Photocatalytic transformation of Rhodamine B to Rhodamine-110 – the mechanism revisited

• N-deethylation of Rhodamine B (Rh-B) leads to Rhodamine-110 (Rh-110) formation. • The photocatalytic RhB transformation and degradation are wavelength dependent. • The mechanism of RhB to Rh-110 transformation has been revisited. • The RhB to Rh-110 transformation does not involve reactive oxygen species. • The reaction involves the photoinduced electron transfer between RhB and TiO 2. Understanding of the TiO 2 -assisted phototransformations observed for fundamentally important derivatives of Rhodamine B is expected to bring consistent and eventually comprehensive knowledge on behavior of this dye. The photocatalytic transformations of Rhodamine B in solution irradiated with visible light embrace an N-deethylation process eventually forming Rhodamine-110 rather than degradation of the chromophore. The N-deethylation of Rhodamine B was studied in solution and for the first time in the solid state. In this work, the influence of the wavelength of incident light on the photocatalytic processes involving Rhodamine dyes, is presented. The results indicate that the selection of wavelength is crucial to govern the pathway of RhB degradation. The N-deethylation process does not require reactive oxygen species, as assumed in literature, but the photoinduced electron transfer between the adsorbed RhB molecule and the TiO 2 support, followed by radical transformations of the dye, plays a key role.