Process for the preparation of metal oxide nanoparticles

Abstract

The application discloses a preparation method of metal oxide nanoparticles. The method comprises the following steps: mixing and contacting at least two reagents, wherein at least one reagent is in a frozen state initially; and controlling the melting phase change rate of the frozen reagent, matching the stirring of a reaction system, accurately controlling the contact rate between the reagents, and then controlling the particle size, particle size distribution and morphology of the obtained metal oxide nanoparticles.

Description

Technical Field

[0001] This invention relates to a method for preparing metal oxide nanoparticles, the method comprising at least two reagents reacting in contact; wherein at least one reagent is initially in a frozen state, and the contact rate between the reagents is controllably adjusted by regulating the phase transition process of the frozen reagent and the stirring conditions of the reaction system. Background Technology

[0002] The preparation and application of metal oxide nanoparticles as catalysts for organic synthesis reactions has become a key research area of ​​great interest in recent years. These materials possess unique physicochemical properties that are significantly different from their corresponding bulk materials, making them highly efficient catalytic media for various reactions.

[0003] This type of material has multiple application advantages: large particle specific surface area and excellent catalyst dispersion in the reaction system; magnetic metal oxide nanoparticles can also be easily recovered through magnetic separation.

[0004] Existing synthesis processes for metal oxide nanocatalysts mainly include the sol-gel method, solution coprecipitation method, and water-oil microemulsion method. The solvothermal method can better control particle size and morphology, but the product yield is low and the synthesis process is cumbersome.

[0005] Taking the synthesis of magnetite (Fe3O4) as an example, the chemical co-precipitation of ferrous and ferric salts with sodium hydroxide solution is the simplest and lowest-cost method, suitable for large-scale production. Applying ultrasonic stirring to the reaction system during co-precipitation can inhibit particle agglomeration and promote the formation of uniformly sized nanoparticles. However, the traditional co-precipitation method still has drawbacks: the resulting nanoparticles have uneven morphology and their sizes are much larger than those obtained by other synthesis methods.

[0006] The industry typically uses the method of adding sodium hydroxide dropwise to iron salt solution to control the size and morphology of nanocrystals. However, this method still results in excessively high local alkali concentration in the iron salt solution, which promotes the rapid nucleation and growth of iron oxide particles.

[0007] Solution coprecipitation is a preferred method for large-scale preparation of nanoparticles due to its simplicity, but an improved process that can precisely control the reagent contact process still needs to be developed.

[0008] US Patent 3681011 discloses a "low-temperature co-precipitation method" for preparing composite metal oxide particles: the process first prepares solid metal salt spheres, then immerses them in a low-temperature alkaline aqueous solution at 0–5°C. The patent states that "the precipitation reaction first occurs on the surface of the spheres, then gradually progresses radially towards the center." The core reaction mechanism of this patent approximates a gradual transformation model of a solid-liquid non-catalytic reaction, making it impossible to achieve precise control over the morphology and particle size of the product nanoparticles.

[0009] Therefore, there is an urgent need in this field for an improved method for preparing metal oxide nanoparticles to overcome at least some of the defects in existing processes and achieve the goal of preparing smaller particle size, narrower particle size distribution, and controllable particle morphology. Summary of the Invention

[0010] This invention provides a method for preparing metal oxide nanoparticles, comprising the following steps: A reaction system is formed by mixing a first reagent containing at least metal ions and a second reagent containing an alkaline salt solution. At least one reagent is initially in a frozen state; By adjusting the temperature of the reaction system and / or applying stirring to the reaction system, the phase change rate of the freezing reagent can be controlled, thereby controlling the contact rate between the freezing reagent and other reagents in the system. Ultimately, the particle size, particle size distribution, and morphology of metal oxide nanoparticles can be controlled.

[0011] In one embodiment, the alkaline salt solution is a sodium hydroxide solution.

[0012] In a preferred embodiment, the second reagent is in a frozen state.

[0013] Preferably, the metal ion is selected from iron, nickel, copper, silver, gold, palladium, platinum, tin, zinc, and combinations thereof.

[0014] Preferably, the metal ions are selected from iron, nickel, copper, and combinations thereof.

[0015] In one embodiment, the temperature of the reaction system is controlled between 0°C and 25°C.

[0016] In a preferred embodiment, the temperature of the reaction system is controlled at 1–20°C, 5–15°C, or 10–15°C.

