Photocatalytic activity and mechanism of bisphenol a removal over TiO2-x/rGO nanocomposite driven by visible light

In the present study, Ti3+ and oxygen vacancies (Ti3+/O-v) self-doped TiO2 and coupled with a reduced graphene oxide (rGO) nanocomposite (TiO2-x/rGO) was successfully synthesized via a facile hydrothermal-calcination method for the efficient degradation of bisphenol A (BPA) under visible light. The results of XPS, ERP and TEM analyses revealed that the presence of Ti3+/O-v in the lattice of TiO2-x/rGO leads to the narrowed band gap and enhanced visible light harvesting. The chemical bonds (TieOeC) between TiO2-x and rGO act as the channel for electron transfer, consequently resulting in the efficient charge separation, which was investigated and confirmed by such methods as PL spectra and time-resolved PL spectra. In addition, the coupling of TiO2-x and rGO could strongly suppress the aggregation of TiO2-x particles and therefore improve the adsorption of organic pollutants. For the synergistic effect of the three preeminent features mentioned above, TiO2-x/rGO exhibited a 6.16-, 2.92-and 2.55-fold faster reaction rate for BPA degradation than that of pristine TiO2, TiO2/rGO and TiO2-x, respectively. Moreover, the effects of the initial substrate concentration, initial solution pH, catalyst dosage and inorganic anions on BPA removal were also investigated in depth. EPR measurements indicated that center dot O-2(-) as the major oxidizing species, is responsible for the degradation of BPA. Next, the feasible pathway of BPA degradation by TiO2-x/rGO was proposed based on the analysis of intermediate products. Finally, the mechanism of the enhanced photocatalytic performance by TiO2-x/rGO under visible light was discussed. Based on these results, the TiO2-x/rGO nanocomposite could be an efficient and promising photocatalyst for the degradation of organic pollutants in water.