Graphene, a lamellar structured material, easily shears at the contact interfaces and exhibits excellent mechanical strength and conductivity, which promises its potential for tribological applications. However, the dispersion of graphene in lube media is a big challenge. Herein, we developed a chemical approach for selective inclusion of long alkyl chains on the edges and defects sites of reduced graphene oxide sheets through the amide linkage, which facilitates their stable dispersion in the lube oil. Chemical and structural features of site-selective chemically functionalized reduced graphene oxide are monitored by FTIR, XPS, XRD, TG-DTA, FESEM, and HRTEM. Tribological test results showed that the chemically functionalized reduced graphene oxide, as an additive to 10W-40 engine oil, significantly reduced both the friction and the wear of steel balls. The stable dispersion of chemically functionalized reduced graphene oxide provides low resistance in a sheared contact owing to weak van der Waals interaction between their lamellas, thus significantly reducing both the friction and the wear.

Graphene oxide was found to be a highly efficient, reusable and cost-effective organocatalyst for the aza-Michael addition of amines to activated alkenes to furnish corresponding β-amino compounds in excellent yields.

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We report on the preparation of alkylated graphenes on a large scale followed by their dispersion in organic solvents. The alkylated graphenes with variable alkyl chain lengths (C n ¼ 8, 12, 18) are prepared by coupling of alkylamine with carboxylic groups of graphene oxide (GrO). The FTIR, UV-Visible, and TGA results reveal that, during alkylation, the oxygen functionalities of GrO are reduced significantly and the average size of the sp 2 carbon domain increased, which is further supported by Raman characteristics. It is observed that the dispersibility of alkylated graphene in hydrocarbon solvents increases on increasing the chain length of (a) hydrocarbon solvents used for the dispersion and (b) alkyl groups attached to the graphene. The van der Waals interaction between methylene units associated with alkylated graphenes and hydrocarbon solvents plays a crucial role in determining their dispersion characteristics, and such an interaction increases with increasing methylene units. Octadecylamine functionalized graphene (ODA-Gr) dispersion in hexadecane is found to have longterm dispersion stability due to its high degree of cohesive interaction. The lubrication characteristics of hexadecane containing ODA-Gr were probed by evaluating its friction and wear properties. The results reveal that hexadecane doped with an optimized dose of 0.06 mg mL À1 ODA-Gr reduced friction and wear by 26% and 9%, respectively, compared to hexadecane. The lubricity enhancement could be attributed to uninterrupted supplies of graphene nanosheets under the rubbing surfaces, where these nanosheets prevent direct contact between the rubbing surfaces, providing low resistance to shear.

Hexagonal boron nitride (h-BN), an isoelectric analogous to graphene multilayer, can easily shear at the contact interfaces and exhibits excellent mechanical strength, higher thermal stability, and resistance toward oxidation, which makes it a promising material for potential lubricant applications. However, the poor dispersibility of h-BN in lube base oil has been a major obstacle. Herein, h-BN powder was exfoliated into h-BN nanoplatelets (h-BNNPs), and then long alkyl chains were chemically grafted, targeting the basal plane defect and edge sites of h-BNNPs. The chemical and structural features of octadecyltriethoxysilane-functionalized h-BNNPs (h-BNNPs-ODTES) were studied by FTIR, XPS, XRD, HRTEM, and TGA analyses. The h-BNNPs-ODTES exhibit long-term dispersion stability in synthetic polyol ester lube base oil because of van der Waals interaction between the octadecyl chains of h-BNNPs-ODTES and alkyl functionalities of polyol ester. Micro- and macrotribology results showed that h-BNNPs-ODTES, as an additive to synthetic polyol ester, significantly reduced both the friction and wear of steel disks. Elemental mapping of the worn area explicitly demonstrates the transfer of h-BNNPs-ODTES on the contact interfaces. Furthermore, insight into the lubrication mechanism for reduction in both friction and wear is deduced based on the experimental results.