Study on the adsorption of CH 4 , CO 2 and N 2 in curved graphite slit pores

Coal and graphite are both carbon-based materials with comparable aromatic carbon frameworks, therefore, flat graphite slit pores are widely used as simplified adsorbent models in adsorption studies. However, coal surfaces are often intrinsically curved at the nanoscale. In this work, we constructed a curved graphite slit-pore model and carried out grand canonical Monte Carlo (GCMC) simulations to investigate the adsorption of three representative coalbed methane (CBM)-related gases (CH₄, CO₂, and N₂), with the results systematically compared against those from a conventional flat graphite slit-pore model and available experimental adsorption data. The results show that curved graphite pores can serve as a useful surrogate for curved carbonaceous surfaces in coal, but curvature does not automatically lead to higher adsorption solely due to a larger geometric surface area. Instead, the relative adsorption performance of curved versus flat pores depends on both the adsorbate species and pressure regime. Microscopic analyses further reveal that the adsorbed molecules form clustered/aggregated distributions in both pore types, and the characteristic cluster size increases with the molecular size of the adsorbate. These findings highlight the importance of incorporating surface curvature when using graphite-based slit pores to rationalise gas adsorption in coal-like carbon frameworks.