Extensively amino-functionalized graphene captures carbon dioxide

Abstract

The development of robust carbon dioxide (CO₂) scavengers is a challenging but paramount problem of modern humanity. In the present work, we report a prospective CO₂ sorbent based on amino-functionalized graphene (FG). Amino-FG retains the favorable physicochemical properties of graphene and acquires the capability of chemically fixing CO₂via the carbamic acid formation mechanism. In the present work, we comprehensively investigate CO₂ capturing prospects by extensively amino-FG using hybrid density functional theory. We show that up to six amino groups can be grafted, remain stable, and subsequently chemisorb CO₂ per benzene ring. Two functional groups above the benzene ring and four such groups below the benzene ring represent a thermodynamically stable molecular configuration in which the number of carbon atoms is equal to the number of functional groups. The thermochemistry of chemisorption is, in general, negatively impacted by the increase in the density of functional groups. However, a less favorable Gibbs free energy is compensated by a several fold higher number of prospective reaction sites. The thermochemistry results are rationalized by considering steric hindrances on the surface of graphene in the context of the states of hybridization and genuine geometries of the amino- and carboxamido functional groups. The functionalization and chemisorption decrease the hydrophobicity of graphene derivatives and, therefore, foster the development of novel and more robust chemical engineering setups.