A method for assembling and stabilizing metal-organic framework nanomaterials using natural pollen as a template

Abstract

The application belongs to the technical field of composite materials, and specifically discloses a method for assembling and stabilizing metal organic framework nanomaterials by using natural pollen as a template, which comprises the following steps: (1) grinding pollen particles, washing, etching by an alkaline solution, centrifugal washing and drying to obtain pretreated pollen; (2) dispersing the pretreated pollen in deionized water, adding a surface modifier and stirring and soaking, and then centrifugal washing to obtain wet surface modified pollen; (3) dispersing the wet surface modified pollen in a soluble copper salt ethanol solution, stirring and heating until the solvent evaporates, and then dispersing the dried solid in N,N-dimethylformamide, adding an ethanolic solution of trimesic acid and an ethanolic solution of polyvinylpyrrolidone to perform hydrothermal reaction; and (4) centrifugal washing and drying the product of the hydrothermal reaction to obtain pollen-assembled metal organic framework nanomaterials. The application uses natural pollen as a biological template, reduces the use of organic solvents in traditional organic templates, and overcomes problems such as high cost and environmental pollution.

Description

Technical Field

[0001] This invention belongs to the field of composite material technology, specifically relating to a method for assembling and stabilizing metal-organic framework nanomaterials using natural pollen as a template. Background Technology

[0002] Metal-organic frameworks (MOFs) are a novel class of porous materials composed of metal ions and organic ligands linked by coordination bonds, forming a highly ordered network structure through self-assembly. Compared to traditional inorganic porous materials, MOFs possess numerous advantages, including high specific surface area, ordered structure, flexible pore structure, and variable functional groups, leading to their widespread application in catalysis, magnetic materials, sensors, drug delivery, and gas adsorption and storage. However, in aqueous environments, the organic ligands in MOF nanomaterials are easily replaced by water molecules, eventually causing the framework to collapse. Therefore, water stability remains a major challenge hindering the practical application of most MOF nanomaterials. For example, Cu-BTC, a common copper-based MOF material, shows great potential in catalysis and gas adsorption and separation, but the Cu in Cu-BTC... 2+ The coordination bonds formed between Cu-BTC and organic ligands through complexation reactions are relatively weak, making them susceptible to attack by water molecules, leading to framework destruction and structural collapse, which limits the practical application of Cu-BTC. Currently, most common modifications to the water resistance of metal-organic framework nanomaterials involve altering the metal ions or organic ligands.

[0003] Chinese patent CN114206993A discloses a water-stable Cu-BTC MOF. The Cu-BTC MOF is modified by replacing some BTC ligands (1,3,5-benzenetricarboxylic acid) with 5-aminoisophthalic acid (AIA), or by occupying the open coordination sites of Cu with ligands such as acetonitrile (CH3CN). However, the new ligands introduced during the post-synthesis modification process of the Cu-BTC MOF prepared in this patent alter the original structure of the MOF.

[0004] To address the above issues, based on the high porosity and compatibility of metal-organic framework (MOF) nanomaterials, some studies have explored assembling MOF nanomaterials with other materials to improve their water stability. Chinese patent CN114870817A discloses a method for preparing Cu-BTC with improved water stability and its application. The specific steps are as follows: Step 1: Dissolve copper salt in deionized water to obtain solution A, disperse nano-ZnO in deionized water to obtain solution B, add solution B to solution A, and stir rapidly to form a hydroxyl double salt solution C. Step 2: Add PVP powder to hydroxyl double salt solution C and stir until dissolved to obtain a mixed solution D. Step 3: Dissolve trimesic acid in a mixture of N,N-dimethylformamide and ethanol to form solution E. Step 4: Add solution E dropwise to mixed solution D, mix and stir, react for a period of time, centrifuge the resulting product and dry it to obtain a PVP@Cu-BTC composite with good water stability encapsulated in PVP. However, the preparation of such composite materials has many problems, such as the complicated preparation steps of traditional artificial materials (such as polymers, mesoporous silica, etc.), the need to use a lot of organic reagents, and the high cost.

