Visible-Light Cr-doped TiO2-XNX Nano Photocatalysts

To use solar or interior light efficiently, we sought a photocatalyst titania with high reactivity under visible light. Titania powders were prepared and doped into chromium or nitrogen atoms via modified sol-gel method. Doped titania have revealed an improvement over pure titania or Degussa P25 photocatalys under visible light(wavelength<550nm) in UV-Vis absorption and photocatalytic activity such as photodegradations of methylene blue and isopropyl alcohol. The rate constants of MB and IPA catalytic reaction with doped titania are 9 and 0.8(μmole/liter-hr-g), which are much higher than those with pure titania, 1.1 and 0(μmole/liter-hr-g), respectively.
Chromium doped into the lattice of titania is responsible for the visible-light response photocatalytic activity because of the isolated narrow bands formed between the valence band and conduction band and lowering the photon energy required to excite the electrons. However excess doped chromium located the interstitial cites in the lattice distorted the original structure and consequently deteriorated the intrinsic photocatalytic activity of titania.
A few amount of nitrogen atoms substituted the lattice oxygen atom and titanium nitride was formed under ammonia-annealing process. Nitrogen doped into substitutional sites of titania has proven to be indispensable for band-gap narrowing and photocatalytic activity. Increasing the nitrogen-doped concentration more than optimum level lowered the quantum yields, indicating the doping sites and oxygen vacancy introduced under the reductive atmosphere could also serve as electron-hole recombination sites.