Luminescence Photocatalysis And Heat Treatment Studies Of MgAl₂O₄ Nanoparticles

Magnesium aluminate（MgAl₂O₄）, as a functional material, has attracted growing interest in diverse applications such as fluorescence, catalyst and preparation of transparent ceramics, etc. Therefore, it is the same as the preparation process of MgAl₂O₄ powders, to research the properties of catalytic and fluorescence in detail has practical significance. In order to improve the dispersion and uniformity, high-temperature calcination route with MgSO₄·7H₂O and NH₄Al（SO₄）₂·12H₂O as raw materials is used to prepare MgAl₂O₄ and Cr3+/Eu3+ doped MgAl₂O₄ powders. In this paper, the photocatalytic and luminescence properties of products, along with the effects of heat treatment on powder performance are studied. And the main conclusions are as follows.First, the powders, prepared with high-temperature calcination route at 1100℃¹200℃for 3 h, having the typical spinel structure with the particle size distribution of 50⁷0 nm, are non-aggregated entities.Second, the MgAl₂O₄ powders prepared at 1150℃ exhibits good photocatalytic properties（90%） for degrading 10 mg/L methyl orange（MO） under UV iiradiation for 2 h. And the photocatalytic ability is attributed to the electron-hole pairs caused by defect level transition. Annealing process in O₂ and N₂ atmosphere removes the surface adsorption of water and accelerates the diffusion for defects, which making degradation of the powders on MO improved to 95% and 98%, respectively.Third, Cr3+/Eu3+ doped MgAl₂O₄ nanophosphors have been prepared via a facile high-temperature calcination route. It is found that Mg Al2-x O4:x Cr3+ can be efficiently excited by visible light（557 nm） and exhibits red emission peaking at 694 nm, corresponding to the 2Egâ†'4A2g transition of Cr3+（3d3） ions. The optimal concentration is 3.0 mol%. The Mg Al2-x O4:x Eu3+ phosphors excited at 398 nm exhibits a strong emission peaking at 620 nm, corresponding to the 7F0â†'5L6 transition of Eu3+（f-f） ions and the optimal concentration is 6.0 mol%.Fourth, after vacuum heat treatment（10-3 Pa） for 2 h, the surface energy and aggregation of the powders decreases, while the sintering activity increases significantly. The MgAl₂O₄ powders after vacuum heat treatment are used to prepared large size ceramics via the two-step sintering route and the transmittance gets up to 80%.