CN101817544B - Method for preparing aluminum-cerium dual-component hydrosol - Google Patents

Abstract

The invention relates to a method for preparing dual-component hydrosol with a dispersed-phase aluminum component of boehmite nanometer crystal grains and a cerium component of cerianite nanometer crystal grains, and belongs to the field of inorganic nanometer materials. The method comprises the following steps of: adding alkali into mixed solution of Al3+ and Ce3+ salts to co-precipitate two kinds of metal ions; adding an oxidizing agent to oxidize Ce(OH)3 in the precipitate into overoxidation hydroxide of Ce4+; performing thermal decomposition on the overoxidation hydroxide of Ce4+ in the precipitate to form Ce(OH)4 (cerium hydroxide (IV)); and adding acid to peptize the precipitate to prepare boehmite-cerianite sol. The clear boehmite-cerianite dual-component hydrosol can be prepared by the method, and the dispersed phase of the hydrosol consists of nanometer crystal grains; and the crystal grains are not agglomerated and are uniform in size, and the size is generally 3 nanometers.

Description

A kind of preparation method of aluminum, cerium two-component hydrosol

technical field

The present invention relates to a kind of aluminum, cerium two-component aqueous sol, particularly a kind of dispersed phase aluminum component is γ-AlOOH (boehmite) nanocrystal, cerium component is CeO ₂ (in the only crystal phase of CeO ₂ cerite phase appears) nanocrystalline two-component hydrosol preparation method, that is, nano-boehmite-peristalite two-component hydrosol (for the sake of brevity, the boehmite-periscite two-component hydrosol is mentioned below. When the component hydrosol is used, it will be referred to as "aluminum cerium sol") wet chemical preparation method. The invention belongs to the field of inorganic nanometer materials.

Background technique

In terms of the sol preparation technology related to the present invention, most of the literature reports focus on the preparation of a single boehmite sol. Since the coarse-grained pericite precipitates are difficult to peptize, it is difficult to prepare a stable CeO ₂ aqueous sol. The prior art in this regard appears in the patent ZL 99114762.6, which relates to a synthetic method of CeO ₂ hydrosol, which uses an aqueous solution of mixed rare earth chloride containing cerium (III) as the starting material, undergoes precipitation-oxidation-selection Steps such as dissolving non-cerium rare earth hydroxides and other steps to obtain CeO ₂ nanometer hydrosol, which can be stored stably for a long time. In addition, Dong Xiangting et al. used ammonia water to precipitate Ce(NO ₃ ) ₃ , and then peptized the precipitation with nitric acid to obtain CeO ₂ nano-hydrosol. The obtained light yellow transparent hydrosol could exist stably for 48 hours [Dong Xiangting et al. CeO ₂ nano-hydrosol Preparation. Rare Metal Materials and Engineering, 2002, 31(3): 229-231]. The preparation method of aluminum and cerium two-component hydrosol, especially the preparation method of aluminum and cerium two-component nano-hydrosol is rarely reported.

The present invention arranges Al ³⁺ , Ce ³⁺ rapid co-precipitation-cerium (III) in the precipitate is oxidized to cerium (IV)-peptization by γ-AlOOH and Ce(OH) ₄ (cerium hydroxide (IV) )) to prepare the aluminum cerium sol, and the aluminum and cerium particles that constitute the dispersed phase of the hydrosol are crystalline compounds of several nanometer scales. Researchers in the technical field know that the solubility of Ce(OH) ₄ and γ-AlOOH is much lower than that of Ce(OH) ₃ under the action of acid solution of the same concentration. Researchers in this technical field also know that the complete dehydration product corresponding to the hydroxide Ce(OH) ₄ of cerium (IV) is CeO ₂ , but Ce(OH) ₄ already has the sole crystal of pericite (CeO ₂ phase), the difference between Ce(OH) ₄ and CeO ₂ is only that the former contains water, that is: Ce(OH) ₄ can be regarded as a kind of CeO ₂ containing water, expressed as dihydrate cerium oxide (CeO ₂ · 2H ₂ O). And Ce(OH) ₄ can be partially dehydrated to CeO ₂ ·mH ₂ O (m<2) at relatively low temperature, for example, under the hydrothermal condition of T≤100°C. That is to say, hydrated cerium oxide (CeO ₂ ·nH ₂ O, n≤2) has the same crystal structure as crystalline CeO ₂ . The thermal analysis results of hydrated ceria are consistent with this understanding: as the temperature rises, hydrated ceria gradually dehydrates, and when the dehydration is complete, it transforms into CeO ₂ , and no phase transition occurs during this process. Different from the above properties of cerium (IV) hydroxide Ce(OH) ₄ , the dehydration product of cerium (III) hydroxide Ce(OH) ₃ is crystalline Ce ₂ O ₃ , crystalline Ce ₂ The crystal structure of O ₃ is different from that of Ce(OH) ₃ ; the product of dehydration of γ-AlOOH is crystalline Al ₂ O ₃ , and the crystal structure of crystalline Al ₂ O ₃ is different from that of γ-AlOOH; here , crystalline hydroxides and their dehydrated corresponding crystalline oxides belong to two types of crystal structures. The present invention just utilizes the characteristics of cerium (IV) hydroxide Ce (OH) ₄ and aluminum hydroxide γ-AlOOH, provides a kind of starting from the mixed solution of Al ³⁺ , Ce ³⁺ salt, synthesizes Process for stable aluminum-cerium bicomponent nanocrystalline sols.

