Nano cerium dioxide as well as preparation method and application thereof

Abstract

The invention discloses nano cerium dioxide as well as a preparation method and application thereof. The preparation method of the nano cerium dioxide comprises the following steps: (1) mixing a cerium salt mother solution and a sodium hypochlorite solution for reaction to obtain a first mixed solution; adding an alkali solution into the first mixed solution for reaction, adjusting the pH value of the reaction system to 6-6.5, continuing stirring for reaction at 80-90 DEG C for 1.5-3 hours, adding a sodium hypochlorite solution for reaction, adjusting the pH value of the reaction system to 6-6.5, and continuing stirring for reaction at 80-90 DEG C for 7-17 hours to obtain a second mixed solution; and (2) acidifying the second mixed solution, centrifuging to obtain a cerium dioxide precipitate, and drying the cerium dioxide precipitate to obtain the nano cerium dioxide. According to the method, the superfine nano spherical cerium dioxide particles with good dispersity, uniform particle size and high purity can be prepared at low temperature without adding any organic reagent. The method is short in production period and suitable for large-scale production.

Description

Technical Field

[0001] The invention relates to nano cerium dioxide and a preparation method and application thereof. Background Art

[0002] Spherical cerium oxide is an important rare earth functional material with good mechanical strength and excellent oxygen ion transmission performance. It is widely used in many fields such as catalysis, polishing, medium-temperature solid oxide fuel cells, ultraviolet shielding, cancer treatment, biological imaging, drug carriers, and biological antioxidants. Especially in the field of polishing, spherical nano-cerium oxide particles are the most ideal polishing abrasives. After polishing optical glass, mobile phone panel glass, display glass and other devices with nano-spherical cerium dioxide abrasives, nano-scale surface roughness can be obtained. Therefore, nano-spherical cerium dioxide is often used for ultra-precision polishing.

[0003] The hydrothermal method uses a specially made closed container (autoclave) as a reaction container and water as a reaction medium. By heating the reaction container (water bath heating or oil bath heating), a high-temperature and high-pressure reaction environment is formed, so that the usually insoluble or insoluble substances are dissolved, and in this process, they are recrystallized to form dispersed nanocrystalline nuclei. Most of the hydrothermal methods currently used to synthesize ultrafine nano-spherical cerium dioxide require a high-temperature and high-pressure reaction environment, and the reaction time is relatively long, and the output is mostly relatively small, which is not conducive to the large-scale production of ultrafine nano-spherical cerium dioxide particles.

[0004] CN113247941A discloses a method for preparing a uniform spherical cerium oxide material. The present invention adopts a low-temperature hydrothermal method, dissolves a certain amount of hexahydrate cerium nitrate, urea, and polyvinyl pyrrolidone-K30 in deionized water at room temperature, mixes and stirs, and then transfers the resulting solution to a stainless steel autoclave for reaction. The autoclave is kept at 80-120°C for 6-12h. After naturally cooling to room temperature, spherical nano cerium dioxide with uniform particle size can be obtained by centrifugation, washing, and calcination. The nano spherical cerium dioxide has mild synthesis temperature conditions, simple operation, and easy control. The average spherical diameter is about 180nm, and the size is uniform. It can be applied to VOCs catalytic degradation, automobile exhaust purification, ultraviolet light shielding and many other aspects. It can be seen from its implementation method that it still needs to react at a temperature of 100°C, and it is also necessary to add an organic dispersant to maintain good dispersibility.

