Zwitterionic carbon quantum dots incorporated ultrafiltration membrane for efficient removal of copper ion

Abstract

Copper, prized for its excellent thermal and electrical conductivity, poses risks when present in wastewater. Treating copper ion-containing wastewater is vital for human and environmental safety. Membrane separation technology offers an eco-friendly and energy-efficient solution. In this study, a mixture of cellulose acetate (CA) and thermoplastic polyurethane (TPU) was used to fabricate the tubular membrane, with quantum dots (QDs) added. Three types of QDs were introduced into the tubular membrane: carbon quantum dots (CQDs), tertiary amine CQDs (TQDs), and zwitterionic CQDs (ZQDs). At pH = 10, copper ions were chelated with sodium dimethyldithiocarbamate (SDDC) at a ratio of SDDC/Cu2+=10 (w/w), signifying a molar concentration (mol.L-1) ratio of SDDC:Cu2+=3:16. This process achieved a 99.8% removal rate of copper ion. The ZQDs-M exhibited high pure water flux of 6,227.4 L.m−2.h−1.bar−1 and 95.4% copper ion-complex rejection rate. The ZQDs-M also demonstrated excellent anti-adhesion properties, with only 4.55% relative fluorescence intensity of E. coli and 34.58% BSA adsorption. The BSA dynamic anti-fouling property of the ZQDs-M was also superior to that of tubular membrane without QDs addition.