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Confined growth of skin layer for high performance reverse osmosis membrane

Yan, Wentao, Shi, Mengqi, Wang, Zhi, Zhao, Song, Wang, Jixiao
Journal of membrane science 2019 v.585 pp. 208-217
polyamides, polymerization, reverse osmosis, roughness, thin film composite membranes
Polyamide (PA) thin film composite membranes consisting of a PA film (skin layer) formed via interfacial polymerization (IP) on a porous support are state of the art reverse osmosis (RO) membranes. The skin layer is thought to provide most resistance for transport and be responsible for separation. An ideal skin layer should be very thin with sufficient selectivity. However, it is challenging to obtain such a kind of skin layer. Herein, a novel concept of confining skin layer growth to reduce the resistance of skin layer significantly without sacrificing the selectivity of skin layer was proposed. The skin layer growth can be confined by a barrier, which can hinder the diffusion of aqueous phase monomers toward the organic phase during IP. Zeolitic imidazolate framework-8 (ZIF-8) particles were used as barriers in this work. By controlling the confinement, the skin layer thickness was reduced, meanwhile the sufficient selectivity of skin layer was maintained. Then, the flux was improved dramatically from 49.8 ± 1.1 L m−2 h−1 to 76.2 ± 3.4 L m−2 h−1 (by 53.0%), meanwhile a high rejection (99.06 ± 0.20%) was retained. Besides, the confinement led to a surface with lower roughness. The comparison of utilizing the barriers (ZIF-8 particles) and shortening the reaction time was also done. The results showed that (1) utilizing the barriers and shortening the reaction time share similarities and (2) utilizing the barriers is superior to shortening reaction time. The performance of membrane fabricated via the concept of confining the skin layer growth exceeds that of many previously reported membranes. This work might inspire the development of high performance membranes fabricated by IP with great potential for applications in molecular separations.