CN103922413B - Method for preparing pyramid-shaped Cr2WO6 microcrystalline by hydrothermal-assisted low-temperature calcination - Google Patents

Abstract

The invention provides a method for preparing pyramid-shaped Cr ₂ WO ₆ microcrystals by hydrothermal assisted low-temperature calcination: adding Cr(NO ₃ ) ₃ solution to Na ₂ WO ₄ solution, adjusting the pH to 7.0-12.0, pouring it into water In a thermal reaction kettle, control the hydrothermal temperature at 100-200°C for 1-24 hours. The product is centrifuged, washed, dried, and put into a muffle furnace for calcination at 400-650°C for 2-4 hours to obtain Cr ₂ WO ₆ micro Crystal, the raw materials for preparing Cr ₂ WO ₆ microcrystals in the present invention are easy to obtain, and the yield is high, the low-temperature calcination time is short, the reaction temperature is low, the reaction energy consumption is small, and the cost is saved. The Cr ₂ WO ₆ microcrystals are completely developed and the purity Higher, uniform in size, better in dispersion, suitable for large-scale production, and has broad development prospects.

Description

A method for preparing pyramid-shaped Cr2WO6 microcrystals by hydrothermally assisted low-temperature calcination

technical field

The invention belongs to the technical field of tungstate nanomaterials, and in particular relates to a method for preparing pyramidal Cr ₂ WO ₆ microcrystals by hydrothermal assisted low-temperature calcination.

Background technique

Tungstate has the characteristics of various types, good performance, changeable crystal morphology, and high added value. With its excellent optical and electrical properties, tungstate is not only widely used in the fields of sensors, optics, scintillation crystals, laser substrates, and acoustic fibers. It has potential applications in corrosion inhibition, electrodes, catalysis, photoanodes, light absorption, coatings and other fields. Chromium tungstate (Cr ₂ WO ₆ ) is one of the tungstate series. Because of its special optical, electrical and magnetic properties, it is considered to be used in optical fibers, scintillators, humidity sensors, magnetic materials and ferroelectric materials, etc. It has potential applications in the field; the study found that its band gap is about 2.52eV, and Cr ₂ WO ₆ has a strong absorption of visible light. It is a new type of photocatalytic material with great potential. It has broad application prospects in water splitting and hydrogen production.

At present, the reports on tungstate mainly focus on Bi ₂ WO ₆ , ZnWO ₄ , CaWO ₄ , FeWO ₄ and other substances, but the reports on chromium tungstate are still rare, and the methods used in the existing reports are mainly solid-phase Reaction method.

G.Bayer adopts the high-temperature solid-phase method, mixes Cr ₂ O ₃ and WO ₃ at a ratio of 1:1, and calcines at 600°C, 750°C, 800°C, 850°C, 900°C, 1000°C, and 1100°C for 20 hours. , found that Cr ₂ WO ₆ started to form at 850°C, and formed completely at 950°C [G.Bayer.Cr ₂ WO ₆ , New Trirutile Compound[J].Journal of The American Ceramic Society,1960:495-496.]; KTJACOB also used the high-temperature solid-state method to prepare Cr ₂ WO ₆ powder by calcining Cr ₂ O ₃ and WO ₃ at a temperature of 1000°C for 24 hours [KTJACOB.Phase relationships in the system Cr-WO and thermodynamic properties of CrWO ₄ and Cr ₂ WO ₆ [J].Journal of Materials Science,1980,15:2167-2174.]; therefore, to prepare Cr ₂ WO ₆ by high-temperature solid phase method, it is necessary to heat the raw material to high temperature and keep it warm for a long time , to get the product. This method not only consumes a lot of energy, but also the particle size of the prepared sample is large, and the specific surface area of the catalyst is greatly reduced. Although visible light response can be achieved, the photocatalytic efficiency is not ideal.

