Immobilized Ag3PO4 photocatalyst for micro-pollutants removal in a continuous flow annular photoreactor

The present work evaluates the efficiency of immobilized silver phosphate (Ag3PO4) catalyst for the removal of emerging micro-pollutants under continuous flow conditions. The Ag3PO4 nanoparticles were grown on TiO2 pellets, which served as supporting material, and incorporated into an annular lab-made photoreactor operating in continuous mode. The photocatalyst was characterized by means of X-Ray diffraction (XRD) and scanning electron microscopy (SEM) acquiring data about its crystallographic structure and chemical composition at different times of irradiation. The activity of the present system was investigated for long-term operation for the destruction of 0.5 mg/L sulfamethoxazole (SMX) at a flow rate of 2 mL/min, which corresponds to a residence time of 11 min. The photocatalyst shows high removal efficiency (ca 75%) even after 74 h of operation. Consecutive experiments using the same photocatalyst were also carried out varying initial SMX concentration, residence time, type of micro-pollutants and the water matrix. SMX removal was found to increase decreasing flow rate in the range 4-1 mL/min and SMX concentration in the range 2-0.5 mg/L. Treatment efficiency in the case of different micro-pollutants like propylparaben and bisphenol A reached 60%, proving the wide-range applicability of Ag3PO4 catalyst. Moreover, when the water matrix was switched from ultrapure water (UPW) to bottled water or UPW spiked with bicarbonate or chloride only a slight deterioration on SMX removal was recorded. However, the presence of humic acid in the water matrix was found to decrease the photocatalytic activity.