Preparation method and application of carboxylic acid functionalized porous organic polymer for adsorbing cationic dye

Abstract

The invention belongs to the technical field of chemistry and new materials, and particularly relates to preparation of a carboxylic acid functionalized porous organic polymer for adsorbing cationic dye and application of the carboxylic acid functionalized porous organic polymer in dye adsorption. The carboxylic acid functionalized porous organic polymer LNU-81 is prepared by taking octaphenyl-POSS as a raw material and taking pyromellitic dianhydride as a reaction external cross-linking agent. The porous organic polymer has the characteristics of a pi-conjugated aromatic system, a hierarchical pore structure, an electronegative skeleton and the like, so that the LNU-81 shows excellent adsorption capacity on malachite green under the synergistic effect of pi-pi accumulation action and hydrogen bond and electrostatic interaction, and the highest adsorption capacity is 1945.36 mg g <-1 >. The carboxyl skeleton shows strong affinity to malachite green, ensures rapid adsorption kinetics, and is beneficial for obtaining higher adsorption efficiency of the material. The invention provides a novel method for directionally designing and preparing the porous organic polymer with high adsorption performance.

Description

Technical Field

[0001] The present invention belongs to the technical fields of chemistry and new materials, and particularly relates to a preparation method of a carboxylic acid-functionalized porous organic polymer and its application in the field of dye adsorption. Background Art

[0002] In recent years, water pollution has become an increasingly serious problem. Among numerous pollutants, organic dye pollutants are widely used in many industries such as papermaking, textile, cosmetics, pharmaceuticals, and food.

[0003] Currently, a variety of water treatment technologies have been widely applied in the field of dye removal, including: photocatalysis, membrane filtration, biodegradation, chemical precipitation, and adsorption method, etc. In contrast, the adsorption method is considered a promising environmental remediation technology due to its advantages such as high adsorption efficiency, low cost, and simple operation. However, the key to the adsorption technology lies in the selection of adsorbents. Traditional adsorbents, such as activated carbon, zeolite, etc., have certain limitations in practical applications due to their low adsorption capacity and poor selectivity. To further improve the dye adsorption performance, various novel adsorbents have been successively developed and reported, such as metal-organic frameworks (MOFs) and porous organic polymers (POPs). Although MOFs have improved in terms of adsorption capacity and selectivity, their coordination bonds are relatively weak, resulting in poor stability of most MOFs under harsh conditions such as acids and alkalis, and even potential secondary pollution may be caused. Porous organic polymers (POPs) are a class of highly cross-linked polymers with nano-pores that have emerged in recent years. They have advantages such as high specific surface area, good chemical stability, low density, and easy functionalization. Therefore, porous organic polymers have broad application prospects in the fields of gas separation, alcohol-water separation, energy storage, pollutant capture, radioactive element enrichment, etc.

[0004] In summary, the present invention uses octaphenyl-POSS as a raw material and pyromellitic dianhydride as a reaction cross-linking agent to prepare a carboxylic acid-functionalized porous organic polymer LNU-81 through a simple Friedel-Crafts reaction, avoiding cumbersome steps such as post-modification. Since the synthesized polymer contains carboxyl functional groups, under certain conditions, the carboxyl groups will ionize and release hydrogen ions, making the polymer have a unique negative charge, which prompts us to further explore its adsorption performance for the cationic dye malachite green (MG). As expected, under the synergistic effect of electrostatic interaction, hydrogen bonding, and π-π stacking interactions, the polymer shows excellent adsorption performance and good adsorption selectivity for malachite green, and is expected to become an ideal material for removing organic pollutants in wastewater. Summary of the Invention

[0005] The object of the present invention is to provide a new design strategy for preparing a carboxylic acid-functionalized porous organic polymer and applying it to the field of adsorption and separation of organic dye malachite green in wastewater.

[0006] The object of the present invention is achieved by the following technical solutions: A carboxylic acid-functionalized porous organic polymer for adsorbing cationic dyes is prepared as follows: Mix the catalyst aluminum trichloride with dichloroethane solvent for activation, dissolve the mixture of the reaction monomers octaphenyl-POSS and pyromellitic dianhydride in dichloroethane and stir, add it to the catalyst solution for reaction, wash the precipitate obtained by suction filtration, perform Soxhlet extraction, and dry to obtain a red powder LNU-81.

