Synthesis, Characteristic And Light-Induced Function Of AB₂O₄ Compounds

The compounds with a molecular formula of AB₂O₄ have drawn attention because these materials have various crystal structures and excellent magnetic, optical, electrical and catalytic properties. In this dissertation, the focus of the studies is on AB₂O₄ compounds with the light-induced function (photocatalysis and photoluminescence) , including two parts: the first is to involve studies on the synthesis, photocatalytic performance under visible light, and characteristics of structure and morphology of AB₂O₄ -spinel materials; the other is on the studies of a one-step process for synthesizing SrAl₂O₄: Eu, Dy long-afterglow luminescent plate, and the luminescence performance of SrAl₂O₄: Eu, Dy composite glasses. Detailes are as follows.1. The synthesis, structure, visible-light photocatalytic activities and the relationship between the structure and performance of spinel compounds, XAl₂O₄ (X = Mg, Zn, Cu) and ZnY₂O₄ (Y = Cr, Mn, Fe), were investigated. Their crystal structure, microscopic morphology and spectral response characteristics were analyzed via. XRD, TEM and UV-Vis diffuse reflectance spectra. The experimental results show that all the samples have spinel structure with particle sizes of 10-40 nm, and their absorption band-edges are able to extend to the visible-light region in varying degrees. In particular, the sample of CUAl₂O₄ has its absorption spectrum covering nearly the whole visible-light region. From photocatalytic degradation of methyl orange, acid red B and reactive red K-2G aqueous dyes, it was found that the sample materials exhibited different visible-light photocatalytic activities due to the differences in crystal structures and band gaps of these materials. Of all these materials, CUAl₂O₄ presented the highest photocatalytic activities with＞98% decolorization rate for all three aqueous dyes after two hours.2. The synthetic process and photocatalytic properties of CUAl₂O₄ with a high activity under visible-light irradiation were studied. The results from XRD, TEM and UV- visible diffuse reflectance spectra show that the precursor was successfully transformed to single-phase CUAl₂O₄ nanoparticles calcined at 700℃for 2 hours in the air, and the products have strong absorption ability in UV and visible light range. Using methyl orange, acid red B and reactive brilliant red K-2G aqueous solution as model compounds, we investigated the effects of calcining temperature, irradiation light source (UV light, visible light, sunlight, and dark room), irradiation wavelength, dye structure, and catalyst dose on the visible-light photocatalytic activity of CUAl₂O₄. In addition, the recycling stability of CuAl₂O₄ was studied. From the experimental results, it is proposed that the decoloration of dyes under irradiation condition is caused by photocatalytic degradation and the decoloration in the absence of light is due to the surface absorption of the dyes by the catalyst. Furthermore, the wavelength dependence of the photocatalytic activity of CuAl₂O₄ can be further suggested that the decorloration reaction is driven by light.3. The morphological formation, the characterizations and the effects on photocatalytic activity of CuAl₂O₄ nanoparticles via. various soft chemistry methods were studied. Nanopowders with various morphologies (such as spherical, rod-like, and irregular grain) were obtained by various methods including the sol-gel, precipitation, polymerizable complex and stearic acid gel. UV-Vis diffuse reflection spectra analysis show that the sample powders with different morphologies exhibited different spectral responses. The morphological irregularity of sample powders was quantitatively described by calculating the fractal dimension D of these samples. The effects of the D value on photoactivity and dynamics process for photocatalytic reaction were discussed.4. A novel one-step systhesis process for making SrAl₂O₄:Eu,Dy(SAED) long-afterglow plate was invented and the luminescence properties of the material were evaluated. A S AED long-afterglow luminescent plate was successfully prepared by solid-state reaction method using Al₂O₃ substrates coated with Eu₂O₃, Dy₂O₃ and Sr (NO₃)₂ materials. The effects of synthetic condition (synthetic atmosphere, calcining temperature and holding time) and additive amount (H₃BO₃) on the surface structures of Al₂O₃ substrates and their luminescence properties were investigated. And the optimal synthetic conditions were obtained.5. SAED(SrAl₂O₄.Eu,Dy) doped SrO-Al₂O₃ borosilicate glass composite materials were synthesized. The luminescent properties with the Al₂O₃ and SrO content, as well as minute amount of iron in glass host were studied. In addition, the influence of synthetic temperature, holding time and atmosphere on their luminescence properties was studied. SEM and emission spectra show that the fluorescence characteristics of these samples were originated from the SAED grains embedded in the glass host. However, the intensity of their luminescence is largely influenced by the glass host compositions. With the increase of Al/Sr ratio in the glass host, the composite luminescence intensity increased significantly. The presence of minute amount of Fe₂O₃ had no influence on the spectral characteristics of the luminescence, but made significant decreases in the luminescence intensity and initial afterglow intensity.