A lithium-rich adsorbent, a preparation method and application thereof

Abstract

The application discloses a lithium-rich adsorbent and a preparation method and application thereof, and belongs to the technical field of metal organic framework material preparation. The lithium-rich adsorbent is a lithium-rich metal organic framework prepared by modifying formate on a six-nuclear metal zirconium cluster in a secondary structure unit of a MOF-808 parent MOF-808 by lithium tricarboxylate [-OOCCH2CH(COOLi)CH(COOLi)CH2(COOLi)]. The lithium tricarboxylate modified MOF-808 metal organic framework material prepared by the application has a smaller crystal size, a higher pore volume and a specific surface area, and a high lithium ion concentration ratio in a molecular channel, and the uniformly distributed carboxylic acid lithium is synergistic, which will give the material stronger application performance in some fields. Compared with a traditional method, the preparation method provided by the application not only simplifies a production process and shortens a reaction period, but also reduces the dependence on high-pressure equipment and the cost, and lays a technical foundation for material large-scale production and industrial application.

Description

Technical Field

[0001] This invention belongs to the field of metal-organic framework material preparation technology, specifically relating to a lithium-rich adsorbent, its preparation method, and its application. Background Technology

[0002] One of the main drivers of global warming is the accumulation of carbon dioxide emissions caused by human industrialization. To curb global warming, it is necessary to reduce carbon dioxide emissions through human activities, and also to consider how to capture, store, and convert already emitted carbon dioxide using non-biological means. In 1999, Lackner proposed the concept of using non-biological means to directly capture ultra-low concentrations of carbon dioxide from the atmosphere to curb global warming; this method is also known as direct aircapture (DAC) technology. DAC technology emphasizes the direct capture of ultra-low concentrations of carbon dioxide from the atmosphere. Its core component is a carbon dioxide adsorbent, and unlike traditional carbon capture, it imposes more stringent standards and advanced requirements on material design and application.

[0003] To effectively capture carbon dioxide from low concentrations (0.04%) of ambient air, highly reactive specific CO2 adsorption sites are essential. In this context, amine functional groups have emerged as promising candidates for chemisorption sites, facilitating the development of highly efficient CO2 capture adsorbents. While current methods involve the chemical binding of CO2 with alkaline aqueous solutions, they suffer from significant drawbacks such as energy-intensive desorption processes and poor recycling capabilities. These issues lead to high energy consumption and unavoidable secondary CO2 emissions, resulting in increased costs. Therefore, developing new materials to address these challenges is of paramount importance.

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

[0005] Metal-organic frameworks (MOFs) are crystalline porous materials formed by the self-assembly of inorganic metal ion nodes and organic ligands, exhibiting a three-dimensional periodic network topology. These materials demonstrate significant application potential in gas storage and separation due to their high porosity, ultra-large specific surface area, and tunable pore size. In recent years, some MOFs containing strong interaction sites have been designed to remove low concentrations (0.04%) of CO2, particularly amine-functionalized MOFs. However, their recycling still requires substantial energy or involves complex steam regeneration processes, limiting their further development.

[0006] To address the current bottlenecks in the capture of low-concentration CO2 (0.04%) by amine-functionalized MOF materials, such as high regeneration energy consumption (requiring steam or high-temperature treatment) and complex processes, there is an urgent need to develop new materials based on strong physical adsorption to achieve low-energy regeneration. Summary of the Invention

[0007] To address the aforementioned problems, this invention provides a lithium-rich adsorbent, its preparation method, and its applications. This invention innovatively uses butanetetracarboxylic acid, which has the highest proportion of carboxylic acid functional groups among tetracarboxylic acid compounds, as a functionalizing modifier. Through a simple synthesis strategy in an aqueous system, a lithium-rich adsorbent containing high-density lithium nodes in its pores was successfully prepared to capture low-concentration CO2 (400 ppm) in air.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] One of the technical solutions of this invention is to provide a lithium-rich adsorbent, which is a lithium-rich metal-organic framework made by modifying and substituting the formate group on the hexanuclear metallic zirconium cluster in the secondary structural unit of the parent MOF-808 with -OOCCH2CH(COOLi)CH(COOLi)CH2(COOLi).

