Preparation of solvent-resistant polyimide membranes for efficient separation of dyes and salts via an “internal drive” strategy

It is extremely difficult to separate salts and dyes from high-salinity printing and dyeing wastewater. In this study, modified montmorillonite (EPTAC-CD-MMT) was obtained by intercalation of 2,3-epoxypropyltrimethylammonium chloride (EPTAC) modified cyclodextrin (CD). PI/EPTAC-CD-MMT membrane was prepared by blending EPTAC-CD-MMT with polyimide (PI). The addition of EPTAC-CD-MMT could inhibit the motion of PI molecular chains and increase the solvent resistance of the membrane. Additionally, EPTAC-CD-MMT exhibited spontaneous "internal drive" during the phase transition and segregated to the membrane surface. The pore structure of the membrane was adjusted to a well-developed "side pore" structure. Thus, solvent-resistant membranes for dye/salt separation with high flux were finally obtained. The successful modification of MMT was demonstrated by FTIR, XRD, TGA and XPS. EDX and SEM were used to characterize the surface segregation phenomena and well-developed pore structures of the membranes. When EPTAC-CD-MMT was added at 3 wt%, the membranes showed a significant increase in pure water flux (138.0 L·m−2·h−1·bar−1), high dye rejection (>98.5 %), low salt rejection (<10.0 %), and good solvent resistance in six organic solvents. This demonstrated the potential of PI/EPTAC-CD-MMT separation membranes for the treatment of dye wastewater containing sophisticated organic solvents.