Effect of anodization time on the growth of twinned pyramid crystals of bismite from polyhedral bismuth particle by facile electrolysis-based oxidation

Nanostructured bismite films were fabricated by both thermal oxidation and electrochemical anodization of Bi film in NaOH aqueous electrolyte. Pure phase of -bismite was obtained by the thermal oxidation technique. Pure-phase and bismites were successfully prepared by varying the anodization time. Truncated polyhedral aggregates of bismuth particles were converted to twinned pyramids particles having nanoscale tips with increase in anodization time. The crystallite size increased with anodization time from 43nm to 79nm. The band gap value lowered from 2.835(2) eV to 2.422(1) eV with anodization time and this is in agreement with the increase in crystallite size obtained from XRD. The shift in the absorption edge to higher wavelength with anodization time was attributed to the smoothening of surface and grain growth.