Process for the preparation of metal oxides and composites thereof

Abstract

The present application provides a preparation method of metal oxide, comprising: (1) melting metal nitrate or metal nitrate hydrate to obtain liquid metal nitrate; or dissolving the metal nitrate or metal nitrate hydrate to obtain a nitrate solution; (2) reacting the liquid metal nitrate or the nitrate solution obtained in step (1) with carbon dioxide to obtain a carbonate; or granulating the liquid metal nitrate or the nitrate solution into solid particles first, and then reacting the solid particles with carbon dioxide to obtain a carbonate; (3) heating and decomposing the metal carbonate obtained in step (2) under vacuum conditions to obtain a metal oxide. Compared with directly heating and decomposing the nitrate, the conversion of the nitrate into the carbonate tends to be spontaneous. The above process can also add an additive to the obtained liquid metal nitrate or the nitrate solution in step (1) or the obtained carbonate in step (2), and finally obtain a metal oxide composite, so as to regulate the composition and function of the metal oxide and the composite.

Description

Technical Field

[0001] This invention relates to the field of materials preparation technology, and specifically to a method for preparing metal oxides and their composites. Background Technology

[0002] Metal oxides and their complexes have wide applications in the metallurgical industry, battery, and catalysis fields. They can be used as raw materials for metal smelting and are also commonly used as catalysts for various applications and functions in catalysis. Furthermore, metal oxides and their complexes with specific morphologies can serve as precursors for positive electrode materials in lithium-ion batteries; there are also research reports on the use of metal oxides and their complexes with specific morphologies as negative electrode materials in lithium-ion batteries.

[0003] Current methods for preparing metal oxides and their complexes mainly include metal powder oxidation, hydrothermal synthesis, combustion synthesis, and spray pyrolysis. However, each method has its own problems, such as low reaction yield, high process requirements making industrialization difficult, high energy consumption, and environmental unfriendliness. Summary of the Invention

[0004] The purpose of this invention is to provide a more energy-efficient, environmentally friendly, homogeneous, less impurity-laden, and industrially suitable preparation method for widely used metal oxides and their composites.

[0005] This invention proposes a method for preparing metal oxides and their complexes. The method involves decomposing carbonates obtained from nitrates and their hydrates under vacuum conditions to prepare the final product, metal oxides. Compared with existing technologies that directly decompose nitrates, this method consumes less energy. Furthermore, the addition of additives during the preparation process can yield metal oxide complexes.

[0006] In the first stage of the above process, nitrate reacts with carbon dioxide to form carbonate. The molar volume of the metallic carbonate is smaller than that of the nitrate, and the formed carbonate does not hinder the contact between nitrate and carbon dioxide, kinetically favoring the decomposition of nitrate. Using carbon dioxide to react with nitrate or its hydrate has two advantages: firstly, it exhibits a greater thermodynamic tendency to react, reducing the difficulty of the chemical reaction; secondly, it shifts the chemical equilibrium in a favorable direction, while simultaneously reducing the residual nitrate content in the resulting oxides and their complexes. The second stage, decomposing the carbonate under vacuum conditions, lowers the decomposition temperature and reduces reaction energy consumption.

[0007] Therefore, nitrates or their hydrates are first reacted with carbon dioxide to obtain solid carbonates with a certain particle size and morphology, and then the carbonates are converted into metal oxides. The metal oxides, as the final product, inherit the particle size and morphology of the carbonates, avoiding the shortcomings of hydrothermal synthesis and other methods that require many control parameters and have long synthesis times.

[0008] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution.

[0009] The first aspect of this invention provides a method for preparing a metal oxide, specifically comprising the following steps:

[0010] (1) Nitrate pretreatment

[0011] Solid metal nitrates or metal nitrate hydrates are physically sieved to obtain solid metal nitrates or metal nitrate hydrates of a certain particle size; or solid metal nitrates or metal nitrate hydrates are heated under stirring conditions at a temperature lower than the decomposition temperature of metal nitrates until the metal nitrates or metal nitrate hydrates are completely melted to obtain liquid metal nitrates; or a solvent is added at a certain temperature to dissolve the nitrates in the solution to obtain a nitrate solution.

[0012] (2) Preparation of carbonates

[0013] The liquid metal nitrate or nitrate solution obtained in step (1) is reacted with carbon dioxide to obtain carbonate; or the liquid metal nitrate or nitrate solution is first granulated into solid particles and then reacted with carbon dioxide to obtain carbonate; or the sieved solid can be directly reacted with carbon dioxide.

