Tannic Acid/Fe³⁺ Nanoscaffold for Interfacial Polymerization: Toward Enhanced Nanofiltration Performance

Conventional thin-film composite (TFC) membranes suffer from the trade-off relationship between permeability and selectivity, known as the “upper bound”. In this work, we report a high performance thin-film composite membrane prepared on a tannic acid (TA)-Fe nanoscaffold (TFC n ) to overcome such upper bound. Specifically, a TA-Fe nanoscaffold was first coated onto a polysulfone substrate, followed by performing an interfacial polymerization reaction between trimesoyl chloride (TMC) and piperazine (PIP). The TA-Fe nanoscaffold enhanced the uptake of amine monomers and provided a platform for their controlled release. The smaller surface pore size of the TA-Fe coated substrate further eliminated the intrusion of polyamide into the substrate pores. The resulting membrane TFC n showed a water permeability of 19.6 ± 0.5 L m 2– h –1 bar –1, which was an order of magnitude higher than that of control TFC membrane (2.2 ± 0.3 L m –2 h –1 bar –1 ). The formation of a more order polyamide rejection layer also significantly enhanced salt rejection (e.g., NaCl, MgCl 2, Na 2 SO 4, and MgSO 4 ) and divalent to monovalent ion selectivity (e.g., NaCl/MgSO 4 ). Compared to conventional TFC nanofiltration membranes, the novel TFC n membrane successfully overcame the longstanding permeability and selectivity trade-off. The current work paves a new avenue for fabricating high performance TFC membranes.