A bimetallic Mg-MOF-74 material, its preparation method and use

Abstract

This invention provides a bimetallic Mg-MOF-74 material, its preparation method, and its applications, relating to the field of adsorption materials technology. The invention involves mixing magnesium acetate, a transition metal salt, 2,5-dihydroxyterephthalic acid, a carboxylic acid, water, N,N-dimethylformamide, and ethanol to obtain a mixed solution; the carboxylic acid includes one or more of benzoic acid, acrylic acid, acetic acid, and oxalic acid; the mixed solution is subjected to a hydrothermal reaction to obtain the bimetallic Mg-MOF-74 material. The bimetallic Mg-MOF-74 material of this invention is prepared using magnesium acetate and a transition metal salt as two metal central ion sources and 2,5-dihydroxyterephthalic acid as a ligand. Compared with pure Mg-MOF-74 material, the bimetallic Mg-MOF-74 material prepared by this invention exhibits excellent CO2 / N2 separation performance, capable of highly selectively adsorbing and separating CO2 from a mixture of CO2 and N2.

Description

Technical Field

[0001] This invention relates to the field of adsorption materials technology, and in particular to a bimetallic Mg-MOF-74 material, its preparation method, and its applications. Background Technology

[0002] With the acceleration of human modernization, energy demand is constantly increasing, and the large amounts of greenhouse gases emitted from the combustion of fossil fuels are causing increasingly serious global environmental problems, such as frequent disasters like climate warming and glacial melting. Greenhouse gases mainly include carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and hydrofluorocarbons (HFCs), among which CO2 contributes the most to the greenhouse effect, reaching up to 70%. As of August 2021, the atmospheric CO2 level had reached 416 ppm, nearly 200 ppm higher than pre-industrial levels. This value far exceeds the capacity of plants to consume carbon in the natural carbon cycle. Therefore, the importance and urgency of reducing carbon emissions have received widespread attention. Given the current non-substitutability of fossil fuels, the development of carbon capture and storage (CCUS) technology has a promising future in the context of energy conservation and emission reduction.

[0003] To date, there are four main CO2 capture technologies: solvent absorption, membrane separation, cryogenic separation, and solid adsorption. Solid adsorption is widely favored due to its high operational flexibility and environmental friendliness. The core of solid adsorption lies in the development of adsorbents. Traditional adsorbents such as activated carbon, zeolite molecular sieves, and silica gel generally suffer from low CO2 adsorption capacity and high regeneration temperatures, failing to meet the separation performance requirements for industrial CO2 capture. Metal-organic frameworks (MOFs), on the other hand, have attracted widespread attention due to their well-defined structures, diverse types, extremely high specific surface area, low density, and chemical tunability. MOF-74, first proposed by Omar M. Yaghi, is widely used in CO2 capture due to its high CO2 adsorption capacity at low temperatures and pressures. Mg-MOF-74 (usually using magnesium nitrate hydrate or magnesium acetate hydrate as the metal salt and 2,5-dihydroxyterephthalic acid as the ligand) exhibits a higher CO2 adsorption capacity compared to other MOF-74 materials due to the ionic characteristics of the Mg-O bond. However, in current industrial production, the volume fraction of CO2 in flue gas is generally 10-15%, and the adsorption effect of pure Mg-MOF-74 on this concentration of CO2 is not ideal. Therefore, to achieve high-efficiency and high-capacity carbon capture, MOF materials need to be modified. However, current research on the selective adsorption properties of modified MOF materials mainly focuses on the separation of CO2 / CH4. Developing MOF materials with better separation effects for CO2 / N2 in industrial applications remains a key technical problem that needs to be solved. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a bimetallic Mg-MOF-74 material, its preparation method, and its applications. The bimetallic Mg-MOF-74 material prepared by this invention exhibits good separation performance for CO2 / N2.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing a bimetallic Mg-MOF-74 material, comprising the following steps:

[0007] Magnesium acetate, a transition metal salt, 2,5-dihydroxyterephthalic acid, a carboxylic acid, water, N,N-dimethylformamide, and ethanol are mixed to obtain a mixture; the carboxylic acid includes one or more of benzoic acid, acrylic acid, acetic acid, and oxalic acid.

[0008] The mixture was subjected to a hydrothermal reaction to obtain the bimetallic Mg-MOF-74 material.

[0009] Preferably, the transition metal salt includes one or more of cobalt acetate, nickel acetate, zinc acetate, manganese chloride, and ferrous chloride.

[0010] Preferably, the molar ratio of magnesium acetate to transition metal salt is 2 to 12:1.

[0011] Preferably, the ratio of the total molar amount of magnesium acetate and transition metal salt to the molar amount of 2,5-dihydroxyterephthalic acid is 3.0 to 3.5:1.

[0012] Preferably, the molar ratio of the carboxylic acid to 2,5-dihydroxyterephthalic acid is 0.2 to 2:1.

[0013] Preferably, the hydrothermal reaction is carried out at a temperature of 100–140°C for a duration of 12–36 hours.

[0014] This invention provides a bimetallic Mg-MOF-74 material prepared by the preparation method described above.

[0015] This invention provides an application of the bimetallic Mg-MOF-74 material described above in selectively adsorbing and separating CO2 from a mixed gas, wherein the mixed gas includes N2.

[0016] Preferably, the volume fraction of CO2 in the mixed gas is 10-15%.

[0017] Preferably, before application, the bimetallic Mg-MOF-74 material is activated in an inert atmosphere at a temperature of 150–300°C for 6–10 hours.

