Zhang Yue, Lucier Bryan E G, Huang Yining
Department of Chemistry, The University of Western Ontario, London, Ontario, Canada N6A 5B7.
Phys Chem Chem Phys. 2016 Mar 28;18(12):8327-41. doi: 10.1039/c5cp04984a.
Microporous metal-organic frameworks (MOFs) have high surface areas and porosities, and are well-suited for CO2 capture. MIL-53 features corner-sharing MO4(OH)2 (M = Al, Ga, Cr, etc.) octahedra interconnected by benzenedicarboxylate linkers that form one-dimensional rhombic tunnels, and exhibits an excellent adsorption ability for guest molecules such as CO2. Studying the behavior of adsorbed CO2 in MIL-53 via solid-state NMR (SSNMR) provides rich information on the dynamic motion of guest molecules as well as their binding strengths to the MOF host, and sheds light on the specific guest adsorption mechanisms. Variable-temperature (13)C SSNMR spectra of (13)CO2 adsorbed within various forms of MIL-53 are acquired and analyzed. CO2 undergoes a combination of two motions within MIL-53; we report the types of motion present, their rates, and rotational angles. (1)H-(13)C CP SSNMR experiments are used to examine the proximity of (1)H atoms in the MOF to (13)C atoms in CO2 guests. By replacing (1)H with (2)H in MIL-53, the location of the CO2 adsorption site in MIL-53 is experimentally confirmed by (1)H-(13)C CP SSNMR. The binding strength of CO2 within these MIL-53 MOFs follows the order MIL-53-NH2 (Al) > MIL-53-NH2 (Ga) > MIL-53 (Al) > MIL-53 (Ga).
微孔金属有机框架材料（MOFs）具有高比表面积和孔隙率，非常适合用于二氧化碳捕获。MIL-53由通过苯二甲酸酯连接体相互连接的共角MO4(OH)2（M = 铝、镓、铬等）八面体组成，形成一维菱形隧道，并且对诸如二氧化碳等客体分子表现出优异的吸附能力。通过固态核磁共振（SSNMR）研究MIL-53中吸附的二氧化碳的行为，可提供有关客体分子动态运动及其与MOF主体结合强度的丰富信息，并有助于阐明特定的客体吸附机制。获取并分析了吸附在各种形式的MIL-53中的（13）CO2的变温（13）C SSNMR光谱。二氧化碳在MIL-53内经历两种运动的组合；我们报告了存在的运动类型、它们的速率和旋转角度。（1）H-（13）C CP SSNMR实验用于检查MOF中的（1）H原子与二氧化碳客体中的（13）C原子的接近程度。通过在MIL-53中用（2）H取代（1）H，通过（1）H-（13）C CP SSNMR实验证实了MIL-53中二氧化碳吸附位点的位置。这些MIL-53 MOF中二氧化碳的结合强度遵循以下顺序：MIL-53-NH2（铝）> MIL-53-NH2（镓）> MIL-53（铝）> MIL-53（镓）。
