Preparation method of small-particle doped cobalt tetroxide material

Abstract

The present invention relates to a preparation method of a small particle doped cobalt tetroxide material, belonging to the technical field of cobalt tetroxide. First, thionyl chloride is used to halogenate methoxypolyethylene glycol to obtain methoxypolyethylene glycol with terminal hydroxyl groups replaced by chlorine atoms. Then, N-vinylimidazole is added, and an ionic liquid containing double bonds is prepared through the action of chlorine atoms and -N=. Next, acrylamide is added for double bond polymerization to obtain a water-soluble polymeric ionic liquid with an amino repeating unit at one end and an ether bond repeating unit at the other end. When it is compounded with cetyltrimethylammonium bromide and undergoes a hydrothermal reaction with deionized water as the solvent, urea as the precipitant, cobalt nitrate hexahydrate as the cobalt source, and in the presence of a dopant, it can exert an excellent dispersing effect on the precursor, and also greatly reduces the interaction force between particles during aging. Finally, the prepared doped cobalt tetroxide material not only has a small particle size but also reduces agglomeration.

Description

Technical Field

[0001] The invention belongs to the technical field of cobalt tetroxide, and in particular relates to a method for preparing a small-particle doped cobalt tetroxide material. Background Art

[0002] Cobalt tetroxide is an inorganic particle in the form of a black or gray-black powder with the chemical formula Co3O4. It is widely used in photocatalysis, batteries, energy, gas sensing and other fields due to its many excellent characteristics such as low band gap energy, high energy storage efficiency and good stability. A large number of studies have shown that compared with pure cobalt tetroxide, cobalt tetroxide materials doped with other metal elements can often exhibit better performance. For example, doping with chromium can enhance catalytic performance, and doping with tin can increase capacitance. Among them, the preparation method of doped cobalt tetroxide materials usually adopts liquid phase precipitation method. The particle size of the doped particles is small and can reach nanometer scale. However, this leads to the fact that the doped cobalt tetroxide materials prepared by liquid phase precipitation method still have certain disadvantages that limit their actual technical effects. This is because the smaller the size of the doped particles, the more obvious the agglomeration problem will be, which will seriously restrict the subsequent performance improvement when used in various fields. Summary of the Invention

[0003] In response to the problems existing in the prior art, the present invention aims to provide a method for preparing a small-particle doped cobalt oxide material. The method comprises the following steps: first, halogen-modifying polyethylene glycol monomethyl ether with thionyl chloride to obtain polyethylene glycol monomethyl ether in which the terminal hydroxyl groups are replaced by chlorine atoms; then, adding N-vinylimidazole to prepare an ionic liquid containing a double bond through the action of the chlorine atoms and -N=; then, adding acrylamide to polymerize the double bonds to obtain a water-soluble polymerized ionic liquid having an amino repeating unit at one end and an ether repeating unit at the other end; and then compounding the liquid with hexadecyltrimethylammonium bromide. When a hydrothermal reaction is carried out in the presence of deionized water as a solvent, urea as a precipitant, and cobalt nitrate hexahydrate as a cobalt source, the liquid can exhibit an excellent dispersing effect on the precursor, and the interaction between particles is greatly reduced during aging. Ultimately, the prepared doped cobalt oxide material has a small particle size and reduced agglomeration.

[0004] The purpose of the present invention can be achieved through the following technical solutions:

[0005] A method for preparing a small particle doped cobalt oxide material, the method comprising the following steps:

[0006] (1) adding cobalt nitrate hexahydrate, urea, hexadecyltrimethylammonium bromide and a water-soluble polymeric ionic liquid to deionized water, and then stirring and mixing at room temperature for 5-10 minutes to obtain material A;

[0007] (2) Add a dopant to the material A and conduct a hydrothermal reaction to obtain material B;

[0008] (3) Naturally cool the material B to room temperature under normal temperature and pressure, then age it for 1 - 1.5 h, filter, remove the filtrate, wash it with deionized water, and dry it to obtain material C;

[0009] (4) Heat up the material C and then calcine it to complete the preparation.

