Bi₁₂TiO₂₀ nanocrystals prepared by electrochemical synthesis exhibit excellent photocatalytic ability under visible light

Although titania (TiO₂) is a good photocatalyst, its use is limited to the ultraviolet range and thus cannot be used in the visible solar light range. Bi₁₂TiO₂₀ has emerged in recent years as a promising alternative that may be used in the visible range. However, current methods to synthesize Bi₁₂TiO₂₀ are not well-suited to prepare ultrafine, well-dispersed, crystalline nanoparticles that are desired for photocatalytic applications. Recent work from the China Building Materials Academy in Beijing has resulted in a new electrochemical route to prepare well-dispersed Bi₁₂TiO₂₀ nanocrystals.

Current solid-state synthesis and wet chemical methods used to prepare Bi₁₂TiO₂₀ require high temperature processing or special equipment that yield large-sized aggregated crystals which are at best sub-optimal for photocatalytic applications. Reporting in the May issue of the Journal of the American Ceramic Society (DOI: 10.1111/j.1551-2916.2011.04505.x; p. 1336), C. Gao, J. Ma, and co-workers prepared Bi₁₂TiO₂₀ nanoparticles by precipitation in an electrolytic solution using Bi and Ti plates as the anode and cathode, respectively. Adjusting the concentration of H₃PO₄ in the electrolyte caused a change in nanoparticle dispersion.

Electron microscopy revealed that a pure body-centered cubic (bcc) phase was formed in the absence of H₃PO₄ where the nanoparticles agglomerate into 2–3 μm spheres. However, increasing the concentration of H₃PO₄ increased the fraction of the face-centered cubic (fcc) phase with a concomitant weakening of the interparticle adhesion resulting in a well-dispersed Bi₁₂TiO₂₀ nanoparticle mixture of bcc and fcc phases.

UV-vis absorption spectra of the prepared samples revealed absorption onset wavelengths exceeding 500 nm, exhibiting good response in the visible light region. The Bi₁₂TiO₂₀ particles also efficiently degraded an RhB dye under visible light facilitated by the high specific surface area of the well-dispersed nanosized particles. Thus, electrochemical synthesis of Bi₁₂TiO₂₀ nanoparticles offers a promising new route to prepare photocatalysts that are responsive to solar light, according to the researchers.