Next-generation tribology: Evaluating hybrid nano-additive enhanced Botryococcus braunii microalgal lubricants

Abstract

This study investigates the physicochemical and tribological performance of Botryococcus braunii microalgae-based bio-nanolubricants enhanced with hybrid nano-additives such as graphene oxide (GO), titanium oxide (TO), aluminium oxide (AO), and multiwalled carbon nanotubes (MWCNTs) using oleic acid as a surfactant. Eight formulations were prepared and evaluated for stability, thermal properties, and lubrication performance. Eta potential and particle size analysis confirmed strong colloidal stability and uniform dispersion of nanoparticles. FTIR spectra indicated strong CH₂/CH₃ stretching and carbonyl peaks, reflecting the presence of long-chain fatty acids and low oxidation products compared to conventional 20 W-40 oil. Physicochemical analysis confirmed improved viscosity, thermal stability, flash point, and pour point, with all samples remaining stable without phase separation for 72 h. Tribological testing using a Pin-on-Disc Tribometer under loads of 20, 80, 140, and 200 N showed that B. braunii oil with hybrid nanoadditives (GO + MWCNTs) exhibited the lowest coefficient of friction of 0.277 at 200 N, minimal wear scar diameter 0.89 mm and specific wear rate 0.0027 × 10⁻³ mm³/N-m, outperforming all other formulations compared to conventional lubricant 20 W-40. Morphological analysis confirmed smoother contact surfaces with minimal grooves. GC–MS analysis revealed a high proportion of C₁₇–C₁₉ fatty acid methyl esters (FAMEs), enhancing oxidation stability and lubricity. B. braunii oil with hybrid nanoadditives (GO + MWCNTs) stands out as a renewable, sustainable, and high-performance lubricant. Its superior tribological behavior demonstrates the potential of microalgae-based bio-nanolubricants to replace petroleum-based oils, offering both environmental benefits and reliable mechanical protection in industrial applications.