A magnesium-chromium hydrotalcite with super large specific surface area and a preparation method and application thereof
Patent Information
- Application Number
- CN202610895460.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-06-22
- Publication Date
- 2026-08-28
AI Technical Summary
[0006]本发明解决的技术问题：解决现有水滑石材料比表面积小、活性基团暴露不充分、对重金属离子吸附容量低和吸附速率慢的技术问题
[0043] 1. The magnesium-chromium hydrotalcite with an ultra-large specific surface area prepared by this invention, through borate intercalation combined with organic solvent washing treatment, achieves a specific surface area as high as 500-600 m². 2 /g, far exceeding that of conventional hydrotalcite materials (typically <100 m³). 2 /g). The extremely large specific surface area significantly increases the exposure density and accessibility of active groups such as hydroxyl groups on the surface of the plates, providing more adsorption sites for heavy metal ions.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of inorganic functional materials technology, and particularly relates to a magnesium-chromium hydrotalcite with an ultra-large specific surface area, its preparation method, and its application. Background Technology
[0002] With rapid industrialization and human activities, heavy metal pollution in water bodies has become increasingly serious, posing a severe threat to the ecological environment and human health. Heavy metal ions such as uranium, arsenic, lead, and cadmium are characterized by high toxicity, reluctance to degrade, and easy bioaccumulation, making their efficient treatment a research hotspot in the environmental field. Meanwhile, uranium, as a key fuel for nuclear power generation, has significant strategic resource value. Therefore, recovering uranium resources from uranium-containing wastewater and seawater, as well as removing heavy metals such as arsenic, lead, and cadmium from polluted water bodies, has dual significance for both environmental remediation and resource recovery.
[0003] Adsorption is considered one of the mainstream technologies for heavy metal pollution control and resource recovery due to its advantages such as simple operation, low energy consumption, low cost, and ease of large-scale application. The core of this technology lies in the development of high-performance adsorption materials. Layered composite metal hydroxides (hydrotalcite, LDH) are a class of two-dimensional layered materials composed of positively charged metal hydroxide plates and exchangeable anions between the layers. Due to their tunable composition, controllable structure, and rich surface hydroxyl groups, they show broad application prospects in the field of heavy metal adsorption.
[0004] However, the adsorption performance of conventional hydrotalcite materials remains significantly insufficient, making it difficult to meet the needs of efficient treatment and resource recovery. The fundamental reason is that hydrotalcite prepared by traditional co-precipitation methods typically has a low specific surface area (generally <100 m²). 2 The low surface area ( / g) results in insufficient exposure of active groups on the surface of the plate, leading to a low density of active sites and limiting its ability to capture and adsorb heavy metal ions. Furthermore, the low specific surface area also causes a long mass transfer path and slow adsorption kinetics, significantly reducing extraction efficiency in low-concentration heavy metal ion environments (such as uranium-containing wastewater and arsenic-polluted water bodies), making it difficult to achieve efficient removal of trace heavy metals.
[0005] Therefore, how to increase the specific surface area of hydrotalcite materials and enhance the exposure density and accessibility of active groups, thereby significantly improving their adsorption capacity and rate for heavy metal ions, is a pressing technical problem to be solved in this field. Developing a novel hydrotalcite material with an ultra-large specific surface area and highly exposed active sites has significant practical implications and application value for heavy metal pollution control and resource recovery. Summary of the Invention
[0006] The technical problem solved by this invention is to address the issues of small specific surface area, insufficient exposure of active groups, low adsorption capacity for heavy metal ions, and slow adsorption rate in existing hydrotalcite materials.
[0007] In view of the technical problems existing in the prior art, the present invention designs an ultra-large specific surface area magnesium chromium hydrotalcite, its preparation method and its application.
[0008] It should be noted that, in this invention, unless otherwise specified, the specific meaning of "comprising" in relation to composition definition and description includes both open-ended meanings such as "comprising," "including," etc., and closed-ended meanings such as "composed of," etc., and similar meanings.
[0009] To solve the aforementioned technical problems, the present invention adopts the following solution:
[0010] [First technical solution]
[0011] A magnesium-chromium hydrotalcite with an ultra-large specific surface area, wherein the specific surface area of the magnesium-chromium hydrotalcite is 500-600 m². 2 / g, the interlayer anion is borate ion, and it has a regular layered structure.
