Method for preparing nano aluminum hydroxide through low-temperature hydrolysis of aluminum isopropoxide precursor

Abstract

The invention discloses a method for preparing nano aluminum hydroxide through low-temperature hydrolysis of an aluminum isopropoxide precursor, and belongs to the field of nano material preparation. The method comprises the following steps: dissolving aluminum isopropoxide in ethanol or isopropanol to prepare a 0.1-1.0 mol / L solution, hydrolyzing at 30-80 DEG C according to a molar ratio of 3: 1-10: 1, adjusting the pH value to 4-8, adding 1-5wt% of a surfactant, aging, washing, and drying in vacuum to obtain the product. A dual-surfactant compounding and gradient heating process is innovatively adopted, agglomeration is inhibited through PAA low-temperature steric hindrance, ammonium bicarbonate is decomposed at high temperature to produce gas and disturbed, and residues are removed in combination with vacuum extraction, so that the average particle size of the product is 20-100 nm, PDI is smaller than or equal to 0.20, and NH4 < + > residue lt is achieved; and 50 ppm. The process is low-temperature and energy-saving, has no salt-containing wastewater, reduces the production cost by 25% compared with the traditional method, and is suitable for the fields of flame-retardant materials, catalyst carriers and the like.

Description

Technical Field

[0001] The invention relates to the technical field of nanomaterials and specifically proposes a method for preparing nano aluminum hydroxide by low-temperature hydrolysis of an aluminum isopropoxide precursor. Background Art

[0002] Nano-aluminum hydroxide is an important inorganic flame retardant and catalyst carrier, and its preparation method has always been a research hotspot. Traditional preparation methods mainly include aluminum salt precipitation method and alcohol salt hydrolysis method. However, these methods have some difficult to overcome problems, such as: 1. The aluminum salt precipitation method requires a large amount of acid-base neutralization reaction, which will produce a large amount of salt-containing wastewater, which does not meet the requirements of green chemistry; 2. Although the alcohol salt hydrolysis method can produce high-purity nano-aluminum hydroxide, particle agglomeration is prone to occur during the hydrolysis process, resulting in poor dispersion of the product; 3. Traditional surfactants such as cetyltrimethylammonium bromide (CTAB) are difficult to remove from the product, affecting the purity and application performance of the product; 4. The gas generated by volatile solvents or low-boiling-point additives during the hydrolysis process can easily form bubbles in the product, resulting in an uneven product structure.

[0003] Therefore, it is of great practical significance to develop a method for preparing nano-aluminum hydroxide that can simultaneously solve the problems of particle agglomeration, surfactant residue and gas interference. Summary of the Invention

[0004] In view of this, the present invention proposes a method for preparing nano-aluminum hydroxide by low-temperature hydrolysis of an aluminum isopropoxide precursor. This method, through a thermal decomposition-type surfactant coordinated gradient control process, can effectively solve the problems of particle agglomeration, surfactant residue and gas interference existing in the prior art, and prepare a high-purity and highly dispersible nano-aluminum hydroxide product.

[0005] The technical solution of the present invention is achieved as follows: The present invention provides a method for preparing nano-aluminum hydroxide by low-temperature hydrolysis of an aluminum isopropoxide precursor, comprising the following steps: S1. Under nitrogen protection, dissolve aluminum isopropoxide with a purity of ≥99% in anhydrous ethanol or isopropanol to prepare a solution with a concentration of 0.1-1.0 mol / L; S2. Maintaining the system temperature at 40-45°C, while mechanically stirring, simultaneously add deionized water and acetic acid buffer dropwise, wherein the molar ratio of deionized water to aluminum isopropoxide is (3-8):1, and the concentration of the acetic acid buffer is 0.01-0.1 mol / L, and the pH value of the system is maintained at 4.5-6.5 by adding the acetic acid buffer dropwise; S3. Add polyacrylic acid and ammonium bicarbonate to the reaction system, wherein the amount of polyacrylic acid is 0.3-0.8 wt % of the mass of aluminum isopropoxide, and the amount of ammonium bicarbonate is 2-3 wt % of the mass of aluminum isopropoxide; S4. After aging at 40-45°C for 0.5-1.5h, the temperature was raised to 60-70°C at a heating rate of 0.5-2°C / min, and the aging was continued for 1-2h under a vacuum degree of -0.07 to -0.09MPa; S5. After aging, the reaction solution is centrifuged to collect the precipitate, which is washed 3-5 times with a 0.05-0.2 mol / L hydrochloric acid-ethanol solution, then washed 2-3 times with anhydrous ethanol, and finally the washed precipitate is vacuum-dried at 50-70° C. for 6-24 hours to obtain a nano-aluminum hydroxide product.

