Method for preparing nano metal oxide by thickening method

Abstract

The present invention discloses a method for preparing nano-metal oxides by thickening. The method comprises the following steps: heating and stirring a saccharide and an organic amine, adding a certain amount of a metal oxide precursor, and continuing to heat and stir to obtain a molten mixture; heating and carbonizing the molten mixture to obtain a dark brown fluffy solid; adding the dark brown fluffy solid to a barrier solution and stirring, wherein the barrier is a saccharide barrier or an inorganic salt barrier; evaporating the water in the solution to obtain a black solid; and calcining and washing the black solid to obtain the nano-metal oxide. The present invention places the barrier addition after carbonization, which allows for secondary dispersion of metal salts that are not fully dispersed during the stirring process, thereby improving the dispersion of the metal salts. The metal oxide has a lower dispersion in the carbon template, resulting in a larger size. The barrier is added later to fix the large-sized particles and prevent sintering and agglomeration due to insufficient stability during the calcination process caused by the reduction of the carbon template.

Description

Technical Field

[0001] The invention relates to the technical field of nano material preparation, in particular to a method for preparing nano metal oxide by a thickening method. Background Art

[0002] Nanomaterial preparation methods can be categorized into three categories: gas-phase, liquid-phase, and solid-phase. Gas-phase methods include chemical vapor deposition, sputtering, and gas-phase combustion; liquid-phase methods include hydrothermal, sol-gel, microemulsion, and precipitation; and solid-phase methods include mechanical pulverization and solid-phase reaction. Nanomaterials prepared by gas-phase methods offer advantages such as uniform particle size, high purity, small particle size, good dispersibility, high chemical reactivity, controllable, and continuous processes. However, their disadvantages remain challenges in engineering applications. Liquid-phase methods offer advantages such as uniform powders, minimal agglomeration, and uniform morphology. However, they are costly, have a limited scope of application, and solvent recycling is difficult, leading to potential pollution. Solid-phase methods are widely used in industry due to their simplicity, low cost, and high yield. However, the resulting powders exhibit uneven particle size, high energy consumption, low efficiency, and are susceptible to contamination by impurities.

[0003] Chinese patent CN112250043A discloses a method for preparing monodisperse nanoparticle materials, which is to mix sugars and urea, and then add metal salts and inorganic salts as barrier agents at the same time, and then dry and heat treat. The barrier agent and sugar urea are added at the same time, that is, the increase of the template agent ensures that the metal oxide precursor is fully dispersed in the solution, and the growth of the grain size can be fully prevented during the calcination process. The particle size of the final product can be controlled within 1-500nm. Adding the barrier agent and sugar urea at the same time has a good effect on the controllable preparation of small-sized nanomaterials, but it is difficult to prepare large-sized nanomaterials. This is because the inorganic salt barrier agent added to the sugar urea precursor solution mainly exists as a crystallizing agent, and its working principle is to reduce the solubility K of the metal salt precursor added later. sp , due to K sp By reducing the particle size, nanoparticles can rapidly crystallize and nucleate, preventing nuclei from growing, thus producing nanomaterials with smaller particle sizes. However, certain metal oxide applications often require larger sizes. For example, in battery materials, micron-sized particles offer improved cycle stability and longevity. The method in patent CN112250043A is suitable for materials under 500nm. To this end, we have improved on the original method and proposed a thickening method for preparing nanometal oxides. Summary of the Invention

[0004] The purpose of the present invention is to address the above-mentioned deficiencies in the prior art and to provide a method for preparing nano-metal oxides by thickening.

[0005] The present invention provides a method for preparing nano-metal oxides by a thickening method, comprising the following steps:

[0006] S1: Heat and stir sugars and organic amines in a certain proportion until a clear and transparent solution is obtained;

[0007] S2: adding a certain amount of metal oxide precursor to the clear transparent solution, and continuing to heat and stir until the metal oxide precursor is completely dissolved to obtain a uniform molten mixture;

[0008] S3: heating the molten mixture to carbonize it to obtain a dark brown fluffy solid;

[0009] S4: preparing a barrier agent solution, and adding the dark brown fluffy solid into the barrier agent solution and stirring, wherein the barrier agent is a carbohydrate barrier agent or an inorganic salt barrier agent;