[0010] A schematic diagram of the lithium tricarboxylate [-OOCCH2CH(COOLi)CH(COOLi)CH2(COOLi)] in the lithium tricarboxylate-modified MOF-808 metal-organic framework and its modified positions (the same applies to formate ions on zirconium clusters in other locations) is shown below. Figure 1 .

[0011] The second technical solution of the present invention provides a method for preparing the above-mentioned lithium-rich adsorbent, comprising the following steps:

[0012] 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 (MOF-808-BTCA) 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.

[0013] Compared with the traditional solvothermal self-generated pressure method (which requires the synthesis of the parent material before modification), the synthesis method of the present invention significantly reduces the use of toxic reagents and lowers reagent costs.

[0014] Optionally, the zirconium-containing metal salt is at least one of zirconium oxychloride octahydrate, zirconium nitrate, zirconium sulfate, zirconium alkoxide, zirconium isopropoxide, zirconium n-butoxide, zirconium chloride, and zirconium acetate.

[0015] Preferably, the molar ratio of zirconium to pyromellitic acid in the zirconium-containing metal salt is 1:0.5~10; and the molar ratio of zirconium to butanetetracarboxylic acid in the zirconium-containing metal salt is 1:0.5~20.

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

[0017] By precisely controlling the ligand ratio, the problems of reduced yield due to insufficient ligand and stagnant conversion rate and increased cost caused by excessive ligand can be effectively solved, ultimately achieving a yield of 85-95% for the metal-organic framework material MOF-808-BTCA.

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

[0019] By controlling the appropriate molar ratio of zirconium to butanetetracarboxylic acid in zirconium-containing metal salts, the proportion of butanetetracarboxylic acid in the MOF-808-BTCA structure can be controlled.

[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 selected from formic acid, acetic acid, nitric acid, and hydrochloric acid.

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

[0023] Compared to the traditional solvothermal autogenous pressure method (which requires DMF as solvent and formic acid as regulator to maintain autogenous pressure for 2-5 days to synthesize MOF-808 precursor, followed by 12-24 hours of aqueous phase for carboxyl modification), the reaction conditions of this invention shorten the preparation cycle, and by reducing the reaction temperature and reacting at atmospheric pressure, a simpler synthesis route is achieved.

[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 difluorooxalate borate.

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

[0026] Preferably, the butanetetracarboxylic acid-modified MOF-808 metal-organic framework is exchanged in a lithium-containing solution for 1 to 600 s.

[0027] The lithium tricarboxylic acid-modified MOF-808 metal-organic frameworks prepared in this invention have small sizes (particle sizes of 50~1000 nm) and high specific surface areas, reaching 600~800 m². 2 / g, making it more suitable as a material for adsorption and separation applications.

[0028] The third technical solution of the present invention provides an application of the above-mentioned lithium-rich adsorbent in the removal of carbon dioxide from the air.

[0029] The lithium-rich adsorbent provided by this invention can capture carbon dioxide concentrations as low as 400 ppm in the air, with an adsorption capacity exceeding 0.4 mmol / g.

[0030] The beneficial technical effects of the present invention are as follows:

[0031] The aqueous phase synthesis method proposed in this invention significantly reduces the reaction temperature of the intermediate product—butanetetracarboxylic acid-modified MOF-808 metal-organic framework. Compared with existing reported carboxylic acid-modified MOF-808 preparation processes, this method achieves green synthesis by avoiding the use of organic solvents and reducing energy consumption. Furthermore, the one-pot synthesis strategy under ambient pressure not only simplifies the production process and shortens the reaction cycle but also reduces dependence on high-pressure equipment, lowering costs and laying a technological foundation for the large-scale production and industrial application of the material.

[0032] The lithium tricarboxylate-modified MOF-808 metal-organic framework material prepared by this invention retains the excellent stability of the parent framework and exhibits significant structural advantages compared with other lithium-modified materials. It has a smaller grain size, higher pore volume and specific surface area, and a high lithium-ion concentration in the molecular channels. The uniformly distributed lithium carboxylate works synergistically, which will endow the material with stronger application performance in some fields.

[0033] In the carbon dioxide adsorption experiment, the lithium tricarboxylate-modified MOF-808 metal-organic framework material prepared in this invention exhibited a very strong affinity for carbon dioxide. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of lithium tricarboxylate in the MOF-808 metal-organic framework modified with lithium tricarboxylate according to the present invention and the modified position thereon.

