Niobium oxide precursors, niobium oxide fibers and yttrium niobate fibers derived therefrom and methods of making

Abstract

The present application relates to niobium oxide precursor, niobium oxide fiber and derived yttrium niobate fiber and preparation method, the preparation of niobium oxide precursor uses anhydrous niobium chloride as niobium source, potassium acetate ligand source, both occur metathesis and coordination reaction, prepare high-quality precursor, then the prepared precursor is mixed with alcohol according to certain proportion, add trace spinning aid, electrostatic spinning and heat treatment can obtain niobium oxide fiber membrane, further can obtain its derived niobate fiber membrane.The method has controllable precursor synthesis process, can quickly prepare high-quality fiber, and is beneficial to industrial production and application.The obtained niobium oxide fiber membrane has potential application in battery energy storage and photocatalysis, and the obtained niobate fiber has potential application in thermal insulation and thermal barrier coating.

Description

Technical Field

[0001] This invention relates to niobium oxide precursors, niobium oxide fibers and their derived yttrium niobate fibers and preparation methods, belonging to the field of functional materials technology. Background Technology

[0002] Niobium pentoxide (Nb₂O₅) is an important inorganic functional material with broad application prospects in multiple fields due to its unique physicochemical properties. This compound possesses various crystal structures, with different crystal phases significantly affecting its performance, thus making it suitable for different application scenarios. Specifically, niobium pentoxide exhibits excellent electrochemical performance and can be used to prepare niobate ceramics and lithium-ion battery anode materials; its excellent oxygen storage capacity makes it suitable for the production of electronic components such as niobium electrolytic capacitors and thin-film transistors. Furthermore, niobium pentoxide possesses outstanding chemical stability, making it suitable as a high-temperature resistant coating or corrosion-resistant additive, and as a catalyst or catalyst support in petroleum refining, organic synthesis, and environmentally friendly catalytic reactions. With its unique chemical stability and multifunctional properties, niobium pentoxide holds an irreplaceable and important position in high-end manufacturing and new material research and development.

[0003] Yttrium niobate (Y3NbO7), with its cubic fluorite structure, exhibits low thermal conductivity, high coefficient of thermal expansion, and excellent thermal shock resistance, making it suitable for use as a thermal barrier coating material. Its wide bandgap characteristic also makes it suitable as a laser matrix material for radiation thermal management. Furthermore, this material demonstrates proton conductivity, making it applicable to sensors and fuel cells. Niobate fibers also show broad application prospects in cutting-edge technologies such as energy, environment, health, and communications. For example, nickel niobate fibers, due to their "zero strain" characteristics, can operate stably over a wide temperature range from extremely cold to high temperatures, making them suitable for high-performance batteries; potassium niobate fibers possess excellent piezoelectric properties and can be used to manufacture flexible generators; niobates, especially high-entropy niobates, exhibit superior thermal radiation protection performance and hold promise for applications in aerospace thermal protection systems.

[0004] Compared to powders, fibers have the following advantages: self-supporting, non-agglomerating, higher specific surface area and porosity, better filtration performance, higher thermal stability and high temperature resistance, lightweight, high strength, and ultra-flexible.

[0005] In summary, fiber morphology exhibits unique advantages over powder morphology in several aspects, giving it potential performance superiority in numerous application fields. Currently, there are few research reports on niobium oxide precursors and niobium oxide fibers, and generally, inorganic salts or alkoxides of niobium are used as precursors, with a large amount of spinning aids (polyvinylpyrrolidone PVP or polyvinyl acetate PVAC) added for spinning. For example, Leindecker et al. (2014) dissolved metallic niobium in hydrofluoric acid and carried out a displacement reaction to obtain niobium fluoride precursor, added PVP, and then performed electrospinning to prepare niobium oxide fibers (Leindecker GC, Alves AK, Bergmann CP. Synthesis of niobium oxide fibers by electrospinning and characterization of their morphology and optical properties[J]. Ceramics International, 2014, 40(10): 16195-16200).

[0006] Inorganic niobium fluoride itself lacks spinnability, and its precursor fibers exhibit a strong tendency to absorb moisture and deliquesce in air, a characteristic that severely restricts the acquisition and stability of the final fiber properties. For example, Viswanathamurthi et al. (2003) reacted niobium ethanol, ethanol, and acetic acid to form a complex, and then prepared PVAC / niobium oxide composite fibers using electrospinning technology. After high-temperature heat treatment, they obtained niobium oxide fibers (Viswanathamurthi P, Bhattarai N, Kim HY, et al. Preparation and morphology of niobium oxide fibres by electrospinning[J]. Chemical physics letters, 2003, 374(1-2): 79-84.). Although niobium ethanol is slightly better than inorganic niobium salts in terms of spinnability, it still has many shortcomings: high raw material cost, poor stability, limited spinnability itself, and complex preparation process. Meanwhile, its poor chemical stability in air and easy hydrolysis result in poor mechanical properties and low yield of the final niobium oxide fibers. In summary, high-quality fibers could not be successfully prepared using either inorganic niobium salts or alkoxides as precursors.

