The development of low cost, stable and efficient materials for solar driven fuel synthesis is a key scientific challenge for addressing global sustainability concerns. My lecture will focus upon separation and recombination dynamics of some of the nanostructured metal oxide photoelectrodes currently being developed for solar water photolysis. A range of experimental techniques will be employed to address some of the key processes limiting the efficiency of water oxidation / reduction on such electrodes. Transient absorption spectroscopy on timescales from femtoseconds to seconds will be correlated with the results of photoelectrochemical impedance analyses. Experimentally, my lecture will be based around our studies of nanostructured hematatite photoelectrodes, and the impact of gallium and cobalt oxide overlayers on this electrodes. The studies will be complimented by studies of a range of other electrode systems, including cuprous oxide, bismuth vanadate, and dye sensitized titania. Recurring themes of my talk will be importance of junctions to separate charge, control of materials structure on the nanometer length scale and the link between carrier dynamics and the thermodynamic efficiency of photoelectrode function.

The lack of efficient sunlight absorption, corrosion of the semiconductor materials and the difficulty of matching the semiconductor band-edge energy levels with the hydrogen and evolution reaction are the principal obstacles to direct photoelectrolysis of water. Tungsten trioxide, WO₃, semiconducting photoanode fulfils the second requirement, having demonstrated remarkable long-term stability during photoelectrolyses performed in appropriate acidic solutions.¹ Despite their optical absorption range restricted to the blue portion (up to 500 nm) of the visible spectrum, the WO₃-based photoanodes supply significant AM 1.5 sunlight-driven water oxidation photocurrents (above 2mA/cm²) attained already under a bias voltage of 1 V. Good photocurrent-voltage performance allowed recently application of semitransparent WO₃ photoanodes in a tandem device in combination with the latest version of dye-sensitized solar cell (DSSC). This work demonstrated for the first time efficient water splitting in a tandem cell operating at a ca 1 V bias voltage provided by a single-junction DSSC.

This presentation will focus upon recent efforts to enhance photocurrent efficiency of semiconducting oxide photoanodes by the use of catalysts and of of plasmonic metal nanoparticles.

These questions will be discussed in a broader context.



1. Renata Solarska, Rafal Jurczakowski and Jan Augustynski, Nanoscale, 4, 1553 (2012).

Sunlight is a clean, renewable and abundant energy source on the earth. Its conversion to hydrogen has been considered an ideal solution to counter the depletion and environmental problems of fossil fuels. Photoelectrochemical water splitting is an ideal technology for the purpose, since H2 could be produced directly from abundant and renewable water and solar light from the process. The key to the technology is photoelectrodes of high efficiency, high stability, and low cost. In addition of the discovery of new materials, the structure and morphology of the known materials could be designed to enhance the performance of the photoelectrodes. In this presentation, the concepts of materials design and their examples are proposed for efficient photoelectrodes of photoelectrochemical (PEC) cells for visible light water splitting. We discuss the material designs including: i) Nanoparticles electrodes to minimize the diffusion length of the minority carrier, ii) p-n heterojunction photoanodes for effective electron-hole separation, iii) electron highway to facilitate interparticle electron transfer, iv) metal doping to improve conductivity of the semiconductor, and v) one-dimensional nanomaterials for vectoral electron transfer. High efficiency has been demonstrated for all these examples due to efficient electron-hole separation. Modern material processing techniques have been explored to materialize these concepts.

Predictability is a key issue in manipulating the electronic properties of materials for various applications, such as photocatalysis. The understanding of electron photo-transition and transport is crucial for the efficient prediction of metal-oxide nano-crystalline photocatalysts. The current understanding at the “nano” level is not very clear, and leads to misleading assumptions to the photocatalytic chemistry for these nano-crystals. Several key issues remain challenging in metal-oxide nano-crystals, such as identification of the fundamental gap and the actual optical gap, the nature of energy levels (“band”) in the nano-crystals, etc. Apart from these challenging issues, metal-oxide nano-crystals can show unpredictable electronic behavior due to their unsaturated and charge uncompensated surface bonds. These charge unpassivated ionic bonds may attract different chemical species to passivate themselves, and hence the electronic properties of the nano-crystals may change significantly. The first principle theories, such as density functional theory (DFT) and time-dependent-DFT (TDDFT), are state of the art theoretical methods to shed light in these aspects. To demonstrate how theoretical studies can guide the path, a unique class of highly stable, self-saturated and self-charge-compensated delafossite nanocrystals has been identified. The DFT study of structural and electronic properties of these nano-crystalline Cu-based delafossites will be presented. To have a better estimate of the electronic excitation energies, and consequently the optical gap, time dependent DFT has been employed as well. The goal is to show, first of all, that these unique set of nanocrystals exists, and to study whether the nano-phase can enhance the electronic properties for its application as photocatalysts.

Metal oxides have the potential to photocatalytically generate hydrogen fuel from water and sunlight. Calcium niobium oxide nanosheets, HCa(subscript)2(subscript)Nb(subscript)3(subscript)O(subscript)10(subscript), have been shown to split pure water into hydrogen and hydrogen peroxide under ultraviolet illumination. The generated hydrogen peroxide coordinates to the Nb(superscript)5+(superscript) on the surface, eventually quenching the photocatalytic activity. Theory predicts that surface ion modification can change the energetics of nanomaterials. This should allow the control of charge transfer across the particle-solution interface. Calcium niobium oxide nanosheets serve as an ideal system to study the effect of ion modification. Since the sheets are negatively charged above pH 2.5, metal cations; e.g. H(superscript)+(superscript), Mg(superscript)2+(superscript), Sr(superscript)2+(superscript), can be readily attached. The use of multivalent cations allows incorporation of anions, including phosphate and sulfate. Photoelectrochemical studies are used to probe the effect of these modifications on the conduction band energy. The effect of these ion modifications on photocatalytic hydrogen evolution from aqueous methanol solutions is also described.

Photocatalytic hydrogen generation is an efficient way of converting solar energy to chemical energy by harvesting sunlight and utilizing solar energy to produce hydrogen from water. Hydrogen can thus be utilized as a high-capacity renewable energy resource for the future.
Quantum confinement effect has been intensively studied for over 30 years since the early 1980s. The utilization of quantum confinement has achieved tremendous successes in tuning the optical, electrical, magnetic properties of semiconductor, and recently in controlling charge generation and separation in nanocrystal solar cells.
Here, we are presenting a quantum size-dependent photocatalytic hydrogen evolution using aqueous solution of CdSe Quantum Dots (QDs). CdSe QDs ranging between 1.8 nm and 6.0 nm were synthesized using an aqueous-based method. Photocatalytic hydrogen evolution can be achieved with these QDs and the activity can be fine tuned by controlling the size via quantum confinement effect. Photoelectrochemistry suggests a significant shift of their conduction band minimum with size. As a result, the thermodynamics and the kinetics are regulated by the change in their energetics. Quantitative investigation reveals that the relationship between the activity and the size can be modeled using well-established kinetic theories, e.g. Marcus theory and Butler Volmer theory, indicating that the electron transfer kinetics at the interface is the rate-limiting step. Overall, this is the first quantitative demonstration of a quantum-confined photocatalytic hydrogen evolution.

Photoelectrochemistry (PEC) is one of the most efficient methods to produce alternative fuels, although lab-scale systems efficiency, cost and durability are currently not at the level required to make this technology economically feasible. The chalcogenide material class, typically identified by its most popular alloy Cu(InGa)Se2 for its use in photovoltaic cells, provides exceptionally good candidates to meet the requirements identified for cheap, sustainable solar fuels (such as hydrogen) production. As we recently reported, co-evaporated CuGaSe2 offers very high saturated photocurrent densities (20mA.cm-not;2, in pH0 under AM1.5G illumination), long durability (up to 420 hours) and solar-to-hydrogen efficiencies up to 4.34% (co-planar integration scheme). In order to improve further water-splitting efficiency and reduce hydrogen production costs, novel alloys and synthesis techniques must be developed. On the material side, the photocatalyst must have a band-gap of 2.0 eV to be integrated into a monolithic hybrid PEC system for water-splitting. A number of chalcogenides with this ideal absorption characteristic have been identified, including CuGa(Se,S)2, Cu(In,Ga)S2 and Cu2(Zn,Ge)S4. Although Cu/In/Ga/Se-based compounds can be routinely synthesized with vacuum-based processes (co-evaporation), Zn- and S-based systems are much more challenging, as phase segregation tends to occur during growth. One solution resides in the use of chemical-based material synthesis methods, where chalcogenide compounds are first created at the nanometer scale, then deposited onto a substrate and finally annealed in a variety of atmospheric conditions.
In the present communication, we report on our search for 2.0 eV band-gap chalcogenide materials synthesized from nanoparticle-based inks. Using Cu2ZnSnS4 photocatalyst as validation, we first demonstrate how nanoparticle “building blocks” can be made with various liquid-based methods, including hot injection and sonochemical processes. As-synthesized nanoparticles were found to be nearly mono-dispersed (8 nm in diameter, 0.7 nm standard deviation) and monocrystalline. Cu2ZnSnS4 thin films were then obtained by spraying the ink onto conductive substrates followed by annealing in sulfur atmosphere at 500°C. Resulting films were single phase Cu2ZnSnS4 (as demonstrated by XRD and Raman scattering) and made of well-defined grains (c.a. 1 micron across). Subsequent PEC characterizations revealed that our Cu2ZnSnS4 films were p-type and photoactive. In the second phase, 2.0 eV CuGa(SeS)2 and Cu2ZnGeS4 where synthesized using similar synthesis protocols. The PEC performances of newly formed thin films will be presented as well as possible integration schemes for efficient low-cost chalcogenide-based PEC hydrogen production.

We report a facile approach to prepare highly conductive and photoactive hematite (α-Fe₂O₃) nanostructure through thermal decomposition of β-FeOOH nanowiresat 550 °C in an oxygen-deficient atmosphere (mixture of N₂ + air). The as-grown hematite sample showed substantially enhanced photoactivity for photoelectrochemical (PEC) water oxidation compared to the pristine hematite prepared in air.The hematite nanowire-arrayed photoanode yields a photocurrent density of 3.37 mA/cm² at 1.50 V vs. RHE, which is the best value reported for pristine hematite materials without the incorporation of dopants or oxygen-evolving catalysts. The enhanced photoactivity is attributed to the improved donor density of hematite nanowires as a result of formation of oxygen vacancies and thereby Fe²⁺ sites confirmed by XPS analysis.Mott-Schottky studies showed that the donor density of this active hematite is an order of magnitude higher that of the pristine hematite prepared in air.This work demonstrated a simple and effective strategy for the preparation of highly photoactive hematite for PEC water oxidation, without the need of dopants and at a relatively low activation temperature.

We report amechanistic studyofthe catalytic effect of Ni(OH)₂ on hematite nanowires for photoelectrochemical water oxidation. Previous studies have shown that the incorporation of Ni(II) catalyst on hematite photoanodescan significantly enhanced their photoelectrochemical performance. However, we found that the photocurrents of Ni catalyst decorated hematite photoelectrodes decay rapidly,indicating the photocurrents were not stable. We revealed that the enhanced photocurrent was mainly due to the photo-induced charging effect. The photoexcited holes generated in hematite efficiently oxidize Ni²⁺ to Ni³⁺ (0.35 V vs. Ag/AgCl), rather than oxidize water. The instability of photocurrent was due to the depletion of Ni²⁺. We proposed that the catalytic mechanism of Ni(II) catalyst for water oxidation is a two-step process that involves the fast initial oxidation of Ni²⁺ to Ni³⁺, and followed by the slow oxidation of Ni³⁺ to Ni⁴⁺, which is the active catalytic species for water oxidation. The catalytic effect of Ni(II) catalyst was limited by the slow formation of Ni⁴⁺. We elucidated the real catalytic performance of Ni(OH)₂ on hematite for photoelectrochemical water oxidation by suppressing the photo-induced charging effect. Furthermore, we also demonstrated that Ni(OH)₂ modified hematite can be used as photoelectrode for solar driven hydrogen releasing from urea and human urine. Ni(OH)₂ catalyze urea oxidation, in which Ni³⁺ species served as the active catalytic sites. These works provide important insights for future studies on Ni based catalystmodified photoelectrodes for water and urea oxidations.

One of the most exciting renewable fuel pathways is solar hydrogen production using a photoelectrochemical water splitting cell. Hematite is a very promising material for use as the photoanode in one of these cells because it is an earth-abundant material, has a band gap of approximately 2.2 eV, is stable in solutions with pH greater than 3 and has a theoretical solar-to-hydrogen efficiency of 16.8%. On the other hand, hematite is a known Mott-Insulator indicating that after charge separation occurs, properties of charge transport are poor. Due to its low light absorption coefficient, enhancement of the incident photon to current efficiency near the band edge is required. The conduction band of hematite falls about 0.2 eV positive of the hydrogen evolution reaction, meaning a bias or engineering of the band edge is required to enable spontaneous water splitting. Though the penetration depth of light into hematite is large, the hole diffusion length is much shorter (below 10 nm), causing most electron hole pairs to recombine if not generated within close proximity of the semiconductor-liquid junction.
Our approach to overcome the drawbacks of hematite has been to nanostructure hematite into nanowire arrays. Nanowire arrays offer several distinct advantages over other morphologies. Nanowires are single crystal structures, which reduces recombination by having little to no grain boundaries that act as electron-hole trap sites. Nanowires are thin in diameter, which causes most electron-hole pairs to be generated near the semiconductor-liquid junction and keeps recombination in the bulk to a minimum. Nanowires also take advantage of the anisotropic conductivity exhibited by hematite because the (001) plane falls along the length of the wire, allowing optimal conductivity to the back contact.
Our group has reliably and repeatedly synthesized highly dense and oriented hematite nanowire arrays via low pressure and atmospheric pressure plasma oxidation of iron foils. Both low pressure plasma oxidation and atmospheric pressure plasma oxidation produced hematite nanowire arrays with significant photoactivities (.38 mA/cm2 at 1.5 V vs. RHE and .06 mA/cm2 at 1.5 V vs. RHE respectively).
Atmospheric plasma oxidation is a very effective technique because it is highly scalable, it operates under ambient temperature and pressure, its only inputs are oxygen and electricity and synthesis time scales are short (1-10 mins). Though nanowire arrays synthesized by atmospheric plasma oxidation show lower photoactivities than under low pressure plasma oxidation, they consistently show better onset potentials than low pressure oxidation. The lower photoactivity is thought to be due to delamination of the thin film from the iron substrate and recombination at the interfacial magnetite layer. Currently, work is underway to understand the upper limit of photoactivity for our NW array system by modifying hematite nanowires via doping and surface passivation.

