CN110424070B - Porous alumina nanofiber and preparation method thereof - Google Patents
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Abstract
The invention relates to the technical field of nano fibers, and provides a porous alumina nano fiber and a preparation method thereof. According to the invention, aluminum hydroxide is used as an aluminum source, ammonium salt or amide compound is used as a modifier, an aluminum oxide precursor is obtained through hydrothermal crystallization of active aluminum hydroxide and the modifier, and porous aluminum oxide nanofibers are obtained after roasting. The preparation method provided by the invention has the advantages of simple steps and low cost, the hydrothermal crystallization mother liquor can be recycled, no waste liquor is discharged, the energy is saved, the environment is protected, and the preparation method is a green process and is suitable for industrial production; in addition, industrial aluminum hydroxide which is cheap and easy to obtain is used as an aluminum source, so that the production cost can be further reduced compared with soluble aluminum salt; the specific surface area of the alumina precursor prepared by the invention is as high as 505.4m2G, pore volume of 2.70cm3The specific surface area of the porous alumina nano fiber after roasting reaches 318.3m2G, pore volume of 2.10cm3/g。
Description
Technical Field
The invention relates to the technical field of nanofiber materials, in particular to porous alumina nanofiber and a preparation method thereof.
Background
Alumina is widely used in catalysts, catalyst supports, adsorbents, or composite materials due to its high specific surface area, abundant pores, and excellent chemical properties. Hydrofining is one of the important means for improving the quality of oil products, and can reduce the impurity content of raw oil. In the hydrofining process, alumina is often used as a carrier of the catalyst, and the alumina has a rich pore structure, so that the catalytic activity and selectivity are improved.
Along with the reduction of the quality of crude oil, the alumina with large pore volume is concerned by the petrochemical industry, the large pore volume can reduce the internal diffusion resistance of heavy oil macromolecules, and the activity and the selectivity of the catalyst can be improved. The macroporous aluminium hydroxide can be synthesized by sol-gel method, precipitation method and other methods, and is roasted at high temperatureThen the alumina with large pore volume can be obtained. The sol-gel method generally uses an organic aluminum source, but the organic aluminum source has high cost and is not environment-friendly. Precipitation method for preparing alumina generally utilizes sodium metaaluminate and an acidic aluminum source (e.g., aluminum sulfate, aluminum nitrate, etc.) to respectively perform precipitation reaction with carbon dioxide gas and alkalis to obtain aluminum hydroxide. However, the alumina prepared in industry has low pore volume, and the specific surface area of the industrial alumina is generally lower than 250m2G, pore volume of 0.5cm3And about/g.
Researches show that the microstructure of the alumina has great influence on the characteristics of the pore structure, the nanofiber structure is randomly stacked, the contact area between fibers is low, a large number of interstitial pores are formed, and the structure shows strong sintering resistance.
The group invented a green process (CN 109292802A) for synthesizing basic ammonium aluminum carbonate and preparing high specific surface alumina by pyrolysis, but the alumina prepared by the method has a low pore volume and is limited in application in hydrofining.
The basic aluminum ammonium carbonate fiber is synthesized by aluminum nitrate and urea under the assistance of an organic template agent in the patent (CN103911686), and the method has the disadvantages of higher cost, environmental friendliness and no contribution to industrial production due to the use of the template agent.
Disclosure of Invention
In view of the above, the present invention aims to provide a porous alumina nanofiber and a preparation method thereof, the porous alumina nanofiber prepared by the present invention has characteristics of high specific surface area, large pore volume, simple preparation method, no need of using an organic template, no waste liquid discharge, environmental friendliness, and suitability for industrial production.
In order to achieve the above object, the present invention provides the following technical solutions:
a preparation method of porous alumina nano-fiber comprises the following steps:
(1) mixing active aluminum hydroxide, a modifier and water for hydrothermal crystallization, and performing solid-liquid separation to obtain an aluminum oxide precursor and a hydrothermal crystallization mother liquor;
(2) roasting the alumina precursor to obtain porous alumina nano fiber;
wherein the active aluminum hydroxide is obtained by activating aluminum hydroxide in an activating atmosphere; the modifier comprises one or more of ammonium salt and amide compounds.
