Rod-like aluminum oxide as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of ceramic material preparation, and discloses rod-like aluminum oxide as well as a preparation method and application thereof. The preparation method comprises the following steps: fully dissolving aluminum chloride hexahydrate in ethylene glycol until the solution is clear; and putting the mixture into a muffle furnace, heating from room temperature to 800-1000 DEG C at a heating rate of 3-5 DEG C / min in an air atmosphere, calcining, keeping the temperature for 3 hours, and carrying out high-temperature calcination to obtain the rod-like aluminum oxide. The average radial length size of the cross section of the rod-like aluminum oxide is 2-5 microns, the average pore size is 5.59-32.15 nm, and the size distribution is wide and is easy to regulate and control; the Congo red dye prepared by the invention has the advantages of regular morphology, good dispersibility and large BET specific surface area (8-81.49 cm < 2 > / g), and can provide a large number of adsorption active sites to interact with Congo red dye molecules, so that the Congo red dye has larger adsorption capacity and high adsorption efficiency on the dye molecules, is convenient to apply to a wastewater treatment process, and realizes comprehensive utilization of resources.

Description

Technical Field

[0001] The invention belongs to the technical field of ceramic material preparation, and in particular relates to rod-shaped aluminum oxide, a preparation method and application thereof. Background Art

[0002] Alumina (Al2O3) is widely used due to its excellent physical properties, including high strength, hardness, high temperature resistance, and wear resistance. Al2O3 powder is not only the raw material for high-end Al2O3 ceramics such as integrated circuit substrates, synthetic gemstones, cutting tools, and artificial bones, but can also be used as a phosphor carrier, advanced refractory material, and specialty abrasive material.

[0003] Existing alumina preparation methods often make it difficult to precisely control the product morphology. For example, rod-shaped alumina often exhibits uneven particle size or dimensional deviations. Furthermore, the product is unstable. Under high temperature, high pressure, or other extreme conditions, some alumina products may undergo phase transitions or changes in particle size, leading to performance degradation. Current alumina preparation processes are complex, making large-scale, stable production difficult. During the alumina preparation process, the product often forms mesoporous, microporous, or other porous structures. These structures may be beneficial for certain applications, such as catalyst supports, but they can compromise performance in applications requiring high mechanical strength or density, such as cutting tools and bone implants.

[0004] In recent years, researchers have been continuously exploring the process of preparing alumina with specific morphology and stable properties. Most of the methods obtained are still in the laboratory stage and have not been further popularized and promoted in actual production.

[0005] The Chinese invention patent application number 201911158244.1 discloses a method in which a certain amount of aluminum nitrate hydrate and ammonium bicarbonate or urea are dissolved in a single liquid of a certain amount of water or ethylene glycol or a mixture of the two as a solvent, and an alumina precursor is obtained after stirring. The precursor is then washed, dried, crushed, and sieved to obtain a precursor powder, which is then calcined to obtain rod-shaped alumina. The shortcomings of this preparation method are that the multi-step process and strict reaction conditions (such as temperature and pH control) increase the process complexity and are difficult to adapt to large-scale production; although this preparation method obtains a rod-shaped structure, it still has deficiencies in particle size uniformity; during the drying and high-temperature treatment process, the nano-alumina particles are prone to agglomeration, which reduces their specific surface area, thereby weakening their adsorption and catalytic activity as a carrier.

[0006] Chinese invention patent application number 201310583217.5 discloses a method for preparing a mesoporous magnetic microchannel alumina dye adsorbent by mixing an organic acid with aluminum nitrate, ferric nitrate, zinc acetate, and nickel acetate in deionized water, stirring, evaporating, and dehydrating the mixture to produce a gel. The gel is then drawn into a precursor filament, which is then calcined to produce a mesoporous magnetic microchannel alumina dye adsorbent. However, this method's shortcomings include an overly complex precursor solution system, strict control of the ratios (molar ratio of citric acid to metal ions, and molar ratio of Al ions to Fe), and complex processes (e.g., evaporation and dehydration, gel drawing), which limit its large-scale application in dye wastewater adsorption. Summary of the Invention

[0007] In order to overcome the shortcomings and deficiencies of the prior art methods for synthesizing rod-shaped alumina, such as complex processes, tedious steps, strict conditions, uneven particle size distribution, and the easy agglomeration of the obtained products, which reduces the specific surface area of the catalyst and weakens its adsorption and catalytic activity as a carrier, the primary purpose of the present invention is to provide a method for preparing rod-shaped alumina; this method has the characteristics of easily available raw materials, low production cost and simple process.

