Converting CO2 to carbon-containing fuels is an effective approach to relieving energy shortages.Carbon quantum dots(CQDs)have shown distinct properties and attracted tremendous interest in CO2 reduction.Herein,we report a joint experimental-computational mechanistic study of photoreduction CO2 to CO on the model catalyst 9-hydroxyphenal-1-one(HPHN)CQDs with known structure.Our theoretical calcula-tions reveal that the rate-determining step is COOH·formation,which is closely related to the proton and electron transfer induced by hydrogen bonding in the excited state.According to the calculated volcano plot,the solution we proposed is addition Zn2+ions.The active center changed from the hydroxyl oxygen atom to the Zn atom and the barrier of the COOH? formation step is noticeably decreased when Zn2+ions are added.It is further confirmed by the experimental data that the activity of CO2 reduction increases 2.9 times when Zn2+ions are added.