Contents of the invention

The object of the present invention is to provide a method for preparing aluminum-cerium sol, especially a two-component aqueous sol in which the aluminum component of the dispersed phase is boehmite nanocrystals and the cerium component is pericite nanocrystals. the

According to above-mentioned invention object, preparation method of the present invention, the preparation method of aluminum cerium sol is realized by following technical scheme, and the feature of this scheme is to have following processing steps:

(1) Take soluble Al ³⁺ salt and Ce ³⁺ salt ingredients according to the molar ratio of n _Al :n _Ce =x:1 to prepare aluminum-cerium two-component solution; under strong stirring, quickly add alkali to the solution Liquid, so that the co-precipitation of Al ³⁺ and Ce ³⁺ occurs instantaneously, and a powdery white jelly-like substance composed of γ-AlOOH and Ce(OH) ₃ is formed;

(2) under strong stirring, add oxidizing agent in the jelly thing that step (2) obtains, oxidize Ce(OH) ₃ be Ce(OOH)(OH) ₃ (Ce ⁴⁺ peroxyhydroxide), Turn the white jelly into a brownish red suspension, and the viscosity is significantly reduced;

(3) Heating and boiling the high-viscosity suspension obtained in step (3) makes the suspension gradually fade to light yellow, and the viscosity is greatly reduced. The solid particles in the light yellow suspension are composed of γ-AlOOH and Ce(OH ) ₄ constitutes;

(4) Slowly add dilute acid dropwise to the low-viscosity suspension obtained in step (3) under vigorous stirring, so that the pH value of the suspension is gradually reduced, and with it, the turbidity of the suspension also increases. Decrease gradually until it turns clear and transparent. The clear liquid is the dispersion system of nano-boehmite-sternite, that is, aluminum cerium sol. the

The Al ³⁺ salt in the above step (1) is one of aluminum chloride, aluminum nitrate, aluminum acetate.

The ^Ce salt in the above step (1) is one of cerous chloride and cerous nitrate.

The lye in the above-mentioned steps (1) is ammoniacal liquor. the

The oxidizing agent in the above-mentioned step (2) is hydrogen peroxide. the

The dilute acid in the above-mentioned step (4) is a kind of in hydrochloric acid, nitric acid. the

The concentration of the dilute acid in the above step (4) is 1.00mol/l-3.00mol/l. the

The pH value of the aluminum-cerium sol obtained in the above step (4) is 1.2-2.0. the

The preparation method of the present invention quickly adds lye into the mixed solution of aluminum and cerium, and the pH value of the solution is instantly raised above the precipitation pH value of Al ³⁺ and Ce ³⁺ ions, so that Al ³⁺ and Ce ³⁺ ions It quickly transforms into a powdery white jelly-like coprecipitate of γ-AlOOH and Ce(OH) ₃ . It is known that the pH value at which the concentration of 1 mol/l aluminum ion begins to precipitate is 3.3, the pH value at which the precipitation is complete is 5.2, and the pH value at which the concentration of 1 mol/l cerium (III) ion begins to precipitate is 7.6. If the way of adding lye is changed, adding lye slowly to the two-component solution will gradually increase the pH value of the solution. During the gradual change of the pH value, Al ³⁺ ions will be precipitated first , Ce ³⁺ ions will not start to precipitate until the precipitation of aluminum ions is complete. Due to the successive formation of the two types of precipitation, there will be differential precipitation and growth of the two types of hydroxides. In a comparative test, when other conditions were the same, the precipitate particles formed by slowly adding alkali solution could not be completely peptized by adding acid in the later stage, even if the pH value of the light yellow suspension obtained in step (3) was changed to Down to below 1.0, the suspension still cannot be dissolved. The above-mentioned condition test shows that it is crucial to suppress the differentiation and precipitation tendency of the two components to finally obtain the clear sol in the present invention.

