Characterisation of Bismuth Oxide via Precipitation Method

A systematic study was carried out in order to investigate the effect of bismuth concentration, precipitating agent concentration, and type of precipitating agent on the microstructural properties of Bi2O3. The formation and properties of the precursors and Bi2O3 were monitored by X-ray powder diffraction (XRD), FTIR spectroscopy, scanning electron microscopy (SEM) and temperature programmed reduction of hydrogen (H2-TPR). Monoclinic β-phase Bi2O3 was precipitated as a single phase in high purity form directly from synthetic route. Upon heat treatment, the morphology shows non-agglomerated small needles in size between 10.8 and 30.5 µm. This was obtained when using NaOH as precipitating agent. Whereas, tetragonal β-phase Bi2O3 was obtained when using NH3 solution as precipitating agent. Nevertheless, this was only successful when using low concentration of bismuth, i.e. 0.1 M, because above that β-phase transformed into β-phase. Metastable β-phase was achieved through multiphase precursors, which upon calcinations at 723 K managed to eliminate all of the unwanted species. From SEM images β-phase Bi2O3 was revealed as plate like particles organised into rosette clusters. The surface area measurement indicated that NH3 solution series of samples give higher value than NaOH series of samples. These values which in accordance to the materials particle size that have an influence on reduction activity. Higher reducing reactivity was displayed by NH3 solution samples due to smaller particle size which activity as an induction factor. Total amount of oxygen removed are about the same in all samples with more than a monolayer oxygen has been removed. Thus, with high reduction activity suggested that the oxygen may originate from sublattice or lattice of the oxide.

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