Membrane technology has emerged as an attractive approach for water purification, while mitigation of fouling is key to lower membrane operating costs. This article reviews various materials with antifouling properties that can be coated or grafted onto the membrane surface to improve the antifouling properties of the membranes and thus, retain high water permeance. These materials can be separated into three categories, hydrophilic materials, such as poly(ethylene glycol), polydopamine and zwitterions, hydrophobic materials, such as fluoropolymers, and amphiphilic materials. The states of water in these materials and the mechanisms for the antifouling properties are discussed. The corresponding approaches to coat or graft these materials on the membrane surface are reviewed, and the materials with promising performance are highlighted.

Polymeric membranes for wastewater reuse are often fouled by suspended solids and dissolved organic matters, resulting in a dramatic decrease in water flux. Fouling can be mitigated by enhancing hydrophilicity of the membrane surface to avoid favorable interactions between the membranes and foulants. However, the modification of the membrane surface is often complicated and difficult to integrate into industrial membrane production processes. Herein we demonstrate a facile one-step coating of superhydrophilic zwitterions on the surface of ultrafiltration (UF) membranes by codepositing dopamine and sulfobetaine methacrylate (SBMA). In the presence of oxygen, dopamine forms polydopamine (PDA) adhering onto the membrane surface and anchors SBMA via Michael addition to form a robust thin superhydrophilic layer, as confirmed by contact angle measurement and X-ray photoelectron spectroscopy (XPS). The modified UF membranes demonstrate up to 80% higher water flux than the uncoated ones, when tested with water containing bovine serum albumin (BSA) as a model foulant in a crossflow system. This facile approach of membrane modification is also adapted for postmodification of a commercial nanofiltration (NF) membrane module, which demonstrates superior antifouling properties when tested with real wastewater at a wastewater treatment plant.

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Hydrogels have been widely utilized to enhance the surface hydrophilicity of membranes for water purification, increasing the antifouling properties and thus achieving stable water permeability through membranes over time. Here, we report a facile method to prepare hydrogels based on zwitterions for membrane applications. Freestanding films can be prepared from sulfobetaine methacrylate (SBMA) with a crosslinker of poly(ethylene glycol) diacrylate (PEGDA) via photopolymerization. The hydrogels can also be prepared by impregnation into hydrophobic porous supports to enhance the mechanical strength. These films can be characterized by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) to determine the degree of conversion of the (meth)acrylate groups, using goniometers for hydrophilicity and differential scanning calorimetry (DSC) for polymer chain dynamics. We also report protocols to determine the water permeability in dead-end filtration systems and the effect of foulants (bovine serum albumin, BSA) on membrane performance.

Hydrogels have been widely utilized to enhance the surface hydrophilicity of membranes for water purification, increasing the antifouling properties and thus achieving stable water permeability through membranes over time. Here, we report a facile method to prepare hydrogels based on zwitterions for membrane applications. Freestanding films can be prepared from sulfobetaine methacrylate (SBMA) with a crosslinker of poly(ethylene glycol) diacrylate (PEGDA) via photopolymerization. The hydrogels can also be prepared by impregnation into hydrophobic porous supports to enhance the mechanical strength. These films can be characterized by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) to determine the degree of conversion of the (meth)acrylate groups, using goniometers for hydrophilicity and differential scanning calorimetry (DSC) for polymer chain dynamics. We also report protocols to determine the water permeability in dead-end filtration systems and the effect of foulants (bovine serum albumin, BSA) on membrane performance.