Anion-exchange synthesis of Ag2S/Ag3PO4 core/shell composites with enhanced visible and NIR light photocatalytic performance and the photocatalytic mechanisms

- Ag2S/Ag3PO4 composites with well-defined core/shell structures were prepared.
- The core/shell structure was dependent on the loaded Ag2S contents.
- Ag2S-5%/Ag3PO4 exhibited the highest visible-light-driven activity.
- Ag2S-50%/Ag3PO4 exhibited the highest NIR-light-driven activity.
- Different mechanisms were proposed for visible and NIR photocatalysis.

A series of Ag2S/Ag3PO4 composites with well-defined core/shell structures were synthesized via an in-situ anion-exchange reaction between Ag3PO4 dodecahedrons and Na2S solutions. The obtained samples were characterized by XRD, BET, AFS, SEM, TEM, EDX, XPS, DRS and PL. The Ag2S/Ag3PO4 composites exhibited excellent photocatalytic activity towards the degradation of MO under both visible and NIR light irradiation. The optimal composite Ag2S-5%/Ag3PO4 exhibited the highest visible-light-driven activity, which could degrade almost all MO within 120 min. Under NIR light irradiation, the Ag2S-50%/Ag3PO4 composite showed the best photocatalytic activity and decomposed more than 30% of MO after 240 min of irradiation. Recycling experiments confirmed that the Ag2S/Ag3PO4 composites had superior cycle performance and stability. The photocatalytic activity was highly dependent on the Ag2S content and the well-defined core/shell structure. The enhancement in photocatalytic activity of Ag2S/Ag3PO4 composites could be mainly ascribed to the efficient separation of photogenerated charge carriers between the intimate interface of Ag2S shell and Ag3PO4 core. The in-situ formed Ag nanoparticles at surfaces of Ag3PO4 and Ag2S during photocatalytic process acted as charge transmission bridges and electron trapping centers, respectively, resulting in the stable Ag2S/Ag/Ag3PO4 Z-scheme system and Ag/Ag2S/Ag3PO4 ternary system. Based on the experimental results, the possible photocatalytic mechanisms for MO degradation over Ag2S/Ag3PO4 composites under both visible and NIR light irradiation were proposed.

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