| Advanced Oxidation Processes（AOPs）are of great interest in the treatment of difficult dye wastewater due to their high oxidation capacity and wide range of applications.AOPs based on ozonation and persulfate oxidation have excellent oxidative degradation performance,and the combined use of ozonation and persulfate oxidation can improve oxidative degradation capacity,and reduce the cost and toxicity of the system.In order to accelerate the mass transfer process of the system and enhance the degradation efficiency of pollutants,it is of great significance to investigate catalysts that can activate both PMS and O3.In this paper,MnFe LDHs were prepared by a simple co-precipitation method,and on this basis,MnFe2O4/LDHs composites with magnetic properties for easy recovery were synthesized.The catalytic performance of MnFe LDHs and their complexes for the coupled PMS/O3 system was investigated in terms of material physicochemical properties,pollutant degradation,and reaction mechanisms.The main work carried out in this thesis is as follows:In order to verify the successful synthesis of MnFe LDHs and MnFe2O4/LDHs materials and to investigate the intrinsic link between the physicochemical properties of the materials and the catalytic degradation reactions,the structure,ionic and elemental composition,specific surface area and magnetic properties of the prepared materials were investigated using a variety of characterization tools.The LDHs and their complexes were found to have a large specific surface area of 184.14 m2/g and97.42 m2/g,respectively,clear crystal structures and abundant functional groups such as O-H,C-O,and M-O,with superior physicochemical properties after compounding.To investigate the catalytic effect of MnFe LDHs on the PMS/O3 system,the MnFe LDHs/PMS/O3 system was used for the removal of the cationic dye Rhodamine B（Rh B）.The degradation rate was 98.4%at 12 min,which was significantly higher than other comparative systems,and the removal rate of TOC was 29.5%.The effects of dosage,initial p H of the solution,coexisting anions,and humic acid on the degradation of Rh B were investigated,and the optimum dosage was determined to be 0.4 g/L for catalyst,0.2 g/L for PMS and 0.3 L/min for O3.Rh B could be completely degraded in10 min.In the range of p H 3-9,the degradation effect was excellent.Common anions in the water had no effect,while humic acid had an inhibitory effect.Meanwhile,the system is generally effective for the degradation of different dyes.To further investigate the reaction mechanism and degradation process,a combination of burst experiments and electron paramagnetic resonance spectroscopy（EPR）revealed that sulfate radicals(SO4·-),hydroxyl radicals（·OH）,superoxide radicals(O2·-)and singlet oxygen（1O2）were all involved in the reaction,with·OH contributing more.The degradation pathway of Rh B was deduced using Liquid Chromatography-Mass Spectrometry（LC-MS）and the biotoxicity of the intermediate was evaluated.In order to verify the stability and availability of the material,four cycles of experiments were carried out,and it was found that the degradation rate of Rh B was basically unchanged,and the leaching rates of Mn and Fe ions were 0.719%and 0.007%,respectively.To investigate the activity of the magnetic MnFe2O4/LDHs composites,they were used to activate the PMS/O3 system for the degradation of Tartrazine（TTZ）,and it was found that the catalytic performance was further improved.The effect of different reaction parameters on the catalytic degradation was investigated and the results showed that the highest TTZ removal rate of 96.1%was achieved at 30 min for MnFe2O4/LDHs concentration of 0.4 g/L,PMS concentration of 0.2 g/L and O3 influx of 0.3 L/min.However,the degradation rate decreased as the initial p H increased,while NO3-,H2PO4-,and HA had inhibitory effects,HCO3-had to promote effects,and Cl-and SO42-had negligible effects.The main active substances involved in the reaction and the degradation mechanism were investigated in combination with EPR tests and bursting experiments,and it was found that·OH,SO4·-,O2·-and 1O2 were all involved in the degradation of TTZ,with·OH and O2·-playing major roles.Based on this,the reaction mechanism and degradation pathways were analyzed,and the biotoxicity of the intermediates was lower than the parent TTZ.In order to verify the stability of MnFe2O4/LDHs,cyclic experiments and ion dissolution tests were carried out.In the fifth cycle,the degradation effect remained at 94.2%,and the ion dissolution rate was lower than that of MnFe LDHs.Finally,in order to investigate the practical effects of the system,the magnetic MnFe2O4/LDHs complex was used to activate the coupled PMS/O3 system to degrade the actual dye wastewater,and it was found that the raw water chromaticity was significantly reduced,and the COD removal rates of raw water and intermediate water reached 46.6%and 54.2%,respectively,which proved the feasibility of the system in practical applications.In conclusion,MnFe LDHs and their complexes have a good catalytic effect on PMS/O3.This work provides a theoretical basis and data support for the synergistic catalysis of PMS/O3 and the deep treatment of dye wastewater. |