[0007] Obtaining high-quality niobium oxide precursors to achieve rapid and efficient preparation of niobium oxide fibers is an urgent problem to be solved; at the same time, ensuring that the fibers produced have excellent mechanical properties has also become another key challenge. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides niobium oxide precursors, niobium oxide fibers, and their derived yttrium niobate fibers, as well as preparation methods.

[0009] This invention utilizes ligand design to obtain high-quality niobium complex precursors, which are then combined with sol-gel and electrospinning to successfully produce high-quality niobium oxide fibers and their derivative yttrium niobate fibers.

[0010] Terminology Explanation:

[0011] Anhydrous niobium chloride (NbCl5) has a relative molecular mass of 270.17.

[0012] Potassium acetate (CH3COOKa) relative molecular mass: 98.15.

[0013] PAY: Polyyttrium acetylacetone, prepared according to the preparation method of polyyttrium acetylacetone in patent document CN108315838A.

[0014] PEO: Polyethylene oxide.

[0015] PENd: Polyniobium acetate, a niobium complex precursor prepared in this invention, with the monomer being CH3COONd(OH)4.

[0016] PANd: Polyacetylacetone-niobium, a niobium complex precursor prepared in this invention, with the monomer being C5H7O2Nd(OH)4.

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

[0018] The first objective of this invention is to provide a method for preparing niobium oxide precursor, comprising the following steps:

[0019] (1) Using anhydrous inorganic salts of niobium as the niobium source, dissolve them in alcohol, stir the reaction, and obtain solution A;

[0020] (2) Add the ligand source to the solvent to obtain solution B. Slowly add solution B to solution A. Filter the supernatant and concentrate it under reduced pressure to obtain niobium oxide precursor powder.

[0021] According to a preferred embodiment of the present invention, in step (1), the anhydrous inorganic salt of niobium is one or a combination of two or more of niobium chloride, niobium bromide, niobium iodide, niobium fluoride, niobium sulfate, and niobium nitrate.

[0022] Most preferably, in step (1), the anhydrous inorganic salt of niobium is niobium chloride.

[0023] According to a preferred embodiment of the present invention, in step (1), the alcohol is one or a mixture of two or more of anhydrous methanol, anhydrous ethanol, and isopropanol. The alcohol acts both as a solvent to dissolve anhydrous niobium chloride and as a protective agent to inhibit the hydrolysis of anhydrous niobium chloride.

[0024] According to a preferred embodiment of the present invention, in step (1), the dissolution temperature is 20~40 °C.

[0025] According to a preferred embodiment of the present invention, in step (1), the mass ratio of niobium source to alcohol is 1:3~10.

[0026] More preferably, in step (1), the mass ratio of niobium source to alcohol is 1:4~6.

[0027] According to a preferred embodiment of the present invention, in step (2), the ligand source is a carboxylate or a β-diketone compound.

[0028] According to a preferred embodiment of the present invention, in step (2), the carboxylate ligand source is selected from one or more of potassium acetate, sodium acetate, potassium propionate, sodium propionate, potassium oxalate, and sodium oxalate.

[0029] Most preferably, in step (2), the carboxylate ligand source is potassium acetate.

[0030] According to a preferred embodiment of the present invention, in step (2), the β-diketone ligand source is selected from one or more of acetylacetone, methyl acetoacetate, ethyl acetoacetate, propyl acetoacetate, isopropyl acetoacetate, and butyl acetoacetate.

[0031] More preferably, in step (2), the ligand source for the β-diketone compound is acetylacetone.

[0032] In a preferred embodiment of the present invention, potassium acetate is used as the ligand source: According to a preferred embodiment of the present invention, in step (2), when potassium acetate is used as the ligand source, potassium acetate is added to the solvent and heated and stirred at 30~90 °C to obtain solution B. Solution B is slowly added to solution A, and the supernatant obtained by filtering to remove potassium chloride is concentrated under reduced pressure to obtain niobium oxide precursor powder.

[0033] According to a preferred embodiment of the present invention, the solvent is a mixture of water and alcohol, wherein the alcohol is methanol or ethanol.

[0034] According to a preferred embodiment of the present invention, the mass ratio of potassium acetate to alcohol is 1:5~10.

[0035] According to a preferred embodiment of the present invention, the mass ratio of potassium acetate to water is 1:0.1~0.5.

[0036] According to a preferred embodiment of the present invention, the molar ratio of niobium source to potassium acetate is 1:1 to 7.

