One-step green synthesis of oil-dispersible carbonized polymer dots as eco-friendly lubricant additives with superior dispersibility, lubricity, and durability.

Chemical functionalization provides effective protocols for inorganic nanomaterials as oil-dispersible lubricant additives. Nevertheless, harsh reaction conditions and arduous post-processing are frequently encountered when adopting this approach. Herein, four types of carbonized polymer dots (CPDs) with admirable dispersibility and long-term stability (more than 6 months without any sediments) in polyethylene glycol (PEG200) were synthesized by a one-step and green solvothermal route using saccharides as the single precursors. The tribological behaviors of CPDs as the lubricant additives of PEG200 were systematically evaluated and compared, confirming that the anti-wear and friction-reducing performances of PEG200 can be effectively enhanced after blended with CPDs. Clarified by the friction evaluations and worn surface detections, the superior lubricity and durability of CPDs-c are mainly attributed to the synergy between the interfacial adsorption of polymeric shells, the nano-lubrication effects of carbon cores, and the establishment of CPDs-inserted tribofilm with a uniform thickness of about 86 nm. This work explores a green and facile strategy for synthesizing the CPDs toward oil lubrication and reveals the lubrication mechanism of CPDs, which facilitates the practical application of CPDs in tribology.

Integration of Functionalized Polyelectrolytes onto Carbon Dots for Synergistically Improving the Tribological Properties of Polyethylene Glycol.

In this work, we carefully designed and synthesized a series of novel polyelectrolyte-functionalized carbon dots (CDs-PEI-X) by a facile and reversible phase transfer method based on the protonation reaction and anion exchange process executed on the surface of polyethylenimine-grafted CDs (CDs-PEI), where X denotes the anionic moieties of polyelectrolyte shells including hexafluorophosphate (PF6-), bis(trifluoromethane)sulfonimide (NTf2-), oleate (OL-), and bis(salicylato)borate (BScB-), respectively. Attributed to the favorable compatibility of these anions and polyethylene glycol (PEG) molecules, the hydrophobic CDs-PEI-X displayed excellent dispersibility and long-term stability in PEG200 base oil. Subsequently, the tribological behaviors of CDs-PEI-X as the lubricant additives of PEG200 were systematically investigated. It was proved that the anionic moieties of the polyelectrolyte shells of CDs-PEI-X played a crucial role in regulating their tribological behaviors. Particularly, CDs-PEI-OL was confirmed as an optimal additive, exhibiting the best lubricity, outstanding load-bearing capacity, long service life, and remarkable operational stability under boundary lubrication regime. Based on the tribological evaluations and worn surface analyses, the lubrication mechanism of CDs-PEI-OL was mainly attributed to the formation of the organic-inorganic hybrid adsorption film, the protective tribofilm, and its nanolubrication functions as scrollable "ball-bearing", i.e., the synergistic lubrication effects of surface polyelectrolyte shells and carbon cores. This study provides a feasible and versatile strategy to rapidly and effectively tailor the surface chemistry of CDs and discloses the essential contribution of carbon cores and surface groups on the lubrication process, which facilitates the development of advanced CDs-based nanolubricant additives.

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.

Ultrahigh yield synthesis of mesoporous carbon nanoparticles as a superior lubricant additive for polyethylene glycol.

Mesoporous carbon nanoparticles (MCNPs), with a particle size of 15-40 nm and pore size of 3-5 nm, were conveniently synthesized in ultrahigh yield (91.7 ± 1.5 wt%) by one-step carbonization of polyoxyethylene sorbitan trioleate (Tween 85) in H2SO4/H3PO4 mixed solution at a mild temperature (150 °C). The MCNPs showed particularly high dispersion stability in polyethylene glycol (PEG200) because their surfaces were abundant in long alkyl chains and ester groups. Considering that PEG200 is a kind of commonly used synthetic oil, the tribological properties of the MCNPs as a lubricant additive for PEG200 were evaluated in steel/steel contact and ball-on-plate reciprocating modes. The MCNPs exhibited the best friction-reducing and antiwear abilities when their concentration was 0.7 wt%, that is, adding 0.7 wt% MCNPs caused the friction coefficient and wear volume of PEG200 to reduce by 49.2% and 71.3%, 49.1% and 67.2%, 48.0% and 48.0%, 47.9% and 23.6%, and 44.4% and 8.1% at loads of 50, 100, 150, 200 and 250 N, respectively. The above results demonstrated that the antiwear function of MCNPs obviously reduced with increasing load despite their friction-reducing function only decaying slightly. Moreover, the performance of MCNPs was barely attenuated when the friction duration prolonged from 20 to 200 min, suggesting their long service life. Wear surface analysis implied that the MCNPs as an additive not only formed physical absorption films on the rubbing surfaces, but also showed rolling, polishing and mending effects under an appropriate load, directly accounting for their outstanding lubrication functions.

Nanocellulose as a sustainable biomass material: structure, properties, present status and future prospects in biomedical applications.

Nanocellulose, extracted from the most abundant biomass material cellulose, has proved to be an environmentally friendly material with excellent mechanical performance owing to its unique nano-scaled structure, and has been used in a variety of applications as engineering and functional materials. The great biocompatibility and biodegradability, in particular, render nanocellulose promising in biomedical applications. In this review, the structure, treatment technology and properties of three different nanocellulose categories, i.e., nanofibrillated cellulose (NFC), nanocrystalline cellulose (NCC) and bacterial nanocellulose (BNC), are introduced and compared. The cytotoxicity, biocompatibility and frontier applications in biomedicine of the three nanocellulose categories were the focus and are detailed in each section. Future prospects concerning the cytotoxicity, applications and industrial production of nanocellulose are also discussed in the last section.