A high-nitrogen Se-COF structural material, a preparation method and application thereof

Abstract

The application relates to the technical field of porous crystal materials, and discloses a high-nitrogen Se-COF structural material, a preparation method and application thereof, the preparation method comprising the following steps: dissolving selenocystamine and aryl formaldehyde ligand in super-dry DMF respectively and reserving; under the protection of inert gas, the selenocystamine solution is added into the aryl formaldehyde ligand solution for reflux reaction, and the product is washed and dried to obtain the high-nitrogen Se-COF structural material. The method takes selenocystamine and aryl formaldehyde ligand as raw materials, prepares selenium-containing COFs containing rich nitrogen elements through a Mannich reaction, has high yield, short reaction time and good crystallinity of the product. The method is expected to realize the adsorption, separation and selective permeation of organic pollutants, and has great potential in the treatment of environmental pollutants.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of porous crystal materials, in particular to a high-nitrogen Se-COF structure material and a preparation method and application thereof. BACKGROUND

[0002] Covalent organic frameworks (COFs) are a new class of crystalline porous materials, which are connected by covalent organic ligands, and have attracted great attention. COFs materials have well-defined two-dimensional (2D) or three-dimensional (3D) crystal structures, in 2D structures, the building blocks are covalently linked to form atomic layers which are further stacked into superimposed layers by π-π interactions, while in 3D structures, COFs materials are covalently linked and arranged into an extended network in three dimensions. COFs materials achieve structural designability by precisely incorporating organic subunits into a pre-determined framework at the atomic level. In addition, as a kind of porous material, they also have the characteristics of low density, high surface area, high thermal stability, adjustable pore size and structure.

[0003] With the gradual maturity of the synthesis technology of COFs materials, the synthesis methods of COFs materials are also more and more diversified. The conventional solvothermal synthesis of COFs usually requires high temperature and long reaction time (3 days or more), which causes great obstacles to the accelerated discovery and exploration of new COFs materials in practical applications. Therefore, from the perspective of cost, time and energy consumption, it is very attractive to rapidly synthesize COFs without compromising their inherent properties.

[0004] In addition, although COFs materials have been proven to be competitive with metal-organic frameworks (MOFs) and zeolites in terms of functional group tolerance, structural tunability and stability in principle, it is still a daunting challenge to achieve these functions in the covalently linked crystalline backbone. The combination of covalent connectivity and crystallinity in COFs materials requires special functional groups and reaction conditions, which are usually suitable for reversible reactions. Therefore, when designing COFs materials based on dynamic covalent chemistry (DCC) for reversible bonding reactions, it is usually difficult to balance between recrystallinity and stability, which has always been a difficulty in designing new COFs and has limited the exploration of COFs materials in practical applications.

[0005] The connecting bonds in most of the currently reported COFs materials are boron-oxygen bonds and imine bonds, which are reversible covalent bonds and will decompose to cause the collapse of the COFs framework in harsh environments, which limits the application of COFs materials. How to construct more stable COFs materials is a difficult problem that restricts the development of COFs materials. Since 2016, COFs based on carbon-carbon double bond connection (sp 2 COFs) have been synthesized for the first time since then, and sp 2The category of COFs and the development of new applications of COFs 2 COFs materials are very important.

[0006] However, there are few reports on COFs materials rich in selenium. For example, CN 113831510A discloses a covalent organic framework based on benzene selenadiazole and a preparation method and application thereof. The covalent organic framework material connected by carbon-carbon double bonds has high specific surface area and strong chemical stability, and has high application value in photoelectric catalysis and separation.

[0007] Therefore, to prepare COFs materials with high crystallinity, good stability and practical application potential, it is necessary to introduce functional structures and functional groups into the materials, and to functionalize COFs materials by changing the functional groups of ligands, so as to prepare COFs materials with high crystallinity and good application performance, which is worthy of further exploration. SUMMARY

[0008] The present application aims at the problems of low crystallinity and poor stability of covalent organic framework materials, and provides a preparation method of Se-COF structure material rich in selenium. The method uses selenocystamine and aryl formaldehyde ligand as raw materials, and prepares selenium COFs containing rich nitrogen elements through Mannich reaction, with high yield, short reaction time and good crystallinity of the product.

