Synthesis of novel sulfonyl covalent organic framework and application of novel sulfonyl covalent organic framework to adsorption of methylene blue

Abstract

The invention belongs to the technical field of novel porous material adsorption, and particularly relates to preparation and application of novel sulfonic COFs. The preparation method comprises the following specific steps: synthesizing an anion sulfonic group COF from an aldehyde group monomer and an amino group monomer by utilizing a solvothermal reaction, and the prepared material COF-SO3H is used for efficiently adsorbing a cationic dye methylene blue and also has a relatively good removal effect on other several water-soluble cationic dyes (methylene blue, crystal violet, brilliant green and malachite green). Wherein the methylene blue adsorption capacity reaches 2799 mg / g and exceeds that of reported COFs, MOFs and composite materials thereof. Adsorption kinetics experiments show that the adsorption of COF-SO3H on methylene blue can quickly reach adsorption equilibrium within 5 minutes, and adsorption thermodynamics shows that the maximum adsorption capacity of the COF-SO3H at 25 DEG C can be 2799 mg / g. Meanwhile, the stable adsorption performance is still kept after five times of circulation, and it is proved that the adsorbent has excellent renewability. The research proves that COF-SO3H can be used as a high-efficiency adsorbent of cationic dyes, and has excellent comprehensive performance and good application potential.

Description

Technical Field

[0001] The present invention belongs to the technical field of novel porous material adsorption, and specifically relates to the preparation of sulfonic acid covalent organic frameworks (COFs) synthesized under solvent thermal conditions, and the adsorption application of COFs to methylene blue (MB) and several other water-soluble cationic dyes in water, including crystal violet (CV), brilliant green (BG), and malachite green (MG). Background Art

[0002] From textiles and leather to cosmetics and make-up, organic dyes are everywhere and flow into environmental water bodies with large-scale production, causing serious damage to the beauty, transparency and gas solubility of water bodies; in addition, organic dyes are usually toxic and can irritate the eyes and skin, causing symptoms such as weakness and dizziness. Since the molecular structure of these organic dyes is generally based on polycyclic aromatics, such as methylene blue, they are very stable in water bodies and will accumulate in organisms, causing great impacts on human and animal health. Therefore, removing water-soluble organic dyes such as MB from aqueous solutions is crucial to environmental protection and human health.

[0003] To date, researchers have adopted a variety of technologies to control the pollution of organic dyes, and the main technologies currently used are catalysis, distillation, cation exchange and adsorption. Among them, adsorption technology is often regarded as the solution with the greatest engineering potential due to its advantages such as simple operation and low operating cost. However, traditional adsorption materials (such as zeolite, clay and activated carbon) generally have problems such as low adsorption capacity, poor cyclic stability and high operating cost, and it is usually difficult to achieve satisfactory results in the treatment of water pollutants. In recent years, porous materials such as MXene and metal organic frameworks (MOFs) have received widespread attention due to their advantages such as good active sites, ultra-high porosity and rich pore structure. However, these porous materials usually have problems such as cumbersome preparation methods and potential metal leaching, which greatly limits their role in practical applications.

[0004] Covalent organic frameworks (COFs) are also porous crystalline materials with all-organic skeleton structures, excellent hydrolysis resistance, and designable nanopores. They also have low density, high stability, and adjustable pore structure. Therefore, they have shown great potential in the field of dye adsorption. In recent years, although COFs materials have received widespread attention in various fields, COFs adsorbents with ultra-high adsorption capacity, fast adsorption kinetics, and excellent reusability are still extremely rare. At present, some studies have reported on the preparation methods of COFs for cationic dye adsorption. The most common method is to modify COFs with functional groups of different electronegativity to improve their own adsorption capacity. For example, Li invented a method for constructing a carboxyl-functionalized clover-like covalent organic framework for the selective adsorption of organic dyes, using the carboxyl groups modified on COFs to promote the charge-induced adsorption of cationic dyes, and the adsorption of MB was only 315 mg / g [Rui L, Xihao T, Jialin W, et al. A sulfonate-functionalized covalent organic framework for record-high adsorption and effective separation of organic dyes [J]. Chemical Engineering Journal, 2023, 464]. In the Chinese patent application CN115449043A, a new type of sulfonate-functionalized covalent organic framework material was disclosed. The electrostatic adsorption of sulfonic acid groups was used to synthesize the COFs material. The maximum adsorption of methylene blue reached 1090 mg / g, which was significantly higher than that of carboxyl-modified COFs for MB, reflecting the electrostatic adsorption ability of sulfonic acid-modified COFs for cationic dyes. The sulfonate-functionalized COFs synthesized in a recent journal report only had an adsorption capacity of 1078 mg / g for methylene blue, and its rapid kinetics required 10 min to reach equilibrium [Li R, Zhang K, Yang X, et al. Construction of a carboxyl-functionalized clover-like covalent organic framework for selective adsorption of organic dyes [J]. Separation and Purification Technology, 2024, 340126765.].

