Nanometer rare earth oxide, efficient preparation method and application thereof

Abstract

The application discloses a kind of nano rare earth oxides and its efficient preparation method and application, belong to nanometer material preparation technical field.The method uses microwave hydrothermal synthesis technology, and soluble rare earth salt is prepared into precursor solution with surfactant, and microwave hydrothermal reaction is carried out after being mixed with precipitator solution, and the rapid and uniform synthesis of nano rare earth oxide is realized by independently controlling microwave output power and reaction system pressure, in combination with surfactant auxiliary dispersion.The preparation method of the application is to mix rare earth salt precursor with precipitator and carry out microwave hydrothermal reaction, and after washing, drying and calcining, D 50 <200 nm of nano rare earth oxide.The application has simple process, short reaction period, controllable product particle size and excellent dispersibility, solves the problems of long reaction time, wide particle size distribution and poor batch repeatability of traditional methods, and has good industrialization promotion prospect.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterial preparation technology, specifically relating to a nano-rare earth oxide and its efficient preparation method and application. Background Technology

[0002] Nano-rare earth oxides, due to their unique 4f electron layer structure and excellent physicochemical properties, have broad application prospects in catalysis, luminescent materials, electronic ceramics, and biomedicine. The properties of rare earth oxides largely depend on their microstructure: structural features directly determine specific surface area, porosity, and permeability, which in turn determine the number of available active sites and ultimately affect actual performance.

[0003] Currently, the main methods for preparing nano-rare earth oxides include precipitation, hydrothermal methods, sol-gel methods, combustion methods, and microemulsion methods. CN111017980A uses a lanthanum chloride-liquid ammonia high-pressure liquid phase system to prepare high-purity nano-lanthanum oxide at 60-250 °C for 50-90 h. However, this method has a long single-batch production cycle and low reactor utilization efficiency. High-temperature heat treatment (650-1000 °C) is completed in an integrated flash drying unit, requiring high precision in equipment materials and atmosphere control. CN102849774A uses a hydrothermal method to prepare nano-cerium oxide, with a reaction time of 2-24 h. The pH value in the reaction system has a significant impact on the product morphology, making scale-up production difficult. CN114477264A uses a sol-gel method, requiring 24-36 h for gel drying. Furthermore, the ethanol washing process involves flammable organic solvents, resulting in high production safety and costs. CN118908263A utilizes organic acid anions to complex rare earth ions to accelerate the nucleation process, but its pH control window is narrow, and deviations in the ratio easily lead to the formation of layered aggregates, making continuous production difficult. CN118145691A employs a flame combustion method to prepare nanoparticles through the atomization and combustion of organic precursors. The reaction temperature is as high as 1000~2500 °C, resulting in high energy consumption and demanding requirements for combustion equipment and exhaust gas treatment systems. CN111018003A, CN108706618A, and CN103450474A all involve microemulsion methods. The implementation of this method depends on the compounding of organic solvents and surfactants, requiring multiple washings for removal, resulting in high wastewater treatment costs. Furthermore, the stability of the microemulsion system is greatly affected by the component ratio, leading to poor batch repeatability.

[0004] In summary, existing methods for preparing nano-rare earth oxides generally suffer from problems such as long process flows, high energy consumption, dependence on harsh reaction conditions or specialized equipment, wide particle size distribution, poor morphology controllability, and poor batch reproducibility, making it difficult to meet the needs of large-scale industrial production. Microwave hydrothermal synthesis technology combines the advantages of rapid, homogeneous bulk heating by microwaves with the high-temperature, high-pressure reaction of hydrothermal methods, significantly accelerating reaction kinetics and achieving rapid nucleation and growth of products. However, the parameter matching relationships in existing microwave hydrothermal synthesis technologies, such as heating rate, isothermal time, and cooling / depressurization stages, are still unclear, resulting in insufficient controllability of the reaction process and affecting product consistency and batch reproducibility. Therefore, there is an urgent need to develop a simple, short-time, highly efficient method for preparing nano-rare earth oxides with controllable particle size and good reproducibility. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a nano-rare earth oxide, its efficient preparation method, and its applications. This method employs a microwave approach, achieving precise temperature control by independently regulating the microwave output power and the upper limit of the reaction system pressure. Combined with the auxiliary dispersing effect of surfactants, highly dispersed nano-rare earth oxides with uniform particle size are prepared. To achieve the above objectives, this invention adopts the following technical solution:

[0006] A method for efficiently preparing nano-rare earth oxides includes the following steps:

[0007] (1) Preparation of rare earth salt precursor solution: Dissolve soluble rare earth salt and surfactant in deionized water and stir until completely dissolved to obtain a homogeneous and transparent rare earth salt precursor solution.