The US Department of Energy&’s (DOE) Fuel Cell Technologies Program (FCT) has made significant progress in fuel cell technology advancement and cost reduction, highlighted by reducing the cost of automotive fuel cells by more than 80% since 2002. Research and development of enabling technologies for the widespread production of affordable renewable hydrogen remains a looming challenge. Near-term utilization of current reforming and electrolytic processes are necessary for early hydrogen markets, but there remains a critical need for transitioning to industrial-scale renewable hydrogen production for the longer term. Central to the long term vision are the solar-to-hydrogen conversion technologies, including the photoelectrochemical, biological, thermochemical and integrated solar-electrolysis routes. In all areas, routes to practical large scale solar hydrogen generation meeting DOE targets will rely on the development of low-cost materials systems with performance and durability properties well-beyond what&’s available today. Innovations in macro-, meso- and nano-scale structures are all needed for pushing forward the state-of-the-art. Specific research and development pathways for advancing materials systems for the solar-to-hydrogen conversion technologies are discussed, and current strategies for leveraging research collaborations across scientific disciplines, and across DOE programs and other federal agencies, are described.

Hematite has a superior solar light absorption property compared to other metal oxide semiconductors, however, Its electron conductivity is relatively lower. Recently, a dramatic improvement of water splitting activity of hematite photoelectrode by changing its electronic structure and morphology was reported.[1] In this study, Two topics are introduced. The one is a metal ion doping effect. The other is an effect of morphology change of hematite photoelectrode. Metal ion doping is one of ways to improve the electron conductivity of metal oxide semiconductors, and various kinds of metal ions have been thus far employed as a dopant for hematite photoelectrode. In this study, solar light water-splitting by Ge4+-doped hematite photoelectrode, prepared by the chemical solution deposition method, has been investigated. Moreover, hematite photoelectrode double -doped with Ge4+ and Ti4+ has been prepared for further improvement of the water splitting activity. The size of hematite particles in the photoelectrode was decreased, and the donor density of photoelectrode was increased by doping of Ge4+ into hematite photoelectrode. Therefore, photocurrent of the hematite photoelectrode improved up to 2.5 times. This improved photocurrent was further enhanced by doping of Ti4+, and the largest photocurrent (1.1 mA/cm2 at 1.5 V vs. NHE) was obtained in the double-doped hematite photoelectrode. Furthermore, by changing the morphology of this hematite photoelecrtrode using organic polymer template, water splitting photocurrent improved up to 1.4 mA/cm2 at 1.5Vvs NHE. Separately, hematite nano-rod photoelectrode was also prepared by the hydrothermal reaction using Fe(NO3)3 as a precursor in the presence of NaCl. Since hematite nano-particle was obtained in the absence of the NaCl, chloride ion must play a crucial role in the growth of hematite nano-rod. Furthermore, metal-ion doped hematite photoelctrodes were prepared by this way, and water splitting photocurrent was improved by doping of Zr4+. The highest photocurrent (0.88 mA/cm2 at 1.5 vs. NHE) was obtained in Zr-doped (10%) hematite nano-rod photoelectrode.
The tandem cells composed of various hematite photoelectrodes and a two-series-connected dye-sensitized solar cell, which could afford 1.5 V to TNR photoelectrode, was applied to solar light water splitting. The obtained best overall efficiency for solar light water splitting (eta;STH) utilizing the hematite tandem cell was 1.7%.
References:
[1] K. Sivula, F. Le Formal, and M. Graetzel, ChemSusChem, 4, 432(2011).

Hematite has long been considered a potential candidate for photocatalytic water splitting because of its favorable valence band edge, reasonably low band gap, high stability and low cost. Unfortunately, only very poor conversion efficiencies have been achieved, which is generally attributed to a short minority carrier collection length. In principle, the short collection length can be overcome through nanostructuring the electrode. Thin films represent ideal model systems of nanostructured electrodes which allow for detailed mechanistic investigations. We utilize atomic layer deposition (ALD) to make conformal thin film hematite electrodes with controllable thickness for this purpose. Films less than 20 nm thick, however, are plagued by a dead layer near the substrate contact. We found that the dead layer can be alleviated by the incorporation of dopant atoms in the hematite film, which lead to dramatically improved water oxidation efficiencies. A series of electrochemical, photoelectrochemical and impedance spectroscopy measurements were employed to elucidate the cause of the improved photoactivity of the doped hematite thin films. This performance enhancement was determined to be a combination of improved bulk properties (hole collection length) and surface properties (water oxidation efficiency). Further improvements in the water oxidation efficiency can be achieved through the addition of water oxidation catalysts to the hematite surface. Results of additional impedance measurements employed to determine the effect of water oxidation catalysts on the photocurrent-determining processes will also be presented.

In order to improve the energy conversion efficiency of α-Fe2O3 (hematite) photoelectrodes in solar water splitting processes, one needs to optimize the generation, transport and extraction of photo-excited electrons to an external circuit. Several ways to achieve this have been reported. For instance, the growth of magnesium-doped, p-type hematite on top of an n-type layer produces a built-in field which results in a substantial increase of the measured photovoltage [1]; high-temperature annealing of hematite nanorod arrays grown on fluorinated tin dioxide (SnO2:F) substrates enhances the photoanodic current by more than two orders of magnitude [2]; and incorporation of titanium ions in hematite photoelectrodes has been known to increase the efficiency of photo-oxidation for a variety of preparation conditions [3]. We have used element- and orbital-sensitive soft x-ray absorption spectroscopy at the Fe L-edges and the O K-edge to investigate various nanorod arrays and thin film structures. The pn-homojunction of Fe2O3 was found to exhibit different orbital occupancies and crystal-field splitting from both n- and p-type bulk hematite, although the introduction of Mg dopants does not alter the structure or morphology of the oxide. In Fe2O3 / SnO2:F electrodes the diffusion of tin into the hematite nanorods was found to induce a change of the electronic structure at the interface by introducing unoccupied O 2p states below the conduction band minimum and reducing the crystal-field splitting. These changes are partly eliminated by high-temperature processing [4]. Furthermore, the incorporation of Ti dopants into hematite was found to be realized in the form of Ti4+ ions, with limited or no simultaneous charge compensation by creation of Fe2+ oxidation states [5]. The implications of our results on the future design of more efficient photoelectrochemical cells will be discussed.
[1] Y. Lin,Y. Xu, M. T. Mayer, Z. I. Simpson, G. McMahon, S. Zhou, and D. Wang, J. Am. Chem. Soc. 134, 5508 (2012)
[2] C. D. Bohn, A. K. Agrawal, E. C. Walter, M. D. Vaudin; A. A. Herzing; P. M. Haney, A. A. Talin, V. A. Szalai, J. Phys. Chem. C, 116, 15290-15296 (2012)
[3] E.g.: N. T. Hahn, and C. B. Mullins, Chem. Mater. 22, 6474 (2010)
[4] C. X. Kronawitter, I. Zegkinoglou, C. Rogero, J. Guo, S. S. Mao, F. J. Himpsel, and L. Vayssieres, J. Phys. Chem. C, Article ASAP, DOI: 10.1021/jp308918e
[5] C. X. Kronawitter, I. Zegkinoglou, S. Shen, J.-H. Guo, F. J. Himpsel, L. Vayssieres, S. S. Mao, in preparation

Our study describes the influence of the thermal treatment on the fundamental properties of the vertical oriented hematite nanorods synthesized under hydrothermal condition. X-ray diffraction and X-ray absorption near edge structure spectra were used to investigate the phase evolution from iron oxyhydroxide to pure hematite phase. The formation of nanorods distributed along of substrate was observed by top-view SEM images and the rod growth preferentially oriented at the highly conductive (001) basal plane of hematite, perpendicular to the substrate. Light absorption capacity increases with the temperature of treatment and the electronic transitions (direct and indirect electronic transition) were estimated from this result. From the electrochemical measurement the hematite/electrolyte interface was evaluated. These findings demonstrated that the temperature plays an important role on the hematite (structural, morphological and catalytic) properties and that many influences must work in great harmony in order to produce a promising hematite photoanode.
Acknowledgements: We gratefully acknowledge financial support from the Brazilian agencies of FAPESP (Grant No. 2010/02464-6 and 2011/18732-2), CAPES, CNPq (555855/2010-4 and 473669/2012-9).

When used as scaffolds onto which semiconductor thin films are deposited, high surface area electrodes (HSEs) made of transparent conductive oxide (TCO) offer the ability to simultaneously maximize internal and external quantum efficiency (IQE and EQE, respectively), key parameters for boosting device performance. TCO HSE substrates serve as a broadly applicable platform for functionalization in many applications. In this work, we have developed optically transparent, electrochemically stable, and physically robust indium tin oxide (ITO) HSE substrates with tunable pore sizes and deposited thin films of hematite onto them for photoelectrochemical (PEC) water splitting.
PEC cells perform photoelectrolysis of water and directly store solar energy in molecular hydrogen. Hematite (α-Fe2O3) is a promising PEC electrode material due to its ideal band gap of ~2.1 eV, high stability, and low cost. However, the performance of hematite is largely limited by its low absorption coefficient and short minority carrier diffusion length. The HSE scaffold allows for enhanced device performance by maintaining short minority carrier path lengths through the hematite while amplifying device optical density.
A facile deposition-annealing technique was employed for the synthesis of titanium-doped hematite films on both HSE and planar substrates made of ITO. A SnO2 interfacial layer introduced between ITO and hematite significantly enhanced both saturated photocurrent density and photocurrent onset potential. The improved photoactivity is attributed to passivation of interface states at the hematite - ITO interface. The performance of these nanoporous hematite films was investigated as a function of thickness, and the optimal thicknesses of both hematite and SnO2 interfacial layers were determined.

Dye-sensitized solar cells have received much attention because of the demand for cheap sources of renewable energy. In general the electrolyte reduction reaction, I₃^- + 2e^- → 3I^- occurs on the counter electrode (CE) surface to provide sufficient iodide anions for dye regeneration. It is well known that coating a thin-layer of Pt on the transparent conducting oxide (TCO) substrate surface increases the electrolyte reduction rate and makes the reduction to be diffusion-controlled. Therefore, Pt films provide low Pt usage and superior catalytic performance is essential for high performance cell. To develop a high catalytic performance Pt film, stabilizing agents are used to control shape and size of nanostructures and to prevent aggregation of nanoparticles. However, the high temperature process for removing the stabilizing molecules such as surfactant and polymer cause great damage to soft substrate of flexible devices. Here we proposed a simple two-step procedure to fabricate Pt monolayer as counter electrodes for DSSC applications, in particular for the flexible devices that facilitate a low-temperature process to cover Pt clusters on soft plastic TCO materials.
Polyol synthesis is a successful method to generate metal nanostructures with well defined and controllable shapes. Uniform Pt NPs were fabricated in ethylene glycol containing Pt precursor and the morphologies are controllable depending on the concentrations of KOH. A self-assembled monolayer (SAM) of Pt nanostructures was fabricated by linking Pt NPs with thio functionalized TCO substrate. Scanning electron microscope top-view images show the Pt nanoparticles homogeneously distributed on the surface of a fluorine doped tin oxide conductive glass. Transmission electron microscopic cross-section images reveal that the Pt nanopaticles are highly crystalline and self-organized on the substrate with a uniform size of 3 nm in diameter. The DSSC device made of SAM CE and optimized TiO₂ photoanode attained an overall power conversion efficiency 9.2% on indium tin oxide substrate, which is slightly higher than the device with a conventional thermal cluster Pt CE on FTO substrate (9.1%); the device made of SAM CE on FTO substrate gives the efficiency 9.0%.
Compared to the traditional thermal decomposition and sputtering method, the proposed two-step self-assembly method of making Pt-SAM counter electrodes has the following advantages: (1) the size distribution of the Pt clusters is more even; (2) the surface area of the Pt-clusters is larger so to provide higher catalytic efficiency; (3) without polymer and surfactant, an appropriate low temperature process is provided so that it is applicable for plastic soft materials; (4) the process is relatively simple and is feasible for industrial mass-production. Therefore, preparation of Pt-coated counter electrode using the proposed two-step process has many advantages over that of TCP or sputtered method for future commercialization.

Silicon has been a dominating material in current microelectronics and solar cell markets due to its earth abundance, non-toxicity, and matured processing technology. Reducing the materials cost of ultrahigh-purity (~99.999999999%, ‘eleven&’ nine) silicon required for improving the cell conversion efficiency is an essential concern in silicon solar cell industries. Of particular interest is to utilize cheap silicon feed stock such as metallurgical silicon (99%~99.999%); however, metal impurities mainly included in low-grade silicon have hindered its useful applications. Here, we demonstrate that metal assisted chemical etching (MaCE), which is well known for wire formation, effectively purifies the metallurgical silicon while removing all kinds of metal impurities inside the wafer. Chemically purified, monocrystalline silicon nanowires (SiNW) could be fabricated in waferscale. We mainly focus on their phototelectrochemical application for water splitting in which sufficient optical absorption along an axial direction of wires was observed while facilitating a radial collection of charge carriers over a distance enough to compromise their short diffusion length. Enhanced photocurrent density (~35% increase) and a reduced onset potential were also obtained with stability better than its bulk counterpart designed for water splitting.

In the last decade the electron transition in quantum dot systems is discussed extensively (especially, in qubits investigation) [1]. An example, one can mention the transition between single-electron Zeeman sublevels or between two-electron triplet-singlet states. In the presented work we are investigating single electron spatial transition in double lateral quantum dots (DLQD) due to an applied constant electric field. The transition means that the electron localization in DQD is changed between the left/right QDs. In the field, for weakly coupled non-identical DQs there are a crossing of single electron energy levels. Degeneracy is avoided by anti-crossing of corresponding levels of DLQD. We demonstrate that in this DLQD the electron transition between the dots occurs due to the electron level anti-crossing induced by the electric field.

The localization of electron in the system (left or right QDs) can be fixed by choosing electric field magnitude. This value is “the transition point”.
Influence of shape asymmetry of the left/right dots to the transition point is studied to find optimal parameters for control of electron position.
Realistic QD geometry for the InAs/GaAs DQDs is applied. Results of numerical simulation for the electron transition are presented.
The double quantum rings (DQR) are also considered as particular case of the non-identical QDs [2]. For DQR we compare the electron transition in both cases of electric and magnetic fields.
The effective potential method proposed in [3] is used for description these hetero-structures.

This work is supported by NSF CREST award; HRD-0833184 and NASA award
NNX09AV07A.