Preferably, the activating atmosphere comprises one or more of hydrogen, oxygen, nitrogen, air, carbon dioxide, argon and helium; the activation temperature is 100-800 ℃, and the activation time is 5-6 h.
Preferably, the ammonium salt comprises one or more of ammonium acetate, ammonium nitrate, ammonium chloride, ammonium sulfate, ammonium citrate, ammonium tartrate, ammonium carbonate, ammonium bicarbonate and ammonium oxalate;
the amide compound comprises one or more of formamide, acetamide, urea and biuret.
Preferably, the molar ratio of the modifier to the Al element in the active aluminum hydroxide is 0.5-20: 1.
Preferably, the temperature of the hydrothermal crystallization is 60-180 ℃, and the time of the hydrothermal crystallization is 6-48 h.
Preferably, after the solid-liquid separation, drying the alumina precursor at 70-200 ℃.
Preferably, the roasting temperature is 250-1300 ℃, and the roasting time is 2-6 h.
Preferably, the hydrothermal crystallization mother liquor is recycled, and the recycling method comprises the following steps: and (3) adding a modifier, active aluminum hydroxide and water into the hydrothermal crystallization mother liquor, and repeating the steps (1) to (2).
Preferably, the molar ratio of the supplemented modifier to the Al element in the supplemented active aluminum hydroxide is 0.5-5: 1, and the molar ratio of the supplemented water to the Al element in the supplemented active aluminum hydroxide is 1-50: 1.
The invention provides the porous alumina nanofiber prepared by the preparation method in the scheme.
The invention provides a preparation method of porous alumina nanofiber, which comprises the steps of taking aluminum hydroxide as an aluminum source, taking ammonium salt or amide compound as a modifier, activating the aluminum hydroxide with gas, carrying out hydrothermal crystallization on the activated aluminum hydroxide and the modifier together to obtain an aluminum oxide precursor, and roasting to obtain the porous alumina nanofiber. The method utilizes the activation atmosphere to activate the aluminum hydroxide, creates defect sites on the surface of the aluminum hydroxide to form active aluminum hydroxide, inserts the modifier into a lamella of an active aluminum hydroxide lattice in the hydrothermal crystallization process to play a role in reaming, and induces an aluminum oxide precursor to form a nanofiber shape; in addition, the hydrothermal crystallization mother liquor in the preparation method provided by the invention can be recycled, no waste liquor is discharged in the whole preparation process, the preparation method is energy-saving and environment-friendly, the preparation method is a green process, the preparation steps are simple, the cost is low, and the preparation method is suitable for industrial production; in addition, industrial aluminum hydroxide which is cheap and easy to obtain is used as an aluminum source, so that the production cost can be further reduced compared with soluble aluminum salt.
The invention also provides the porous alumina nanofiber prepared by the preparation method in the scheme, the porous alumina nanofiber provided by the invention has high specific surface area and large pore volume, and the example result shows that the specific surface of the alumina precursor synthesized by the invention is up to 505.4m2G, pore volume of 2.70cm3The specific surface area of the alumina nano fiber obtained after high-temperature roasting reaches up to 318.3m2G, pore volume of 2.10cm3/g。
Drawings
FIG. 1 shows N of alumina precursors obtained in example 1, example 1-1 to example 1-3, example 2-1 to example 2-32Adsorption and desorption isotherm diagram;
FIG. 2 shows N of the alumina precursors obtained in example 3, example 3-1 to example 3-22Adsorption and desorption isotherm diagram;
FIG. 3 is a graph showing pore size distributions of alumina precursors obtained in example 1, example 1-1 to example 1-3, example 2-1 to example 2-3;
FIG. 4 is a graph showing pore size distributions of alumina precursors obtained in example 3, example 3-1 to example 3-2;
FIG. 5 is a graph showing N of the porous alumina nanofibers obtained in examples 1 to 22Adsorption and desorption isotherm diagram;
FIG. 6 is a graph showing pore size distribution of the porous alumina nanofibers obtained in examples 1-2;
figure 7 is an XRD pattern of the porous alumina nanofibers from example 1.
