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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-Bi2O3nanoparticles with an aim to uncover the origin of property degradation when bismuth oxides that contain traces of secondary phase α-Bi2O3were exposed in either air or aqueous solutions. First, α-Bi2O3nanoparticles with spherical and rod-like morphologies were prepared by developing solution chemistries. It was found that α-Bi2O3transformed partially to Bi2O2CO3when stored in air for 6 months. Such transformation was further accelerated when α-Bi2O3nanoparticles were exposed to water or methylene blue (MB) solution, probably because α-Bi2O3reacts with the species HCO3−as formed by dissolution of CO2from air. Bi2O3surfaces had an unusual tendency to adsorb MB molecules, which in turn prevented the reaction between α-Bi2O3and 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. [ABSTRACT FROM AUTHOR]