Quantum mechanical analysis of adsorption for CH4 and CO2 onto graphene oxides

Abstract

Graphene oxide (GO) surfaces with rich and diverse oxygen-containing functional groups might endow GOs with unique chemical adsorption activity. Exploring the adsorption behavior of gas molecules on GOs with different degrees of oxidation can help design highly efficient adsorbents and catalysts. Herein, the interaction energies between two kinds of gas molecules, CH4 and CO2, and the GO surfaces with varied oxidization degrees were simulated by density functional theory. It is numerically demonstrated that CO2 has a stronger interaction strength than CH4. More specifically, the interaction energies for the gases on GO surfaces do not show monotonous variation with the degree of oxidization. The results suggest that there exists an appropriate range of oxidized degrees on GOs, which can impose higher adsorption interaction. The AIM (atom in molecule) and NOCV (natural orbital for chemical valence) analyses were applied to reveal the interaction mechanisms between the gas molecules and GO surfaces. The adsorption free energy and adsorption coverage of CH4 and CO2 on GO surfaces were calculated. Generally, the gas adsorption on GO is thermodynamically unfavorable under standard conditions. The computational results provide an improved understanding of the adsorption mechanism, which might be valuable for the application of high-performance GO-based adsorbents and catalysts.