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

• K1.6Ca2Nb3O9.4N0.6·1.1H2O oxynitride was synthesized by ammonolysis of KCa2Nb3O10.
• The oxynitride showed good stability even after a long time of exposure to air.
• The material was protonated and exfoliated into nanosheets with good cristallinity.
• These nanosheets are potential building blocks to new nanostructured materials.
• The band gap makes these materials promising photocatalysts with visible radiation.

A new oxynitride Ruddlesden-Popper phase K1.6Ca2Nb3O9.4N0.6.1.1H2O was synthesized by the topochemical ammonolysis reaction at 700 °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) Å and c = 17.90(8) Å for the most hydrated phase and a = 3.927(6) Å and c = 17.09(2) Å 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.

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