[0012] Furthermore, the pore size distribution of the ultra-large specific surface area magnesium chromium hydrotalcite is mesoporous, with an average pore size of 3-4 nm.
[0013] [Second Technical Solution]
[0014] A method for preparing the above-mentioned magnesium-chromium hydrotalcite with ultra-large specific surface area includes the following steps:
[0015] Step (1): Mix magnesium salt, chromium salt, borate ion source with water to obtain a mixed salt solution;
[0016] Step (2): Mix the alkaline solution with the mixed salt solution from step (1) to carry out a co-precipitation reaction to obtain borate-intercalated magnesium chromium hydrotalcite;
[0017] Step (3): The borate-intercalated magnesium chromium hydrotalcite obtained in step (2) is washed with an organic solvent and dried to obtain the magnesium chromium hydrotalcite with ultra-large specific surface area.
[0018] Further, in step (1), the magnesium salt is at least one of magnesium nitrate, magnesium chloride, and magnesium sulfate; the chromium salt is at least one of chromium nitrate, chromium chloride, and chromium sulfate; and the borate ion source is at least one of boric acid, borax, and sodium metaborate.
[0019] Further, in step (1), the molar ratio of magnesium ions in magnesium salt to chromium ions in chromium salt is (2-5):1; the molar ratio of chromium ions to borate ions is 1:(1-3).
[0020] Furthermore, in step (2), the alkaline solution is a sodium hydroxide solution with a concentration of 0.5-2 mol / L.
[0021] The pH value of the coprecipitation reaction is 8.5-10, the reaction temperature is room temperature to 80℃, and the reaction time is 0.5-2 hours.
[0022] Furthermore, in step (3), the organic solvent is one of acetone, methanol, ethanol, or a mixture thereof;
[0023] The drying method is vacuum drying, the drying temperature is 40-80℃, and the drying time is 6-24 hours.
[0024] Furthermore, in step (3), the organic solvent washing is performed by washing with acetone and ethanol in sequence, or by washing with acetone and methanol in sequence.
[0025] In this invention, the number of washing cycles is generally 1-5 times to ensure the washing effect and effectively remove water molecules and impurities between layers.
[0026] The mechanism by which this invention can successfully synthesize magnesium-chromium hydrotalcite with ultra-large specific surface area is as follows:
[0027] The core mechanism by which this invention successfully prepares magnesium-chromium hydrotalcite with ultra-large specific surface area lies in the synergistic effect of two points.
[0028] Firstly, the intercalation effect of borate ions: Compared with traditional carbonate ions, borate ions have a larger spatial volume and a unique charge distribution. When these ions intercalate between the layers of hydrotalcite, they can more effectively open up the layers, increase the interlayer spacing, weaken the electrostatic attraction and hydrogen bonding between the layers, thereby inhibiting the tight stacking of the layers.
[0029] Secondly, the key aspect of organic solvent washing: Conventional water washing retains a large number of interlayer water molecules. These water molecules are connected to the layers through hydrogen bonds, leading to a reduction in interlayer distance and layer recombination. This invention uses organic solvents such as acetone and ethanol for washing, which can effectively remove interlayer water molecules and impurities, significantly weaken the hydrogen bond forces between the layers, promote partial delamination of the layers, and form a rich mesoporous structure, thereby synergistically achieving an ultra-large specific surface area.
[0030] The mechanism by which the magnesium-chromium hydrotalcite with ultra-large specific surface area prepared in this invention has a large adsorption capacity for heavy metal ions is as follows:
[0031] The excellent adsorption performance of the material of this invention for heavy metal ions stems from its ultra-large specific surface area, abundant surface active sites, and unique layer electronic structure, but the specific adsorption mechanisms of different heavy metal ions vary.
[0032] For heavy metal ions such as uranium and lead, which are mainly captured by hydroxyl coordination, the ultra-large specific surface area allows for full exposure of hydroxyl active sites on the plate surface, significantly increasing the hydroxyl density. The high density and high accessibility of these active sites effectively overcome mass transfer resistance in the liquid phase, enabling the target ions to diffuse rapidly and bind to hydroxyl groups. This achieves rapid and efficient extraction with ultra-high adsorption capacity, making it particularly suitable for the extraction of extremely low concentrations of uranium from seawater.
