CN113184887B - Micron-sized three-dimensional scaly alumina prepared by taking wheat straws as template and preparation method thereof - Google Patents

Micron-sized three-dimensional scaly alumina prepared by taking wheat straws as template and preparation method thereof Download PDF

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CN113184887B
CN113184887B CN202110417578.7A CN202110417578A CN113184887B CN 113184887 B CN113184887 B CN 113184887B CN 202110417578 A CN202110417578 A CN 202110417578A CN 113184887 B CN113184887 B CN 113184887B
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CN113184887A (en
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刘一军
黄剑锋
钟辛子
曹丽云
黄玲艳
潘利敏
汪庆刚
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Monalisa Group Co Ltd
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    • C—CHEMISTRY; METALLURGY
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    • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
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    • C01F7/02—Aluminium oxide; Aluminium hydroxide; Aluminates
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    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
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Abstract

The invention discloses micron-sized three-dimensional fish scale-shaped alumina prepared by taking wheat straws as a template and a preparation method thereof. The method comprises the following steps: pickling wheat straw to etch it; adopting a glucose solution to attach and fill etching point positions of the pickled wheat straws, and then drying to obtain a wheat straw precursor; immersing a wheat straw precursor into a double precipitator solution containing multiple heterogeneous functional groups to attach the heterogeneous functional groups of the precipitator to the interior of the wheat straw in a chemical bond form, so as to obtain a modified solution of the wheat straw precursor; carrying out micro-polymerization on the modified solution of the wheat straw precursor in a rotary micro-polymerization reactor; and collecting the micro-polymerized reaction product, and sintering the micro-polymerized reaction product, aluminum fluoride and silicon dioxide to obtain the micron-sized three-dimensional scaly aluminum oxide. The method is simple and low in cost, and the product has high purity and good orientation.

Description

Micron-sized three-dimensional scaly alumina prepared by taking wheat straws as template and preparation method thereof
Technical Field
The invention belongs to the field of materials, and particularly relates to micron-sized three-dimensional scaly aluminum oxide prepared by taking wheat straws as a template and a preparation method thereof.
Background
The wheat straw is used as a biomass energy material, and the storage yield of the wheat straw in China is up to hundreds of millions of tons every year. However, most of wheat straw materials are wasted in manual incineration at present, and gases such as sulfur dioxide, nitrogen dioxide and the like released in the incineration process pollute the environment and cause serious damage. Therefore, how to reasonably use the wheat straw and exert the maximum value thereof is one of the key issues discussed by scientific researchers.
In the existing preparation of micron-scale alumina, a micro-emulsion method, a detonation method, a precipitation method, a sol-gel method and the like are mainly adopted, but the methods often involve high-pollution reagent raw materials, and the size of the alumina prepared by production is difficult to control. In addition, most of the methods are limited to laboratory stage, and cannot be popularized and popularized in actual production. How to effectively combine the preparation of alumina with the biomass material of wheat straw and to find out a micro-nano alumina production technology with low cost and high practicability becomes a target which is reached by a plurality of scientific researchers.
Disclosure of Invention
Aiming at the problems, the invention provides micron-sized three-dimensional fish scale alumina prepared by using wheat straws as a template and a preparation method thereof.
In a first aspect, the invention provides a method for preparing micron-sized three-dimensional fish-scale alumina by using wheat straws as a template, which comprises the following steps:
pickling wheat straw to etch it;
adopting a glucose solution to attach and fill etching point positions of the pickled wheat straws, and then drying to obtain a wheat straw precursor;
immersing a wheat straw precursor into a double precipitator solution containing multiple heterogeneous functional groups to attach the heterogeneous functional groups of the precipitator to the interior of the wheat straw in a chemical bond form, so as to obtain a modified solution of the wheat straw precursor;
carrying out micro-polymerization on the modified solution of the wheat straw precursor in a rotary micro-polymerization reactor;
and collecting the micro-polymerized reaction product, and sintering the micro-polymerized reaction product, aluminum fluoride and silicon dioxide to obtain the micron-sized three-dimensional scaly aluminum oxide.
