CN102583467B - Method for using hydrotalcite-like substance with low zinc-aluminum molar ratio as precursor to manufacture zinc-aluminum spinel - Google Patents

Abstract

The invention relates to a method for preparing nano-ZnAl ₂ O ₄ spinel, which comprises the steps of (1) weighing divalent zinc salt, trivalent aluminum salt and CO(NH ₂ ) ₂ , adding deionized water to obtain a mixed salt solution, Heating in an oil bath at 70°C to 110°C, stirring, standing, and cooling; the obtained filter cake is ground to obtain a zinc-aluminum hydrotalcite precursor; (2) the obtained zinc-aluminum hydrotalcite precursor is placed in a muffle furnace, and the temperature is raised to 700℃～1000℃, keep warm for 1～5 hours, cool to room temperature, and get ZnAl ₂ O ₄ spinel; if it contains Al ₂ O ₃ or ZnO impurities, it can be treated with alkali solution with a molar concentration of 5～15mol/L to remove high Dispersed _{Al2O3 or} ZnO. The invention utilizes the urea hydrolysis method to prepare the zinc-aluminum low molar ratio hydrotalcite-like layered precursor without adjusting and controlling the pH value, the obtained precursor has a large grain size, good crystallinity and dispersibility, and the prepared ZnAl ₂ O ₄ The spinel components are uniform and the particle size is small.

Description

A method for preparing zinc-aluminum spinel with zinc-aluminum low molar ratio hydrotalcite as precursor

technical field

The invention relates to the technology for preparing nano-zinc-aluminum spinel, in particular to a method for preparing nano-zinc-aluminum spinel (ZnAl ₂ O ₄ ) by using hydrotalcites with a low molar ratio of zinc and aluminum as precursors.

Background technique

ZnAl ₂ O ₄ spinel is a widely used inorganic non-metallic material, because of its high thermal stability, low surface acidity and strong mechanical resistance, it is used as a catalyst or catalytic carrier on the catalytic reverse side, At the same time, because of its wide-bandgap semiconductor properties, it is expected to be used as an ultraviolet transparent semiconductor, sensor and dielectric material. At present, the methods for preparing this type of spinel mainly include ceramic method, sol-gel method, etc. The traditional ceramic method requires a higher calcination temperature, and the product is easy to agglomerate during calcination, the overall uniformity is poor, and the specific surface area is small. The glue method generally uses expensive metal alkoxide as the reaction starting material, which makes the preparation cost higher, and the calcination process is more dangerous, requires corresponding protection measures, and has a great impact on the environment. In order to overcome the shortcomings of the ceramic method and the sol-gel method, the literature LuZou, Feng Li, XuXiang, David G.Evans, Xue Duan, Self-generated template pathway to high-surface-area zinc aluminate spinel with mesopore network from a single-source Inorganic precursor, Chem. Mater., 18, 5852 (2006) proposed to obtain ZnAl ₂ O ₄ spinel with high specific surface area by calcining zinc-aluminum hydrotalcite. However, the zinc-aluminum molar ratio in the precursor used in this method is relatively large, and the content of impurities in the calcined product is relatively large. Further chemical treatment is required to obtain pure phase ZnAl ₂ O ₄ spinel, and the utilization rate of raw materials is relatively small. , increasing the preparation cost.

Zinc-aluminum hydrotalcite is the precursor material for preparing ZnAl ₂ O ₄ spinel. The common method for the preparation of zinc-aluminum hydrotalcite is to drop the mixed salt solution of zinc salt and aluminum salt and sodium hydroxide solution into the In ionized water, the pH value is controlled to be 6-10, then sodium carbonate is added, stirred to obtain a precipitate, suction filtered and washed to obtain a zinc-aluminum hydrotalcite filter cake. Such methods need to control the pH value, and the zinc-aluminum hydrotalcite obtained has small crystal grains, poor crystallinity and dispersibility, and is not conducive to the preparation of pure phase ZnAl ₂ O ₄ spinel as a precursor.

Contents of the invention

Aiming at the disadvantages of using hydrotalcite-like precursor technology to prepare nano-ZnAl ₂ O ₄ spinel calcined products, the impurity content is relatively large and the utilization rate of raw materials is low. A method for preparing nano ZnAl ₂ O ₄ spinel with talc as precursor.

