Crosslinked β‐<scp>CD</scp>/<scp>TMC</scp> Thin Film as Interlayer for Improving Water Flux in Forward Osmosis Membranes With Microfiltration Substrate

ABSTRACT This study presents a novel thin‐film composite (TFC) membrane with significantly improved performance synthesized by an interlayer composed of β‐cyclodextrin (β‐CD) and trimesoyl chloride (TMC) onto a polyethersulfone microfiltration (PES‐MF) substrate. The top surface of the PES‐MF is coated with a crosslinked thin film via a conventional interfacial reaction, where β‐CD and TMC monomers are dissolved in aqueous and organic phases, respectively. The successful synthesis of the crosslinked β‐CD/TMC film and the change in surface characteristics of the substrate are verified by various analysis methods. SEM images verify that a thin layer of β‐CD/TMC effectively coats the surface pores of the substrate. This coating alters the substrate's surface properties and serves as a new reaction interface, facilitating the formation of a defect‐free polyamide‐selective layer. Results show that the β‐CD/TMC interlayer promotes the formation of a thin and smooth polyamide layer, which is critical for improving membrane performance. The effect of β‐CD/TMC interlayer on the FO performance of the TFC membrane is studied using DI water feed and 1 M NaCl draw solutions. The interlayered TFC‐CD.2 membrane exhibits a water flux of 22.1 LMH, which is three times higher than that of the control membrane (7.8 LMH), and its selectivity is also improved. This method emphasizes the crucial role of the interlayer in forming a defect‐free polyamide selective layer on a microfiltration substrate.