A method for universally synthesizing monodisperse metal oxide nanoparticle clusters and products a prepared using the method

Abstract

The application discloses a method for universally synthesizing monodisperse metal oxide nanoparticle clusters and a product A prepared by using the method. The method comprises the following steps: dissolving metal inorganic salt precursors and small molecule ligands in water to form a complex by coordination, adding an alkali source and a hydrophilic polymer after the alkali source is dissolved to obtain an A solution; and performing a hydrothermal reaction on the A solution to synthesize metal oxide nanoparticle clusters corresponding to the precursors. The one-step hydrothermal method is used to synthesize a series of metal oxide nanoparticle clusters. The small molecule ligands are coordinated with metal ions to form a "metal-ligand" complex, so that the concentration of free metal ions in the aqueous solution is greatly reduced. The alkali source provides hydroxyl ions to promote the dissociation of the complex and help the metal ions to hydrolyze to form metal oxides. The hydrophilic polymer is coated on the surface of the formed original nanoparticles to provide van der Waals force and electrostatic repulsion, and the two forces interact to jointly control the self-assembly process of the nanoparticles, so that the nanoparticles are gathered into clusters with uniform morphology and size and good monodispersity.

Description

Technical Field

[0001] The present invention relates to the technical field of nanoparticle clusters, in particular to a method for synthesizing monodisperse metal oxide nanoparticle clusters. Background Art

[0002] Nanoparticle clusters (NPCs) are superparticles with secondary structures composed of numerous primary nanoparticles. They exhibit not only the intrinsic physical properties of the original nanoparticles but also collective properties of the nanoparticles, and even new physical and chemical properties derived from the interactions between the original nanoparticles. These unique properties make NPCs promising for a wide range of applications in optoelectronics, catalysis, sensing, biomedicine, magnetism, and renewable energy. The controllable synthesis of NPCs is crucial for exploring their properties and applications.

[0003] The mainstream method for obtaining NPCs is a two-step process, which involves first synthesizing nanoparticles and then assembling the nanoparticles into clusters by regulating the interaction forces between the nanoparticles. This two-step synthesis method allows the use of various nanoparticles as basic building blocks to prepare clusters with controllable structures. However, this method involves tedious procedures such as complex nanoparticle synthesis, surface functionalization, purification and assembly processes, and the high requirements for assembly conditions usually lead to poor reproducibility of cluster formation. To avoid these problems, there is an urgent need to develop a one-step synthesis method to synthesize nanoparticle clusters. The one-step method combines synthesis and assembly into one step, simplifying the synthesis steps. However, the currently available one-step method is only applicable to individual metal oxides and is difficult to generalize. In addition, due to the uncontrolled reaction rate in the aqueous phase and the mismatch in the reactivity of different metal organic precursors, it is difficult to control the size, composition and structure of the clusters in a one-step synthesis. Summary of the Invention

[0004] In order to overcome the above shortcomings and deficiencies, the purpose of the present invention is to propose a general strategy for the one-step synthesis of monodisperse metal oxide nanoparticle clusters (MONPCs) with adjustable size, composition and structure in aqueous phase. The main idea of ​​this method is to rely on small molecule ligands and water-soluble polymers to co-mediate the hydrolysis of metal ions to form metal oxide nanoparticles and the self-assembly of particles into clusters. Based on this idea, nanoparticle clusters with uniform morphology and good monodispersity are obtained. This method can not only synthesize various MONPCs, including high-entropy spinel phase metal oxide NPCs containing multiple metal elements, but also regulate the size of MONPCs, ranging from tens of nanometers to hundreds of nanometers, and can deposit different types of metal oxide nanoparticles on pre-prepared MONPCs to form core-shell heterostructures, which provides great possibilities for designing and regulating the unique properties of MONPCs to meet the application needs of different fields.

[0005] The present invention provides a universal method for synthesizing monodisperse metal oxide nanoparticle clusters, the method comprising:

[0006] The metal inorganic salt precursor and the small molecule ligand are dissolved in water and coordinated to form a complex, an alkali source is added, and after the alkali source is dissolved, a hydrophilic polymer is added to obtain solution A;

[0007] Solution A is subjected to a hydrothermal reaction to synthesize a metal oxide corresponding to the precursor.

[0008] In the above technical solution, a series of metal oxides are synthesized using a one-step hydrothermal method. The concentration of free metal ions is greatly reduced by introducing ligands that easily coordinate with metal ions. The introduction of an alkaline source provides hydroxide, which accelerates the dissociation of the complex and helps the metal ions hydrolyze to form metal oxides. A hydrophilic polymer is coated on the surface of the formed original nanoparticles. Due to the high water dispersibility of the polymer and the negative charge carried by the polymer groups themselves, electrostatic repulsion is generated between the nanoparticles, allowing the nanoparticles to be uniformly dispersed in the solution. At the same time, the polymer further provides the van der Waals force required for self-assembly. The interaction between electrostatic repulsion and van der Waals forces jointly regulates the self-assembly process, causing the nanoparticles to aggregate and form clusters. As the self-assembly proceeds, when the clusters reach a certain size, that is, when the van der Waals force and electrostatic repulsion are balanced, the assembly stops, and metal oxide nanoparticle clusters with uniform morphology and good monodispersity are obtained. The method comprises the following steps: dissolving a metal inorganic salt precursor (metal chloride, metal nitrate, etc.) and a small molecule ligand in an aqueous solution, stirring them to fully dissolve them, and performing coordination. While stirring continuously, an alkaline substance is added to provide an alkaline source for the overall reaction environment. Once fully dissolved, an appropriate amount of hydrophilic polymer is added to control cluster growth. The mixture is then heated in a reactor for a period of time. After the reaction is complete, the mixture is cooled to room temperature and washed and dried to obtain the product.

