Highly selective separation and resource recovery using forward osmosis membrane assembled by polyphenol network

Abstract

We report a novel forward osmosis (FO) membrane prepared by a green tannic acid/iron (TA/Fe) coordination chemistry to selectively separate and recover organic source from salty water. The microscopic and x-ray photoelectron spectroscopy (XPS) characterizations confirmed the formation of a thin continuous TA/Fe rejection layer with a thickness of 20–30 nm on a polyacrylonitrile (PAN) substrate. This TA/Fe-PAN membrane showed a high water permeability (A) of 14.2 ± 1.7 Lm−2h−1bar−1, a high rejection of 99.5 ± 0.1% for a low-molecular dye sunset yellow and low rejection of 27.6 ± 2.7% for NaCl under reverse osmosis (RO) mode. The membrane selectivity to sunset yellow was nearly three orders of magnitude greater than that of NaCl, revealing its preference towards organic dye retention and salt passage. As a result of its higher water permeability and the prevention of salt accumulation during FO tests, the TA/Fe-PAN membrane showed significantly higher FO water flux compared to that of a commercially available polyamide thin film composite membrane. It could concentrate sunset yellow from a salty FS solution with a concentration ratio of 9.6 and mild salt accumulation at the water recovery ratio of 90%. The results demonstrated the feasibility of selective separation and resource recovery for target solutes from salty even more complicated water matrix via proper membrane chemistry design in FO.