[0008] (2) Preparation of precipitant solution: Dissolve the precipitant in deionized water and stir until completely dissolved to obtain a homogeneous and transparent precipitant solution;

[0009] (3) Microwave hydrothermal synthesis: The solutions obtained in steps (1) and (2) are mixed evenly and transferred to the reaction vessel of a microwave hydrothermal synthesizer. After sealing, a microwave hydrothermal reaction is carried out. The reaction temperature is controlled at 90 °C~180 °C, the reaction time is 0.1 h~9 h, the upper limit of the pressure inside the vessel is 0.5 MPa~5.0 MPa, the microwave output power is 0~1000 W, and the stirring speed is 100 rpm~300 rpm. After the reaction is completed, the mixture is cooled, filtered, washed, dried, and calcined to obtain nano-rare earth oxides.

[0010] Preferably, in step (1), the soluble rare earth salt is one or more of lanthanum salt, cerium salt, and yttrium salt, and the lanthanum salt, cerium salt, and yttrium salt are each independently a nitrate, a chloride, or an acetate; the concentration of the rare earth salt precursor solution is 0.05 mol / L to 0.5 mol / L.

[0011] Preferably, in step (1), the surfactant is selected from one or more of sodium dodecyl sulfate (SDS), sodium dodecylbenzene sulfonate (SDBS), hexadecyltrimethylammonium chloride (CTAC), hexadecyltrimethylammonium bromide (CTAB), polyvinylpyrrolidone K30 (PVP K30), and polyethylene glycol-20000 (PEG-20000), and the amount of surfactant added is controlled within the range of 0.5% to 3.0% of the total mass of the precursor solution.

[0012] Preferably, in step (2), the precipitant is one or more of urea, hexamethylenetetramine, and ammonium carbonate, and the molar ratio of the precipitant to rare earth ions is 4:1 to 24:1.

[0013] Preferably, in step (3), the organic solvent is one or more of anhydrous ethanol, methanol, and acetone.

[0014] Preferably, in step (3), the drying temperature is 60 °C to 80 °C and the drying time is 6 h to 24 h.

[0015] Preferably, in step (3), the calcination heating rate is 1 °C / min to 10 °C / min, the calcination temperature is 300 °C to 900 °C, and the holding time is 1 h to 6 h.

[0016] The microwave hydrothermal synthesizer used in this invention has functions such as continuously adjustable microwave output power (0~1000 W), real-time pressure monitoring and upper limit control, and closed-loop temperature feedback regulation. It can automatically adjust the microwave output power according to the set temperature and work in conjunction with the pressure upper limit control unit to ensure that the reaction temperature is stable within the set value ±1 °C range, effectively avoiding the temperature overshoot problem caused by thermal inertia or power fluctuations in traditional oil baths or ordinary ovens.

[0017] A highly dispersed nano-rare earth oxide, prepared using the aforementioned efficient method for preparing nano-rare earth oxides, product D 50 <200 nm.

[0018] Applications of a highly dispersed nano-rare earth oxide in catalysis, luminescent materials, electronic ceramics, and biomedicine.

[0019] The beneficial effects of this invention are as follows:

[0020] (1) This invention uses microwave hydrothermal synthesis technology to prepare nano-rare earth oxides. The microwave bulk heating effect enables the rapid and uniform heating of the reaction system, which significantly accelerates the reaction kinetics and shortens the reaction time from several days in the traditional hydrothermal method to several hours or even minutes, greatly improving the synthesis efficiency.

[0021] (2) This invention ensures batch-to-batch consistency through continuously adjustable microwave output power, real-time pressure monitoring, and closed-loop temperature feedback control; by adjusting the molar ratio of precipitant to rare earth ions, reaction temperature, reaction time, and type of surfactant, the product D can be controlled. 50 Precise control within the 100 nm to 200 nm range results in a narrow particle size distribution.

[0022] (3) The process of this invention is simple, efficient, uniform in particle size and good repeatability; the in-situ modification of surfactant effectively inhibits calcination agglomeration and the product redispersibility is good; the precise temperature control of the single reactor facilitates the establishment of a reaction kinetic model, and the raw material ratio can be directly scaled up to the industrial-grade large-capacity microwave reactor, which has good prospects for industrial promotion. Attached Figure Description

[0023] Figure 1 This is a scanning electron microscope (SEM) image of the rare earth nano-oxide prepared in Example 1 of the present invention.