[0009] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0010] A preparation method of high-nitrogen Se-COF structure material, comprising the steps of: dissolving selenocystamine and aryl formaldehyde ligand in super-dry DMF respectively for standby; under the protection of inert gas, the selenocystamine solution is added dropwise into the aryl formaldehyde ligand solution for reflux reaction, and the product is washed and dried to obtain the high-nitrogen Se-COF structure material.

[0011] In the present application, selenocystamine is used as the linking ligand of COFs material, and Se-Se structure is introduced into COFs material. Through Mannich reaction, high-efficiency and rapid synthesis effect can be achieved. By controlling the temperature and the dropping rate of the ligand, the Se-rich COF structure material prepared under heating reflux has good crystallinity, high nitrogen content and good charge transfer effect, and has good application prospect in the fields of pollutant adsorption and photoelectric catalysis. In addition, the material can be prepared into a self-supporting film, which is expected to realize the adsorption, separation and selective permeation of organic pollutants, and has great potential in environmental pollutant treatment.

[0012] The aryl formaldehyde ligand includes one or more of 2-hydroxy-1,3,5-benzene triformaldehyde, 1,3,5-benzene triformaldehyde, 2,4,6-trihydroxy-1,3,5-benzene triformaldehyde and [1,1'-biphenyl]-3,3',5,5'-tetracarboxaldehyde.

[0013] Preferably, the aryl aldehyde ligand is 2,4,6-trihydroxy-1,3,5-benzene tricarboxaldehyde, since this ligand has high symmetry, and the hydroxyl functional groups on the ligand can easily promote the nucleophilic addition reaction of the surrounding aldehyde groups, so the COFs material prepared by this ligand has more excellent crystallization performance.

[0014] The total molar ratio of the amino group of selenocystamine to the hydroxyl and aldehyde groups of the aryl aldehyde ligand is 3:1-1:3.

[0015] Preferably, the total molar ratio of the amino group of selenocystamine to the hydroxyl and aldehyde groups of the aryl aldehyde ligand is 1:1, which is the best effect, and there is no naked amino group or hydroxyl / aldehyde end defect in the COF structure, so that the COF material has more excellent crystallization performance.

[0016] The molar concentration of selenocystamine in the selenocystamine solution is 1.5-4 mmol / L. The molar concentration of aryl aldehyde ligand in the aryl aldehyde ligand solution is 1-3 mmol / L. The higher the concentration of the two raw materials, the higher the contact probability and the faster the reaction, but the crystallinity of the product may decrease slightly. The synthesis efficiency is high in this range, and the crystallization performance of the obtained product is good.

[0017] The dropwise addition speed of the selenocystamine solution is 2-10 mL / h. Preferably, the dropwise addition speed is 3-7 mL / h. The dropwise addition speed in the reaction process has an effect on the yield and structure of the COFs material. The sample is added at this speed to control the local reaction rate, so that the functional groups of the ligand can be fully contacted, so that the reaction is always kept in a dynamic balance process, and the generation of carbon-nitrogen bonds is maximized.

[0018] The reflux reaction temperature is 130-150℃, and the time is 12-36h. The continuous reaction at this temperature can ensure that the reaction proceeds smoothly, and the reaction can be ensured to proceed sufficiently within this time period.

[0019] The preparation method of the present application has high yield, short time, relatively mild reaction conditions, and does not require high equipment requirements, and can achieve a yield of more than 70%, or even more than 80%.

[0020] On the other hand, the present application also provides a high-nitrogen Se-COF structure material prepared by the preparation method.

[0021] In another aspect, the present application also provides the application of the high-nitrogen Se-COF structure material in electrocatalysis or photocatalysis.

[0022] The application also provides application of the high-nitrogen Se-COF structure material as an adsorption material in adsorbing heavy metal pollutants or transition metals, and the adsorption efficiency is high, the heavy metal pollutants include metals or metal salts containing Pb, Pd, Pt or Cr, and the transition metals include metals or metal salts containing Ni, As, Cd or Hg.

[0023] Compared with the prior art, the application has the following beneficial effects:

[0024] In the application, selenium cystamine is connected with aromatic formaldehyde ligands, Se-Se structures are introduced into COFs materials through Mannich reaction, a series of Se-COF structure materials containing rich nitrogen elements are successfully prepared, the preparation method is simple and has high yield, and the product can greatly promote charge transfer in a chemical reaction, and has great application prospect in the fields of electrocatalysis and photocatalysis. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a nuclear magnetic resonance carbon spectrum (C NMR) of Se-COF-1 obtained in Example 1. 13

[0026] Figure 2 is an X-ray powder diffraction (XRD) diagram of Se-COF-2 obtained in Example 2.

