Rubidium and cesium ion selective adsorbent based on porous metal organic framework material and preparation method of rubidium and cesium ion selective adsorbent

Abstract

The invention belongs to the field of selective adsorbents, and particularly relates to a rubidium cesium ion selective adsorbent based on a porous metal organic framework material and a preparation method thereof, and the preparation method comprises the following steps: covalently embedding a crown ether derivative functional monomer into a zirconium-based MOF skeleton, and carrying phosphomolybdic acid or phosphotungstic acid in a limited range. The adsorbent realizes high-selectivity adsorption of rubidium and cesium ions under the background of high-concentration alkali metal through the size matching effect of crown ether and the ion exchange synergistic effect of heteropoly acid, and has structural stability and cyclic regeneration performance.

Description

Technical Field

[0001] This invention relates to the field of selective adsorbent technology, specifically to a rubidium-cesium ion selective adsorbent based on porous metal-organic framework materials and its preparation method. Background Technology

[0002] Currently, common extraction methods for rubidium and cesium from salt lake brines mainly include precipitation, extraction, and adsorption, each with its own advantages and disadvantages. Precipitation is complex, the precipitate is unstable, the precipitant is expensive, and separation is difficult. Extraction uses expensive extractants that are easily lost, causing environmental pollution. Adsorption, if using powdered adsorbents, presents industrial separation difficulties; however, considering the high content and low concentration characteristics of salt lake brines, this method offers high selectivity, convenient operation, simple process, high recovery rate, and ease of industrialization, making it considered the most promising production method for separating and extracting rubidium and cesium from salt lake brines. Considering the characteristics of salt lake brines, adsorption is a more suitable method for extracting rubidium and cesium resources from complex brines.

[0003] The key to adsorption methods lies in the preparation of high-performance adsorbents to overcome the interference of numerous coexisting alkali / alkaline earth metal ions in brine. The adsorbents also require stable adsorption-desorption performance, suitability for large-scale cyclic operation, ease of manufacture, and environmental friendliness. Currently, common porous materials include zeolites, activated carbon, mesoporous silica, carbon nanotubes, graphene oxide, metal-organic frameworks, and porous organic polymers, which have received widespread attention in wastewater treatment. However, while activated carbon has a high specific surface area and porosity, its amorphous pore structure leads to low adsorption selectivity. Although zeolite molecular sieves possess ordered porous structures and are widely used in porous material research, their selectivity for specific alkali metals (such as rubidium and cesium) is not very high. Furthermore, traditional porous adsorbents, represented by zeolites, are limited by low production efficiency, demanding synthesis conditions, and difficulties in post-functionalization. In addition, their application is hampered by low adsorption capacity and poor selectivity due to a lack of effective adsorption sites.

[0004] Metal-organic frameworks (MOFs) have shown promising applications in ion adsorption and separation due to their high specific surface area, tunable pore structure, and abundant functionalization sites. In recent years, researchers have attempted to combine MOFs with highly selective inorganic adsorption components to address the extraction needs of rare alkali metal ions such as rubidium and cesium, in order to balance structural stability and adsorption performance.

[0005] Patent CN115703060A proposes a magnetic bimetallic MOF rubidium and cesium adsorbent (Fe3O4@CMC@FeMn-MOF), which achieves rapid separation of the adsorbent by introducing Fe3O4 magnetic cores and utilizes the bimetallic MOF to enhance structural stability and adsorption capacity. However, the functional recognition unit of this adsorbent is still the metal node or ligand of the MOF itself, lacking targeted design based on the size and coordination characteristics of rubidium and cesium ions. Furthermore, the introduction of magnetic components may occupy part of the pore space, affecting mass transfer efficiency. In addition, the magnetic particles pose a risk of oxidation or dissolution when used in strong acid or high salt systems for a long time, which may affect the material's cycle stability.