Preferably, the double precipitant is sulfanilamide and melamine. Preferably, the molar ratio of sulfanilamide to melamine is 1: (0.5-3).
Preferably, the dual precipitant solution comprises: the aluminum source is 50-70%, the sulfanilamide 5-12%, the melamine 6-18%, the pH regulator 3-6%, and the balance of deionized water.
Preferably, the reaction time of the micro-polymerization is 6-8 h.
Preferably, the micro-polymerization is divided into two stages, the reaction temperature of the second stage is 80-120 ℃ higher than that of the first stage, and the reaction time of the second stage is 3-4h higher than that of the first stage.
Preferably, the pressure of the first stage of the micro polymerization is 20-40Pa, the temperature is 60-100 ℃, the rotation rate is 40-100r/min, and the micro polymerization reaction time is 1-2 h; the pressure of the second stage is 30-50Pa, the temperature is 160-200 ℃, the rotation rate is 80-120r/min, and the micro-polymerization reaction time is 5-6 h.
Preferably, the mass ratio of the reaction product of the micro-polymerization, aluminum fluoride and silicon dioxide is (0.8-1.2): (1.2-1.8): (1.5-2.2).
Preferably, the sintering temperature is 1100-1300 ℃, and the sintering time is 0.5-2 h.
In a second aspect, the invention provides micron-sized three-dimensional fish-scale aluminum oxide obtained by the preparation method described in any one of the above. The micron-sized three-dimensional scaly alumina has a scaly shape formed by directionally growing alumina grains. The diameter of the alumina crystal grain is 1-5 μm, the thickness is 0.2-0.8 μm, the specific surface area is 200-2·g-1. Wherein, the alumina crystal grains are dispersed uniformly without obvious agglomeration.
Preferably, the micron-sized three-dimensional fish scale-shaped alumina has a three-dimensional ordered pore structure, and the pore volume is 0.5-1.2cm3·g-1The pore size distribution is 8-30 nm.
Drawings
FIG. 1 is a scanning electron micrograph of the micron-sized three-dimensional fish-scale aluminum oxide of the product of example 1;
FIG. 2 is an X-ray diffraction pattern of the product micron-sized three-dimensional fish-scale aluminum oxide of example 1;
FIG. 3 is a scanning electron micrograph of aluminum oxide grains formed by the micropolymerization reaction of example 1;
FIG. 4 is a scanning electron micrograph of the product micron-sized alumina of comparative example 2;
FIG. 5 is an X-ray diffraction pattern of the product micron-scale alumina of comparative example 2;
FIG. 6 is a scanning electron micrograph of the product micron-sized alumina of comparative example 3;
FIG. 7 is a scanning electron micrograph of the product micron-sized alumina of comparative example 5.
Detailed Description
The present invention is further illustrated by the following examples, which are to be understood as merely illustrative of, and not restrictive on, the present invention. Unless otherwise specified, each percentage means a mass percentage.
The following is an exemplary illustration of the method for preparing micron-sized three-dimensional fish-scale alumina using wheat straw as a template according to the present invention.
Wheat straw was acid-washed to etch it. The three-dimensional pore structure in the wheat straw is developed, and the microstructure of the wheat straw can be optimized through acid washing and etching. For example, wheat straw is washed with an acid solution. The acid solution must not be a strong oxidizing acid, otherwise the templating agent and the glucose filler will carbonize. The pH of the acid liquor is preferably 7.5-8.5. The acid solution can be hydrochloric acid, nitric acid, acetic acid, etc. Dilute nitric acid of 0.5-0.8mol/L may be used. The washing times of the acid liquor can also be adaptively changed according to the etching condition. For example, the washing with an acid solution may be carried out 2 to 8 times. Of course, alternate washing with acid solution and absolute ethanol may be used. The acid liquor is used for etching the surface layer structure of the wheat straw to generate nano-scale etching point positions, and the original three-dimensional pore structure of the wheat straw is not damaged. In some embodiments, the etching time is 5-20 min.
