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^•-), hydroxyl radicals (•OH) and superoxide anion free radicals (•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.

Developing monolithic carbon-based catalyst with low cost, easy separation and high performance to degrade pollutants via PMS activation is crucial. In this work, a series of novel monolithic Me-CA catalysts based on biomass derived carbon aerogel were prepared by hydrothermal method using waste watermelon peel as raw material. Co-CA catalyst showed excellent performance to activate PMS for 2, 4-DCP degradation in different temperature and different water matrices. Different pollutants, such as ciprofloxacin (CIP), bisphenol A (BPA), and 2, 4-dichlorophenoxyacetic acid (2, 4-D) could also be removed in the Co-CA/PMS system. As expected, Co-CA could be easily separated from degraded solution, and show high stability and reusability for PMS activation with a lower cobalt leaching. Based on the results of the quenching tests, electron paramagnetic resonance (EPR) spectra, Chronoamperometric test (i-t curves) and electro-chemical impedance spectroscopy (EIS), the PMS activation mechanism was proposed. The phytotoxicity assessment determined by germination situation of mung bean indicated that PMS activation could eliminate the hazards of 2, 4-D. Therefore, this study provides a low cost, efficient and environmental-friendly monolithic biomass carbon aerogel catalyst for different pollutants degradation, which further advances monolithic catalyst for practical wastewater treatment.

A LaCoO ₃ /g-C ₃ N ₄ catalyst with high stability was designed and used for PMS activation to degrade TC.

Metal-organic frameworks (MOFs) have unique properties and stable structures, which have been widely used as templates/precursors to prepare well developed pore structure and high specific surface area materials. In this article, an innovative and facile method of crystal reorganization was designed by using MOFs as sacrificial templates to prepare a layered double hydroxide (LDH) nano-layer sheet structure through a pseudomorphic conversion process under alkaline conditions. The obtained CoMn-LDH and CoFe-LDH catalysts broke the ligand of MOFs and reorganized the structure on the basis of retaining a high specific surface area and a large number of pores, which had higher specific surface area and well developed pore structure compared with LDH catalysts prepared by traditional methods, and thus provide more active sites to activate peroxymonosulfate (PMS). Due to the unique framework structure of MOFs, the MOF-derived CoMn-LDH and CoFe-LDH catalysts could provide more active sites to activate PMS, and achieve a 2,4-dichlorophenol degradation of 99.3% and 99.2% within 20 minutes, respectively. In addition the two LDH catalysts displayed excellent degradation performance for bisphenol A, ciprofloxacin and 2,4-dichlorophenoxyacetic acid (2,4-D). X-ray photoelectron spectroscopy indicated that the valence state transformation of metal elements participated in PMS activation. Electron paramagnetic resonance manifested that sulfate radical () and singlet oxygen (1O2) were the main species for degrading pollutants. In addition, after the three-cycle experiment, the CoMn-LDH and CoFe-LDH catalysts also showed long-term stability with a slight activity decrease in the third cycle. The phytotoxicity assessment determined by the germination of mung beans proved that PMS activation by MOF-derived LDH catalysts can basically eliminate the phytotoxicity of a 2,4-D solution. This research not only developed high-activity LDH catalysts for PMS activation, but also expanded the environmental applications of MOF derivants.