Magnesium-based metal organic framework composite cellulose aerogel material based on ex-situ synthesis as well as preparation method and application of magnesium-based metal organic framework composite cellulose aerogel material

Abstract

The invention discloses a magnesium-based metal organic framework composite cellulose aerogel material based on ex-situ synthesis as well as a preparation method and application thereof, and belongs to the technical field of gas adsorption materials and carbon capture. The invention aims to solve the problem that the MOF powder is difficult to process and form. According to the invention, Mg2 (dobpdc) is distributed in cellulose aerogel in a rod-like structure, the length of a rod body is 500-800 nm, the diameter is 50-100 nm, and the structure is loose and porous; according to the aerogel material loaded with Mg2 (dobpdc) and nanocellulose, CO2 chemical adsorption is achieved through [Mg-O = C = O] coordinate bonds formed by unsaturated metal sites Mg < 2 + > in MOF and CO2, and physical adsorption is achieved through hydrogen-bond interaction formed by carboxyl in carboxyl modified nanocellulose and CO2. The adsorbent is applied to adsorption of CO2.

Description

Technical Field

[0001] The present invention belongs to the technical field of gas adsorption materials and carbon capture, and specifically relates to a magnesium-based metal-organic framework (Mg2(dobpdc)) composite cellulose aerogel material based on non-in-situ synthesis and a preparation method thereof; as well as the application of the material in the efficient adsorption and recycling of carbon dioxide. Background Art

[0002] Carbon dioxide (CO2) is one of the main gases contributing to the greenhouse effect, and its emission reduction technologies are crucial for mitigating climate change. Traditional adsorbent materials (such as activated carbon and zeolites) suffer from low adsorption capacity, poor selectivity, and high regeneration energy consumption. Metal-organic frameworks (MOFs) show great potential for CO2 adsorption due to their high surface area, tunable pore size, and chemical functionalization. However, MOF powders are difficult to form and prone to agglomeration, limiting their practical applications. Aerogels, with their three-dimensional porous structure, are ideal supports for MOFs, but the composite process and performance optimization of MOFs and aerogels remain to be solved.

[0003] Prior attempts have been made to combine cellulose aerogels with MOFs, but none have involved efficient CO₂ capture at atmospheric pressure. Research has found that Mg₂(dobpdc) (dobpdc = 4,4'-dioxybiphenyl-3,3'-dicarboxylic acid), a MOF with open metal sites, has a high affinity for CO₂. However, few reports exist on the preparation of its composite with aerogels and the optimization of its adsorption properties. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention provides a method for preparing a cellulose aerogel composite material with Mg2(dobpdc) as a core support and its application. By ex situ growing Mg2(dobpdc) within the cellulose aerogel, the present invention aims to achieve efficient CO2 adsorption and recycling through the synergistic effect of the microporous properties of Mg2(dobpdc) and the macroporous structure of the aerogel.

[0005] The technical difficulty that needs to be overcome in the process of non-in situ synthesis of Mg2(dobpdc) cellulose aerogel in the present invention is: how to stably grow MOF on the surface of the aerogel material and retain the performance of MOF.

[0006] To achieve the above-mentioned purpose of the invention, the present invention provides a cellulose aerogel material loaded with Mg2(dobpdc), which is composited by oxidized nanocellulose, polyvinyl alcohol and MOF materials for adsorbing CO2. The Mg2(dobpdc) is distributed in the cellulose aerogel in a rod-like structure, with a rod length of 500nm-800nm and a diameter of 50nm-100nm, and the structure presents a loose and porous appearance. The preparation method of the present invention is simple, and the prepared composite aerogel material has the advantages of high stability and is expected to be used in industrial production. The preparation method of the magnesium-based metal-organic framework composite cellulose aerogel material based on non-in situ synthesis is carried out according to the following steps: Step 1: extracting cellulose from wood powder, adding a solution of 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) and sodium bromide to the cellulose, stirring at room temperature for at least 12 hours, adjusting the pH value to 10, washing with deionized water, and ultrasonically dispersing to obtain a TEMPO-oxidized nanocellulose dispersion; Step 2: ultrasonically disperse 4,4'-dihydroxy[1,1'-biphenyl]-3,3'-dicarboxylic acid and magnesium nitrate in DMF and methanol solvents, perform hydrothermal reaction, cool, and then wash with DMF and methanol at least three times, respectively, and vacuum dry to obtain Mg2(dobpdc) powder; Step 3: Mix the cellulose dispersion obtained in step 1 with the PVA solution and ionized water, add the Mg2(dobpdc) powder obtained in step 2, stir at room temperature for 8h-15h, and perform gradient freeze-drying to obtain the cellulose aerogel material.

