Atomistic Simulation Study of Polyarylate/Zeolitic-Imidazolate Framework Mixed-Matrix Membranes for Water Desalination

Mixed-matrix membranes (MMMs) have received considerable interest because of their capability to synergize polymeric and nanomaterials. Extensive experimental and a handful of simulation studies on MMMs have been conducted for gas separation; however, there is scarce simulation endeavor for liquid separation. Herein, we report an atomic simulation study to examine the swelling of MMMs in water and subsequently explore their performance for water desalination. The MMMs are composed of a polyarylate (coined as “PAR”) and two zeolitic-imidazolate frameworks (ZIF-8 and ZIF-93, respectively) with various PAR/ZIF ratios. After swelling, the bulk region of PAR in different PAR/ZIF MMMs exhibits similar swelling degree and void size distribution, implying the microstructure of PAR is nearly not affected by the presence of ZIF. However, remarkably different behavior at the PAR/ZIF interface is observed between PAR/ZIF-8 and PAR/ZIF-93. It is revealed that hydrophobic ZIF-8 possesses comparable interaction with PAR and water; by contrast, hydrophilic ZIF-93 interacts preferentially with water and negligibly with PAR. Consequently, PAR is compactly packed near the ZIF-8 surface but displaced by water near ZIF-93 surface during swelling process. For water desalination, water permeabilities through the swollen PAR/ZIF-8 MMMs are found to drop with increasing PAR/ZIF-8 ratio due to the blockage of ZIF-8 pores by PAR; intriguingly, water permeabilities through the swollen PAR/ZIF-93 MMMs remain almost unchanged. Moreover, all the MMMs exhibit the capability of complete salt rejection. This simulation study provides molecular insight into the microstructure and performance of PAR/ZIF MMMs, reveals the crucial role of ZIF functionality in the swelling and permeation of PAR/ZIF MMMs, and would facilitate the development of MMMs for high-performance water desalination.