Controlled Synthesis of Calcium Tungstate Hollow Microspheres via Ostwald Ripening and Their Photoluminescence Property
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Abstract
Nearly monodispersed CaWO4 hollow microspheres with controlled diameters were successfully prepared by a facile one-step hydrothermal method using CaCl2, Na2WO4, and sodium dodecyl sulfate (SDS) as the starting reaction reagents and distilled water as solvent. The crystal structure, morphology, macroporous and photoluminescence properties of the as-synthesized products are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, selected-area electron diffraction, nitrogen adsorption−desorption isotherm technique, and fluorescence spectrometer. The hollow microspheres have an average diameter of 2.2 μm and hollow interior of 0.5−1 μm. The shell is consisting of numerous nanoparticles 45 nm in diameter. The effects of SDS amount, pH value, concentrations of reaction reagents, and reaction durations have been studied systematically. The results indicate that a certain SDS amount plays a key important role in the final formation of hollow microspheres. It is also found that the average diameters of the hollow spheres can also be tuned by increasing the SDS amount in the range of 0.2−1 g into the reaction system. Based on the detailed investigation on the influences of experimental parameters, the formation mechanism of the hollow interiors by a SDS-induced Ostwald ripening process is proposed for the CaWO4 hollow microspheres. The Brunauer−Emmett−Teller (BET) surface areas and pore volume of the CaWO4 hollow microspheres are 14.4 m2/g and 0.087 cm3/g, respectively. Furthermore, photoluminescence spectrum of the CaWO4 hollow microspheres reveals a strong and broadband from 350 to 450 nm with an emission peak at 413 nm originating from the WO42− groups. This Ostwald ripening process could open novel and efficient pathway for the preparation of ternary metal oxides with hollow interiors.
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