Preparation method of nano porous rare earth oxide material

Abstract

The invention relates to the technical field of preparation of functionalized inorganic nano materials, in particular to a preparation method of a nano porous rare earth oxide material, which comprises four synergistic steps of precursor preparation, molecular directional modification, secondary construction of a pore structure and high-temperature roasting conversion. The material prepared by the process has a mesopore-macropore composite hierarchical pore structure, is high in specific surface area and large in saturated adsorption capacity on forbidden substance molecules, and can specifically recognize at least three forbidden substances such as morphine, methylamphetamine and ketamine; when the material is applied to a prohibited article detection probe, non-invasive sampling can be realized through surface scratching, and high-throughput analysis is carried out by matching with an in-situ mass spectrometry detection device. The process parameters are controllable, large-scale production is easy, and the application prospect in the field of trace contraband detection is wide.

Description

Technical Field

[0001] This invention relates to the field of functionalized inorganic nanomaterials preparation technology, specifically a method for preparing nanoporous rare earth oxide materials. Background Technology

[0002] Rare earth oxides, due to their unique electronic structure and chemical stability, have wide applications in catalysis, adsorption, and optics. Among them, nanoporous rare earth oxide materials, with their high specific surface area and abundant active sites, have become a research hotspot in the field of trace substance detection. For example, rare earth oxide aerogels can achieve a specific surface area >200 m² using the sol-gel method. 2 While porous structures with a density of / g are available, their preparation relies on metal alkoxide precursors, resulting in high costs and complex processes. Furthermore, the application of rare earth oxides in trace detection often faces the challenge of balancing high adsorption capacity with structural stability. Traditional hard-template methods require high-temperature etching of the template, which can easily lead to pore collapse; the sol-gel method suffers from difficulty in precisely controlling porosity due to capillary forces during drying. Existing technologies exhibit the following bottlenecks:

[0003] Structural control is challenging: traditional methods struggle to achieve precise and coordinated control from the molecular scale to the macroscopic structure; materials prepared by some processes are prone to particle aggregation, resulting in insufficient exposure of active sites; while other methods can construct ordered channels, the template removal process is complex, easily introducing impurities or damaging the pore structure, affecting the stability of material performance.

[0004] The contradiction between stability and porosity: Rare earth oxides are prone to structural collapse under high temperature treatment or extreme environments, resulting in a decrease in specific surface area and porosity; single-stage calcination or treatment processes often fail to balance structural stability and porosity, causing materials to perform poorly in complex application scenarios.

[0005] Therefore, a method for preparing nanoporous rare earth oxide materials is proposed to address the above problems. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing nanoporous rare earth oxide materials to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A method for preparing a nanoporous rare earth oxide material includes the following steps:

[0009] S1. Precursor preparation: Rare earth raw materials and polymeric precipitants are reacted by liquid-phase precipitation, organic polymeric dispersants are added to inhibit agglomeration, and the pH of the system is adjusted to >4 to obtain rare earth hydroxide powder with a particle size of 5-10μm.

[0010] S2. Molecular-directed modification: The rare earth hydroxide obtained in step S1 is assembled with organic ligands containing carboxyl groups or cyano groups under hydrothermal conditions to form a metal-organic coordination polymer network.

[0011] S3. Secondary construction of pore structure: Mix the product of step S2 with the auxiliary salt in a weight ratio, and perform high-energy ball milling for 2-10 hours at a ball-to-material ratio of 2-4. Then, acid wash, water wash, and dry.

[0012] S4. High-temperature roasting and conversion: The product from step S3 is roasted in a confined isolation device in two stages.

[0013] Dehydroxylation reaction was carried out at 400-450℃ in a weak oxidizing atmosphere for 3-6 hours to fix the byproducts;

[0014] The porous structure is solidified by heating to above 500℃ and holding for 4-5 hours, ultimately achieving a specific surface area ≥80m². 2 / g of nanoporous rare earth oxide materials.

[0015] As a preferred option, in step S1:

[0016] The polymeric precipitant is a functionalized polymer with protonated amine groups;

[0017] The long-chain alkyl content of the organic polymer dispersant is ≥50wt%.

[0018] After precipitation, the surface tension is reduced by washing with anhydrous ethanol.

[0019] As a preferred option, in step S2:

[0020] The molar ratio of organic ligands to rare earth hydroxides is 1:1 to 1:3;

[0021] Metal-organic coordination polymer networks specifically bind carbonyl or amine functional groups through bidentate coordination bonds of carboxylate groups.

[0022] As a preferred option, in step S3:

[0023] The auxiliary salt is a water-soluble inorganic salt, and its addition amount is 10-30% of the weight of rare earth hydroxide;

[0024] The high-energy ball mill operates at a speed of 300-500 rpm, and the pore size distribution is controlled and particle agglomeration is prevented through the salt template effect.

[0025] As a preferred option, the pickling process in step S3 involves treating with hydrochloric acid at pH=1 for 0.5 hours to remove auxiliary salt residues.

[0026] As a preferred embodiment, the confined isolation device in step S4 includes a multi-stage cyclone separator to achieve gas-solid separation during the dehydroxylation and structural shaping stages.

[0027] As a preferred embodiment, the product of step S4 has a mesoporous-macroporous composite hierarchical pore structure with a pore size range of 2-50 nm.

[0028] As a preferred option, nanoporous rare earth oxide materials are used to prepare non-invasive trace sampling probes with an operating temperature range of -10℃ to 400℃.

[0029] As can be seen from the above technical solution provided by the present invention, the beneficial effects of the preparation method of the nanoporous rare earth oxide material provided by the present invention are:

[0030] I. Innovative Breakthroughs in Technology and Processes:

[0031] Multi-level structural synergistic regulation mechanism: Through a four-step synergistic process of "precursor preparation - molecular modification - pore structure construction - confined calcination", precise regulation of nanoporous rare earth oxide materials from the molecular scale to the macroscopic structure is achieved. Compared with traditional preparation methods, this process effectively solves the problems of easy agglomeration and unstable pore structure of rare earth oxide porous materials, significantly improves the specific surface area and pore structure integrity of the material, and overcomes the technical bottleneck of "difficulty in balancing high specific surface area and structural stability".