The invention uses the wheat straw with the pore structure as the template, and has the following advantages compared with other template agents without the pore structure, such as P123: the wheat straw biomass material is green and environment-friendly, has wide resources and great industrialization potential, and the chemical template agent inevitably damages human health and ecological environment; secondly, the wheat straw has a micro-nano pore structure, and can play a role in providing space orientation for the growth of the alumina product along a specific structure by being assisted by a precipitator and a surfactant, and the chemical template mostly guides the generation of the alumina products with different shapes by changing the surface energy of the alumina product.
In order to improve the acid-washing and etching effects of the wheat straws, the wheat straws can be cut into strips before acid washing. In some embodiments, 6 to 12g of fresh wheat straw is cut into strips with the length, width and height of 3 to 5mm, 3 to 5mm and 5 to 8mm respectively, and the obtained strips are washed alternately by using a dilute nitric acid solution with the concentration of 0.5 to 0.8mol/L and absolute ethyl alcohol until the total washing times are 6 times.
And (3) attaching and filling etched points of the pickled wheat straws by using a glucose solution, and then drying to obtain a wheat straw precursor. The pipe wall of the wheat straw has certain roughness, and glucose can be attached to the outer surface of the pipe wall to fill acid etching points. In addition, free groups such as hydroxyl, aldehyde and the like exist at etching points after acid cleaning, and the combination of glucose groups and the free groups can play a role in filling the acid etching points. In addition, the glucose is not used as a carbon source to prepare the colloidal carbon, but the glucose solution also washes and cleans the internal structure while filling the glucose, and the wheat straw structure which is possibly blocked by foreign matters is broken through by virtue of the micro-structure capillary phenomenon, so that the method can be similar to a smooth water pipe. Namely, glucose is introduced to attach and fill etching point positions, so that the rich internal tubular structure of the wheat straw is smooth, and the subsequent precipitator containing heterogeneous functional groups is favorably attached to the internal part of the wheat straw template in a chemical bond mode, thereby providing a space foundation for the growth of the micron-sized three-dimensional fish scale-shaped alumina seed crystals along the internal structure of the template.
The filling time may be 8 to 12 hours. This filling time is favorable to glucose to carry out complete attached and filling to the sculpture point position, washs and gets through the wheat straw structure that probably is blockked up by the foreign matter.
The concentration of the glucose solution can be 2.5-3.5 mol/L. The glucose solution may be an aqueous glucose solution. In some embodiments, the mass ratio of the wheat straw and the glucose solution after the acid washing can be 1: (1-3).
The above-mentioned drying manner is not limited. For example, oven drying, spray drying, freeze drying, far infrared drying, microwave drying, etc. may be mentioned. Preferably far infrared drying. For example, the wheat straw filled and treated by the glucose solution is placed in a far infrared drying box and dehydrated for 18-24h at the temperature of 120-160 ℃.
And (3) immersing the wheat straw precursor into a double precipitator solution containing multiple heterogeneous functional groups to attach the heterogeneous functional groups of the precipitator to the interior of the wheat straw in a chemical bond form, so as to obtain a modified solution of the wheat straw precursor. Compared with the use of urea, ethylenediamine and other micromolecular ammonium salts, the method uses the precipitator with larger molecular weight and more structural functional groups with the same mole number, and is favorable for realizing the attachment of the precipitator in the internal structure of the wheat straw under the condition of assisting the glucose combination action. In the experimental process, the experimental effect of the small molecular ammonium salts such as urea, ethylenediamine and the like is poor, and the yield is low. And the sulfanilamide and the melamine are used as double precipitants, compared with a single precipitator, the precipitating efficiency of the alumina seed crystal can be effectively improved, the precipitating width and the purity of the seed crystal are improved, and the uniform precipitation of the micron-sized three-dimensional scaly alumina seed crystal is facilitated. The expression of increasing the precipitation width means that the nucleation barrier and the seed crystal precipitation temperature are reduced, which is beneficial to precipitating the seed crystal under the reaction condition of wider range.
