Urchin-like Nb2O5 hollow microspheres enabling efficient and selective photocatalytic C–C bond cleavage in lignin models under ambient conditions

Selective cleavage of robust C−C bonds to harvest value-added aromatic oxygenates is an intriguing but challenging task in lignin depolymerization. Photocatalysis is a promising technology with the advantages of mild reaction conditions and strong sustainability. Herein, we show a novel urchin-like Nb2O5 hollow microsphere (U-Nb2O5 HM), prepared by one-pot hydrothermal method, are highly active and selective for Cα−Cβ bond cleavage of lignin β-O-4 model compounds under mild conditions, achieving 94% substrate conversion and 96% C−C bond cleavage selectivity. Systematic experimental studies and density functional theory (DFT) calculations revealed that the superior performance of U-Nb2O5 HMs arises from more exposed active sites, more efficient free charge separation and the active (001) facet, which facilitates the activation of Cβ−H bond of lignin models and generate key Cβ radical intermediates by photogenerated holes, further inducing the Cα−Cβ bond cleavage to produce aromatic oxygenates. This work could provide some suggestions for the fabrication of hierarchical photocatalysts in the lignin depolymerization system.