Origin of Activity and Stability Enhancement for Ag(3)PO(4) Photocatalyst after Calcination

Pristine Ag(3)PO(4) microspheres were synthesized by a co-precipitation method, followed by being calcined at different temperatures to obtain a series of calcined Ag(3)PO(4) photocatalysts. This work aims to investigate the origin of activity and stability enhancement for Ag(3)PO(4) photocatalyst after calcination based on the systematical analyses of the structures, morphologies, chemical states of elements, oxygen defects, optical absorption properties, separation and transfer of photogenerated electron-hole pairs, and active species. The results indicate that oxygen vacancies (V(O)˙˙) are created and metallic silver nanoparticles (Ag NPs) are formed by the reaction of partial Ag(+) in Ag(3)PO(4) semiconductor with the thermally excited electrons from Ag(3)PO(4) and then deposited on the surface of Ag(3)PO(4) microspheres during the calcination process. Among the calcined Ag(3)PO(4) samples, the Ag(3)PO(4)-200 sample exhibits the best photocatalytic activity and greatly enhanced photocatalytic stability for photodegradation of methylene blue (MB) solution under visible light irradiation. Oxygen vacancies play a significantly positive role in the enhancement of photocatalytic activity, while metallic Ag has a very important effect on improving the photocatalytic stability. Overall, the present work provides some powerful evidences and a deep understanding on the origin of activity and stability enhancement for the Ag(3)PO(4) photocatalyst after calcination.