[0033] For heavy metal ions such as cadmium that rely on isomorphous substitution, the structural stability of ultra-large specific surface area magnesium-chromium hydrotalcite is relatively reduced due to its thinner and smaller layers and the introduction of more defect sites. The Mg in the layers... 2+ It is more likely to dissolve and form vacancies. Subsequently, Cd in the solution... 2+ Through isomorphous substitution, Mg vacancies are introduced, forming a stable Cd-doped mineralization structure, significantly reducing Cd content. 2+ Migration and biotoxicity.
[0034] For heavy metals such as arsenic that exist in the form of oxygen-containing anions, the ultra-large specific surface area provides abundant adsorption sites for surface hydroxyl groups, which have a strong electrostatic attraction and coordination effect on negatively charged oxygen-containing anions. At the same time, borate intercalation not only expands the laminations but also modulates the electronic structure of the lamination metals, inducing electron transfer from Cr to O, increasing the electron cloud density on oxygen atoms, enhancing the nucleophilicity of surface hydroxyl groups, and making it easier to form stable chemical bonds with arsenic oxygen-containing anions, thereby significantly improving adsorption capacity and affinity.
[0035] Furthermore, in a mixed system where cadmium, arsenic, and lead coexist, the adsorption capacity of the material of this invention for both is further enhanced. The possible mechanism is as follows: the material surface first adsorbs lead and cadmium through hydroxyl coordination or isomorphous substitution. These adsorbed metal cations act as "bridging" sites, further complexing with negatively charged arsenite ions to form Cr-O-Cd / Pb-As ternary surface complexes, resulting in a synergistic adsorption effect.
[0036] [Third technical solution]
[0037] Application of the above-mentioned magnesium-chromium hydrotalcite with ultra-large specific surface area in the adsorption of uranium, arsenic, lead and cadmium.
[0038] Furthermore, the specific applications include uranium extraction from seawater, treatment of uranium-containing wastewater, or treatment of wastewater containing arsenic, lead, or cadmium.
[0039] The application method can be adjusted according to specific needs. For example, its application can be as follows:
[0040] Application 1: Uranium extraction from seawater: The ultra-large specific surface area magnesium chromium hydrotalcite is added to natural seawater or uranium-containing wastewater at a dosage of 10-50 mg / L and stirred at room temperature for 0.5-2 hours to achieve efficient adsorption and extraction of uranyl ions. After adsorption is completed, the material is recovered by filtration or centrifugation.
[0041] Application of arsenic-containing wastewater treatment: The ultra-large specific surface area magnesium chromium hydrotalcite is added to arsenic-containing wastewater with a pH of 6-8 at a dosage of 1-5 g / L. After stirring at room temperature for 1-3 hours, the concentration of arsenic (arsenite or arsenate) in the wastewater can be reduced to below the national emission standard. The treated material is then separated by precipitation or filtration.
[0042] This invention provides a magnesium-chromium hydrotalcite with ultra-large specific surface area, its preparation method, and its application, which have the following beneficial effects:
[0043] 1. The magnesium-chromium hydrotalcite with an ultra-large specific surface area prepared by this invention, through borate intercalation combined with organic solvent washing treatment, achieves a specific surface area as high as 500-600 m². 2 / g, far exceeding that of conventional hydrotalcite materials (typically <100 m³). 2 / g). The extremely large specific surface area significantly increases the exposure density and accessibility of active groups such as hydroxyl groups on the surface of the plates, providing more adsorption sites for heavy metal ions.
[0044] 2. The magnesium-chromium layered double hydroxide (TLH) with ultra-large specific surface area prepared by this invention exhibits excellent adsorption performance for heavy metal ions. Experiments show that the maximum adsorption capacity of the LDH prepared by this invention for uranium can reach 2542 mg / g; in real seawater, the uranium extraction efficiency exceeds 90% within 1 hour. In single heavy metal ion systems, the adsorption capacity of this material for cadmium, arsenic, and lead is significantly improved; in mixed systems where cadmium, arsenic, and lead coexist, it still exhibits broad-spectrum and efficient removal capabilities for multiple heavy metal ions, and the adsorption performance is further improved in mixed systems.
[0045] 3. In the preparation method of the present invention, borate ions are directly inserted into the interlayer of hydrotalcite during the co-precipitation process, without the need for additional ion exchange steps. The process is simple, easy to operate, and low in cost.