Technical scheme of the present invention is as follows:

A preparation method of nanometer ZnAl ₂ O ₄ spinel, comprising steps as follows:

(1) Preparation of zinc-aluminum hydrotalcite precursors

^{Weigh divalent} _zinc salt ^, trivalent _aluminum salt ^and CO(NH ₂ ) ₂ is placed in a beaker, and deionized water is added to obtain a mixed salt solution, so that the concentration of divalent zinc salt in the mixed salt solution is 0.02-0.25mol/L, and the concentration of trivalent aluminum salt is 0.08-0.25mol/L L. The concentration of CO(NH ₂ ) ₂ is 0.3-2.0mol/L; transfer the mixed salt solution to a three-necked flask, heat in an oil bath at 70°C-110°C, stir for 6-18 hours, and keep at 70°C- Stand in an oil bath at 110°C for 3-48 hours, then cool to room temperature, filter and rinse with deionized water, dry the filter cake at 60°C-80°C for 6-24 hours, and grind to obtain the zinc-aluminum hydrotalcite precursor Crystalline powder.

(2) Preparation of ZnAl ₂ O ₄ spinel

a. When the molar ratio of Zn ²⁺ /Al ³⁺ in the mixed salt solution in step (1) is 0.5, place the obtained zinc-aluminum hydrotalcite precursor in a muffle furnace at 3-15°C/min Raise the temperature to 700°C-1000°C at a high speed, keep it warm for 1-5 hours, and cool down to room temperature naturally with the furnace temperature to obtain pure-phase ZnAl ₂ O ₄ spinel nanopowder; no other post-treatment is required.

b. When 0.25<Zn ²⁺ /Al ³⁺ molar ratio<0.5 in the mixed salt solution in step (1), or 0.5<Zn ²⁺ /Al ³⁺ molar ratio<1, the resulting zinc-aluminum water The talc precursor is placed in a muffle furnace, heated to 700-1000°C at a rate of 3-15°C/min, kept at a temperature of 1-5 hours, and naturally cooled to room temperature with the furnace temperature to obtain Al ₂ O ₃ or ZnO-containing Powder material of ZnAl ₂ O ₄ spinel. Treat the obtained product with an alkali solution with a molar concentration of 5-15 mol/L at 25-35°C for 24-96 hours, and then wash it with _deionized water until neutral to remove highly dispersed _Al2O3 or ZnO to obtain a pure phase of ZnAl ₂ O ₄ spinel nano powder.

According to the method of the present invention, the acid ion in the divalent zinc salt and trivalent aluminum salt in the salt mixed solution in step (1) is Cl ^- , NO ₃ ^- or SO ₄ ^2- , and the acid ion can be the same or different , as long as the Zn ²⁺ /Al ³⁺ molar ratio in the solution is 0.25<Zn ²⁺ /Al ³⁺ <1. Preferably, the divalent zinc salt is Zn(NO ₃ ) ₂ ·6H ₂ O, and the trivalent aluminum salt is selected from Al(NO ₃ ) ₃ ·9H ₂ O or AlCl ₃ ·6H ₂ O.

According to the method of the present invention, the alkali used in the alkali solution in step (2) b. is NaOH or KOH.

According to the present invention, preferably, a kind of preparation method of nano ZnAl ₂ O ₄ spinel, the steps are as follows:

Weigh 2.97～3.97g Zn(NO ₃ ) ₂ 6H ₂ O, 7.5～10g Al(NO ₃ ) ₃ 9H ₂ O and 7.2～9.6g CO(NH ₂ ) ₂ in a beaker, add 200ml deionized water to obtain a mixed salt solution, the Zn ²⁺ /Al ³⁺ molar ratio in the mixed salt solution is 0.5, and the CO(NH ₂ ) ₂ /(Zn ²⁺ +Al ³⁺ ) molar ratio is 4; the mixed salt solution is transferred Put the three-necked bottle into the three-necked bottle and immerse the three-necked bottle in a 100°C oil bath, stir and heat for 12 hours, keep the temperature of the 100°C oil bath for 12 hours, cool to room temperature, filter and rinse with deionized water several times, and finally dry at 60°C After 12 hours, the zinc-aluminum hydrotalcite precursor was obtained. Place the obtained zinc-aluminum hydrotalcite precursor in a muffle furnace, raise the temperature to 700°C-900°C at a rate of 5°C/min, keep the temperature for 3 hours, and naturally cool to room temperature with the furnace temperature to obtain pure phase ZnAl ₂ O ₄ spinel, the grain size is 10-40nm.

