(569b) Fouling Resistant Ultrafiltration Membranes with Ultrathin Hydrogel Selective Layers Containing Zwitterionic Moieties

Membrane separation processes are of paramount importance in water and wastewater treatment. However, membrane fouling by organic compounds is still one of the main obstacles to more extensive use of membrane separation processes. Hydrogels are materials that can absorb large quantities of water and swell. This high degree of hydration makes them inherently fouling resistant. Hydrogels also have tunable mesh size – enabling control of their permeation selectivity – and are functionalizable. These features make them excellent membrane materials. However, the applicability of hydrogels as fouling-resistant selective layers of thin film composite membranes has, so far, been hindered by the lack of a fabrication process that allows for the formation of a thin, defect-free hydrogel layer on a porous support. We have recently demonstrated a new method, namely Interfacially Initiated Free Radical Polymerization (IIFRP), to address this challenge. In IIFRP, an ultrathin hydrogel selective layer, as thin as ~80 nm, is synthesized on top of a porous support by separating the monomer and photoinitiator into two immiscible phases. The hydrogel is formed at the interface of these two phases. The goal of the present study was to explore the incorporation of other hydrophilic functional groups, particularly zwitterionic (ZI) groups, into hydrogel selective layers by IIFRP. We have shown that the incorporation of ZI moieties can further increase membrane fouling resistance and improve membrane properties. For instance, the partial substitution of poly(ethylene glycol) diacrylate (PEGDA) units in the hydrogel layer with the zwitterionic monomer sulfobetaine methacrylate (SBMA) led to a permeance increase of almost an order of magnitude (from 3.9±0.4 L/h.m².bar to 34.7±0.8 L/h.m².bar). Although the addition of SBMA also decreased the crosslinking density of the hydrogel selective layer, the rejection properties of these membranes remained essentially constant (99.2±0.6% and 98.7±0.6% myoglobin rejection, respectively). Moreover, the zwitterionic hydrogel membranes have shown higher fouling resistance to oil emulsions compared to both commercial membranes and the zwitterion-free hydrogel membranes. Consequently, zwitterionic containing hydrogel selective layer obtained by IIFRP are very promising membrane materials.