[0037] Further preferred, the molar ratio of niobium source to potassium acetate is 1:2~5.

[0038] When solution B is added dropwise to solution A, niobium chloride and potassium acetate react chemically to form potassium chloride. Potassium chloride has low solubility in alcohol, so it precipitates out as a white precipitate. Potassium acetate acts as a ligand source to coordinate with anhydrous niobium chloride, maintaining an acidic environment and preventing the hydrolysis of anhydrous niobium chloride.

[0039] According to a preferred embodiment of the present invention, the carboxylate is dissolved in an alcohol solvent, and the amount of alcohol solvent used is the amount dissolved, without particular limitation.

[0040] In a preferred embodiment of the present invention, β-diketone compounds are used as the ligand source:

[0041] According to a preferred embodiment of the present invention, in step (2), when β-diketone compounds are used as ligand sources, the β-diketone compound ligand source and the dechlorinating agent are dissolved in a solvent and then added to transparent solution A. The mixture is stirred and reacted for 0.5 to 2 hours. The supernatant is concentrated under reduced pressure and evaporated to dryness. The dry powder is then soaked in an extractant for 12 to 48 hours and filtered. The resulting supernatant is concentrated under reduced pressure to form a powder, thus obtaining the niobium oxide precursor.

[0042] According to a preferred embodiment of the present invention, the solvent is methanol or ethanol.

[0043] According to a preferred embodiment of the present invention, the molar ratio of the anhydrous niobium chloride to the β-diketone ligand source is 1:0.5~3.

[0044] According to a preferred embodiment of the present invention, the dechlorinating agent is one or a mixture of two or more of triethylamine, ethylenediamine, ethanolamine, and aniline.

[0045] According to a preferred embodiment of the present invention, the ethanolamine is monoethanolamine, diethanolamine, or triethanolamine.

[0046] According to a preferred embodiment of the present invention, the molar ratio of the anhydrous niobium chloride to the dechlorinating agent is 1:3~6.

[0047] According to a preferred embodiment of the present invention, after reacting with the dechlorinating agent, the vacuum concentration and evaporation is carried out at 38~42 °C.

[0048] According to a preferred embodiment of the present invention, after the extractant removes the byproduct triethylamine hydrochloride, the supernatant is concentrated under reduced pressure at 32-35 °C.

[0049] According to a preferred embodiment of the invention, the extractant is acetone and / or tetrahydrofuran.

[0050] The precursor prepared by this invention has a stable structure, obvious synthesis process phenomena, easily adjustable reaction, and strong spinnability.

[0051] The second objective of this invention is to provide a niobium oxide precursor, which is prepared using the above-described method.

[0052] The third objective of this invention is to provide a niobium oxide fiber membrane, which is prepared by electrospinning and heat treatment using the aforementioned niobium oxide precursor as raw material and adding a spinning aid.

[0053] The fourth objective of this invention is to provide a method for preparing the above-mentioned niobium oxide fiber membrane, comprising the following steps:

[0054] 1) Dissolve the niobium oxide precursor in methanol at 40-50℃ and stir thoroughly to form a sol. Then add a spinning aid and continue stirring and aging at 40-50℃ for 10-15 hours to obtain a uniform and transparent precursor sol spinning solution. Electrospin the sol spinning solution to obtain a niobium oxide precursor fiber membrane.

[0055] 2) The niobium oxide precursor fiber membrane is heat-treated in an air atmosphere to obtain the niobium oxide fiber membrane.

[0056] According to a preferred embodiment of the present invention, in step 1), the electrospinning environment temperature is 20~40 ℃, the relative humidity is 15~60%, the applied voltage is between 10~20kV, the spinning solution flow rate is 0.3~3.5 mL / h, the positive electrode stainless steel needle is of model G20~G25, the yarn taking is carried out using a roller taking device, and the distance between the needle and the roller is 10~35 cm.

[0057] According to a preferred embodiment of the present invention, in step 2), the heat treatment is to heat to 600-900°C at a heating rate of 1-10°C / min and hold at that temperature for 1-3 hours.

[0058] The fifth objective of this invention is to provide a yttrium niobate fiber membrane derived from a niobium oxide fiber membrane. This fiber membrane is prepared by electrospinning and heat treatment using a niobium oxide precursor as raw material, adding polyacetylacetone yttrium (PAY) and a spinning aid.

[0059] The sixth objective of this invention is to provide a method for preparing the above-mentioned yttrium niobate fiber membrane, comprising the following steps:

[0060] S1. Niobium oxide precursor and polyacetylacetonate PAY are dissolved in methanol at 40-50℃ and stirred thoroughly to form a sol. Then, a spinning aid is added, and the mixture is stirred and aged at 40-50℃ for 10-15 hours to obtain a uniform and transparent precursor sol spinning solution. The sol spinning solution is then electrospun to obtain yttrium niobate precursor fiber membrane.

