A metal-doped functionalized mil-53 type metal-organic framework adsorbent and its application in lithium extraction and lithium isotope separation

Abstract

The application discloses a metal-doped functionalized MIL-53 type metal organic framework adsorbent and application thereof in lithium extraction and lithium isotope separation, and a preparation method thereof. + The adsorbent is Li The application provides a specific adsorption microenvironment, so that lithium ions in a lithium-containing aqueous solution can be adsorbed and enriched. Through a continuous optimization route of "metal center screening-ligand functionalization-heterometal in-situ doping", the lithium adsorption performance of the MIL-53 type MOF can be effectively improved.

Description

Technical Field

[0001] This invention belongs to the technical fields of lithium resource extraction, adsorption and separation materials, bi / multi-metal-organic framework materials, lithium isotope separation, and resource utilization of salt lake brine. Specifically, it relates to a metal-doped functionalized MIL-53 type metal-organic framework adsorbent, its preparation method, and its application. Background Technology

[0002] Lithium, as a core element in new energy batteries, controlled nuclear fusion, and strategic nuclear energy devices, has seen its resource security elevated to a national strategic level. Liquid resources such as salt lake brines, underground brines, seawater concentrates, and leachate from spent batteries contain enormous lithium reserves. However, these complex water bodies generally contain extremely high background levels of sodium (Na). + K + Ca 2+ Mg 2+ Coexisting interfering ions. Especially in complex salt lake systems with high magnesium-to-lithium ratios, Mg 2+ The high concentration of lithium and its hydration radius, which is very close to that of Li+, make it extremely difficult for conventional materials to selectively capture lithium.

[0003] Metal-organic frameworks (MOFs) have shown great promise in solid-phase lithium extraction due to their porous crystalline characteristics and tunable pore microenvironments. However, most current research is still limited to a parent framework with a single metal center or simple ligand surface modification. The local electron cloud density tuning space of a single metal site is limited, making it difficult to handle extremely complex interfering ions or demanding applications. 6 Li / 7 When Li isotopes separate, a single coordination center often cannot provide sufficient zero-point energy difference and spatial confinement barrier.

[0004] Metal doping offers a novel approach to overcoming these bottlenecks. By introducing a second transition metal in situ into the crystal lattice, the original symmetrical local lattice can be broken, constructing non-uniform bimetallic active sites (Fe-OM bridging units) at the nanoscale, thereby drastically altering the degree of electronic localization within the channels. This synergy between the bimetallic center and the ligand functional groups enables stronger short-range asymmetric electrostatic trapping of desolvated Li+, and is significantly amplified by lattice distortion. 6 Li / 7 The difference in vibration frequency between Li.

[0005] However, there is still a lack of systematic and in-depth process and materials science solutions on how to precisely control the in-situ doping ratio of dissimilar metals in the flexible MIL-53 framework and use them in combination for efficient lithium extraction and isotope solid-phase separation.

[0006] The existing technology has the following main shortcomings: (1) Traditional lithium adsorbents have limited structural tuning space, making it difficult to precisely optimize Li at the level of metal nodes, ligand functional groups, and pore microenvironment. + Identification site.

[0007] (2) Existing MOF lithium extraction materials mainly focus on the total adsorption of lithium ions, and have little effect on the adsorption of other materials. 6 Li / 7 There is insufficient research on the separation or enrichment capabilities of Li isotopes.

[0008] (3) Although the MIL-53 type MOF has flexible channels and adjustable structure, the influence of different metal centers and different functional groups on lithium adsorption and lithium isotope fractionation is still unclear.

[0009] (4) Na in complex lithium-containing water systems + K + Mg 2+ Ca 2+ Coexisting ions can interfere with lithium adsorption and subsequent isotope separation.

[0010] (5) Existing lithium isotope separation methods usually have problems such as complex processes, high reagent consumption, high environmental risks or limited separation efficiency. Summary of the Invention

[0011] The purpose of this invention is to overcome the shortcomings of the prior art and provide a metal-doped functionalized MIL-53 type metal-organic framework adsorbent.

[0012] The second objective of this invention is to provide a method for preparing a metal-doped functionalized MIL-53 type metal-organic framework adsorbent.