[0005] CN107651703A discloses a method for preparing nano cerium oxide with {111} crystal plane orientation. A certain amount of cerium nitrate hexahydrate is dissolved in a certain amount of deionized water, and an appropriate amount of NaOH is dissolved in a certain amount of deionized water to form two uniform solutions; the NaOH solution is added to the cerium nitrate solution under stirring conditions, and the pH value is adjusted to 5-7 to form a suspension; the suspension is placed in a blast drying oven at 160°C-200°C for hydrothermal reaction; the obtained product is washed and dried to obtain a white or light yellow solid, and then ground to obtain nano cerium dioxide powder. Although this method does not add organic reagents, it still needs to be hydrothermally reacted at high temperature, which is not suitable for large-scale production. Summary of the invention

[0006] In view of this, one object of the present invention is to provide a method for preparing nano-cerium dioxide, which can prepare ultrafine nano-spherical cerium dioxide particles with good dispersibility, uniform particle size and high purity. The reaction temperature is low. Another object of the present invention is to provide a nano-cerium dioxide prepared by the above preparation method. Another object of the present invention is to provide an application of sodium hypochlorite in improving the dispersibility and particle size uniformity of the obtained nano-cerium dioxide.

[0007] The above technical objectives are achieved through the following technical solutions.

[0008] In one aspect, the present invention provides a method for preparing nano-cerium dioxide, comprising the following steps:

[0009] (1) mixing a cerium salt mother solution and a sodium hypochlorite solution to react to obtain a first mixed solution; then adding an alkali solution to the first mixed solution for reaction, adjusting the pH value of the reaction system to 6 to 6.5, and then continuing to stir and react at 80 to 90° C. for 1.5 to 3 hours, then adding a sodium hypochlorite solution for reaction, and then adjusting the pH value of the reaction system to 6 to 6.5, and then continuing to stir and react at 80 to 90° C. for 7 to 17 hours to obtain a second mixed solution;

[0010] (2) Acidifying and centrifuging the second mixed solution to obtain a cerium dioxide precipitate, and then drying the cerium dioxide precipitate to obtain nano-cerium dioxide.

[0011] According to the preparation method of the present invention, preferably, in step (1), the cerium salt mother solution is obtained by mixing a trivalent cerium salt solution and a tetravalent cerium salt; the concentration of the trivalent cerium salt solution is 1 to 3 mol / L; and the molar ratio of tetravalent cerium to the total cerium in the cerium salt mother solution is 1:50000 to 300000.

[0012] According to the preparation method of the present invention, preferably, in step (1), the trivalent cerium salt is selected from one of cerium nitrate, cerium chloride and cerium sulfate.

[0013] According to the preparation method of the present invention, preferably, the tetravalent cerium salt is selected from one of ammonium cerium nitrate, ammonium cerium sulfate, cerium (IV) nitrate and cerium (IV) sulfate.

[0014] According to the preparation method of the present invention, preferably, in step (1), the cerium salt mother liquor and the sodium hypochlorite solution are mixed at 15 to 35° C., and then the temperature is raised to 80 to 90° C. for reaction to obtain a first mixed solution.

[0015] According to the preparation method of the present invention, preferably, in step (1), the alkaline solution is selected from one of sodium hydroxide solution, potassium hydroxide solution or ammonia water.

[0016] According to the preparation method of the present invention, preferably, in step (2), acidification is performed using an acid solution, and the pH value of the second mixed solution after acidification is 0.5-2.

[0017] According to the preparation method of the present invention, preferably, the drying temperature is 80 to 300° C. and the drying time is 1 to 2 hours.

[0018] On the other hand, the present invention provides a nano-cerium dioxide prepared by the above-mentioned preparation method.

[0019] In another aspect, the present invention provides an application of a sodium hypochlorite solution in improving the dispersibility and particle size uniformity of the obtained nano-cerium dioxide, comprising the following steps:

[0020] (1) mixing a cerium salt mother solution and a sodium hypochlorite solution to react to obtain a first mixed solution; then adding an alkali solution to the first mixed solution for reaction, adjusting the pH value of the reaction system to 6 to 6.5, and then continuing to stir and react at 80 to 90° C. for 1.5 to 3 hours, then adding a sodium hypochlorite solution for reaction, and then adjusting the pH value of the reaction system to 6 to 6.5, and then continuing to stir and react at 80 to 90° C. for 7 to 17 hours to obtain a second mixed solution;

[0021] (2) Acidifying and centrifuging the second mixed solution to obtain a cerium dioxide precipitate, and then drying the cerium dioxide precipitate to obtain nano-cerium dioxide.

