We prepared a graphene/ionic liquid (G/IL) composite material by the hybridization of G and an IL for use as a lubricating oil additive. The friction coefficient and wear volume of a base oil containing 0.04 wt% of the G/IL composite was reduced by 45% and 90%, respectively. Furthermore, the base oil containing the G/IL composite exhibited better lubricating properties than the base oil containing G, IL, or a mixture of IL and G at the same mass fraction. A synergistic lubrication mechanism was also revealed. The G/IL composite was adsorbed and deposited on the wear surface, forming a more ordered protective film and a unique tribochemical reaction film during rubbing. Therefore, the G/IL composite exhibited the synergistic lubricating effects of G and IL, which significantly improved the lubricating performance of the base oil. This study also suggested a way to limit the out-of-plane puckering of G at the macroscale.

Graphene’s many excellent properties have cemented it as an essential research topic in materials science and beyond. It is widely used in photoelectric materials, sensors, battery electrode materials, composites, and so on. Graphene has attracted particular attention in the field of tribology. However, graphene agglomerates easily, limiting its performance when used directly. Therefore, considerable research has focused on methods of modifying the surface of graphene to improve its tribological performance, by improving the dispersion stability, friction reduction, wear resistance, or a combination of these. This paper focuses on the research progress of surface modification of graphene-based materials for tribological applications. According to the reaction principles, surface modification methods can be divided into covalent surface modification, noncovalent surface modification, and surface modification by nanoparticles doping. Herein, the typical reaction processes of these modification methods and the anti-wear mechanism of modified graphene-based materials are introduced, and current research on the surface modification of graphene used in tribology is discussed.

The large-scale preparation of stable graphene aqueous dispersion has been a challenge in the theoretical research and industrial applications of graphene. This study determined the suitable exfoliation agent for overcoming the van der Waals force between the layers of expanded graphite sheets using the liquid-phase exfoliation method on the basis of surface energy theory to prepare a single layer of graphene. To evenly and stably disperse graphene in pure water, the dispersants were selected based on Hansen solubility parameters, namely, hydrophilicity, heterocyclic structure and easy combinative features. The graphene exfoliation grade and the dispersion stability, number of layers and defect density in the dispersion were analysed under Tyndall phenomenon using volume sedimentation method, zeta potential analysis, scanning electron microscopy, Raman spectroscopy and atomic force microscopy characterization. Subsequently, the long-chain quaternary ammonium salt cationic surfactant octadecyltrimethylammonium chloride (0.3 wt.%) was electrolyzed in pure water to form ammonium ions, which promoted hydrogen bonding in the remaining oxygen-containing groups on the surface of the stripped graphene. Forming the electrostatic steric hindrance effect to achieve the stable dispersion of graphene in water can exfoliate a minimum of eight layers of graphene nanosheets; the average number of layers was less than 14. The 0.1 wt.% (sodium dodecylbenzene sulfonate: melamine = 1:1) mixed system forms π–π interaction and hydrogen bonding with graphene in pure water, which allow the stable dispersion of graphene for 22 days without sedimentation. The findings can be beneficial for the large-scale preparation of waterborne graphene in industrial applications.

Nanopesticides can facilitate controlled release kinetics and efficiently enhance the permeability of active ingredients to reduce the dosage and loss of pesticides. To clarify the synergistic mechanism of graphene–insecticide nanocarriers against cotton bollworm, treatment groups, namely, control, graphene (G), insecticide (lambda-cyhalothrin (Cyh) and cyfluthrin (Cyf)), and graphene-delivered insecticide groups were used to treat the third-instar larvae of cotton bollworm. The variations in phenotypes, namely, the body length, body weight, and mortality of the cotton bollworm, were analyzed. The results show that graphene enhances the insecticidal activity of lambda-cyhalothrin and cyfluthrin against cotton bollworm. The two graphene-delivered insecticides with optimal compositions (3:1) had the strongest inhibitory effects and the highest mortality rates, with the fatality rates for the 3/1 Cyh/G and Cyf/G mixture compositions being 62.91% and 38.89%, respectively. In addition, the 100 μg/mL Cyh/G mixture had the greatest inhibitory effect on cotton bollworm, and it decreased the body length by 1.40 mm, decreased the weight by 1.88 mg, and had a mortality rate of up to 61.85%. The 100 and 150 μg/mL Cyh/G mixtures achieved the same mortality rate as that of lambda-cyhalothrin, thus reducing the use of the insecticide by one-quarter. The graphene-delivered insecticides could effectively destroy the epicuticle spine cells of the cotton bollworm by increasing the permeability and, thus, the toxicity of the insecticides.