One-pot synthesis of a reduced graphene oxide–ZnO nanorod composite and dye decolorization modeling

In this paper, reduced graphene oxide (rGO)–ZnO nanorod composite was fabricated by one-pot hydrothermal method and used for photocatalytic decolorization of anionic (Direct Red 80, DR80) and cationic (Basic Red 18, BR18) dyes. The composite was characterized using FESEM, XRD, FTIR, TGA, and UV–vis. Response surface methodology (RSM) was used to model the decolorization efficiency. The optimization of the process was carried out using a genetic algorithm (GA) in order to find the maximum yield of photodecolorization. Maximum value of photodecolorization yield based on optimization of the input space by RSM integrated GA approach is obtained with a yield as high as 90.87% for DR80 and 88.33% for BR18 at initial dye concentration 17.68 and 20.39 mg/L, initial pH 5.68 and 5.37, rGO–ZnO dosage 0.0221 and 0.0308 g/L, and irradiation time 186.30 and 189.60 min for DR80 and BR18, respectively. The photostability of rGO–ZnO nanorod composite and ZnO was evaluated and compared after the three consecutive cycles for decolorization. The results revealed that presence of graphene in the composite, can greatly improve the dye photodecolorization ability due to retardation of electron–hole recombination and also concentrating of dyes around the surface by enhancing adsorption ability.