[0024] Figure 2 The figure shows the particle size test results of the rare earth oxide nanoparticles prepared in Example 1 of this invention.

[0025] Figure 3 The figure shows the particle size test results of the rare earth oxide nanoparticles prepared in Example 2 of this invention.

[0026] Figure 4 The figure shows the particle size test results of the nano-rare earth oxide particles prepared in Example 3 of the present invention.

[0027] Figure 5 The figure shows the particle size test results of the nano-rare earth oxide particles prepared in Example 4 of this invention.

[0028] Figure 6 The figure shows the particle size test results of the nano-rare earth oxide particles prepared in Example 5 of the present invention.

[0029] Figure 7 The figure shows the particle size test results of the nano-rare earth oxide particles prepared in Example 6 of the present invention.

[0030] Figure 8 The figure shows the particle size test results of the nano-rare earth oxide particles prepared in Example 7 of the present invention.

[0031] Figure 9 The figure shows the particle size test results of the nano-rare earth oxide particles prepared in Example 8 of the present invention.

[0032] Figure 10 The figure shows the particle size test results of the nano-rare earth oxide particles prepared in Example 9 of the present invention.

[0033] Figure 11 The figure shows the particle size test results of the rare earth oxides obtained in Comparative Example 1 of this invention.

[0034] Figure 12 The figure shows the particle size test results of the rare earth oxides obtained in Comparative Example 2 of this invention.

[0035] Figure 13 The figure shows the particle size test results of the rare earth oxides obtained in Comparative Example 3 of this invention. Detailed Implementation

[0036] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. However, the following embodiments are only for explaining the present invention, and the scope of protection of the present invention should include all the contents of the claims. Moreover, through the description of the following embodiments, those skilled in the art can fully implement all the contents of the claims of the present invention.

[0037] In the following examples, the amount of surfactant added is expressed as a percentage of the total mass of soluble rare earth salts, surfactants, and deionized water in the precursor solution. The amounts of each component added in the examples are based on accurate weighing.

[0038] Example 1:

[0039] (1) Preparation of rare earth salt precursor solution: 216.50 g of lanthanum nitrate hexahydrate (0.5 mol) and 12.16 g of SDS (1.0% of the total mass of the precursor solution) were added to 1.0 L of distilled water and stirred until completely dissolved to obtain a homogeneous and transparent rare earth salt precursor solution (La). 3+ (Concentration is 0.50 mol / L), for later use.

[0040] (2) Preparation of precipitant solution: Add 240.20 g of urea (4.0 mol, urea / La) to the solution. 3+ Add (8:1) to 1.0 L of distilled water and stir until completely dissolved to obtain a homogeneous and transparent precipitant solution for later use.

[0041] (3) Microwave hydrothermal synthesis and calcination: The solutions obtained in steps (1) and (2) were mixed evenly and transferred to a microwave reactor. The reaction temperature was set at 140 °C, the upper limit of the pressure was 2.5 MPa, the reaction time was 4 h, the stirring rate was 180 rpm, and the upper limit of the microwave output power was 1000 W. After the reaction was completed, the mixture was naturally cooled to room temperature. The resulting suspension was filtered and washed alternately with deionized water and anhydrous ethanol to obtain nano-rare earth oxide precursors. The precursors were placed in a drying oven and dried at 75 °C for 10 h. The dried product was then placed in a muffle furnace and heated to 600 °C at a heating rate of 4 °C / min. The temperature was maintained for calcination for 3 h, and the nano-rare earth oxides were obtained after natural cooling. The microstructure of the nano-rare earth oxides is shown in the figure below. Figure 1 As shown, the product D was determined by a laser particle size analyzer. 50 The particle size is 0.114 μm (114 nm), indicating good dispersibility.

[0042] Example 2:

[0043] (1) Preparation of rare earth salt precursor solution: 217.10 g of cerium nitrate hexahydrate (0.5 mol) and 22.30 g of SDBS (1.0% of the total mass of the precursor solution) were added to 2.0 L of distilled water and stirred until completely dissolved to obtain a homogeneous and transparent rare earth salt precursor solution (Ce). 3+ (Concentration is 0.25 mol / L), for later use.

[0044] (2) Preparation of precipitant solution: 280.40 g hexamethylenetetramine (2.0 mol, hexamethylenetetramine / Ce 3+ Add the precipitant solution (4:1 ratio) to 1.0 L of distilled water and stir until completely dissolved to obtain a homogeneous and transparent precipitant solution for later use.

