In situ healing of damaged polyethersulfone ultrafiltration membranes with microgels

The damage of water treatment membranes under operation is a thorny problem, resulting in a great reduction of separation performance and compromised water quality. Here, we shall report a facile method for in-situ reparation of damaged membranes by using damaged polyethersulfone (PES) ultrafiltration (UF) flat membranes as model systems and quaternized crosslinked microgels coded as PNI6 microgels as the healing materials. The PNI6 microgels were synthesized via surfactant free emulsion polymerization of N-isopropylacrylamide (NIPAM) and 1-vinylimidazole (VIM) in the presence of 1,6-dibromohexane (BrCH). The obtained PNI6 microgel suspension was used as the feeding liquid to successfully heal the wound of damaged PES UF flat membranes by filtration deposition. An absorbed microgel layer was formed on the wound site of membranes and hence healed the wound. The rejection performances of microgel-healed PES UF membranes were recovered to the original level of pristine membranes although the water flux decreased from 588.6 L/(m(2) h bar) for the pristine membrane to 228.8 L/(m(2) h bar) for the healed membranes. It was also demonstrated that the microgel-healed PES UF membranes were chemically stable in both strong acidic and basic conditions and durable in a wide temperature range from 25 to 70 degrees C with a long-term stability.