Ag incorporated nano BiPO4: sonochemical synthesis, characterization and improved visible light photocatalytic properties

We report an efficient route for the sonochemical synthesis of undoped BiPO4, Ag3PO4 and silver doped BiPO4:Ag(x%) (x = 2, 5, 10 and 20) nanostructures using bismuth/silver nitrate and ammonium dihydrogen phosphate as precursors. The products obtained have been characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (UV-vis DRS) and X-ray photoelectron spectroscopy (XPS). The size and morphology of BiPO4 exhibited drastic changes on Ag doping. The surface areas of the samples have been estimated using the Brunauer-Emmett-Teller (BET) method. The catalytic activities of all the samples for the rhodamine-B degradation were investigated systematically under UV and visible-light irradiation. Undoped BiPO4 exhibited excellent photocatalytic activity under UV light but the degradation of RhB was only similar to 60% under visible light, while Ag doped BiPO4 samples showed almost complete degradation of the dye under visible light. Amongst all of them, BiPO4:Ag(10%) exhibited the best photocatalytic activity. Furthermore, after photocatalysis, the nanoparticles could be readily separated from the reaction system by low-speed centrifugation and reused. Stability of the photocatalysts was ascertained using FT-IR and Raman spectroscopy. After five recycles, the nanoparticles did not exhibit any apparent loss in activity, confirming its stability despite recycling. By tuning the band gap and measuring the surface area of the nanoparticles using BET tests, we found that the combined effect of these two factors resulted in good performance of the BiPO4:Ag(10%) photocatalyst under visible light irradiation.