So far, there are various synthesis methods of tungstate. Lee prepared sheet-like Bi ₂ WO ₆ nanocrystals at 160°C by hydrothermal method [Wen-Lian William Lee, Shiuh-Tsuen Huang, et al. Photodegradation of CV over nanocrystalline bismuth tungstate prepared by hydrothermal synthesis[J].J.Mol.Catal.A:Chem,2012,361-362:80-90.]; MAPAlmeid prepared pure FeWO ₄ by microwave hydrothermal method at 170℃ Nano powder [MAP Almeida,LS Cavalcante,C.Morilla-Santos,et al.Electronic structure and magnetic properties of FeWO ₄ nanocrystals synthesized by the microwave-hydrothermal method[J].Mater.Charact,2012,73:124-129.] ; Fan Dong prepared hollow PbWO ₄ microspheres by ultrasonic spray pyrolysis [Fan Dong, Yu Huang, Shichun Zou, Jiang Liu, and SCLee.Ultrasonic spray pyrolysis fabrication of solid and hollow PbWO ₄ spheres with structure-directed photocatalytic activity [J].J.Phys.Chem.C,2011,115(1):241-247]; In addition, there are sol-gel method, microemulsion method, solvothermal method, etc. The low-temperature liquid-phase synthesis method has many advantages such as controllable conditions, low cost, and mild environment. The morphology, structure, and crystallinity present special effects, so the tungstate photocatalytic material synthesized by the low-temperature liquid phase method shows superior photocatalytic performance than the same photocatalytic material prepared by other preparation techniques.

Contents of the invention

The object of the present invention is to provide a method for preparing pyramid-shaped Cr ₂ WO ₆ microcrystals by hydrothermal assisted low-temperature calcination. The Cr ₂ WO ₆ microcrystals prepared by this method have complete morphology, uniform size, and controllable particle size. Low, good repeatability, suitable for mass production.

To achieve the above object, the present invention adopts the following technical solutions:

Step 1: Add Cr(NO ₃ ) ₃ ·9H ₂ O into deionized water, and keep stirring to prepare a transparent solution A (Cr(NO ₃ ) ₃ solution) with a Cr ³⁺ concentration of 0.2-0.6 mol/L ;

Step 2: Add Na ₂ WO ₄ ·2H ₂ O into deionized water, and keep stirring to prepare a transparent solution B (Na ₂ WO ₄ solution) with a WO ₄ ^2- concentration of 0.2-0.6 mol/L;

Step 3: According to the ratio of transparent solution A: transparent solution B volume ratio of 1:2 to 2:1, add transparent solution A to transparent solution B, and form a green precursor suspension by stirring (about 30 minutes) liquid;

Step 4: adjusting the pH of the precursor suspension to 7.0-12.0 with an aqueous sodium hydroxide solution to obtain a mixture;

Step 5: Pour the mixture into a hydrothermal reaction kettle, then seal the hydrothermal reaction kettle and put it into a homogeneous reactor, and react for 1 to 24 hours at a controlled hydrothermal temperature of 100-200°C. After the reaction Natural cooling to room temperature;

Step 6: After step 5, open the hydrothermal reaction kettle, centrifuge the product obtained from the reaction to obtain a precipitate, wash the precipitate with deionized water and absolute ethanol in turn, and dry it at 50-80°C for 2-4 hours to obtain an intermediate product ;

Step 7: put the intermediate product into a muffle furnace and calcinate at 400-650° C. for 2-4 hours to obtain Cr ₂ WO ₆ microcrystals.

The concentration of the aqueous sodium hydroxide solution is 0.5˜1 mol/L.

In the fifth step, the filling degree of the hydrothermal reactor is controlled at 40-60%.

The beneficial effects of the present invention are reflected in:

1) In the present invention, the precursor reaction is completed in the liquid phase, and the operation is simple, and then the prepared precipitate is subjected to low-temperature calcination, which is a method for synthesizing pyramidal Cr ₂ WO ₆ microcrystals with hydrothermal assisted low-temperature calcination. The technical scope of the synthesis of Cr ₂ WO ₆ microcrystals;

2) The raw materials for preparing Cr ₂ WO ₆ microcrystals in the present invention are easy to obtain, and the low-temperature calcination time is short, the reaction temperature is low, the reaction energy consumption is small, and the cost is saved;

3) The pyramid-shaped Cr ₂ WO ₆ microcrystals obtained by the method of the present invention are fully developed, have high purity, uniform size, good dispersibility, and controllable product particle size;

4) The preparation of pyramid-shaped Cr ₂ WO ₆ microcrystals in the present invention has high repeatability, low pollution, is suitable for large-scale production, and has broad development prospects.

Description of drawings

Figure 1 is the XRD pattern of the Cr ₂ WO ₆ microcrystal prepared in Example 1, and the product corresponds to the standard JCPDS card number No.35-0791;

FIG. 2 is an SEM photo of Cr ₂ WO ₆ microcrystals prepared in Example 1.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and embodiments.

