Cerium oxide precursor sol spinning solution and preparation method of cerium oxide fiber membrane

Abstract

The invention relates to a cerium oxide precursor sol spinning solution and a preparation method of a cerium oxide fiber membrane. The method comprises the steps of synthesis of a cerium oxide precursor, preparation of sol, electrostatic spinning and heat treatment. Anhydrous cerium chloride and basic cerium carbonate are used as cerium sources, an oxidation-reduction reaction is innovatively adopted to promote dissolution coordination of cerium so as to synthesize a high-quality precursor, then the prepared precursor and an alcohol solvent are mixed according to a certain proportion, a trace amount of a spinning auxiliary agent is added, and the cerium oxide fiber membrane with excellent performance can be obtained through electrostatic spinning and heat treatment. The method has the advantages that the precursor synthesis process is controllable, high-quality fibers can be rapidly prepared, and industrial production and application are facilitated. The cerium oxide fiber membrane has potential application in the aspects of thermal radiation resistance, thermal insulation, photocatalysis and the like.

Description

Technical Field

[0001] The present invention relates to a preparation method of a cerium oxide precursor sol spinning solution and a cerium oxide fiber membrane, belonging to the technical field of nano-functional materials. Background Art

[0002] Cerium oxide (CeO2), as an important lanthanide rare earth oxide, has unique physical and chemical properties and broad application prospects. Cerium oxide has a fluorite-type structure, which is a fluorescent crystal structure, making it important in many fields.

[0003] Excellent oxygen storage capacity: Cerium oxide has excellent oxygen storage and release properties due to its oxygen vacancies, which makes it widely used in fields such as fuel cells. Excellent thermal stability: Cerium oxide exists stably in a single fluorite crystal phase, with an extremely high melting point (2397 °C) and high heat resistance. Good electrochemical properties: The excellent electrochemical performance of cerium oxide makes it an ideal electrode material for applications such as lithium-ion batteries, electrochemical sensors, electrocatalysis, and supercapacitors. Due to these properties, CeO2 exhibits multi-enzyme mimicking activity in fields such as three-way catalysts for automotive exhaust treatment, oxygen storage materials, photocatalysts, and sensor materials, becoming a promising material. And cerium oxide plays an increasingly important role in industrial and scientific research fields due to its unique properties and functions.

[0004] Compared with nano-powders, one-dimensional nano-fibers have the following advantages: self-supporting, non-agglomerating, higher specific surface area and porosity, better filtration performance, higher thermal stability and heat resistance, lightweight, high strength, and super flexibility.

[0005] In summary, nanofibers have many unique advantages compared to nanometer powders, making them potentially superior in many application fields. Currently, there are very few reports on cerium oxide precursors. The prepared cerium oxide fibers are basically made from cerium chloride heptahydrate and then a large amount of spinning aids (such as PVP) are added, and then spinning is carried out. Since the inorganic salts of cerium itself do not have spinnability, and the precursor fibers are extremely hygroscopic in air, it will have a great impact on the properties of the fibers. In the applicant's previous literature CN 111187424A, a lanthanide rare earth-organic polymer precursor, lanthanide rare earth oxide fibers, and their preparation methods and applications, using lanthanide crystalline chlorides and anhydrous chlorides as lanthanum sources, and using one or several of β-diketones such as acetylacetone, ethyl acetoacetate, and methyl acetoacetate as ligands, triethylamine as a dechlorinating agent, and acetone or a mixture of tetrahydrofuran as an extractant, the precursor is prepared and then the precursor fibers are prepared by electrospinning, and then the lanthanide oxide fibers are obtained by high-temperature sintering. However, for cerium sources, although the corresponding precursors can be obtained, through in-depth research, it is found that this process does not consider the dissolution process and the influence of water in the raw materials. Among them, anhydrous cerium chloride is insoluble in methanol, while cerium chloride heptahydrate has a very high water content. The relative molecular mass of cerium chloride heptahydrate is 372.6, and its water content is 126.1, accounting for more than 1 / 3 of the relative molecular mass. Moreover, rare earth chlorides are extremely hygroscopic, which leads to difficult control of the hydrolysis and polycondensation process. Precipitation will inevitably occur in the precursor, which will affect the degree of polymerization and purity, and the electron transport efficiency of the obtained cerium oxide fibers is relatively reduced, and the catalytic activity needs to be further improved.

[0006] Surprisingly, in subsequent experiments, it was found that since cerium itself has two valence states, Ce 3+ and Ce 4+ and they can be mutually transformed. When trying to dissolve anhydrous cerium chloride in methanol, after vigorous heating and stirring, the white methanol suspension of undissolved cerium chloride will turn into a pale yellow suspension. At this time, adding a small amount of water can dissolve it and subsequent synthesis steps can be carried out. This may be due to oxygen in the air converting Ce 3+ to Ce 4+ . At the same time, the applicant was pleasantly surprised to find that after the valence transformation, the conversion rate of the raw materials is higher, and it is easier to synthesize and obtain high-quality precursors. After that, by precisely controlling the use of oxidants and the influence of water in the precursor synthesis process, high-quality precursors can be quickly prepared. Therefore, inducing the valence change of cerium elements is the key to synthesizing high-quality cerium precursors.

[0007] Currently, there are at least the following two problems in the work of preparing cerium oxide nanofibers by electrospinning technology: one is that the solid content of the precursor fibers is not high and the preparation efficiency is low; the other is that the mechanical properties of the obtained fibers are poor. They only have the morphology of one-dimensional fibers, but do not exhibit the excellent properties of one-dimensional fibers themselves.

