阅读说明：本技术 一种分级多孔zif-9的合成方法 (Synthesis method of hierarchical porous ZIF-9 ) 是由 庄赞勇 李虎 张元鸣 庄国鑫 于岩 于 2021-08-30 设计创作，主要内容包括：本发明公开了一种分级多孔ZIF-9的合成方法,其利用价格低廉、绿色无毒、易获得的原料,采用胶体盐模板法,一步合成了分级多孔的ZIF-9。其中,通过改变Co/苯并咪唑的比例、钠盐的浓度和超声时间,可调控盐模板颗粒及其内部孔道的大小,从而实现分级多孔ZIF-9在形貌和孔道尺寸的精细调控。本发明制备过程经济高效、简便快捷,可实现大规模生产。(The invention discloses a method for synthesizing hierarchical porous ZIF-9, which synthesizes the hierarchical porous ZIF-9 in one step by using raw materials which are low in price, green, nontoxic and easy to obtain and adopting a colloidal salt template method. The ratio of Co/benzimidazole, the concentration of sodium salt and the ultrasonic time are changed, the size of the salt template particles and the size of the inner pore channel of the salt template particles can be regulated, and therefore fine regulation and control of the morphology and the pore channel size of the hierarchical porous ZIF-9 are achieved. The preparation process is economic, efficient, simple, convenient and quick, and can realize large-scale production.)

1. A method for synthesizing a hierarchical porous ZIF-9 is characterized by comprising the following steps: the method comprises the following steps:

(1) mixing Co (CH)₃COO)₂And NaNO₃Or CH₃COONa and Co (NO)₃)₂Adding the mixture of (a) to DMF to form a solution A; adding benzimidazole to DMF to form solution B; respectively stirring the solution A and the solution B at room temperature and then carrying out ultrasonic treatment;

(2) pouring the solution B into the solution A for stirring reaction, and using DMF or H to react the obtained product₂O cleaning;

(3) and (3) soaking the cleaned product into a dichloromethane water solution to remove DMF molecules, and then centrifuging and vacuum drying to obtain the hierarchical porous ZIF-9.

2. The method of synthesizing a hierarchical porous ZIF-9 as claimed in claim 1, wherein: the molar ratio of Co to Na in the mixture used in the step (1) is 1:1-1: 3.

3. The method of synthesizing a hierarchical porous ZIF-9 as claimed in claim 1, wherein: the amount of benzimidazole used in step (1) is converted according to the molar ratio of benzimidazole to Co of 5:1-1: 5.

4. The method for regulating and controlling synthesis of the hierarchical porous ZIF-9 as claimed in claim 1, wherein: the amount of DMF in the solution A in the step (1) is 0.7 to 9mL per mmol of Na.

5. The method of synthesizing a hierarchical porous ZIF-9 as claimed in claim 1, wherein: the rotating speed of the stirring treatment in the step (1) is 500 rpm, and the time is 20-30 min.

6. The method of synthesizing a hierarchical porous ZIF-9 as claimed in claim 1, wherein: the ultrasonic treatment time in the step (1) is 10-50 min.

7. The method of synthesizing a hierarchical porous ZIF-9 as claimed in claim 1, wherein: the rotation speed of the stirring reaction in the step (2) is 500 rpm, and the time is 3-12 h.

8. The method of synthesizing a hierarchical porous ZIF-9 as claimed in claim 1, wherein: and (4) soaking for 3d in the step (3).

9. The method of synthesizing a hierarchical porous ZIF-9 as claimed in claim 1, wherein: the concentration of the aqueous methylene chloride solution used in step (3) was 0.012 mol/ml.

10. The method of synthesizing a hierarchical porous ZIF-9 as claimed in claim 1, wherein: and (3) the vacuum drying temperature is 120 ℃, and the time is 8-12 h.

Technical Field

The invention belongs to the field of nano material preparation, and particularly relates to a synthesis method of a hierarchical porous ZIF-9.

Background

MOFs are three-dimensional and highly ordered crystal structures assembled by coordination of metal components and organic bridging ligands, have the characteristics of large specific surface area, porosity, adjustable structural components and the like, and are ideal materials in the fields of gas adsorption/separation, organic catalysis, photoelectricity and the like. However, conventional MOFs are often microporous (< 2 nm) materials, which are not conducive to rapid diffusion of reactants, limit rapid mass transfer of reactants to the interior, prevent active metal centers in the interior from participating in reactions, and greatly limit applications of the MOFs in various aspects such as catalysis. Therefore, introducing mesopores/macropores into the microporous MOFs material to form a hierarchical porous structure, improving mass transfer of reactants and increasing exposure of internal active metal centers while maintaining high specific surface area and abundant metal center sites, becomes one of the current research hotspots.

