S-scheme electron transfer promoted by novel indium oxide quantum dot-loaded carbon nitride heterojunctions promoted using oxidized indium monomers.

The graphitic carbon nitride (g-CN) photocatalysis has emerged as a clean method for cleaving lignin-linked bonds due to its mild and sunlight-driven reaction conditions. The fast electron-hole pair complex of g-CN constrains its degradation efficiency, making the heterojunction construction a popular solution. The conventional methods of preparing g-CN heterojunctions by physical mixing destroy π-conjugations in g-CN, reducing the adsorption of lignin containing benzene rings. In this study, a novel indium oxide (InO) quantum dot-g-CN 0D/2D heterojunction was prepared through the high-temperature oxidation of pre-prepared indium-doped g-CN. The introduction of InO at the quantum dot level minimizes the interference with lignin adsorption capacity. The strong combination of the two (InO and g-CN) increases the intersection interface area, promoting the S-scheme transfer route of the photogenerated electrons. Consequently, this enhances the photoelectric conversion efficiency and carrier lifetime of the heterojunction, and inhibits the rapid recombination of photogenerated electron-hole pairs in g-CN. The proposed heterojunction was 3 times more efficient than g-CN alone for selective cleavage of lignin β-O-4 bonds after 2 h of sunlight irradiation. Combined with inhibitor experiments and gas chromatography-mass spectrometry analysis, this paper defines the reactive oxides and proposes a cleavage pathway for the lignin β-O-4 bonds in InO-g-CN heterojunction system.