The degradation of methylene blue was chosen as the test reaction for the photocatalytic activity because the reaction is very simple and allows a quick initial statement about the photocatalytic activity of the coated plates. Figure shows the degradation rate of methylene blue achieved with the different coatings. It is clear that the samples with the TTIP-derived photocatalytic layer perform much better than the ones derived from P25 particles. In the latter case, the degradation rate constant was only 0.015 mM min -1 and even declined further with laser-annealing and additional coating steps. The plates that have been coated with P25 are very unstable. Each time the laser was used, a small part of the coated layer flaked off, which is why the degradation rate of methylene blue decreases. On the contrary, the TTIP-derived coatings showed a much higher degradation rate constant of 0.033 mM min -1 even after a single coating step without annealing. Laser annealing increased this by 27% to 0.042 mM min -1 . A second and third subsequent coating step further increased the degradation rate constant to 0.064 and 0.072 mM min -1 , respectively.