[0009] The advantages of this method are:

[0010] (1) A simple, green, and economical universal method for synthesizing metal oxide nanoparticle clusters is proposed, which can precisely control the size, composition, and structure of nanoparticle clusters; a series of metal oxides (including transition metal oxides, group III, group IV, and lanthanide and actinide metal oxides) are synthesized using a one-step hydrothermal method. This strategy relies on the co-mediation of small molecule ligands and water-soluble polymers to hydrolyze metal ions to form metal oxide nanoparticles and the self-assembly of particles into clusters. Since the hydrolysis rate of metal ions under hydrothermal conditions is very fast, it is extremely challenging to directly treat metal ions to obtain monodisperse nanostructured metal oxides using traditional hydrothermal methods. The present invention uses small molecule ligands to form "metal-ligand" complexes with metal ions to significantly reduce the concentration of free metal ions in the solution, slow down the formation rate of nanoparticles, and thus provide sufficient time for the nanoparticles to self-assemble into spherical clusters. The hydrophilic polymer coats the surface of the formed nanoparticles. Due to the polymer's high water dispersibility and the negative charge of its groups, the electrostatic repulsion between the nanoparticles causes the nanoparticles to be evenly dispersed in the solution. The polymer also provides the van der Waals forces required for self-assembly. The interaction between these forces regulates the self-assembly process, causing the nanoparticles to aggregate and form clusters. As the self-assembly proceeds, when the clusters reach a certain size, where the van der Waals forces and electrostatic repulsion are balanced, assembly ceases, resulting in metal oxide nanoparticle clusters with uniform morphology and size and good monodispersity.

[0011] (2) Achieve precise control of cluster size. The present invention can control the size of metal oxide nanoparticle clusters by varying the concentration of the precursor or the reaction time. Size control is achieved by regulating the concentration of the precursor. The lower the concentration, the fewer the total number of nanoparticles formed, and the smaller the size of the nanoparticle clusters. The higher the concentration of the precursor, the larger the size of the nanoparticle clusters, ranging from tens to hundreds of nanometers, and very uniform. This means that NPCs can be controlled to meet the size requirements of specific applications.

[0012] (3) Achieve precise control of cluster composition. A variety of metal oxides doped with different components are obtained. The doping does not affect the cluster morphology and still has good dispersion and size uniformity. Doping methods include Co:ZnO, Mg:ZnO, Mg:Ga2O3, Co:Ga2O3, Zn:Ga2O3, Mg:Ga2O3, Co:Ga2O3, Ni:Ga2O3, Cu:Ga2O3.

[0013] It is worth mentioning that it is also applicable to the synthesis of spinel-type (AB2O4) oxides with adjustable composition and high-entropy oxide nanoparticle clusters, to obtain multi-metal oxide nanoparticle clusters with good monodispersity and size uniformity.

[0014] (4) The present invention not only regulates the size and composition of a series of metal oxide nanoparticle clusters, but also further enables the regulation of cluster structure. By incorporating pre-synthesized clusters as the core of a core-shell structure, and then successfully coating the core with a shell material using the synthesis method of the present invention, a core-shell structure is formed. This lays a solid foundation for the diverse applications of nanoparticle clusters.

[0015] (5) The synthesis method provided by the present invention has mild reaction conditions, high yield, simple and easy reaction process, great cost savings, strong universality, and is suitable for further promotion.

[0016] In summary, the present invention provides a universal method for synthesizing metal oxide nanoparticle clusters, which is not only applicable to various types of metal oxides (including polynary oxides), but also achieves the same control of size, composition, and structure. Compared with the prior art, the present invention not only can obtain a series of metal oxide nanoparticle clusters with uniform morphology and good monodispersity, but also achieves more precise control of size, composition, and structure, creating a systematic and efficient nanoparticle cluster synthesis strategy in an aqueous solution system. The entire reaction conditions are mild, simple and easy to operate. Compared with the solvothermal method, the aqueous solution system is more economical and green, and is suitable for promotion.

[0017] In some embodiments, the metal inorganic salt precursor is metal chloride, metal nitrate, etc.; the concentration of the metal inorganic salt is 0.02M to 0.5M.

[0018] In the above technical solution, metal inorganic salts usually have good solubility in water, which helps to form a uniform solution during the hydrothermal synthesis process. Compared with some toxic or harmful precursors, metal inorganic salts are relatively safe in handling and use, and the by-products produced during the synthesis process are also easier to handle. Furthermore, according to the coordination ratio design of the ligand and the metal ion, the molar ratio of the metal ion and the complex is: 1:1~10, and the concentration of the metal precursor is 0.02M~0.50M. This setting is to ensure that the ion concentration is moderate. Too low or too high a concentration will affect whether metal oxides are formed and the morphology of the formed metal oxides. At the same time, the effect of concentration on morphology is obtained by controlling a single variable experiment, so as to determine in what ratio range nanoparticle clusters with uniform morphology and good dispersion can be formed.

[0019] In some embodiments, the small molecule ligand is one of trisodium citrate, citric acid, and metal cyanide.

[0020] In the above technical solution, the ligand is essential for the formation of monodisperse NPCs. Without citrate, only particles with random shapes can be obtained. Further, other small molecule ligands that tend to coordinate with metal ions to form stable complexes can also be used to reduce the concentration of free metal ions. Further, -CN - plays the same role as the citrate ligand, i.e. coordinates with metal ions to form a complex, which is conducive to the slow hydrolysis of metal ions.

[0021] In some embodiments, the alkali source is one of urea, sodium carbonate, potassium carbonate, and sodium bicarbonate, and the concentration of the alkali source in the A solution is 0.1M-0.5M.

[0022] In the above technical solution, the inventors have found that a too high concentration of the alkali source will affect the morphology, and a too low concentration will not allow the formation of metal oxides; therefore, the above molar ratio is set. Meanwhile, the above alkali sources cannot be mixed together. The role of the alkali source is to increase the pH value of the solution and promote the hydrolysis and polycondensation of metal ions into metal oxides.

[0023] In some embodiments, the process parameters of the hydrothermal reaction are as follows:

[0024] The reaction temperature is 120-200℃, and the preset reaction time is 20-720min.

[0025] In the above technical solution, based on the method proposed by the present application, the hydrothermal reaction is adjusted, and the above suitable temperature range is determined through a control variable experiment.

[0026] In some embodiments, the hydrophilic polymer is one of poly(methyl methacrylate sodium), polyacrylamide, polyacrylic acid, polyacrylic acid sodium, and polyvinylpyrrolidone. The concentration of the hydrophilic polymer is 1wt%-5wt%.