Example 1:

Step 1: Add 6 mmol of analytically pure Cr(NO ₃ ) ₃ 9H ₂ O into 15 mL of deionized water, and keep stirring to prepare a transparent solution A;

Step 2: Add 3 mmol of analytically pure Na ₂ WO ₄ ·2H ₂ O into 15 mL of deionized water, and keep stirring to prepare a transparent solution B;

Step 3: According to the volume ratio of transparent solution A: transparent solution B is 2:1, slowly add transparent solution A to transparent solution B, and stir with a magnetic stirrer for 30 minutes to form a green precursor suspension;

Step 4: adjust the pH of the green precursor suspension to 8.0 with 0.8mol/L sodium hydroxide aqueous solution to obtain a mixture;

Step 5: Pour the mixture into the hydrothermal reaction kettle, and control the filling degree at 40%; then seal the hydrothermal reaction kettle, put it into a homogeneous reactor, control the hydrothermal temperature at 160°C for 12 hours, and naturally cool to room temperature;

Step 6: Open the hydrothermal reaction kettle, centrifuge the product obtained from the reaction to obtain a precipitate, then wash the precipitate with deionized water and absolute ethanol for 3 to 5 times, and place the washed precipitate in an electric blast drying oven at 60 ℃ drying for 2 hours to obtain the intermediate product;

Step 7: put the intermediate product into a muffle furnace for calcination at 650° C. for 2 hours to obtain the final product Cr ₂ WO ₆ crystallite.

It can be seen from Figure 1 that the prepared Cr ₂ WO ₆ microcrystals have good crystallinity and high purity. It can be seen from Figure 2 that the prepared Cr ₂ WO ₆ crystallites are well developed and pyramid-shaped, and the diameter of the Cr ₂ WO ₆ crystallites is about 1 μm.

Example 2:

Step 1: Add 8 mmol of analytically pure Cr(NO ₃ ) ₃ 9H ₂ O into 15 mL of deionized water, and keep stirring to prepare a transparent solution A;

Step 2: Add 4 mmol of analytically pure Na ₂ WO ₄ ·2H ₂ O into 15 mL of deionized water, and keep stirring to prepare a transparent solution B;

Step 3: According to the volume ratio of transparent solution A: transparent solution B is 1:1, slowly add transparent solution A to transparent solution B, and stir with a magnetic stirrer for 30 minutes to form a green precursor suspension;

Step 4: adjust the pH of the green precursor suspension to 7.0 with 1mol/L sodium hydroxide aqueous solution to obtain a mixture;

Step 5: Pour the mixture into the hydrothermal reaction kettle, and control the filling degree at 40%; then seal the hydrothermal reaction kettle, put it into a homogeneous reactor, control the hydrothermal temperature at 180°C for 12 hours, and naturally cool to room temperature;

Step 6: Open the hydrothermal reaction kettle, centrifuge the product obtained from the reaction to obtain a precipitate, then wash the precipitate with deionized water and absolute ethanol for 3 to 5 times, and place the washed precipitate in an electric blast drying oven at 60 ℃ drying for 2 hours to obtain the intermediate product;

Step 7: put the intermediate product into a muffle furnace for calcination at 600° C. for 2 hours to obtain the final product Cr ₂ WO ₆ crystallite. The crystallite diameter of Cr ₂ WO ₆ is about 1 μm.

Example 3:

Step 1: Add 6 mmol of analytically pure Cr(NO ₃ ) ₃ 9H ₂ O into 20 mL of deionized water, and keep stirring to prepare a transparent solution A;

Step 2: Add 6 mmol of analytically pure Na ₂ WO ₄ ·2H ₂ O into 20 mL of deionized water, and keep stirring to prepare a transparent solution B;

Step 3: Slowly add transparent solution A to transparent solution B according to the volume ratio of transparent solution A:transparent solution B of 1:2, and stir with a magnetic stirrer for 30 minutes to form a green precursor suspension;

Step 4: adjust the pH of the green precursor suspension to 10.0 with 1mol/L sodium hydroxide aqueous solution to obtain a mixture;

