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Mono-dispersed monoclinic bismuth vanadate (m-BiVO 4 ) octahedral single crystals were synthesized by a simple hydrothermal route in the presence of sodium dodecyl benzene sulfonate (SDBS). Electron microscope observation revealed that the synthesized m-BiVO 4 octahedral single crystals were grown with preferentially facets {120} and {021}. The size of these single crystalline octahedra could be facially adjusted in a broad range from 5 mm to less than 200 nm. The influences of additive SDBS, reaction time and acid concentration were studied to understand the formation process, and hence a typical super-saturation process combined Oswald ripening process was proposed. Furthermore, these octahedral single crystals exhibited excellent photocatalytic performance determined by the degradation of rhodamine B (RhB) under visible light irradiation.

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In this paper, g-Bi 2 O 3 , considered as the best photocatalyst among all Bi 2 O 3 polymorphs, was successfully prepared on the surface of m-BiVO 4 octahedral crystals through an alkaline "etching" process. Extensive XRD, SEM and TEM characterization revealed the formation of a p-n junction in the form of m-BiVO 4 @g-Bi 2 O 3 core-shell heterostructure. In addition, the alkaline concentration and reaction time during the etching process were studied and found to be critical parameters in the formation and yield of the Bi 2 O 3 phase. The visible-light photocatalytic activities of these heterogeneous samples with different g-Bi 2 O 3 /m-BiVO 4 phase ratios were evaluated for the degradation of Rhodamine B (RhB). The results indicated that with an optimum amount of g-Bi 2 O 3 on the m-BiVO 4 surface, the powders showed superior photocatalytic performance over pure m-BiVO 4 octahedral crystals. The enhancement mechanisms were discussed based on the specific surface area and g-Bi 2 O 3 shell thickness, as well as the influences of improved charge carrier transfer on the p-n heterostructure.