[0013] The third objective of this invention is to provide an application of a metal-doped functionalized MIL-53 type metal-organic framework adsorbent in lithium extraction.

[0014] The fourth objective of this invention is to provide an application of a metal-doped functionalized MIL-53 type metal-organic framework adsorbent in lithium isotope separation.

[0015] The technical solution of this invention is summarized as follows: A method for preparing a metal-doped functionalized MIL-53 type metal-organic framework adsorbent includes the following steps: (1) Dissolve the main metal salt and the doped metal salt in N,N-dimethylformamide, add 2-hydroxyterephthalic acid, stir until completely transparent, then add hydrofluoric acid aqueous solution dropwise. After the addition is complete, transfer the material into a polytetrafluoroethylene-lined reactor and react at a constant temperature of 120-180 °C for 12-36 h. (2) Cool the product obtained in step (1) to room temperature, separate the solid and liquid, wash the solid with N,N-dimethylformamide at 60-100℃ to remove the liquid on the surface of the solid or between the particles; perform solvent exchange with ethanol; vacuum dry to obtain a metal-doped functionalized MIL-53 type metal-organic framework adsorbent.

[0016] Preferably, the ratio of the main metal salt, doped metal salt, N,N-dimethylformamide, 2-hydroxyterephthalic acid and hydrofluoric acid in step (1) is 0.80-0.95 mmol: 0.05-0.20 mmol: 8-12 mL: 1 mmol: 1 mmol.

[0017] Preferably, the cation of the main metal salt is Fe. 3+ Al 3+ or In 3+ .

[0018] Preferably, the cation of the doped metal salt is Ni. 2+ Co 2+ Mn 2+ Zn 2+ Cu 2+ Mg 2+ or Ca 2+ .

[0019] The above preparation method produces a metal-doped functionalized MIL-53 type metal-organic framework adsorbent.

[0020] The above-mentioned application of a metal-doped functionalized MIL-53 type metal-organic framework adsorbent in lithium extraction.

[0021] The above-mentioned metal-doped functionalized MIL-53 metal-organic framework adsorbent is used in lithium isotope separation.

[0022] Advantages of this invention: This invention provides a metal-doped functionalized MIL-53 type metal-organic framework adsorbent that benefits from the flexible and tunable pore structure of MIL-53 type MOF, the designable bimetallic nodes, the modifiable ligand functional groups, and the localized asymmetric coordination environment introduced by heterometallic doping. This adsorbent can be used for Li... + A specific adsorption microenvironment is provided to achieve the adsorption and enrichment of lithium ions in lithium-containing aqueous solutions. Experimental results show that the lithium adsorption performance of MIL-53 type MOFs can be effectively improved through a continuous optimization route of "metal center screening – ligand functionalization – in-situ heterometallic doping". Among them, Ni10%-OH-MIL-53(Fe) was selected as the preferred adsorbent. Hydroxyl functionalization and in-situ Ni heterometallic doping can synergistically enhance the oxygen-containing sites, asymmetric active units and Li within the pores. +The interaction between the two resulted in an equilibrium lithium adsorption capacity of 34.30 mg·g⁻¹. -1 It can reach adsorption equilibrium in about 120 minutes. In addition, Co10%-OH-MIL-53(Fe) has a maximum lithium isotope separation coefficient of 1.043. Attached Figure Description

[0023] Figure 1 Lithium adsorption capacity of MIL-53 metal-organic framework adsorbents with different metal doping functionalizations.

[0024] Figure 2 The adsorption capacity and separation coefficient of Ni10%-OH-MIL-53(Fe) (prepared in Example 1) for Li+ and coexisting ions.

[0025] Figure 3 The lithium adsorption equilibrium capacity of Ni10%-OH-MIL-53(Fe) in the cyclic regeneration experiment.

[0026] Figure 4 Lithium isotope separation factor for MIL-53 metal-organic framework adsorbents functionalized with different metal doping.

[0027] Figure 5 XRD patterns of M1n-OH-MIL-53(Fe) doped with different metals. Detailed Implementation

[0028] The present invention will be further described below through specific embodiments.