[0010] As a preferred technical solution of the present invention, the mass ratio of the deionized water, cobalt nitrate hexahydrate, urea, cetyltrimethylammonium bromide, and the water-soluble polymeric ionic liquid in step (1) is 80:2 - 3:5:0.5:1 - 1.5.

[0011] As a preferred technical solution of the present invention, the water-soluble polymeric ionic liquid in step (1) is prepared through the following steps:

[0012] Step A: Add 8 - 10 parts by weight of polyethylene glycol monomethyl ether and 2 - 2.5 parts by weight of pyridine to 80 - 100 parts by weight of toluene, then dropwise add 4 - 5 parts by weight of thionyl chloride dropwise with stirring in an ice bath under an argon atmosphere. After the dropping is completed, raise the temperature to 100 - 110 °C, then keep stirring for 48 h, naturally cool to room temperature, and remove impurities to obtain component A;

[0013] Step B: Stir 4 - 5 parts by weight of component A and 1 part by weight of N-vinylimidazole at 90 - 100 °C for 24 - 26 h under an argon atmosphere, then wash it alternately with ethyl acetate and diethyl ether 2 - 3 times, and finally vacuum dry it at 50 - 70 °C until constant weight to obtain component B;

[0014] Step C: Add 15 - 20 parts by weight of deionized water to 40 parts by weight of tetrahydrofuran, then stir and mix at room temperature for 5 - 10 min, then add 4 - 5 parts by weight of component B, 1 - 1.5 parts by weight of acrylamide, and 0.1 - 0.2 parts by weight of potassium persulfate, and finally stir at 60 - 65 °C for 4 - 6 h, carry out reduced pressure distillation, filter, and remove the insoluble matter to complete the preparation.

[0015] Furthermore, the polyethylene glycol monomethyl ether in step A is at least one of polyethylene glycol monomethyl ether 350 and polyethylene glycol monomethyl ether 600.

[0016] Furthermore, the dropping rate in step A is controlled at 1 - 3 drops / s.

[0017] Furthermore, the heating rate in step A is controlled at 3 - 5 °C / min.

[0018] Further, the impurity removal in step A means collecting the upper liquid, then adding an aqueous solution of sodium bicarbonate saturated at room temperature in an amount of 2.5% by volume, stirring for 5 - 10 min for mixing, then adding 40 - 50 parts by weight of dichloromethane, shaking 5 - 7 times, standing for 5 - 10 min, taking the lower liquid, distilling at 40°C until all volatiles are completely removed, washing with deionized water, and finally drying in vacuo at 50 - 70°C until constant weight.

[0019] Further, the reduced-pressure distillation in step C means distilling at 50°C under a vacuum degree of -0.06 MPa until all volatiles are completely removed.

[0020] As a preferred technical solution of the present invention, the mass ratio of cobalt nitrate hexahydrate in step (1) to the dopant in step (2) is 1:0.005 - 0.01; the dopant in step (2) is one of potassium nitrate, iron nitrate, magnesium nitrate, lithium nitrate, and nickel nitrate.

[0021] As a preferred technical solution of the present invention, the reaction conditions of the hydrothermal reaction in step (2) are a pressure of 25 - 28 kPa, a temperature of 100 - 105°C, and a time of 10 - 12 h.

[0022] As a preferred technical solution of the present invention, the drying in step (3) means drying in vacuo at 105°C until constant weight.

[0023] As a preferred technical solution of the present invention, the calcination after heating in step (4) means heating at a heating rate of 8 - 10°C / min in an oxygen atmosphere to 350 - 400°C and then calcining for 3 - 3.5 h.

[0024] Advantages of the present invention:

[0025] (1) In the present invention, thionyl chloride is first used to halogenate polyethylene glycol monomethyl ether to obtain polyethylene glycol monomethyl ether with the terminal hydroxyl group replaced by a chlorine atom, then N-vinylimidazole is added, and an ionic liquid containing a double bond is prepared through the action of the chlorine atom and -N=, and then acrylamide is added for double bond polymerization to obtain a water-soluble polymeric ionic liquid with an amino repeating unit at one end and an ether bond repeating unit at the other end. When it is compounded with cetyltrimethylammonium bromide and undergoes a hydrothermal reaction in the presence of deionized water as a solvent, urea as a precipitant, cobalt nitrate hexahydrate as a cobalt source, and a dopant, it can exert an excellent dispersing effect on the precursor, and also greatly reduces the intermolecular force during aging. Finally, the prepared cobalt tetroxide doped material not only has a small particle size but also reduces aggregation.