[0007] For the above-mentioned carboxylic acid-functionalized porous organic polymer for adsorbing cationic dyes, the activation is carried out at 70 °C for 3 hours.

[0008] For the above-mentioned carboxylic acid-functionalized porous organic polymer for adsorbing cationic dyes, the reaction is carried out at 80 °C for 24 hours.

[0009] Application of the above-mentioned carboxylic acid-functionalized porous organic polymer for adsorbing cationic dyes in the adsorption of organic dyes.

[0010] For the above-mentioned application, the organic pollutant is malachite green.

[0011] For the above-mentioned application, the method is as follows: Add LNU-81 to an aqueous solution of malachite green with a pH value of 2-10 for adsorbing malachite green.

[0012] For the above-mentioned application, the concentration of the malachite green aqueous solution is 100-400 ppm.

[0013] We carry out targeted design on the material, use aromatic monomers as raw materials and acid anhydrides as external cross-linking agents to prepare a carboxylic acid-functionalized porous organic polymer by Friedel-Crafts acylation reaction. The π-π interaction and hydrogen bond interaction between the porous material and the guest molecule enhance the intermolecular binding force, and the swelling behavior provides more adsorption space, thus greatly improving the adsorption selectivity of the polymer for dyes. The present invention provides a new method for the directional design and preparation of functional porous organic polymers with high adsorption performance.

[0014] The present invention prepares a keto-carbonyl polymer by Friedel-Crafts acylation reaction, introduces carboxyl functional groups, and forms strong electrostatic interactions with guest molecules through porous materials, thereby greatly improving the adsorption performance and adsorption selectivity of cationic dyes. The unique swelling behavior of LNU-81 is due to the formation of hydrogen bonds between the carboxyl functional groups in LNU-81 and water molecules, resulting in an increase in the internal voids of the material and thus causing the material volume to expand. The above characteristics can provide more adsorption sites for malachite green molecules, thereby improving the adsorption efficiency.

[0015] The beneficial effects of the present invention are as follows:

[0016] The monomers and catalysts used in the present invention are relatively inexpensive, the preparation method is relatively simple and mild, and has general applicability. The prepared porous organic polymer has excellent thermochemical stability and can be used for adsorption under relatively harsh conditions such as acids and alkalis. Due to the characteristics of the polymer such as π-conjugated aromatic system, hierarchical pore structure, and negatively charged skeleton, efficient and selective capture of the cationic dye malachite green can be achieved under the synergistic effect of π-π stacking interaction, hydrogen bond, and electrostatic interaction. This material not only has the advantages of high adsorption efficiency and good selectivity, but also is green and pollution-free, which is of great significance for the development of environmentally friendly and efficient solid adsorbents.

[0017] The present invention uses octaphenyl-POSS as an organic monomer and pyromellitic dianhydride as an external cross-linking agent, and successfully prepares a carboxylic acid-functionalized porous organic polymer LNU-81 through a simple Friedel-Crafts reaction, avoiding cumbersome synthesis steps such as post-modification. The obtained polymer exhibits high thermal stability and chemical stability, and can be used as a novel and efficient solid adsorbent to remove the organic dye malachite green in wastewater under harsh environments, with a maximum adsorption capacity of 1945.36 mg / g. -1 Even under the condition of mixing dyes with different charges, the polymer can still achieve selective adsorption of the cationic dye malachite green and exhibits excellent cycle stability, showing good application prospects in the field of sewage treatment. Description of the Drawings

[0018] Figure 1 : Infrared spectra of the porous organic polymer LNU-81 and reaction monomers synthesized in the present invention;

[0019] Figure 2 : Thermogravimetric diagram of the porous organic polymer LNU-81 synthesized in the present invention;

[0020] Figure 3 : Powder X-ray diffraction pattern of the porous organic polymer LNU-81 synthesized in the present invention;

[0021] Figure 4: Zate diagram of the porous organic polymer LNU-81 synthesized in the present invention;

[0022] Figure 5 : Adsorption performance test of the porous organic polymer LNU-81 synthesized in the present invention for malachite green under different pH conditions;

[0023] Figure 6 : Adsorption isotherm of the porous organic polymer LNU-81 synthesized in the present invention for malachite green;

[0024] Figure 7 : UV-visible spectra of the porous organic polymer LNU-81 synthesized in the present invention before and after adsorbing a mixed dye solution of malachite green and methyl orange;

[0025] Figure 8 : UV-visible spectra of the porous organic polymer LNU-81 synthesized in the present invention before and after adsorbing a mixed dye solution of malachite green and calcein;

