Three-dimensional gold nanoparticles-modified graphene hydrogel for high-sensitive NO2 and NH3 detection with enhanced resistance to humidity

A one-step, facile hydrothermal approach was developed to synthesize gold nanoparticles (Au NPs) modified reduced graphene oxide hydrogel (Au-RGOH) with three-dimensional (3D) porous microstructures for sensitive NO2 and NH3 monitoring. It was found that the Au-RGOH displayed an order of magnitude higher sensitivity and much lower limit of detections (LODs) than the unmodified RGOH counterpart, demonstrating the remarkable role of Au NPs in boosting the responsivity toward NO2 and NH3. To address the disturbance of humidity on gas sensing, an integrated microheater platform was exploited to quench the response to humidity without impairing the response to target gas, enhancing the resistance to humidity. The mechanisms of Au NPs decoration effect and temperature-assisted screening effect were elucidated by molecular dynamics and density functional theory simulations for the first time. It revealed that Au NPs were active adsorption sites for NO2 molecules, and the strong and weak dependence of the adsorption of H2O and NO2 molecules on temperature, respectively, providing theoretical evidences for experimental results. Benefiting from the chemical sensitization effect of Au NPs, 3D porous structure, and localized temperature modulation, the Au-RGOH gas sensor exhibited high sensitivity, low LODs (1.16 NO2 and 55.3 ppb NH3), excellent selectivity, reversibility, fast recovery speed, etc. This study offers a facile and practical solution to boost the gas sensing performance by engineering the surface, structure and operation temperature of transducing materials, as well as understand the sensing behaviors via theoretical simulations.