CO2 Capture and Conversion into Carbon-Based Tribofilm by In Situ Tribochemical Reaction for Green Lubrication

The capture and conversion of CO2 are of great significance for mitigating the greenhouse effect and achieving sustainable development. Unlike previous CO2 utilization methods, this work develops a novel CO2 utilization strategy that directly converts captured CO2 to a carbon-based tribofilm through in situ tribochemical reactions. Monoethanolamine (MEA) aqueous solution is used as the absorbent for CO2 capture, and tribological experiments have shown that its lubrication performance is significantly enhanced under various loads and speeds after absorbing CO2. After absorbing CO2 for 40 min, the friction and wear of 75 wt % MEA solution are decreased by 45.31 and 40.38%, respectively, compared to the unabsorbed MEA solution. The CO2 undergoes a chemical reaction with MEA to produce carbamates. Anions of carbamates adsorb onto the substrate through carboxylate groups to form a molecular brush structure, decreasing friction coefficient. Meanwhile, the strong interaction between carboxylate groups and the substrate also makes carboxylate groups prone to tribochemical reactions, forming a carbon-based tribofilm and reducing wear. This work successfully achieves green lubrication by converting CO2 into carboxylate groups, which are further in situ converted into carbon-based tribofilms through tribochemical reactions. This study not only reveals the potential value of CO2 in tribology but also opens up a new path for the value-added utilization of CO2.