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

The selective breaking of the Cβ–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 Cβ–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 Cα–OH to form Cα═O initially, followed by the activation of Cβ–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.