Issue 4, 2024

Z-scheme heterojunction g-C3N4/CQD/CdZnS with high redox capability for enhancing visible light-driven photocatalytic depolymerization of lignin into aromatic monomers

Abstract

The photocatalytic depolymerization of lignin is a sustainable strategy to produce high-value aromatic chemicals. The selective and efficient cleavage of β-O-4 bonds under mild conditions remains one of the challenges in lignin valorization. Herein, an efficient and mild strategy was employed for one-step photocatalytic depolymerization of lignin and β-O-4 model compounds over novel Z-scheme heterojunction g-C3N4/carbon quantum dot/CdZnS (CN/CQD/CZS) under simulated solar light. The total yield of vanillin and vanillic acid from lignin depolymerization was 36.3 mg g−1 lignin when the volume ratio of SDS-8 (sodium dodecyl sulfate solution with a mass fraction of 0.08%) to HCOOH was 4 : 1 within 2 h. The depolymerization mechanism of lignin was investigated using β-O-4 model compounds. The β-O-4 model compounds were converted into phenolic monomers over optimized CN/CQD/CZS, yielding 84% substrate conversion and ∼100% C–O bond cleavage selectivity. Three extractive natural lignin samples were applied to this system and successfully depolymerized. A combination of experimental results and theoretical calculations illustrated that CQDs played a crucial role in accelerating photogenerated electron transfer at the CN/CZS interface via the Z-scheme electron pathway, which effectively promoted the separation and transfer of photoexcited hole–electron pairs. Mechanistic studies demonstrated that the selective cleavage of the β-O-4 bond mainly involved a photogenerated electron–hole coupled redox mechanism. The construction of the Z-scheme CN/CQD/CZS heterojunction is essential to enhance the kinetics of electron transport and maintain strong redox ability. The approach in this work offers a useful guidance for the construction of Z-scheme heterojunction photocatalysts with a carbon-based electron mediator and the selective breakage of C–O bonds in lignin.

Graphical abstract: Z-scheme heterojunction g-C3N4/CQD/CdZnS with high redox capability for enhancing visible light-driven photocatalytic depolymerization of lignin into aromatic monomers

Supplementary files

Article information

Article type
Paper
Submitted
15 Oct 2023
Accepted
21 Dec 2023
First published
22 Dec 2023

Green Chem., 2024,26, 1935-1948

Z-scheme heterojunction g-C3N4/CQD/CdZnS with high redox capability for enhancing visible light-driven photocatalytic depolymerization of lignin into aromatic monomers

X. Liu, Z. Jiang, X. Cao, Z. Shen, W. Zhao, F. Wang, M. Cui and C. Liang, Green Chem., 2024, 26, 1935 DOI: 10.1039/D3GC03929C

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