[0026] (2) On the basis of not changing that deionized water is mostly used as the solvent for preparing the precursor in the existing liquid phase precipitation method, the present invention creatively prepares a water-soluble polymeric ionic liquid, which can produce an excellent synergistic effect when compounded with cetyltrimethylammonium bromide and dissolved in deionized water, and jointly play a role in dispersing the precursor. On the one hand, the addition of the water-soluble polymeric ionic liquid can disperse the precursor by reducing the surface tension of the whole system. On the other hand, due to the existence of a certain degree of polymerization structure, it has stronger hydrogen bond interactions and a large number of hydrogen bond networks, which can "cover" the surface of the precursor in the system and hinder the occurrence of agglomeration. Especially during the aging process, it can greatly reduce the mutual force between particles during growth, thereby reducing the agglomeration situation. At the same time, compared with directly using ionic liquid to replace deionized water as the solvent in the existing technology, the water-soluble polymeric ionic liquid of the present invention has stronger universality and is added to the system in the form of an auxiliary agent, without considering the solubility problems of other substances such as cobalt source and dopant in it. Detailed implementation mode

[0027] To further elaborate on the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following combines examples to elaborate in detail on the specific implementation mode, structure, characteristics and effects of the present invention.

[0028] Example 1

[0029] A preparation method of a small particle doped cobalt ferrite material, the preparation method comprising the following steps:

[0030] (1) Add cobalt nitrate hexahydrate, urea, cetyltrimethylammonium bromide and water-soluble polymeric ionic liquid to deionized water, and then stir and mix at room temperature for 5 min to obtain material A;

[0031] (2) Add a dopant to the material A and perform a hydrothermal reaction to obtain material B;

[0032] (3) Naturally cool the material B to room temperature at normal temperature and pressure, then age for 1 h, filter, remove the filtrate, wash with deionized water, and dry to obtain material C;

[0033] (4) Heat up the material C and calcine it to complete the preparation.

[0034] The mass ratio of the deionized water, the cobalt nitrate hexahydrate, the urea, the cetyltrimethylammonium bromide and the water-soluble polymeric ionic liquid in step (1) is 80:2:5:0.5:1.

[0035] The water-soluble polymeric ionic liquid in step (1) is prepared by the following steps:

[0036] Step A: Add 8 parts by weight of polyethylene glycol monomethyl ether and 2 parts by weight of pyridine to 80 parts by weight of toluene, and then dropwise add 4 parts by weight of thionyl chloride while stirring in an ice bath under an argon atmosphere. After the addition is complete, raise the temperature to 100 °C, then keep stirring for 48 h, naturally cool to room temperature, and remove impurities to obtain Component A;

[0037] Step B: Stir 4 parts by weight of Component A and 1 part by weight of N-vinylimidazole at 90 °C for 24 h under an argon atmosphere, then wash twice alternately with ethyl acetate and diethyl ether, and finally dry under vacuum at 50 °C until a constant weight is obtained to obtain Component B;

[0038] Step C: Add 15 parts by weight of deionized water to 40 parts by weight of tetrahydrofuran, then stir and mix at room temperature for 5 min, then add 4 parts by weight of Component B, 1 part by weight of acrylamide, and 0.1 part by weight of potassium persulfate, and finally stir at 60 °C for 4 h, carry out reduced-pressure distillation, filter, and remove insoluble substances, thus the preparation is completed.

[0039] The polyethylene glycol monomethyl ether described in Step A is polyethylene glycol monomethyl ether 350.

[0040] The dropping rate described in Step A is controlled at 1 drop / s.

[0041] The heating rate described in Step A is controlled at 3 °C / min.

[0042] The impurity removal described in Step A means collecting the upper layer liquid, then adding saturated sodium bicarbonate aqueous solution at room temperature according to 2.5% by volume, stirring and mixing for 5 min, then adding 40 parts by weight of dichloromethane, shaking 5 times, standing for 5 min, taking the lower layer liquid, distilling at 40 °C until all volatiles are completely removed, washing with deionized water, and finally drying under vacuum at 50 °C until a constant weight is obtained.