[0005] The present invention introduces abundant negatively charged sulfonate groups into the COFs framework, and utilizes the electrostatic effect of the sulfonic acid groups to adsorb methylene blue (MB) and several other water-soluble cationic dyes, including crystal violet (CV), brilliant green (BG), and malachite green (MG). Among them, COFs has the highest adsorption capacity for MB, reaching the highest so far at 2799 mg / g, and can reach adsorption equilibrium within 5 minutes. 3 H still maintains excellent adsorption performance after five cycles of use. Summary of the invention

[0006] The purpose of the present invention is to provide a novel sulfonic acid covalent organic framework material, and to apply it to the adsorption of methylene blue MB and various water-soluble cationic dyes such as crystal violet (CV), brilliant green (BG), and malachite green (MG). The purpose is to construct a COFs material adsorbent with ultra-high adsorption capacity, fast adsorption kinetics, and excellent reusability by utilizing various functional groups in functional monomers through design and regulation.

[0007] Compared with the prior art, the present invention has the following characteristics and benefits:

[0008] (1) Sulfonic acid COFs (COF-SO 3 H) was synthesized by solvothermal method. As an anionic COFs, it has good adsorption effect on various cationic dyes such as methylene blue, crystal violet, brilliant green, malachite green, etc., among which the adsorption amount of MB reaches 2799 mg / g, which exceeds the reported COFs, MOFs and their composites.

[0009] (2)COF-SO 3 H on MB can quickly reach adsorption equilibrium in 5 minutes.

[0010] (3)COF-SO 3 H has excellent reusability and maintains stable adsorption performance after five cycles.

[0011] The purpose of the present invention is achieved through the following technical solutions.

[0012] (1) COF-SO 3 Preparation of H materials:

[0013] COF-SO 3 H was synthesized by solvothermal method. Aldehyde monomer and amino monomer were added to a long glass test tube. Under the catalysis of 1M sodium acetate (NaOAc) solution, after three cycles of liquid nitrogen cooling-vacuuming-thawing, the test tube was sealed with flame and reacted at 100-120°C for 3-5 days. Finally, an orange-yellow powder product (COF-SO 3 H).

[0014] (2)COF-SO 3 Application of H materials to adsorb various cationic dyes:

[0015] COF-SO 3 H was placed in four cationic dyes, namely methylene blue (MB), brilliant green (BG), crystal violet (CV) and malachite green (MG), respectively, and after ultrasonic dispersion, it was shaken for 30 min and centrifuged, and then the absorbance of the supernatant was measured by UV-visible spectrophotometer. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] [ Figure 1 ] is COF-SO 3 Schematic diagram of the preparation process of H material:

[0017] [ Figure 2 ] is COF-SO 3 Powder X-ray diffraction pattern of material H;

[0018] [ Figure 3 ] is COF-SO 3 Zeta potential and Fourier transform infrared spectrum of H material;

[0019] [ Figure 4 ] is COF-SO 3 Scanning electron microscope image of material H;

[0020] [ Figure 5 ] is COF-SO 3 Adsorption diagram of H material to different dyes;

[0021] [ Figure 6 ] is COF-SO 3 The effect of the amount of H material input on the removal rate of MB;

[0022] [ Figure 7 ] is the effect of pH and cation strength on COF-SO 3 Effect of H on the removal efficiency of MB;

[0023] [ Figure 8 ] is COF-SO 3 Adsorption equilibrium rate curve of H on MB;

[0024] [ Fig. 9 ] is COF-SO 3 Adsorption isotherm curve of H on MB;

[0025] [ Fig.10 ] is COF-SO 3 Figure 2. Study on the adsorption-desorption cycle of MB by H. Specific implementation plan

[0026] The specific implementation scheme of the present invention is described in detail with reference to the accompanying drawings and examples.