[0006] In some embodiments, the molecular weight of the polyacrylic acid is 1000-5000.

[0007] In some embodiments, the flow rate of the nitrogen gas is 0.1-1 L / min.

[0008] In some embodiments, the speed of the mechanical stirring is 300-1000 rpm.

[0009] In some embodiments, the centrifugal separation is performed at a rotation speed of 6000-10000 rpm and a time of 10-30 min.

[0010] In some embodiments, the volume ratio of hydrochloric acid to ethanol in the hydrochloric acid-ethanol solution is 1:(10-50).

[0011] The present invention also provides nano aluminum hydroxide prepared by the method.

[0012] The nano aluminum hydroxide prepared by the above preparation method can be used in technical fields such as plastics, rubber, coatings, fiber materials or medical carriers.

[0013] The present invention has the following beneficial effects compared to the prior art: The present invention realizes low-temperature green preparation of nano-aluminum hydroxide by compounding dual-functional surfactants and gradient process control. The method uses the gas disturbance generated by thermal decomposition of ammonium bicarbonate to inhibit particle agglomeration, combines vacuum extraction and acid washing to remove residues, and controls the average particle size of the product to 20-50nm. + Residue <50ppm, specific surface area up to 150-200m 2 / g, resulting in improved dispersibility and flame retardant efficiency compared to traditional methods. The low-temperature process consumes less energy than traditional methods, and combined with ethanol recovery and zero wastewater discharge, it reduces production costs. It combines high purity, high dispersibility, and environmental friendliness, making it suitable for diverse applications such as flame retardancy and catalytic supports. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0015] Figure 1 This is the particle size distribution diagram of Example 1 of the present invention; Figure 2 This is the particle size distribution diagram of Example 2 of the present invention; Figure 3 The particle size distribution diagram of comparative example A2 of the present invention. DETAILED DESCRIPTION

[0016] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0017] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which embodiments of the present invention belong. If the definitions set forth in this section are contrary to or otherwise inconsistent with definitions set forth in the patents, patent applications, published patent applications, and other publications incorporated herein by reference, the definitions listed in this section take precedence over the definitions incorporated herein by reference.

[0018] Unless otherwise specified, the methods used in the following examples are conventional methods. The materials, reagents, and instruments used are conventional materials, reagents, and instruments in the art, unless otherwise specified, and can be obtained commercially by those skilled in the art.

[0019] When an amount, concentration or other value or parameter is expressed as a range, a preferred range or a range defined by a series of upper preferred values ​​and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pairing of any upper range limit or preferred value with any lower range limit or preferred value, regardless of whether the range is disclosed alone. For example, when a range "1 to 5" is disclosed, the described range should be interpreted as including the ranges "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5", etc. When a numerical range is described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within the range. In the present specification and claims, range definitions may be combined and / or interchanged, and if not otherwise stated, such ranges include all subranges contained therein.

[0020] Example 1 step: S1, 0.5 mol / L aluminum isopropoxide-ethanol solution (120 g aluminum isopropoxide dissolved in 1 L ethanol), nitrogen flow (0.5 L / min) at 40°C; S2, add 54 mL of deionized water (water-aluminum ratio 5:1) and 0.05 mol / L acetic acid buffer (maintain pH 5.5); S3, add 0.6g PAA (Mw = 1800, 0.5wt%) + 3g NH4HCO3 (2.5wt%), stir for 30min; S4, aging at 40℃ for 1h → heating to 60℃ at 1℃ / min → aging under -0.08MPa vacuum for 1h; S5. Wash with 0.1 mol / L hydrochloric acid-ethanol (1:20) three times, wash with ethanol twice, and dry in vacuum at 60°C for 12 h.

[0021] Comparative Example A1 On the basis of Example 1, step S3 was changed to: adding 0.6 g PAA, omitting NH 4 HCO 3 , and the remaining conditions were the same as in Example 1.