[0027] Figure 3 is an X-ray powder diffraction (XRD) diagram of Se-COF-3 obtained in Example 3.

[0028] Figure 4 is an ultraviolet-visible (UV-vis) spectrum diagram of adsorbing transition metal Ni 2+ in Application Example 1.

[0029] Figure 5 is a removal rate diagram of adsorbing Pb, Pd and Pt metal salts in Application Example 2.

[0030] Figure 6 is a UV-vis diagram of adsorbing heavy metal pollutants CrO4 2- in Application Example 3. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical scheme and advantages of the application more clear, the application will be further described in detail below in combination with examples. It should be understood that the specific examples described herein are only used to explain the application, and are not used to limit the application. Those skilled in the art can modify or replace the equivalent without departing from the spirit and scope of the technical scheme of the application, and all should be covered in the protection scope of the application.

[0032] ​The raw materials used in the following specific embodiments are all purchased from the market.

[0033] Example 1

[0034] A preparation method of a Se-COF structure material includes the following steps:

[0035] 0.2g of 2,4,6-trihydroxy-1,3,5-benzene tricarboxaldehyde is dissolved in 20mL of super dry DMF solution, placed in a round bottom flask, and water and oxygen are removed by N2, ready for use; 0.6g of selenocystamine is dissolved in 10mL of super dry DMF and stored under N2 atmosphere, then the selenocystamine solution is dropped into the aryl aldehyde ligand solution at a speed of 5mL / h by using a syringe, heated to 150℃, refluxed for 12h, washed by ordinary 60mL DMF and 60mL ethanol to remove unreacted substrates, and a Se-COF structure material with high nitrogen content is prepared, which is placed in a vacuum drying box at 75℃ for drying for 6h, and the obtained product is recorded as Se-COF-1, with a yield of up to 90%.

[0036] The Se-rich COFs prepared in the present application have high stability, and the product is tested by solid nuclear magnetic carbon spectrum to obtain the successful generation of C-N single bond and C-N double bond, and the carbon spectrum is as shown in Figure 1 , in which the positions of a, b, c, d and e represent the chemical environment of the carbon bonds at a, b, c, d and e in the structural formula, and it can be seen that the target structure COFs are successfully prepared.

[0037] Example 2

[0038] A preparation method of a Se-COF structure material includes the following steps: 0.3g of 1,3,5-benzene tricarboxaldehyde is dissolved in 20mL of super dry DMF solution, placed in a round bottom flask, and water and oxygen are removed by N2, then 0.3g of selenocystamine is dissolved in 10mL of super dry DMF and stored under N2 atmosphere, then the selenocystamine solution is dropped into the aryl aldehyde ligand solution at a speed of 4mL / h by using a syringe, heated to 150℃, refluxed for 15h, washed by ordinary 50mL DMF and 50mL ethanol to remove unreacted substrates, and a Se-COF structure material with high nitrogen content is prepared, which is placed in a vacuum drying box at 75℃ for drying for 6h, and the obtained product is recorded as Se-COF-2, with a yield of up to 87%. The X-ray powder diffraction (XRD) pattern thereof is as shown in Figure 2 , and the sharp peak at 2.74° proves that the material has good crystallization performance.

[0039] Example 3

[0040] A preparation method of a Se-COF structure material includes the following steps:

[0041] Firstly, 0.5 g of [1,1'-biphenyl]-3,3',5,5'-tetracarboxaldehyde was dissolved in 20 mL of super dry DMF solution, placed in a round bottom flask, and dehydrated and deoxygenated by N2, secondly, 0.3 g of selenocystamine was dissolved in 10 mL of super dry DMF and stored under N2 atmosphere, then the selenocystamine solution was dropped into the aryl aldehyde ligand solution at a speed of 5 mL / h, heated to 150°C, refluxed for 12 h, washed with ordinary 100 mL DMF and 100 mL ethanol to remove unreacted substrate, and a Se-COF structure material with high nitrogen content was prepared. The material was placed in a vacuum drying oven at 75°C for 6 h, and the obtained product was recorded as Se-COF-3, with a yield of up to 90%. The X-ray powder diffraction (XRD) pattern thereof is shown in Figure 3 As can be seen from the figure, Se-COF-3 has good crystallization performance.

