Diamine-Functionalization of a Metal–Organic Framework Adsorbent for Superb Carbon Dioxide Adsorption and Desorption Properties

For real-world postcombustion applications in the mitigation of CO₂ emissions using dry sorbents, adsorption and desorption behaviors should be controlled to design and fabricate prospective materials with optimal CO₂ performances. Herein, we prepared diamine-functionalized Mg₂(dobpdc) (H₄dobpdc=4,4′-dihydroxy-(1,1′-biphenyl)-3,3′-dicarboxylic acid). (1-diamine) with ethylenediamine (en), primary–secondary (N-ethylethylenediamine—een and N-isopropylethylenediamine—ipen), primary–tertiary, and secondary–secondary diamines. A slight alteration of the number of alkyl substituents on the diamines and their alkyl chain length dictates the desorption temperature (T_des) at 100 % CO₂, desorption characteristics, and ΔT systematically to result in the tuning of the working capacity. The existence of bulky substituents on the diamines improves the framework stability upon exposure to O₂, SO₂, and water vapor, relevant to real flue-gas conditions. Bulky substituents are also responsible for an interesting two-step behavior observed for the ipen case, as revealed by DFT calculations. Among the diamine-appended metal–organic frameworks, 1-een, which has the required adsorption and desorption properties, is a promising material for sorbent-based CO₂ capture processes. Hence, CO₂ performance and framework durability can be tailored by the judicial selection of the diamine structure, which enables property design at will and facilitates the development of desirable CO₂-capture materials.