粘土表面自由基产生机理及其降解邻苯二甲酸酯的研究

Clay minerals are a group of phyllosilicate minerals with negative charged surfaces due to isomorphous substitution. The high ratios of surface areas and negative surfaces make clay minerals adsorb large amount of organic contaminants (such as phthalate esters, PAEs) and heavy metal cations. Many researches focus on the adsorption and desorption of PAEs to clay minerals, however, limited attention is paid to the degradation of PAEs adsorbed. In this proposed protocol, five different clay minerals with different structures, iron contents will be selected, including ferruginous smectite NAu-2, montmorillonite smectite SWy-3 and SAz-2, kaolinite KGa-1b and illite IMt-2. In the study, the experiments will be conducted in an anaerobic condition without light or a dry anaerobic condition with UV light. The degradation kinetics, reaction pathways and products of three phthalate esters (diethyl phthalate, di-n-butyl phthalate and di-(2-ethylhexyl) phthalate) will be studied with state-of-the-art experiment techniques and instruments, including HPLC-UV or MS/MS, GC-FID/MS, UV-Vis, ATR-FTIR, and EPR spectroscopy. In this proposed protocol, electrochemistry station will be applied to investigate electron transfer between reduced dissolved organic matter/phenolic acids and clay minerals, interactions between DOC and transition metal cations; the impacts of redox status on the degradation of phthalate esters will be discussed; radicals produced on clay surfaces would be detected with EPR to explore reaction mechanisms of electron transfer from organics to clay structure Fe(III). We will also collect soil samples at different depths in facility agriculture to examine the relationships between redox potential, soil components and phthalate esters’ degradation rates. The results of this proposed protocol will be helpful in understanding the transport and transformation of phthalate esters in contaminated agriculture soils, and will inform efforts to remediate plasticizers in soils.

在还原条件下含铁粘土对有机污染物的降解有促进作用，有关这方面的研究比较少。邻苯二甲酸酯(PAEs)是一类广泛存在的土壤污染物，对人类的健康有危害作用。在本项目研究中，我们将以绿蛭石，蒙皂石、高岭石和伊利石为例，研究它们与常见的小分子酚酸或土壤可溶性有机质（DOC）作用产生表面自由基的可能性；研究不同环境条件下自由基生成的影响因素，包括小分子酚酸的结构、粘土结构铁的位置和含量、吸附的过渡金属阳离子、溶液pH、氧气的存在和干湿条件，以及这些自由基对PAEs的降解途径的影响。在研究中，我们将通过电子顺磁共振技术捕捉粘土产生的自由基，阐明粘土的活性位点。在研究中，我们还将通过对设施农业土壤进行实地采样分析不同深度土壤层中PAEs降解与土壤粘土成分、氧化还原电位的相关性。本项目的研究结果将有助于理解PAEs分子在土壤表层和亚表层的迁移转化途径，为土壤污染治理提供科学依据。

土壤是许多有机污染物的汇，同时土壤的不同组分与有机污染物间有相互作用，对污染物的迁移转化产生影响，但是由于土壤成分的复杂性，其间的作用机制非常不清晰。本研究主要针对土壤主要成分之一的粘土开展研究，在还原条件下含铁粘土对有机污染物的降解有促进作用，有关这方面的研究比较少。在本项目研究中，我们以绿蛭石，蒙皂石、高岭石和伊利石为粘土代表，研究了它们与常见的小分子酚酸或土壤可溶性有机质（DOC）相互作用，产生表面自由基的性质，及其对常见有机污染的去除影响（以邻苯二甲酸酯为主）。结果表明，小分子酚酸在含铁粘土表面会发生电子传递，产生高活性的瞬态自由基和持久性自由基，并且电子传递改变粘土结构铁的价态和构型，粘土结构铁的位置和含量影响粘土的活性，从而促进污染物的去除；吸附的过渡金属阳离子（Fe3+）、溶液pH、氧气浓度会影响粘土表面吸附有机物（如对乙酰氨基酚）的反应途径和产物，而且空气干湿条件、光照等环境因子也会改变表面自由基的生成量和种类。在研究中，我们研发了原位电子顺磁共振装置和技术由于观测和解析粘土产生的自由基，也开发了系列高效的环保粘土材料和高效活性电极用于产生更大量的自由基，促进土壤中有机污染物的原位降解。本项目的研究结果有助于解决土壤有机污染，为土壤污染治理提供科学依据。