Manipulating the mussel-inspired co-deposition of tannic acid and amine for fabrication of nanofiltration membranes with an enhanced separation performance.

Nanofiltration (NF) membranes with tannic acid (TA) based selective layers have been intensively studied in recent years, but they still suffer from poor inorganic salt rejection. This study provided a first report on mussel-inspired co-deposition of TA and amine to obtain high-performance NF membranes. The inorganic salt separation performance of the as-prepared NF membrane was significantly improved by optimising the amine molecular weight. The membranes prepared by TA and various amines were characterised by X-ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier transform infrared (ATR-FTIR), scanning electron microscopy (SEM), zeta potential, and water contact angle measurement. It was found that amines with low molecular weight, such as ethylenediamine (EDA) and diethylenetriamine (DETA) facilitated the co-deposition onto the membrane surface, while polyethylene polyamine (PEPA) and branched polyethylenimine 600 (PEI600) enhanced the precipitation in solution. The TA/DETA co-deposited membrane showed an MgCl2 rejection of 83.5% and a pure water permeance of 4.5 L m-2 h-1 bar-1. The rejection was higher than the reported TA based NF membranes in the literature. In addition to demonstrating a TA based NF membrane with the improved inorganic salt rejection, this study provided new insights into the mussel-inspired co-deposition for material surface engineering towards various applications.