[0010] S5: Evaporating the water from the solution in step S4 to obtain a black solid;

[0011] S6: If the barrier agent used in step S4 is a carbohydrate barrier agent, the black solid is calcined in an inert atmosphere at a first calcination temperature to decompose the metal salt into metal oxides, and then calcined in an oxidizing atmosphere at a second calcination temperature to remove the carbon template to obtain nano-metal oxides;

[0012] If the barrier agent used in step S4 is an inorganic salt barrier agent, the black solid is calcined at high temperature in an oxidizing atmosphere to directly remove the carbon template to obtain a nano-metal oxide wrapped in the barrier agent, and then washed with water to remove the barrier agent to obtain the nano-metal oxide.

[0013] Furthermore, in step S1, the sugars are one or more of glucose, sucrose, fructose, lactose, starch, lactose, maltose and ribose; and the organic amines are one or more of aliphatic amines, alcohol amines, amides, alicyclic amines, aromatic amines and naphthyl amines.

[0014] Furthermore, in step S1, the temperature of heating and stirring is 80-150°C.

[0015] Furthermore, the metal oxide precursor in step S2 is a metal salt of one or more of metal nitrates, sulfates, oxalates, acetates, phosphates, hypochlorites or halides; the metal of the metal salt is selected from at least one of Mg, Al, Pb, In, Sn, Sb, Zr, Nb, La, Ce, Ta, W, Re, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ag, Pt, Pd, Ir, Ru, Rh, Y, Ba, Sr or Os, and heating and stirring are continued at 80-150°C.

[0016] Furthermore, the molar ratio of the sugar to the metal element in the metal oxide precursor is 1:(0.01-100); the molar ratio of the organic amine to the metal element in the metal oxide precursor is 1:(0.01-100).

[0017] Furthermore, the molar ratio of the barrier agent to the metal element in the metal oxide precursor is (0.1-20):1.

[0018] Furthermore, the heating carbonization method in step S3 is one of oven carbonization, hydrothermal carbonization, and microwave carbonization; during oven carbonization, the molten mixture is placed at 50-300° C. and treated for 0.5-48 hours; during hydrothermal carbonization, the molten mixture is placed in a hydrothermal reactor and treated at 50-220° C. for 0.5-24 hours; during microwave carbonization, the molten mixture is treated in a 100w-800kw microwave processor for 60-600s.

[0019] Furthermore, the carbohydrate barrier includes one or more of glucose, sucrose, fructose, lactose, starch, lactose, maltose, and ribose, and the inorganic salt barrier includes but is not limited to one or more of potassium sulfate, sodium chloride, potassium chloride, sodium fluoride, and lithium chloride. The barrier used in step S4 is a carbohydrate barrier, the first calcination temperature is 300-1800°C, the calcination time is 1-48 hours, the second calcination temperature is 200-1800°C, the calcination time is 1-48 hours, and the barrier is an inorganic salt barrier, the high-temperature calcination temperature is 300-1800°C, and the time is 1-48 hours.

[0020] Furthermore, the barrier agent used in step S4 is a carbohydrate barrier agent, the first calcination temperature is 300-1800°C, the calcination time is 1-48h, the second calcination temperature is 200-1000°C, the calcination time is 1-24h, the second calcination temperature is lower than the first calcination temperature, the barrier agent is an inorganic salt barrier agent, the high temperature calcination temperature is 300-1500°C, and the time is 1-48h.

[0021] This patent adds inorganic salts such as sodium chloride after carbonization. It does not add inorganic salts during the heating and stirring of the sugar-urea mixed solution to promote nucleation and limit the growth of precursor grains. Instead, it simply adds a "wall" to the carbonized carbon template to further confine the particles and prevent them from growing in contact during calcination. This does not restrict the nucleation of the metal oxide in the sugar-urea salt solution. The inorganic salts added after carbonization serve only as a barrier to prevent sintering, thereby enabling the preparation of larger nano-metal oxides.