[0017] In one embodiment, the stirring method used is selected from mechanical stirring, ultrasonic stirring, and combinations thereof.

[0018] In one embodiment, the ultrasonic stirring power is controlled at 50–100 W.

[0019] In one embodiment, when the metal ion is iron ion, the average particle size of the iron oxide nanoparticles obtained by the method of the present invention is reduced by at least 70% compared with the average particle size of the product obtained by the conventional co-precipitation method of adding reagent dropwise in liquid-liquid.

[0020] In another embodiment, when the metal ion is copper ion, the average particle size of CuO nanoparticles obtained by the method of the present invention is reduced by at least 45% compared with the average particle size of the product obtained by the conventional co-precipitation method of adding reagent dropwise in liquid-liquid.

[0021] In another embodiment, when the metal ion is nickel ion, the average particle size of the NiO nanoparticles obtained by the method of the present invention is at least 15% smaller than the average particle size of the product obtained by the conventional co-precipitation method of adding reagent dropwise in a liquid-liquid manner. The present invention also provides metal oxide nanoparticles prepared by the above method.

[0022] The present invention also provides a catalytic reaction method, which uses metal oxide nanoparticles prepared by the above process as a catalyst. Attached Figure Description

[0023] The present invention will now be described in more detail with reference to non-limiting embodiments and accompanying drawings, wherein: Figure 1 The image shows a comparison of the average particle size of iron oxide nanoparticles. Among them, CR is the control group (reagent added drop by drop), NA15 is the 15℃ unstirred experimental group, NA10 is the 10℃ unstirred experimental group, A15 is the 15℃ stirred experimental group, and A10 is the 10℃ stirred experimental group. Figure 2 The image shows a comparison of the average particle size of copper oxide nanoparticles; CR represents the control group (reagent added dropwise), NA15 represents the 15℃ unstirred experimental group, NA10 represents the 10℃ unstirred experimental group, A15 represents the 15℃ stirred experimental group, and A10 represents the 10℃ stirred experimental group. Figure 3 The image shows a comparison of the average particle size of nickel oxide nanoparticles; CR represents the control group (reagent added dropwise), NA15 represents the 15℃ unstirred experimental group, NA10 represents the 10℃ unstirred experimental group, A15 represents the 15℃ stirred experimental group, and A10 represents the 10℃ stirred experimental group. Figure 4 The image shows a comprehensive comparison of the average particle size of iron oxide, copper oxide, and nickel oxide nanoparticles; CR represents the control group (reagents added dropwise), NA15 represents the 15℃ unstirred experimental group, NA10 represents the 10℃ unstirred experimental group, A15 represents the 15℃ stirred experimental group, and A10 represents the 10℃ stirred experimental group. Figure 5 The graph shows the comparison of dye removal rates of iron oxide nanoparticles; CR is the control group (reagent added drop by drop), NA15 is the 15℃ unstirred experimental group, NA10 is the 10℃ unstirred experimental group, A15 is the 15℃ stirred experimental group, and A10 is the 10℃ stirred experimental group. Figure 6 The graph shows the comparison of dye removal rates of copper oxide nanoparticles; CR is the control group (reagent added drop by drop), NA15 is the 15℃ unstirred experimental group, NA10 is the 10℃ unstirred experimental group, A15 is the 15℃ stirred experimental group, and A10 is the 10℃ stirred experimental group. Figure 7The graph shows the comparison of dye removal rates of nickel oxide nanoparticles; CR is the control group (reagent added drop by drop), NA15 is the 15℃ unstirred experimental group, NA10 is the 10℃ unstirred experimental group, A15 is the 15℃ stirred experimental group, and A10 is the 10℃ stirred experimental group. Figure 8 This is a comparative chart of the average particle size of iron oxide, copper oxide, and nickel oxide nanoparticles; CR is the control group (reagent added dropwise), NA15 is the 15℃ unstirred experimental group, NA10 is the 10℃ unstirred experimental group, A15 is the 15℃ stirred experimental group, and A10 is the 10℃ stirred experimental group. Detailed Implementation

[0024] The following embodiments of the present invention are not intended to limit the present invention. Those skilled in the art can make minor modifications to the embodiments or derive other implementation methods within the scope of the present invention, all of which fall within the protection scope of the present invention.

