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Hexagonal boron nitride nanosheets (h‐BNNSs) are obtained by a chemical exfoliation method from bulk h‐BN powders. The surface of h‐BNNSs is functionalized with 3‐aminopropyltriethoxysilane (APTS). Further, the amino functional groups on the surface of APTS‐modified h‐BNNSs (APTS‐BNNSs) are reacted with 4‐carboxyphenylboronic acid (CPBA) to obtain the covalently linked CPBA‐BNNSs. The morphology and structure of h‐BNNSs, APTS‐BNNSs, and CPBA‐BNNSs are comprehensively discussed. Of all the above four additives, the CPBA‐BNNSs can most outstandingly improve friction‐reducing and antiwear capacities of 150N base oil. The CPBA‐BNNSs possess excellent dispersion stability in base oil due to the phenylboronic acid groups on the surface of h‐BNNSs. Only 0.075 wt% CPBA‐BNNSs is added into the base oil, the coefficient of friction is decreased by 32.3%, and the wear scar diameter and mean wear volume of the rubbing surface are reduced by 42.9% and 88.4%. The analysis of the worn scar surface demonstrates that CPBA‐BNNSs can form a protective tribofilm containing boron and nitrogen elements on the rubbing surfaces, thereby decreasing the friction and protecting the surfaces from wear. Thus, the CPBA‐BNNSs may be recommended as a potential lubricant additive in practical applications.

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