Tungstate Nanomaterials Preparation by Low Temperature Hydrothermal Method

Tungstate nanomaterials have been widely used in many fields, such as optics, electricity, magnetism, conductor/superconductor, catalysis, biology and so on. The synthesis methods of transition metal tungstate materials include sol-gel method, copolymer assisted synthesis, reversed micellar soft template, wet chemical method and solution synthesis.

Some scholars have provided a low temperature hydrothermal preparation method for tungstic acid series nanometer photocatalytic materials. The following steps are included:

（1） Sodium tungstate (Na₂WO₄·2H₂O) and polyvinylpyrrolidone (PVP-30) were dissolved into the deionized water of 70ml in proportion, the 4 mol/L hydrochloric acid solution was slowly added to the mixed solution under the condition of full mixing, the pH was adjusted to 1.

（2） The mixed phase is loaded into a 100 ml polytetrafluoroethylene autoclave. After the hydrothermal reaction, the precipitated sediment is washed with deionized water. The vacuum drying 12h, the temperature is 80°C, and the reaction precursor WO₃ 0.33H₂O is obtained.

（3） In the state of magnetic stirring, the precursor was added to 70ml deionized water. After 10 min, 0.0569g ammonium fluoride (NH4F) was added into the mixed solution, and the solution A was fully stirred.

（4） According to the stoichiometric ratio of different tungstates, the metal ion reactants were dissolved in nitric acid (HNO₃) solution with 3 mL concentration of 4 mol/L and the solution B was obtained.

（5） The mixture of solution A and solution B was adjusted with 25% ammonia (NH₃·H₂O) to adjust the pH value of solution to 7.
（6） The tungstate nano-photocatalytic materials were prepared by transferring the mixed phase to a 100 ml PTFE autoclave and then washing and drying after hydrothermal reaction.

The low temperature hydrothermal method has the advantages of simple process, simple operation, low cost and so on. Several nanostructured tungstate materials with controllable morphology can be prepared by parameter adjustment.

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