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

The synthesis of nanoscaled β-Bi(2)O(3) starting from the bismuth oxido clusters [Bi(6)O(4)(OH)(4)](NO(3))(6)·H(2)O, [Bi(22)O(26)(OSiMe(2)(t)Bu)(14)], [Bi(38)O(45)(NO(3))(20)(DMSO)(28)](NO(3))(4)·4DMSO and [Bi(38)O(45)(OMc)(24)(DMSO)(9)]·2DMSO·7H(2)O (OMc = O(2)CC(3)H(5)) under ambient conditions is reported. The metal oxido clusters are regarded as ideal precursors for β-Bi(2)O(3) 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 α-Bi(2)O(3) whereas after 3 min an amorphous material is observed. Annealing of the amorphous material at 370 °C gave nanoscaled β-Bi(2)O(3). An unusual high reactivity of the β-Bi(2)O(3) particles with SiO(2) and Al(2)O(3) is observed at temperatures above 400 °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 β-Bi(2)O(3) nanoparticles. The properties of the β-Bi(2)O(3) nanoparticles depend on the starting bismuth oxido clusters with regard to particle size and optical band gap. The β-Bi(2)O(3) nanoparticles show excellent photocatalytic activity as demonstrated by dye decomposition (rhodamine B, methyl orange, methylene blue and orange G) under visible light.