CN100522816C - Preparing process of nano gamma-alumina powder with intraparticle mesoporous structure - Google Patents

Abstract

The invention discloses a preparation method of γ-alumina nanopowder with inner mesoporous structure of particles. Surfactants and adjust the pH of the ammonium bicarbonate solution. Add the aluminum salt dropwise to the ammonium bicarbonate under magnetic stirring, and continue to stir until the reaction is complete. After separation, washing, drying, azeotropic distillation and dehydration, high-temperature calcination, the particle size distribution is relatively uniform, and the average particle size in the particle is 20-63nm, γ-Al ₂ O ₃ nanometer powder with intra-particle mesoporous structure, with an average particle internal pore diameter of 2.8-7.4nm and a specific surface area locally adjustable within the range of 95-212m ² /g. The invention has the advantages of simple and convenient operation, mild production conditions, low energy consumption and low cost, and is suitable for industrialized production. The prepared alumina powder has nanometer size, γ nanocrystalline phase and mesoporous characteristics at the same time, and has broad application prospects in adsorption, separation, catalyst and its carrier, and chromatographic column materials.

Description

A kind of preparation method of γ-alumina nanopowder with particle inner mesoporous structure

technical field

The invention relates to a method for preparing gamma-alumina nanoparticles with an inner mesoporous structure, and belongs to the field of mesoporous inorganic nanometer materials.

Background technique

Nano-alumina (Al ₂ O ₃ ) refers to alumina products with a particle size of less than 100nm. Due to its small particle size and large specific surface area, it has high chemical activity and is widely used in artificial gemstones, reagents, catalysts and carriers, and luminescence. materials, electronic ceramic substrates, and aerospace fields. At present, the industrial preparation of alumina powder mainly adopts methods such as the Bell method and the thermal decomposition of aluminum ammonium alum, which require special heating equipment and increase the difficulty of synthesis. However, it is difficult to effectively control the size and microstructure of particles by traditional wet chemical methods, so it is difficult to prepare real nano-alumina powder by traditional wet chemical methods.

In the 1970s, Mobile Company first synthesized the M41S series of silica inorganic mesoporous materials with mesoporous structure by using the principle of self-assembly of surfactants (the pore size distribution is called mesoporous materials in the range of 2-50nm). At present, surfactants have been successfully prepared in the aspect of mesoporous or porous γ-alumina. Mesoporous or porous γ-alumina has been widely used in industrial adsorbents, chromatographic separation column materials, catalysts and their supports. However, the porous Al ₂ O ₃ prepared by the surfactant template method usually has an amorphous structure with poor thermal stability, which will lead to the collapse of the porous structure during its crystallization into γ-phase alumina, which greatly reduces the The specific surface area of the material is reduced, which seriously affects its application in catalysts and adsorbents. It can be seen that the preparation of γ-alumina mesoporous materials with high thermal stability and specific surface area has important practical significance. At present, there are no literatures and reports about the preparation and application of nanometer γ-alumina nanopowder with intraparticle mesoporous structure at home and abroad.

Contents of the invention

The purpose of the present invention is to provide a preparation method of γ-alumina nanopowder with mesoporous structure in the particles. The method is easy to operate and low in cost. All in one, with high thermal stability and specific surface area.

The technical solution provided by the present invention is a method for preparing gamma-alumina nanopowder with an inner mesoporous structure comprising the following specific steps:

(1), take aluminum ammonium sulfate, aluminum chloride and ammonium bicarbonate according to needs, dissolve in secondary water respectively, make aluminum chloride solution or aluminum ammonium sulfate and aluminum ion total concentration 0.3-0.5mol/L A mixed solution of aluminum chloride, the molar ratio range of ammonium aluminum sulfate/aluminum chloride in the mixed solution is 0-3, and the ammonium bicarbonate solution with a concentration of 0.3-0.6mol/L is used to filter out the solution with a microporous membrane impurities;

