Incorporation of Core–Shell-Structured Zwitterionic Carbon Dots in Thin-Film Nanocomposite Membranes for Simultaneously Improved Perm-Selectivity and Antifouling Properties

The development of highly efficient thin-film nanocomposite (TFN) membranes with superior water permeability, maintained rejection performance, and excellent antifouling capacity is critical to meeting the ever-escalating demand for fresh water. Herein, carbon dots (CDs) grafted with hyperbranched zwitterions, denoted as CDs-ZPEI0.6–10k, were first prepared by the hydrothermal treatment of citric acid in the presence of zwitterionic hyperbranched polyethylenimine (ZPEI0.6–10k) with different molecular weights (0.6, 1.8, and 10 kDa). Subsequently, the synthesized nanoparticles were introduced in membrane fabrication to form CDs-ZPEI0.6–10k-embedded TFN (TFN-CDs-ZPEI0.6–10k) membranes. The grafted shells of superhydrophilic ZPEI not only increased the chemical compatibility of CDs in the polyamide layer to suppress the formation of nonselective voids but also created a densely packed network for efficient water transportation and effective divalent salt rejection. The TFN-CDs-ZPEI10k membrane demonstrated a 2.8-fold enhancement in the permeate flux with an increased Na2SO4 rejection rate of 98.1% and improved antifouling properties than the pristine thin-film composite (TFC) membrane. This work provides an insight into the development of functionalized core–shell structured nanoparticles to effectively overcome the permeability-selectivity trade-off limitations and fouling problems in TFC membranes.