[0061] S2. The yttrium niobate precursor fiber membrane is heat-treated in an air atmosphere to obtain the yttrium niobate fiber membrane.

[0062] According to a preferred embodiment of the present invention, in step S1, the electrospinning environment temperature is 20~40 ℃, the relative humidity is 15~60%, the applied voltage is between 10~20kV, the spinning solution flow rate is 0.3~3.5 mL / h, the positive electrode stainless steel needle is of model G20~G25, the yarn taking is carried out using a roller taking device, and the distance between the needle and the roller is 10~35 cm.

[0063] According to a preferred embodiment of the present invention, in step S2, the heat treatment involves heating to 600-1200 °C at a heating rate of 1-10 °C / min and holding at that temperature for 1-3 h.

[0064] In the preparation of the above-mentioned niobium oxide fiber membrane and yttrium niobate fiber membrane, the spinning aid used is PEO.

[0065] This invention fully utilizes chemical equilibrium, such as acid-base balance, precipitation-dissolution balance, and coordination-dissociation balance, to prepare precursors, promotes the dissolution and coordination of anhydrous niobium chloride, and obtains an niobium oxide precursor with extremely stable structure and strong spinnability. Furthermore, by utilizing redox balance and heat treatment, niobium oxide fibers and its derivative yttrium niobate fibers are successfully obtained.

[0066] This invention uses carboxylates as both a ligand source and a dechlorinating agent, which shortens the reagents required for precursor preparation. At the same time, the prepared precursor has a high solid content and can be used as an optimal raw material for preparing niobium oxide and yttrium niobate fiber membranes with superior strength and performance.

[0067] Technical features and superior effects of the present invention:

[0068] 1. In the precursor preparation process of this invention, anhydrous inorganic salts of niobium are used as niobium sources, and carboxylates or β-diketone compounds are used as ligand sources. The two undergo metathesis and coordination reactions to prepare high-quality precursors. The addition of ligand sources in this invention, especially potassium acetate, enables the formation and stabilization of the precursor structure. The precursor prepared by this invention has a stable structure, obvious synthesis process phenomena, and easily adjustable reactions. The extremely stable precursor has strong spinnability.

[0069] 2. In this invention, anhydrous inorganic salts of niobium are used as the niobium source and potassium acetate is used as the ligand source. The reaction phenomenon is obvious during the preparation of the precursor, and the reaction process can be clearly observed, which is beneficial for the control of subsequent operations.

[0070] 3. The niobium oxide fiber prepared by this invention can be used as a photocatalytic material for recycling, overcoming the problems of existing powder catalysts being difficult to recycle and prone to secondary pollution.

[0071] 4. This invention allows for the use of various ligand sources to prepare a variety of niobium oxide precursors. The prepared niobium oxide precursors are of high quality, enriching the variety of niobium oxide precursors.

[0072] 5. The niobium oxide precursor synthesized in this invention can be used with other metal compounds to prepare niobate precursor sol spinning solutions. In addition to preparing the yttrium niobate fiber of this invention, other niobate fibers can also be prepared. Attached Figure Description

[0073] Figure 1 This is a powder photograph of the polyniobium acetate precursor obtained in Example 1.

[0074] Figure 2 This is a photograph of the polyniobium acetate spinning solution obtained in Example 1 after being left at room temperature for 4 weeks.

[0075] Figure 3 The image shows the TG-DSC curve of the polyniobium acetate precursor obtained in Example 1.

[0076] Figure 4 An optical photograph of the polyniobium acetate precursor fiber membrane obtained in Example 1.

[0077] Figure 5 An optical photograph of the niobium oxide fiber membrane obtained by heat treatment at 800°C for 2 hours using the method of Example 1.

[0078] Figure 6 The image shows a SEM image of niobium oxide fibers obtained by heat treatment at 800°C for 2 hours using the method of Example 1.

[0079] Figure 7 This is an optical photograph of the yttrium niobate precursor fiber membrane obtained in Example 2.

[0080] Figure 8 An optical photograph of the yttrium niobate fiber membrane obtained by heat treatment at 1100°C for 2 hours using the method of Example 2.

[0081] Figure 9 The image shows a SEM image of yttrium niobate fibers obtained by heat treatment at 1100°C for 2 hours using the method of Example 2.

[0082] Figure 10 The XRD pattern of niobium oxide fibers obtained by heat treatment at 800℃ for 2 hours using the method in Example 1.