[0014] Furthermore, the liquid metal nitrate or nitrate solution obtained in step (1) can be physically atomized into small droplets. The atomized droplets react with carbon dioxide gas to produce solid metal carbonate and a gas mixture whose main components are oxygen and nitrogen dioxide. The atomization method can be spray atomization. Alternatively, the liquid metal nitrate or nitrate solution obtained in step (1) can be granulated to obtain solid nitrate particles with a defined particle size and morphology. Then, it reacts with carbon dioxide gas to produce a gas-solid reaction. The reaction products are the same as those of the gas-liquid reaction described above. The granulation method can be spray drying granulation.

[0015] The above-mentioned gas-liquid and gas-solid reactions can be represented by chemical reaction formulas:

[0016]

[0017]

[0018] Where ① is the reaction equation for a gas-liquid reaction, and ② is the reaction equation for a gas-solid reaction. M is a metallic element, water is in a gaseous or liquid state, x and a are numbers greater than 0, and b and c can be 0.

[0019] Taking the decomposition of lithium nitrate as an example: During direct heating, the reaction is 4LiNO3(s) → 2Li2O(s) + O2(g) + 4NO2(g), ΔG r Θ=4ΔG f Θ NO2 +ΔG f Θ O2 +2ΔG f Θ Li2O -4ΔG f Θ LiNO3 = 607.28 kJ / mol; The reaction of lithium nitrate with carbon dioxide is 4LiNO3(s) + 2CO2(g) → 2Li2CO3(s) + O2(g) + 4NO2(g), ΔG r Θ =4ΔG f Θ NO2 +ΔG f Θ O2 +2ΔG f Θ Li2CO3 -4ΔG f Θ LiNO3 -2ΔG f Θ CO2 = -534.48 kJ / mol. Compared with direct heating decomposition, the Gibbs free energy of the reaction between carbon dioxide and lithium nitrate becomes negative, indicating that the reaction has a spontaneous tendency. Therefore, the addition of carbon dioxide changed the direction of the lithium nitrate decomposition reaction.

[0020] Taking the decomposition of zinc nitrate as an example: During direct heating, the reaction is 2Zn(NO3)2(s) → 2ZnO(s) + O2(g) + 4NO2(g), ΔG Θ =4ΔG f Θ NO2 +ΔG f Θ O2 +2ΔG f Θ ZnO -2ΔG f Θ Zn(NO3)2 = -431.36 kJ / mol, when the reaction reaches equilibrium, ΔG r =0=ΔG Θ +RTln KΘ , The reaction of zinc nitrate with carbon dioxide is 2Zn(NO3)2(s) + 2CO2 → 2ZnCO3(s) + O2(g) + 4NO2(g), ΔGr Θ =4ΔG f Θ NO2 +ΔG f Θ O2 +2ΔG f Θ ZnCO3 -2ΔG f Θ Zn(NO3)2 -2ΔG f Θ CO2 = -469.082 kJ / mol; when the reaction reaches equilibrium, ΔG r =0=ΔG Θ +RTln KΘ , Where ΔG r Θ For the Gibbs free energy change of the reaction under standard conditions, ΔG r This represents the Gibbs free energy change under equilibrium conditions. The above reaction process illustrates that although the direct heating and decomposition of zinc nitrate has a spontaneous tendency, increasing the carbon dioxide pressure can shift the decomposition reaction towards decomposition.

[0021] In summary, using carbon dioxide to react with nitrates or their hydrates offers two advantages: firstly, it exhibits a greater thermodynamic tendency to react, reducing the difficulty of the chemical reaction; secondly, it shifts the chemical equilibrium in a favorable direction while simultaneously reducing the residual nitrate content in the resulting oxide. It should be noted that the reaction of nitrates or nitrate hydrates with carbon dioxide has a lower standard Gibbs free energy change ΔG. r Θ This is a universally existing law.

[0022] (3) Preparation of metal oxides

[0023] The metal carbonate obtained in step (2) is decomposed by heating under vacuum to obtain metal oxide.

[0024] After the above-mentioned heating and decomposition is completed, an inert gas is used to break the vacuum to obtain metal oxides and a gas with carbon dioxide as the main component. The obtained metal oxides are protected in an inert atmosphere.