[0042] Comparative Example 1

[0043] According to the process of Example 1, the dropping speed of the selenocystamine solution was modified to 50 mL / h, and it was observed that the speed of solution to solid increased, and the yield was less than 50% after the same reaction time.

[0044] Comparative Example 2

[0045] According to the process of Example 1, the reflux reaction temperature was modified to 200°C, and it was also observed that the speed of solid generation increased, and the yield was less than 70% after the same reaction time.

[0046] Application Example 1

[0047] 10 mg of the material of Example 1 was weighed and placed in a prepared 20 mL 100 ppm NiCl2 solution for stirring and adsorption, and samples were taken at 30 min, 5 h and 10 h, respectively. Under the monitoring of UV-Vis spectrum, it was found that the adsorption of transition metal Ni 2+ was up to more than 80% within 10 h. The ultraviolet-visible (UV-vis) spectrum of the transition metal Ni 2+ adsorbed is shown in Figure 4 The figure shows that the material has an absorption of transition metal Ni 2+ half an hour, a wide range of absorption at about 5 hours, and an absorbance minimum at 10 h, with an absorbance weakening of more than 80%, achieving an adsorption effect of Ni 2+ of more than 80%.

[0048] Application Example 2

[0049] The material of Example 3 was each taken 10 mg, which was placed in the prepared 20 mL 100 ppm PbCl2, PdCl2and K2PtCl6solution respectively, and stirred for 10 h. Under the monitoring of ICP spectrum, the adsorption amount of Pb 2+ , Pd 2+ , Pt 2+ salt was up to 90%, 85%, 80% or more. The removal rate graph of adsorbing Pb, Pd and Pt metal salt is shown in Figure 5 , which shows that it has nearly 90% adsorption effect on Pb 2 + , Pd 2+ , Pt 2+ salt.

[0050] Application Example 3

[0051] The material of Example 3 was taken 10 mg, which was placed in the prepared 20 mL 100 ppm Na2CrO4solution and stirred for adsorption. The samples were taken at 1 h, 5 h and 10 h respectively, and tested under the monitoring of UV-vis spectrum. The removal rate of heavy metal pollutant CrO4 2- was up to 98% or more within 10 h at low concentration. The UV-vis graph of adsorbing heavy metal pollutant CrO4 2- is shown in Figure 6 .

Claims

1. A method for preparing a high nitrogen-containing Se-COF structure material, characterized in that, The method comprises the steps of: dissolving selenocystamine and aryl aldehyde ligand in super dry DMF respectively; under the protection of inert gas, dropping the selenocystamine solution into the aryl aldehyde ligand solution for reflux reaction; and washing and drying the product to obtain the high nitrogen Se-COF structure material. The molar concentration of selenocystamine in the selenocystamine solution is 1.5-4 mmol / L. The molar concentration of aryl aldehyde ligand in the aryl aldehyde ligand solution is 1-3 mmol / L. The dropping speed of the selenocystamine solution is 2-10 mL / h. The reflux reaction temperature is 130-150 DEG C, and the reaction time is 12-36 h.

2. The method for preparing the high-nitrogen-content Se-COF structural material according to claim 1, characterized in that, The aryl aldehyde ligand includes one or more of 2-hydroxy-1,3,5-benzene tricarboxaldehyde, 1,3,5-benzene tricarboxaldehyde, 2,4,6-trihydroxy-1,3,5-benzene tricarboxaldehyde and [1,1'-biphenyl]-3,3',5,5'-tetracarboxaldehyde.

3. The method for preparing the high-nitrogen-content Se-COF structural material according to claim 1, characterized in that, The total molar ratio of the amino group of selenocystamine to the hydroxyl group and aldehyde group of aryl aldehyde ligand is 3:1-1:

3.

4. The high nitrogen Se-COF structure material prepared by the method according to any one of claims 1-3.

5. The application of the high nitrogen Se-COF structure material according to claim 4 in electrocatalysis or photocatalysis.

6. Use of the high nitrogen-containing Se-COF structure material according to claim 4 as an adsorbent material for adsorbing heavy metal pollutants or transition metals, characterized in that, The heavy metal pollutants include metals or metal salts containing Pb, Pd, Pt or Cr; and the transition metals include metals or metal salts containing Ni, Cd or Hg.

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