[0008] Another object of the present invention is to provide a rod-shaped alumina prepared by the above-mentioned preparation method; the rod-shaped alumina has a rich pore structure, and the capillary action in the pores produces a large adsorption driving force, so that the adsorbed substance can be quickly "absorbed" into the pores; the larger specific surface area increases the contact area with the adsorbate, which helps to improve the adsorption performance of the rod-shaped alumina and has potential application value in the adsorption field.

[0009] Another object of the present invention is to provide an application of the above-mentioned rod-shaped alumina.

[0010] The purpose of the present invention is achieved through the following technical solutions:

[0011] A method for preparing rod-shaped aluminum oxide comprises the following steps:

[0012] (1) fully dissolving aluminum chloride hexahydrate in ethylene glycol by heating and stirring until the solution becomes clear and transparent to obtain a precursor salt solution with a concentration of 0.45 mol / L;

[0013] (2) Pour the precursor salt solution into an alumina crucible, then place the alumina crucible in a muffle furnace, and in an air atmosphere, heat the temperature from room temperature to 800-1000°C at a heating rate of 3-5°C / min, and then keep the temperature for 3 hours for high-temperature calcination to obtain rod-shaped alumina powder of γ phase, θ phase, α phase or their adjacent mixed phases.

[0014] A rod-shaped alumina prepared by the above preparation method, wherein the cross-sectional radial average length of the rod-shaped alumina is 2 to 5 μm, the average pore size is 5.59 to 32.15 nm; the BET specific surface area of the rod-shaped alumina is 8 to 81.49 cm 2 / g, pore volume of 0.008~0.115cm 3 / g.

[0015] The above-mentioned rod-shaped aluminum oxide is used in the field of dye wastewater adsorption, wherein the dye wastewater contains Congo red and / or methyl blue. During the application process, the rod-shaped aluminum oxide is placed in the dye wastewater, ultrasonically adsorbed for 1 hour, and then allowed to stand until the adsorption is completed.

[0016] The present invention has the following advantages and beneficial effects compared to the prior art:

[0017] (1) The raw materials required for the present invention are purchased from commercial sources and are all cheap and readily available products, with low production costs and high safety factors of the raw materials.

[0018] (2) The calcination involved in the present invention only uses a common commercial muffle furnace, the required calcination temperature is relatively low, no toxic products are released during the reaction process, and no protective atmosphere or raw materials with low safety factors are used.

[0019] (3) The present invention can prepare rod-shaped alumina of γ phase, θ phase and α phase by controlling the heating rate and holding time of the calcination process; the average radial length of the cross section of the rod-shaped alumina is 2 to 5 μm, the average pore size is 5.59-32.15 nm, and the distribution is uniform and the morphology is regular. The prepared Al2O3 rod has a large BET specific surface area (8 to 81.49 cm 2 / g), which can provide a larger adsorption contact area and has broad application prospects in the fields of catalysis and adsorption. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the SEM image of the rod-shaped alumina prepared in Example 1.

[0021] Figure 2 This is the heat treatment process diagram in Example 2-6.

[0022] Figure 3 This is the SEM image of the rod-shaped alumina prepared in Example 2.

[0023] Figure 4 This is the SEM image of the rod-shaped alumina prepared in Example 3.

[0024] Figure 5 This is the SEM image of the rod-shaped alumina prepared in Example 4.

[0025] Figure 6This is the SEM image of the rod-shaped alumina prepared in Example 5.

[0026] Figure 7 SEM image of rod-shaped alumina prepared in Example 6

[0027] Figure 8 This is the XRD pattern of the rod-shaped alumina prepared in Example 2-6.