[0027] In the above technical solution, this setting is because if the concentration of the hydrophilic polymer is too low, the nanoparticles cannot self-assemble into clusters with uniform morphology. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the following embodiment or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0029] Figure 1 is a flowchart of an embodiment of a method for universally synthesizing monodisperse metal oxide nanoparticle clusters according to the present application;

[0030] Figure 2 This is one of the SEM images of Ga2O3NPCs of an embodiment of a universal method for synthesizing monodisperse metal oxide nanoparticle clusters of the present invention;

[0031] Figure 3 This is an SEM image of different metal oxide NPCs in an embodiment of a universal method for synthesizing monodisperse metal oxide nanoparticle clusters of the present invention;

[0032] Figure 4 This is the second SEM image of Ga2O3NPCs of an embodiment of a universal method for synthesizing monodisperse metal oxide nanoparticle clusters of the present invention;

[0033] Figure 5 This is the third SEM image of Ga2O3NPCs of an embodiment of a universal method for synthesizing monodisperse metal oxide nanoparticle clusters of the present invention;

[0034] Figure 6 This is the fourth SEM image of Ga2O3NPCs of an embodiment of a universal method for synthesizing monodisperse metal oxide nanoparticle clusters of the present invention;

[0035] Figure 7 FTIR spectra of Ga2O3NPCs (orange) and sodium polymethacrylate (blue) according to an embodiment of a universal method for synthesizing monodisperse metal oxide nanoparticle clusters of the present invention;

[0036] Figure 8 This is an SEM image and size distribution diagram of gallium oxide nanoparticle cluster size control according to an embodiment of a method for universally synthesizing monodisperse metal oxide nanoparticle clusters of the present invention;

[0037] Figure 9 This is an XRD pattern of Ga2O3NPCs doped with Co at different molar ratios according to an embodiment of a method for universally synthesizing monodisperse metal oxide nanoparticle clusters of the present invention;

[0038] Figure 10 TEM and EDS element distribution diagrams of Ga2O3NPCs doped with Co at different molar ratios according to an embodiment of a universal method for synthesizing monodisperse metal oxide nanoparticle clusters of the present invention;

[0039] Figure 11 1 is a SEM image of Zn-Ga-O NPCs with different Zn:Ga ratios according to an embodiment of a universal method for synthesizing monodisperse metal oxide nanoparticle clusters of the present invention;

[0040] Figure 12This is an SEM image of MgGa2O4, CoGa2O4 and NiGa2O4 NPCs according to an embodiment of a method for universal synthesis of monodisperse metal oxide nanoparticle clusters of the present invention;

[0041] Figure 13 The SEM, TEM, and EDS element distribution images of high-entropy metal oxide nanoparticle clusters (MgAICrMnFeCoNiCuZnYInSn)Ga2O4NPCs according to one embodiment of a universal method for synthesizing monodisperse metal oxide nanoparticle clusters of the present invention are shown;

[0042] Figure 14 The SEM, TEM, HRTEM, and EDS element distribution diagrams of core-shell structured Fe3O4@Ga2O3NPCs according to one embodiment of a universal method for synthesizing monodisperse metal oxide nanoparticle clusters of the present invention are shown;

[0043] Figure 15 The XRD patterns of core-shell structures Fe3O4@Ga2O3NPCs, Fe3O4@In2O3NPCs, and Fe3O4@ZnO NPCs according to one embodiment of a method for universally synthesizing monodisperse metal oxide nanoparticle clusters of the present invention are shown;

[0044] Figure 16 The SEM, TEM, and size distribution images of core-shell structured Fe3O4@Ga2O3NPCs, Fe3O4@In2O3NPCs, and Fe3O4@ZnO NPCs according to one embodiment of a universal method for synthesizing monodisperse metal oxide nanoparticle clusters of the present invention are shown; DETAILED DESCRIPTION

[0045] The present invention will be described in further detail below with reference to the accompanying drawings and examples. It is particularly noted that the following examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention. Similarly, the following examples are only some embodiments of the present invention and are not intended to be exhaustive. All other embodiments obtained by those of ordinary skill in the art without creative effort are intended to fall within the scope of protection of the present invention.

[0046] The present invention provides a universal method for synthesizing monodisperse metal oxide nanoparticle clusters. The method's key concept is to slow the hydrolysis rate and utilize a hydrophilic polymer to regulate cluster growth. This approach enables the synthesis of uniformly sized, monodisperse metal oxide nanoparticle clusters. This method can control cluster size and composition, including the synthesis of high-entropy oxides, and is also applicable to the synthesis of clusters with core-shell structures.

[0047] Example 1

[0048] See also Figure 1 , a method for universally synthesizing monodisperse metal oxide nanoparticle clusters, the method comprising:

[0049] The metal inorganic salt and the small molecule ligand are dissolved in water and coordinated to form a complex, and a hydrophilic polymer is added after the dissolution to obtain a solution A; wherein an alkali source is added during the dissolution process;

[0050] Performing a hydrothermal reaction on solution A to synthesize a metal oxide corresponding to the precursor;

[0051] in,

[0052] The concentration of metal precursor is 0.02M~0.50M;

[0053] The molar ratio of metal ions to small molecule ligands is 1:1 to 10;

[0054] The concentration of the alkali source in the solution A is 0.1M to 0.5M.

[0055] The concentration of the hydrophilic polymer is 1 wt% to 5 wt%.

[0056] In the above technical solution, a series of metal oxide nanoparticle clusters with uniform morphology and good monodispersity are synthesized by a one-step hydrothermal method, such as Figure 2 and Figure 3 The hydrolysis rate is controlled by adding a small molecule ligand to coordinate with the metal ion to form a complex, so that the particles are formed slowly. Then, the cluster growth is controlled by adding a water-soluble polymer to obtain clusters of uniform size and uniform dispersion. The method includes the following steps: dissolving the metal inorganic salt precursor and the small molecule ligand in an aqueous solution, stirring them to fully dissolve them, and then coordinating them. While constantly stirring, an alkaline substance is added to provide an alkaline source for the overall reaction environment; after sufficient dissolution, an appropriate amount of hydrophilic polymer is continued to be added to control the growth of the clusters. The product is then placed in a reactor and heated for a period of time. When the reaction is completed, it is cooled to room temperature and washed and dried to obtain the product.

[0057] In this embodiment, the metal inorganic salt is a metal chloride, metal nitrate, etc.; the concentration of the metal inorganic salt is 0.02M to 0.50M. Metal inorganic salts generally have good solubility in water, which helps to form a uniform solution during the hydrothermal synthesis process. Compared with some toxic or harmful precursors, metal inorganic salts are relatively safe in handling and use, and the byproducts produced during the synthesis process are also easier to handle. Furthermore, according to the coordination ratio of the ligand to the metal ion, the molar ratio of the metal ion to the small molecule ligand in the precursor is designed to be: 1:1 to 10, and the concentration of the metal precursor is 0.02M to 0.50M. This setting is to ensure that the ion concentration is moderate. Too low or too high a concentration will affect whether a metal oxide is formed and the morphology of the formed metal oxide. At the same time, the effect of concentration on morphology is obtained by controlling a single variable experiment, so as to determine the ratio range in which uniform morphology and well-dispersed nanoparticle clusters can be formed. It should be noted that the above setting is a specific range. When those skilled in the art need to clearly select the ratio, they can set it according to actual needs. The optimal ratio of different metal oxides is different and should be set according to actual conditions.