[0006] In summary, existing MOF-based rubidium-cesium adsorbents still have room for improvement in terms of specific recognition site construction, selectivity in complex brine systems, and long-term operational stability. Therefore, it is necessary to develop a rubidium-cesium ion adsorbent based on porous metal-organic framework materials that combines high selective recognition with excellent stability, as well as its preparation method. Summary of the Invention

[0007] The purpose of this invention is to provide a rubidium-cesium ion selective adsorbent based on porous metal-organic framework materials and its preparation method, thereby solving the aforementioned problems. This can be achieved through the following technical solutions: A method for preparing a rubidium-cesium ion selective adsorbent based on porous metal-organic framework materials includes the following steps: S1: A precursor mixed solution is formed by dissolving a zirconium source, a carboxylic acid organic ligand, and a crown ether derivative functional monomer in a polar aprotic solvent; the zirconium source is zirconium oxychloride or zirconium nitrate. S2: Add a regulator to the precursor mixture solution, heat the reaction to obtain zirconium-based metal-organic framework crystals containing crown ether functionalized sites; S3: The obtained zirconium-based metal-organic framework crystal containing crown ether functionalized sites was washed with a polar solvent and then dried under vacuum to obtain crown ether functionalized MOF; S4: Disperse the crown ether functionalized MOF in deionized water, add phosphomolybdic acid or phosphotungstic acid to react; allow the heteropolyacid anions to combine with the protonated hydroxyl groups in the MOF framework through electrostatic interaction, and achieve in-situ loading through the MOF channel confinement effect; S5: Centrifuge the reaction product obtained in step S4, wash it alternately with deionized water and ethanol, and vacuum dry it to obtain the rubidium-cesium ion selective adsorbent based on porous metal-organic framework material.

[0008] Further, in step S1, the carboxylic acid organic ligand is 2,5-dihydroxyterephthalic acid or 2-aminoterephthalic acid.

[0009] Furthermore, the crown ether derivative functional monomer is 4′-carboxybenzo-15-crown-5 or 4′-carboxybenzo-18-crown-6.

[0010] Furthermore, the polar aprotic solvent is N,N-dimethylformamide or N,N-dimethylacetamide.

[0011] Furthermore, in step S1, the molar ratio of zirconium source, carboxylic acid organic ligand and crown ether derivative functional monomer is 1:0.8~1.2:0.1~0.3.

[0012] Further, in step S1, the concentration of the zirconium source in the precursor mixed solution is 0.01~0.05 mol / L.

[0013] Further, in step S2, the regulator is formic acid or acetic acid, the molar ratio of regulator to zirconium source is 30~100:1, and the hydrothermal reaction is carried out at 80~120℃ for 24~72h.

[0014] Furthermore, in step S3, the vacuum drying temperature is 70~90℃ and the drying time is 16~20h.

[0015] Furthermore, in step S4, phosphomolybdic acid or phosphotungstic acid participates in the reaction in solution form, and the concentration of the phosphomolybdic acid solution or phosphotungstic acid solution is 0.01~0.1 mol / L; The mass ratio of phosphomolybdic acid or phosphotungstic acid to crown ether functionalized MOF is controlled at 0.1~0.5:1, and the reaction is carried out by stirring at 25~40℃ for 6~24h. In step S5, the vacuum drying temperature is 50~80℃ and the vacuum drying time is 12~24h.

[0016] Secondly, a rubidium-cesium ion selective adsorbent based on porous metal-organic framework materials is prepared using the above-mentioned preparation method.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The adsorbent of this invention comprises a zirconium-based metal-organic framework, covalently intercalated crown ether derivative functional groups, and phosphomolybdic acid or phosphotungstic acid anions confined within the pores. After soaking in an aqueous solution with pH 3-10 for 7 days, the adsorbent retains a framework crystallinity of over 90% and a heteropolyacid loss rate of less than 5%. The partition coefficient Kd of the adsorbent for rubidium ions is not less than 15000 ml / g in simulated brine containing 1000 mg / L potassium ions, and the Kd value for cesium ions is not less than 12000 ml / g. After 5 adsorption-desorption cycles, the adsorbent retains an adsorption capacity of not less than 92% for rubidium and cesium.

[0018] 2. This invention constructs a dual recognition mechanism in a single material by covalently integrating a molecular recognition unit (crown ether) into the MOF framework and synergistically confining and loading a highly selective inorganic adsorbent phase (heteropolyacid acid salt). On the one hand, the crown ether ring provides specific recognition based on ion size and coordination geometry; on the other hand, the heteropolyacid anion captures rubidium and cesium cations through an ion exchange mechanism. The synergistic effect of these two mechanisms significantly improves the performance of rubidium adsorption at high Na+ concentrations. + K + Selectivity in this context. Simultaneously, the high stability of zirconium-based MOFs and the confined encapsulation of heteropolyacids effectively suppress the loss of active components, ensuring long-term operational performance. This technical solution does not rely on magnetic components, avoiding the risks of pore blockage and metal leaching, and is suitable for the efficient extraction of rubidium and cesium resources from complex systems such as strongly acidic brine lakes and nuclear waste liquids. Detailed Implementation

[0019] The present invention will be further described in detail below through specific embodiments.

