Enhancement of CO2 separation efficiency in mixed matrix membranes through zinc ion modified g‐C3N4 nanosheets

Abstract This study employed modified graphitic carbon nitride (g‐C 3 N 4 ) nanosheets and polyether block amide (Pebax) to prepare mixed matrix membranes (MMMs) aiming to enhance CO 2 separation efficiency. Through sulfonation and zinc ion (Zn 2+ ) modification of g‐C 3 N 4 nanosheets, high Zn 2+ loaded nanofillers (SCN‐Zn 2+ ) were synthesized. Compared to g‐C 3 N 4 , MMMs with SCN‐Zn 2+ as nanofiller showed a CO 2 permeance of 462 Barrer as well as the CO 2 /N 2 selectivity of 47.5 at the feed gas pressure of 2 bar, which surpassed the 2008 Robeson upper bound. Additionally, the Pebax/SCN‐Zn 2+ (30) membrane was subjected to continuous gas permeability experiments for 70 h and showed good stability. The results showed that SCN‐Zn 2+ nanosheets played an important role in enhancing the gas selectivity of the membranes. SEM confirmed that the SCN‐Zn 2+ nanosheets had good compatibility with the Pebax substrate and the presence of hydrophilic sulfonic acid groups effectively suppressed the interfacial defects. The increase in the free volume fraction of the membranes as well as the solubility and diffusion coefficient suggested that the introduction of g‐C 3 N 4 nanosheets led to more tortuous gas transport paths, which enhanced the permeability and selectivity of CO 2 .