Promotion of Photocatalytic Lignin Models Cβ–O Bond Cleavage by Cr-Doped Zinc Indium Sulfide in Alkaline Solvent

Photocatalytic valorization of lignin to aromatic monomers by cleaving the Cβ–O bond is a promising approach for the utilization of biomass resources. Herein, we achieved nearly 100% conversion of the model compound 2-phenoxy-1-phenylethanol (PP-ol), and the selectivity of phenol and acetophenone reached 96 and 95%, respectively, using water and Cr-doped ZnIn2S4(CZIS) as the hydrogen source and photocatalyst, respectively. Density functional theory calculations showed that Cr present on the CZIS surface can provide appropriate free energy for the target reaction intermediate, reducing the uphill ΔGfor cleaving the Cβ–O ether bond reaction of the Cαradical (Cα•) intermediate to form acetophenone and phenol (from 2.15 to −0.81 eV), which facilitate the photocatalytic PP-ol conversion. In addition, controlling the competitive hydrogen evolution on the photocatalyst surface by adjusting the alkalinity of the reaction solvent is also a key factor to improve the photocatalytic performance.