Ligand Substitution: An Effective Way for Tuning Structures of ZIF-7 Nanoparticles (NPs) and Improving Energy Recovery Performance of ZIF/PA TFN Membranes

It is an important initiative to reduce the building energy consumption using energy recovering ventilation (ERV) systems. The application of ERV systems is hindered by the low CO2 barrier performance of commercial total heat exchange membranes (THEMs) that lead to unsatisfactory indoor air refreshing rate, and there is an urgent need for THEMs that have improved CO2 barrier properties and effective energy recovery efficiencies. Here, we report the formation of novel ZIF/PA TFN THEMs based on ZIF-7-X nanoparticles (NPs) with "core-shell" structures and tunable particle sizes, formed from benzimidazole (BIM) ligands and BIM substituted by -NH2, -CH3, -C2H5, and -C3H7 functional groups. The NPs were mixed with pyr omellitic triformyl chloride (TMC) in the organic phase during the interface polymerization process to form ZIF/PA TFN membranes. The total heat exchange performance of ZIF/PA TFN membranes could be effectively modified by the type and quantity of ZIF-7-X NPs added. The CO2 barrier properties and water vapor permeability of ZIF/PA TFN membranes could be improved by the addition of optimal levels of ZIF-7-X NPs, showing low CO2 permeance of 7.76 GPU, high H2O permeance of 663.8 GPU, and excellent enthalpy exchange efficiency of 72.1%. This work provided an effective strategy for tuning not only the nanostructures of ZIF-7 fillers but also the CO2 barrier properties of the formed ZIF/PA TFN membranes.