Preparation of Tantalum-Based Oxynitride Nanosheets by Exfoliation of a Layered Oxynitride, CsCa_2Ta_3O_(10-x)N_y, and Their Photocatalytic Activity

摘要

Calcium tantalum oxynitride [Ca_2Ta_3O_(9.7)N_(0.2)] nanosheets were prepared by exfoliating a layered perovskite oxynitride (CsCa_2Ta_3O_(9.7)N_(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_(9.7)N_(0.2)]~- nanosheets exhibited photocatalytic activity for H_2 evolution from water under visible light irradiation. In contrast, CsCa_2Ta_3O_(9.7)N_(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_(9.7)N_(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.