[0018] This invention provides a method for preparing a bimetallic Mg-MOF-74 material, comprising the following steps: mixing magnesium acetate, a transition metal salt, 2,5-dihydroxyterephthalic acid, a carboxylic acid, water, N,N-dimethylformamide, and ethanol to obtain a mixture; subjecting the mixture to a hydrothermal reaction to obtain the bimetallic Mg-MOF-74 material; wherein the carboxylic acid includes one or more of benzoic acid, acrylic acid, acetic acid, and oxalic acid. The bimetallic Mg-MOF-74 material of this invention is prepared using magnesium acetate and a transition metal salt as two metal central ion sources and 2,5-dihydroxyterephthalic acid as a ligand. Compared with pure Mg-MOF-74 material, bimetallic Mg-MOF-74 exhibits improved CO2 / N2 separation performance due to the addition of more stable coordinating unsaturated sites in the framework, resulting in a higher synergistic effect of the pore structure and a higher density of unsaturated metal sites within the framework. Furthermore, the present invention incorporates the aforementioned carboxylic acid during the synthesis process. The competitive coordination of the carboxylic acid and the 2,5-dihydroxyterephthalic acid ligand with the metal affects the coordination process during the material's self-assembly, thereby altering the crystallinity, morphology (specific surface area, pore structure), and stability of the final product, thus regulating the material's adsorption and selectivity. In addition, the preparation method provided by the present invention is simple, environmentally friendly, and has good reproducibility, facilitating industrial scale-up.

[0019] This invention provides a bimetallic Mg-MOF-74 material prepared by the method described above. The bimetallic Mg-MOF-74 material provided by this invention exhibits excellent CO2 / N2 separation performance, capable of selectively adsorbing and separating CO2 from a mixture of CO2 and N2. Furthermore, the adsorption between the bimetallic Mg-MOF-74 material and the gas is physisorption, therefore regeneration is easy, requires no additional energy input, and is beneficial for industrial scale-up. Detailed Implementation

[0020] This invention provides a method for preparing a bimetallic Mg-MOF-74 material, comprising the following steps:

[0021] Magnesium acetate, a transition metal salt, 2,5-dihydroxyterephthalic acid, a carboxylic acid, water, N,N-dimethylformamide, and ethanol are mixed to obtain a mixture; the carboxylic acid includes one or more of benzoic acid, acrylic acid, acetic acid, and oxalic acid.

[0022] The mixture was subjected to a hydrothermal reaction to obtain the bimetallic Mg-MOF-74 material.

[0023] Unless otherwise specified, all raw materials involved in this invention are commercially available products well known to those skilled in the art.

[0024] The present invention involves mixing magnesium acetate, transition metal salt, 2,5-dihydroxyterephthalic acid, carboxylic acid, water, N,N-dimethylformamide and ethanol to obtain a mixture.

[0025] In this invention, the transition metal salt preferably includes one or more of cobalt acetate, nickel acetate, zinc acetate, manganese chloride, and ferrous chloride. In embodiments of this invention, both magnesium acetate and the transition metal salt are added in their hydrated form. In this invention, the molar ratio of magnesium acetate to the transition metal salt is preferably 2–12:1, more preferably 3–10:1, further preferably 4–9:1, and most preferably 5–8:1. In this invention, magnesium acetate serves as a first metal central ion source, and the transition metal salt serves as a second metal central ion source.

[0026] In this invention, 2,5-dihydroxyterephthalic acid is used as a ligand. In this invention, the ratio of the total molar amount of magnesium acetate and the water-soluble transition metal salt to the molar amount of 2,5-dihydroxyterephthalic acid is preferably 3.0–3.5:1, specifically 3.0:1, 3.1:1, 3.2:1, 3.3:1, 3.4:1, or 3.5:1. In this invention, the carboxylic acid includes one or more of benzoic acid, acrylic acid, acetic acid, and oxalic acid, and the molar ratio of the carboxylic acid to 2,5-dihydroxyterephthalic acid is preferably 0.2–2:1, more preferably 0.5–1.5:1, and even more preferably 0.5–1:1.

[0027] In this invention, the water is preferably deionized water, and the volume ratio of N,N-dimethylformamide, ethanol and water is preferably 5:1:1. N,N-dimethylformamide, ethanol and water are used as solvents. This invention does not have any special requirements on the total amount of N,N-dimethylformamide, ethanol and water added, as long as it can ensure sufficient dissolution.

[0028] In this invention, the preferred mixing method is as follows: mixing magnesium acetate, transition metal salt, water and carboxylic acid to obtain a mixed metal salt solution; mixing 2,5-dihydroxyterephthalic acid, N,N-dimethylformamide and ethanol to obtain a ligand solution; and then mixing the mixed metal salt solution and the ligand solution.

[0029] In this invention, the preferred method for mixing magnesium acetate, transition metal salt, water, and acetic acid is to dissolve the magnesium acetate and transition metal salt in water, and then add the carboxylic acid and stir. The stirring time is preferably 10 to 30 minutes, specifically until the magnesium acetate and water-soluble transition metal salt are fully dissolved.

[0030] In this invention, the preferred method for mixing 2,5-dihydroxyterephthalic acid, N,N-dimethylformamide, and ethanol is as follows: mixing N,N-dimethylformamide and ethanol to obtain a mixed solvent; adding 2,5-dihydroxyterephthalic acid to the mixed solvent and stirring; the stirring time is preferably 10 to 30 minutes, specifically until the 2,5-dihydroxyterephthalic acid is completely dissolved.

[0031] In this invention, the mixing of the mixed metal salt solution and the ligand solution is preferably carried out by stirring, and the stirring time is preferably 10 to 30 minutes.