[0027] The following examples are used to illustrate the present invention, but do not limit the scope of application and extension of the present invention.

[0028] Example 1

[0029] (1) COF-SO 3 Preparation of H

[0030] according to Figure 1 The specific experimental operation method is as follows: take a long heat-resistant glass test tube, put 4,4',4"-(1,3,5-triazine-2,4,6-triyl) tribenzaldehyde (0.067mmol) and 4,4'-diaminobenzylbenzene-2,2'-disulfonic acid (0.07mmol) into the test tube, add 1.6mL methanol and 0.4mL o-dichlorobenzene, and ultrasonicate for 3min to make the monomers evenly dispersed. Add 0.2mL 1M sodium acetate (NaOAc) solution and then continue ultrasonication for 3 minutes. After that, put the glass test tube into liquid nitrogen for freezing, evacuate the inner tube to a vacuum state, and then transfer the glass test tube to methanol for thawing. After three cycles, seal the test tube with a flame. Subsequently, react the test tube at 100-120°C for 3-5 days. After the reaction is completed, cool the glass test tube to room temperature, take out the sample, wash it three times with tetrahydrofuran (THF) and methanol each to remove the unreacted monomers, and dry the product in a 50°C vacuum drying oven for 12 hours to obtain an orange-yellow powder product.

[0031] (2)COF-SO 3 Characterization of H Materials

[0032] Figure 2 It is COF-SO 3 The powder X-ray diffraction pattern of the H material shows obvious characteristic diffraction peaks at 2θ=4.0° and 7.4°, indicating that COF-SO with a clear crystalline structure has been successfully prepared. 3 H. Among them, the strong diffraction peak at 2θ = 4.0° confirms the existence of a highly ordered mesoporous structure in the material, corresponding to the characteristic diffraction of the (100) crystal plane. The diffraction peak at 2θ = 7.4° further verifies that the formation of the layered stacking structure belongs to the interlayer stacking diffraction of the (002) plane, indicating that there is π-π ordered stacking between adjacent covalent organic framework layers.

[0033] Figure 3 a is COF-SO 3 Zeta potential distribution diagram of H material in aqueous solution with different pH (3-11). It can be seen from the figure that COF-SO 3The pHzpc of H is around pH = 9.0, and it maintains a negative potential in a wide pH range, effectively capturing cationic pollutants through strong electrostatic effects.

[0034] Figure 3 b is COF-SO 3 The Fourier transform infrared spectrum of H material, comparing the infrared spectrum of the raw material monomer and the final product, can clearly observe the characteristic functional group transformation during the formation of COFs material: 3 The infrared spectrum of H does not contain the stretching vibration band of NH in the amino monomer (3070–3175 cm -1 ) and the characteristic stretching vibration peak of C=O in the aldehyde monomer (1695cm -1 ), which marks the completion of the Schiff base condensation reaction. 3 The infrared spectrum of H is at 1024 cm -1 There is a characteristic absorption peak at , indicating that the sulfonic acid amino monomer has been successfully introduced into COFs. This result matches the molecular structure characteristics of the sulfonic acid amino monomer, indicating that the sulfonic acid group has been successfully introduced into the COFs skeleton structure.

[0035] Figure 4 It is COF-SO 3 Scanning electron microscope image of H material. As shown in the figure, COF-SO 3 The H material presents a fluffy coral-like stacking structure, which can provide diffusion channels for pollutants and expose more adsorption sites.

[0036] Example 2

[0037] In order to study COF-SO 3 In this study, six common organic dyes with different molecular sizes were selected, including four cationic dyes: methylene blue (MB), brilliant green (BG), crystal violet (CV), malachite green (MG) and two anionic dyes: methyl orange (MO) and Congo red (CR). In the adsorption experiment, 2.0 mg of COF-SO prepared in Example 1 was weighed. 3 The H adsorbent was placed in 6 mL of 200 mg / L six organic dye solutions, respectively, and after ultrasonic dispersion, it was shaken for 30 min and centrifuged, and then the absorbance of the supernatant was measured by UV-visible spectrophotometer.