[0045] (3) Microwave hydrothermal synthesis and calcination: The solutions obtained in steps (1) and (2) were mixed evenly and transferred to a microwave reactor. The reaction temperature was set at 160 °C, the upper limit of the pressure was 3.5 MPa, the reaction time was 2 h, the stirring rate was 220 rpm, and the upper limit of the microwave output power was 1000 W. After the reaction was completed, the mixture was naturally cooled to room temperature. The resulting suspension was filtered and washed alternately with deionized water and anhydrous ethanol to obtain nano-rare earth oxide precursors. The precursors were placed in a drying oven and dried at 80 °C for 8 h. The dried product was then placed in a muffle furnace and heated to 750 °C at a heating rate of 6 °C / min. The temperature was maintained for calcination for 2.5 h. After natural cooling, nano-rare earth oxides were obtained. The product D was measured by a laser particle size analyzer. 50 It has a particle size of 0.120 μm (120 nm) and good dispersibility.

[0046] Example 3:

[0047] (1) Preparation of rare earth salt precursor solution: 169.08 g yttrium acetate tetrahydrate (0.5 mol) and 98.20 g CTAC (3.0% of the total mass of the precursor solution) were added to 3.0 L of distilled water and stirred until completely dissolved to obtain a homogeneous and transparent rare earth salt precursor solution (Y). 3+ (Concentration is 0.167 mol / L), for later use.

[0048] (2) Preparation of precipitant solution: Add 192.20 g of ammonium carbonate (2.0 mol, ammonium carbonate / Y) 3+ Add the precipitant solution (4:1 ratio) to 2.0 L of distilled water and stir until completely dissolved to obtain a homogeneous and transparent precipitant solution for later use.

[0049] (3) Microwave hydrothermal synthesis and calcination: The solutions obtained in steps (1) and (2) were mixed evenly and transferred to a microwave reactor. The reaction temperature was set at 130 °C, the upper limit of the pressure was 2.0 MPa, the reaction time was 5 h, the stirring rate was 140 rpm, and the upper limit of the microwave output power was 1000 W. After the reaction was completed, the mixture was naturally cooled to room temperature. The resulting suspension was filtered and washed alternately with deionized water, anhydrous ethanol, and acetone to obtain nano-rare earth oxide precursors. The precursors were placed in a drying oven and dried at 70 °C for 14 h. The dried product was then placed in a muffle furnace and heated to 500 °C at a heating rate of 8 °C / min. The temperature was maintained for calcination for 4 h, and the nano-rare earth oxides were obtained after natural cooling. The product D was measured by a laser particle size analyzer. 50 The particle size is 0.141 μm (141 nm), indicating good dispersibility.

[0050] Example 4:

[0051] (1) Preparation of rare earth salt precursor solution: 216.50 g of lanthanum nitrate hexahydrate (0.5 mol) and 63.25 g of CTAB (1.5% of the total mass of the precursor solution) were added to 4.0 L of distilled water and stirred until completely dissolved to obtain a homogeneous and transparent rare earth salt precursor solution (La). 3+ (Concentration is 0.125 mol / L), for later use.

[0052] (2) Preparation of precipitant solution: Add 192.10 g of ammonium carbonate (2.0 mol, ammonium carbonate / La) 3+ Add the precipitant solution (4:1 ratio) to 1.5 L of distilled water and stir until completely dissolved to obtain a homogeneous and transparent precipitant solution for later use.

[0053] (3) Microwave hydrothermal synthesis and calcination: The solutions obtained in steps (1) and (2) were mixed evenly and transferred to a microwave reactor. The reaction temperature was set to 100 °C, the upper limit of the pressure was 1.5 MPa, the reaction time was 8 h, the stirring rate was 110 rpm, and the upper limit of the microwave output power was 1000 W. After the reaction was completed, the mixture was naturally cooled to room temperature. The resulting suspension was filtered and washed alternately with deionized water and methanol to obtain nano-rare earth oxide precursors. The precursors were placed in a drying oven and dried at 65 °C for 20 h. The dried product was then placed in a muffle furnace and heated to 400 °C at a heating rate of 2 °C / min. The temperature was maintained for 5 h and then naturally cooled to obtain nano-rare earth oxides. The product D was measured by a laser particle size analyzer. 50 It has a particle size of 0.126 μm (126 nm) and good dispersibility.

[0054] Example 5:

[0055] (1) Preparation of rare earth salt precursor solution: 185.50 g of lanthanum chloride heptahydrate (0.5 mol) and 128.07 g of PVP K30 (2.4% of the total mass of the precursor solution) were added to 5.0 L of distilled water and stirred until completely dissolved to obtain a homogeneous and transparent rare earth salt precursor solution (La). 3+ (Concentration is 0.10 mol / L), for later use.