Detailed Description
The invention provides a preparation method of porous alumina nano-fiber, which comprises the following steps:
(1) mixing active aluminum hydroxide, a modifier and water for hydrothermal crystallization, and performing solid-liquid separation to obtain an aluminum oxide precursor and a hydrothermal crystallization mother liquor;
(2) and roasting the alumina precursor to obtain the porous alumina nanofiber.
The invention mixes active aluminum hydroxide, modifier and water for hydrothermal crystallization, and obtains an aluminum oxide precursor and hydrothermal crystallization mother liquor after solid-liquid separation. In the invention, the active aluminum hydroxide is obtained by activating aluminum hydroxide in an activating atmosphere; the activating atmosphere preferably comprises one or more of hydrogen, oxygen, nitrogen, air, carbon dioxide, argon and helium; the activation temperature is preferably 100-800 ℃, more preferably 200-400 ℃, and the activation time is preferably 5-6 h. According to the invention, the aluminum hydroxide is activated through the activating atmosphere, so that a defect site can be created on the surface of the aluminum hydroxide to obtain the active aluminum hydroxide, and the defect site on the surface of the active aluminum hydroxide can provide a position for the insertion and reaming of a subsequent modifier; the invention has no special requirement on the source of the aluminum hydroxide, and only needs to use industrial aluminum hydroxide; the invention takes industrial aluminum hydroxide as an aluminum source, and can further reduce the preparation cost.
In the invention, the modifier preferably comprises one or more of ammonium salt and amide compounds, and the ammonium salt preferably comprises one or more of ammonium acetate, ammonium nitrate, ammonium chloride, ammonium sulfate, ammonium citrate, ammonium tartrate, ammonium carbonate, ammonium bicarbonate and ammonium oxalate; the amide compound preferably comprises one or more of formamide, acetamide, urea and biuret; when the modifier is a mixture of multiple modifiers, the molar amounts of each modifier in the mixture are preferably equal.
In the invention, the molar ratio of the modifier to the Al element in the active aluminum hydroxide is preferably 0.5-20: 1, more preferably 1-15: 1, and further preferably 5-10: 1; the molar ratio of the water to the Al element in the active aluminum hydroxide is preferably 1: 50-100, and more preferably 1: 60-80.
The invention preferably dissolves the modifier in water, then adds active aluminum hydroxide, stirs evenly and then carries out hydrothermal crystallization. In the invention, the temperature of the hydrothermal crystallization is preferably 60-180 ℃, more preferably 80-130 ℃, and the time of the hydrothermal crystallization is preferably 6-48 h, more preferably 12-24 h; the hydrothermal crystallization is preferably carried out in a hydrothermal crystallization kettle. In the hydrothermal crystallization process, a modifier is inserted into a lamella of an aluminum hydroxide crystal lattice in the reaction process to play a role in hole expansion, so that an aluminum oxide precursor with high specific surface area and large pore volume can be obtained, and under the high-temperature hydrothermal condition and the action of the modifier, the aluminum oxide precursor crystal grows directionally along a certain direction to finally form the shape of the nanofiber.
After the hydrothermal crystallization is finished, the invention carries out solid-liquid separation on the hydrothermal crystallization product system to obtain an alumina precursor and a hydrothermal crystallization mother liquor. In the present invention, the solid-liquid separation is preferably performed by filtration; after filtering, the alumina precursor is preferably dried to obtain a dried alumina precursor, wherein the drying temperature is preferably 70-200 ℃, and more preferably 100-150 ℃.
After the alumina precursor is obtained, the porous alumina nanofiber is obtained by roasting the alumina precursor. In the invention, the roasting temperature is preferably 250-1300 ℃, more preferably 300-1200 ℃, further preferably 500-1000 ℃, and the roasting time is preferably 2-6 hours, more preferably 3-5 hours, further preferably 3.5-4 hours; the heating rate for heating to the roasting temperature is preferably 2 ℃/min; the calcination is preferably carried out in an air atmosphere. According to the invention, the modifier is decomposed and removed by roasting, and the nano fibrous alumina precursor is formed into porous alumina nano fiber.