[0022] Comparative Example A2 On the basis of Example 1, step S3 was changed to: adding 3 g NH 4 HCO 3 , omitting PAA, and the other conditions were the same as in Example 1.

[0023] Comparative Example B1 On the basis of Example 1, in step S4, the temperature is raised to 60° C. and then aged at normal pressure for 1 hour. The other conditions are the same as in Example 1.

[0024] Comparative Example C1 On the basis of Example 1, in step S4, after aging at 40°C for 1 hour, the temperature was directly and quickly (within 2 minutes) raised to 60°C, and aged in a vacuum at -0.08 MPa for 2 hours. The other conditions were the same as in Example 1.

[0025] Example 2 On the basis of Example 1, in step S3, 2.4 g NH 4 HCO 3 (2 wt %) was used, and the other conditions were the same as in Example 1.

[0026] Example 3 On the basis of Example 1, in step S3, 3.6 g NH 4 HCO 3 (3 wt %) was used, and the other conditions were the same as in Example 1.

[0027] Comparative Example D1 On the basis of Example 1, in step S2, the pH value was controlled to be 4.0 by dropwise addition, and the other conditions were the same as in Example 1.

[0028] Comparative Example D2 On the basis of Example 1, in step S2, the pH value was controlled to be 7.0 by dropwise addition, and the other conditions were the same as in Example 1.

[0029] Comparative Example E1 On the basis of Example 1, in step S5, washing three times with 0.1 mol / L hydrochloric acid-ethanol (1:20) was changed to washing three times with deionized water, and the other conditions were the same as in Example 1.

[0030] Comparative Example F1 On the basis of Example 1, in step S3, 3 g of CTAB was added instead, and the vacuum operation was omitted in step S4. The other conditions were the same as in Example 1.

[0031] The performance of the nano-aluminum hydroxide prepared by the above different methods was tested: Average particle size and particle size distribution: 5 mg of the product was dispersed in 10 mL of anhydrous ethanol and ultrasonically dispersed for 10 min (power 100 W, frequency 40 kHz); Transfer to a 1 cm pathlength quartz cuvette and measure at 25°C. Dynamic light scattering was performed using a Malvern Zetasizer Nano ZS90 with a laser wavelength of 633 nm, a scattering angle of 90°, and an equilibrium time of 120 s. Three measurements were repeated and the average value was calculated. The software automatically fits the particle size distribution curve and outputs the Z-average particle size and PDI value.

[0032] NH4 + Residue detection: Ion chromatography was used to detect ions, and the NH4 + Standard curve.

[0033] Specific surface area: Low temperature nitrogen adsorption method, detection by specific surface area analyzer.

[0034] Limiting Oxygen Index (LOI) Nano-Al(OH)3 was blended with polypropylene (PP) pellets at a ratio of 30 wt% using an oxygen index meter; pelletized using a twin-screw extruder (temperature 180-200°C) and injection molded into standard specimens (size 80×10×4 mm).

[0035] The spline is fixed vertically in the combustion tube, and an O2 / N2 mixed gas (total flow rate 10L / min) is introduced; Ignite the upper end for 30 seconds, remove the fire source, and record the minimum oxygen concentration required for the specimen to continue burning for ≥3 minutes or the burning length ≥50 mm.

[0036] Drying agglomeration rate: Laser particle size analyzer Take 1 g of dry sample, disperse it in 50 mL of anhydrous ethanol, and sonicate for 10 min; Immediately take samples to determine the initial particle size distribution D1; The same sample was dried at 105 °C for 2 h, and then dispersed and measured repeatedly to obtain the particle size distribution D2; Agglomeration rate = (D2-D1) / D1×100% The above D1 and D2 are both D90.

[0037]

[0038] In Example 1, NH₄HCO₃ (2.5 wt%) decomposes during aging and heating to produce CO₂ and NH₃ gases, forming a bubble template that promotes the formation of a mesoporous structure. In Comparative Example A1, omitting NH₄HCO₃ significantly reduces the specific surface area of ​​the product, due to a lack of bubble-forming pores and a reduced pore structure.

[0039] The NH3 produced by the decomposition of NH4HCO3 can buffer the pH of the system, maintain the stability of the hydrolysis and condensation reaction, and avoid particle agglomeration caused by local acid-base imbalance.

