High-flux polyamide nanofiltration membranes via phosphate saline-buffered polymerization

Controlling the structure and charge of nanofiltration membranes is vital for removing emerging contaminants in both point-of-use and industrial wastewater treatment. However, the challenge is finding a viable method to regulate interfacial polymerization for high-permeance polyamide membranes with tailored selectivity and reduced scaling potential. Here we propose a simple and straightforward approach to creating an ultra-thin, highly charged polyamide membrane through protonation-regulated interfacial polymerization with phosphate saline buffer (PB-IP). The resulting thin films exhibit a long-term permeation performance with permeance >110 L m−2 h−1 bar−1 without pore collapsing. Within these membranes, the polyamide network is composed of loosely crosslinked chains with high charge density, providing sub-1 nm pore sizes that are effective for separating small molecules, such as perfluorooctanoic acid (PFOA) and different antibiotics. The PB-IP methodology allows for tailored membrane functionality, particularly for reducing the rate of surface mineral deposition. We examined the inorganic scaling propensity of these membranes by systematically quantifying the rejection of different salt species and studying the change in hydraulic flux using the solution with high gypsum saturation index. Furthermore, the fouling characteristics of the membranes were stimulated with common foulants to demonstrate the antifouling characteristic. This work provides a feasible strategy to adjust the structure-property-performance relationship profile for polyamide membranes, and to enable their use in water purification under a more dynamic range of water conditions.