[0007] It is further defined that in step 1, the wood powder is eucalyptus wood powder, basswood wood powder, balsa wood powder or poplar wood powder.

[0008] Further defined, in step 1, cellulose is extracted from wood powder: 2 g of wood powder is weighed and dispersed in a solution containing NaClO2 and glacial acetic acid. The mixture is placed in a 75°C waterbath, heated for 1 hour, cooled, heated again for 1 hour, and cooled to room temperature. This process is repeated three times until the wood powder turns white to completely remove the lignin. The mixture is then washed multiple times with deionized water to remove any NaClO2 remaining on the surface of the holocellulose. The cellulose is then soaked in a 5 wt%-8 wt% KOH solution at room temperature for 12 hours, filtered and washed, and then redispersed in a 6 wt% KOH solution. The mixture is heated for 2 hours and then washed with deionized water and dried.

[0009] The sodium chlorite concentration is 1 wt%; glacial acetic acid is used to adjust the solution pH. The sodium hypochlorite solution concentration is 10%; 2 g of cellulose corresponds to 60 mmol of sodium hypochlorite solution. The volume ratio of sodium chlorite to glacial acetic acid in the mixed solution is 1:2.

[0010] It is further defined that in step 1, the mass ratio of cellulose to 2,2,6,6-tetramethylpiperidin-1-oxyl is 2:0.016.

[0011] It is further defined that in step 1, the mass ratio of cellulose to sodium bromide solution is 2:0.1.

[0012] It is further defined that in step 2, the molar ratio of 4,4'-dihydroxy[1,1'-biphenyl]-3,3'-dicarboxylic acid and magnesium nitrate is 1:(1-5), preferably 1:2.5; when DMF / methanol is mixed, the volume ratio of DMF and methanol is 55:45; the hydrothermal reaction is carried out at 100°C-200°C for 12 hours; the soaking time is 2 hours, preferably, the hydrothermal reaction temperature is 120°C; and the vacuum drying is carried out at 80°C-120°C, preferably, the vacuum drying temperature is 120°C.

[0013] It is further defined that in step 3, the cellulose dispersion is mixed with the PVA solution and ionized water in a mass ratio of 1:1:1; and the mass concentration of the PVA solution is 5%.

[0014] It is further defined that in step 3, the gradient freeze drying in step 3 is: pre-freezing at -80°C for 1 hour, and freeze drying at -60°C for 48 hours.

[0015] The application of the non-in-situ synthesized magnesium-based metal organic framework composite cellulose aerogel material in the adsorption of CO2 is particularly suitable for adsorbing CO2 in the air.

[0016] The large number of carboxyl groups on the cellulose surface of the present invention can not only form hydrogen bonds with CO2 to enhance adsorption, but also the unsaturated metal sites Mg in the MOF material can form hydrogen bonds with CO2 to enhance adsorption. 2+ It can also form coordination bonds with CO2 to promote adsorption.

[0017] The aerogel material loaded with Mg2(dobpdc) and nanocellulose of the present invention is prepared by the unsaturated metal site Mg in MOF. 2+ The chemical adsorption of CO2 is achieved by forming a [Mg-O=C=O] coordination bond with CO2, and the physical adsorption is achieved by forming hydrogen bonds between the carboxyl groups in the carboxyl-modified nanocellulose and CO2. The two can also produce a synergistic adsorption effect through the pore confinement effect.

[0018] Compared with the prior art, the present invention has the following beneficial effects: Compared with the existing technology, the present invention grows MOF materials non-in situ in cellulose aerogel, solving the problem that MOF powder is difficult to process and shape. At the same time, the open metal sites in MOF and the porous structure of aerogel promote CO2 adsorption. At a temperature of 25°C and a pressure of 1 bar, the CO2 adsorption capacity is ≥32cm3 / g. The material's performance remained stable after 10 adsorption-desorption cycles, with a capacity retention rate of ≥95%.