[0040] PAA (Mw=1800) is used as a polymer dispersant, which binds to Al 3+ Coordination inhibits the rapid aggregation of aluminum hydroxide sol and forms a uniform sol network. In comparative example A2, after omitting PAA, TEM observations show that the particles are severely agglomerated, the specific surface area decreases, and the pore size distribution becomes wider.

[0041] The steric hindrance effect of PAA can also regulate the crystal growth direction. The XRD spectrum of Example 1 shows that the (100) crystal plane diffraction peak is stronger, corresponding to an ordered mesoporous structure, while A2 has disordered crystal orientation due to agglomeration.

[0042] Example 1 was aged under a vacuum of -0.08 MPa, which lowered the solvent boiling point and promoted uniform solvent volatilization. Simultaneously, the CO2 bubbles expanded more evenly under negative pressure, forming regular pores. Comparative Example B1, when aged at ambient pressure, experienced uneven solvent volatilization, increased pore collapse, and decreased pore connectivity as observed by SEM.

[0043] The vacuum environment can also accelerate the escape of NH4HCO3 decomposition products (CO2, NH3), avoiding pore blockage caused by gas residue. In comparative example B1, macropore defects appeared in the pore size distribution due to gas retention.

[0044] In Example 1, the temperature was slowly increased at 1°C / min, providing a uniform thermal field and gradually condensing the AlOOH sol to form an ordered skeleton. XRD showed high crystallinity (the (100) peak intensity was 30% higher than that of C1). In Comparative Example C1, the rapid temperature increase (to 60°C within 2 minutes) resulted in local overheating, instantaneous condensation of the sol, and internal stress. TEM observations revealed skeleton fracture, a decrease in specific surface area, and a bimodal pore size distribution, corresponding to uneven growth.

[0045] When pH=4.0, H + Increased concentration accelerates Al 3+ Hydrolysis generates [Al(OH)2] + The rate of polycondensation reaction is accelerated, resulting in a sudden increase in the particle size of the sol and a decrease in the specific surface area.

[0046] The strong acid environment inhibits the decomposition of NH4HCO3, the generation of CO2 bubbles is delayed, the pores are formed unevenly, and the BET pore size distribution shows that the proportion of macropores larger than 10 nm increases to 40% (20% in Example 1).

[0047] When pH=7.0, OH - As the concentration increases, Al 3+ Easy to form [Al(OH)4] - Anions, sol stability decreased, and agglomeration and precipitation occurred (the turbidity of the supernatant after centrifugation was 50% higher than that of Example 1). XRD showed that the amorphous peak of D2 was enhanced and the crystallinity was reduced. This is because the growth of AlOOH crystals is hindered under alkaline conditions, forming an amorphous aluminum hydroxide precursor.

[0048] The alkaline environment also promotes the premature decomposition of NH4HCO3, which is not synchronized with the sol condensation, resulting in pore collapse and a decrease in pore volume. A dense and non-porous structure was observed by SEM.

[0049] Example 1 uses 0.1 mol / L hydrochloric acid-ethanol for washing. HCl can neutralize the NH3 remaining on the surface of the product, and ethanol can dissolve the residual organic matter to avoid carbon pollution after calcination. Comparative Example E1 uses deionized water for washing. The residual NH4 +and HCO3 - Thermogravimetric analysis showed that the weight loss rate at 600°C was 15% higher than that in Example 1, and XRD showed a calcium carbonate peak (derived from residual HCO3 - reacts with CO2 in the air).

[0050] The low surface tension of ethanol helps to maintain the pore structure. After E1 is washed with water, the pores shrink due to capillary forces, the pore volume decreases, and the BET specific surface area decreases.

[0051] PAA binds to Al through carboxyl groups 3+ The coordination forms a flexible template, while CTAB (cationic surfactant) forms a rigid micelle template through hydrophobic chain aggregation, causing the mesoporous structure to change from disordered worm-like (Example 1) to ordered hexagonal arrangement (XRD of F1 shows characteristic peaks (100) and (110)). However, the size of CTAB micelles is large (about 20 nm), the pore size increases, and the specific surface area decreases.

[0052] After omitting the vacuum operation, the gas generated by the decomposition of CTAB micelles cannot be discharged, and a closed-pore structure appears in the pores (the closed-pore ratio of F1 measured by mercury intrusion porosimetry is 30%, and that of Example 1 is 5%), which affects the adsorption performance of the material.

