In situ hydrothermal synthesis of TiO 2 –RGO nanocomposites for 4-nitrophenol degradation under sunlight irradiation

Different amounts (0, 1.0, 3.0, 5.0 and 10.0 wt%) of reduced graphene oxide (RGO) were successfully immobilized to the surface of TiO2 nanoparticles through a hydrothermal process. With addition of RGO, the particle size decreased and the surface area and pore volume increased, resulting in improvement of the reactants’ diffusion and contact area. RGO could be hybridized with titanium atoms, leading to decreasing of the gap energy of TiO2 and more efficient utilization of the solar energy. Hence, the photocatalytic activity of TiO2–RGO composites for 4-nitrophenol degradation was improved accordingly. However, excess amount of RGO (≥ 10.0 wt%) brought about easier recombination of photoelectrons and holes, causing a lower quantum efficiency and photocatalytic activity. The ·OH radicals were the main active species during the degradation process, but the involvement of ·O2− radicals could not be neglected. The pathways for mineralizing of 4-nitrophenol over TiO2–RGO composites under sunlight irradiation were also proposed.