Mixed matrix membranes by incorporating methyl-functionalized covalent organic framework into PDMS for high flux ethanol/water separation

Polydimethylsiloxane (PDMS) membranes are commonly utilized for ethanol-water separation. However, the separation performance is insufficient owing to the inherent trade-off between permeability and selectivity. In this study, we reported the incorporation of methyl-functionalized covalent organic framework (COF, TpBD-CH₃) into PDMS membranes to prepare mixed matrix membranes (MMMs), greatly increasing ethanol flux by 2.7 times. Under testing conditions of 60 ​°C with a feed solution containing 5 ​wt% ethanol in water, the permeation flux of the membrane incorporating 0.1 ​wt% TpBD-CH₃ significantly increased from 1738 ​g/(m²·h) to 4648 ​g/(m²·h) compared to the original PDMS membrane, while the separation factor improved from 7.32 to 8.40. The improved separation performance is attributed to that the incorporation of the COF enhances the hydrophobicity as well as the free volume cavities of the membranes as evidenced by the significantly increased gas permeability (CO₂ permeability reaches 26,720 Barrer). This study indicates the potential of COF in the development of PDMS-based MMMs for the separation of organic aqueous solutions or gas components.