Milner Phillip J, Martell Jeffrey D, Siegelman Rebecca L, Gygi David, Weston Simon C, Long Jeffrey R
Department of Chemistry , University of California , Berkeley , CA 94720 , USA . Email:
Department of Chemistry and Chemical Biology , Harvard University , Cambridge , MA 02138 , USA.
Chem Sci. 2017 Oct 26;9(1):160-174. doi: 10.1039/c7sc04266c. eCollection 2018 Jan 7.
Alkyldiamine-functionalized variants of the metal-organic framework Mg(dobpdc) (dobpdc = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) are promising for CO capture applications owing to their unique step-shaped CO adsorption profiles resulting from the cooperative formation of ammonium carbamate chains. , (1°,2°) alkylethylenediamine-appended variants are of particular interest because of their low CO step pressures (≤1 mbar at 40 °C), minimal adsorption/desorption hysteresis, and high thermal stability. Herein, we demonstrate that further increasing the size of the alkyl group on the secondary amine affords enhanced stability against diamine volatilization, but also leads to surprising two-step CO adsorption/desorption profiles. This two-step behavior likely results from steric interactions between ammonium carbamate chains induced by the asymmetrical hexagonal pores of Mg(dobpdc) and leads to decreased CO working capacities and increased water co-adsorption under humid conditions. To minimize these unfavorable steric interactions, we targeted diamine-appended variants of the isoreticularly expanded framework Mg(dotpdc) (dotpdc = 4,4''-dioxido-[1,1':4',1''-terphenyl]-3,3''-dicarboxylate), reported here for the first time, and the previously reported isomeric framework Mg-IRMOF-74-II or Mg(pc-dobpdc) (pc-dobpdc = 3,3'-dioxidobiphenyl-4,4'-dicarboxylate, pc = -carboxylate), which, in contrast to Mg(dobpdc), possesses uniformally hexagonal pores. By minimizing the steric interactions between ammonium carbamate chains, these frameworks enable a single CO adsorption/desorption step in all cases, as well as decreased water co-adsorption and increased stability to diamine loss. Functionalization of Mg(pc-dobpdc) with large diamines such as -(-heptyl)ethylenediamine results in optimal adsorption behavior, highlighting the advantage of tuning both the pore shape and the diamine size for the development of new adsorbents for carbon capture applications.
金属有机框架Mg(dobpdc)（dobpdc = 4,4'-二氧代联苯-3,3'-二羧酸酯）的烷基二胺功能化变体因其独特的阶梯状CO吸附曲线而在CO捕获应用中颇具前景，这种曲线是由氨基甲酸铵链的协同形成导致的。(1°,2°)烷基乙二胺附加变体尤其令人关注，因为它们的CO阶梯压力较低（40℃时≤1毫巴），吸附/解吸滞后最小，且热稳定性高。在此，我们证明进一步增大仲胺上烷基的尺寸可提高抗二胺挥发的稳定性，但也会导致令人惊讶的两步CO吸附/解吸曲线。这种两步行为可能是由Mg(dobpdc)不对称六边形孔引起的氨基甲酸铵链之间的空间相互作用导致的，并且会导致CO工作容量降低以及在潮湿条件下水共吸附增加。为了最小化这些不利的空间相互作用，我们针对首次在此报道的等规扩展框架Mg(dotpdc)（dotpdc = 4,4''-二氧代-[1,1':4',1''-三联苯]-3,3''-二羧酸酯）的二胺附加变体，以及先前报道的异构框架Mg-IRMOF-74-II或Mg(pc-dobpdc)（pc-dobpdc = 3,3'-二氧代联苯-4,4'-二羧酸酯，pc = -羧酸酯），与Mg(dobpdc)相比，其具有均匀的六边形孔。通过最小化氨基甲酸铵链之间的空间相互作用，这些框架在所有情况下都能实现单一的CO吸附/解吸步骤，以及减少水共吸附并提高对二胺损失的稳定性。用大的二胺如-(-庚基)乙二胺对Mg(pc-dobpdc)进行功能化可导致最佳吸附行为，突出了调整孔形状和二胺尺寸对于开发用于碳捕获应用的新型吸附剂的优势。
