BDD-Fe-NADE电芬顿系统降解磺胺类抗生素的作用机理

Degradation mechanism of sulfa antibiotics by H_(2)O_(2) and PS in BDD-Fe-NADE system

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)、H_(2)O_(2)、·OH、S_(2)O_(8)^(2-)和·SO_(4)^(-)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Fe^(2+)催化S_(2)O_(8)^(2-)产生的·SO_(4)^(-)起主要氧化作用,贡献率分别为49.02%和35.29%;在阴极室中,Fe^(2+)催化H_(2)O_(2)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S_(2)O_(8)^(2-)浓度在180 min时可达到0.4 mmol·L^(-1),阴极室积累的H_(2)O_(2)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H_(2)O_(2)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.

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),H_(2)O_(2),·OH,S_(2)O_(8)^(2-)and·SO_(4)^(-)to sulfadiazine degradation in anode and cathode chambers were calculated.The results show that·SO_(4)^(-)produced by S_(2)O_(8)^(2-)catalyzed by Fe^(2+)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 H_(2)O_(2)catalyzed by Fe^(2+)plays a major role in oxidation,contributing 99.61%.In the absence of contaminants,the concentration of S_(2)O_(8)^(2-)accumulated can reach 0.4 mmol·L^(-1)at 180 min in the anode chamber,and the concentration of H_(2)O_(2)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 H_(2)O_(2),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.