Preparation of PIM-1 thin film composite membranes with enhanced organic solvent resistance via thermal crosslinking

Abstract

PIM-1 thin film composite (TFC) membrane has attracted great attention for organic solvent nanofiltration (OSN) because of its high porosity and excellent solution process-ability. However, the PIM-1 thin selective layer may swell excessively in polar solvents such as methanol and acetone, and thus it makes the connection between the PIM-1 selective layer and the porous support unstable, which can significantly impair its separation performance. In this work, a series of novel PIM-1 TFC membranes was obtained by spin-coating of PIM-1/tetrahydrofuran solution onto α-Al2O3 ceramic supports followed by a thermal treatment process. Since the nitrile group within PIM-1 tends to experience a thermal crosslinking reaction forming stable triazine rings after heat treatment, thus the organic solvent resistance ability of PIM-1 TFC membrane was greatly enhanced. Results showed that the thermally treated PIM-1 TFC membranes possess better chemical stability in polar solvents and acceptable permeances for various solvents (e.g., 2 ∼ 4.2 L·m−2·h−1·bar−1 for methanol, and 4.3 ∼ 6.8 L·m−2·h−1·bar−1 for toluene). For instance, the PIM-1 TFC membrane termed as PIM-1-3 wt%-1h TFC showed a methanol permeance of 3.8 L·m−2·h−1·bar−1 with a rejection of 96.5% towards Congo red (Mw = 697 Da). Moreover, compared to the pristine PIM-1 TFC membrane, the thermally treated PIM-1 TFC membrane possesses better separation stability after the long-term static immersion test in acetone and DMF for 7 days, and it also exhibit good stability in the continuous filtration test using 20 mg·L−1 Congo Red methanol solution, demonstrating a promising outlook in OSN fields.