Bismuth Tungstate Preparation by Solvothermal Method
Bismuth tungstate (Bi2WO6) is an oxide with perovskite like structure, and is a typical n-type semiconductor.
Because of its unique crystal structure, Bi2WO6 has the properties of thermoelectric, ferroelectric, piezoelectric, oxygen ion conductor, luminescence, nonlinear dielectric induction and catalysis.
The preparation methods of bismuth tungstate include solvothermal method, precipitation method, microemulsion method, hydrothermal method, etc.. Among the many methods of liquid phase preparation, hydrothermal process has high utilization ratio of material and less energy consumption because of its simple operation process. But there is a clear flaw in hydrothermal methods, that is, the water sensitive compounds are not satisfactory, so people will use organic solvents instead of "water" in hydrothermal method, which is called solvothermal method.
The principle of solvothermal method is similar to thydrothermal method. It also works in a special sealed reaction vessel (autoclave), the difference is that other organic solvents are used instead of water as the reaction medium, organic solvents also play a role in the media, mineralization and transmission of pressure.
The main difference between solvothermal and hydrothermal methods is that: 1. The solvothermal method uses organic solvent, while hydrothermal method uses water; 2. Under normal circumstances, the boiling point of organic solvents is relatively low, so the reaction temperature required in the preparation process is relatively low, less energy consumption; 3. The reaction activity of the solvent is high, and the quality of the synthesized bismuth tungstate is better; 4. Organic solvents used in solvothermal methods are toxic and less environmentally friendly.
The most common organic solvent used in the preparation of bismuth tungstate is ethylene glycol, Bi2WO6 with an average grain size of 12 nm was synthesized by solvothermal method using ethylene glycol as solvent, the Bi2WO6 samples prepared by hydrothermal method were compared under the same conditions, it is found that the Bi2WO6 powder prepared by solvothermal method has smaller grain size and larger specific surface area than hydrothermal method, so the photocatalytic degradation of B powder is better under visible light.
In recent years, the use of solvothermal method is more and more widespread, but the gap is still very obvious. Organic solvent as reaction solvent will bring security risks to the stability of reaction system, in addition, organic solvents are generally toxic, improper use is liable to harm the body and the environment, so for the use of this method, enterprises often have to consider carefully.
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