Brilliant Yellow, Transparent Pure, and SiO₂-Coated BiVO₄ Nanoparticles Made in Flames

Transparent, yellow bismuth vanadate nanoparticles were made by flame spray pyrolysis. These materials are of special interest as brilliant yellow pigments. The structural properties of the as-prepared powders were characterized by X-ray diffraction, Raman spectroscopy, nitrogen adsorption, transmission electron microscopy, zeta potential measurements, and photospectroscopy. Depending on the particle collection temperature, either pale, amorphous materials or brilliant yellow-green, crystalline BiVO 4 with particle size of about 50 nm were formed by direct calcination above 300 °C. The addition of Si during flame synthesis of BiVO 4 resulted in smaller such crystals of about 20 nm that were embedded in silica. This prevented sintering of the BiVO 4 particles during calcination at 400 °C and resulted in thermally stable, highly transparent, yellow particles.