[0008] Based on this, obtaining high-quality precursors to achieve rapid and efficient preparation of cerium oxide fibers is a major problem to be solved. At the same time, whether the fibers have excellent mechanical properties has also become a major problem to be solved. Summary of the Invention

[0009] Aiming at the deficiencies of the prior art, the present invention provides a class of cerium oxide precursor sol spinning solutions and a preparation method of cerium oxide fibers.

[0010] The present invention obtains high-quality cerium oxide precursors through valence regulation and ligand design, and combines sol-gel and electrospinning to prepare cerium oxide fiber membranes with high quality and excellent properties.

[0011] Term Explanation:

[0012] Cerium chloride heptahydrate (CeCl3·7H2O) relative molecular mass: 372.6

[0013] Anhydrous cerium chloride (CeCl3) relative molecular mass: 246.5

[0014] Hydrogen peroxide solution: An aqueous solution of hydrogen peroxide (H2O2). The hydrogen peroxide solution used in the present invention is a hydrogen peroxide solution with a mass concentration of 30 wt%.

[0015] Effective solid content of CeO2: Refers to the mass ratio of CeO2 transformed from the precursor fiber membrane after heat treatment.

[0016] Molar ratio of hydrogen peroxide: Calculated based on the recalculated average relative molecular mass of hydrogen peroxide.

[0017] The technical solution of the present invention is as follows:

[0018] A preparation method of a class of cerium oxide precursor sol spinning solutions, including the following steps:

[0019] (1) Using anhydrous cerium chloride or basic cerium carbonate as a cerium source, adding it to an alcohol solvent, heating and stirring to react, slowly adding an oxidant to carry out an oxidation-reduction reaction to make Ce 3+ To Ce 4+ Undergo a transformation, and then adding a ligand source to carry out a coordination reaction to obtain a cerium oxide precursor;

[0020] (2) Dissolving the cerium oxide precursor in an alcohol solvent, adding a spinning aid, stirring and dissolving, and aging to obtain a uniform cerium oxide sol spinning solution.

[0021] According to the preference of the present invention, in step (1), the alcohol solvent is one or more of methanol, ethanol, and isopropanol.

[0022] According to the preference of the present invention, in step (1), the heating and stirring reaction temperature is 30-90 °C.

[0023] Preferably according to the present invention, in step (1), the oxidant is selected from chlorine gas (Cl2), potassium permanganate (KMnO4), dry air (O2), pure oxygen (O2), ozone (O3), hydrogen peroxide (H2O2) or chlorine dioxide (ClO2).

[0024] More preferably, in step (1), the oxidant is selected from dry air (O2), pure oxygen (O2), ozone (O3) or hydrogen peroxide (H2O2).

[0025] Preferably according to the present invention, the addition condition of the oxidant in step (1): The reaction system is stirred for 12 - 32 h at a temperature of 30 - 90 °C and then added. The undissolved white suspension turns into a light yellow suspension. In addition, water is added to the system as a cosolvent and ligand source to promote the dissolution and coordination of anhydrous cerium chloride. The molar ratio of cerium source to water = 1:1 - 10, and then the ligand source is added for the coordination reaction.

[0026] More preferably, in step (1), the molar ratio of cerium source to water = 1:1.1 - 3.

[0027] The oxidant introduced in the present invention undergoes an oxidation-reduction reaction to promote the dissolution and coordination of anhydrous cerium chloride to prepare the precursor. The change of the undissolved white suspension into a light yellow suspension indicates that Ce 3+ To Ce 4+ Undergoes a transformation.

[0028] Preferably according to the present invention, in step (1), the addition condition of hydrogen peroxide as the oxidant: The reaction system is heated and stirred at a temperature of 30 - 90 °C, and then hydrogen peroxide is added. The molar ratio of cerium source to hydrogen peroxide = 1:1 - 7. After obtaining a transparent solution, the ligand source is added for coordination without adding water.

[0029] More preferably, in step (1), the molar ratio of cerium source to hydrogen peroxide = 1:1.3 - 5.

[0030] Preferably according to the present invention, in step (1), using hydrogen peroxide as the oxidant can not only carry out the oxidation-reduction reaction, but also the H2O after the reaction can be directly used as a cosolvent and ligand source, greatly shortening the time required for the dissolution reaction.

[0031] The present invention prepares the precursor by introducing an oxidant and making full use of the four major chemical equilibria (oxidation-reduction equilibrium, coordination equilibrium, acid-base equilibrium, precipitation-dissolution equilibrium) to promote the dissolution and coordination of anhydrous cerium chloride, obtaining a precursor with extremely stable structure and excellent spinnability.

[0032] Preferred embodiment of using anhydrous cerium chloride as the cerium source:

[0033] Preferably according to the present invention, in step (1), when anhydrous cerium chloride is used as the cerium source, the ligand source is a β-diketone compound or a carboxylate salt.

[0034] Preferably according to the present invention, in step (1), the β-diketone compound ligand source is selected from one or more mixtures of acetylacetone, methyl acetoacetate, ethyl acetoacetate, propyl acetoacetate, isopropyl acetoacetate, and butyl acetoacetate.

[0035] More preferably, in step (1), the β-diketone compound ligand source is acetylacetone.

