Tuning Intrinsic Electronic Properties via Size-Controlled Hydrothermal 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.