Hydrothermal Synthesis And Photocatalytic Properties Of Stannate Nano Materials

In the 21th century, environment and energy are the considerably serious problems for human beings. Therefore, photocatalytic materials and the development of related technology have gradually become one of the most hot spots of science investigated fields. Recently, in order to resolve this problem, a large number of new type photocatalytic nano-materials have been explored. Although the photocatalytic materials have good activities, their preparation methods or synthesis conditions are rather harsh. Therefore, how to improve these materials preparation pathways and explore the high-performance of other photo- catalytic materials is an urgent issue. Generally, the main point of this thesis rests with exploring novel hydrothermal methods to synthesize functional stannate composite oxides nano-materials, and studying the formation and morphology controlled mechanism of the composite oxides nano-materials under hydrothermal conditions. The main research achievements are summed up as follows:(1)According to the testing needs of photocatalytic hydrogen-generation, we have designed and set up a suit of photocatalytic H2-generation equipments with external light irradiation. This system adopts water-excluded method to collect generated gas and the expansion of gas which is arising from temperature increasing, so that the pressure in the reaction system can be kept consistent. By measuring the displacement to chalk up the total volume of gas, it can calculate the content of hydrogen with respect to the peak area obtained in the chromatogram by the external standard method;(2)Using NaOH as the mineralization, La₂Sn₂O₇ and Zn₂SnO₄ photo- catalytic nano-materials have been successfully synthesized via a one-pot hydrothermal method. By changing the concentration of mineralization, hydrothermal temperature, duration time and surfactants, we investigated the mutual relationship between the reaction parameters and the configuration of products. Based on the characterization results from TEM/SEM/XRD/SAED/ HRTEM/Raman/FT-IR, the particular phase conversion process and the possible growth mechanism of nanocrystals under the hydrothermal conditions were proposed. At the same time, by comparing the differences of phase structure, morphology and size of the product which was synthesized with different surfactants, we elucidated the probable effect of these surfactants. Otherwise, UV-Vis diffusion reflection spectroscopy was used to elucidate the effect of particle size for their optical absorption properties and band gap;(3)Under the UV-light irradiation, a systematic photocatalytic testing was applied to character activities of the hydrothermally synthesized La₂Sn₂O₇ and Zn₂SnO₄ nanocrystals. Especially, we summarized the functionary law of crystal structure, particle size and morphology for their photocatalytic properties. Finally, by in-depth analysis of photocatalytic H₂-generation and photodegradation performance of La₂Sn₂O₇ and Zn₂SnO₄, we proposed that the photodegradation of organic dye obeyed the pseudo-first-order kinetics law and the relevant photocatalytic mechanism and the reaction process were discussed in detail.