Technical characteristics of the present invention and principle are described as follows:

Hydrotalcite-like precursors are a new class of nano-inorganic functional materials with a layered structure, in which the chemical composition can be expressed as [M ^II _1-x M ^III _x (OH) ₂ ] ^x+ [A ^n- _x/n ]·mH ₂ O, wherein M ^II is a divalent metal cation, M ^II is selected from Ca ²⁺ , Mg ²⁺ , Mn ²⁺ , Fe ²⁺ , Co ²⁺ , Ni ²⁺ , Cu ²⁺ , Zn ²⁺ ; M ^III It is a trivalent metal cation, M ^III is selected from Al ³⁺ , Cr ³⁺ , Mn ³⁺ , Fe ³⁺ , Co ³⁺ ; ^An- is an interlayer anion, ^{An- is} selected from CO ₃ ^2- , SO ₄ ^2- , NO ₃ ^- , Cl ^- or organic anions; x is the molar ratio of M ^III to the total metal cations; m is the number of interlayer water molecules. In the hydrotalcite-like crystal structure, due to the influence of the lowest energy effect of the lattice and its lattice positioning effect, the metal ions are evenly distributed on the laminate in a certain way, that is, in every tiny structural unit on the laminate, Its chemical composition and structure remain unchanged. Due to the controllability and overall uniformity of the chemical composition and microstructure of hydrotalcite-like materials, materials with this special structure and composition are good precursors for the synthesis of nano-spinel-like materials with uniform components. Since the Zn ²⁺ /Al ³⁺ molar ratio of metal ions in zinc-aluminum hydrotalcites prepared by traditional methods is 1 to 4, which is much higher than that of spinel Zn ²⁺ /Al ³⁺ = 0.5, the direct roasting product is spinel A mixture of divalent metal oxides with good dispersibility, wherein the molar ratio of divalent metal oxides to roasted products is above 1:2, the impurity content is high, and the utilization rate of raw materials is low. The method of urea hydrolysis prepares pure-phase zinc-aluminum hydrotalcite under the condition that the raw material zinc-aluminum molar ratio is 0.25<Zn ²⁺ /Al ³⁺ <1, and the hydrotalcite can be roasted to obtain ZnAl ₂ O ₄ spinel and The two-phase mixture of Al ₂ O ₃ or ZnO can be removed by alkaline solution by utilizing the amphoteric properties of Al ₂ O ₃ and ZnO. Especially when the raw material zinc-aluminum molar ratio Zn ²⁺ /Al ³⁺ is equal to 0.5, the pure-phase ZnAl ₂ O ₄ spinel can be directly obtained without post-treatment of alkaline solution, which greatly saves the production cost.

The urea method uses urea hydrolyzate as a reaction precipitant. Compared with NaOH and ammonia water, urea is slowly hydrolyzed under heating, so that the supersaturation of the solution is low, the product has a large grain size and a good crystallinity. The hydrolysis reaction of urea is shown in the following formula:

H ₂ N-CO-NH ₂ →NH ₄ ⁺ +NCO ^- (1)

NCO ^- +2H ₂ O→NH ₄ ⁺ +CO ₃ ^2- (2)

In the preparation process of zinc-aluminum hydrotalcites, with the gradual decomposition of urea, the pH value of the solution increases slowly, and the solution first produces boehmite (AlOOH) with a layered structure, and then Zn ²⁺ enters the AlOOH layer to form a layered Zinc-aluminum hydrotalcites.

The nano ZnAl ₂ O ₄ spinel of the present invention is prepared by first preparing a single compound with uniform overall, microscopically adjustable chemical composition and structure, and high activity as a precursor, and then roasting and purifying. It solves the problems of easy agglomeration and small specific surface area of the ceramic method and the disadvantages of high preparation cost, dangerous calcination process and great impact on the environment of the sol-gel method. The present invention has the following excellent effects:

1. The zinc-aluminum low molar ratio hydrotalcite-like layered precursor was prepared by the method of urea hydrolysis, without adjusting and controlling the pH value. The obtained precursor has a large grain size, good crystallinity and dispersibility.