[0043] The reduced-pressure distillation described in Step C means distilling at 50 °C under a vacuum degree of -0.06 MPa until all volatiles are completely removed.

[0044] The mass ratio of cobalt nitrate hexahydrate described in Step (1) to the dopant described in Step (2) is 1:0.005; the dopant described in Step (2) is potassium nitrate.

[0045] The reaction conditions of the hydrothermal reaction described in Step (2) are a pressure of 25 kPa, a temperature of 100 °C, and a time of 10 h.

[0046] The drying described in Step (3) means drying under vacuum at 105 °C until a constant weight is obtained.

[0047] The calcination after heating described in Step (4) means heating to 350 °C at a heating rate of 8 °C / min in an oxygen atmosphere and then calcining for 3 h.

[0048] Example 2

[0049] A preparation method of a small particle doped cobalt tetroxide material, the preparation method comprising the following steps:

[0050] (1) Add cobalt nitrate hexahydrate, urea, cetyltrimethylammonium bromide and water-soluble polymeric ionic liquid to deionized water, and then stir and mix at room temperature for 10 min to obtain material A;

[0051] (2) Add a dopant to the material A, and carry out a hydrothermal reaction to obtain material B;

[0052] (3) Naturally cool the material B to room temperature under normal temperature and pressure, then age for 1.5 h, filter, remove the filtrate, wash with deionized water, and dry to obtain material C;

[0053] (4) Heat up the material C and then calcine it to complete the preparation.

[0054] The mass ratio of the deionized water, the cobalt nitrate hexahydrate, the urea, the cetyltrimethylammonium bromide and the water-soluble polymeric ionic liquid in step (1) is 80:3:5:0.5:1.5.

[0055] The water-soluble polymeric ionic liquid in step (1) is prepared by the following steps:

[0056] Step A: Add 10 parts by weight of polyethylene glycol monomethyl ether and 2.5 parts by weight of pyridine to 100 parts by weight of toluene, then dropwise add 5 parts by weight of thionyl chloride while stirring in an ice bath under an argon atmosphere. After the dropping is completed, heat up to 110 °C, then keep stirring for 48 h, naturally cool to room temperature, and remove impurities to obtain component A;

[0057] Step B: Stir 5 parts by weight of component A and 1 part by weight of N-vinylimidazole at 100 °C under an argon atmosphere for 26 h, then wash alternately with ethyl acetate and diethyl ether 3 times, and finally vacuum dry at 70 °C until constant weight to obtain component B;

[0058] [[ID=3º]]Step C: Add 20 parts by weight of deionized water to 40 parts by weight of tetrahydrofuran, then stir and mix at room temperature for 10 min, then add 5 parts by weight of component B, 1.5 parts by weight of acrylamide and 0.2 parts by weight of potassium persulfate, and finally stir at 65 °C for 6 h, carry out reduced pressure distillation, filter, and remove insoluble substances to complete the preparation.

[0059] The polyethylene glycol monomethyl ether in step A is polyethylene glycol monomethyl ether 350.

[0060] The dropping rate in step A is controlled at 3 drops / s.

[0061] The heating rate in Step A is controlled at 5 °C / min.

[0062] The impurity removal in Step A means collecting the upper liquid, then adding an aqueous solution of sodium bicarbonate saturated at room temperature in an amount of 2.5% by volume, stirring for 10 min for mixing, then adding 50 parts by weight of dichloromethane, shaking 7 times, standing for 10 min, taking the lower liquid, distilling at 40 °C until all volatiles are completely removed, washing with deionized water, and finally drying under vacuum at 70 °C until a constant weight is achieved.

[0063] The vacuum distillation in Step C means distilling at 50 °C under a vacuum degree of -0.06 MPa until all volatiles are completely removed.

[0064] The mass ratio of cobalt nitrate hexahydrate in Step (1) to the dopant in Step (2) is 1:0.01; the dopant in Step (2) is potassium nitrate.

[0065] The reaction conditions for the hydrothermal reaction in Step (2) are a pressure of 28 kPa, a temperature of 105 °C, and a time of 12 h.

