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

The reactions between amines and carbon dioxide (CO) 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 () of amines. In this work, we confirmed that the presence of ammonium bicarbonate (NHHCO) in ESI microdroplets significantly increased the of amines. The went up remarkably with the increase in the concentration of NHHCO from 0.5 to 20 mM. The of ,-dibutyl-1,3-propanediamine (DBPA) reached 93.7% under 20 mM NHHCO, which was significantly higher than previous reports. The rise in became insignificant when the concentration of NHHCO was increased beyond 20 mM. Further investigations were made on the mechanism of the phenomenon. According to the results, it was suggested that NHHCO decomposed into CO and formed microbubbles within the microdroplets of ESI. The microbubbles acted as direct internal CO sources. The conversion reactions occurred at the liquid-gas interface. The formation of CO microbubbles remarkably increased the total area of the interface, thus promoting the conversion reactions. C-labeled experiments confirmed that NHHCO acted as an internal CO source. Factors that influenced the 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 . It determined the initial sizes of the microdroplet. Lower flow rates ensured higher of amines. The present work implied that NHHCO could be a superior medium for CO capture and utilization. It might offer an alternative choice for future CO conversion research studies. In addition, our study also provided evidence that NHHCO decomposed and generated microbubbles in the droplets during ESI. Attention should be paid to this when using NHHCO as an additive in mass spectrometry-based analysis.