[0025] Taking the decomposition of zinc carbonate as an example: Zn(CO3)2(s) → ZnO(s) + CO2(g), the relationship between the decomposition temperature T and the decomposition pressure p is as follows: This indicates that decomposing carbonates under vacuum conditions can lower the decomposition temperature, further reducing reaction energy consumption.

[0026] Preferably, in step (1), the metal element in the metal nitrate or metal nitrate hydrate is capable of forming a stable nitrate or its hydrate, and simultaneously forming a stable carbonate. The metal element is selected from at least one of Li, Be, Mg, Sc, Zr, Hf, Cr, Mn, Ni, Fe, Co, Ni, Cu, Zn, Cd, Tl, Pb, Bi, and Th, and at least one of the lanthanide metals in the periodic table other than La and Pm.

[0027] Preferably, in step (1), the solid metal nitrate or metal nitrate hydrate is physically sieved to obtain a solid metal nitrate or metal nitrate hydrate with a certain particle size, wherein the particle size of the solid metal nitrate or metal nitrate hydrate is 1 mm or less.

[0028] Preferably, in step (1), the heating method is heat source conduction heating or microwave heating.

[0029] Preferably, in step (1), the solvent does not participate in the chemical reaction and does not appear in the final product. The solvent has a solubility of more than 0.1 mol / L for the selected nitrate at 25°C and a boiling point of less than 101°C at 0.1 MPa. The solvent includes, but is not limited to, water, alcohol, or ketone. Typical characteristics of nitrates or their hydrates are low melting points and high solubility in water. Some nitrates or their hydrates have high solubility in organic solvents such as methanol and ethanol. Heating and using specific solvents can conveniently melt or dissolve nitrates, while using alcohol solvents can inhibit the hydrolysis of metal salts.

[0030] Preferably, the amount of solvent v used in step (1) can be calculated using the following formula:

[0031] At 25°C, the solubility of nitrates or their hydrates in a solvent is m grams per liter. The mass M of nitrates or their hydrates used and the amount of solvent used, v, satisfy the following equation: v = a * M / m. The unit of solvent amount v is liters, a is the solvent coefficient, a is greater than or equal to 5%, and the units of M and m are grams. When multiple nitrates or their hydrates are used, the amount of solvent is the sum of the corresponding amounts of solvent for each nitrate or its hydrate.

[0032] Preferably, in step (2), the temperature of the carbon dioxide gas is 30℃-500℃, more preferably 30℃-370℃.

[0033] Preferably, in step (2), the flow rate of the carbon dioxide gas is 27-50 m³ / h. 3 / h, the ratio of the molar amount of nitrate metal to the molar amount of carbon dioxide injected per unit time is less than 2.

[0034] Preferably, in step (2), a gas mixture containing carbon dioxide is added, wherein the partial pressure of the carbon dioxide gas is greater than 0.01 MPa.

[0035] Preferably, in step (3), the heating temperature under vacuum conditions is 40℃-600℃, more preferably 40℃-450℃.

[0036] Preferably, in step (3), the vacuum degree is any value below 0.1 MPa absolute pressure, and the heating decomposition reaction time is 1-10 h. The heating can be continuous throughout the entire vacuum reaction process, or it can be intermittent during the reaction process.

[0037] Preferably, in step (3), after the heating decomposition is completed, an inert gas is used to break the vacuum, and the resulting metal oxide is protected in an inert atmosphere. The inert gas contains at least one of carbon dioxide, nitrogen, and argon. The pressure of the inert atmosphere is not limited, and it contains at least one of carbon dioxide, nitrogen, and argon.

[0038] A second aspect of the present invention provides a metal oxide prepared by the method, wherein the metal oxide is composed of a metal element and an oxygen element, and the metal element and the oxygen element are bonded together by chemical bonds.

[0039] The third aspect of the present invention provides a method for preparing a metal oxide composite, wherein, compared with the above-described method for preparing metal oxides, additives are added to the intermediate products obtained in steps (1) and (2).

[0040] The additive is added either during the nitrate pretreatment in step (1) or after the preparation of the carbonate in step (2).

[0041] Preferably, additives can be added to the liquid metal nitrate melt or nitrate solution obtained in step (1), and after mixing evenly, a liquid mixture of nitrate and additives can be obtained.