[0022] The method provided by the present invention can prepare ultrafine nano-spherical cerium dioxide particles with good dispersibility, uniform particle size and high purity at low temperature without adding any organic reagent. The D50 of the obtained cerium dioxide particles is 8-9nm. It can be applied to the precision polishing of optical glass, mobile phone panel glass and display glass. The production cycle is short and it is suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is the transmission electron microscope image of Example 1-3; Among them, Figure 1(a) is a transmission electron microscope image of Example 1; Figure 1 (b) is a transmission electron microscope image of Example 2; Figure 1 (c) is the transmission electron microscope image of Example 3.

[0024] Figure 2 The XRD diagrams of Examples 1 to 3 are shown in FIG.

[0025] Figure 3 TEM images of Comparative Examples 1 to 3; wherein, Figure 3 (a) is a transmission electron microscope image of Comparative Example 1; Figure 3 (b) is a transmission electron microscope image of Comparative Example 2; Figure 3 (c) is the transmission electron microscope image of Comparative Example 3.

[0026] Figure 4 These are the XRD patterns of Comparative Examples 1 to 3. DETAILED DESCRIPTION

[0027] The present invention is described in more detail below, but the present invention is not limited thereto.

[0028] <Preparation method of nano cerium dioxide>

[0029] The method for preparing nano-cerium dioxide of the present invention comprises the following steps: (1) a solution preparation step; (2) a hydrothermal reaction step; and (3) a step of forming nano-cerium dioxide. The following is a detailed description.

[0030] Solution preparation steps

[0031] The cerium salt mother solution can be prepared from a soluble cerium salt, for example, a trivalent cerium salt solution is mixed with a tetravalent cerium salt to prepare the cerium salt mother solution.

[0032] The trivalent cerium salt may be one of cerium nitrate, cerium chloride and cerium sulfate; preferably cerium chloride or cerium nitrate; more preferably cerium chloride. The concentration of the trivalent cerium salt solution may be 1 to 3 mol / L; preferably 1.5 to 2.5 mol / L; more preferably 1.8 to 2.2 mol / L. This is more conducive to the formation of cerium dioxide with good dispersibility and crystallinity.

[0033] The tetravalent cerium salt may be one of ammonium cerium nitrate, ammonium cerium sulfate, cerium (IV) nitrate and cerium (IV) sulfate; preferably ammonium cerium nitrate or cerium (IV) nitrate; more preferably ammonium cerium nitrate.

[0034] The molar ratio of tetravalent cerium to total cerium can be 1:50000-300000; preferably 1:80000-250000; more preferably 1:100000-200000; tetravalent cerium salt has the functions of solidification and precipitation assistance, and can be first recrystallized to form nanocrystalline cores during the subsequent hydrothermal reaction.

[0035] Hydrothermal reaction steps

[0036] The present invention uses a cerium salt mother liquor of appropriate concentration as a reaction liquid, sodium hypochlorite as an oxidant and a precipitant, and sodium hydroxide as an auxiliary precipitant, and prepares nano-scale spherical cerium dioxide particles by a hydrothermal method at low temperature and low pressure without adding any organic reagents. Compared with the high temperature and high pressure or low temperature in the prior art, which requires the addition of organic reagents and has a long reaction cycle, the method of the present invention is suitable for large-scale production.

[0037] In the present invention, it can be divided into several reaction stages:

[0038] Reaction stage 1: mixing the cerium salt mother solution and the sodium hypochlorite solution to obtain a first mixed solution.

[0039] Reaction stage two: add alkaline solution to the first mixed solution for reaction, adjust the pH value of the reaction system to 6-6.5, and then continue to stir and react at 80-90° C. for 1.5-3 h (first reaction time), then add sodium hypochlorite solution for reaction, and then adjust the pH value of the reaction system to 6-6.5, and then continue to stir and react at 80-90° C. for 7-17 h (second reaction time) to obtain a second mixed solution.