2. Since the metal atoms in the precursor are evenly dispersed between the layers, the ZnAl ₂ O ₄ spinel prepared by this method has the characteristics of uniform composition and small particle size.

3. The molar ratio of zinc ions to aluminum ions in the zinc-aluminum hydrotalcite precursor obtained in the present invention is close to the metal ion ratio in ZnAl ₂ O ₄ spinel, so that Al ₂ O ₃ or ZnO impurities in the calcined product The content is less, especially when Zn ²⁺ /Al ³⁺ = 0.5 in the original mixed salt solution, the precursor obtained can be directly calcined to obtain pure phase ZnAl ₂ O ₄ spinel, which greatly improves the utilization of raw materials Rate.

Description of drawings

Fig. 1 is an XRD pattern of zinc-aluminum hydrotalcite prepared by the urea method of the present invention under the condition that the molar ratio of Zn ²⁺ /Al ³⁺ is 0.5.

Fig. 2 is an XRD pattern of the ZnAl ₂ O ₄ spinel product after the zinc-aluminum hydrotalcite in Example 1 was calcined at 900°C.

Fig. 3 is a scanning electron microscope image (SEM) of the ZnAl ₂ O ₄ spinel product after the zinc-aluminum hydrotalcite in Example 1 was calcined at 900°C.

Detailed ways

The present invention will be further described below in conjunction with the examples, but not limited thereto. All raw materials used in the examples are commercially available and analytically pure.

Example 1:

Weigh 3.97g of Zn(NO ₃ ) ₂ ·6H ₂ O, 10.00g of Al(NO ₃ ) ₃ ·9H ₂ O and 9.60g of CO(NH ₂ ) ₂ in a beaker, add 200ml of deionized water to obtain a mixed salt solution, in the solution The molar ratio of Zn ²⁺ /Al ³⁺ is 0.5, the molar ratio of CO(NH ₂ ) ₂ /(Zn ²⁺ +Al ³⁺ ) is 4, and the molar concentration of Zn(NO ₃ ) ₂ ·6H ₂ O is 0.067mol/ L, the molar concentration of Al(NO ₃ ) ₃ 9H ₂ O is 0.133mol/L, the molar concentration of CO(NH ₂ ) ₂ is 0.8mol/L, the mixed salt solution is transferred to the three-necked flask and the three-necked flask Immerse in an oil bath at 100°C, stir and heat for 12 hours, keep at the temperature of the oil bath at 100°C for 12 hours, cool to room temperature, filter and rinse with deionized water several times, and finally dry at 60°C for 12 hours to obtain zinc-aluminum hydrotalcites Precursor, the yield is about 82%.

The obtained zinc-aluminum hydrotalcite precursor was placed in a muffle furnace, and the temperature was raised to 700°C, 800°C or 900°C at a rate of 5°C/min, respectively, kept for 1 hour, and naturally cooled to room temperature with the furnace temperature to obtain Pure phase ZnAl ₂ O ₄ spinel, the XRD spectrum of the product is shown in Figure 2, and the scanning electron microscope (SEM) is shown in Figure 3. According to the XRD pattern and the scanning electron microscope (SEM) pattern, it can be seen that the spinel grain size obtained by calcining is 10-40nm.

Example 2:

Weigh 3.97g Zn(NO ₃ ) ₂ 6H ₂ O, 6.25g AlCl ₃ 6H ₂ O and 9.00g CO(NH ₂ ) ₂ into a beaker, add 200ml deionized water to obtain a mixed salt solution, in which Zn ²⁺ /Al ³⁺ molar ratio is 0.8, CO(NH ₂ ) ₂ /(Zn ²⁺ +Al ³⁺ ) molar ratio is 4, where Zn(NO ₃ ) ₂ ·6H ₂ O molar concentration is 0.067mol/L, Al The molar concentration of (NO ₃ ) ₃ ·9H ₂ O is 0.083mol/L, and the molar concentration of CO(NH ₂ ) ₂ is 0.6mol/L; transfer the mixed salt solution to a three-necked flask and immerse the three-necked flask in 100°C oil Stirring and heating in the bath for 18 hours, then standing at the same temperature for 3 hours, cooling to room temperature, filtering and rinsing with deionized water several times, and finally drying at 60°C for 18 hours to obtain a zinc-aluminum hydrotalcite precursor. The obtained zinc-aluminum hydrotalcite precursor was placed in a muffle furnace, and the temperature was raised to 900°C at a rate of 10°C/min, kept for 2 hours, and then naturally cooled to room temperature with the furnace temperature to obtain ZnAl ₂ O ₄ spinel and A mixture of ZnO, wherein ZnO accounts for about 20% of the mass of the calcined product, and the calcined product is treated with 5 mol/L KOH solution for 24 hours to remove ZnO to obtain a pure phase ZnAl ₂ O ₄ spinel.

Example 3:

Weigh 3.57g Zn(NO ₃ ) ₂ 6H ₂ O, 9.00g AlCl ₃ 6H ₂ O and 10.80g CO(NH ₂ ) ₂ in a beaker, add 200ml deionized water to obtain a mixed salt solution, in which Zn ²⁺ /Al ³⁺ molar ratio is 0.5, CO(NH ₂ ) ₂ /(Zn ²⁺ +Al ³⁺ ) molar ratio is 5, where Zn(NO ₃ ) ₂ ·6H ₂ O molar concentration is 0.06mol/L, Al The molar concentration of (NO ₃ ) ₃ ·9H ₂ O is 0.12mol/L, and the molar concentration of CO(NH ₂ ) ₂ is 0.9mol/L; transfer the mixed salt solution to a three-necked bottle and immerse the three-necked bottle in 100°C oil Stirring and heating in the bath for 18 hours, then standing at the same temperature for 3 hours, cooling to room temperature, filtering and rinsing with deionized water several times, and finally drying at 60°C for 24 hours to obtain a zinc-aluminum hydrotalcite precursor. Place the obtained zinc-aluminum hydrotalcite precursor in a muffle furnace, heat up to 1000°C at a rate of 10°C/min, keep it warm for 1 hour, and naturally cool to room temperature with the furnace temperature to obtain a pure phase ZnAl ₂ O ₄ spinel stone.

Example 4:

Weigh 2.23g of Zn(NO ₃ ) ₂ ·6H ₂ O, 8.44g of Al(NO ₃ ) ₃ ·9H ₂ O and 7.2g of CO(NH ₂ ) ₂ in a beaker, add 200ml of deionized water to obtain a mixed salt solution, in the solution The molar ratio of Zn ²⁺ /Al ³⁺ is 1/3, the molar ratio of CO(NH ₂ ) ₂ /(Zn ²⁺ +Al ³⁺ ) is 4, and the molar concentration of Zn(NO ₃ ) ₂ ·6H ₂ O is 0.0375mol/L, _Al (NO ₃ ) ₃ .9H ₂ O molar concentration is 0.1125mol/L, CO(NH ₂ ) The molar concentration of 0.6mol/L; This mixed salt solution is transferred in the there-necked flask and The three-neck flask was immersed in an oil bath at 100°C for 8 hours, stirred and heated for 8 hours, then stood at the same temperature for 16 hours, cooled to room temperature, filtered and rinsed with deionized water several times, and finally dried at 70°C for 12 hours to obtain zinc-aluminum hydrotalcites Precursor. The obtained zinc-aluminum hydrotalcite precursor was placed in a muffle furnace, and the temperature was raised to 900°C at a rate of 8°C/min, kept for 2 hours, and then naturally cooled to room temperature with the furnace temperature to obtain ZnAl ₂ O ₄ spinel and A mixture of Al ₂ O ₃ , wherein Al ₂ O ₃ accounts for about 21% of the mass of the calcined product, is treated with 10 mol/L NaOH solution for 36 hours to remove Al ₂ O ₃ , and a pure phase ZnAl ₂ O ₄ spinel is obtained.