References

1. R. Hanson, L. P. Kouwenhoven, J. R. Petta, S. Tarucha, and L. M. K. Vandersypen, Rev.
Mod. Phys. 79, 1217 (2007).

2. I. Filikhin, S. G. Matinyan, J. Nimmo and B. Vlahovic, Physica E: Low-dimensional
Systems and Nanostructures 43, 1669 (2011).

3. I. Filikhin, V. M. Suslov and B. Vlahovic, Phys. Rev. B 73, 205332 (2006).

Epitaxial growth on planar substrates has been pursued for creating single crystal layers of new materials. In many important materials systems, such as heteroepitaxy onto planar substrates leads to phase segregation and misfit dislocations due to lattice mismatch-induced stresses and strain. Recently, our group showed that using hetero-epitaxy on nanowire substrates, thick layers (~200 nm) can be grown without the problems associated with planar substrates due to the lower interfacial contact area and stress relaxation. Specifically, using hetero-epitaxy, we were able to obtain single crystalline layers of InxGa1-xN alloys with composition over the entire range for indium from 0 to 100%.1 InxGa1-xN alloys with indium composition from 45-65 % can have the right band gap between 1.7-2.2 eV necessary for photoelectrochemical water splitting applications.
The hetero-epitaxial growth of InGaN alloys on GaN nanowire substrates exhibited different growth morphologies depending upon nanowire growth direction. Typically, the “c” plane-oriented GaN nanowires exhibit stacking faults perpendicular to growth direction where as the “a” plane oriented GaN nanowires exhibit stacking faults parallel to growth direction. Similarly, the hetero-epitaxial InGaN layers on “c” plane-oriented nanowires developed stacking faults perpendicular to growth direction. The photocurrent for InGaN epilayers on GaN nanowire arrays was found to be on the order of only 100-150 micro-A/cm2. In some cases, there was no photoactivity. This “poor” photoelectrochemical performance is attributed to the extension of defects in the epilayers grown using “c” wires and the corresponding poor conductivity of the “c” direction wires.2 In order to address this problem, we have been creating “a” plane oriented nanowire arrays on both stainless steel and sapphire substrates and use them for producing InGaN epilayers. In this presentation, we will highlight work our results on photoelectrochemical properties of InGaN layers grown specifically on “a” direction nanowire arrays. Several properties such as flat band potential and stability are of interest as a function of indium composition in InGaN alloys in addition to photoactivity.
Acknowledgements: Financial support from US DOE (DE-FG02-07ER46375) is acknowledged.
1. 1. C. Pendyala, J. B. Jasinski, J. H. Kim, V. K. Vendra, S. Lisenkov, M. Menon and M. K. Sunkara, “Nanowires as semi-rigid substrates for growth of thick, InxGa1-xN (x>0.4) epi-layers without phase segregation for photoelectrochemical water splitting”, Nanoscale, DOI: 10.1039/C2NR32020G (2012).
2. M.K. Sunkara, R. Makkena, H. Li and B. Alphenaar, “Direction Dependent Electrical and Optical Properties of Gallium Nitride Nanowires”, ECS Trans., 3 (5) 421 (2006).

Rare earth materials such as europium and terbium are utilized as phosphors in fluorescent lamps and plasma displays. Department of Energy has classified such rare earths as critical materials, because they are supplied by only a few mines around the world and the production is plagued with environmental problems such as radioactive waste [1]. It is desirable to find more abundant and environmentally sustainable alternatives to rare earths.
The objective of this research is to investigate whether clusters of potassium (K) might serve as substitutes for rare earth phosphors. Alkali elements are known to be good emitters of light. For example sodium lamp which emits primarily yellow light at 589 nm is widely adopted in outdoor lighting because of its high efficiency. Potassium atoms emit primarily in the near infrared (767 nm), therefore potassium has not found any applications in lighting. However clustering of potassium atoms can change the emission spectrum.
Optical properties of potassium clusters are investigated by first principle quantum mechanical calculations using the configuration interaction method with Pople type basis sets augmented with polarization functions. Results indicate that optical spectra of the clusters change from the characteristic near infrared to visible colors from red to blue, as the cluster size increases from a few atoms to tens of atoms. Furthermore oscillator strength of the spectral lines increases in proportion to the number of atoms in the cluster. Hence each atom added to the cluster makes a contribution to the light output. These results are promising to utilize potassium clusters as phosphors which can emit broadband white light, possibly with a color rendering better than that of the rare earths.
The potassium atom which has one electron in the outer shell, can share that electron with other atoms in a cluster to attain a more stable state. Bond energy of K2 is 0.9 eV which is small as compared to that of H2 (~4.5 eV). Heat of vaporization of potassium is 490 cal/g which yields a bonding energy of 0.8 eV for the surface atoms of the cluster. One way of achieving greater stability is to enclose potassium clusters in a porous host [2]. Such a host physically confines the clusters to the pores, as well as protecting them from the environment.
[1] “Critical Materials Strategy,” report by US Department of Energy, December 2011
[2] M. Shatnawi, et al., "Structures of Alkali Metals in Silica Gel Nanopores: New Materials for Chemical Reductions and Hydrogen Production," Journal of American Chemical Society, 129, p.1386, 2007

The overall carbon footprint will exceed 40 Gt/year of CO2 emissions by 2030. In this context, their valorizations constitute a complementary strategy to CO2 geological sequestration and captured CO2 can be valorized and converted into high value chemical products starting in the C1-based building block, which can play the role of chemical storage molecule for renewable fuels and also used for the synthesis of high added value products such as acetic acid, formaldehyde, olefinshellip; In this scenario, electro reduction of CO2 constitutes one plausible option. However the use of system with photon activation of catalysts from the solar radiation will promote lower electricity consumption and an enhancement of the conversion rate and selectivity obtaining outstanding energy balance and decreasing cost. The general concept relies on the optimization of the photo-catalytic materials for the photo anode, as a source of solar-to-electricity conversion, providing enough energy to the cathode to carry out the electro reduction of CO2. In this contribution, photo reactor implementation and associated nanomaterial characteristics will be reviewed. 1D MOx nanostructures with an excellent surface-to-volume ratio as well as an easy collection of the electrons by the supporting substrate as well as new hierarchical structures, enhancing the efficiency of the photoanode, taking the advantage of 1D semiconductors over a 3D electrode for increasing the global surface area will be analyzed.
Levels of photocurrent (mA/cm2) and IPCE(%) will be evaluated and compared for different metal oxide photo anodes based on modified metal oxides nanomaterials considering the global PCE cell energetic balance. Likewise, influence of the morphological control at the nanoscale for increasing charge transport from the surface of the photo anode to the cathode, doping of the nanostructures and use of catalyst will also be presented as elements to scale up CO2 conversion photo reactor to high productivity levels, several m3/h.

The light-induced conversion and electrochemical storage of energy critically depend on the appropriate design of nanostructured materials and interfaces to achieve efficient transport of the respective charge carriers and ions. Here we discuss different strategies for the synthesis of nanoporous materials with tunable pore systems, wall thickness and domain sizes that are being studied in the context of energy conversion and storage. We will address the non-aqueous synthesis and assembly of ultrasmall metal oxide nanoparticles to create mesoporous materials with extremely high surface areas, hierarchical scaffold structures (1), and biotemplating with shape-persistent templates. We ask how the nano-morphology of such systems affects the transport behavior and the efficiency of dye-sensitized solar cells containing different hole-transport materials, and of anode structures for light-induced electrochemical water splitting. Moreover, we will discuss multi-level templating strategies for the formation of nanostructured mesoporous carbon phases for applications in lithium-sulfur batteries, featuring very high storage capacity and good cycle stability (2).
(1) Mandlmeier, B., Szeifert, J., Fattakhova-Rohlfing, D., Amenitsch, H., Bein, T., J. Am. Chem. Soc. 133 (2011) 17274-17282.
(2) Schuster, J., He, G., Mandlmeier, B., Taeeun, Y., Lee, K. T., Bein, T., Nazar, L. F., Angew. Chem. Int. Ed. 51 (2012) 3591-3595.

The field of Solid State Ionics, dealing with materials exhibiting significant ionic or mass transport under electrical or chemical potential gradients, is receiving a great deal of attention, given the needs for improved energy storage and conversion devices and robust environmental monitoring devices. We report on advances made in our laboratory in achieving improved insights into the defect, transport and electrocatalytic properties of films of interest in solid oxide fuel cell cathodes, membranes and automotive catalysts by taking advantage of controlled morphology and geometry of thin films including the use of oxide superlattices and the application of in-situ analytical tools including impedance, optical and scanning tunneling spectroscopy.
Acknowledgements: Collaborative contributions from colleagues Prof. Bilge Yildiz (MIT) and Prof. Sean Bishop (I2CNER, MIT) and students Di Chen, Jae Jin Kim, Johanna Engel, Nick Thompson and Yan Chen are appreciated.

Inorganic nanostructured metal oxides and sulfides are being extensively studied for their application potential in energy storage and generation (e.g., batteries, supercapacitors, solar cells, photocatalysts). Of various power-source devices, supercapacitors, also known as electrochemical capacitors (ECs), have attracted great interest due to their merits of fast charging-discharging rates, long cycle life and the ability to deliver up to ten times more power than conventional batteries. High performance relies largely on scrupulous design of nanoarchitectures and smart hybridization of dissimilar active materials.
We will present our recent research in strategic fabrication of hierarchical and heterogeneous oxide nanomaterials with either core-shell or stem-branch structure directly on various conductive substrates. The obtained metal oxide/hydroxides, or metal sulfides have the combined properties of direct electron-flow path, high surface areas, and functional synergy. Many examples show the advantage of core-shell hybrid nanostructures over individual components in their charge storage performance. Strategies in achieving microporous and nangaps, and their positive roles in EC will be discussed in detail. We demonstrate the atomic layer deposition (ALD) is a useful technique for this research direction.
References
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Toxic organic pollutants produced by industrial sources are harmful to the environment and human health. Photocatalysis is an efficient, broadly applicable, green technique that has shown great potential for the complete elimination of toxic chemicals in the environment. Nanostructured semiconductor metal oxides (SMOs) have been shown to degrade various organic pollutants when irradiated with solar light. Although these materials have been used extensively as ultraviolet (UV) light-sensitive photocatalysts, they can only utilize approximately 5% of the total solar spectrum. In addition rapid recombination of photo-generated electron-hole pairs also hinders the industrial application of SMOs. To solve these limitations, hybrid nanostructure materials have been studied to be activated at visible light spectrum by reducing band-gap and reduce recombination of electron-hole pairs by expanding photo-responsive range and enhancing charge separation rate. However, one-pot syntheses of hybrid SMO composites consisting of a primary material with modified surfaces are difficult. As a result, facile and simple processes are needed to decorate SMO surfaces.
In this presentation, we suggest a facile strategy for fabricating hybrid SnO2 nanofibers decorated with N-doped ZnO nanonodules using a single-nozzle co-electrospinning with a phase-separated, mixed polymer composite solution. Firstly, core (poly(acrylonitrile), PAN) and shell (poly(vinylpyrrolidone), PVP) structured nanofibers were fabricated by co-electrospinning, and then hybrid semiconductor metal oxide (SMO) nanofibers were formed by calcination. Consequently, the hybrid SMO nanofibers that were 50 nm diameters of SnO2 core nanofiber decorated N-doped nanonodules on the surface were fabricated without additional synthesis. Furthermore, this method can precisely control the fiber diameter and the population density of the nanonodules. The SnO2/N-doped ZnO hybrid nanofibers were evaluated as UV and visible light-sensitive photocatalysts for the decomposition of organic pollutants. The hybrid nanofibers exhibited excellent photocatalytic activity superior to that of commercial TiO2 (Degussa P-25). This was attributed to an enlarged interfacial area and enhanced surface area, both of which increased with increasing degrees of N-doped ZnO nanonodule decoration. It is the first experimental demonstration of an efficient, visible light-sensitive photocatalyst based on SnO2/N-doped ZnO hybrid nanofibers using a single-nozzle co-electrospinning process.

Dye-sensitized solar cells (DSSCs) have attracted interest over the past two decades due to their low cost, simple fabrication, and eco-friendliness. In a conventional DSSC system, the device includes a nanocrystalline semiconductor (NCS) electrode, dye-sensitizer, redox electrolyte, and counter electrode (CE). Various efforts have been made to enhance the overall performance of DSSCs, such as modifying the morphology of NCS and the molecular structures of organic sensitizers as well as using low-volatility electrolytes and new CE materials.
The role of the CE is to facilitate the reduction of triiodide ions (I3-) from iodide ions (I-) in the redox electrolytes. Platinum (Pt)-coated transparent conductive oxides (TCOs), such as indium-doped tin oxide (ITO) or fluorine-doped tin oxide (FTO), have generally been used as CEs in DSSCs due to the high electro-catalytic activity for triiodide reduction of Pt and high conductivity of TCOs. However, Pt-coated TCOs are expensive to produce and are incompatibility with the I-/I3- redox electrolyte. Various CEs based on carbon materials, metals, conductive polymers, and hybrid-structured materials have been made to substitute the Pt and TCO. However, most candidates have relatively low conversion efficiency compared to Pt CEs, and many depend heavily on mechanically brittle TCO glass substrates. Therefore, it is desirable to develop simple and cost-effective method for fabricating CEs in DSSCs.
In this presentation, we report a novel method for the fabrication of porous PANI/CSA nanostructured CEs for high-performance DSSCs. Porous nanostructures of PANI/CSA CEs were readily obtained via decomposition of embedded porogens. Gases such as oxygen (O2) from BPO and nitrogen (N2) were emitted from the surface of the PANI/CSA by porogen decomposition via thermal treatment, generating pores with different diameters and shapes on the PANI/CSA CEs. In the case of BPO, porous PANI/CSA CEs fabricated by the new method exhibited an increased Brunauer-Emmett-Teller (BET) surface area of 36.98 m2 g-1 and enhanced electro-catalytic activity compared to both pristine PANI/CSA and Pt-coated ITO. Furthermore, they were successfully used as Pt- and TCO-free CEs in DSSCs, resulting in a power-conversion efficiency (PCE) of eta; = 6.23% and excellent efficiency of 101.0% compared to a DSSC with a conventional Pt-coated ITO CE (eta;pt = 6.17%).