[0056] (2) Preparation of precipitant solution: Add 720.70 g of urea (12.0 mol, urea / La) 3+ Add a 24:1 ratio of precipitant to 2.0 L of distilled water and stir until completely dissolved to obtain a homogeneous and transparent precipitant solution for later use.

[0057] (3) Microwave hydrothermal synthesis and calcination: The solutions obtained in steps (1) and (2) were mixed evenly and transferred to a microwave reactor. The reaction temperature was set at 170 °C, the upper limit of the pressure was 4.0 MPa, the reaction time was 1 h, the stirring rate was 280 rpm, and the upper limit of the microwave output power was 1000 W. After the reaction was completed, the mixture was naturally cooled to room temperature. The resulting suspension was filtered and washed alternately with deionized water and acetone to obtain nano-rare earth oxide precursors. The precursors were placed in a drying oven and dried at 60 °C for 18 h. The dried product was then placed in a muffle furnace and heated to 850 °C at a heating rate of 1 °C / min. The temperature was maintained for calcination for 1.5 h, and the nano-rare earth oxides were obtained after natural cooling. The product D was measured by a laser particle size analyzer. 50 The particle size is 0.139 μm (139 nm), indicating good dispersibility.

[0058] Example 6:

[0059] (1) Preparation of rare earth salt precursor solution: 185.65 g of cerium acetate trihydrate (0.5 mol) and 49.27 g of PEG-20000 (0.79% of the total mass of the precursor solution) were added to 6.0 L of distilled water and stirred until completely dissolved to obtain a homogeneous and transparent rare earth salt precursor solution (Ce). 3+ (Concentration is 0.083 mol / L), for later use.

[0060] (2) Preparation of precipitant solution: Add 360.40 g urea (6.0 mol) and 140.20 g hexamethylenetetramine (1.0 mol) to 3.0 L of distilled water and stir until completely dissolved to obtain a homogeneous and transparent precipitant solution (total precipitant / Ce). 3+ =14:1), for backup.

[0061] (3) Microwave hydrothermal synthesis and calcination: The solutions obtained in steps (1) and (2) were mixed evenly and transferred to a microwave reactor. The reaction temperature was set at 110 °C, the upper limit of the pressure was 1.0 MPa, the reaction time was 7 h, the stirring rate was 130 rpm, and the upper limit of the microwave output power was 1000 W. After the reaction was completed, the mixture was naturally cooled to room temperature. The resulting suspension was filtered and washed alternately with deionized water, anhydrous ethanol, and methanol to obtain nano-rare earth oxide precursors. The precursors were placed in a drying oven and dried at 75 °C for 16 h. The dried product was then placed in a muffle furnace and heated to 800 °C at a heating rate of 5 °C / min. The temperature was maintained for 2 h, and the product was naturally cooled to obtain nano-rare earth oxides. The product D was measured by a laser particle size analyzer. 50 The particle size is 0.132 μm (132 nm), indicating good dispersibility.

[0062] Example 7:

[0063] (1) Preparation of rare earth salt precursor solution: 108.30 g lanthanum nitrate hexahydrate (0.25 mol), 92.80 g lanthanum chloride heptahydrate (0.25 mol), 64.53 g SDS and 64.53 g CTAB (the total amount of surfactant added is 1.8% of the total mass of the precursor solution) were added to 7.0 L of distilled water and stirred until completely dissolved to obtain a homogeneous and transparent rare earth salt precursor solution (total rare earth ion concentration is 0.07 mol / L) for later use.

[0064] (2) Preparation of precipitant solution: 841.14 g hexamethylenetetramine (6.0 mol, hexamethylenetetramine / La) 3+ =12:1) and 576.54 g ammonium carbonate (6.0 mol, ammonium carbonate / La) 3+Add a 12:1 ratio of total precipitant to 2.0 L of distilled water and stir until completely dissolved to obtain a homogeneous and transparent precipitant solution (total precipitant / La). 3+ =24:1), for backup.