[0032] The integration of molecular recognition and structural design: introducing organic ligands containing specific functional groups for molecular-directed modification, and endowing the material with the ability to specifically recognize target molecules through coordination bond interaction, breaks through the limitation of traditional adsorption materials that rely solely on physical adsorption, realizes the transformation from "non-selective adsorption" to "targeted capture", and significantly improves the material's selectivity for specific substances.

[0033] II. Comprehensive optimization of material properties:

[0034] Synergistic enhancement of adsorption and stability: The mesoporous-macroporous composite hierarchical pore structure provides an efficient channel for molecular diffusion. Combined with the abundant active sites on the material surface, it significantly enhances the adsorption capacity for target substances. At the same time, the material maintains structural and performance stability over a wide temperature range, which can adapt to the application requirements under different environmental conditions and solves the problem of performance degradation of traditional materials at extreme temperatures.

[0035] Broad spectrum of specific recognition capabilities: By leveraging coordination, spatial matching effects and the synergy of surface chemical properties, the material can specifically recognize a variety of target substances, effectively reducing the influence of irrelevant interfering substances, improving the accuracy of identifying trace targets in complex systems, and broadening the application range of the material.

[0036] III. Significantly Enhanced Application Value:

[0037] Driving the upgrade of detection technology: The detection probe based on this material realizes non-invasive sampling without damaging the object being tested, and can be adapted to rapid detection equipment, simplifying the sampling and analysis process, improving detection efficiency, and providing a new technical path for the rapid and accurate detection of trace substances;

[0038] Expanding the application scenarios of materials: The high performance and stability of materials make them not only suitable for the detection of prohibited items, but also have potential application value in fields such as environmental monitoring and biomedicine, providing a new direction for the functional application of porous rare earth oxide materials;

[0039] IV. Advantages in industrialization feasibility:

[0040] The preparation process has clear steps and controllable parameters. The raw materials and equipment used have a good industrialization foundation and do not require special harsh conditions, which facilitates large-scale production. At the same time, the material has stable performance and controllable cost, which is conducive to promoting its transformation from laboratory research to practical application. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the preparation steps of a nanoporous rare earth oxide material according to the present invention. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0043] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific embodiments.

[0044] like Figure 1 As shown, this embodiment of the invention provides a method for preparing nanoporous rare earth oxide materials, comprising the following steps:

[0045] S1. Precursor preparation: Rare earth raw materials and polymeric precipitants are reacted by liquid-phase precipitation, organic polymeric dispersants are added to inhibit agglomeration, and the pH of the system is adjusted to >4 to obtain rare earth hydroxide powder with a particle size of 5-10μm.

[0046] S2. Molecular-directed modification: The rare earth hydroxide obtained in step S1 is assembled with organic ligands containing carboxyl groups or cyano groups under hydrothermal conditions to form a metal-organic coordination polymer network.

[0047] S3. Secondary construction of pore structure: Mix the product of step S2 with the auxiliary salt in a weight ratio, and perform high-energy ball milling for 2-10 hours at a ball-to-material ratio of 2-4. Then, acid wash, water wash, and dry.

[0048] S4. High-temperature roasting and conversion: The product from step S3 is roasted in a confined isolation device in two stages.

[0049] Dehydroxylation reaction was carried out at 400-450℃ in a weak oxidizing atmosphere for 3-6 hours to fix the byproducts;

[0050] The porous structure is solidified by heating to above 500℃ and holding for 4-5 hours, ultimately achieving a specific surface area ≥80m². 2 / g of nanoporous rare earth oxide materials.

[0051] In this embodiment, in step S1:

[0052] The polymeric precipitant is a functionalized polymer with protonated amine groups;

[0053] The long-chain alkyl content of the organic polymer dispersant is ≥50wt%.

[0054] After precipitation, the surface tension is reduced by cleaning with anhydrous ethanol.

[0055] Furthermore, step S1 aims to obtain a precursor with uniform particle size (5-10 μm) and good dispersibility by precisely controlling the preparation process of rare earth hydroxide powder. This provides a stable reaction substrate for subsequent molecular-oriented modification and pore structure construction, ensuring the structural controllability and performance stability of the final nanoporous rare earth oxide material. The detailed steps are as follows:

[0056] Step S1-1: Raw material screening and pretreatment:

[0057] Rare earth raw material purity control: Rare earth oxides (such as La2O3, CeO2) or rare earth salts (such as rare earth nitrates, rare earth chlorides) are selected as raw materials, and the purity is detected by inductively coupled plasma mass spectrometry (ICP-MS). The total purity of rare earth elements is required to be ≥99.9%, and the content of transition metal impurities (Fe, Cu, Ni, etc.) is ≤0.01wt% to avoid impurities interfering with coordination reactions.

[0058] Pretreatment of polymeric precipitant: Select functionalized polymers with protonated amine groups (such as polyethyleneimine and polyallylamine), dialyze (with a molecular weight cutoff of 5000 Da) to remove oligomer impurities before use, dry and prepare a 0.2-0.4 mol / L aqueous solution, seal and refrigerate (4℃) for later use to prevent amine oxidation;

[0059] Raw material ratio calculation: based on rare earth ions (such as La) 3+ Ce 3+The stoichiometric ratio of the amino groups in the precipitant to the precipitant (1:1.2-1:1.4) is used to calculate the amount of both added using the molar concentration formula to ensure complete precipitation reaction (the reaction endpoint is verified by EDTA titration, and the residual rare earth ions are ≤0.001mol / L).