The dual precipitant solution comprises: the aluminum source is 50-70%, the sulfanilamide 5-12%, the melamine 6-18%, the pH regulator 3-6%, and the balance of deionized water.
The composition of the aluminum source is not limited, and it is preferable to use inorganic aluminum salts including, but not limited to, aluminum chloride, aluminum nitrate, aluminum sulfate, sodium metaaluminate, aluminum potassium sulfate, and the like. The aluminum source may be aluminum chloride hexahydrate.
The double precipitant solution is controlled to be slightly alkaline, and the pH value is preferably between 8.2 and 9.2. In this case, the pH regulator may be ammonia water with a mass fraction of 20-40%.
In the preparation process of the double precipitant solution, the components of all the double precipitant solutions can be uniformly mixed, and the double precipitant solution can also be prepared by stages. For example, firstly, sequentially adding aluminum chloride hexahydrate and sulfanilamide into a potassium hydroxide solution, and stirring until the aluminum chloride hexahydrate and the sulfanilamide are completely dissolved; and then continuously adding the mixed solution of melamine, ammonia water and deionized water. In some embodiments, 6.4-8.4g of aluminum chloride hexahydrate and 8.2-10.8g of sulfanilamide are sequentially added into a potassium hydroxide solution with the concentration of 0.8-1.2mol/L, and then the mixture is magnetically stirred at the temperature of 120-180 ℃ and the stirring speed of 400-500r/min until white granular substances (possibly precipitated sulfanilamide) in the solution are completely dissolved; gradually dropwise adding melamine according to the volume ratio: ammonia water: deionized water ═ (40-60): (20-40): (20-40) preparing a mixed solution of melamine so that the pH is 8.2-9.2.
The soaking time of the precursor of the wheat straw in the double-precipitator solution is 18-24 h.
The sulfanilamide and the melamine contain various heterogeneous functional groups such as hydroxyl, carbonyl, amino and the like, and the various functional groups can generate a combined reaction of free chemical bonds with wheat straws containing a large number of attachment sites inside under a slightly alkaline condition, so that the double precipitator is ensured to successfully enter the inside of the template, and alumina seed crystals with specific orientation are separated, separated and grown at specific spatial point positions, the occurrence rate of non-template precipitation reaction in the solution is reduced, and the yield of the micron-sized three-dimensional fish scale seed crystals is improved.
Carrying out micro-polymerization on the modified solution of the wheat straw precursor in a rotary micro-polymerization reactor. The reaction time of the micro-polymerization is 6-8 h. The existing hydrothermal method is often used for preparing micron-scale alumina. The rotary micropolymerization reaction compared to the hydrothermal reaction: (1) has larger reaction specific surface area and yield. The specific surface area of the reaction is improved by the unique microchannel structure of the micro-polymerization reactor, the effective collision of reaction particles and the uniform dispersion of products in the thermal motion process are promoted by synchronous rotation and pressurization, the reaction efficiency is improved while the process steps are simplified, and the target product loss possibly existing in the multi-step reaction process is reduced. (2) The rotary micro-polymerization reaction can provide larger external pressure for solution reaction, is beneficial to reducing nucleation barrier and precipitation of micro-nano seed crystal, and the product of the hydrothermal reaction has larger size and is difficult to accurately control.
The micropolymerization can be divided into two stages. Wherein the reaction temperature of the second stage is preferably higher than 80-120 ℃ than that of the first stage, and the reaction time of the second stage is preferably higher than that of the first stage for 3-4 h. The temperature control in the first stage effectively ensures that reaction particles uniformly permeate into the internal structure of the wheat straw through thermal motion, provides a material basis for uniform precipitation and directional growth of alumina seed crystals attached to a template in the main reaction in the second stage, and ensures the yield of micron-sized three-dimensional scaly alumina seed crystals.
