Research On Effect And Mechanism Of Sulfadiazine Degradation In A Multi-electrode Paralleling Dielectric Barrier Discharge Plasma System Catalyzed By ZnO/Cellulose Acetate Films

With the development of animal husbandry,aquaculture and other industries,sulfonamide antibiotics represented by sulfadiazine have been widely used,and the corresponding problems caused by antibiotics has attracted many attentions.At present,the sulfadiazine（SDZ）concentrations detected in the water environment are increasing.It is difficult of the traditional wastewater treatment technology to remove the antibiotics efficiently,which poses a threat to human health and ecological environment.Therefore,it is very research clean and efficient technologies to treat the wastewater polluted by the antibiotics.Advanced oxidation technologies（AOTs）is a kind of technology that can produce hydroxyl radical（·OH）to treat wastewater under the conditions of high pressure,electricity,sound,light or catalyst addition.As a kind of AOTs,dielectric barrier discharge plasma（DBDP）technology has the virtue of high treatment efficiency,no secondary pollution and mild reaction conditions.However,DBDP technology still has the disadvantage of low energy utilization in the practical application.The utilization of ultraviolet light（UV）,ozone（O₃）and hydrogen peroxide（H₂O₂）is also limited.In this study,on the basis of setting up the DBDP system assembled with multi electrode paralleling structure electrodes instead of single high-voltage electrode,ZnO/cellulose acetate（CA）film was introduced as catalyst to improve the SDZ degradation as well as the energy utilization efficiency of the DBDP system.Firstly,the optimum number of high-voltage electrodes in the DBDP system was determined according to results of the discharge characteristics analysis,O₃output detection and corresponding energy yield calculation.The decolorization of methyl orange（MO）under different conditions of the electrode number was then investigated to verify the results.Secondly,nano ZnO/CA films were prepared and characterized and then taking SDZ as the target pollutant,the effect of nano ZnO loading amount and the number of films on the SDZ degradation were investigated.Finally,the SDZ degradation in the DBDP-ZnO/CA synergistic system under different solution parameters were studied and the degradation mechanism of SDZ by the synergistic effect was analyzed.The main results are summarized as follows:（1）Setting up and optimization of the multi-electrode paralleling DBDP system.Comparing the O₃production and calculating the corresponding energy yield under the conditions of the five kinds of DBDP systems with the high-voltage electrode number ranging from 1 to 5,it can be concluded that the DBDP system with five high-voltage electrodes could produce more O₃and energy yield,the values were0.539 mg/L and 2.96 g/k Wh,respectively,which were higher than those obtained in the DBDP system with a single high-voltage electrode（0.254 mg/L and 1.58 g/k Wh）.The decolorization of MO in the DBDP system with five high-voltage electrodes reached to the maximum value of 96.1%,which verified the higher efficiency of the DBDP system with multi-electrodes.（2）Research on the catalytic effect of the prepared ZnO/CA films and the critical parameters analysis.The ZnO/CA films were firstly prepared successfully.The characterization results show that the nano-ZnO particles were dispersed uniformly in the CA matrix,and the ZnO/CA films has better light utilization performance than the nano-ZnO.SDZ was taken as the target pollutant,and the degradation rate,kinetic analysis,degradation energy efficiency and the synergistic factors of catalytic degradation between ZnO/CA films and DBDP were taken as the evaluation indicators.The effects of the nano-ZnO loading amount and the number of the ZnO/CA films on the SDZ degradation showed that the optimal loading amount of the nano-ZnO was 3%of the mass of the CA,and the optimal number of the films was 4.Under the conditions,the maximum degradation rate of the SDZ in the DBDP-ZnO/CA system was 97.2%,which was 9.3%higher than that in DBDP alone system.The effects of the initial concentration and initial p H value of the SDZ solution showed that the degradation rate of SDZ decreased with the increase of the initial concentration of the solution,and a lower initial concentration（20 mg/L）was conducive to the SDZ degradation;the neutral solution condition was favorable for the SDZ degradation.The catalytic effect of ZnO/CA films was slightly higher than that of the powder ZnO.After four cycles using,the ZnO/CA films still has good catalytic effect in the DBDP system,and its surface morphology and internal structure remained stable.（3）Research on the catalytic mechanism of the ZnO/CA films in the DBDP system for the SDZ degradation.The obtained results showed that the solution p H increased with the reaction time during the SDZ degradation process in the DBDP alone system and the change of the solution conductivity presented the contrary trend.The addition of the ZnO/CA films could strengthen the changing trend.The mineralization,the biodegradability of the SDZ solutions and the concentrations of O₃and·OH in deionized water increased by the addition of the ZnO/CA films into the DBDP system.The TOC removal increased from 16.26%to 21.36%,the COD removal increased from 34.26%to 47.77%,and the concentrations of O₃and·OH increased by 0.143 mg/L and 0.2 mg/L,respectively.The results of the ESR analysis proved the promotion of the ZnO/CA films addition on the formation of the·OH and the ¹O₂.The scavenger addition could inhibit the SDZ degradation.The ion chromatographic analysis showed that the inorganic ions including NO₂^-,NO₃^-and SO₄^2-could be formed by the SDZ degradation and the SO₄^2-concentration was the highest.Four possible degradation pathways were inferred by analyzing the organic intermediates with the LC-MS analysis.The catalytic mechanism of ZnO/CA films in the DBDP system for the SDZ degradation was finally speculated:electron-hole pairs could be formed by the UV light in the DBDP system and then reacted with O₂,H₂O,O₃and H₂O₂to produce more O₃,·OH,¹O₂and O₂·^-.The combination of ZnO and CA could reduce the band gap energy of the ZnO and then broaden the response range of the catalyst to the light.Furthermore,the CA films could inhibit the agglomeration of the powder ZnO and then improve the catalytic effect further.