[0032] After obtaining the mixture, the present invention subjectes the mixture to a hydrothermal reaction to obtain the bimetallic Mg-MOF-74 material. In the present invention, the temperature of the hydrothermal reaction is preferably 100–140°C, more preferably 110–130°C, and even more preferably 120°C; the time is preferably 12–36 h, more preferably 18–24 h. The present invention preferably transfers the mixture to a polytetrafluoroethylene liner and performs the hydrothermal reaction at the specified temperature. During the hydrothermal reaction, the ligand 2,5-dihydroxyterephthalic acid and the carboxylic acid first undergo a deprotonation reaction, and then coordinate with metal ions in the solution. The carboxylic acid and the ligand 2,5-dihydroxyterephthalic acid compete for coordination, and this competition controls the reaction rate and crystallization process, ultimately altering the morphology and pore structure of the product. Increased specific surface area and micropore volume both increase the adsorption capacity of the final product; and the different coordination rates of different metal ions ultimately result in different amounts actually incorporated into the material. Through the aforementioned hydrothermal reaction, bimetallic MOF materials with different metal ions coordinated to O atoms of ligands were finally formed.

[0033] In this invention, after the hydrothermal reaction is completed, the obtained product is preferably cooled to room temperature and then washed and dried sequentially to obtain the bimetallic Mg-MOF-74 material. In this invention, the washing is preferably performed by centrifugation three times each with N,N-dimethylformamide and ethanol; the drying can be ordinary drying at room temperature or vacuum heating drying, and this invention does not impose any particular requirements on this.

[0034] This invention provides a bimetallic Mg-MOF-74 material prepared by the preparation method described above. The bimetallic Mg-MOF-74 material provided by this invention is a MOF material formed with magnesium as the first metal central ion, a transition metal as the second metal central ion, and 2,5-dihydroxyterephthalic acid ligand.

[0035] This invention provides an application of the bimetallic Mg-MOF-74 material described above in selectively adsorbing and separating CO2 from a mixed gas, wherein the mixed gas includes N2.

[0036] Before application, the present invention preferably activates the bimetallic Mg-MOF-74 material. The activation is preferably carried out in an inert atmosphere, preferably argon, at a temperature preferably 150–300°C, more preferably 200–250°C, and for a time preferably 6–10 hours, more preferably 8–10 hours. The activation can be carried out under normal pressure. The present invention preferably first compresses the bimetallic Mg-MOF-74 material into tablets and sieves them to obtain 40–60 mesh particles before performing the activation.

[0037] In this invention, the volume fraction of CO2 in the mixed gas is preferably 10-15%. In an embodiment of this invention, the CO2 / N2 adsorption and separation performance of the bimetallic Mg-MOF-74 material is tested under 25°C and normal pressure conditions for a CO2 / N2 mixed gas. The adsorption and separation performance data are obtained using adsorption breakthrough curves. Existing technologies for the separation selectivity of adsorbent materials are mainly calculated based on the isothermal adsorption lines of pure components and the Ideal Adsorption Solution Theory (IAST). This method, due to certain assumptions in the calculation, results in final data that does not closely approximate the actual separation situation. This invention uses adsorption breakthrough curves to derive the CO2 / N2 adsorption selectivity of MOF materials, which is more practical than the IAST selectivity calculated using isotherms and models.

[0038] The bimetallic Mg-MOF-74 material provided by this invention exhibits excellent CO2 / N2 separation performance, capable of selectively adsorbing and separating CO2 from a mixture of CO2 and N2. Furthermore, the adsorption between the bimetallic Mg-MOF-74 material and the gas is physisorption, thus facilitating regeneration.

[0039] To further illustrate the present invention, the bimetallic Mg-MOF-74 material, its preparation method, and its applications provided by the present invention are described in detail below with reference to examples, but these should not be construed as limiting the scope of protection of the present invention.

[0040] Example 1

[0041] 0.3 g of ligand 2,5-dihydroxyterephthalic acid was dissolved in a mixture of 100 mL N,N-dimethylformamide and 20 mL ethanol and stirred for 10 min. 0.673 g of magnesium acetate tetrahydrate and 0.391 g of cobalt acetate tetrahydrate were dissolved in 20 mL of deionized water, and then 0.037 g of benzoic acid was added and stirred for 10 min. The two solutions were mixed and stirred for 10 min, then transferred to a polytetrafluoroethylene liner and reacted at 100 °C for 24 h. After cooling to room temperature, the mixture was washed by centrifugation with N,N-dimethylformamide and ethanol. The product was dried in a vacuum oven to obtain the bimetallic Mg-MOF-74 material, denoted as MOFs-1.

[0042] The above-mentioned bimetallic Mg-MOF-74 adsorbent material was pressed into tablets and sieved. 0.4 g of the tablets was placed in a quartz tube, and adsorption separation experiments were conducted using a multicomponent adsorption breakthrough analyzer. First, the adsorbent material was activated at 250℃ under an argon atmosphere for 8 hours. Then, the CO2 / N2 separation performance (mixed gas volume ratio CO2:N2 = 15% / 85%) was tested at 25℃ and atmospheric pressure. The CO2 / N2 separation coefficients are shown in Table 1.

