Preparation of tantalum-based oxynitride nanosheets by exfoliation of a layered oxynitride, CsCa ₂Ta ₃O _10-xN _y, and their photocatalytic activity

Calcium tantalum oxynitride [Ca ₂Ta ₃O _9.7N _0.2] ^- nanosheets were prepared by exfoliating a layered perovskite oxynitride (CsCa ₂Ta ₃O _9.7N _0.2) via proton exchange and two-step intercalation of ethylamine and tetrabutylammonium ions. Monolayer nanosheet was prepared by the above processes, although some bilayer or trilayer nanosheets were also produced. The [Ca ₂Ta ₃O _9.7N _0.2] ^- nanosheets exhibited photocatalytic activity for H ₂ evolution from water under visible light irradiation. In contrast, CsCa ₂Ta ₃O _9.7N _0.2 exhibited very low photocatalytic activity for H ₂ evolution under the visible light irradiation, even when methanol was added to water as a sacrificial agent. The improved photocatalytic activity originates from the characteristics of nanosheets such as their molecular thickness and large surface area. Further, the Rh-loaded [Ca ₂Ta ₃O _9.7N _0.2] ^- nanosheets restacked with protons exhibited photocatalytic activity for H ₂ and O ₂ evolution from pure water under UV-light irradiation. The ratio of H ₂/O ₂ evolved was around 3. The ratio of N/O in the catalyst remained the same after the photocatalytic reaction, signifying that there was no decomposition of the catalyst during the reaction. This indicates that the present N-doped nanosheet is stable in the photocatalytic reaction.