In the present invention, the components of the hydrothermal crystallization mother liquor include water, residual modifier, and dissolved aluminum ions, etc., and the crystallization mother liquor is preferably recycled by the following method: and (3) adding a modifier, active aluminum hydroxide and water into the hydrothermal crystallization mother liquor, and repeating the steps (1) to (2), wherein the molar ratio of the Al element in the added modifier to the Al element in the added active aluminum hydroxide is preferably 0.5-5: 1, more preferably 1-4: 1, and the molar ratio of the Al element in the added water to the Al element in the added active aluminum hydroxide is preferably 1-50: 1, more preferably 5-40: 1. The method recycles the hydrothermal crystallization mother liquor, avoids waste liquid discharge, is green and pollution-free, and reduces the preparation cost.
The invention also provides the porous alumina nano fiber prepared by the preparation method in the scheme. The specific surface area of the porous alumina nano fiber provided by the invention is up to 318.3m2G, pore volume of 2.10cm3The diameter is 30-50 nm, and the length-diameter ratio is 20-40.
The embodiments of the present invention will be described in detail with reference to the following examples, but they should not be construed as limiting the scope of the present invention.
Example 1
Preparing a biuret solution with the mass fraction of 30% at room temperature, and then mixing the biuret solution with Al according to the molar ratio of 10:1 adding active aluminum hydroxide powder (aluminum hydroxide is activated for 5 hours at 100 ℃ in a nitrogen atmosphere), uniformly stirring, transferring to a crystallization kettle, crystallizing for 14 hours at 80 ℃, filtering and washing a solid obtained after crystallization, drying for 12 hours at 80 ℃ to obtain an alumina fiber precursor, and recording the precursor as A-1 and a mother liquor obtained after crystallization as mother liquor (1). The specific surface area of A-1 obtained was 505.4m2G, pore volume of 2.7cm3/g。
Heating the obtained A-1 solid to 650 ℃ at the heating rate of 2 ℃/min in the air atmosphere, and roasting at the constant temperature for 6 hours to obtain porous alumina nano-fiber, and recording as Al2O3-1, specific surface area 318.3m2Per g, pore volume of 2.10cm3/g。
Examples 1 to 1
The mother liquor (1) obtained in example 1 was supplemented with biuret, and then with activated aluminum hydroxide powder (oxyhydrogen) in an amount equivalent to that of example 1Activating aluminum at 150 ℃ for 4h) and water in a carbon dioxide atmosphere, and uniformly stirring, wherein the molar ratio of the supplemented biuret to Al in the supplemented active aluminum hydroxide is 4:1, and the molar ratio of the supplemented water to Al in the supplemented active aluminum hydroxide is 20-30: 1; and (3) transferring the precursor to a crystallization kettle for crystallization at 130 ℃ for 12 hours, filtering and washing the crystallized solid, and drying the crystallized solid at 100 ℃ for 12 hours to obtain a nano fibrous alumina precursor, namely A-1-1, and marking the crystallized mother liquor as mother liquor (2). The specific surface area of the obtained A-1-1 was 325.9m2G, pore volume of 1.42cm3/g。
Examples 1 to 2
Supplementing urea to the mother liquor (2) obtained in the example 1-1, then supplementing active aluminum hydroxide powder (activated at 200 ℃ for 3 hours in an air atmosphere) and water which are equal to those in the example 1-1, and uniformly stirring, wherein the molar ratio of the supplemented urea to Al in the supplemented active aluminum hydroxide is 5:1, and the molar ratio of the supplemented water to Al in the supplemented active aluminum hydroxide is 20-30: 1; and (3) transferring the precursor to a crystallization kettle for crystallization at 90 ℃ for 24 hours, filtering and washing the crystallized solid, and drying the solid at 100 ℃ for 12 hours to obtain a nano fibrous alumina precursor, namely A-1-2, and marking the crystallized mother liquor as mother liquor (3). The specific surface area of the obtained A-1-2 was 405.1m2Per g, pore volume of 2.36cm3/g。
