Dual-facet modulation involving surface carboxyl functionalization and interlayer regulation by CQDs in g-C3N4 for enhanced xylose photooxidation

Abstract

Photocatalytic oxidation of biomass-derived xylose to xylonic acid provides a sustainable route for producing high-value sugar acids under mild conditions. However, its practical application is often limited by poor selectivity caused by uncontrolled radical reactions promoting Csingle bondC bond cleavage and deep oxidation. Herein, we propose that bamboo-derived carbon precursors are employed to construct an in-plane heterojunction between conjugated carbon domains and graphitic carbon nitride (g-C3N4), in which bamboo-derived carbon quantum dots (CQDs) act as electron bridges to facilitate interlayer charge transport and thereby enhance surface-directed electron migration. This effect is evidenced by enhanced photocurrent responses, reduced charge-transfer resistance, prolonged carrier lifetimes, and increased electron delocalization. Meanwhile, carbonyl groups on the CQD surface promote the adsorption and activation of xylose at the reaction interface through an electron-withdrawing effect. Mechanistic investigations further identify superoxide (·O2−) and singlet oxygen (1O2) as the dominant reactive oxygen species responsible for selective xylose oxidation. Consequently, the optimized catalyst achieves an 84.4% yield of xylonic acid under visible-light irradiation with excellent stability. This work establishes reaction-demand-oriented charge-transport engineering as a key design principle for the selective photocatalytic upgrading of biomass-derived sugars.