At present, the methods for forming hierarchical porous MOFs composed of mesopores and micropores are mainly through an organic bridged ligand extension method and a template method. Although the organic bridging ligand extension method can prepare hierarchical porous MOFs to a certain extent, the mesoporous size of the hierarchical porous MOFs is limited (generally less than 8 nm). In addition, too long organic bridged ligands can cause an interpenetration effect in the internal network structure, resulting in further reduction of the mesoporous size, and further limit the industrial application thereof due to the higher synthesis cost of the long organic bridged ligands. The template method mainly comprises a soft template and a hard template, and is one of the conventional strategies for preparing the graded porous material. The soft template method generally realizes the synthesis of the hierarchical porous MOFs material by using an organic surfactant or mixing immiscible solvents, namely, the synthesis of the hierarchical porous MOFs is realized by providing a domain-limiting effect through the organic surfactant or immiscible organic reagents, but the process needs to use a large amount of the surfactant or the organic reagents, is high in price and difficult to expand to other MOFs, and the surfactant or the organic reagents are easily adsorbed on active sites and are not easily removed, so that the catalytic activity of the hierarchical porous MOFs is low. The hard template method is to provide a confinement effect through a solid precursor, and finally remove the hard template through high-temperature calcination or acid-base etching to prepare the hierarchical porous MOFs. Although hard templates can be extended to other MOFs, high temperature processing and acid-base etching tend to damage the graded porous MOFs structure. Therefore, there is an urgent need to find a suitable hard template method capable of preparing graded porous MOFs under mild conditions.

Disclosure of Invention

The invention aims to provide a method for synthesizing hierarchical porous ZIF-9, which utilizes low-price, green, nontoxic and easily-obtained raw materials, realizes fine regulation and control of the hierarchical porous ZIF-9 on the appearance and pore size under the conditions of no addition of any surfactant and no adoption of complicated high-temperature calcination steps, has low cost, economic, simple, convenient and efficient process, good economic and environmental benefits, and can be applied to large-scale production.

In order to achieve the purpose, the invention adopts the following technical scheme:

a method for synthesizing hierarchical porous ZIF-9 comprises the steps of adding sodium salt into a cobalt salt solution of a reaction precursor by utilizing different solubility of different salts in a DMF solvent, enabling the cobalt salt solution to spontaneously form a colloidal sodium salt template, and preparing hierarchical porous ZIF-9 (containing micropores and mesopores or micropores and macropores) with adjustable pore passage size in one step; which comprises the following steps:

(1) mixing Co (CH)₃COO)₂And NaNO₃Or CH₃COONa and Co (NO)₃)₂Adding the mixture of (a) to DMF to form a solution A; adding benzimidazole to DMF to form solution B; respectively stirring the solution A and the solution B at room temperature and then carrying out ultrasonic treatment;

(2) pouring the solution B into the solution A for stirring reaction, and using DMF or H to react the obtained product₂O cleaning;

(3) and (3) soaking the cleaned product into a dichloromethane water solution to remove DMF molecules, and then centrifuging and vacuum drying to obtain the hierarchical porous ZIF-9.

Further, the molar ratio of Co to Na in the mixture used in the step (1) is 1:1 to 1: 3.

Further, the amount of benzimidazole used in the step (1) is converted in terms of its molar ratio to Co of 5:1 to 1: 5.

Further, the amount of DMF in the solution A in the step (1) is 0.7 to 9mL per mmol of Na.

Further, the rotation speed of the stirring treatment in the step (1) is 500 rpm, and the time is 20-30 min.

Further, the ultrasonic treatment time in the step (1) is 10-50 min.

Further, the rotation speed of the stirring reaction in the step (2) is 500 rpm, and the time is 3-12 h.

Further, the number of times of washing in the step (2) is 3.

Further, the soaking time in the step (3) is 3 d.

Further, the concentration of the methylene chloride aqueous solution used in the step (3) was 0.012 mol/ml.

Further, the temperature of the vacuum drying in the step (3) is 120 ℃, and the time is 8-12 h.

The invention has the following remarkable advantages:

(1) the invention utilizes the raw materials which are low in price, green, nontoxic and easily available, and adopts a colloidal salt template method to synthesize the hierarchical porous ZIF-9 with the pore size distribution of 1.1-1.8 and 34.0-34.5nm in one step. The preparation process is economic, simple, convenient and efficient, and does not need to add any surfactant.

