Fabrication of a novel nanofiltration membrane using an Mg-Fe layered double hydroxide for dye/salt separation

Mg-Fe layered hydroxide (LDH) was synthesized by the double titration method and added to trimesoyl chloride (TMC) to prepare an Mg-Fe LDH-modified polyamide nanofiltration (NF) membrane by interfacial polymerization (IP). Compared to the pure polyamide NF membrane, the Mg-Fe LDH-modified membrane presented a wrinkled structure and a comparatively smooth surface. Additionally, the permeation flux and rejection rate of the modified NF membrane for 1000 mg L^-1 Na₂SO₄ solution were 61.7 L m^-2 h^-1 and 95.9%, respectively. When the Mg-Fe LDH modified NF membrane was used to separate dye/NaCl mixed solutions, the rejection of NaCl was less than 17% and the rejection rate of Coomassie Brilliant Blue (CBB) molecules was close to 100%. At the same time, the concentration of CBB increased from 500 mg L^-1 to 1151 mg L^-1 which means that the LDH modified NF membrane could separate CBB/NaCl effectively and could concentrate CBB at the same time.