[0028] Figure 9 This is the N2 adsorption-desorption isotherm of the rod-shaped alumina prepared in Example 2-6.

[0029] Figure 10 This is the DFT model pore size analysis of the rod-shaped alumina prepared in Examples 2-6.

[0030] Figure 11 BJH adsorption branch pore size analysis of rod-shaped alumina prepared in Examples 2-6.

[0031] Figure 12 This figure shows the application of the rod-shaped aluminum oxide prepared in Examples 2 to 6 in the adsorption of 100 mg / L Congo red dye. DETAILED DESCRIPTION

[0032] The present invention will be further described below in conjunction with specific examples, but should not be construed as limiting the present invention. Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0033] Aluminum chloride hexahydrate used in the following examples was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. with a purity of ≥97%; ethylene glycol was purchased from Tianjin Damao Chemical Reagent Factory with a purity of ≥99%.

[0034] The heat treatment process of step (2) of the following examples 2-6 is as follows Figure 2 shown.

[0035] Example 1:

[0036] (1) A certain proportion of aluminum chloride hexahydrate is fully dissolved in ethylene glycol by heating and stirring until the solution becomes clear and transparent, thereby obtaining precursor salt solutions of different concentrations;

[0037] (2) Pour the precursor salt solution obtained in step (1) into an alumina crucible, then place the alumina crucible in a muffle furnace, and heat it from room temperature to 300°C at a heating rate of 3-5°C / min in an air atmosphere, and then keep it warm for 0.5 and 3 hours respectively for high-temperature calcination to obtain a calcined product.

[0038] Figure 1These are SEM images of the products calcined at 300°C for 0.5h and 3h in precursor salt solutions with different concentrations.

[0039] Figure 1 (a) is the sample with a holding time of 0.5h. Only the calcined product of 0.6mol / L precursor salt solution has a rod-like morphology, while the products obtained by calcining other low concentration precursor salt solutions are agglomerated blocks.

[0040] Figure 1 (b) is a sample with a holding time of 3h. When the precursor salt concentration changes from 0.3-0.6mol / L, the number of rod-shaped particles increases and the size becomes more uniform as the nucleation points increase.

[0041] Calcining a 0.3 mol / L precursor salt solution yielded a product with a rod-like morphology, indicating that this concentration is critical for rod-like particles. Holding the precursor salt solution at 0.45 mol / L for 3 hours resulted in the most uniform rod-like particles. Therefore, 0.45 mol / L was selected as the optimal concentration, and a holding time of 3 hours was selected for subsequent experiments.

[0042] Example 2:

[0043] (1) fully dissolving a certain proportion of aluminum chloride hexahydrate in ethylene glycol by heating and stirring until the solution becomes clear and transparent, thereby obtaining a precursor salt solution with a concentration of 0.45 mol / L;

[0044] (2) Pour the precursor salt solution obtained in step (1) into an alumina crucible, then place the alumina crucible in a muffle furnace, and heat it from room temperature to 800°C at a heating rate of 3-5°C / min in an air atmosphere, and then keep it at this temperature for 3 hours for high-temperature calcination to obtain a calcined product, which is a rod-shaped alumina powder.

[0045] (3) The calcined products were characterized by N2 adsorption method, the specific surface area was calculated by BET method, the mesopore and macropore distribution of the samples were analyzed by BJH theoretical model, and the full pore distribution of the samples was analyzed by DFT density functional theory model.

[0046] (4) 50 mg of the rod-shaped alumina powder obtained above was placed in a 100 mg / L Congo red solution, ultrasonicated for 1 h, and then allowed to stand for adsorption until adsorption was complete.

[0047] Figure 3 The morphology of the rod-shaped alumina produced in Example 2 was observed under a scanning electron microscope. The powder after calcination was completely rod-shaped, with regular morphology, uniform long and long diameters, and good dispersibility.

[0048] Figure 8This is the XRD diagram of rod-shaped alumina, which shows that the sample obtained in Example 2 is γ-Al2O3 and has a high degree of crystallinity.

