CN109052451B - Cerium dioxide nanosheet and preparation method and application thereof - Google Patents

Cerium dioxide nanosheet and preparation method and application thereof Download PDF

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CN109052451B
CN109052451B CN201811317889.0A CN201811317889A CN109052451B CN 109052451 B CN109052451 B CN 109052451B CN 201811317889 A CN201811317889 A CN 201811317889A CN 109052451 B CN109052451 B CN 109052451B
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cerium dioxide
hydroxide
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杨蓉
刘学良
王琛
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National Center for Nanosccience and Technology China
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Abstract

The invention relates to a cerium dioxide nanosheet and a preparation method and application thereof, wherein the preparation method comprises the following steps: (1) precipitating a cerium nitrate aqueous solution by using an alkaline solution to obtain a cerium hydroxide nanosheet precursor; (2) drying and roasting the cerium hydroxide nanosheet precursor obtained in the step (1) to obtain a cerium dioxide nanosheet; the alkaline solution in the step (1) comprises a sodium hydroxide solution and/or a potassium hydroxide solution; the molar ratio of hydroxide ions in the alkaline solution to the cerium nitrate in the cerium nitrate aqueous solution is (8-27): 1. The cerium dioxide nanosheet obtained by the method can be used as various nano metal carriers, and has a wide application prospect in the fields of energy, environment and catalysis. The method has the advantages of no need of high-temperature and high-pressure equipment for hydrothermal reaction and the like, no addition of any organic modifier or organic solvent, environmental friendliness, mild reaction conditions, low cost and the like, and is favorable for industrial large-scale production.

Description

Cerium dioxide nanosheet and preparation method and application thereof
Technical Field
The invention belongs to the field of composite material preparation, relates to a nano composite material, a preparation method and application thereof, and particularly relates to a cerium dioxide nanosheet and a preparation method and application thereof.
Background
Ce4+/Ce3+The oxidation-reduction transformation and abundant oxygen vacancies lead the nano-cerium dioxide to be widely applied to the fields of energy, environment, catalysis and the like as a catalyst and a catalyst carrier. The catalytic activity of the nano-ceria is closely related to the exposed crystal face, and as a catalyst and a catalyst carrier, the (100) crystal face and the (110) crystal face of the ceria have higher activity than the (111) crystal face, so that the preparation of the nano-ceria with the exposed crystal face with high activity is called as a hotspot of research. At present, the methods for preparing nano cerium dioxide mainly comprise a precipitation method, a water (solvent) thermal method, a sol-gel method, a microemulsion method and the like.
Liu Zi En et al published an article titled preparation and catalytic performance of noble metal-cerium dioxide nano-materials of different structure types (scientific report, 2015(24):2288-2Is unique in propertyThe rare earth oxide has excellent catalytic activity, good thermal stability and chemical stability and electron and oxygen vacancy transfer capacity, and is often used as a carrier of a noble metal catalyst to improve the catalytic performance of the material. Noble metal-cerium dioxide (M-CeO)2) The composite catalyst is widely applied to CO catalytic oxidation, water gas conversion and NOxThe fields of reduction, solid oxide fuel cells and the like make important contributions to the treatment of environmental pollution and the solution of energy crisis. CeO (CeO)2There is a complex interaction with noble metals, the interaction being M-CeO2The catalytic performance of the composite catalyst has important influence, the structure type of the M-CeO2 has close relation with the interaction, and different structure types can influence the stability, the activity, the selectivity and the like of the catalyst.
An article entitled Shape-selective synthesis and oxygen storage cerium oxide, nanorods, and nanocubes (Journal of Physical Chemistry B,2005,109(51): 24380-.
CN 101407330B proposes a method for preparing nano-ceria nanorods, the ceria prepared by the method has higher specific surface area and carbon monoxide catalytic activity, but the reaction period of the method is long, and the obtained ceria has poor crystallinity. The research finds that the surface of the cerium dioxide with the sheet structure has a large number of defects, a high specific surface area and more active sites, and shows high catalytic activity.
CN 105668606A takes cerous nitrate hexahydrate, sodium oleate, oleylamine, trioctylamine and the like as raw materials to prepare square cerium dioxide nanosheets at the high temperature of 360 ℃; the preparation process uses a large amount of oil-soluble solvent and needs high-temperature and high-pressure equipment, and the problems of high energy consumption, serious pollution, safety and the like exist.
CN 106186036B takes cerous nitrate hexahydrate, sodium fluoborate, sodium hydroxide and the like as raw materials, and prepares hexagonal cerium dioxide nanosheets with the thickness of 8-10nm and the side length of 50-60nm through hydrothermal reaction. However, the cerium dioxide nanosheet prepared by the method is high in thickness, long in reaction time and high in energy consumption.
Both CN 101734706A and CN 103991891B adopt a precipitation method to prepare the sheet-shaped nano cerium dioxide, but the obtained nano cerium dioxide sheet has larger thickness and low specific surface area.
Noble metal nanoparticles (such as nano platinum, gold, palladium, and the like) have very wide application in the fields of energy, environment, biology, and the like. The metal nanoparticles are easy to agglomerate due to the large specific surface area and the high surface energy of the metal nanoparticles, so that the reaction activity of the metal nanoparticles is greatly reduced, and the application of the metal nanoparticles is limited. The noble metal nanoparticles are modified by the surfactant, so that the dispersity of the nanoparticles can be effectively improved, but a large number of surfactant molecules occupy active sites of the metal nanoparticles, so that the interaction between substrate molecules and the nanoparticles is hindered, the activity of the noble metal nanoparticles is reduced, and meanwhile, a large number of surfactants used in the preparation process are harmful to the environment. By using cerium dioxide nanosheets as carriers and loading noble metal nanoparticles onto the cerium dioxide nanosheet carriers, the agglomeration of the metal nanoparticles can be effectively inhibited and the reaction activity of the metal nanoparticles can be improved.
Therefore, the method for preparing the ultrathin cerium dioxide nanosheet and the precious metal nanocomposite thereof has very important significance and wide application prospect, and is low in preparation cost and simple in process.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a cerium dioxide nanosheet and a preparation method and application thereof. The cerium dioxide nanosheet is large in specific surface area, rich in surface active sites, capable of effectively loading noble metal nanoparticles, simple in preparation method process, simple and convenient to operate, environment-friendly, mild in reaction conditions and beneficial to industrial amplification production.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a method for preparing a cerium dioxide nanosheet, the method comprising the steps of:
(1) precipitating a cerium nitrate aqueous solution by using an alkaline solution to obtain a cerium hydroxide nanosheet precursor;
(2) and (3) drying and roasting the cerium hydroxide nanosheet precursor obtained in the step (1) to obtain the cerium dioxide nanosheet.