Examples 1 to 3
And (3) adding ammonium carbonate into the mother liquor (3) obtained in the example 1-2, then adding aluminum hydroxide powder (activated at 150 ℃ for 4 hours in a nitrogen atmosphere) and water which are equal to those in the example 1-2, and uniformly stirring, wherein the molar ratio of the added ammonium carbonate to Al in the added active aluminum hydroxide is 4:1, and the molar ratio of the added water to Al in the added active aluminum hydroxide is 20-30: 1. And (3) transferring the mixture to a crystallization kettle for crystallization at the temperature of 80 ℃ for 24 hours, filtering and washing the crystallized solid, and drying the solid at the temperature of 100 ℃ for 12 hours to obtain a nano fibrous alumina precursor, namely A-1-3, and marking the crystallized mother liquor as mother liquor (2). The obtained A-1-3 had a specific surface area of 596.9m2Per g, total pore volume of 2.70cm3/g。
Example 2
Preparing modifier solution with the mass fraction of 50% according to the mol ratio of ammonium carbonate to ammonium chloride of 1:1 at room temperature, and then preparing modifier according to the weight fraction of the modifierThe molar ratio to Al is 10:1 adding active aluminum hydroxide powder (activated for 6h at 150 ℃ under the nitrogen atmosphere), uniformly stirring, transferring to a crystallization kettle, crystallizing for 12 h at 100 ℃, carrying out suction filtration and washing on the crystallized solid, drying for 12 h at 100 ℃ to obtain a nano fibrous alumina precursor, marked as A-2, and marking the mother liquor obtained after crystallization as mother liquor (1). The specific surface area of A-2 obtained was 473.9m2G, pore volume of 1.9cm3/g。
Heating the obtained A-2 solid to 550 ℃ at the heating rate of 2 ℃/min in the air atmosphere, and roasting at the constant temperature for 6 hours to obtain the porous alumina nanofiber, and recording the porous alumina nanofiber as Al2O3-2, specific surface 254.5m2G, pore volume of 1.85cm3/g。
Example 2-1
Supplementing urea to the mother liquor (1) obtained in the example 2, then supplementing active aluminum hydroxide powder (activated for 5 hours at 300 ℃ in an argon atmosphere) and a certain amount of water which are equal to those in the example 2, and uniformly stirring; wherein the molar ratio of the supplemented urea to Al in the supplemented active aluminum hydroxide is 5:1, and the molar ratio of the supplemented water to Al in the supplemented active aluminum hydroxide is 20-30: 1. And (3) transferring the precursor to a crystallization kettle for crystallization at the temperature of 80 ℃ for 24 hours, filtering and washing the crystallized solid, and drying the solid at the temperature of 100 ℃ for 12 hours to obtain a nano fibrous alumina precursor, namely A-2-1, and marking the crystallized mother liquor as mother liquor (2). The specific surface area of the obtained A-2-1 was 320.0m2(g) total pore volume of 0.92cm3/g。
Examples 2 to 2
Supplementing urea to the mother liquor (2) obtained in the example 2-1, then supplementing active aluminum hydroxide powder (activated at 350 ℃ for 3 hours in a hydrogen atmosphere) and water which are equal to those in the example 2-1, and uniformly stirring, wherein the molar ratio of the supplemented urea to Al in the supplemented active aluminum hydroxide is 6:1, and the molar ratio of the supplemented water to Al in the supplemented active aluminum hydroxide is 20-30: 1. And (3) transferring the precursor to a crystallization kettle for crystallization at the temperature of 80 ℃ for 24 hours, filtering and washing the crystallized solid, and drying the solid at the temperature of 100 ℃ for 12 hours to obtain a nano fibrous alumina precursor, namely A-2-2, and marking the crystallized mother liquor as mother liquor (3). The specific surface area of the obtained A-2-2 film was 577.5m2G, pore volume of 1.30cm3/g。
Examples 2 to 3
