Lithium-rich adsorbent as well as preparation method and application thereof

Abstract

The invention discloses a lithium-rich adsorbent as well as a preparation method and application thereof, and belongs to the technical field of preparation of metal organic framework materials. The lithium-rich adsorbent is a lithium-rich metal organic framework prepared by modifying and replacing formate on a hexanuclear metal zirconium cluster in a secondary structural unit of a parent MOF-808 with lithium tricarboxylate [-OOCCH2CH (COOLi) CH (COOLi) CH2 (COOLi)]. Compared with other lithium modified materials, the lithium tricarboxylate modified MOF-808 metal organic framework material prepared by the preparation method disclosed by the invention shows remarkable structural advantages on the basis of retaining excellent stability of a parent framework, has relatively small grain size, high pore volume and specific surface area, meanwhile, the concentration ratio of lithium ions in a molecular pore channel is high, and the lithium tricarboxylate modified MOF-808 metal organic framework material has a good application prospect. And the uniformly distributed lithium carboxylate is mutually cooperated, so that the material is endowed with stronger application performance in some fields. Compared with the traditional method, the preparation method provided by the invention not only simplifies the production process and shortens the reaction period, but also reduces the dependence on high-voltage equipment, reduces the cost, and lays a technical foundation for large-scale production and industrial application of materials.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of preparation of metal organic framework materials, and particularly relates to a lithium-rich adsorbent and a preparation method and application thereof. BACKGROUND

[0002] One of the main driving forces of global warming is the accumulation of carbon dioxide emissions caused by human industrial activities. To suppress global warming, it is necessary to artificially reduce the amount of carbon dioxide emissions, and in addition, it is necessary to consider how to capture, store and convert the already emitted carbon dioxide by non-biological means. Lackner proposed in 1999 the concept of directly capturing ultra-low concentration carbon dioxide from air to suppress global warming by using non-biological means, which is also known as DAC (direct air capture) technology. DAC technology emphasizes the direct capture of ultra-low concentration carbon dioxide from air, and its core is a carbon dioxide adsorbent, which is different from traditional carbon capture and requires more stringent standards and advanced requirements for material design and application.

[0003] In order to effectively capture carbon dioxide from low-concentration (0.04%) ambient air, specific CO2 adsorption sites with high reactivity must be present. In this case, amine functional groups have become promising candidates for chemical adsorption sites, helping to develop efficient CO2 capture adsorbents. Although current methods involve the use of basic aqueous solutions to chemically bind with CO2, they have significant drawbacks such as energy-intensive desorption processes and poor cycleability. These problems lead to high energy consumption and unavoidable secondary carbon dioxide emissions, resulting in rising costs. Therefore, it is urgent to develop new materials to study and address these challenges.

[0004] Many classes of solid-state materials have been extensively explored to meet the demand for efficient CO2 adsorbents, and CO2 adsorption chemistry has been proposed, including zeolites, polymers, silicas, metal-organic frameworks (MOFs), and covalent organic frameworks (COFs).

[0005] Metal-Organic Frameworks (MOFs) are crystalline porous materials formed by self-assembly of inorganic metal ion nodes and organic ligands, with a three-dimensional periodic network topology. This class of materials has important application potential in the field of gas storage and separation due to its high porosity, ultra-large specific surface area and controllable pore size. In recent years, a part of MOFs containing strong force sites have been used to remove low-concentration (0.04%) CO2, especially amine-functionalized MOFs, but their cyclic regeneration still requires a lot of energy, or a complex steam regeneration process, which limits their development.

[0006] Aiming at the problems of high regeneration energy consumption (steam or high temperature treatment is needed) and complex process of current amine functionalized MOF materials in the field of low concentration CO2 (0.04%) capture, it is urgent to develop new materials based on strong physical adsorption to realize low energy consumption regeneration. SUMMARY

[0007] To solve the above problems, the present application provides a lithium-rich adsorbent and a preparation method and application thereof. The present application innovatively uses butane tetracarboxylic acid with the highest proportion of carboxylic acid functional groups in tetracarboxylic acid substances as a functional modification agent, and successfully prepares a lithium-rich adsorbent containing high-density lithium nodes in the pore by constructing a simple synthesis strategy in an aqueous system to capture air-grade low-concentration CO2 (400 ppm).

