The dc thermal plasma synthesis of ZnO nanoparticles for visible-light photocatalyst

It is known that ZnO is an n-typed semiconductor with band-gap energy of ∼3.2 eV and thus only absorbs UV light with the wavelength ≤385 nm. However, as far as photocatalytic efficiency and practical applications are concerned, it is desirable that ZnO absorbs not only UV but also visible light. In the present study, a novel dc thermal plasma reactor was used to synthesize ZnO nano-particles. We found that the kind of plasma affects the nanoparticle morphology and N2 plasma favors formation of the spherical nanoparticles. Visible light absorption of the ZnO nano-particles was achieved by doping up to a few thousands ppm of nitrogen into the material. The effect of doping concentration and particle morphology on photocatalytic characteristics of the ZnO nanoparticles will be described.