BiVO₄ hollow nanospheres: Anchoring synthesis, growth mechanism, and their application in photocatalysis

An anchoring method was developed to synthesize monoclinic BiVO₄ (m-BiVO₄) hollow spheres with a size of about 700 nm by employing colloidal carbon spheres (CCSs) as hard templates. The influence of synthesis conditions and the growth mechanism were investigated with XRD, TEM, and SEM through a series of comparison experiments. It was found that two-stage heat treatment was essential for the synthesis of BiVO₄ hollow nanospheres. The Bi³⁺ ions were firstly adsorbed on the surface of the CCSs and worked as anchors in the first stage (80 °C). In the second stage (100 °C), the VO₃^- ions reacted with the anchored Bi³⁺ ions, and amorphous BiVO₄ nanoparticles were thus precipitated on the CCSs surface. The analysis on the calcination process revealed that calcination promoted the crystallization of amorphous BiVO ₄ into In-BiVO₄ crystals at 236 °C and removed the CCSs at 353 °C. The as-prepared BiVO₄ hollow nanospheres exhibited higher photocatalytic activity than BiVO₄ prepared by the aqueous method and by a solid-state reaction in the degradation of rhodamine B and acetaldehyde, which could be attributed to their higher BET surface area (5.85 m²g^-1) and larger band gap (2.36 eV). Given the general adsorption of metal ions on the CCSs surface, this anchoring method could be extended to synthesize other hollow-structured multicomponent oxides.