[0060] Step S1-2: Construction of the liquid-phase precipitation reaction system:

[0061] Reaction apparatus setup: A double-walled glass reactor (2-10L capacity) is used, equipped with a polytetrafluoroethylene stirring paddle (to avoid metal ion contamination), a constant temperature water bath (temperature control accuracy ±1℃), an online pH monitor (accuracy ±0.01), and a condenser reflux device (to prevent solvent evaporation);

[0062] Feeding and stirring control: First, add deionized water (conductivity ≤5μS / cm) to the reactor, then add the pretreated rare earth raw materials, and start stirring (300-400rpm) until completely dissolved; then slowly add the polymer precipitant solution through a constant pressure dropping funnel, controlling the dropping rate at 1.5-2mL / min to avoid excessive local concentration leading to particle agglomeration;

[0063] Reaction temperature control: The system temperature is maintained at 60-70℃ by a constant temperature water bath. At this temperature, the amine matrix protonation can be accelerated (increasing the coordination activity with rare earth ions) while inhibiting the hydrolysis of the precipitant (experimental verification: the hydrolysis rate of the precipitant at 60℃ is ≤5%, which is significantly lower than 15% at room temperature).

[0064] Steps S1-3: Introduction and Enhancement of the Function of Organic Polymer Dispersants:

[0065] Dispersant selection and concentration determination: Select organic polymer dispersants with long carbon chain alkyl content ≥50wt% (such as polyethylene stearate, polyhexyl methacrylate), whose long carbon chains can hinder particle aggregation through steric hindrance effect; the dispersant concentration is controlled at 0.8-1.5wt% of the total mass of the system (determined by orthogonal experiments: within this range, the absolute value of the Zeta potential ≥35mV indicates the best dispersion stability);

[0066] Timing of addition and dispersion treatment: When the precipitation reaction reaches 40% (as monitored by a turbidimeter: the turbidity of the system reaches 40% of the final value), add the dispersant, and then turn on ultrasonic-assisted dispersion (power 250W, frequency 40kHz) for 10-15 minutes to allow the dispersant to be uniformly adsorbed on the particle surface (verified by X-ray photoelectron spectroscopy XPS: the carbon content on the particle surface increases by 8-10 at%, proving the adsorption of the dispersant).

[0067] Steps S1-4: Precise adjustment and stabilization of system pH:

[0068] pH adjustment agent selection and use: Use dilute ammonia (5wt%) as pH adjustment agent (avoid introducing metal ions), and slowly inject it into the reaction system through a micro peristaltic pump (flow rate accuracy ±0.1mL / h). The adjustment rate is controlled at 0.8-1mL / min to prevent local pH surges that could lead to particle coarsening.

[0069] pH control range and maintenance: Adjust the pH of the system to 4.5-5.5 (pH>4 can avoid the dissolution of rare earth hydroxides. Experiments show that the solubility at pH=4 is 0.002 g / L, which is significantly lower than 0.01 g / L at pH=3); After adjustment, continue stirring for 60 min, and monitor the pH value in real time. If the fluctuation exceeds ±0.1, add ammonia water to make fine adjustments to ensure pH stability.

[0070] Steps S1-5: Separation, washing, and drying of rare earth hydroxide powder:

[0071] Solid-liquid separation process: High-speed centrifugation is used (9000 rpm, 12 min). After separation, the wet powder at the bottom is collected (the supernatant is detected by UV-Vis spectrophotometer, and the rare earth ion concentration is ≤0.0001 g / L to ensure complete separation).

[0072] Anhydrous ethanol cleaning: Mix wet powder with anhydrous ethanol at a solid-liquid ratio of 1:8, ultrasonically disperse for 10 min, and then centrifuge again. Repeat the operation 3 times (verified by contact angle measuring instrument: after cleaning, the contact angle of the powder surface increased from 55° to 92°, and the surface tension was significantly reduced) to remove residual impurities and free dispersants.

[0073] Vacuum drying parameters: The cleaned powder was placed in a vacuum drying oven and dried at 70℃ and a vacuum of -0.095MPa for 10 hours (thermogravimetric analysis (TG) showed that the residual moisture was ≤0.5wt% under these conditions and there was no powder sintering).

[0074] Step S1-6: Verification of powder particle size and dispersibility:

[0075] Particle size distribution detection: The dried powder was analyzed using a laser particle size analyzer (test range 0.1-100μm). The required D50 (median particle size) was 5-10μm, and the particle size distribution span SPAN = (D90-D10) / D50 ≤ 1.2 (to ensure particle size uniformity).

[0076] Dispersibility assessment: The powder was dispersed in deionized water at 0.5 wt%, and after sonication for 10 min, it was tested by dynamic light scattering (DLS). The average agglomeration particle size was required to be ≤15 μm (agglomeration ratio ≤1.5 times), and the suspension was allowed to stand for 24 h without significant sedimentation.

[0077] Handling of non-conforming products: If the particle size or dispersibility does not meet the standards, the powder is redispersed in an ethanol solution containing 0.5 wt% dispersant, sonicated for 30 min, and then dried and tested again until it meets the requirements (experiments show that the pass rate after secondary treatment is ≥95%).

[0078] In this embodiment, in step S2:

[0079] The molar ratio of organic ligands to rare earth hydroxides is 1:1 to 1:3;

[0080] Metal-organic coordination polymer networks specifically bind carbonyl or amine functional groups through bidentate coordination bonds of carboxylate groups;

[0081] Furthermore, step S2 serves to construct an ordered metal-organic coordination polymer network through the specific coordination interaction between organic ligands and rare earth hydroxides, providing a molecular-level template for subsequent secondary construction of the pore structure. Simultaneously, it introduces functional groups (carboxylate or cyano groups) to endow the material with the ability to recognize target molecules. The detailed steps are as follows:

[0082] Step S2-1: Screening and pretreatment of organic ligands:

[0083] Ligand type selection: Select organic ligands containing carboxylic acid groups (such as terephthalic acid and citric acid) or cyano groups (such as cyanobenzoic acid and oxonitrile). Aromatic ligands with bidentate coordination ability (such as 1,4-phthalic acid) are preferred, as their rigid structure can enhance the stability of the coordination network (experimental verification: the thermal decomposition temperature of the network formed by aromatic ligands is 30-50℃ higher than that of aliphatic ligands).

[0084] Ligand purity control: The purity of ligands is detected by high performance liquid chromatography (HPLC) and is required to be ≥99%, with impurities (such as unreacted monomers and solvent residues) content ≤0.5wt%. If the purity does not meet the standard, it is purified by recrystallization (e.g., terephthalic acid is recrystallized three times with N,N-dimethylformamide).

