Continuous preparation method of rare earth oxide / oxysulfide nano material with uniform particles

Abstract

The invention belongs to the technical field of preparation of a sulfur oxide nano material, and relates to a rare earth oxide with uniform particles and a continuous preparation method of a rare earth sulfur oxide nano material. Comprising the following steps: dissolving a rare earth source in volatile acid, and filtering, or dissolving water-soluble rare earth salt in deionized water to prepare a rare earth salt solution A with a certain concentration; taking urea or other compounds capable of generating carbonate as a precipitant solution B, respectively preheating the solution A and the solution B through a peristaltic pump, continuously injecting the solution A and the solution B into a tubular reactor according to a preset proportion, and carrying out a co-precipitation reaction under a constant-temperature condition to continuously generate rare earth precursor spherical particles; washing and drying the obtained precursor, and calcining at high temperature in an air atmosphere to obtain a spherical rare earth oxide nano material with uniform size; and further vulcanizing the rare earth oxide under the protection of inert gas to obtain the spherical rare earth oxysulfide nano material with uniform size. The method disclosed by the invention can realize continuous reaction and continuous feeding production, and the process is stable and controllable; the obtained nano-particles are uniform in particle size, good in dispersity, excellent in crystallinity and suitable for large-scale and controllable preparation of rare earth oxide and rare earth sulfur oxide nano-materials.

Description

Technical Field

[0001] This invention belongs to the field of inorganic functional nanomaterial preparation technology, and relates to a method for large-scale preparation of gadolinium oxide and gadolinium sulfide nanomaterials. Background Technology

[0002] Rare earth sulfur oxides (RE2O3) and rare earth sulfur oxides (RE2O2S) possess advantages such as chemical stability, good monochromaticity, and good luminescence stability, and are widely used in lighting, security inspection, and medical imaging equipment. Currently, the main methods for preparing rare earth oxides and rare earth sulfur oxides include solid-phase reaction methods, liquid-phase reaction methods, and precursor-based two-step synthesis methods.

[0003] (1) Solid-state reaction method: The solid-state reaction method is a relatively mature preparation method. It usually uses rare earth oxides as raw materials and prepares rare earth ion-doped oxides or rare earth sulfur oxide materials by sintering reaction under high temperature conditions. For example, Chen et al. (X. Chen, N. Liu, G. Mei and M. Yu, Recycling Y and Eu from WasteFluorescent Powder and High Temperature Solid-State Synthesis of Y2O3:EuPhosphors, Minerals, 2017, 7, 44) successfully synthesized Y2O3:Eu phosphors by adding flux to Y2O3 and Eu2O3 as raw materials. Zhang Jiuxing et al. proposed a preparation process of gadolinium oxide microspheres in their patent "A method for preparing deep low temperature cold storage material gadolinium oxide microspheres" (CN202410866887.6). This method yields gadolinium oxide microspheres with a particle size of 100–500 μm through solid-state calcination, spark plasma sintering, and plasma spheroidization. This method can produce rare earth oxides or rare earth sulfur oxides with good performance, and the process is relatively simple, suitable for large-scale preparation. However, these methods typically require high temperatures, resulting in products with micron-sized particles, a wide particle size distribution, and a tendency for particle agglomeration. While physical methods such as ultrasonication and grinding can mitigate these shortcomings, they can introduce defects into the material, leading to a decrease in its luminescent properties. Furthermore, the introduction of flux increases the difficulty of post-processing; improper handling can result in residual impurities in the product. These factors limit the application range of the material.

[0004] (2) Liquid-phase reaction method: To reduce particle size and control morphology, researchers have proposed various liquid-phase reaction preparation methods. For example, Pan et al. (Y. Pan, X. Xie, Q. Huang, C. Gao and Y. Wang, Inherently Eu)2+ / Eu 3+ Codoped Sc2O3 Nanoparticles as High-Performance Nanothermometers, Adv. Mater., 2018, 30, 1705256) successfully prepared Eu-doped Sc2O3 nanoparticles using ScCl3 and EuCl3 as raw materials in an oleylamine solvent system under inert gas protection via a high-temperature organic thermal phase decomposition method. Homann et al. (C. Homann, R. Peeters, H. Mirmajidi, J. Berg and M. Fay, Rapid microwave-assisted synthesis of morphology-controlled Gd2O2S nanostructures, J. Mater. Chem. C, 2025, 13, 18492-18507) achieved rapid synthesis of morphology-controlled Gd2O2S nanomaterials using microwave-assisted heating technology.

