Thickness-dependent carrier separation in Bi2Fe4O9 nanoplates with enhanced photocatalytic water oxidation

Herein, Bi2Fe4O9 nanoplates (BFO NPs) with controllable thickness are successfully synthesized via a facile hydrothermal method with varied content of sodium dodecyl benzene sulfonate (SDBS). The thickness along the [001] direction of the BFO NPs can be controlled by varying the SDBS content, and the decreased thickness plays multiple roles in improving the photocatalytic water oxidation performance: (1) increasing the distortion and asymmetries of the FeO4 tetrahedral and FeO6 octahedral units, and enhancing the built-in electric field in the BFO NPs accordingly, to facilitate the efficient separation of photogenerated electron-hole pairs; (2) reducing the migration distance of holes to the surface of the both oxygen- and bismuth-enriched {001} facets; (3) promoting the exposure of {001} facets of the BFO NPs which facilitates hole accumulation and provides more active sites to accelerate surface oxidation reaction. As a result, the as-prepared BFO-2 sample with optimized thickness exhibits the best photocatalytic water oxidation performance under visible-light irradiation, achieving the O2 evolution rate of 461.08 µmol g−1 h−1, about 7.87 times higher than BFO NPs prepared without using SDBS. The built-in electric field for BFO and its role in photocatalytic water oxidation process are reported for the first time. This work provides new insights into improving intrinsic activity of individual semiconductor photocatalyst by morphology and structure modulation and charge behavior regulation.