[0029] Preparation of control example OH-MIL-53(Fe): (1) Dissolve the main metal salt (FeCl3·6H2O, 1 mmol) in N,N-dimethylformamide (10 mL), add 2-hydroxyterephthalic acid (1 mmol), stir until completely transparent, and then add hydrofluoric acid aqueous solution (wherein, the amount of hydrofluoric acid is 1 mmol in HF). After the addition is complete, transfer the material into a polytetrafluoroethylene-lined reactor and react at 150 °C for 24 h in a constant temperature solvothermal environment. (2) Cool the product obtained in step (1) to room temperature, separate the solid and liquid, wash the solid with N,N-dimethylformamide at 80°C to remove the liquid on the surface of the solid or between the particles; wash with ethanol; vacuum dry to obtain OH-MIL-53(Fe).

[0030] Example 1 A method for preparing a metal-doped functionalized MIL-53 type metal-organic framework adsorbent (Ni10%-OH-MIL-53(Fe)) includes the following steps: (1) Dissolve the main metal salt (FeCl3·6H2O, 0.9 mmol) and the doped metal salt (NiCl2·6H2O, 0.1 mmol) in N,N-dimethylformamide (10 mL), add 2-hydroxyterephthalic acid (1 mmol), stir until completely transparent, and then add hydrofluoric acid aqueous solution (wherein, the amount of hydrofluoric acid is 1 mmol in HF). After the addition is complete, transfer the material into a polytetrafluoroethylene-lined reactor and react at a constant temperature of 150 °C for 24 h. (2) Cool the product obtained in step (1) to room temperature, separate the solid and liquid, wash the solid with N,N-dimethylformamide at 80°C to remove the liquid on the surface of the solid or between the particles; perform solvent exchange with ethanol; vacuum dry to obtain a metal-doped functionalized MIL-53 type metal-organic framework adsorbent (Ni10%-OH-MIL-53(Fe)).

[0031] Replacing NiCl2·6H2O with Mn(NO3)2·4H2O, Zn(NO3)2·6H2O, Cu(NO3)2·3H2O, Mg(NO3)2·6H2O, and Ca(NO3)2·4H2O respectively, while keeping other aspects the same as in this embodiment, yields: Mn10%-OH-MIL-53(Fe), Zn10%-OH-MIL-53(Fe), Cu10%-OH-MIL-53(Fe), Mg10%-OH-MIL-53(Fe), or Ca10%-OH-MIL-53(Fe).

[0032] Replacing FeCl3·6H2O with Al(NO3)3·9H2O or In(NO3)3·5H2O respectively, while keeping the other aspects the same as in this embodiment, yields: Ni10%-OH-MIL-53(Al) or Ni10%-OH-MIL-53(In).

[0033] Referring to this embodiment, the following can be prepared: Co10%-OH-MIL-53(Fe), Co15%-OH-MIL-53(Fe), Co20%-OH-MIL-53(Fe), Ni20%-OH-MIL-53(Fe), Mn5%-OH-MIL-53(Fe), Mn10%-OH-MIL-53(Fe), and Mn15%-OH-MIL-53(Fe).

[0034] Example 2 A method for preparing a metal-doped functionalized MIL-53 type metal-organic framework adsorbent (Co5%-OH-MIL-53(Fe)) includes the following steps: (1) Dissolve the main metal salt (FeCl3·6H2O, 0.95 mmol) and the doped metal salt (Co(NO3)2·6H2O, 0.05 mmol) in N,N-dimethylformamide (8 mL), add 2-hydroxyterephthalic acid (1 mmol), stir until completely transparent, and then add hydrofluoric acid aqueous solution (wherein, the amount of hydrofluoric acid is 1 mmol in HF). After the addition is complete, transfer the material into a polytetrafluoroethylene-lined reactor and react at 120 °C for 36 h in a constant temperature solvothermal environment. (2) Cool the product obtained in step (1) to room temperature, separate the solid and liquid, wash the solid with N,N-dimethylformamide at 60 °C to remove the liquid on the surface of the solid or between the particles; perform solvent exchange with ethanol; vacuum dry to obtain a metal-doped functionalized MIL-53 type metal-organic framework adsorbent (Co5%-OH-MIL-53(Fe)).

