Photocatalyst g-C3N4 for efficient cleavage of lignin C[sbnd]C bonds in micellar aqueous medium

Abstract

Depolymerizing lignin to prepare aromatic high-value chemicals is beneficial to solve the problem of energy shortage and waste of resources. However, cleavage of lignin CC bonds still faces greater challenges due to the recalcitrance of CC bonds in lignin. Photocatalysis is considered to be a promising way to break lignin CC bonds under mild conditions. Here, the micellar aqueous medium (SDS) composed of sodium lauryl sulfonate and water was prepared. 1, 2-Diphenylethanol (lignin model compound, Dpol) and dioxanesolv poplar lignin can be well dispersed in SDS-8 (mass fraction of 0.08% for sodium lauryl sulfate). Photocatalyst g-C3N4 can efficiently break the lignin CC bonds in SDS-8 and very high photocatalytic efficiency can be obtained. A small amount of acetic acid can further improve photocatalytic efficiency. The main products produced by photocatalytic breaking lignin CC bonds are benzaldehyde and benzoic acid. The mechanism of photocatalytic cleavage of lignin CC bonds mainly follows a photogenerated electron-hole coupled redox mechanism. Thereinto, the hydrogen provided by SDS-8 has powerfully promoted photocatalytic efficiency. Our work provides a new direction for photocatalytic cleavage of lignin CC bonds into aromatic high-value chemicals.