【作者】 杨波；

【导师】 张永丽；

【作者基本信息】 四川大学 ， 土木工程， 2022， 博士

【摘要】 抗生素类物质在水环境中的广泛残留,在世界范围内已引起了人们的重点关注,尤其是对长期暴露于该环境中的水生物种所面临的生态毒性以及相关衍生耐药性。抗生素类物质的双电离结构特性使其能够与水中的溶解性有机质(DOM,Dissolved organic matter)和金属离子(Mn+)发生相互作用,导致水环境中抗生素同时存在自由态和结合态两种状态。以往的研究中DOM常作为光敏剂或自由基竞争剂,Mn+常作为催化剂参与反应,且多关注自由态抗生素的化学转换过程,而DOM和Mn+与抗生素的结合作用对其在水环境中的迁移、转化和降解等均会产生显著且复杂的影响,相关结合作用对抗生素化学转化的影响研究较少。本论文旨在系统性分析结合态四环素(TET,Tetracycline)分别在DOM和三价铁离子(Fe3+)背景水体下的赋存和去除机制。(1)论文选取水环境中四种典型的溶解性有机质,包括牛血清蛋白BSA(蛋白质类)、海藻酸钠SAA(多糖类)、腐植酸HA和富里酸FA(腐殖质类),考察其在不同离子强度IS和pH条件下与TET的结合作用。分别采用平衡透析袋技术和傅里叶红外光谱(FTIR)测定TET的结合浓度以及DOM参与结合的作用位点,并通过UV-Vis光谱、总有机碳(TOC)、三维荧光光谱(EEM)、Zeta电位和动态光散射等技术表征分析IS和pH对结合作用的影响。结果表明,羧基和酚羟基是DOM结合TET的主要位点,DOM与TET结合能力由大到小依次为HA>FA>>BSA>SAA。相比于BSA和SAA,HA和FA具有更大的结合能力,这主要由于羧基和酚羟基的数量更多,Zeta电位更低且分子尺寸更大。离子强度通过压缩分子结构和表面双电层显著抑制结合作用,pH则通过改变DOM表面官能团水解和TET离子分布形态产生影响。结合Donnan模型和多元线性回归分析,论文建立了修正后的Karickhoff模型,该模型可有效预测不同IS和pH条件下DOM的结合性能。最后通过实验测定logKDOC与模型计算logKoc之间的线性拟合以验证了模型的稳定性和准确性。(2)研究进一步选取结合性能较强的HA作为目标溶解性有机质,考察了 HA/TET体系中自由态TET和结合态TET-HA分别在UV、UV/H2O2、UV/PS和UV/PMS氧化工艺的氧化降解过程。FTIR和核磁共振氢谱(1H NMR)分析表明,HA中的羧基和酚羟基,以及TET分子的-N(CH3)2基团是参与结合的主要位点。二维相关光谱(2D-COS)分析表明,相比于酚羟基,HA中的羧基在与TET的结合过程中具有更强的结合倾向。随着离子强度的增加,自由态和结合态TET的表观降解速率差值(Δkobs)减小。随着Ca2+和Mg2+的引入,由于TET-C a2+/Mg2+复合物的形成,其表观降解速率差值逐渐增大。通过自由基淬灭实验以及理论计算验证了典型工艺体系(UV/PS、UV/PMS和UV/H2O2)中降解TET的主导氧化活性物质占比分别为·OH/SO4·-(58.6%)、PMS(59.2%)和UV辐射(60.6%)。原位荧光时间扫描和紫外差分吸收光谱分析表明除UV/PS体系外,自由态TET优先于结合态TET-HA被氧化降解。(3)研究进一步分析了 HA的结合效应对TET在UV、UV/H2O2、UV/PS和CNTs/PS氧化工艺中的降解途径、降解产物和产物毒性的影响。通过UPLC-QTOF-MS/MS分析,结合双键当量(DBE)和芳香度指数(AI)计算,分别确定了自由态、混合态和结合态TET在不同氧化体系中降解途径,并鉴定出TET的33种降解产物。含N分子二维核密度变化以及密度泛函理论(DFT)计算分析表明,HA与TET的结合作用削弱了氧活性物质对二甲基氨基(-N(CH3)2)的攻击,并进一步诱导了结合态TET的A环和B环直接裂解生成具有较高毒性的双环结构产物。毒性评估和统计分析表明,中等分子量(230≤m/z≤380)的中间产物毒性相对较高,且产物毒性与分子结构的环数密切相关,产物毒性由大到小分别为双环>>三环>单环/四环结构产物。论文构建了毒性累积模型(PTAM)以计算氧化过程中整体毒性变换,结果表明结合作用通过削弱TET的氧化降解及减少降解产物的浓度,显著降低了 UV和UV/H2O2体系中TET降解的整体毒性。然而,在UV/PS和CNTs/PS体系中,HA的结合作用会促进毒性更高的降解中间产物的生成。(4)论文选取水环境中常见的Fe3+作为目标金属离子,考察Fe3+与TET的微观结合作用机制。研究结果表明Fe3+会与水环境中TET迅速发生结合作用形成Fe3+-TET配合物,TET与Fe3+的结合作用会显著抑制Fe3+的水解过程。论文分别采用1HNMR、2D-FTIR-COS、XPS和Raman技术表征分析Fe3+与TET的结合作用,结果表明TET分子中的-N(CH3)2和-OH基团是参与结合的主要位点。通过紫外差分光谱分析表明,Fe3+-TET配合物的摩尔比为1:1。而含两个-N(CH3)2官能团的二甲胺四环素(MC)分子与Fe3+的配合摩尔比为1:2,再次验证了-N(CH3)2在结合过程中的关键作用。通过结合Benesi-Hildebrand模型和分子/离子物料平衡原理,论文准确计算了不同Fe3+和TET浓度条件下Fe3+和TET各自的结合浓度和比例。(5)论文最后考察了在紫外辐射下Fe3+的结合效应对TET的化学转化机制的影响,并系统研究了其降解途径、降解产物和产物毒性。研究结果表明,Fe3+与TET通过结合作用形成了 Fe3+-TET配合物,通过不完全水解转化为Fe(OH)2+-TET,并会在紫外辐射条件下快速生成·OH,实现TET的快速降解,同时Fe(OH)2+-TET被还原为Fe2+-TET。Fe2+-TET配合物可以进一步被氧化为Fe3+-TET配合物实现氧化还原循环。与自由态TET相比,与Fe3+结合的TET具有更高的降解效率。通过与MC的降解对比以及EDTA的竞争实验,证实了 TET的结合率与降解速率呈正相关。通过UPLC-QTOF-MS鉴定了 10种主要转化降解产物,解析了 TET的降解途径。原位荧光时间扫描和毒性评估分析结果表明,提高Fe3+浓度可有效减少毒性较高的中间体的产生。本论文系统地研究了水环境中DOM和Fe3+与典型抗生素TET在微界面的结合特性,分析了结合态TET在不同氧化工艺下的微界面去除效能,并揭示了结合作用对TET的降解途径、降解产物和产物毒性的影响机制,从而为水环境中结合态残留污染物的表征分析及其化学转换机制分析提供重要的理论支持。更多还原

【Abstract】 Residual antibiotics are widespread in the aquatic environment,drawing extensive attention due to the ecotoxicity and related derivative drug resistance.Antibiotics with a double ionization structure show a strong tendency to complex with dissolved organic matter(DOM)and metal ions(Mn+),leading to the simultaneous existence of free and bound state antibiotics in the aquatic environment.In previous studies,DOM mainly served as photosensitizers or radical scavengers,and Mn+ were generally adopted as catalysts to participate in reactions.More importantly,the studies mainly focused on the chemical conversion process of free-state antibiotics.However,few studies referred to the binding effect of DOM and Mn+on the migration,transformation and degradation of antibiotics in the aquatic environment.This work aims to systematically analyze the occurrence and interface removal mechanisms of bound tetracycline(TET)in DOM and ferric ion(Fe3+)background water.