Adsorption Properties and Microscopic Mechanism of CO2 Capture in 1,1-Dimethyl-1,2-ethylenediamine-Grafted Metal-Organic Frameworks

Hui Zhang; Li-Ming Yang; Eric Ganz

doi:10.1021/acsami.0c01927

Adsorption Properties and Microscopic Mechanism of CO₂ Capture in 1,1-Dimethyl-1,2-ethylenediamine-Grafted Metal-Organic Frameworks

ACS Appl Mater Interfaces. 2020 Apr 22;12(16):18533-18540. doi: 10.1021/acsami.0c01927. Epub 2020 Apr 13.

Authors

Hui Zhang¹, Li-Ming Yang¹, Eric Ganz²

Affiliations

¹ Hubei Key Laboratory of Bioinorganic Chemistry and Materia Medica; Key Laboratory of Material Chemistry for Energy Conversion and Storage, Ministry of Education; Hubei Key Laboratory of Materials Chemistry and Service Failure; School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Wuhan 430074, China.
² School of Physics and Astronomy, University of Minnesota, 116 Church Street Southeast, Minneapolis, Minnesota 55455, United States.

PMID: 32227842
DOI: 10.1021/acsami.0c01927

Abstract

The adsorption properties and microscopic mechanism of CO₂ adsorption in 1,1-dimethyl-1,2-ethylenediamine (dmen) functionalized M₂(dobpdc) (dobpdc^4-=4,4'-dioxidobiphenyl-3,3'-dicarboxylate; M = Mg, Sc-Zn) have been completely unveiled for the first time via comprehensive investigations based on first-principles density functional theory (DFT) calculations. The results show that for the primary-primary amine, dmen prefers to interact with the open metal site of M₂(dobpdc) via the end with smaller steric hindrance. The binding energies of dmen with MOFs are in the range of 104-174 kJ/mol. In presence of CO₂, it fully inserts into the metal-N bond, forming ammonium carbamate. The CO₂ binding energies vary from 53 to 89 kJ/mol, showing strong metal dependence. Among the 11 metals, dmen-Sc₂(dobpdc) and dmen-Mg₂(dobpdc) have the highest CO₂ binding energies of 89 and 84 kJ/mol, respectively, and may have large CO₂ adsorption capacity for practical applications. More importantly, the microscopic CO₂ capture process of dmen-M₂(dobpdc) is revealed at the atomic level. The whole reaction process includes two steps, that is, formation of zwitterion intermediate (step 1) and rearrangement of the zwitterion intermediate (step 2). The first step in which nucleophilic addition between CO₂ and the metal-bound amine and proton transfer from the metal-bound amine to free amine simultaneously occur is a rate-determining step, with higher energy barriers (0.99-1.35 eV). The second step with much lower barriers (maximum of 0.16 eV) is extremely easy, which can promote the whole CO₂ uptake process in dmen-M₂(dobpdc). This study provides a fundamental understanding of the underlying mechanism of the rather complicated CO₂ adsorption process and sheds important insights on design, synthesis, and optimization of highly efficient CO₂ capture materials.

Keywords: CO2 capture; density functional theory (DFT) calculations; dmen−M2(dobpdc), adsorption properties; reaction mechanism.