The preparation method of the present invention is by adding hydrogen peroxide rapidly in the above-mentioned powdery white jelly, and the Ce(OH) in the oxidized precipitate ₃ The microparticles are Ce(OOH)(OH) ₃ of cerium(IV) peroxide hydroxide, and simultaneously make The pH of the solution dropped to ~7.

The preparation method of the present invention decomposes the peroxygen bond of the perhydroxide oxide of cerium (IV) by heating and boiling the brownish-red high-viscosity suspension obtained in step (2) to convert it into the hydroxide of cerium (IV). Compound Ce(OH) ₄ .

In the preparation method of the present invention, dilute acid is slowly added dropwise to the suspension containing γ-AlOOH and Ce(OH) ₄ precipitates obtained in step (3), so that the aggregate particles constituting the precipitates are peptized. Peptization is a process in which colloidal particles temporarily aggregated into aggregates are redispersed in the liquid phase to form a colloidal solution (sol). The structural feature of the agglomerate as the peptization object of the present invention is that two kinds of nanoparticles of γ-AlOOH and Ce(OH) ₄ are distributed adjacent to each other in the agglomerate particles. During the peptization process, the detachment and dispersion of one type of nanoparticle from the surface of such aggregate particles will facilitate the detachment and dispersion of the other type of particle, thereby facilitating the final formation of a two-component nanosol. The peptization process of the present invention involves the effects of two aspects at the same time: on the one hand, part of the boehmite is dissolved to destroy the aggregation structure of aggregate particles, and on the other hand, the detachment and dispersion of nanoparticles from the surface of the aggregate. Within the peptization pH value range arranged by the present invention, the Ce(OH) _particles in the aggregates can exist stably, and part of the boehmite will be dissolved, and this part of the boehmite should be relatively poor in structural integrity, This dissolution will facilitate the disintegration of aggregate particles; as the amount of acid solution increases, the nanoparticles on the surface of the aggregate are charged due to the adsorption of cations and tend to form a stable surface charge layer outside the particles. Under the action of (such as stirring), these charged particles will be detached from the surface of the aggregate and dispersed in the liquid phase. Under the synergy of these two aspects, the final result is that the aggregate particles are completely disintegrated to form an aluminum-cerium sol with Ce(OH) ₄ as the main dispersed phase and γ-AlOOH as the secondary.

The substantive feature of the present invention is that the agglomerate particle as the peptization object has the structure feature that γ-AlOOH and Ce(OH) ₄ two kinds of nanoparticles are adjacent to each other, and the structure feature is that Al ³⁺ And Ce ³⁺ ions quickly and synchronously form hydroxide precipitates, and then convert Ce(OH) ₃ particles in the co-precipitate into Ce(OH) ₄ in time. _Because the acid solution of the same concentration is far less than its dissolving ability to Ce(OH) ₄ to Ce(OH) , therefore, Ce(OH) ₃ particles are changed into Ce(OH) ₄ , it is the present invention The preparation method is one of the key conditions for obtaining aluminum cerium sol. If there is no such transformation, when acid is added to lower the pH value of γ-AlOOH-Ce(OH) ₃ suspension, Ce(OH) ₃ particles are easily dissolved, and the peptized product generated in this case will be It is boehmite sol dispersed in CeCl ₃ -AlCl ₃ solution, but cannot form aluminum cerium sol.

The present invention has following advantage and remarkable effect:

1. The aluminum-cerium sol prepared in the present invention is a nano-boehmite (γ-AlOOH)-periscite (CeO ₂ ) sol, that is, the aluminum and cerium oxide particles constituting the dispersed phase of the sol are all nanocrystals. The aluminum cerium sol is transparent and stable, and can be placed for a long time without turbidity, gelation and the like. The nanocrystalline aluminum cerium sol prepared by the method has two uses. One is to use this sol to dip-coat the surface of carriers of various shapes (such as balls, tubes, plates, rods, etc.), and to generate a crystalline boehmite-sputum surface film on the carrier surface; The thickness of the crystalline coating film on the surface of the carrier can be controlled by the number of times of coating. The second is to directly coagulate and precipitate nano-boehmite-galena powder from this sol. Since the aluminum-cerium sol is a dispersion system of boehmite and pericite nanoparticles, the film layer and powder prepared by using the sol are in a crystalline state without being calcined; if the obtained film layer or powder is calcined, the An increase in temperature will dehydrate boehmite, one of the components, and transform it into a series of isomers of alumina, that is, the formation from γ-Al ₂ O ₃ (low temperature product) to α-Al ₂ O ₃ (high temperature product) A series of phase transition products, while pericite has no phase transition and valence change during calcination. It is known that CeO ₂ -based composite oxides are the basic components of catalytic converters for treating automobile exhaust, and when CeO ₂ is doped with γ-Al ₂ O ₃ , the oxygen buffering capacity of CeO ₂ can be optimized. At the same time, the γ-Al ₂ O ₃ -CeO ₂ composite is also an excellent acidic catalyst and a combustion catalyst for aromatic compounds. Starting from the crystalline aluminum-cerium sol prepared by this method, it is easy to obtain dense films or fine powders of nano-γ-AlOOH-CeO ₂ and nano-Al ₂ O ₃ -CeO ₂ composites, because of their high specific surface area and high activity to optimize the function of the complex.