[0005] As is well known, bio-template materials possess advantages such as good reproducibility, high biocompatibility, low cost and availability, environmental friendliness, and compliance with sustainable development principles, making them ideal alternatives to artificial materials. The exine of natural pollen is primarily composed of sporophytin, providing strong mechanical strength; its surface contains phospholipids and proteins, which facilitate precursor attachment and provide a medium for the doping of other elements. However, untreated bio-templates have fewer functional groups on their surface, resulting in lower loading efficiency. Summary of the Invention

[0006] The purpose of this invention is to overcome the defects of the existing technology and provide a method for assembling and stabilizing metal-organic framework nanomaterials using natural pollen as a template. By adding a surface modifier to modify the pollen surface, the loading capacity of the metal-organic framework nanomaterials is increased. The surface of natural pollen is modified to grow metal-organic framework nanomaterials in situ inside the pollen, so that the pollen acts as a protective shell and improves its water resistance stability, thereby solving the dilemma of metal-organic framework nanomaterials in practical applications.

[0007] To achieve the above objectives, one of the technical solutions of the present invention is: a method for assembling and stabilizing metal-organic framework nanomaterials using natural pollen as a template, comprising the following steps:

[0008] (1) The pollen grains were crushed, washed with anhydrous ethanol, etched with an alkaline solution, and then centrifuged, washed and dried to obtain pretreated pollen.

[0009] (2) Disperse the pretreated pollen obtained in step (1) in deionized water, add surface modifier, stir and soak for 2-5 hours, centrifuge and wash to obtain wet surface modified pollen.

[0010] (3) The wet surface-modified pollen obtained in step (2) is dispersed in a soluble copper salt ethanol solution, stirred and heated until the solvent is completely evaporated, and the dried solid is redispersed in N,N-dimethylformamide (DMF). Trimethylolpropionic acid ethanol solution and polyvinylpyrrolidone ethanol solution are added and stirred to carry out a hydrothermal reaction.

[0011] (4) The suspension obtained from the hydrothermal reaction in step (3) is centrifuged, washed and dried to obtain pollen-assembled metal-organic framework nanomaterials.

[0012] In a preferred embodiment of the present invention, the pollen in step (1) is at least one of camellia pollen, rapeseed pollen or sunflower pollen.

[0013] In a preferred embodiment of the present invention, the alkaline solution in step (1) is at least one of sodium hydroxide solution, potassium hydroxide solution and calcium hydroxide solution, and the concentration of the alkaline solution is 0.1 to 10 wt%.

[0014] In a preferred embodiment of the present invention, the surface modifier in step (2) is at least one of ethylenediaminetetraacetic acid, 3-aminopropyltrimethoxysilane and hexadecyltrimethylammonium bromide.

[0015] In a preferred embodiment of the present invention, the ratio of surface modifier, pretreated pollen and deionized water in step (2) is (0.01-1) mL: (0.1-1) g: 8 mL.

[0016] In a preferred embodiment of the present invention, the soluble copper salt in step (3) is at least one of copper nitrate, copper chloride, and copper acetate.

[0017] In a preferred embodiment of the present invention, in step (3), the concentration of soluble copper salt in the ethanol solution of soluble copper salt is 0.01-2 wt%, the concentration of trimesic acid in the ethanol solution of trimesic acid is 0.1-4 wt%, and the concentration of polyvinylpyrrolidone in the ethanol solution of polyvinylpyrrolidone is 0.1-2 wt%.

[0018] In a preferred embodiment of the present invention, the ratio of the soluble copper salt ethanol solution, wet surface-modified pollen, N,N-dimethylformamide (DMF), trimesic acid ethanol solution and polyvinylpyrrolidone ethanol solution in step (3) is (0.1-20) mL:(0.01-0.2) g:(0.1-20) mL:(0.01-20) mL:(0.01-5) mL.

[0019] In a preferred embodiment of the present invention, the etching time in step (3) is 3 to 8 hours, the hydrothermal reaction temperature is 60 to 120°C, and the reaction time is 12 to 24 hours.

