Using zeolite imidazole frameworks as ionic cross-linkers to improve the performance of composite SPEEK membrane

SPEEK (sulfonated poly ether ether keton) is a type of very attractive polymeric material in membrane applications. Properties of SPEEK membranes can be tailored through controlling its sulfonation degree. However, the sulfonation degree affects the mechanical strength and membrane stability. SPEEK/PES composite membranes were prepared via a surface coating method. Those membranes show lower retentions due to the swelling of SPEEK. ZIF-8, constructed from zinc centers and 2-methlimidazole ligands, was incorporated into SPEEK to improve their performance. Sulfonation groups in SPEEK closely link to ZIF-8 through the coordination and electrostatic interactions, proved by ATR-IR characterizations and IEC measurements. The ionic crosslinked ZIF-8-SPEEK composite membranes show a higher desulfonation temperature and a lower swelling, evidenced by the TGA results and the water uptake values of ZIF-8-SPEEK composites. The crossflow filtrations show the ionic crosslinked ZIF-8-SPEEK composite membranes have good retentions of PEG1000 (70-90%), dyes ( > 90%) and salts (30-40%). The membrane retentions increase, whereas the permeances decrease after filling of ZIF-8. More than 100 h filtrations indicate that those membranes have a good stability. Although ZIF-8 particles are believed providing extra permeating channels, the strong ionic interactions have a domain effect on the membrane permeance.