[0083] Figure 11 XRD pattern of yttrium niobate fiber obtained by heat treatment at 1100℃ for 2 hours using the method in Example 2. Detailed Implementation

[0084] The invention will be further explained below with reference to the embodiments, aiming to elucidate the mechanism and phenomena in the preparation process, but it is not limited thereto. The scope of various raw materials used only indicates that they can be used to synthesize better precursors and fiber membranes, but the scope is not limited to this. Even if the proportions are appropriately relaxed, although it will affect the yield, it still falls within the scope of this invention.

[0085] Example 1: Preparation of niobium oxide precursor and niobium oxide fiber membrane using anhydrous niobium chloride as the niobium source and potassium acetate as the ligand source.

[0086] (1) Preparation of polyniobium acetate precursor

[0087] 1) Weigh 20g of anhydrous niobium chloride and add 100g of ethanol. Heat and stir at 60℃ for 1h. The solution changes from pale yellow to white transparent.

[0088] 2) Weigh 29g of potassium acetate, add 250g of ethanol and 5g of water, heat and stir at 60℃ until the potassium acetate is completely dissolved to obtain a clear and transparent solution.

[0089] 3) Add the clear and transparent solution from step 2) dropwise to the system from step 1) to form a suspension; filter the suspension, take the supernatant and concentrate it under reduced pressure at 45°C to make powder, and obtain the poly(niobium acetate) precursor (niobium oxide precursor).

[0090] Optical photographs of the obtained polyniobium acetate precursor are shown below. Figure 1 .

[0091] Stability test of polyniobium acetate precursor:

[0092] The prepared niobium acetate precursor powder was dissolved in methanol to form a transparent sol. Optical photographs were taken after 4 weeks of storage. Figure 2 ,from Figure 2 It can be seen that the polyniobium acetate precursor exhibits good stability after continuous storage for more than 4 weeks. The TG-DSC curve of the obtained polyniobium acetate precursor is shown below. Figure 3 According to TG-DSC curve analysis, the polyniobium acetate precursor crystallizes at 600℃, and the thermal decomposition is mainly divided into three parts: the first part is the removal of organic solvent from room temperature to 100℃, the second part is the carbonization and decomposition of ligands from 100-400℃, and the third part is the removal of residual carbon from 400-600℃.

[0093] (2) Preparation of spinning solution

[0094] 10g of the prepared niobium acetate precursor and 0.02g of PEO were dissolved in 20g of methanol, stirred thoroughly at 45℃ and aged for 12h to obtain a uniform and transparent niobium acetate precursor sol spinning solution.

[0095] (3) Electrospinning

[0096] The poly(niobium acetate) precursor sol-spinning solution was transferred to an electrospinning apparatus. The apparatus was operated at 24°C and 25% relative humidity, with an applied voltage of 11kV, a stainless steel needle (model G23), a micro-injection pump flow rate of 2mL / h, and a needle-to-roll distance of 20cm, to obtain a poly(niobium acetate) precursor fiber membrane.

[0097] Optical photographs of the prepared poly(niobium acetate) precursor fiber membrane are shown below. Figure 4 ,pass Figure 4 It can be seen that the precursor fiber membrane has a good morphology. Based on the phenomenon of membrane formation by roller collection, it can also be reflected that the precursor fiber membrane has good flexibility, which lays the prerequisite for the preparation of niobium oxide fiber membrane.

[0098] (4) Heat treatment

[0099] The poly(niobium acetate) precursor fiber membrane was heat-treated in a muffle furnace under air atmosphere, heated to 800°C at a heating rate of 2°C / min and held for 2 hours to fully remove the ligands in the precursor fiber membrane and crystallize it into niobium oxide fiber membrane, thus obtaining niobium oxide fiber membrane.

[0100] Optical and SEM images of the niobium oxide fiber membrane are shown below. Figure 5 , Figure 6 It can be seen that the fiber diameter is approximately 200-300µm.

[0101] Example 2: Preparation of niobium oxide precursor and niobium oxide fiber membrane using anhydrous niobium chloride as the niobium source and potassium acetate as the ligand source.

[0102] (1) The preparation of the polyniobium acetate precursor is the same as in Example 1.

[0103] (2) Preparation of spinning solution

[0104] The prepared 2g poly(niobium acetate) precursor and 6.5g PAY precursor were dissolved in 20g methanol at 45°C and stirred thoroughly to form a sol. Then, 0.08g PEO was added to the sol, and the mixture was stirred and aged at 45°C for 12 h to obtain a uniform and transparent precursor sol spinning solution.

[0105] (3) Electrospinning is the same as in Example 1.

[0106] Optical photographs of the prepared yttrium niobate precursor fiber membranes are shown below. Figure 7 .