In some embodiments, the micropolymerization is in two stages: the pressure of the first stage is 20-40Pa, the temperature is 60-100 ℃, the rotation rate is 40-100r/min, and the micro-polymerization reaction time is 1-2 h; the pressure of the second stage is 30-50Pa, the temperature is 160-200 ℃, the rotation rate is 80-120r/min, and the micro-polymerization reaction time is 5-6 h.
The micro-polymerized reaction product was collected. In some embodiments, the reaction product of the micropolymerization may be washed with deionized water, absolute ethanol, and dried sequentially. For example, the reaction product of the micro-polymerization is washed by deionized water and absolute ethyl alcohol in sequence until the pH value of the washing liquid is 6.8-7.6, and then the washing liquid is moved into a far infrared drying oven and dried for 12-18h at the temperature of 80-120 ℃.
And sintering the micro-polymerized reaction product, aluminum fluoride and silicon dioxide to obtain the micron-sized three-dimensional scaly aluminum oxide. In the high-temperature solid-phase reaction, aluminum fluoride can simultaneously act on a plurality of adjacent coordination polyhedral units, and under the same orientation condition, the growth speeds of various crystal grains on different crystal faces are different, so that seed crystals are guided to be converted into micron-sized three-dimensional fish-scale aluminum oxide; the silicon dioxide is attached to the crystal face of the seed crystal, so that the interfacial surface energy is adjusted, and the seed crystal is promoted to be converted into the micron-sized three-dimensional fish-scale aluminum oxide more quickly.
The sintering temperature can be 1100-1300 ℃, and the sintering time can be 0.5-2 h. Aluminum fluoride and silicon dioxide are introduced in the high-temperature sintering reaction to provide guidance for the oriented growth of alumina seed crystals, the crystal form transformation of alumina and the generation of micron-sized three-dimensional scaly alumina are efficiently promoted under the combined action of a template agent, ammonia gas, fluoride and the like, the reaction efficiency is improved, and the abnormal growth of crystal grains caused by long-time high-temperature solid-phase reaction is avoided.
The mass ratio of the reaction product of the micro-polymerization, aluminum fluoride and silicon dioxide may be (0.8-1.2): (1.2-1.8): (1.5-2.2). The mass ratio of the three components is not in the range, so that the phase balance of the high-temperature solid phase reaction is easily damaged, and the growth is incomplete or products with other appearances are grown.
For example, the reaction product of the micropolymerization is: aluminum fluoride: silica ═ (0.8-1.2): (1.2-1.8): (1.5-2.2), uniformly mixing and flatly paving the mixture to the bottom of the crucible, then moving the sealed crucible to a muffle furnace, heating the mixture from room temperature to 400-600 ℃ at the heating rate of 6-10 ℃/min, keeping the temperature for 0.5-1h, heating the mixture to 1100-1300 ℃ at the heating rate of 5-8 ℃/min, keeping the temperature for 0.5-2h, and naturally cooling the mixture to room temperature to obtain the micron-sized three-dimensional scaly aluminum oxide.
Of course, after sintering, the sintered product can be washed by deionized water and absolute ethyl alcohol in sequence.