[0042] The subsequent preparation process is the same as the preparation method of metal oxides, that is, in step (2), the liquid mixture obtained in step (1) is reacted with carbon dioxide to obtain a carbonate complex containing additives; in step (3), the carbonate complex containing additives is heated and decomposed under vacuum conditions to obtain a metal oxide complex.

[0043] Preferably, the additive is selected from at least one of metal carbonates, metal oxides, and inorganic substances whose chemical composition is elemental carbon.

[0044] Preferably, the metal carbonate and metal oxide can be prepared by the technical solution provided in the first aspect of the present invention.

[0045] The additives may undergo physical or chemical changes during preparation. Generally, metal oxides and inorganic substances with elemental carbon do not undergo chemical changes during preparation and remain as metal oxides and carbon in the final product. Metal carbonates, however, undergo corresponding chemical reactions during preparation and remain as metal oxides in the final product.

[0046] The fourth aspect of the present invention provides a metal oxide composite prepared by the method, wherein the metal oxide composite contains two or more metal oxides, or contains at least one metal oxide and carbon.

[0047] Based on the above technical solution, the present invention has the following beneficial effects:

[0048] This invention provides a method for preparing metal oxides by converting metal nitrates or nitrate hydrates into carbonates, and further preparing the carbonates by vacuum thermal decomposition. Due to the low melting point and high solubility in water of metal nitrates and their hydrates, and the significant solubility of some nitrates or their hydrates in organic solvents such as methanol and ethanol, metal ions can achieve atomic-level mixing in liquids, ensuring the uniformity of chemical composition of the subsequent metal carbonates and metal oxides. Simultaneously, the molar volume of the metal carbonate is smaller than that of the corresponding metal nitrate. When nitrates react with carbon dioxide, the resulting carbonates do not impede the diffusion of carbon dioxide gas, providing a certain kinetic advantage.

[0049] Based on Gibbs free energy calculations from chemical reaction thermodynamics, the conversion of nitrates to carbonates is more spontaneous than the direct thermal decomposition of nitrates. Furthermore, decomposition under vacuum conditions reduces the energy consumption of carbonate decomposition and avoids non-oxide impurities generated from reactions with air. The particle size of metal carbonates can be initially controlled by atomizing or granulating liquid metal nitrates or nitrate solutions into solid particles, thereby producing oxides of specific particle sizes. Additional additives can be added during the melting or dissolving stages of the metal nitrates or nitrate hydrates and the decomposition stages of the carbonates to achieve specific oxide structures and functions. The nitric acid, oxygen, and carbon dioxide produced in the reaction can be recovered and reused.

[0050] Furthermore, this invention can also add additives to metal nitrates or nitrate solutions to regulate the composition and function of metal oxides and their complexes. This effectively solves the problems of high energy consumption and complex reaction conditions in the preparation of existing metal oxides. At the same time, the required equipment and raw materials are simple and readily available, and the synthesis method is straightforward. Detailed Implementation

[0051] The following embodiments further illustrate the above-mentioned content of the present invention in detail. However, the subject matter of the present invention is not limited to the following embodiments, and all technologies implemented based on the above-mentioned content of the present invention fall within the scope of the present invention.

[0052] Example 1

[0053] This embodiment proposes a method for preparing nickel oxide, which is specifically carried out according to the following steps:

[0054] (1) Nitrate pretreatment

[0055] Solid nickel nitrate hexahydrate was sieved through a 16-mesh sieve, and the undersize material was collected.

[0056] (2) Preparation of carbonates

[0057] The undersize obtained in step (1) is reacted with carbon dioxide gas in a fluidized reactor at a temperature of 80°C and a partial pressure of 1 MPa to produce a mixture of nickel carbonate and gas, the main components of which are oxygen and nitrogen dioxide.

[0058] (3) Preparation of metal oxides

[0059] The nickel carbonate obtained in step (2) was decomposed by heating under vacuum at a temperature of 80°C. The absolute pressure of the vacuum reactor was maintained below 700 Pa for 4 hours. After decomposition, nitrogen was used to break the vacuum, producing nickel oxide and a gas mainly composed of carbon dioxide. The produced nickel oxide was protected in nitrogen.

