Differently modified TiO2 nanotubes were used to achieve a drastic change in the selectivity of a photocatalytic reaction. For the photocatalytic oxidation of toluene, depending on the electronic properties of TiO2 (anatase, rutile, Ru-doped), a strong change in the main reaction product (namely benzoic acid versus benzaldehyde) can be achieved, and certain undesired reaction pathways can be completely shut down.