[0035] Figure 2 The XRD patterns are of MOF-808-BTCA-Li prepared in Examples 1-3.

[0036] Figure 3 The images shown are SEM images of the adsorbents prepared in Examples 1-3 and Comparative Example 1, where 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.

[0037] Figure 4 The adsorption curves of N2 for the adsorbents prepared in Example 3 and Comparative Example 1 are shown.

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

[0039] Figure 6 The adsorption curves of carbon dioxide prepared by the adsorbents in Comparative Examples 1-4 are shown. Detailed Implementation

[0040] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0041] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0042] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0043] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar to or equivalent to those described herein may be used in the implementation or testing of this invention.

[0044] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0045] The model and manufacturer information of the equipment involved in this invention are as follows:

[0046] Oven I, model DZF-6050, manufactured by Shanghai Jinghong Real Estate Equipment Co., Ltd.

[0047] Vacuum Oven II, model number DHG-9053-A, manufactured by Shanghai Jinghong Real-Time Equipment Co., Ltd.

[0048] High-performance physical adsorption analyzer, ASAP-2020-PLUS model, McMurray Instruments (Shanghai) Co., Ltd.;

[0049] Steam adsorption unit, BEL-MAX, Macquarie (Japan) Co., Ltd.

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

[0051] Zirconium oxychloride octahydrate, pyromellitic acid, acetic acid, DMF, and butanetetracarboxylic acid were 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 butanetetracarboxylic acid (BTCA) were mechanically ground and mixed in a molar ratio of 1:1:10 to obtain a white mixed powder, wherein the amount of ZrOCl2·8H2O was 2 mmol.

[0055] (2) Add deionized water to the mixed powder and control the molar ratio of ZrOCl2·8H2O to water to be 1:5000. Then add acetic acid as a reaction regulator to maintain the molar ratio of ZrOCl2·8H2O to acetic acid at 1:2000 to form a homogeneous reaction system.

[0056] (3) The mixed solution was heated to 100℃ and reacted under normal pressure for 16h to promote the coordination reaction between the metal node and the organic ligand, and MOF-808-BTCA crystals were generated to obtain the crude product.

[0057] (4) The crude product obtained in step (3) is washed three times by centrifugation with deionized water (8000 rpm, 10 min / time) to remove residual H3BTC, BTCA and acetic acid, and high-purity MOF-808-BTCA powder is obtained. The powder is further exchanged by soaking in 0.1 M lithium hydroxide solution for 300 s to obtain 1 g 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 is that the amount of ZrOCl2·8H2O in step (1) was adjusted to 10 mmol, and the molar ratio of ZrOCl2·8H2O to H3BTC and BTCA was still 1:1:10; the amount of deionized water and acetic acid in step (2) was scaled up proportionally, and the final mass of MOF-808-BTCA-Li was 4.91 g, with a yield of 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 is that the amount of ZrOCl2·8H2O in step (1) was adjusted to 20 mmol, and the molar ratio of ZrOCl2·8H2O to H3BTC and BTCA was still 1:1:10; the amount of deionized water and acetic acid in step (2) was scaled up proportionally, and the final mass of MOF-808-BTCA-Li was 9.51 g, with a yield of about 89.3%.

[0064] XRD analysis was performed on the MOF-808-BTCA-Li prepared in Examples 1-3. The results are shown in the figure. Figure 2 . Figure 2 The results show that even when the amount of ZrOCl2·8H2O added is increased to 50 mmol (Example 3), the resulting 10g MOF-808-BTCA-Li still maintains a single crystal phase structure and no impurity diffraction peaks appear, proving that the synthesis strategy provided by the present invention has good scalability.

[0065] Comparative Example 1

[0066] Preparation of MOF-808:

[0067] The MOF-808 was prepared according to the method 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 gram-scale 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 is that BTCA in step (1) is replaced with an equimolar 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 BTCA in step (1) is replaced with an equimolar amount of malic acid (MA).