[0035] Replacing Co(NO3)2·6H2O in this embodiment with Mn(NO3)2·4H2O or NiCl2·6H2O respectively, while keeping the rest the same as in this embodiment, yields (Mn5%-OH-MIL-53(Fe)) and (Ni5%-OH-MIL-53(Fe)).

[0036] Example 3 A method for preparing a metal-doped functionalized MIL-53 type metal-organic framework adsorbent (Mn15%-OH-MIL-53(Fe)) includes the following steps: (1) Dissolve the main metal salt (FeCl3·6H2O, 0.85 mmol) and the doped metal salt (Mn(NO3)2·4H2O, 0.15 mmol) in N,N-dimethylformamide (12 mL), add 2-hydroxyterephthalic acid (1 mmol), stir until completely transparent, and then add hydrofluoric acid aqueous solution (wherein, the amount of hydrofluoric acid is 1 mmol in HF). After the addition is complete, transfer the material into a polytetrafluoroethylene-lined reactor and react at a constant temperature of 180 °C for 12 h. (2) Cool the product obtained in step (1) to room temperature, separate the solid and liquid, wash the solid with N,N-dimethylformamide at 100°C to remove the liquid on the surface of the solid or between the particles; perform solvent exchange with ethanol; vacuum dry to obtain a metal-doped functionalized MIL-53 type metal-organic framework adsorbent (Mn15%-OH-MIL-53(Fe)).

[0037] Replacing Mn(NO3)2·4H2O with NiCl2·6H2O, while keeping the rest the same as in this embodiment, yields: (Ni15%-OH-MIL-53(Fe)).

[0038] Example 4 A method for preparing a metal-doped functionalized MIL-53 type metal-organic framework adsorbent (Ni20%-OH-MIL-53(Fe)) includes the following steps: (1) Dissolve the main metal salt (FeCl3·6H2O, 0.8 mmol) and the doped metal salt (NiCl2·6H2O, 0.2 mmol) in N,N-dimethylformamide (10 mL), add 2-hydroxyterephthalic acid (1 mmol), stir until completely transparent, and then add hydrofluoric acid aqueous solution (wherein, the amount of hydrofluoric acid is 1 mmol in HF). After the addition is complete, transfer the material into a polytetrafluoroethylene-lined reactor and react at 150 °C for 24 h in a constant temperature solvothermal environment. (2) Cool the product obtained in step (1) to room temperature, separate the solid and liquid, wash the solid with N,N-dimethylformamide at 80 °C to remove the liquid on the surface of the solid or between the particles; perform solvent exchange with ethanol; vacuum dry to obtain a metal-doped functionalized MIL-53 type metal-organic framework adsorbent (Ni20%-OH-MIL-53(Fe)).

[0039] Replacing NiCl2·6H2O in this embodiment with Mn(NO3)2·4H2O or Co(NO3)2·6H2O, while keeping the other conditions the same as in this embodiment, yields: Mn20%-OH-MIL-53(Fe) or Co20%-OH-MIL-53(Fe).

[0040] The XRD patterns of the above-mentioned metal-doped functionalized MIL-53 metal-organic framework adsorbent are shown in [reference needed]. Figure 5 .

[0041] Example 5 Application of metal-doped functionalized MIL-53 metal-organic framework adsorbent in lithium extraction.

[0042] Prepare a 1.0 g / L LiCl aqueous solution as a simulated lithium-containing solution.

[0043] 20 mg of OH-MIL-53 (Fe) prepared in the control example and 20 mg of metal-doped functionalized OH-MIL-53 metal-organic framework adsorbent (Ni10%-OH-MIL-53(Fe)) prepared in Example 1 were weighed and added to 20 mL of simulated lithium-containing solution, respectively. Adsorption was carried out by shaking at 25 °C at a shaking rate of 140 rpm for 24 h. After adsorption, the supernatant was filtered through a microporous membrane to obtain the test solution. 1 mL of the simulated lithium-containing solution and the test solution were respectively added to 100 mL volumetric flasks and diluted to the mark with deionized water. The lithium concentration was determined by ICP-OES, and the lithium adsorption capacity of the metal-organic framework adsorbent was calculated using the formula. (See [reference]). Figure 1 (Take 20 mg of each of the metal-doped functionalized MIL-53 metal-organic framework adsorbents prepared in the other embodiments and follow the steps described above.) Prepare Li separately + / Na + Li + / Mg 2+ and Li + / K + A binary mixed solution, with each ion concentration of 1 g / L, was prepared in 20 mL portions. 20 mg of Ni10%-OH-MIL-53(Fe) was weighed and added to the mixed solution. The solution was then shaken and adsorbed at 25 ℃ and 140 rpm for 24 h. After adsorption, the concentrations of each ion were measured, and the adsorption capacity and separation coefficient were calculated. (See attached table). Figure 2 .