[0066] The drying in Step (3) means drying under vacuum at 105 °C until a constant weight is achieved.

[0067] The calcination after heating in Step (4) means heating at a heating rate of 10 °C / min in an oxygen atmosphere to 400 °C and then calcining for 3.5 h.

[0068] Example 3

[0069] A preparation method of a small particle doped cobalt tetroxide material, the preparation method comprising the following steps:

[0070] (1) Add cobalt nitrate hexahydrate, urea, cetyltrimethylammonium bromide, and a water-soluble polymeric ionic liquid to deionized water, and then stir at room temperature for 8 min for mixing to obtain Material A;

[0071] (2) Add a dopant to the Material A and perform a hydrothermal reaction to obtain Material B;

[0072] (3) Naturally cool the Material B to room temperature at normal temperature and pressure, age for 1.3 h, filter, remove the filtrate, wash with deionized water, and dry to obtain Material C;

[0073] (4) Heat the Material C and then calcine to complete the preparation.

[0074] The mass ratio of the deionized water, the cobalt nitrate hexahydrate, the urea, the cetyltrimethylammonium bromide, and the water-soluble polymeric ionic liquid in Step (1) is 80:2.5:5:0.5:1.3.

[0075] The water-soluble polymeric ionic liquid described in step (1) is prepared through the following steps:

[0076] Step A: Add 9 parts by weight of polyethylene glycol monomethyl ether and 2.3 parts by weight of pyridine to 90 parts by weight of toluene, then dropwise add 4.5 parts by weight of thionyl chloride dropwise with stirring in an ice bath under an argon atmosphere. After the addition is completed, raise the temperature to 105 °C, then keep stirring for 48 h, cool naturally to room temperature, remove impurities, and obtain component A;

[0077] Step B: Stir 4.5 parts by weight of component A and 1 part by weight of N-vinylimidazole at 95 °C for 25 h under an argon atmosphere, then wash alternately with ethyl acetate and diethyl ether 3 times in sequence, and finally dry in vacuo at 60 °C until a constant weight is obtained to obtain component B;

[0078] Step C: Add 18 parts by weight of deionized water to 40 parts by weight of tetrahydrofuran, then stir and mix at room temperature for 8 min, then add 4.5 parts by weight of component B, 1.3 parts by weight of acrylamide, and 0.15 parts by weight of potassium persulfate. Finally, stir at 63 °C for 5 h, carry out vacuum distillation, filter, and remove insoluble substances, and the preparation is completed.

[0079] The polyethylene glycol monomethyl ether described in step A is polyethylene glycol monomethyl ether 350.

[0080] The dropping rate described in step A is controlled at 2 drops / s.

[0081] The heating rate described in step A is controlled at 4 °C / min.

[0082] The impurity removal described in step A means collecting the upper layer liquid, then adding saturated sodium bicarbonate aqueous solution at room temperature by 2.5% of the volume, stirring and mixing for 8 min, then adding 45 parts by weight of dichloromethane, shaking 6 times, standing for 8 min, taking the lower layer liquid, distilling at 40 °C until all volatiles are completely removed, washing with deionized water, and finally drying in vacuo at 60 °C until a constant weight is obtained.

[0083] The vacuum distillation described in step C means distilling at 50 °C under a vacuum degree of -0.06 MPa until all volatiles are completely removed.

[0084] The mass ratio of cobalt nitrate hexahydrate described in step (1) to the dopant described in step (2) is 1:0.008; the dopant described in step (2) is potassium nitrate.

[0085] The reaction conditions of the hydrothermal reaction described in step (2) are a pressure of 26 kPa, a temperature of 103 °C, and a time of 11 h.

[0086] The drying described in step (3) means drying in vacuo at 105 °C until a constant weight is obtained.

[0087] The post - heating calcination described in step (4) means heating to 380 °C at a heating rate of 9 °C / min in an oxygen atmosphere and then calcining for 3.2 h.

[0088] Comparative Example 1

[0089] Based on Example 1, cetyltrimethylammonium bromide was replaced with an equal weight of water - soluble polymeric ionic liquid, and the rest remained unchanged.

