Amino acid ionic liquids for effective removal of crotonaldehyde and acetaldehyde from cigarette mainstream smoke

A series of amino acid-based ionic liquids (AAILs) have been synthesized by acid-base neutralization reaction of tetraalkylammonium hydroxides and amino acids. The pendent chain length and groups of AAILs were well adjusted by using glycine (Gly), L-alanine (L-Ala), L-valine (L-Val), L-leucine (L-Leu), L-Phenylalanine (L-Phe), L-glutamic acid (L-Glu) and L-lysine (L-Lys) as amino acid precursors. These AAILs was used for the effective removal of aldehydes in cigarette smoke, 41-66% of crotonaldehyde and 12-39% of acetaldehyde could be removed from the cigarette smoke with these AAILs as adsorbents. With the increasing of the pendent chain length, the remove efficiency of acetaldehyde and crotonaldehyde decreased from 32%, 66% to 16%, 41%, respectively due to the increase of steric hindrance. [N3333][Gly], the AAILs with the smallest chain length, has a highest removal efficiency of 66% for crotonaldehyde and 32% for acetaldehyde. The AAILs with pendent benzene groups, [N3333][Phe], has high crotonaldehyde removal efficiency of crotonaldehyde due to the strong π-π interaction, which could overcome the higher steric resistance of pendent chain. AAILs with pendent amino groups, [N3333][Lys], could reduce 60% of crotonaldehyde and 39% of acetaldehyde due to the enhanced chem-adsorption of the aldehydes by the pendent amino groups. Its excellent performance stems from the synergy between amino chemical adsorption and polar side chain solubility. The high aldehydes removal efficiency of these AAILs, such as [N3333][Gly], [N3333][Phe], [N3333][Lys], demonstrates the great potential of these AAILs as adsorbents for the removal of aldehydes in cigarette smoke.