Sarkar Sougata, Dutta Soumen, Bairi Partha, Pal Tarasankar
Department of Chemistry, Indian Institute of Technology , Kharagpur 721302, India.
Langmuir. 2014 Jul 8;30(26):7833-41. doi: 10.1021/la501309m. Epub 2014 Jun 23.
Herein, we report a new strategy to remove toxic Cr(VI) ion from aqueous solution using metal-organic hybrid gel as sorbent. The gel could be easily synthesized from the commercially available organic ligand 2-mercaptobenzimidazole (2-MBIm) and copper(II) chloride in alcoholic medium. The synthesis involves one-electron reduction of Cu(II) to Cu(I) by 2-MBIm, and then gel formation is triggered through Cu(I)-ligand coordination and extensive hydrogen-bonding interactions involving the "-NH" protons (of 2-MBIm ligand), solvent molecules, and chloride ions. The gel shows entangled network morphology. Different microanalytical techniques (FTIR, powder XRD, FESEM, TEM, rheology etc.) have been employed for complete characterizations of the gel sample. Both Cu(I) (in situ formed) and Cl(-) ions trigger the gel formation as demonstrated from systematic chemical analyses. The gel also exhibits its stimuli-responsive behavior toward different interfering chemical parameters (pH, selective metal ions and anions, selective complexing agents, etc.). Finally the gel shows its redox-responsive nature owing to the distinguished presence of Cu(I) metal centers throughout its structural backbone. And this indeed helps in the effective removal of Cr(VI) ions from aqueous solution. Reduction of Cr(VI) to Cr(III) ions and its subsequent sorption take place in the gel matrix. The reductive removal of Cr(VI) has been quantitatively interpreted through a set of different kinetic measurements/models, and the removal capacity of the gel matrix has been observed to be ∼331 mg g(-1) at pH ∼ 2.7, which is admirably higher than the commonly used adsorbents. However, the capacity decreases with the increase in pH of the solution. The overall removal mechanism has been clearly demonstrated. Again, the gel could also be recycled. Thus, the low-cost and large-scale fabrication of the redox-active metallogel makes it an efficient matrix for the toxic ion removal and hence indicates the high promise of this new generation hybrid material for environmental pollution abatement.
在此，我们报道了一种使用金属有机杂化凝胶作为吸附剂从水溶液中去除有毒六价铬离子的新策略。该凝胶可在醇介质中由市售有机配体2-巯基苯并咪唑（2-MBIm）和氯化铜（II）轻松合成。合成过程包括2-MBIm将Cu（II）单电子还原为Cu（I），然后通过Cu（I）-配体配位以及涉及（2-MBIm配体的）“-NH”质子、溶剂分子和氯离子的广泛氢键相互作用引发凝胶形成。该凝胶呈现出缠结的网络形态。已采用不同的微观分析技术（傅里叶变换红外光谱、粉末X射线衍射、场发射扫描电子显微镜、透射电子显微镜、流变学等）对凝胶样品进行全面表征。系统化学分析表明，原位形成的Cu（I）离子和Cl（-）离子均引发凝胶形成。该凝胶还对不同的干扰化学参数（pH值、选择性金属离子和阴离子、选择性络合剂等）表现出刺激响应行为。最后，由于在其整个结构主链中存在独特的Cu（I）金属中心，该凝胶表现出氧化还原响应特性。这确实有助于从水溶液中有效去除六价铬离子。六价铬还原为三价铬离子及其随后的吸附在凝胶基质中发生。通过一系列不同的动力学测量/模型对六价铬的还原去除进行了定量解释，并且在pH约为2.7时观察到凝胶基质的去除容量约为331 mg g(-1)，这明显高于常用吸附剂。然而，容量随溶液pH值的增加而降低。整体去除机制已得到清晰证明。此外，该凝胶还可回收利用。因此，低成本且大规模制备的氧化还原活性金属凝胶使其成为去除有毒离子的有效基质，从而表明这种新一代杂化材料在减少环境污染方面具有很高的前景。
