Tungsten Trioxide by Sol-Gel Method

Sol-gel method is a more commonly used and effective preparation method of nano-semiconductor tungsten trioxide powder. Its general procedure is to hydrolyze tungstic acid inorganic salts or metal alkoxides and then polymerize and gel. Or in the preparation of tungstic acid solution system by adding organic acids as a ligand, inorganic acid and alkali tungstic acid solution system to adjust the p H value. Finally, the solvent was slowly evaporated and a gel was obtained. The gel was dried and calcined to give the final product. The advantage of the sol-gel method is that the tungsten oxide product has the advantages of smaller particle size, good uniformity and high purity, and is suitable for industrial production. Its disadvantage is that it is difficult to control the transformation of sol-gel, such as poor transformation, the gel tends to agglomerate after drying, and the synthesis period is generally longer.

Sol-gel method for the preparation of tungsten trioxide step: a certain amount of sodium tungstate crystal powder dissolved in deionized water. Concentrated hydrochloric acid was added dropwise to the solution while stirring. After stirring to obtain a clear and transparent tungstate sol. Continue dropping a certain amount of concentrated hydrochloric acid, or increase the mixing time will form jelly gel. The resulting gel was filtered, washed and then allowed to settle to the bottom of the beaker after being placed for a week. After discarding the supernatant, the product is placed in a forced air oven at 60 ºC and dried. Visible product color is yellow. Finally, the product was placed in air 500 ° C calcined 2 hours, you can get light yellow nano-tungsten trioxide powder. Other sol-gel methods include tungsten peroxide poly-tungstic acid, ion exchange, tungsten alkoxide hydrolysis, and the like. In the post treatment process, the sol-gel method can not be removed by high temperature calcination to remove organic components. However, the calcination process may increase the particle size of the sample and greatly reduce the surface hydroxyl group, which is not conducive to the improvement of the photocatalytic performance of the sample.

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