(376j) Membrane Surface Modification Using Acrylate- and Thiol-Containing Zwitterionic Materials Via Polydopamine

Fouling is one of the major challenges for the use of membrane technology for water purification. One effective way to mitigate the fouling is to chemically modify membrane surface to reduce its favorable interactions with foulants, such as grafting with superhydrophilic zwitterions. However, zwitterionic materials are water-soluble, and it is challenging to graft or coat zwitterions for long-term underwater operation. In this work, we demonstrate facile covalent grafting of zwitterionic materials (functionalized by acrylate and thiol) on the surface of ultrafiltration (UF) membranes using dopamine. Specifically, dopamine is deposited with sulfobetaine methacrylate (SBMA) or a thiol-containing zwitterionic polymer (p(MPC₁₆₀-co-DTMAEL₄₂, or PMD). In the presence of oxygen, dopamine forms polydopamine (PDA) adhering onto the membrane surface and covalently grafts SBMA or PMD via Michael addition to form a robust thin superhydrophilic layer, as confirmed by contact angle measurement and X-ray photoelectron spectroscopy (XPS). Interestingly, the coating does not completely cover the pores (as evidenced by the SEM) and thus, the modified membranes still exhibit reasonably high water permeance. The antifouling properties of the membranes were determined using a crossflow system and bovine serum albumin (BSA) as a model foulant. The modified UF membrane with SBMA and dopamine demonstrates up to 30% higher water flux than the uncoated one when tested with 1 g/L BSA. Moreover, the membrane modified with PMD and dopamine exhibits less flux decline (38% reduction) than the unmodified membrane (53% reduction). The facile approach of membrane modification employing SBMA/dopamine is also adapted for post‑modification of a commercial nanofiltration (NF) membrane module, which demonstrates enhanced antifouling properties when tested with real wastewater at a wastewater treatment plant.