Investigating Molecular Structure Modulation To Enhance The Co-catalytic Mechanism Of MoS₂-activated Peroxymonosulfate

Molybdenum disulphide（MoS₂）is widely used in iron-based catalysts for activation of PMS systems due to its excellent co-catalytic properties,effectively solving the problem of low Fe（III）/Fe（II）cycle efficiency.However,it still faces research bottlenecks.Firstly,only the edge-exposed Mo（IV）can be used for the reduction of high-valent to low-valent metal ions,and the basal inactive Mo cannot be used effectively;secondly,the function of the non-metallic component（S）in molybdenum disulphide was ignored in most research,resulting in its co-catalytic function not being efficiently performed and a large amount of wasted co-catalyst.In this thesis,the molecular structure of molybdenum disulphide has been modulated by adjusting the combination of catalytic and co-catalytic components,the basal inactive low-valent molybdenum and terminal unsaturated sulphur was used.The co-catalytic mechanism of molybdenum disulphide in a two-part system is explored.The results are as follows.（1）An iron-doped molybdenum disulphide（Fe-MoS₂）catalyst was prepared by a one-step hydrothermal method,which provides continuous activation of PMS for the removal of tetracycline hydrochloride（TCH）from aqueous solutions.The prepared Fe-MoS₂catalyst has dual metal active site of Fe and Mo atoms to enhance the regeneration of Fe（II）and to prevent the leakage of iron.In addition,the Fe-MoS₂catalysts exhibit good recyclability and could undergo multiple TCH degradation cycles in the activated PMS system.The generated radicals(SO₄^·-,O₂^·-,and·OH)and non-radical species（¹O₂）are responsible for the TCH degradation as confirmed by radical trapping experiments and molecular probe experiments.LC-MS was used to identify intermediates in the degradation of TCH and to propose a pathway for TCH degradation.The present work takes full advantage of the low activity of Mo（IV）at the basal plane,ensuring the continued production of divalent iron for a certain number of cycles.The shortcoming is the bulk catalyst results in a failure to effectively function as a terminal unsaturated sulphur in molybdenum disulphide.（2）A particulate Fe₃O₄supported by wrinkled MoS₂with discernible sulfur vacancy（S_V）was prepared by a one-step hydrothermal method,forming a flower-like Fe₃O₄-MoS₂composite catalyst.The first time,a strong affinity of S_Vto PMS was demonstrated,facilitating the formation of an intermediate Fe ^III-PMS*while also modulating the generation of pivotal active species.The simultaneous production of sulphate radicals,high-valent iron-oxygen species(≡Fe ^IV=O)and singlet oxygen（¹O₂）during the activation of PMS with Fe₃O₄-MoS₂catalysts was confirmed by various characterisation techniques.In addition,the≡Fe ^IV=O stemmed from the Fe ^III-PMS*precursor through heterolytic cleavage and concomitant rearrangement of the O–O bond were proposed.Meanwhile,the ¹O₂is excited by PMS from the active oxygen（O*）which is liberated from the lattice oxygen(O_lat)in iron oxides.Further,the impressive performance of Fe₃O₄-MoS₂catalysts in removing typical micropollutants from real water sources such as secondary effluent from wastewater treatment plants,tap water,and surface water stream was showed.This study takes full advantage of the role of Mo（IV）with terminal unsaturated sulphur,using both free radical and non-free radical pathways for the removal of pollutants.