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 assynthesized 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 O-center dot(2)-, (OH)-O-center dot 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.