[0020] The following detailed description of embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0021] Example 1 Selection of functional monomers for crown ether derivatives: In this example, the crown ether is 4′-carboxybenzo-15-crown-5 (CAS No. 56683-55-7).

[0022] Adsorbent preparation: S1: Add 1.23g (4mmol) zirconium oxychloride, 0.82g (4mmol) 2-aminoterephthalic acid, and 0.28g (0.8mmol) of the above crown ether derivative functional monomers to 40ml of N,N-dimethylformamide and sonicate for 20min to obtain a clear solution.

[0023] S2: Add 1.44g (30mmol) of formic acid, transfer to a 50ml polytetrafluoroethylene reactor, and hydrothermally react at 100℃ for 48h.

[0024] S3: Collect crystals by centrifugation, wash three times with N,N-dimethylformamide, and dry under vacuum at 80℃ for 18h to obtain crown ether functionalized MOF.

[0025] S4: Take 0.5g of crown ether functionalized MOF and ultrasonically disperse it in 50ml of deionized water. Add 0.15g of phosphomolybdic acid and stir at 30℃ and 300r / min for 12h.

[0026] S5: Centrifuge, wash three times with alternating water and ethanol, and vacuum dry at 60℃ for 18h to obtain adsorbent A1.

[0027] Example 2 The crown ether derivative functional monomer was 4′-carboxybenzo-18-crown-6 (CAS No. 60835-75-8), and the rest was the same as in Example 1, to obtain adsorbent A2.

[0028] Example 3 In step S4, phosphomolybdic acid is replaced with phosphotungstic acid, and the rest is the same as in Example 1, to obtain adsorbent A3.

[0029] Reference ratio 1 In this example, the crown ether derivative functional monomer is 4′-nitrobenzo-15-crown-5 (CAS No. 34508-51-7), and the rest is the same as in Example 1, resulting in adsorbent A4.

[0030] Reference ratio 2 In this example, the crown ether derivative functional monomer is 4′-aminobenzo-18-crown-6 (CAS No. 68833-70-3), and the rest is the same as in Example 1, resulting in adsorbent A5.

[0031] Comparative Example 1 Without adding crown ether derivative functional monomers, the rest is the same as in Example 1, resulting in adsorbent D1.

[0032] Comparative Example 2 Without performing step S4, i.e. without loading heteropoly acid (phosphomolybdic acid), the rest is the same as in Example 1, yielding adsorbent D2.

[0033] Comparative Example 3 First, MOF was synthesized, and then crown ether derivative functional monomers and heteropoly acids were added by physical mixing method. The rest was the same as in Example 1 to obtain adsorbent D3.

[0034] Comparative Example 4 In this example, the crown ether derivative functional monomer is 4′,4′′-dicarboxy-dibenzo-18-crown-6 (CAS No. 66814-87-1), and the rest is the same as in Example 1, to obtain adsorbent D4.

[0035] In this example, the core of the crown ether derivative functional monomer is dibenzo-18-crown-6, which has one more benzene ring than a monobenzo-ring; it has two carboxyl groups and can be used to construct more complex coordination networks or polymers.

[0036] Comparative Example 5 In this example, the crown ether derivative functional monomer is 4′-carboxybenzo-12-crown-4 (CAS No. 131069-91-7), and the rest is the same as in Example 1, to obtain adsorbent D5.

[0037] In this example, the parent nucleus of the crown ether derivative functional monomer is benzo-12-crown-4, and the crown ether ring is smaller (12-membered ring).

[0038] The adsorbent of the present invention comprises a zirconium-based metal-organic framework, covalently intercalated crown ether derivative functional groups (crown ether derivative functional monomers), and phosphomolybdic acid or phosphotungstic acid anions confined and loaded within the pores.