[0058] In this embodiment, the small molecule ligand is one of trisodium citrate and citric acid. The inventors found that the ligand is crucial for the formation of monodisperse NPCs. Figure 4 , SEM images of Ga2O3NPCs were obtained by adjusting the concentration of trisodium citrate to (a) 0mM, (b) 100mM, (c) 200mM, and (d) 300mM, while other reaction conditions were the same as those of the typical synthesis. Without citrate, only particles with random shapes were obtained. When citrate was combined with Ga 3+ When the ratio of Ga to Mg gradually increased to 3:1, monodisperse spherical particles with uniform size distribution appeared. 3+ The coordinated citrate significantly reduced the free Ga in the solution 3+ The concentration was reduced from 0.05 to 1.90x10 -11 M, which greatly slows down the formation rate of oxide nanoparticles, thus providing sufficient time for the nanoparticles to self-assemble into spherical clusters. In fact, other small molecule ligands that tend to coordinate with metal ions to form stable complexes can also be used to reduce the concentration of free metal ions. For example, using Fe(CN)3 as a metal precursor, free Fe 3+ The concentration decreased from 0.05 to 4.28×10 -9 M, can generate spherical Fe2O3NPCs. In addition, we can also use Co(CN)6 3- As a precursor to synthesize spherical Co3O4NPCs. Obviously, -CN - It plays the same role as the citrate ligand, that is, it coordinates with metal ions to form a complex, which is beneficial to the slow hydrolysis of metal ions.

[0059] In this embodiment, the alkali source is one of urea, sodium carbonate, potassium carbonate, and sodium bicarbonate, and the concentration of the alkali source in the A solution is 0.1M to 0.5M. The inventors have found through testing that too high a concentration of the alkali source will affect the morphology, and too low a concentration will not form metal oxides; therefore, the above molar ratio is set. At the same time, the above alkali sources cannot be mixed in multiple ways. The role of the alkali source is to increase the pH value of the solution and promote the hydrolysis of metal ions into metal oxides. It has been proved through experiments, please refer to Figure 5 , SEM images of Ga2O3NPCs obtained by adjusting the urea concentration: (a) 0mM, (b) 50mM, (c) 150mM, (d) 250mM, (e) 350mM, (f) 450mM, while the other reaction conditions are the same as the typical synthesis. When there is no urea in the synthesis, we can only obtain trace amounts of solid products, which are composed of irregular particles of tens of microns in size ( Figure 5 a). When the concentration is 50 mM, spherical nanoparticle clusters are formed ( Figure 5 b). When the concentration increases to 150 mM, the uniformity of the nanoparticle clusters increases ( Figure 5 c). Further increasing the concentration to 250 mM or even higher can produce severely aggregated nanoparticles ( Figure 5 df). Obviously, spherical nanoparticle clusters can only be obtained within an appropriate urea concentration range. Urea, as an alkaline source, promotes the dissociation of Ga complexes and the formation of Ga 3+ of the urea to form Ga2O3. If the concentration is too low, the pH is too low to drive the hydrolysis reaction, resulting in a low synthesis yield. If the urea concentration is too high, the hydrolysis reaction is too fast and the nanoparticles do not have enough time to self-assemble into thermodynamically stable spherical nanoparticle clusters, resulting in irregular aggregation of the nanoparticles. Other alkaline sources such as Na2CO3 can also be used to adjust the pH and regulate the hydrolysis of metal ions. For example, in zinc oxide NPCs, Na2CO3 is used instead of urea as an alkaline source. Therefore, by selecting suitable ligands and alkaline sources, we will be able to expand our strategy to synthesize various metal oxide NPCs.

[0060] In this embodiment, the process parameters of the hydrothermal reaction are as follows:

[0061] The reaction temperature is 120°C to 200°C, and the preset reaction time is 20 min to 720 min. Based on the method proposed by the present invention, the hydrothermal reaction is adjusted, and the above-mentioned suitable temperature range is determined through controlled variable experiments.

[0062] In this embodiment, the hydrophilic polymer is one of sodium polymethacrylate, polyacrylamide, polyacrylic acid, sodium polyacrylate, and polyvinylpyrrolidone. The concentration of the hydrophilic polymer is 1 wt% to 5 wt%. This is because if the concentration of the hydrophilic polymer is too low, the nanoparticles cannot self-assemble into clusters with uniform morphology. Using a surfactant containing groups (OH, COOH, etc.) that can coordinate with metal ions, such as sodium polymethacrylate, prevents the growth of nanoparticles and avoids the random aggregation of the formed nanoparticles. Figure 6 , SEM images of Ga2O3NPCs obtained by adjusting the concentration of sodium polymethacrylate: (a) 0wt%, (b) 0.5wt%, (c) 1.25wt% and (d) 2wt%, while other reaction conditions were the same as the typical synthesis. The lack of sodium polymethacrylate in our synthesis resulted in irregular clusters randomly aggregated together ( Figure 6 a). When the amount of sodium polymethacrylate is increased to 1.25 wt% and above, monodisperse spheres are obtained ( Figure 6 bd). The hydrophilicity of the surface-coated sodium polymethacrylate makes the prepared MONPCs highly water-dispersible. During the hydrothermal treatment, the hydrolysis of metal ions leads to the nucleation of metal oxides, and then the metal ions diffuse to the surface of the formed cores to form nanoparticles. In this process, sodium polymethacrylate always reacts with COO through metal ions. - The coordination between the groups is coated on the surface of the nanoparticles. The presence of sodium polymethacrylate in Ga2O3NPCs can be confirmed by Fourier transform infrared (FTIR) analysis ( Figure 7 , FTIR spectra of gallium oxide NPCs (orange) and sodium polymethacrylate (blue).

