Preparation method of nano cerium oxide

Abstract

The invention relates to the technical field of nano material synthesis, in particular to a preparation method of nano cerium oxide, which comprises the steps of rare earth carbonate preparation, fused salt mixing, high-temperature calcination and post-treatment. The method can be used for preparing nano cerium oxide with uniform particle size and excellent dispersity, is a molten salt method which is simple in process, low in equipment requirement and capable of realizing mixing homogenization of cerium salt and fluxing salt, and is suitable for market popularization and application.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nanometer material synthesis, and particularly relates to a preparation method of nanometer cerium oxide. BACKGROUND

[0002] Nanometer cerium oxide (CeO2) is an important functional material, which has application value in the fields of catalyst, polishing agent, solid oxide fuel cell, ultraviolet absorption material, etc. due to its unique oxygen storage capacity, excellent oxidation-reduction performance and optical properties. Its performance depends largely on the size, morphology, dispersibility and crystallinity of the particles.

[0003] At present, many methods have been developed for the preparation of nanometer cerium oxide. For example: hydrothermal / solvothermal method (CN113247941A, CN105480999A): the morphology can be controlled, but usually requires high-temperature and high-pressure equipment, the reaction time is long, and organic surfactants may be used, increasing the cost and complexity of subsequent processing. Precipitation method (CN118289796A): simple process, but the precipitate is prone to hard agglomeration during drying and calcination, resulting in increased particle size and broadened distribution. Microemulsion method (CN116251562A): uniform particle size, good dispersibility, controllable morphology, mild reaction conditions, low yield, large amount of organic solvents used, and difficulties in scale-up. Supergravity method (CN119528201A): intensifies the mass transfer process and can obtain small particle size products, but requires a supergravity reactor, which has special requirements for equipment. Salt isolation method (CN119569099A): uses magnesium sulfate and other salts as isolation medium to effectively prevent high-temperature sintering, and can prepare ultra-small particle size (3-4 nm) cerium oxide, but cerium nitrate has a certain solubility in ethanol, which may affect the yield.

[0004] Salt melting method is an effective crystal growth method, which uses low-melting-point salt to form a liquid phase environment at high temperature to provide mass transfer medium and reaction site for reactants, thereby inhibiting particle agglomeration and promoting crystal growth. However, there are few reports on the combination of salt melting method with specific rare earth carbonate precursors for the preparation of nanometer cerium oxide with good dispersibility and uniform particle size. CN115140756A discloses a preparation method of spherical-like nanometer cerium oxide, which uses cerium carbonate or cerium acetate as precursor, mixes with an aqueous solution of sodium chloride, ammonium chloride and other fluxing salts, stirs, dries, and calcines to prepare spherical-like nanometer cerium oxide. This method mixes cerium salt and fluxing salt by stirring, which is difficult to ensure uniform mixing and dense wrapping at the microscale.

[0005] Therefore, it is crucial to develop a salt melting method with simple process, low equipment requirement, and high uniformity of cerium salt and fluxing salt mixing, for the preparation of nanometer cerium oxide with uniform particle size and excellent dispersibility. Summary of the Invention

[0006] In view of this, the purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing nano-cerium oxide that is simple in process, low in cost, can effectively suppress the agglomeration of nanoparticles, and produces a product with good dispersibility and high crystallinity.

[0007] To achieve the above-mentioned technical objectives, the technical content of this invention is as follows: A method for preparing nano-cerium oxide, the method specifically includes the following steps: Preparation of rare earth carbonates: A soluble cerium salt solution is reacted with an ammonium bicarbonate precipitant solution to generate rare earth carbonates. After filtration, washing, and drying, cerium carbonate powder is obtained. The soluble cerium salt is cerium nitrate or cerium chloride.

[0008] Molten salt mixing: Industrial-grade or prepared cerium carbonate powder is thoroughly mixed with molten salt and surfactant by ball milling or rotary evaporation; the mass ratio of molten salt to cerium carbonate powder is 0.1:1 to 5:1, the molten salt is at least one of sodium chloride, potassium chloride, ammonium chloride, and magnesium sulfate, and the surfactant is at least one of polyethylene glycol, sodium dodecyl sulfate, polyvinylpyrrolidone, and hexadecyltrimethylammonium bromide, and the amount used is 1% to 10% of the mass of cerium carbonate and molten salt.

[0009] When using ball milling, the milling medium is zirconia balls, the ball-to-material ratio is 2:1 to 10:1, the rotation speed is 100 to 500 r / min, and the milling time is 1 to 6 hours. When using rotary evaporation, cerium carbonate powder is dispersed in an aqueous solution of molten salt and evaporated to dryness under reduced pressure at 50 to 80°C, so that the molten salt and cerium carbonate are uniformly mixed.