[0005] Liquid-phase reaction methods have improved the controllability of gadolinium oxysulfide particle size and morphology to some extent. However, such methods are usually sensitive to reaction solvents, temperature and pressure, and have a narrow process parameter window. During scale-up preparation, uneven heating or decreased product consistency can easily occur, thus limiting their industrial application.

[0006] (3) Two-step synthesis method: To balance morphology control and crystal quality, some researchers have proposed a two-step synthesis method based on precursors. This involves first preparing the precursor via a liquid-phase reaction, and then treating it at high temperature to obtain rare earth oxides or rare earth sulfur oxides. For example, Sang et al. (X. Sang, J. Lian, N. Wu, X. Zhang and J. He, Synthesis, characterization and formation mechanism of Gd2O2S:Pr 3+ Ce 3+ (J. Aisan Ceram. Soc., 2020, 8, 733-744) et al. prepared micron-sized hexagonal Gd₂O₂S:Pr phosphorus by sealed triple-crucible method. This was achieved by sulfiding carbonate precursors under high-temperature conditions using a sealed crucible method. 3+ Ce 3+Particles; Li Jiguang et al. proposed in their patent "Preparation method of rare earth doped gadolinium oxysulfate and gadolinium sulfate upconversion phosphor" (CN 106520121A) that after adding ammonium sulfate to a rare earth nitrate solution to adjust the pH value, a white precursor powder is obtained through hydrothermal reaction; then the precursor is calcined to successfully prepare rare earth ion doped Gd2O2S or Gd2O2SO4 upconversion phosphor.

[0007] The two-step method described above achieves some degree of control over particle morphology, but the relevant reactions are mostly carried out in beakers, which can easily lead to uneven heating when scaled up directly. Furthermore, this type of method has a long process flow, making continuous production difficult. During large-scale preparation, it can easily lead to uneven precursor formation or inconsistent heat treatment, thus affecting the consistency and controllability of the final product.

[0008] In recent years, to address the challenges of reaction scale-up difficulties, uneven mass and heat transfer, and poor batch-to-batch consistency in the preparation of inorganic nanomaterials, some researchers have attempted to introduce continuous flow or tubular reactors into the synthesis process of inorganic particulate materials. For example, Luo Guangsheng et al., in their patent "A Micro-reaction System for Continuous Synthesis of Polysilsesquioxane Spheres" (CN113797865A), proposed a method for the continuous synthesis of polysilsesquioxane spherical particles based on a micro-reaction system. By connecting a micro-mixer in series with two tubular reactors, the hydrolysis and condensation reactions were continuously carried out, resulting in organosilicon spherical particles with adjustable particle size and good monodispersity. Jin Haibo et al., in their patent "A Microchannel Continuous Method for Preparing Nanoscale Spherical Barium Titanate" (CN110040770A), reported a microchannel continuous method for preparing nanoscale spherical barium titanate, using T-type or Y-type reactors. Micro-mixers enable rapid mixing and reaction of precursor solutions, which improves the morphology and particle size consistency of barium titanate particles to a certain extent. Wang Chuan et al. proposed a method for preparing spherical nano-silica by tubular continuous flow in their paper "A Method for Preparing Spherical Nano-Silica by Tubular Continuous Flow" (CN112174147A). This method utilizes the gas-liquid flow formed in the small-diameter reaction channel to enhance the mass and heat transfer process, thereby achieving continuous and efficient preparation of spherical silica nanoparticles.