(2), add Polyethylene Glycol 400 in aluminum chloride solution or the mixed solution of Aluminum Ammonium Sulfate and Aluminum Chloride, the Al3 ⁺ concentration that is mixed with 4-8wt% Polyethylene Glycol 400 is 0.3-0.5mol /L aluminum salt A solution, add polyethylene glycol 2000 in ammonium bicarbonate solution, be made into 0.3-0.6mol/L ammonium bicarbonate B solution containing 1-8wt% polyethylene glycol 2000, and add ammoniacal liquor Adjust its pH value to 9-10;

(3) Under magnetic stirring, add dropwise 1/2 volume to an equal volume of aluminum salt A solution to the ammonium bicarbonate B solution. After the titration is completed, continue to stir until the reaction is complete, centrifuge to separate the precipitate, and wash with secondary water until Detect that there is no SO ₄ ^2- , and then dry to obtain a dry powder;

(4) Add the obtained dry powder to a sufficient amount of n-butanol, after ultrasonic dispersion, fully reflux, distill and remove the n-butanol-water azeotrope at 93-95 °C, when the fraction temperature rises to normal When the boiling point of butanol is 115-120°C, stop the distillation, continue to reflux, and then recover n-butanol by distillation under reduced pressure to obtain loose γ-Al ₂ O ₃ nanopowder;

(5) Calcining the obtained γ-Al ₂ O ₃ nanometer powder at 850-900° C. to obtain γ-Al ₂ O ₃ nanometer powder with an intra-particle mesopore structure.

And, in the step (3), under the magnetic stirring of 1000-1300r/min, drop 1/2 volume to the aluminum salt A solution of equal volume in the ammonium bicarbonate B solution with the speed of 250-350 drop/min, and The precipitate separated by centrifugation was washed twice with water, detected with 1-2% barium nitrate until no SO ₄ ^2- was detected, then washed several times with ethanol and dried at 70-90° C. for 3-4 hours to obtain a dry powder. The calcination time in step (5) is 2-3 hours, and the particle size distribution of the obtained γ-Al ₂ O ₃ nanopowder with the mesoporous structure in the particle is uniform, and the average particle size in the particle is 20-63nm, and the average particle size is The pore diameter is 2.8-7.4nm, and the specific surface area is 95-212m ² /g.

It can be seen from the above technical scheme that the present invention effectively adjusts the particle size, pore size, and specific _surface area of the _Al2O3 product by optimizing the type and concentration of the precipitation reaction initiator, and appropriately adding a surfactant. Relatively stable γ-Al ₂ O ₃ nanopowder with mesoporous structure. The method of the invention can prepare gamma-alumina nanometer powder with an average particle diameter of 20-63nm, an average pore diameter of 2.8-7.4nm, a specific surface area of 95-212m ² /g, and high thermal stability and specific surface area. And this kind of mesoporous nanometer γ-alumina, which combines nanometer size, γ-phase nanocrystal and mesoporous characteristics, is bound to be used in adsorption, separation, catalyst and its carrier, automobile three-way catalytic conversion device, chromatographic separation column material and so on show broad application prospects.

Compared with the prior art, the present invention has the following advantages and effects:

1. Wide source of raw materials, mild production conditions, low energy consumption and cost, suitable for industrial production.

2. Using the template effect of surfactants, the particle size, inner pore size and distribution of nano-Al ₂ O ₃ powder can be controlled locally by adjusting the concentration and type of polyethylene glycol surfactant and aluminum salt .

3. When calcined at 850-900°C, the mesoporous wall can be crystallized while maintaining the mesoporous structure, thereby obtaining a high surface area. However, the mesoporous pores prepared by the usual method collapsed completely when calcined at 900 °C.

4. The alumina powder prepared by this method integrates nanometer size and mesoporous properties, and has broad application prospects in catalysts and their supports, automotive three-way catalytic conversion devices, and chromatography separation column materials.

Description of drawings

Fig. 1 is the transmission electron micrograph of the product obtained in embodiment 1.

Fig. 2 is the transmission electron micrograph of the product obtained in embodiment 2.

Fig. 3 is the transmission electron micrograph of the product obtained in embodiment 3.

Fig. 4 is the transmission electron micrograph of the product obtained in embodiment 4.

Figure 5 is a transmission electron micrograph of the product obtained in Example 5.