[0043] Example 2

[0044] 0.3 g of ligand 2,5-dihydroxyterephthalic acid was dissolved in a mixture of 100 mL N,N-dimethylformamide and 20 mL ethanol and stirred for 20 min. 0.866 g of magnesium acetate tetrahydrate and 0.168 g of cobalt acetate tetrahydrate were dissolved in 20 mL of deionized water, and then 0.185 g of benzoic acid was added and stirred for 20 min. The two solutions were mixed and stirred for 20 min, then transferred to a polytetrafluoroethylene liner and reacted at 120 °C for 18 h. After cooling to room temperature, the mixture was washed by centrifugation with N,N-dimethylformamide and ethanol, and the product was dried at room temperature to obtain the bimetallic Mg-MOF-74 material, denoted as MOFs-2.

[0045] The above-mentioned bimetallic Mg-MOF-74 adsorbent material was pressed into tablets and sieved. 0.4 g of the tablets was placed in a quartz tube, and adsorption separation experiments were conducted using a multicomponent adsorption breakthrough analyzer. First, the adsorbent material was activated at 150℃ under an argon atmosphere for 6 hours. Then, the CO2 / N2 separation performance (mixed gas volume ratio CO2:N2 = 15% / 85%) was tested at 25℃ and atmospheric pressure. The CO2 / N2 separation coefficients are shown in Table 1.

[0046] Example 3

[0047] 0.3 g of ligand 2,5-dihydroxyterephthalic acid was dissolved in a mixture of 100 mL N,N-dimethylformamide and 20 mL ethanol and stirred for 30 min. 0.898 g of magnesium acetate tetrahydrate and 0.130 g of cobalt acetate tetrahydrate were dissolved in 20 mL of deionized water, and then 0.164 g of acrylic acid was added and stirred for 30 min. The two solutions were mixed and stirred for 30 min, then transferred to a polytetrafluoroethylene liner and reacted at 110 °C for 36 h. After cooling to room temperature, the mixture was washed by centrifugation with N,N-dimethylformamide and ethanol. The product was dried in a vacuum oven to obtain the bimetallic Mg-MOF-74 material, denoted as MOFs-3.

[0048] The above-mentioned bimetallic Mg-MOF-74 adsorbent material was pressed into tablets and sieved. 0.4 g of the tablets was placed in a quartz tube, and adsorption separation experiments were conducted using a multicomponent adsorption breakthrough analyzer. First, the adsorbent material was activated at 200℃ under an argon atmosphere for 10 h. Then, the CO2 / N2 (mixed gas volume ratio CO2:N2 = 15% / 85%) separation performance was tested at 25℃ and atmospheric pressure. The CO2 / N2 separation coefficients are shown in Table 1.

[0049] Example 4

[0050] 0.3 g of ligand 2,5-dihydroxyterephthalic acid was dissolved in a mixture of 100 mL N,N-dimethylformamide and 20 mL ethanol and stirred for 30 min. 0.808 g of magnesium acetate tetrahydrate and 0.207 g of zinc acetate dihydrate were dissolved in 20 mL of deionized water, and then 0.022 g of acrylic acid was added and stirred for 30 min. The two solutions were mixed and stirred for 30 min, then transferred to a polytetrafluoroethylene liner and reacted at 120 °C for 12 h. After cooling to room temperature, the mixture was washed by centrifugation with N,N-dimethylformamide and ethanol. The product was dried in a vacuum oven to obtain the bimetallic Mg-MOF-74 material, denoted as MOFs-4.

[0051] The above-mentioned bimetallic Mg-MOF-74 adsorbent material was pressed into tablets, sieved, and 0.4 g was placed in a quartz tube for adsorption separation experiments on a multicomponent adsorption breakthrough instrument. First, the adsorbent material was activated at 200℃ under an argon atmosphere for 10 h, followed by CO2 / N2 separation at 25℃ and atmospheric pressure (mixed gas volume ratio CO2:N2 = 15% / 85%). The CO2 / N2 separation coefficients are shown in Table 1.

[0052] Example 5

[0053] 0.3 g of ligand 2,5-dihydroxyterephthalic acid was dissolved in a mixture of 100 mL N,N-dimethylformamide and 20 mL ethanol and stirred for 30 min. 0.898 g of magnesium acetate tetrahydrate and 0.115 g of zinc acetate dihydrate were dissolved in 20 mL of deionized water, and then 0.136 g of oxalic acid was added and stirred for 30 min. The two solutions were then mixed and stirred for 30 min, and then transferred to a polytetrafluoroethylene liner and reacted at 110 °C for 24 h. After cooling to room temperature, the mixture was washed by centrifugation with N,N-dimethylformamide and ethanol. The product was dried in a vacuum oven to obtain the bimetallic Mg-MOF-74 material, denoted as MOFs-5.

[0054] The above-mentioned bimetallic Mg-MOF-74 adsorbent material was pressed into tablets, sieved, and 0.4 g was placed in a quartz tube for adsorption separation experiments on a multicomponent adsorption breakthrough instrument. First, the adsorbent material was activated at 150℃ under an argon atmosphere for 6 h. Then, the CO2 / N2 separation performance (mixed gas volume ratio CO2:N2 = 15% / 85%) was tested at 25℃ and atmospheric pressure. The CO2 / N2 separation coefficients are shown in Table 1.

[0055] Example 6

[0056] 0.3 g of ligand 2,5-dihydroxyterephthalic acid was dissolved in a mixture of 100 mL N,N-dimethylformamide and 20 mL ethanol and stirred for 20 min. 0.918 g of magnesium acetate tetrahydrate and 0.107 g of nickel acetate tetrahydrate were dissolved in 20 mL deionized water, and 0.018 g of acetic acid was added and stirred for 20 min. The two solutions were then mixed and stirred for 20 min, and then transferred to a polytetrafluoroethylene liner. The mixture was reacted at 100 °C for 18 h. After cooling to room temperature, the mixture was washed by centrifugation with N,N-dimethylformamide and ethanol. The product was dried at room temperature to obtain the bimetallic Mg-MOF-74 material, denoted as MOFs-6.

