Growing environmental regulations that limit sulphur and phosphorus in engine lubricants have created an urgent need to reduce or replace zinc dialkyldithiophosphate, commonly used anti wear additive, without compromising tribological performance. This thesis tackles that challenge head on. It develops and explains, at a mechanistic level, a new multi additive lubricant formulation that combines glycerol monooleate, carboxylated nanodiamonds, and two families of two dimensional MXenes, namely Mo₂TiC₂Tₓ and Ti₃C₂Tₓ, dispersed in a polyalphaolefin base oil. The central hypothesis is that well-designed interactions between these additives can promote the formation of durable, low-shear tribofilms under boundary lubrication conditions that can match or even surpass the protection traditionally provided by ZDDP-based formulations.The research is structured into four experimental phases, each building toward lubricant systems with progressively lower sulphur and phosphorus content. In the first phase, blending nanodiamonds, glycerol monooleate, and a small amount of ZDDP in the base oil led to marked reductions in both friction and wear compared with conventional formulations. A key outcome was the discovery of tribochemical interactions between carboxylated nanodiamonds and glycerol monooleate at around 80°C, which significantly accelerated tribofilm formation. The observed reduction in friction was linked to nanodiamonds becoming embedded within a glycerol monooleate derived tribofilm, along with rolling effects, mechanical interlocking, and micro scale surface polishing.The second phase explored how nanodiamonds perform in combination with molybdenum dithiocarbamate. The results showed that optimal tribological behaviour occurs when nanodiamonds are fully incorporated within MoDTC derived tribofilms containing MoS₂. Performance was found to depend strongly on the surrounding additive package, highlighting that synergistic formulation design is not accidental but essential for reliable and repeatable performance.In the third phase, attention shifted to the use of Mo₂TiC₂Tₓ MXene together with glycerol monooleate and reduced ZDDP content. Although dispersion proved challenging, these formulations formed multilayered tribofilms enriched with MXene, leading to substantial reductions in friction and wear compared with the base oil alone. These results demonstrate a technically viable route to lowering sulphur and phosphorus while maintaining effective anti-wear performance in realistic lubricant systems.The fourth and final phase investigated a formulation that was almost free of ZDDP, consisting of Ti₃C₂Tₓ MXene, nanodiamonds, and glycerol monooleate. This system produced uniform and continuous tribofilms with an average thickness of about 150 nanometres, exhibited excellent wear resistance under high contact pressure.Overall, this work provides the first systematic examination of multi additive synergy involving glycerol monooleate, nanodiamonds, and MXenes under boundary lubrication conditions. It delivers nanoscale insight into how interactions between additives influence tribofilm composition, thickness, and shear behaviour. The findings show that newly developed additive formulation reduced or eliminated ZDDP and in some cases outperform, conventional anti wear benchmarks. Importantly, the thesis lays out a clear and evidence-based pathway toward next-generation lubricants that balance environmental requirements with high tribological performance, with clear relevance to automotive, aerospace, and industrial applications.