Two, the preparation technology that the present invention adopts can suppress the differentiation precipitation tendency of aluminum, cerium component in co-precipitation step, and make as peptization object γ-AlOOH and Ce(OH) ₄ The microscopic characteristic of individual remains until peptization Before, thus ensuring that the final peptization can be carried out smoothly. In the arrangement of specific process steps, after the rapid co-precipitation of Al ³⁺ and Ce ³⁺ is realized, an oxidizing agent is added to the system in time to oxidize Ce(OH) ₃ to Ce(OOH)(OH) ₃ , and make the system Viscosity decreased significantly, and pH value dropped rapidly to near neutral. This treatment, combined with the subsequent heating and boiling treatment, effectively converts Ce(OH) ₃ co-existing with γ-AlOOH in the precipitated particles into Ce(OH) ₄ . This process arrangement enables the γ-AlOOH and Ce(OH) ₄ particles as peptization objects to maintain their fine characteristics, and ensures that the cerium compound can remain stable during the peptization process. During the peptization process, the partial dissolution of boehmite and the peptization of hydroxide particles are achieved by adding dilute acid, thereby destroying the contiguous structure of γ-AlOOH and Ce(OH) ₄ nanoparticles in the aggregate particles , so that Ce(OH) ₄ , which is usually difficult to peptize, is dissociated smoothly from the precipitated particles, dispersed and suspended as nanocrystals, and together with peptized and dispersed nano-boehmite, forms a two-component nano-hydrosol. This preparation process overcomes the problem that Ce(OH) ₄ is difficult to be peptized, and does not need to use auxiliary peptization methods such as heating reflux and ultrasonic dispersion.

Three, the sol preparation process of the present invention is simple and easy. From the co-precipitation of Al ³⁺ and Ce ³⁺ ions to the peptization of aggregate particles, the four steps are completed in the same reaction vessel at one go, realizing a one-pot synthesis.

Detailed ways

The preparation method of the present invention will be further described below in conjunction with the examples. The following examples will help to understand the present invention, but do not limit the content of the present invention. the

Example 1

A kind of method for preparing nano aluminum cerium sol of the present invention, its processing step is as follows:

(1) Use CeCl ₃ 7H ₂ O to prepare 600ml of a solution with a concentration of 0.20mol/l, add AlCl ₃ 6H ₂ O to it according to the molar ratio of Al:Ce=0.25:1, and obtain a colorless and transparent solution after dissolution . Under vigorous stirring, pour 60ml of concentrated ammonia water into the solution, so that the solution instantly turns into a powdery white jelly.

(2) Quickly add 30ml of hydrogen peroxide to make the white jelly-like substance into a maroon high-viscosity suspension. the

(3) Heat and boil the obtained suspension until the suspension fades to light yellow and its viscosity is greatly reduced. the

(4) Under stirring, slowly add dilute hydrochloric acid with a concentration of 2.00 mol/l dropwise while hot to peptize the slurry, so that it gradually turns into a yellow-green transparent sol, and its pH value is 1.55. the

Determined by chemical analysis, in the sol obtained in this embodiment, sol-state aluminum (i.e. boehmite particles) accounts for 15.3% of the total aluminum moles, and sol-state cerium (i.e. pericite particles) accounts for 97.7% of the total cerium moles. %, indicating that the dispersed phase of the sol prepared in this example is mainly composed of pericite particles and boehmite particles are secondary components. The high-resolution transmission electron microscope (HRTEM) image of the sol prepared in this example shows that there is no agglomeration among the crystal grains, the size of the crystal grains is uniform, approximately 3nm, and the cation arrangement of the nanocrystal grains is generally regular, and the lattice fringes can be distinguished. ; Carry out Fourier transform images of some nanocrystal individuals, and index the diffraction spots, and then determine that they are the diffraction patterns of pericite single crystals. the