[0008] To achieve the above object, the present application provides the following technical scheme:

[0009] One of the technical schemes of the present application: a lithium-rich adsorbent is provided, which is a lithium-rich metal organic framework prepared by modifying formate on the six-nuclear zirconium cluster in the secondary structure unit of the parent MOF-808 by -OOCCH2CH(COOLi)CH(COOLi)CH2(COOLi).

[0010] The schematic diagram of the lithium tricarboxylate [-OOCCH2CH(COOLi)CH(COOLi)CH2(COOLi)] in the lithium tricarboxylate modified MOF-808 metal organic framework and the modified position (formate on the zirconium cluster of other parts) is shown in Figure 1 .

[0011] The second technical scheme of the present application: a preparation method of the above lithium-rich adsorbent is provided, comprising the following steps:

[0012] The zirconium-containing metal salt, trimesic acid and butane tetracarboxylic acid ground into powder are added to an acid solution, and after reaction, a butane tetracarboxylic acid modified MOF-808 metal organic framework (MOF-808-BTCA) is obtained. The butane tetracarboxylic acid modified MOF-808 metal organic framework is immersed in a lithium-containing solution for exchange to obtain the lithium-rich adsorbent.

[0013] The synthesis method of the present application significantly reduces the use of toxic reagents and reduces the cost of reagents compared with the traditional solvent thermal autogenous pressure method (which needs to synthesize the parent first and then modify).

[0014] Alternatively, the zirconium-containing metal salt is at least one of zirconium oxychloride octahydrate, zirconium nitrate, zirconium sulfate, zirconium alkoxide, zirconium isopropyl alcohol, zirconium n-butyl alcohol, zirconium chloride and zirconium acetate.

[0015] Preferably, the molar ratio of zirconium in the zirconium-containing metal salt to the trimesic acid is 1:0.5-10; the molar ratio of zirconium in the zirconium-containing metal salt to the butane tetracarboxylic acid is 1:0.5-20.

[0016] More preferably, the molar ratio of zirconium in the zirconium-containing metal salt to the trimesic acid is 1:0.5-2, most preferably 1:0.8-1.2.

[0017] By precisely regulating the ligand ratio, the problems of reduced yield caused by insufficient ligand and conversion stagnation and cost increase caused by excessive ligand can be effectively solved, and finally the yield of the metal-organic framework material MOF-808-BTCA reaches 85-95%.

[0018] More preferably, the molar ratio of zirconium in the zirconium-containing metal salt to the butane tetracarboxylic acid is 1:3-10.

[0019] Controlling the molar ratio of zirconium in the appropriate zirconium-containing metal salt to the butane tetracarboxylic acid can control the proportion of the butane tetracarboxylic acid in the MOF-808-BTCA structure.

[0020] Preferably, the molar ratio of zirconium in the zirconium-containing metal salt to water in the acid solution is 1:3000-10000; the molar ratio of zirconium in the zirconium-containing metal salt to acid in the acid solution is 1:300-1000.

[0021] Optionally, the acid is at least one of formic acid, acetic acid, nitric acid, and hydrochloric acid.

[0022] Preferably, the temperature of the reaction is 80-120℃, and the time is 10-48h.

[0023] Compared with the traditional solvothermal autogenous pressure method (which needs to use DMF as a solvent and formic acid as a regulator to synthesize the MOF-808 parent under autogenous pressure for 2-5 days, and then to complete the carboxyl modification through a water phase post-synthesis method for 12-24 hours), the reaction conditions of the present application shorten the preparation period, and through reducing the reaction temperature and normal pressure reaction, a more simple synthesis path is realized.

