Investigation of methane adsorption onto metal–organic frameworks under subcritical condition employing adsorption isotherm models

Analysis of methane (CH4) adsorption isotherms for metal–organic framework (MOF) adsorbents in the subcritical regions has been reported in this article. In this study, virgin MIL-101-(Cr) MOF, which is doped with alkali ions, are used to comprehend the influence of alkali dopants on CH4 sorption behaviour. MIL-101-(Cr) MOF and its derivatives with alkali ion dopants were prepared by the benign hydrothermal synthesis route, which was characterized by powder X-ray diffraction method. The equilibrium uptakes of CH4 under the subcritical condition were evaluated by fitting the isotherms with Langmuir, Toth and Dubinin–Astakohv adsorption models to determine the adsorption parameters. The adsorption parameters were correlated with the surface-induced heterogeneity, which can be attributed to the introduction of alkali dopants in the MOF structure. It is apparent from the analysis that the isosteric heat of adsorption diminishes with increasing alkali dopant size, while the induced surface structural heterogeneity increases with increasing alkali dopant size.