Polyamide membranes with a ZIF-8@Tannic acid core-shell nanoparticles interlayer to enhance nanofiltration performance

Polyamide nanofiltration membranes with an interlayer of either a plant polyphenol tannic acid (TA) coating to improve polyamide formation or zeolitic imidazolate framework-8 (ZIF-8) nanoparticles (NPs) as a sacrificial template have been recently attracting great interest, although none has reported such a dual-functional interlayer. In this study, we demonstrated a facile and controllable one-pot synthesis of novel ZIF-8@TA core-shell NPs. Mixing Zn2+, Hmim, and TA in an aqueous solution could readily give rise to these NPs. Microscopy characterizations showed that composition and morphology of NPs could be easily controlled by the amount of TA used. Comparing with the thin film nanocomposite (TFN) membrane prepared with ZIF-8 NPs as an interlayer, which had significant defects in its polyamide layer due to the aggregation of hydrophobic ZIF-8 NPs, the homogeneous and hydrophilic ZIF-8@TA NPs interlayered TFN membranes demonstrated intact polyamide layers. It was found that when 0.5 mg ZIF-8@TA1.0 NPs were used, the obtained TFN membrane showed a high water permeance of 20.7 L m- 2 h-1 bar-1 and Na2SO4 rejection of 96.6 %, typically outperforming other interlayer-based PA membranes reported elsewhere. This work provided not only a novel interlayer material but also deep insights into design of high-performance polyamide membranes.