[0025] The specific terminology used in this invention is for general description only and does not constitute a limitation.

[0026] In this specification and claims, the singular forms “a,” “the,” and “the” have plural meanings unless the context explicitly limits it to a single object.

[0027] As used in this invention, the terms “comprising,” “containing,” “having,” “including,” and variations thereof mean to cover the components described below, their equivalents, and other additional components.

[0028] In this invention, the terms "frozen" and "frozen reagent" should be understood to refer to the following phase transition process or state: a reagent that is normally liquid at room temperature, but transforms into a solid state when the temperature drops below its freezing point, or is provided in solid form.

[0029] This invention provides a method for preparing metal oxide nanoparticles, comprising the following steps: At least two reagents are mixed and brought into contact, wherein at least one reagent is initially in a frozen state; and the degree of contact between the reagents is controlled by controlling the melting or phase change of the frozen reagent and stirring the reaction mixture, thereby controlling the particle size, particle size distribution and morphology of the resulting metal oxide nanoparticles.

[0030] The phase change process (including the phase change rate) of the freezing reagent is precisely controlled by selecting appropriate parameters, including the initial temperature of the liquid (non-freezing) reagent, the ratio and volume of the freezing reagent and the liquid reagent, the temperature difference between the temperature of the reaction mixture and the temperature of the temperature control device, and specific stirring devices and stirring parameters.

[0031] One of the reagents is an alkaline salt solution, selected from sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, ammonium hydroxide, and combinations thereof. In one embodiment, the alkaline salt solution is a sodium hydroxide solution. These types of alkaline salt solutions exhibit similar properties in the frozen state and during the phase transition from the frozen state to the liquid state.

[0032] According to the present invention, at least one reagent is added in a frozen state to control the contact degree of each reagent in the reaction mixture and subsequent reactions. The melting rate, i.e., the phase change rate, of the frozen reagent can be adjusted as needed based on the temperature of the remaining reaction mixture, the temperature control conditions provided by the dedicated reaction apparatus, and various stirring parameters.

[0033] In one embodiment, the alkaline salt solution is in a frozen state.

[0034] One of the reagents is a metal ion-containing reagent, wherein the metal ion is selected from iron, nickel, copper, silver, gold, palladium, platinum, tin, zinc, and combinations thereof. Iron, nickel, and copper are used as examples in this invention because these types of metal nanoparticles have significant commercial value. For example, iron oxides are commonly used as conventional catalysts and photocatalysts, and can also be applied in the field of medical diagnostics; copper oxides are preferred for environmental remediation applications; and nickel oxides are widely used in hydrogen-containing systems.

[0035] However, those skilled in the art will know that the method of the present invention described herein can also reasonably be expected to be successful in treating other metal ions (including silver, gold, palladium, platinum, tin, zinc, cobalt, titanium, chromium, ruthenium, and rhodium).

[0036] For example, in one embodiment, the alkaline salt solution is added in a frozen state, and the reagent containing metal ions, such as the metal salt solution, is in the liquid phase. This embodiment does not require consideration of the solidification characteristics of the metal salt. After the frozen alkaline salt solution is heated and melted to undergo a phase change, it can react with the metal salt solution in a conventional manner to undergo a precipitation reaction. The degree of reagent contact can be controlled throughout the process by the phase change rate of the frozen reagent.

[0037] The temperature of the reaction solution is controlled within the range of 5℃ to 25℃. Preferably, the temperature of the reaction solution is controlled within the range of 5℃ to 20℃, 5℃ to 15℃, or 10℃ to 15℃. The reaction system temperature of this invention refers to the average temperature of the entire system, including the freezing reagent undergoing a melting phase change. Any known conventional method in the field of industrial equipment temperature control can be used to regulate the temperature of the reaction solution. The aforementioned temperature range of 5℃ to 25℃ is merely one implementation example of the core technical solution of this invention; the actual reaction temperature and heating rate can be adjusted according to the type of reagent, reactor structure, and reagent dosage, and such adjustments all fall within the protection scope of this invention.

[0038] The degree of contact between the freezing reagent undergoing the melt phase change and the other reagents in the system is controlled by the stirring method and parameters. Any one or more stirring techniques in the art can be used. In specific embodiments, conventional mechanical stirring, ultrasonic stirring, or a combination of mechanical and ultrasonic stirring are employed to stir the reaction mixture. The power of the ultrasonic stirring needs to be determined according to the other parameters of the preparation method based on this invention, including reagent type, relative ratio and volume of reagents, temperature control conditions, etc. In one example, the power of the ultrasonic stirring is set to 50–100 W.

