Characterization and performance evaluation of synthesized ZnO nanoflowers, nanorods, and their hybrid nanocomposites with graphene oxide for degradation of Orange G.

Nanoflowers and nanorods of ZnO were synthesized via hydrothermal route. These morphologies of zinc oxide (ZnO) were then decorated over graphene oxide (GO) to yield hybrid nanocomposites, namely, GO-ZnOnR and GO-ZnOnF. The decoration of ZnO nanorods and nanoflowers on GO layers was confirmed through FESEM images. The synthesized nanocomposites were subjected to degrade the Orange G under identical conditions. The band gap energies determined using diffused reflectance spectra were 2.87, 2.89 eV for GO-ZnOnR, and GO-ZnOnF, whereas, for both ZnOnR and ZnOnF, it was 3.14 eV. For 50 min of UV irradiations (at 6 pH), 100% degradation was achieved corresponding to GO-ZnOnR (44.1 m2 g-1) followed by 90.1%, 70.2%, and 68.3% with GO-ZnOnF (35.9 m2 g-1), ZnOnR (20 m2 g-1), and ZnOnF (15.1 m2 g-1), respectively. Significant boost in the degradation of Orange G, with GO-ZnOnR, was attributed to its reduced band gap, higher surface area, and enhanced charge separation. Kinetic study confirms the pseudo-first-order reaction rate. Mineralization efficiency of 91% in 120 min indicated the efficient reduction of Orange G and its intermediates. Further, reactive species trapping experiments revealed that photo-induced •OH are dominant radicals for the degradation followed by •O2- and h+. Liquid chromatography mass spectra data has been used to predict the plausible reaction pathways. Reusability studies indicated that GO-ZnOnR can be used for four successive degradation cycles, without any significant activity loss.