Improvement of photocatalytic activity of tantalum nitride by ammonothermal treatment at high pressure

Morphological change and enhanced photocatalytic activity of tantalum nitride (Ta₃N₅) by ammonothermal treatment with mineralizer

“…However, for the samples treated above 823 K, the intensity of absorption in the longer wavelength region increased due to the presence of reduced Ta species 18) at higher treatment temperatures. Similar increases in the absorption intensity of Ta 3 N 5 have been previously observed following ammonothermal post-treatment at 823 K 24) and highpressure N 2 post-treatment above 873 K, 29) suggesting that Ta 3 N 5 partially decomposes even under high-pressure conditions. Therefore, on the basis of the results of the UVvis DRS analysis, it was concluded that Ta 3 N 5 is partially decomposed during the ammonothermal post-treatment with NaI above 823 K. Figure 5 shows the dependence of photocatalytic activity for hydrogen evolution of the Ta 3 N 5 samples ammonothermally posttreated with NaI on treatment temperature.…”

“…We previously reported that after ammonothermal post-treatment without mineralizers, the crystallite size of Ta 3 N 5 remains nearly unchanged. 24) By contrast, as can be seen in Fig. 2, ammonothermal post-treatment with NaI monotonically increased the crystallite size of Ta 3 N 5 with the treatment temperature.…”

“…All of post-treated Ta 3 N 5 showed increased hydrogen evolution activity in comparison with as-prepared Ta 3 N 5 . As in the case without mineralizers, 24) this increase in photocatalytic activity may result from decrease in surface defects by exposure to high-pressure ammonia and the accompanying improvement in electron transfer from the surface of Ta 3 N 5 to the loaded Pt co-catalyst. The hydrogen evolution activity initially increased with the treatment temperature, reaching a maximum value at 823 K, and then decreased above 873 K. Although the Ta 3 N 5 samples treated above 873 K showed obvious changes in their morphologies, as observed in the SEM images [ Figs. 3(e) and 3(f )], the photocatalytic activity were lower than that of the samples treated at 823 K, which did not experience a morphology change.…”

“…In contrast, heat treatment under high-pressure ammonia, i.e., ammonothermal treatment, has been reported only as a post-treatment method for enhancing the photocatalytic activity of Ta 3 N 5 without altering the crystallinity, morphology, and specific surface area. 23), 24) The ammonothermal method uses ammonia instead of water, similar to that in the hydrothermal method, thus providing the advantages that the hydrothermal method offers in oxide preparation to nitride synthesis. That is, using a suitable mineralizer, the ammonothermal treatment can change the morphology of nitrides as effectively as hydrothermal treatment of TiO 2 with NaOH.…”

Low-temperature synthesis of BaTaO₂N by an ammonothermal method

“…Moreover, the method is applied to a post-treatment of Ta 3 N 5 photocatalyst, enhancing the photo-catalytic activity by improving the surface characteristics of its particles. 16) To the best of our knowledge, only few studies have successfully synthesized multinary oxynitride materials using an ammonothermal method. Herein, we report the first synthetic approach for obtaining highly crystalline BaTaO 2 N by an ammonothermal method.…”