A comparative study of mechanisms of the adsorption of CO2 confined within graphene–MoS2 nanosheets: a DFT trend study

Abstract

The space within the interlayer of 2-dimensional (2D) nanosheets provides new and intriguing confined environments for molecular interactions. However, atomic level understanding of the adsorption mechanism of CO₂ confined within the interlayer of 2D nanosheets is still limited. Herein, we present a comparative study of the adsorption mechanisms of CO₂ confined within graphene–molybdenum disulfide (MoS₂) nanosheets using density functional theory (DFT). A comprehensive analysis of CO₂ adsorption energies (E_AE) at various interlayer spacings of different multilayer structures comprising graphene/graphene (GrapheneB) and MoS₂/MoS₂ (MoS₂B) bilayers as well as graphene/MoS₂ (GMoS₂) and MoS₂/graphene (MoS₂G) hybrids is performed to obtain the most stable adsorption configurations. It was found that 7.5 Å and 8.5 Å interlayer spacings are the most stable conformations for CO₂ adsorption on the bilayer and hybrid structures, respectively. Adsorption energies of the multilayer structures decreased in the following trend: MoS₂B > GrapheneB > MoS₂G > GMoS₂. By incorporating van der Waals (vdW) interactions between the CO₂ molecule and the surfaces, we find that CO₂ binds more strongly on these multilayer structures. Furthermore, there is a slight discrepancy in the binding energies of CO₂ adsorption on the heterostructures (GMoS₂, MoS₂G) due to the modality of the atom arrangement (C–Mo–S–O and Mo–S–O–C) in both structures, indicating that conformational anisotropy determines to a certain degree its CO₂ adsorption energy. Meanwhile, Bader charge analysis shows that the interaction between CO₂ and these surfaces causes charge transfer and redistributions. By contrast, the density of states (DOS) plots show that CO₂ physisorption does not have a substantial effect on the electronic properties of graphene and MoS₂. In summary, the results obtained in this study could serve as useful guidance in the preparation of graphene–MoS₂ nanosheets for the improved adsorption efficiency of CO₂.