[0039] The zirconium-based metal-organic framework consists of a three-dimensional network structure formed by the coordination linkage of Zr6O4(OH)4 metal clusters with carboxylic acid organic ligands and crown ether derivative functional monomers, with a specific surface area of ​​800~1500 m². 2 / g, with pore size distribution concentrated in 0.8~1.5nm; the crown ether derivative functional group is coordinated with the zirconium cluster through the carboxyl group, and its crown ether ring faces the inside of the pore, forming a size-selective recognition cavity; the phosphomolybdic acid or phosphotungstic acid anion forms an ion pair with the protonated amino or hydroxyl groups on the framework and is confined in the MOF micropore space, and cannot migrate freely.

[0040] In some embodiments, the grafting density of crown ether functional groups in the adsorbent is 0.3~0.8 mmol / g material, and the loading of phosphomolybdic acid or phosphotungstic acid is 8~25 wt%. The grafting density is determined by elemental analysis combined with titration, and the loading is calculated by converting the molybdenum or tungsten content determined by inductively coupled plasma optical emission spectrometry (ICP-OES).

[0041] After being soaked in an aqueous solution with a pH of 3-10 for 7 days, the adsorbent retained more than 90% of its framework crystallinity and less than 5% of its heteropolyacids. Crystallinity was calculated by comparing the integral area of ​​the main peak intensity in the X-ray powder diffraction (XRD) pattern with that of the original sample, and the loss rate was calculated by measuring the concentration of molybdenum or tungsten in the soaking solution.

[0042] The partition coefficient Kd of the adsorbent for rubidium ions is not less than 15000 ml / g in simulated brine containing 1000 mg / L potassium ions, and the Kd value for cesium ions is not less than 12000 ml / g. The Kd value is calculated using the formula Kd = (C... D - C e ) / C e Calculated by × V / m, where C D and C e The initial and adsorption equilibrium concentrations are (mg / L), V is the solution volume (mL), and m is the adsorbent mass (g).

[0043] After five adsorption-desorption cycles, the adsorbent retains at least 92% of its rubidium and cesium adsorption capacity. The desorption process utilizes a 0.5–2 mol / L ammonium nitrate or ammonium chloride solution, eluted at 25–40°C for 1–3 hours with shaking, achieving selective desorption of rubidium and cesium ions and adsorbent regeneration.

[0044] The adsorbent has a particle size of 0.5~5μm and can be made into millimeter-sized particles for use in fixed-bed adsorption columns by tableting or granulation. During granulation, a 5% (w / w) polyvinyl alcohol aqueous solution is added as a binder, and the tableting pressure is 10MPa.

[0045] The above adsorbent was placed in a solution containing 1000 mg / L K + 100 mg / L Rb + 100 mg / L Cs + The adsorption performance was tested in simulated brine (pH=5), and the results are shown in Table 1: Table 1

[0046] As shown in the table, the adsorbent obtained in the embodiments of the present invention performs well at high K. + Background of Rb + Cs + All three exhibited high Kd values ​​and excellent cycling stability. Comparative Example 1 showed a significant decrease in selectivity due to the lack of crown ether recognition sites; Comparative Example 2 had insufficient adsorption capacity and stability due to the absence of heteropolyacid synergy; and Comparative Example 3 had the worst cycling performance due to the easy loss of active components caused by non-covalent integration.

[0047] As can be seen from reference ratios 1 and 2, compared to carboxyl groups, amino and nitro groups are generally difficult to coordinate with zirconium clusters to form a stable structure.

[0048] As shown in Comparative Examples 4 and 5, for functional monomers of crown ether derivatives containing the same carboxyl group but with different crown ether cores, the spatial dimensions of the size-selective recognition cavity formed by the coordination of the carboxyl group with the zirconium cluster are not significantly different. Therefore, for Rb + Cs + The Kd values ​​exhibited by all examples were not significantly different from those in Example 1; however, the different crown ether core structures had a significant impact on the complexity and stability of the three-dimensional network structure, which in turn greatly affected the capacity retention rate after multiple cycles of use.

[0049] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the invention.