The alkaline solution in the step (1) comprises a sodium hydroxide solution and/or a potassium hydroxide solution.
The molar ratio of hydroxide ions in the alkaline solution to cerium nitrate in the aqueous cerium nitrate solution is (8-27):1, and may be, for example, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, 20:1, 21:1, 22:1, 23:1, 24:1, 25:1, 26:1 or 27:1, preferably (10-25):1, and more preferably (12-21): 1.
According to the invention, an alkaline solution composed of a sodium hydroxide solution and/or a potassium hydroxide solution is mixed with a cerium nitrate aqueous solution, wherein the molar ratio of hydroxide ions in the alkaline solution to cerium nitrate in the cerium nitrate aqueous solution is (8-27):1, so that a cerium hydroxide nanosheet precursor meeting the requirements of the invention can be obtained. Drying and roasting the cerium hydroxide nanosheet precursor to obtain cerium dioxide nanosheets, wherein the thickness of the prepared cerium dioxide nanosheets is not more than 3nm, the specific surface area is high and can reach 182m2The cerium dioxide nano composite material prepared from the cerium dioxide nano sheets can uniformly load more noble metal catalysts, and the catalytic efficiency is high.
Preferably, the precipitation in step (1) is carried out under the protection of a non-oxidizing gas.
Preferably, the non-oxidising gas comprises any one or a combination of at least two of nitrogen, helium or argon, preferably nitrogen.
Preferably, the molar concentration of cerium nitrate in the aqueous cerium nitrate solution in the step (1) is 0.01-0.1mol/L, and may be, for example, 0.01mol/L, 0.02mol/L, 0.03mol/L, 0.04mol/L, 0.05mol/L, 0.06mol/L, 0.07mol/L, 0.08mol/L, 0.09mol/L or 0.1mol/L, preferably 0.02-0.08 mol/L.
Preferably, the alkaline solution of step (1) comprises a sodium hydroxide solution and/or a potassium hydroxide solution.
Preferably, the molar concentration of the hydroxide ion in the alkaline solution is 0.5 to 6mol/L, and may be, for example, 0.5mol/L, 1mol/L, 1.5mol/L, 2mol/L, 2.5mol/L, 3mol/L, 3.5mol/L, 4mol/L, 4.5mol/L, 5mol/L, 5.5mol/L or 6mol/L, preferably 1 to 5mol/L, and more preferably 2 to 4 mol/L.
Preferably, the alkaline solution is added dropwise to the aqueous cerium nitrate solution.
Preferably, the dropping rate is 10 to 20mL/h, and may be, for example, 10mL/h, 12mL/h, 14mL/h, 16mL/h, 18mL/h or 20mL/h, preferably 12 to 18 mL/h.
Preferably, the precipitation process of step (1) is also accompanied by stirring.
Preferably, the stirring speed is 600-1500r/min, such as 600r/min, 650r/min, 700r/min, 750r/min, 800r/min, 850r/min, 900r/min, 950r/min, 1000r/min, 1050r/min, 1100r/min, 1150r/min, 1200r/min, 1250r/min, 1300r/min, 1350r/min, 1400r/min, 1450r/min or 1500r/min, preferably 1200-1500 r/min.
Preferably, the stirring time is 2 to 15 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours or 15 hours, preferably 4 to 12 hours, and more preferably 6 to 8 hours.
Preferably, the precipitate obtained in step (1) is washed to neutrality.
Preferably, the precipitation temperature in step (1) is 0-40 ℃, for example, 0 ℃, 5 ℃,10 ℃, 15 ℃,20 ℃, 25 ℃, 30 ℃, 35 ℃ or 40 ℃, preferably 10-30 ℃, more preferably 15-25 ℃.
Preferably, the drying of step (2) comprises freeze drying, spray drying or oven drying, preferably freeze drying.
Preferably, the temperature of the calcination in step (2) is 380-.
Preferably, the roasting time in the step (2) is 0.5-4.2h, for example, 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h or 4.2h, preferably 1-4h, and more preferably 2-3 h.
If the roasting temperature is lower, the porosity of the cerium dioxide nanosheet is not favorably improved, so that the subsequent loading of the precious metal catalyst on the cerium dioxide nanosheet is influenced. If the temperature for calcination is too high, the sheet structure of the cerium dioxide nanosheet is destroyed, which is also not beneficial to the loading of the noble metal catalyst on the cerium dioxide nanosheet.
In a second aspect, the invention also provides the cerium dioxide nanosheet prepared by the preparation method of the first aspect.
Preferably, the thickness of the cerium oxide nanosheet is 0.8-3.2nm, and may be, for example, 0.8nm, 1nm, 1.2nm, 1.4nm, 1.6nm, 1.8nm, 2nm, 2.4nm, 2.7nm, 3nm or 3.2nm, preferably 1-3nm, and more preferably 1.2-2.7 nm.
Preferably, the equivalent diameter of the cerium dioxide nanosheet is 150-1200nm, and can be 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 550nm, 600nm, 650nm, 700nm, 750nm, 800nm, 850nm, 900nm, 950nm, 1000nm, 1050nm, 1100nm, 1150nm or 1200nm, preferably 200-1000nm, and more preferably 250-800 nm.
Preferably, the cerium dioxide nanosheets are distributed with nanometer-scale holes.
The cerium dioxide nanosheet prepared by the method has a large specific surface area and is full of nanoscale holes, and the cerium dioxide nanosheet has a large number of active sites, so that precious metals can be better loaded.
Preferably, the pore size of the nanoscale pores is 1-6nm, and may be, for example, 1nm, 2nm, 3nm, 4nm, 5nm or 6nm, preferably 2-5nm, and more preferably 3-4 nm.
In a third aspect, the present invention also provides a ceria nanocomposite comprising ceria nanoplatelets as described in the second aspect of the invention.