[0036] Preferably according to the present invention, in step (1), the carboxylate salt ligand source is selected from one or more mixtures of potassium acetate, sodium acetate, potassium propionate, sodium propionate, potassium oxalate, and sodium oxalate.

[0037] More preferably, in step (1), the carboxylate salt ligand source is potassium acetate.

[0038] Preferably according to the present invention, in step (1), when a β-diketone compound is used as the ligand source, the β-diketone compound ligand source and the dechlorinating agent are respectively added to the transparent solution formed by introducing an oxidant, stirred and reacted for 0.5 to 4 h, the supernatant is taken and concentrated under reduced pressure until dry, the dry powder is taken and soaked in an extractant for 12 to 72 h and then filtered, and the obtained supernatant is concentrated under reduced pressure to form a powder to obtain a cerium oxide precursor.

[0039] Preferably according to the present invention, the molar ratio of anhydrous cerium chloride:β-diketone compound ligand source = 1:0.8 to 4.

[0040] Preferably according to the present invention, the dechlorinating agent is one or more mixtures of triethylamine, ethylenediamine, ethanolamine, and aniline.

[0041] Preferably according to the present invention, the molar ratio of anhydrous cerium chloride:dechlorinating agent = 1:1.1 to 3.

[0042] Preferably according to the present invention, after adding the dechlorinating agent and reacting, the concentration under reduced pressure until dry is carried out under reduced pressure at 38 to 42 °C.

[0043] Preferably according to the present invention, the concentration of the supernatant under reduced pressure is carried out under reduced pressure at 32 to 35 °C.

[0044] Preferably according to the present invention, the extractant is acetone and / or tetrahydrofuran.

[0045] Preferably according to the present invention, in step (1), when a carboxylate salt is used as the ligand source, the carboxylate salt is dissolved in an alcohol solvent, added to the transparent solution formed by introducing an oxidant, filtered, and the supernatant is taken and concentrated under reduced pressure to form a powder to obtain a cerium oxide precursor.

[0046] Preferably according to the present invention, the molar ratio of anhydrous cerium chloride to carboxylate is 1:0.8 to 4, and the supernatant is concentrated under reduced pressure at 32 to 35 °C.

[0047] Preferably according to the present invention, the carboxylate is dissolved in an alcohol solvent, and the amount of the alcohol solvent used is the dissolution amount, without particular limitation.

[0048] Preferred embodiment of cerium hydroxide carbonate as the cerium source:

[0049] Preferably according to the present invention, in step (1), when using cerium hydroxide carbonate as the cerium source, the ligand source is one or a mixture of two or more of formic acid, acetic acid, and propionic acid.

[0050] Preferably according to the present invention, in step (1), when using cerium hydroxide carbonate as the cerium source, an oxidant is slowly added while adding the ligand source to form a clear solution, and the clear solution is concentrated under reduced pressure until dry to obtain a cerium oxide precursor.

[0051] Preferably according to the present invention, in step (1), the molar ratio of cerium hydroxide carbonate to ligand source is 1:1 to 4, and the temperature for concentration under reduced pressure is 35 to 70 °C;

[0052] Preferably according to the present invention, in step (2), the mass ratio of the cerium oxide precursor: spinning aid: alcohol solvent is 100:(0.7 to 5):(100 to 400).

[0053] Preferably according to the present invention, in step (2), the alcohol solvent is one or a combination of two or more of methanol, ethanol, and isopropanol.

[0054] Preferably according to the present invention, in step (2), the spinning aid is selected from one or a combination of two or more of polyethylene oxide, polyacrylic acid, polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl butyral, polyethyleneimine, polyacrylamide, polyethylene glycol, polyethylene terephthalate, polyurethane, polyglycolic acid, and polylactic acid.

[0055] Preferably according to the present invention, in step (2), stirring and dissolving and aging are carried out by stirring at a temperature of 10 to 60 °C, and the aging time is 12 to 24 h.

[0056] In the preparation process of the cerium oxide precursor of the present invention, after the cerium source is added to the alcohol solvent and heated and stirred for reaction, an oxidant is added to carry out an oxidation-reduction reaction to make Ce 3+ To Ce 4+ Undergo a transformation. At the same time, water acts as a co-solvent and ligand source to promote dissolution while coordinating to stabilize the system; the addition of the ligand source further supplements the coordination stable structure. The precursor prepared by the present invention has an extremely stable structure, obvious phenomena in the synthesis process and easy adjustment of the reaction, and the precursor with an extremely stable structure has extremely strong spinnability.

[0057] A kind of cerium oxide precursor is prepared by the above method step (1).

[0058] The cerium oxide precursor sol spinning solution is prepared by the above method.

[0059] A cerium oxide fiber membrane is prepared by electrospinning and heat treatment using the above cerium oxide precursor sol spinning solution.

[0060] The preparation method of the above cerium oxide fiber membrane includes the following steps:

[0061] 1) Preparation of the precursor fiber membrane: Electrospin the sol spinning solution to obtain a cerium oxide precursor fiber membrane.

[0062] 2) Place the precursor fiber membrane in a muffle furnace for heat treatment in an air atmosphere, heat it to 400 - 1000 °C at a heating rate of 0.5 - 10 °C / min and hold for 1 - 3 h to obtain a cerium oxide fiber membrane.

[0063] Preferably according to the present invention, in step 1), the electrospinning environment temperature is 22 - 38 °C, the relative humidity is 10 - 60%, the applied voltage is between 10 - 24 kV, the flow rate of the spinning solution is 0.5 - 3.5 mL / h, the positive stainless steel needle head model is G20 - G25, and the distance between the needle head and the roller is 8 - 35 cm.

