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 0.21 min(-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. (C) 2015 Elsevier B.V. All rights reserved.