[0046] 4. In the preparation method provided by the present invention, an organic solvent washing step is used instead of traditional water washing, which effectively removes excess water molecules and impurities between layers, promotes the peeling of layers and the formation of pore structures, and further increases the specific surface area and porosity.
[0047] 5. The hydrotalcite material prepared by this invention has the dual functions of environmental remediation and resource recycling. It can be used for uranium extraction from seawater, treatment of uranium-containing wastewater, and remediation of heavy metal pollution such as arsenic, lead, and cadmium. It has a wide range of applications and good economic and social benefits. Attached Figure Description
[0048] Figure 1 : XRD comparison diagram of the ultra-large specific surface area magnesium-chromium hydrotalcite prepared in Example 1 of the present invention and the conventional magnesium-chromium hydrotalcite prepared in Comparative Example 1.
[0049] Figure 2 : TEM image of the magnesium-chromium hydrotalcite with ultra-large specific surface area prepared in Example 1 of this invention;
[0050] Figure 3 : Nitrogen adsorption-desorption isotherm of the ultra-large specific surface area magnesium-chromium hydrotalcite prepared in Example 1 of this invention;
[0051] Figure 4 : Pore size distribution curve of the ultra-large specific surface area magnesium-chromium hydrotalcite prepared in Example 1 of the present invention;
[0052] Figure 5 : FTIR comparison image of the ultra-large specific surface area magnesium-chromium hydrotalcite prepared in Example 1 of the present invention and the conventional magnesium-chromium hydrotalcite prepared in Comparative Example 1;
[0053] Figure 6 : This is a comparison chart of the BET specific surface area of the ultra-large specific surface area magnesium-chromium hydrotalcite prepared in Example 1 of the present invention and the conventional magnesium-chromium hydrotalcite prepared in Comparative Example 1.
[0054] Figure 7 : XPS full spectrum of the ultra-large specific surface area magnesium-chromium hydrotalcite prepared in Example 1 of this invention before and after uranium adsorption;
[0055] Figure 8 : This is a fitting diagram of the adsorption isotherm of uranium on the ultra-large specific surface area magnesium-chromium hydrotalcite prepared in Example 1 of this invention;
[0056] Figure 9 : This is a graph showing the uranium extraction efficiency of the ultra-large specific surface area magnesium-chromium hydrotalcite prepared in Example 1 of this invention in real seawater;
[0057] Figure 10 : This is a bar chart showing the adsorption capacity of ultra-large specific surface area magnesium-chromium hydrotalcite for cadmium, arsenic, and lead in an application example of this invention.
[0058] Figure 11 : This is a bar chart showing the adsorption capacity of ultra-large specific surface area magnesium-chromium hydrotalcite for cadmium, arsenic, and lead in a mixed system in an application example of the present invention. Detailed Implementation
[0059] The present invention will be further described below with reference to specific embodiments and accompanying drawings:
[0060] Example 1
[0061] The preparation method of magnesium-chromium hydrotalcite with ultra-large specific surface area provided in this embodiment includes the following specific steps:
[0062] (1) Dissolve 30 mmol magnesium nitrate hexahydrate, 10 mmol chromium nitrate nonahydrate and 20 mmol boric acid in 50 mL of ultrapure water and stir until completely dissolved to obtain a mixed salt solution. The molar ratio of magnesium ions to chromium ions is 3:1.
[0063] (2) Prepare a 1 mol / L sodium hydroxide solution as an alkaline solution. Under nitrogen protection, the mixed salt solution and alkaline solution from step (1) are simultaneously added dropwise to the reaction vessel, and the mixture is stirred vigorously. The addition rate is controlled to maintain the pH of the reaction system at 9.0. After the addition is complete, the mixture is stirred at room temperature for 1 hour to obtain a borate-intercalated magnesium chromium hydrotalcite precipitate.
[0064] (3) The precipitate obtained in step (2) was separated by centrifugation, washed twice with acetone and once with ethanol, and then vacuum dried at 60°C for 12 hours to obtain magnesium chromium hydrotalcite with ultra-large specific surface area (sample number MgCr-H).
[0065] Testing revealed that the specific surface area of the magnesium-chromium hydrotalcite prepared in this embodiment was 530 m². 2 / g, with a mesoporous structure and an average pore size of about 3-4 nm. The interlayer anion is borate ion, and it has a regular layered structure.
