Zwitterionic material for construction of an antifouling polyamide thin film composite membrane

Zwitterionic materials containing equal proportions of positively and negatively charged groups have been used to provide membranes with antifouling capabilities. This study focuses on the modification of a commercially available polyamide thin-film composite membrane with a zwitterionic material and investigates its effectiveness in fouling mitigation. The zwitterionic material, sulfobetaine vinylimidazole (SBVI), was synthesized by reacting 1,3-propane sulfone with 1-vinyl imidazole. A NF90 polyamide membrane functionalized with propagyl bromide was modified by the polymerization of SBVI on its surface. Various techniques were used to verify the successful modification of membranes. The water flux and salt rejection of the pristine and modified membranes were measured under comparable stabilization conditions, and showed an increase in salt rejection and a decrease in permeability for the modified membrane because of additional membrane resistance. However, fouling tests conducted with a wide range of foulants in cross-flow filtration mode showed a lower fouling ratio and higher recovery ratio for the modified membrane than for the pristine membrane. The enhancement in the antifouling characteristics of the modified membrane was mainly attributed to the improvement in hydrophilicity resulting from the zwitterionic brushes. Our results demonstrated the fouling resistance is further reinforced in an ionic environment through the "salting-in" effect.