[0024] Optionally, the lithium salt in the lithium-containing solution is at least one of lithium tert-butoxide, lithium hydroxide, lithium sulfate, lithium chloride, lithium lactate, and lithium difluoro(oxalato)borate.

[0025] Preferably, the concentration of lithium in the lithium-containing solution is 0.01-0.5M.

[0026] Preferably, the time for the butane tetracarboxylic acid modified MOF-808 metal-organic framework to exchange in the lithium-containing solution is 1-600s.

[0027] The MOF-808 metal organic framework modified by lithium tricarboxylate prepared by the method has small size (particle size is 50-1000 nm), high specific surface area, and can reach 600-800 m 2 / g, and is more suitable as an application material in the fields of adsorption and separation.

[0028] The application also provides application of the lithium-rich adsorbent in removal of carbon dioxide in air.

[0029] The lithium-rich adsorbent can capture carbon dioxide in air with a concentration as low as 400 ppm, and the adsorption amount is more than 0.4 mmol / g.

[0030] The application has the following beneficial technical effects:

[0031] The water-phase synthesis method significantly reduces the reaction temperature of the intermediate product, butane tetracarboxylic acid modified MOF-808 metal organic framework, compared with the preparation process of the carboxylic acid modified MOF-808 reported in the prior art, and realizes green synthesis by avoiding the use of organic solvents and reducing energy consumption. Meanwhile, based on the one-pot synthesis strategy under normal pressure, the production process is simplified, the reaction period is shortened, the dependence on high-pressure equipment is reduced, the cost is reduced, and a technical foundation is laid for material scale production and industrial application.

[0032] The MOF-808 metal organic framework material modified by lithium tricarboxylate prepared by the method has the advantages of small crystal size, high pore volume and specific surface area, and high concentration of lithium ions in the molecular channel, and the uniform distribution of lithium carboxylate is synergistic, which will give the material stronger application performance in some fields.

[0033] In the carbon dioxide adsorption experiment, the MOF-808 metal organic framework material modified by lithium tricarboxylate prepared by the method exhibits strong affinity for carbon dioxide. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 The figure is a schematic diagram of lithium tricarboxylate in the MOF-808 metal organic framework modified by lithium tricarboxylate and the modified position.

[0035] Figure 2 The figure is an XRD graph of the MOF-808-BTCA-Li prepared in Examples 1-3.

[0036] Figure 3 The figure is a SEM graph of the adsorbent prepared in Examples 1-3 and Comparative Example 1, wherein a is the SEM graph of Comparative Example 1, b is the SEM graph of Example 1, c is the SEM graph of Example 3, and d is the SEM graph of Example 2.

[0037] Figure 4 Adsorption curves of the adsorbents prepared in Example 3 and Comparative Example 1 for N2.

[0038] Figure 5 Adsorption curves (a) of the adsorbents prepared in Example 3 and Comparative Example 1 for carbon dioxide, and carbon dioxide adsorption curves (b) in the low pressure region.

[0039] Figure 6 Adsorption curves of the adsorbents prepared in Comparative Examples 1 to 4 for carbon dioxide. DETAILED DESCRIPTION

[0040] The detailed description set forth below describes various illustrative embodiments of the application and is not intended to represent the only embodiments in which the application can be practiced. The detailed description is intended only to provide a more complete understanding of the application, and is not intended to limit the scope of the application.

[0041] It should be noted that the present application does not describe in detail the conventional operation means in the art, and is not the focus of the present application.

[0042] In addition, for the numerical range in the present application, it should be understood that each intermediate value between the upper limit and the lower limit of the range is also specifically disclosed. Each smaller range between any stated value or intermediate value in the stated range, and any other stated value or intermediate value in the stated range, is also encompassed within the scope of the present application. The upper limit and the lower limit of these smaller ranges can be independently included or excluded from the range.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application, preferred methods and materials are described. Any and all

[0044] As used herein, the terms "comprises", "comprising", "includes", "including", "has", "having", and the like are open-ended terms that are intended to mean including, but not limited to.

