Multifunctional poly(lactic acid) membrane assisted by coal-based carbon dots for efficient separation of oil-in-water emulsions and dyes

Superhydrophilic separation membranes have broad application prospects in oil-water separation and wastewater purification. However, the accumulation of pollutants on the membrane surface and the secondary environmental pollution caused by waste membranes remain inevitable challenges. In this study, a superhydrophilic self-cleaning multifunctional membrane was fabricated by hydrolytic co-deposition of carbon dots, tetrabutyl titanate (TBT), and tannic acid on the surface of a degradable poly(lactic acid) (PLA) membrane for efficient separation of dye/oil/water emulsions. The results indicate that the superhydrophilic crosslinking network is formed on the surface of PLA-based membranes through co-deposition of TA-based coating, enabling the multifunctional membrane to possess a stable and ultra-strong oleophobic hydrophilic layer. As a result, the membrane exhibits strong underwater oil resistance and excellent performance in the separation of oil-in-water emulsions (rejection rate > 99%). More importantly, the surface of the superhydrophilic crosslinking network is negatively charged, which facilitates the selective removal of positively charged organic soluble substances in water through electrostatic adsorption. For instance, the removal rate of cationic dye MB and amphoteric dye RhB can reach as high as 99.93%. Additionally, with the catalysis of TiO₂, the organic pollutants on the membrane surface can be decomposed under UV irradiation, indicating the ideal self-cleaning property of the multifunctional membrane. This novel strategy for constructing a multifunctional surface deposition layer is expected to provide broader prospects for the application of superhydrophilic membranes in oil-water separation and wastewater purification.