High-performance carbonized ZIF-8-doped hybrid carbon molecular sieve membrane for CO2/N2 separation

Incorporating functional materials into polymer precursors is an effective way to prepare carbon molecular sieve (CMS) membranes for solving the trade-off problem between permeability and selectivity of gas separation. In this work, we induced ZIF-8 nanoparticles (from 5 to 20 wt%) as a doping agent to construct a series of phenolphthalein-based cardo poly (arylene ether ketone) (PEK-C) -based hybrid carbon molecular sieve (ZCMS) membranes for CO2/N2 separation via an oxidation and a carbonization process with pyrolysis temperature in the range of 500–700 °C. The carbonized ligand and metal centre of ZIF-8 offered additional pores of carbon matrix, which tailored the ultramicropores of ZCMS membranes for both excellent CO2 permeability and selectivity. By treating with the temperature of 600 °C, ZCMS-600-15 (ZCMS membrane based on 15 wt% of ZIF-8-doped PEK-C) exhibited the highest CO2 permeability of 8902 Barrer, which was 1.8 times higher than that of CMS-600 (CMS membrane based on naked PEK-C). ZCMS-600-15 showed an ideal CO2/N2 selectivity value of 42.2, which is also higher than that of other samples, indicating that the appropriate doping amount of ZIF-8 is 15 wt% and the proper carbonization temperature is 600 °C. Moreover, among all the samples, ZCMS-600-15 also showed a superior CO2 permeability of 8285 Barrer and the highest CO2/N2 selectivity of 24.08 for an equimolar mixture of CO2 and N2, far exceeding the 2008 Robeson upper bound. Therefore, our results suggest that incorporating MOFs into polymer precursors to prepare hybrid carbon molecular sieve membranes by carbonization process could solving the trade-off problem between permeability and selectivity, introducing new possibilities for industrial application.