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

In this study, we succeeded, for the first time, in changing the particle morphology of a transition metal nitride using ammonothermal post-treatment with a mineralizer. Tantalum (V) nitride (Ta3N5) was post-treated using NaI as a mineralizer under ammonothermal conditions with an ammonia pressure of 100 MPa at 673–973 K for 24 h. Post-treatment above 873 K changed the particle morphology of Ta3N5 markedly; the particle size was reduced, the crystallite size was increased, and the specific surface area was decreased compared to the as-prepared Ta3N5, suggesting the dissolution of particle surface during post-treatment. In addition, all treated Ta3N5 samples showed enhanced photocatalytic activity for hydrogen evolution from an aqueous methanol solution under visible light irradiation compared to untreated Ta3N5. However, the hydrogen evolution activity for the samples post-treated above 873 K was less than that of the samples post-treated at lower temperatures due to the increase in lattice defects in Ta3N5 resulting from thermal decomposition.