[0060] Example 2

[0061] This embodiment proposes a method for preparing a nickel-cobalt oxide composite, which is specifically prepared according to the following steps:

[0062] (1) Nitrate pretreatment

[0063] Nickel nitrate hexahydrate and cobalt nitrate hexahydrate with a molar ratio of Ni:Co = 1:1 were weighed and heated under stirring. Simultaneously, a methanol solution with a mass fraction of 85% was added at a solvent coefficient a = 20%. The heating temperature was 60℃ until the metal nitrate hydrates completely became liquid. The addition of methanol solution serves two purposes: firstly, it utilizes the solubility of nickel nitrate and cobalt nitrate in methanol to accelerate the conversion of the nickel nitrate and cobalt nitrate hydrates into a liquid state; secondly, it inhibits the hydrolysis of nickel and cobalt ions. The amount of solvent added also has a certain influence on the morphology of nickel cobalt carbonate and nickel cobalt oxide.

[0064] (2) Preparation of carbonates

[0065] Using spray drying granulation technology, the nitrate liquid obtained in step (1) is made into solid particles with a certain particle size. Then, the solid particles react with carbon dioxide gas at a temperature of 80°C and a partial pressure of 1 MPa to produce a mixture of nickel cobalt carbonate and gas. The main components of the gas mixture are oxygen and nitrogen dioxide.

[0066] (3) Preparation of metal oxide composites

[0067] The nickel cobalt carbonate obtained in step (2) was decomposed by heating under vacuum conditions at a temperature of 200°C. The absolute pressure of the vacuum reactor was maintained below 700 Pa for 4 hours. After decomposition, nitrogen was used to break the vacuum, producing nickel oxide and a gas mainly composed of carbon dioxide. The produced nickel cobalt oxide was protected in nitrogen.

[0068] Example 3

[0069] This embodiment proposes a method for preparing a nickel-cobalt-lithium oxide composite, which is specifically prepared according to the following steps:

[0070] Steps (1) and (2) of Example 3 are the same as steps (1) and (2) of Example 2; the difference is that in step (3), the nickel cobalt carbonate obtained in step (2) is weighed according to the metal molar ratio of lithium:(nickel+cobalt)=1:1, and ethanol is added to mix the lithium carbonate and nickel cobalt carbonate. After ball milling for 5 hours to make the composition uniform, a lithium carbonate and nickel cobalt carbonate composite is obtained.

[0071] The composite was then decomposed under vacuum conditions at 150°C, with the absolute pressure in the vacuum reactor maintained below 700 Pa for 2 hours. The temperature was then increased to 260°C, with the absolute pressure in the vacuum reactor maintained below 700 Pa for another 2 hours. After decomposition, a mixed gas comprising 70% nitrogen was used to break the vacuum, producing lithium nickel cobalt manganese oxide and a gas primarily composed of carbon dioxide. The produced lithium nickel cobalt oxide was protected in nitrogen.

[0072] Example 4

[0073] This embodiment proposes a method for preparing a nickel-cobalt-lithium oxide and graphite composite, which is specifically prepared according to the following steps:

[0074] The steps in Example 4 were the same as those in Example 3, except that in step (1), after the nitrate was completely dissolved into a liquid, stirring was continued for 30 minutes, and 0.01% by mass of graphite powder (sieved through a 12500 mesh sieve) was added while stirring was maintained. After 1 hour, the process of repeating steps (2), (3), and (4) of Example 3 was started.

[0075] Example 5

[0076] This embodiment proposes a method for preparing a zinc oxide-coated nickel-cobalt-lithium oxide and graphite composite, which is specifically prepared according to the following steps:

[0077] The composite of lithium nickel cobalt manganese oxide and graphite prepared in Example 4 was further used as an additive in Example 5.

[0078] (1) Preparation of nitrate mixtures

[0079] A zinc nitrate solution was prepared using zinc nitrate hexahydrate and 95% ethanol solution, with a concentration of 15 g / L. The nickel cobalt lithium oxide and graphite composite obtained in Example 3 was added to the zinc nitrate solution to ensure that the solution could completely submerge the nickel cobalt lithium oxide and graphite composite obtained in Example 4, and that the nickel cobalt lithium oxide and graphite composite obtained in Example 4 could be completely dispersed in the solution.

[0080] (2) Preparation of carbonates

[0081] Using spray drying granulation technology, the zinc nitrate solution obtained in step (1) and the mixture of lithium nickel cobalt manganese oxide and graphite composite are made into solid particles. Then, the solid particles are reacted with carbon dioxide gas at a temperature of 100°C and a partial pressure of 1 MPa to produce a mixture of lithium nickel cobalt manganese oxide and graphite composite coated with zinc carbonate and gas. The main components of the gas mixture are oxygen and nitrogen dioxide.

