(136b) Atomistic Study of Effect of Defects on the Thermal Conductivity of Metal-Organic Frameworks

Metal-organic frameworks (MOFs) are crystalline, nanoporous, highly tunable materials that are promising for gas storage and separations applications among others. However, their usefulness, especially for gas storage applications depends on how quickly they can dissipate the significant amount of thermal energy produced during the typically exothermic adsorption process. Over the past decade, the structure-property relationships of MOFs have been studied extensively but mainly with regards to their gas adsorption capacity and selectivity. In contrast, comparatively limited studies have focused so far on understanding thermal transport in MOFs. Past studies on thermal properties of MOFs have investigated the effect of pore size and shape, interpenetration, and functional groups on thermal conductivity. In all those studies, MOF structures were assumed to be “ideal crystals” with no defects. In practice, defect sites are always present in real MOFs and are known to affect their chemical and physical properties. Here we report our investigations on the effect of defects in MOFs on their thermal conductivities, where defect sites can be responsible for phonon-lattice-defect scattering. We show that defect density, if controlled, can be helpful in tuning thermal properties. Hence defect site density can provide us with an additional lever along with other structural parameters (e.g. pore size and shape) to control thermal properties in MOFs. In this work, we used molecular dynamics simulations and the equilibrium Green-Kubo method to study the effect of defects, and their density, on the thermal conductivity of MOFs.