Effect of surface grafting with quaternized carbon quantum dots on nanofiltration membrane removing contaminants from micro-polluted river water

It is highly encouraged to efficiently and stably remove heavy metals (HMs) and pharmaceutical active compounds (PhACs) from practical micro-polluted river water by one-stage process based on novel customized nanomaterials. For this purpose, the effect of grafting 0D quaternized carbon quantum dots (QCDs) on the resultant nanofiltration membrane microstructure, macroscopic removal performance and associated environmental risk reduction features was explored detailly, compared with the unmodified, doping-modified and other reported counterparts. The results showed that membrane skin characteristics including wettability, smoothness and positive charge could be better optimized through surface grafting (with water contact angle, root mean square roughness and isoelectric point of 39.4o, 7.39 ± 0.52 nm and 8.6, respectively) than embedding modification (46.5o, 9.10 ± 0.48 nm and 8.1) by the tailored 0D QCDs. Consequently, the optimal QCDs-grafted nanofiltration membrane exhibited excellent antiadhesion (Rir = 1.39%), satisfactory rejection (all above 98.5% for target HMs and PhACs) and relatively higher water permeability (20.8 L·m−2·h−1·bar−1) in a 40-hour test. Also, it was capable of reducing raw river water with medium/low pollution level to a non-polluting state. More interestingly, it was found that rejections for target micropollutants in practical water environment were always slightly higher than those in ideal water environment. In brief, this study convincingly demonstrated that nanocomposite membranes prepared by QCDs grafting rather than doping modification was more suitable for reliably and stably removing a range of specific small-sized contaminants in practical wastewater scenarios.