[0057] The above-mentioned bimetallic Mg-MOF-74 adsorbent material was pressed into tablets, sieved, and 0.4 g was placed in a quartz tube for adsorption separation experiments on a multicomponent adsorption breakthrough instrument. First, the adsorbent material was activated at 150℃ under an argon atmosphere for 8 hours. Then, the CO2 / N2 separation performance (mixed gas volume ratio CO2:N2 = 15% / 85%) was tested at 25℃ and atmospheric pressure. The CO2 / N2 separation coefficients are shown in Table 1.

[0058] Example 7

[0059] 0.3 g of ligand 2,5-dihydroxyterephthalic acid was dissolved in a mixture of 100 mL N,N-dimethylformamide and 20 mL ethanol and stirred for 10 min. 0.898 g of magnesium acetate tetrahydrate and 0.130 g of nickel acetate tetrahydrate were dissolved in 20 mL deionized water, and 0.091 g of acetic acid was added and stirred for 10 min. The two solutions were then mixed and stirred for 30 min, and then transferred to a polytetrafluoroethylene liner. The mixture was reacted at 120 °C for 24 h. After cooling to room temperature, the mixture was washed by centrifugation with N,N-dimethylformamide and ethanol. The product was dried in a vacuum oven to obtain the bimetallic Mg-MOF-74 material, denoted as MOFs-7.

[0060] The above-mentioned bimetallic Mg-MOF-74 adsorbent material was pressed into tablets, sieved, and 0.4 g was placed in a quartz tube for adsorption separation experiments on a multicomponent adsorption breakthrough instrument. First, the adsorbent material was activated at 150℃ under an argon atmosphere for 8 hours. Then, the CO2 / N2 separation performance (mixed gas volume ratio CO2:N2 = 15% / 85%) was tested at 25℃ and atmospheric pressure. The CO2 / N2 separation coefficients are shown in Table 1.

[0061] Example 8

[0062] 0.3 g of ligand 2,5-dihydroxyterephthalic acid was dissolved in a mixture of 100 mL N,N-dimethylformamide and 20 mL ethanol and stirred for 10 min. 0.808 g of magnesium acetate tetrahydrate and 0.234 g of nickel acetate tetrahydrate were dissolved in 20 mL of deionized water, and then 0.136 g of oxalic acid was added and stirred for 10 min. The two solutions were mixed and stirred for 10 min, then transferred to a polytetrafluoroethylene liner and reacted at 140 °C for 24 h. After cooling to room temperature, the mixture was washed by centrifugation with N,N-dimethylformamide and ethanol, and the product was dried at room temperature to obtain the bimetallic Mg-MOF-74 material, denoted as MOFs-8.

[0063] The above-mentioned bimetallic Mg-MOF-74 adsorbent material was pressed into tablets and sieved. 0.4 g of the tablets was placed in a quartz tube, and adsorption separation experiments were conducted using a multicomponent adsorption breakthrough analyzer. First, the adsorbent material was activated at 150℃ under an argon atmosphere for 8 hours. Then, the CO2 / N2 separation performance (mixed gas volume ratio CO2:N2 = 15% / 85%) was tested at 25℃ and atmospheric pressure. The CO2 / N2 separation coefficients are shown in Table 1.

[0064] Example 9

[0065] 0.3 g of ligand 2,5-dihydroxyterephthalic acid was dissolved in a mixture of 100 mL N,N-dimethylformamide and 20 mL ethanol and stirred for 30 min. 0.673 g of magnesium acetate tetrahydrate and 0.311 g of manganese chloride tetrahydrate were dissolved in 20 mL of deionized water, and then 0.091 g of acetic acid was added and stirred for 30 min. The two solutions were then mixed and stirred for 30 min, and then transferred to a polytetrafluoroethylene liner and reacted at 120 °C for 24 h. After cooling to room temperature, the mixture was washed by centrifugation with N,N-dimethylformamide and ethanol. The product was dried in a vacuum oven to obtain the bimetallic Mg-MOF-74 material, denoted as MOFs-9.

[0066] The above-mentioned bimetallic Mg-MOF-74 adsorbent material was pressed into tablets and sieved. 0.4 g of the tablets was placed in a quartz tube, and adsorption separation experiments were conducted using a multicomponent adsorption breakthrough analyzer. First, the adsorbent material was activated at 250℃ under an argon atmosphere for 6 hours. Then, the CO2 / N2 (mixed gas CO2:N2 = 15% / 85%) separation performance was tested at 25℃ and atmospheric pressure. The CO2 / N2 separation coefficients are shown in Table 1.

[0067] Example 10

[0068] 0.3 g of ligand 2,5-dihydroxyterephthalic acid was dissolved in a mixture of 100 mL N,N-dimethylformamide and 20 mL ethanol and stirred for 30 min. 0.866 g of magnesium acetate tetrahydrate and 0.133 g of manganese chloride tetrahydrate were dissolved in 20 mL of deionized water, and then 0.204 g of oxalic acid was added and stirred for 30 min. The two solutions were then mixed and stirred for 30 min, and then transferred to a polytetrafluoroethylene liner and reacted at 140 °C for 12 h. After cooling to room temperature, the mixture was washed by centrifugation with N,N-dimethylformamide and ethanol. The product was dried in a vacuum oven to obtain the bimetallic Mg-MOF-74 material, denoted as MOFs-10.

