The Preparation Of Fenton-like Catalysts Based On Transition Metals And Their Catalytic Degradation Performance Studies For Activating Peroxymonosulfate

A series of studies using transition metal ions for the activation of permonosulfate?PMS?to degrade various organic contaminants has attracted much attention recently.However,the homogeneous metallic ion catalysts are prone to secondary pollution due to the difficulty in recycling.Therefore,the heterogeneous metallic salt catalysts are the better choices,especially cobalt and manganese-based salts.In order to solve the problems of low activation efficiency and poor stability of heterogeneous transition metal catalysts,graphitic carbon nitride?g-C₃N₄?and zeolitic imidazolate mental-organic framework?ZIF-8?have been used as the substrates to immobilize different cobalt or manganese catalysts on their surfaces in this thesis for activating PMS to degrade pollutants.Based on this,the following three aspects of studies have been carried out in this dissertation.In the second chapter,Mn₃O₄/g-C₃N₄ with different mass fractions of Mn₃O₄were prepared by loading Mn₃O₄ on the surface of g-C₃N₄ nanosheets through the hydrothermal method and high-temperature calcination method.It was found that the catalytic activity of Mn₃O₄/g-C₃N₄ was significantly higher than that of single g-C₃N₄or Mn₃O₄ in the presence of PMS under visible light irradiation on RhB degradation.30%Mn₃O₄/g-C₃N₄ showed optimal catalytic activity,with a kinetic constant 47 and2.2 times higher than that of g-C₃N₄ and Mn₃O₄,respectively.The quenching experiments confirmed that SO₄·^-and h⁺were the major reactive species,while·O₂^-and·OH are involved in the degradation process,but their effect is not obvious.Cyclic experiments showed that Mn₃O₄/g-C₃N₄ possessed excellent stability.Based on the above experimental results and combined with the literature,a feasible activation mechanism of the catalytic reaction over Mn₃O₄/g-C₃N₄ was proposed.In chapter three,ZIF-67/g-C₃N₄ composite catalysts were prepared.Bulk g-C₃N₄was synthesized through high-temperature calcination.The product was grinded and then heated again to obtain g-C₃N₄ nanosheet.ZIF-67/g-C₃N₄ with different mass fraction of ZIF-67 was prepared by attaching ZIF-67 on the surface of g-C₃N₄nanosheet via a hydrothermal method.It was found that the catalytic activity of ZIF-67/g-C₃N₄ was significantly higher than that of single g-C₃N₄ or ZIF-67 in the presence of PMS under visible light irradiation on RhB degradation.20%ZIF-67/g-C₃N₄ exhibited optimal catalytic activity,with a kinetic constant 41 and 1.4times higher than that of single g-C₃N₄ and mechanical mixture of 20%ZIF-67/g-C₃N₄,respectively.The quenching experiments confirmed that SO₄·^-and·O₂^-was the major reactive radicals,while·OH and h⁺played little roles.Based on the above experimental results and in combination with the literature,a feasible catalytic raection mechanism over ZIF-67/g-C₃N₄ was proposed.In chapter four,a cobalt-iron bimetallic Prussian blue analogue?PBA?was immobilized in situ on the surface of ZIF-8 to produce a PBA-ZIF8 composite catalyst via a facile in-situ growth method.The catalytic activity of PBA-ZIF8 was significantly higher than that of ZIF-8 or PBA alone.The catalytic rate constant of RhB degradation using PBA-ZIF8 was 3.3 times higher than that using PBA alone when PMS was directly activated in the absence of light for the catalytic degradation of RhB.By exploring the various experimental parameters,it was found that the degradation efficiency of RhB was effectively promoted at relatively higher PBA-ZIF8 dosage and PMS concentration,as well as at near-neutral pH environment.The quenching experiments confirmed that SO₄·^-was the major reactive radical and·OH played a minor role.Based on the above experimental results and combined with the literature,a feasible catalytic reaction mechanism over PBA-ZIF8 was proposed.Cyclic experiments with cobalt ion leaching indicated that PBA-ZIF8possessed excellent stability.In this thesis,different cobalt and manganese-based catalysts were supported on g-C₃N₄ or ZIF-8,respectively.It avoids the problem of difficult recovery and secondary pollution of homogeneous catalysts.Therefore,it has broad application prospects in the field of wastewater treatment.