结构和价态调控的Ce-MOFs及其衍生物吸附水中氟离子的机理

Adsorption mechanism of fluorion removal from water by structure and valence-regulated Ce-MOFs and their derivatives

严控饮水氟浓度,可以有效降低人体罹患氟骨症和氟牙症的风险。近年来,铈基吸附材料在解决氟污染问题中表现优异,而铈盐与有机酸反应生成的铈基金属有机框架材料(Ce-MOFs)或其衍生物,能有效去除水中的氟离子。硝酸铈铵(Ce(NH_(4))_(2)(NO3)6)和均苯三甲酸(H_(3)BTC)在不同反应时长下生成了Ce-MOFs CeT1及其衍生物CeT2,更换H_(3)BTC为对苯二甲酸(H2BDC),反应生成2种Ce-MOFs,CeD1和CeD2。利用XRD、BET、SEM、XPS和FTIR对材料的结构、比表面积、元素含量和组成基团,进行系统的表征;通过控制吸附时间、溶质初始浓度、溶液pH值和竞争离子种类研究4种材料的吸附性能;对实验数据进行吸附动力学模型和吸附等温模型拟合,探究吸附机理。表征结果显示,CeT1为高度配位不饱和的Ce(Ⅳ)-MOFs,CeD1为比表面积最大(1 003.10 m^(2)/g)的Ce(Ⅳ)-MOFs,而CeT2和CeD2则同为Ce(Ⅲ)占比较高的吸附材料。吸附实验中,CeT1、CeT2、CeD1和CeD2的最大吸附容量分别为99.38 mg/g、142.45 mg/g、60.45 mg/g和124.55 mg/g,CeT1、CeT2和CeD2符合假二级动力学模型,CeD1符合假一级动力学模型。4种材料对氟离子的吸附机理主要为静电吸引、离子交换和沉淀。其中,CeT1的不饱和配位可提供吸附位点进行离子交换和静电吸引,CeD1的大比表面积增加了污染物与材料的碰撞几率,而CeT2和CeD2中含有的Ce(Ⅲ),可通过形成溶度积常数极小的CeF3(K_(sp)=8×10^(-16)),以沉淀作用固定氟离子。实验分析了4种材料的特点与吸附性能之间的关系,为Ce-MOFs及其衍生物的制备与优选提供参考。

Controlling the concentration of fluorion in drinking water is crucial for reducing the risk of bone and dental fluorosis.In recent years,cerium-based adsorption materials,particularly cerium organic framework materials(Ce-MOFs)and their derivatives,have emerged as effective solutions for fluorion pollution.In this study,Ce-MOFs,namely CeT1 and CeT2 were synthesized using ammonium cerium nitrate(Ce(NH_(4))_(2)(NO3)6)and homophenic acid(H_(3)BTC)at different reaction times,while CeD1 and CeD2 were generated by replacing H_(3)BTC with terephthalic acid(H2BDC).Structural,surface area,elemental content and constituent group analyses were conducted using XRD,BET,SEM,XPS and FTIR techniques.Adsorption properties of the four materials were studied by controlling adsorption parameters,such as time,initial solute concentration,pH,and competing ions.Kinetic and isothermal models were employed to explore the adsorption mechanism.Characterization showed CeT1 as Ce(Ⅳ)-MOFs with high coordination unsaturation,CeD1 as Ce(Ⅳ)-MOFs with the largest specific surface area(1003.10 m^(2)/g),and CeT2 and CeD2 as Ce(Ⅲ)adsorption materials.Maximum adsorption capacities for CeT1,CeT2,CeD1 and CeD2 were determined as 99.38 mg/g,142.45 mg/g,60.45 mg/g and 124.55 mg/g,respectively.CeT1,CeT2 and CeD2 conformed to the pseudo-second-order kinetic model,while CeD1 conformed to the pseudo-first-order kinetic model.Adsorption mechanisms of fluorion in the four materials involved electrostatic attraction,ion exchange and precipitation,with CeT1 providing adsorption sites for ion exchange and electrostatic attraction due to unsaturated coordination.CeD1’s large specific surface area increases collision probability between pollutants and materials,while Ce(Ⅲ)in CeT2 and CeD2 facilitated precipitation by forming CeF3(K_(sp)=8×10^(-16))with minimal solubility product constant.The study provides insights into the characteristics and defluorination abilities of Ce-MOFs and their derivatives,offering valuable reference for their preparation and optimization.