Rapid Hydroxyl Radical Generation on (001)-Facet-Exposed Ultrathin Anatase TiO2 Nanosheets for Enhanced Photocatalytic Lignocellulose-to-H2 Conversion

Photocatalytic lignocellulose-to-H2 conversion is highly attractive but remains a huge challenge due to the absence of efficient photocatalysts. Herein we report the use ultrathin anatase TiO2 nanosheets with a thickness of 2.1 nm and 94.5% exposed (001) facets (TiO2-1) as highly active photocatalysts for photocatalytic lignocellulose-to-H2 conversion. The ultrathin structure of TiO2 not only provides abundant active sites for the photocatalytic H2 production reaction but also benefits photogenerated charge transfer to the surface. Furthermore, as proven by theoretical calculations and fluorescence experiments, the ●OH radicals acting as the key species for the oxidation of lignocelluloses can be easily generated on the (001) facets owing to the low activating energy for the ●OH generation reaction. Notably, the highest photocatalytic H2 generation rates of 275 and 26 μmol·h–1·g–1 were achieved, respectively, in 250 mL of 4g·L–1 α-cellulose solution and poplar wood chip aqueous solution consisting of 100 mg of 1.0% Pt-loaded TiO2-1 photocatalyst, and an apparent quantum yield of 1.89% at 380 nm was achieved in α-cellulose aqueous solution. The photocatalytic H2 production activity of TiO2-1 is about 2.4 and 2.1 times higher than that of reference TiO2 nanosheets (TiO2-2) in α-cellulose solution and poplar wood chip solution, respectively. Our findings demonstrate the feasibility of establishing rapid ●OH generation to boost the oxidation of lignocelluloses and to enhance lignocellulose-to-H2 conversion.