And (3) supplementing acetamide to the mother liquor (3) obtained in the example 2-2, then adding active aluminum hydroxide powder (activated at 250 ℃ for 3 hours in an oxygen atmosphere) with the same amount as that of the mother liquor obtained in the example 2-2, and uniformly stirring, wherein the molar ratio of the supplemented acetamide to Al in the supplemented active aluminum hydroxide is 5:1, and the molar ratio of the supplemented water to Al in the supplemented active aluminum hydroxide is 20-30: 1. And (3) transferring the precursor into a crystallization kettle for crystallization at 60 ℃ for 24 hours, carrying out suction filtration and washing on the crystallized solid, and drying at 100 ℃ for 12 hours to obtain a nano fibrous alumina precursor, which is marked as A-2-3. The specific surface area of the obtained A-2-3 was 401.1m2G, total pore volume 2.30cm3/g。
Example 3
At room temperature, as ammonium carbonate: preparing a modifier solution with the mass fraction of 50% according to the molar ratio of ammonium bicarbonate of 1:1, adding active aluminum hydroxide powder (activated for 6 hours at 450 ℃ in a nitrogen atmosphere) according to the molar ratio of the modifier to Al of 15:1, uniformly stirring, transferring to a crystallization kettle, crystallizing for 12 hours at 100 ℃, carrying out suction filtration and washing on a solid obtained after crystallization, drying for 12 hours at 100 ℃, obtaining a nano fibrous alumina precursor, and marking the precursor as A-3, and marking a mother liquor obtained after crystallization as mother liquor (1). The specific surface area of A-3 obtained was 473.9m2G, pore volume of 1.9cm3/g。
Example 3-1
And (2) supplementing acetamide to the mother liquor (1) obtained in the example 3, then adding activated aluminum hydroxide powder (activated at 400 ℃ for 3 hours in an oxygen atmosphere) with the same amount as that of the mother liquor obtained in the example 3, and uniformly stirring, wherein the molar ratio of the supplemented acetamide to Al in the supplemented activated aluminum hydroxide is 4:1, and the molar ratio of the supplemented water to Al in the supplemented activated aluminum hydroxide is 20-30: 1. And (3) transferring the precursor into a crystallization kettle for crystallization at 60 ℃ for 24 hours, carrying out suction filtration and washing on the crystallized solid, drying the washed solid at 100 ℃ for 12 hours to obtain a nano fibrous alumina precursor A-3-1, and marking the mother liquor obtained after crystallization as mother liquor (2). The specific surface area of the obtained A-3-1 was 401.1m2G, total pore volume 2.30cm3/g。
Examples 3 to 2
Mother liquor (2) obtained in example 3-1 was supplemented with ammonium carbonateAnd then adding active aluminum hydroxide powder (activated at 500 ℃ for 3 hours in an air atmosphere) which is equal to that in the embodiment 3-1, and uniformly stirring, wherein the molar ratio of the supplemented ammonium carbonate to Al in the supplemented active aluminum hydroxide is 6:1, and the molar ratio of the supplemented water to Al in the supplemented active aluminum hydroxide is 20-30: 1. And (3) crystallizing at 70 ℃ for 12 hours in a crystallization kettle, carrying out suction filtration and washing on the crystallized solid, and drying at 100 ℃ for 12 hours to obtain the alumina fiber precursor A-3-2. The specific surface area of the obtained A-3-2 was 401.1m2G, total pore volume 2.30cm3/g。
And (3) characterization:
(1) characterization of the alumina precursor
FIG. 1 shows N of alumina precursors obtained in example 1, example 1-1 to example 1-3, example 2-1 to example 2-32Adsorption and desorption isotherm diagram; FIG. 2 shows N of the alumina precursors obtained in example 3, example 3-1 to example 3-22Adsorption and desorption isotherm diagram;
according to the graphs in fig. 1-2, all samples have IV-type nitrogen adsorption and desorption isotherms, which indicates that the alumina precursors obtained in the above embodiments are typical mesoporous materials; P/P0After 0.9, the curve adsorption capacity is obviously increased, which shows that the sample has a large mesoporous structure.