Claims (1)

1. a nanometer Zn Al ₂o ₄the preparation method of spinel, comprises that step is as follows:

(1) preparation of zinc-aluminum gavite presoma

0.25 < Zn in molar ratio ²⁺/ Al ³⁺< 1, CO (NH ₂) ₂/ (Zn ²⁺+ Al ³⁺the proportioning of)=3～5 takes divalent zinc salt, trivalent aluminium salt and CO (NH ₂) ₂be placed in beaker, add deionized water to obtain mixing salt solution, making divalent zinc salt concentration in mixing salt solution is that the concentration of 0.02 ~ 0.25 mol/L, trivalent aluminium salt is 0.08 ~ 0.25mol/L, CO (NH ₂) ₂concentration be 0.3 ~ 2.0mol/L; Described mixing salt solution is transferred in there-necked flask, 70 ℃～110 ℃ oil bath heating, stir 6～18 hours, keep under 70 ℃～110 ℃ oil bath temperatures standing 3～48 hours, then cool to room temperature, filter and use deionized water rinsing, filter cake is dried to 6～24 hours at 60 ℃～80 ℃, grind and obtain zinc-aluminum gavite presoma grains powder;

In described divalent zinc salt, trivalent aluminium salt, acid ion is Cl ^-, NO ₃ ^-or SO ₄ ^2-;

(2) ZnAl ₂o ₄the preparation of spinel

A. work as Zn in the middle mixing salt solution of step (1) ²⁺/ Al ³⁺mol ratio is 0.5 o'clock, and resulting zinc-aluminum gavite presoma is placed in to retort furnace, with the speed of 3～15 ℃/min, is warming up to 700 ℃～1000 ℃, is incubated 1～5 hour, with furnace temperature, naturally cools to room temperature, obtains the ZnAl of pure phase ₂o ₄spinel nano powder;

B. work as 0.25 < Zn in the middle mixing salt solution of step (1) ²⁺/ Al ³⁺mol ratio < 0.5, or 0.5 < Zn ²⁺/ Al ³⁺during mol ratio < 1, resulting zinc-aluminum gavite presoma is placed in to retort furnace, with 3～15 ° of speed of C/ minute, is warming up to 700 ° of C～1000 ℃, be incubated 1～5 hour, with furnace temperature, naturally cool to room temperature, obtain containing Al ₂o ₃or the ZnAl of ZnO ₂o ₄the powder body material of spinel; Products therefrom is processed 24～96 hours at 25～35 ℃ with the alkaline solution of volumetric molar concentration 5～15mol/L, then with deionized water wash, to neutrality, removed the Al of high dispersive ₂o ₃or ZnO, obtain the ZnAl of pure phase ₂o ₄spinel nano powder.

2 .nanometer Zn Al as claimed in claim 1 ₂o ₄the preparation method of spinel, is characterized in that the described divalent zinc salt of step (1) is Zn (NO ₃) ₂6H ₂o, trivalent aluminium salt is selected from Al (NO ₃) ₃9H ₂o or AlCl ₃6H ₂o.

3 .nanometer Zn Al as claimed in claim 1 ₂o ₄the preparation method of spinel, is characterized in that the alkaline solution alkali used in step (2) b. is NaOH or KOH.

4 .nanometer Zn Al as claimed in claim 1 ₂o ₄the preparation method of spinel, is characterized in that, step is as follows:

Take 2.97～3.97g Zn (NO ₃) ₂6H ₂o, 7.5～10g Al (NO ₃) ₃9H ₂o and 7.2～9.6g CO (NH ₂) ₂be placed in beaker, add 200mL deionized water to obtain mixing salt solution, Zn in mixing salt solution ²⁺/ Al ³⁺mol ratio is 0.5, CO (NH ₂) ₂/ (Zn ²⁺+ Al ³⁺) mol ratio is 4; Described mixing salt solution is transferred in there-necked flask and there-necked flask is immersed in 100 ℃ of oil baths to stirring heating 12 hours, keep under 100 ℃ of oil bath temperatures standing 12 hours, after cool to room temperature, filter and with deionized water rinsing number time, finally at 60 ℃, be dried and within 12 hours, obtain zinc-aluminum gavite presoma; Resulting zinc-aluminum gavite presoma is positioned in retort furnace, with the speed of 5 ℃/min, is warming up to 700 ℃ ~ 1000 ℃, be incubated 3 hours, obtain pure phase ZnAl after naturally cooling to room temperature with furnace temperature ₂o ₄spinel, grain-size is 10～40nm.

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