Nanofiltration (NF), as an emerging membrane technology, has gained increasing attention in water treatment and desalination, etc. NF membranes exhibit high rejection for molecules (MW&gt;300 Da) and multivalent ions, but the monovalent ion rejection rate is relatively low, generally in 10~60%. Besides, great challenges remain for conventional NF membranes to achieve high ion rejection without sacrificing water flux. Herein, novel carbon nanotube (CNT) and graphene oxide (GO) based NF membranes were fabricated, and electrochemical assistance as a new strategy was employed for improving the water flux and ion rejection performance. When the external voltage applied on an electro-conductive polyaniline/CNT NF membrane was increased from 0 to 2.5 V, the rejection rate for Na2SO4 increased from 81.6 to 93.0% and that for NaCl improved from 53.9 to 82.4%; meanwhile, the membrane retained high permeances of ~14.0 LMH bar-1. The analysis based on Donnan steric pore model suggested that the improved ion rejection was attributed to enhanced membrane surface charge under electrochemical assistance. Furthermore, by applying an electric field (3.0 V, 3.75 V/mm) across a GO/CNT asymmetric membrane, co-enhancement of water flux from 9.1 to 17.4 LMH bar-1 and NaCl rejection from 52.4 to 78.3% was exhibited. Numerical analysis revealed that the co-enhancement phenomenon was ascribed to the electrokinetic effect generated under external electric field. Our studies provide new insight into the development of advanced NF technologies for water treatment and desalination.

Electrochemically assisted nanocarbon-based nanofiltration membranes for improving water flux and ion rejection

ACS Fall 2021

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