[0063] The advantages of this method are:

[0064] (1) A simple, green, and economical method for synthesizing universal metal oxide nanoparticle clusters is proposed, which can precisely control the size, composition, and structure of nanoparticle clusters; a series of metal oxides (including transition metal oxides, group III, group IV, and lanthanide and actinide metal oxides) are synthesized using a one-step hydrothermal method. This strategy relies on small molecule ligands and water-soluble polymers to co-mediate the hydrolysis of metal ions to form metal oxide nanoparticles and the self-assembly of particles into clusters. Since the hydrolysis rate of metal ions under hydrothermal conditions is very fast, it is extremely challenging to directly treat metal ions with traditional hydrothermal methods to obtain monodisperse nanostructured metal oxides. The present invention utilizes small molecule ligands to form "metal-ligand" complexes with metal ions to significantly reduce the concentration of free metal ions in the solution, slow down the formation rate of nanoparticles, and provide sufficient time for the nanoparticles to self-assemble into spherical clusters. The hydrophilic polymer coats the surface of the original nanoparticles. Due to the polymer's high water dispersibility and the negative charge of its groups, the electrostatic repulsion between the nanoparticles causes them to be evenly dispersed in the solution. The polymer also provides the van der Waals forces required for self-assembly. The interaction between these forces regulates the self-assembly process, causing the nanoparticles to aggregate and form clusters. As the self-assembly proceeds, when the clusters reach a certain size, where the van der Waals forces and electrostatic repulsion are balanced, assembly ceases, resulting in metal oxide nanoparticle clusters with uniform morphology and good monodispersity.

[0065] (2) Achieve precise control of cluster size. Figure 8 The present invention can control the size of metal oxide nanoparticle clusters by varying the concentration of the precursor or the reaction time. By adjusting the concentration of the precursor, size control is achieved. The lower the concentration, the fewer nanoparticles are formed, and the smaller the size of the nanoparticle clusters. The higher the concentration of the precursor, the larger the size of the nanoparticle clusters. The size ranges from tens to hundreds of nanometers and is very uniform, meaning that NPCs can be tailored to meet the size requirements of specific applications.

[0066] (3) Achieve precise control of cluster composition. To obtain metal oxides doped with various components, please refer to Figure 9-10 After doping, the morphology of the clusters is still not affected, and they still have good dispersion and size uniformity. The doping methods include Co:ZnO, Mg:ZnO, Mg:Ga2O3, Co:Ga2O3, Zn:Ga2O3, Mg:Ga2O3, Co:Ga2O3, Ni:Ga2O3, Cu:Ga2O3.

[0067] It is worth mentioning that it is also applicable to the synthesis of spinel-type (AB2O4) oxides with adjustable composition and high-entropy oxide nanoparticle clusters, to obtain multi-metal oxide nanoparticle clusters with good monodispersity and size uniformity.

[0068] (4) The present invention can not only regulate the size and composition of a series of metal oxide nanoparticle clusters, but also further achieve the regulation of the cluster structure. By adding a pre-synthesized cluster as the core of the core-shell structure, and then successfully coating the shell material on the core using the synthesis method of the present invention, a core-shell structure is formed, such as Figure 14-16 , which lays a solid foundation for the multifaceted applications of nanoparticle clusters.

[0069] (5) The synthesis method provided by the present invention has mild reaction conditions, high yield, simple and easy reaction process, great cost savings, strong universality, and is suitable for further promotion.

[0070] In summary, the present invention provides a universal strategy for synthesizing metal oxide nanoparticle clusters, which is not only applicable to various types of metal oxides (including polynary oxides), but also achieves the same control of size, composition, and structure. Compared with the existing technology, the present invention not only can obtain a series of metal oxide nanoparticle clusters with uniform morphology and good monodispersity, but also achieves more precise control of size, composition, and structure, creating a systematic and efficient strategy for synthesizing nanoparticle clusters in an aqueous solution system. The entire reaction conditions are mild, simple and easy to operate. Compared with the solvothermal method, the aqueous solution system is more economical and green, and is suitable for promotion.

[0071] One of the specific examples

[0072] The purpose of this specific example is to synthesize gallium oxide nanoparticle clusters with good dispersion and uniform size and morphology, as follows:

[0073] Gallium chloride was prepared into an aqueous solution with trisodium citrate, urea, and sodium polymethacrylate. The molar ratio of gallium chloride to trisodium citrate was 1:6, which resulted in the most uniform cluster morphology and the best monodispersity. Once the solution was fully dissolved and transparent, it was transferred to a reactor and heated at 180°C for 12 hours at a heating rate of 6°C / minute. After the reaction was completed, the reaction solution was cooled to room temperature, removed from the reactor, transferred to a centrifuge tube, and centrifuged for washing. The washed sample was then dried in a vacuum drying oven at 60°C for 360 minutes to obtain the desired product.

[0074] The above gallium oxide nanoparticle clusters were characterized, and the scanning electron microscopy results showed that Figure 2 , the scale bar is 6μm, and gallium oxide clusters with good dispersion, no agglomeration, and very uniform size and morphology were synthesized.

[0075] Calculation shows that the particle size of the cluster is 447 nm, and the original grain size of the cluster is 8.3 nm.

[0076] Specific example two

[0077] The purpose of this specific example is to synthesize Fe3O4 nanoparticle clusters with good dispersion and uniform size and morphology, as follows:

[0078] An aqueous solution of 1 mmol of FeCl₃·6H₂O and trisodium citrate at a molar ratio of 1:2 was prepared with 3 mmol of urea and 0.25 mL of sodium polymethacrylate. The solution was then transferred to a reactor and heated at 200°C for 12 hours at a heating rate of 6°C / minute. After the reaction was completed, the solution was cooled to room temperature, transferred to a centrifuge tube, and centrifuged for washing. The washed sample was then dried in a vacuum drying oven at 60°C for 360 minutes to obtain the desired product.

[0079] For the characterization of the above Fe3O4 nanoparticle clusters, please refer to Figure 3 c, scale bar = 1 μm. Scanning electron microscopy results show that well-dispersed, agglomerated, and uniform Fe3O4 clusters were synthesized. The calculated particle size of the clusters is 114 nm, and the size of the individual crystals constituting the clusters is 8 nm.

[0080] Specific example three

[0081] The purpose of this specific example is to synthesize metal oxides Co:Ga2O3 with good dispersion and uniform size and morphology after being doped with different components, such as Figure 9 、 10 .

[0082] Co-doped Ga2O3 NPCs were synthesized by dissolving CoCl2, 1 mmol GaCl3, 6 mmol trisodium citrate, and 3 mmol urea at molar ratios of 0, 1%, 3%, 5%, and 10%, respectively, in 19.75 mL of distilled water. 0.25 mL of sodium polymethacrylate was then added under magnetic stirring to prepare Co-doped Ga2O3 NPCs. The remaining steps were identical to those for Ga2O3 NPCs (Note: Other dopants were similar to this example, requiring only the corresponding doping metal chloride and host chloride to be modified, such as Co:ZnO, Mg:ZnO, Mg:Ga2O3, Zn:Ga2O3, Mg:Ga2O3, Co:Ga2O3, Ni:Ga2O3, and Cu:Ga2O3).