[0022] The present invention places the barrier agent in the order of adding after carbonization, which can secondary disperse the metal salt that is not fully dispersed during the stirring process, thereby improving the dispersion degree of the metal salt. Moreover, by adding the barrier agent after carbonization, the dispersion degree of the metal oxide in the carbon template is lower, and thus the size is larger. The barrier agent is added later to fix large-sized particles and prevent sintering and agglomeration due to insufficient stability during the calcination process caused by the reduction of the carbon template. Its main purpose is to increase the particle size (micrometers) while effectively maintaining monodispersity. In short, the purposes of adding first and adding later are different. Adding first reduces the particle size, while adding later increases the particle size and maintains monodispersity, thereby preventing sintering between large particles. Figure 6 、 7 This is also proven.

[0023] The formation temperature of some metal oxides exceeds 1000°C, which exceeds the melting point of most inorganic salt barriers and therefore cannot provide a barrier effect. Moreover, in some fields that require high purity of nano-metal oxides, such as cerium oxide grinding and polishing, the presence of chloride ions and sodium ions will seriously affect its polishing performance. The melting point of carbon is 3700°C. Therefore, sugar barriers can be used. First, calcination in an inert atmosphere at a high temperature can produce metal oxide particles. At the same time, the presence of the carbon template prevents the agglomeration of nano-metal oxides during high-temperature thermoforming. The carbon template can then be directly removed at a lower temperature to obtain nano-metal oxides with good dispersion and high purity, without the presence of impurities.

[0024] If an inorganic salt barrier is used, high-temperature calcination is carried out in an oxidizing atmosphere below its melting point to directly remove the carbon template, avoiding secondary calcination at high temperature followed by low temperature. The inorganic salt still exists in solid phase due to its high melting point and can fully block the nano-metal oxide to obtain metal oxide wrapped in the inorganic salt barrier. The barrier is then removed by water washing to obtain nano-metal oxide. The product obtained by this method has high dispersibility and uniform particle size. The entire preparation process is simple to operate, the raw materials are cheap and easily available, it is environmentally friendly, and easy to scale up production. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the XRD pattern of nano-yttrium oxide prepared in Example 1;

[0026] Figure 2 This is the SEM image of nano-yttrium oxide prepared in Example 1;

[0027] Figure 3 This is the XRD pattern of nano zinc oxide prepared in Example 2;

[0028] Figure 4 This is the XRD pattern of nano-cerium oxide prepared in Example 3;

[0029] Figure 5This is the SEM image of nano-cerium oxide prepared in Example 3;

[0030] Figure 6 This is the DLS image of nano-cerium oxide prepared in Example 4;

[0031] Figure 7 This is the DLS graph of nano-cerium oxide prepared in Comparative Example 1;

[0032] Figure 8 This is the XRD pattern of nano copper oxide prepared in Example 5;

[0033] Figure 9 The nano Cu prepared in Example 6 0.4 Zn 0.6 Fe2O4 XRD pattern.

[0034] Figure 10 This is the XRD pattern of nano-alumina prepared in Example 7. DETAILED DESCRIPTION

[0035] The following are specific embodiments of the present invention and the accompanying drawings to further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments.

[0036] Unless otherwise specified, experimental drugs were obtained from commercial sources and were not further purified;

[0037] Example 1: Nano-yttrium oxide

[0038] Synthetic raw materials: sucrose, ethylenediamine, yttrium chloride hexahydrate

[0039] (1) Weigh 1.0 g (0.0029 mol) of sucrose and 10 g (0.166 mol) of ethylenediamine in a beaker, mix them, and heat and stir at 100°C until the drugs in the beaker are molten;

[0040] (2) Weigh and add 1.22 g (0.004 mol) of yttrium chloride hexahydrate, heat and stir at 100°C for 40 min; the molar ratio of sucrose to the yttrium element in yttrium chloride hexahydrate is 1:1.38, and the molar ratio of urea to the yttrium element in yttrium chloride hexahydrate is 41.5:1;

[0041] (3) Place the beaker in a microwave oven for 4 min, then take out the beaker and grind the sample;

[0042] (4) Weigh 5 g of anhydrous glucose and dissolve it in 20 ml of deionized water to prepare a glucose solution;

[0043] (5) Add the ground sample in (3) to the glucose solution and stir for 24 h;

[0044] (6) Place the beaker in an oven at 60°C and dry;

[0045] (7) The dried sample was calcined in a tube furnace under nitrogen at 800 °C for 4 h;

[0046] (8) The calcined sample was placed in a muffle furnace and calcined at 500 °C for 3 h to obtain the yttrium oxide sample.

