Abstract
High-performance sulfonated polysulfone (SPSf) mixed-matrix membranes (MMMs) were fabricated via a nonsolvent-induced phase separation (NIPS) method using zeolitic imidazolate frameworks-67 (ZIF-67) as a crosslinker. Acid-base crosslinking occurred between the sulfonic acid groups of SPSf and the tertiary amine groups of the embedded ZIF-67, which improved the dispersion of ZIF-67 and simultaneously improved the membrane strzcture and permselectivity. The dispersion of ZIF-67 in the MMMs and the acid-base crosslinking reaction were verified by energy-dispersive X-ray spectroscopy (EDX), X-ray diffractometry (XRD), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The pore structure analysis of MMMs indicated that filling ZIF-67 into SPSf enhanced the average surface pore sizes, surface porosities and more micropore in cross-sections. The crossflow filtrations showed the MMMs have higher pure water fluxes (57 to 111 L m-2 h-1) than the SPSf membrane (55 L m-2 h-1) but also higher bovine serum albumin (BSA) rejection rate of 93.9-95.8%, a model protein foulant. The MMMs showed a higher water contact angle than the SPSf membrane due to the addition of hydrophobic ZIF-67 and acid-base crosslinking, and also maintained high thermal stability evidenced by the thermogravimetric analysis (TGA) results. At the optimal ZIF-67 concentration of 0.3 wt%, the water flux of the SPSf-Z67-0.3 membrane was 82 L m-2 h-1 with a high BSA rejection rate of 95.3% at 0.1 MPa and better antifouling performance (FRR = 70%).
Highlights
In recent years, sulfonated polymers have been widely used for membrane fabrication due to their hydrophilicity, high proton conduction capacity, selective ion transport, and chlorine tolerance (Luo et al 2017; Liu et al 2019)
When a highly-sulfonated polymer is used as the membrane matrix, the hydrophilic sulfonic acid groups destabilize the membrane at high pressures because they allow water to plasticize and swell the membranes, which compromises the mechanical properties (Peeva et al 2011; Ma et al 2013)
The surface area and pore size of zeolitic imidazolate frameworks-67 (ZIF-67) were characterized by the Brunauer-Emmett-Teller (BET) method
Summary
In recent years, sulfonated polymers have been widely used for membrane fabrication due to their hydrophilicity, high proton conduction capacity, selective ion transport, and chlorine tolerance (Luo et al 2017; Liu et al 2019). The weak acid-base reaction between the imidazole ligands and the sulfonic acid groups contributed to the good dispersion of ZIF-67, which would produce membranes surface with larger average surface pore sizes and higher porosities.
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