Research On Bisphenol A Degradation In A Dielectric Barrier Discharge Plasma System Catalyzed By Nano Metal Oxide

With the continuous development of organic chemical industry,the components of wastewater discharged from factories become more and more complex.Wastewater contains a large number of refractory organic compounds,which are difficult to be effectively removed by the traditional wastewater treatment methods.The research depends on the characteristics of the dielectric barrier discharge plasma(DBDP)can generate hydroxyl radicals(·OH),ozone(O3)and hydrogen peroxide(H2O2),and other reactive oxygen species(ROS)to degradate refractory organic pollutants in water,combined with the multi-catalytic advantages of the nano-metals(photocatalysis,and catalysis for O3 and H2O2),hence introduce nano-metal oxides into the DBDP system.A reaction system combined with nano-metal oxides and DBDP was established in the paper to degrade organic pollutants in water,and then to improve the energy utilization efficiency of the DBDP system and the degradation efficiency of the organic compounds.In the paper,a DBDP system was established firstly;then two kinds of nano-metal oxides,including ZnO and WO3,were prepared and characterized;bisphenol A(BPA)was used as the target pollutant to investigate the catalytic effect of different catalysts thirdly and then to optimize the solution parameters on BPA degradation;finally the degradation mechanism of BPA and the catalytic mechanism of nano-metal oxides were analyzed.The specific research results are summarized as follows:(1)Preparation and characterization of ZnO.Taking BPA as the target pollutant,the effects of different ZnO dosage,solution initial pH,carrier gas type,chemical collectors’ addtiont on the BPA degradation and corresponding energy utilization efficiency in DBDP/ZnO system were investigated as well as kinetic analysis were carried out.The optimum operating conditions for the BPA degradation were obtained as follows:the optimal dosage of ZnO was 50 mg/L,compared with the sole DBDP system,the degradation rate of the BPA was increased by 17.0%;compared with the alkaline solution,the acidic and weak acidic solution were favorable for the BPA degradationcan;when the carrier gas was O2,the degradation rate of the BPA in the catalytic system was the highest,and the degradation rate could reach 100%after 20 min treatment;102,electrons,·OH and O2·-all play a crucial role for the BPA degradation in the catalytic system,of which the role of O2·-was more significant;UV-Vis full-band scanning analysis of the BPA solutions at different discharge time showed that the absorption peak of BPA presented a gradual downward trend with the prolong of discharge time,and the peaks of by-products gradually increased.The detection of TOC and COD after 40 minutes of degradation demonstrated that the addition of ZnO could increase the removal rate of the TOC and the COD.(2)Preparation and characterization of WO3,and then establish the DBDP/WO3 system to investigate the effect of different WO3 dosage,solution initial pH,carrier gas type and collectors’ additon on the BPA degradation.The obtained results showed that:with the increase of the catalyst dosage,the degradation rates of the BPA exhibited a tendency of increasing first and then decreasing,the optimum additive amount of the WO3 was 175 mg/L,when the treatment time was 60 min,BPA degradation rate coulde reach 83.0%;neutral conditions were more conducive to the BPA degradation,both acidic and alkaline solution could produce inhibitory effects;when the carrier gas was oxygen,the degradation rate could be improved greatly,and reached 100%after 30 min reaction.The addition of radical scavenger was not conducive to the BPA degradation.Studies confirmed that.OH played a major role for the BPA degradation.Cycling test and characterization comparison of the WO3 before and after reaction showed that the WO3 had good stability(3)Catalytic mechanism of the nano-WO3 was investigated.The results showed that after adding WO3 into the DBDP system,the O3 concentration in the liquid phase decreased from 0.206 mg/L to 0.121 mg/L,while the H2O2 concentration of increased accordingly,which proved that the addition of catalyst could convert O3 to ·OH;the addition of WO3 could also improve the removal rate of TOC by 11.8%and the removal rate of COD by 14.6%;LC-MS analysis showed that the main degradation products of BPA were 1,4-benzenediol,fumaric acid,phenylacetone,4-p-hydroxyacetophenone,isopropylphenol,4-cumylphenol.And the catalytic mechanism of WO3 was speculated:the photo effect produced in the DBDP system could activate WO3 to generate electron-hole pairs,and then electrons and holes could catalyze the active substance(O3 and H2O2)formed in the DBDP system to form ·OH,which finally improved the degradation efficiency of the BPA.