[0047] from Figure 1 It can be seen that the yttrium oxide prepared in this example has a good crystal form and does not contain impurity peaks. Figure 2 It can be seen that the prepared nano-yttrium oxide is spherical and dispersed, with a particle size of about 20nm.

[0048] Example 2: Nano zinc oxide

[0049] Synthetic raw materials: sucrose, urea, zinc sulfate heptahydrate

[0050] (1): Weigh 50 g (0.2775 mol) of sucrose and 5 g (0.0831 mol) of urea in a beaker, mix them, and heat and stir at 90°C until the drugs in the beaker are molten;

[0051] (2) Weigh and add 15 g (0.0243 mol) of zinc sulfate heptahydrate, heat and stir at 90°C for 20 min, the molar ratio of sucrose to zinc in zinc sulfate heptahydrate being 11.4:1, and the molar ratio of urea to zinc in zinc sulfate heptahydrate being 3.42:1;

[0052] (3) Place the beaker in an oven at 180°C for 24 h, then remove the beaker and grind the sample;

[0053] (4) Weigh 15 g of fructose and dissolve it in 50 ml of deionized water to prepare a fructose solution;

[0054] (5) Add the ground sample in (3) to the fructose solution and stir with a magnetic stirrer for 4 h;

[0055] (6) Place the beaker in an oven and dry at 120°C;

[0056] (7) The dried sample was placed in a tube furnace and calcined at 700 °C in an argon atmosphere for 8 h;

[0057] (8) The sample calcined in argon gas was calcined in a muffle furnace at 700 °C for 5 h to obtain a sample of zinc oxide.

[0058] from Figure 3 It can be seen that the zinc oxide prepared in this example has a good crystal form and does not contain impurity peaks, and the calculated particle size is 70 nm.

[0059] Example 3: Nano-cerium oxide

[0060] Synthetic raw materials: fructose, polyethyleneimine, cerium oxalate nonahydrate

[0061] (1) Weigh 1 g (0.0056 mol) of fructose and 2.51 g (0.0084 mol) of polyethyleneimine in a beaker, mix them, and heat and stir at 90°C until the drugs in the beaker are molten.

[0062] (2) Weigh and add 1.01 g (0.0018 mol) of cerium oxalate nonahydrate, heat and stir at 108°C for 30 min, the molar ratio of fructose to the cerium element in cerium oxalate nonahydrate is 3.1:1, and the molar ratio of polyethyleneimine to the cerium element in cerium oxalate nonahydrate is 4.6:1;

[0063] (3) The sample was transferred to a hydrothermal reactor and dried at 150 °C for 3 h, and the sample was taken out and ground;

[0064] (4) Weigh 20 g of anhydrous glucose and heat to 160°C to melt;

[0065] (5) Add the ground sample in (3) to the glucose solution and stir with a magnetic stirrer for 30 min;

[0066] (6) Place the beaker in an oven at 200°C for 10 h;

[0067] (7) The dried sample was placed in a tube furnace and calcined at 800 °C for 5 h under nitrogen atmosphere;

[0068] (8) The sample calcined in an inert atmosphere was calcined at 300°C in a muffle furnace for 3 h to obtain a cerium oxide sample.

[0069] from Figure 4 It can be seen that the cerium oxide prepared in this example has a good crystal form and does not contain impurity peaks. Figure 5 It can be seen that the prepared nano-cerium oxide is spherical and dispersed, with a particle size of about 30nm.

[0070] Example 4 (Comparative Example 1): Nano-cerium oxide

[0071] Synthetic raw materials: glucose, urea, cerium nitrate hexahydrate, sodium chloride

[0072] (1) Weigh 10 g (0.0555 mol) of glucose and 5 g (0.0833 mol) of urea in a beaker, mix them, and heat and stir at 100°C for 20 min until the drugs in the beaker are molten.

