The Research Of Niobate By Modification And Its Photocatalytic Properties

With the research of solar energy, photocatalytic technology have received lardge attention as an extremely versatile material. Due to its unique highly ordered array structure, good mechanical and chemical stability, which is widely applied in environmental purification, photolysis water and gas sensor. The photocatalytic oxidation of harmful organic compounds by using semiconductors is becoming a promising treatment strategy nowadays. However, most of the semiconductor photocatalysts have a wide band-gap energy, which limit their efficient utilization of sunlight and more practical applications. So, the developing of visible-light sensitivity is one of the most important objectives in the field of material science research. As an important photocatalytic material, perovskite niobate showed great catalytic activity in water photolysis and degradation of organic pollutants.In this thesis, the low cost Nb₂O₅ as Nb source, we investigated the synthesis of perovskite AgNbO₃ and NaNbO₃ in the mild hydrothermal conditions, systematically. Then we used some methods by modifying two niobate modification to improve their activity. The major research work are summarized as follows:With a mild hydrothermal synthesis of AgNbO₃ substrate, a new visible-light-driven plasmonic photocatalyst Ag@AgCl/AgNbO₃ is prepared via loading with Ag@AgCl nanoparticles by an impregnating precipitation photoreduction method. The experimental results showed that the degradation rate for MB of AgNbO₃（AgNO₃ concentrations was 0） catalyst was only 20.2%. We can see that when concentration of AgNO₃ was 1.5 M, the photocatalytic effect was optimum, and the degradation rate of 2 h reached to 56.9%. Compared with the AgNbO₃ on the degradation rate of MB, it increased by 36.7%. After the loading Ag@AgCl nanoparticles on the surface of AgNbO₃, the optical response of the photocatalyst was extended, which was due to the SPR effect. The photocatalytic activity of the Ag@AgCl/ AgNbO₃ composite was increased observably with the increasing AgNO₃ content. The photocatalytic activity decreased when AgNO₃ concentration was over 1.5 M. Mainly because large amounts of Ag@AgCl were loaded on the part of active center of AgNbO₃, which reduces the reactive group in the solution and decreases photocatalytic performance.While the preparation of AgNbO₃ is relatively expensive, we have put the above modification methods applied in the NaNbO₃. An efficient and stable visible-light-driven photocatalyst Ag@AgCl/NaNbO₃ is synthesized via depositing Ag@AgCl nanoparticles on the surface of NaNbO₃, and NaNbO₃ is prepared by the hydrothermal method. The experimental results show that the photocatalytic efficiency increased with AgNO₃ loading up to 1.5 M. After that, the photocatalytic activity was decreased with continuously increasing the content of AgNO₃. We can see that when concentration of AgNO₃ was 1.5 M, the photocatalytic effect was optimum, and the degradation rate of 2 h reached to 87.5%. It increased by 78.0% compared with the NaNbO₃ on the degradation rate of MB. Compared with the Ag@AgCl/AgNbO₃, we prepared Ag@AgCl/NaNbO₃ have lower cost and higher catalytic activity.In order to improve the photocatalytic activity of NaNbO₃, we modify the photocatalytic activity of the composite semiconductor photocatalyst. The Ag₃PO₄/NaNbO₃ composite photocatalyst was successfully prepared by a facile hydrothermal method with an in situ precipitation route. The experimental results show that the composite Ag₃PO₄/NaNbO₃ catalyst with molar ratio 4:1 exhibited the highest degradation efficiency. The degradation rate of half an hour reached to 92.4 %.