MARTINI-Based Force Fields for Predicting Gas Separation Performances of Metal–Organic Framework/Polymer Composites

Metal-organic framework (MOF)/polymer composites have been widely investigated in the past decade for gas separation applications. However, the impact of the MOF nanoparticle morphology and size in gas separation has not yet been systematically studied by computer simulation techniques. In this work, coarse-grained simulations are deployed to study gas adsorption in ZIF-8/PVDF at the nanoparticle level as a test case. ZIF-8 nanoparticles of different morphologies and sizes are explored, and single-gas adsorption of CO2, N2, and CH4 is investigated throughout the extension of the bulk and surface of the nanoparticle as well as of the polymer phase. The adsorption sites of all guest molecules in bulk ZIF-8 are reproduced with remarkable accuracy, despite the reduction of degrees of freedom. The expected preference for CO2 over the other two gases is also captured. Nanoparticles of smaller sizes provide a better separation performance under ambient conditions, while rhombic dodecahedron nanoparticles perform better than cubic ones. This work presents a perspective on the merits and limitations of modeling gas adsorption in MOF/polymer composites at the nanoparticle level via particle-based coarse graining approaches and provides a methodological setup which can be integrated into high-throughput schemes, bringing us closer to reaching time- and length scales that can be directly compared with experimental data.