In a fourth aspect, the present invention also provides a method for preparing a cerium oxide nanocomposite material as described in the third aspect, the method comprising the steps of:
(I) preparing cerium dioxide nanosheets by adopting the preparation method of the cerium dioxide nanosheets;
(II) immersing the cerium dioxide nanosheet obtained in the step (I) into a reducing solution to obtain a cerium dioxide dispersion liquid;
(III) adding a precious metal precursor solution into the cerium dioxide dispersion liquid obtained in the step (II) to obtain a mixed liquid;
(IV) heating and stirring the mixed solution obtained in the step (III), cooling, centrifugally separating, washing and drying to obtain the cerium dioxide nano composite material.
Preferably, the reducing solution comprises any one of, or a combination of at least two of, anhydrous ethylene glycol, an ethylene glycol solution of sodium hydroxide, or an ethylene glycol solution of potassium hydroxide, with typical but non-limiting combinations including a combination of an ethylene glycol solution of sodium hydroxide and an ethylene glycol solution of potassium hydroxide.
The ethylene glycol solution has reducibility, and can completely reduce the noble metal in the noble metal precursor solution. As an optimized technical scheme, the addition of sodium ions and potassium ions in the glycol solution of sodium hydroxide and the glycol solution of potassium hydroxide can avoid the occurrence of noble metal clustering phenomenon, thereby improving the catalytic performance of the prepared cerium dioxide nano composite material.
Preferably, the molar concentration of hydroxide ions in the ethylene glycol solution of sodium hydroxide or the ethylene glycol solution of potassium hydroxide is 0.8 to 1.2mol/L, and may be, for example, 0.8mol/L, 0.9mol/L, 1mol/L, 1.1mol/L or 1.2mol/L, preferably 0.9 to 1.1 mol/L.
Preferably, the noble metal precursor solution in step (III) includes one or a combination of at least two of a chloroplatinic acid solution, a chloroauric acid solution, a chloroiridic acid solution or a potassium chloroplatinate solution, and typical but non-limiting combinations include a combination of a chloroplatinic acid solution and a chloroauric acid solution, a combination of a chloroauric acid solution, a chloroiridic acid solution and a potassium chloroplatinate solution, and a combination of a chloroplatinic acid solution, a chloroauric acid solution, a chloroiridic acid solution and a potassium chloroplatinate solution.
Preferably, the mass fraction of the noble metal element in the noble metal precursor solution is 0.5 to 15 wt%, and may be, for example, 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, or 12 wt%, preferably 1 to 12 wt%, and more preferably 3 to 10 wt%.
Preferably, the mass ratio of the noble metal element to the ceria nanosheets in the noble metal precursor solution is 1 (5-60), and may be, for example, 1:5, 1:10, 1:15, 1:20, 1:25, 1:30, 1:35, 1:40, 1:45, 1:50, 1:55, or 1:60, preferably 1 (10-50), and more preferably 1 (20-40). The noble metal elements in the noble metal precursor solution are not too much, otherwise, the particle size of the reduced noble metal is increased, and the catalytic activity is reduced.
Preferably, the heating temperature in step (IV) is 100-.
Preferably, the stirring time in step (IV) is 0.3-2.1h, such as 0.3h, 0.5h, 0.8h, 1h, 1.2h, 1.4h, 1.6h, 1.8h, 2h or 2.1h, preferably 0.5-2h, and more preferably 0.8-1.6 h.
As a preferred technical scheme of the invention, the preparation method comprises the following steps:
(a) under the protection of non-oxidizing gas, dropwise adding a sodium hydroxide aqueous solution and/or a potassium hydroxide aqueous solution with the molar concentration of hydroxide ions of 0.5-6mol/L into a cerium nitrate aqueous solution with the molar concentration of cerium nitrate of 0.01-0.1mol/L within the temperature range of 0-40 ℃, wherein the molar ratio of the hydroxide ions to the cerium nitrate is (10-25):1, the dropwise adding speed is 10-20mL/h, the cerium nitrate aqueous solution is stirred in the precipitation process, the stirring time is 2-15h, the stirring speed is 600-;
(b) roasting the cerium hydroxide nanosheet precursor obtained in the step (a) by freeze drying at the temperature of 380-800 ℃, wherein the roasting time is 0.5-4.2h, so as to obtain cerium dioxide nanosheets;
(c) immersing a cerium dioxide nanosheet into a reducing solution to obtain a cerium dioxide dispersion liquid;
(d) adding a precious metal precursor solution with the mass fraction of precious metal elements of 0.5-15 wt% into the cerium dioxide dispersion liquid obtained in the step (c) to obtain a mixed liquid, wherein the mass ratio of the precious metal elements in the precious metal precursor solution to the cerium dioxide nanosheets is 1 (5-60);
(e) stirring the mixed solution obtained in the step (d) at the temperature of 100 ℃ and 210 ℃, cooling, centrifugally separating, washing and drying to obtain the cerium dioxide nano composite material, wherein the stirring time is 0.3-2.1 h.
In a fifth aspect, the invention also provides the use of the ceria nanocomposite for the catalytic oxidation of formaldehyde.
The recitation of numerical ranges herein includes not only the above-recited numerical values, but also any numerical values between non-recited numerical ranges, and is not intended to be exhaustive or to limit the invention to the precise numerical values encompassed within the range for brevity and clarity.
Compared with the prior art, the invention has the following beneficial effects:
the preparation method of the cerium dioxide nanosheet is simple, the operation is simple and convenient, the thickness of the prepared cerium dioxide nanosheet is 0.8-3.2nm, the equivalent diameter of the cerium dioxide nanosheet is 150-1200nm, the cerium dioxide nanosheet is fully distributed with nanoscale holes with the aperture of 1-6nm, and the cerium dioxide nanocomposite prepared by loading the precious metal catalyst on the cerium dioxide nanosheet is large in specific surface area and can provide more active sites, so that the catalytic efficiency is improved.
Drawings
FIG. 1 is a transmission electron microscope image of a cerium hydroxide nanosheet precursor prepared in example 8;
FIG. 2 is a transmission electron microscope image of cerium oxide nanosheets prepared in example 8;
FIG. 3 is a transmission electron microscope image of cerium oxide nanosheets prepared in example 9;
FIG. 4 is a transmission electron microscope photograph of the cerium oxide nanocomposite prepared in example 10;
FIG. 5 is a transmission electron microscope photograph of the cerium oxide nanocomposite prepared in example 11.
Detailed Description
The technical solution of the present invention is further explained by the following embodiments.
