Metastable β-Bi2O3 nanoparticles with high photocatalytic activity from polynuclear bismuth oxido clusters

The synthesis of nanoscaled beta-Bi2O3 starting from the bismuth oxido clusters [Bi6O4(OH)(4)](NO3)(6)center dot H2O, [Bi22O26((OSiMe2Bu)-Bu-t)(14)], [Bi38O45(NO3)(20)(DMSO)(28)](NO3)(4)center dot 4DMSO and [Bi38O45(OMc)(24)(DMSO)(9)]center dot 2DMSO center dot 7H(2)O (OMc = O2CC3H5) under ambient conditions is reported. The metal oxido clusters are regarded as ideal precursors for beta-Bi2O3 due to their structural relationship with the latter. Nevertheless, different bismuth oxide polymorphs are accessible dependent on the hydrolysis protocol. Hydrolysis over a period of 18 h gave stable alpha-Bi2O3 whereas after 3 min an amorphous material is observed. Annealing of the amorphous material at 370 degrees C gave nanoscaled beta-Bi2O3. An unusual high reactivity of the beta-Bi2O3 particles with SiO2 and Al2O3 is observed at temperatures above 400 degrees C. Powder X-ray diffraction studies, transmission electron microscopy, diffuse reflectance UV/Vis spectroscopy and nitrogen adsorption measurements are used for characterization of the as-prepared beta-Bi2O3 nanoparticles. The properties of the beta-Bi2O3 nanoparticles depend on the starting bismuth oxido clusters with regard to particle size and optical band gap. The beta-Bi2O3 nanoparticles show excellent photocatalytic activity as demonstrated by dye decomposition (rhodamine B, methyl orange, methylene blue and orange G) under visible light.