[0083] Specific example four

[0084] The purpose of this specific example is to synthesize spinel-type (AB2O4) oxides and high-entropy oxide nanoparticle clusters with adjustable composition, and to obtain multi-metal oxide nanoparticle clusters with good monodispersity and size uniformity.

[0085] Spinel structures include: (B site is Ga)

[0086] Typically, 0.5 mmol ZnCl2 (0.025 M), 1 mmol GaCl3 (0.05 M), 6 mmol trisodium citrate (0.3 M) and 3 mmol urea (0.15 M) were dissolved in 19.75 mL distilled water. Then 0.25 mL of sodium polymethacrylate aqueous solution was added under magnetic stirring. The remaining steps were the same as those for synthesizing Ga2O3NPCs. In order to adjust the stoichiometric ratio of Zn and Ga in the spinel phase Zn-Ga-O, the molar ratio of ZnCl2 and GaCl3 was adjusted to the desired value, while the total amount of the two precursors was kept at 1.5 mmol, and Zn could be obtained. 0.1 Ga 2.9 O4,Zn 0.6 Ga 2.4 O4, ZnGa2O4, such as Figure 11 .

[0087] Among them, other spinel structures can be obtained by changing ZnCl2 to other metal chlorides, see Figure 12 For example, when synthesizing spinel phase CoGa2O4, NiGa2O4, and MgGa2O4 NPCs, 0.5 mmol CoCl2, NiCl2, and MgCl2 were used instead of ZnCl2, and the other reaction parameters and steps were the same as those for synthesizing ZnGa2O4 NPCs.

[0088] Specific example five

[0089] This specific example differs from the fourth specific example in that the B position is Fe.

[0090] When synthesizing spinel phase XFe2O4 (X = Ni, Mg, Zn, Cu, Co, etc.) NPCs, use 0.5 mmol of XCl2 and 1 mmol of FeCl3, 3 mmol of trisodium citrate, and the heating temperature is 200°C. The other reaction parameters and steps are the same as those for synthesizing ZnGa2O4NPCs, and Fe-based spinel structure oxides with uniform size and good monodispersity can be obtained.

[0091] Specific example six

[0092] The purpose of this specific example is to synthesize clusters of ternary spinel oxides to obtain multi-component metal oxide nanoparticle clusters with good monodispersity and size uniformity. The following are two different oxide synthesis examples.

[0093] 1. Prepare (MgZn)Ga2O4NPCs by dissolving 0.25mmol MgCl2·6H2O, 0.25mmol ZnCl2, 1mmol GaCl3, 6mmol trisodium citrate, and 3mmol urea in 19.75mL distilled water. Then, add 0.25mL sodium polymethacrylate under magnetic stirring. The remaining steps are identical to those for the synthesis of Ga2O3NPCs. Replace MgCl2·6H2O with 0.25mmol CoCl2, NiCl2·6H2O, or CuCl2·2H2O, and follow the same reaction parameters and steps as for the synthesis of (MgZn)Ga2O4NPCs to obtain (CoZn)Ga2O4, (NiZn)Ga2O4NPCs, and (CuZn)Ga2O4:NPCs. (The A-site element can be modified as desired).

[0094] 2. Synthesis of (CoNi)Fe2O4. Dissolve 0.25 mmol CoCl2, 0.25 mmol NiCl2·6H2O, 1 mmol FeCl3·6H2O, 3 mmol trisodium citrate, and 3 mmol urea in 19.75 mL of distilled water. Then, add 0.25 mL of sodium polymethacrylate under magnetic stirring. The remaining steps are identical to those for the synthesis of Fe3O4NPCs. Substitute the following metal precursors for the following synthesis: (CoCu)Fe2O4, (CoMg)Fe2O4, (CoZn)Fe2O4, (CoMn)Fe2O4, (NiCu)Fe2O4, (NiMg)Fe2O4, (NiZn)Fe2O4, (NiMn)Fe2O4 (the A-site element can be freely changed).

[0095] Specific example seven

[0096] The difference from the sixth specific example is that the present specific example prepares a quaternary spinel structure oxide. The following are two different examples of oxide synthesis.

[0097] 1. Dissolve 0.167 mmol MgCl2·6H2O, 0.167 mmol CoCl2, 0.167 mmol ZnCl2, 1 mmol GaCl3, 6 mmol trisodium citrate, and 3 mmol urea in 19.75 mL distilled water to synthesize (MgCoZn)Ga2O4NPCs. Then, add 0.25 mL sodium polymethacrylate under magnetic stirring. The remaining steps are the same as those for synthesizing Ga2O3NPCs. (The A-site element can be changed at will.)

[0098] 2. Dissolve 0.167 mmol CoCl2, 0.167 mmol NiCl2·6H2O, 0.167 mmol ZnCl2, 1 mmol FeCl3·6H2O, 3 mmol trisodium citrate, and 3 mmol urea in 19.75 mL of distilled water to synthesize (CoNiZn)Fe2O4NPCs. Then, add 0.25 mL of sodium polymethacrylate under magnetic stirring. The remaining steps are identical to those for Fe3O4NPCs. By varying the precursors, (CoNiCu)Fe2O4NPCs, (CoNiMn)Fe2O4NPCs, (CuNiZn)Fe2O4NPCs, (MnNiZn)Fe2O4NPCs, and (CoCuZn)Fe2O4NPCs can be obtained (the A-site element can be freely changed).

[0099] Specific example eight

[0100] The difference from the sixth specific example is that the present specific example prepares a five-element spinel structure oxide.

[0101] 1. Dissolve 0.125 mmol MgCl2·6H2O, 0.125 mmol CoCl2, 0.125 mmol NiCl2·6H2O, 0.125 mmol ZnCl2, 1 mmol GaCl3, 6 mmol trisodium citrate, and 3 mmol urea in 19.75 mL distilled water to synthesize (MgCoNiZn)Ga2O4NPCs. Then, add 0.25 mL sodium polymethacrylate under magnetic stirring. The remaining steps are the same as those for synthesizing Ga2O3NPCs. (The A-site element can be changed at will.)

