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-C 3 N 4 ) 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-C 3 N 4 constrains its degradation efficiency, making the heterojunction construction a popular solution. The conventional methods of preparing g-C 3 N 4 heterojunctions by physical mixing destroy π-conjugations in g-C 3 N 4 , reducing the adsorption of lignin containing benzene rings. In this study, a novel indium oxide (In 2 O 3 ) quantum dot–g-C 3 N 4 0D/2D heterojunction was prepared through the high-temperature oxidation of pre-prepared indium-doped g-C 3 N 4 . The introduction of In 2 O 3 at the quantum dot level minimizes the interference with lignin adsorption capacity. The strong combination of the two (In 2 O 3 and g-C 3 N 4 ) 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-C 3 N 4 . The proposed heterojunction was 3 times more efficient than g-C 3 N 4 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 In 2 O 3 –g-C 3 N 4 heterojunction system.