†Department of Chemistry, Virginia Tech, Blacksburg, Virginia 24061, United States.
‡Department of Chemical Engineering, Virginia Tech, Blacksburg, Virginia 24061, United States.
Inorg Chem. 2015 May 4;54(9):4328-36. doi: 10.1021/ic503047y. Epub 2015 Apr 21.
Two Zn-based metal organic frameworks have been prepared solvothermally, and their selectivity for CO2 adsorption was investigated. In both frameworks, the inorganic structural building unit is composed of Zn(II) bridged by the 2-carboxylate or 5-carboxylate pendants of 2,5-pyridine dicarboxylate (pydc) to form a 1D zigzag chain. The zigzag chains are linked by the bridging 2,5-carboxylates across the Zn ions to form 3D networks with formulas of Zn4(pydc)4(DMF)2·3DMF (1) and Zn2(pydc)2(DEF) (2). The framework (1) contains coordinated DMF as well as DMF solvates (DMF = N,N-dimethylformamide), while (2) contains coordinated DEF (DEF = N,N-diethylformamide). (1) displays a reversible type-I sorption isotherm for CO2 and N2 with BET surface areas of 196 and 319 m(2)/g, respectively. At low pressures, CO2 and N2 isotherms for (2) were not able to reach saturation, indicative of pore sizes too small for the gas molecules to penetrate. A solvent exchange to give (2)-MeOH allowed for increased CO2 and N2 adsorption onto the MOF surface with BET surface areas of 41 and 39 m(2)/g, respectively. The binding of CO2 into the framework of (1) was found to be exothermic with a zero coverage heat of adsorption, Qst(0), of −27.7 kJ/mol. The Qst(0) of (2) and (2)-MeOH were found to be −3 and −41 kJ/mol, respectively. The CO2/N2 selectivity for (1), calculated from the estimated KH at 296 K, was found to be 42. At pressures relevant to postcombustion capture, the selectivity was 14. The thermodynamic data are consistent with a mechanism of adsorption that involves CO2 binding to the unsaturated Zn(II) metal centers present in the crystal structures.
两种基于锌的金属有机骨架已通过溶剂热法制备，并研究了它们对 CO2 吸附的选择性。在这两种骨架中，无机结构构建单元由 Zn(II) 通过 2-羧酸盐或 5-羧酸盐桥联的 2,5-吡啶二甲酸酯（pydc）组成，形成 1D 之字形链。之字形链通过桥联的 2,5-羧酸盐在 Zn 离子之间连接，形成具有化学式 Zn4(pydc)4(DMF)2·3DMF（1）和 Zn2(pydc)2(DEF)（2）的 3D 网络。骨架（1）含有配位的 DMF 和 DMF 溶剂化物（DMF = N,N-二甲基甲酰胺），而（2）含有配位的 DEF（DEF = N,N-二乙基甲酰胺）。（1）对 CO2 和 N2 表现出可逆的 I 型吸附等温线，比表面积分别为 196 和 319 m2/g。在较低的压力下，（2）的 CO2 和 N2 吸附等温线未能达到饱和，表明孔径太小，气体分子无法穿透。溶剂交换得到（2）-MeOH 后，MOF 表面上的 CO2 和 N2 吸附量增加，比表面积分别为 41 和 39 m2/g。发现 CO2 与（1）骨架的结合是放热的，零覆盖吸附热 Qst(0)为-27.7 kJ/mol。（2）和（2）-MeOH 的 Qst(0)分别为-3 和-41 kJ/mol。（1）的 CO2/N2 选择性，根据 296 K 下的估计 KH 计算，为 42。在与后燃烧捕获相关的压力下，选择性为 14。热力学数据与吸附机制一致，该机制涉及 CO2 与晶体结构中未饱和的 Zn(II)金属中心结合。
