溶解性黑碳促进水环境中四环素的光降解

Dissolved Black Carbon Enhanced the Photodegradation of Tetracycline in Aqueous Solution

具有固碳功能的生物炭材料在土壤修复和水体污染治理中的大规模施用导致了溶解性黑碳的(dissolved black carbon,DBC)的大量释放,其在污染物的环境地球化学过程发挥着重要作用.相比于天然溶解有机质,DBC稠环度高、芳香性强、分子量小,有更高的光电转化效率,更易产生活性中间体促进有机污染物的光降解.但不同热解温度(heating temperature,HTT)和生物质类型的DBC对水环境中抗生素(antibiotics,ATs)的光降解影响尚有待深入研究.本文选取不同HTT(300—600℃)的芦苇和芦竹生物炭制备DBC,表征其基本理化性质及结构特征,研究其对水环境中典型ATs四环素(tetracycline,TC)光降解过程的影响,探究关键水环境条件的影响.结果表明,随着HTT升高,两类DBC的有机碳含量呈先升高后降低趋势,平均分子量呈先降低后增加趋势;芳香性官能团含量增加,芳香性增强,腐殖酸和富里酸类物质含量升高.所有DBC均促进了TC的光降解(16.3%—97.0%),促进效果随HTT的升高而呈上升趋势.HTT相同时,芦竹DBC对TC光降解的促进效果高于芦苇DBC.水环境中常见阴离子(NO_(3)^(-)、HCO_(3)^(-)、SO_(4)^(2-)、Cl^(-))及阳离子(Fe^(3+)、Ca^(2+))均在不同程度上抑制了TC的光降解;碱性(pH 7—11)环境中DBC对TC光降解的促进作用强于酸性(pH 3—5)环境.活性中间体猝灭实验表明DBC对TC光降解的促进作用主要由三重激发态DBC(3DBC*)主导.本研究拓展了人们对水环境中DBC环境行为及其对共存ATs归趋的理解,为水环境中ATs环境过程和生态风险的预测提供了理论依据.

The large-scale application of biochars with the function of carbon sequestration in soil remediation and water pollution control has resulted in the discharges of dissolved black carbon(DBC),which plays an important role in the environmental geochemical process of various pollutants.Compared with natural dissolved organic matter(NOM),DBC with higher condensed degrees,stronger aromaticity,smaller molecular weight,higher photoelectric activity,potentially generates more active intermediates to facilitate the photodegradation of organic pollutants.However,the effects of DBCs produced from different biomass under different heating temperature(HTT)on the photodegradation of antibiotics in water environment was poorly understood.Therefore,the biochars derived from reed and giant reed at 300—600℃were selected to prepare the DBCs,and their basic physical,chemical properties and structural characteristics were also characterized to investigate the effects of DBCs on photodegradation process of typical antibiotic tetracycline(TC)in the water environment,and the influences of related key environmental factors were also considered.With increasing HTT,the organic carbon content of DBC increased first and then decreased,molecular weight decreased first and then increased,the aromaticity,contents of aromatic functional groups,and humic acid and fulvic acid substance increased.All the tested DBCs consistently promoted the photodegradation of TC by 16.3%—97.0%,and the promoting effect was elevated by the increasing HTT.At the same HTT,DBCs derived from giant reed showed a greater promoted effect on the TC photodegradation relative to the DBCs derived from reed.Anions(NO_(3)^(-),HCO_(3)^(-),SO_(4)^(2-),Cl^(-))and cations(Fe^(3+),Ca^(2+))that are frequently detected in the water environment generally inhibited the TC photodegradation to the different extent.DBC showed a greater promoted effect on TC degradation in alkaline(pH 7—11)environment than acidic(pH 3—5)environment.The quenching experiment of reactive intermediates revealed that the TC photodegradation by DBC was mainly mediated by the triple excited state DBC(3DBC*).These findings expand our understanding regarding the environmental behavior of DBC and the fate of coexisted ATs in water environment,and provide the theoretical basis for predicting ATs environmental process and ecological risk in water environment.