Green carbon quantum dots as eco-friendly nano-additives for tribological enhancement of Pongamia oil

Carbon quantum dots (CQDs) offer various advantages - biodegradability, non-toxicity, lower cost and are used as a replacement for various metal oxide-based nanoparticles. Despite these advantages, the use of CQDs remains limited. This study investigates the synthesis of CQDs using cowpea seeds and their application as nano-additives in bio-based Pongamia oil as a lubricant. The addition of CQDs enhanced the lubricating properties of Pongamia oil. At a concentration of 0.15 wt% CQDs, the nanofluid improved the viscosity and anti-wear properties while reducing the friction compared to the base oil. The enhancement in tribological properties of Pongamia oil after the addition of CQDs was rationalised based on the correlation among viscosity, activation energy, wear, friction, thermal conductivity, flash point, and fire point. The analysis of the wear scar surface revealed lower wear and fewer grooves on the metal surface lubricated with CQD-modified Pongamia oil compared to the base oil. The results offer a simple and effective strategy for using CQDs in base oil as nanoadditives, thereby increasing the tribological properties.