The efficient capture and sequestration of CO2 from fossil-fuel-burning power plants has been studied and practiced for decades because anthropogenic CO2 emissions have become a serious concern in relation to global warming. Zeolites, activated carbons, calcium oxides, hydrotalcites, metal-organic frame (MOF) materials, aminopolymers, and organic-inorganic hybrid materials make up the main classes of adsorbents for CO2 sequestration. In those adsorbents, zeolites, activated carbons, and organic-inorganic hybrids are operated in room temperature. Zeolites and organic-inorganic hybrids show higher CO2 adsorption capacity than activated carbons. To desorb CO2 adsorbed on the adsorbent for the reuse, zeolites require higher energy than organic-inorganic hybrids due to the desorption-operating conditions of controlled pressure and temperature. For these reasons, the organic-inorganic hybrid materials have been well studied by numerous research groups as a CO2 adsorbent. There have been a number of amine types investigated for immobilization or physisorption onto porous silica particles such as MCM-x, SBA-x, etc. to capture CO2.
Herein, we report on the effect of primary (1o), secondary (2o), and tertiary (3o) amines for CO2 capture with 1o, 2o, and 3o amines immobilized on highly ordered mesoporous silica particles which is prepared with the colloidal template. And based on the results of good efficient amine types for CO2 adsorption, polyamines were surface-immobilized on porous silica particles. A study related with the type of amines (1o, 2o, and 3o amines) has not been reported although it is very critical for the designing of amino-functionalized CO2 adsorbents. We focused our efforts on studying the effects of the type of amines for the CO2 capture, and analyzing from a basis to the performance of synthesized amino-functionalized CO2 adsorbents. The all reaction was performed at least three times to verify the reproducibility of the reaction through the XPS wide-scan and the XPS high resolution spectra. The nitrogen amount of amino-functionalized silica particles was obtained using an elemental analyzer. CO2 adsorption-desorption measurements for amino-functionalized silica particles were performed using thermogravimetric analyser (TGA).
The adsorbed CO2 is easily desorbed from the adsorbent with the low energy consumption in the order of 3o, 2o, and 1o amino-adsorbents while the adsorption amount and the bonding-affinity increase in the reverse order. This work on the CO2 adsorption on 1o, 2o, and 3o amino adsorbents lays the foundation for potential applications to design various CO2 adsorbents efficiently. Based on these results, polyamines consisting of only primary amines were synthesized on the surface of porous silica particles, and exhibited the high amount of CO2 adsorption.

Metal-organic frameworks (MOFs) are crystalline porous materials consisting of metal ions or clusters linked by organic molecules. Owing to their high surface area, adjustable pore size and dimensions, and tuneable properties, MOFs have been explored for many potential applications. One of the most promising applications is gas storage or capture, with gases such as methane, carbon dioxide and hydrogen. In addition, they can be used in molecular separations, catalysis, thin-film devices, biomedical imaging, drug storage and delivery etc. The study of thermal stability of MOFs under various gas atmospheres such as methane, carbon dioxide, and hydrogen is presented in this paper. Our interest is in investigating the decomposition products and temperatures of the MOFs in order to obtain a better understanding of the framework robustness. This should allow future syntheses of MOFs to be tailored better to give the characteristic properties required and hence allow preparation of materials with enhanced performance. Firstly, the thermal stability of some well-known MOFs such as ZIF-8 will be studied under an inert atmosphere and then under some more reactive atmospheres such as hydrogen, methane and carbon dioxide. The decomposition temperature will be determined using thermogravimetric analysis and the decomposition products will be characterised by mass spectrometry. Secondly, novel MOFs containing silicon based linking molecules will be investigated using the same techniques.^1,2 These linking molecules are more synthetically accessible than their carbon-based analogues and their chemical and structural properties can be modified to allow synthesis of a range of novel Si-containing MOFs.
(1) R. P. Davies, R. Less, P. D. Lickiss, K. Robertson, and A. J. P. White, Crystal Growth & Design, 2010, 10, 4571-4581.
(2) R. P. Davies, P. D. Lickiss, K. Robertson, and A. J. P. White, CrystEngComm, 2012, 14, 758-760.

Synthesis of photoactive materials has recently turned in a new direction, driven by the desire to design architectures in nanoscale with specific chemical functionalities. Recent researches in photoactive composites have been focused to increase the photoactivity performance by means of nanostructuring and electronic modification. Last years, a wide range of chemical reactions using microwave heating have been reported. The microwave assisted synthesis is a green chemical route to produce toxic-free materials for many technological branches and a power growth technique that allow synthesized faster and more efficient than the traditional methods used on the industry today.
In this work, semiconductor nanoparticles-zeolite composites were synthesized as photoactive materials. Different zeolite-like powders were synthesized via Sol-Gel variation method using solutions of Na2SiO3 and Al2(SO4)3 as a gel precursor. The synthesis was carried out in an Anton Paar Synthos 3000 microwave oven at different temperature conditions (from 393 to 500 K) during 6h. ZnS nanoparticles were grown via ion exchange by using zinc nitrate [Zn(NO3)2] solutions, and warmed up by microwave radiation; then, the samples were dehydrated at 623 K for 24 h and finally sulphurized with H2S atmosphere at room temperature for 48 h. Morphological, structural and chemical properties of the composites were characterized by X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy, electron diffraction, energy dispersive X-Ray spectroscopy, and isothermal nitrogen adsorption. Spectral-Optic responses were characterized by UV-Vis absorption, infrared, and Raman spectroscopies. In dependence of the process temperature and the reaction time, powders with different morphologies and grain sizes were obtained. An evolution from nanocrystallines to crystalline materials is discussed in dependence of process parameters. Photoactive performance attributable to ZnS nanoparticles grown and homogeneously dispersed on zeolite matrix, can be modulated by the control of the zinc and sulfur concentration in the ion exchange solutions.
The authors thank to E. Aparicio, F. Ruiz, and I. Gradilla, for their technical assistance. Support from CoNaCyT (Grant 127633 and 102907) and DGAPA-UNAM (Grant IN113312) is acknowledged.

Metallic foams have recently attracted significant attention for service in functional applications such as a substrate for catalytic reaction, sensing, heat exchanging application, etc., owing to their high surface area. In particular, nanoporous metallic foams with an exceptionally high specific surface area can be a perfect solution for those applications. Indeed, the latest research has paid much attention to the processing and characterization of nanoporous noble metallic foams (Pt and Au) through the conventional dealloying technique. On the other hand, this study proposes a new and innovative method of processing nanoporous non-noble metallic foams: A technique that combines the conventional electroless plating with three-dimensional proximity-field nanopatterning. The nanoporous non-noble metallic foams processed and characterized include copper, nickel, and tungsten foams.

Aluminum is among the most significant lightweight metals worldwide. Together with copper as alloying addition high tensile ultimate stresses can be obtained, compared with pure aluminum. Furthermore AlCu compounds belong to the heat-treatable alloys, along this aging process coherent precipitates are formed. Depending on the aging time those precipitates consist of single layer copper disks, so called Guinier-Preston-1 (GP-1) zones, several layers of GP-1 zones which form the GP-2 zones and later on the semi-coherent Θ&’ phase and finally the incoherent Θ phase. The influence of the GP-1 and GP-2 zones on the stress-strain behavior is investigated via atomistic simulation. Molecular Dynamics (MD) simulations were performed for single and polycrystalline nanocrystals. The simulation package IMD (ITAP Molecular Dynamics) [1] is applied to investigate the tensile behavior of the systems made from these practically relevant alloys. The grain size varies up to diameters of 50nm. Our systems contained up to 500 grains, therefore we obtained simulation samples with over 40 million atoms. We analyzed the influence of several parameters of the GP-zones, such as amount of zones per grain, type of zone and different radii. The study of grain size effects is a further focus of the present work. Hence, the results obtained were compared to each other and with simulations of the tensile behavior of single crystals.
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We demonstrated the combination of QDs (e.g. CdTe and InP) and ZnO nanowires for photoelectrochemical water splitting. Employment of QDs in water splitting system has major advantage. The efficiency for water splitting reaction can be exactly measured in aqueous system without sacrificial reagents. The maximum photoconversion efficiency of 1.83% was observed at an applied potential of ~ 0.25 V. Moreover, the photocurrent response were almost identical for 50 cycles, which was demonstrated very good stability of this structure and used as photoanodes were relatively stable in the photo-oxidation process in aqueous solution. The utilization of gold nanord-ZnO nanostructure photoelectrode exhibited a maximum photoconversion efficiency 3.9% for water splitting in neutral medium, which is more than approximately 110% higher than that of traditional Pt electrode. Several strategies have been successfully employed to reveal plasmonic-inducing effects under solar irradiation, indicating that coupling of plasmonic-inducing hot electron and electromagnetic field can effectively increase the probability of photochemical reaction in water splitting.

At the nanoscale, MoS2 exhibits excellent turnover frequencies for the hydrogen evolution reaction (HER) due to the presence of undercoordinated edge sites with high catalytic activity. In order to achieve high electrode current densities, the density of these edge sites must be increased and vertically integrated into a conductive architecture. In this paper, we will describe several synthesis routes to produce interesting nano-architectures of MoS2, including nanowires, mesoporous structures, as well as nanoparticles. We will describe how one can control the atomic-scale features of the surface by directing the morphology of the material at the nano-scale. We will also describe how the different features factor into electrocatalytic activity for H2 evolution, in some cases yielding extremely high activity within 100-200 mV of the best precious metal catalysts, in a stable manner. We also present strategies as to how to engineer architectures that eliminates charge transport limitations. We also describe impacts of nano-structure on optical absorption properties as well as electronic band structure. Finally, we discuss how surface states can be both beneficial and detrimental simultaneously toward photoelectrochemical water-splitting.

We report an atmospheric, cost-effective and scalable flame synthesis method for the growth and doping of metal oxide nanowires and these nanowires (NWs) exhibit superior photoelectrochemical (PEC) performance due to their high crystallinity, great morphology tunability and chemical composition control. First, arrays of tungsten trioxide (WO3) NWs are synthesized on fluorinated tin oxide (FTO) coated glass substrates by rapid, atmospheric flame vapor deposition, in which a flame oxidizes and evaporates tungsten metal to produce tungsten oxide vapors that condense onto a colder FTO substrate with tunable morphologies of NWs. Importantly, the WO3 NWs synthesized by flame have higher areal number density and longer length than state-of-the-art WO3 NW photoanodes grown by chemical vapor deposition and hydrothermal methods, resulting in stronger light absorption and doubled saturation photocurrent. Second, the flame synthesized WO3 NWs are further coated with thin BiVO4 shells to form a core/shell heterojunction NW array. The WO3/BiVO4 heterojunction NW array utilizes the individual strengths of WO3 (good electron transport) and BiVO4 (strong light absorption) and outperforms all other WO3 or BiVO4-based photoanodes in the literature, regardless of doping, heterojunction, or catalyst. Finally, we report a novel ex-situ method to codope rutile TiO2 with (W, C) pair by sequentially annealing tungsten (W)-precursor coated TiO2 nanowires in flame and CO. The unique advantages of the flame annealing are that the high temperature and heating rate of flame enable rapid diffusion of W into TiO2 that prevents the damage of TiO2 nanowire morphology and crystallinity, and the delicate glass substrate. Significantly, this is the first experimental demonstration that the codoped TiO2:(W, C) nanowires doubles the saturation photocurrent of undoped TiO2 for PEC.

A device with 10% solar-to-hydrogen (STH) conversion efficiency and lasting for 10 years was referred as the “Holy Grail” of chemistry [1], and is still a significant challenge for photoelectrochemical (PEC) water splitting.
While metal oxides based photoelectrodes may be stable in aqueous solutions, key issues are wide band gap, band-edges mismatch and their low STH efficiencies. A combinatorial screening could be a relevant approach to search for metal oxides with suitable band gap [2]. Moreover, different tandem cells [3-6] have been developed to solve the band-edges mismatch of metal oxides. The intrinsic low STH efficiency, the biggest hurdle, can be related to wide band gap, absorption, charge mobility, recombination, interfacial kinetics, etc. To overcome, approaches should consider many aspects, including band gap engineering, quantum confinement, doping and co-doping, nanostructuring, and catalyst, etc.
On the other hand, semiconducting materials like III-V have suitable band gaps and high STH efficiencies. The band edge mismatch was successfully solved by a monolithic p-GaInP2/n/p-GaAs PEC-PV tandem cell device demonstrating a 12.4% STH efficiency [7]. However, the trade-off is the stability of III-V materials in aqueous solution. We at NREL tested the III-V material in different solutions to investigate the photo-corrosion and to extend the durability of the top layer. Different techniques were used to analyze the surfaces and the tested solutions. Different surface modification methods including coating, ion bombardment and surface nitridation were tested for protecting the III-V. A combined surface treatment, both solid and electrolyte, may be required to approach the “Holy Grail”.
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Hydrogen production from water is one of the most promising methods to secure renewable sources for energy in general and chemical industry in particular. There are many methods for producing hydrogen from water and these include reducible oxide materials (solar thermal material) [1], combined PV/electrolysis [2,3], artificial photosynthesis [4] and photocatalysis[5]. At present about ½ of the total amount of hydrogen produced in the world (30 million metric tons/year) is used in the ammonia synthesis process. If humanity can succeed in making hydrogen from water, ammonia and therefore fertilizers will be made from totally renewable sources. In this work we are comparing two methods for making hydrogen from water one based on oxidation/reduction cycles of reducible oxides (solar thermal) and the other photocatalytic using Au-Pd/TiO2 catalysts. The extent of reduction of Ce4+ to Ce3+ has been found to be dramatically enhanced by the incorporation of U4+ cations within the CeO2 fluorite structure [6,7]. The reasons for these are at present investigated at the experimental level using core and valence level spectroscopy and computational study using Density Functional Theory with PBE exchange-correlation functional and onsite Coulomb correction (GGA+U) to describe the localized electronic states of Ce ions. Evidence of increased charge localisation around Ce3+ cations is seen upon mixing with U4+ cations as well as a considerable decrease in the oxygen vacancy formation energy. Photocatalytic reactions are also studied where the plasmonic effect of Au together with the synergistic effect of both phases of TiO2 (rutile and anatase) [8,9], have resulted in considerable enhancement of hydrogen production.
[1] W. C. Chueh, C. Falter, M. Abbott, D. Scipio, P. Furler, S. M. Haile, A. Steinfeld, Science, 330, 1797 (2010)
[2] An introduction to energy sources; National Centre for Catalysis Research, Department of Chemistry, Indian Institute of Technology, Madras, India (ebook)
[3] J. R. Thompson, R. D. McConnell, M. Mosleh, Cost analysis of a concentrator photovoltaic hydrogen production system, International Conference on Solar Concentrators for the Generation of Electricity or Hydrogen, 1-5 May 2005, Arizona (NREL/CD-520-38172).
[4] A. Sartorel, M. Carraro, F. Maria, T. M. Prato, M. Bonchio, Energy Environ. Sci. 5, 5592 (2012).
[5] M. Murdoch, G.W.N. Waterhouse, M.A. Nadeem, M.A. Keane, R.F. Howe, J. Llorca, H. Idriss, Nature Chem. 3, 489 (2011).
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[8] Idriss, H; Wahab, A.K., European Procedure (12CHEM0012-EP-EPA) filed at the Patent Office on 03-09-2012 as Serial Number 12006217.9. (2012)
[9] K. Connelly, H. Idriss, Materials for Renewables and Sustainable Energy, in press, 2012.

