A novel electrical double-layer ion transport carbon-based membrane with 3D porous structure: High permselectivity for dilute zinc ion separation

Abstract

A novel electrical double-layer (EDL) ion transporting carbon-based membrane system was proposed for the selective separation of dilute zinc ion (Zn2+). The three-dimensional (3D) porous carbon-based membrane was fabricated by facile pressure filtering the core-shell graphite-nitride (g-C3N4)@multi-walled carbon nanotubes (MWCNTs) dispersed solution through a polytetrafluoroethylene (PTFE) membrane. In order to realize the continuous separation of Zn2+, a smart electrochemically switched ion permselective (ESIP) system was designed and made by modulating positive and negative charge density on EDL of g-C3N4@MWCNTs membrane coupling with an external electric field. In particular, the fast charge-discharge process of EDL in these materials could result in the high-rate and high-throughput of Zn2+ enrichment and depletion. The effects of cell voltage, pulse width and initial concentration on the flux of Zn2+ and the membrane permselectivity were investigated. It is discovered that the system had a high-flux (about 10 g m−2 h−1) with a high current efficiency (38%) for the continuous separation of Zn2+ with good stability under optimal operating parameters owing to the capillary tunnel effect of the g-C3N4@MWCNTs composite membrane. Such an EDL carbon-based membrane with the 3D porous structure should be a promising material for the separation of Zn2+ in a practical wastewater treatment.