[0066] Example 2
[0067] The preparation method of magnesium-chromium hydrotalcite with ultra-large specific surface area provided in this embodiment includes the following specific steps:
[0068] (1) Dissolve 30 mmol magnesium chloride hexahydrate, 10 mmol chromium chloride pentahydrate and 10 mmol borax in 50 mL of ultrapure water and stir until completely dissolved to obtain a mixed salt solution. The molar ratio of magnesium ions to chromium ions is 2:1.
[0069] (2) Prepare a 0.5 mol / L sodium hydroxide solution as an alkaline solution. Under nitrogen protection, the mixed salt solution and alkaline solution from step (1) are simultaneously added dropwise to the reaction vessel, and the mixture is stirred vigorously. The dropwise addition rate is controlled to maintain the pH value of the reaction system at 8.5. After the addition is complete, the reaction is stirred in an 80℃ water bath for 0.5 hours to obtain magnesium chromium hydrotalcite with a large specific surface area.
[0070] (3) The precipitate obtained in step (2) is separated by centrifugation, washed twice with acetone and three times with methanol, and then vacuum dried at 80°C for 12 hours to obtain magnesium chromium hydrotalcite with ultra-large specific surface area.
[0071] Testing revealed that the specific surface area of the magnesium-chromium hydrotalcite prepared in this embodiment was 502 m². 2 / g, with a mesoporous structure and an average pore size of about 3-4 nm. The interlayer anion is borate ion, and it has a regular layered structure.
[0072] Example 3
[0073] The preparation method of magnesium-chromium hydrotalcite with ultra-large specific surface area provided in this embodiment includes the following specific steps:
[0074] (1) Dissolve 50 mmol magnesium sulfate, 10 mmol hydrated chromium sulfate and 30 mmol sodium metaborate in 50 mL of ultrapure water and stir until completely dissolved to obtain a mixed salt solution. The molar ratio of magnesium ions to chromium ions is 5:1.
[0075] (2) Prepare a 2 mol / L sodium hydroxide solution as an alkaline solution. Under nitrogen protection, the mixed salt solution and alkaline solution from step (1) are simultaneously added dropwise to the reaction vessel, and the mixture is stirred vigorously. The dropwise addition rate is controlled to strictly maintain the pH value of the reaction system at 10. After the addition is complete, the mixture is stirred at 40°C for 2 hours to obtain magnesium chromium hydrotalcite with a large specific surface area.
[0076] (3) The precipitate obtained in step (2) is separated by centrifugation, washed twice with acetone and once with ethanol, and then vacuum dried at 80°C for 6 hours to obtain magnesium chromium hydrotalcite with ultra-large specific surface area.
[0077] Testing revealed that the specific surface area of the magnesium-chromium hydrotalcite prepared in this embodiment was 512 m². 2 / g, with a mesoporous structure and an average pore size of about 3-4 nm. The interlayer anion is borate ion, and it has a regular layered structure.
[0078] Comparative Example 1
[0079] This comparative example provides a conventional method for preparing carbonate-intercalated magnesium chromium hydrotalcite, the specific steps of which are as follows:
[0080] (1) Dissolve 30 mmol magnesium nitrate hexahydrate and 10 mmol chromium nitrate nonahydrate in 50 mL of ultrapure water and stir until completely dissolved to obtain a mixed salt solution.
[0081] (2) Preparation of alkaline solution: a mixed solution of 1 mol / L sodium hydroxide and 0.1 mol / L sodium carbonate. Under nitrogen protection, the mixed salt solution and alkaline solution from step (1) were simultaneously added dropwise to the reaction vessel, and the mixture was stirred vigorously. The addition rate was controlled to maintain the pH of the reaction system at 9.0. After the addition was complete, the reaction was stirred for another hour to obtain magnesium chromium hydrotalcite precipitate with carbonate intercalation.
[0082] (3) The precipitate obtained in step (2) was separated by centrifugation, washed twice with acetone and twice with methanol, and then vacuum dried at 60°C for 12 hours to obtain conventional magnesium chromium hydrotalcite (sample number MgCr-LDH).
[0083] Testing showed that the specific surface area of the conventional magnesium-chromium hydrotalcite prepared in this comparative example was 40.7 m². 2 / g.
