本研究构建了以BDD电极为阳极，自然空气扩散电极(natural air diffusion electrode，NADE)为阴极，零价铁作为催化剂的电芬顿系统，深入探索了该系统对磺胺嘧啶(sulfadiazine，SD)的降解效果和机理。相较于其他系统，BDD-Fe-NADE系统降解优势明显。为进一步探索系统的作用机理，在BDD阳极和NADE阴极之间加入质子交换膜，构建双室降解系统，分别计算阳极室和阴极室中直接电子转移(direct electron transfer，DET)、H2O2、·OH、S2O82-和·SO4-等氧化性粒子对于磺胺嘧啶降解的贡献率。结果表明，在阳极室中，电极氧化和Fe2+催化S2O82-产生的·SO4-起主要氧化作用，贡献率分别为49。02％和35。29％;在阴极室中，Fe2+催化H2O2产生的·OH起主要氧化作用，贡献率达99。61％。在不添加污染物的条件下，阳极室积累的S2O82-浓度在180min时可达到0。4mmol·L-1，阴极室积累的H2O2浓度在120 min时可达到8 mmol·L-1。在初始pH为3时，阴极室pH会随H2O2的生成逐渐增大，阳极室pH由于·OH的生成缓慢降低。利用Gaussian软件在B3LYP/6-31+g(d，p)水平优化SD分子构象，结合密度泛函理论(Density functional theory，DFT)计算电子云密度和福井函数，确定了 SD分子中的反应活性位点，利用高效液相色谱串联质谱(Liquid chromatograph mass spectrometer)对中间产物测定，检测到质荷比(m/z)为225、279、185、171等6种中间产物，推测了 SD的三种可能降解途径。
Degradation mechanism of sulfa antibiotics by H2O2 and PS in BDD-Fe-NADE system
This paper explores the degradation effect and oxidation mechanism of the electro oxidation system with BDD as anode,NADE as cathode and zero valent Fe as catalyst.Compared with other systems,BDD-Fe-NADE system has obvious advantages in degradation.In order to further explore the mechanism of the system,a proton exchange membrane was added between BDD anode and NADE cathode to construct a two-compartment degradation system.The contributions of Direct Electron Transfer(DET),H2O2,OH,S2O82-and SO4-to sulfadiazine degradation in anode and cathode chambers were calculated.The results show that SO4-produced by S2O82-catalyzed by Fe2+and electrode oxidation play a major role in the anodic chamber,contributing 35.29％and 49.02％respectively.In the cathode chamber,OH produced by H2O2 catalyzed by Fe2+plays a major role in oxidation,contributing 99.61％.In the absence of contaminants,the concentration of S2O82-accumulated can reach 0.4 mmol·L-1at 180 min in the anode chamber,and the concentration of H2O2 accumulated can reach 8 mmol·L-1 at 120 min in the cathode chamber.When the initial pH is 3,the pH of the cathode chamber gradually increases with the generation of H2O2,while the pH of the anode chamber decreases slowly due to the generation of OH.The conformation of SD molecule was optimized at the B3LYP/6-31+g(d,p)level by Gaussian software,and the Fukui function and electron cloud density were calculated with density functional theory(DFT),and the reactive sites in SD molecule were determined.Liquid Chromatograph Mass Spectrometer(LC-MS)was used for the determination of intermediates.The Mass charge ratio(m/z)of intermediates was 225,279,317,185,171.Three possible degradation pathways were detected finally.
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