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.