[0064] Preferably according to the present invention, in step 2), heat treatment fully removes the organic matter in the precursor fiber membrane to ensure the crystallization of the fiber membrane.

[0065] The cerium oxide fiber membrane prepared by the present invention has a diameter of 300 - 1000 nm and a length of 3 - 18 cm, and is a cerium oxide fiber membrane with excellent mechanical properties and a large aspect ratio.

[0066] The present invention introduces an oxidant, fully utilizes the four major chemical equilibria to prepare the precursor, promotes the dissolution and coordination of anhydrous cerium chloride, regulates the influence of the valence change of anhydrous cerium chloride on dissolution during the precursor synthesis process, the influence of the amount of water on dissolution, as a ligand hydroxyl donor and on hydrolysis, and increases the cerium oxide solid content in the precursor fiber membrane; on the premise based on redox reactions, carboxylate is used as both a ligand source and a dechlorinating agent, shortening the time required for preparing the precursor; further, using basic cerium carbonate as the cerium source, combining redox, acid-base neutralization, and coordination dissociation equilibria further shortens the time required for precursor preparation, and at the same time, the prepared precursor has a high solid content and few impurity ions, and can be used to prepare a cerium oxide fiber membrane with excellent strength and performance.

[0067] The technical features and excellent effects of the present invention:

[0068] 1. During the preparation of the precursor of the present invention, adding an oxidant for redox reaction makes Ce3+ Turning to Ce 4+ A transformation occurs. Meanwhile, water acts as a co-solvent and ligand source to promote dissolution while coordinating, stabilizing the system. The addition of ligand sources such as β-diketone compounds, carboxylates, and carboxylic acids enables the formation and stabilization of the precursor structure. The precursor prepared by the present invention has an extremely stable structure, obvious phenomena during the synthesis process, and easy adjustment of the reaction. The precursor with an extremely stable structure has extremely strong spinnability.

[0069] 2. The present invention preferably selects anhydrous cerium chloride and cerium basic carbonate as the cerium source, greatly avoiding the influence of excessive moisture in cerium chloride heptahydrate on the high-quality synthesis of the precursor.

[0070] 3. During the preparation process of the precursor of the present invention, the reaction phenomena are obvious, and the reaction process can be clearly observed, which is beneficial for the regulation and control of subsequent operations.

[0071] 4. After high-temperature treatment, the cerium oxide fiber membrane prepared by the present invention has stable mechanical properties and no impurities, and is a fiber membrane that can play a role in multiple fields.

[0072] 5. The cerium oxide fiber membrane of the present invention is easy to recycle when used as a photocatalytic material, overcoming the problem that the existing nano-powder catalyst is difficult to recycle and prone to secondary pollution.

[0073] 6. Based on different cerium sources, the present invention selects a variety of ligand sources, enabling the preparation of various types of cerium oxide precursors. Moreover, the prepared cerium oxide precursors have high quality, greatly enriching the types of cerium oxide precursors and making up for the lack of high-quality cerium oxide precursors.

[0074] 7. The present invention relies on redox reactions, continuously explores and innovates, and prepares high-quality cerium oxide precursors based on regulating the four major equilibrium reactions in chemistry, and proposes a series of preparation methods for cerium oxide precursors. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] Figure 1 Optical photograph of the cerium acetylacetonate precursor obtained in Example 1.

[0076] Figure 2 Optical photograph of the sol formed by dissolving the cerium acetylacetonate precursor powder obtained in Example 1 in methanol after standing for four weeks.

[0077] Figure 3 Optical photograph of the cerium acetylacetonate precursor fiber membrane obtained in Example 1.

[0078] Figure 4 Optical photograph of the cerium oxide fiber membrane obtained by heat-treating at 700 °C for 2 h using the method of Example 1.

[0079] Figure 5SEM photograph of the cerium oxide fiber membrane obtained by subjecting the method of Example 1 to heat treatment at 700 °C for 2 h with heat preservation.

[0080] Figure 6 SEM photograph of a single bendable cerium oxide fiber obtained by subjecting the method of Example 1 to heat treatment at 700 °C for 2 h with heat preservation.

[0081] Figure 7 TG-DSC curve of the cerium acetylacetonate precursor obtained in Example 1.

[0082] Figure 8 XRD pattern of the cerium oxide fiber membrane obtained by subjecting the method of Example 1 to heat treatment at 700 °C for 2 h with heat preservation.

[0083] Figure 9 UV-Vis-NIR diffuse reflectance spectrum of the cerium oxide fiber membrane obtained by subjecting the method of Example 1 to heat treatment at 700 °C for 2 h with heat preservation.

[0084] Figure 10 UV-Vis absorption spectrum of the cerium oxide fiber membrane obtained by subjecting the method of Example 1 to heat treatment at 700 °C for 2 h with heat preservation. Detailed implementation mode

[0085] The present invention will be further explained and illustrated below in conjunction with examples, aiming to elaborate on problems such as mechanism phenomena during the preparation process, but not limited thereto. The usage ranges of various raw materials only represent that better precursors and fiber membranes can be synthesized and prepared, but the ranges are not limited thereto. Even if the ratio is appropriately relaxed, although the yield will be affected, it still falls within the scope of the present invention.

