Preparation and mechanism investigation of highly sensitive humidity sensor based on two-dimensional porous Gold/Graphite carbon nitride nanoflake

Abstract In this study, a humidity sensor with high performance based on two dimensional porous graphite carbon nitride (2D Au/g-C3N4) by stripping methods was designed. It solves the problem that g-C3N4 does not easily dissociate water molecules to form conductive ions (H3O+). Density functional theory (DFT) simulation results show that Au nanoparticles on the surface of g-C3N4 can promote the decomposition of water to form hydroxyl groups and reduce the band gap of Au/g-C3N4 when the hydroxyl group is adsorbed on the surface of Au/g-C3N4. The narrower band gap makes the electrons more easily to be excited and promotes the formation of H3O+, hence improving the conductivity of the sensor. Experiments show that an appropriate amount of Au nanoparticles between the g-C3N4 layers can provide a large number of adsorption/active sites to accelerate the decomposition of water molecules and enhance the conductivity of g-C3N4. The conductivity of Au/g-C3N4 (0.5 mM) humidity sensor achieves more than 5 orders of magnitude in impedance change with low hysteresis (1.38 %) and high stability when the relative humidity is varied from 11%–95%. This study provides a theoretical basis and guidance for the development of resistive humidity sensors based on g-C3N4.