Non-Polyamide Based Nanofiltration Membranes Using Green Metal–Organic Coordination Complexes: Implications for the Removal of Trace Organic Contaminants

Abstract

Polyamide-based thin film composite (TFC) membranes are generally optimized for salt rejection but not for the removal of trace organic contaminants (TrOCs). The insufficient rejection of TrOCs such as endocrine disrupting compounds (EDCs) by polyamide membranes can jeopardize product water safety in wastewater reclamation. In this study, we report a novel nonpolyamide membrane chemistry using green tannic acid–iron (TA–Fe) complexes to remove TrOCs. The nanofiltration membrane formed at a TA–Fe molar ratio of 1:3 (TA–Fe3) had a continuous thin rejection layer of 10–30 nm in thickness, together with a water permeability of 5.1 Lm2–h–1bar–1 and a Na2SO4 rejection of 89.7%. Meanwhile, this membrane presented significantly higher rejection of EDCs (up to 99.7%) than that of polyamide membranes (up to 81.8%). Quartz crystal microbalance results revealed that the sorption amount of a model EDC, benzylparbaen, by TA–Fe3 layer was nearly 2 orders of magnitude less than that by polyamide, leading to reduced transmission and higher rejection. Further analysis of membrane revealed a much greater water/EDC selectivity of the TA–Fe3 membrane compared to the polyamide membranes.