Study on gas adsorption and separation performance of alkyl functionalized MOF materials under wet conditions

Metal-organic framework materials exhibit significant potential for diverse applications in gas adsorption and separation. We have studied the performance changes of Cu-BTC, Cu-MBTC and Cu-EBTC under different water-containing conditions. GCMC studies shows that, compared with Cu-BTC, the water absorption properties of Cu-MBTC and Cu-EBTC have a certain degree of decline, which is consistent with the experimental results. The incorporation of alkyl groups led to a decrease in the heat of adsorption for both Cu-MBTC and Cu-EBTC when exposed to water. The gas adsorption performance of Cu-BTC, Cu-MBTC and Cu-EBTC exhibits inconsistent variations in gas adsorption performance under water-containing conditions. The addition of coordinated water molecules enhances the ability of Cu-BTC to adsorb CO₂. The capacity of Cu-MBTC with 4 wt% water to adsorb CO₂ increased, but the capacity of Cu-MBTC with 8 wt% water to adsorb CO₂ decreased. The presence of coordinated water molecules reduces the CO₂ adsorption performance of Cu-EBTC. The study of the heat of adsorption explains this phenomenon from the mechanism. At the same time, we found an interesting phenomenon. The existence of trace water molecules can greatly improve the adsorption selectivity of Cu-EBTC to CO₂/N_2, while the pressure and gas ratio have little effect. It can provide more possibilities for the widespread use of MOF in the fields of gas adsorption and separation.