[0039] The ultrasonic stirring parameters should be matched according to the type of reagent, the ratio, and the temperature control conditions, with an optimal power of 50-100 W.

[0040] This invention is not bound by any specific theory, but believes that ultrasonic stirring helps to control the phase transition process, namely the melting and transformation of the freezing reagent, so that the reaction between the alkali salt and the metal salt can occur at the phase interface. In addition, ultrasonic stirring can prevent the agglomeration of nanoparticles after the reaction in the liquid medium, ensuring that the final product has a uniform particle size distribution and a specific morphology (the particle size distribution and morphology are determined by temperature and stirring rate).

[0041] The present invention will be described more fully below with reference to several non-limiting embodiments.

[0042] General experimental operating procedures: Experimental materials: ultrafine steel wool, copper shavings, 10.2 M hydrochloric acid (HCl), 12.3 M nitric acid (HNO3), sodium hydroxide granules, hydrogen peroxide (30 vol%), nickel powder (99.7 wt%), methylene blue (99 wt%). All materials were used directly without pretreatment.

[0043] To prepare a 1 M NaOH standard solution: Dissolve 40 g of sodium hydroxide granules in 1 L of deionized water; freeze 10 mL of the 1 M NaOH standard solution into a block-shaped freezing reagent using an ice tray mold and store it in a laboratory freezer.

[0044] Preparation of ferric ion solutions: Dilute 10.2 M HCl to prepare 1 L of 3.9 M and 2.6 M hydrochloric acid solutions respectively. Weigh two 1 g portions of steel wool and place them in two separate 50 mL beakers. Add 12.5 mL of 3.9 M hydrochloric acid solution to the first beaker to obtain Fe ions. 2+ Solution; Add 25 mL of 2.6 M hydrochloric acid solution to the second beaker to prepare Fe. 3+ Solution. Both systems were allowed to stand until the steel wool was completely dissolved (approximately 15–20 minutes). The resulting solutions were then filtered separately to remove residual carbonaceous solids. Add 25 mL of Fe... 3+ Add 1 mL of hydrogen peroxide dropwise to the solution to remove Fe.3+ Reduced to Fe 2+ The solution changes from light green to golden orange, indicating that the ion valence state transformation is complete. Mixing the two solutions yields a bright yellow mixture.

[0045] Preparation of copper ion solution: Weigh 2 g of pure copper shavings and place them in a beaker. Dilute 12.3 M HNO3 to prepare 2 M HNO3. Add 35 mL of this diluted nitric acid dropwise to the beaker until the copper shavings are completely dissolved. Filter the resulting copper ion solution to remove any undissolved copper shavings.

[0046] Preparation of nickel ion solution: Weigh 2 g of 99.7% nickel powder and place it in a beaker; dilute with nitric acid to 2 M, and add 25 mL of the solution dropwise to the nickel powder until the nickel powder is completely dissolved, resulting in a dark green nickel ion solution; filter the mixture to remove undissolved nickel powder.

[0047] Comparative Example 1 Preparation of iron, copper, and nickel metal oxide nanoparticles by coprecipitation method The comparative sample underwent a precipitation reaction at normal pressure and 25°C.

[0048] Preparation of ferric oxide: 20 mL of deionized water and 20 mL of 1 M sodium hydroxide solution were added dropwise to a pre-prepared ferric ion solution, resulting in the formation of a black precipitate. The pH of the system was monitored to ensure the formation of the target ferric hydroxide product. Sodium hydroxide solution was continuously added dropwise until the pH reached 14, for a total of 300 mL. The resulting solution was then aerated using an air pump for 1 h, followed by filtration for 1 h. The precipitate was then allowed to stand and dry overnight to obtain the final product.

[0049] Preparation of copper oxide: 60 mL of 1 M sodium hydroxide solution and 60 mL of distilled water were added sequentially to a copper ion solution. The 1 M sodium hydroxide solution was continuously added dropwise until the solution turned turbid blue and the pH reached 13–14. A total of 300 mL of sodium hydroxide solution was consumed in the process. The solution was aerated using an air pump for 1 h, allowed to stand overnight, and then filtered. The filtered precipitate was placed in a 100°C oven until the blue particles completely turned black.

