Fabrication of S-Scheme g-C₃N₄/Zn₄In₂S₇ Heterojunction Photocatalyst for Enhancing Selective Cleavage of β-O-4 Bond in Lignin Model Compounds and Lignin

Abstract

The photocatalytic cleavage of the C–O bonds between the β-O-4 structure in natural lignin is still very challenging. Regrettably, the efficiency and selectivity of the photocatalysts for lignin valorization need to be further improved due to the fast recombination of the photogenerated carriers and unsuitable redox potential. To address these challenges, an efficient approach for promoting the one-step Cβ–O bond cleavage in β-O-4 lignin model compounds and lignin by using a g-C3N4/Zn4In2S7 (CN/ZIS) photocatalyst with a step-scheme (S-scheme) heterojunction was employed under visible-light illumination. The construction of the S-scheme CN/ZIS heterojunction was essential to efficiently separate the photoexcited carriers and then improve their redox capability. Due to its ingenious design, the lignin β-O-4 model compound was completely converted under mild conditions with 99% C–O bond cleavage selectivity, which affords high selectivity of phenol (93.4%) and acetophenone (75.2%). The mechanistic studies and density functional theory calculation demonstrated that the efficient cleavage of Cβ–O bonds mainly involved a photoexcited electron–hole-coupled redox mechanism. After optimizing the reaction conditions, real lignin samples were applied to this system and successfully depolymerized. This study elucidated the high-performance charge transfer mechanism of heterogeneous interfaces and provided an effective strategy to produce aromatic resources by utilizing both lignin and photoenergy.

Harnessing the Synergistic Power of Ce2S3/TiO2 S-Scheme Heterojunctions for Profound C–O Bond Cleavage in Lignin Model Compounds

“…For our preliminary investigations, we followed the experimental protocols established by previous researchers in this domain, using 5 mg of the catalyst and 2 mL of the solvent (a 1:1 mixture of acetonitrile and water) in a nitrogen atmosphere. Our investigation focused on determining photocatalytic activity under 420 nm visible-light irradiation in the presence of nitrogen (N 2 ).…”

Efficient Photocatalytic Cleavage of C–C Bonds in β-1 Lignin Models and Aromatic Vicinal Diols by Combining Alkali Metal-Treated Graphitic Carbon Nitride and Persulfate

“…However, the study of depolymerizing lignin by breaking lignin C–C bonds to obtain high-value chemicals seems to have been limited, which is not conducive to high-value utilization of lignin. Previous studies have shown that the dissociation energy of lignin C–C bonds is higher than that of lignin C–O bonds. , At the same time, the lignin C–C bond is sandwiched between two benzene rings, which makes it more stable and therefore requires more energy to break it. So far, there is still huge room for improvement in obtaining high-value chemicals by breaking lignin C–C bonds.…”