Tuning IntrinsicElectronic Properties via Size-ControlledHydrothermal Crystalline Transformation from Tetragonal BiVO₄ Spheroids to Monoclinic Plates

This study reports the synthesis of monoclinic clinobisvanite BiVO₄ crystals with well-defined {010} and {110} facets and nanometer sizes through controlled reactant addition and hydrothermal treatment. By adjustment of the Bi³⁺ precursor addition rate, nanoplates with significantly reduced edge length and thickness were obtained compared to conventional microplates. The formation process involves the nucleation of surfactant-coated tetragonal zircon BiVO₄ nanocrystals, which aggregate into spheroids before being transformed into monoclinic clinobisvanite plates. A proposed model explains this size-tuning mechanism through partial dissolution, phase transformation, and facet-selective growth. Reducing the size of tetragonal zircon BiVO₄ spheroids enhanced photocatalytic water oxidation, while for monoclinic clinobisvanite BiVO₄ plates, size reduction had the opposite effect. Photoelectrochemical analysis revealed a shift from n-type behavior in microplates to p-type behavior in nanoplates under negative bias. These findings highlight the need to integrate size control with surface chemistry, bulk doping, and defect engineering to optimize BiVO₄ for catalytic and electronic applications.