金属-有机骨架类Fenton体系去除水中难降解有机污染物机理研究

Appropriate organic ligands can accelerate the degradation process of a pollutant in Fenton reaction and broaden the reaction pH value, which is valuable for wastewater treatment. Metal-organic frameworks (MOFs) are coordination polymers composed of organic ligands and inorganic metal ions through self assembly. The organic ligands in MOFs are self-contained activators, whereas the metal units are the active center for catalytic activation of hydrogen peroxide. This makes MOFs as potential self-activation catalyst in heterogeneous Fenton-like reaction. In this project, iron-based MOFs were constructed by changing the type of an organic ligand and its ratio to metal ions to obtain MOFs structure with excellent adsorption performance for methylene blue, methyl orange and rhodamine dyes, which were used as the model refractory organic contaminants. Then, MOFs-based heterogeneous Fenton-like system was established. The degradation characteristics of this system for model containments were investigated, including reaction kinetics, intermediate products and degradation pathways. By figuring out the main active intermediate species, conversion of different iron forms and the effect of dissolved oxygen on cycles of ferrous and ferric species, the mechanism underlying the MOFs promoted adsorption of organic pollutants and enhanced the cycles efficiency of active centers was clarified to effectively regulate the MOFs-based Fenton-like catalytic reaction for degradation of a pollutant. The results from this project will not only help us to deeply understand the MOFs-based heterogeneous Fenton-like system, but also promise theoretical and practical values for water purification.

合适的有机配体可加速芬顿反应中污染物的降解进程、拓宽反应pH值，有应用价值。金属-有机骨架(MOFs)是由有机配体与无机金属离子自组装而成的配位聚合物，其有机配体是“自备”的活化剂；金属组分可作为催化活化过氧化氢的活性中心，是潜在的“自活化”多相类芬顿催化剂。本项目拟以亚甲蓝、甲基橙及罗丹明类染料等为模型难降解有机污染物，以铁基MOFs为对象，通过改变构成铁基MOFs的有机配体及其与活性中心的比例，获得吸附性能优良的MOFs结构；据此建立MOFs多相类芬顿体系，研究其对模型污染物的降解特性，包括反应动力学、中间产物及降解途径。查明反应中的主要活性中间体、铁的形态转化规律及溶解氧对铁循环的作用。在此基础上，阐明MOFs促进有机污染物的吸附及提高催化活性中心的循环效率的原理，从而实现对MOFs类芬顿降解污染物的有效调控。本项目研究结果有利于加深对MOFs多相类芬顿的理解，有理论和应用价值。

MOFs是由有机配体与金属离子自组装而成的配位聚合物，其有机配体是自备的活化剂；金属可作为催化活化H2O2的活性中心，是潜在的自活化多相类芬顿催化剂。主要研究内容为：1. 通过改变铁与配体比例、利用溶剂热法及微波法等制备了MOF-235(Fe)、NH2-MIL-88B(Fe)、MIL-101(Fe)及NH2-MIL-53(Fe)等不同结构的铁基MOFs材料，研究它们对亚甲蓝、甲基橙、罗丹明B、四环素等染料及抗生素的吸附及去除特性、有无外加配体对催化过程中铁形态转化的影响规律及污染物降解机理；结果表明，铁基MOFs活化H2O2去除难降解污染物有如下特点：MOFs的孔结构特性有利于吸附富集污染物、宽pH适应范围、降解过程中均有羟基自由基产生、存在三价铁与二价铁的循环、配体加入有助于实现三价铁与二价铁的快速循环。2. 直接利用铁基MOFs作为多相类芬顿催化剂存在回收难（通常要用离心进行分离）、活性中心持续溶出及溶解氧作用复杂等问题，提出以MOFs为前体制备磁性多相类芬顿催化剂、静电纺丝固定MOFs催化剂及根据理论计算指导设计高效活化溶解氧及PMS的催化剂解决以上问题，主要内容包括：1)基于NH2-MIL-88(Fe)衍生物、ZIF-67衍生物及普鲁士蓝类似物分别构筑CoNPs/MC、FeNPs@Co3O4中空纳米笼及FeCo@NC磁性类芬顿催化剂；2)基于MOF衍生的铁钴双金属氧化物双壳纳米笼磁性多功能类酶及类芬顿催化剂；3)利用静电纺丝制备MIL-101(Fe)@PAN类芬顿膜催化剂去除亚甲蓝；4)DFT计算指导设计钴基双金属纳米笼类芬顿催化剂及铁铋MOF衍生的双金属单原子类芬顿催化剂。结果表明，以MOFs为前体制备的磁性多相类芬顿催化剂有稳定性高、易分离等优点，是一类高效类芬顿催化剂。通过静电纺丝将MIL-101(Fe)固定在聚丙烯腈纳米纤维上，铁溶出下降85%以上，有很好的稳定性，反应后MIL-101(Fe)@PAN纤维可直接从溶液中取出，无需外加分离手段，是一类极具应用潜力的类芬顿膜催化剂。3. 开展了基于MOFs类芬顿催化剂构建环境中重要活性化合物如H2O2等的快速检测及酶活性筛选平台。以上结果有助于阐明基于MOFs的多相类芬顿体系去除污染物的机理及溶解氧对铁基MOFs多相类芬顿体系中铁循环的作用机制等科学问题，从而实现对MOFs类芬顿降解污染物的有效调控。