[0085] Ligand dissolution treatment: Add the organic ligand to deionized water or ethanol-water mixed solvent (volume ratio 1:1), sonicate (power 300W) for 30min to promote dissolution, prepare a 0.05-0.2mol / L solution, and adjust the pH to 5-7 with dilute NaOH or HCl (avoid extreme pH to prevent damage to ligand structure).

[0086] Step S2-2: Ratio and mixing of rare earth hydroxides and ligands:

[0087] Precise control of molar ratio: Weigh the organic ligands to rare earth hydroxides at a molar ratio of 1:1 to 1:3 (determine the concentration of rare earth ions in the rare earth hydroxides using inductively coupled plasma optical emission spectrometry (ICP-OES) and calculate the required amount of ligands), with a 1:2 ratio preferred (experiments show that the coordination network integrity reaches over 90% at this ratio).

[0088] Mixing method optimization: The rare earth hydroxide powder prepared in step S1 was added to the ligand solution and mechanical stirring (500 rpm) and ultrasonic dispersion (200 W power, 10 min interval, 5 min of ultrasonication) were alternated for 30 min to ensure uniform dispersion of powder (particle agglomerates ≤50 μm observed by optical microscope);

[0089] Dispersant compatibility verification: Test the Zeta potential of the mixture (it should be maintained between -30 and -40 mV). If the absolute value of the potential drops by more than 10 mV, 0.1-0.3 wt% of the original dispersant (used in step 1) needs to be added to prevent the particles from re-agglomerating.

[0090] Step S2-3: Construction and parameter control of the hydrothermal reaction system:

[0091] Reactor selection and sealing: Use a hydrothermal reactor with a polytetrafluoroethylene liner (volume 50-200mL), and control the material filling degree at 60%-80% (to avoid excessive pressure during the reaction); check the sealing performance after tightening the reactor lid (pressure holding test: no leakage at 1MPa pressure for 30 minutes);

[0092] Temperature and time control: Place the reactor in a programmed temperature oven, set the heating rate to 2℃ / min, raise it to 120-180℃ (150℃ is preferred for carboxylate ligands, and 120℃ for cyano ligands), and hold it at this temperature for 6-12 hours (determined by kinetic experiments: more than 95% of the coordination reaction can be completed at 150℃ for 8 hours).

[0093] Pressure monitoring: During the reaction, a pressure sensor is connected to the vessel body through a reserved interface to monitor the pressure inside the vessel in real time (usually 0.5-2MPa). If the pressure rises suddenly by more than 10% of the set value, heating will be stopped immediately and the vessel will cool down naturally. The raw material ratio or sealing problem should be investigated.

[0094] Step S2-4: Formation and verification of metal-organic coordination polymer networks:

[0095] Coordination bond type confirmation: After the reaction is complete, a small amount of product is taken for Fourier transform infrared spectroscopy (FTIR) analysis. The carboxylate ligand should be within the range of 1550-1650 cm⁻¹. -1 (asymmetric stretching vibration of carboxylate group) and 1400-1450 cm -1The (symmetric stretching vibration) exhibits a characteristic peak, and the peak position shifts by ≥20cm compared to the free ligand. -1 This proves the formation of bidentate coordination bonds; the cyano ligand needs to be in the range of 2200-2250 cm⁻¹. -1 Coordination characteristic peaks appear;

[0096] Network structure characterization: The crystal structure of the product was detected by X-ray diffraction (XRD) and compared with the simulated metal-organic framework (MOF) standard card. The main characteristic peak matching degree was ≥85%, which proved that an ordered network was formed. The particle surface should form a nanoscale sheet-like or rod-like coordination structure (thickness / diameter 50-200nm) when observed by scanning electron microscopy (SEM).

[0097] Verification of reaction completeness: Take the supernatant and detect it with a UV-Vis spectrophotometer. The intensity of the characteristic absorption peak of the ligand should be ≤5% of the initial value (proving that the ligand has almost completely reacted). Otherwise, the reaction time needs to be extended by 2-4 hours or the temperature needs to be increased by 10-20℃.

[0098] Step S2-5: Product separation and purification:

[0099] Solid-liquid separation: Cool the material after hydrothermal reaction to room temperature and separate it by centrifugation (8000 rpm, 15 min). Collect the metal-organic coordination polymer solid at the bottom (the pH of the supernatant should be maintained between 5 and 7. If it deviates, record and analyze the reason).

[0100] Multi-stage cleaning: First, wash three times with deionized water (solid-liquid ratio 1:10 each time, sonicate for 10 min and then centrifuge) to remove unreacted free ligands; then wash twice with anhydrous ethanol to reduce surface tension (contact angle increased from 70° to 85°) and prevent the network structure from collapsing during drying.

[0101] Low-temperature drying: The cleaned product was placed in a vacuum drying oven and dried at 60℃ and a vacuum of -0.09MPa for 12 hours (thermogravimetric analysis showed that the weight loss rate was ≤2% and no coordinate bond breakage occurred under these conditions). After drying, the product was sealed and stored in a desiccator (relative humidity ≤30%).

[0102] Step S2-6: Coordination network stability test:

[0103] Thermal stability assessment: Thermogravimetric-differential scanning calorimetry (TG-DSC) analysis showed that the weight loss of the product below 200℃ should be ≤5% (only physically adsorbed water was lost), and there was no obvious exothermic peak (proving that the coordination network did not decompose).

[0104] Chemical stability verification: The product was soaked in buffer solutions with pH=3, 7 and 11 for 24 hours respectively. After centrifugation, the concentration of rare earth ions in the supernatant was detected (it should be ≤0.01g / L), and the XRD characteristic peaks showed no significant change (proving that the network is stable in acidic and alkaline environments).

[0105] Handling of non-conforming products: If the stability does not meet the standard, the hydrothermal temperature (±20℃) or ligand ratio (±0.5) needs to be optimized again, and steps S2-2 to S2-5 are repeated until the requirements are met (the pass rate after optimization is ≥90%).

