Construction of MIL-53(Fe) metal-organic framework modified by silver phosphate nanoparticles as a novel Z-scheme photocatalyst: Visible-light photocatalytic performance and mechanism investigation

Novel heterostructure photocatalysts consisted of MIL-53(Fe) and silver phosphate (Ag3PO4) were successfully developed through a simple in situ precipitation strategy in this work. The photocatalytic activities of the as-synthesized samples were assessed via multiple antibiotics degradation, including tetracycline (TC), oxytetracycline (OTC), chlortetracycline (CTC) and deoxytetracycline (DCL). All the obtained Ag3PO4/MIL-53(Fe) composites exhibited much more superior photocatalytic activities than pure MIL-53(Fe) and Ag3PO4. Especially, the optimal composite with 1:3 mass ratio of Ag3PO4:MIL-53(Fe) (APM-3) displayed the best photocatalytic activity, for which the removal of antibiotics was 93.72% (TC), 90.12% (OTC), 85.54% (CTC) and 91.74% (DCL) under visible light irradiation for 1 h. The APM-3 also exhibited good photostability and recyclability. Three-dimensional (3D) EEMs (excitation-emission matrix fluorescence spectroscopy) was applied to further investigate the TC degradation process, and the TC intermediates were identified by high-performance liquid-mass spectrometry (HPLC-MS). The possible degradation pathway for TC was also discussed. In addition, electron spin resonance (ESR) measurement and quenching experiments verified that O2−, OH and h+ radicals all worked during the degradation process. In the end, a possible Z-scheme heterostructure model composed of MIL-53(Fe), metallic Ag and Ag3PO4 was proposed, in which the small reducible Ag nanoparticles functioned as a center for charge transmission. Powerful redox ability and effective separation of photoinduced carriers can be achieved in this Z-scheme heterostructure system. The findings of this work could offer a novel way to design MOF-based materials for remediation of contaminated water.