CO2 adsorption thermodynamics over N-substituted/grafted graphanes: a DFT study

Area of Science:

• Materials Science
• Computational Chemistry
• Environmental Science

Background:

• Graphane, a hydrogenated graphene, offers a versatile 2D platform for chemical functionalization.
• Developing efficient carbon capture materials is crucial for mitigating climate change.

Purpose of the Study:

• To investigate the CO2 adsorption properties of N-substituted and N-grafted graphanes.
• To elucidate the role of nitrogen functionalities and coadsorbed water in CO2 adsorption.
• To guide the rational design of novel graphane-based adsorbents for carbon capture.

Main Methods:

• Density Functional Theory (DFT) calculations were employed to model CO2 adsorption.
• Various N-functionalization strategies on the graphane surface were systematically studied.
• Adsorption energies and mechanisms were analyzed for different functional groups and coadsorbed species.

Main Results:

• Single, isolated N- or NH2-sites on graphane exhibit weak CO2 adsorption.
• Coadsorbed water significantly enhances CO2 adsorption on both N- and NH2-functionalized sites, with exothermic energies around -50 kJ mol(-1).
• Geometric restrictions hinder CO2 adsorption stabilization with directly grafted -NH2 or -OH groups adjacent to other -NH2 sites.
• Introducing a linker (n(-CH2-), n ≥ 1) between the graphane surface and -NH2 or -OH groups greatly enhances CO2 adsorption, reaching -58.8 kJ mol(-1) for -NH2 and -43.1 kJ mol(-1) for -OH at n=2.

Conclusions:

• The presence and proximity of functional groups, along with linker strategies, are critical for optimizing CO2 adsorption on graphanes.
• DFT-driven insights provide a pathway for designing tailored N-based graphane materials for efficient CO2 capture.