(1)Four typical kinds of DOM(including bovine serum proteins(BSA),sodium alginate(SAA),humic acid(HA)and fulvic acid(FA))were selected to investigate the binding effects on zwitterionic TET under various conditions of ionic strength(IS)and pH.The dialysis equilibration technique was employed to determine the binding concentrations of TET,and the influence of IS and pH on binding performance was evaluated via UV-Vis spectroscopy,total organic carbon(TOC),Excitation-Emission-Matrix spectra(EEM),Zeta potentials and molecule size distribution analysis.As a result,the carboxyl and phenolic hydroxyl groups were identified as the main binding sites based on the Fourier transform infrared spectroscopy(FTIR)analysis,and the binding capability of four DOMs followed as HA>FA>>BSA>SAA.Compared to BSA and SAA,HA and FA possessed higher binding capabilities due to the richer functional groups,lower Zeta potential and larger molecular size.The ionic distribution of TET was affected by IS via inhibiting the binding interaction by compressing the molecular structure and the surface electric double layer and by pH via affecting the surface functional groups.By combining the Donnan model and the multiple linear regression analysis,a modified Karickhoff model was established to effectively predict the binding performance of DOM under different IS and pH conditions.The higher R2 values of linear fitting between experiment-measured logKDOC and model-calculated logKoc indicated the stability and accuracy of the modified Karickhoff model.(2)HA was chosen as the target DOM to further investigate the performance of both free TET and bound TET-HA oxidation by UV,UV/H2O2,UV/PS and UV/PMS processes in the HA/TET systems.FTIR data showed that the carboxyl and phenolic hydroxyl groups in HA were the main binding sites of TET,while nuclear magnetic resonance(NMR)analysis showed the binding of TET engages its-N(CH3)2 groups.Two-dimensional correlation spectroscopy(2D-COS)data showed that the carboxyl groups in DOM were more sensitive than phenolic groups in the binding of TET.The difference in the degradation rates(Δkobs)between the free and bound TET decreased with the increase of ionic strength(NaNO3),but it increased with the addition of metal ions(Ca2+and Mg2+)due to the formation of TET-Ca2+/Mg2+complexes.Quenching experiments showed that the free radicals(·OH and SO4·-),PMS oxidant and UV light were the main contributors to the TET degradation in UV/PS,UV/PMS and UV/H2O2 processes,respectively.In-situ fluorescence time scanning and differential absorbance spectra showed that free TET was preferentially oxidized over the bound TET in all the tested treatments except UV/PS.