[0086] Example 1: Preparation using anhydrous cerium chloride as the cerium source and acetylacetone as the ligand source

[0087] (1) Preparation of the cerium acetylacetonate precursor

[0088] a. Weigh 100 g of anhydrous cerium chloride, add 400 g of methanol, heat and stir at 60 °C for 18 h while continuously introducing dry air to obtain a pale yellow suspension, indicating that the valence state of Ce 3+ has changed;

[0089] b. Mix 14 g of water and 32 g of methanol and gradually add them dropwise to the pale yellow suspension. As the water is added and stirring proceeds, the color of the suspension continuously changes, and finally a reddish-brown transparent solution is obtained and stirring is continued for 1 h;

[0090] c. Weigh 50 g of acetylacetone, stir and dissolve it with 90 g of methanol, then gradually add it dropwise to the system in step b and stir and react for 0.5 h to obtain a black-brown solution;

[0091] d. Weigh 105 g of triethylamine and dissolve it in 200 g of methanol. Then, add the solution drop by drop to the dark brown solution and react for 1 h. Concentrate under pressure at 42 °C to obtain a mixed solid of the precursor and impurities.

[0092] e. Add 150 g of acetone extractant to the mixed solid and soak for 24 h. Filter to obtain the supernatant, and concentrate under reduced pressure at 34 °C to obtain a solid powder, namely the poly(acetylacetonato)cerium precursor.

[0093] The optical photograph of the obtained poly(acetylacetonato)cerium precursor is shown in Figure 1 , and through Figure 1 It can be seen that the method of the present invention can prepare the poly(acetylacetonato)cerium precursor in a large scale, and at the same time, the yield of the precursor is also greatly improved, providing conditions for the large-scale preparation of cerium oxide fibers in the future.

[0094] Stability test of the poly(acetylacetonato)cerium precursor:

[0095] Dissolve the obtained poly(acetylacetonato)cerium precursor powder in methanol to form a sol. The optical photograph after standing for four weeks is shown in Figure 2 , and from Figure 2 It can be seen that after continuous standing for more than 4 weeks, the precursor has good stability. The TG-DSC curve of the obtained poly(acetylacetonato)cerium precursor is shown in Figure 7 .

[0096] (2) Preparation of the spinning solution

[0097] Dissolve 10 g of the prepared poly(acetylacetonato)cerium precursor in 20 g of methanol at 45 °C and stir well to form a solution. Then, add 0.2 g of polyethylene oxide to the solution and continue to stir and age at 45 °C for 12 h to obtain a homogeneous and transparent poly(acetylacetonato)cerium precursor sol spinning solution.

[0098] (3) Electrospinning

[0099] Transfer the poly(acetylacetonato)cerium precursor sol spinning solution to an electrospinning device. At a temperature of 25 °C, a relative humidity of 32%, an applied voltage of 11 kV, a stainless steel needle model of G23, a flow rate of the micro-injection pump of 2 mL / h, and a distance between the needle and the roller of 20 cm, a poly(acetylacetonato)cerium precursor fiber membrane is obtained. The optical photograph of the prepared poly(acetylacetonato)cerium precursor fiber membrane is shown in Figure 3 , and through Figure 3 It can be seen that the precursor fiber membrane has a good morphology. Based on the phenomenon of collecting and forming a film by the roller, it can also be reflected that the precursor fiber membrane has good flexibility, laying a prerequisite for the preparation of the cerium oxide fiber membrane.

[0100] (4) Heat treatment

[0101] The poly(acetylacetonato)cerium precursor fiber membrane was heat-treated in a muffle furnace under an air atmosphere. It was heated at a rate of 1 °C / min to 700 °C and held for 2 h, so that the ligands in the precursor fiber membrane were fully removed and crystallized to transform into a cerium oxide fiber membrane.

[0102] The optical photograph and SEM photograph of the cerium oxide fiber membrane prepared in Example 1 are shown in Figure 4 and Figure 5 respectively. It can be seen from Figure 4 that the cerium oxide fibers have good macroscopic and microscopic morphologies. It can be seen from Figure 5 that a single cerium oxide fiber is a fiber with a smooth surface and uniform diameter, with a diameter of 500 - 900 nm and a length of 5 - 13 cm. The fiber membrane has good morphology and mechanical properties.

[0103] The SEM photograph of the obtained single bendable cerium oxide fiber is shown in Figure 6 and it can be seen from Figure 6 that the cerium oxide fiber has good flexibility.

[0104] The XRD pattern of the cerium oxide fiber membrane prepared in Example 1 is shown in Figure 8 and it can be seen from Figure 8 that the cerium oxide fiber was successfully prepared.

[0105] Example 2: Using anhydrous cerium chloride as the cerium source and acetylacetone as the ligand source to prepare

[0106] It was carried out according to the method described in Example 1, except that:

[0107] Steps a and b were carried out as follows: Weigh 100 g of anhydrous cerium chloride and add 400 g of methanol. Heat and stir at 60 °C, and gradually add 20 g of hydrogen peroxide dropwise. The color of the white suspension changed continuously and finally dissolved to form a reddish-brown transparent solution. Stir for 0.5 h, and the subsequent steps were carried out according to Example 1.

