Ti-MOF-derived titanium oxide-modified carbon nitride: A Z-scheme heterostructure for the selective photocatalytic cleavage of lignin CC bonds

Abstract

The utilization of solar energy to break the C_αC_β bonds in lignin under mild conditions is highly important for lignin valorization. This work presents an MIL-125-derived titanium oxide (M-TiO₂)-modified carbon nitride (g-C₃N₄) heterostructure for selective photocatalytic lignin C_αC_β bond cleavage at room temperature. The conversion of lignin model 2-phenoxy-1-phenylethanol (PP-ol) reached 90.8 % over M-TiO₂/g-C₃N₄ composites, which is visibly higher than that of bare M-TiO₂ (33.2 %) and g-C₃N₄ (57.3 %). Furthermore, the selectivity of C_αC_β bond breakage reached 96.8 %, and the yield of benzaldehyde was as high as 86.4 %. A mechanistic study innovatively demonstrated that lignin C_αC_β bond cleavages are achieved by the cooperative effect between holes and ¹O₂, where holes dominate PP-ol conversion, whereas ¹O₂ governs C_αC_β bond cleavages. M-TiO₂ has relatively large surface areas and high porosities, and the Z-scheme heterojunctions retard charge carrier recombination and outfit strong redox abilities, which separately prompt O₂ adsorption and evolution to generate ¹O₂, accounting for the high selectivity of C_αC_β bond breakages over M-TiO₂/g-C₃N₄ composites. This study sheds new light on the potential of metal–organic framework-derived materials in photocatalysis and provides valuable insights into the photocatalytic cleavage of lignin C_αC_β bonds.