[0073] (2) Weigh and add 1 g (0.0023 mol) of cerium nitrate hexahydrate, heat and stir at 100°C for 3 h, the molar ratio of glucose to cerium in cerium nitrate hexahydrate being 24.1:1, and the molar ratio of urea to cerium in cerium nitrate hexahydrate being 36.2:1;

[0074] (3) Place the beaker in a microwave oven for 5 min, then take out the beaker and grind the sample;

[0075] (4) Weigh 20 g of saturated potassium chloride solution;

[0076] (5) Add the ground sample in (3) to a saturated potassium chloride solution and stir with a magnetic stirrer for 3 h;

[0077] (6) Place the beaker in an oven and dry at 150°C;

[0078] (7) The dried sample was calcined in a muffle furnace at 600 °C for 7 h to obtain cerium oxide coated with sodium chloride;

[0079] (8) The potassium chloride-coated cerium oxide was washed three times with 200 ml of deionized water and dried to obtain nano-cerium oxide.

[0080] from Figure 6 It can be seen that the particle size distribution of cerium oxide prepared in this embodiment is 10 μm.

[0081] Comparative Example 1

[0082] Cerium oxide was prepared according to the preparation method in patent CN112250043A, and the specific steps are as follows:

[0083] (1) Weigh 10 g (0.0555 mol) of glucose and 5 g (0.0833 mol) of urea in a beaker, mix them, and heat and stir at 100°C for 20 min until the drugs in the beaker are molten.

[0084] (2) Weigh and add 1 g (0.0023 mol) of cerium nitrate hexahydrate and 20 g of saturated potassium chloride solution, heat and stir at 100°C for 3 h;

[0085] (3) Place the beaker in a microwave oven for 5 min, then take out the beaker and grind the sample;

[0086] (7) The ground sample was calcined in a muffle furnace at 600 °C for 7 h to obtain sodium chloride-coated cerium oxide;

[0087] (8) The potassium chloride-coated cerium oxide was washed three times with 200 ml of deionized water and dried to obtain nano-cerium oxide.

[0088] Figure 7 This is the DLS graph of nano-cerium oxide prepared in Comparative Example 1, and its particle size distribution is around 30 nm.

[0089] The raw materials, raw material content, reaction temperature and time, calcination temperature and time used in Example 4 and Comparative Example 1 are the same, and only the order of adding the inorganic salt barrier potassium chloride solution is adjusted. Figure 6 and Figure 7 A comparison shows that the cerium oxide particles prepared in Example 4 have a particle size distribution of approximately 10 μm, while the cerium oxide particles prepared in Comparative Example 1 have a particle size distribution of approximately 30 nm. This comparison also shows that changing the order in which the barrier agents are added can significantly alter the particle size of the nanomaterials: adding the barrier agents first results in smaller nanoparticles, while adding them later results in larger particles.

[0090] Example 5: Nano-copper oxide

[0091] Synthetic raw materials: glucose, ethanolamine, copper oxalate, potassium sulfate

[0092] (1) Weigh 100.01 g (0.56 mol) of glucose and 1.01 g (0.01662 mol) of ethanolamine in a beaker, mix them, and heat and stir at 108°C until the drugs in the beaker are molten;

[0093] (2) Weigh and add 2.01 g (0.0132 mol) of copper oxalate, heat and stir at 80°C for 120 min, and heat and stir at 80°C until the drug in the beaker is molten. The molar ratio of glucose to copper in copper oxalate is 42.42:1, and the molar ratio of ethanolamine to copper in copper oxalate is 1.26:1.

[0094] (3) Place the beaker in a microwave oven for 5 minutes. Then remove the beaker and grind the sample.

[0095] (4) Weigh 5 g of potassium sulfate and dissolve it in 200 ml of deionized water to prepare a potassium sulfate solution;

[0096] (5) Add the ground sample in step (3) to the potassium sulfate solution and stir with a magnetic stirrer for 120 min;

[0097] (6) Place the beaker in an oven and dry at 180°C;

[0098] (7) The dried sample was calcined in a muffle furnace at 520 °C for 5 h to obtain potassium sulfate-coated cerium oxide;

[0099] (8) The potassium sulfate-coated cerium oxide was washed 20 times with 200 ml of deionized water and dried to obtain nano-copper oxide.

