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

Abstract

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.