Efficient Activation Of PMS By Bimetallic Compounds And Their Composite Membranes For Degradation Of Sulfonamides In Water

Sulfonamides（SAs）have been widely distributed in environment,which even at trace level have potential threat to the human health and the whole eco-system.Sulfate radical SO₄^·-based advanced oxidation process（SR-AOPs）shows strong capacity in decomposing emerging contaminants owing to its high oxidization ability for a wide range of refractory organics.In consideration for the practical utilization and operation cost,the activation of PMS by heterogeneous-based catalysts provides an alternative route for pollution removal in aqueous solution,in which the enhanced efficiencies of PMS activation and contaminants degradation can be achieved.However,the heterogeneous nanocatalyst has problems in not only recovery,but also agglomeration phenomenon,which is not conducive to the exposure of active sites.In this thesis,cobalt-copper layered double hydroxides（CoCu LDHs）,cobalt-iron Prussian blue analogs（CoFe PBAs）and corresponding calcined derivatives were prepared and used as PMS activators for the degradation of SAs.Besides,the mechanism of SAs degradation was clarified.More importantly,the optimized bimetal compounds were assembled on membrane.The nanocatalyst@PVDF membrane and nanocatalyst@fiber membrane were constructed to improve the reusability of catalyst and its practical application potential.The main works of this thesis are as follows:CoCu LDHs were synthesized and optimized through the co-participation methods.Following,CoCu LDOs were fabricated by calcination treatment.The physiochemical properties of the catalysts were systemically measured by various characterization methods.In particular,Co1Cu1 LDH possessed a typical three-dimensional shuttle-like nanosheet layered stacking micromorphology with plentiful mesoporous structure,and exhibited more excellent electron transfer performance.And then,the catalytic performances of as-prepared catalysts were evaluated via degradation process of sulfamethoxazole（SMX）.It was demonstrated that Co1Cu1 LDH possessed the superior PMS activation performance for SMX degradation and mineralization compared with CoCu LDOs and other CoCu LDHs.Under the optimized conditions of 150 mg L-1 PMS concentration,60 mg L-1 catalyst dosage at reaction temperature of 25℃,the SMX degradation efficiency and mineralization efficiency reached 95.2%and 64.9%,respectively.Moreover,the negligible effects of pH value and common coexisting substances（Cl-,NO3-,HCO3-and humic acid）on the reaction system were determined.In addition,the quenching experiments implied SO₄^·-,·OH,·O2-and 1O2 were the predominant reactive oxide species responsible for SMX degradation.Therefore,the degradation of SMX in the Co1Cu1 LDH/PMS system was completed by synergistic process of free radicals and non-free radicals.More importantly,Co1Cu1 LDH nanocatalysts showed good stability of catalytic performance and crystal structure.A series of CoFe PBAs nanomaterials were prepared by co-precipitation method as well,and Co1Fe1 PBA derivatives were synthesized via calcination treatment.The obtained catalysts were all block structure mainly composed of clustered nanoparticles,and with good electron transfer performance and rich mesoporous structure,which would promote the PMS activation process by as-obtained catalysts.Moreover,the optimal reaction condition was confirmed as the PMS concentration of 300 mg L-1,and Co1Fe1 PBA dosage of 60 mg L-1 in sulfacetamide（SAM）solution（10 mg L-1）,76.1%of SAM was eliminated within initial 40 min.Based on the results of XPS and electrochemical property characterization,the electron transfer occurred on the surface of Co1Fe1 PBA to activate PMS.Therefore,Co1Fe1 PBA/PMS reaction system was a radical-based oxidation system.Besides,co-existing inorganic ions（Cl-,NO3-,HCO3-）and common organics（humic acid）in water with diverse concentrations did not significantly affect SAM degradation efficiency.The stability,which is conducive to catalyst recovery and reuse,of Co1Fe1 PBA nanocomposite was demonstrated.In order to further expand the practical application of nanocatalysts,the optimized bimetal compounds were used to construct nanocatalyst@PVDF membranes and nanocatalyst@fiber membranes.The physicochemical property of as-obtained composite membranes was detected,confirming that the catalyst nanoparticles were bound to membrane substrate tightly and distributed on the surface evenly.And then,the PMS activation performance of these composite membranes was evaluated to remove organic pollutants in water,concluding SAs simulation wastewater and medical wastewater.The experimental results proved that composite membrane/PMS reaction system could be applied not only for the oxidative degradation of a specific antibiotic,but also for the treatment of actual medical wastewater,degrading and mineralizing organic pollutants efficiently.In detail,in the medical wastewater treatment process by LDH@PVDF/PMS,PBA@PVDF/PMS,LDH（9.09%）@PAN/PMS and PBA（6.25%）@PAN/PMS reaction system,TOC removal efficiency reached 89.7%,93.5%,93.1%and 98.4%,respectively.Moreover,the dissolution percentages of Co ions of Co1Cu1 LDH,Co1Fe1 PBA,LDH@PVDF,PBA@PVDF,LDH（9.09%）@PAN and PBA（6.25%）@PAN were 0.26%,0.43%,0.22%,0.09%,0.27%and 1.36%,respectively.Obviously,the dissolution concentration of metal ions in theses composite membrane-based reaction systems were pretty low,part of them even lower than that of the corresponding nanocatalyst-based PMS activation system.In addition,the composite membranes could maintain excellent catalytic performance after repeated activation reaction.Consequently,the performance of nanocatalyst@PVDF membrane and nanocatalyst@fiber membrane are excellent and stable,and it is easy to recover from water.So that these composite membranes can meet the needs of practical applications.Moreover,the construction of the composite membranes greatly improves the practical applicability of nanocatalysts in wastewater treatment process.Therefore,this work provides a theoretical basis not only for the design and preparation of PMS heterogeneous catalysts,but also for the study of PMS activation mechanism and the treatment of wastewater containing antibiotics.