Facile synthesis of TiO 2 /Ag 3 PO 4 composites with co-exposed high-energy facets for efficient photodegradation of rhodamine B solution under visible light irradiation.

In this study, TiO 2 /Ag 3 PO 4 composites based on anatase TiO 2 nanocrystals with co-exposed {101}, {010}/{100}, {001} and [111]-facets and Ag 3 PO 4 microcrystals with irregular and cubic-like polyhedron morphologies were successfully synthesized by combining hydrothermal and ion-exchange methods. The anatase TiO 2 nanocrystals with different high-energy facets were controllably prepared via hydrothermal treatment of the exfoliated [Ti 4 O 9 ] 2- /[Ti 2 O 5 ] 2- nanosheet solutions at desired pH values. The Ag 3 PO 4 microcrystal with different morphologies was prepared via the ion-exchange method in the presence of AgNO 3 and NH 4 H 2 PO 4 at room temperature, which was used as a substrate to load the as-prepared anatase TiO 2 nanocrystals on its surface and to form TiO 2 /Ag 3 PO 4 heterostructures. The apparent rate constant of the pH 3.5-TiO 2 /Ag 3 PO 4 composite was the highest at 12.0 × 10 -3 min -1 , which was approximately 1.1, 1.2, 1.4, 1.6, 13.3, and 24.0 fold higher than that of pH 0.5-TiO 2 /Ag 3 PO 4 (10.5 × 10 -3 min -1 ), pH 7.5-TiO 2 /Ag 3 PO 4 (10.2 × 10 -3 min -1 ), pH 11.5-TiO 2 (8.8 × 10 -3 min -1 ), Ag 3 PO 4 (7.7 × 10 -3 min -1 ), blank sample (0.9 × 10 -3 min -1 ), and the commercial TiO 2 (0.5 × 10 -3 min -1 ), respectively. The pH 3.5-TiO 2 /Ag 3 PO 4 composite exhibited the highest visible-light photocatalytic activity which can be attributed to the synergistic effects of its heterostructure, relatively small crystal size, large specific surface area, good crystallinity, and co-exposed high-energy {001} and [111]-facets. The as-prepared TiO 2 /Ag 3 PO 4 composites still exhibited good photocatalytic activity after three successive experimental runs, indicating that they had remarkable stability. This study provides a new way for the preparation of TiO 2 /Ag 3 PO 4 composite semiconductor photocatalysts with high energy crystal surfaces and high photocatalytic activity.