[0106] In this embodiment, in step S3:

[0107] The auxiliary salt is a water-soluble inorganic salt, and its addition amount is 10-30% of the weight of rare earth hydroxide;

[0108] The high-energy ball mill operates at a speed of 300-500 rpm, and the pore size distribution is controlled and particle agglomeration is prevented through the salt template effect.

[0109] The pickling process in step S3 involves treating with hydrochloric acid at pH=1 for 0.5 hours to remove auxiliary salt residues;

[0110] Furthermore, step S3 aims to regulate the pore structure of the metal-organic coordination polymer network through the synergistic effect of the template effect of the auxiliary salt and the mechanical force of high-energy ball milling, thereby refining the particle size and inhibiting agglomeration. This also lays the foundation for subsequent calcination to form a mesoporous-macroporous composite structure. The detailed steps are as follows:

[0111] Step S3-1: Screening and pretreatment of auxiliary salts:

[0112] Salt type selection: Water-soluble inorganic salts (such as NaCl, KCl, Na2CO3) are selected as auxiliary salts. Preferential selection is given to cubic crystal system salts with a melting point ≥800℃ (such as NaCl, melting point 801℃). Its rigid particles can form a uniform template in ball milling (experimental verification: the pore size distribution deviation formed by NaCl template is ≤15%, which is better than the 25% of Na2CO3).

[0113] Salt purity and particle size control: The salt purity was ≥99.5% and the water-insoluble matter was ≤0.1wt% by X-ray fluorescence spectroscopy (XRF); the salt was pulverized to a particle size of 1-5μm using an air jet mill (D50 = 3μm measured by a laser particle size analyzer) to ensure that the particle size matched that of the product in step S2 (to avoid uneven pore size due to excessive differences in template size).

[0114] Drying and dehydration: Place the auxiliary salt in a muffle furnace and dry at 120°C for 4 hours (thermogravimetric analysis shows that the residual water of crystallization is ≤0.5wt% under this condition). After cooling, seal and store to prevent moisture absorption.

[0115] Step S3-2: Mixing the product and auxiliary salt in the specified proportions:

[0116] Precise control of weight ratio: Weigh the product and auxiliary salt in step S2 at a weight ratio of 10:1-10:3 (i.e., the amount of auxiliary salt added is 10-30%), and ensure that the ratio error is ≤±0.5% by using an electronic balance (accuracy 0.1mg); a ratio of 10:2 is preferred (experimental data: the pore size distribution is the most uniform under this ratio, and the proportion of mesopores reaches 65%).

[0117] Premixing process: Add both to an agate mortar and grind manually for 10 minutes until initially mixed (observed under an optical microscope, no obvious salt particle agglomeration); then transfer to a V-type mixer (30 rpm) and mix for 30 minutes to ensure the uniformity of the system (sampled at 3 points, salt content deviation ≤2%).

[0118] Anti-agglomeration agent supplementation: If the absolute value of the Zeta potential of the mixed system is <30mV, add 0.2-0.5wt% of polyvinylpyrrolidone (PVP, molecular weight 50000), and ultrasonically disperse for 5 minutes (power 200W) to enhance dispersion stability.

[0119] Step S3-3: Optimization and Execution of High-Energy Ball Milling Parameters:

[0120] Ball milling equipment and media selection: A planetary ball mill is used, equipped with a polyurethane or zirconia ball mill jar (50-200mL volume) to avoid metal contamination; zirconia balls (density 6.0g / cm³) are selected as the milling media. 3 Mix them in a ratio of 5mm:10mm in diameter (to improve grinding efficiency);

[0121] Key parameter settings:

[0122] Particle-to-material ratio (total mass of balls to total mass of materials): 2-4 (preferably 3:1; experiments show that this ratio produces the best particle refinement without over-grinding).

[0123] Rotation speed: 300-500 rpm (adjust according to the hardness of the material; 400 rpm is preferred for rare earth coordination polymers);

[0124] Time: 2-10 hours (determined by phased sampling: the particle size decreases rapidly in the first 2 hours, then tends to stabilize, and the total time can be controlled within 6 hours to achieve the optimal pore structure precursor state);

[0125] Intermittent mode: Pause for 10 minutes every 30 minutes of operation (to prevent the temperature inside the tank from exceeding 60°C and to avoid premature salt dissolution or ligand decomposition);

[0126] Ball milling process monitoring: The temperature inside the mill is monitored by the temperature sensor built into the ball mill. If it exceeds 60°C, the mill is immediately stopped and cooled to room temperature. Samples are taken every 2 hours and the particle morphology is observed using a scanning electron microscope (SEM) to ensure that there is no obvious sintering phenomenon.

[0127] Step S3-4: Acid washing and desalting of the ball-milled product:

[0128] Pickling system preparation: Prepare a hydrochloric acid solution with pH=1 (concentration of approximately 0.1 mol / L), calibrate it with a precision pH meter (error ±0.02) to ensure stable hydrogen ion concentration (affecting salt dissolution efficiency);

[0129] Pickling process parameters: The ball milling product and hydrochloric acid solution are mixed at a solid-liquid ratio of 1:10 and placed in a constant temperature water bath (30℃). The mixture is mechanically stirred (200 rpm) for 0.5 hours (determined by dissolution kinetics experiments: more than 99% of soluble salts can be removed in 0.5 hours).

[0130] Salt residue detection: Take the supernatant after acid washing and use an ion chromatograph to detect the salt ion concentration (e.g., Cl-). The requirement is ≤10ppm. If it does not meet the standard, replace it with fresh hydrochloric acid solution and repeat the acid washing once (extend the time to 0.5 hours) until it meets the standard.

[0131] Step S3-5: Washing and drying:

[0132] Multi-stage washing: The acid-washed solid is washed 3 times with deionized water (conductivity ≤5μS / cm), each time with a solid-liquid ratio of 1:15. After stirring for 10 minutes, it is centrifuged (8000rpm, 10 minutes) until the pH of the supernatant is ≥5 (tested with precision pH test paper to avoid residual acid corroding subsequent equipment).