[0045] The model and manufacturer information of the equipment involved in the present application is as follows:

[0046] Oven I, model DZF-6050, Shanghai Jinghong Realization Equipment Co., Ltd.

[0047] Vacuum oven II, model DHG-9053-A, Shanghai Jinghong Realization Equipment Co., Ltd.

[0048] High performance physisorption analyzer, ASAP-2020-PLUS, Micromeritics (Shanghai) Instrument Co., Ltd.

[0049] Vapor sorption analyzer, BEL-MAX, BEL Japan, Ltd.

[0050] The raw material information involved in the embodiments of the present application is as follows:

[0051] Zirconium oxychloride octahydrate, trimesic acid, acetic acid, DMF, butane tetracarboxylic acid are all purchased from Beijing Inokai Technology Co., Ltd.

[0052] Example 1

[0053] The preparation method of the lithium-rich adsorbent MOF-808-BTCA-Li is as follows:

[0054] (1) Zirconium oxychloride octahydrate (ZrOCl2·8H2O), trimesic acid (H3BTC) and butane tetracarboxylic acid (BTCA) are mechanically ground and mixed at a molar ratio of 1:1:10 to obtain a white mixed powder, wherein the amount of ZrOCl2·8H2O is 2 mmol.

[0055] (2) Deionized water is added to the mixed powder, and the molar ratio of ZrOCl2·8H2O to water is controlled to be 1:5000. Then acetic acid is added as a reaction regulator, and the molar ratio of ZrOCl2·8H2O to acetic acid is maintained at 1:2000 to form a homogeneous reaction system.

[0056] (3) The mixed solution is heated to 100°C and reacted at normal pressure for 16h to promote the coordination reaction of metal nodes and organic ligands, and MOF-808-BTCA crystals are generated to obtain a crude product.

[0057] (4) The crude product obtained in step (3) is centrifuged with deionized water three times (8000 rpm, 10 min / time) to remove residual H3BTC, BTCA and acetic acid, and high-purity MOF-808-BTCA powder is obtained. Further exchange by soaking in 0.1 M lithium hydroxide solution for 300s to obtain 1g of MOF-808-BTCA-Li, with a yield of about 93.9%.

[0058] Example 2

[0059] The preparation method of the lithium-rich adsorbent MOF-808-BTCA-Li is as follows:

[0060] Compared with Example 1, the difference lies in that the feeding amount of ZrOCl2·8H2O in step (1) is adjusted to 10 mmol, and the molar ratio of ZrOCl2·8H2O, H3BTC and BTCA is still 1:1:10; the amounts of deionized water and acetic acid in step (2) are proportionally enlarged, and finally the mass of the prepared MOF-808-BTCA-Li is 4.91 g, and the yield is about 92.2%.

[0061] Example 3

[0062] The preparation method of the lithium-rich adsorbent MOF-808-BTCA-Li is as follows:

[0063] Compared with Example 1, the difference lies in that the feeding amount of ZrOCl2·8H2O in step (1) is adjusted to 20 mmol, and the molar ratio of ZrOCl2·8H2O, H3BTC and BTCA is still 1:1:10; the amounts of deionized water and acetic acid in step (2) are proportionally enlarged, and finally the mass of the prepared MOF-808-BTCA-Li is 9.51 g, and the yield is about 89.3%.

[0064] The MOF-808-BTCA-Li prepared in Examples 1-3 is subjected to XRD analysis, and the analysis results are shown in Figure 2 . Figure 2 It is shown that even if the feeding amount of ZrOCl2·8H2O is increased to 50 mmol (Example 3), the obtained 10 g level MOF-808-BTCA-Li still maintains a single crystal phase structure, and no impurity diffraction peak is generated, which proves that the synthesis strategy provided by the present application has good scalability.

[0065] Comparative Example 1

[0066] Preparation of MOF-808:

[0067] According to the preparation method of MOF-808 published by Peng, Y., Huang, H., Zhang, Y. et al. A versatile MOF-based trap for heavy metal ion capture and dispersion. Nat Commun 9, 187 (2018).), which is a common method for preparing kilogram-level parent MOF-808.