[0050] Preparation of nickel oxide: Add 1 M sodium hydroxide solution dropwise to nickel nitrate ion solution until the solution turns light green and the pH reaches 13-14; aerate with an oxygen pump for 1 h, and let stand overnight. Filter the nickel oxide mixture and place the precipitate in a 100℃ oven for 1 h. Example 2

[0051] Iron, copper, and nickel metal oxide nanoparticles were prepared using a frozen reagent (sodium hydroxide). In this embodiment, 10 mL of 1 M sodium hydroxide reagent in block form was frozen, and experiments were carried out at 10℃ and 15℃ respectively.

[0052] Those skilled in the art will foresee that similar effects can be obtained by setting the metal ion solution to a frozen state; the reaction system temperature is not limited to 10℃ or 15℃, but can be adjusted in the range of 0℃ to 25℃, preferably 1~20℃, 5~15℃, or 10~15℃, and the temperature is matched according to the performance of the target nanoparticles.

[0053] Iron oxide preparation: A pre-prepared iron ion solution was fixed in a constant-temperature water bath using a clamp and allowed to stand until thermal equilibrium was reached. After the system reached thermal equilibrium, two sodium hydroxide freezing blocks were added and allowed to melt completely; then 20 mL of deionized water was added to the solution. Two sodium hydroxide freezing blocks were added in batches, and more were added after each melting until the pH of the system reached 14. The resulting solution was then aerated, filtered, and dried, following the same procedures as in Comparative Example 1. The entire process was repeated under conditions of 10℃, 15℃ ultrasonic water bath, and 10℃ ultrasonic water bath.

[0054] Preparation of copper oxide: A pre-prepared copper ion solution was placed in a 10°C constant temperature water bath and allowed to stand until thermal equilibrium was reached. Six pre-prepared 1 M sodium hydroxide cryo-blocks were added to the solution, and after they completely melted, 60 mL of distilled water was added. 1 M sodium hydroxide cryo-blocks were continued to be added until the pH of the system reached 13–14 and a blue precipitate formed. A total of 30 sodium hydroxide cryo-blocks were added in the process. The solution was aerated for 1 h and then allowed to stand overnight. The copper oxide mixture was filtered, and the solid particles were placed in a 100°C oven until the blue particles completely turned black. The above procedure was repeated at 15°C, 10°C with ultrasonic stirring, and 15°C with ultrasonic stirring, respectively.

[0055] Nickel oxide preparation: A pre-prepared nickel ion solution was placed in a 10°C constant temperature water bath and allowed to stand until the system reached thermal equilibrium. Then, 1 M sodium hydroxide freezing blocks were added to the solution until the pH reached 13–14 and a green precipitate formed; a total of 30 sodium hydroxide freezing blocks were added. The solution was aerated for 1 h and then allowed to stand overnight. The nickel oxide mixture was filtered, and the solid particles were placed in a 100°C oven and kept at that temperature for 1 h. The above procedure was repeated at 15°C, 10°C with ultrasonic stirring, and 15°C with ultrasonic stirring, respectively.

[0056] Synthesis and characterization of iron-based nanoparticles: Iron oxide nanoparticles prepared using the method of this invention were compared with iron oxide nanoparticles prepared by the traditional co-precipitation method. Energy dispersive spectroscopy (EDX) analysis confirmed that the obtained product was the target iron oxide nanoparticle, with no impurities generated. Particle size, morphology, and particle size distribution were used as comparative evaluation indicators. The average particle size of the magnetite particles obtained in each group of experiments is shown below. Figure 1 As shown.

[0057] Depend on Figure 1 As can be seen, the average particle size of magnetite synthesized using the method of this invention is significantly and consistently smaller than that of the product prepared by the traditional co-precipitation method. The average particle size data for each group are as follows: the average particle sizes for the control group, 15℃ without stirring, 10℃ without stirring, 15℃ with ultrasonic stirring, and 10℃ with ultrasonic stirring are 79.38 nm, 19.04 nm, 13.91 nm, 14.91 nm, and 11.93 nm, respectively. This clearly demonstrates that even under the condition of 15℃ without stirring, ideal particle size and particle size distribution can still be obtained. The particle size distribution curves of the samples prepared using the method of this invention show that, compared to the co-precipitation method, the particle size distribution uniformity of the product obtained by this invention is significantly improved.