[0107] (4) Heat treatment

[0108] The prepared precursor fiber membrane was heat-treated in a muffle furnace under air atmosphere, heated to 1100°C at a heating rate of 2°C / min and held for 2 hours to completely remove the ligands in the precursor fiber membrane and crystallize it into a yttrium niobate fiber membrane. SEM images showed that the fiber diameter was approximately 200-300 µm, with a smooth surface. After repeated folding with tweezers, the fiber could recover its shape, indicating that the fiber has a certain degree of flexibility and strength.

[0109] Optical and SEM images of the yttrium niobate fiber membrane prepared in Example 2 are shown below. Figure 8 , Figure 9 .

[0110] Example 3: Preparation of niobium oxide precursor and niobium oxide fiber membrane using anhydrous niobium chloride as the niobium source and acetylacetone as the ligand source.

[0111] (1) Preparation of polyacetylacetone-niobium precursor

[0112] a. Weigh 20g of anhydrous niobium chloride and add 100g of ethanol. Heat and stir at 60℃ for 1h. The solution changes from pale yellow to white and transparent.

[0113] b. Weigh 15g of acetylacetone and 20g of ethanol, stir and mix to dissolve, then add dropwise to the system in step a and stir for 0.5h to obtain a pale yellow solution.

[0114] c. Weigh 34g of triethylamine and 50g of ethanol, mix and dissolve them, then add the mixture dropwise to a pale yellow solution. React for 12 hours, then concentrate under reduced pressure at 42℃ to obtain a mixed solid of the precursor and triethylamine hydrochloride.

[0115] d. The mixed solid was soaked in 60 g of acetone extractant for 24 h, filtered, and the supernatant was concentrated under reduced pressure at 34 °C to obtain a solid powder, which is a polyacetylacetone niobium precursor (niobium oxide precursor).

[0116] (2) Preparation of spinning solution, (3) Electrospinning, (4) Heat treatment are carried out according to Example 1.

[0117] Example 4: Preparation of niobium oxide precursor and niobium oxide fiber membrane using niobium acetate oxide obtained in Example 1 as niobium source and acetylacetone as ligand source.

[0118] (1) Preparation of polyacetylacetone-niobium precursor

[0119] a. Weigh 20g of the polyniobium acetate precursor prepared in Example 1 and add 100g of methanol, then heat and stir at 60°C.

[0120] b. Weigh 10g of acetylacetone and 20g of methanol, mix and stir well, then add dropwise to the system in step a and stir for 0.5h to obtain a pale yellow solution;

[0121] c. Weigh 45g of triethylamine and 90g of methanol, mix and stir evenly, add the pale yellow solution dropwise, react fully for 12h, concentrate under reduced pressure at 38℃ to obtain a mixed solid of precursor and triethylamine hydrochloride.

[0122] d. Add 50 g of acetone extractant to the mixed solid and soak for 24 h. Filter and take the supernatant. Concentrate under reduced pressure at 34 °C to obtain solid powder, which is the polyacetylacetone niobium precursor.

[0123] (2) Preparation of spinning solution, (3) Electrospinning, (4) Heat treatment are carried out according to Example 1.

[0124] Example 5:

[0125] The method described in the same way as in Example 1 differs in that:

[0126] In step (1) of preparing the polyniobium acetate precursor, 20g of anhydrous niobium chloride was weighed and added to 100g of ethanol, and 22g of potassium acetate was weighed and added to 230g of ethanol. The potassium acetate solution was added dropwise to obtain a white suspension. The subsequent steps were carried out according to Example 1.

[0127] Example 6: Preparation using anhydrous niobium chloride as the niobium source and potassium acetate as the ligand source

[0128] The method described in the same way as in Example 1 differs in that:

[0129] Step (2) Preparation of spinning solution: Dissolve 4g of poly(niobium acetate) precursor and 5g of PAY precursor in 20g of methanol at 45°C and stir thoroughly to form a solution. Then add 0.09g of PEO to the solution and continue stirring and aging at 45°C for 10h to obtain a uniform and transparent precursor sol spinning solution.

[0130] Example 7: Preparation using anhydrous niobium chloride as the niobium source and potassium acetate as the ligand source

[0131] The method described in the same way as in Example 1 differs in that:

[0132] Step (2) Preparation of spinning solution: Dissolve 4g of the prepared niobium acetate precursor and 8g of yttrium nitrate hexahydrate in 20g of methanol at 45°C and stir thoroughly to form a sol. Then add 0.04g of PEO to the sol and continue stirring at 45°C for 2 hours to obtain a uniform and transparent precursor sol spinning solution.

[0133] Example 8: Preparation using anhydrous niobium chloride as the niobium source and acetylacetone as the ligand source

[0134] The method described in the same way as in Example 3 differs in that:

[0135] In step (1) of the preparation of polyacetylacetone-niobium precursor, 40g of triethylamine and 80g of ethanol were mixed and dissolved, and then added dropwise to a pale yellow solution. The reaction was carried out for 12h, and the mixture was concentrated under reduced pressure at 42℃ to obtain a mixed solid of the precursor and triethylamine hydrochloride. The mixed solid was soaked in 60g of acetone extractant for 24h, filtered, and the supernatant was collected. The supernatant was concentrated under reduced pressure at 34℃ to obtain a solid powder, which is the polyacetylacetone-niobium precursor. The subsequent steps were carried out according to Example 3.

