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

We report the use of 1,2,3-triazole (Tz)-containing water microdroplets for gas-phase carbon dioxide (CO2) reduction at room temperature. Using a coaxial sonic spraying setup, the CO2 can be efficiently captured by Tz and converted to formic acid (HCOOH; FA) at the gas–liquid interface (GLI). A mass spectrometer operated in negative ion mode monitors the capture of CO2 to form the bicarbonate anion (HCO3–) and conversion to form the formate anion (HCOO–). Varied FA species were successfully identified by MS/MS experiments including the formate monomer ([FA – H]−, m/z 45), the dimer ([2FA – H]−, m/z 91; [2FA + Na – 2H]−, m/z 113), the trimer ([3FA – H]−, m/z 137), and some other adducts (such as [FA – H + H2CO3]−, m/z 107; [2FA + Na – 2H + Tz]−, m/z 182). The reaction conditions were systematically optimized to make the maximum conversion yield reach over 80% with an FA concentration of approximately 71 ± 3.1 μM. The mechanism for the reaction is speculated to be that Tz donates the proton and the hydroxide (OH–) at the GLI, resulting in a stepwise yield of electrons to reduce gas-phase CO2 to FA.