[0053] Example 2 (2 wt% NH4HCO3): The gas-producing template is reduced and the pore volume decreases because the number of CO2 bubbles is insufficient and the mesoporous network is sparse.

[0054] Example 3 (3 wt% NH4HCO3): Excessive gas production resulted in bubble merging, an increase in the proportion of macropores, and a decrease in specific surface area.

[0055] The principle of the optimal content (2.5wt%): the gas production rate matches the sol condensation rate, forming a uniform mesoporous structure with a pore size of 5-10nm, taking into account both specific surface area and adsorption performance.

[0056] The experimental design manipulated the template (NH4HCO3, PAA), aging kinetics (temperature, pressure, rate), interfacial chemistry (pH, detergent), and template mechanism (surfactant type) to influence nucleation, growth, pore formation, and structural solidification during the sol-gel process, ultimately achieving precise control of the microstructure (pore size, pore volume, crystallinity) and macroscopic properties of the mesoporous material. The synergistic effect of NH4HCO3 and PAA, as well as the kinetic control of vacuum aging, were key factors in enhancing the material's ordered mesoporous structure.

[0057] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing nano-aluminum hydroxide by low-temperature hydrolysis of an aluminum isopropoxide precursor, characterized in that: The steps include: S1. Under nitrogen protection, dissolve aluminum isopropoxide with a purity of ≥99% in anhydrous ethanol or isopropanol to prepare a solution with a concentration of 0.1-1.0 mol / L; S2. Maintaining the system temperature at 40-45°C, while mechanically stirring, simultaneously add deionized water and acetic acid buffer dropwise, wherein the molar ratio of deionized water to aluminum isopropoxide is (3-8):1, and the concentration of the acetic acid buffer is 0.01-0.1 mol / L, and the pH value of the system is maintained at 4.5-6.5 by adding the acetic acid buffer dropwise; S3. Add polyacrylic acid and ammonium bicarbonate to the reaction system, wherein the amount of polyacrylic acid is 0.3-0.8 wt % of the mass of aluminum isopropoxide, and the amount of ammonium bicarbonate is 2-3 wt % of the mass of aluminum isopropoxide; S4. After aging at 40-45°C for 0.5-1.5h, the temperature was raised to 60-70°C at a heating rate of 0.5-2°C / min, and the aging was continued for 1-2h under a vacuum degree of -0.07 to -0.09MPa; S5. After aging, the reaction solution is centrifuged to collect the precipitate, which is washed 3-5 times with a 0.05-0.2 mol / L hydrochloric acid-ethanol solution, then washed 2-3 times with anhydrous ethanol, and finally the washed precipitate is vacuum-dried at 50-70° C. for 6-24 hours to obtain a nano-aluminum hydroxide product.

2. The method for preparing nano-aluminum hydroxide by low-temperature hydrolysis of an aluminum isopropoxide precursor as claimed in claim 1, characterized in that: The molecular weight of the polyacrylic acid is 1000-5000.

3. The method for preparing nano-aluminum hydroxide by low-temperature hydrolysis of an aluminum isopropoxide precursor as claimed in claim 1, characterized in that: The flow rate of the nitrogen is 0.1-1 L / min.

4. The method for preparing nano-aluminum hydroxide by low-temperature hydrolysis of an aluminum isopropoxide precursor as claimed in claim 1, wherein: The speed of the mechanical stirring is 300-1000 rpm.

5. The method for preparing nano-aluminum hydroxide by low-temperature hydrolysis of an aluminum isopropoxide precursor as claimed in claim 1, characterized in that: The centrifugal separation conditions are: rotation speed 6000-10000 rpm, time 10-30 min.

6. The method for preparing nano-aluminum hydroxide by low-temperature hydrolysis of an aluminum isopropoxide precursor as claimed in claim 1, characterized in that: The volume ratio of hydrochloric acid to ethanol in the hydrochloric acid-ethanol solution is 1:(10-50).

7. A nano aluminum hydroxide, characterized in that The nano aluminum hydroxide is prepared by the method according to any one of claims 1 to 6.

8. Use of the nano-aluminum hydroxide according to claim 7 in the fields of plastics, rubber, coatings, fiber materials or medical carriers.

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