Adsorption and Diffusion Properties of Functionalized MOFs for CO2 Capture: A Combination of Molecular Dynamics Simulation and Density Functional Theory Calculation

The capture of carbon dioxide (CO₂) from fuel gases is a significant method to solve the global warming problem. Metal-organic frameworks (MOFs) are considered to be promising porous materials and have shown great potential for CO₂ adsorption and separation applications. However, the adsorption and diffusion mechanisms of CO₂ in functionalized MOFs from the perspective of binding energies are still not clear. Actually, the adsorption and diffusion mechanisms can be revealed more intuitively by the binding energies of CO₂ with the functionalized MOFs. In this work, a combination of molecular dynamics simulation and density functional theory calculation was performed to study CO₂ adsorption and diffusion mechanisms in five different functionalized isoreticular MOFs (IRMOF-1 through -5), considering the influence of functionalized linkers on the adsorption capacity of functionalized MOFs. The results show that the CO₂ uptake is determined by two elements: the binding energy and porosity of MOFs. The porosity of the MOFs plays a dominant role in IRMOF-5, resulting in the lowest level of CO₂ uptake. The potential of mean force (PMF) of CO₂ is strongest at the CO₂/functionalized MOFs interface, which is consistent with the maximum CO₂ density distribution at the interface. IRMOF-3 with the functionalized linker -NH₂ shows the highest CO₂ uptake due to the higher porosity and binding energy. Although IRMOF-5 with the functionalized linker -OC₅H₁₁ exhibits the lowest diffusivity of CO₂ and the highest binding energy, it shows the lowest CO₂ uptake. Accordingly, among the five simulated functionalized MOFs, IRMOF-3 is an excellent CO₂ adsorbent and IRMOF-5 can be used to separate CO₂ from other gases, which will be helpful for the designing of CO₂ capture devices. This work will contribute to the design and screening of materials for CO₂ adsorption and separation in practical applications.