[0133] Drying parameter control: The washed solid was placed in a vacuum drying oven and dried at 60℃ and a vacuum of -0.09MPa for 12 hours (thermogravimetric analysis showed that the residual moisture was ≤1wt% under these conditions and the non-porous structure collapsed); after drying, it was passed through a 200-mesh sieve (75μm sieve opening) to remove any possible large particle agglomerates.

[0134] Step S3-6: Preliminary characterization and verification of pore structure:

[0135] Particle size distribution detection: The dried powder was analyzed using a laser particle size analyzer. The required particle size distribution range was D50 = 1-3 μm (5-10 times finer than the product in step S2), and the particle size distribution range was SPAN ≤ 1.0 (to prove the uniformity of ball milling).

[0136] Preliminary surface area test: Measured using a low-temperature nitrogen adsorption analyzer (BET method), the specific surface area should be ≥50 m². 2 / g (laying the foundation for high specific surface area after subsequent calcination); if it is lower than this value, the ball milling time needs to be extended by 2-4 hours.

[0137] Salt template residue verification: X-ray diffraction (XRD) should be used to detect the presence of characteristic peaks of auxiliary salts (such as the 2θ = 28.3° and 47.3° peaks of NaCl), which proves that the salt has been completely removed.

[0138] Handling of non-conforming products: If the pore structure parameters do not meet the standards, readjust the ball-to-material ratio (±0.5) or the ball milling time (±2 hours), and repeat steps S3-3 to S3-5 until the requirements are met (optimized pass rate ≥92%).

[0139] In this embodiment, the confined isolation device in step S4 includes a multi-stage cyclone separator to achieve gas-solid separation during the dehydroxylation and structural shaping stages.

[0140] The product of step S4 has a mesoporous-macroporous composite hierarchical pore structure with a pore size range of 2-50 nm.

[0141] Furthermore, step S4 aims to achieve the controllable removal of organic components and the directional shaping of the porous structure of rare earth oxides through a two-stage calcination process under confined isolation conditions, ultimately obtaining a specific surface area ≥80m². 2 / g and with a reasonable pore size distribution, nanoporous rare earth oxide materials; the detailed steps are as follows:

[0142] Step S4-1: Construction and commissioning of the confined isolation device:

[0143] The core components of the device: The confined isolation device consists of a feeding unit (screw feeder, speed 0.5-2 kg / h), a multi-stage cyclone separator (2-3 stages in series, separation efficiency ≥95%), a calcining furnace (programmed temperature rise accuracy ±5℃), an atmosphere control system (oxygen / nitrogen mixing device, flow rate accuracy ±0.1 L / min), and a product collection unit; among them, the cyclone separator is lined with high-temperature resistant ceramic (temperature resistance ≥1000℃) to avoid metal contamination;

[0144] Air tightness and temperature control verification: After assembly, an air tightness test was conducted (0.1MPa nitrogen was introduced, and the pressure drop was ≤5% after 30 minutes); the temperature curve of the empty furnace was adjusted by raising the temperature from room temperature to 600℃ and then cooling it down to verify the temperature control stability (fluctuation ≤±3℃) of each temperature zone (400-450℃, above 500℃).

[0145] Atmosphere mixing calibration: Weak oxidizing atmosphere (oxygen content 5-10 vol%, nitrogen balance) and inert atmosphere (nitrogen purity ≥99.999%) are calibrated using a gas flow meter and monitored in real time with an oxygen analyzer to ensure that the mixing error is ≤±0.5 vol%.

[0146] Step S4-2: First stage roasting – dehydroxylation in a weak oxidizing atmosphere at 400-450℃:

[0147] Feeding and initial temperature control: The product from step S3 is fed into the calcination furnace through a screw feeder. The initial temperature is set to 200℃ (to avoid water vapor condensation at low temperatures). The feeding rate is matched with the airflow speed inside the furnace (material residence time ≥ 30 min).

[0148] Heating and holding parameters: Heating to 400-450℃ at a rate of 5℃ / min (420℃ is preferred for carboxylate ligand-derived precursors, and 450℃ is preferred for cyano ligand-derived precursors), and holding in a weak oxidizing atmosphere (5 vol% oxygen) for 3-6 hours (as determined by thermogravimetric analysis: more than 90% of hydroxyl groups and organic ligands can be removed at 420℃ for 4 hours, with residual carbon ≤2 wt%).

[0149] Byproduct fixation and separation: Removed hydroxyl groups (H2O), organic decomposition products (CO2, NO) x (etc.) enter the first-stage cyclone separator with the airflow, where water vapor is condensed and separated by cooling (150℃). Small molecule gases are further purified by the second-stage cyclone separator (removing entrained powder particles, with a separation efficiency of ≥98%), avoiding the re-adsorption of by-products in the pores.

[0150] Step S4-3: Second stage roasting – shaping the porous structure at temperatures above 500℃:

[0151] Atmosphere switching and heating: After the first stage, quickly switch the furnace atmosphere to inert (nitrogen) and raise it to 550-700℃ at a rate of 10℃ / min (adjust according to the type of rare earth oxide: La2O3 preferred 600℃, CeO2 preferred 650℃) to avoid structural collapse caused by high temperature oxidation.

[0152] Heat preservation and crystallization control: Heat preservation at a set temperature for 4-5 hours promotes the crystallization of rare earth oxides (X-ray diffraction monitoring: after heat preservation for 4 hours, the characteristic peak half width at half maximum is ≤0.3°, and the crystallinity is ≥85%). At the same time, surface tension shrinkage is used to shape the mesoporous-macroporous composite structure (pore size 2-50nm).

[0153] Enhanced confinement effect: Gas-solid separation is achieved through the local negative pressure (-5 to 10 kPa) formed by the cyclone, avoiding the reverse diffusion of calcination products and by-products, and ensuring the integrity of the pore structure (experimental comparison: pore collapse rate under confinement conditions ≤15%, significantly lower than 40% in open systems);

[0154] Step S4-4: Cooling and Product Collection

[0155] Programmed cooling control: After calcination, maintain an inert atmosphere and cool to 200℃ at a rate of 5℃ / min (to avoid thermal stress cracking caused by rapid cooling), and then allow it to cool naturally to room temperature;

[0156] Product classification and collection: The first-stage cyclone separator collects the main products with a particle size of 1-5μm (accounting for ≥90%), and the second-stage cyclone separator collects the fine powder (particle size <1μm), and they are sealed and stored in a desiccator (relative humidity ≤30%).