The unrestrained combustion of fossil fuels has resulted in vast pollution at the local scale throughout the world, while contributing to global warming at a rate that seriously threatens the stability of many of the world's ecosystems. Solar photovoltaic (PV) technology is a clean, sustainable and renewable energy conversion technology that can help meet the energy demands of the world&’s growing population. Although PV technology is mature with commercial modules obtaining over 20% conversion efficiency there remains considerable opportunities to improve performance. The nearly global access to the solar resource coupled to nanotechnology innovation-driven decreases in the costs of PV, provides a path for a renewable energy source to significantly reduce the adverse anthropogenic impacts of energy use by replacing fossil fuels. This study explores several approaches to improving PV efficiency with nanotechnology: optical enhancement, microstructural optimization for electronic material quality and increasing the spectral response via bandgap engineering. Recent progress in these approaches is summarized with examples using 3rd generation PV materials and thin film PV devices. The results and impediments to widespread deployment and commercialization are discussed including technical viability, intellectual property laws and licensing, material resource scarcities, and economics. Future work is outlined and conclusions are drawn to overcome these limitations and improve PV device performance using methods that can scale to the necessary terawatt level.

Dye-sensitized solar cells (DSCs) are promising next-generation alternatives to conventional silicon-based photovoltaic devices owing to their low cost, easy fabrication, and environmental friendliness. Although great progresses have been developed on DSCs, further improving the conversion efficiency is still an important task for commercialization of this kind of solar cell as power generation devices. It is well known that the conversion efficiency of a DSC usually depends on three major parameters: short circuit density (Jsc), open circuit voltage (Voc) and fill factor (FF). In this presentation, our work on improvement of these important parameters for higher conversion efficiency is introduced.
We investigated the principle of dye-sensitized solar cells (DSCs) with an equivalent circuit model by electrochemical impedance spectroscopy (EIS). On the basis of the analyses of this equivalent circuit model, researches aimed at achieving high efficiency were carried out. To increase Jsc, we developed new dyes with high molar extinction coefficient to improve the light harvesting efficiency, and synthesized aggregation free dyes preventing aggregation of dyes to enhance the electron collection efficiency. To increase Voc, new co-adsorbents were developed to reduce interfacial charge recombination at the TiO2 surface and improve shunt resistance.
Finally, we report our new achievement on higher Jsc, Voc, and FF in the DSC with black dye and a new co-adsorbent. An overall conversion efficiency of 11.4% was achieved which is the highest certified efficiency.

One dimensional (1D) noble metal nanostructures represent a key new structural paradigm in the ongoing quest for designing and constructing effective electrocatalysts with high activity and durability. Despite increasing interest in the use of these uniquely anisotropic catalysts, there has been a surprising lack of effort expended in thoroughly and rationally examining the influence of various physicochemical properties of 1D electrocatalysts with respect to their intrinsic performance. In this presentation, we address this important issue by investigating and summarizing recent progress aimed at precisely deducing the nature of the complex interplay amongst size, chemical composition, and electrocatalytic performance in high-quality elemental and bimetallic 1D noble metal nanowire systems. The fundamental insights acquired are then utilized to discuss future and potentially very exciting new directions towards the continuous improvement and optimization of 1D catalysts.

Scanned nanopipettes have undergone a period of tremendous development over the past decade, with research scaling down from the micrometer to the nanometer regimes and finding application in materials science. These probes are at the heart of the scanned ion conductance microscope (SICM). In this presentation, I will describe the development and application of highly localized SICM-type probes for materials science research, focusing in particular on localized electrochemistry and discussing implications for energy related systems. Various operational modes will be considered, and the robustness and flexibility of the techniques will be detailed, including the characterization of material interfaces, ion exchange, polymer membranes and fuel cell catalysts.

ZnO-X alloys reveal intriguing material properties. Incorporation of X = GaN or InN in ZnO narrows the energy gap. Although the incorporation implies broken crystalline symmetry and semi-local band states, the strong exciton peak of ZnO is not diminished. Moreover, the presence of InN-like nanoclusters enhances the effect on the electronic structure and significantly narrows the band gap. Hence, by properly growing and designing ZnO-X, the compound can be suitable for a variety of novel integrated nano-systems. Ref: M. Dou, G. Baldissera, and C. Persson, Int. J. Hydrogen Energy (2013), accepted; ibid J. Cryst. Growth 350, 17 (2012).

A novel and greener fuel to replace foundry coke in cupolas was developed using nanotechnology from waste anthracite fines briquetted with Si-containing materials such as silicon metal and bio-based waste products such as rice hull ash or raw rice hulls, lignin and collagen. When the briquettes were treated under carbothermal reduction conditions to simulate the cupola preheat zone, silicon carbide nanowires (SCNWs) were formed. The SiC nanowires formed as meshes during high temperature pyrolysis to maintain the mechanical strength of briquette. Progressive thermal tests exhibited that the formation of the SCNWs started from 1100°C but favored at 1400°C. No extra metal catalyst was needed for the growth of the SCNWs. Characterizations were performed by XRD, SEM, EDS, TEM, and SAED. The SCNWs were 30-60 nm in diameter and were typically grown by stacking the (1 1 1) lattice plane of 3C-SiC along the [1 1 1] direction. Many non-epitaxial branches of the nanowires were also formed through this one-step process as observed by TEM. The results suggest that the SCNWs were most likely grown through the vapor-solid mechanism. The formation of SiC nanowires is crucial to the mechanical integrity of the briquette during high temperature pyrolysis for complete burning of anthracite fines and bio-based products to generate high temperatures for melting of metal ores. Experimental results confirmed that the redox level of the Si source significantly affected the formation of SiC. Using zerovalent silicon led to ideal redox conditions for the formation of SCNWs. In a full-scale demonstration, bricks made from anthracite fines and zerovalent silicon successfully replaced a part of the foundry coke in an actual cupola. In addition to saving in fuel cost, replacing coke by waste anthracite fines can reduce energy consumption and CO2 and other pollution associated with conventional coking as the coke is produced by pyrolyzing bituminous coal at 1000°C for 16-36 hours wasting about 20% of coke&’s energy and leading to CO2 emissions. The development of the above new fuel source involves nanotechnology while saving energy and the environment for a sustainable future.

Extensive research on fuel cell stack materials has led to advances in lower cost, high performing materials. With the decrease in the cost of stack materials, lowering the cost of the balance of plant (BOP) components has increased in importance. In order to decrease the overall cost of the automotive and stationary fuel cell systems and make them as competitive as possible, low-cost system component materials that provide similar function, performance and durability are needed. However, intelligently selecting low cost materials for application in polymer electrolyte membrane fuel cell (PEMFC) systems requires understanding the potential adverse effects that system contaminants may have on the fuel cell performance and durability. Limited work in this area has been conducted to-date [1-7].
Families of material chosen for the study include structural materials, elastomers for seals and (sub)gaskets, and assembly aids (adhesives, lubricants). Furthermore, different grades of BOP materials, containing different polymer resin grades and additives from different manufacturers were selected for this study.
The contaminants can come from the parent polymer material or the additives that were added to provide specific physical properties, such as glass fiber for structural reinforcement. Hence, it is important to determine what species leached out of the BOP materials, where the contaminating species come from, their impact on fuel cell performance, and whether the contaminating species can be removed or substituted via communication with the supplier manufacturer. These results would help the fuel cell industry in selecting appropriate BOP material for fuel cell applications.
To quantify the impact of system contaminants on fuel cell performance, many prospective fuel cell system relevant BOP materials were screened, using a suite of ex-situ and in-situ techniques. This talk will give a general overview of the results for the assembly aids materials as well as focus on the catalytic effect of selected assembly aids materials.
The authors would like to acknowledge funding from the U.S. Department of Energy under Contract No. AC36-08GO28308 and collaborations with colleagues at GM.
References
[1]. O&’Leary, K. A., B. Lakshmanan, and M. Budinski, “Methodologies for Evaluating Automotive PEM Fuel Cell System Contaminants”, Canada-US PEM Network Research Workshop, February, 16, 2009.
[2]. O&’Leary, K. A., B. Lakshmanan, “Methods for Screening Balance of Plant Materials for Fuel Cell Contamination”, 2010 Fall ECS Meeting.
[3]. Guo, Q., R. Pollard, and J. Ruby, "Compatibility and Durability of Fuel Cell Materials", ECS Transactions, 2007. 5(1): p. 187-196.
[4]. Tan, J., et al., "Degradation of elastomeric gasket materials in PEM fuel cells", Materials Science and Engineering: A, 2007. 445-446: p. 669-675.
[5]. Macomber, C.S, et al, Characterizing polymeric leachants for potential system contaminants of fuel cells, ECS Transactions 2010, 33(1) 1637-1643.
[6]. Wang, H., et al, Evaluating polymeric materials as potential sources of PEMFC system contaminants, ECS Transactions 2010, 33(1) 1617-1625.
[7]. H.-S. Cho, M. Ohashi, and J. W. Van Zee, “The Effect on PEMFC Contamination of Functional Groups of Some Organic Contaminants,” ECS Transactions, 2011, 41 (1), 1487-1499

Sustainability implies a rationale and more effective use of energy. In this respect, fuel cells can play a major role since this technology allows producing power with the largest efficiency. In addition, the efficiency of fuel cells does not depend on size, which allows deployment in small scale power applications, including powering of portable devices. In particular, solid oxide fuel cells may offer the additional advantage of fuel flexibility, due to the higher operating temperature with respect to the other fuel cell technologies.
In this framework, the development of micro-solid oxide fuel cells (SOFCs) open new scenarios for portable unit power generation. Micro-SOFCs are likely to produce energy densities per volume and specific energy per weight up to four times larger than state-of-the-art batteries. Reducing the operation temperature is critical for practical use of miniaturized SOFCs and can be achieved using thin-film electrolytes. Pulsed laser deposition (PLD) is very promising for the fabrication of tailored oxide thin films, because it allows to obtain single crystal or polycrystalline films, with tailored microstructure from dense to highly porous. A rapidly growing attention is being directed towards the investigation of the ionic conducting properties of oxide thin films and hetero-structures. Experimental evidence has been reported showing that interfacial phenomena at hetero-phase interfaces, including film-substrate interfaces, give rise to faster ion conduction pathways than the bulk or homo-phase interfaces. This has been ascribed either to the building up of space charge regions at the interfaces or to interfacial strains derived from the lattice mismatch between the two adjacent materials. However, controversial results have been reported: in some cases the nature of the ionic carriers has been questioned, or the presence of strains did not enhance the ionic conductivity. These findings show the need of a deeper understanding of the interface transport properties to unravel the interfacial conduction mechanisms.
This talk will present the recent efforts performed in our lab towards the PLD fabrication of ionic (both proton or oxygen-ion) conducting oxide thin films and superlattices, and their electrochemical characterization to clarify the causes for enhanced ionic conductivity at oxide hetero-interfaces.

LiquiScan-ES is a versatile nanoparticle sizing system that relies on first-principle size analysis to determine the particle size distribution of nanoparticles in the range of 2.5 to 1000 nm. This mature technology neutralizes droplets produced from an electrosprayed suspension, resulting primarily in singly-charged particles. The sizing of nanoparticles in the aerosol state is accomplished by differential mobility analysis in an electrical field, followed by subsequent detection by condensation particle counting.
The advantages of the LiquiScan-ES system include rapid and reproducible sample analysis, in addition to high resolution, sensitivity, and accuracy in comparison with standard analytical methods. The shear stress exerted during electrospraying is minimal relative to that required to break up aggregates, making the LiquiScan-ES well-suited for measuring aggregated samples. This technique is also independent of the optical properties of the particle and solvent, and can produce an accurate measurement of multimodal distributions, making it a powerful alternative to light-scattering techniques. LiquiScan-ES has proven to be a valuable tool for analyzing and quantifying particles such as metals, metal oxides, polymers, and aggregates. Particle size distribution measurements of SiO2 nanoparticles are presented, demonstrating the high-resolution sizing and concentration quantification capabilities of LiquiScan-ES.

Iron-containing nanomaterials are mainly consisted of zero-valent iron (ZVI is currently a classic term, as well as NZVI (nano zero-valent iron)), iron nanoalloys or core-shell nanoparticles, and oxides, among others, such as, for example, ferrites. Iron typically exists in the environment as iron(II) and iron(III)-oxides. Iron oxides is also a collective term for oxides, hydroxides, and oxy-hydroxides composed of Fe(II) and/or Fe(III) cations and O2- and/or OH- anions. Sixteen pure phases of iron oxides, i.e., oxides, hydroxides or oxy-hydroxides are known to date. The nanomaterials on their basis are used for remediation of organic contaminants (chlorine-containing pollutants, benzoic and formic acids, dyes) and inorganic cations (Zn(II), Cu(II), Cd(II) and Pb(II)) and anions (nitrates, bromates, arsenates), as well as water disinfection (against viruses and bacteria).
In this work, we have prepared NZVI and iron oxide nanoparticles by soft “greener” methods starting from iron salts as precursors and a series of natural plant extracts in 1) room temperature conditions and 2) by hydrothermal-microwave method (equipment MARS-5). The prepared materials were characterized by electron microscopy techniques and applied for water disinfection against E. Coli. The results have shown more than 90-95% elimination of bacteria from water.
References
Boris I. Kharisov, Rasika Dias, Victor Manuel Jimenez-Perez, Oxana V. Kharissova, Betsabee Olvera Perez, Blanca Muñoz Flores. Iron-containing nanomaterials: synthesis, properties, and environmental applications. RSC Advances, 2012, 2, 9325-9358.
Li, Q.; Mahendra, S.; Lyon, D.Y. ; Brunet, L. ; Liga, M.V. ; Li, D. ; Alvarez, P.J.J. Antimicrobial nanomaterials for water disinfection and microbial control: Potential applications and implications. Water Research, 2008, 42, 4591-4602.