[0100] from Figure 8 It can be seen that the copper oxide prepared in this example has a good crystal form and does not contain impurity peaks, and the calculated particle size is about 200 nm.

[0101] Example 6: Nano Cu 0.4 Zn 0.6 Fe2O4

[0102] Synthetic raw materials: lactose, urea, ferric nitrate nonahydrate, copper sulfate, zinc chloride, sodium fluoride

[0103] (1) Weigh 10 g (0.56 mol) of lactose and 30 g (0.5 mol) of urea in a beaker, mix them, and heat and stir at 150°C until the drugs in the beaker are molten;

[0104] (2) Weigh and add 1.4315 g (0.0035 mol) of ferric nitrate nonahydrate, 0.1498 g (0.0006 mol) of copper sulfate pentahydrate, and 0.2195 g (0.0015 mol) of zinc chloride, and heat and stir at 150°C for 120 min. The molar ratios of lactose to the iron element in ferric nitrate nonahydrate, the copper element in copper oxalate, and the zinc element in zinc chloride are 160:1, 933.33:1, and 373.33:1, respectively. The molar ratios of urea to the iron element in ferric nitrate nonahydrate, the copper element in copper oxalate, and the zinc element in zinc chloride are 142.86:1, 833.33:1, and 333.33:1, respectively.

[0105] (3) Place the beaker in a microwave oven for 10 minutes. Then remove the beaker and grind the sample.

[0106] (4) Weigh 10% sodium fluoride and dissolve it in 200 ml of deionized water to prepare a sodium fluoride solution;

[0107] (5) Add the ground sample in step (3) to the sodium fluoride solution and stir with a magnetic stirrer for 120 min;

[0108] (6) Place the beaker in an oven and dry at 180°C;

[0109] (7) The dried sample was calcined in a muffle furnace at 800 °C for 5 h to obtain sodium fluoride-coated Cu 0.4 Zn 0.6 Fe2O4;

[0110] (8) Wash the sodium fluoride-wrapped cerium oxide 20 times with 200 ml of deionized water and dry it to obtain nano Cu 0.4 Zn 0.6 Fe2O4.

[0111] from Figure 9 It can be seen that the Cu prepared in this embodiment 0.4 Zn 0.6 The Fe2O4 has good crystal form and does not contain impurity peaks, and the calculated particle size is about 5μm.

[0112] Example 7: Nano-Al2O3

[0113] Synthetic raw materials: glucose, urea, aluminum nitrate nonahydrate

[0114] (1) Weigh 3 g (0.016 mol) of glucose and 5 g (0.083 mol) of urea in a beaker, mix them, and heat and stir at 110°C until the drugs in the beaker are molten;

[0115] (2) Weigh and add 6.67 g (0.0098 mol) of aluminum nitrate nonahydrate, heat and stir at 150°C for 120 min, the molar ratio of glucose to aluminum in aluminum nitrate nonahydrate is 1.63:1, and the molar ratio of urea to aluminum in aluminum nitrate nonahydrate is 8.47:1.

[0116] (3) Place the beaker in a microwave oven for 5 minutes. Then remove the beaker and grind the sample.

[0117] (4) Weigh 50 g of glucose and dissolve it in 200 ml of deionized water to prepare a glucose solution;

[0118] (5) Add the ground sample in step (3) to the glucose solution and stir with a magnetic stirrer for 120 min;

[0119] (6) Place the beaker in an oven at 200°C for drying;

[0120] (7) The dried sample was calcined in a tube furnace at 1600 °C for 8 h under an argon atmosphere to obtain carbon-coated Al2O3;

[0121] (8) The carbon-coated Al2O3 was calcined at 500 °C in a muffle furnace for 4 h to obtain nano-Al2O3.

[0122] from Figure 10 It can be seen that the Al2O3 prepared in this example has a good crystal form and does not contain impurity peaks, and the calculated particle size is about 800 nm.

[0123] Any matters not mentioned above shall be subject to the existing technology.

