Advanced synthesis of hBN/TiO ₂ nanocomposites for water-based lubricants: tribological performance and mechanism

Abstract In this study, hexagonal boron nitride/titanium dioxide (hBN/TiO 2 ) nanocomposites were synthesised using a novel, facile, and eco-friendly method. The preparation method consisted of oxygen plasma treatment and sonochemical processes. The as-synthesised nanocomposites are thoroughly characterised via XRD, XPS, and TEM-EDS. Oxygen functional groups are introduced on the surfaces and edges of hBN by B-O interactions and are targeted for further chemical grafting with TiO 2 via B-O-Ti interactions. The addition of hBN/TiO 2 nanocomposites to water-based lubricants presented an influence on 1D 1 H NMR resonance, suggesting a shift in the chemical environment, especially in SDBS proton signals. The overall mechanism of all the additives in water regulated the formation of an interconnected network through hydrogen bonding, hydrophobic, and π – π interactions, which resulted in stable dispersion of hBN/TiO 2 for up to 8 days after preparation. Tribological test results revealed that an optimal sonochemical duration of 15 min for hBN/TiO 2 nanocomposite synthesis improved the lubrication performance of water-based lubricants, as it significantly reduced the average COF and wear rate by 73.7% and 84.09%, respectively, compared with those of pure water. Worn track analysis demonstrated that the hBN/TiO 2 nanocomposites have a superior ability to adhere to and form a thick, continuous, and synergistic lubricating tribofilm at the steel-steel interfaces.