[0068] Comparative Example 2

[0069] The preparation method of the lithium-rich adsorbent MOF-808-CA-Li is as follows:

[0070] Compared with Example 3, the difference lies in that the BTCA in step (1) is replaced by an equal molar amount of citric acid (CA).

[0071] Comparative Example 3

[0072] The preparation method of the lithium-rich adsorbent MOF-808-MA-Li is as follows:

[0073] Compared with Example 3, the difference is that the BTCA in step (1) is replaced by equimolar amount of malic acid (MA).

[0074] Comparative Example 4

[0075] The MOF-808-BTCA-Li is prepared by a post-synthesis method:

[0076] The MOF-808 prepared in Comparative Example 1 is put into a 6 g / L BTCA solution, and stirred at 60°C for 24 h, and a white powder is obtained by filtration, and washed with pure water for 24 h, and the pure water is replaced for three times to obtain the intermediate MOF-808-BTCA. Further exchange by 0.1 M lithium hydroxide solution for 300 s to obtain MOF-808-BTCA-Li.

[0077] Application Example

[0078] The final products prepared in Examples 1-3 and Comparative Example 1 are observed by a scanning electron microscope, and the obtained SEM images are shown in Figure 3 , wherein a is the SEM image of Comparative Example 1, b is the SEM image of Example 1, c is the SEM image of Example 3, and d is the SEM image of Example 2.

[0079] Figure 3 It can be seen that the particle size of the adsorbent prepared in Comparative Example 1 is mostly in the range of 500-2000 nm, while the particle size of the adsorbent prepared in Examples 1-3 is mostly in the range of 50-1000 nm, and the particle size of the adsorbent prepared in the examples is smaller.

[0080] The specific surface area of the adsorbents prepared in Example 3 and Comparative Example 1 is compared, and the adsorption capacity of N2 of the adsorbents prepared in Example 3 and Comparative Example 1 is tested at 77 K, and the adsorption results are shown in Figure 4 .

[0081] It can be seen from Figure 4 that the BET specific surface area of the two samples calculated according to the isotherm is 615 m 3 / g and 1750 m 3 / g, respectively, and the specific surface area of Example 3 is significantly smaller than that of Comparative Example 1, which is due to the occupation of a large amount of lithium carboxylate in the pores.

[0082] Further carbon dioxide adsorption experiments are carried out on the adsorbents prepared in Example 3 and Comparative Example 1, and the experimental results are shown in Figure 5wherein a is the adsorption curve of the adsorbent prepared in Example 3 for carbon dioxide, and b is the adsorption curve of carbon dioxide at low pressure region.

[0083] From Figure 5 it can be seen that the adsorption curve of the adsorbent prepared in Example 3 for carbon dioxide becomes steeper obviously, especially at low pressure region, which means that the adsorbent prepared in Example 3 has very strong affinity for carbon dioxide. Subsequent analysis of adsorption at low pressure region can find that the adsorption amount of the adsorbent prepared in Example 3 is 11.5 cm 3 ·g -1 (0.51 mmol·g -1 ) at 400 ppm carbon dioxide partial pressure, while the adsorption amount of the adsorbent prepared in Comparative Example 1 is negligible at 400 ppm carbon dioxide partial pressure, which means that the modification by lithium tricarboxylate enables the material to capture carbon dioxide at low concentration.

[0084] Based on the experiments of Comparative Examples 2-4, further carbon dioxide adsorption experiments (the same method as above) were carried out on the adsorbents prepared in Comparative Examples 1-4, and the results are shown in Figure 6 .

