The sensitization of a semiconductor-based oxidoreduction photocatalyst is carried out by fixing at its surface a colour carrier comprised of a fragment of a transition metal complex such as ruthenium, chromium or iron and of a ligand of the bipyridyl or phenanthrolyl type. The fixing of such a colour carrier results in the displacement of the light absorption band of the photocatalyst towards the visible light. Utilisation of such a catalyst for the photooxidation of aqueous liquids or organic aqueous liquids or for the photodecomposition of aqueous liquids in visible light.