Synthesis And Characterization Of Several Metal Tungstates With Nano/Micro Structure

Metal tungstates have attracted much interest due to its application in variousareas such as catalyst, photoluminescence, humidity sensor. The investigation onmetal tungstates nano/micro structures is important both in fundamental theory andindustrial areas. Herein, we synthesized BaWO₄twin-spheres viahydrothermal/solvethermal approach. The photoluminescence property of rare earthmetal doped BaWO₄was investigated. We also synthesized a series of transtionmetal tungstate via chemical transformation method, using as prepared BaWO₄twin-spheres as precursors. This provide a new approach for synthesizing metaltungstates which cannot be synthesized directly. This is quite useful in thefundametal theory and application of metal tungstates.We synthesized BaWO₄twin-spheres via solvethermal approach with EG assolvent. The phase and morphology of the product was investigated by XRD andSEM. The BaWO₄twin-spheres are approximately2μm in length and1μm indiameter. The twin-spheres were composed of nanoparticles of about100nm.Experimental results show the surface of BaWO₄twin-spheres became rough andthe nanoparticles became large as the temperature increases. When the concentrationof reactants was decreased, the product became twin-spheres with rod-shaped microstructures and dumbbells. The formation mechanism of dumbbells was proposed tobe rod to dumbbells to twin-spheres.The photoluminescence property of rare earth metal (Eu³⁺/Tb³⁺) doped BaWO₄was investigated. When BaWO₄was doped with Eu³⁺, it would possess strongphotoluminescence property. When excited with ultra-violet,394nm and464nmphotons it will emit visible photons, which is the characteristic emission of Eu³⁺.When the doping concentration was increased, the emission intensity increases first.After reaching the maximum, the intensity decreases. When BaWO₄was doped withTb³⁺, it will also possess strong photoluminescence property. When the Tb³⁺dopedBaWO₄was excited with ultra-violet photons it would emit visible photons. Theemission wavelength is the characteristic emission wavelength of Tb³⁺. When thedoping concentration was increased, the emission intensity increases first. Afterreaching the maximum, the intensity decreases.Using the as-prepared BaWO₄twin-spheres as template, making it react withtransition metal under hydrothermal condition, we got a series of transition metaltungstates including CuWO₄, CoWO₄, MnWO₄. The morphology of the templatewas inherited to the product. Temperature and amount of transition metal ions havegreat influence on the transformation. In the case of CuWO₄, the transformation became easier at high temperature. Also, the transformation extent increases as theamount of Cu2+increases.