Novel in-situ zwitterionization of carbon quantum dots on membrane surface for oil/water separation

Industrial growth led to an increase in the release of hazardous oily wastewater that seriously threatens human health and the ecosystem. Developing polymeric membranes for treating such wastewater has garnered significant attention, yet their fouling resistance remains a challenge. In this study, an anti-fouling zwitterionic cellulose acetate (CA) membrane, called ZQDs-g-CA, was fabricated by grafting carbon quantum dots (CQDs) on the surface of the CA membrane, followed by zwitterionization of CQDs (Zwitterionic carbon quantum dots, ZQDs). The grafting of ZQDs increased the hydrophilicity and oleophobicity of the membrane due to the hydrophilic functional groups present in the nanomaterial. The surface roughness was increased, allowing a greater surface area for contact between water molecules and the membrane. The modified CA membrane demonstrated excellent water flux (602.2 ± 30.2 L m−1 h−1 bar−1 (LMHB)) and oil/water emulsion separation performance, with a permeation flux of 426.1 ± 9.6 LMHB and oil rejection of 99.4 %. Additionally, the anti-fouling tests demonstrated remarkable performance with more than 96 % flux recovery ratio (FRR), 30.35 % reversible fouling ratio (Rr), and 3.05 % irreversible fouling ratio (Rir). The results showed that the in-situ ZQDs on the CA membrane exceeded the 96 % rejection rate for different oil/water emulsions. ZQDs were successfully applied on the CA membrane, which would provide a reference for the application of ZQDs-g-CA in oil/water separation.