UV and visible light acrylate photopolymerisation initiated by nitrogen- or carbon-doped titanium dioxide

Nitrogen and carbon doped titania powders initiate acrylate polymerisation upon UV excitation. Time resolved photovoltage measurements afford surface charge carrier lifetimes of 7-8 ms for undoped and N-doped titania, whereas 12 ms are observed for the C-doped semiconductor. These values correlate with the observation that the polymerisation rate constants are similar for titania or N-doped titania but about two times larger for the C-doped material. Wavelength dependent polymerisation experiments indicate that visible light polymerisation is possible only with carbon-doped titania. This suggests that hole relaxation to dopant-centered surface states is much more efficient in nitrogen-doped titania. These experimental findings are in accord with the assumption that polymerisation is initiated by hole oxidation of the acrylate.