Step 5: Pour the mixture into the hydrothermal reaction kettle, and the filling degree is controlled at 50%; then seal the hydrothermal reaction kettle, put it into a homogeneous reactor, control the hydrothermal temperature at 170°C for 24 hours, and naturally cool to room temperature;

Step 6: Open the hydrothermal reaction kettle, centrifuge the product obtained from the reaction to obtain a precipitate, then wash the precipitate with deionized water and absolute ethanol for 3 to 5 times, and place the washed precipitate in an electric blast drying oven at 70 ℃ drying for 2 hours to obtain the intermediate product;

Step 7: put the intermediate product into a muffle furnace for calcination at 650° C. for 2 hours to obtain the final product Cr ₂ WO ₆ crystallite. The crystallite diameter of Cr ₂ WO ₆ is about 1 μm.

Example 4:

Step 1: Add 6 mmol of analytically pure Cr(NO ₃ ) ₃ 9H ₂ O into 20 mL of deionized water, and keep stirring to prepare a transparent solution A;

Step 2: Add 12mmol of analytically pure Na ₂ WO ₄ ·2H ₂ O into 20mL of deionized water, and keep stirring to prepare a transparent solution B;

Step 3: According to the volume ratio of transparent solution A: transparent solution B is 1:1, slowly add transparent solution A to transparent solution B, and stir with a magnetic stirrer for 30 minutes to form a green precursor suspension;

Step 4: adjust the pH of the green precursor suspension to 9.0 with 1mol/L sodium hydroxide aqueous solution to obtain a mixture;

Step 5: Pour the mixture into the hydrothermal reaction kettle, and the filling degree is controlled at 50%; then seal the hydrothermal reaction kettle, put it into a homogeneous reactor, control the hydrothermal temperature at 180°C for 12 hours, and naturally cool to room temperature;

Step 6: Open the hydrothermal reaction kettle, centrifuge the product obtained from the reaction to obtain a precipitate, then wash the precipitate with deionized water and absolute ethanol for 3 to 5 times, and place the washed precipitate in an electric blast drying oven at 80 ℃ drying for 2 hours to obtain the intermediate product;

Step 7: put the intermediate product into a muffle furnace for calcination at 600° C. for 2 hours to obtain the final product Cr ₂ WO ₆ crystallite. The crystallite diameter of Cr ₂ WO ₆ is about 1 μm.

Claims (3)

1. A method for preparing pyramid-shaped Cr ₂ WO ₆ microcrystals by hydrothermal assisted low-temperature calcination, characterized in that: comprising the following steps: Step 1: adding Cr(NO ₃ ) ₃ ·9H ₂ O into deionized water to prepare a transparent solution A with a Cr ³⁺ concentration of 0.2-0.6 mol/L; Step 2: adding Na ₂ WO ₄ ·2H ₂ O into deionized water to prepare a transparent solution B with a WO ₄ ^2- concentration of 0.2-0.6 mol/L; Step 3: Add transparent solution A to transparent solution B according to the volume ratio of transparent solution A: transparent solution B in the ratio of 1:2 to 2:1, and form a green precursor suspension by stirring; Step 4: adjusting the pH of the precursor suspension to 7.0-12.0 with an aqueous sodium hydroxide solution to obtain a mixture; Step 5: Pour the mixture into a hydrothermal reaction kettle, then seal the hydrothermal reaction kettle and put it into a homogeneous reactor, and react for 1 to 24 hours at a controlled hydrothermal temperature of 100-200°C. After the reaction Natural cooling to room temperature; Step 6: Open the hydrothermal reaction kettle, centrifuge the product obtained from the reaction to obtain a precipitate, wash the precipitate with deionized water and absolute ethanol in turn, and then dry it at 50-80°C for 2-4 hours to obtain an intermediate product; Step 7: put the intermediate product into a muffle furnace and calcinate at 400-650° C. for 2-4 hours to obtain Cr ₂ WO ₆ microcrystals. 2 . A method for preparing pyramid-shaped Cr ₂ WO ₆ microcrystals by hydrothermally assisted low-temperature calcination according to claim 1 , wherein the concentration of the aqueous sodium hydroxide solution is 0.5-1 mol/L. 3. A method for preparing pyramid-shaped Cr ₂ WO ₆ microcrystals by hydrothermal assisted low-temperature calcination according to claim 1, characterized in that: in step 5, the filling degree of the hydrothermal reaction vessel is controlled at 40-60% .