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

Abstract

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.

Emerging Materials to Prepare Mixed Matrix Membranes for Pollutant Removal in Water

“…However, some filler materials tend to agglomerate (e.g., due to inherent hydrophobicity), and empirical evidence suggests that agglomeration is usually more pronounced under high filler or additive concentrations [ 23 , 24 ]. Hence, methods such as oxidation or modification of filler properties (to increase compatibility with the polymer matrix), ultrasonication as well as the addition of surfactants are typically employed to physically disperse the filler materials in the liquid phase prior to the membrane fabrication process [ 25 , 26 , 27 ].…”

Advances in Integrating Carbon Dots With Membranes and Their Applications

“…Studies have found that the zwitterionic hyperbranched polyethyleneimine (ZPEI) is integrated into the polyamide layer of the membrane to form a tightly packed network, which can effectively remove salt. As shown in Figure 4, Zheng et al [35] . synthesized CDs doped with ZPEI (CDs‐ZPEI) via hydrothermal citric acid and ZPEI at 200 °C, and then introduced the prepared composite nanoparticles into the thin film composite (TFC) membranes (CDs‐ZPEI@membranes).…”

High‐Precision and High‐Flux Separation by Rationally Designing the Nanochannels and Surface Nanostructure of Polyamide Nanofiltration Membranes

“…A number of TFN membranes with high flux, retained or improved selectivity, and enhanced antifouling and antichlorination capability have been developed by incorporating CDs with different functional groups. [35][36][37] Nonetheless, none of the research works aimed at tailoring the pore sizes and surface nanostructure of polyamide layers using CDs to achieve desired sieving capacity for targeted solutes and higher water flux. Meanwhile, the mechanisms of the altered membrane properties and hence the enhanced filtration performance by the incorporation of CDs require comprehensive investigations.…”