Example 1
The embodiment provides a preparation method of a cerium dioxide nano composite material, which comprises the following steps:
(1) dropwise adding sodium hydroxide aqueous solution with the molar concentration of hydroxide ions of 3mol/L into cerium nitrate aqueous solution with the molar concentration of 0.05mol/L at the temperature of 20 ℃ under the protection of nitrogen, wherein the molar ratio of the hydroxide ions to the cerium nitrate is 18:1, the dropwise adding speed is 14mL/h, the cerium nitrate aqueous solution is stirred in the precipitation process, the stirring time is 9h, the stirring speed is 1000r/min, and washing and precipitating to be neutral to obtain a cerium hydroxide nanosheet precursor;
(2) roasting the cerium hydroxide nanosheet precursor obtained in the step (1) by freeze drying at 600 ℃, wherein the roasting time is 2h, so as to obtain cerium dioxide nanosheets;
(3) immersing the cerium dioxide nanosheets obtained in the step (2) into a glycol solution of sodium hydroxide to obtain a cerium dioxide dispersion liquid, wherein the molar concentration of hydroxide ions in the glycol solution of sodium hydroxide is 1 mol/L;
(4) adding a chloroplatinic acid solution with the mass fraction of precious metal elements of 6 wt% into the cerium dioxide dispersion liquid obtained in the step (3) to obtain a mixed solution, wherein the mass ratio of platinum elements in the chloroplatinic acid solution to the cerium dioxide nanosheets is 1: 30;
(5) and (3) stirring the mixed solution obtained in the step (4) at 180 ℃, cooling, performing centrifugal separation, washing and drying to obtain the cerium dioxide nano composite material, wherein the stirring time is 1 h.
Example 2
The embodiment provides a preparation method of a cerium dioxide nano composite material, which comprises the following steps:
(1) dropwise adding a sodium hydroxide aqueous solution with the molar concentration of hydroxyl ions of 4mol/L into a cerium nitrate aqueous solution with the molar concentration of 0.06mol/L at 25 ℃ under the protection of argon, wherein the molar ratio of the hydroxyl ions to the cerium nitrate is 12:1, the dropwise adding speed is 16mL/h, stirring the cerium nitrate aqueous solution in the precipitation process for 12h at the stirring speed of 1200r/min, and washing and precipitating to be neutral to obtain a cerium hydroxide nanosheet precursor;
(2) roasting the cerium hydroxide nanosheet precursor obtained in the step (1) by freeze drying at the temperature of 420 ℃ for 3h to obtain cerium dioxide nanosheets;
(3) immersing the cerium dioxide nanosheets obtained in the step (2) into a glycol solution of potassium hydroxide to obtain a cerium dioxide dispersion liquid, wherein the molar concentration of hydroxide ions in the glycol solution of potassium hydroxide is 0.9 mol/L;
(4) adding a chloroauric acid solution with the mass fraction of precious metal elements of 10 wt% into the cerium dioxide dispersion liquid obtained in the step (3) to obtain a mixed liquid, wherein the mass ratio of gold elements in the chloroauric acid solution to the cerium dioxide nanosheets is 1: 40;
(5) and (3) stirring the mixed solution obtained in the step (4) at the temperature of 200 ℃, cooling, centrifugally separating, washing and drying to obtain the cerium dioxide nano composite material, wherein the stirring time is 2 hours.
Example 3
The embodiment provides a preparation method of a cerium dioxide nano composite material, which comprises the following steps:
(1) dropwise adding a potassium hydroxide aqueous solution with the molar concentration of hydroxide ions of 2mol/L into a cerium nitrate aqueous solution with the molar concentration of 0.02mol/L at 15 ℃ under the protection of helium, wherein the molar ratio of the hydroxide ions to the cerium nitrate is 10:1, the dropwise adding speed is 12mL/h, the cerium nitrate aqueous solution is stirred in the precipitation process, the stirring time is 6h, the stirring speed is 800r/min, and washing and precipitating to be neutral to obtain a cerium hydroxide nanosheet precursor;
(2) roasting the cerium hydroxide nanosheet precursor obtained in the step (1) by freeze drying at 400 ℃, wherein the roasting time is 1h, so as to obtain cerium dioxide nanosheets;
(3) immersing the cerium dioxide nanosheets obtained in the step (2) into anhydrous glycol to obtain cerium dioxide dispersion liquid;
(4) adding a chloroiridic acid solution with the mass fraction of noble metal elements being 3 wt% into the cerium dioxide dispersion liquid obtained in the step (3) to obtain a mixed liquid, wherein the mass ratio of iridium elements in the chloroiridic acid solution to the cerium dioxide nanosheets is 1: 20;
(5) and (3) stirring the mixed solution obtained in the step (4) at 150 ℃, cooling, centrifugally separating, washing and drying to obtain the cerium dioxide nano composite material, wherein the stirring time is 1 h.
Example 4
The embodiment provides a preparation method of a cerium dioxide nano composite material, which comprises the following steps:
(1) dropwise adding a mixed aqueous solution of potassium hydroxide and sodium hydroxide with the molar concentration of hydroxide ions of 5mol/L into a cerium nitrate aqueous solution with the molar concentration of 0.08mol/L at the temperature of 30 ℃ under the protection of argon, wherein the molar ratio of the hydroxide ions to the cerium nitrate is 21:1, the dropwise adding speed is 18mL/h, the cerium nitrate aqueous solution is stirred in the precipitation process, the stirring time is 12h, the stirring speed is 1300r/min, and washing and precipitating to be neutral to obtain a cerium hydroxide nanosheet precursor;
(2) roasting the cerium hydroxide nanosheet precursor obtained in the step (1) at 750 ℃ for 4h to obtain cerium dioxide nanosheets;
(3) immersing the cerium dioxide nanosheets obtained in the step (2) into a glycol solution of sodium hydroxide to obtain a cerium dioxide dispersion liquid, wherein the molar concentration of hydroxide ions in the glycol solution of sodium hydroxide is 1.1 mol/L;
(4) adding a potassium chloroplatinate solution with the mass fraction of precious metal elements of 12 wt% into the cerium dioxide dispersion liquid obtained in the step (3) to obtain a mixed liquid, wherein the mass ratio of platinum elements in the potassium chloroplatinate solution to the cerium dioxide nanosheets is 1: 50;
(5) and (3) stirring the mixed solution obtained in the step (4) at the temperature of 200 ℃, cooling, centrifugally separating, washing and drying to obtain the cerium dioxide nano composite material, wherein the stirring time is 2 hours.