[0108] Example 3: Using anhydrous cerium chloride as the cerium source and potassium acetate as the ligand source to prepare

[0109] It was carried out according to the method described in Example 1, except that:

[0110] The precursor prepared in step (1) should be a poly(cerium oxyacetate) precursor, and the specific steps are as follows

[0111] a. Weigh 100 g of anhydrous cerium chloride and add 200 g of ethanol. Heat and stir at 60 °C for 18 h and continuously pass in dry air to obtain a pale yellow suspension, indicating that Ce 3+ has undergone a valence change;

[0112] b. Add 14 g of water to the pale yellow suspension. As the water is added and stirred, the color of the suspension continuously changes until a reddish-brown transparent solution is obtained, and continue stirring for 1 h;

[0113] c. Weigh 100 g of potassium acetate and mix it with 1000 g of ethanol by stirring, and then add it dropwise to the system in step b to form a suspension;

[0114] d. Filter the suspension obtained in step c, take the supernatant and concentrate it under reduced pressure at 50 °C to make a powder, thus obtaining the cerium acetate oxide precursor;

[0115] After that, the cerium oxide precursor sol spinning solution is carried out according to step (2).

[0116] Example 4: Using cerium basic carbonate as the cerium source and acetic acid as the ligand source to prepare

[0117] Carry out according to the method described in Example 1, the difference is:

[0118] The precursor prepared in step (1) should be the cerium acetate oxide precursor, and the specific steps are as follows

[0119] a. Weigh 100 g of cerium basic carbonate, add 200 g of ethanol, heat and stir at 60 °C, add 60 g of acetic acid and 30 g of hydrogen peroxide, and stir for 10 h to obtain a clear solution.

[0120] b. Concentrate and evaporate the above solution to dryness under reduced pressure at 60 °C to obtain the cerium acetate oxide precursor;

[0121] After that, the cerium oxide precursor sol spinning solution is carried out according to step (2).

[0122] Example 5: Using anhydrous cerium chloride as the cerium source and acetylacetone as the ligand source to prepare

[0123] Carry out according to the method described in Example 1, the difference is:

[0124] Steps a and b are carried out as follows: Weigh 100 g of anhydrous cerium chloride, add 400 g of methanol, heat and stir at 60 °C, and gradually add 12 g of hydrogen peroxide dropwise. The color of the white suspension continuously changes until it finally dissolves to form a reddish-brown solution, stir for 0.5 h, and the subsequent steps are carried out according to Example 1.

[0125] Example 6: Using anhydrous cerium chloride as the cerium source and acetylacetone as the ligand source to prepare

[0126] Carry out according to the method described in Example 1, the difference is:

[0127] Step e is carried out as follows: Add 200 g of the extractant tetrahydrofuran and soak for 36 h, filter, take the supernatant and concentrate it under reduced pressure at 36 °C to obtain a solid powder, namely the cerium acetylacetonate precursor.

[0128] Example 7: Cerium acetylacetonate was prepared using anhydrous cerium chloride as the cerium source and acetylacetone as the ligand source

[0129] It was carried out according to the method described in Example 1, except that:

[0130] Preparation of the spinning solution in step (2): 10 g of the precursor was dissolved in 15 g of methanol at 45 °C and stirred thoroughly to form a solution. Then, 0.2 g of polyethylene oxide was added to this solution, and stirring was continued at 45 °C to obtain a uniform transparent spinning solution, which was aged for 18 h.

[0131] Example 8: Cerium acetylacetonate was prepared using anhydrous cerium chloride as the cerium source and acetylacetone as the ligand source

[0132] It was carried out according to the method described in Example 1, except that:

[0133] Electrospinning in step (3): The sol spinning solution was transferred to an electrospinning device. At a temperature of 22 °C, relative humidity of 25%, an applied voltage of 12 kV, a stainless steel needle model G23, a flow rate of the micro-injection pump of 2.5 mL / h, and a distance between the needle and the roller of 27 cm, a cerium acetylacetonate precursor fiber membrane was obtained, with a diameter in the range of 0.7 - 1.2 μm.

[0134] Example 9: Cerium acetylacetonate was prepared using anhydrous cerium chloride as the cerium source and acetylacetone as the ligand source

[0135] It was carried out according to the method described in Example 1, except that:

[0136] Heat treatment in step (4): The precursor fiber membrane was heat-treated in a muffle furnace under an air atmosphere. It was heated to 900 °C at a heating rate of 1 °C / min and held for 2 h, so that the ligands in the precursor fiber membrane were fully removed and crystallized to transform into a cerium oxide fiber membrane, and the fiber membrane had good morphology and mechanical properties.

[0137] Comparative Example 1:

[0138] The same method as described in Example 1, the difference is that:

[0139] During the preparation process of the cerium acetylacetonate precursor, in step a, anhydrous cerium chloride was replaced with cerium chloride heptahydrate. After weighing 151 g of cerium chloride heptahydrate and stirring it with 400 g of methanol to obtain a colorless transparent solution, heating and stirring were continued, but a reddish-brown transparent solution could not be obtained. Due to the presence of a large amount of water in cerium chloride heptahydrate, step b was omitted, that is, no water was added, and other methods and conditions were carried out according to Example 1.

[0140] The yield of the precursor obtained in this comparative example was extremely low. This was because cerium chloride heptahydrate was extremely hygroscopic itself, resulting in a relatively high water content in the solution obtained after mixing with methanol. Although the relatively high water content could promote its direct dissolution in methanol, it also made it impossible for the valence state transformation to occur during the heating and stirring process. As a result, after the subsequent addition of the ligand source, the structure remained unstable. At the same time, the presence of a large amount of water also easily caused hydrolysis and precipitation during the subsequent preparation process, thus having a serious negative impact on the synthesis of the precursor.