Detailed ways

First, weigh aluminum ammonium sulfate, aluminum chloride and ammonium bicarbonate as required, dissolve them in secondary water respectively, and make aluminum chloride solution or aluminum ammonium sulfate and aluminum chloride with a total concentration of aluminum ions of 0.3-0.5mol/L The mixed solution, the molar ratio range of ammonium aluminum sulfate/aluminum chloride in the mixed solution is 0-1, and the ammonium bicarbonate solution with a concentration of 0.3-0.6mol/L, and the impurities in the solution are filtered by a microporous membrane.

Then add Polyethylene Glycol 400 in aluminum chloride solution or the mixed solution of Aluminum Ammonium Sulfate and Aluminum Chloride, be mixed with the Al3 ⁺ concentration that contains 4-8wt% Polyethylene Glycol 400 and be 0.3-0.4mol/L , adding polyethylene glycol 2000 to the ammonium bicarbonate solution to prepare 0.3-0.6mol/L ammonium bicarbonate B solution containing 1-8wt% polyethylene glycol 2000, and adding ammonia water to adjust its pH value to 9- 10.

The above two steps are to prepare the stock solution, which will be repeated in the following examples. To make the examples concise, these two steps are listed separately, and will not be repeated in each example.

Embodiment 1: Under the magnetic stirring of 1300r/min, the concentration that will contain 4.5wt% polyethylene glycol (PEG) 400 is that the solution of _0.3mol /LAlCl is added as aluminum salt A solution with the speed of 300 drops/min. Containing the concentration of 4.6wt% polyethylene glycol (PEG) 2000 is in the ammonium bicarbonate B solution (pH is 9.3) of 0.6mol/L, after titration is finished, continue stirring 0.5h; Centrifugal separation, with secondary water washing 3 times, washed with ethanol for 3 times, dried at 80°C for 4 hours, and the surface water was removed to obtain a dry powder. Add the obtained dry powder into 80ml of n-butanol, after ultrasonic dispersion, reflux for 2h, distill and remove the n-butanol-water azeotrope at 93°C, when the fraction temperature rises to the boiling point of n-butanol at 117°C, After stopping the distillation and continuing to reflux for 2 h, the n-butanol was recovered by distillation under reduced pressure to obtain a loose powder.

The γ-Al ₂ O ₃ product was obtained by calcining at 900°C for 2 hours, and its particle morphology is shown in Figure 1. The particle distribution is relatively uniform, the particle size range is 18-68nm, and the average particle size is 38nm; the particle inner pore size ranges from 2-12nm, and the particle inner average pore size is 3.8nm. The specific surface area is 121m ² /g, and the crystallization degree of the pore wall is relatively high.

Example 2: Under magnetic stirring at 1000r/min, a solution containing 4.5wt% PEG400 with an Al ³⁺ concentration of 0.30mol/L (AlCl ₃ : NH ₄ Al(SO ₄ ) ₂ =1:1 molar ratio) was used as aluminum Add the salt A solution at a rate of 250 drops/min into an equal volume of ammonium bicarbonate B solution (pH 9.3) containing 4.6 wt% PEG2000 at a concentration of 0.60 mol/L. After the titration is completed, continue stirring for 0.5 h; , washed 3 times with secondary water and 3 times with ethanol, dried at 80°C for 4 hours, removed surface water, and obtained dry powder. Add the obtained dry powder into 80ml of n-butanol, after ultrasonic dispersion, reflux for 2h, distill and remove the n-butanol-water azeotrope at 93°C, when the fraction temperature rises to the boiling point of n-butanol at 117°C, After stopping the distillation and continuing to reflux for 2 h, the n-butanol was recovered by distillation under reduced pressure to obtain a loose powder.

Calcined at 850°C for 3 hours to obtain the γ-Al ₂ O ₃ product, the particle morphology of which is shown in Figure 2. The particle distribution is relatively uniform, the particle size range is 56-87nm, and the average particle size is 63nm; the particle inner pore size ranges from 2-9nm, the particle inner average pore size is 4.7nm, the specific surface area is 153m ² /g, and the degree of crystallization of the pore wall higher.

