Efficient removal of heavy metal ions by forward osmosis membrane with a polydopamine modified zeolitic imidazolate framework incorporated selective layer.

A novel thin film nanocomposite (TFN) forward osmosis (FO) membrane with a positively charged and nano-functional selective layer has been developed for effective heavy metal ions removal. The selective layer is constructed by penetrating the polydopamine modified zeolitic imidazolate framework (ZIF-8@PDA) in the poly(ethyleneimine)/1,3,5-benzenetricarboxylic acid chloride (PEI/TMC) crosslinked matrix. Compared with the pristine thin film composite (TFC) membrane, the thin film nanocomposite membrane (0.05 wt % nanofillers loading) exhibits a higher water flux (20.8 vs12.8 LMH) without losing of selectivity in terms of Js/Jw ratio (0.25 vs 0.20 g L-1) in FO mode. This improvement of the permeability is mainly attributed to the optimized selective layer with good wettability and loose structure. Besides, the modified PDA layer facilitates the affinity between the nanofillers and selective layer, which results in an ideal selectivity. In addition, this modified membrane shows a high heavy metal ion (Cu2+, and Ni2+ and Pb2+) rejection (>96%) in FO mode. Our finding offers a simple and efficient method to enhance the FO performance of membrane by designing the selective layer for treating heavy metal wastewater.