The Application Of Supercritical Water System On Preparation Of Multicomponent Oxide Materials With Micro And Nano Scale

Recently, with the development of chemistry, chemistry engineering, energy and materials, plenty of novel structural and functional materials have been prepared, and accordingly the problems about environment pollution have become more and more severe. Therefore, people started to pay much more attention to the sustainable development such as protection of environment. People not only had high requirements on the safety and environmental conservation of materials themselves, such as the replace of toxic materials with non-toxic or lower-toxic ones, but also proposed the concept of green chemistry for synthetic methods, which focused on making the process of preparation "green" and environmental friendly. This solved the pollutions in the process of material synthesis in the beginning, and avoided the problems which might exist in waste treatment from a long-term perspective. Green chemistry, one of the most important parts of society sustainable development, is necessary and significant for the survival and development of human beings. The most representative green chemistry is supercritical fluids technology, which has been developed rapidly in the past several decades. Supercritical fluids technology is green and novel, and until now the research and application were mostly focused on supercritical water technology and supercritical carbon dioxide technology. Owing primarily to its special chemical and physical properties supercritical water has attracted people's attention. Supercritical water has been proved to be a fast, effective, environmental friendly and energy-saving reaction medium in the fields of energy, environment and materials. Especially the prepared fine particle materials in supercritical water system usually had high crystallinity, single phase, uniform morphology and high dispersivity.In this thesis, we focus on the application of supercritical water system on the synthesis of multicomponent oxide materials including YVO4, Y3Al5O12 and BaTeMo2O9 with micro and nano scale.(1) We have successfully synthesized pure YVO4 and rare earth-doped YVO4 ultra-fine nanoparticles with single phase, high crystallinity and high dispersivity in supercritical water system by using high-temperature and high- pressure autoclave. The influence of system conditions to the phase and morphology of final products, such as doped rare earth ion, addition of KOH, reaction temperature and reaction time, was examined in detail. Furthermore, the luminescent properties of YVO4:Eu and YVO4:Tb powders excited by UV irradiation were characterized.(2) YAG nano-particles and micro-particles with single phase, high crystallinity and high dispersivity were obtained from a novel synthesis process by employing supercritical water system. The synthesis process includes two steps, precursor precipitation and treatment in supercritical water system by using high-temperature and high-pressure autoclave. Factors influencing the phase and morphology of the final products, such as experimental method, precursor, reaction temperature, reaction time and addition of precipitant, were investigated in detail.(3) We have successfully synthesized novel BaTeMo2O9 micro-plate materials with single phase and uniform morphology in supercritical water system by using high-temperature and high-pressure autoclave. The factors influencing the phase and morphology of final products, such as adding order of reactants, addition of KOH, reaction temperature, reaction time, cooling time, and addition of reactants, were investigated in detail. The novel BaTeMo2O9 micro-plate materials were characterized and tested in detail for the first time. From the successful preparation of BaTeMo2O9 micro-plate materials, experience that might lead to the synthesis of quaternary oxide materials with nano or micro scale in the future were accumulated, the application range of green supercritical water technology in materials synthesis was extended, and a green, environmental friendly and effective synthetic method was provided to prepare ultrafine particles of quaternary oxide materials.Here we explored and studied the application of a novel reaction medium supercritical water on the area of materials synthesis. From a unique angle of view, the research about the preparation of novel functional materials was carried out and an environmental friendly technical route was built and developed. Then the research of materials science, environmental protection, energy conservation and sustainable chemical engineering was combined. The research results have outstanding practical significance in the fields of both fundamental science and application technology.