[0019] In order to further understand the features and technical contents of the present invention, please refer to the following detailed description of the present invention and the accompanying drawings. However, the accompanying drawings are provided for reference and illustration only and are not intended to limit the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 XRD patterns of cellulose aerogels loaded with Mg2(dobpdc) prepared in Examples 1-5 of the present invention and Comparative Example 1 Figure 2 SEM images of aerogels prepared in Examples 1-5 of the present invention and Comparative Example 1; Figure 3 The magnified SEM images of the aerogel surfaces prepared in Examples 1-5 of the present invention and Comparative Example 1 are shown; Figure 4 Pure CO2 adsorption diagram of aerogels prepared in Examples 1-5 of the present invention and Comparative Example 1. DETAILED DESCRIPTION

[0021] The following examples and accompanying drawings are intended to provide further detailed descriptions of the present invention. Unless otherwise specified below, all technical and scientific terms used in the present invention, including the processes, conditions, and experimental methods, are common knowledge and general understanding in the art and are not intended to be limiting.

[0022] All examples shown and discussed herein are described and explained by way of example only and not by way of limitation. Therefore, other examples of the exemplary embodiments may have different values.

[0023] As introduced in the background technology, although there are studies on the adsorption of CO2 by MOF / cellulose composite aerogel materials in the prior art, the research on the adsorption effect of CO2 under low partial pressure conditions in the air needs to be strengthened.

[0024] In the following embodiment, the method for extracting cellulose from wood powder is as follows: 2 g of poplar wood powder is purified and dispersed in a mixed solution of sodium chlorite and glacial acetic acid in a volume ratio of 1:2, heated in a water bath at 75°C for at least 3 times, each heating for 1 hour with an interval of 30 minutes, immersed in a 6 wt% KOH solution for 12 hours, washed with deionized water 5 times, filtered, dried, and then dispersed in 60 mmol, approximately 40 mL, 0.6 mol / L sodium hypochlorite solution, and the holocellulose is immersed in a 6 wt% KOH solution and placed at room temperature for 12 hours. Finally, the holocellulose soaked for 12 hours is filtered and washed, and then dispersed in a 6 wt% KOH solution again, heated for 2 hours, washed with deionized water, and dried for use.

[0025] Example 1: The preparation method of the MOF-loaded cellulose aerogel material in this example is carried out according to the following steps: Step 1: Extract cellulose from 2 g of poplar wood powder, add 0.016 g of 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) and 0.1 g of sodium bromide to 200 ml of a solution, stir at room temperature, adjust the pH to 10 with 0.5 M sodium hydroxide solution, wash with deionized water, and disperse by ultrasonication to obtain a TEMPO-oxidized nanocellulose dispersion; Step 2: Ultrasonic dispersion of 4,4'-dihydroxy[1,1'-biphenyl]-3,3'-dicarboxylic acid and magnesium nitrate in a DMF / methanol mixed solvent (volume ratio 55:45) in a molar ratio of 1:1 until uniform, and then placed in a polytetrafluoroethylene-lined reactor, hydrothermally reacted at 120°C for 12 hours, and then washed with DMF and methanol three times, respectively, and dried in vacuo at 120°C for 12 hours to obtain Mg2(dobpdc); Step 3: Mix 5 g of cellulose dispersion with 5 g of 5 wt% PVA solution and 5 g of deionized water, add 100 mg of Mg2(dobpdc) powder, stir at room temperature for 12 h, and perform gradient freeze-drying (pre-freezing at -80 °C for 1 h, freeze-drying at -60 °C for 48 h) to obtain a cellulose aerogel material loaded with MOF.

[0026] Example 2: The preparation method of the MOF-loaded cellulose aerogel material in this example is carried out according to the following steps: Step 1: Extract cellulose from 2 g of poplar wood powder, add 0.016 g of 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) and 0.1 g of sodium bromide to 200 ml of a solution, stir at room temperature, adjust the pH to 10 with 0.5 M sodium hydroxide solution, wash with deionized water, and disperse by ultrasonication to obtain a TEMPO-oxidized nanocellulose dispersion; Step 2: Ultrasonic dispersion of 4,4'-dihydroxy[1,1'-biphenyl]-3,3'-dicarboxylic acid and magnesium nitrate in a DMF / methanol mixed solvent (volume ratio 55:45) in a molar ratio of 1:1 until uniform, hydrothermally react at 120°C for 12 hours, and then wash with DMF and methanol three times, respectively, and vacuum dry at 120°C for 12 hours to obtain Mg2(dobpdc); Step 3: Mix 5 g of cellulose dispersion with 5 g of 5 wt% PVA solution and 5 g of deionized water, add 200 mg of Mg2(dobpdc) powder, stir at room temperature for 12 hours, and perform gradient freeze-drying to obtain a cellulose aerogel material loaded with MOF.