[0069] The above-mentioned bimetallic Mg-MOF-74 adsorbent material was pressed into tablets and sieved. 0.4 g of the tablets was placed in a quartz tube, and adsorption separation experiments were conducted using a multicomponent adsorption breakthrough analyzer. First, the adsorbent material was activated at 250℃ under an argon atmosphere for 8 hours. Then, the CO2 / N2 separation performance (mixed gas volume ratio CO2:N2 = 15% / 85%) was tested at 25℃ and atmospheric pressure. The CO2 / N2 separation coefficients are shown in Table 1.

[0070] Example 11

[0071] 0.3 g of ligand 2,5-dihydroxyterephthalic acid was dissolved in a mixture of 100 mL N,N-dimethylformamide and 20 mL ethanol and stirred for 30 min. 0.808 g of magnesium acetate tetrahydrate and 0.187 g of ferrous chloride tetrahydrate were dissolved in 20 mL of deionized water, and then 0.277 g of benzoic acid was added and stirred for 30 min. The two solutions were mixed and stirred for 30 min, then transferred to a polytetrafluoroethylene liner and reacted at 120 °C for 18 h. After cooling to room temperature, the mixture was washed by centrifugation with N,N-dimethylformamide and ethanol. The product was dried in a vacuum oven to obtain the bimetallic Mg-MOF-74 material, denoted as MOFs-11.

[0072] The above-mentioned bimetallic Mg-MOF-74 adsorbent material was pressed into tablets and sieved. 0.4 g of the tablets was placed in a quartz tube, and adsorption separation experiments were conducted using a multicomponent adsorption breakthrough analyzer. First, the adsorbent material was activated at 300℃ under an argon atmosphere for 8 hours. Then, the CO2:N2 separation performance (mixed gas volume ratio CO2:N2 = 15% / 85%) was tested at 25℃ and atmospheric pressure. The CO2 / N2 separation coefficients are shown in Table 1.

[0073] Example 12

[0074] 0.3 g of ligand 2,5-dihydroxyterephthalic acid was dissolved in a mixture of 100 mL N,N-dimethylformamide and 20 mL ethanol and stirred for 30 min. 0.918 g of magnesium acetate tetrahydrate and 0.085 g of ferrous chloride tetrahydrate were dissolved in 20 mL deionized water, and then 0.164 g of acrylic acid was added and stirred for 30 min. The two solutions were mixed and stirred for 30 min, then transferred to a polytetrafluoroethylene liner and reacted at 110 °C for 24 h. After cooling to room temperature, the mixture was washed by centrifugation with N,N-dimethylformamide and ethanol. The product was dried in a vacuum oven to obtain the bimetallic Mg-MOF-74 material, denoted as MOFs-12.

[0075] The above-mentioned bimetallic Mg-MOF-74 adsorbent material was pressed into tablets and sieved. 0.4 g of the tablets was placed in a quartz tube, and adsorption separation experiments were conducted using a multicomponent adsorption breakthrough analyzer. First, the adsorbent material was activated at 200℃ under an argon atmosphere for 6 hours. Subsequently, the CO2 / N2 (mixed gas CO2:N2 = 15% / 85%) separation performance was tested at 25℃ and atmospheric pressure. The CO2 / N2 separation coefficients are shown in Table 1.

[0076] Example 13

[0077] 0.3 g of ligand 2,5-dihydroxyterephthalic acid was dissolved in a mixture of 100 mL N,N-dimethylformamide and 20 mL ethanol and stirred for 30 min. 0.808 g of magnesium acetate tetrahydrate and 0.235 g of cobalt acetate tetrahydrate were dissolved in 20 mL of deionized water, and then 0.218 g of acrylic acid was added and stirred for 30 min. The two solutions were mixed and stirred for 30 min, then transferred to a polytetrafluoroethylene liner and reacted at 120 °C for 36 h. After cooling to room temperature, the mixture was washed by centrifugation with N,N-dimethylformamide and ethanol. The product was dried in a vacuum oven to obtain the bimetallic Mg-MOF-74 material, denoted as MOFs-13.

[0078] The above-mentioned bimetallic Mg-MOF-74 adsorbent material was pressed into tablets and sieved. 0.4 g of the tablets was placed in a quartz tube, and adsorption separation experiments were conducted using a multicomponent adsorption breakthrough analyzer. First, the adsorbent material was activated at 200℃ under an argon atmosphere for 6 hours. Then, the CO2 / N2 separation performance (mixed gas volume ratio CO2:N2 = 15% / 85%) was tested at 25℃ and atmospheric pressure. The CO2 / N2 separation coefficients are shown in Table 1.

[0079] Example 14

[0080] 0.3 g of ligand 2,5-dihydroxyterephthalic acid was dissolved in a mixture of 100 mL N,N-dimethylformamide and 20 mL ethanol and stirred for 20 min. 0.918 g of magnesium acetate tetrahydrate and 0.107 g of nickel acetate tetrahydrate were dissolved in 20 mL of deionized water, and then 0.273 g of oxalic acid was added and stirred for 20 min. The two solutions were then mixed and stirred for 20 min, and then transferred to a polytetrafluoroethylene liner and reacted at 100 °C for 36 h. After cooling to room temperature, the mixture was washed by centrifugation with N,N-dimethylformamide and ethanol. The product was dried in a vacuum oven to obtain the bimetallic Mg-MOF-74 material, denoted as MOFs-14.