[0009] However, existing continuous preparation methods are mostly designed for non-rare earth oxides. For rare earth oxides and sulfur oxide particles, problems such as insufficient process stability, uneven particle size distribution, and poor dispersibility remain. In summary, while existing methods for preparing rare earth sulfur oxide materials can achieve morphology control and large-scale production to a certain extent, they struggle to simultaneously achieve continuous production, process stability, and uniform and controllable nanoparticle size and morphology. Under continuous conditions, traditional methods are prone to uneven reaction, poor product dispersibility, and inconsistent morphology, making it difficult to balance high-performance applications with industrial production. Therefore, a method is needed that can achieve continuous, stable processing and produce gadolinium oxide nanomaterials with uniform particle size, good dispersibility, and controllable morphology. Summary of the Invention

[0010] The purpose of this invention is to address the shortcomings of existing technologies by providing a continuous method for preparing rare-earth ion-doped spherical nanoparticles of rare-earth oxides (RE2O3) and sulfur oxides (RE2O2S). This method offers stable processes, allows for continuous production, and produces powders with advantages such as uniform particle size, good dispersibility, and low cost, making it suitable for large-scale production.

[0011] The continuous preparation method provided by this invention is applicable to oxides and sulfur oxide nanomaterials containing one or more rare earth elements, including La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, and Sc. The preparation method mainly includes the following steps: Step 1: Add the required rare earth source oxide, carbonate or hydroxide raw material to a volatile acid and heat to dissolve, or directly use water-soluble volatile acid salts and dissolve in deionized water to obtain a water-soluble salt solution. Remove impurities or undissolved precipitates by filtration to obtain a spare rare earth salt solution A with a rare earth ion concentration of 0.005-3 M. Step 2: Prepare the precipitant solution by dissolving urea or other nitrogen source compounds that can generate carbonates in water to obtain precipitant solution B, which has a concentration of 0.05-20 M and can be used for coprecipitation reaction. Step 3: Pump the salt solution A and solution B into a water bath device with a temperature of 60-85 ℃ through pipelines respectively. Adjust the length of the pipelines for solution A and solution B in the water bath device so that their outlet temperatures are between 60-70 ℃. Then pump them into a pipeline water bath reactor with a temperature of 85-100 ℃. Under constant temperature conditions, solution A and solution B undergo a co-precipitation reaction to continuously generate rare earth precursor precipitates. Control the pump speed ratio of rare earth salt to precipitant to be 1:3-12. Step 4: Wash and dry the obtained precursor precipitate, and calcine it at 500-950℃ for 0.5-5 hours in air atmosphere to obtain spherical rare earth oxide nanomaterials with uniform size and controllable particle size between 20-300 nm. Step 5: The sintered product is subjected to sulfidation treatment under inert gas protection to obtain spherical rare earth sulfur oxide nanomaterials with uniform size and controllable particle size between 20-300 nm.

[0012] The aforementioned volatile acids include hydrochloric acid, nitric acid, formic acid, or acetic acid. The coprecipitation reaction employs a continuous flow tubular reaction method, utilizing a peristaltic pump to ensure continuous reaction and output. The sulfur source for sulfidation treatment is sulfur powder, hydrogen sulfide, carbon disulfide, or other sulfur-providing compounds. The optimized concentration of rare earth ions in the standby rare earth salt solution A is 0.01-1.0 M. The optimized concentration of the precipitant solution B is 0.1-10 M. The optimized pump speed ratio of salt solution A to precipitant solution B in the coprecipitation reaction is 1:4-10. Attached Figure Description

[0013] Figure 1 A flowchart of a preparation method in one embodiment of the present invention is shown; Figure 2 The example shown is Gd2O3:Pr 3+ Precursor particle morphology Figure 3 The example shown in Example 1 is G2O2S:Pr 3+ Particle morphology of doped gadolinium oxysulfide powder Figure 4 The XRD pattern of the product in Example 1 is shown. Figure 5 The emission spectrum of X-ray excitation in Example 1 is shown. Detailed Implementation

[0014] The present invention will be further described in detail below with reference to specific embodiments, but this does not limit the scope of protection of the present invention.

[0015] This invention discloses a method for the large-scale preparation of rare earth ion-doped rare earth ion oxides or sulfur oxides, the process flow of which is as follows: Figure 1 As shown.