[0020] To achieve the above objectives, the second technical solution of the present invention is: a pollen-assembled metal-organic framework composite material prepared by a method of assembling and stabilizing metal-organic framework nanomaterials using natural pollen as a template.

[0021] In a preferred embodiment of the present invention, the pollen contains embedded metal-organic framework nanomaterials.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. By adopting the technical solution of the present invention, natural pollen is used as a biological template, which is inexpensive, readily available, green and environmentally friendly, reducing the use of organic solvents in traditional organic template agents and overcoming problems such as high cost and environmental pollution.

[0024] 2. In this invention, the surface-modified pollen can be used as a template to induce the growth of metal-organic framework nanomaterials inside the pollen, thereby providing a robust protective shell to resist adverse reaction conditions, improve water resistance and stability, extend service life, and give pollen-assembled metal-organic framework composite materials a promising prospect for multifunctional applications.

[0025] 3. The metal-organic framework nanomaterials prepared by this invention have a multi-level spatial structure, and the method is simple, easy to operate, and has good reproducibility, and has broad application prospects in catalysis, adsorption and other fields. Attached Figure Description

[0026] Figure 1 This is a scanning electron microscope (SEM) image of the Cu-BTC@pollen material prepared in Example 1 of the present invention;

[0027] Figure 2 Scanning electron microscope (SEM) images of the Cu-BTC@pollen material prepared in Example 1 of this invention before and after soaking in water at 60°C for 24 hours;

[0028] Figure 3 The X-ray diffraction (XRD) spectra of the Cu-BTC@pollen material prepared in Example 1 of this invention before and after soaking in water at 60°C for 24 hours.

[0029] Figure 4 The X-ray diffraction (XRD) spectra of Cu-BTC@pollen (without NaOH) material prepared in Comparative Example 1 of this invention before and after soaking in water at 60°C for 24 hours are shown. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in more detail below with reference to the accompanying drawings and specific embodiments. However, the scope of protection of this invention is not limited to these embodiments. The same reference numerals throughout the text always represent the same elements, and similar reference numerals represent similar elements.

[0031] A method for assembling and stabilizing metal-organic framework nanomaterials using natural pollen as a template includes the following steps:

[0032] (1) The pollen grains were crushed, washed with anhydrous ethanol, etched with an alkaline solution, and then centrifuged, washed and dried to obtain pretreated pollen.

[0033] (2) Disperse the pretreated pollen obtained in step (1) in deionized water, add surface modifier, stir and soak for 2-5 hours, centrifuge and wash to obtain wet surface modified pollen.

[0034] (3) The wet surface-modified pollen obtained in step (2) is dispersed in a soluble copper salt ethanol solution, stirred and heated until the solvent is completely evaporated, and the dried solid is redispersed in N,N-dimethylformamide (DMF). Trimethylolpropionic acid ethanol solution and polyvinylpyrrolidone ethanol solution are added and stirred to carry out a hydrothermal reaction.

[0035] (4) The suspension obtained from the hydrothermal reaction in step (3) is centrifuged, washed and dried to obtain pollen-assembled metal-organic framework nanomaterials.

[0036] The pollen in step (1) is at least one of camellia pollen, rapeseed pollen, or sunflower pollen.

[0037] The alkaline solution in step (1) is at least one of sodium hydroxide solution, potassium hydroxide solution and calcium hydroxide solution, and the concentration of the alkaline solution is 0.1 to 10 wt%.

[0038] The surface modifier in step (2) is at least one of ethylenediaminetetraacetic acid, 3-aminopropyltrimethoxysilane, and hexadecyltrimethylammonium bromide.

[0039] In step (2), the ratio of surface modifier, pretreated pollen and deionized water is (0.01-1) mL: (0.1-1) g: 8 mL.

[0040] In step (3), the soluble copper salt is at least one of copper nitrate, copper chloride, and copper acetate.

[0041] In step (3), the concentration of soluble copper salt in the ethanol solution of soluble copper salt is 0.01-2 wt%, the concentration of pyromellitic acid in the ethanol solution of pyromellitic acid is 0.1-4 wt%, and the concentration of polyvinylpyrrolidone in the ethanol solution of polyvinylpyrrolidone is 0.1-2 wt%.