[0102] 2. Dissolve 0.125 mmol MnCl2·4H2O, 0.125 mmol CoCl2, 0.125 mmol NiCl2·6H2O, 0.125 mmol ZnCl2, 1 mmol FeCl3·6H2O, 3 mmol trisodium citrate, and 3 mmol urea in 19.75 mL of distilled water to synthesize (MnCoNiZn)Fe2O4NPCs. Then, add 0.25 mL of sodium polymethacrylate under magnetic stirring. The remaining steps are identical to those for Fe3O4NPCs. By varying the precursors, you can obtain (MnCoNiCu)Fe2O4NPCs, (CuCoNiZn)Fe2O4NPCs, and other compounds (the A-site element can be freely varied).

[0103] Specific example nine

[0104] The difference from the sixth specific example is that this specific example prepares a hexavalent spinel structure oxide. The following are two different oxide synthesis examples: (MgAlCoNiZn)Ga2O4NPCs and (MgMnCoNiZn)Fe2O4NPCs

[0105] Dissolve 0.1 mmol MgCl2·6H2O, 0.1 mmol AlCl3, 0.1 mmol CoCl2, 0.1 mmol NiCl2·6H2O, 0.1 mmol ZnCl2, 1 mmol GaCl3, 6 mmol trisodium citrate, and 3 mmol urea in 19.75 mL of distilled water. Then, add 0.25 mL of sodium polymethacrylate aqueous solution under magnetic stirring. Transfer the mixture to a 50 mL hydrothermal autoclave and heat at 180°C for 12 h. Wash the resulting sample by centrifugation and dry it.

[0106] 2. Dissolve 0.1 mmol MgCl2·6H2O, 0.1 mmol MnCl2·4H2O, 0.1 mmol CoCl2, 0.1 mmol NiCl2·6H2O, 0.1 mmol ZnCl2, 1 mmol FeCl3·6H2O, 3 mmol trisodium citrate, and 3 mmol urea in 19.75 mL of distilled water. Then, add 0.25 mL of sodium polymethacrylate under magnetic stirring. Transfer the mixture to a 50 mL hydrothermal autoclave and heat at 200°C for 12 h. Wash the resulting sample by centrifugation and dry.

[0107] Specific examples ten

[0108] The difference from Specific Example 6 is that this specific example prepares a seven-membered spinel structure oxide.

[0109] (MgVMnCoNiZn)Fe2O4: (MVMnCoNiZn)Fe2O4 NPCs were synthesized by dissolving 0.083 mmol MgCl2·6H2O, 0.083 mmol VCl3, 0.083 mmol MnCl2·4H2O, 0.083 mmol CoCl2, 0.083 mmol NiCl2·6H2O, 0.083 mmol ZnCl2, 1 mmol FeCl3·6H2O, 3 mmol trisodium citrate, and 3 mmol urea in 19.75 mL of distilled water. 0.25 mL of sodium polymethacrylate was then added under magnetic stirring. The remaining steps were identical to those for the synthesis of Fe3O4 NPCs.

[0110] Specific Example 11

[0111] The difference from Specific Example 6 is that this specific example prepares a nine-membered spinel structure oxide.

[0112] (MgAlMnFeCoNiCuZn)Ga2O4NPCs were synthesized by dissolving 0.125 mmol of MgCl2·6H2O, 0.125 mmol of AlCl3, 0.125 mmol of MnCl2·4H2O, 0.125 mmol of FeCl3·6H2O, 0.125 mmol of CoCl2, 0.125 mmol of NiCl2·6H2O, 0.125 mmol of CuCl2·2H2O, 0.125 mmol of ZnCl2, 2 mmol of GaCl3, 12 mmol of trisodium citrate, and 3 mmol of urea in 19.75 mL of distilled water. 0.25 mL of sodium polymethacrylate was then added under magnetic stirring. The remaining steps were identical to those for the synthesis of Ga2O3NPCs.

[0113] Specific Example 12

[0114] The difference from Specific Example 6 is that this specific example prepares a ten-membered spinel structure oxide.

[0115] (MgAlMnFeCoNiCuZnY)Ga2O4NPCs

[0116] To synthesize (MgAlMnFeCoNiCuZnY)Ga2O4:NPCs, 0.11 mmol MgCl2·6H2O, 0.11 mmol AlCl3, 0.11 mmol MnCl2·4H2O, 0.11 mmol FeCl3·6H2O, 0.11 mmol CoCl2, 0.11 mmol NiCl2·6H2O, 0.11 mmol CuCl2·2H2O, 0.11 mmol ZnCl2, 0.11 mmol YCl3·6H2O, 2 mmol GaCl3, 12 mmol trisodium citrate, and 3 mmol urea were dissolved in 19.75 mL of distilled water. Then, 0.25 mL of sodium polymethacrylate was added under magnetic stirring. The remaining steps were identical to those for the synthesis of Ga2O3NPCs.

[0117] Specific example thirteen

[0118] The difference from the sixth specific example is that the present specific example prepares a 13-membered spinel structure oxide. (MgAlMnFeCoNiCuZnY)Ga2O4NPCs

[0119] To synthesize (MgAlCrMnFeCoNiCuZnYInSn)Ga2O4NPCs, such as Figure 13In 19.75 mL of distilled water, dissolve 0.11 mmol MgCl₂·6H₂O, 0.11 mmol AlCl₃, 0.11 mmol CrCl₃·6H₂O, 0.11 mmol MnCl₂·4H₂O, 0.11 mmol FeCl₃·6H₂O, 0.11 mmol CoCl₂, 0.11 mmol NiCl₂·6H₂O, 0.11 mmol CuCl₂·2H₂O, 0.11 mmol ZnCl₂, 0.11 mmol YCl₃·6H₂O, 0.11 mmol InCl₃, 0.11 mmol SnCl₄·5H₂O, 2 mmol GaCl₃, 12 mmol trisodium citrate, and 3 mmol urea. Then, add 0.25 mL of sodium polymethacrylate under magnetic stirring. The remaining steps are the same as those for the synthesis of Ga₂O₃NPCs.

[0120] Specific Example 14

[0121] In this specific example, a pre-synthesized cluster is added to the precursor as the core of the core-shell structure, and then the shell material is successfully coated on the core using the synthesis method of the present invention to form a core-shell structure, wherein both the core metal oxide and the shell metal oxide can be replaced. This specific example uses Fe3O4 as the core to list three specific example methods, such as Figure 14-16 :

[0122] (1)Fe3O4@Ga2O3

[0123] Mix 10 mg of prepared Fe₃O₄NPCs with 10 mL of distilled water and sonicate for 30 minutes. Dissolve 0.1 mmol of GaCl₃, 0.6 mmol of trisodium citrate, and 3 mmol of urea in 15 mL of distilled water. Add 0.25 mL of sodium polymethacrylate and mix the resulting solution with 5 mL of a 1 mg / mL Fe₃O₄NPCs dispersion. A 20 mL mixture is obtained. The remaining steps are identical to those for synthesizing Ga₂O₃NPCs.