[0141] Comparative Example 2:

[0142] The same method as described in Example 1, except that:

[0143] During the preparation process of the cerium acetylacetonate precursor, step a was carried out according to Example 1, and in step b, no water was added, or 50 g of water was added, and then it was carried out according to Example 1.

[0144] Although a certain amount of precursor could also be prepared in this comparative example during the subsequent preparation process, the yield was very low.

[0145] This was because the addition of water not only served as a cosolvent to dissolve the cerium chloride after the valence state transformation, but also played the role of a ligand source. If no water was added, the synthesis of the precursor could hardly proceed, thus resulting in a decrease in the yield. While adding a large amount of water promoted the better dissolution of anhydrous cerium chloride, it also caused precipitation during the subsequent preparation process, thereby affecting the yield.

[0146] In summary, during the preparation process, the amount of water used should be strictly controlled, as too much or too little water will have a great negative impact on the synthesis of the precursor.

[0147] Comparative Example 3:

[0148] The same method as described in Example 1, except that:

[0149] During the preparation process of the cerium acetylacetonate precursor, in step a, it was not heated, stirred at room temperature, and at the same time, the system was sealed, no oxidation was introduced, and no dry air (O2) was passed through. The anhydrous cerium chloride was not able to undergo valence state transformation and would not dissolve, ultimately resulting in the failure to successfully synthesize the precursor.

[0150] This shows that during the preparation of the precursor, the occurrence of the redox reaction is an extremely important step. In Comparative Example 3, without carrying out the redox reaction to promote the dissolution and coordination of anhydrous cerium chloride and without undergoing valence state transformation, it is extremely difficult to synthesize the precursor.

[0151] Comparative Example 4:

[0152] The same method as described in Example 1, except that:

[0153] In the preparation process of the cerium acetylacetonate precursor, in step c, the amount of the ligand source acetylacetone is 120 g. It is directly poured in and stirred briefly before proceeding to the next step. A large amount of precipitation will occur during this process because the ligand source is excessive and the addition rate is too fast, directly forming cerium acetylacetonate, which will also affect the quality and yield of the precursor.

[0154] Comparative Example 5:

[0155] The method is the same as that described in Example 1, except that:

[0156] In the preparation process of the cerium acetylacetonate precursor, in step d, the amount of the dechlorinating agent triethylamine is 200 g. It is directly poured in and stirred. A large amount of precipitation will also occur during this process because excessive triethylamine makes the solution alkaline and insoluble hydroxides are produced.

[0157] Comparative Example 6:

[0158] The method is the same as that described in Example 1, except that:

[0159] In the preparation process of the cerium acetylacetonate precursor, triethylamine is first mixed with cerium chloride, and then the ligand source is added. This feeding sequence is not favorable for the precursor and the final fiber.

[0160] In summary, for Comparative Examples 1 - 6, the successful progress of the redox reaction during the synthesis of the precursor is a prerequisite for synthesizing a high-quality precursor. Among them, if there is an excessive amount of ligand sources such as acetylacetone in β-diketone compound ligands, a large amount of precipitation will occur regardless of whether the stirring is uniform; at the same time, the dosages of various reagents required for the reaction must be strictly controlled, and improper operations and dosages will have a huge negative impact on the synthesis of the precursor.

[0161] Comparative Example 7:

[0162] The method is the same as that described in Example 1, except that:

[0163] In step (2), 10 g of the precursor is dissolved in 50 g of methanol. The use of a large amount of solvent will cause the fiber to be too thin and powdered, resulting in a decrease in strength and failure to obtain a high-quality precursor and cerium oxide fiber membrane.

[0164] Experimental Example 1

[0165] Select the cerium oxide fiber membrane obtained in Example 8 and heat-treated at 900 °C for 2 h to test the near-infrared diffuse reflection spectrum. The results are as Figure 9 shown. The high near-infrared reflectivity indicates that the cerium oxide fiber membrane has potential applications in anti-thermal radiation and heat insulation materials.

[0166] Experimental Example 2

[0167] The cerium oxide fiber membrane obtained in Example 8 and heat-treated at 900 °C for 2 h was selected to test the ultraviolet-visible absorption spectrum. The results are as Figure 10 shown. The fiber membrane exhibits good ultraviolet absorption in the range of 250-400 nm, indicating that the prepared cerium oxide fiber membrane is expected to find applications in the field of photocatalysis.

Claims

1. A preparation method of a cerium oxide precursor sol spinning solution, comprising the following steps: (1) Using anhydrous cerium chloride or cerium basic carbonate as the cerium source, add it to an alcohol solvent, heat and stir the reaction, and slowly add an oxidant to carry out an oxidation-reduction reaction to cause the transformation of Ce 3+ Add to Ce 4+ to undergo a transformation, and then add a ligand source to carry out a coordination reaction to obtain a cerium oxide precursor; (2) Dissolve the cerium oxide precursor in an alcohol solvent, add a spinning aid, stir to dissolve and age to obtain a uniform cerium oxide sol spinning solution.

2. The preparation method according to claim 1, characterized in that, In step (1), the alcohol solvent is one or a mixture of two or more of methanol, ethanol, and isopropanol, the heating and stirring reaction temperature is 30-90 °C, and the oxidant is selected from chlorine gas (Cl2), potassium permanganate (KMnO4), dry air (O2), pure oxygen (O2), ozone (O3), hydrogen peroxide (H2O2), or chlorine dioxide (ClO2). Further preferably, in step (1), the oxidant is selected from dry air (O2), pure oxygen (O2), ozone (O3), or hydrogen peroxide (H2O2).