[0049] Figure 9 is the N2 adsorption-desorption isotherm of rod-shaped alumina. Figure 10 This is the DFT model pore size analysis of rod-shaped alumina. Figure 11 It is the BJH adsorption branch pore size analysis of rod-shaped aluminum oxide. Figure 9-11 It can be seen that the pore structure of the rod-shaped alumina obtained in Example 2 is: BET specific surface area 81.49 cm 2 / g, pore volume 0.114cm 3 / g, and the average pore diameter is 5.59nm.

[0050] Figure 12 This is an application diagram of rod-shaped alumina powder being placed in a 100 mg / L Congo red solution and adsorbed for 48 hours. It shows that the solution has been adsorbed by the porous alumina powder to become clear and transparent, and the removal rate of Congo red dye molecules is high.

[0051] Example 3:

[0052] The specific method and steps are the same as those in Example 2, except that in step (2), after the temperature is raised to 300° C., the temperature is maintained for 3 hours for high-temperature calcination.

[0053] pass Figure 4 It can be seen that although the heat treatment temperature is only 300℃, a rod-like structure has been obtained. Figure 8 It can be seen that the sample is amorphous at this time.

[0054] from Figure 9-11 It can be seen that the pore structure of the rod-shaped alumina obtained in Example 3 is: BET specific surface area 6.5cm 2 / g, micropore specific surface area 4.54cm 2 / g, pore volume 0.008cm 3 / g, and the average pore diameter is 5.14nm.

[0055] Figure 12 This is an application diagram of rod-shaped alumina powder placed in a 100 mg / L Congo red solution for 48 hours of adsorption, showing that the Congo red solution has good adsorption and tends to become clearer and more transparent than the Congo red solution without powder.

[0056] Example 4:

[0057] The specific method and steps are the same as those in Example 2, except that in step (2), after the temperature is raised to 400° C., the temperature is maintained for 3 hours for high-temperature calcination.

[0058] pass Figure 5It can be seen that although the heat treatment temperature is further increased, the surface morphology of the rod-like structure does not change significantly.

[0059] from Figure 9-11 It can be seen that the pore structure of the rod-shaped alumina obtained in Example 1 is: BET specific surface area 135.83 cm 2 / g, micropore specific surface area 112.21cm 2 / g, pore volume 0.079cm 3 / g, and the average pore diameter is 2.32nm.

[0060] Figure 12 This is an application diagram of rod-shaped alumina powder placed in a 100 mg / L Congo red solution for 48 hours of adsorption, showing that the Congo red solution has good adsorption and tends to become clearer and more transparent than the Congo red solution without powder.

[0061] Example 5:

[0062] The specific method and steps are the same as those in Example 2, except that in step (2), after the temperature is raised to 600° C., the temperature is maintained for 3 hours for high-temperature calcination.

[0063] pass Figure 6 It can be seen that as the heat treatment temperature is further increased, the surface morphology of the rod-like structure still does not change significantly, indicating that a certain increase in treatment temperature will not destroy the surface morphology of the sample. Figure 8 It can be seen that the sample is still amorphous at this time.

[0064] from Figure 9-11 It can be seen that the pore structure of the rod-shaped alumina obtained in Example 1 is: BET specific surface area 127.04 cm 2 / g, micropore specific surface area 21.98cm 2 / g, pore volume 0.115cm 3 / g, and the average pore diameter is 3.61nm.

[0065] Figure 12 This is an application diagram of rod-shaped alumina powder placed in a 100 mg / L Congo red solution for 48 hours of adsorption, showing that the Congo red solution has good adsorption and tends to become clearer and more transparent than the Congo red solution without powder.

[0066] Example 6:

[0067] The specific method and steps are the same as those in Example 1, except that in step (2), after heating to 1000° C., the temperature is maintained for 3 hours for high-temperature calcination.

[0068] pass Figure 7 It can be seen that as the heat treatment temperature is further increased, the particle size of the sample becomes significantly smaller at 1000°C and the sample uniformity increases.

[0069] from Figure 9-11 It can be seen that the pore structure of the rod-shaped alumina obtained in Example 1 is: BET specific surface area 8.43cm 2 / g, micropore specific surface area 1.20cm 2 / g, pore volume 0.068cm 3 / g, and the average pore diameter is 32.15nm.