[0010] High-temperature calcination: The mixture is calcined in air to decompose cerium carbonate into cerium oxide; the heating rate of calcination is 1~10℃ / min, the calcination temperature is 500~900℃, and the holding time is 1~20h.

[0011] When using molten salts with low thermal stability, such as ammonium chloride, a staged calcination method is adopted. First, the temperature is held at 300~400℃ to melt the molten salt and coat the precursor. Then, the temperature is raised to 500~900℃ to decompose and crystallize the precursor.

[0012] Post-processing: The calcined product is rinsed with deionized water or hot water until no chloride ions are detected in the aqueous solution to completely remove the molten salt. Then, it is filtered and dried to obtain the final product, nano-cerium oxide. The drying method is freeze drying or vacuum drying, and the drying temperature is 50~100℃.

[0013] As can be seen from the above technical solution, compared with the prior art, the beneficial effects achieved by the present invention are as follows: (1) Molten salt forms a liquid environment at the calcination temperature, which physically isolates the cerium carbonate / cerium oxide particles, fundamentally preventing the sintering and agglomeration of nanoparticles.

[0014] (2) The ball milling method achieves uniform mixing between solid particles through the impact and shearing of grinding beads and materials, ensuring that molten salt fully coats cerium carbonate particles; the rotary evaporation method starts from the solution state and can achieve uniform composite of molten salt and precursor.

[0015] (3) The use of inexpensive ammonium bicarbonate as a precipitant and widely available, low-cost sodium chloride, potassium chloride, ammonium chloride, magnesium sulfate, etc. as molten salts greatly reduces the cost of raw materials. This method does not require complex equipment and is suitable for large-scale production.

[0016] (4) Through process optimization, the obtained nano-cerium oxide product has good dispersibility, high crystallinity and narrow particle size distribution. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0018] Figure 1 This is a flow chart of the preparation process of nano-cerium oxide according to the present invention.

[0019] Figure 2 The image shows the X-ray diffraction (XRD) pattern of cerium oxide prepared in Example 1 of this invention.

[0020] Figure 3 This is a scanning electron microscope (SEM) image of cerium oxide prepared in Example 1 of the present invention.

[0021] Figure 4 This is a SEM image of the cerium oxide prepared in Example 2 of the present invention.

[0022] Figure 5 This is a SEM image of the cerium oxide prepared in Example 3 of the present invention.

[0023] Figure 6 This is a SEM image of the cerium oxide prepared in Example 4 of the present invention.

[0024] Figure 7 This is a SEM image of the cerium oxide prepared in Comparative Example 1 of this invention.

[0025] Figure 8 This is a SEM image of the cerium oxide prepared in Comparative Example 2 of this invention. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] This invention discloses a method for preparing nano-cerium oxide.

[0028] To better understand the present invention, the following embodiments are provided for further detailed description of the present invention, but they should not be construed as limiting the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above-described invention are also considered to fall within the protection scope of the present invention.

[0029] Example 1 S1: Weigh 127.48g of cerium chloride heptahydrate (CeCl3·7H2O), dissolve it in 1L of water, add 1mL of glacial acetic acid, stir and heat to 80℃; prepare a saturated solution of ammonium bicarbonate (NH4HCO3) as a precipitant; slowly add the precipitant dropwise to the rare earth salt solution using a peristaltic pump until pH=7; after the reaction is complete, filter to separate the precipitate, wash the precipitate with water, and finally freeze-dry to obtain the cerium carbonate precursor.

[0030] S2: Weigh 25g of the dried cerium carbonate precursor, 50g of sodium chloride (NaCl), and 7.5g of polyethylene glycol (PEG-10000), place them in a ball mill jar, use zirconia balls as the ball milling medium, the ball-to-material ratio is 8:1, the rotation speed is 250r / min, and the ball milling process is carried out for 1 hour.

[0031] S3: Place the ball-milled mixture in an alumina crucible, put it in a muffle furnace, heat it to 800°C at a rate of 5°C / min, and hold it at this temperature for 2 hours, then cool it to room temperature.

[0032] S4: Crush the calcined block product, rinse with hot deionized water at 60-80℃ and filter until no white precipitate (AgCl) is formed in the washing solution when tested with silver nitrate solution, indicating that the molten salt has been completely removed. For molten salts containing sulfate (such as magnesium sulfate), rinse until no white precipitate (BaSO4) is formed when tested with barium chloride. Dry the obtained solid under vacuum at 80℃ for 6 hours to obtain nano-cerium oxide powder.

[0033] Example 2 S1: Same as Example 1.

[0034] S2: Disperse the dried cerium carbonate precursor powder in an aqueous NaCl solution at a mass ratio of 1:1 and stir to form a uniform suspension; transfer the suspension to a rotary evaporator and perform rotary evaporation under reduced pressure in an 80°C water bath until the water is completely evaporated to obtain a uniform cerium carbonate / sodium chloride composite powder.