[0027] Example 3: The preparation method of the MOF-loaded cellulose aerogel material in this example is carried out according to the following steps: Step 1: Extract cellulose from 2 g of poplar wood powder, add 0.016 g of 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) and 0.1 g of sodium bromide to 200 ml of a solution, stir at room temperature, adjust the pH to 10 with 0.5 M sodium hydroxide solution, wash with deionized water, and disperse by ultrasonication to obtain a TEMPO-oxidized nanocellulose dispersion; Step 2: Ultrasonic dispersion of 4,4'-dihydroxy[1,1'-biphenyl]-3,3'-dicarboxylic acid and magnesium nitrate in a DMF / methanol mixed solvent (volume ratio 55:45) in a molar ratio of 1:1 until uniform, hydrothermally react at 120°C for 12 hours, and then wash with DMF and methanol three times, respectively, and vacuum dry at 120°C for 12 hours to obtain Mg2(dobpdc); Step 3: Mix 5 g of cellulose dispersion with 5 g of 5 wt% PVA solution and 5 g of deionized water, add 300 mg of Mg2(dobpdc) powder, stir at room temperature for 12 h, and perform gradient freeze-drying (pre-freezing at -80 ° C for 1 h, freeze-drying at -60 ° C for 48 h) to obtain a cellulose aerogel material loaded with MOF.

[0028] Example 4: The preparation method of the MOF-loaded cellulose aerogel material in this example is carried out according to the following steps: Step 1: Extract cellulose from 2 g of poplar wood powder, add 0.016 g of 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) and 0.1 g of sodium bromide to 200 ml of a solution, stir at room temperature, adjust the pH to 10 with 0.5 M sodium hydroxide solution, wash with deionized water, and disperse by ultrasonication to obtain a TEMPO-oxidized nanocellulose dispersion; Step 2: Ultrasonic dispersion of 4,4'-dihydroxy[1,1'-biphenyl]-3,3'-dicarboxylic acid and magnesium nitrate in a DMF / methanol mixed solvent (volume ratio 55:45) in a molar ratio of 1:1 until uniform, hydrothermally react at 120°C for 12 hours, and then wash with DMF and methanol three times, respectively, and vacuum dry at 120°C for 12 hours to obtain Mg2(dobpdc); Step 3: Mix 5 g of cellulose dispersion with 5 g of 5 wt% PVA solution and 5 g of deionized water, add 400 mg of Mg2(dobpdc) powder, stir at room temperature for 12 h, and perform gradient freeze-drying (pre-freezing at -80 ° C for 1 h, freeze-drying at -60 ° C for 48 h) to obtain a cellulose aerogel material loaded with MOF.

[0029] Example 5: The preparation method of the MOF-loaded cellulose aerogel material in this example is carried out according to the following steps: Step 1: Extract cellulose from 2 g of poplar wood powder, add 0.016 g of 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) and 0.1 g of sodium bromide to 200 ml of a solution, stir at room temperature, adjust the pH to 10 with 0.5 M sodium hydroxide solution, wash with deionized water, and disperse by ultrasonication to obtain a TEMPO-oxidized nanocellulose dispersion; Step 2: Ultrasonic dispersion of 4,4'-dihydroxy[1,1'-biphenyl]-3,3'-dicarboxylic acid and magnesium nitrate in a DMF / methanol mixed solvent (volume ratio 55:45) in a molar ratio of 1:1 until uniform, hydrothermally react at 120°C for 12 hours, and then wash with DMF and methanol three times, respectively, and vacuum dry at 120°C for 12 hours to obtain Mg2(dobpdc); Step 3: Mix 5 g of cellulose dispersion with 5 g of 5 wt% PVA solution and 5 g of deionized water, add 500 mg of Mg2(dobpdc) powder, stir at room temperature for 12 h, and perform gradient freeze-drying (pre-freezing at -80 ° C for 1 h, freeze-drying at -60 ° C for 48 h) to obtain a cellulose aerogel material loaded with MOF.

[0030] (1) The purified poplar wood powder was heated in a sodium chlorite / glacial acetic acid mixture at 75°C for three times, each time for one hour. It was then soaked in a 6 wt% KOH solution for 12 hours, washed, heated, and dried. The powder was oxidized with TEMPO / NaBr / NaClO, the pH was adjusted to 10, and the powder was washed and dispersed to obtain TEMPO-oxidized nanocellulose. (2) 5 g of cellulose dispersion was mixed with 5 g of 5 wt% PVA solution and 5 g of deionized water, stirred at room temperature for 12 h, and then subjected to gradient freeze-drying to obtain cellulose aerogel material.