[0157] Treatment of calcination residue: If a small amount of sintered lumps (≤5wt%) appear on the furnace wall, they should be crushed by ball milling (300 rpm, 30 minutes) and then tested. If the specific surface area is ≥60 m², the residue should be removed. 2 / g can be mixed into the main product; otherwise, it should be treated as waste.

[0158] Step S4-5: Characterization of porous structure and properties:

[0159] Specific surface area and pore size analysis: Tested using a low-temperature nitrogen adsorption-desorption apparatus (BET method), requiring a specific surface area ≥ 80 m². 2 / g (Optimal embodiment reaches 112m) 2 / g), the proportion of mesopores and macropores with a pore size of 2-50nm is ≥80% (calculated by BJH model);

[0160] Phase verification: X-ray diffraction (XRD) analysis showed characteristic peaks of rare earth oxides (such as 2θ = 27.8° and 32.2° for La2O3) and no impurity phase peaks (proving that the organic ligands were completely decomposed); high-resolution transmission electron microscopy (HRTEM) observed clear lattice fringes (the interplanar spacing matched the standard card);

[0161] Microscopic morphology observation: Scanning electron microscopy (SEM) shows that the material has a loose porous structure with no obvious agglomeration; transmission electron microscopy (TEM) can observe interconnected mesopores (2-50nm) and macropores (50-200nm) channels.

[0162] Step S4-6: Performance Compliance Verification and Optimization

[0163] Key indicator testing: If the specific surface area is <80m² 2 / g, the second stage calcination temperature needs to be adjusted (reduced by 50℃) or the holding time shortened (reduced by 1 hour), and steps S4-3 to S4-4 should be repeated; if the pore size distribution deviation is >20%, the first stage dehydroxylation time needs to be optimized (±1 hour);

[0164] Stability test: The product was placed in air for 72 hours, and the specific surface area was tested again (the decrease rate should be ≤5%) to prove the structural stability; the pore volume was measured by mercury porosimetry (it should be ≥0.3 cm³). 3 / g), ensuring the basic adsorption performance;

[0165] Final qualification standard: Requires a specific surface area ≥ 80 m² 2 / g, mesoporous-macroporous ratio ≥80%, crystallinity ≥85%, all three indicators must meet the standards before it can enter the subsequent application stage (pass rate ≥88%).

[0166] In this embodiment, nanoporous rare earth oxide materials are used to prepare non-invasive trace sampling probes with an operating temperature range of -10℃ to 400℃.

[0167] Furthermore, nanoporous rare earth oxide materials are functional porous materials with a unique hierarchical pore structure, excellent adsorption performance, and specific recognition ability. Their specific characteristics are as follows:

[0168] I. Composition and Microstructural Characteristics:

[0169] Chemical composition: Primarily composed of single or composite rare earth oxides (such as La2O3, CeO2, Nd2O3, or their solid solutions), with a total rare earth element content ≥95wt% and a total impurity content (Fe, Si, Al, etc.) ≤0.5wt% (detected by X-ray fluorescence spectroscopy). Among these, CeO2-based materials exhibit variable valence states (Ce... 3+ / Ce 4+ During the adsorption process, the interaction with the target molecule can be enhanced through redox reactions;

[0170] Hierarchical porous structure: It exhibits a mesoporous-macroporous composite interconnected structure—mesoporous pores (2-50nm) account for 60%-70%, mainly due to the template effect of metal-organic coordination polymer networks; macropores (50-200nm) account for 30%-40%, formed by the mechanical force of high-energy ball milling and the space after the removal of salt templates; the pores are interconnected (pore connectivity index measured by mercury porosimeter ≥0.8), providing efficient channels for the diffusion of target molecules;

[0171] Particle size and morphology: The particles are generally spherical or irregular in shape, with a secondary particle size distribution of 1-5 μm (D50 of laser particle size analyzer = 3 μm). The particle surface is densely covered with nanoscale pores (SEM observation: pore density ≥ 10). 4 per μm 2 No obvious hard agglomeration phenomenon was observed (agglomeration fold measured by dynamic light scattering instrument DLS ≤1.2);

[0172] II. Physicochemical properties:

[0173] Specific surface area and pore volume: determined by low-temperature nitrogen adsorption-desorption (BET) method, with a specific surface area ≥80m². 2 / g (Optimal embodiment reaches 112m) 2 / g), pore volume ≥0.3cm³ 3 / g (calculated using the BJH model), where the specific surface area contributed by mesopores accounts for ≥70% (ensuring adsorption capacity for small molecule prohibited substances);

[0174] Surface functional groups: The surface contains a small amount of hydroxyl (-OH) and unsaturated coordinated rare earth ions (detected by X-ray photoelectron spectroscopy XPS: hydroxyl oxygen accounts for 15%-20% in the O1s spectrum, and rare earth ions have some unsaturated coordination sites). These active sites can interact specifically with illicit molecules (such as compounds containing amine or carbonyl groups) through hydrogen bonds and coordination bonds.

[0175] Crystallinity and thermal stability: X-ray diffraction (XRD) analysis showed that it was highly crystalline, with the main diffraction peaks matching the corresponding rare earth oxide standard cards (such as PDF#34-0394 for CeO2), and crystallinity ≥85% (calculated by the full width at half maximum). Thermogravimetric analysis (TG) showed that the weight loss rate in air below 400℃ was ≤3% (only physically adsorbed water was lost), and there was no obvious structural collapse below 800℃ (suitable for use in high-temperature environments).

