Enhanced degradation of tetracycline under natural sunlight through the synergistic effect of Ag3PO4/MIL-101(Fe) photocatalysis and Fenton catalysis: Mechanism, pathway, and toxicity assessment

Here, we show that the adverse environmental and health effects of tetracycline (TC) can be efficiently reduced by encapsulating Ag3PO4 into MIL-101(Fe) to construct a Ag3PO4/MIL-101(Fe) heterojunction composite through advanced oxidation processes, such as Fenton catalysis, photocatalysis, and photo-Fenton catalysis. Notably, the reaction can be driven by natural sunlight and does not require any artificial energy source. Remarkably, the optimal degradation of TC can be achieved under different compositions of the composite system through photocatalysis and photo-Fenton catalysis. For photo-Fenton catalysis, the maximum degradation rate of TC (2.5730 min−1) is achieved when the mass ratio of MIL-101(Fe) to Ag3PO4 in the composite is 5:1, which is 31.65- and 3.12-fold of that in the Ag3PO4 + PDS + Sunlight and MIL-101(Fe) + PDS+ Sunlight catalyst systems, respectively. Moreover, the internal conversion of matrix during photocatalysis and Fenton catalysis processes inhibits the photocorrosion of Ag3PO4 and improves the reusability of the composite. Furthermore, it is found that both radical and non-radical species participate in the TC degradation. Besides, the degradation products and catalytic mechanism of Ag3PO4 and Ag3PO4/MIL-101(Fe) systems are explored. The toxicity evaluation results suggest that the intermediates produced during Ag3PO4/MIL-101(Fe) catalysis have a lower biotoxicity than those produced during Ag3PO4 catalysis. Overall, this work provides an effective strategy to inhibit the inherent photocorrosion of Ag3PO4 and establishes an efficient catalytic system for the treatment of organic-contaminated wastewater under natural sunlight conditions.