[0058] This invention is not limited by any specific theory; the particle size difference of magnetite (iron-based) nanoparticles can be attributed to the contact mode between the reagents. In the traditional coprecipitation method, sodium hydroxide solution is added dropwise, and localized high concentration regions of sodium hydroxide are observed within the iron ion solution. This phenomenon promotes rapid nucleation and growth of particles, ultimately resulting in nanoparticles with higher aggregation, larger particle size, and spherical shape.

[0059] Figure 1 The error bars in the figure represent the population standard deviation, and the statistical population consists of all particles generated under each experimental condition in the three parallel experiments. Clearly, compared to the method of this invention, which uses freezing reagents and controllable reagent contact, the traditional co-precipitation method produces a wider particle size distribution range.

[0060] In this invention, the melting rate of the frozen cube is controlled by adjusting the solution temperature, thereby regulating the reaction rate and ion diffusion process, ultimately producing particles with smaller particle size and better spherical morphology uniformity compared to traditional coprecipitation methods. Figure 1 It is evident that the lower the synthesis temperature, the smaller the particle size. When the synthesis temperature is reduced from 15℃ to 10℃, the particle size decreases by 26.79% under no-stirring conditions and by 19.99% under stirred conditions. Under the same temperature conditions, introducing stirring can further reduce the particle size; the particle size of the stirred group at 15℃ is 21.69% smaller than that of the unstirred group, and the particle size of the stirred group at 10℃ is 14.23% smaller than that of the unstirred group.

[0061] Synthesis and characterization of copper-based nanoparticles: Energy dispersive X-ray spectroscopy (EDX) analysis confirmed that the obtained product was the target copper oxide nanoparticles, free of impurities. The comparison results of the average particle size of copper particles corresponding to different preparation methods are shown below. Figure 2 As shown. By Figure 2 As can be seen, the average particle size of copper oxide synthesized using the method of this invention is significantly smaller than that of the product obtained by the traditional co-precipitation method. The average particle sizes of each group are as follows: control group: 147.86 nm, 15℃ without stirring: 81.18 nm, 10℃ without stirring: 65.60 nm, 15℃ with stirring: 47.28 nm, 10℃ with stirring: 33.26 nm. The smallest particle size of 33.26 nm can be obtained by low temperature combined with stirring; even the experimental results under the 15℃ without stirring condition show significant advantages.

[0062] The particle size distribution curves of the samples prepared using this invention show that, compared with the traditional co-precipitation method, the particle size distribution uniformity of the product obtained by this invention is significantly improved; moreover, the particle size distribution range obtained by this invention under low temperature and stirring conditions is narrower. Figure 2 The dimensions of the error bars also confirm this conclusion.

[0063] The particles prepared by the traditional co-precipitation method have a very large average particle size, severe agglomeration, and a wide particle size distribution, with the particles being rod-shaped. Particle size distribution data shows that the vast majority of particles obtained by this method have a particle size greater than 100 nm, with only a small number of particles smaller than 100 nm. When using the technical solution of this invention, although the products of the unstirred experimental group are still rod-shaped particles, their size is smaller than that of the co-precipitation method; the low-temperature stirring experimental group can obtain spherical particles with even smaller size and higher uniformity. This morphology is an ideal product form due to its high specific surface area.

[0064] Synthesis and characterization of nickel-based nanoparticles: Consistent with experiments involving iron and copper, energy dispersive spectroscopy (EDX) analysis confirmed that the obtained product was the target nickel oxide nanoparticles, with no impurities generated. The average particle size of the nickel nanoparticles corresponding to different preparation methods is shown below. Figure 3 As shown.

[0065] Depend on Figure 3 It is evident that the average particle size of the product synthesized using the method of this invention is smaller than that of the traditional co-precipitation method. The average particle sizes of each group are as follows: control group: 29.15 nm, 15℃ without stirring: 24.68 nm, 10℃ without stirring: 22.15 nm, 15℃ with stirring: 17.24 nm, 10℃ with stirring: 14.62 nm. The smallest particle size, 14.62 nm, can be obtained under the condition of low temperature combined with stirring.