[0050] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing a rubidium and cesium ion selective adsorbent based on a porous metal-organic framework material, characterized in that, The method comprises the following steps: S1: dissolving a zirconium source, a carboxylic organic ligand and a crown ether derivative functional monomer in a polar aprotic solvent to form a precursor mixed solution; the zirconium source is zirconyl chloride or zirconium nitrate, S2: adding an adjusting agent to the precursor mixed solution and heating to react to obtain a zirconium-based metal organic framework crystal containing a crown ether functional site; S3: washing the obtained zirconium-based metal organic framework crystal containing a crown ether functional site with a polar solvent and vacuum drying to obtain a crown ether functional MOF; S4: dispersing the crown ether functional MOF in deionized water and adding phosphomolybdic acid or phosphotungstic acid to react; S5: centrifuging the reaction product obtained in step S4, washing with deionized water and ethanol alternately, and vacuum drying to obtain the rubidium and cesium ion selective adsorbent based on the porous metal organic framework material.

2. The method of claim 1, wherein the method comprises: (a) providing a porous metal-organic framework material; (b) modifying the porous metal-organic framework material with a functional group; (c) modifying the functional group with a polyamine; and (d) modifying the polyamine with a quaternary ammonium group. In step S1, the carboxylic organic ligand is 2,5-dihydroxyterephthalic acid or 2-amino terephthalic acid.

3. The method of claim 1, wherein the method comprises: (a) synthesizing a porous metal organic framework material; (b) modifying the porous metal organic framework material with a functional group; (c) modifying the functional group with a polyamine; and (d) modifying the polyamine with a quaternary ammonium group. The crown ether derivative functional monomer is 4'-carboxybenzo-15-crown-5 or 4'-carboxybenzo-18-crown-6.

4. The method of claim 1, wherein the method comprises: (a) synthesizing a porous metal organic framework material; (b) modifying the porous metal organic framework material with a functional group; (c) modifying the functional group with a polyamine; and (d) modifying the polyamine with a quaternary ammonium group. The polar aprotic solvent is N,N-dimethylformamide or N,N-dimethylacetamide.

5. The method of claim 1, wherein the method comprises: (a) synthesizing a porous metal organic framework material; (b) modifying the porous metal organic framework material with a functional group; (c) modifying the functional group with a polyamine; and (d) modifying the polyamine with a quaternary ammonium group. In step S1, the molar ratio of the zirconium source, the carboxylic organic ligand and the crown ether derivative functional monomer is 1:0.8-1.2:0.1-0.

3.

6. The method of claim 1, wherein the method comprises: (a) synthesizing a porous metal organic framework material; (b) modifying the porous metal organic framework material with a functional group; (c) modifying the functional group with a polyamine; and (d) modifying the polyamine with a quaternary ammonium group. In step S1, the concentration of the zirconium source in the precursor mixed solution is 0.01-0.05 mol / L.

7. The method of claim 1, wherein the method comprises: (a) synthesizing a porous metal organic framework material; (b) modifying the porous metal organic framework material with a functional group; (c) modifying the functional group with a polyamine; and (d) modifying the polyamine with a quaternary ammonium group. In step S2, the adjusting agent is formic acid or acetic acid, the molar ratio of the adjusting agent to the zirconium source is 30-100:1, and the hydrothermal reaction is carried out at 80-120°C for 24-72h.

8. The method of claim 1, wherein the method comprises: (a) synthesizing a porous metal organic framework material; (b) modifying the porous metal organic framework material with a functional group; (c) modifying the functional group with a polyamine; and (d) modifying the polyamine with a quaternary ammonium group. In step S3, the vacuum drying temperature is 70-90°C, and the drying time is 16-20h.

9. The method of claim 1, wherein the method comprises: (a) synthesizing a porous metal organic framework material; (b) modifying the porous metal organic framework material with a functional group; (c) modifying the functional group with a polyamine; and (d) modifying the polyamine with a quaternary ammonium group. In step S4, the phosphomolybdic acid or phosphotungstic acid participates in the reaction in the form of a solution, and the concentration of the phosphomolybdic acid solution or the phosphotungstic acid solution is 0.01-0.1 mol / L; and / or, The mass ratio of the phosphomolybdic acid or phosphotungstic acid to the crown ether functional MOF is controlled to be 0.1-0.5:1, and the stirring reaction is carried out at 25-40°C for 6-24h; and / or, In step S5, the vacuum drying temperature is 50-80°C, and the vacuum drying time is 12-24h.

10. A rubidium and cesium ion selective adsorbent based on a porous metal organic framework material, characterized in that: The preparation method is prepared by any one of claims 1-9. The preparation method is prepared by any one of claims 1-9.

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