The wide bandgap layered perovskites A5M4O15 (A = Ba, Sr; M = Ta, Nb) are shown do be very active in photocatalytic water splitting under UV-light, resulting from the additional reaction sites in the crystal structure.[1] The activity can be improved either by the formation of heterojunctions such as Ba5Ta4O15-Ba3Ta5O15 or Ba5Ta4O15-Ba3Ta5O15-BaTa2O6.[2,3] Preparation of nanofibers can additionally solve the problem of the large mismatch between the small charge carrier diffusion length and the much larger light penetration depth, resulting in higher photocatalytic activity.[4,5] Visible light activity can be gained by the formation of heterojunctions such as Ba5Ta4O15-AgVO3[6] and Ba5Ta4O15-C3N4[7] and via ammonolysis[8].

We are combining the positive effects of the nanofiber structure and the ammonolysis by preparing (111) layered perovskites nanofibers of Ba5Ta4O15 and Ba5Nb4O15 and converting them into perovskite oxynitrides (Figure 1).

The samples were characterized with XRD and the conversion degree was determined. SEM characterization was performed, and Kr physisorption measurements were done to determine the BET surface area before and after ammonolysis. UV-Vis spectroscopy as well as hydrogen evolution measurements in water/methanol were performed.
In first experiments, conversion degrees of nearly 100% were obtained, yielding in a decrease of the band from 4.0 eV down to 2.0 eV for the niobium compound and from 4.6 eV down to 1.9 eV for the tantalum compound; giving visible light absorption abilities. The surface area is slightly increased. Morphology changes will be discussed in detail.