[0040] In the present invention, sodium hypochlorite is used as an oxidant and a precipitant to oxidize part of the trivalent cerium ions into tetravalent cerium, and crystal nuclei can be synthesized first in the reaction. At the same time, it can be used as an oxidant to achieve more precise control.

[0041] In the first reaction stage of the present invention, the cerium salt mother liquor is mixed with the sodium hypochlorite solution, and the anti-backflow device and the tail gas treatment device equipped with a saturated sodium hydroxide solution are connected. The content of available chlorine in the sodium hypochlorite can be 8-15wt%, preferably 10-12wt%, and more preferably 10wt%. It can be kept in a fume hood at room temperature and under stirring for 20-40min, preferably 25-30min. Then the temperature is raised to 80-90°C within 0.5-1.5h to obtain a first mixed solution. During this period, a large amount of gas will be generated, and the next stage of reaction will be carried out after no bubbles are generated in the tail gas treatment device and the anti-backflow device is no longer backflowing.

[0042] In the reaction stage 2 of the present invention, the concentration of the sodium hydroxide solution can be 0.04-0.08 mol / L, preferably 0.05-0.07 mol / L, and more preferably 0.05-0.06 mol / L. The pH value can be 6-6.5, preferably 6. According to a specific embodiment of the present invention, the pH value is 6. The pH value of the hydrothermal reaction has an important influence on the formation of nano-cerium dioxide particles. Only a suitable pH value can form nano-cerium dioxide particles with good crystallinity and good dispersibility.

[0043] In the present invention, the temperature of the hydrothermal reaction may be 80 to 90° C., preferably 80 to 85° C. The hydrothermal reaction temperature of the present invention is low, and is more suitable for large-scale production than the high temperature of the prior art.

[0044] In the present invention, the first reaction time may be 1.5 to 3 hours, preferably 1.8 to 2.5 hours, and more preferably 2 to 2.2 hours, which is more conducive to the formation of cerium hydroxide precipitate.

[0045] In the present invention, the second reaction time can be 7 to 17 hours, preferably 9 to 15 hours, and more preferably 12 to 14 hours. Sodium hypochlorite is added in the second reaction stage to completely convert the cerous hydroxide precipitate into a cerium hydroxide precipitate (quadrivalent), and then a second mixed solution with a cerium dioxide precipitate is obtained through a hydrothermal reaction.

[0046] In the present invention, the stirring speed may be 900 to 1500 r / min, preferably 1100 to 1300 r / min.

[0047] Steps for forming nano-cerium dioxide

[0048] The second mixed solution is acidified, centrifuged and washed to obtain a cerium dioxide precipitate, and then the cerium dioxide precipitate is dried to obtain nano-cerium dioxide.

[0049] In the present invention, the second mixed solution can be acidified with an acid solution, and the pH of the second mixed solution after acidification is 0.5-2, which is conducive to removing soluble salts in the product.

[0050] In the present invention, there is no special requirement for the centrifugal method, and any method commonly used in the art can be used. For example, a centrifuge can be used for centrifugation, and the centrifugal speed can be 10000-15000 r / min, preferably 11000-12000 r / min.

[0051] In the present invention, the precipitate of cerium dioxide can be dried in a dryer to obtain bulk cerium dioxide. The drying temperature can be 80 to 300° C., preferably 100 to 250° C., and more preferably 120 to 180° C. The drying time can be 1 to 2 hours, preferably 1.2 to 2 hours, and more preferably 1.5 to 2 hours.

[0052] In the present invention, the blocky cerium dioxide is placed in a grinding device for grinding to obtain cerium dioxide powder. The grinding device can be selected from a ball mill, a vertical mill, and a vibration mill; preferably a ball mill or a vibration mill, more preferably a ball mill. The grinding time can be 2 to 6 hours, preferably 2.5 to 6 hours, and more preferably 4.5 to 5.5 hours.