[0090] Comparative Example 2

[0091] Based on Example 1, the water - soluble polymeric ionic liquid was replaced with an equal weight of cetyltrimethylammonium bromide, and the rest remained unchanged.

[0092] Comparative Example 3

[0093] Based on Example 1, in step (1), neither cetyltrimethylammonium bromide nor water - soluble polymeric ionic liquid was added, and they were added after the hydrothermal reaction in step (2) ended, and the rest remained unchanged.

[0094] Comparative Example 4

[0095] Based on Example 1, cetyltrimethylammonium bromide was replaced with an equal weight of water - soluble polymeric ionic liquid. At the same time, in step (1), the water - soluble polymeric ionic liquid was not added and was added after the hydrothermal reaction in step (2) ended, and the rest remained unchanged.

[0096] Comparative Example 5

[0097] Based on Example 1, the water - soluble polymeric ionic liquid was replaced with an equal weight of cetyltrimethylammonium bromide. At the same time, in step (1), cetyltrimethylammonium bromide was not added and was added after the hydrothermal reaction in step (2) ended, and the rest remained unchanged.

[0098] Comparative Example 6

[0099] Based on Example 1, in step C, 1 part by weight of acrylamide was changed to 0.6 part by weight of acrylamide, and the rest remained unchanged.

[0100] Comparative Example 7

[0101] Based on Example 1, both cetyltrimethylammonium bromide and water - soluble polymeric ionic liquid were replaced with an equal weight of deionized water, and the rest remained unchanged.

[0102] Test Example 1

[0103] Performance test:

[0104] The sensitivity tests were carried out on the small particle-doped cobalt tetroxide materials prepared in Examples 1-3 and Comparative Examples 1-7 using a CGS-MT type intelligent gas sensing test system. The sensitivity = R1 / R0, where R1 is the resistance value of the sensor in the response gas and R0 is the resistance value of the sensor in the air.

[0105] Table 1. Performance test results

[0106]

[0107]

[0108] Comparing Example 1 with Comparative Examples 1-7 shows that:

[0109] The difference between Comparative Example 1 and Example 1 is that cetyltrimethylammonium bromide is replaced with a water-soluble polymeric ionic liquid of equal weight.

[0110] The difference between Comparative Example 2 and Example 1 is that the water-soluble polymeric ionic liquid is replaced with cetyltrimethylammonium bromide of equal weight.

[0111] The difference between Comparative Example 3 and Example 1 is that cetyltrimethylammonium bromide and the water-soluble polymeric ionic liquid are added after the hydrothermal reaction ends.

[0112] The difference between Comparative Example 4 and Example 1 is that cetyltrimethylammonium bromide is replaced with a water-soluble polymeric ionic liquid of equal weight, and at the same time, the water-soluble polymeric ionic liquid is added after the hydrothermal reaction ends.

[0113] The difference between Comparative Example 5 and Example 1 is that the water-soluble polymeric ionic liquid is replaced with cetyltrimethylammonium bromide of equal weight, and at the same time, cetyltrimethylammonium bromide is added after the hydrothermal reaction ends.

[0114] The difference between Comparative Example 6 and Example 1 is that the number of amino repeating units in the water-soluble polymeric ionic liquid is reduced.

[0115] The difference between Comparative Example 7 and Example 1 is that both cetyltrimethylammonium bromide and the water-soluble polymeric ionic liquid are replaced with deionized water of equal weight.

[0116] From Test Example 1, comparing Example 1 with Comparative Examples 1-7 shows that the small particle-doped cobalt tetroxide material prepared by the present invention has more excellent performance, indicating that the agglomeration situation is relatively less, and correspondingly, the obtained technical effect is better.

