Fast photocatalytic degradation of bisphenol A by Ag3PO4/TiO2 composites under solar radiation

In this work, the photocatalytic degradation of bisphenol A (BPA) was investigated. Silver orthophosphate (Ag-3 PO4) and its composites with P25 TiO2 (Ag-3 PO4/TiO2) at various molar ratios were prepared and used as the photocatalyst, while radiation was provided by a solar simulator. The physicochemical and optical properties of the synthesized samples were investigated employing the BET method, X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy (DRS) and scanning electron microscopy (SEM/EDS). High performance liquid chromatography (HPLC) was employed to monitor changes in BPA concentration. Pure Ag3PO4 and its composites with TiO2 were found to be highly responsive in the visible spectral region owing to the narrow band gap of silver orthophosphate (2.33 eV). Optimal photocatalytic performance for the title reaction was observed for the Ag3PO4/TiO2 photocatalyst with a molar ratio 75:25. This material resulted in complete degradation of 220 mu g/L BPA in pure water with an apparent rate constant of 0.91 min(-1), which was much higher than that obtained with pure Ag-3 PO4 (0.43 min(-1)) or P25 TiO2 (0.27 min(-1)). Reaction rates were found to increase with increasing catalyst concentration in the range 50-500 mg/L and decreasing BPA concentration in the range 2200-440 mu g/L. The rate was affected negatively by the water matrix in the order pure water > drinking water > wastewater. However, spiking pure water with bicarbonate or humic acid had no measurable effect on BPA degradation. The catalysts partially lost their activity upon repeated use for 5 consecutive runs, i.e. the rate decreased by 80% and 65% for Ag3PO4 and Ag3PO4/TiO2, respectively, due to irreversible reduction of silver orthophosphate by photogenerated electrons. (C) 2016 Elsevier B.V. All rights reserved.