Controllable adsorption groups on amine-functionalized carbon nitride for enhanced photocatalytic CO2 reduction

CO2 photoreduction by carbon nitride (CN) is an appealing idea, but its current efficiency remains daunting for practical viability. The amine-functionalized CN with controllable adsorption groups was prepared by carboxylation and acylation reactions. The carboxylation and amine-functionalization process preserved the crystalline structure of CN but exfoliated bulk CN to thin layers avoiding its agglomeration. With the successful graft of EDA, the amounts of –NH2 groups for 24-CN-EDA increased remarkably compared with bulk CN. EDA-functionalization benefited CO2 reduction activity of CN with varying amounts of amino groups. The CO yield of 24-CN-EDA was 5.92 folds to bulk CN. The enhancement was mainly triggered by the enlarged CO2 adsorption capacity and reduced charge transfer resistance, rather than band structure and light absorption. Moreover, DFT calculations suggest that the graft of EDA on CN nanosheets possesses reduced energy barrier for CO2 reduction into CO via enhancing CO* desorption and CO formation.