(2) The hierarchical porous ZIF-9 obtained by the invention not only can keep higher specific surface area and rich active sites of micropores, but also can provide a rapid mass transfer path through mesopores, thereby avoiding the problem of slow mass transfer of the micropores.

(3) The preparation method has the advantages of easily obtained equipment and materials, simple process operation, concise process conditions, low cost, safety and high efficiency; the invention obtains an eco-friendly material, which has good popularization and application values.

Drawings

FIG. 1 is an SEM image of hierarchical porous ZIF-9 synthesized by sonication for different times in example 1;

FIG. 2 is a comparison of XRD patterns of graded porous ZIF-9 synthesized in example 1 (10 min sonication) and microporous ZIF-9 synthesized in comparative example 1;

FIG. 3 is a graph showing N of the hierarchical porous ZIF-9 (ultrasonic 10 min) obtained in example 1₂-sorption-desorption curve and pore size distribution profile;

FIG. 4 is a view showing N of microporous ZIF-9 obtained in comparative example 1₂-sorption-desorption curve and pore size distribution profile;

FIG. 5 is SEM and TEM images of a hierarchical porous ZIF-9 synthesized in example 1 (10 min sonication);

FIG. 6 is SEM and TEM images of microporous ZIF-9 synthesized in comparative example 1;

FIG. 7 is SEM and TEM images of the hierarchical porous ZIF-9 obtained in example 2;

FIG. 8 is an SEM image of a hierarchical porous ZIF-9 synthesized in example 3;

FIG. 9 is SEM and TEM images of a hierarchical porous ZIF-9 synthesized in example 4;

FIG. 10 is an SEM photograph of bulk ZIF-9 obtained in comparative example 2;

FIG. 11 shows different ZIF-9 photocatalysed reductions of CO in the application examples₂The rate of CO is plotted against the rate of CO.

Detailed Description

A method for synthesizing hierarchical porous ZIF-9 comprises the following steps:

(1) 0.13-0.44 g of Co (CH)₃COO)₂And 0.12-0.64 g NaNO₃A mixture of constituents, or 0.11-0.41 g CH₃COONa and 0.13-0.46 g Co (NO)₃)₂Adding the mixture (the molar ratio of Co to Na in the mixture is 1: 2) into 6-12 mL of DMF to form a solution A; adding 0.015-0.060 g of benzimidazole into 6-12 mL of DMF to form a solution B; respectively stirring the solution A and the solution B at room temperature and then carrying out ultrasonic treatment; the rotation speed of stirring treatment is 500 rpm, the time is 20-30 min, and the time of ultrasonic treatment is 10-50 min;

(2) pouring the solution B into the solution A, stirring at 500 rpm for reaction for 3-12H, and reacting the obtained product with DMF or H₂O cleaning for 3 times;

(3) and soaking the cleaned product in dichloromethane water solution with the concentration of 0.012 mol/mL for 3d to remove DMF molecules, centrifuging, and vacuum drying at 120 ℃ for 8-12 h to obtain the hierarchical porous ZIF-9.

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features mentioned in the embodiments of the present invention described below may be combined as long as they do not conflict with each other.

Example 1

(1) 0.44 g of Co (CH)₃COO)₂And 0.42 g NaNO₃(Co/Na =1: 2) was added to 9mL of DMF to form solution A, 0.060 g of benzimidazole (benzimidazole/Co =1: 5) was added to 9mL of DMF to form solution B, and solution A and solution B were stirred at 500 rpm for 20 min at room temperature, followed by sonication for 10min, 20 min, and 30 min, respectively;

(2) pouring the solution B into the solution A, stirring and reacting at the room temperature for 3 hours at the rotating speed of 500 rpm, and using DMF or H to obtain a product₂O cleaning for 3 times;

(3) and soaking the cleaned product in a dichloromethane water solution with the concentration of 0.012 mol/mL for 3d to completely remove DMF molecules in the sample, centrifuging, and performing vacuum drying at 120 ℃ for 10h to obtain the hierarchical porous ZIF-9.

Example 2

(1) 0.18 g of Co (NO)₃)₂And 0.16 g CH₃Adding COONa (Co/Na =1: 2) into 9mL of DMF to form a solution A, adding 0.060 g of benzimidazole (benzimidazole/Co =1: 2) into 9mL of DMF to form a solution B, stirring the solution A and the solution B at the rotating speed of 500 rpm for 20 min at room temperature respectively, and then carrying out ultrasonic treatment for 10 min;

(2) pouring the solution B into the solution A, stirring and reacting at the room temperature for 3 hours at the rotating speed of 500 rpm, and using DMF or H to obtain a product₂O cleaning for 3 times;

(3) and soaking the cleaned product in a dichloromethane water solution with the concentration of 0.012 mol/mL for 3d to completely remove DMF molecules in the sample, centrifuging, and performing vacuum drying at 120 ℃ for 10h to obtain the hierarchical porous ZIF-9.