The micron-sized three-dimensional fish scale-shaped alumina prepared by the method has a three-dimensional controllable pore structure, and the pore volume is 0.5-1.2cm3·g-1The pore size distribution is 8-30 nm. As can be seen from SEM, the micron-sized three-dimensional scaly alumina has a scaly shape formed by oriented growth of alumina grains. The diameter of the alumina crystal grain is 1-5um, the thickness is 0.2-0.8 μm, and the specific surface area is 200-600cm2·g-1。
The preparation method of the invention has the following beneficial effects:
according to the invention, biomass raw material wheat straw with wide natural reserves is used as a template, and a micro-nano self-communicated pore structure inside the wheat straw is used as a growth template of the alumina seed crystal, so that compared with chemical templates such as polyethylene glycol and the like which are commonly used at present, the template agent has the advantages of easily available raw materials, non-toxic and harmless products, lower production and manufacturing cost, simple production process, capability of perfectly conforming to national policy requirements on energy conservation and environmental protection, and potential for realizing large-scale production. In addition, the existing micro-nano-scale alumina preparation technology is mainly completed by a one-step precipitation method such as a microemulsion method, a hydrothermal method and the like, and alumina seed crystals have the defects of low yield, poor growth orientation and the like. The invention creates a double-substance coprecipitation system, introduces melamine and sulfanilamide to participate in precipitation reaction in sequence, avoids the problems that a single precipitator is insensitive to product separation and has lower precipitation efficiency in solution reaction, and effectively improves the preparation efficiency of the product. Meanwhile, the double-precipitator introduced by the invention has better chemical inertness, reduces the occurrence of side reactions in the system, improves the stability of the preparation technology and the purity of the product, and has better popularization value and application prospect technically.
The present invention will be described in detail by way of examples. It is also to be understood that the following examples are illustrative of the present invention and are not to be construed as limiting the scope of the invention, and that certain insubstantial modifications and adaptations of the invention by those skilled in the art may be made in light of the above teachings. The specific process parameters and the like of the following examples are also only one example of suitable ranges, i.e., those skilled in the art can select the appropriate ranges through the description herein, and are not limited to the specific values exemplified below.
Example 1
The method comprises the following steps: cutting 6-12g of fresh wheat straw into strips with the length, width and height of 3-5mm, 3-5mm and 5-8mm respectively, washing the obtained strips for 6 times by using a dilute nitric acid solution with the concentration of 0.5-0.8mol/L and absolute ethyl alcohol in sequence, then soaking the washed strips into a glucose solution with the concentration of 2.5-3.5mol/L for filling treatment for 8-12h, finally transferring the obtained strips into a far infrared drying box for dehydration for 18-24h at the temperature of 160 ℃, and collecting a product to obtain a wheat straw precursor A;
step two: sequentially adding 6.4-8.4g of aluminum chloride hexahydrate and 8.2-10.8g of sulfanilamide into 0.8-1.2mol/L potassium hydroxide solution, and magnetically stirring at the temperature of 120-180 ℃ and the stirring speed of 400-500r/min until white granular substances in the solution are completely dissolved to obtain solution B;
step three: gradually dropwise adding melamine according to the volume ratio: ammonia water: deionized water ═ (40-60): (20-40): (20-40) soaking the wheat straw precursor A in the melamine mixed solution until the pH value is 8.2-9.2, and soaking for 18-24 hours to obtain a mixed solution C;
step four: the solution C was transferred to a rotary micropolymerization reactor and the reaction was carried out for 6-8h in two stages with the following split: the pressure of the first stage is 20-40Pa, the temperature is 60-100 ℃, the rotation rate is 40-100r/min, and the micro-polymerization reaction time is 1-2 h; the pressure of the second stage is 30-50Pa, the temperature is 160-200 ℃, the rotation rate is 80-120r/min, the micro-polymerization reaction time is 5-6h, and finally the product is collected to obtain a solid D;
step five: washing the solid D with deionized water and absolute ethyl alcohol in sequence until the pH is 6.8-7.6, then transferring the product into a far infrared drying oven, drying at 80-120 ℃ for 12-18h, and collecting to obtain a white powdery solid E;
step six: solid E in mass ratio: aluminum fluoride: silica ═ (0.8-1.2): (1.2-1.8): (1.5-2.2) uniformly mixing the three substances and flatly paving the three substances to the bottom of a crucible, then moving the sealed crucible to a muffle furnace, heating the crucible to 400-600 ℃ at the heating rate of 6-10 ℃/min, keeping the temperature for 0.5-1h, heating the crucible to 1100-1300 ℃ at the heating rate of 5-8 ℃/min, keeping the temperature for 0.5-2h, naturally cooling the crucible to room temperature, finally collecting a sintering product, washing the sintering product for 6-8 times by using deionized water and absolute ethyl alcohol in sequence, and drying the sintering product to obtain the micron-sized three-dimensional fish scale aluminum oxide.