Example 5
The embodiment provides a preparation method of a cerium dioxide nano composite material, which comprises the following steps:
(1) dropwise adding a mixed aqueous solution of potassium hydroxide and sodium hydroxide with the molar concentration of hydroxide ions of 1mol/L into a cerium nitrate aqueous solution with the molar concentration of 0.02mol/L at 10 ℃ under the protection of nitrogen, wherein the molar ratio of the hydroxide ions to the cerium nitrate is 25:1, the dropwise adding speed is 12mL/h, the cerium nitrate aqueous solution is stirred in the precipitation process, the stirring time is 6h, the stirring speed is 800r/min, and washing and precipitating to be neutral to obtain a cerium hydroxide nanosheet precursor;
(2) roasting the cerium hydroxide nanosheet precursor obtained in the step (1) at 780 ℃ to obtain cerium dioxide nanosheets, wherein the roasting time is 1 h;
(3) immersing the cerium dioxide nanosheets obtained in the step (2) into a glycol solution of sodium hydroxide to obtain a cerium dioxide dispersion liquid, wherein the molar concentration of hydroxide ions in the glycol solution of sodium hydroxide is 1.2 mol/L;
(4) adding a mixed solution of chloroplatinic acid and chloroauric acid with the mass fraction of the precious metal elements being 1 wt% into the cerium dioxide dispersion liquid obtained in the step (3) to obtain a mixed solution, wherein the mass ratio of the precious metal elements to the cerium dioxide nanosheets in the mixed solution is 1: 10;
(5) and (3) stirring the mixed solution obtained in the step (4) at 120 ℃, cooling, centrifugally separating, washing and drying to obtain the cerium dioxide nano composite material, wherein the stirring time is 0.5 h.
Example 6
The embodiment provides a preparation method of a cerium dioxide nano composite material, which comprises the following steps:
(1) dropwise adding a potassium hydroxide aqueous solution with the molar concentration of hydroxide ions of 0.5mol/L into a cerium nitrate aqueous solution with the molar concentration of 0.01mol/L at 0 ℃ under the protection of nitrogen, wherein the molar ratio of the hydroxide ions to the cerium nitrate is 8:1, the dropwise adding speed is 10mL/h, the cerium nitrate aqueous solution is stirred in the precipitation process, the stirring time is 2h, the stirring speed is 600r/min, and washing and precipitating to be neutral to obtain a cerium hydroxide nanosheet precursor;
(2) roasting the cerium hydroxide nanosheet precursor obtained in the step (1) by freeze drying at 380 ℃ for 4.2h to obtain cerium dioxide nanosheets;
(3) immersing the cerium dioxide nanosheets obtained in the step (2) into a glycol solution of sodium hydroxide to obtain a cerium dioxide dispersion liquid, wherein the molar concentration of hydroxide ions in the glycol solution of sodium hydroxide is 0.8 mol/L;
(4) adding a chloroplatinic acid solution with the mass fraction of noble metal elements of 0.5 wt% into the cerium dioxide dispersion liquid obtained in the step (3) to obtain a mixed solution, wherein the mass ratio of platinum elements in the chloroplatinic acid solution to the cerium dioxide nanosheets is 1: 5;
(5) and (3) stirring the mixed solution obtained in the step (4) at the temperature of 100 ℃, cooling, centrifugally separating, washing and drying to obtain the cerium dioxide nano composite material, wherein the stirring time is 2.1 h.
Example 7
The embodiment provides a preparation method of a cerium dioxide nano composite material, which comprises the following steps:
(1) dropwise adding a sodium hydroxide aqueous solution with the molar concentration of hydroxide ions of 6mol/L into a cerium nitrate aqueous solution with the molar concentration of 0.1mol/L at 40 ℃ under the protection of nitrogen, wherein the molar ratio of the hydroxide ions to the cerium nitrate is 27:1, the dropwise adding speed is 20mL/h, the cerium nitrate aqueous solution is stirred in the precipitation process, the stirring time is 15h, the stirring speed is 1500r/min, and washing and precipitating to be neutral to obtain a cerium hydroxide nanosheet precursor;
(2) roasting the cerium hydroxide nanosheet precursor obtained in the step (1) by freeze drying at 800 ℃, wherein the roasting time is 0.5h, so as to obtain cerium dioxide nanosheets;
(3) immersing the cerium dioxide nanosheet obtained in the step (2) into anhydrous ethylene glycol to obtain a cerium dioxide dispersion liquid;
(4) adding a chloroplatinic acid solution with the mass fraction of noble metal elements of 15 wt% into the cerium dioxide dispersion liquid obtained in the step (3) to obtain a mixed solution, wherein the mass ratio of platinum elements in the chloroplatinic acid solution to the cerium dioxide nanosheets is 1: 60;
(5) and (3) stirring the mixed solution obtained in the step (4) at the temperature of 210 ℃, cooling, centrifugally separating, washing and drying to obtain the cerium dioxide nano composite material, wherein the stirring time is 0.3 h.
Example 8
The embodiment provides a preparation method of a cerium dioxide nanosheet, which comprises the following steps:
(1) dropwise adding 20mL of aqueous solution of sodium hydroxide with the molar concentration of hydroxide ions of 1.25mol/L into 30mL of aqueous solution of cerium nitrate with the molar concentration of 0.033mol/L at 25 ℃ under the protection of nitrogen, wherein the dropwise adding speed is 20mL/h, stirring the aqueous solution of cerium nitrate in the precipitation process for 6h at the stirring speed of 1500r/min, washing the precipitate to be neutral to obtain a cerium hydroxide nanosheet precursor, and a transmission electron microscope image of the obtained cerium hydroxide nanosheet precursor is shown in FIG. 1;
(2) and (2) roasting the cerium hydroxide nanosheet precursor obtained in the step (1) at 600 ℃ to obtain cerium dioxide nanosheets, wherein the roasting time is 2h, and the transmission electron microscope image of the obtained cerium dioxide nanosheets is shown in fig. 2.
As can be seen from fig. 1, the cerium hydroxide nanosheet precursor prepared in step (1) is seriously layered, and as can be seen from fig. 2, the cerium oxide nanosheet prepared from the cerium oxide nanosheet provided in example 8 has a uniform morphology and a complete structure.
