Multi-function adsorbent-photocatalyst MXene-TiO2 composites for removal of enrofloxacin antibiotic from water

MXenes, a new family of two-dimensional transition metal carbides or nitrides, have attracted tremendous attention for various applications due to their unique properties such as good electrical conductivity, hydrophilicity, and ion intercalability. In this work, Ti₃C₂ MXene, or MX, is converted to MX-TiO₂ composites using a simple and rapid microwave hydrothermal treatment in HCl/NaCl mixture solution that induces formation of fine TiO₂ particles on the MX parent structure and imparts photocatalytic activity to the resulting MX-TiO₂ composites. The composites were used for enrofloxacin (ENR), a frequently found contaminating antibiotic, removal from water. The relative amount of the MX and TiO₂ can be controlled by controlling the hydrothermal temperature resulting in composites with tunable adsorption/photocatalytic properties. NaCl addition was found to play important role as composites synthesized without NaCl could not adsorb enrofloxacin well. Adding NaCl into the hydrothermal treatment causes sodium ions to be simultaneously intercalated into the composite structure, improving ENR adsorption greatly from 1 to 6 mg ENR/g composite. It also slows down the MX to TiO₂ conversion leading to a smaller and more uniform distribution of TiO₂ particles on the structure. MX-TiO₂/NaCl composites, which have sodium intercalated in their structures, showed both higher ENR adsorption and photocatalytic activity than composites without NaCl despite the latter having higher TiO₂ content. Adsorbed ENR on the composites can be efficiently degraded by free radicals generated from the photoexcited TiO₂ particles, leading to high photocatalytic degradation efficiency. This demonstrates the synergetic effect between adsorption and photocatalytic degradation of the synthesized compounds.     

恩诺沙星在鲫鱼肝微粒体中的代谢及代谢关键酶的确定

抗生素因具有抗菌谱广、杀菌性强等特点使其被广泛应用于人类医药、畜牧业、农业和水产养殖业。其进入水生生物体内后,会在药物代谢酶的作用下发生代谢转化,产生生态毒性。本研究采用鲫鱼肝微粒体体外孵育法,探究恩诺沙星细胞色素P450酶作用下的代谢转化过程,并通过代谢抑制实验确定关键的代谢酶。实验结果表明,恩诺沙星体外代谢过程符合一级动力学方程,当恩诺沙星暴露浓度为1 mg·L-1时,其在肝微粒体中的消除速率常数k最大为0.00303 min-1,半衰期t1/2最短为228.8 min,应用HPLC-MS/MS技术,检测到了恩诺沙星脱乙基产物和羟基化产物;代谢抑制实验结果表明,CYP3A4在恩诺沙星代谢过程中起主要作用,是恩诺沙星代谢的关键酶。本研究结果为深入了解恩诺沙星在水生生物体内的代谢转化及其生态风险提供了基础数据。