[0044] Lithium adsorption experiments were conducted on Ni10%-OH-MIL-53(Fe) prepared in Example 1. 20 mg of Ni10%-OH-MIL-53(Fe) was added to 20 mL of a simulated lithium-containing solution. Adsorption was performed by shaking at 25 °C at a shaking rate of 140 rpm for 24 h. After adsorption, the adsorbent was immersed in 0.1 mol / L hydrochloric acid solution overnight for desorption. It was then washed three times with deionized water and ethanol, respectively, dried under vacuum at 80 °C, and activated under vacuum at 100 °C overnight before the next adsorption experiment. The above adsorption-desorption process was repeated four times. (See attached table). Figure 3 .

[0045] Example 6 Application of metal-doped functionalized MIL-53 metal-organic framework adsorbent in lithium isotope separation.

[0046] Formulated with natural abundance 6 Li and 7 LiCl aqueous solution was used as the raw solution for lithium isotope separation, in which Li + The concentration is 1 g / L.

[0047] 20 mg of OH-MIL-53(Fe) prepared in the control example and 20 mg of metal-doped functionalized OH-MIL-53(Fe) were weighed and added to 20 mL of lithium isotope separation stock solution, respectively. The mixture was shaken and adsorbed at 25 °C at a shaking rate of 140 rpm for 24 h. After adsorption, the supernatant was filtered through a microporous membrane to obtain the test solution. 100 μL of both the lithium isotope separation stock solution and the test solution were added to 100 mL volumetric flasks and diluted to the mark with deionized water. The concentrations were determined by ICP-MS. 6 Li and 7 The isotopic abundance of Li was calculated.6 Li / 7 Li isotope separation factor, see Figure 4 .

Claims

1. A method for preparing a metal-doped functionalized MIL-53 type metal-organic framework adsorbent, characterized in that... Includes the following steps: (1) Dissolve the main metal salt and the doped metal salt in N,N-dimethylformamide, add 2-hydroxyterephthalic acid, stir until completely transparent, then add hydrofluoric acid aqueous solution dropwise. After the addition is complete, transfer the material into a polytetrafluoroethylene-lined reactor and react at a constant temperature of 120-180 °C for 12-36 h. (2) Cool the product obtained in step (1) to room temperature, separate the solid and liquid, wash the solid with N,N-dimethylformamide at 60-100℃ to remove the liquid on the surface of the solid or between the particles; perform solvent exchange with ethanol; vacuum dry to obtain a metal-doped functionalized MIL-53 type metal-organic framework adsorbent.

2. The preparation method according to claim 1, characterized in that: In step (1), the ratio of the main metal salt, the doped metal salt, N,N-dimethylformamide, 2-hydroxyterephthalic acid and hydrofluoric acid is 0.80-0.95 mmol: 0.05-0.20 mmol: 8-12 mL: 1 mmol: 1 mmol.

3. The preparation method according to claim 1 or 2, characterized in that the cation of the main metal salt is Fe. 3+ Al 3+ or In 3+ .

4. The preparation method according to claim 1 or 2, characterized in that: The cations of the doped metal salt are Ni2+, Co2+, and Mn. 2+ Zn 2+ Cu 2+ Mg 2+ or Ca 2+ .

5. A metal-doped functionalized MIL-53 type metal-organic framework adsorbent prepared by the preparation method according to any one of claims 1-4.

6. The application of the metal-doped functionalized MIL-53 type metal-organic framework adsorbent of claim 5 in lithium extraction.

7. The application of a metal-doped functionalized MIL-53 type metal-organic framework adsorbent according to claim 5 in lithium isotope separation.

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