[0042] The ratio of the soluble copper salt ethanol solution, wet surface-modified pollen, N,N-dimethylformamide (DMF) solution, trimesic acid ethanol solution, and polyvinylpyrrolidone ethanol solution is (0.1–20) mL: (0.01–0.2) g: (0.1–20) mL: (0.01–20) mL: (0.01–5) mL.

[0043] In step (3), the etching time is 3 to 8 hours, the hydrothermal reaction temperature is 60 to 120°C, and the reaction time is 12 to 24 hours.

[0044] A pollen-assembled metal-organic framework composite material prepared by assembling and stabilizing metal-organic framework nanomaterials using natural pollen as a template.

[0045] The pollen contains embedded metal-organic framework nanomaterials.

[0046] The SEM characterization tests used in the following examples and comparative examples were performed using a Hitachi SU5000 field emission scanning electron microscope.

[0047] The XRD characterization tests used in the following examples and comparative examples were performed using a SmartLab X-ray powder diffractometer from Rigaku Corporation, Japan.

[0048] Example 1

[0049] A method for assembling and stabilizing metal-organic framework nanomaterials using natural pollen as a template includes the following steps:

[0050] Step (1):

[0051] (a) Commercially available rapeseed pollen granules were crushed using a pulverizer to obtain pollen powder, which was then soaked in anhydrous ethanol for 2 hours to remove dust from the pollen, and then dried at 80°C for 8 hours.

[0052] (b) Take 1.5g of dried rapeseed pollen powder, add 30mL of 7.5wt% sodium hydroxide aqueous solution, stir thoroughly for 5h, wash twice by centrifugation with ethanol, and then dry at 80℃ for 8h.

[0053] Step (2): Disperse 0.1g of the pretreated pollen obtained in step (1) in 8mL of deionized water, add 0.01mL of 3-aminopropyltrimethoxysilane surface modifier, stir and soak for 4h, then wash twice by centrifugation with ethanol to obtain wet surface modified pollen.

[0054] Step (3):

[0055] (a) Disperse all the wet surface-modified pollen obtained in step (2) in 15 mL of 0.02 wt% copper nitrate ethanol solution, stir and heat until the solvent evaporates;

[0056] (b) The solid sample obtained in step (a) of step (3) was redispersed in 15 mL of N,N-dimethylformamide (DMF), and stirred continuously. After 2 min, 15 mL of 0.1 wt% pyromellitic acid ethanol solution and 3 mL of 0.15 wt% polyvinylpyrrolidone ethanol solution were added. After stirring for 10 min, the mixture was placed in an 80 °C oven for hydrothermal reaction for 20 h.

[0057] The suspension obtained from the hydrothermal reaction in step (4) and step (3) (b) was washed twice by centrifugation with ethanol and dried at 80°C for 8 hours to obtain the pollen-assembled metal-organic framework nanomaterial.

[0058] SEM images of the metal-organic framework nanomaterials prepared in this embodiment are attached. Figure 1 As shown in the figure, the metal-organic framework nanomaterials prepared by this method grow within the cavities of the pollen template. The metal-organic framework nanomaterials are octahedral with a particle size of approximately 250 nm. The SEM and XRD patterns of the prepared Cu-BTC@pollen material before and after immersion in water at 60℃ for 24 h are shown in the figure. Figure 2 , 3 As shown in the figure, the metal-organic framework (MOF) nanomaterials remained structurally intact before and after immersion in water, demonstrating the improved water resistance of pollen-assembled MOF nanomaterials. A 10 mg sample was used to catalyze the degradation of Rhodamine B (100 ppm, 50 mL) with hydrogen peroxide. Within 60 minutes, the decolorization rate approached 100%, significantly higher than that of powdered MOF nanomaterials (approximately 75%). After seven cycles under the same conditions, the decolorization rate of the pollen-assembled MOF nanomaterials remained above 90%, while the decolorization rate of the powdered MOF nanomaterials approached 0% by the third cycle due to excessive sample loss. The sample was mixed with a polymer and used as ink for 3D printing. The tensile properties of the sample were tested. Compared to powdered MOF nanomaterials, the tensile strength and elongation at break of the pollen-assembled MOF nanomaterials were increased by 7 times and 5 times, respectively. This indicates that the pollen-assembled MOF nanomaterials exhibit significant improvements in both mechanical stability and catalytic degradation performance.

