Polyamide nanofiltration membrane with high separation performance prepared by EDC/NHS mediated interfacial polymerization

Composite nanofiltration membranes comprising polyamide active layer and polyacrylonitrile (PAN) support were prepared by 1-ethyl-(3-3-dimethylaminopropyl) carbodiimide hydrochloride (EDC)/N-hydroxysuccinimide (NHS) mediated interfacial polymerization. PAN support was first hydrolyzed to create carboxyl groups on surface, which were then activated by EDC/NHS to enhance reactivity with amine groups. Afterwards, activated PAN support was impregnated in aqueous phase containing piperazine (PIP). Finally, PIP impregnated PAN support was immersed in organic phase containing trimesoyl chloride (TMC), where the polyamide active layer was formed on the hydrolyzed PAN support. Fourier Transform Infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS) analysis verified the formation of amide bonds between PIP molecules and carboxyl groups on the hydrolyzed PAN support. Variation energy positron annihilation spectroscopy (VEPAS) measurement manifested that the active layer and interfacial zone of composite membrane became denser owing to EDC/NHS activation. The water flux slightly decreased but the rejection of Orange GII remarkably increased with an increase in EDC concentration. The composite membrane prepared at EDC concentration 100 mM and PIP concentration 0.20 wt% exhibited a flux of MgSO4 solution as high as 511 L/(m2 h MPa) while the rejection reached 98.5%. The structural stability of the composite membranes after EDC/NHS treatment was greatly enhanced as tested by alcohol treatment.