[0074] Comparative Example 4

[0075] MOF-808-BTCA-Li was prepared by post-synthesis method:

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

[0077] Application examples

[0078] The final products obtained in Examples 1-3 and Comparative Example 1 were observed using a scanning electron microscope (SEM). The resulting SEM images are shown below. 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 The results show that the adsorbent particles prepared in Comparative Example 1 are mostly in the range of 500~2000 nm, while the adsorbent particles prepared in Examples 1~3 are mostly in the range of 50~1000 nm. The adsorbent particles prepared in the Examples are even smaller.

[0080] The specific surface area of ​​the adsorbents prepared in Example 3 and Comparative Example 1 was compared. The adsorption capacity of the adsorbents prepared in Example 3 and Comparative Example 1 for N2 was tested at 77K. The adsorption results are as follows: Figure 4 As shown.

[0081] from Figure 4 As can be seen from this, the BET specific surface areas of the two samples, calculated based on this isotherm, are 615 m² and 615 m², respectively. 3 / g、1750m 3 / g, the specific surface area of ​​Example 3 is significantly smaller than that of Comparative Example 1, which is due to the large amount of carboxyl lithium occupying the channels.

[0082] Further carbon dioxide adsorption experiments were conducted on the adsorbents prepared in Example 3 and Comparative Example 1. The experimental results are shown in [Figure 1]. Figure 5Where, a is the adsorption curve of carbon dioxide by the adsorbents prepared in Example 3 and Comparative Example 1, and b is the carbon dioxide adsorption curve under low pressure.

[0083] from Figure 5 As can be seen, the adsorption curve for carbon dioxide by the adsorbent prepared in Example 3 is significantly steeper, especially in the low-pressure region. This indicates that the adsorbent prepared in Example 3 has a very strong affinity for carbon dioxide. Subsequent analysis of the adsorption in the low-pressure region revealed that at a carbon dioxide partial pressure of 400 ppm, the adsorbent prepared in Example 3 had an adsorption capacity of 11.5 cm³. 3 ·g -1 (0.51 mmol·g) -1 The adsorbent prepared in Comparative Example 1 had a negligible adsorption capacity at a carbon dioxide partial pressure of 400 ppm, which means that the material was modified with tricarboxylic acid lithium to capture low concentrations of carbon dioxide.

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

[0085] Combination Figure 5 and Figure 6 It can be seen that the adsorbent prepared in Example 3 exhibits irreplaceable comprehensive advantages: Comparative Examples 2 and 3 (different carboxylic acid ligands) have an adsorption capacity of only 0.1 mmol·g at 400 ppm CO2. -1 The adsorbent prepared in Comparative Example 4 (post-synthetic modification method) increased to 0.46 mmol·g. -1 (reaching 90% of Example 3), but Example 3 achieved 0.51 mmol·g at a low concentration of 400 ppm by constructing high-density lithium carboxylate cooperating sites in situ (lithium atomic spacing <3.5 Å). -1 The breakthrough adsorption performance is improved by more than 700% compared to Comparative Examples 2 and 3, and by 10% compared to Comparative Example 4. In terms of preparation process, the green aqueous one-pot method of Example 3 completely eliminates the use of DMF solvent, and the time is shortened to 20h (16h + about 4h of the previous mixing steps), which is only 26.3% of Comparative Example 4 (time 76h, specifically the preparation time of Comparative Example 1 52h + 60℃ stirring reaction 24h), and the total life cycle cost is reduced by 22.7% (energy consumption reduced by 71.4%) through integrated synthesis.

[0086] In summary, the preparation method of MOF-808-BTCA-Li provided by this invention is simple and rapid, has low requirements for reaction conditions, a short preparation cycle, and requires no organic solvents. The MOF-808-BTCA-Li obtained by this method can capture low concentrations of carbon dioxide and can be easily scaled up to the 10-gram level. All of the aforementioned advantages contribute to the development of MOF-808-BTCA-Li MOFs materials and their commercial production.

[0087] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

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). The preparation steps of the lithium-rich adsorbent include: adding zirconium-containing metal salt, pyromellitic acid and butanetetracarboxylic acid ground into powder to an acid solution, reacting to obtain a butanetetracarboxylic acid-modified MOF-808 metal-organic framework, immersing the butanetetracarboxylic acid-modified MOF-808 metal-organic framework in a lithium-containing solution for exchange, and obtaining the lithium-rich adsorbent.

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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