CdS–SH/TiO2 Heterojunction Photocatalyst Significantly Improves Selectivity for C–O Bond Breaking in Lignin Models

Abstract

The selective breaking of the C_β–O bond has great potential for the conversion of lignin into high-value aromatic monomers. In the present work, we designed a CdS–SH/TiO₂ heterojunction photocatalyst for the efficient selective breaking of the C_β–O bond. The surface modification of CdS by –SH promoted close contact between the catalyst and lignin and further promoted the Fermi level matching with TiO₂. A type-II heterojunction was constructed by CdS–SH and TiO₂ nanosheets to enhance the light absorption range and further increase the separation of photogenerated electron–hole pairs, resulting in high catalytic activity. Finally, 85% phenol and 87% acetophenone yields were obtained under mild light irradiation using 2-phenoxy-1-phenylethanol as the model substrate. Several control experiments, along with DFT calculations, indicate that the reaction pathway is more likely to involve the oxidation of C_α–OH to form C_α═O initially, followed by the activation of C_β–O, which is then reduced to further form aromatic monomers. This work achieves the efficient selectivity of lignin depolymerization and provides a reference for the design of heterojunction photocatalysts in the valorization of lignin.