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.
Competing Interests: The authors declare no conflict of interest.
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