Carbon dots-incorporated composite membrane towards enhanced organic solvent nanofiltration performance

Herein, a series of composite membranes hybridized by sub-5 nm carbon dots (CDs) in polymer active layer were fabricated for organic solvent nanofiltration. The CDs with tailored functional groups were facilely synthesized and embedded into polyethyleneimine (PEI) matrix, and then dip-coated on polyacrylonitrile support to prepare composite membranes through interfacial polymerization. The resultant membranes were characterized by scanning electron microscopy, atomic force microscopy, fourier transform infrared spectroscopy, contact angle, thermal gravity analysis and tensile testing. The nanofiltration performances of membranes were evaluated by solvent uptake behavior, solvent flux and solute rejection, confirming that hybridization of small-sized CDs could well exert the advantages of PEI and CDs: the completely cross-linked PEI networks assured excellent solvent resistance and solute rejection ability, whilst CDs worked as selective nano-accelerators for solvent transfer via their functional groups. Carbonation degree acutely governed the acceleration ability of CDs for different solvents. And for instance, lowly carbonated CDs could efficiently adsorb polar solvents by the hydrophilic groups, thus providing a 54.3% permeance increase for isopropanol to 42.6 L m(-2) h(-1). Meanwhile, this kind of CDs also suppressed the transport of non-polar solvents and thereby enhanced membrane selectivity. In contrast, obvious increase of non-polar solvent uptaking and permeation was achieved by high-carbonation-degree CDs via their hydrophobic domains.