Controllable synthesis of phosphate-modified BiPO₄nanorods with high photocatalytic activity: Surface hydroxyl groups concentrations effects

Surface properties of photocatalysts are crucial to improve their efficiency in the removal of wastewater pollutants. In this study, phosphate-modified BiPO4photocatalysts with different PO43-/Bi molar ratios were controllably synthesized through a one-pot hydrothermal method. The concentrations of surface hydroxyl groups on BiPO4samples can be tuned by adjusting the PO43-/Bi3+molar ratios. XRD results showed that surface modification by phosphate could boost the crystallinity of BiPO4, which was beneficial to photocatalytic performance. XPS and IR spectra revealed that PO43-modified only the surface of BiPO4. The optical absorption of phosphate-modified BiPO4samples showed an obvious blue shift compared with that of bare BiPO4. Photocatalytic activities of the as-prepared samples were evaluated by the decomposition of methylene orange (MO) under ultraviolet light and simulated solar-light irradiation. Experimental results demonstrated that the photocatalytic performance of the modified samples significantly improved after the BiPO4surface was modified by different amounts of PO43-. Both an indirect scavenger method and an electron spin resonance method were adopted to determine the production and intensity of free radicals during photocatalytic degradation. Results suggested that MO was removed predominantly through oxidation by OH radicals, as confirmed by theoretical calculations. Moreover, the mechanism of photocatalytic degradation of MO over the as-prepared phosphate-modified BiPO4was proposed.