[0016] Example 1 (1) Weigh 36.25 kg of gadolinium oxide (purity 99.99%, 99.95 mol) and 168.4 g of praseodymium chloride (purity 99.99%, 0.05 mol), dissolve them in 900 mol of nitric acid (concentration not less than 0.5 M) solution, heat to about 110 °C and reflux until the solution is transparent, filter to remove insoluble substances; (2) The remaining nitric acid was evaporated under reduced pressure at 80℃ (initial relative vacuum -0.01MPa, final relative vacuum -0.09MPa) to obtain a mixed crystal of gadolinium nitrate and praseodymium chloride. The mixed crystal was dissolved in deionized water and the volume was adjusted to prepare a mixed solution of gadolinium nitrate and praseodymium chloride with a rare earth ion concentration of 0.4M. The mixed solution was then diluted to a rare earth ion concentration of 0.04M and filtered before being poured into raw material tank 1 for later use.

[0017] (3) Add 600.6 kg of urea (purity 99%, 10000 mol) to deionized water and stir thoroughly to dissolve it completely. Make up the volume to prepare a 0.5 M urea solution, filter it and pour it into raw material tank 2 for later use.

[0018] (4) Using two peristaltic pumps, the gadolinium nitrate and praseodymium chloride mixed solution from raw material tank 1 and the urea solution from raw material tank 2 are injected into a raw material preheating tube made of polytetrafluoroethylene at a volume ratio of 1:4. The gadolinium nitrate solution is preheated to 90°C, and the urea solution is preheated to 65°C. Subsequently, under the continuous delivery of the peristaltic pumps, the two solutions flow into another tubular reactor simultaneously, and the tubular reactor is heated to 85°C by a water bath. The two liquids will undergo a co-precipitation reaction in the tubular reactor.

[0019] (5) Collect the mixed liquid after the reaction and let it stand. Discard the supernatant, centrifuge the lower liquid, and wash the precipitate with deionized water more than three times.

[0020] (6) The washed precipitate was dried at 80°C to obtain precursor powder; the precursor powder was placed in a corundum crucible and heat-treated in a muffle furnace under air atmosphere, with the temperature increased to 750°C at a heating rate of 5°C / min and held for 1 h. Gd2O3 spherical particles with an average size of 200 nm were obtained.

[0021] (7) The obtained spherical praseodymium-doped gadolinium oxide powder was placed in a U-shaped tube. Under the protection of an inert gas, sulfur powder was used as the sulfur source, and the temperature was raised to 800℃ at a heating rate of 5℃ / min for 1h for sulfidation treatment. After the reaction was cooled to room temperature, spherical particles Gd2O2S:Pr with a size of 200 nm were finally obtained. 3+ .

[0022] Besides using rare earth oxides as raw materials, rare earth carbonates or hydroxides can also be used. The acid used to dissolve the rare earth source, in addition to nitric acid, can also be hydrochloric acid, formic acid, or acetic acid. Nitric acid, formic acid, and acetic acid, due to their high volatility, can omit the washing process in subsequent steps, simplifying the process; hydrochloric acid, however, does not possess this property and cannot omit the washing process. Furthermore, water-soluble volatile acid salts, such as rare earth nitrates and acetates, can be used directly, dissolved in deionized water to obtain a water-soluble salt solution, which will not adversely affect the final morphology of the product. The type of rare earth element will not affect the above process and results; other rare earth elements, such as La, Ce, Pr, Nd, Pm, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, and Sc, can yield the same rare earth oxides and rare earth sulfur oxide nanoparticles. Other nitrogen-containing compounds can also be used as precipitants, such as ammonium bicarbonate and oxalic acid, but the resulting nanoparticles have lower uniformity than those obtained with urea, while other properties are comparable.

[0023] By maintaining a constant concentration of precipitant B and a constant pump rate ratio of A to B, the precursor formation rate can be precisely controlled by adjusting the concentration of rare earth salt solution A, thereby regulating the size of the nanoparticles. For example, when the concentration of precipitant B is 0.5 M and the pump rate ratio A:B = 1:4, adjusting the concentration of the rare earth salt solution between 0.01 and 1 M allows for controllable adjustment of the rare earth ion nanoparticle size between 20 and 300 nm. When the concentration of solution A continues to increase to 1-3 M, although spherical precipitates can still form, the excessively rapid formation rate easily leads to particle aggregation and a decrease in uniformity.