Alkyl CyanoAcrylates are highly reactive acrylic functional monomers undergoing very fast anionic polymerizations in the presence of traces of weak bases. Poly-Alkyl CyanoAcrylates are FDA approved materials for biomedical applications, such as tissue adhesives and raw materials for drug delivery systems (mainly nanoparticles). Despite the attractive final properties of these materials, extremely high reactivity and very fast degradation rates limit their uses. Recently, the possibility to copolymerize Alkyl CyanoAcrylates with Methacrylates by free radical polymerization disclosed new opportunities towards controlling such polymers degradation rates. In the first part of this work the anionic polymerization of n-Butyl CyanoAcrylate (BCA) has been studied in detail in order elucidate its underlying kinetic mechanism. This analysis was carried out in order to suppress such parasitic reaction during the free radical polymerization. Namely, the living characteristic of the anionic polymerization of BCA has been confirmed using different initiators. The produced polymers samples were characterized by GPC as well as MALDI-TOF and different compounds (such as dichloroacetic acid) have been experimentally established as effective to prevent the anionic polymerization.
Since no experimental data are available in the literature for this monomer pair, the reactivity of BCA and Methyl Methacrylate (MMA) has been firstly investigated through ab initio simulations. The estimated values of the reactivity ratios (r_BCA=0.40 and r_MMA=0.009) have been used to guide the experimental investigation of the system. An experimental kinetic study was then carried out and the copolymer composition data and reaction rates were measured by NMR, GPC and MALDI TOF. Interestingly, it has been found that the computational results are in remarkably agreement with the experimental ones.
Finally, a series of copolymers with different composition were synthesized through free radical solution polymerization in DMF. The produced copolymers have been fully characterized and then used to prepare nanoparticles (NPs) through a nanoprecipitation process. The polymer degradation behavior has been studied in vitro in different solutions of biological interest (isotonic solution, PBS solution) and the effect of MMA content on the degradation process has been characterized. Finally, biocompatibility and degradation behavior of the nanoparticles have been studied in in vitro experiments. Specifically, PBCA-based NPs were loaded in human fetal amniotic fluid derived stem cells characterized by high proliferative rate. Flow cytometric analyses of the main biochemical parameters (apoptosis and cell cycle) as well as cell proliferation and metabolic rate assessed the biocompatibility of NPs. These data also sustain the possible use of these materials for stem cell housing/culture.

In various industrial productions, volatile organic compounds (VOCs) are massively used and included in reagents, solvents, additives, intermediates, or even final products. VOCs are typically dangerous, explosive, flammable, toxic, and environmental hazardous. Therefore, real-time detection of the VOCs storage, transport or usage is hence important which ensures the safety of human health and human properties and also avoids environmental disasters.
Numerous methodologies have been applied to commercial VOCs sensors such as semiconductor sensing, catalytic combustion, electrochemistry sensing, infrared sensing, etc. However, according to our investigation most of the sensors are extremely expensive, e.g. an infrared sensor costs over 130,000 U.S. dollar. Specifically, to our best knowledge there is no commercial VOC senor to date that can be massively equipped anywhere such as each joint between transporting pipes or each switch of storage tanks which are all high risky regions of VOC leakage.
The present work demonstrates a high efficient and low cost sensor for sensing volatile organic compounds (VOCs). We utilize conjugated polymer/nanoparticles blends to sense various VOCs by detecting the variation of optical properties. The three dimensional nanomorphology of the as deposited film through fast drying process is relatively unstable due to the limited time for molecular ordering. Therefore, the exposure of organic solvent vapors can lead to the rearrangement of thin film nanomorphology and thus results in the change of optical properties. This methodology is widely applicable in different conjugated polymer/nanoparticle blend or hybrid materials, including commercially available materials such as P3HT/PCBM, or our own developed materials PBCN/PCBM, PBCN/Cu2S nanoparticles. The sensing effect is quantified herein with different VOCs in different concentrations and exposure time as a comprehensive database. The detecting limit of the sensor has achieved the permissible exposure limits (PELs) ruled by Occupational Safety and Health Administration (OSHA), U.S.A.. We have practically fabricated a device to exhibit the practical sensing of VOCs by transferring the optical signal variation to electronic signals. A recorded movie demonstrated that under the condition of 50 ppm chloroform vapor, the alarm can be delivered within 3 minutes. It indicates that real-time sensing is achievable based on the instant response and detectable low concentration of VOCs&’ vapor down to ppm level. The developed sensor features high sensitivity, high accuracy, quick response, broad sensing range, and very low cost. Furthermore, it is easy of fabrication into a sensing chip and can be placed anywhere such as pipe joints and tank switches that are high risk of VOCs leakage. The demonstrated low cost and high efficient VOCs sensor significantly advance the current technology of protecting human and environment from risky damage of VOCs.

Due to the rising number of applications using carbon nanotubes (CNT) in aqueous solutions it has become a key issue to investigated their cytotoxicity. We have investigated this factor through the study of interactions of CNT with model bacteria of different strains, namely 4J6 (marine), Pseudomonas PAO1 (medical), Escherichia coli and salmonella (food). Bacteria have been grown on the one hand onto gelose in aqueous medium with different concentrations of CNT (1.2, 2 et & 4 mg.L-1) and on the second had onto CNT random networks sprayed layer by layer from aqueous solution of CNT of different concentration (0, 4, 8, 12, 16, 20, 40 mg.L-1). Both bacteria adhesion (after washing) and growth were observed by laser confocal scanning microscopy (LCSM). The impact of CNT on bacteria adhesion and growth is found to depend on both bacteria strain and CNT concentration. First results show that the marine bacteria 4J6 is more sensitive than the others to CNT. Nevertheless the mechanisms of growth or adhesion of bacteria due to their interactions with CNT is not fully understood. It may be related to the strength of bacteria membrane as suggested by some authors [1].

1. S Liu, L Wei, L Hao, N Fang, MW Chang, R Xu, Yanhui Yang, Yuan Chen, ACS Nano, 2009, 3, 12, 3891-3902

Three topics of the author&’s own research are selected and summarized to illustrate the breath of nanotechnology, in particular the variety of nanostructured materials, on the development of sustainable energy technologies. These three technologies are light-emitting diodes with quantum dot-polymer nanocomposites, anti-fogging coatings with self-similar porous nanostructures, and photocatalytic hydrogen production with disorder-engineered nanocrystals.

Inorganic-organic nanohybrids contain inorganic as well as organic constituents. Thus, such hybrid can be established by an inorganic cation and an organic anion. While the organic anion entails certain functionality (e.g., gas separation, luminescence, pH indication), the inorganic cation guarantees for nucleation of an insoluble hybrid compound that can be precipitated as a nanoparticles [1]. In sum, inorganic-organic hybrids comprise the best of two world&’s - inorganic and organic materials. The underlying concept is illustrated below with two examples:
1. The nanohybrid Mg(AEP)(H2O) [2] (AEP: aminoethylphosphonate) is formally composed of the inorganic cation [Mg]2+ and the anionic amine [AEP]2-. This inorganic-organic hybrid exhibits a particle diameter of 20 nm and shows reversible CO2 sorption (152 mg/g) at high pressure (le;120 bar). In contrast, the N2 uptake remains below 1 mg/g over the complete pressure range (1-120 bar). Based on this CO2:N2 selectivity (~100%), Mg(AEP)(H2O) may expand the range of materials available for CO2 sorption and sequestration.
2. The nanohybrid ZrO(FMN) [3] (FMN: flavine mononucleotide) is formally composed of the inorganic cation [ZrO]2+ and the fluorescent dye anion [FMN]2-. ZrO(FMN) nanoparticles exhibit a diameter of 50-60 nm and show intense green fluorescence when excited with UV-light or via blue-light of an LED. As the [FMN]2- anion represents an intrinsic constituent of the compound, it is available in molar quantities - thus, allowing for intense spot-light emission of each single nanoparticle. While the synthesis of ZrO(FMN) can be performed in water, the biocompatible nanoparticles can be ideal as a fluorescent marker for medical purposes. Other emission colors (blue, red, infrared) are possible based on hybrid nanoparticles containing other fluorescent dyes, and will be presented, as well.
This presentation will address inorganic-organic nanohybrids as a general concept. Different compositions as well as different properties will be discussed (e.g., gas sorption and gas sequestration, fluorescent nanoparticles, drug-delivery).
References
[1] H. Goesmann, C. Feldmann, Angew. Chem. Int. Ed. 2010, 49, 1362minus;1395 (Review).
[2] P. Leidinger, S. Simonato, C. Feldmann, Chem. Commun. 2012, 48, 7046-7048.
[3] M. Roming, H. Lünsdorf, K. E. J. Dittmar, C. Feldmann, Angew. Chem. Int. Ed. 2010, 49, 632minus;637.

Efficient, reproducible low cost methods for preparation of highly complex nano-materials is a requisite for practical application in many areas of sustainable energy conversion and storage, such as photo-catalysts for H2 and fuel production, solar cells, solar thermal absorbers, batteries, low friction coatings for efficient transmission of mechanical energy and corrosion resistance. Solution based processing routes allowing for designed multi-phase, multi-elemental nano-materials in one or few steps are probably the best suited for achieving this. Here we describe two approaches to solution based synthesis of complex oxides, metals and nano-composites; (A) Metal alkoxides yielding pure complex composition oxides as nano-particles, thin or ultra-thin films and coatings, core-shells, wires and mixed nano-phase materials. Precursors and synthesis routes to different oxide systems relevant for energy materials will be described including doped and non-doped Fe2O3, TiO2, ZnO, WO3, spinels and perovskites. The use of purely alkoxide based routes provide many beneficial possibilities such as formation of pure CoFe2O4 spinel at <300oC, doping levels beyond the thermodynamic range for e.g. Co doped ZnO, as well as oxide formation at down to room temperature and ultra-thin oxide coatings on wires and nano-structured electrodes. The influence of the choice of precursor and processing parameters on the target oxide purity and structure will be discussed. (B) Low-cost routes based on metal salt complexes have been developed that yield thin or ultra-thin films and coatings, core-shells, and sponge or foam-like materials. Many useful structures have been prepared with these routes including: nano-structured metals and alloys with <10 nm Co crystallites in films and sponges, down to 1 nm ultra-thin Ni coatings on wires and nano-structured oxide electrodes as well as metal-in-ceramic composite films and thin or ultra-thin coatings on wires and porous oxide electrodes with a wide range of metals (Ni, Co, Cu, Ru, Pthellip;) and oxide matrixes, having particle sizes down a few nm and loadings up to >80%. The processes have been up-scaled to large industrial or pilot 50 m roll-to-roll scale, with the former resulting in superior hardness/toughness WC-Co mining and excavation tools and the latter in record efficiency spectrally selective solar thermal absorbers with Ni-Al2O3 films. The Ni-Al2O3 composites have also been proven for methane activation in the dry-reforming reaction of CO2 + CH4 to CO + 2H2, which requires all sub 6-9 nm sized Ni particles to avoid carbon filament growth deactivating the catalyst.

This presentation is aimed at underlying the principles, synthesis, characterization and applications of inorganic nanotubes (INT) and fullerene-like (IF) nanoparticles (NP) from 2-D layered compounds. While the high temperature synthesis and study of IF materials and INT from layered metal dichalcogenides, like WS₂ and MoS₂ remain a major challenge, progress with the synthesis of IF and INT structures from various other compounds has been realized, as well. Scaling-up efforts in collaboration with "NanoMaterials" resulted in multikilogram production of (almost) pure multiwall WS₂ nanotube phases and commercial production of “industrial grade” IF-WS₂ nanoparticles.
IF-MS₂ (M=W,Mo, etc) were shown to be superior solid lubricants in variety of forms, including an additive to various lubricating fluids/greases and for various self-lubricating coatings. Doping of the IF nanoparticles with Re atoms produced negatively-charged IF nanoparticles which exhibit very low friction and wear. Following scaling-up efforts, initial commercialization of products based on this technology have taken place in the automotive, aerospace, food, machining and other industries. New potential applications have been realized, e.g. in the field of medical technology. Major progress has been recently reported with polymer nanocomposites reinforced with both carbon nanotubes and IF-WS₂ nanoparticles.

Our current objective is the realization on surfaces of self-assembled molecular architectures specifically designed to exhibit specific properties resulting from their nanometric structure.
This is why we developed a strategy aimed at the positioning of functional molecules a few Å above the surface while maintaining the lateral organization of the array. We introduced the concept of Janus-like 3D molecular tectons, which are dual-functionalized building blocks exposing two opposite faces (A and B) linked by a rigid spacer: A is a pedestal designed for steering 2D self-assembly on the substrate (HOPG) and B a functional moiety. The organization of various 3D Janus conjugated tectons is determined by scanning tunneling microscopy (STM). The highly versatile synthetic approach presented allows, through modification of face B, for preparing a wide range of Janus tectons exposing various functional units opening interesting perspectives for applications in different fields of nanotechnology or in energy storage.

Thanks to the size of its band gap and its relative position toward HO-/HO#9679; and O2/O2#9679;- redox potentials, TiO2 is one of the most efficient photocatalyst under UV irradiation and anatase is the active polymorph. The particles used must have a relatively high specific surface tailored to efficiently interact with the pollutant. Moreover, a good stacking of atoms constituting the crystalline structure is mandatory to display high activity since defects may act as recombination centre between photogenerated electrons and holes.1 Recent works on that phase demonstrated in addition to an influence of the nanoparticles size, an effect related to the nature of the exposed surfaces.2
We used the sol-gel method to obtain a wide range of anatase nanoparticles sizes and morphologies by changing the concentrations, ions in solution, solution acidity, and aging parameters and by new activation methods such as microwave heating.3
Especially, different shapes of pure anatase nanoparticles have been synthesized by selective adsorption of organic molecules during the syntheses.4 The influence of synthesis parameters and the organic molecules nature on the nanoparticles structure and morphology have been analysed with various techniques, such as XRD and HRTEM.
The photocatalytic efficiency of the different morphologies was probed by the degradation of Rhodamine B in aqueous solution and the activity was correlated to the surface composition. The adsorption of the dye as well as his degradation has been discussed.
Pyridine adsorption on anatase surfaces in order to get acidity properties have been done and compared to MUSIC model.5 Reactive Oxygen Species production of each morphology has been studied.
The approach presented here can be extended to other application in which the nature of the material surface is a key parameter, such as Dye-Sensitized Solar Cells.6
[1] 1. G. Benko, B. Skarman, R. Wallenberg, A. Hagfeldt, V. Sundstrom, and A.P. Yartsev, J. Phys. Chem. B 107, 1370 (2003),
[2] D. Q. Zhang, G. S. Li, H. B. Wang, K. M. Chan, J. C. Yu, Cryst. Growth Des., 2010, 10, 1130
[3] F. Dufour, S. Cassaignon, O. Durupthy, C. Chanéac, Eur. J. Inorg. Chem, 2012, accepted
[4] T. Sugimoto, X.P. Zhou, A. Muramatsu, Journal of Colloid and Interface Science, 2003, 259, 53
[5] T. Hiemstra, P. Venema and W. H. V. Riemsdijk, J. Colloid Interface Sci. 184, 680 (1996)
[6] C. Magne, F. Dufour, F. Labat, G. Lancel, O. Durupthy , S. Cassaignon, T. Pauporté, J. Photochem. Photobiol. A, 2012, 232, pp 22-31

For last few decades, many research groups have put much effort to synthesize various self-organized semiconductive structures. Among these synthesis approaches self-organized porous structures have contributed to a broad area of scientific and engineering fields due to some outstanding physical, chemical and geometric properties. In order to synthesize such self-organized nanostructures, various approaches are used like hydrothermal, sol-gel, and electro deposition. However, self-ordering anodization has several advantages over other approaches: It allows highly defined controllable and ordered formation, using simple experimental apparatuses. Some valve metals (such as Al, Ti, Ta, Nb and so on) have shown extremely promising materials to fabricate anodic porous oxide structure. In particular, TiO2 has attracted attention because of its suitable band gap energy (3.2 eV), and chemical stability to be used in wide applications such as photocatalysts, solar cells, biomedical applications and water splitting. Such highly ordered anodic TiO2 nanostructures can be fabricated in fluoride ion containing electrolytes. Nevertheless, this anodization approach can be transferred to to other materials to form ordered anodic nanostructures. Even more, new anodization approaches, without fluoride ion containing electrolytes (such as hot glycerol/K2HPO4 electrolytes) can be deliver even more defined nanostructure. This presentation, shows that from a commercial metallic Ti/Ta and Ti/Nb multilayer substrate, under optimized anodization conditions a TiO2/Ta2O5 and TiO2/Nb2O5 “superlattice” nanotube/nanoporous structure can be obtained, and these structure shows a drastic improvement of the (photo)electrochemical properties over TiO2 nanotubes.

