Uncovering the structural stabilities of the functional bismuth containing oxides: a case study of α-Bi2O3nanoparticles in aqueous solutions

Abstract

The majority of bismuth containing oxides have been taken as important functional materials for applications including photocatalytic water splitting and highly conductive solid electrolytes, which however suffer from property degradation owing to the presence of intermediates. This work initiated a case study on α-Bi₂O₃ nanoparticles with an aim to uncover the origin of property degradation when bismuth oxides that contain traces of secondary phase α-Bi₂O₃ were exposed in either air or aqueous solutions. First, α-Bi₂O₃ nanoparticles with spherical and rod-like morphologies were prepared by developing solution chemistries. It was found that α-Bi₂O₃ transformed partially to Bi₂O₂CO₃ when stored in air for 6 months. Such transformation was further accelerated when α-Bi₂O₃ nanoparticles were exposed to water or methylene blue (MB) solution, probably because α-Bi₂O₃ reacts with the species HCO₃⁻ as formed by dissolution of CO₂ from air. Bi₂O₃ surfaces had an unusual tendency to adsorb MB molecules, which in turn prevented the reaction between α-Bi₂O₃ and HCO₃⁻. Consequently, MB solution became clear even without light irradiation. The results reported in this work may help to fully comprehend the property degradation of bismuth containing oxides when used in aqueous solutions.