[0136] Example 9: Preparation using anhydrous niobium chloride as the niobium source and potassium acetate as the ligand source

[0137] The method described in the same way as in Example 1 differs in that:

[0138] Step (4) Heat treatment: The precursor fiber membrane is placed in a muffle furnace under air atmosphere and heated to 1100 °C at a heating rate of 1 °C / min and held for 2 h to fully remove the ligands in the precursor fiber membrane and crystallize it into yttrium niobate fiber membrane. After picking up the fiber with tweezers, it is repeatedly folded and the fiber can be restored. The fiber membrane has good morphology and mechanical properties.

[0139] Comparative Example 1:

[0140] The method described in the same way as in Example 1 differs in that:

[0141] In the preparation of the polyniobium acetate precursor, step b involves weighing 45g of potassium acetate and dissolving it in 400g of anhydrous ethanol to obtain a solution. Other methods and conditions are carried out according to Example 1.

[0142] The precursor yield obtained in this comparison was extremely low because excess potassium acetate reacted with anhydrous niobium chloride. Anhydrous niobium chloride is chemically unstable and readily hydrolyzed. Some of the anhydrous niobium chloride hydrolyzed to form niobium hydroxide precipitate, which was filtered out along with the potassium chloride, resulting in a decrease in precursor yield.

[0143] Comparative Example 2:

[0144] The method is the same as that described in Example 1, except that:

[0145] In preparing the spinning solution, 2g of the prepared niobium acetate precursor and 11.5g of yttrium nitrate hexahydrate were dissolved in 15g of methanol at 45°C and stirred thoroughly to form a sol. Then, 0.04g of PEO was added to the sol, and the mixture was stirred and aged at 45°C for 12 h to obtain a uniform and transparent precursor sol spinning solution. Other methods and conditions were carried out as in Example 1.

[0146] The yttrium niobate fibers obtained in this comparative example have poor mechanical properties. This is mainly because, in addition to the fact that yttrium nitrate hexahydrate itself is not spinnable, the precursor fibers obtained are prone to deliquescence leading to fiber clumping, and they also undergo violent decomposition during heat treatment, resulting in uneven fiber diameter shrinkage, fiber deformation, and increased brittleness.

[0147] Comparative Example 3:

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

[0149] In the preparation of polyacetylacetone niobium precursor, in step b, the amount of acetylacetone as the ligand source is 50g, which is directly added to the stirring for the next step. This process makes the solution turbid. This is because too much ligand source is added too quickly, which directly generates acetylacetone niobium, affecting the quality and yield of the precursor.

[0150] Comparative Example 4:

[0151] The method is the same as that described in Example 1, except that:

[0152] In the preparation of polyacetylacetone-niobium precursor, in step d, the amount of dechlorinating agent triethylamine is 60 g, which is directly poured in and stirred. This process also makes the solution turbid and produces precipitation. This is because excessive triethylamine makes the solution alkaline and produces insoluble hydroxides, resulting in a decrease in the precursor yield.

[0153] Comparative Example 5:

[0154] The method is the same as that described in Example 1, except that:

[0155] In the preparation of the polyniobium acetate precursor, in step b, 22g of potassium acetate is weighed and dissolved in 400g of anhydrous ethanol to obtain a solution, which is then directly poured into anhydrous niobium chloride solution. After a short stirring, the next step is carried out. Other methods and conditions are the same as in Example 1.

[0156] The precursor yield obtained in this comparison was extremely low because potassium acetate did not react sufficiently with niobium chloride. Some niobium chloride remained in molecular form, and some niobium chloride was hydrolyzed, resulting in a very small amount of niobium chloride undergoing coordination, which reduced the quality and yield of the precursor.

[0157] Comparative Example 6:

[0158] The method described in the same way as in Example 1 differs in that:

[0159] In step (2), 10g of polyniobium acetate precursor and 20g of yttrium nitrate hexahydrate are dissolved in 50g of methanol. The use of a large amount of solvent will cause the fiber to be too fine and the strength to decrease, resulting in the failure to obtain a high-quality precursor and yttrium niobate fiber membrane.

Claims

1. A method for preparing niobium oxide precursor, comprising the following steps: (1) Using anhydrous inorganic salts of niobium as the niobium source, dissolve them in alcohol, stir the reaction, and obtain solution A; (2) Add the ligand source to the solvent to obtain solution B. Slowly add solution B to solution A. Filter the supernatant and concentrate it under reduced pressure to obtain niobium oxide precursor powder.

