Covalently Linked Hexagonal Boron Nitride-Graphene Oxide Nanocomposites as High-Performance Oil-Dispersible Lubricant Additives

The present study demonstrates an improved and facile method for the exfoliation and chemical oxidation of bulk hexagonal boron nitride (h-BN) powder. Further, chemical functionalization of oxidized h-BN with (3-aminopropyl) trimethoxysilane (APTMS) as a bifunctional chemical linker has been undertaken to prepare APTMS-grafted h-BN (h-BNAS). Amino-terminated functional groups on the basal plane defect and edge sites of h-BNAS were targeted for further chemical grafting with graphene oxide (GO) through covalent interaction to achieve an h-BN/GO nanocomposite (h-BNAS@GO). The chemical structure and morphology of h-BN, oxidized h-BN, h-BNAS, and h-BNAS@GO were investigated through standard spectroscopic and microscopic analyses. The macro- and microtribological results depicted that the h-BNAS@GO hybrid composite (0.5 wt %) as an oil-dispersible additive significantly reduced the coefficient of friction (COF) and wear of the steel-steel tribopair, revealing superior tribological properties. The COF of h-BNAS@GO nanocomposite exhibited a reduction of 50.7% (at Pm ≈ 1.95 GPa) than that of base paraffin oil and showed a lower specific wear rate (1 × 10–8 mm3/N-m) at macrotribological trials, revealing the best wear-resistance performance. At microtribological reciprocating sliding, the composite nanolubricant was observed to diminish the COF by ∼41.18% (at Pm ≈ 2.15 GPa) compared to base oil. The post-tribological analysis of the worn tribotracks demonstrates that the h-BNAS@GO nanocomposite has a superior ability to adhere and form a thicker, continuous, synergetic lubricating tribofilm at the interfaces, thereby effectively reducing COF and protecting the tribopairs from wear. Therefore, the h-BNAS@GO nanocomposite has a great prospect as a load-bearing lubricating advanced material in convenient industrial application.