Micropore engineering of polyamide loose nanofiltration membrane for efficient dye/salt separation

Loose nanofiltration membranes (LNF) with efficient sieving and excellent permeance are desirable for dye/salt separation, and engineering the micropore of the LNF membranes is a promising approach to maximize membrane performance. Herein, we present a highly permeable and sieving polyamide LNF membrane with high porosity and suitable pore size that is prepared by interfacial polymerization using twisted aqueous phase monomer and subsequent alkali-treatment. The large-size, rigid and twisted structure of the adamantane-1,3-diamine effectively inhibits the dense-packing of polymer chain segments, resulting in a polyamide membrane with enhanced porosity and enlarged pore size. The alkali treatment hydrolyzes the partial amide linkage to further enlarge the membrane pore size, increasing the flux while maintaining high dye rejection. The optimum membrane exhibits a high salt/dye selective factor of 735 for Na2SO4/ Evans blue and an excellent water permeance of 87.72 L m-2 h-1 bar-1. This study is expected to provide a valuable guidance for the targeted design and fabrication of LNF membranes.