2. The preparation method according to claim 1, characterized in that, In step (1), the anhydrous inorganic salt of niobium is one or a combination of two or more of niobium chloride, niobium bromide, niobium iodide, niobium fluoride, niobium sulfate, and niobium nitrate. In step (1), the alcohol is one or a mixture of two or more of anhydrous methanol, anhydrous ethanol, and isopropanol. The dissolution temperature is 20~40 ℃, and the mass ratio of niobium source to alcohol is 1:3~10.

3. The preparation method according to claim 1, characterized in that, In step (2), the ligand source is a carboxylate or a β-diketone compound. The carboxylate ligand source is selected from one or more of potassium acetate, sodium acetate, potassium propionate, sodium propionate, potassium oxalate, and sodium oxalate. Preferably, the carboxylate ligand source is potassium acetate. The β-diketone compound ligand source is selected from one or more of acetylacetone, methyl acetoacetate, ethyl acetoacetate, propyl acetoacetate, isopropyl acetoacetate, and butyl acetoacetate. Preferably, in step (2), the β-diketone compound ligand source is acetylacetone.

4. The preparation method according to claim 3, characterized in that, In step (2), when potassium acetate is used as the ligand source, potassium acetate is added to the solvent and heated and stirred at 30~90 °C to obtain solution B. Solution B is slowly added to solution A, and the supernatant obtained by filtering to remove potassium chloride is concentrated under reduced pressure to obtain niobium oxide precursor powder. The solvent is a mixture of water and alcohol, where the alcohol is methanol or ethanol. The mass ratio of potassium acetate to alcohol is 1:5~10, the mass ratio of potassium acetate to water is 1:0.1~0.5, and the molar ratio of niobium source to potassium acetate is 1:1~7.

5. The preparation method according to claim 3, characterized in that, In step (2), when using β-diketone compounds as ligand sources, the β-diketone compound ligand source and the dechlorinating agent are dissolved in a solvent and then added to transparent solution A. The mixture is stirred and reacted for 0.5 to 2 hours. The supernatant is collected, concentrated under reduced pressure, and evaporated to dryness. The dry powder is collected and soaked in an extractant for 12 to 48 hours, then filtered. The supernatant is collected under reduced pressure and concentrated to form a powder, thus obtaining the niobium oxide precursor. The solvent is methanol or ethanol. The molar ratio of the anhydrous niobium chloride to the β-diketone ligand source is 1:0.5~3. The dechlorinating agent is one or more of triethylamine, ethylenediamine, ethanolamine, and aniline. The ethanolamine is monoethanolamine, diethanolamine, or triethanolamine. The molar ratio of the anhydrous niobium chloride to the dechlorinating agent is 1:3~6. After the dechlorinating agent is added and reacted, the mixture is concentrated under reduced pressure at 38~42 °C. After the byproduct triethylamine hydrochloride is removed by the extractant, the supernatant is concentrated under reduced pressure at 32~35 °C. The extractant is acetone and / or tetrahydrofuran.

6. Niobium oxide precursor, prepared by any one of the preparation methods described in claims 1-5.

7. A niobium oxide fiber membrane, wherein the fiber membrane is prepared by electrospinning and heat treatment using the niobium oxide precursor obtained according to claim 1 as raw material and adding a spinning aid.

8. The method for preparing the niobium oxide fiber membrane according to claim 7, comprising the following steps: 1) Dissolve the niobium oxide precursor in methanol at 40-50℃ and stir thoroughly to form a sol. Then add a spinning aid and continue stirring and aging at 40-50℃ for 10-15 hours to obtain a uniform and transparent precursor sol spinning solution. Electrospin the sol spinning solution to obtain a niobium oxide precursor fiber membrane. 2) The niobium oxide precursor fiber membrane is heat-treated in an air atmosphere to obtain the niobium oxide fiber membrane.

9. A yttrium niobate fiber membrane derived from a niobium oxide fiber membrane, wherein the fiber membrane is prepared by electrospinning and heat treatment using the niobium oxide precursor obtained in claim 1 as raw material, adding PAY and a spinning aid.

10. The method for preparing the yttrium niobate fiber membrane according to claim 9, comprising the following steps: S1. Dissolve niobium oxide precursor and PAY in methanol at 40-50℃ and stir thoroughly to form a sol. Then add spinning aid, continue stirring at 40-50℃ and age for 10-15 hours to obtain a uniform and transparent precursor sol spinning solution. Electrospin the sol spinning solution to obtain yttrium niobate precursor fiber membrane. S2. The yttrium niobate precursor fiber membrane is heat-treated in an air atmosphere to obtain the yttrium niobate fiber membrane.

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