Synthesis And Characterization Of CaTiO₃Particles With Controlled Shape And Size

Perovskite-type oxides (ABO3) is a class of functional materials with colorful structure and performance, while changing the elements of A bit and B bit, its structure (such as orthogonal, cubic, rhombohedral and monoclinic etc.) and performance (such as ferroelectric, ferromagnetic, giant magnetoresistance, semiconductor, photoluminescence, photoelectric and photocatalytic etc.) will change also. Because of the properties of the materials are significantly influenced by the structure, the researches on the controllable morphology and size of the perovskite-type oxide materials have been a hot spot. CaTiO3compound as one of the representatives has a stable crystal structure, good dielectric characteristics, a high thermal stability, superior catalytic, gas sensing and optical characteristics, and therefore it is widely used in the photocatalytic, sensors and other research areas and as dielectric material and the high-frequency equipment are widely used in the electronics industry. To better understand the structure and nature of the perovskite-type oxide, and then guide the applications, the research about their morphology is given a great deal of concern. So it is a rewarding job to synthesis CaTiO3micro/nano-structures with different morphology and size in a controlled way and research the interaction among the natures, morphology and size. In this thesis, we have produced the CaTiO3powders with different morphologies (spherical, octahedral, rectangular and cubic, etc.) by using the sol-gel method, the traditional and improved solvothermal method, and then explored the different experimental parameters such as reaction time, reaction temperature, initial concentration of NaOH and different solvents how to effect the morphologies of the samples, and the X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) are used to characterize the structures and morphologies of the samples.(1) Ca(NO3)24H2O as the calcium source, Ti(OC4H9)4as the titanium source, they were dissolved in absolute ethanol respectively, added PEG-1000to the mixing as a dispersing agent, we obtained the spherical CaTiO3nanoparticles with average size of50nm by sol-gel method. Through changing the pH value, the content of the dispersing agent, the calcination temperature, the water bath temperature and the other experimental parameters, we discovered the optimal experimental parameters were:pH=2.5, the content of the dispersing agent was0.3fold (multiples=mPEG/(mTi+mca)), the calcining temperature was800℃and the water bath temperature was60℃.(2) Ca(NO3)2·4H2O as the calcium source, Ti(OC4H9)4as the titanium source, added NaOH to the mixing, we prepared the CaTiO3particles with better dispersion in the PEG-200solvent by the conventional solvothermal. With the reaction temperature increased from180℃to200℃and220℃respectively, we obtained the CaTiO3particles with spherical shape, octahedron and cubic morphologies, the SEM analysis showed that the spherical particles formed at180℃had walnut-shaped with average size of150nm, the particles were picked up by the nanocubes with the average size of10nm. Voids appeared on the surface of the particles when the temperature arised. With the NaOH concentration increased from1M to2M, we obtained the rectangular CaTiO3particles. Through a series of experiments, the reaction time had not a particularly significant impact on the morphology and size of the products.(3) Solvent PEG-200was partial replaced by the aqueous, the total amount of reaction solution was unchanged and the other reaction parameters were constant, the CaTiO3cubic particles with better crystallinity were obtained by this improved solvothermal method. With the water content increased from0.25ml to0.5ml, the particle size was significantly reduced, as the temperature increased at200℃and220℃, this tendency becomed more apparently, but in a higher water content (such as1ml), the influence of the temperature to the particle size was reduced. At the same time, the shape of the CaTiO3particles becomed more regularly when increased the water content, and the surface becomed more smoother. In the aqueous environment, the reaction time had a significant effect on the CaTiO3particles, the CaTiO3particles with better dispersivity and higher crystallinity were produced when extended the reaction time.(4) Selected the spherical, cubic and rectangular shape CaTiO3particles synthesized by the traditional and improved solvothermal method, and then studied their photocatalytic properties. The experimental results showed that after30min UV irradiation, spherical, cubic and rectangular CaTiO3particles degraded82%,89%and94%of the methylene blue solution respectively. Photocatalytic reaction followed the first-order kinetics:c=coexp (-kt). The reaction rate k of the spherical, cubic and rectangular shape CaTiO3particles were2.70,3.71and4.50h-1respectively. Rectangular CaTiO3particles exhibited the highest photocatalytic activity.