Example 9
The embodiment provides a preparation method of a cerium dioxide nanosheet, which comprises the following steps:
(1) dropwise adding 20mL of aqueous solution of sodium hydroxide with the molar concentration of hydroxide ions of 2mol/L into 80mL of aqueous solution of cerium nitrate with the molar concentration of 0.025mol/L at 25 ℃ under the protection of nitrogen, wherein the dropwise adding speed is 20mL/h, stirring the aqueous solution of cerium nitrate in the precipitation process, the stirring time is 8h, the stirring speed is 1500r/min, and washing and precipitating to be neutral to obtain a cerium hydroxide nanosheet precursor;
(2) and (2) roasting the cerium hydroxide nanosheet precursor obtained in the step (1) at 600 ℃ to obtain cerium dioxide nanosheets, wherein the roasting time is 2h, and the transmission electron microscope image of the obtained cerium dioxide nanosheets is shown in fig. 3.
As can be seen from fig. 3, the cerium dioxide nanosheets prepared from the cerium dioxide nanosheets provided in example 9 have uniform morphology and complete structure.
Example 10
The embodiment provides a preparation method of a cerium dioxide nano composite material, which comprises the following steps:
(1) immersing 30mg of the cerium dioxide nanosheet obtained in example 8 into a glycol solution of sodium hydroxide with a molar concentration of hydroxide ions of 1mol/L to obtain a cerium dioxide dispersion;
(2) adding a chloroplatinic acid solution into the cerium dioxide dispersion liquid obtained in the step (1) to obtain a mixed solution, wherein the mass ratio of platinum elements in the chloroplatinic acid solution to the cerium dioxide nanosheets is 1: 30;
(3) and (3) stirring the mixed solution obtained in the step (2) at 180 ℃, cooling, centrifugally separating, washing and drying to obtain the cerium dioxide nano composite material, wherein the stirring time is 2 hours, and the transmission electron microscope image of the obtained cerium dioxide nano composite material is shown in fig. 4.
As can be seen from fig. 4, the ceria nanocomposite prepared by the method of example 10 has a uniform morphology and a complete structure, and the noble metal platinum having a particle size of not more than 3nm is uniformly supported on the ceria nanosheet prepared in example 8.
Example 11
The embodiment provides a preparation method of a cerium dioxide nano composite material, which comprises the following steps:
(1) immersing 30mg of the cerium dioxide nanosheet obtained in example 8 into a glycol solution of sodium hydroxide with a molar concentration of hydroxide ions of 1mol/L to obtain a cerium dioxide dispersion;
(2) adding a chloroauric acid solution into the cerium dioxide dispersion liquid obtained in the step (1) to obtain a mixed liquid, wherein the mass ratio of the platinum element in the chloroauric acid solution to the cerium dioxide nanosheet is 1: 30;
(3) and (3) stirring the mixed solution obtained in the step (2) at 140 ℃, cooling, centrifugally separating, washing and drying to obtain the cerium dioxide nano composite material, wherein the stirring time is 2 hours, and the transmission electron microscope image of the obtained cerium dioxide nano composite material is shown in fig. 5.
As can be seen from fig. 5, the ceria nanocomposite prepared by the method of example 11 has a uniform morphology and a complete structure, and the noble metal gold having a particle size of not more than 5nm is supported on the ceria nanosheet prepared in example 8. However, the particle size of the noble metal gold supported by the ceria nanosheets is larger than that of the noble metal platinum supported in fig. 4.
Example 12
This example provides a method for preparing a cerium oxide nanocomposite, which is the same as that of example 3, except that the firing temperature in step (2) is 350 ℃.
Example 13
This example provides a method for preparing a cerium oxide nanocomposite, which is the same as that of example 3, except that the firing temperature in step (2) is 840 ℃.
Example 14
The present example provides a preparation method of a cerium oxide nanocomposite, which is the same as in example 3 except that the mass ratio of the platinum element in the chloroplatinic acid solution in step (4) to the cerium oxide nanosheet is 1: 3.
Example 15
The present example provides a preparation method of a cerium oxide nanocomposite, which is the same as in example 3 except that the mass ratio of the platinum element in the chloroplatinic acid solution in step (4) to the cerium oxide nanosheet is 1: 65.
Comparative example 1
This comparative example provides a preparation method of a cerium oxide nanocomposite, which is the same as that of example 3, except that the molar ratio of hydroxide ions to cerium nitrate in step (1) is 5: 1.
Comparative example 2
This comparative example provides a preparation method of a cerium oxide nanocomposite, which is the same as that of example 3, except that the molar ratio of hydroxide ions to cerium nitrate in step (1) is 30: 1.
The thickness and specific surface area of the cerium oxide nanocomposite prepared in examples 1 to 7 and 10 to 15 according to the present invention and comparative examples 1 to 2 were measured, and the measurement results are shown in table 1:
TABLE 1
Figure BDA0001856776590000181
Figure BDA0001856776590000191
As is apparent from Table 1, the ceria nanocomposites prepared in examples 1 to 7 and 10 to 11 had a thickness of not more than 2.5nm and a specific surface area of more than 150m2/g。
In example 12, the calcination temperature in the step (2) was 350 ℃, the thickness of the cerium oxide nanocomposite prepared in example 12 was 2.8nm, which was 1.8nm higher than that of the cerium oxide nanocomposite prepared in example 3, and the specific surface area of the cerium oxide nanocomposite prepared in example 12 was 146m2(per gram), less than 182m, the specific surface area of the cerium oxide nanocomposite prepared in example 32Therefore, the lower roasting temperature of the cerium hydroxide nanosheet precursor is not beneficial to reducing the thickness of the cerium dioxide nanocomposite and improving the specific surface area of the cerium dioxide nanocomposite.
In example 13, the calcination temperature in step (2) was relatively high at 840 ℃, the thickness of the cerium oxide nanocomposite prepared in example 13 was 5.2nm, which was 1.8nm higher than that of the cerium oxide nanocomposite prepared in example 3, and the specific surface area of the cerium oxide nanocomposite prepared in example 13 was 121m2(per gram), less than 182m, the specific surface area of the cerium oxide nanocomposite prepared in example 32Therefore, the higher roasting temperature of the cerium hydroxide nanosheet precursor is not beneficial to reducing the thickness of the cerium dioxide nanocomposite and improving the specific surface area of the cerium dioxide nanocomposite.
In example 14, the mass ratio of the platinum element to the cerium oxide nanosheet in the chloroplatinic acid solution in the step (4) is 1:3, the thickness of the prepared cerium oxide nanocomposite is 2.7nm, which is 1.8nm higher than that of the cerium oxide nanocomposite prepared in example 3, and the specific surface area of the cerium oxide nanocomposite prepared in example 14 is 146m2(g) lower than the ratio of the cerium oxide nanocomposite prepared in example 3Surface area 182m2Therefore, the higher content of platinum element in the chloroplatinic acid solution is not favorable for reducing the thickness of the cerium dioxide nano composite material and improving the specific surface area of the cerium dioxide nano composite material.
