Solvothermal Synthesis And Performance Of Tantalate Photocatalysts

A series of tantalate photocatalysts were successfully synthesized via solvothermal method. X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM) and Uv-vis diffuse reflectance spectra (UV-DRS) were used to characterize the morphology and structure of samples, and the photocatalitic performance of the tantalates was also studied by decomposing safranine T solution under UV light.The main results are as follows:(1) Nanosize NaTaO₃ photocatalysts have been synthesized by a single-step hydrothermal method. The influence of reaction temperature and time, as well as alkaline concentration, on the structure and photocatalysis was investigated. The results showed that pure-phase NaTaO₃ could be synthesized in a 0.75 mol/L NaOH at 140°C for 12 h. This process was dominated by a dissolution/precipitation mechanism, in which the growth mechanism of the NaTaO₃ nanoparticles was also discussed based on its crystal structure. The NaTaO₃ nanostructures show a higher photocatalytic activity in the degradation of safranine T dye due to their perfective crystallinity and larger surface areas.(2) NaTaO₃ photocatalysts were modified by loading NiO on surface and doping with La3+. Photocatalytic performance evaluation results show the photogenerated electrons in the conduction band of the NaTaO₃ photocatalyst are able to transfer to the conduction band of a NiO cocatalyst which is an active site for hydrogen evolution and enhances charge separation. Therefore, NiO-loading was effective for the NaTaO₃ photocatalyst even without special pretreatment.(3) Ethanol-water and hexane-water mixed solvents were employed in the solvothermal synthesis of pyrochlore and perovskite KTaO₃ powders. The mixed solvents played a significant role in the phase transformation of KTaO₃ products by easily changing the ratio of the solvents, even with the same quantity of starting materials and in the same reaction conditions. In the ethanol-water system, the real activity of hydroxyl ions in the solution can be controlled easily by changing the ratio of the solvents. While in the hexane-water system, there are two phases and the KOH concentration in the water phase, which can act as a lot of tiny reactors in the solution, is corresponding to the solvents'ratio, too. This way also can be used in the synthesis of some other important substances, such as niobates, titanate, and so on. The photocatalytic results show that the pyrochlore KTaO₃ has high reactivity.