[0082] (3) Preparation of metal oxides

[0083] The zinc carbonate-coated lithium nickel cobalt oxide and graphite composite obtained in step (2) was decomposed under vacuum conditions at 100°C. The absolute pressure of the vacuum reactor was maintained below 700 Pa for 2 hours. After decomposition, nitrogen was used to break the vacuum, producing the zinc carbonate-coated lithium nickel cobalt oxide and graphite composite and a gas mainly composed of carbon dioxide. The produced zinc carbonate-coated lithium nickel cobalt oxide and graphite composite was protected in nitrogen.

[0084] Comparative Example 1

[0085] This comparative example uses direct heating to decompose nickel nitrate, and high-temperature air is introduced to decompose nickel nitrate into nickel oxide.

[0086] (1) Preparation of liquid nickel nitrate

[0087] Solid nickel nitrate hexahydrate was sieved through a 16-mesh sieve, and the undersize material was collected.

[0088] (2) Decomposition of nickel nitrate

[0089] The undersize obtained in step (1) is reacted with high-temperature air in a fluidized reactor at a temperature of 280°C and a pressure of 1 MPa to produce a mixture of nickel oxide and gas. The main components of the gas mixture are oxygen and nitrogen dioxide. The produced product has a certain degree of adhesion.

[0090] Comparative Example 2

[0091] The steps in this comparative example are the same as those in Example 1. The difference from Example 1 is that in step (3), nickel carbonate is decomposed under normal pressure and heated to 300°C. The remaining steps are the same as those in Example 1.

[0092] In the above examples and comparative examples, the carbonate content in the carbonate or carbonate complex and the apparent molar conversion rate of nitrate are shown in Table 1. The carbonate content in the oxide or oxide complex, the apparent molar decomposition rate of carbonate, and the nitrate content in the oxide or oxide complex are shown in Table 2.

[0093] Table 1

[0094]

[0095] Table 2

[0096]

[0097]

[0098] The data comparison in Table 1 shows that the introduction of carbon dioxide is a key influencing factor on the conversion rate of nitrate to carbonate, and the conversion rate of nitrate is higher after the introduction of carbon dioxide.

[0099] The data comparison in Table 2 shows that decomposing carbonates under vacuum conditions can achieve a higher decomposition rate at lower temperatures than decomposing at atmospheric pressure and high temperature, while also producing less nitrate residue in the products.

[0100] The apparent conversion rate is calculated as follows: calculate the theoretical carbonate mass fraction (m%) per mole of carbonate, the actual carbonate mass fraction (m1%) per mole of carbonate, and the carbonate mass fraction (m2%) per mole of oxide.

[0101] This invention provides a method for preparing metal oxides and their complexes. By selectively using different metal oxide nitrates and their hydrates and adding different additives during the preparation stage of liquid nitrates or nitrate solutions and the carbonate decomposition stage, metal oxides and their complexes with different compositions and structures are prepared.

[0102] Furthermore, the reaction of carbon dioxide with nitrates exhibits a greater thermodynamic tendency, which significantly reduces the temperature required for the decomposition of nitrates in practical operation.

[0103] Vacuum decomposition of carbonates reduces the energy consumption required for carbonate decomposition.

[0104] The resulting nitrogen dioxide gas can be recycled, and the carbon dioxide gas can be reused. Through the combination of embodiments of the present invention, metal oxides and their complexes with different compositions, structures, and uses can be produced.

[0105] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this invention, and these modifications or substitutions should all be covered within the scope of protection of this invention. Therefore, the scope of protection of this invention should be determined by the scope defined in the claims.