In example 15, the mass ratio of the platinum element to the cerium oxide nanosheet in the chloroplatinic acid solution in the step (4) is 1:65, the thickness of the prepared cerium oxide nanocomposite is 2.7nm, which is 1.8nm higher than that of the cerium oxide nanocomposite prepared in example 3, and the specific surface area of the cerium oxide nanocomposite prepared in example 15 is 144m2(per gram), less than 182m, the specific surface area of the cerium oxide nanocomposite prepared in example 32Therefore, the lower content of platinum element in the chloroplatinic acid solution is not beneficial to reducing the thickness of the cerium dioxide nano composite material and improving the specific surface area of the cerium dioxide nano composite material.
In comparative example 1, the molar ratio of hydroxide ions in the alkaline solution to cerium nitrate in the aqueous cerium nitrate solution was 5:1, and the amount of hydroxide ions added was lower than that in example 3. The thickness of the cerium oxide nanocomposite prepared in comparative example 1 was 3.1nm, which was 1.8nm higher than that of the cerium oxide nanocomposite prepared in example 3, and the specific surface area of the cerium oxide nanocomposite prepared in comparative example 1 was 133m2(per gram), less than 182m, the specific surface area of the cerium oxide nanocomposite prepared in example 32Therefore, the addition amount of hydroxide ions is not favorable for reducing the thickness of the ceria nanocomposite and for increasing the specific surface area of the ceria nanocomposite.
In comparative example 2, the molar ratio of hydroxide ions in the alkaline solution to cerium nitrate in the aqueous cerium nitrate solution was 30:1, and the amount of hydroxide ions added was lower than that in example 3. The thickness of the cerium oxide nanocomposite prepared in comparative example 1 was 3.2nm, which was 1.8nm higher than that of the cerium oxide nanocomposite prepared in example 3, and the specific surface area of the cerium oxide nanocomposite prepared in comparative example 1 was 132m2(per gram), less than 182m, the specific surface area of the cerium oxide nanocomposite prepared in example 32Therefore, a higher amount of hydroxide ions is not favorable for reducing the thickness of the ceria nanocomposite and for increasing the specific surface area of the ceria nanocomposite.
In conclusion, the preparation method of the cerium dioxide nanosheet provided by the invention is simple, the operation is simple and convenient, the prepared cerium dioxide nanosheet is low in thickness, the cerium dioxide nanosheet is full of nano-scale holes with the aperture of 1-6nm, the thickness of the cerium dioxide nanocomposite prepared by the cerium dioxide nanosheet supporting the noble metal catalyst is not more than 2.5nm, and the specific surface area of the obtained cerium dioxide nanocomposite is higher than 150m2More precious metals can be uniformly loaded, so that the catalytic efficiency is improved, the consumption of metal cerium can be reduced, and the production cost of the cerium dioxide nano composite material is reduced.
The applicant states that the present invention is illustrated by the above examples to show the detailed process equipment and process flow of the present invention, but the present invention is not limited to the above detailed process equipment and process flow, i.e. it does not mean that the present invention must rely on the above detailed process equipment and process flow to be implemented. It should be understood by those skilled in the art that any modification of the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.

Claims (52)

1. A preparation method of cerium dioxide nanosheets is characterized by comprising the following steps:
(1) precipitating a cerium nitrate aqueous solution by using an alkaline solution to obtain a cerium hydroxide nanosheet precursor;
(2) freeze-drying and roasting the cerium hydroxide nanosheet precursor obtained in the step (1) to obtain a cerium dioxide nanosheet;
the alkaline solution in the step (1) comprises a sodium hydroxide solution and/or a potassium hydroxide solution;
the molar ratio of hydroxide ions in the alkaline solution to cerium nitrate in the cerium nitrate aqueous solution is (8-27) to 1;
the molar concentration of the cerium nitrate in the cerium nitrate aqueous solution in the step (1) is 0.01-0.1 mol/L; the molar concentration of hydroxide ions in the alkaline solution in the step (1) is 0.5-6 mol/L;
the roasting temperature in the step (2) is 380-800 ℃, and the roasting time is 0.5-4.2 h.
2. The method according to claim 1, wherein the precipitation in step (1) is carried out under a non-oxidizing gas atmosphere.
3. The method of claim 2, wherein the non-oxidizing gas comprises any one of nitrogen, argon, or helium, or a combination of at least two thereof.
4. The method according to claim 3, wherein the non-oxidizing gas is nitrogen.
5. The preparation method according to claim 1, wherein the molar concentration of the cerium nitrate in the aqueous solution of cerium nitrate in step (1) is 0.02 to 0.08 mol/L.
6. The method according to claim 1, wherein the molar concentration of hydroxide ions in the alkaline solution of step (1) is 1 to 5 mol/L.
7. The method according to claim 6, wherein the molar concentration of hydroxide ions in the alkaline solution of step (1) is 2 to 4 mol/L.
8. The method of claim 1, wherein the molar ratio of hydroxide ions to cerium nitrate is (10-25): 1.
9. The method of claim 8, wherein the molar ratio of hydroxide ions to cerium nitrate is (12-21): 1.
10. The production method according to claim 1, wherein the basic solution is added dropwise to the aqueous cerium nitrate solution.
11. The method according to claim 10, wherein the dropping is carried out at a rate of 10 to 20 mL/min.
12. The method according to claim 11, wherein the dropping is carried out at a rate of 12 to 18 mL/min.
13. The method according to claim 1, wherein the precipitation in step (1) is accompanied by stirring.
14. The method as claimed in claim 13, wherein the stirring speed is 600-1500 r/min.
15. The method as claimed in claim 14, wherein the stirring speed is 1200-1500 r/min.
16. The method of claim 13, wherein the stirring time is 2 to 15 hours.
17. The method of claim 16, wherein the stirring time is 4 to 12 hours.
18. The method of claim 17, wherein the stirring time is 6 to 8 hours.
19. The method according to claim 1, wherein the precipitate obtained in step (1) is washed to neutrality.
20. The method according to claim 1, wherein the precipitation temperature in step (1) is 0 to 40 ℃.
21. The method according to claim 20, wherein the precipitation temperature in step (1) is 10 to 30 ℃.
22. The method of claim 21, wherein the precipitation temperature in step (1) is 15-25 ℃.
23. The method as claimed in claim 1, wherein the temperature of the calcination in step (2) is 400-780 ℃.
24. The method as claimed in claim 23, wherein the temperature of the calcination in step (2) is 420-750 ℃.
25. The preparation method of claim 1, wherein the roasting time in the step (2) is 1-4 h.
26. The method as claimed in claim 25, wherein the roasting time in step (2) is 2-3 h.
27. Cerium oxide nanoplates prepared by the method of any one of claims 1-26;
the thickness of the cerium dioxide nano-sheet is 0.8-3.2nm, and the equivalent diameter is 150-1200 nm; the cerium dioxide nanosheets are fully distributed with nanoscale holes, and the aperture of each nanoscale hole is 1-6 nm.