3. The preparation method according to claim 2, characterized in that, The addition conditions of the oxidant in step (1): The reaction system is stirred at a temperature of 30-90 °C for 12-32 h and then added. The undissolved white suspension becomes a light yellow suspension. In addition, water is added to the system as a cosolvent and ligand source to promote the dissolution and coordination of anhydrous cerium chloride. The molar ratio of cerium source to water = 1:1-10, and then a ligand source is added for coordination; The addition conditions of hydrogen peroxide as an oxidant: The reaction system is heated and stirred at a temperature of 30-90 °C, and then hydrogen peroxide is added. The molar ratio of cerium source to hydrogen peroxide = 1:1-7. After obtaining a transparent solution, a ligand source is added for coordination, and there is no need to add water.

4. The preparation method according to claim 1, wherein, In step (1), when anhydrous cerium chloride is used as the cerium source, the ligand source is a β-diketone compound or a carboxylate; The β-diketone compound ligand source is selected from one or a mixture of two or more of acetylacetone, methyl acetoacetate, ethyl acetoacetate, propyl acetoacetate, isopropyl acetoacetate, and butyl acetoacetate; The carboxylate ligand source is selected from one or a mixture of two or more of potassium acetate, sodium acetate, potassium propionate, sodium propionate, potassium oxalate, and sodium oxalate.

5. The preparation method according to claim 4, characterized in that, In step (1), When using a β-diketone compound as the ligand source, add the β-diketone compound ligand source and a dechlorinating agent to the transparent solution formed by introducing the oxidant, stir and react for 0.5-4 h, take the supernatant, concentrate it under reduced pressure until dry, take the dry powder, soak it in an extractant for 12-72 h, and then filter. Concentrate the obtained supernatant under reduced pressure to form a powder to obtain the cerium oxide precursor; the molar ratio of anhydrous cerium chloride to the β-diketone compound ligand source = 1:0.8-4; the dechlorinating agent is one or a mixture of two or more of triethylamine, ethylenediamine, ethanolamine, and aniline; the molar ratio of anhydrous cerium chloride to the dechlorinating agent = 1:1.1-3; after adding the dechlorinating agent and reacting, concentrate it under reduced pressure until dry at 38-42 °C; concentrate the supernatant under reduced pressure at 32-35 °C; the extractant is acetone and / or tetrahydrofuran; In step (1), when using a carboxylate as the ligand source, dissolve the carboxylate in an alcohol solvent, add it to the transparent solution formed by introducing the oxidant, filter, take the supernatant, concentrate it under reduced pressure to form a powder to obtain the cerium oxide precursor, the molar ratio of anhydrous cerium chloride to the carboxylate ligand source = 1:0.8-4, and concentrate the supernatant under reduced pressure at 32-35 °C.

6. The preparation method according to claim 1, characterized in that, In step (1), when cerium hydroxide carbonate is used as the cerium source, the ligand source is formic acid, acetic acid, propionic acid, or a mixture of two or more of them. When cerium hydroxide carbonate is used as the cerium source, an oxidant is slowly added while adding the ligand source to form a clear solution. The clear solution is concentrated under reduced pressure until dry to obtain a cerium oxide precursor. The molar ratio of cerium hydroxide carbonate to the ligand source = 1:1 to 4, and the temperature for concentration under reduced pressure is 35 to 70 °C.

7. The preparation method according to claim 1, wherein In step (2), the mass ratio of the cerium oxide precursor: spinning aid: alcohol solvent = 100:(0.7 to 5):(100 to 400). The alcohol solvent is one or a combination of two or more of methanol, ethanol, and isopropanol. The spinning aid is selected from one or a combination of two or more of polyethylene oxide, polyacrylic acid, polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl butyral, polyethyleneimine, polyacrylamide, polyethylene glycol, polyethylene terephthalate, polyurethane, polyglycolic acid, and polylactic acid. Stir and dissolve, and age by stirring at a temperature of 10 to 60 °C for an aging time of 12 to 24 h.

8. A class of cerium oxide precursors prepared by using the method step (1) of any one of claims 1-7.

9. A cerium oxide precursor sol spinning solution prepared by using the method of any one of claims 1-7.

10. A cerium oxide fiber membrane prepared by electrospinning and heat treatment using the above-mentioned cerium oxide precursor sol spinning solution; A method for preparing a cerium oxide fiber membrane, comprising the following steps: 1) Preparation of a precursor fiber membrane: Electrospin the sol spinning solution to obtain a cerium oxide precursor fiber membrane; 2) Place the precursor fiber membrane in a muffle furnace for heat treatment in an air atmosphere, heat it at a heating rate of 0.5 to 10 °C / min to 400 to 1000 °C and hold for 1 to 3 h to obtain a cerium oxide fiber membrane; In step 1), the electrospinning environmental temperature is 22 to 38 °C, the relative humidity is 10 to 60%, the applied voltage is between 10 and 24 kV, the flow rate of the spinning solution is 0.5 to 3.5 mL / h, the positive stainless steel needle head model is G20 to G25, and the distance between the needle head and the drum is 8 to 35 cm; In step 2), heat treatment fully removes the organic matter in the precursor fiber membrane to ensure the crystallization of the fiber membrane.

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