Yttrium–decorated C₂₈B₂₈ tetragonal graphene nanocapsule: a promising candidate for CO₂ capture

Abstract

In this study, a modified C₂₈B₂₈ tetragonal graphene nanocapsule is proposed and systematically explored as a high-capacity carbon dioxide (CO₂) capture system using density functional theory (DFT) calculations. The initial investigation of CO₂ adsorption on the pristine C₂₈B₂₈ tetragonal graphene nanocapsule revealed weak physisorption, with an adsorption energy of –0.10 eV at a distance of approximately 3.0 Å. To enhance CO₂ affinity, the nanocapsule was functionalized with a transition metal atom (yttrium), which significantly increased the adsorption strength. For the functionalized structure, the adsorption energy for a single CO₂ molecule reached –0.78 eV. Further calculations showed that up to six CO₂ molecules could effectively bind to each metal site. To evaluate maximum adsorption capacity, a multi-functionalized nanocapsule incorporating six metal atoms was modeled, enabling the adsorption of up to 36 CO₂ molecules, equivalent to an outstanding gravimetric storage capacity of approximately 61 wt.%. The average adsorption energy in this fully loaded complex was calculated to be –0.59 eV, indicating the system’s potential for efficient and reversible CO₂ capture. To gain deeper insight into the interaction mechanisms, additional electronic structure analyses were carried out using the quantum theory of atoms in molecules (QTAIM), natural bond orbital (NBO) analysis, frontier molecular orbital (FMO) analysis, and Independent Gradient Model based on Hirshfeld partitioning (IGMH) analysis. These results suggest a partially covalent character of the interactions and emphasize the role of electronic modulation in enhancing CO₂ adsorption performance.