Ammonium Bicarbonate Significantly Accelerates the Microdroplet Reactions of Amines with Carbon Dioxide

Abstract

The reactions between amines and carbon dioxide (CO2) are among the most commonly used and important carbon fixation reactions at present. Microdroplets generated by electrospray ionization (ESI) have been proved to increase the conversion ratio (R C) of amines. In this work, we confirmed that the presence of ammonium bicarbonate (NH4HCO3) in ESI microdroplets significantly increased the R C of amines. The R C went up remarkably with the increase in the concentration of NH4HCO3 from 0.5 to 20 mM. The R C of N,N-dibutyl-1,3-propanediamine (DBPA) reached 93.7% under 20 mM NH4HCO3, which was significantly higher than previous reports. The rise in R C became insignificant when the concentration of NH4HCO3 was increased beyond 20 mM. Further investigations were made on the mechanism of the phenomenon. According to the results, it was suggested that NH4HCO3 decomposed into CO2 and formed microbubbles within the microdroplets of ESI. The microbubbles acted as direct internal CO2 sources. The conversion reactions occurred at the liquid–gas interface. The formation of CO2 microbubbles remarkably increased the total area of the interface, thus promoting the conversion reactions. 13C-labeled experiments confirmed that NH4HCO3 acted as an internal CO2 source. Factors that influenced the R C of the reaction were optimized. Pure water was proved to be the optimal solvent. Lower temperature of the mass spectrometer’s entrance capillary was beneficial to the stabilization of the product carbamic acids. The sample flow rate of ESI was crucial to the R C. It determined the initial sizes of the microdroplet. Lower flow rates ensured higher R C of amines. The present work implied that NH4HCO3 could be a superior medium for CO2 capture and utilization. It might offer an alternative choice for future CO2 conversion research studies. In addition, our study also provided evidence that NH4HCO3 decomposed and generated microbubbles in the droplets during ESI. Attention should be paid to this when using NH4HCO3 as an additive in mass spectrometry-based analysis.

Simultaneous and Spontaneous Oxidation and Reduction in Microdroplets by the Water Radical Cation/Anion Pair

“…To validate the fact that formic acid is produced from CO 2 , we provide a CO 2 -rich environment for the water microdroplets, and a clear response of the formate signal to CO 2 "on" and "off" was found (see Supporting Information, Figure S5). This reaction suggests the possibility of application of microdroplets in CO 2 fixation; [37,45] to the best our knowledge there is no precedent for this in the literature. Inductive nESI analysis was performed and both the water radical cation and formic acid were identified (see Supporting Information, Figure S6).…”

Spraying Water Microdroplets Containing 1,2,3-Triazole Converts Carbon Dioxide into Formic Acid

“…Previous investigations have revealed that amines and nitrogen-containing aromatic heterocycles such as pyridine, imidazole, triazole, and tetrazole in porous materials have a high affinity for the capture of CO 2 . − In particular, the 1,2,3-triazole (Tz)-incorporated metal–organic framework (MOF) can remarkably enhance CO 2 uptake capacity . Tz mainly serves as the ligand in the above-mentioned MOF materials.…”

Aqueous microdroplets enable abiotic synthesis and chain extension of unique peptide isomers from free amino acids

“…Five-membered heterocycles, similar to the proposed structures, have been suggested as important prebiotic biomolecule precursors ( 81 ). The initial condensation reaction is likely driven by the extremely low interfacial pH of the microdroplet surface, as previously suggested for the condensation of o -phenyl diamines and carboxylic acids to form benzimidazoles and for the sequestration of carbon dioxide as the carbamic acids using free amines ( 41 , 43 , 82 ). Two ion-neutral complexes 2 and 3 ( 83 , 84 ) are accessible from fully covalent oxazolidinone ion 1.…”