It is known that atomically flat, Au 111 surfaces are inactive for gas phase CO oxidation. Several decades ago, it was found that when gold is nanoscaled to less than 5 nm in diameter on certain metal oxide supports, it becomes one of the most active CO oxidation catalysts. Gold has also been shown to be electrocatalytically active for CO oxidation. The physical origins are widely debated. Possible explanations are: 1. Size dependent coordination number effects; 2. Support directed coordination number effects; 3. Gold lattice strain; 4. Support electronic promotion; 5. Gold surface oxidation; 6. Support activation of oxygen. It is our objective to establish a nanoscaling factor hierarchy from this list by measuring the physical, electronic, and electrocatalytic factors for the highly active Au on TiO2 system.
Our approach entails the design of a well defined, flat TiO2 support and the deposition of Au nanoparticles using a contamination free, size controlled e-beam technique. This design approach is well suited for determination of size, shape and lattice strain that we measure by Scanning Electron Microscopy and Transmission Electron Microscopy. Additionally, we measure the electronic structure using the 5d subshell sensitive hard x-ray valence band photoelectron spectroscopy to help disentangle the previous nanoscaling effects. There is a trend in the valence band electronic structure that we attribute to a surface coordination number effect. Finally, we measure the CO electrocatalytic oxidation activity versus Au nanoparticle size on TiO2 in both base and acid. We have found and seek to overcome limitations derived from the inherent instability of small gold nanoparticles within aqueous environments. By carefully designing our experiments to mitigate this instability, we hope to obtain fundamental knowledge in the size dependent CO electro-oxidation activity of TiO2 supported gold nanoparticles.

Efficient solar hydrogen production via water photoelectrolysis is a long-standing challenge with a great promise for solar energy conversion and storage in the form of solar fuels. Important advances in developing semiconductor photoelectrodes have been achieved in the last four decades since Fujishima and Honda&’s seminal report on photo-induced water splitting using TiO2 photoanodes. Despite these advances no photoelectrochemical system for solar hydrogen production has met the technological requirements in terms of efficiency (ge; 10% solar to hydrogen conversion efficiency), durability (ge; 5000 h) and cost ($3 per kg of H2). So far, the most promising photoanode candidates are iron oxide (α-Fe2O3), tungsten oxide (WO3), and bismuth vanadate (BiVO4). These oxide semiconductors are stable in aqueous solutions and they can oxidize water to form oxygen and protons (the protons form hydrogen at the cathode) in basic, acidic or neutral aqueous solutions, respectively, without corrosion or decomposition. In this presentation, we introduce an electrospinning processing strategy for producing various semiconducting metal oxide nanofibers (α-Fe2O3, WO3, TiO2, BiVO4, Co3O4, RuO2, LaCoO3, catalyst-decorated metal oxide fibers etc.) which can be potentially optimized for application in water oxidation catalysts. Novel synthesis of tailored metal oxide composite nanofibers which offer dual advantages in terms of suppression of charge recombination and fast reaction kinetics, and their microstructural evolution will be highlighted to emphasize the performance of one dimensional oxygen evolving catalysts.

Hydrogen is used in a wide variety of industrial process and its wider use in the society is expected to increase rapidly due to the crucial role H₂ is anticipated to play in future as a clean energy carrier. Thus there is a growing need to develop reliable, inexpensive and easy to use H₂ sensors because H₂ is highly flammable and explosive in the presence of oxygen at certain concentrations. Hydrogen sensing can also play a role as an indicator for certain diseases, for detection of environmental pollution and indicator for food quality [1].
Thin film optical H₂ sensors have recently attracted much attention due to their advantages over conventional H₂ sensors [2, 3]. Unlike most conventional H₂ sensors which are bulky and operate at 150-450 °C, thin film optical sensors are compact and can operate at room temperatures. Furthermore they can be used remotely, making it safer in an explosive environment and also suitable for biochemical/biomedical purposes due to absence of electrical connections in the sensing area. However, most thin film optical H₂ sensors still require a transducer or electrical readout which increases their power consumption and cost.
We have developed a very sensitive, low cost and easy to use H₂ detector which is eye-readable thus circumventing the need for an electrical readout. The indicator consists of nanostructured Y/Pd_xAu_y thin films; it can detect as low as 10ppm H₂ and can be used for various applications. We will discuss the sensor&’s properties such as response/recovery times (H₂ sorption kinetics), stability and selectivity towards H₂ in the presence of O₂, air, moisture, CH₄ and CO₂. We will show how these properties can be tuned by varying the thickness and/or concentration of the Pd/Au and the use of a protective Teflon coating.
[1] C.A. Grimes, et al. Sensors 3 (2003), 69
[2] T. Hübert et al. Sensors and Actuators B, 157, (2011), 329
[3] M.A. Butler., Appl. Phys. Lett. 45, (1984), 1007

Spraying layer by layer (sLbL) Conductive Polymer nanoComposites (CPC) dispersions onto interdigitated electrodes is a versatile way to fabricate low cost Quantum Resistive vapour Sensors (QRS) that can be implemented into e-noses for applications such as anticipated disease diagnosis [1] or smart packaging [2]. However, although spray [3] or electrostatic [4] LbL both allow to structure step by step the CPC conducting network in three dimensions, it is still tempting to be able to adjust a nanometric parameter such as the tunnel junctions&’ gap between nanofillers. This makes possible to tune the QRS sensors macroscopic chemo-resistive properties, i.e., sensitivity and selectivity to volatile organic compounds (VOC). Therefore, we have investigated different types of assemblies of natural macromolecules with multiwall carbon nanotubes (CNT), which allow to control the CNT/CNT junction gap, such as grafting from CNT by in-situ polymerization of ε-caprolactone [5], surface cross-linking of chitosan chains [6] and non covalent bonding (Fig. 1) of amylose helices of amylopectine [7]. Interestingly, most strategies are enhancing the sensitivity of CNT transducers compared to bulk polymer matrices. Moreover, these results suggest that changing the conformation of macromolecules on CNT not only allows to tailor CPC chemo-resistive sensors sensitivity by changing the gap but also their selectivity by specifically orientating chemical groups.
1. J. W. Gardner, H. W. Shin, E. L. Hines, Sensors & Actuators B: Chemical 70 (2000) 19-24.
2. M. Peris, L. Escuder-Gilabert, Analytica Chimica Acta 638 (2009) 1-15.
3. B. Kumar, M. Castro, J. F. Feller, Sensors & Actuators B: Chemical 161 (2012) 621-628.
4. B. Kumar, Y. T. Park, M. Castro, J. C. Grunlan, J. F. Feller, Talanta 88 (2012) 396-402.
5. M. Castro, J. Lu, S. Bruzaud, B. Kumar, J. F. Feller, Carbon 47 (2009) 1930-1942.
6. B. Kumar, M. Castro, J. F. Feller, Journal of Materials Chemistry (2012) 22 (21), 10656-10664.
7. B. Kumar, M. Castro, J. F. Feller, Carbon (2012) 50 (10), 3627-3634.

Carbon nanotubes (CNTs) based gas sensors have been extensively investigated over the last decade and have shown excellent potential for detecting toxic gas molecules at low concentrations. While single walled carbon nanotubes (SWCNTs) have been demonstrated to be promising sensing nanomaterials for the detection of electron donating (NH3) and electron withdrawing (NO2) gases, they are relatively limited in sensing performance due to weak interactions between the SWNTs and gas molecules. To overcome this limitation, carbon nanotubes can be modified using several different approaches.
We report on a novel gas sensing material based on hybrid metal nanostructures/carbon nanotube composites that exhibits enhanced sensitivity and excellent sensor recovery compared to sensors fabricated from pure single walled carbon nanotubes. Sensors fabricated from platinum nanobox (PtNB) and semiconducting SWCNT composites showed increased sensitivity and recovery time as compared to the sensors that only contained SWCNTs, when exposed to chlorine gas at room temperature. The enhanced gas sensor response is attributed to the increase in efficiency of the charge transfer process between the non-polar electron withdrawing gas molecule and the semiconducting SWCNT with the introduction of the metal nanostructures.

Desalination is one of the most promising approaches for new fresh water supply. One of the most promising methods for improving desalination is the nanoporous membrane, which can leverage multiple mechanisms to reject ions while permeating water much faster than nonporous Reverse Osmosis (RO) membranes. We recently showed that nanoporous graphene could exhibit 100-1000 times higher permeability than conventional polyamide membranes in reverse osmosis while still rejecting salt ions [1].
However, several crucial questions remain regarding the relevance of two-dimensional nanomaterials such as graphene in real-world desalination systems. In particular, graphene consists of a single layer of carbon, and questions have been raised about the ability of this material to withstand the high mechanical pressures (dozens of bars) required for reverse osmosis.
In addition, the permeation kinetics of water molecules and salt ions must be investigated in further detail in order to understand how they evolve at realistic hydrostatic pressures. Finally, the improvements in water permeability achievable with two-dimensional nanomaterials will result more efficient desalination processes. But the quantitative efficiency gains have not been determined before. How would this material's superior performance translate into actual energy savings and cost reductions?
We will present results from semi-empirical system modeling and molecular dynamics simulations to answer these outstanding questions that may help bring next-generation membranes closer to reality.
[1] Cohen-Tanugi and Grossman, Nano Letters, 2012, 12 (7)

Millions of people die from waterborne diseases caused by contaminant pathogens every year. It is extremely important for people in areas without water treatment plants or regions of post-disaster reconstruction to have simple, affordable and high-efficiency water disinfection means. Here we demonstrate a fast-disinfection filter which is easily fabricated using robust, low-cost substrates such as textiles/sponges coated with one dimensional nanomaterials such as carbon nanotubes, silver nanowires. By adding a small external voltage of several volts to the filters, 100% inactivation of bacteria and 99.6% inactivation of virus were achieved with contact time of filters to pathogens within one second and energy consumption of only 100-200J/L.

Abstract
Research work on the synthesis, designing and characterization of nanostructures has been extensively documented in the last decades. This in-depth documentation not only enabled researchers to understand the relationship between the nanostructures properties, size, shape, and composition but have also given them immense control over their manufacturing. This enhanced knowledge, cemented the switching of academic nanotechnology research into industrial products. However; despite of the recent accomplishment in the synthesis, characterization and application of the nanostructure materials, a complete knowledge/information of their interactions with biological systems is still not available. Hence, it is difficult to forecast the injurious biological responses of these novel nanostructures to humans, animals, insects and plants. Due to this hesitancy, safety regulatory authorities and general public have raised their concerns to the manufacturing and use of nanostructure-based products. Consequently, it is vital for the researchers to concentrate more on safe designing, manufacturing and characterization of nanostructures before these could meet human and communal needs. This review is taking an overview of the increasing investment into nanotechnology, designing, synthesis and characterization of nanostructures and their in-vitro and in-vivo toxicity.
Keywords
Carbonaceous NPs; Metal oxide NPs, Toxicity, In-vitro, In-vivo, NPs Synthesis

One major obstacle plaguing the field of nanotechnology is the unknown consequences resulting from the introduction of nanomaterials (NM) into the environment and the resultant impact on human health and safety. As this concern has emerged, it has become clear that a mechanism is needed to accurately translate in vitro exposure data to a prediction of real world implications. In an effort to enhance the efficacy of information gathered from an in vitro environment, a chronic NM exposure scenario was designed and implemented in which human keratinocyte cells (HaCaT) were dosed with 50 nm silver nanoparticles (Ag-NP) 8 h a day, 5 days a week, for 3 months. Working concentrations were based off the permissible exposure limits set by OSHA and the known degree of Ag-NP retention and were 0.4, 4, and 400 pg/ml. The HaCaT stress response of the chronically treated cells was directly compared to a 24 h acute exposure at a concentration equal to the cumulative Ag-NP dosage encountered over the 3 months. Cellular endpoints evaluated include activation of Heat shock protein-27 signal transduction, ki67 expression, pro-inflammatory cytokine secretion, actin inflammation, and alterations in gene regulation. Results indicated that the chronically dosed HaCaT cells were functioning under sustained, augment cellular stress: as seen with increased reactive oxygen species levels, HSP-27 signaling, cytosolic ki67 expression, and actin inflammation and disorganization. Furthermore, considerable IL-6 secretion was observed throughout the experiment, indicating a continuous inflammatory response. Most notably, these stress indicators were all significantly higher in chronically dosed cells vs. their acute counterparts, demonstrating a more severe response. Additionally, chronically dosed cells demonstrated a vastly higher modification to gene regulation, again representing the potential for a serious long term impact. In conclusion, this study was the first to identify significant variations in the cellular stress response following chronic Ag-NP exposure at extremely low doses. As such, these results underscore the utmost importance oflimiting and identifying NM waste into the environment as we demonstrated the potential for arising health issues from continual exposure.