[0066] The particle size distribution curves of the samples prepared using this invention show that, compared to the co-precipitation method, the particle size distribution uniformity of the product of this invention is significantly improved; the particle size distribution range of the product obtained using the freezing reagent preparation process under low-temperature stirring conditions is narrower. Although the average particle size of the particles obtained by the co-precipitation method is relatively small, the particle size distribution range is wide, and the particles are spherical. The experimental group using this invention in conjunction with stirring can obtain spherical particles with smaller size and higher uniformity.

[0067] Figure 4 This is a size comparison chart of various transition metal nanoparticles. Figure 4 As can be seen, by using at least one freezing reagent to control the contact degree between reagents, this invention can produce metal oxide nanoparticles with smaller particle size, better uniformity, and narrower particle size distribution range compared to the traditional co-precipitation method. Examples of this invention have been given based on iron, copper, and nickel. However, those skilled in the art, based on the disclosure herein, can reasonably expect without extensive experimentation that this invention can also produce metal nanoparticles with superior performance to conventional processes for other metals such as silver, gold, palladium, platinum, tin, and zinc.

[0068] The type of precursor reagent, reaction pH, reaction temperature, and precursor concentration are all adjustable process parameters. These parameters affect the formation rate of various hydroxides, thereby altering the properties of the final metal nanoparticles. Example 3

[0069] Degradation performance test of iron, copper, and nickel metal oxide nanoparticle dyes: Weigh an appropriate amount of methylene blue dye and dissolve it in 1 L of deionized water to prepare standard dye solutions with concentrations of 20, 40, 60, 80, and 100 mg / L. Set the spectrophotometer wavelength to 662 nm, which corresponds to the characteristic absorption wavelength of methylene blue dye. Select the absorbance 100% (A) / transmittance 0% (T) mode. Add deionized water to a cuvette and place it in the spectrophotometer to measure the reference value. Then, measure the absorbance values ​​of each standard solution sequentially, plot the absorbance-solution concentration standard curve, and complete the instrument calibration.

[0070] 20 mg of iron, copper, and nickel oxide nanoparticles were weighed and added to 60 mL of dye solution. The top stirrer was set to 500 rpm, and the dye solution containing the adsorbent was stirred for 1 h at room temperature. After stirring, the solution was drawn off with a syringe, filtered through a microporous membrane, and transferred to a cuvette for absorbance measurement using a spectrophotometer. The above operation was repeated for the control group, the experimental groups prepared at 10℃, and the experimental groups prepared at 15℃. The dye removal test was used to evaluate the performance of the synthesized metal oxide nanoparticles. All experimental groups used the same process parameters to facilitate comparison of performance differences between different nanoparticles. Iron, copper, and nickel oxide nanoparticles prepared by the above processes were selected for testing. Each experiment was repeated 3 times to ensure the reproducibility of the test results.

[0071] The dye removal performance comparison test of each group of samples was conducted under the following conditions: top stirrer speed 500 rpm, initial dye concentration 60 mg / L, contact time between dye solution and sample 1 h, dye solution volume 60 mL, and sample dosage 20 mg.

[0072] The dye removal performance of iron oxide nanoparticles in aqueous solution: The dye removal rate test results of each group of iron oxide nanoparticle samples are as follows: Figure 5 As shown in Figure 5, the dye adsorption rate of the iron-based (magnetite) nanoparticles synthesized using the method of this invention is significantly higher than that of the samples prepared by the traditional co-precipitation method. The dye removal rates of each group of samples are as follows: control group: 29.87%, 15℃ unstirred group: 49.90%, 10℃ unstirred group: 69.93%, 15℃ stirred group: 66.06%, 10℃ stirred group: 83.57%.

[0073] also, Figure 5 The error bars represent the sample standard deviation of three parallel tests for each process, reflecting the fluctuation range of dye adsorption rate in three parallel tests under the same preparation process. They visually demonstrate the repeatability of dye adsorption data for each group, and the experiment has good reproducibility.

[0074] The dye removal performance of copper oxide nanoparticles in aqueous solution: The results of dye removal rates of copper oxide nanoparticles in each group are shown below. Figure 6 .Depend on Figure 6 It is evident that the copper oxide nanoparticles synthesized using the method of this invention exhibit a higher dye removal rate than those prepared by the traditional co-precipitation method. The dye removal rates of each group of samples are as follows: control group: 16.73%, 15℃ unstirred group: 27.51%, 10℃ unstirred group: 36.94%, 15℃ stirred group: 44.85%, 10℃ stirred group: 56.13%.