[0038] The results are as follows Figure 5 As shown in a, COF-SO 3 H has good adsorption for four cationic dyes, but poor adsorption for two anionic dyes, methyl orange (MO) and Congo red (CR). 3The adsorption force of H on organic dyes mainly comes from electrostatic interaction. 3 There are abundant sulfonic acid groups in the H channel, which maintains a stable negative charge on the surface in a wide pH range and generates strong electrostatic attraction with cationic dyes. 3 H exhibits excellent adsorption capacity for cationic dyes in dye wastewater treatment.

[0039] The MB concentration was fixed at 100 mg / mL, and MO and CR with a concentration of 100 mg / mL were added to prepare two different binary dye solutions (MB / MO and MB / CR) for binary dye competitive adsorption experiments. Figure 5 As shown in b, in MB / MO and MB / CR binary dye solutions, COF-SO 3 H can selectively adsorb MB, and the removal rate can reach 99%.

[0040] Example 3

[0041] In an 800 mg / mL methylene blue (MB) aqueous solution, the solution volume was fixed at 6 mL, and the adsorbent inputs (1, 2, 3, 4, and 5 mg) were added to study the COF-SO 3 The effect of H dosage on adsorption performance. Figure 6 As shown, when COF-SO 3 As the H input increases from 2 mg to 5 mg, we can see that COF-SO 3 The removal efficiency of MB by H remained almost unchanged.

[0042] Example 4

[0043] When the MB concentration was 1000 mg / mL, the pH value of the system was adjusted to the range of 3-9 using 0.1 M HCl / NaOH solution, and the COF-SO 3 The removal rate of methylene blue (MB) by H at different solution pH values. Figure 7 As shown in a, when the pH value increases from 3 to 9, the effect on the removal rate of methylene blue (MB) is very small, indicating that COF-SO 3 The material has good stability at pH 3-9.

[0044] At 298K, the MB concentration was fixed at 200 mg / mL, the total volume of the solution was 6 mL, and 2 mg of COF-SO was added to four different NaCl concentrations of 1 M, 0.5 M, 0.1 M, and 0.01 M. 3 H, in order to investigate the effect of cation strength on COF-SO 3 The results are shown in Figure 7As shown in b, in four different NaCl solution systems, COF-SO 3 The removal efficiency of MB by H was stable at about 99%, indicating that the cation competition effect had a significant impact on the COF-SO 3 The effect of H adsorption process can be neglected.

[0045] Example 5

[0046] Weigh 2.0 mg of COF-SO prepared in Example 1 3 H was placed in 6 mL of 950 mg / L MB solution, and then ultrasonically dispersed and shaken. The absorbance of the MB solution at the preset time points (1 min-35 min) was measured by UV spectrophotometer, and the concentration of the MB solution at different time points was calculated by substituting it into the MB standard linear equation. Figure 8 As shown, COF-SO 3 H adsorbs very quickly within 1-3 minutes, and removes most of the MB in the solution within 5 minutes, with an adsorption capacity of up to 2585.555 mg / g. 3 The adsorption rate of H for the organic dye methylene blue is faster than that of other adsorbent materials, which is beneficial for practical applications.

[0047] In order to further evaluate the kinetics of the dye molecules on the adsorbent, the adsorption process was fitted using the pseudo-first-order kinetic model and the pseudo-second-order kinetic model. The adsorption kinetics fitting data are shown in Table 1. The experimental results show that the pseudo-second-order kinetic model can better describe the adsorption of MB on COF-SO 3 The adsorption process on H. That is, the adsorption process may include physical adsorption and chemical adsorption, and the chemical adsorption process plays a major role. 3 This is consistent with the strong electrostatic interaction mechanism between the sulfonic acid group in H and the MB cation.

[0048] Table 1 COF-SO 3 Parameters of pseudo-first-order and pseudo-second-order kinetic models for H adsorption of methylene blue

[0049]

[0050] Example 6

[0051] Weigh 2.0 mg of COF-SO prepared in Example 1 3 H adsorbent was dispersed in 6.0 mL of MB solution with gradient concentration (50-1000 mg / L). Thermodynamic equilibrium experiments were carried out at 298 K, 310 K and 328 K. The absorbance of the solution after adsorption equilibrium was measured by UV-visible spectrophotometer. The residual MB concentration was calculated based on the MB standard solution curve. The results are shown in Figure 2. Fig. 9 shown.

