抗生素在粘土矿物表面的光降解行为及机理研究

As emerging pollutants, photochemical behavior of antibiotics in the environment attracted great attention. Many studies have been conducted to investigate the photolysis of antibiotics. However, most of these studies were mainly focused on the photolysis of antibiotics in aqueous solution. Few works were performed to examine the photolysis of antibiotics adsorbed on solid matrices. By now, little information is available about the photochemistry of antibiotics on solid matrices, and the difference of photolytic behavior and mechanism between the adsorbed molecules and the free molecules in aqueous solution is still unknown. Considering clay minerals are the main constituents of soil and sediment, this study will be focused on the photolysis of antibiotics on clay minerals, aiming at investigating the photodegradation of antibiotics on suspended clay mineral particles and solid layer. The main objectives of this research are to propose a kinetic model for photodegradation of antibiotics on solid matrices, and investigate the influence of environmental factors on the photodegradation. Moreover, the photolytic mechanism is expected to be elucidated via identification of photoproducts, and the difference of photoreactivity and photochemical behavior between the adsorbed molecules and the free molecules can be clarified by comparing the photochemistry of antibiotics on solid matrices with that in aqueous solution. The research findings could lead to a better understanding of the photodegradation of antibiotics on solid matrices, and lay a solid foundation for further study on the photolysis of antibiotics on multi-component media such as soil and sediment.

作为一种新兴污染物，抗生素在环境中的光化学行为受到研究者的广泛关注。目前抗生素的光降解研究绝大部分都集中在水相，而对存在于固相介质（土壤、沉积物）表面的抗生素光解却很少关注，尤其对其光解行为和机理以及与水相光解的差异缺乏认识。鉴于粘土矿物是土壤和沉积物的重要组分，本项目围绕单一组分固相介质——粘土矿物表面抗生素的光解开展研究。项目着重对悬浮粘土矿物颗粒表面和干燥粘土矿物薄层表面的抗生素光解行为进行研究，建立抗生素在粘土矿物表面的光解动力学模型，分析环境因素对光解的影响；借助中间产物的鉴定，阐明抗生素的光解路径及机理；进一步通过与水相中抗生素的光解进行对比分析，探讨吸附态抗生素分子与水相中自由分子的光活性、光解产物及光解路径差异，阐释产生差异的内在机制。研究成果将为认识抗生素在固相介质表面光解提供有价值的参考，同时为后续研究抗生素在多组分固相介质表面光解奠定坚实的基础。

抗生素在水相中的光解已经取得大量研究成果，而对吸附于固—液界面上的抗生素的光解行为及反应机理却知之甚少。本项目以揭示固—液界面上吸附态抗生素的光降解规律，探讨其与水相光解的差异为研究目标，重点研究了以下几个方面的内容：（1）选择2:1型粘土矿物—蒙脱石模拟固相介质，研究氟喹诺酮抗生素—环丙沙星（CIP）在其表面的光解行为及反应机理，并与水相光解进行对比。考察了CIP在蒙脱石晶格层间的光解动力学，发现吸附于蒙脱石晶格层间的CIP分子在太阳光照射下能够被逐步降解，且其动力学过程满足一级动力学方程。通过与水相光解进行对比，发现CIP在蒙脱石层间的光解速率大于水相，这主要是由于蒙脱石的光催化特性。通过UV-vis光谱分析和自由基淬灭实验，证实了蒙脱石晶格层间CIP的光解反应机理主要包括直接光解和羟基自由基诱导的间接光解。利用LC-MS/MS对光解产物进行了分离鉴定，并基于中间产物推测CIP在晶格层间以及水相中的光解路径，结果表明，CIP在蒙脱石晶格层间的光解产物及路径相对于水相存在明显差异。（2）选择1:1型粘土矿物—高岭石为研究对象，研究CIP在高岭石表面的光解行为及反应机理，并分析了环境因素对光解的影响。考察了CIP在高岭石表面的光解动力学，发现吸附于高岭石表面的CIP在太阳光的照射下能够被逐渐光解，其动力学过程也符合一级动力学方程。与水相光解相比，CIP在高岭石表面的光解速率稍慢，主要是由于高岭石颗粒的对光的遮蔽和吸收造成的。分析了高岭石的加入量，溶液的pH值以及溶解氧对光解的影响。结果表明，高岭石投入量的增加会导致高岭石表面CIP光解速率的减缓；酸性环境和溶解氧促进了高岭石表面CIP的光解。自由基淬灭实验表明羟基自由基参与了CIP的降解，但不是主要的光解机制。LC-MS/MS分析表明，高岭石表面吸附态CIP的光解产物和光解路径与水相不同。总体而言，由于固相介质、吸附作用的影响以及分子所处微环境的变化，抗生素分子在固—液界面上的光化学行为及反应机理不同于水相，需要开展更全面和深入的研究。