[0065] (3) Microwave hydrothermal synthesis and calcination: The solutions obtained in steps (1) and (2) were mixed evenly and transferred to a microwave reactor. The reaction temperature was set at 150 °C, the upper limit of the pressure was 3.0 MPa, the reaction time was 3.5 h, the stirring rate was 200 rpm, and the upper limit of the microwave output power was 1000 W. After the reaction was completed, the mixture was naturally cooled to room temperature. The resulting suspension was filtered and washed alternately with deionized water, methanol, and acetone to obtain nano-rare earth oxide precursors. The precursors were placed in a drying oven and dried at 80 °C for 10 h. The dried product was then placed in a muffle furnace and heated to 700 °C at a heating rate of 10 °C / min. The temperature was maintained for calcination for 3 h, and the nano-rare earth oxides were obtained after natural cooling. The product D was measured by a laser particle size analyzer. 50 It has a particle size of 0.115 μm (115 nm) and good dispersibility.

[0066] Example 8:

[0067] (1) Preparation of rare earth salt precursor solution: 151.70 g yttrium chloride hexahydrate (0.5 mol), 83.03 g SDBS and 83.03 g CTAC (the total amount of surfactant added is 2.0% of the total mass of the precursor solution) were added to 8.0 L of distilled water and stirred until completely dissolved to obtain a homogeneous and transparent rare earth salt precursor solution (Y). 3+ (Concentration is 0.0625 mol / L), for later use.

[0068] (2) Preparation of precipitant solution: Add 450.50 g of urea (7.5 mol, urea / Y) 3+ Add a 15:1 ratio of precipitant to 1.5 L of distilled water and stir until completely dissolved to obtain a homogeneous and transparent precipitant solution for later use.

[0069] (3) Microwave hydrothermal synthesis and calcination: The solutions obtained in steps (1) and (2) were mixed evenly and transferred to a microwave reactor. The reaction temperature was set to 180 °C, the upper limit of the pressure was 5.0 MPa, the reaction time was 0.1 h, the stirring rate was 300 rpm, and the upper limit of the microwave output power was 1000 W. After the reaction was completed, the mixture was naturally cooled to room temperature. The resulting suspension was filtered and washed alternately with deionized water and acetone to obtain nano-rare earth oxide precursors. The precursors were placed in a drying oven and dried at 60 °C for 22 h. The dried product was then placed in a muffle furnace and heated to 900 °C at a heating rate of 4 °C / min. The temperature was maintained for calcination for 1 h, and the nano-rare earth oxides were obtained after natural cooling. The product D was measured by a laser particle size analyzer. 50 The particle size is 0.108 μm (108 nm), indicating good dispersibility.

[0070] Example 9:

[0071] (1) Preparation of rare earth salt precursor solution: 108.30 g lanthanum nitrate hexahydrate (0.25 mol), 79.10 g anhydrous lanthanum acetate (0.25 mol), 25.47 g PVP K30 and 25.47 g PEG-20000 (the total amount of surfactant added is 0.5% of the total mass of the precursor solution) were added to 10 L of distilled water and stirred until completely dissolved to obtain a homogeneous and transparent rare earth salt precursor solution (total rare earth ion concentration is 0.05 mol / L) for later use.

[0072] (2) Preparation of precipitant solution: 140.20 g hexamethylenetetramine (1.0 mol) and 96.10 g ammonium carbonate (1.0 mol) were added to 2.0 L of distilled water and stirred until completely dissolved to obtain a homogeneous and transparent precipitant solution (total precipitant / La). 3+ =4:1), for backup.

[0073] (3) Microwave hydrothermal synthesis and calcination: The solutions obtained in steps (1) and (2) were mixed evenly and transferred to a microwave reactor. The reaction temperature was set to 90 °C, the upper limit of the pressure was 0.5 MPa, the reaction time was 9 h, the stirring rate was 100 rpm, and the upper limit of the microwave output power was 1000 W. After the reaction was completed, the mixture was naturally cooled to room temperature. The resulting suspension was filtered and washed alternately with deionized water and anhydrous ethanol to obtain nano-rare earth oxide precursors. The precursors were placed in a drying oven and dried at 65 °C for 24 h. The dried product was then placed in a muffle furnace and heated to 300 °C at a heating rate of 6 °C / min. The temperature was maintained for 6 h and then naturally cooled to obtain nano-rare earth oxides. The product D was measured by a laser particle size analyzer. 50 It has a size of 0.104 μm (104 nm) and good dispersibility.

[0074] Comparative Example 1:

[0075] (1) Preparation of rare earth salt precursor solution: Add 216.50 g lanthanum nitrate hexahydrate (0.5 mol) and 22.30 g SDBS (1.0% of the total mass of the precursor solution) to 2.0 L of distilled water and stir until completely dissolved.

[0076] (2) Preparation of precipitant solution: Add 240.20 g of urea (4.0 mol) to 1.0 L of distilled water and stir until completely dissolved.