[0053] In the present invention, in order to facilitate subsequent characterization, a part of the obtained cerium dioxide precipitate can be depolymerized to prepare a cerium dioxide suspension; the other part can be dried to obtain nano cerium dioxide powder. The obtained cerium dioxide precipitate can be mixed with deionized water and depolymerized, and then deionized water is added to the depolymerized cerium dioxide suspension to prepare it into a cerium dioxide suspension. The content of cerium dioxide in the cerium dioxide suspension can be 9.5-12wt%, preferably 10-11wt%. The depolymerization method can be selected from one of an ultrasonic treatment device, a double impact jet treatment device or a wet grinding device; preferably an ultrasonic treatment device or a double impact jet treatment device; more preferably an ultrasonic treatment device.

[0054] <Nano-cerium dioxide>

[0055] The nano cerium dioxide particles prepared by the above method have an average particle size D50 of 8-9 nm and can be used in the precision polishing of optical glass, mobile phone panel glass and display glass.

[0056] <Application of Sodium Hypochlorite>

[0057] The present invention also provides an application of sodium chlorate in improving the dispersibility and particle size uniformity of the obtained nano cerium dioxide. It should be noted that not all oxidants can be used to prepare cerium dioxide. For example, hydrogen peroxide is selected as an oxidant in the prior art, which is theoretically feasible, but in the actual operation process, it is found that hydrogen peroxide as an oxidant has a strong variability and is not well controlled. In addition, it is still necessary to react at high temperature to generate nano cerium dioxide particles with good dispersibility and uniform particle size. The present invention unexpectedly found that the use of sodium hypochlorite to participate in the reaction can achieve good control. When the cerium salt mother liquor is used as the reaction liquid, sodium hypochlorite is used as the oxidant and precipitant, and an alkaline solution is used, it can be achieved at low temperature and low pressure without adding any organic reagents. Still can prepare nano cerium dioxide particles with good dispersibility and uniform particle size. Although the specific reasons and mechanisms are not clear, it is speculated that it may be because the oxidation conditions are easy to control and the uniform charge distribution leads to good dispersibility and particle size, but the detailed scientific reasons need further study.

[0058] Nano-cerium dioxide is prepared by the following steps:

[0059] (1) mixing a cerium salt mother solution and a sodium hypochlorite solution to react to obtain a first mixed solution; then adding an alkali solution to the first mixed solution for reaction, adjusting the pH value of the reaction system to 6 to 6.5, and then continuing to stir and react at 80 to 90° C. for 1.5 to 3 hours, then adding a sodium hypochlorite solution for reaction, and then adjusting the pH value of the reaction system to 6 to 6.5, and then continuing to stir and react at 80 to 90° C. for 7 to 17 hours to obtain a second mixed solution;

[0060] (2) Acidifying and centrifuging the second mixed solution to obtain a cerium dioxide precipitate, and then drying the cerium dioxide precipitate to obtain nano-cerium dioxide.

[0061] Here is the test method:

[0062] (1) XRD analysis: A MiniFlex 600 desktop X-ray diffractometer manufactured in Japan was used for analysis and characterization.

[0063] (2) TEM morphology analysis: The morphology of nano-cerium dioxide powder was characterized using a JEM-2100F transmission electron microscope.

[0064] Example 1

[0065] 40 mL of 1.5 mol / L cerium chloride solution was mixed with cerium ammonium nitrate to prepare a cerium salt mother solution.

[0066] The cerium salt mother liquor is added into the reactor, and the anti-backflow device and the tail gas treatment device filled with a saturated sodium hydroxide solution are connected.