[0176] III. Adsorption performance and specific recognition mechanism:

[0177] Saturated adsorption capacity: The saturated adsorption capacity for typical prohibited molecules (morphine, methamphetamine, ketamine, etc.) is ≥50mg / g (equilibrium adsorption capacity determined by UV-Vis spectrophotometry), of which the adsorption capacity for fentanyl can reach 65mg / g (significantly higher than 20mg / g of activated carbon), which is due to the synergistic effect of high specific surface area and surface active sites.

[0178] Specific recognition capability: selective adsorption of target molecules is achieved through the following mechanisms:

[0179] Coordination effect: Unsaturated rare earth ions on the material surface can form coordination bonds with amine groups (-NH2) and carbonyl groups (C=O) in the narcotic molecule (stability constant K≥10). 4 L / mol, determined by isothermal titration calorimetry (ITC);

[0180] Spatial matching: The pore size of the mesopores (2-50nm) matches the molecular size of the prohibited substances (such as morphine molecules with a diameter of about 0.8nm), resulting in a size sieving effect, and the adsorption capacity of large molecular impurities (such as proteins) is ≤5mg / g;

[0181] Hydrogen bonding: Surface hydroxyl groups (-OH) form hydrogen bonds with phenolic hydroxyl groups in narcotic molecules (such as morphine), further enhancing adsorption selectivity;

[0182] In actual testing, it can specifically identify at least three of morphine, methamphetamine, ketamine, cocaine, fentanyl, and synthetic cannabinoids (verified by high performance liquid chromatography, cross-adsorption rate ≤10%).

[0183] IV. Stability and Usage Conditions:

[0184] Chemical stability: After soaking in aqueous solution with pH = 3-11 for 24 hours, the amount of rare earth ions dissolved is ≤0.01g / L (detected by inductively coupled plasma mass spectrometry ICP-MS), and the change rate of pore structure parameters (specific surface area, pore size distribution) is ≤5% (suitable for sampling in complex environments);

[0185] Mechanical stability: After tap density test (vibration at 200 times / min for 30 min), the bulk density change rate is ≤8%, and there is no obvious powder breakage phenomenon (meets the requirements of probe coating process);

[0186] Operating temperature range: -10℃ to 400℃. Within this range, the adsorption performance remains stable (the adsorption capacity decrease rate at low temperatures is ≤10%, and the specific surface area retention rate after treatment at 400℃ is ≥90%). It can adapt to the sampling needs of extreme environments (such as cold chain transportation and high temperature storage).

[0187] V. Application Adaptability Features:

[0188] Sampling compatibility: The powder particle size and surface roughness (Ra = 50-100 nm as measured by atomic force microscopy AFM) are suitable for collecting trace samples by scraping (sampling efficiency ≥ 80%, that is, 80% of the target molecules remaining on the surface can be transferred by scraping);

[0189] Detection compatibility: Compatible with in-situ mass spectrometry detection devices—the material does not interfere with mass spectrometry ion sources (such as ESI, APCI), and the adsorbed prohibited molecules can be rapidly desorbed at 50-200℃ (desorption rate ≥95%, verified by thermal desorption-mass spectrometry), meeting the needs of high-throughput analysis (single sample detection time ≤30 seconds).

[0190] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a nanoporous rare earth oxide material, characterized in that: Includes the following steps: S1. Precursor preparation: Rare earth raw materials and polymeric precipitants are reacted by liquid-phase precipitation, organic polymeric dispersants are added to inhibit agglomeration, and the pH of the system is adjusted to >4 to obtain rare earth hydroxide powder with a particle size of 5-10μm. S2. Molecular-directed modification: The rare earth hydroxide obtained in step S1 is assembled with organic ligands containing carboxyl groups or cyano groups under hydrothermal conditions to form a metal-organic coordination polymer network. S3. Secondary construction of pore structure: Mix the product of step S2 with auxiliary salt in a weight ratio, and perform high-energy ball milling for 2-10 hours at a ball-to-material ratio of 2-4. Then, acid wash, water wash, and dry. S4. High-temperature roasting and conversion: The product from step S3 is roasted in a confined isolation device in two stages. Dehydroxylation reaction was carried out at 400-450℃ in a weak oxidizing atmosphere for 3-6 hours to fix the byproducts; The porous structure is solidified by heating to above 500℃ and holding for 4-5 hours, ultimately achieving a specific surface area ≥80m². 2 / g of nanoporous rare earth oxide materials.

2. The method for preparing a nanoporous rare earth oxide material according to claim 1, characterized in that: In step S1: The polymeric precipitant is a functionalized polymer with protonated amine groups; The organic polymer dispersant contains ≥50 wt% long-chain alkyl groups; After precipitation, the surface tension is reduced by washing with anhydrous ethanol.

3. The method for preparing a nanoporous rare earth oxide material according to claim 1, characterized in that: In step S2: The molar ratio of the organic ligand to the rare earth hydroxide is 1:1 to 1:3; Metal-organic coordination polymer networks specifically bind carbonyl or amine functional groups through bidentate coordination bonds of carboxylate groups.

4. The method for preparing a nanoporous rare earth oxide material according to claim 1, characterized in that: In step S3: The auxiliary salt is a water-soluble inorganic salt, and its addition amount is 10-30% of the weight of rare earth hydroxide; The high-energy ball mill operates at a speed of 300-500 rpm, and the pore size distribution is controlled and particle agglomeration is prevented through the salt template effect.

5. The method for preparing a nanoporous rare earth oxide material according to claim 4, characterized in that: The pickling process in step S3 involves treating the sample with hydrochloric acid at pH=1 for 0.5 hours to remove residual auxiliary salts.

6. The method for preparing a nanoporous rare earth oxide material according to claim 1, characterized in that: The confined isolation device in step S4 includes a multi-stage cyclone separator to achieve gas-solid separation during the dehydroxylation and structural shaping stages.

7. The method for preparing a nanoporous rare earth oxide material according to claim 1, characterized in that: The product of step S4 has a mesoporous-macroporous composite hierarchical pore structure with a pore size range of 2-50 nm.

8. The method for preparing a nanoporous rare earth oxide material according to claim 1, characterized in that: The nanoporous rare earth oxide material is used to prepare a non-invasive trace sampling probe with an operating temperature range of -10℃ to 400℃.

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