Novel thin-film composite membrane with polydopamine-modified polyethylene support and tannic acid-Fe3+ interlayer for forward osmosis applications

Polyethylene (PE) has recently gained attention as an advantageous support material in forward osmosis (FO) owing to its low structural parameters. A novel thin-film composite (TFC) membrane for FO was fabricated by introducing a tannic acid (TA)-Fe 3+ interlayer on a polydopamine (PDA)-modified PE support via interfacial polymerization. The TA-Fe 3+ interlayer influenced the diffusion of m -phenylenediamine, causing a unique worm-like morphology of the polyamide (PA) layer, distinct from the traditional “ridge and valley” morphology. Worm-like structures provided more permeation sites and improved the water flux (71.2 L⋅m −2 ⋅h −1 ). Furthermore, the TA-Fe 3+ interlayer prevented some salt molecules from passing through and resulted in a low specific salt flux (0.03 g⋅L −1 ). The TA-Fe 3+ interlayer was the key to overcoming the trade-off between permeability and selectivity. It functioned as a bridge connecting the PA layer and the PDA-modified PE support through chemical bonding, and the adhesion strength between PA layer and PDA-modified PE support was enhanced. This resulted in the excellent stability of the obtained TFC membrane. This study presents a new method for the design of a TFC membrane with excellent perm-selectivity and manipulatable morphologies of the PA layer for FO applications.