Constructing functionalized carbon quantum dots on amino-rich graphitic carbon nitride to enhance CO2 photocatalytic reduction: Critical role of functional group modulation

Carbon quantum dots (CQDs) decoration have been widely acknowledged as promising strategy in photocatalysis, yet in-depth understanding of the effect of different functionalized CQDs on CO 2 photocatalytic reduction is still lacked. Herein, three kinds of functionalized CQDs, i.e. carboxylic CQDs (CCQDs), amino CQDs (NCQDs) and sulfonated CQDs (SCQDs), were homogeneously anchored on amino-rich g-C 3 N 4 (U1W1-CN) to investigate their CO 2 reduction behaviors under simulated solar-light illumination. Structural analysis demonstrated that potential amide covalent bonds formed between U1W1-CN and CCQDs, and noncovalent conjugations might exist between U1W1-CN and SCQDs, while strong electrostatic attraction between U1W1-CN and NCQDs. Performance tests showed CQDs decoration greatly enhanced the CO 2 reduction activity, with 7%CCQDs/U1W1-CN exhibiting the optimal CO and CH 4 productions of 40.94 μmol g −1 and 2.2 μmol g −1 under 4 h light irradiation, markedly higher than those of 7%SCQDs/U1W1-CN and 7%NCQDs/U1W1-CN. After comprehensive analysis, it was found that CCQDs decoration endowed U1W1-CN with better CO 2 adsorption and activation. And due to the potential amide covalent bonds formed between CCQDs and U1W1-CN, 7%CCQDs/U1W1-CN delivered the largest electron density and most abundant COOH – intermediates, contributing much to its superior CO 2 reduction activity over 7%NCQDs/U1W1-CN and 7%SCQDs/U1W1-CN. It is expected that the critical role of functional group modulation on CQDs in enhancing CO 2 photocatalytic reduction revealed in this work can provide valuable insights into the rational design of more advanced photocatalysts for targeted reactions.