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

Abstract

The cleavage of lignin C−C bonds is of great significance for the high-value utilization of lignin. However, it still faces great challenges due to the stubbornness and complexity of lignin C−C bonds. Herein, the cyano group with an electronwithdrawing effect is successfully introduced into the graphitic carbon nitride (BCN) photocatalyst by alkali metal molten salt methods, and it is labeled KLCN. Compared with pure BCN, the micromorphology and electronic structure of KLCN have undergone significant changes. Markedly, KLCN with a short rod-like micromorphology has excellent photogenerated electron−hole pair separation ability and stronger photogenerated electron reduction ability. By combining KLCN and persulfate, the C−C bond in β-1 lignin models and aromatic vicinal diols was efficiently broken. Mechanistic studies have shown that the active radicals in the photocatalytic reaction are regulated and that the hydroxyl radicals are the main active radicals. It promotes the participation of water in the photocatalytic reaction and provides H and O atoms for breaking of the lignin C−C bonds. The photocatalytic reaction mainly follows a single-electron-transfer mechanism, which is rare in breaking lignin C−C bonds by using a heterogeneous photocatalyst. The current work provides helpful guidelines for designing effective photocatalysts for lignin C−C bond cleavage.