[0059] Example 2

[0060] In step (b) of step (1) of Example 1, the concentration of 30 mL of 7.5 wt% sodium hydroxide aqueous solution was adjusted to 3 wt%; in step (a) of step (3) of Example 1, the concentration of 15 mL of 0.02 wt% copper nitrate ethanol solution was adjusted to 5 mL of 0.02 wt% copper acetate ethanol solution, and the remaining process parameters were the same as in Example 1. The pollen-assembled metal-organic framework nanomaterials can be obtained.

[0061] Example 3

[0062] In step (2) of Example 1, the 0.01 mL of 3-aminopropyltrimethoxysilane surface modifier was replaced with 0.01 g of ethylenediaminetetraacetic acid surface modifier, and the remaining process parameters were the same as in Example 1. The metal-organic framework nanomaterials prepared by this method grow within the cavity of the pollen template. The metal-organic framework nanomaterials are octahedral, thus obtaining the pollen-assembled metal-organic framework nanomaterials.

[0063] Example 4

[0064] In step (2) of Example 1, the 0.01 mL of 3-aminopropyltrimethoxysilane surface modifier was changed to 0.01 g of hexadecyltrimethylammonium bromide surface modifier, and the remaining process parameters were the same as in Example 1. The pollen-assembled metal-organic framework nanomaterials can be obtained.

[0065] Example 5

[0066] In step (a) of step (1) of Example 1, rapeseed pollen was replaced with sunflower pollen; in step (2) of Example 1, 0.01 mL of 3-aminopropyltrimethoxysilane surface modifier was replaced with 0.02 mL of 3-aminopropyltrimethoxysilane surface modifier, so that the mass ratio of surface modifier to pollen was 1:5, and the remaining process parameters were the same as in Example 1. The pollen-assembled metal-organic framework nanomaterials can be obtained.

[0067] Example 6

[0068] In step (a) of step (1) of Example 1, rapeseed pollen was replaced with camellia pollen; in step (2) of Example 1, 0.01 mL of 3-aminopropyltrimethoxysilane surface modifier was replaced with 0.05 mL of 3-aminopropyltrimethoxysilane surface modifier, so that the mass ratio of surface modifier to pollen was 1:2, and the remaining process parameters were the same as in Example 1. The pollen-assembled metal-organic framework nanomaterials can be obtained.

[0069] Comparative Example 1

[0070] In step (b) of step (1) of Example 1, no sodium hydroxide aqueous solution is added; in step (a) of step (3) of Example 1, 15 mL of 0.02 wt% copper nitrate ethanol solution is adjusted to 5 mL of 0.02 wt% copper acetate ethanol solution, and the remaining process parameters are the same as in Example 1, to prepare pollen-assembled metal-organic framework nanomaterials.

[0071] In the pollen-assembled metal-organic framework nanomaterial prepared in Comparative Example 1, most of the Cu-BTC nanoparticles were dispersed on the outside of the pollen; and the water stability and mechanical stability were also worse than those in Example 1. Figure 4 The XRD patterns of the prepared Cu-BTC@pollen (without NaOH) material before and after soaking in water at 60℃ for 24h are shown in the figure. It can be seen from the figure that the intensity of the characteristic peak of the metal-organic framework nanomaterial decreased before and after soaking in water, but the crystal structure did not change significantly.

