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.