腐殖质作用下锑(III)光化学氧化机理研究

Antimony(Sb) has been considered as a globally emerging contaminant. The toxicity of Sb is assumed to be similar to that of arsenic and depends on its chemical species. However, there is limited knowledge available regarding chemical transformation of Sb. As an important carrier of contaminants in aquatic environments, humic substances significantly affects chemical species, bioavailability and toxicity of contaminants. The information on the influences of humic substances on the chemical transformation of Sb is limited. The main objective of this study is to elucidate the mechanisms regarding photoinduced oxidation of Sb(III) in the interface of humic substances and water. Different types of humic substances, originated from river, soil, coal and peat, and two fractions of humic substances (HA and FA) are selected. The reaction kinetics for the photooxidation of Sb(III) to Sb(V) in the presence of humic substances are examined under various environmental parameters. Furthermore, the mechanisms regarding photoinduced oxidation of Sb(III) in the presence of humic substances are to elucidate based on the modern equipment techniques, such as FT-IR, ESR, 3D-EEM and so on. The complexation of Sb(III, V) with humic substances in the photooxidative reaction system is to be investigated. The prevailing photooxidants and intermediates involved in the reaction are to be identified. The reaction pathways and electron transfer for the photooxidation of Sb(III) are expected to be clarified. This project is beneficial to further understand the environmental fates, distribution of chemical speciation of Sb in aquatic systems. The present study enriches the knowledge on toxicity, bioavailability and environmental risk assessment of Sb and is advantageous to expound or forecast the biogeochemical behaviors of Sb in aquatic systems.

锑是"新兴"的全球性污染物，锑的毒性效应与其化学价态密切相关，而目前关于锑形态转化的研究还很少。腐殖质是地表水环境中污染物的重要载体，是影响污染物形态、生物有效性和毒性的重要因素，腐殖质对Sb形态转化的影响机制还不清楚。本项目以Sb(III)为对象，对比研究光照条件下不同来源（水体、土壤、煤炭、泥炭）、不同组分（HA和FA）腐殖质-水界面Sb(III)的光化学氧化动力学特征与主要影响因素；采用FT-IR、ESR、三维荧光等技术多角度揭示腐殖质作用下Sb(III)光化学氧化反应微观机理及其差异，结合对反应体系中不同价态Sb与腐殖酸络合行为的研究，共同揭示起氧化作用的腐殖酸中间体与氧化反应途径，探明具氧化作用的活性自由基和电子传递过程。研究成果对于深入了解水环境中Sb形态分布、迁移转化和归趋，以及毒性与生物有效性评价具有重要的理论和实际意义，为预测Sb在水体中的环境地球化学行为提供科学依据。

锑已被认为是“新兴”的全球性污染物，目前关于锑在环境中形态转化的研究还很少。腐殖质是地表水环境中污染物的重要载体，是影响污染物形态、生物有效性和毒性的重要因素。本项目以Sb为研究对象，对比研究光照条件下不同类型腐殖质-水界面Sb(III)的光化学氧化动力学特征及其环境影响因素；采用电子顺磁共振技术揭示光化学氧化反应微观机理；采用平衡透析法分离自由态和络合态Sb，考察环境条件（腐殖酸浓度、pH值、竞争性离子的存在）对腐殖质与Sb(III、V)络合特征的影响及络合机理，并对比不同类型腐殖质与Sb(III、V)络合能力的差异并阐述其原因。本研究发现：五价Sb化学性质相对稳定，不易与腐殖酸发生络合反应与光化学反应。研究结果表明：腐殖酸作为光敏化剂，当紫外光照射时腐殖酸自身发生光解反应产生具有活性的超氧自由基和羟基自由基促使Sb(III)发生氧化反应生成Sb(V)，氧化作用在pH4.0时达到最大值。此外，本研究还发现：pH值对Sb(III)与腐殖质的络合能力具有显著影响，在pH为4.0时具有最大分配系数，当pH在4.0~8.0之间时，随pH值增加，二者络合能力显著降低，络合作用还随腐殖酸浓度的增加而加强，Na+和Ca2+显著抑制Sb(III)与腐殖酸的络合作用；机理研究表明腐殖酸分子结构中的酚羟基和羧基是络合作用的主要结合位点。本研究成果对于深入了解水环境中Sb 形态分布、迁移转化和归趋，以及毒性与生物有效性评价具有重要的理论和实际意义，为预测Sb 在水体中的环境地球化学行为提供科学依据。