An electrochemically-switched BPEI-CQD/PPy/PSS membrane for selective separation of dilute copper ions from wastewater

The continuous separation of dilute Cu 2+ from wastewater was performed by using a branched poly(ethylenimine) (BPEI)-functionalized carbon quantum dots (BPEI-CQD)/polypyrrole (PPy)/ polystyrenesulfonate (PSS) membrane in an electrochemically switched ion permselective (ESIP) process. The membrane with a high selectivity for Cu 2+ separation was prepared by pressure filtering BPEI-CQD/PPy/PSS solution through a polytetrafluoroethylene (PTFE) membrane. In this ESIP system, the directional uptake/release of Cu 2+ was realized by modulating the redox state of the membrane coupling with an external electric field. The effects of the operating parameters on the flux of Cu 2+ and membrane permselectivity were investigated. The BPEI-CQD/PPy/PSS composite electrode showed excellent permselectivity for Cu 2+ with a flux of 0.108   mg·cm −2 ·h −1 , a current efficiency of 39.9% and an excellent cycling stability. The Cu 2+ concentration in the solution was reduced from 30 to 0.82   ppm with a removal efficiency of 97.2%. Furthermore, the effects of BPEI-CQD content and the membrane thickness on the separation properties of the membrane from a mixed nitrate solution containing Cu 2+ , Ni 2+ and Cd 2+ were investigated. It is expected to understand the sorption-diffusion mechanism of such a membrane and provide more information on the design of it for a practical metal ion separation process.