Electron transfer mediated photo-Fenton-like synergistic catalysis of Fe,Cu-doped MIL-101 coupled with AgPO: Quantitative evaluation and DFT calculations.

Widespread use of tetracycline (TC) results in its persistent residue and bioaccumulation in aquatic environments, posing a high toxicity to non-target organisms. In this study, a bimetal-doped composite material AgPO/MIL-101(Fe,Cu) has been designed for the treatment of TC in aqueous solutions. As the molar ratio of Fe/Cu in composite is 1:1, the obtained material AP/MFeCu is placed in an aqueous environment under visible light irradiation in the presence of 3 mM peroxydisulfate (PDS), which forms a photo-Fenton-like catalytic system that can completely degrade TC (10 mg/L) within 60 min. Further, the degradation rate constant (0.0668 min) is 5.66 and 7.34 times higher than that of AP/MFe and AP/MCu, respectively, demonstrating a significant advantage over single metal-doped catalysts. DFT calculations confirm the strong adsorption capacity and activation advantage of PDS on the composite surface. Therefore, the continuous photogenerated electrons (e) accelerate the activation of PDS and the production of SO, resulting in the stripping of abundant photogenerated h  for TC oxidation. Meanwhile, the internal circulation of Fe/Fe and Cu/Cu in composite also greatly enhances the photo-Fenton-like catalytic stability. According to the competitive dynamic experiments, SO have the greatest contribution to TC degradation (58.93%), followed by O (23.80%). The degradation intermediates (products) identified by high-performance liquid chromatography-mass spectrometry (HPLC/MS) technique indicate the involvement of various processes in TC degradation, such as dehydroxylation, deamination, N-demethylation, and ring opening. Furthermore, as the reaction proceeds, the toxicity of the intermediates produced during TC degradation gradually decreases, which can ensure the safety of the aquatic ecosystem. Overall, this work reveals the synergy mechanism of PDS catalysis and photocatalysis, as well as provides technical support for removal of TC-contaminated wastewater.