[0084] Application Example 1
[0085] The magnesium chromium hydrotalcite (MgCr-H) with ultra-large specific surface area prepared in Example 1 was used for the adsorption isotherm experiment of uranyl ions.
[0086] Six mg of MgCr-H was placed in a 100 mL beaker, and 100 mL of uranyl nitrate solution with different initial concentrations (10-200 mg / L) was added. The mixture was magnetically stirred at room temperature for 24 hours until adsorption equilibrium was reached. The supernatant was filtered through a 0.22 μm filter membrane, and the concentration of remaining uranium was determined by ICP-OES. The results showed that the maximum adsorption capacity of MgCr-H for uranium was 2542 mg / g.
[0087] Application Example 2
[0088] Natural seawater (uranium concentration approximately 3.24 μg / L) was collected. 10 mg of MgCr-H was added to a 100 mL beaker, followed by 100 mL of natural seawater. The mixture was magnetically stirred at room temperature for 1 hour. The supernatant was filtered, and the uranium concentration was determined by ICP-MS. The results showed that MgCr-H had an extraction efficiency of over 90% for uranium from seawater.
[0089] Application Example 3
[0090] The MgCr-H prepared in Example 1 was used for single adsorption experiments of cadmium, arsenic and lead.
[0091] Prepare Cd-containing 2+ AsO2 - Pb 2+ The initial concentration of each salt solution was 1000 mg / L. 50 mg of MgCr-H was added to 50 mL of the above solution, and the mixture was magnetically stirred at room temperature for 24 hours until adsorption equilibrium was reached. The supernatant was filtered, and the concentration of remaining metal ions was determined by ICP-OES. The results showed that MgCr-H had an adsorption capacity of 1053.4 mg / g for cadmium, 667.2 mg / g for arsenic, and 1414.6 mg / g for lead.
[0092] Application Example 4
[0093] The MgCr-H prepared in Example 1 was used for a mixed adsorption experiment of cadmium and arsenic.
[0094] Formulating Pb 2+ Cd 2+ and AsO2 - A mixed solution was prepared, with each of the three components initially concentrated at 500 mg / L. 25 mg of MgCr-H was added to 50 mL of this mixed solution, and the mixture was magnetically stirred at room temperature for 24 hours until adsorption equilibrium was reached. The supernatant was filtered, and the concentration of remaining metal ions was determined by ICP-OES. The results showed that MgCr-H had an adsorption capacity of 519.8 mg / g for cadmium, 449.1 mg / g for arsenic, and 596.2 mg / g for lead.
[0095] The materials and test results in the embodiments, comparative examples, and application examples are further illustrated with reference to the accompanying drawings:
[0096] Figure 1 XRD comparison diagram of the ultra-large specific surface area magnesium-chromium hydrotalcite prepared in Example 1 of the present invention and the conventional magnesium-chromium hydrotalcite prepared in Comparative Example 1.
[0097] from Figure 1 It can be seen that the ultra-large specific surface area magnesium chromium hydrotalcite (MgCr-H) prepared in Example 1 of the present invention exhibits typical characteristic diffraction peaks such as (003) and (006) in the low-angle region. The peaks are sharp and the baseline is stable, indicating that the material has a regular layered structure and good crystallinity.
[0098] Figure 2 This is a TEM image of the magnesium-chromium hydrotalcite with ultra-large specific surface area prepared in Example 1 of the present invention;
[0099] from Figure 2 As can be seen, the ultra-large specific surface area magnesium chromium hydrotalcite prepared in Example 1 of the present invention exhibits an ultra-thin two-dimensional sheet-like morphology with uniform sheet size, curled edges, and a thickness of about 5-10 nm, showing typical few-layer / monolayer characteristics.
[0100] Figure 3 The nitrogen adsorption-desorption isotherm of the magnesium-chromium hydrotalcite with ultra-large specific surface area prepared in Example 1 of this invention;
[0101] from Figure 3 It can be seen that the nitrogen adsorption-desorption isotherm of the ultra-large specific surface area magnesium chromium hydrotalcite prepared in Example 1 of the present invention belongs to the type IV isotherm. A significant H3 type hysteresis loop appears in the relative pressure range of P / P0=0.4-1.0, indicating that there is a rich mesoporous structure in the material.