[0085] It can be seen from Figure 5 and Figure 6 that the adsorbent prepared in Example 3 exhibits irreplaceable comprehensive advantages: the adsorption amount of Comparative Examples 2 and 3 (different carboxylic acid ligands) for carbon dioxide at 400 ppm is only 0.1 mmol·g -1 ; the adsorbent prepared in Comparative Example 4 (post-synthetic modification method) is improved to 0.46 mmol·g -1 (reaching 90% of Example 3), but Example 3 realizes a breakthrough adsorption performance of 0.51 mmol·g -1 at 400 ppm low concentration by in-situ construction of high-density lithium carboxylate and coordination sites (lithium atom spacing < 3.5 Å), which is more than 700% higher than Comparative Examples 2 and 3 and 10% higher than Comparative Example 4. In terms of preparation process, the green aqueous one-pot method of Example 3 completely eliminates the use of DMF solvent, shortens the time to 20 h (16 h + about 4 h of the previous mixing step), which is only 26.3% of Comparative Example 4 (time 76 h, specifically 52 h of the preparation time of Comparative Example 1 + 24 h of stirring reaction at 60 °C), and reduces the total life cycle cost by 22.7% (energy consumption is reduced by 71.4%) through integrated synthesis.

[0086] In summary, the preparation method of the MOF-808-BTCA-Li is simple and fast, has low requirements for reaction conditions, has a short preparation period, and is free of organic solvents. The MOF-808-BTCA-Li obtained by the method can capture low-concentration carbon dioxide and can be easily scaled up to 10 grams for synthesis. All the foregoing advantages are conducive to promoting the development of the MOF-808-BTCA-Li MOFs material and commercialized production thereof.

[0087] The above-described embodiments are merely preferred modes of the present application and are not intended to limit the scope of the present application. Various modifications and improvements to the technical solutions of the present application made by those of ordinary skill in the art without departing from the design spirit of the present application shall fall within the protection scope of the present application as defined by the claims.

Claims

1. A lithium-rich adsorbent, characterized in that, The lithium-rich adsorbent is a metal-organic framework made by modifying and substituting the formate group on the hexanuclear zirconium cluster in the secondary structural unit of the parent MOF-808 with -OOCCH2CH(COOLi)CH(COOLi)CH2(COOLi).

2. A method for preparing the lithium-rich adsorbent according to claim 1, characterized in that, Includes the following steps: Zirconium-containing metal salts, trimesic acid, and butanetetracarboxylic acid, ground into powder, are added to an acid solution. After reaction, a butanetetracarboxylic acid-modified MOF-808 metal-organic framework is obtained. The butanetetracarboxylic acid-modified MOF-808 metal-organic framework is then immersed in a lithium-containing solution for exchange to obtain the lithium-rich adsorbent.

3. The method for preparing the lithium-rich adsorbent according to claim 2, characterized in that, The molar ratio of zirconium to trimethylbenzene in the zirconium-containing metal salt is 1:0.5~10; the molar ratio of zirconium to butanetetracarboxylic acid in the zirconium-containing metal salt is 1:0.5~20.

4. The method for preparing the lithium-rich adsorbent according to claim 3, characterized in that, The molar ratio of zirconium to trimethylbenzene in the zirconium-containing metal salt is 1:0.5~2.

5. The method for preparing the lithium-rich adsorbent according to claim 3, characterized in that, The molar ratio of zirconium to butanetetracarboxylic acid in the zirconium-containing metal salt is 1:3~10.

6. The method for preparing the lithium-rich adsorbent according to claim 2, characterized in that, The molar ratio of zirconium in the zirconium-containing metal salt to water in the acid solution is 1:3000~10000; the molar ratio of zirconium in the zirconium-containing metal salt to acid in the acid solution is 1:300~1000.

7. The method for preparing the lithium-rich adsorbent according to claim 2, characterized in that, The reaction is carried out at a temperature of 80-120°C for a time of 10-48 hours.

8. The method for preparing the lithium-rich adsorbent according to claim 2, characterized in that, The lithium concentration in the lithium-containing solution is 0.01~0.5M.

9. The method for preparing the lithium-rich adsorbent according to claim 2, characterized in that, The butanetetracarboxylic acid-modified MOF-808 metal-organic framework has an exchange time of 1–600 s in lithium-containing solutions.

10. The application of the lithium-rich adsorbent of claim 1 in the removal of carbon dioxide from air.

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