Silver-doped ZnO embedded reduced graphene oxide hybrid nanostructured composites for superior photocatalytic hydrogen generation, dye degradation, nitrite sensing and antioxidant activities

Abstract

Doped semiconductor metal oxide-rGO mediated photocatalysts have exhibited fascinating potentiality and utilized in a variety of applications. This could be attributed to their large surface area, unique morphologies and thickness-dependent characteristics. In this study, we focused on the green synthesis of ZnO, Ag-ZnO and Ag-ZnO-rGO nanocomposite using Cucumis melo fruit juice as fuel via solution combustion synthesis method. The synthesized materials were characterized thoroughly using PXRD, TEM, SEM, FTIR, UV-DRS, EDX and Raman spectroscopic techniques. As prepared materials were evaluated for photocatalytic H2 evolution by water splitting, dye degradation using visible light, photoluminescence, nitrite sensing and antioxidant activities. It was found that Ag-ZnO-rGO nanocomposite exhibited 3.2 and 1.7 times higher H2 evolution property than ZnO and Ag-ZnO nanoparticles respectively. Further, the composite material was found to be superior visible light active photocatalyst towards degradation of methylene blue (MB) dye compared to pure and Ag doped ZnO NPs. Photoluminescence studies revealed that Ag-ZnO-rGO nanocomposite showed remarkable reduction in the peak intensity of PL spectrum compared to ZnO and Ag-ZnO due to better charge separation. Ag-ZnO-rGO showed superior electrocatalytic performance towards the detection of NaNO2 and radical scavenging activity by inhibiting the activity of DPPH compared to ZnO and Ag-ZnO NPs. The superior activities of Ag-ZnO-rGO is probably due to lowering of bandgap by rGO, crystal lattice incorporated and ZnO-rGO interface accumulated Ag and also possibly due to the ability of rGO to facilitate the electron transport that suppress the recombination rate of photogenerated charge carriers. This study gives a concise methodology for the development of visible light responsive photocatalyst for various applications such as H2 evolution, dye degradation, photoluminescence and electrocatalytic nitrite sensing & antioxidant activities.