[0102] Figure 4The pore size distribution curve of the ultra-large specific surface area magnesium-chromium hydrotalcite prepared in Example 1 of the present invention is shown.
[0103] from Figure 4 It can be seen that the pore size distribution of the ultra-large specific surface area magnesium chromium hydrotalcite prepared in Example 1 of the present invention is mainly concentrated in 3-4 nm, showing a narrow distribution characteristic, which further confirms that the material has a uniform mesoporous structure.
[0104] Figure 5 The image shows a comparison of the FTIR of the ultra-large specific surface area magnesium-chromium hydrotalcite prepared in Example 1 of the present invention and the conventional magnesium-chromium hydrotalcite prepared in Comparative Example 1.
[0105] from Figure 5 It can be seen that, compared with the MgCr-LDH prepared in Comparative Example 1, the MgCr-H prepared in Example 1 of this invention has a temperature range of ~1387 cm⁻¹. -1 A new BO characteristic absorption peak appeared at the point, while the characteristic peak of carbonate was significantly weakened, indicating that borate ions successfully inserted into the interlayer of hydrotalcite.
[0106] Figure 6 A comparison chart of the BET specific surface area of the ultra-large specific surface area magnesium-chromium hydrotalcite prepared in Example 1 of the present invention and the conventional magnesium-chromium hydrotalcite prepared in Comparative Example 1.
[0107] from Figure 6 It can be seen that the BET specific surface area of MgCr-H prepared in Example 1 of this invention is as high as 530 m². 2 / g, while the specific surface area of MgCr-LDH prepared in Comparative Example 1 was only 40.7 m². 2 / g, the former is about 13 times that of the latter, indicating that the method of the present invention significantly improves the specific surface area of the material.
[0108] Figure 7 The XPS full spectrum of the magnesium-chromium hydrotalcite with ultra-large specific surface area prepared in Example 1 of this invention before and after uranium adsorption.
[0109] from Figure 7 As can be seen, after the magnesium-chromium hydrotalcite with ultra-large specific surface area prepared in Example 1 of the present invention adsorbs uranium, a significant U 4f characteristic peak appears in the XPS full spectrum, indicating that uranium has been successfully adsorbed onto the material surface; at the same time, the peaks of elements such as Mg, Cr, O, and B still exist, indicating that the material structure remains stable during the adsorption process.
[0110] Figure 8 This is a fitted diagram of the adsorption isotherm of uranium on the ultra-large specific surface area magnesium-chromium hydrotalcite prepared in Example 1 of this invention.
[0111] from Figure 8It can be seen that the adsorption isotherm of uranium by the ultra-large specific surface area magnesium chromium hydrotalcite prepared in Example 1 of the present invention conforms to the Langmuir model, and the theoretical maximum adsorption capacity obtained by fitting is 2542 mg / g, indicating that the material has excellent adsorption capacity for uranyl ions.
[0112] Figure 9 The graph shows the uranium extraction efficiency of the ultra-large specific surface area magnesium-chromium hydrotalcite prepared in Example 2 of this invention in real seawater.
[0113] from Figure 9 As can be seen, in real seawater (initial uranium concentration of about 3.24 μg / L), the uranium extraction efficiency of the ultra-large specific surface area magnesium chromium hydrotalcite prepared in Example 1 of this invention exceeds 90% within 1 hour, demonstrating a rapid and efficient trace uranium capture capability.
[0114] Figure 10 The bar chart shows the adsorption capacity of cadmium, arsenic, and lead for the ultra-large specific surface area magnesium-chromium hydrotalcite in Application Example 3 of this invention.
[0115] from Figure 10 As can be seen, the magnesium-chromium hydrotalcite with ultra-large specific surface area prepared in Example 1 of the present invention has single adsorption capacities of 667.2 mg / g, 1414.6 mg / g and 1053.4 mg / g for arsenic, lead and cadmium respectively, and exhibits excellent removal performance for a variety of heavy metal ions.
[0116] Figure 11 This is a bar chart showing the adsorption capacity of cadmium and arsenic in a mixed system using magnesium-chromium hydrotalcite with a large specific surface area in Application Example 4 of this invention.
