Effect of reduced graphene oxide load into TiO2 P25 on the generation of reactive oxygen species in a solar photocatalytic reactor. Application to antipyrine degradation

TiO2-based photocatalysis is intensively investigated for efficient degradation of emerging environmental contaminants, but the generation of reactive oxygen species during such photocatalytic reactions is often under-researched. In this paper, we study the formation of reactive oxygen species under real solar irradiation on TiO2 P25 loaded with reduced graphene oxide (rGO). TiO2/rGO composites were prepared by mixing graphene oxide and TiO2 P25, followed by hydrothermal treatment. The band gap of TiO2 was not affected in the composites but the optical properties of the systems changed due to the morphology and presence of rGO. When these composites were studied under solar irradiation, the generation rate of hydroxyl HO center dot radicals under solar light was higher in pure TiO2 than in TiO2/rGO, but also their decay with time, so TiO2/rGO eventually presented higher HO center dot concentration at longer times. Moreover, adding rGO to TiO2 also affected the concentration of superoxide O-2(center dot-) and singlet oxygen O-1(2) radicals, which we assign to the charge transfer between TiO2 and rGO and the presence of remaining holes on the surface. The amount of generated hydrogen peroxide H(2)O(2 )and consumed in these systems was practically the same, so its concentration remained low. The catalytic systems developed were tested in the solar photocatalytic degradation of antipyrine, demonstrating the relationship between the evolution of generated reactive oxygen species along the reaction time and the consumption of antipyrine. The TiO2 valence band holes were also found to be the responsible primary species along the course of reaction especially in the final mineralization step.