Example 3: under 1300r/min magnetic stirring, a solution containing 8wt% PEG400 with an Al ³⁺ concentration of 0.4mol/L (AlCl ₃ : NH ₄ Al(SO ₄ ) ₂ =1:1) was used as the aluminum salt A solution Add 2 times the volume of ammonium bicarbonate B solution (pH is 9.3) containing 8wt% PEG2000 with a speed of 350 drops/min of 0.40mol/L, after the titration is completed, continue to stir for 0.5h; Wash with water for 3 times, add the obtained precipitate into 80ml of n-butanol, after ultrasonic dispersion, reflux for 2h, distill and remove the azeotrope of n-butanol-water at 93°C, when the fraction temperature rises to n-butanol When the boiling point was 117°C, the distillation was stopped, and after continuing to reflux for 2 hours, n-butanol was recovered by distillation under reduced pressure to obtain a loose powder.

Calcined at 880°C for 2.5 hours to obtain the γ-Al ₂ O ₃ product, the particle morphology of which is shown in Figure 3. The surface of the particles is rough, and the mesoporous nanoparticles are connected to form a fibrous structure. The particle size ranges from 25-75nm, with an average particle size of 51nm; the inner particle diameter ranges from 2.2-9nm, with an average pore size of 5.2nm, and a specific surface area of 212m ² /g, the degree of crystallization of the pore wall is higher.

Example 4: under 1300r/min magnetic stirring, a solution containing 8wt% PEG400 with an Al ³⁺ concentration of 0.3 mol/L (AlCl ₃ : NH ₄ Al(SO ₄ ) ₂ = 1:1) was used as the aluminum salt A solution Add 2 times of volume containing 1.4wt% PEG2000 concentration in the ammonium bicarbonate B solution (pH is 9.3) of 0.30mol/L with the speed of 300 drops/min, after the titration is completed, continue to stir for 0.5h; Wash twice with water for 3 times, ethanol for 3 times, and dry at 80°C for 4 hours to remove surface water to obtain a dry powder. Add the obtained dry powder into 80ml of n-butanol, after ultrasonic dispersion, reflux for 2h, distill and remove the n-butanol-water azeotrope at 93°C, when the fraction temperature rises to the boiling point of n-butanol at 117°C, After stopping the distillation and continuing to reflux for 2 h, the n-butanol was recovered by distillation under reduced pressure to obtain a loose powder.

Calcined at 900°C for 2 hours to obtain the γ-Al ₂ O ₃ product, the particle morphology is shown in Figure 4, the particle distribution is relatively uniform, the particle size range is 10-50nm, and the average particle size is 20nm; The average pore diameter is 2.8nm, the specific surface area is 132m ² /g, and the crystallization degree of the pore wall is relatively high. .

Example 5: Under the magnetic stirring of 1300r/min, the Al ^{3 +} concentration of 0.4mol/L (AlCl ₃ : NH ₄ Al(SO ₄ ) ₂ = 1:3) solution containing 7wt% PEG400 was used as the aluminum salt A solution to Add an equal volume of ammonium bicarbonate B solution (pH is 9.3) containing 5.2wt% PEG2000 at a speed of 300 drops/min at a concentration of 0.30mol/L. After the titration is completed, continue to stir for 0.5h; Wash with water for 3 times, add the obtained precipitate into 80ml of n-butanol, after ultrasonic dispersion, reflux for 2h, distill off the azeotrope of n-butanol-water at 93°C, when the fraction temperature rises to the boiling point of n-butanol At 117°C, the distillation was stopped, and after reflux was continued for 2 hours, n-butanol was recovered by distillation under reduced pressure to obtain a loose powder.

The γ-Al ₂ O ₃ product was obtained by calcining at 900°C for 2 hours, and its particle morphology is shown in Fig. 5 . The particle surface is rough, the particle size range is 10-75nm, and the average particle size is 25nm; the particle inner pore size ranges from 2-18nm, the average pore size is 7.4nm, the specific surface area is 96m ² /g, and the crystallization degree of the pore wall is relatively high .

