Montmorillonite/Graphene Composite Based Resistive Humidity Sensor

The needs about precise humidity sensor are getting higher gradually in numerous major industries for insuring optimal performance of electrical devices and safety in diverse environments.<br/>Graphene, the two-dimensional material, has extraordinary electrical properties due to its π-bonding of sp³ hybrid orbital. Recent study has shown possibility of graphene-based material as the humidity sensing material because of its ultrahigh surface area. However, the results reported thus far are limited in recovery time and long-term stability due to irreversible adsorption of water molecules on graphene’s surface during humidity sensing. Its high price also can be challenge for the practical application. Although doping other sensitive material to graphene is one of the possible ways that can improve recovery property, but it not that effective way to improve sensor’s sensitivity.<br/>In this study, we propose a stable humidity sensor based on a montmorillonite/graphene composite to overcome these recovery, stability, and price problem. As a natural clay mineral, montmorillonite has attracted interest because of its abundance and unique ability to absorb large amounts of water by an increase in the c-axis of the layer lattice structure.<br/>The incorporation of graphene into montmorillonite, at the point where graphene’s concetration exceeds electrical percolation threshold, forms a cost-effective composite material compared to carbon materials like GO or rGO that exhibits enhanced electrical resistance changes for humidity sensing. Additionally, the hydrophilic nature of montmorillonite facilitates the absorption of water molecules into the composite, whereas the hydrophobic nature of pristine graphene facilitates the desorption of water molecules. This combination of properties can contribute to the reduction of both response and recovery time in the composite.<br/>The montmorillonite/graphene composite was fabricated using a simple solution-based method. The composite was then coated on an electrode deposited substrate. The best ratio of montmorillonite/graphene of composite sensor was confirmed through observation of distinct electrical resistance change in variation of ratio. And then, the sensor was characterized by measuring its resistance in response to different humidity levels ranging from 20% to 80%. The results showed that the sensor had a linear response to humidity, with a sensitivity of 10% per RH. Moreover, we find out the sensor was reversible and stable over time.<br/>Overall, the montmorillonite/graphene composite is a promising candidate for highly efficient humidity sensor with plenty of advantages over traditional humidity sensors. The sensor is highly sensitive, reversible, and inexpensive. It is also easy to fabricate and can be scaled up for mass production. The sensor has potential applications in a wide range of fields, including civil engineering, agriculture, and industrial processes.