[0072] Comparative Example 2

[0073] In step (2) of Example 1, no 3-aminopropyltrimethoxysilane surface modifier was added, and the remaining process parameters were the same as in Example 1 to prepare pollen-assembled metal-organic framework nanomaterials. This method can obtain the pollen-assembled metal-organic framework nanomaterials, but the loading of the metal-organic framework nanomaterials is low, and they lack regular morphology, mostly growing along the outer wall of the pollen template. 10 mg of the sample was used to catalyze the degradation of Rhodamine B (100 ppm) with hydrogen peroxide; the decolorization rate was close to 80% within 60 minutes, a slight improvement compared to powdered metal-organic framework nanomaterials (approximately 75%). The sample was mixed with a polymer as ink for 3D printing, and the tensile properties of the sample were tested. Compared to powdered metal-organic framework nanomaterials, the tensile strength and elongation at break of the pollen-assembled metal-organic framework nanomaterials were increased by 50% and 20%, respectively.

[0074] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for assembling and stabilizing metal-organic framework nanomaterials using natural pollen as a template, characterized in that, Includes the following steps: (1) The pollen grains were crushed, washed with anhydrous ethanol, etched with an alkaline solution, centrifuged, washed and dried to obtain pretreated pollen. (2) Disperse the pretreated pollen obtained in step (1) in deionized water, add surface modifier, stir and soak for 2-5 h, centrifuge and wash to obtain wet surface modified pollen; (3) Disperse the wet surface-modified pollen obtained in step (2) in a soluble copper salt ethanol solution, stir and heat until the solvent is completely evaporated, take the dried solid and redisperse it in N,N-dimethylformamide, add pyromellitic acid ethanol solution and polyvinylpyrrolidone ethanol solution and stir to carry out hydrothermal reaction. (4) The suspension obtained from the hydrothermal reaction in step (3) is centrifuged, washed and dried to obtain pollen-assembled metal-organic framework nanomaterials; The surface modifier is at least one of ethylenediaminetetraacetic acid, 3-aminopropyltrimethoxysilane, and hexadecyltrimethylammonium bromide; The ratio of the surface modifier, pretreated pollen and deionized water is (0.01~1) mL: (0.1~1) g: 8 mL.

2. The method for assembling and stabilizing metal-organic framework nanomaterials using natural pollen as a template according to claim 1, characterized in that: The pollen in step (1) is at least one of camellia pollen, rapeseed pollen, or sunflower pollen.

3. The method for assembling and stabilizing metal-organic framework nanomaterials using natural pollen as a template according to claim 1, characterized in that: The alkaline solution in step (1) is at least one of sodium hydroxide solution, potassium hydroxide solution and calcium hydroxide solution, and the concentration of the alkaline solution is 0.1~10 wt%.

4. The method for assembling and stabilizing metal-organic framework nanomaterials using natural pollen as a template according to claim 1, characterized in that: In step (3), the soluble copper salt is at least one of copper nitrate, copper chloride, and copper acetate.

5. The method for assembling and stabilizing metal-organic framework nanomaterials using natural pollen as a template according to claim 1, characterized in that: In step (3), the concentration of soluble copper salt in the soluble copper salt ethanol solution is 0.01~2 wt%, the concentration of pyromellitic acid in the pyromellitic acid ethanol solution is 0.1~4 wt%, and the concentration of polyvinylpyrrolidone in the polyvinylpyrrolidone ethanol solution is 0.1~2 wt%.

6. The method for assembling and stabilizing metal-organic framework nanomaterials using natural pollen as a template according to claim 1, characterized in that: In step (3), the ratio of soluble copper salt ethanol solution, wet surface-modified pollen, N,N-dimethylformamide, trimesic acid ethanol solution and polyvinylpyrrolidone ethanol solution is (0.1~20) mL: (0.01~0.2) g: (0.1~20) mL: (0.01~20) mL: (0.01~5) mL.

7. The method for assembling and stabilizing metal-organic framework nanomaterials using natural pollen as a template according to claim 1, characterized in that: In step (3), the etching time is 3-8 h, the hydrothermal reaction temperature is 60-120℃, and the reaction time is 12-24 h.

8. A pollen-assembled metal-organic framework composite material prepared by the method of assembling and stabilizing metal-organic framework nanomaterials using natural pollen as a template as described in any one of claims 1 to 7.

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