Polyoxometalates modified g-C3N4 promotes efficient photocatalytic cleavage of C−C bond in lignin model compounds

Abstract

Lignin stands out as the largest natural reservoir of renewable aromatic compounds, positioning it as a highly potential substitute for fossil fuels. However, due to the complex structure of lignin, achieving lignin depolymerization under mild conditions is still challenging. Phosphomolybdic acid (PMo₁₂) was introduced as an electron acceptor, and phosphomolybdic acid/carbon nitride (PMo₁₂/g-C₃N₄) composite photocatalysts with varying phosphomolybdic acid loadings were synthesized by a straightforward hydrothermal process. PMo₁₂/g-C₃N₄ composite photocatalysts efficiently cleave C−C bonds in the β−O−4 lignin model compounds at room temperature and pressure under simulated sunlight irradiation. The 15 % PMo₁₂/g-C₃N₄ composite photocatalyst has far higher catalytic efficiency than pure g-C₃N₄, with optimal yields of benzaldehyde and phenyl formate of 81 % and 66 %, respectively, and the selectivity of C−C cleavage could reach 94 %. The results demonstrate that loading PMo₁₂ greatly enhances the separation of photoinduced carriers within the 15 % PMo₁₂/g-C₃N₄ composite photocatalyst, which substantially increases its photocatalytic performance. This research introduces a novel method to efficiently cleave C−C bonds in lignin, which could have important implications for its high-value utilization.