28. Cerium oxide nanoplatelets according to claim 27 wherein the thickness of the cerium oxide nanoplatelets is 1-3 nm.
29. Cerium oxide nanoplatelets according to claim 28 wherein the thickness of the cerium oxide nanoplatelets is 1.2-2.7 nm.
30. Cerium oxide nanoplatelets according to claim 27 wherein the cerium oxide nanoplatelets have an equivalent diameter of 200-1000 nm.
31. Cerium oxide nanoplatelets according to claim 30 wherein the equivalent diameter of the cerium oxide nanoplatelets is 250-800 nm.
32. Cerium oxide nanoplatelets according to claim 27 wherein the nanoscale pores have a pore size of 2-5 nm.
33. Cerium oxide nanoplatelets according to claim 32 wherein the nanoscale pores have a pore size of 3-4 nm.
34. A ceria nanocomposite comprising ceria nanoplates as defined in any one of claims 27 to 33.
35. A method for preparing a cerium oxide nanocomposite according to claim 34, comprising the steps of:
(I) preparing cerium dioxide nanoplates using the preparation method of any one of claims 1-26;
(II) immersing the cerium dioxide nanosheet obtained in the step (I) into a reducing solution to obtain a cerium dioxide dispersion liquid;
(III) adding a precious metal precursor solution into the cerium dioxide dispersion liquid obtained in the step (II) to obtain a mixed liquid;
(IV) heating and stirring the mixed solution obtained in the step (III), cooling, performing centrifugal separation, washing and drying to obtain the cerium dioxide nano composite material;
the reducing solution comprises any one or the combination of at least two of anhydrous ethylene glycol, ethylene glycol solution of sodium hydroxide or ethylene glycol solution of potassium hydroxide.
36. The method according to claim 35, wherein the molar concentration of hydroxide ions in the ethylene glycol solution of sodium hydroxide or the ethylene glycol solution of potassium hydroxide is 0.8 to 1.2 mol/L.
37. The method according to claim 36, wherein the molar concentration of hydroxide ions in the ethylene glycol solution of sodium hydroxide or the ethylene glycol solution of potassium hydroxide is 0.9 to 1.1 mol/L.
38. The production method according to claim 35, wherein the noble metal precursor solution of step (III) includes one or a combination of at least two of a chloroplatinic acid solution, a chloroauric acid solution, a chloroiridic acid solution, or a potassium chloroplatinate solution.
39. The production method according to claim 38, wherein the mass fraction of the noble metal element in the noble metal precursor solution is 0.5 to 15 wt%.
40. The method according to claim 39, wherein the noble metal precursor solution contains the noble metal element in an amount of 1 to 12 wt%.
41. The method according to claim 40, wherein the noble metal precursor solution contains the noble metal element in an amount of 3 to 10 wt%.
42. The preparation method of claim 35, wherein the mass ratio of the noble metal element in the noble metal precursor solution to the cerium dioxide nanosheets is 1 (5-60).
43. The preparation method of claim 42, wherein the mass ratio of the noble metal element in the noble metal precursor solution to the cerium dioxide nanosheets is 1 (10-50).
44. The preparation method of claim 43, wherein the mass ratio of the noble metal element in the noble metal precursor solution to the cerium dioxide nanosheets is 1 (20-40).
45. The method as claimed in claim 35, wherein the heating temperature in step (IV) is 100-210 ℃.
46. The method as claimed in claim 45, wherein the heating temperature in step (IV) is 120-200 ℃.
47. The method as claimed in claim 46, wherein the heating temperature in step (IV) is 150-180 ℃.
48. The method of claim 35, wherein the stirring time of step (IV) is 0.3 to 2.1 hours.
49. The method of claim 48, wherein the stirring time of step (IV) is 0.5-2 h.
50. The method of claim 49, wherein the stirring time of step (IV) is 0.8-1.6 h.
51. The method of claim 35, comprising the steps of:
(a) under the protection of non-oxidizing gas, dropwise adding a sodium hydroxide aqueous solution and/or a potassium hydroxide aqueous solution with the molar concentration of hydroxide ions of 0.5-6mol/L into a cerium nitrate aqueous solution with the molar concentration of cerium nitrate of 0.01-0.1mol/L within the temperature range of 0-40 ℃, wherein the molar ratio of the hydroxide ions to the cerium nitrate is (10-25):1, the dropwise adding speed is 10-20mL/min, stirring the cerium nitrate aqueous solution in the precipitation process, the stirring time is 2-15h, the stirring speed is 600-;
(b) roasting the cerium hydroxide nanosheet precursor obtained in the step (a) by freeze drying at the temperature of 380-800 ℃, wherein the roasting time is 0.5-4.2h, so as to obtain cerium dioxide nanosheets;
(c) immersing a cerium dioxide nanosheet into an ethylene glycol solution to obtain a cerium dioxide dispersion liquid;
(d) adding a precious metal precursor solution with the mass fraction of precious metal elements of 0.5-15 wt% into the cerium dioxide dispersion liquid obtained in the step (c) to obtain a mixed liquid, wherein the mass ratio of the precious metal elements in the precious metal precursor solution to the cerium dioxide nanosheets is 1 (5-60);
(e) stirring the mixed solution obtained in the step (d) at the temperature of 100 ℃ and 210 ℃, cooling, centrifugally separating, washing and drying to obtain the cerium dioxide nano composite material, wherein the stirring time is 0.3-2.1 h.
52. Use of a cerium oxide nanocomposite material according to claim 34 or a cerium oxide nanocomposite material prepared by a preparation method according to any one of claims 35 to 51 for the catalytic oxidation of formaldehyde.
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