Tannic acid reinforced interfacial polymerization fabrication of internally pressurized thin-film composite hollow fiber reverse osmosis membranes with high performance

Internally pressurized thin-film composite (TFC) hollow fiber (HF) reverse osmosis (RO) membranes have the merits of easy scaling-up and no flow dead zone, etc. In this work, we used tannic acid (TA) as a reinforced additive in m-phenylenediamine (MPD) aqueous solution to assist the interfacial polymerization process to construct a polyamide separation skin layer with high separation performance on the inner surface of polysulfone hollow fiber substrate. Due to many phenolic hydroxyl groups on tannic acid molecules, they could form hydrogen bonds with MPD molecules and thus greatly hinders MPD diffusion towards the interface, and greatly helps to manipulate the interfacial polymerization process. In this way, we obtained a TA-reinforced TFC HF RO membrane having super hydrophilicity (contact angle of merely 26.4°), much thinner skin layer (about 100 nm in thickness), as well a much smoother surface (roughness of about 35 nm) under the optimized ultra-low concentration (100 mg L−1) for tannic acid in the MPD solution. The prepared TA-reinforced membrane achieves a water permeance of 20.4 L m−2 h−1 MPa−1, which is more than 50 % higher than that of the TA-free membrane, and a NaCl rejection of about 98 % with 2000 mg L−1 NaCl solution as feed. The TA-reinforced membrane has excellent fouling resistance, chlorine resistance, as well as long-term operation stability, thus showing a broad application prospect in brackish water desalination and tap water treatment.