Effect of electric field intensity on the performance of poly(piperazine amide) nanofiltration membranes

Abstract

Nanofiltration membrane has high flux and rejection to inorganic salts at relative low operation pressure, which is widely used in desalination and wastewater treatment. Negatively charged nanofiltration membrane prepared with interfacial polymerization method has high rejection to anion with high valence because of Donnan effect. In this work, negatively charged poly(piperazine amide) nanofiltration membranes with different rejections were used in separation of salt solution and low voltage direct current (LVDC) electric field was involved to increase the surface electric charge density to improve the membrane rejections to inorganic salts. When the forward electric field intensity was increased from 0 to 16 V/cm, the membrane rejections were all increased. The rejection to Na2SO4 of membrane (NO2) increased from 68 to 93%, while the membrane flux did not change obviously. At the same time, when the forward electric intensity is elevated, the membranes with low rejections show obvious elevation of permselectivity while the membranes with high rejections have limited elevation of performance. When reversed electric field was applied, the rejection to Na2SO4 of membrane (NO5) was decreased from 68 to 36%, while the flux changed little. It was demonstrated that the applied LVDC electric field can affect the surface charge density and change the permselectivity of negatively charged nanofiltration membranes, which is meaningful in desalination.