FIG. 1 is a scanning electron micrograph of the micron-sized three-dimensional fish-scale aluminum oxide prepared in example 1. It can be seen that the three-dimensional fish scale-like alumina is uniformly dispersed, the agglomeration among the particles is less, the particles are fish scale-like in appearance, and the abnormal growth of alumina crystal grains is not generated, which indicates that the three-dimensional fish scale-like alumina is successfully synthesized by using the wheat straws as the template in example 1.
FIG. 2 is an X-ray diffraction pattern of the three-dimensional fish-scale alumina prepared in example 1. An obvious sharp peak can be seen, which indicates that the prepared alumina has higher purity and crystallinity. The diffraction angles of 25.58 °, 35.16 °, 43.47 °, 52.55 °, 57.56 °, 66.76 ° and 68.42 ° correspond to the characteristic peak positions of alumina, and it was verified that the resultant substance was alumina.
The micron-sized three-dimensional fish-scale product prepared with the double precipitant in example 1 was collected, weighed and calculated to calculate the yield:
TABLE 1 comparison of yield data
Figure BDA0003026533100000081
Comparative example 1 was prepared with reference to example 1, except that only the precipitant melamine was introduced. The yield of the embodiment 1 is obviously higher than that of the comparative example, because the precipitation efficiency of the alumina seed crystal of the product can be effectively improved by adopting the double precipitating agents, and the precipitation width and the yield of the target product are improved.
Comparative example 2
Essentially the same as in example 1, except that: comparative example 2 used a templating agent P123 that did not contain a pore structure. The scanning electron micrograph of the alumina product prepared at this time is shown in FIG. 4 and the X-ray diffraction pattern is shown in FIG. 5. It can be seen that the alumina prepared in this comparative example does not appear to be fish-scaly.
Comparative example 3
Essentially the same as example 1, except that: comparative example 3 the micro-polymerized reaction product was directly sintered. The sintering temperature is 1100-1300 ℃, and the sintering time is 0.5-2 h.
Comparing fig. 6 and fig. 1, it can be seen that under the conventional calcination condition, the alumina product presents irregular thick plate shape, the separation between the sheets is not clear, and obvious agglomeration phenomenon exists, while the micron-sized three-dimensional fish-scale alumina in fig. 1 has less agglomeration and does not have the condition of excessive growth of crystal grains. As can be seen from Table 2, the grain diameter, thickness, pore volume and other data of the product obtained in comparative example 3 are all larger than those of example 1, which proves that the great difference exists between the microstructures of the two shown in the attached FIG. 6 and FIG. 1, and therefore, the conventional calcination system is difficult to meet the preparation requirement of the micron-sized three-dimensional scaly alumina.
TABLE 2 comparison of product Properties
Figure BDA0003026533100000082
Comparative example 4
Essentially the same as example 1, except that: comparative example 4 the filling step of glucose was omitted.
TABLE 3 comparison of yield data
Figure BDA0003026533100000091
Comparative example 5
Essentially the same as example 1, except that: comparative example 5 a one-step sintering was used.
Step six: solid E in mass ratio: aluminum fluoride: silica ═ (0.8 to 1.2): (1.2-1.8): (1.5-2.2) uniformly mixing the three substances and flatly paving the three substances to the bottom of a crucible, then moving the sealed crucible to a muffle furnace, heating to 1100-1300 ℃ at a heating rate of 5-8 ℃/min, keeping the temperature for 2-4 h, then naturally cooling to room temperature, finally collecting a sintered product, washing for 6-8 times by using deionized water and absolute ethyl alcohol in sequence, and drying to obtain the micron-sized three-dimensional fish scale-shaped alumina.
