(545e) Synthesis and Characterization of Nitrogen-Dope Sr4Nb2O9 by Mechanochemical Method

Perovskite-type oxynitride often exhibit intense colors and have potential for applications such as visible light driven photocatalyst. Conventionally, these oxynitride have been synthesized by the direct nitridation method which require very severe reaction conditions such as high temperature (900-1100℃) under ammonia flow for long time (e.g., 10 h). Nitrogen-doped Sr₄Nb₂O₉ is one of them_, and Wu et al. reported its high oxygen generation efficiency for water splitting under visible light irradiation.

Therefore, in this study, we attempted to develop a more safer and simple synthesis method of perovskite type oxynitride such as nitrogen-doped Sr₄Nb₂O₉ by using the mechanochemical method. under various conditions and evaluated characteristics of the resulting samples. The mechanochemical method does not need to treat sample under ammonia high temperature under ammonia flow for long time to dope nitrogen, and instead, solid materials such as CO(NH₂)₂ can be utilized as nitrogen sources.

At first, Sr₄Nb₂O₉ was synthesized by a solid-state reaction method using SrCO₃ and Nb₂O₅ as raw materials at 1000℃ for 9 h in air. Then, nitrogen-doped Sr₄Nb₂O₉ was synthesized by the mechanochemical treatment. In the experiment, a planetary ball mill (Frisch, P-7) was used to grind Sr₄Nb₂O₉ and CO(NH₂)₂ (15wt%) at a speed of 700 rpm for 180 min and then the obtained samples were heated at 400℃ in air for 1 h to remove the unreacted CO(NH₂)₂. In order to determine the crystalline structure of the obtained sample, the X-ray diffraction pattern was measured. The result showed that the structures of both before and after the mechanochemical treated samples were Sr₄Nb₂O_9, however, the peak of the mechanochemical treated sampleshifted to a higher angle by 0.1°than the original_. In addition, the absorption spectrum was shifted to the visible light region. These results demonstrated that nitrogen-doped Sr₄Nb₂O₉ was successfully synthesized by using the mechanochemical method with much safer reaction condition than the conventional method.