[0081] The above-mentioned bimetallic Mg-MOF-74 adsorbent material was pressed into tablets and sieved. 0.4 g of the tablets was placed in a quartz tube, and adsorption separation experiments were performed using a multicomponent adsorption breakthrough analyzer. First, the adsorbent material was activated at 300℃ under an argon atmosphere for 6 hours. Subsequently, CO2 / N2 separation (mixed gas volume ratio CO2:N2 = 15% / 85%) was performed at 25℃ and atmospheric pressure. The CO2 / N2 separation coefficients are shown in Table 1.

[0082] Example 15

[0083] 0.3 g of ligand 2,5-dihydroxyterephthalic acid was dissolved in a mixture of 100 mL N,N-dimethylformamide and 20 mL ethanol and stirred for 10 min. 0.866 g of magnesium acetate tetrahydrate and 0.168 g of cobalt acetate tetrahydrate were dissolved in 20 mL of deionized water, and 0.091 g of acetic acid was added and stirred for 10 min. The two solutions were then mixed and stirred for 10 min, and then transferred to a polytetrafluoroethylene liner. The mixture was reacted at 120 °C for 24 h. After cooling to room temperature, the mixture was washed by centrifugation with N,N-dimethylformamide and ethanol. The product was dried at room temperature to obtain the bimetallic Mg-MOF-74 material, denoted as MOFs-15.

[0084] The above-mentioned bimetallic Mg-MOF-74 adsorbent material was pressed into tablets and sieved. 0.4 g of the tablets was placed in a quartz tube, and adsorption separation experiments were conducted using a multicomponent adsorption breakthrough analyzer. First, the adsorbent material was activated at 250℃ under an argon atmosphere for 8 hours. Then, the CO2 / N2 separation performance (mixed gas volume ratio CO2:N2 = 15% / 85%) was tested at 25℃ and atmospheric pressure. The CO2 / N2 separation coefficients are shown in Table 1.

[0085] Example 16

[0086] 0.3 g of ligand 2,5-dihydroxyterephthalic acid was dissolved in a mixture of 100 mL N,N-dimethylformamide and 20 mL ethanol and stirred for 10 min. 0.918 g magnesium acetate tetrahydrate and 0.107 g cobalt acetate tetrahydrate were dissolved in 20 mL deionized water, and then 0.277 g benzoic acid was added and stirred for 10 min. The two solutions were mixed and stirred for 10 min, then transferred to a polytetrafluoroethylene liner and reacted at 130 °C for 18 h. After cooling to room temperature, the mixture was washed by centrifugation with N,N-dimethylformamide and ethanol. The product was dried in a vacuum oven to obtain the bimetallic Mg-MOF-74 material, denoted as MOFs-16.

[0087] The above-mentioned bimetallic Mg-MOF-74 adsorbent material was pressed into tablets and sieved. 0.4 g of the tablets was placed in a quartz tube, and adsorption separation experiments were performed using a multicomponent adsorption breakthrough analyzer. First, the adsorbent material was activated at 300℃ under an argon atmosphere for 6 hours. Subsequently, CO2 / N2 separation (mixed gas volume ratio CO2:N2 = 15% / 85%) was performed at 25℃ and atmospheric pressure. The CO2 / N2 separation coefficients are shown in Table 1.

[0088] Example 17

[0089] The difference from Example 7 is that the amount of acetic acid added is 0.136g, and the rest is the same as in Example 7. The resulting MOF material is designated as MOFs-17.

[0090] The above-mentioned adsorbent material was pressed into tablets and sieved. 0.4 g of the tablets was placed in a quartz tube, and adsorption separation experiments were conducted using a multicomponent adsorption breakthrough analyzer. First, the adsorbent was activated at 150℃ under an argon atmosphere for 8 hours. Then, the CO2 / N2 (mixed gas CO2:N2 = 15% / 85%) separation performance was tested at 25℃ and normal pressure. The CO2 / N2 separation coefficients are shown in Table 1.

[0091] Example 18

[0092] The difference from Example 8 is that the reaction temperature is 130°C, and the rest is the same as Example 8. The resulting MOF material is denoted as MOFs-18.

[0093] The above-mentioned adsorbent material was pressed into tablets and sieved. 0.4 g of the tablets was placed in a quartz tube, and adsorption separation experiments were conducted using a multicomponent adsorption breakthrough analyzer. First, the adsorbent was activated at 150℃ under an argon atmosphere for 8 hours. Then, the CO2 / N2 separation performance (mixed gas volume ratio CO2:N2 = 15% / 85%) was tested at 25℃ and atmospheric pressure. The CO2 / N2 separation coefficients are shown in Table 1.

[0094] Example 19

[0095] The difference from Example 9 is that the activation temperature is 200℃, otherwise it is the same as Example 9, and the corresponding MOFs material is designated as MOFs-19. Details are as follows:

[0096] The bimetallic Mg-MOF-74 adsorbent material prepared in Example 9 was pressed into tablets and sieved. 0.4 g of the tablets was placed in a quartz tube and subjected to adsorption separation experiments using a multicomponent adsorption breakthrough analyzer. First, the adsorbent was activated at 200°C under an argon atmosphere for 6 hours. Then, the separation performance of the CO2 / N2 mixed gas (CO2:N2 = 15% / 85%) was tested at 25°C and atmospheric pressure. The CO2 / N2 separation coefficients are shown in Table 1.

[0097] Example 20

[0098] The difference from Example 11 is that the reaction time is 24 hours, and the rest is the same as Example 11. The resulting MOF material is denoted as MOFs-20.

