Abstract
Pristine Ag&sub3;PO&sub4; microspheres were synthesized by a co-precipitation method, followed by being calcined at different temperatures to obtain a series of calcined Ag&sub3;PO&sub4; photocatalysts. This work aims to investigate the origin of activity and stability enhancement for Ag&sub3;PO&sub4; 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 (VO˙˙) are created and metallic silver nanoparticles (Ag NPs) are formed by the reaction of partial Ag⁺ in Ag&sub3;PO&sub4; semiconductor with the thermally excited electrons from Ag&sub3;PO&sub4; and then deposited on the surface of Ag&sub3;PO&sub4; microspheres during the calcination process. Among the calcined Ag&sub3;PO&sub4; samples, the Ag&sub3;PO&sub4;-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&sub3;PO&sub4; photocatalyst after calcination.