Preparation of niobium based oxynitride nanosheets by exfoliation of Ruddlesden-Popper phase precursor

A new oxynitride Ruddlesden-Popper phase K1.6Ca2Nb3O9.4N0.6.1.1H(2)O was synthesized by the topochemical ammonolysis reaction at 700 degrees C from the oxide Dion-Jacobson phase KCa2Nb3O10 in the presence of K2CO3. The oxynitride showed good stability with a little loss of nitrogen, even after a few months of exposure to air. Its crystal structure was solved by Rietveld refinement of X-ray powder diffraction data in space group P4/mmm and considering a two-phase mixture, due to the difference in the degree of hydration, with a = 3.894(2) angstrom and c = 17.90(8) angstrom for the most hydrated phase and a = 3.927(6) angstrom and c = 17.09(2) angstrom for the less one. Optical band gaps were measured by diffuse reflectance in the UV-Visible range indicating a red shift of Eg to the visible region. The oxynitride layered perovskite was then protonated and exfoliated into nanosheets. TEM images and SAED patterns of the nanosheets proved that exfoliation was successful, showing lattice parameters quite compatible with the Rietveld refinement. (C) 2015 Elsevier Masson SAS. All rights reserved.