Enormous enhancement in photocatalytic performance of Ag₃PO₄/HAp composite: A Z-scheme mechanism insight

For the first time, the Ag₃PO₄/HAp composite catalysts were synthesized through a facile in-situ ion exchange method and carefully studied by various techniques including XRD, BET, SEM & TEM, DRS, ICP, XPS, ESR, and photocurrent measurements. It was found that the well dispersed small Ag₃PO₄ particles were loaded on the HAp support, and the surface area was slightly increased after the ion exchange process. Importantly, the coupling of the Ag₃PO₄ and HAp significantly enhanced the separation efficiency of the photogenerated electron-hole pairs and then promoted the activity for the photodegradation of RhB or 4-CP under visible light irradiation. What is more, the effect of calcination temperature of the HAp support on the catalytic performance was also discussed. It is interesting to find that the apparent rate constant of Ag₃PO₄/HAp-773 composite photocatalyst was 0.21min^-1, which was 10 times higher than that of pristine Ag₃PO₄. The radical trapping experiments revealed that the introduction of HAp transformed the photocatalytic mechanism, which was obviously different from that of pure Ag₃PO₄. The enormous enhancement in catalytic performance may be attributed to the vacancy of HAp that resulted from the alternation in electronic state of surface PO₄ group under irradiation. Ultimately, a possible Z-scheme mechanism for the efficient Ag₃PO₄/HAp composite was proposed.