Covalent Functionalized Boron Nitride Nanosheets as Efficient Lubricant Oil Additives

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.