The strive to reduce harmful emissions from transport has resulted in an increased emphasis on minimising friction in lubricated contacting components to improve the energy efficiency of automotive engines. In this sense, it is of particular interest to investigate whether a synergistic tribological performance could be achieved by combining two or more friction modifier additives with nanoparticles. This study conducts a comprehensive investigation into the tribological characteristics of lubricant formulations enriched with nanodiamonds (NDs), combined with organic (Glycerol Monooleate, GMO) and inorganic (molybdenum dithiocarbamate, MoDTC) friction modifiers and a low-concentration anti-wear additive (Zinc dialkyl dithio-phosphate, ZDDP). The interaction between NDs and MoDTC has been evaluated using reciprocal sliding tests at two different temperatures. The outcomes of the tribological experiments revealed that the interaction of NDs and MoDTC can enhance the friction and wear performance of steel pairs. However, this enhanced performance is shown to highly depend on other additives present in the lubricant mixture. Analysis of wear scars using High-Resolution Transmission Electron Microscopy (HRTEM), Atomic Force Microscopy (AFM) and Raman spectroscopy reveals that when NDs are fully entrapped into the formed tribofilm that contains the MoDTC-derived MoS₂ layer, the lowest friction coefficient can be achieved.

Two-dimensional MXenes have emerged as promising candidates for advanced lubricant additives, owing to their distinctive surface chemistry and exceptional tribological performance. Nevertheless, their incorporation into lubricant formulations remains challenging due to dispersion stability and complex interactions with conventional additives. This study systematically evaluates the tribological behaviour of Mo2TiC2Tx MXene-based additive systems combined with glycerol monooleate (GMO) and low concentrations of zinc dialkyldithiophosphate (ZDDP) under boundary lubrication conditions using a TE77 reciprocating tribometer. The formulated oil demonstrated marked reductions in friction and wear relative to base oil formulations. High-resolution SEM and HRTEM analyses of wear tracks revealed the formation of robust, multilayered tribofilms enriched with MXene-derived elements, supporting beneficial interactions between Mo2TiC2Tx MXenes and conventional additives at the sliding interface. These findings underscore the potential of MXene–GMO–ZDDP combinations to deliver superior tribological performance whilst providing a pathway to reduce phosphorus and sulfur content in lubricant systems, in line with emerging environmental and regulatory requirements.

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