[0052] In order to further study COF-SO 3 The adsorption mechanism of H on MB was investigated by using the Langmuir and Freundlich models to perform nonlinear fitting on the experimental data. The fitting data are shown in Table 2. The Langmuir model showed better fitting under the three temperature conditions, confirming that COF-SO 3 The adsorption process of H on MB is mainly monolayer adsorption. According to the Langmuir model, COF-SO 3 The theoretical maximum adsorption capacity of H at 298K, 310K and 328K are 2968.68mg / g, 2920.45mg / g and 2589.46mg / g, respectively.

[0053] Table 2 Related parameters of the two adsorption isotherm models

[0054]

[0055] Example 7

[0056] To study COF-SO 3 The practical application performance of H was tested by testing its reusability in removing methylene blue (MB). 3 The H regeneration process is as follows: COF-SO 3 H was immersed in acetone solvent, treated with constant temperature oscillation at 37°C, and then centrifuged and eluted repeatedly until the supernatant was colorless and transparent. Finally, the regenerated COF-SO was obtained after vacuum drying at 50°C. 3 H. Fig.10 As shown in Figure 2, five consecutive cycles of experiments showed that the removal rate of the regenerated material for 200 mg / L MB solution was always maintained above 93%, and the removal rate only dropped by 6.39% in the fifth cycle. This phenomenon was attributed to the high stability of the COFs framework. The above results prove that COF-SO 3 H has stable reusability and has important application value in wastewater treatment.

Claims

1. A novel solvothermal preparation method of sulfonic acid COFs (COF-SO3H) and adsorption application, characterized in that: Sulfonic acid COFs were synthesized using aldehyde monomers and amino monomers and used to adsorb water-soluble cationic dyes.

2. The preparation of the adsorbent according to claim 1, characterized in that: First, add aldehyde monomer and amino monomer to a long heat-resistant glass test tube, then add reaction solvent and ultrasonicate to evenly disperse the monomers. Then, add catalyst and continue ultrasonicate. After that, put the glass test tube into liquid nitrogen for freezing, vacuumizing, and thawing. After three cycles, seal the test tube with flame. Finally, react the test tube at 100-120℃ for 3-5 days. After the reaction is over, the final product sulfonic acid COFs is generated.

3. The method for preparing an adsorbent according to claim 2, characterized in that: The synthesized aldehyde monomer is 4,4',4"-(1,3,5-triazine-2,4,6-triyl) tribenzaldehyde, the amino monomer is 4,4'-diaminostilbene-2,2'-disulfonic acid, and the molar ratio of the added aldehyde monomer (TRZ22) and the amino monomer (4,4'-diaminostilbene-2,2'-disulfonic acid) is 1:

1.

4. The sulfonic acid COFs (COF-SO3H) prepared by the method of claim 2, characterized in that: The reaction solvent added was methanol and o-dichlorobenzene in a volume ratio of 4:

1.

5. The method for preparing sulfonic acid COFs (COF-SO3H) according to claim 2, characterized in that ,During the solvothermal reaction, sodium acetate (NaOAc) solution was added as a catalyst, the concentration of the added NaOAc solution was 1 M and the volume was 0.2 mL.

6. The method for preparing sulfonic acid COFs (COF-SO3H) according to claim 2, characterized in that During the solvent thermal reaction, the reaction temperature is 100-120°C and the reaction time is 3-5 days.

7. The method for preparing sulfonic acid COFs (COF-SO3H) according to claim 2, characterized in that After the reaction was completed, the sample was cooled to room temperature and then washed with tetrahydrofuran (THF) and methanol several times to remove the unreacted monomers, and finally dried.

8. The use of sulfonic acid COFs (COF-SO3H) for adsorption of organic dyes according to claim 2, characterized in that: The dye types adsorbed by COF-SO3H are cationic dyes, including methylene blue (MB), crystal violet (CV), brilliant green (BG) and malachite green (MG).

9. The use of sulfonic acid COFs (COF-SO3H) for adsorption of organic dyes according to claim 2, characterized in that: The eluent after adsorption is acetone solution.

10. The use of sulfonic acid COFs (COF-SO3H) for adsorption of organic dyes according to claim 2, characterized in that: The optimal pH range for MB adsorption by COF-SO3H is 3-9.

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