Photocatalysis of sprayed nitrogen-containing Fe2O3–ZnO and WO3–ZnO composite powders in gas-phase acetaldehyde decomposition

Two series of nano-sized N-containing MOx–ZnO (M: Fe, W) composite powders were synthesized by spray pyrolysis. The nitrogen content was controlled from 500 to 2100 ppm by changing the powder ingredients and spray pyrolysis temperature. Ultraviolet-visible (UV-Vis) spectra indicated that the N-containing MOx–ZnO powders absorbed not only ultraviolet light (λ<387 nm) like pure ZnO powder, but also part of visible light (λ<650 nm). Acetaldehyde decomposition was used as a probe reaction to evaluate the photocatalysis of these composite powders. The photocatalytic activity of the N-containing ZnO powder was pronouncedly enhanced by the WO3 addition under both UV and visible-light irradiation. However, that of the N-containing ZnO powder was suppressed by the Fe2O3 addition. A model of the semiconductor energy-band structure is proposed to explain the enhancement and suppression of photocatalytic activity.