[0035] S3: Place the composite powder in an alumina crucible, put it into a muffle furnace, heat it to 800℃ at 5℃ / min, hold it for 2 hours, and then cool it to room temperature.

[0036] S4: Same as Example 1.

[0037] Example 3 Same as Example 1, except that the mass ratio of cerium carbonate precursor to molten salt in S2 is changed from 1:2 to 1:1.5.

[0038] Example 4 S1: Same as Example 1.

[0039] S2: Weigh 25g of the dried cerium carbonate precursor, 2.5g of ammonium chloride (NH4Cl), and 0.55g of cetyltrimethylammonium bromide (CTAB), place them in a ball mill jar, use zirconia balls as the ball milling medium, the ball-to-material ratio is 8:1, the rotation speed is 250r / min, and the ball milling process is carried out for 2 hours.

[0040] S3: Place the ball-milled mixture in an alumina crucible and put it into a muffle furnace for a segmented calcination process. First, heat the mixture to 400°C at a rate of 5°C / min and hold for 20 minutes to melt the molten salt and fully coat the cerium carbonate precursor. Then, continue heating the mixture to 800°C at a rate of 5°C / min and hold for 1 hour to completely decompose the cerium carbonate into cerium oxide. Finally, cool the mixture to room temperature with the furnace.

[0041] S4: Same as Example 1.

[0042] Comparative Example 1 S1: Same as Example 1.

[0043] S2: Omit the molten salt mixing step and directly take the dry cerium carbonate precursor.

[0044] S3: Calcine the cerium carbonate precursor at 800℃ for 2 hours.

[0045] S4: No rinsing is required; the product is obtained directly.

[0046] Comparative Example 2 S1: Same as Example 1.

[0047] S2: The dried cerium carbonate precursor is ball-milled.

[0048] S3: The ball-milled cerium carbonate precursor was calcined at 800℃ for 2 hours.

[0049] S4: No rinsing is required; the product is obtained directly.

[0050] The above embodiments illustrate that the present invention significantly improves the dispersibility of nano-cerium oxide by introducing molten salt and surfactant, and combining it with ball milling or rotary evaporation, effectively suppressing particle agglomeration during high-temperature calcination.

[0051] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing nano-cerium oxide, characterized in that, The preparation method specifically includes the following steps: Preparation of rare earth carbonates: A soluble cerium salt solution is reacted with an ammonium bicarbonate precipitant solution to generate rare earth carbonates, which are then filtered, washed, and dried to obtain cerium carbonate powder. Molten salt mixing: Industrial-grade or prepared cerium carbonate powder is thoroughly mixed with molten salt and surfactant by ball milling or rotary evaporation to obtain a mixture; High-temperature calcination: The mixture is calcined in air atmosphere to decompose cerium carbonate into cerium oxide; Post-processing: The calcined product is rinsed with deionized water or hot water until no chloride ions are detected in the aqueous solution to completely remove the molten salt. Then, it is filtered and dried to obtain the final product, nano-cerium oxide.

2. The method for preparing nano-cerium oxide according to claim 1, characterized in that, Soluble cerium salts are cerium nitrate or cerium chloride.

3. The method for preparing nano-cerium oxide according to claim 1, characterized in that, The mass ratio of molten salt to cerium carbonate powder is 0.1:1 to 5:

1. The molten salt is at least one of sodium chloride, potassium chloride, ammonium chloride, and magnesium sulfate. The surfactant is at least one of polyethylene glycol, sodium dodecyl sulfate, polyvinylpyrrolidone, and hexadecyltrimethylammonium bromide. The amount of surfactant used is 1% to 10% of the mass of cerium carbonate and molten salt.

4. The method for preparing nano-cerium oxide according to claim 1 or 3, characterized in that, When using ball milling, the milling media are zirconia balls, the ball-to-material ratio is 2:1 to 10:1, the rotation speed is 100 to 500 r / min, and the milling time is 1 to 6 hours. When using rotary evaporation, cerium carbonate powder is dispersed in an aqueous solution of molten salt and then evaporated to dryness under reduced pressure at 50-80°C, so that the molten salt and cerium carbonate are uniformly mixed.

5. The method for preparing nano-cerium oxide according to claim 1, characterized in that, The heating rate for high-temperature calcination is 1~10℃ / min, the calcination temperature is 500~900℃, and the holding time is 1~20h.

6. The method for preparing nano-cerium oxide according to claim 1 or 5, characterized in that, When using molten salt with low thermal stability, a staged calcination method is adopted. First, the temperature is held at 300~400℃ to melt the molten salt and coat the precursor. Then, the temperature is raised to 500~900℃ to decompose and crystallize the precursor.

7. The method for preparing nano-cerium oxide according to claim 1, characterized in that, The drying method is freeze drying or vacuum drying, and the drying temperature is 50~100℃.

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