[0070] Figure 12 This is an application diagram of rod-shaped alumina powder being placed in a 100 mg / L Congo red solution and adsorbed for 48 hours. It shows that the solution has been adsorbed by the porous alumina powder to become clear and transparent, and the removal rate of Congo red dye molecules is high.

[0071] Figure 8 The XRD patterns of the rod-shaped alumina powder samples obtained at various calcination temperatures in Examples 2-6 are shown. The rod-shaped alumina obtained by calcination at 300-600°C exhibits an amorphous structure; when calcined at temperatures above 800°C, the product exhibits distinct crystalline diffraction peaks. The product calcined at 800°C is typical γ-phase alumina; the product calcined at 1000°C is a mixture of θ- and α-phase alumina. The temperature range of 800-1000°C is the transition period from γ-phase to α-phase alumina.

[0072] Figure 9 The N2 adsorption-desorption isotherms of the rod-shaped alumina powder samples obtained at various calcination temperatures in Examples 2-6 are Type IV curves. Samples calcined at 300°C and 1000°C exhibit H3-type hysteresis loops, indicating that these samples are mesoporous or macroporous materials with slits. Samples calcined at 400°C exhibit H4-type hysteresis loops, indicating that the samples contain a large number of slit-like pores. Samples calcined at 600°C and 800°C exhibit H2-type hysteresis loops, indicating that the samples contain a large number of mesopores.

[0073] Figure 10 Figure 2 shows the micropore diameters of the rod-shaped alumina powders obtained at various calcination temperatures in Examples 2-6, calculated based on DFT. As can be seen, samples calcined at 400°C, 600°C, and 800°C contain micropores. The pore diameters of the 400°C sample are concentrated between 0.6 and 1.2 nm, while those of the 600°C and 800°C samples are concentrated around 1.2 nm.

[0074] Figure 11 This figure shows the adsorption branch pore size analysis of rod-shaped alumina powders obtained at various calcination temperatures in Examples 2-6, calculated using BJH. As can be seen, samples calcined at 600°C and 800°C contain a large number of mesopores, with mesopore diameters concentrated around 5 nm. The sample calcined at 1000°C primarily contains macropores.

[0075] Figure 12The diagram shows the adsorption effect of the rod-shaped alumina powder obtained at various calcination temperatures in Examples 2-6 placed in a 100 mg / L Congo red solution after 48 hours of adsorption. Among them, the adsorption effects at 800°C and 1000°C are the best, with high removal rates of Congo red dye molecules and clear solutions, indicating good practical application value in the field of catalytic adsorption.

[0076] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for preparing rod-shaped aluminum oxide, characterized in that The following steps are included: (1) fully dissolving aluminum chloride hexahydrate in ethylene glycol by heating and stirring until the solution becomes clear, to obtain a precursor salt solution with a concentration of 0.45 mol / L; (2) Pour the precursor salt solution into an alumina crucible, then place the alumina crucible in a muffle furnace, and in an air atmosphere, heat the temperature from room temperature to 800-1000°C at a heating rate of 3-5°C / min, and then keep the temperature for 3 hours for high-temperature calcination to obtain rod-shaped alumina powder of γ phase, θ phase, α phase or their adjacent mixed phases.

2. A rod-shaped aluminum oxide prepared by the preparation method according to claim 1, characterized in that: The cross-sectional radial average length of the rod-shaped aluminum oxide is 2 to 5 μm, and the average pore size is 5.59 to 32.15 nm; the BET specific surface area of the rod-shaped aluminum oxide is 8 to 81.49 cm 2 / g, pore volume of 0.008~0.115cm 3 / g.

3. The use of the rod-shaped alumina according to claim 2 in the field of dye wastewater adsorption, characterized in that: The dye wastewater contains Congo red and / or methyl blue; during the application process, rod-shaped aluminum oxide is placed in the dye wastewater, ultrasonically adsorbed for 1 hour, and then allowed to stand until the adsorption is completed.

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