[0031] XRD test: XRD test confirmed that Examples 1-5 of the present invention successfully achieved the composite of MOF and cellulose aerogel. As the content of MOF material increased, the characteristic peak became more and more obvious. Figure 1 .

[0032] SEM test: Through SEM test, it can be observed that the aerogel materials prepared in Examples 1-5 of the present invention and Comparative Example 1 all present a loose porous structure, and the composite cross-linking phenomenon of the rod-shaped MOF material and the cellulose base material can also be observed. Figure 2 .

[0033] Further observation revealed that a large number of rod-like structures existed on the surface of the aerogel materials of Examples 1-5 of the present invention, which were the Mg2(dobpdc) synthesized by the present invention. The surface of the control example 1 was relatively smooth. Figure 3 .

[0034] The CO2 adsorption test was conducted in a tube furnace. First, the aerogel material was placed in a tube furnace, the temperature was adjusted to 130°C for vacuum activation, nitrogen was introduced to evacuate, and then CO2 was introduced for a period of time to allow the material to fully contact with CO2. The temperature was then adjusted to 130°C again, nitrogen was introduced at a fixed rate, the CO2 content at the outlet was recorded in real time, and the CO2 adsorption amount was calculated using the formula. The results are as follows: Figure 4 As shown, compared with the blank group without MOF material, Examples 1-5 of the present invention can effectively adsorb CO2, and Example 2 of the present invention can adsorb 32.06 cm 3 / g of CO2.

[0035] Although the specific embodiments of the present invention are described in conjunction with the text description and the drawings, this does not limit the scope of protection of the present invention. For those skilled in the art, various modifications or variations that can be made on the basis of the technical solution of the present invention without expending creative labor are still within the scope of protection of the present invention.

Claims

1. A method for preparing a magnesium-based metal-organic framework composite cellulose aerogel material based on non-in-situ synthesis, characterized in that: The following steps are involved: Step 1: extracting cellulose from wood powder, adding 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) and sodium bromide solution to the cellulose, stirring at room temperature for at least 12 hours, adjusting the pH value to 10, washing with deionized water, and ultrasonically dispersing to obtain a TEMPO-oxidized nanocellulose dispersion; Step 2: ultrasonically disperse 4,4'-dihydroxy[1,1'-biphenyl]-3,3'-dicarboxylic acid and magnesium nitrate in DMF and methanol solvents, perform hydrothermal reaction, cool, and then wash with DMF and methanol at least three times, respectively, and vacuum dry to obtain Mg2(dobpdc) powder; Step 3: Mix the cellulose dispersion obtained in step 1 with the PVA solution and ionized water, add the Mg2(dobpdc) powder obtained in step 2, stir at room temperature for 8h-15h, and perform gradient freeze-drying to obtain the cellulose aerogel material.

2. The method according to claim 1, characterized in that The wood powder is eucalyptus wood powder, basswood wood powder, balsa wood powder or poplar wood powder.

3. The method according to claim 1, characterized in that The mass ratio of cellulose to 2,2,6,6-tetramethylpiperidin-1-oxyl is 2:0.

016.

4. The method according to claim 1, characterized in that The mass ratio of cellulose to sodium bromide solution is 2:0.

1.

5. The method according to claim 1, characterized in that: In step 2, 4,4'-dihydroxy[1,1'-biphenyl]-3,3'-dicarboxylic acid and magnesium nitrate are in a molar ratio of 1:(1-5); when DMF / methanol is mixed, the volume ratio of DMF to methanol is 55:45; the reaction is hydrothermally reacted at 100°C-200°C for 12 hours; the soaking time is 2 hours; and the mixture is vacuum dried at 80°C-120°C.

6. The method according to claim 1, characterized in that In step 3, the cellulose dispersion is mixed with the PVA solution and ionized water in a mass ratio of 1:1:1; the mass concentration of the PVA solution is 5%; in step 3, the step 3 is subjected to gradient freeze drying: pre-freezing at -80°C for 1 hour, and freeze drying at -60°C for 48 hours.

7. A magnesium-based metal-organic framework composite cellulose aerogel material based on ex situ synthesis prepared by the method according to any one of claims 1 to 8, wherein Mg2(dobpdc) in the composite aerogel material is distributed in the cellulose aerogel in a rod-like structure, the rod length is 200nm-500nm, the diameter is 50nm-100nm, and the structure presents a loose and porous appearance.

8. Use of a magnesium-based metal-organic framework composite cellulose aerogel material prepared by the method according to any one of claims 1 to 8 based on ex-situ synthesis in the adsorption of CO2.

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