Origins of Negative Gas Adsorption

Negative gas adsorption by a porous crystalline solid, DUT-49, observed by spontaneous desorption of gas during a pressure increase raises fundamental questions on the physical origin of this puzzling behavior. Importantly, a framework that can transform a large amount of strain into pressure has many possible technological applications. To address this question, we studied the mechanics and thermodynamics of DUT-49 at both the molecular unit and framework scales by applying quantum density functional theory and extensive classical molecular-dynamics simulations. We demonstrate that negative gas adsorption originates from molecular buckling of the organic structural unit and thus allows a colossal framework transformation. Methane adsorption is subsequently shown to activate this transition, in full agreement with experimental observations. The molecular insight presented here unveils the mechanics and thermodynamics responsible for negative gas adsorption and provides unparalleled understanding to aid the discovery of new examples of similarly responsive porous metamaterials.