(3)The distribution and toxicity assessment of the transformation products of TET in free,mixed and bound states by UV,UV/H2O2,UV/PS and CNTs/PS processes was further systematically investigated.A total of 33 major transformation products were identified by UPLC-QTOF-MS/MS analysis,combining the double bond equivalence and aromaticity index calculations.The binding interaction would weaken the attack on the dimethylamino(-N(CH3)2)group and induce the direct destruction of rings A and B of TET through the analysis of 2D Kernel Density changes and density functional theory(DFT)calculations.Toxicity assessment and statistics revealed that the intermediate products with medium molecular weight(230≤m/z ≤380)exhibited higher toxicity,which was closely related to the number of rings of molecular structures(followed as 2>>3>1≈4).A predicted toxicity accumulation model(PTAM)was established to evaluate the overall toxicity changes during various oxidation processes.(4)Fe3+was selected as the target metal ion to probe the micro-combination mechanism between Fe3+ and TET.The results suggested that Fe3+would rapidly combine with TET in water to form Fe3+-TET complexes.The binding effect would significantly inhibit the hydrolysis of Fe3+,and weaken the HPLC chromatographic peak area of TET.The binding interaction was characterized via 1H NMR,2DFTIR-COS,XPS and Raman techniques,indicating that the-N(CH3)2 and-OH groups of TET molecule were the main sites involved in the binding process.Based on the UV differential spectroscopy,the molar ratio of Fe3+-TET complex was 1:1,while the molar ratio of minocycline(MC)molecules containing two-N(CH3)2 functional groups to Fe3+is 1:2,further confirming the critical role of-N(CH3)2 in the binding interaction.By combining the Benesi-Hildebrand equation and the principle of molecular/ion balance,the binding concentration and ratio of both Fe3+and TET under different conditions of Fe3+and TET concentrations were accurately calculated.(5)This study is devoted to systematically revealing the transformation mechanism of Fe3+-TET complexes induced by UV irradiation.The results suggested that the complexation between Fe3+and TET would effectively inhibit the hydrolysis of Fe3+,accelerate the Fe3+-TET/Fe2+-TET redox cycle,and enhance the generation of hydroxyl radicals(·OH)under UV irradiation to promote the degradation of Fe3+-TET and TET.By combining the complex ratio of Fe3+and TET at various conditions,a theoretical model was established to predict the oxidation rate constants of Fe3+-TET complexes.A total of 10 main transformation intermediates were identified via UPLC-QTOF-MS analysis,and the degradation pathway was proposed.The results of the time fluorescence scan and Ecological Structure Activity Relationships(ECOSAR)analysis indicated that increasing the Fe3+concentration could effetely reduce the generation of toxic intermediate.In this work,the binding properties of DOM and Fe3+with typical antibiotic TET at the micro-interface in water environment were systematically investigated;the micro-interface removal efficiency of bound TET under different oxidation processes was compared;and the influence mechanism of the binding effect on the degradation pathway,degradation products formation and toxicity were investigated.This study provided some important theoretical basis for the characterization and chemical transformation mechanism analysis of bound residual pollutants in the water environment.更多还原