The plasma synthesis, characterization, and photocatalytic activity of WO3, which consisted of a mixture of gamma WO3 and epsilon WO3 (gamma/epsilon-WO3), and physically mixed WO3 and CeO2 (WO3/CeO2) were investigated. Synergistic effects were observed in acetaldehyde photocatalysis experiments using gamma/epsilon-WO3 or WO3/CeO2. The synergistic effect in the gamma/epsilon-WO3 photocatalyst system is proposed to be the concurrent reduction of oxygen at gamma WO3 and oxidation of acetaldehyde at epsilon WO3. It is hypothesized that acetaldehyde preferentially interacts with epsilon WO3 over gamma WO3 because of dipole dipole interactions between them. In the case of the WO3/CeO2 photocatalyst, the electron scavenging property of CeO2 aided charge carrier separation. As a result, WO3/CeO2 exhibited excellent photocatalytic activity in volatile organic compound decomposition under visible light at room temperature. (C) 2017 Elsevier Ltd. All rights reserved.