FIG. 3 is a graph showing pore size distributions of alumina precursors obtained in example 1, example 1-1 to example 1-3, example 2-1 to example 2-3; FIG. 4 is a graph showing pore size distributions of the alumina precursors obtained in example 3, example 3-1 to example 3-2.
As can be seen from FIGS. 3 to 4, the pore size distribution of the sample is wide and has a bimodal distribution.
(2) Porous alumina nanofiber characterization
FIG. 5 is a graph showing N of the porous alumina nanofibers obtained in examples 1 to 22Adsorption and desorption isotherm diagram; as can be seen from FIG. 5, the alumina nanofibers obtained after calcination still have high adsorption capacity, indicating that the sample still retains large pore volume.
FIG. 6 is a graph showing pore size distribution of the porous alumina nanofibers obtained in examples 1-2; as can be seen from fig. 6, the sample still retained a broad pore size distribution after firing.
FIG. 7 is an XRD pattern of the porous alumina nanofibers from example 1; figure 7 shows that the calcined sample was gamma alumina.
According to the embodiment, the preparation method provided by the invention has the advantages that the porous alumina nanofiber is prepared by taking the aluminum hydroxide as the aluminum source and the ammonium salt or the amide compound as the modifier through hydrothermal crystallization and roasting, the preparation steps are simple, the hydrothermal crystallization mother liquor can be recycled, no waste liquid is discharged, the energy is saved, the environment is protected, and the prepared porous alumina nanofiber has the advantages of high specific surface area, large pore volume and wide application prospect.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (10)
1. A preparation method of porous alumina nano-fiber is characterized by comprising the following steps:
(1) mixing active aluminum hydroxide, a modifier and water for hydrothermal crystallization, and performing solid-liquid separation to obtain an aluminum oxide precursor and a hydrothermal crystallization mother liquor;
(2) roasting the alumina precursor to obtain porous alumina nano fiber;
wherein the active aluminum hydroxide is obtained by activating aluminum hydroxide in an activating atmosphere; the activating atmosphere comprises one or more of hydrogen, oxygen, nitrogen, air, carbon dioxide, argon and helium; the activation temperature is 100-500 ℃; the modifier comprises one or more of ammonium salt and amide compounds.
2. The method according to claim 1, wherein the activation time is 5 to 6 hours.
3. The preparation method according to claim 1, wherein the ammonium salt comprises one or more of ammonium acetate, ammonium nitrate, ammonium chloride, ammonium sulfate, ammonium citrate, ammonium tartrate, ammonium carbonate, ammonium bicarbonate and ammonium oxalate;
the amide compound comprises one or more of formamide, acetamide, urea and biuret.
4. The preparation method according to claim 1, wherein the molar ratio of the modifier to Al element in the active aluminum hydroxide is 0.5-20: 1.
5. The preparation method according to claim 1, wherein the temperature of the hydrothermal crystallization is 60-180 ℃ and the time of the hydrothermal crystallization is 6-48 h.
6. The preparation method according to claim 1, further comprising drying the alumina precursor after the solid-liquid separation, wherein the drying temperature is 70 to 200 ℃.
7. The preparation method of claim 1, wherein the roasting temperature is 250-1300 ℃ and the roasting time is 2-6 h.
8. The preparation method according to claim 1, wherein the hydrothermal crystallization mother liquor is recycled, and the recycling method comprises the following steps: and (3) adding a modifier, active aluminum hydroxide and water into the hydrothermal crystallization mother liquor, and repeating the steps (1) to (2).
9. The preparation method according to claim 8, wherein the molar ratio of the Al element in the supplemented modifier to the supplemented active aluminum hydroxide is 0.5-5: 1, and the molar ratio of the Al element in the supplemented water to the supplemented active aluminum hydroxide is 1-50: 1.
10. The porous alumina nanofiber prepared by the preparation method of any one of claims 1 to 9.
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