A loose hybrid nanofiltration membrane fabricated via chelating-assisted in-situ growth of Co/Ni LDHs for dye wastewater treatment

A nano-filtration membrane with a loose LDHs/polymer hybrid layer which aimed at the desalination of textile wastewater was fabricated by chelating-assisted in-situ growth of layered double hydroxides (LDHs) on the organic substrate. The positively charged polyethyleneimine (PEI) with excellent chelating ability to metal ions was initially deposited on the hydrolyzed polyacrylonitrile (PAN) membrane surface by electrostatic interaction. Then, Co²⁺ ions were immobilized on the modified membrane though chelating reaction to form a Co²⁺/PEI complex layer, which provided a Co²⁺ source for the in-situ growth of Co/Ni LDHs at a lower temperature. Besides, the LDHs/PEI hybrid membrane prepared at optimized condition achieved a sufficient permeability (198.6 L/(m²·h·MPa)), high rejection for dyes (methyl blue 97.9% and acid fuchsin 97.5%) and low salt rejection (less than 3%). Meanwhile, this membrane possessed good hydrophilicity, satisfactory antifouling performance (flux recovery ratio was 89.5% for humic acid (HA)) and remarkable long-term stability. The loose LDHs/polymer hybrid layer was conducive to the transport of ions and water molecules, since the ridge-and-valley surface structure enhanced the steric hindrance effect and consequently increased the rejection of macromolecules. Therefore, this surface modification strategy can be applied to construct a ridge-and-valley porous structure on substrate for desalination of textile wastewater.