[0124] Although some specific embodiments of the present invention have been described in detail through examples, those skilled in the art should understand that the above examples are for illustration only and are not intended to limit the scope of the present invention. Those skilled in the art of the present invention may make various modifications or additions to the described specific embodiments or replace them in similar ways, but they will not deviate from the direction of the present invention or exceed the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent replacements, improvements, etc. made to the above embodiments based on the technical essence of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing nano metal oxides by thickening method, characterized in that: The steps include: S1: Heat and stir sugars and organic amines in a certain proportion until a clear and transparent solution is obtained; S2: adding a certain amount of metal oxide precursor to the clear transparent solution, and continuing to heat and stir until the metal oxide precursor is completely dissolved to obtain a uniform molten mixture; S3: heating the molten mixture to carbonize it to obtain a dark brown fluffy solid; S4: preparing a barrier agent solution, and adding the dark brown fluffy solid into the barrier agent solution and stirring, wherein the barrier agent is a carbohydrate barrier agent or an inorganic salt barrier agent; S5: Evaporating the water from the solution in step S4 to obtain a black solid; S6: If the barrier agent used in step S4 is a carbohydrate barrier agent, the black solid is calcined in an inert atmosphere at a first calcination temperature to decompose the metal salt into metal oxides, and then calcined in an oxidizing atmosphere at a second calcination temperature to remove the carbon template to obtain nano-metal oxides; If the barrier agent used in step S4 is an inorganic salt barrier agent, the black solid is calcined at high temperature in an oxidizing atmosphere to directly remove the carbon template to obtain a nano-metal oxide wrapped in the barrier agent, and then washed with water to remove the barrier agent to obtain a nano-metal oxide; The barrier agent used in step S4 is a carbohydrate barrier agent, the first calcination temperature is 300-1800°C, the calcination time is 1-48h, the second calcination temperature is 200-1000°C, the second calcination temperature is lower than the first calcination temperature, the calcination time is 1-24h, the barrier agent is an inorganic salt barrier agent, the high temperature calcination temperature is 300-600°C, and the time is 1-48h; The organic amines are one or more of aliphatic amines, alcohol amines, amides, alicyclic amines, aromatic amines and naphthyl amines; The inorganic salt barrier agent includes one or more of potassium sulfate, sodium chloride, potassium chloride, sodium fluoride, and lithium chloride; When the metal of the metal oxide precursor is cerium, the barrier agent is an inorganic salt barrier agent; When the metals of the metal oxide precursor are Cu, Zn, and Fe at the same time, the barrier agent is an inorganic salt barrier agent; When the metal of the metal oxide precursor is Al, the barrier agent is a sugar barrier agent.

2. The method for preparing nano metal oxide by thickening method according to claim 1, wherein The sugar in step S1 is one or more of glucose, sucrose, fructose, lactose, starch, lactose, maltose and ribose.

3. The method for preparing nano metal oxide by thickening method according to claim 1, wherein In step S1, the temperature for heating and stirring is 80-150°C.

4. The method for preparing nano metal oxide by thickening method according to claim 1, wherein The metal oxide precursor in step S2 is one or more metal salts selected from metal nitrates, sulfates, oxalates, acetates, phosphates, hypochlorites or halides.

5. The method for preparing nano metal oxide by thickening method according to claim 1, wherein The molar ratio of the sugar to the metal element in the metal oxide precursor is 1: (0.01-100); the molar ratio of the organic amine to the metal element in the metal oxide precursor is 1: (0.01-100).

6. The method for preparing nano metal oxide by thickening method according to claim 1, wherein The molar ratio of the barrier agent to the metal element in the metal oxide precursor is (0.1-20):

1.

7. The method for preparing nano metal oxide by thickening method according to claim 1, wherein: The heating carbonization method in step S3 is one of oven carbonization, hydrothermal carbonization, and microwave carbonization; during oven carbonization, the molten mixture is placed in a hydrothermal reactor and treated at 50-300° C. for 0.5-48 hours; during hydrothermal carbonization, the molten mixture is placed in a hydrothermal reactor and treated at 50-220° C. for 0.5-24 hours; during microwave carbonization, the molten mixture is treated in a microwave processor with a power of 100w-800kw for 60-600s.

8. The method for preparing nano metal oxide by thickening method according to claim 1, wherein The carbohydrate blocker includes one or more of glucose, sucrose, fructose, lactose, starch, lactose, maltose and ribose.

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