[0117] from Figure 11 It can be seen that in the mixed system where cadmium, arsenic, and lead coexist, the magnesium chromium hydrotalcite with ultra-large specific surface area prepared in Example 1 of this invention has adsorption capacities of 449.1 mg / g, 596.2 mg / g, and 519.8 mg / g for arsenic, lead, and cadmium, respectively, showing a significant synergistic adsorption effect.
[0118] The magnesium-chromium layered double hydroxide (TLH) with ultra-large specific surface area prepared in this invention exhibits excellent adsorption performance for heavy metal ions. Experiments show that the LDH prepared in this invention has a large adsorption capacity for uranium; in real seawater, the uranium extraction efficiency is high. In single heavy metal ion systems, the adsorption capacity of this material for cadmium, arsenic, and lead is significantly improved; in mixed systems where cadmium, arsenic, and lead coexist, it still demonstrates a broad-spectrum and highly efficient removal ability for multiple heavy metal ions, and the adsorption performance is further improved in mixed systems.
[0119] The present invention has been described above by way of example with reference to the embodiments and accompanying drawings. Obviously, the implementation of the present invention is not limited to the above-described manner. Any improvements made by adopting the inventive concept and technical solution of the present invention, or the direct application of the inventive concept and technical solution of the present invention to other occasions without modification, are all within the protection scope of the present invention.
Claims
1. A magnesium-chromium hydrotalcite with an ultra-large specific surface area, characterized in that: The specific surface area of the aforementioned magnesium-chromium hydrotalcite with ultra-large specific surface area is 500-600 m². 2 / g, the interlayer anion is borate ion, and it has a regular layered structure.
2. The magnesium-chromium hydrotalcite with ultra-large specific surface area according to claim 1, characterized in that: The pore size distribution of the ultra-large specific surface area magnesium chromium hydrotalcite is mesoporous, with an average pore size of 3-4 nm.
3. A method for preparing the ultra-large specific surface area magnesium-chromium hydrotalcite according to any one of claims 1-2, characterized in that, Includes the following steps: Step (1): Mix magnesium salt, chromium salt, borate ion source with water to obtain a mixed salt solution; Step (2): Mix the alkaline solution with the mixed salt solution from step (1) to carry out a co-precipitation reaction to obtain borate-intercalated magnesium chromium hydrotalcite; Step (3): The borate-intercalated magnesium chromium hydrotalcite obtained in step (2) is washed with an organic solvent and dried to obtain the magnesium chromium hydrotalcite with ultra-large specific surface area.
4. The method for preparing ultra-large specific surface area magnesium-chromium hydrotalcite according to claim 3, characterized in that: In step (1), the magnesium salt is at least one of magnesium nitrate, magnesium chloride, and magnesium sulfate; the chromium salt is at least one of chromium nitrate, chromium chloride, and chromium sulfate; and the borate ion source is at least one of boric acid, borax, and sodium metaborate.
5. The method for preparing ultra-large specific surface area magnesium-chromium hydrotalcite according to claim 3, characterized in that: In step (1), the molar ratio of magnesium ions in magnesium salt to chromium ions in chromium salt is (2-5):1, and the molar ratio of chromium ions to borate ions is 1:(1-3).
6. The method for preparing ultra-large specific surface area magnesium-chromium hydrotalcite according to claim 3, characterized in that: In step (2), the alkaline solution is a sodium hydroxide solution with a concentration of 0.5-2 mol / L; The pH value of the coprecipitation reaction is 8.5-10, the reaction temperature is room temperature to 80℃, and the reaction time is 0.5-2 hours.
7. The method for preparing ultra-large specific surface area magnesium-chromium hydrotalcite according to claim 3, characterized in that: In step (3), the organic solvent is one of acetone, methanol, ethanol, or a mixture thereof; The drying method is vacuum drying, the drying temperature is 40-80℃, and the drying time is 6-24 hours.
8. The method for preparing ultra-large specific surface area magnesium-chromium hydrotalcite according to claim 7, characterized in that: In step (3), the organic solvent washing is performed by washing with acetone and ethanol in sequence, or by washing with acetone and methanol in sequence.
9. The application of the ultra-large specific surface area magnesium-chromium hydrotalcite as described in any one of claims 1-2 in the adsorption of uranium, arsenic, lead, and cadmium.
10. The application according to claim 9, characterized in that, The specific applications are seawater uranium extraction, uranium-containing wastewater treatment, or treatment of wastewater containing arsenic, lead, or cadmium.