[0124] (2)Fe3O4@In2O3

[0125] Dissolve 0.1 mmol of InCl₃, 0.2 mmol of trisodium citrate, and 3 mmol of urea in 15 mL of distilled water. Then, add 0.1 mL of sodium polymethacrylate. Mix this solution with 5 mL of a 1 mg / mL Fe₃O₄ dispersion. The remaining steps are identical to those for synthesizing In₂O₃NPCs.

[0126] (3)Fe3O4@ZnO

[0127] Dissolve 0.05 mmol of ZnCl₂, 0.1 mmol of trisodium citrate, and 1 mmol of Na₂CO₃ in 15 mL of distilled water. Then, add 0.25 mL of sodium polymethacrylate. Mix this solution with 5 mL of a 1 mg / mL Fe₃O₄ dispersion. The remaining steps are identical to those for synthesizing ZnO NPCs.

[0128] Specific Example 15

[0129] In this specific example, a pre-synthesized cluster is added to the precursor as the core of the core-shell structure, and then the shell material is successfully coated on the core using the synthesis method of the present invention to form a core-shell structure. This specific example uses In2O3 as the core and lists three specific examples:

[0130] (1)In2O3@Ga2O3

[0131] Mix 10 mg of the prepared In2O3 NPCs with 10 mL of distilled water and sonicate for 30 minutes to prepare a 1 mg / mL In2O3 NPC dispersion. Dissolve 0.1 mmol of GaCl3, 0.6 mmol of trisodium citrate, and 3 mmol of urea in 15 mL of distilled water. Then, add 0.25 mL of sodium polymethacrylate. Mix this solution with 5 mL of the 1 mg / mL In2O3 dispersion. The remaining steps are identical to those for synthesizing Ga2O3 NPCs.

[0132] (2)In2O3@ZnO

[0133] Dissolve 0.05 mmol of ZnCl₂, 0.1 mmol of trisodium citrate, and 1 mmol of Na₂CO₃ in 15 mL of distilled water. Then, add 0.25 mL of sodium polymethacrylate. Mix this solution with 5 mL of a 1 mg / mL In₂O₃ dispersion. The remaining steps are identical to those for synthesizing ZnO NPCs.

[0134] (3)In2O3@SnO2

[0135] Dissolve 0.3 mmol of SnCl₄·5H₂O, 1.2 mmol of trisodium citrate, and 3 mmol of urea in 15 mL of distilled water. Then, add 0.25 mL of sodium polymethacrylate. Mix the solution with 5 mL of a 1 mg / mL In₂O₃ dispersion. The remaining steps are identical to those for synthesizing SnO₂NPCs.

[0136] Specific Example 16

[0137] In this specific example, a pre-synthesized cluster is added to the precursor as the core of the core-shell structure, and then the shell material is successfully coated on the core using the synthesis method of the present invention to form a core-shell structure. This specific example uses SnO2 as the core and lists three specific examples:

[0138] (1)SnO2@Ga2O3

[0139] Mix 10 mg of the prepared SnO2NPCs with 10 mL of distilled water and sonicate for 30 minutes to obtain a 1 mg / mL SnO2NPCs dispersion. Dissolve 0.1 mmol of GaCl3, 0.6 mmol of trisodium citrate, and 3 mmol of urea in 15 mL of distilled water. Then, add 0.25 mL of sodium polymethacrylate. Mix this solution with 5 mL of the 1 mg / mL SnO2 dispersion. The remaining steps are identical to those for synthesizing Ga2O3NPCs.

[0140] (2)SnO2@ZnO

[0141] Dissolve 0.05 mmol of ZnCl₂, 0.1 mmol of trisodium citrate, and 1 mmol of Na₂CO₃ in 15 mL of distilled water. Then, add 0.25 mL of sodium polymethacrylate. Mix this solution with 5 mL of a 1 mg / mL SnO₂ dispersion. The remaining steps are identical to those for synthesizing ZnO NPCs.

[0142] (3)SnO2@In2O3

[0143] Dissolve 0.1 mmol of InCl₃, 0.2 mmol of trisodium citrate, and 3 mmol of urea in 15 mL of distilled water. Then add 0.1 mL of sodium polymethacrylate. Mix this solution with 5 mL of a 1 mg / mL SnO₂ dispersion. The remaining steps are identical to those for synthesizing In₂O₃NPCs.

[0144] The above descriptions are only some embodiments of the present invention and do not limit the scope of protection of the present invention. Any equivalent device or equivalent process transformation made by using the contents of the description and drawings of the present invention, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A universal method for synthesizing monodisperse metal oxide nanoparticle clusters, characterized in that: The method comprises: The metal inorganic salt precursor and the small molecule ligand are dissolved in water and coordinated to form a complex, an alkali source is added, and after the alkali source is dissolved, a hydrophilic polymer is added to obtain solution A; Performing a hydrothermal reaction on solution A to synthesize a metal oxide corresponding to the precursor; The small molecule ligand is one of trisodium citrate and citric acid; The molar ratio of the metal ion to the small molecule ligand in the metal inorganic salt precursor is 1:1-10.

2. The method for universally synthesizing monodisperse metal oxide nanoparticle clusters according to claim 1, characterized in that: The metal inorganic salt precursor is a metal chloride or a metal nitrate; The concentration of the metal inorganic salt precursor is 0.02M to 0.50M.

3. The method for universally synthesizing monodisperse metal oxide nanoparticle clusters according to claim 1, characterized in that: The alkaline source is one of urea, sodium carbonate, potassium carbonate and sodium bicarbonate; The concentration of the alkali source in the solution A is 0.1M to 0.5M.

4. The method for universally synthesizing monodisperse metal oxide nanoparticle clusters according to claim 1, characterized in that: The process parameters of the hydrothermal reaction are as follows: The reaction temperature is: 120℃~200℃; the preset reaction time is: 20min~720min.

5. The method for universally synthesizing monodisperse metal oxide nanoparticle clusters according to claim 1, characterized in that: The hydrophilic polymer is one of sodium polymethacrylate, polyacrylamide, polyacrylic acid, sodium polyacrylate, and polyvinyl pyrrolidone.

6. A product A, characterized in that Product A is prepared using the method for universal synthesis of monodisperse metal oxide nanoparticle clusters as described in any one of claims 1 to 5.

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