Shape-controlled ZnO nanocrystals synthesized via auto combustion method and enhancement of the visible light catalytic activity by decoration on graphene

Abstract Several shapes of ZnO nanocatalysts have been acquired by the alteration of auto combustion method parameters in order to obtain the most efficient catalyst towards 2-nitrophenol degradation under UV-C. Thereafter, the procedure with tuned parameters was employed to decorate ZnO on graphene nanosheets to improve its visible light driven catalytic performance. Characterization results of the as-prepared nanocatalysts revealed that initial pH, fuel to metal ratio, and calcination temperature have influenced different growth and agglomeration directions. However, XRD patterns indicated the monocrystalline hexagonal phase of all tested products. Furthermore, UV–Vis and FTIR spectra exhibited the red-shift of ZnO absorption towards the visible light region upon loading on graphene and confirmed the successful reduction of graphene oxide by the subsequent preparation steps. Indeed, 2-nitrophenol degradation under visible light irradiation has shown a considerable enhancement with all graphene oxide weights utilized. Moreover, the kinetics of the reaction that fitted to the pseudo first-order kinetic and Langmuir-Hinshelwood models elaborated the dominance of pollutant catalytic degradation over its adsorption despite the improved adsorption in the presence of graphene. Finally, the degradation mechanism we suggested involves mainly the surface complexation of 2-NP on the catalyst surface to enable the absorption of visible light through ligand-to-metal charge transfer.