Through the examples and a large number of experiments, it is found that the particle size and pore size and their distribution are related to the concentration and degree of polymerization of the surfactant and the composition and concentration of the inorganic salt. Polyethylene glycol surfaces with different proportions and degrees of polymerization can be selected as required. Active agent and aluminum salt or mixture thereof. Within a certain range (such as: polyethylene glycol 400 concentration 4-8wt%, polyethylene glycol 2000 concentration 1-8wt%), the greater the concentration of PEG, the smaller the particle size, the larger the pore size and specific surface area. The main diffraction peaks of the X-ray powder diffraction pattern of γ-Al ₂ O ₃ nanopowder obtained by calcination at 900°C are: 46.0°(100), 67.1°(90), 37.0°(60), 49.0°(58), 39.7 °(53) is the characteristic peak of γ-Al ₂ O ₃ , and no other characteristic diffraction peaks were found. The specific surface area varies in the range of 95-212m ² /g with the concentration and type of aluminum salt and PEG. The specific surface area, degree of crystallization, and particle size are related to the setting of the temperature zone. With the increase of the calcination temperature, nanopowders with a gradually decreasing specific surface area and gradually increasing crystallization degree, crystal grains and particle size can be obtained. After calcination at 1000℃ for 2 hours, the main crystal phase is still γ-Al ₂ O ₃ .

Claims (3)

1. A method for preparing gamma-alumina nanopowder with an inner mesoporous structure, characterized in that it comprises the following specific steps: (1), take aluminum ammonium sulfate, aluminum chloride and ammonium bicarbonate according to needs, dissolve in secondary water respectively, make aluminum chloride solution or aluminum ammonium sulfate and aluminum ion total concentration 0.3-0.5mol/L A mixed solution of aluminum chloride, the molar ratio range of ammonium aluminum sulfate/aluminum chloride in the mixed solution is 0-3, and the ammonium bicarbonate solution with a concentration of 0.3-0.6mol/L is used to filter out the solution with a microporous membrane impurities; (2), add Polyethylene Glycol 400 in aluminum chloride solution or the mixed solution of Aluminum Ammonium Sulfate and Aluminum Chloride, the Al3 ⁺ concentration that is mixed with 4-8wt% Polyethylene Glycol 400 is 0.3-0.5mol /L aluminum salt A solution, add polyethylene glycol 2000 in ammonium bicarbonate solution, be made into 0.3-0.6mol/L ammonium bicarbonate B solution containing 1-8wt% polyethylene glycol 2000, and add ammoniacal liquor Adjust its pH value to 9-10; (3) Under magnetic stirring, add dropwise 1/2 volume to an equal volume of aluminum salt A solution to the ammonium bicarbonate B solution. After the titration is completed, continue to stir until the reaction is complete, centrifuge to separate the precipitate, and wash with secondary water until Detect that there is no SO ₄ ^2- , and then dry to obtain a dry powder; (4) Add the obtained dry powder to a sufficient amount of n-butanol, after ultrasonic dispersion, fully reflux, distill and remove the n-butanol-water azeotrope at 93-95 °C, when the fraction temperature rises to normal When the boiling point of butanol is 115-120°C, stop the distillation, continue to reflux, and then recover n-butanol by distillation under reduced pressure to obtain loose γ-Al ₂ O ₃ nanopowder; (5) Calcining the obtained γ-Al ₂ O ₃ nanometer powder at 850-900° C. to obtain γ-Al ₂ O ₃ nanometer powder with an intra-particle mesopore structure. 2. The preparation method of γ-alumina nanopowder with inner mesoporous structure according to claim 1, characterized in that: in step (3), under the magnetic stirring of 1000-1300r/min, 250-350 Add 1/2 volume to an equal volume of aluminum salt A solution to the ammonium bicarbonate B solution at a rate of drop/minute, and wash the centrifuged precipitate with secondary water, and detect no SO with 1-2% barium nitrate ₄ ^2- , and then washed several times with ethanol and dried at 70-90°C for 3-4 hours to obtain a dry powder. 3. The preparation method of γ-alumina nanopowder with intra-particle mesoporous structure according to claim 1, characterized in that: the calcination time in step (5) is 2-3 hours, and the obtained γ-alumina nano-powder with intra-particle The γ-Al ₂ O ₃ nanometer powder with mesoporous structure has a uniform particle size distribution, the average particle size in the particles is 20-63nm, the average particle internal pore size is 2.8-7.4nm, and the specific surface area is 95-212m ² /g.

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