Enhanced CO2 photocatalytic reduction on alkali-decorated graphitic carbon nitride

In this work, visible-light photocatalytic reduction performance of carbon dioxide (CO2) on graphitic carbon nitride (g-C3N4) was significantly promoted by the decoration of potassium hydroxide (KOH) on g-C3N4. More importantly, the role of KOH was thoroughly discussed via various characterizations, control experiments and density functional theory (DFT) calculations. It was found that KOH decoration did not result in any significant difference regards to the morphology, elemental states, BET surface area and light adsorption of g-C3N4 except a drastically enhanced CO2 adsorption capacity. The promotion effect of KOH on g-C3N4 was mainly contributed by the hydroxide ion (OH−) functioning as both a hole accepter and a driving force to keep a dynamically stable amount of H2CO3 (probably the major form of CO2 to be reduced) on the surface of the catalyst. Moreover, the different extents of influence of NaOH and KOH on g-C3N4 were revealed and further explained using computational results. This study supplements current understanding on alkali-promoted photocatalytic processes and provides new insights into the mechanism of CO2 photocatalytic reduction.