[0117] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Although the present invention has been disclosed above with the preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to equivalent embodiments of equivalent changes within the scope of the technical solution of the present invention by using the technical content disclosed above. However, as long as it does not depart from the content of the technical solution of the present invention, any brief modifications, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A preparation method of a small particle-doped cobalt tetroxide material, characterized in that: The preparation method comprises the following steps: (1) Cobalt nitrate hexahydrate, urea, cetyltrimethylammonium bromide and a water-soluble polymeric ionic liquid are added to deionized water, and then stirred at room temperature for 5 - 10 min for mixing to obtain material A; (2) A dopant is added to the material A, and hydrothermal reaction is carried out to obtain material B; (3) The material B is naturally cooled to room temperature at normal temperature and pressure and then aged for 1 - 1.5 h, filtered, the filtrate is removed, washed with deionized water, and dried to obtain material C; (4) The material C is heated and then calcined to complete the preparation; Among them, the water-soluble polymeric ionic liquid in step (1) is prepared by the following steps: Step A: 8 - 10 parts by weight of polyethylene glycol monomethyl ether and 2 - 2.5 parts by weight of pyridine are added to 80 - 100 parts by weight of toluene, and then 4 - 5 parts by weight of thionyl chloride are added dropwise with stirring in an ice bath under an argon atmosphere. After the addition is completed, the temperature is raised to 100 - 110 °C, and then stirred for 48 h while keeping warm, and naturally cooled to room temperature for impurity removal to obtain component A; Step B: 4 - 5 parts by weight of component A and 1 part by weight of N-vinylimidazole are stirred at 90 - 100 °C for 24 - 26 h under an argon atmosphere, and then washed alternately with ethyl acetate and diethyl ether for 2 - 3 times, and finally vacuum dried at 50 - 70 °C until constant weight to obtain component B; Step C: 15 - 20 parts by weight of deionized water are added to 40 parts by weight of tetrahydrofuran, and then stirred at room temperature for 5 - 10 min for mixing, and then 4 - 5 parts by weight of component B, 1 - 1.5 parts by weight of acrylamide and 0.1 - 0.2 parts by weight of potassium persulfate are added. Finally, stirred at 60 - 65 °C for 4 - 6 h, subjected to reduced pressure distillation, filtered, and the insoluble matters are removed to complete the preparation.

2. The preparation method of a small particle doped cobalt tetroxide material according to claim 1, characterized in that: The mass ratio of the deionized water, the cobalt nitrate hexahydrate, the urea, the cetyltrimethylammonium bromide and the water-soluble polymeric ionic liquid in step (1) is 80:2 - 3:5:0.5:1 - 1.

5.

3. The preparation method of a small particle doped cobalt tetroxide material according to claim 1, characterized in that: The polyethylene glycol monomethyl ether in step A is at least one of polyethylene glycol monomethyl ether 350 and polyethylene glycol monomethyl ether 600.

4. The preparation method of a small-particle doped cobalt tetroxide material according to claim 1, characterized in that: The impurity removal in step A means collecting the upper layer liquid, then adding 2.5% by volume of saturated sodium bicarbonate aqueous solution at room temperature, stirring for 5 - 10 min for mixing, then adding 40 - 50 parts by weight of dichloromethane, shaking 5 - 7 times, standing for 5 - 10 min, taking the lower layer liquid, distilling at 40 °C until all volatiles are completely removed, washing with deionized water, and finally vacuum drying at 50 - 70 °C until constant weight.

5. The preparation method of a small-particle doped cobalt tetroxide material according to claim 1, wherein: The reduced pressure distillation in step C means distilling at 50 °C under a vacuum degree of -0.06 MPa until all volatiles are completely removed.

6. The preparation method of a small particle doped cobalt tetroxide material according to claim 1, characterized in that: The mass ratio of the cobalt nitrate hexahydrate in step (1) to the dopant in step (2) is 1:0.005 - 0.01; the dopant in step (2) is one of potassium nitrate, iron nitrate, magnesium nitrate, lithium nitrate and nickel nitrate.

7. The preparation method of a small particle doped cobalt tetroxide material according to claim 1, characterized in that: The reaction conditions of the hydrothermal reaction in step (2) are a pressure of 25 - 28 kPa, a temperature of 100 - 105 °C, and a time of 10 - 12 h.

8. The preparation method of a small-particle doped cobalt tetroxide material according to claim 1, characterized in that: The drying described in step (3) means vacuum drying at 105°C until constant weight is achieved.

9. The preparation method of a small-particle doped cobalt tetroxide material according to claim 1, wherein: The calcination after heating described in step (4) means heating to 350 - 400°C at a heating rate of 8 - 10°C / min in an oxygen atmosphere and then calcining for 3 - 3.5 h.

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