Example 3

(1) 0.44 g of Co (CH)₃COO)₂And 0.64 g NaNO₃(Co/Na =1: 3) in 9mL of DMF to form a solution a, 0.060 g of benzimidazole (benzimidazole/Co =1: 5) in 9mL of DMF to form a solution B, stirring the solution a and the solution B at 500 rpm for 20 min at room temperature, followed by sonication for 10 min;

(2) pouring the solution B into the solution A, stirring and reacting at the room temperature for 3 hours at the rotating speed of 500 rpm, and using DMF or H to obtain a product₂O cleaning for 3 times;

(3) and soaking the cleaned product in a dichloromethane water solution with the concentration of 0.012 mol/mL for 3d to completely remove DMF molecules in the sample, centrifuging, and performing vacuum drying at 120 ℃ for 10h to obtain the hierarchical porous ZIF-9.

Example 4

(1) 0.44 g of Co (CH)₃COO)₂And 0.42 g NaNO₃(Co/Na =1: 2) was added to 9mL of DMF to form a solution A, 0.150 g of benzimidazole (benzimidazole/Co =1: 2) was added to 9mL of DMF to form a solution B, and the solution A and the solution B were stirred at 500 rpm for 20 min at room temperature, followed by sonication for 10 min;

(2) pouring the solution B into the solution A, stirring and reacting at the room temperature for 3 hours at the rotating speed of 500 rpm, and using DMF or H to obtain a product₂O cleaning for 3 times;

(3) and soaking the cleaned product in a dichloromethane water solution with the concentration of 0.012 mol/mL for 3d to completely remove DMF molecules in the sample, centrifuging, and performing vacuum drying at 120 ℃ for 10h to obtain the hierarchical porous ZIF-9.

Comparative example 1

(1) 0.18 g of Co (CH)₃COO)₂Adding into 9mL DMF to form solution A, adding 0.060 g benzimidazole into 9mL DMF to form solution B, stirring solution A and solution B at 500 rpm for 20 min at room temperature, and then performing ultrasonic treatment for 10 min;

(2) pouring the solution B into the solution A, stirring and reacting at the room temperature for 3 hours at the rotating speed of 500 rpm, and using DMF or H to obtain a product₂O cleaning for 3 times;

(3) and soaking the cleaned product in a dichloromethane water solution with the concentration of 0.012 mol/mL for 3d to completely remove DMF molecules in the sample, centrifuging, and performing vacuum drying at 120 ℃ for 10h to obtain the microporous ZIF-9.

Comparative example 2

(1) 0.18 g of Co (NO)₃)₂And 0.060 g benzimidazole to 18 mL DMF to form a mixed solution, and the mixed solution is stirred for 30-60 min at room temperature;

(2) charging the stirred mixed solution into a 25 mL stainless steel autoclave, heating to 130 ℃ at the speed of 5 ℃/min, carrying out solvothermal reaction for 48H, then cooling along with the furnace, and using DMF or H to obtain a product₂O cleaning for 3 times;

(3) and washing the washed product with ethanol until the centrifugate is transparent, washing with deionized water, and freeze-drying at-50 ℃ for 8 h to obtain the blocky ZIF-9.

FIG. 1 is an SEM image of the hierarchical porous ZIF-9 synthesized in example 1 by sonication for different times. As can be seen from the figure, the size of the hierarchical porous ZIF-9 is not greatly changed along with the extension of the ultrasonic time of the colloidal salt solution, but the morphology is gradually changed from a hexagonal prism or an octagonal prism to a tetradecahedron, and the distribution of mesopores is more dense, which is probably because the crystal face of the growth is changed due to the change of the concentration of acetate ions in the solution.

FIG. 2 is a comparison XRD of the hierarchical porous ZIF-9 synthesized in example 1 (10 min sonication) and the microporous ZIF-9 synthesized in comparative example 1. As can be seen from the figure, both have similar crystallinity and no hetero phase exists.

FIG. 3 is a graph showing N of the hierarchical porous ZIF-9 (ultrasonic 10 min) obtained in example 1₂Adsorption-desorption curves and pore size distribution plots. As can be seen from the figure, the adsorption and desorption curves of the hierarchical porous ZIF-9 belong to the IV-type isotherm, and an obvious hysteresis loop exists, which indicates that a mesopore/micropore structure exists, and the sizes of micropores and mesopores are respectively and intensively distributed at 1.6 nm and 34.3 nm.

