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

The effects of adding dispersed powders of various forms of titanium(IV) dioxide on the photodegradation of polystyrene have been examined using FT-IR spectroscopy from the following points of view: effect of crystal form, concentration of pigment, transition metal ion, dopant concentration, calcination temperature of pigment, and pigment coating. The rate of photodegradation of polystyrene is reduced by adding certain grades of TiO 2 such as coated TiO 2 particles or TiO 2 doped with small percentages of Cr or Mn ions. The rate is increased on adding TiO 2 doped with V and especially Mo or W ions. The anatase form of TiO 2 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.