Microwave Hydrothermal Synthesis of Rod-shaped Manganese Tungstate Microcrystal

Manganese tungstate (MnWO₄) crystal has tungsten-manganese iron structure and belongs to the direct bandgap semiconductor material. Because of its special optical, electrical and magnetic properties, it has been widely used in the fields of photoluminescence, optical fibers, scintillators, humidity sensors, magnetic materials and ferroelectric materials.

Some scholars have tried to synthesize rod-like manganese tungstate microcrystals by microwave hydrothermal method. The process steps are as follows:

1) The analytical pure manganese nitrate (Mn(NO₃)₂) was added into deionized water and stirred continuously to prepare a transparent solution A with Mn₂⁺ concentration of 0.2-0.8mol/L.

2) Analytical pure ammonium tungstate ((NH₄)₂WO₄) was added into deionized water and stirred continuously to prepare transparent solution B with WO₄² concentration of 0.2-0.8mol/L.

3) Solution A was slowly added to solution B at the volume ratio of 1:2 to 2:1, and stirred continuously to form precursor precipitation solution C.

4) NaOH solution was used to adjust the pH of precursor precipitation solution C to 8.0-11.0 to obtain precipitation solution D.

5) The precipitation solution D is poured into the microwave hydrothermal reactor, and the filling degree is controlled to 60-70%. Then the microwave hydrothermal reactor is sealed and put into the temperature-pressure dual-control microwave hydrothermal reactor. The temperature control mode is selected for the reaction, and the hydrothermal temperature is controlled at 120-260 ℃ for 10-120 min. After the reaction, it is cooled naturally to room temperature.

6) Open the microwave hydrothermal reactor, collect the products by centrifugation, then wash them with deionized water and absolute ethanol for 3-5 times, and dry them at 50-80 ~℃ to obtain rod-like manganese tungstate microcrystals.

The rod-like manganese tungstate microcrystals with diameters of 10-30 nm and lengths of 30-200 nm can be prepared by microwave hydrothermal synthesis. The method has the advantages of low reaction temperature, short reaction period, low energy consumption, low cost, simple operation and good repeatability. It is suitable for large-scale production of MnWO₄ microcrystals.

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