FIG. 4 is a view showing N of microporous ZIF-9 obtained in comparative example 1₂Adsorption-desorption curves and pore size distribution plots. From the figureIt can be seen that the adsorption curve of the microporous ZIF-9 is represented by a class I isotherm having a BET specific surface area of 8.67 m²·g^-1 Significantly smaller than the BET specific surface area (33.71 m) of the hierarchical porous ZIF-9² g^-1) (ii) a The pore size distribution pattern indicated that only micropores were present and the pore size distribution was mainly centered at 1.6 nm.

FIG. 5 is SEM and TEM images of the hierarchical porous ZIF-9 synthesized in example 1 (10 min sonication). From the figure, it can be seen that the particle size distribution of the hierarchical porous ZIF-9 synthesized from the colloidal solution of inorganic salt is in the range of 1-1.5 μm, but its surface has wormhole-like pores uniformly distributed over the entire outer surface of the nanoparticles. It is also found that the interior of the bulk phase has uniform pores and is interconnected from inside to outside. The different magnification bright and dark field images of TEM further confirm the presence of mesopores in the bulk phase.

FIG. 6 is SEM and TEM images of the microporous ZIF-9 synthesized in comparative example 1. As can be seen from the figure, the microporous ZIF-9 directly synthesized from the solution is a smooth surfaced rice-like particle with a particle size of about 1-1.5 μm. The micropore ZIF-9 particle presents uniform bright and dark brightness under bright field images and dark field images of a TEM, and is proved to be a solid micropore material, which is consistent with nitrogen adsorption and desorption data, and shows that only micropores exist.

FIG. 7 is SEM and TEM images of the hierarchical porous ZIF-9 obtained in example 2. Among them, the SEM shows that ZIF-9 prepared is a spherical sample assembled orderly from small nanoparticles to about 200 nm, and a significant void can be observed. The TEM images further confirmed that there were a large number of mesopores above the spherical particles and exhibited a hollow character.

FIG. 8 is an SEM image of the hierarchical porous ZIF-9 synthesized in example 3, and from a comparison with FIG. 5, it can be seen that the variation of the sodium nitrate concentration does not have much influence on the morphology of the hierarchical porous ZIF-9, but there is a difference in the sizes of the mesopores of the two, and the higher concentration of sodium nitrate causes the pore size of the mesopores to become larger.

FIG. 9 is an SEM and TEM image of the hierarchical porous ZIF-9 synthesized in example 4, as seen by comparison with FIG. 5, with Co²⁺Reduction of the ratio, grading of the porosity ZThe morphology of IF-9 changes and the mesopore size decreases.

FIG. 10 is an SEM photograph of bulk ZIF-9 obtained in comparative example 2. As can be seen from the figure, ZIF-9 prepared by directly hydrothermally synthesizing a solution consisting of cobalt nitrate and benzimidazole is a bulk material with the size of 60 mu m, and no mesopores exist.

Application examples

(1) 2 mg of the hierarchical porous ZIF-9 (sonicated for 10 min) synthesized in example 1 and the microporous ZIF-9 synthesized in comparative example 1 were added to a solution containing 3000. mu. L C, respectively₂H₃N and 1000. mu. L H₂Forming a solution A in a 25 mL photocatalytic reactor of the O mixed solution;

(2) adding 8 mg of terpyridyl ruthenium and 1000 mu L of triethanolamine into the solution A, and sealing the reactor by using vacuum grease;

(3) repeatedly circulating the air extraction and the air ventilation for 3 times to ensure that the air in the reactor is completely removed, and then introducing CO₂And stirred for 30 min to make CO₂Fully dissolving into the reaction liquid;

(4) placing the reactor under a 300W xenon light source, controlling the temperature at 28-30 deg.C, and using every 1 h

Agilent gas chromatography detects product (CO) in 500. mu.L of the reaction gas phase.

FIG. 11 is a hierarchical porous ZIF-9 and microporous ZIF-9 photocatalytic reduction of CO₂The rate of CO is plotted against the rate of CO. As can be seen from the figure, the hierarchical porous ZIF-9 catalyzes the reduction of CO₂The activity as CO (CO yield 9011.5. mu. mol g)^-1·h^-1) Is obviously higher than that of microporous ZIF-9 (the CO yield is 7149.4 mu mol g)^-1 h^-1) This shows that the hierarchical porous structure can effectively improve the photocatalytic reduction of CO₂Activity of (2).

The above description is only a preferred embodiment of the present invention, and all equivalent changes and modifications made in accordance with the claims of the present invention should be covered by the present invention.