Silk fibroin-coated polyamide thin-film composite membranes with anti-scaling properties

Scaling inevitably occurs on the reverse osmosis (RO) membrane's surface due to the increased salt concentration during the filtration of a saline solution containing various kinds of ions. Particularly, scaling becomes more likely when an RO membrane's surface possesses many carboxyl groups capable of interacting with multivalent cations. Herein, we developed a thin-film composite (TFC) membrane by coating silk fibroin (SF) on a polyamide (PA) active layer. Since SF consists of a large number of hydroxyl groups, the SF-coated PA TFC membrane (SF-PA-TFC) revealed a smaller absolute value (−17.7 mV) of surface zeta potential than half of that (−40.3 mV) of the PA TFC membrane (PA-TFC), thereby effectively preventing carboxyl groups from stepping in scaling. Furthermore, SF coating made a PA active layer more hydrophilic and smoother. Thanks to the desirable features, the SF-PA-TFC was accompanied by several strengths such as 5 times lower irreversible scaling resistance, 50% higher flux recovery ratio, and 4 times longer operation duration till cleaning under the condition for heterogeneous nucleation. We hope this finding could facilitate the development of anti-scaling RO membranes by making the most of natural resources that can minimize the economic and environmental burdens imposed by a manufacturing process.