An acrylate polymerisation initiated by iron doped titanium dioxide

Fe3+ ion doped anatase samples with homogenously distributed Fe3+ ions within the TiO2 particles were prepared using a sol–gel technique followed by a thermal treatment of the resulting powders.The photocatalytic initiation of the polymerisation of an ethoxylated trisacrylate was investigated as a function of the Fe3+ content of TiO2 pigment grains. The polymerisation rate slightly increases with increasing Fe3+ content of the TiO2 in the concentration range from 0.1 to 1 mol% Fe3+. Maximum polymerisation rate rpmax is observed at 1 mol% Fe3+ followed by decreasing rates at increasing Fe3+ contents. A TiO2 sample containing 10 mol% Fe3+ does not show any photocatalytic activity.For the polymerisation the heterogeneous photocatalytic formation of initiating radicals is essential. Thus the results of the photopolymerisation experiments may be explained on the basis of the charge carrier lifetime in the surface/subsurface region and the UV–vis absorption properties of the samples: Photo-EMF investigations reveal that Fe3+ doping decreases the charge carrier lifetime in the surface region of TiO2 from about 23 ms for the undoped material down to about 1.5 ms for samples containing 3 mol% or more Fe3+ indicating a very fast capturing of photochemically produced electrons by Fe3+. For homogeneously distributed Fe3+ contents ranging up to 1 mol% this detrimental effect of Fe3+ doping may be compensated by an improvement of light absorption properties of the TiO2 crystallites in the visible range. At higher Fe3+ concentrations XRD amorphous Fe2O3- or iron-rich TiO2-phases are formed at the grain boundaries. These iron-rich phases act as light filters, so reducing the light absorption by the photocatalytically active TiO2 crystallites. These amorphous phases should not show any photocatalytic activity.