[0099] The above-mentioned adsorbent material was pressed into tablets and sieved. 0.4 g of the tablets was placed in a quartz tube, and adsorption separation experiments were conducted using a multicomponent adsorption breakthrough analyzer. First, the adsorbent was activated at 300℃ under an argon atmosphere for 8 hours. Then, the CO2 / N2 separation performance (mixed gas volume ratio CO2 / N2 = 15% / 85%) was tested at 25℃ and atmospheric pressure. The CO2 / N2 separation coefficients are shown in Table 1.

[0100] Example 21

[0101] The difference from Example 10 is that the activation time is 6 hours; otherwise, it is the same as Example 10. The corresponding MOF material is designated MOFs-21. Details are as follows:

[0102] The bimetallic Mg-MOF-74 adsorbent material prepared in Example 10 was pressed into tablets and sieved. 0.4 g of the tablets was placed in a quartz tube, and adsorption separation experiments were conducted using a multicomponent adsorption breakthrough analyzer. First, the adsorbent was activated at 250°C under an argon atmosphere for 6 hours. Then, the CO2 / N2 separation performance (mixed gas volume ratio CO2 / N2 = 15% / 85%) was tested at 25°C and atmospheric pressure. The CO2 / N2 separation coefficients are shown in Table 1.

[0103] Comparative Example 1

[0104] The difference from Example 15 is that only 1.01g of magnesium acetate tetrahydrate was added as a metal salt, while the rest was the same as in Example 15, resulting in MOFs material, denoted as MOFs-a.

[0105] The above-mentioned adsorbent material was pressed into tablets and sieved. 0.4 g of the tablets were placed in a quartz tube, and adsorption separation experiments were conducted using a multicomponent adsorption breakthrough analyzer. First, the adsorbent was activated at 250℃ under an argon atmosphere for 8 hours. Then, the CO2 / N2 separation performance (mixed gas volume ratio CO2 / N2 = 15% / 85%) was tested at 25℃ and normal pressure. The CO2 / N2 separation coefficients are shown in Table 1.

[0106] Comparative Example 2

[0107] The difference from Example 15 is that only 2,5-dihydroxyterephthalic acid is added, and no other acids are added. The rest is the same as in Example 15, and MOFs material is obtained, which is denoted as MOFs-b.

[0108] The above-mentioned adsorbent material was pressed into tablets and sieved. 0.4 g of the tablets were placed in a quartz tube, and adsorption separation experiments were conducted using a multicomponent adsorption breakthrough analyzer. First, the adsorbent was activated at 250℃ under an argon atmosphere for 8 hours. Then, the CO2 / N2 separation performance (mixed gas volume ratio CO2 / N2 = 15% / 85%) was tested at 25℃ and normal pressure. The CO2 / N2 separation coefficients are shown in Table 1.

[0109] Table 1. CO2 / N2 separation performance of different bimetallic Mg-MOF-74 materials in the examples and comparative examples.

[0110]

[0111]

[0112] Cyclic stability test:

[0113] The bimetallic Mg-MOF-74 adsorbent material MOFs-7 prepared in Example 7 was tested for its recycling performance as an adsorbent under conditions of 25 °C and 100 kPa. The desorption conditions were 200 °C for 2 h. The CO2 / N2 separation coefficients after 5 adsorption / desorption cycles are shown in Table 2.

[0114] Table 2. Cyclic Separation Performance of MOFs-7

[0115]

[0116] In summary, the bimetallic Mg-MOF-74 material prepared in this invention achieves high CO2 / N2 separation efficiency. Compared with pure Mg-MOF-74, bimetallic MOF-74 significantly improves the separation selectivity of CO2 / N2 and exhibits better cycle stability. Furthermore, as an adsorbent, the bimetallic MOF material prepared in this invention can reduce environmental pollution, has minimal corrosiveness to equipment, is easy to regenerate, and is readily recyclable.

[0117] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a bimetallic Mg-MOF-74 material, characterized in that, Includes the following steps: Magnesium acetate, transition metal salts, 2,5-dihydroxyterephthalic acid, carboxylic acid, water, N,N-dimethylformamide, and ethanol are mixed to obtain a mixture; the carboxylic acid includes one or more of benzoic acid, acrylic acid, acetic acid, and oxalic acid; the transition metal salt includes one or more of cobalt acetate, nickel acetate, zinc acetate, manganese chloride, and ferrous chloride. The mixture was subjected to a hydrothermal reaction to obtain the bimetallic Mg-MOF-74 material.

2. The preparation method according to claim 1, characterized in that, The molar ratio of magnesium acetate to transition metal salt is 2~12:

1.

3. The preparation method according to claim 1, characterized in that, The ratio of the total molar amount of magnesium acetate and transition metal salt to the molar amount of 2,5-dihydroxyterephthalic acid is 3.0~3.5:

1.

4. The preparation method according to claim 1 or 3, characterized in that, The molar ratio of the carboxylic acid to 2,5-dihydroxyterephthalic acid is 0.2 to 2:

1.

5. The preparation method according to claim 1, characterized in that, The hydrothermal reaction is carried out at a temperature of 100~140℃ for a duration of 12~36h.

6. The bimetallic Mg-MOF-74 material prepared by the preparation method according to any one of claims 1 to 5.

7. The application of the bimetallic Mg-MOF-74 material of claim 6 to selectively adsorb and separate CO2 from a mixed gas, characterized in that, The mixed gas includes N2.

8. The application according to claim 7, characterized in that, The volume fraction of CO2 in the mixed gas is 10-15%.

9. The application according to claim 7, characterized in that, Before application, the bimetallic Mg-MOF-74 material is activated in an inert atmosphere at a temperature of 150-300°C for 6-10 hours.

Images