Deep eutectic solvents for effective removal of indoor formaldehyde: Theoretical design, experiment, and adsorption mechanism study

Formaldehyde (HCHO) represents a prevalent indoor air pollutant, and its efficient removal continues to be an area of significant concern. Adsorption is a typical technique to capture this pollutant gas. In this work, the COSMO-RS theoretical framework guided the selection of three deep eutectic solvents (DES): L-arginine/glyc-erol, L-lysine/glycerol, and L-proline/glycerol, from a pool of 416 combinations involving 16 amino acids and 26 alcohols. These DES were used for the first time to adsorb HCHO. The adsorption experiments of HCHO illus-trated that the DES system had a higher HCHO adsorption capacity than the pure fraction. Among them, L-arginine-glycerol-1:5 (A-G-DES) had the highest adsorption efficiency, requiring only 0.1 g to remove 92.7% HCHO in 6 h, which is consistent with the predicted results. The nucleophilic addition reaction between amino acids and HCHO during the adsorption was revealed by FT-IR and 13C NMR. DFT calculations analyzed the interaction strength of HCHO at different adsorption sites, and the formation of DES system was demonstrated to produce more favorable HCHO adsorption behavior through the interaction energy calculation. The molecular dynamics simulations (MD) verified that the main mode of HCHO adsorption was the non-covalent interaction between polar functional groups (such as-COOH,-NH and-OH) in DES system and O and/or C atoms in the HCHO molecules.