Ahamad M Naqi, Khan M Shahnawaz, Shahid M, Ahmad Musheer
Functional Inorganic Materials Lab (FIML), Department of Chemistry, Aligarh Muslim University, Aligarh 202002, India.
Department of Applied Chemistry (ZHCET), Aligarh Muslim University, Aligarh 202002, India.
Dalton Trans. 2020 Oct 27;49(41):14690-14705. doi: 10.1039/d0dt02949a.
In this report, metal organic frameworks (MOFs) are designed and tuned for structural variations in order to induce metal capture which in turn directs dye adsorption properties. The three MOFs, Cu-MOF-2COOH, Ni-MOF-COOH and Cd-MOF, are synthesized by employing 1,3,5-benzenetricarboxylic acid (H3-BTC) as the main ligand and 4,4'-dipyridyl (bipy) as the spacer. The MOFs have been characterized using various spectral techniques and single crystal X-Ray studies. A topological analysis using TOPOS Pro reveals that the MOFs possess varying topologies i.e.hcb, hxl, sql and 2C1. Cu-MOF-2COOH and Ni-MOF-COOH contain two and three uncoordinated carboxylic acid groups, respectively, and in Cd-MOF, all three -COOH groups are utilized in bonding. The dye adsorption properties of the MOFs with free carboxylate group(s) were checked and we found that both MOFs are unable to adsorb any of the dyes significantly. The free carboxylate group(s) in the MOFs inspire us to elaborate their metal capturing properties. In different solvents we checked the metal capturing properties of Cu-MOF-2COOH and Ni-MOF-COOH with different metal salts. Surprisingly, both MOFs show better metal capturing properties towards the hard and highly polarizing Fe3+ ion in aqueous medium. Theoretical studies show that the free carboxylate(s) are involved in binding with metals. The post synthetically modified materials (Fe@Cu-MOF-2COOH and Fe@Ni-MOF-COOH) were further checked for their dye adsorption properties and both the doped MOFs show better adsorption properties towards the MB and MO. Furthermore, three kinetic models were employed to understand the reaction mechanism of adsorption and the pseudo second order kinetic model fits the best in both cases. The uncoordinated carboxylate groups in the channels act as post synthetic modification sites for metal capture and the post synthetically modified material thus formed attracts organic dyes following the HSAB concept. The strong interaction existing between the hard Fe3+ ion and hard donors of the dyes is responsible for the enhanced adsorption.
在本报告中，为了诱导金属捕获从而指导染料吸附性能，对金属有机框架（MOF）进行了结构变化的设计和调整。采用1,3,5-苯三甲酸（H3-BTC）作为主要配体，4,4'-联吡啶（bipy）作为间隔物，合成了三种MOF，即Cu-MOF-2COOH、Ni-MOF-COOH和Cd-MOF。使用各种光谱技术和单晶X射线研究对这些MOF进行了表征。使用TOPOS Pro进行的拓扑分析表明，这些MOF具有不同的拓扑结构，即hcb、hxl、sql和2C1。Cu-MOF-2COOH和Ni-MOF-COOH分别含有两个和三个未配位的羧酸基团，而在Cd-MOF中，所有三个-COOH基团都用于键合。检查了具有游离羧酸根基团的MOF的染料吸附性能，我们发现这两种MOF都不能显著吸附任何一种染料。MOF中的游离羧酸根基团促使我们详细研究它们的金属捕获性能。在不同溶剂中，我们用不同的金属盐检查了Cu-MOF-2COOH和Ni-MOF-COOH的金属捕获性能。令人惊讶的是，在水性介质中，这两种MOF对硬的、高极化的Fe3+离子都表现出更好的金属捕获性能。理论研究表明，游离羧酸根参与了与金属的结合。对合成后修饰的材料（Fe@Cu-MOF-2COOH和Fe@Ni-MOF-COOH）的染料吸附性能进行了进一步检查，两种掺杂的MOF对亚甲基蓝（MB）和甲基橙（MO）都表现出更好的吸附性能。此外，采用三种动力学模型来理解吸附反应机理，在两种情况下，伪二级动力学模型拟合效果最佳。通道中未配位的羧酸基团作为金属捕获的合成后修饰位点，由此形成的合成后修饰材料按照硬软酸碱（HSAB）概念吸引有机染料。硬的Fe3+离子与染料的硬供体之间存在的强相互作用是吸附增强的原因。
