Hydrothermal synthesis of potassium niobate photocatalysts under subcritical and supercritical water conditions

Hydrothermal synthesis of potassium niobate powders was carried out under various subcritical and supercritical water conditions using crystalline Nb2O5 powder as a starting material. A single phase of K4Nb6O17 was formed under subcritical water conditions, while mixed phases of K4Nb6O17 and KNbO3 were obtained under supercritical water conditions where KNbO3 was predominant over K4Nb6O17 as the heating duration was increased. Characterization of these hydrothermally synthesized potassium niobates by XRD, SEM, and TG-DTA analyses revealed that fine hydrated powders can be obtained under subcritical and supercritical water conditions. The hydrothermally synthesized potassium niobate powders were used for photocatalytic hydrogen evolution from water decomposition. The crystallinity is responsible for the high photocatalytic performance of the hydrothermally synthesized potassium niobate powders. The maximal hydrogen evolution rate was achieved for the potassium niobate hydrothermally synthesized at 400 degreesC for 4 hours. Besides, the hydrogen evolution rate was enhanced more than 10-fold by Ni loading for the hydrothermally synthesized potassium niobate powder which was much higher in comparison with the Ni loaded solid-state synthesized photocatalyst.