Nitrogen-Doped Carbon Dot as a Lubricant Additive in Polar and Non-polar Oils for Superior Tribological Properties via Condensation Reaction

Abstract

Nitrogen-doped lubricating additives have been proved to be an effective strategy to improve the tribological properties of lubricating oil. However, the traditional preparation methods of nitrogen-doped lubricating additives have the defects including harsh preparation conditions and a time-consuming preparation process. Herein, we report a preparation method of nitrogen-doped carbon dot (NCD) lubricating additives in a short time by one-step aldehyde condensation reaction at room temperature. The small size effect and nitrogen-containing functional groups of NCD lubricating additives provide favorable conditions for their dispersion and low friction in base oil. The tribological properties of NCD lubricating additives in sunflower oil (SFO) and PAO10 were systematically evaluated. The results show that NCD lubricating additives could reduce the average friction coefficient of SFO from 0.15 to 0.06 and PAO10 oil from 0.12 to 0.06, and the wear width is also decreased by 50–60%. In particular, the friction curve is very stable, and the friction coefficient was maintained at about 0.06 even under the working time of 5 h. By analyzing the morphology and chemical properties of the worn surface, the lubrication effect of NCDs is attributed to its small size effect and adsorption, which was easy to enter the friction gap to fill and repair. Furthermore, the doping of nitrogen induces the occurrence of friction chemical reactions, forming a friction film of nitrides and metal oxides at the friction interface, which effectively reduces the friction and wear of the surface. These findings provide a possibility for the convenient and effective preparation of NCD lubricating additives.

Fabrication of Zwitterionic Polymer-Functionalized Onion-like Carbon Nanoparticles as Aqueous Lubricant Additives

“…During the friction process, Fe 2+ and Fe 3+ positive ions are generated on the friction contact surface as a result of the friction heat-induced charge mission so that the PEIS@OLC nanoparticles with the opposite of the negative charge are easily adsorbed on the friction pairs through electrostatic action . As the continuous progress of adsorption and deposition, tribochemical reaction takes place under the friction heat and heat force, while PEIS@OLC randomly fills into the damaged surface to cause the repairing effect, leading to the formation of a continuous and uniform tribo-film, in which N and S atoms contained in PEIS are able to enhance the antifriction effect . In addition, benefitted by the zwitterionic polymer PEIS, a dense and stable hydration layer is encapsulated on the surface of the OLC spheres, which cooperates with the onion-like structure to bear load .…”

Tribological and Rheological Study of Thixotropic Gels of 2D Nanoparticles

“…Moreover, the smaller the particle, the more likely it is to interact with the friction pair and reduce the coefficient of friction (CoF) and wear. , Nano lubricants’ tribological behavior is also affected by their viscosity, which rises as the concentration of nanoparticles rises . Various kinds of nanoparticles that have been used as additives in base lubricant can be categorized as metals, , metallic oxides, , nonmetallic oxides, , sulfides, , fullerene, , and other carbon materials. − More specifically, 2D layered-structured materials have attracted attention as lubrication nanoadditives because of their excellent tribological characteristics. The typical examples of such 2D materials are graphene, hexagonal boron nitride, black phosphorus, natural hydrate clay minerals (i.e., layered vermiculite), silicene, and MXenes. , For lubricity in industrial applications, e.g., drilling fluids, suspensions containing organic and inorganic nanoparticles ranging in diameter from 1 to 100 nm in the base fluids, such as water, oil, paraffin, glycerol, etc., are usually investigated. , The incorporation of these particles into the base fluid alters its rheology and lubricity .…”

Carbon Dot-Based Nanofluids as Additives for Mechanical Lubrication

“…The application of CDs as additives of nonpolar oil such as polyalphaolefin (PAO) was more difficult than their application in PEG as the CDs are usually derived from various precursors with polar oxygen-containing groups. To obtain the hydrophobic CD-based additives, the nonpolar solvents were used as both reaction mediums and modifiers, which brought in big challenges for separation and purification of CD from reaction mediums. − In some cases, the dispersants were used to disperse the amphipathic CDs as the additives of PAO. , The double modification was even needed to realize the application of CDs in PAO . Therefore, exploring a simple, economical, and high-yield route for synthesizing the oil-soluble versatile CD-based additives is highly desirable and urgently needed.…”