Influence of transition metal-doped titanium(IV) dioxide on the photodegradation of polystyrene

The rate of photodegradation of polystyrene is reduced by adding certain grades of TiO2 such as coated TiO2 particles or TiO2 doped with small percentages of Cr or Mn ions. The rate is increased on adding TiO2 doped with V and especially Mo or W ions. The anatase form of TiO2 is more photoactive than the rutile form, as is the effect of increasing the calcination temperature of the pigment. The concentration dependences of the degradation rates are complex, but can be directly related to the percentage of anatase achieved after calcination. Even the most aggressive of the metal-doped pigments are less photoactive than a Degussa P25 material, containing rutile and anatase.