[0077] (3) Conventional heating reaction and calcination: The solutions obtained in steps (1) and (2) were mixed evenly, transferred to a reactor, and heated to 140 °C in a conventional oil bath for 4 h without mechanical stirring or pressure control. After the reaction, the product was filtered, washed, dried at 75 °C for 10 h, and then calcined at 650 °C for 3 h at a rate of 3 °C / min. The product D was determined by a laser particle size analyzer. 50 It is 4.850 μm.

[0078] Comparative Example 2:

[0079] (1) Preparation of rare earth salt precursor solution: Add 216.50 g of lanthanum nitrate hexahydrate (0.5 mol) to 2.0 L of distilled water without adding any surfactant, stir until completely dissolved, and set aside.

[0080] (2) Preparation of precipitant solution: Add 240.20 g of urea (4.0 mol) to 1.0 L of distilled water without adding any surfactant, stir until completely dissolved, and set aside.

[0081] (3) Microwave hydrothermal synthesis and calcination: The solutions obtained in steps (1) and (2) were mixed evenly and transferred to a microwave reactor. The reaction temperature was set at 140 °C, the upper limit of the pressure was 2.5 MPa, the reaction time was 4 h, the stirring rate was 180 rpm, and the upper limit of the microwave output power was 1000 W. After the reaction was completed, the mixture was naturally cooled to room temperature. The resulting suspension was filtered and washed alternately with deionized water and anhydrous ethanol to obtain nano-rare earth oxide precursors. The precursors were placed in a drying oven and dried at 75 °C for 10 h. The dried product was then placed in a muffle furnace and calcined at 650 °C for 3 h at a rate of 3 °C / min. The product D was measured by a laser particle size analyzer. 50 It is 3.290 μm.

[0082] Comparative Example 3:

[0083] (1) Preparation of rare earth salt precursor solution: Same as in Example 1.

[0084] (2) Preparation of precipitant solution: Same as in Example 1.

[0085] (3) Oven heating reaction and calcination: The solutions obtained in steps (1) and (2) were mixed evenly and transferred to a conventional hydrothermal reactor. After sealing, the reactor was placed in a conventional oven at 140 °C and allowed to heat naturally for 4 hours without microwave output power adjustment or pressure control. After the reaction, the product was filtered, washed, and dried at 75 °C for 10 hours. Then, it was calcined at 650 °C for 3 hours with a heating rate of 3 °C / min. The product D was measured by a laser particle size analyzer. 50 It is 2.160 μm.

[0086] Examples 1-9 employed different rare earth salt precursors (nitrates, chlorides, acetates of lanthanum, cerium, and yttrium, and their blends), surfactant types (SDS, SDBS, CTAC, CTAB, PVP K30, PEG-20000, and their blends), precipitant types (urea, hexamethylenetetramine, ammonium carbonate, and their blends), and reaction conditions (temperature 90–180 °C, time 0.1–9 h) to verify the universality of the method under different process parameters. Comparative Examples 1-3 verified the key effects of microwave synthesis technology, surfactants, and closed-loop temperature and pressure control on the product particle size. The particle size of the prepared samples was measured using a laser particle size analyzer. The particle size test results for Examples 1 to 9 and Comparative Examples 1–3 are shown below. Figures 2 to 13 D 50 The results are shown in Table 1.

[0087] Table 1 D 50 Particle size test results

[0088] Example 1 0.114 Example 2 0.120 Example 3 0.141 Example 4 0.126 Example 5 0.139 Example 6 0.132 Example 7 0.115 Example 8 0.108 Example 9 0.104 Comparative Example 1 4.850 Comparative Example 2 3.290 Comparative Example 3 2.160

[0089] As shown in Table 1, the nano-rare earth oxides prepared in Examples 1-9 have a D 50 The results showed particle sizes between 104 and 141 nm, indicating uniform particle size, all within the nanomaterial range (<200 nm), and good dispersibility. In contrast, the D particles in Comparative Examples 1-3... 50 The particle sizes were 4.850 μm, 3.290 μm, and 2.160 μm, respectively, all much larger than 200 nm, indicating severe particle agglomeration and poor dispersibility, making it impossible to obtain nano-rare earth oxide particles within the target particle size range.