Claims

1. A method for preparing a metal oxide, characterized in that, Includes the following steps: (1) Nitrate pretreatment: Solid metal nitrates or solid metal nitrate hydrates are physically sieved to obtain solid metal nitrates or solid metal nitrate hydrates of a certain particle size; or solid metal nitrates or solid metal nitrate hydrates are heated under stirring conditions at a temperature lower than the decomposition temperature of metal nitrates until the metal nitrates or metal nitrate hydrates are completely melted to obtain liquid metal nitrates; or a solvent is added at a certain temperature to dissolve the metal nitrates in the solution to obtain a nitrate solution. In step (1), the metal element in the metal nitrate or metal nitrate hydrate can form a stable nitrate or its hydrate, and at the same time can form a stable carbonate; (2) Preparation of metal carbonates: The liquid metal nitrate or nitrate solution obtained in step (1) is first granulated into solid particles, and then reacted with carbon dioxide gas to obtain metal carbonate; or the sieved solid is directly reacted with carbon dioxide gas. The temperature of the carbon dioxide gas is 30℃-500℃; If a gas mixture containing carbon dioxide is added, the partial pressure of the carbon dioxide gas is greater than 0.01 MPa; (3) Preparation of metal oxides: The metal carbonate obtained in step (2) is decomposed by heating under vacuum to obtain metal oxide; The heating temperature under the vacuum conditions is 40℃-450℃, and the vacuum degree is any value below 0.1Mpa absolute pressure.

2. The method for preparing the metal oxide according to claim 1, characterized in that, In step (1), the metal element is selected from at least one of Li, Be, Mg, Sc, Zr, Hf, Cr, Mn, Ni, Fe, Co, Cu, Zn, Cd, Tl, Pb, Bi, Th, and at least one of the lanthanide metal elements other than La and Pm in the periodic table.

3. The method for preparing the metal oxide according to claim 1, characterized in that, In step (1), the solvent has a solubility of more than 0.1 mol / L for the selected metal nitrate at 25°C and a boiling point of less than 101°C at 0.1 MPa pressure.

4. The method for preparing the metal oxide according to claim 3, characterized in that, In step (1), the solvent is water, alcohol or ketone.

5. The method for preparing the metal oxide according to claim 4, characterized in that, In step (1), the alcohol is methanol or ethanol.

6. The method for preparing the metal oxide according to claim 1, characterized in that, Step (2) involves spray drying to granulate the obtained liquid metal nitrate or nitrate solution into solid nitrate particles, which then react with carbon dioxide gas.

7. The method for preparing the metal oxide according to claim 1, characterized in that, In step (2), the temperature of the carbon dioxide gas is 30℃-370℃; The flow rate of the carbon dioxide gas is 27–50 m³ / h. 3 / h, the ratio of the molar amount of nitrate metal to the molar amount of carbon dioxide injected per unit time is less than 2.

8. The method for preparing the metal oxide according to claim 1, characterized in that, In step (3), the heating decomposition reaction time is 1-10h.

9. A metal oxide prepared by the method according to any one of claims 1 to 8, wherein the metal oxide is composed of a metal element and an oxygen element, and the metal element and the oxygen element are bonded together by chemical bonds.

10. A method for preparing a metal oxide composite, characterized in that, Includes the following steps: (1) Nitrate pretreatment: Solid metal nitrates or solid metal nitrate hydrates are heated under stirring conditions at a temperature lower than the decomposition temperature of the metal nitrates until the metal nitrates or metal nitrate hydrates are completely melted to obtain liquid metal nitrates; or water or organic solvents are added at a certain temperature to dissolve the metal nitrates in the solution to obtain a nitrate solution. Additives are added to the obtained liquid metal nitrate or metal nitrate solution, and after mixing evenly, a liquid mixture of nitrate and additives is obtained. In step (1), the metal element in the metal nitrate or metal nitrate hydrate can form a stable nitrate or its hydrate, and at the same time can form a stable carbonate; The additive is selected from at least one of metal carbonates, metal oxides, and inorganic substances whose chemical composition is elemental carbon; (2) Preparation of carbonates: The liquid mixture obtained in step (1) is first granulated into solid particles, and then reacted with carbon dioxide gas to obtain a carbonate complex containing additives. The temperature of the carbon dioxide gas is 30℃-500℃; If a gas mixture containing carbon dioxide is added, the partial pressure of the carbon dioxide gas is greater than 0.01 MPa; (3) Preparation of metal oxides: The carbonate complex containing additives obtained in step (2) is decomposed by heating under vacuum to obtain a metal oxide complex. The heating temperature under the vacuum conditions is 40℃-450℃, and the vacuum degree is any value below 0.1Mpa absolute pressure.

11. The metal oxide composite prepared by the method of claim 10, wherein the metal oxide composite contains two or more metal oxides, or contains at least one metal oxide and carbon.

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