Pebax®1657-based membranes with organic gatekeepers for effective CO2 capture

Due to the population growth and industrial development, CO2 emissions have emerged as an undeniable environmental issue for climate change. In this study, sulfocalix[6]arene (SCA6), an organic macrocyclic cavitand, was utilized as the gatekeeper with an open cavity of 6 similar to 6.3 & Aring; and introduced into the Pebax (R) 1657 membranes for efficient CO2 capture. The addition of SCA6 into the pristine membrane at a weight ratio of 0.01:1 significantly increases the CO2 permeability from 166.04 Barrer to 224.62 Barrer (i.e., an increase of 45%), while the ideal CO2/N-2 selectivity only slightly drops from 72.13 to 66.28 (i.e., a dip of 2%). The Pebax/SCA6 membrane also possesses a good ideal selectivity of 9.03 for CO2/H-2 separation. On the other hand, Pebax and SCA6 appear to be compatible at a molecular level as confirmed by FTIR, thermal and EDX analyses. Sorption studies indicate that the gas separation mechanism shifts from being solubility-dominated to diffusivity-dominated in the Pebax/SCA6-1% membrane. However, the SCA6 loading more than 1% may induce crystallization of polyethylene oxide and jeopardizes the permeability and selectivity, as validated by XRD and PALS. The optimal Pebax/SCA6-1% membrane displays stable long-term mixed gas performance over 108 h using a CO2/N-2 feed of 15/85 (v/v%) at 6 bar and 25 degrees C. It has an average CO2 permeability of 228.67 Barrer and a CO2/N-2 selectivity of 70.01. The enhanced gas separation performance by incorporating SCA6 into Pebax arises from both gatekeepers and synergistic effects between them in MMMs, highlighting their potential for gas separation applications.