Nanotechnology has been explored for applications in wide areas such as energy, environment, agriculture, healthcare and consumer goods. Due to its antibacterial properties, silver nanoparticles (Ag NPs) are the most commonly used nanomaterials in commercial products, which include wound dressings and catheters. This enhances the possibilities of Ag NPs entering into blood stream of the patients and transfer to the whole body. Human embryonic stem cells (hESCs), obtained from the inner cell mass of the blastocyst have shown the capability of differentiating into nearly all kinds of cells, and are sensitive to the outside environment. In our study, the cellular response of hESCs treated with Ag NPs was studied on both undifferentiated cells (2D) and embryo body (3D)—differentiated cells. The toxicity of Ag NPs was evaluated using changes in cell morphology, metabolic activity and gene expression. The mitochondria activity of hESCs was not affected by Ag NPs in both 2D and 3D at low concentrations. Further the damage of cells was checked by the changes of EGF genes, which provide information on the mechanism of toxicity. Our new results may help to people, especially pregnant women, make a learned decision on nanoparticle incorporated products.
Acknowledgement: The authors acknowledge technical and funding support from National University of Singapore (NUS) and WC thanks NUS for a PhD scholarship.

The increasing use of portable electronic devices and electrical vehicles has enhanced the need of effective energy storage devices significantly. The substrates/electrodes prepared from nanofibrillated cellulose (NFC) with a cross-section of 2-3 nm and a length of 2 mu;m demonstrate many advantages for the electronic applications, compared to expensive conventional substrates, due to their unique properties such as flexibility, transparency, high mechanical strength, low thermal expansion and high specific surface area. Following a brief introduction to the NFC preparation, a general overview on the NFC nano-paper based flexible energy storage devices such as capacitors, supercapacitors, Li-ion batteries and transistors will be discussed. The discussion on NFC paper-based graphene or carbon nanotube ultracapacitors with enhanced conductivities is presented. The influence of embedded, integrated stainless steel mesh backbones on the conductivity and material integrity is discussed. Power densities in excess of 100.000 W/kg can be achieved both for CNT and graphene based devices, and CNT devices can achieve energy densities in excess of 10 Wh/kg based on active material masses. Graphene-based samples exhibit excellent cycling performance with roughly 90% of the original capacity retained after 48.000 cycles. In the second part of the presentation the preparation of a NFC-based flexible and transparent optoelectronic device is discussed and it is shown that some unique optical properties of NFC nanopaper such as light scattering and transparency allow the preparation of efficient solar cells. The power conversion efficiency of the solar cell is found to be 0.40%. The cell efficiency could be further improved by stabilizing the nanopaper to maintain the surface smoothness in the device fabrication.

Thermochromic and electrochromic materials are the foundations for "smart" windows that are able to vary thieir throughput of visible light and solar energy in accordance with dynamic needs and thereby create energy efficiency as well as indoor comfort. This paper reviews a number of recent investigations of ours which include nanoparticles of transparent conductors, in particular of Indium Tin Oxide (ITO) and Vanadium Dioxide. Specifically, we cover (i) thermochromics based on VO2, VO2:Mg and VO2-ITO composites, (ii) polaronic electrochromism with near-infrared transmittance blockage due to ITO-containing polymer electrolytes, and (iii) plasmonic electrochromism. Underlying principles, theoretical results and experimental data will be reported.

Magnetic refrigeration is an environmentally friendly cooling technology that does not use ozone-depleting and global-warming volatile liquid refrigerants. The majority of magnetic refrigeration is to find materials that exhibit both large magnetocaloric effect (MCE) and large refrigerant capacity (RC). In addition, a magnetic refrigerator often acquires a higher amount of heat absorption/extraction per volume than in a conventional gas-based cooling system. Since a magnetic material is the working body of a cooling system, it is required to have a large heat transfer area to provide high heat exchange efficiency. In this context, exploring magnetocaloric materials on the nanoscale can be of great importance. Relative to their bulk counterparts, the nanomaterials possess enhanced surface area, thus providing better heat transfer. The particle size distribution, as well as interparticle interactions in them, can broaden MCE over a wide temperature range, thus enhancing RC. From a materials engineering perspective, nanomaterials can easily be assembled as thin films through self-assembly, which are essential for applications of a cooling device for microelectromechanical systems (MEMS) and nanoelectromechanical systems (NEMS). While exploring nanoscale magnetocaloric materials shows a potential for achieving this goal, the conventional trend is reduction of the magnetization that leads to the decrease in MCE and/or RC with nanostructuring. In this talk, we will give an overview and outlook for research into functional nanostructured magnetocaloric materials, with a focus on the advantages and limitations of existing nanomaterials for active magnetic refrigeration technology. We will then discuss novel approaches developed by us thus far for enhancing both MCE and RC in magnetic nanostructures [1,2] and future research directions in this exciting area.
References: [1] M.H. Phan et al., Appl. Phys. Lett. 97, 242506 (2010); [2] N. S. Bingham et al., Appl. Phys. Lett. 101, 102407 (2012).
Supports: The research at USF was supported by the DOE through Grant No. DE-FG02-07ER46438 and the Florida Cluster for Advanced Smart Sensor Technologies (FCASST).

Ternary group III-Nitrides semiconductors, in particular InGaN, have attracted great interest in the past decade owing to their novel material properties and tunable bandgap. These unique material properties provide opportunities for novel device structures in many energy related applications such as light emitting diodes, Thermoelectricity (TE) and Photovoltaic (PV) solar cells. In this talk, the multi-functionality of ternary group III-nitride alloys for high temperature TE and PV applications will be addressed.
The operational temperatures of current TE materials and devices are typically limited to< 800K. It is critical to develop a new class of TE materials with mechanical and chemical stability at high temperatures to harvest significant energy from commonly available waste heat sources. Wide band-gap based TE materials, such as the III-Nitrides, provide one solution that minimizes the excitation of minority carriers and the loss of n- or p-type character of materials at high temperatures. Our recent work has shown that GaN:Si exhibited a maximum power factor of 9.1x10-4 W/m-K with a carrier concentration of 1.6x1018 cm-3, and In0.1Ga0.9N exhibited a maximum power factor of 109x10-4 W/m-K with a carrier concentration of 1.2x1018 cm-3. These results indicate that GaN and InGaN-based materials could be a new class of TE materials for high temperature applications provided their inherent high phonon conductivity can be further reduced by low dimensional nanostructuring.
Tandem solar cells consisting of materials with multiple band gaps are needed to improve the efficiency limit of conventional solar cells. The ternary InGaN based material is the most promising candidate owing to its direct band gap, high absorption coefficient, and tunable bandgaps covering the majority of the solar spectrum from 0.7 eV to 3.4 eV. Therefore, tandem solar cells with a single material system can be realized by using InGaN with different indium and gallium compositions to achieve a series of different bandgaps needed for tandem structures. Our group reported the first InGaN solar cell devices and these cells had EQE max of 43% and Voc as 2.40 V at 5% indium composition. The most recent work has reported a MQW structure of InGaN solar cells at 28% indium composition, with EQE max as 70% and Voc as 2.40 V.

Thermoelectric (TE) materials have historically been an intriguing topic of materials science because of their potential applications in temperature measurement, temperature control, energy harvesting and power generation. In the global drive to develop sustainable energy, TE energy storage and generation technologies have attracted a tremendous interest. For practical energy harvesting and power generation applications, a TE efficiency (determined by the dimensionless figure of merit, ZT = α²σT/κ, where α is the Seebeck coefficient, σ is the electrical conductivity, κ is the thermal conductivity, and T is the absolute temperature) approaching ZT ~ 3 is required. Unfortunately, however, the existing bulk TE materials have much lower ZT value (ca. ~ 1) mainly because of the interdependence of σ and κ which defines the limitation in the ZT value. Recently, it has been widely recognized that the nanostructured TE materials with well-defined nanoscale grain boundaries can have reduced κ without much decrease in σ through the phonon scattering/carrier transmission phenomenon. With this in mind, TE nanoparticles (NPs) have become intensely investigated as promising building blocks for high-ZT nanostructured TE materials. While there are a host of different synthesis approaches toward the creation of TE NPs, the chemical synthesis-based approaches offer the most versatility in manipulation of the individual particle characteristics including size, shape, structure, or surface properties. Among many TE materials, Zn-Sb systems consist of relatively abundant elements and exhibit excellent TE performance because of the remarkably low κ arising from their disordered local structure. Nanostructured Zn-Sb, therefore, is expected to have extremely low κ due to the multiplier effect of intrinsic disordered structure and nanograin boundaries which makes it a promising material for energy harvesting purposes. To achieve this, we have developed a synthetic method towards Zn-Sb NPs via a sequential reduction of metal precursors and subsequent alloying. Sb cores were first synthesized followed by the growth of Zn shell onto the cores and subsequent alloying. Structure and thermoelectric properties of the resulting NPs were characterized by various methods including TEM, Scanning TEM, XRD, TEM-EDS, XPS and PPMS-TTO.

Despite years of advancement in making energy systems more efficient, the predominant mode of condensation seen in large-scale industrial processes is still filmwise condensation. Replacing the filmwise condensation mode with dropwise condensation promises large improvements in heat transfer that will lead to large cost savings in material, water consumption and decreased size of the systems. In this regards, use of superhydrophobic surfaces fabricated by texturing surfaces with nano/microstructures has been shown to lead decrease in contact line pinning of millimetric drops resulting in fast shedding. However, these useful properties are lost during condensation where droplets that nucleate within texture grow by virtue of condensation to large sized droplets while still adhering to the surface. Recently we have shown that liquid impregnated surfaces can overcome many limitations of conventional superhydrophobic surfaces during condensation. Here we discuss aspects related to condensation on liquid surfaces, and show how relations among surface tension of encapsulating liquid and condensing liquid determine the condensation and subsequent shedding behavior for condensing droplets. We compare the characteristics of condensed droplet behavior on these surfaces with their behavior on conventional un-impregnated superhydrophobic surfaces and show how use of lubricant impregnated surfaces may lead to large enhancement in heat transfer and energy efficiencies.

Nanofluids are nano-size-powder suspensions in liquids that are of interest for their enhanced thermal transport properties. They are studied as promising alternatives as compared to ordinary cooling fluids, particularly for critical cooling as in nuclear systems, large engine radiators, and microchip cooling, but the effects of nanofluids on wall materials are largely unknown. The authors developed an instrument that uses a low-speed jet on material targets to test such effects.
The work is presented of the authors&’ experimental research on the early interactions of selected nanofluids (2% weight of alumina nanopowders in distilled water, and in solutions of ethylene glycol in water) with aluminum and copper samples as typical cooling-system materials. The observed surface changes (and possible nanoparticle deposition) for test periods as long as 14 hours were assessed by roughness and wear (i.e., volumetric-removal wear) measurements, and by microscope studies. Comparative roughness measurements indicate that alumina nanofluids can produce significant surface changes on copper surfaces, but negligible effects on aluminum for the same testing conditions. These investigations set a baseline for further research and provide a suitable method for testing of nanofluids effects in cooling system-materials.

Without an ordered atomic structure, a glassy material possesses the lowest possible lattice thermal conductivity of its composition, also called the Einstein&’s limit [1]. In physics, this limit is reached when the phonon mean free paths decrease to half of the phonon wavelength and thus invalidate the wave description of lattice vibrations. Depending on the material composition and the extent of disorder, the lattice thermal conductivity of a bulk glass can be down to 0.1-0.3 W/m-K at room temperature [2,3]. This represents some of the lowest thermal conductivities among existing solids. Along this line, an even lower thermal conductivity is anticipated in a glass-based nanocomposite, with a high volumetric interface area and a large interface thermal resistance between nano-domains of different constituent materials to cut off the heat flow. In this work, nanocomposites cold pressed from Ge-Se-Te glass nanopowder and commercial oxide nanoparticles (10-20 nm in diameter) are investigated as next-generation thermal insulation materials for large-scale thermal energy conservation. Compared with highly porous thermal insulation materials (e.g. polyurethane foam, mineral wool), these new composites have superior mechanical strength and high durability in harsh environments. In pursuit of a remarkably low thermal conductivity, the pressure and temperature of the cold press can be used as two “knobs” to adjust the nanoporosity and interfacial constitution of the obtained nanocomposites. Systematic studies have been carried out on a series of glass-oxide nanocomposites, with phonon transport analysis to elucidate the contribution of nanoporosity and glass-oxide interface thermal resistance.
References:
1 A. Einstein, Ann. Phys. 35, 679 (1911).
2 A. P. Goncalves, E. B. Lopes, O. Rouleau, and C. Godart, J. Mater. Chem. 20, 1516 (2010).
3 S. N. Zhang, J. He, T. J. Zhu, X. B. Zhao, and T. M. Tritt, Journal of Non-Crystalline Solids 355, 79 (2009).

Strategies for improving sustainability and economic development rely on using nanotechnology to develop alternatives for certain in-demand materials. In the area of energy critical elements, quantum dots have been synthesized to replace existing lighting materials, and high-performance metal alloys and magnetic materials are being engineered through control of nanoparticle behavior. Successful development of these new sustainable nanotechnologies requires consideration of appropriate levels of life cycle assessment, theory, computation, and experiment, as well as the explicit incorporation of a manufacturability perspective throughout the product research, development, demonstration, and deployment cycles. To accelerate the discovery and development of material, in particular nanomaterials, it is critical to integrate these factors seamlessly into a comprehensive approach. However, success in this endeavor depends on the development of improved tools to characterize nanomaterials at all stages of their development to ensure that processes are scalable and that desired material properties are escorted to and throughout manufacturing to become an ensconced part of the nanotechnology.
A class of versatile characterization techniques that are essential to the development of sustainable nanomaterials important to energy are those provided by synchrotron radiation-based approaches. In the soft x-ray regime, x-ray absorption spectroscopy, x-ray emission spectroscopy, resonant inelastic x-ray scattering, and hard x-ray diffraction along with x-ray scattering are the core approaches currently being utilized. Perhaps the most impactful of these methods towards nanotechnology is soft x-ray spectromicroscopy with the scanning transmission x-ray microscope (STXM) at the Molecular Environmental Science (MES) Beamline 11.0.2 of the Advanced Light Source (ALS). The MES STXM is capable of imaging with a spatial resolution approaching 10 nm, can directly probe the light element K-edges below 2 keV via x-ray absorption, and can be employed on a diverse range of samples including particulates and highly air-sensitive materials. Representative results from several particulate-based systems will be presented highlighting the utility of the STXM for a broad range of materials research. A critical discussion will follow on future developmental opportunities for STXM, as well as other soft x-ray methods, to bridge research and manufacturing efforts to foster more rapid growth in sustainable nanotechnology.