[0067] Under stirring at a speed of 1200r / min, 15mL of sodium hypochlorite solution with an effective chlorine content of 10wt% was added to the cerium salt mother solution, and the reaction was continued to be stirred for 30min at room temperature, and then the temperature was raised to 85°C for reaction until no bubbles were generated in the tail gas treatment device, thereby obtaining a first mixed solution. Then 40mL of 0.05mol / L sodium hydroxide solution was added to the first mixed solution, and the reaction system completely turned purple at this time, and the pH value of the reaction system was adjusted to 6, and then the reaction was continued to be stirred at 85°C for 2h (first reaction time), and then 40mL of sodium hypochlorite solution with an effective chlorine content of 10wt% was slowly added to the reaction system, and a large number of bubbles were generated in the tail gas treatment device, and the purple color of the reaction system completely disappeared at this time, and the pH value of the reaction system was adjusted to 6, and the reaction was continued to be stirred at 85°C for 7h (second reaction time), thereby obtaining a second mixed solution.

[0068] The second mixed solution was cooled to room temperature, and then 68 wt % nitric acid was added to the second mixed solution for acidification, and the pH value was adjusted to 2, and then centrifuged to obtain a cerium dioxide precipitate. The cerium dioxide precipitate was dried at 150° C. for 2 h to obtain a block of cerium dioxide, and the block of cerium dioxide was placed in a ball mill and ground for 5 h to obtain a nano cerium dioxide powder.

[0069] Example 2

[0070] The process is the same as in Example 1 except that the concentration of the cerium chloride solution is 2 mol / L and the second reaction time is 9.5 h.

[0071] Example 3

[0072] The above steps are the same as those in Example 1 except that the concentration of the cerium chloride solution is 2.5 mol / L and the second reaction time is 12 h.

[0073] Comparative Example 1

[0074] Except that the pH value is 5, the rest is the same as Example 1.

[0075] Comparative Example 2

[0076] Except that the concentration of the cerium chloride solution is 2.5 mol / L and the pH value is 7, the rest is the same as Example 1.

[0077] Comparative Example 3

[0078] Except that the concentration of the cerium chloride solution is 3 mol / L and the pH value is 12, the rest is the same as Example 1.

[0079] The characterization results are as follows Figures 1 to 4 shown.

[0080] Depend on Figure 1 As shown in (a) to (c), the cerium dioxide synthesized in Examples 1 to 3 are spherical particles with an average particle size of 8 to 9 nm, with sharp edges but not particularly sharp, and the particles are relatively uniform, with relatively small agglomerations, and even monodisperse cerium dioxide particles appear. In terms of dispersibility, the monodisperse particles of Examples 2 and 3 are more than those of Example 1, and the monodisperse particles of Example 3 are the fullest and have better dispersibility.

[0081] Depend on Figure 2 It can be seen that the XRD spectra of Examples 1 to 3 conform to the positions of the peaks in the standard PDF card 34-0394, and the intensity of the diffraction peaks of the spectra does not change much, and there are no other impurity peaks. The intensity of the diffraction peaks is very large, indicating that the degree of crystallization is very good.

[0082] Depend on Figure 3 (a) to (c) show that, under a pH of 5, the cerium dioxide synthesized in Comparative Example 1 is a spherical particle with an average particle size of 8-9 nm, with sharp edges but not particularly sharp, and the particles are relatively uniform, with relatively small agglomerations, and monodispersed cerium dioxide particles also appear. Under a pH of 7, the cerium dioxide particles synthesized in Comparative Example 2 are a mixture of spheres and a small amount of rods, and the agglomeration is more serious. Under a pH of 12, the cerium dioxide particles synthesized in Comparative Example 3 are a mixture of spheres and a large amount of rods, and the agglomeration is more serious.

[0083] Depend on Figure 4It can be seen that the XRD spectrum of Comparative Example 1 conforms to the positions of the peaks in the standard PDF card 34-0394, but the diffraction peak intensity is strong, the diffraction peak is also sharp, and there are no other miscellaneous peaks, but compared with Example 1, the diffraction peak intensity is lower, indicating that the degree of crystallization is lower than that of Example 1. The XRD spectra of Comparative Examples 2 and 3 conform to the positions of the peaks in the standard PDF card 34-0394, but the diffraction peak intensity is weak, the width is large, the (222) peak, (400) peak, and (420) peak are not obvious, and there are many fine burrs, indicating that the degree of crystallization is low.

