Efficient Use of a Polyamine Carboxylate Ligand to Probe the Extent of Incorporation of Stereochemically Active Bi3+ in ThO2

Realizing the advantages of atomic level mixing, high homogeneity precise stoichiometric control and low processing temperatures, co-precipitation route employing the polyamine carboxylate, ethylenediamine tetra acetic acid (EDTA) has been followed to determine the extent of dissolution of bismuth in ThO2 adopting fluorite structure. While the precursors containing varying amounts of Th4+ and Bi3+ were X-ray amorphous, calcining them at 800 degrees C for 6 h yielded crystalline oxides with fluorite structure till Th0.40Bi0.60O2-delta. This was supported by Raman spectral measurements in which defect band due to oxygen vacancies was present at around 590 cm(-1) in addition to the band due to fluorite at around 460 cm(-1). An increasing trend of cubic lattice constant with progressive substitution of bismuth in ThO2 was observed. The direct band gap was found to decrease with increase in bismuth content and was lying in the range of 2.54-3.62 eV. Porous morphology of the samples was evident in their scanning electron microscopic images and they were macro porous as determined from surface area analysis measurements. Th0.50Bi0.50O2-delta was found to efficiently catalyze the reduction of some nitroaromatics for nearly six cycles.