Methane adsorption on specially designed TiC and Mo2C derived carbons with different pore size and surface morphology

Abstract

The effect of pore size and surface morphology of carbon materials on the adsorption of methane was studied selecting three microstructurally different carbide-derived carbons (CDC), synthesized from titanium carbide (TiC-CDC 950 °C and TiC-CDC 1100 °C HCl) and molybdenum carbide (Mo2C-CDC 1000 °C). Nitrogen sorption and Raman spectroscopy methods were used to obtain the specific surface area, ratio of micro- and mesopores, the pore size distribution and disorder in structure, respectively. Studied CDCs had high surface area (>800 m2 g−1), but the pore size distribution was remarkably different. TiC-CDC 950 °C contains mainly micropores (from 0.5 to 1 nm), TiC-CDC 1100 °C HCl both micro- and mesopores (from 1.5 to 5 nm) and Mo2C-CDC 1000 °C mainly mesopores (from 2.5 to 10 nm). Structural correlation lengths calculated from Raman spectra showed that CDC with the smallest pores (TiC-CDC 950 °C) was the most disordered of carbon materials studied. Excess isotherms (EI) of methane adsorption were measured at different temperatures (from −100 to 40 °C) and pressures (from 0.03 to 1.35 MPa) and modelled with modified Langmuir equation to obtain the absolute adsorption isotherms, enthalpies and entropies of methane adsorption. It was concluded that the change in entropy is the key factor determining the amount of gas adsorbed per unit of surface area of CDC and up to 55% more methane can be adsorbed if the structure of carbon material is optimized.