The storage stability of the aluminum-cerium sol prepared by this method is good. A cup of the sol sample prepared in Example 1 has been sealed and stored for more than one year, and it is still clear and transparent without any precipitation and no gel formation. the

Example 2

A kind of method for preparing nano-aluminum cerium sol of the present invention, its raw material and process step are similar to embodiment 1, but in step (1) according to the molar ratio of Al: Ce=0.11 _: 1, add AlCl in CeCl ₃ solution. 6H ₂ O, step (4) Peptize the slurry with dilute hydrochloric acid with a concentration of 1.00 mol/l, so that it gradually turns into a yellow-green transparent sol.

The pH value of the sol prepared in this embodiment is 1.24, the sol-state aluminum accounts for 29.8% of the total aluminum moles, and the sol-state cerium accounts for 98.2% of the total cerium moles. the

Example 3

A kind of method for preparing nano aluminum cerium sol of the present invention, its raw material and process step are similar to embodiment 1, but in step (1) according to the molar ratio of Al: Ce=0.43: 1 to CeCl ₃ solution is added AlCl ₃ . 6H ₂ O, step (4) Peptize the slurry with dilute hydrochloric acid with a concentration of 3.00 mol/l, so that it gradually turns into a yellow-green transparent sol.

The pH value of the sol prepared in this embodiment is 1.96, the sol-state aluminum accounts for 20.2% of the total aluminum moles, and the sol-state cerium accounts for 97.4% of the total cerium moles. the

Example 4

A kind of method for preparing nano-aluminum cerium sol of the present invention, its process step is similar to embodiment 1, but the raw material used is different from embodiment 1, uses Ce(NO ₃ ) ₃ 6H ₂ O and Al(NO _{3 )} 3.9H ₂ O is used as the starting material, according to the molar ratio of Al: Ce = 0.25: 1, step (4) peptize the slurry with dilute nitric acid with a concentration of 2.00 mol/l, so that it gradually transforms into Yellow-green transparent sol.

The pH value of the sol prepared in this embodiment is 1.33, the sol-state aluminum accounts for 17.5% of the total aluminum moles, and the sol-state cerium accounts for 96.8% of the total cerium moles. the

Claims (8)

1. a preparation method of boehmite-peristalite two-component hydrosol, is characterized in that following process step is arranged: (1) According to the molar ratio of n _Al : n _Ce = x: 1 ingredients, in the formula, the composition parameter x is 0.11 ~ 0.43, prepare the aqueous solution of soluble Al ³⁺ salt and Ce ³⁺ salt, in the solution under stirring Quickly add alkali by pouring to obtain the co-precipitate of Al ³⁺ and Ce ³⁺ ; (2) under stirring, quickly add the oxidant in time to obtain a suspension containing boehmite and cerium (IV) hydroxide precipitate; (3) under stirring, heating and boiling the suspension obtained in step (2) to obtain a suspension containing boehmite and cerium hydroxide (IV) precipitates; (4) Slowly add acid under stirring until the precipitate is completely peptized to obtain a boehmite-peristalite two-component aqueous sol. 2. the preparation method of boehmite-peristalite hydrosol according to claim 1 is characterized in that the soluble ^Al of described step (1) Salt is aluminum chloride, aluminum nitrate or aluminum acetate, soluble Ce The ³⁺ salt is cerous chloride or cerous nitrate. 3. the preparation method of boehmite-peristalite hydrosol according to claim 1, is characterized in that the alkali of described step (1) is ammoniacal liquor. 4. the preparation method of boehmite-peristalite hydrosol according to claim 1, is characterized in that the oxidizing agent of described step (2) is hydrogen peroxide. 5. The preparation method of boehmite-scarcite hydrosol according to claim 1, characterized in that the acid in the step (4) is hydrochloric acid or nitric acid. 6 . The method for preparing boehmite-scarcite hydrosol according to claim 1 , characterized in that the acid concentration in the step (4) is 1.00 mol/l˜3.00 mol/l. 7 . The method for preparing the pericite-boehmite sol according to claim 1 , characterized in that the pH value for completely peptizing the precipitate in the step (4) is 1.2˜2.0. 8. the preparation method of boehmite-peristalite hydrosol according to claim 1 is characterized in that the dispersed phase of described boehmite-peristalite hydrosol is made of boehmite and pericite nano-single crystal constitute.