[0084] Comparative Example 4

[0085] Except that the sodium hypochlorite solution was replaced by 10 wt % hydrogen peroxide, the rest was the same as Example 1. When the experiment was conducted with hydrogen peroxide, the oxidation conditions were very difficult to control, and the crystallinity and uniformity of the cerium dioxide particles finally formed were poor.

[0086] The present invention is not limited to the above-mentioned embodiments. Without departing from the essential content of the present invention, any deformation, improvement and substitution that can be conceived by those skilled in the art shall fall within the scope of the present invention.

Claims

1. A method for preparing nano cerium dioxide, It is characterized in that The steps include: (1) mixing a cerium salt mother solution and a sodium hypochlorite solution to react to obtain a first mixed solution; then adding an alkali solution to the first mixed solution for reaction, adjusting the pH value of the reaction system to 6 to 6.5, and then continuing to stir and react at 80 to 90° C. for 1.5 to 3 hours, then adding a sodium hypochlorite solution for reaction, and then adjusting the pH value of the reaction system to 6 to 6.5, and then continuing to stir and react at 80 to 90° C. for 7 to 17 hours to obtain a second mixed solution; (2) Acidifying and centrifuging the second mixed solution to obtain a cerium dioxide precipitate, and then drying the cerium dioxide precipitate to obtain nano-cerium dioxide.

2. The preparation method according to claim 1, It is characterized in that In step (1), the cerium salt mother solution is obtained by mixing a trivalent cerium salt solution and a tetravalent cerium salt; the concentration of the trivalent cerium salt solution is 1 to 3 mol / L; and the molar ratio of tetravalent cerium to the total cerium in the cerium salt mother solution is 1:50,000 to 300,000.

3. The preparation method according to claim 2, It is characterized in that In step (1), the trivalent cerium salt is selected from one of cerium nitrate, cerium chloride and cerium sulfate.

4. The preparation method according to claim 2, It is characterized in that The tetravalent cerium salt is selected from one of ammonium cerium nitrate, ammonium cerium sulfate, cerium (IV) nitrate and cerium (IV) sulfate.

5. The preparation method according to claim 1, It is characterized in that In step (1), the cerium salt mother solution and the sodium hypochlorite solution are mixed at 15-35° C., and then the temperature is raised to 80-90° C. to react to obtain a first mixed solution.

6. The preparation method according to claim 1, It is characterized in that In step (1), the alkaline solution is selected from one of sodium hydroxide solution, potassium hydroxide solution or ammonia water.

7. The preparation method according to claim 1, It is characterized in that In step (2), an acid solution is used for acidification, and the pH value of the second mixed solution after acidification is 0.5-2.

8. The preparation method according to claim 1, It is characterized in that The drying temperature is 80-300°C; the drying time is 1-2h.

9. A nano cerium dioxide, It is characterized in that The compound is prepared by the preparation method according to any one of claims 1 to 8.

10. Application of a sodium hypochlorite solution in improving the dispersibility and particle size uniformity of the obtained nano-cerium dioxide. It is characterized in that The steps include: (1) mixing a cerium salt mother solution and a sodium hypochlorite solution to react to obtain a first mixed solution; then adding an alkali solution to the first mixed solution for reaction, adjusting the pH value of the reaction system to 6 to 6.5, and then continuing to stir and react at 80 to 90° C. for 1.5 to 3 hours, then adding a sodium hypochlorite solution for reaction, and then adjusting the pH value of the reaction system to 6 to 6.5, and then continuing to stir and react at 80 to 90° C. for 7 to 17 hours to obtain a second mixed solution; (2) Acidifying and centrifuging the second mixed solution to obtain a cerium dioxide precipitate, and then drying the cerium dioxide precipitate to obtain nano-cerium dioxide.

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