Synthesis of δ-bismuth oxide stable at room temperature for use in industrial applications

The current research reports an inexpensive and effective method of synthesising δ bismuth oxide stable at room temperature by reacting monoclinic α-Bi₂O₃ and 5.25% sodium hypochlorite at 100 °C. The resultant product was washed, dried and characterized using optical imaging, microstructural analysis by scanning electron microscopy (SEM), thermographic assessment (TGA), X-ray diffraction (XRD), infrared spectroscopy (FT-IR), X-ray absorption fine structure (XAFS) and synchrotron XRD. The interaction with sodium hypochlorite resulted in a change in bismuth oxide microstructure and a colour change from yellow to dark brown/black. TGA showed a change in mass and colour with reversal at ~ 450 °C. Further analysis of bismuth oxide reacted with sodium hypochlorite revealed a stable δ-phase at room temperature with reformation of the α polymorph at 500 °C. The δ-bismuth oxide was modelled to show a defective fluorite structure similar to that proposed by Sillen. The current research is the first to report a cheap and effective method of stabilising the δ phase which is useful for a number of industrial processes such as an oxide ion conductor.