Functionalization of Diamine-Appended MOF-Based Adsorbents by Ring Opening of Epoxide: Long-Term Stability and CO 2 Recyclability under Humid Conditions.

Although diamine-appended metal-organic framework (MOF) adsorbents exhibit excellent CO 2 adsorption performance, a continuous decrease in long-term capacity during repeated wet cycles remains a formidable challenge for practical applications. Herein, we present the fabrication of diamine-appended Mg 2 (dobpdc)-alumina beads ( een-MOF/Al - Si - C x ; een = N -ethylethylenediamine; x = number of carbon atoms attached to epoxide) coated with hydrophobic silanes and alkyl epoxides. The reaction of epoxides with diamines in the portal of the pore afforded sufficient hydrophobicity, hindered the penetration of water vapor into the pores, and rendered the modified diamines less volatile. een-MOF/Al-Si-C17-200 ( een-MOF/Al-Si-C17- y ; y = 50, 100, and 200, denoting wt % of C17 with respect to the bead, respectively), with substantial hydrophobicity, showed a significant uptake of 2.82 mmol g -1 at 40 °C and 15% CO 2 , relevant to flue gas concentration, and a reduced water adsorption. The modified beads maintained a high CO 2 capacity for over 100 temperature-swing adsorption cycles in the presence of 5% H 2 O and retained CO 2 separation performance in breakthrough tests under humid conditions. This result demonstrates that the epoxide coating provides a facile and effective method for developing promising adsorbents with high CO 2 adsorption capacity and long-term durability, which is a required property for postcombustion applications.