Selective adsorption, structure and dynamics of CO2-CH4 mixture in Mg-MOF-74 and the influence of intercrystalline disorder

Mg-MOF-74 is a highly efficient adsorbent for CO2. We use molecular simulations to study the effects of disorder in Mg-MOF-74 on the selective adsorption, structure, and dynamics of a CO2-CH4 mixture. Positional disorder is introduced in the adsorbent by separating individual Mg-MOF-74 crystallites via inserting intercrystalline space between them. Rotating a crystallite with respect to others by different extents provides the orientational disorder (OD). Disorder is observed to enhance the adsorption selectivity of CO2 over CH4. The additional adsorption sites available by exposing crystallite surfaces may provide added selectivity for CO2. Disorder is found to affect both the translational as well as rotational motion of CO2 in Mg-MOF-74. This behavior follows a systematic pattern dictated by the interplay of the pore geometry of Mg-MOF-74 and Mg2+ - CO2 interactions. Our results provide a guide on how to tailor Mg-MOF-74 adsorption behavior with desired properties by purposeful introduction of disorder.