The scanning electron microscope image of the alumina prepared by the comparative example is shown in fig. 7, and it can be seen that the appearance of the obtained alumina product is in a molten worm shape, and a remarkable tumor-shaped structure appears at the connection part of the seed crystal, which is the result of abnormal growth of the alumina seed crystal at high temperature. In addition, the agglomeration phenomenon of the alumina product in fig. 7 is serious, and the alumina is melted due to the overhigh temperature and overlong time of the high-temperature solid-phase reaction, which affects the directional growth of the final product. In conclusion, the two-step sintering reaction is very important for preparing the micron-sized three-dimensional fish-scale alumina.

Claims (8)

1. A method for preparing micron-sized three-dimensional fish-scale alumina by taking wheat straws as a template is characterized by comprising the following steps:
pickling wheat straw to etch it;
adopting a glucose solution to attach and fill etching point positions of the pickled wheat straws, and then drying to obtain a wheat straw precursor;
immersing a wheat straw precursor into a double precipitator solution containing multiple heterogeneous functional groups to attach the heterogeneous functional groups of the precipitator to the interior of the wheat straw in a chemical bond form, so as to obtain a modified solution of the wheat straw precursor; the dual precipitant solution comprises: the aluminum source is 50-70%, the sulfanilamide 5-12%, the melamine 6-18%, the pH regulator 3-6% and the balance of deionized water in percentage by mass;
carrying out micro-polymerization on the modified solution of the wheat straw precursor in a rotary micro-polymerization reactor;
collecting a micro-polymerization reaction product, and sintering the micro-polymerization reaction product, aluminum fluoride and silicon dioxide to obtain micron-sized three-dimensional scaly aluminum oxide; the sintering is as follows: raising the temperature from the room temperature to 400-1300 ℃, keeping the temperature for 0.5-1h, then raising the temperature to 1100-1300 ℃, keeping the temperature for 0.5-2h, and then naturally cooling to the room temperature.
2. The process according to claim 1, characterized in that the molar ratio of sulfanilamide and melamine is 1: (0.5-3).
3. The method according to claim 1, wherein the micro-polymerization is carried out for a reaction time of 6 to 8 hours.
4. The process according to claim 1, wherein the micro-polymerization is divided into two stages, the second stage having a reaction temperature 80-120 ℃ higher than the first stage and a reaction time 3-4 hours higher than the first stage.
5. The method of claim 4, wherein the micro-polymerization first stage is at a pressure of 20-40Pa, a temperature of 60-100 ℃, a rotation rate of 40-100r/min, and a micro-polymerization reaction time of 1-2 h; the pressure of the second stage is 30-50Pa, the temperature is 160-200 ℃, the rotation rate is 80-120r/min, and the micro-polymerization reaction time is 5-6 h.
6. The method according to claim 1, wherein the mass ratio of the reaction product of the micro-polymerization, aluminum fluoride and silicon dioxide is (0.8-1.2): (1.2-1.8): (1.5-2.2).
7. The micron-sized three-dimensional fish-scale-shaped alumina obtained by the preparation method according to any one of claims 1 to 6, wherein the micron-sized three-dimensional fish-scale-shaped alumina has a fish-scale-shaped morphology formed by oriented growth of alumina grains; the diameter of the alumina crystal grain is 1-5 μm, the thickness is 0.2-0.8 μm, the specific surface area is 200-2·g-1。
8. The micron-sized three-dimensional fish-scale aluminum oxide as claimed in claim 7, wherein the micron-sized three-dimensional fish-scale aluminum oxide has a three-dimensional controllable pore structure with a pore volume of 0.5-1.2cm3·g-1The pore size distribution is 8-30 nm.
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CN111554926A (en) * 2020-05-15 2020-08-18 陕西科技大学 Preparation method of wheat straw/carbon nanotube for long-cycle nitrogen-doped lithium battery negative electrode material
CN112054196A (en) * 2020-08-11 2020-12-08 绍兴诺鼎卫浴洁具股份有限公司 Waste paper-based porous carbon-coated S-Co3O4The positive electrode material of the lithium-sulfur battery and the preparation method thereof

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