In order to develop low-cost photocatalyst, commercial Bi2O3 was utilized as raw material to prepare alpha-Bi2O3/BiOCI core-shell heterojunction via a facile in situ chemical transformation method. To clarify experimentally the band alignment relationships between the alpha-Bi2O3 and BiOCl (0 0 1), the alpha-Bi2O3/BiOCI (0 0 1) core-shell heterojunction band offsets were analyzed by X-ray photoelectron spectroscopy (XPS). Here based on energy gaps, valence band values of alpha-Bi2O3 and BiOCI (0 0 1), core levels difference of Bi 4f in alpha-Bi2O3/BiOCI (0 0 1) heterojunction, we demonstrate that band alignment of 0.28 eV exists between alpha-Bi2O3 and BiOCl with cx-Bi2O3 possessing the higher valence band potential or electron affinity which is a driving force of valence band holes from alpha-Bi2O3 to BiOCI (0 0 1). While, the electrons in conduction band were driven to migrate through conduction band potential difference (0.49 eV) from BiOC1 (0 0 1) to alpha-Bi2O3. (C) 2015 Elsevier B.V. All rights reserved.