Oxidation of tetracycline hydrochloride with a photoenhanced MIL-101 (Fe)/g-C3N4/PMS system: Synergetic effects and radical/nonradical pathways

MIL-101(Fe)-based catalysts have been widely used for degradation of organic pollutants based on peroxymonosulfate (PMS) activation. Hence, a facile calcination and hydrothermal method was used in this study to prepare a MIL-101(Fe)/g-C3N4 composite catalyst with high activity and high stability for PMS activation to degrade tetracycline hydrochloride (TC) under visible-light irradiation. We clearly elucidated the mechanism involved in the MIL-101(Fe)/g-C3N4 photo Fenton-catalyzed PMS activation process by separating the PMS activation and pollutant oxidation processes. The synergetic effects of MIL-101(Fe) and g-C3N4 involved MIL-101 (Fe) acting as an electron shuttle mediating electron transfer from the organic substrate to PMS, accompanied by redox cycling of the surface Fe(II)/Fe(III). Multiple experimental results indicated that PMS was bound to the surface of MIL-101(Fe)/g-C3N4 during visible irradiation and generation of sulfate radicals (SO4 center dot-), hydroxyl radicals (center dot OH) and superoxide anion free radicals (center dot O2- ) for the radical pathway and singlet oxygen (1O2) and holes (h+) for the nonradical pathway. The major degradation pathways for TC can be described as demethylation, deamination, deamidation and carbonylation. This work provides valuable information and advances the fundamental understanding needed for design and syntheses of metal-free conjugated polymers modified by metal-organic frameworks for heterogeneous photo-Fenton reactions.

Automated summary

A facile calcination and hydrothermal method was used in this study to prepare a MIL-101(Fe)/g-C3N4 composite catalyst for the degradation of tetracycline hydrochloride (TC) using peroxymonosulfate (PMS) activation. The mechanism of the MIL-101(Fe)/g-C3N4 photo Fenton-catalyzed PMS activation process was elucidated, demonstrating the involvement of various radicals and nonradicals. This research provides valuable insights for the design and synthesis of metal-free conjugated polymers modified by metal-organic frameworks for heterogeneous photo-Fenton reactions.