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

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) (H₄ dobpdc=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.