Large enhancement in humidity sensing performance and photocatalytic efficiency of Ag-doped ZnO/GO nanocomposites

In this study, we demonstrate the multifunctional property of a nanocomposite (NC) synthesized by combining Ag-doped ZnO with graphene oxide (GO) nanosheets. The Ag-ZnO/GO NC works as an efficient photocatalyst to remove methylene blue (MB) dye (a common water pollutant) from water, and functions also as a good sensing material to detect relative humidity (RH) of air. X-ray diffraction confirmed hexagonal wurtzite crystal structure of ZnO whereas scanning and transmission electron microscopies revealed the successful integration of Ag-ZnO nanoparticles (NPs) onto GO sheets forming well-defined NC. The optimized Ag-ZnO/10%GO NC (AZO-10%GO NC) exhibited 98.95% degradation efficiency for MB dye under sunlight within just 40 min, a remarkably improved performance compared to only 82.99% degradation by pure ZnO NPs. Interestingly, the same Ag-ZnO/10%GO NC also exhibits a high sensing response of ~ 406 at 74% RH along with fast response and recovery times of 7 s and 21 s, respectively when tested as a chemi-resistive film to sense RH of air. Thus, this work demonstrates the utility of the Ag-ZnO/10%GO NC for both water and air quality monitoring as it can not only remove organic pollutants from water bodies but also can monitor RH of air.