Green and Economical Bet-Based Natural Deep Eutectic Solvents: A Novel High-Performance Lubricant

Developing halogen-free and green lubricants is an impending research topic for achieving energy conservation and pollution reduction. Inspired by the sustainable and ecofriendly characteristics of natural deep eutectic solvents (NADESs), Bet-based NADESs were successfully synthesized using betaine (Bet) and sugars or sugar alcohols. The as-synthesized Bet-based NADESs presented superior kinematic viscosity, viscosity index, thermostability, and anticorrosion properties, which promised their potential as green lubricants. The as-prepared NADESs showed favorable lubrication properties compared with the traditional choline chloride (ChCl)-Urea DES and commercial G13830 ester. The friction and wear rate of Bet-Suc NADES are only 69.70 and 53.46% of G13830 ester even under 2.16 GPa, owing to the formed fluid lubrication film and excellent kinematic viscosity. The half-maximal effective concentration value (EC50) of Bet-Sor NADES toward Vibrio fischeri is 270 000 mg L–1, indicating that the toxicity is low. NADESs represent the first promising, halogen-free, and cost-effective lubricants constructed by Bet and sugars, which can be applied to real-world lubrication.