[0075] The dye removal rate test results for each group of nickel oxide nanoparticle samples are shown in Figure 7. As can be seen from Figure 7, the dye removal rate of the nickel oxide nanoparticles synthesized using the method of this invention is higher than that of the product prepared by the traditional co-precipitation method. The dye removal rates of each group of samples are as follows: control group: 55.62%, 15℃ unstirred group: 61.85%, 10℃ unstirred group: 65.72%, 15℃ stirred group: 66.57%, 10℃ stirred group: 76.33%.

[0076] The purpose of the dye removal experiment is to verify whether the metal oxide nanoparticles prepared using the process of this invention (by controlling the contact between reagents with at least one freezing reagent) have a superior effect on the removal of organic dyes compared to the traditional co-precipitation method. This dye test can serve as a representative experimental method for the performance of nanoparticles; based on the superior basic particle properties of the product of this invention, it is expected that it will also have an improving effect in other catalytic scenarios. Figure 8 This is a comparison of the dye removal test results for three types of metal oxide nanoparticles. Figure 8 It can be seen that the performance of various nanoparticle samples prepared by the method of the present invention is improved.

[0077] The above embodiments are only used to illustrate the preparation and implementation of the present invention. Those skilled in the art can modify the process details to derive other implementation methods, all of which fall within the scope of protection of the present invention. For example, those skilled in the art will clearly understand after reading the disclosure herein that the present invention is not limited to the raw materials described herein; other metal ions and alkaline salt solutions can also be adapted to this process.

Claims

1. A method for preparing metal oxide nanoparticles, characterized in that, Includes the following steps: A reaction system is formed by mixing a first reagent containing at least metal ions and a second reagent containing an alkaline salt solution. At least one reagent is initially in a frozen state; By adjusting the temperature of the reaction system and / or applying stirring to the reaction system, the phase change rate of the freezing reagent can be controlled, thereby controlling the contact rate between the freezing reagent and other reagents in the system. Ultimately, the particle size, particle size distribution, and morphology of metal oxide nanoparticles can be controlled.

2. The method for preparing metal oxide nanoparticles as described in claim 1, characterized in that, The alkaline salt solution is a sodium hydroxide solution.

3. The method for preparing metal oxide nanoparticles as described in claim 1, characterized in that, The second reagent is in a frozen state.

4. The method for preparing metal oxide nanoparticles as described in claim 1, characterized in that, The metal ions are selected from iron, nickel, copper, silver, gold, palladium, platinum, tin, zinc, and combinations thereof.

5. The method for preparing metal oxide nanoparticles as described in claim 4, characterized in that, The metal ions are selected from iron, nickel, copper, and combinations thereof.

6. The method for preparing metal oxide nanoparticles as described in claim 1, characterized in that, The temperature of the reaction system is controlled between 0℃ and 25℃.

7. The method for preparing metal oxide nanoparticles as described in claim 6, characterized in that, The temperature of the reaction system is controlled at 1–20℃, 5–15℃, or 10–15℃.

8. The method for preparing metal oxide nanoparticles as described in claim 1, characterized in that, The stirring method used is selected from mechanical stirring, ultrasonic stirring, and combinations thereof.

9. The method for preparing metal oxide nanoparticles as described in claim 8, characterized in that, The ultrasonic stirring power should be controlled between 50 and 100 W.

10. The method for preparing metal oxide nanoparticles as described in claim 1, characterized in that, When the metal ion is iron ion, the average particle size of the iron oxide nanoparticles obtained is reduced by at least 70% compared to the average particle size of the product obtained by the traditional coprecipitation method of adding reagent dropwise from liquid to liquid.

11. The method for preparing metal oxide nanoparticles as described in claim 1, characterized in that, When the metal ion is copper ion, the average particle size of CuO nanoparticles obtained by the method of the present invention is reduced by at least 45% compared with the average particle size of the product obtained by the traditional co-precipitation method of adding reagent dropwise in liquid-liquid.

12. A metal oxide nanoparticle, characterized in that, The metal oxide nanoparticles were prepared using the preparation method described in any one of claims 1 to 11.

13. A catalytic reaction method, wherein the metal oxide nanoparticles prepared by the method of any one of claims 1 to 11 are used as catalysts.

Images