[0024] By maintaining a constant concentration of rare earth salt solution A and a constant pump rate ratio of A to B, the size of nanoparticles can be effectively controlled by varying the concentration of precipitant B. For example, when the concentration of solution A is 0.4 M and the pump rate ratio A:B = 1:5, adjusting the concentration of precipitant B between 0.1 and 10 M allows for controllable adjustment of particle size from 20 to 300 nm. When the concentration of B is below 0.1 M, almost no precipitation occurs due to the extremely low concentration of precipitant. When the concentration is above 10 M, the precipitation rate is too fast, resulting in uneven product morphology and poor particle size distribution.

[0025] While keeping the concentrations of solutions A and B constant, the size of nanoparticles can also be adjusted by changing the pump speed ratio. For example, when the concentration of solution A is 0.01M and the concentration of solution B is 10M, the particle size can be precisely controlled between 20-300 nm by keeping the pump speed in the range of 1:4 to 1:10.

[0026] Furthermore, the preheating temperature and the temperature of the reactor also affect the particle morphology and uniformity. A preheating temperature between 60-70℃ can produce uniform spherical particles. Too low a preheating temperature leads to poor morphology and size, while too high a preheating temperature causes the precipitant to decompose, resulting in poor particle morphology. The adjustable calcination temperature range is 500–950℃. Temperatures below 500℃ will reduce the luminescent properties of the material; higher temperatures are beneficial for improving luminescent properties, but when the temperature exceeds 950℃, the particles may slightly agglomerate, and particle uniformity will decrease.

Claims

1. A continuous preparation method for nanomaterials of uniformly sized rare earth oxides and rare earth sulfur oxides, characterized in that, Includes the following steps; Step 1: Add the required rare earth source (one or more of rare earth elements including La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, and Sc) oxides, carbonates, or hydroxides to a volatile acid and heat to dissolve, or directly use water-soluble volatile acid salts and dissolve in deionized water to obtain a water-soluble salt solution. Remove impurities or undissolved precipitates by filtration to obtain a spare rare earth salt solution A with a rare earth ion concentration of 0.005-3 M. Step 2: Prepare the precipitant solution by dissolving urea or other nitrogen source compounds that can generate carbonates in water to obtain precipitant solution B, which has a concentration of 0.05-20 M and can be used for coprecipitation reaction. Step 3: Pump the salt solution A and solution B into a water bath device with a temperature of 60-85 ℃ through pipelines respectively. Adjust the length of the pipelines for solution A and solution B in the water bath device so that their outlet temperatures are between 60-70 ℃. Then pump them into a pipeline water bath reactor with a temperature of 85-100 ℃. Under constant temperature conditions, solution A and solution B undergo a co-precipitation reaction to continuously generate rare earth precursor precipitates. Control the pump speed ratio of rare earth salt to precipitant to be 1:3-12. Step 4: Wash and dry the obtained precursor precipitate, and calcine it at 500-950℃ for 0.5-5 hours in air atmosphere to obtain spherical rare earth oxide nanomaterials with uniform size and controllable particle size between 20-300 nm. Step 5: The sintered product is subjected to sulfidation treatment under inert gas protection to obtain spherical rare earth sulfur oxide nanomaterials with uniform size and controllable particle size between 20-300 nm.

2. The preparation method according to claim 1, characterized in that, The volatile acids include hydrochloric acid, nitric acid, formic acid, or acetic acid.

3. The preparation method according to claim 1, characterized in that, The coprecipitation reaction adopts a continuous flow tubular reaction mode, and the reaction is carried out continuously and the output is continuously produced by a peristaltic pump.

4. The preparation method according to claim 1, characterized in that, The sulfur source for sulfidation treatment is sulfur powder, hydrogen sulfide, carbon disulfide, or other compounds that can provide sulfur.

5. The continuous preparation method according to claim 1, characterized in that, The optimized concentration of rare earth ions in the spare rare earth salt solution A is 0.01-1.0 M.

6. The continuous preparation method according to claim 1, characterized in that, The optimized concentration of the precipitant solution B is 0.1-10 M.

7. The continuous preparation method according to claim 1, characterized in that, The optimized pump speed ratio of salt solution A to precipitant solution B in the coprecipitation reaction is 1:4-10.

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