Nanosized N-containing MOx-ZnO (M = W, V, Fe) composite powders were synthesized by spray pyrolysis. These powders were orange in color and absorbed not only ultraviolet light (lambda < 387 nm) like pure ZnO powder did, but also part of the visible-light spectrum (lambda < 650 nm). The nitrogen content was varied from 500 to 2600 ppm by changing the powder ingredients and spray pyrolysis temperature. The visible-light photocatalytic activity of the N-containing ZnO powder for acetaldehyde decomposition was pronouncedly enhanced by adding WO3 or V2O5. However, it was suppressed by adding Fe2O3. A model for the semiconductor energy-band structure was proposed to explain the enhancement and suppression of photocatalytic activity. The potential application of these sprayed powders to air purification was also investigated by simulating a commercial air cleaner system. (C) 2004 Elsevier B.V. All rights reserved.