[0090] It should be noted that different types of surfactants in this invention exert different dispersion mechanisms: anionic surfactants (SDS, SDBS) inhibit aggregation through electrostatic repulsion, cationic surfactants (CTAC, CTAB) guide crystal growth through electrostatic adsorption, and nonionic surfactants (PVP K30, PEG-20000) stabilize the system through steric hindrance. The combination of these three surfactants can achieve a synergistic dispersion effect. During the microwave hydrothermal synthesis process, the equipment uses a closed-loop temperature control system to stabilize the reaction temperature within ±1 °C of the set value, inhibiting rapid coarsening and Ostwald ripening of the crystals, and ensuring uniform nucleation and growth of nanoparticles. Under microwave radiation conditions, urea and hexamethylenetetramine gradually hydrolyze, slowly releasing OH-. − Ammonium carbonate has both precipitation and buffering functions. The difference in hydrolysis rate among the three precipitants allows for flexible control of the precipitation rate, thus broadening the process window.

[0091] In summary, the technology involved in this invention prepares nano-rare earth oxides by employing precise closed-loop temperature and pressure control in a microwave hydrothermal synthesizer. Utilizing the uniformity and speed of microwave bulk heating, combined with the in-situ modification of nanoparticle surfaces by surfactants, and employing electrostatic repulsion or steric hindrance effects to separate the nanoparticles, the surface energy between nanoparticles is reduced, and the aggregation effect between nanoparticles is suppressed, ultimately yielding highly dispersed, D... 50 Rare earth oxides with a particle size of <200 nm. The preparation method provided by this invention is simple, efficient, produces uniform particle size, has good repeatability, and is easy to industrialize.

[0092] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for efficiently preparing nano-rare earth oxides, characterized in that, The microwave hydrothermal synthesis technique includes the following steps: (1) Preparation of rare earth salt precursor solution: Dissolve soluble rare earth salt and surfactant in deionized water and stir until completely dissolved to obtain rare earth salt precursor solution; (2) Preparation of precipitant solution: Dissolve the precipitant in deionized water and stir until completely dissolved to obtain precipitant solution; (3) Microwave hydrothermal synthesis: The solutions obtained in steps (1) and (2) are mixed evenly and transferred to the reaction vessel of the microwave hydrothermal synthesizer. After sealing, the microwave hydrothermal reaction is carried out. The reaction temperature is controlled at 90 °C~180 °C, the reaction time is 0.1 h~9 h, the upper limit of the pressure inside the vessel is 0.5 MPa~5.0 MPa, the microwave output power is 0~1000 W, and the stirring speed is 100 rpm~300 rpm. After the reaction is completed, the mixture is cooled, filtered, washed, dried, and calcined to obtain nano-rare earth oxides.

2. The method for efficiently preparing nano-rare earth oxides according to claim 1, characterized in that: In step (1), the soluble rare earth salt is selected from one or more of rare earth nitrates, rare earth chlorides, and rare earth acetates, and the rare earth element in the soluble rare earth salt is selected from one or more of lanthanum, cerium, and yttrium; the concentration of the soluble rare earth salt is 0.05 mol / L to 0.5 mol / L.

3. The method for efficiently preparing nano-rare earth oxides according to claim 1, characterized in that: In step (1), the surfactant is selected from one or more of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, hexadecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide, polyvinylpyrrolidone K30, and polyethylene glycol-20000, and the amount added is 0.5% to 3.0% of the total mass of the precursor solution.

4. The method for efficiently preparing nano-rare earth oxides according to claim 1, characterized in that: In step (2), the precipitant is one or more of urea, hexamethylenetetramine, and ammonium carbonate, and the molar ratio of the precipitant to rare earth ions is 4:1 to 24:

1.

5. The method for efficiently preparing nano-rare earth oxides according to claim 1, characterized in that: In step (3), the organic solvent used for washing is one or more of anhydrous ethanol, methanol, and acetone.

6. The method for efficiently preparing nano-rare earth oxides according to claim 1, characterized in that: In step (3), the drying temperature is 60 °C to 80 °C and the drying time is 6 h to 24 h.

7. The method for efficiently preparing nano-rare earth oxides according to claim 1, characterized in that: In step (3), the calcination heating rate is 1 °C / min to 10 °C / min, the calcination temperature is 300 °C to 900 °C, and the holding time is 1 h to 6 h.

8. The method according to claim 1, characterized in that, The microwave hydrothermal synthesizer features continuously adjustable microwave output power, real-time pressure monitoring and upper limit control, and closed-loop temperature feedback regulation, with the reaction temperature controlled within the set value ±1 °C range.

9. A highly dispersed nano-rare earth oxide, characterized in that, The product D is prepared using the efficient method for preparing nano-rare earth oxides according to any one of claims 1 to 8. 50 <200 nm.

10. The application of the highly dispersed nano-rare earth oxides according to claim 9 in the fields of catalysis, luminescent materials, electronic ceramics, and biomedicine.

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