Ag/AgX (X = Cl, Br, or I) Nanocomposite Loaded on Ag3PO4 Tetrapods as a Photocatalyst for the Degradation of Contaminants

A silver phosphate (Ag3PO4)/silver (Ag)/silver halide (AgX, X = Cl, Br, or I) ternary composite photocatalysts were prepared by loading Ag nanoparticles on Ag3PO4 tetrapods followed with in situ halogenation. The interface charge transfer behavior in the Ag3PO4/Ag/AgX nanocomposite was studied, and the photocatalytic performance was also evaluated. The results show that the Ag3PO4/Ag/AgI photocatalyst exhibits higher photocatalytic activity than the other two photocatalysts due to the more matched band structure between AgI and Ag3PO4. An internal electric field (IEF) from Ag3PO4 to AgI is formed at the heterogeneous interface, so the photogenerated electrons at the conduction band of AgI can rapidly transfer to the valence band of Ag3PO4 and recombine with photogenerated holes, which is consistent with the S-scheme charge transfer mechanism. Meanwhile, the photogenerated electrons left at the conduction band of Ag3PO4 can transfer to Ag nanoparticles due to the Schottky junction and react with oxygen to produce •O2–, which is proved to be the main active species in the photocatalytic procedure. This tandem junction modulated between the S-scheme heterojunction and Schottky junction promotes the efficient separation of photogenerated carriers, thus significantly increasing the average PL lifetime of electrons by 2.95 times. Therefore, the Ag3PO4/Ag/AgI photocatalyst exhibits excellent photocatalytic activity for the degradation of methylene blue and norfloxacin. The seven consecutive cyclic tests prove the good stability of the photocatalyst, thus showing the application potential in the field of sewage treatment.