Dispersion of reduced nanodiamond and its application in lubrication

Nanodiamonds (ND) possess remarkable properties derived from both bulk diamonds and nanoparticles. However, their full potential has been impeded by spontaneous particle agglomeration caused by high surface energy. To address this, we have developed a facile, cost-effective, and contaminant-free method to homogenize the ND surface by incorporating sodium borohydride (NaBH4) reduction in a mechanochemical process. Throughout this study, we extensively investigated various influencing factors, such as grinding time, reducing agent ratio, and surface charge, to successfully modify the ND surface. The results demonstrated that the introduction of hydroxyl functional groups significantly improved dispersibility and enabled the re-dispersion of modified ND into the water and other common solvents, achieving particle sizes below 200 nm. Notably, our reduced ND exhibited potential as an additive in lubricating oil, contributing to energy saving and emission reduction. For instance, when 0.02% reduced ND was supplemented into PAO6 lubricant oil, it cannot only reduce the oil consumption by 7.72% but also significantly lower CO, HC, and NOX emissions by 20.2% and 12.7%, respectively. This suggests that the proposed strategy for ND surface chemical modification can enhance colloidal stability and find practical applications in the lubricating oil industry.