Direct Air Capture of CO2 via Ionic Liquids Derived from “Waste” Amino Acids

Abstract

Direct capture of CO2 from anthropogenic emissions is an imperative societal task as the concentration of global atmospheric CO2 continues to increase drastically. The long-term goal of negative emission requires methods to remove carbon directly from the atmosphere, oceanwater, and nonpoint sources. Ionic liquids (ILs) have had a pivotal impact on finding and implementing innovative solutions that enable a more sustainable future. Here, we report the first example of an IL-enabled approach for direct CO2 capture from the atmosphere on a laboratory scale. These de novo bioderived materials represent an ideal milieu for direct carbon capture applications because of their nonvolatility and a priori low toxicity. Easily prepared liquid salts based on a mixture of three common amino acids, valine, leucine, and isoleucine, were found to be effective sorbents for ready and reversible CO2 sequestration from air despite its very low concentration. Collectively known as branched-chain amino acid, they are commonly derived from biowaste products, for example, feathers, fur, and even human hair. Therefore, the resultant ILs from the “waste” amino acids provide an exciting prospect in terms of CO2 transformation and waste utilization. We provided valuable design insights for engineering structure–property relationships in amino acid-based ILs. The impact of moisture on the absorption characteristics and capacity was evaluated in ambient conditions. We postulate that the high capture efficiency and stability of these ILs make them superior to present amine- and alkali-assisted approaches for the direct air capture of CO2 as a scalable process.