Bi2WO6 with different Bi3+ ion concentrations (0-30 mol%) is incorporated with the ZnWO4 photocatalyst to improve the photocatalytic efficiency by forming a ZnWO4/Bi2WO6 composite photocatalyst with hierarchical heterostructure via a one-step hydrothermal method. X-ray diffraction and Raman spectroscopy analyses confirm the presence of ZnWO4 and Bi2WO6 as main phases in the composite photocatalyst. Scanning electron microscopy and transmission electron microscopy observations reveal that the rice- and plate-like Bi2WO6 nanoparticles were either separate or attached to the surface of quasi-spherical ZnWO4 particles. A gradual increase in the Bi2WO6 content of the composite photocatalyst results in a monotonic shift of the absorption edge from ca. 355 nm to longer wavelengths up to ca. 450 nm. The photocatalytic performance of the ZnWO4/Bi2WO6 composite photocatalyst was evaluated by investigating the degradation of gaseous acetaldehyde (AcH) under UV light irradiation. Only the composite photocatalyst synthesized with 30 mol% Bi3+ exhibits higher photo catalytic activity under UV light irradiation compared with both individual ZnWO4 and Bi2WO6, and with a mechanically mixed ZnWO4/Bi2WO6 composite photocatalyst. The enhanced photocatalytic activity is attributed to the n-n isotype junction formed between the two semiconductors and the charge separation of each semiconductor. (c) 2013 Elsevier B.V. All rights reserved.