[0026] Figure 9 : Influence of the porous organic polymer LNU-81 synthesized in the present invention on the adsorption efficiency of malachite green in different water quality environments;

[0027] Figure 10 : Study on the recycling performance of the porous organic polymer LNU-81 synthesized in the present invention for adsorbing malachite green. Detailed implementation mode

[0028] The following are examples of the present invention, which are helpful for understanding the present invention, but the protection scope of the present invention is not limited to this content. Example 1 Preparation of a carboxylic acid-functionalized porous organic polymer LNU-81

[0029] 1. Synthesis of the sample:

[0030] Under nitrogen conditions, aluminum trichloride (1.1664 mmol, 1.8514 g) as the catalyst was added to the prepared reaction flask, and then 10 mL of dichloroethane solvent was injected and activated at 70 °C for 3 hours. Then, a mixture of the reaction monomers octaphenyl-POSS (0.1946 mmol, 200 mg) and pyromellitic dianhydride (0.7764 mmol, 171 mg) was dissolved in 20 mL of dichloroethane, placed in another reaction flask, and stirred at room temperature for 3 hours. After the activation reaction of the catalyst was completed, the reaction monomer mixture dissolved in dichloroethane was injected into the activated catalyst solution and reacted at 80 °C for 24 hours.

[0031] 2. Post-treatment of the sample:

[0032] After the reaction was completed, the precipitate was separated from the reaction solution by suction filtration and washed repeatedly with tetrahydrofuran, N,N-dimethylformamide, and dichloromethane to remove unreacted monomers and catalysts. The crude product was further subjected to Soxhlet extraction with tetrahydrofuran and dichloromethane for 72 hours, which is a more thorough purification step that can remove more residual organic solvents and impurities. Finally, the washed and purified product was dried under vacuum at 100 °C for 12 hours, and the resulting reddish-brown powder was LNU-81.

[0033] The synthesis schematic diagram of the porous organic polymer LNU-81 prepared in the present invention is shown as follows:

[0034]

[0035] Figure 1 This is the infrared spectrum of the porous organic polymer LNU-81 and the reaction monomer synthesized in the present invention. It can be clearly observed from the figure that the Si-O-Si bending vibration peak of the octaphenyl-POSS monomer at ~1198 cm -1 is present and this peak is still visible in LNU-81. In addition, the C=O absorption at ~1806 cm -1 of the anhydride disappears, while LNU-81 shows C=O absorption peaks at ~1649 cm -1 (related to ketone), ~1705 cm -1 (related to carboxyl group), and the O-H stretching peak at ~3227 cm -1 also proves the existence of the carboxyl group in LNU-81, which means that the Friedel-Crafts reaction between octaphenyl-POSS and pyromellitic dianhydride was successfully carried out. The above results indicate the successful polymerization of LNU-81.

[0036] Figure 2 This is the thermogravimetric graph of the porous organic polymer LNU-81 under air atmosphere test conditions. It can be seen that the polymer backbone begins to decompose at 300 °C, and obvious weight loss occurs in the range of 350 - 500 °C, which is mainly due to the decomposition of the polymer and the oxidation of the benzene ring, indicating that LNU-81 has very good thermal stability.

[0037] Figure 3 This is the powder X-ray diffraction pattern of the porous organic polymer LNU-81 synthesized in the present invention. It can be seen from the figure that there are no obvious sharp peaks in the spectrum of the porous organic polymer LNU-81, indicating that the polymer is an amorphous structure. This may be because the material is prepared under dynamic condensation conditions. Due to the fast reaction rate, the building units (monomers or polymer chains) do not have enough time to arrange orderly, thus forming an amorphous structure.

[0038] Figure 4Zeta potential diagram of the porous organic polymer LNU-81 synthesized in the present invention. It can be found from the spectrum that the zero potential of LNU-81 is approximately at pH = 3, and its potential becomes more negative with the increase of pH value. Since the pyromellitic dianhydride structure is negatively charged, the surface potential of the material shows a negative value in a relatively wide pH range. In addition, the results also show that when the pH increases, the Zeta potential becomes lower, and the adsorption efficiency of cationic dyes will increase due to electrostatic interaction.

[0039] Example 2 Adsorption of malachite green by carboxylic acid-functionalized porous organic polymer LNU-81

[0040] Figure 5 This is the test of the adsorption performance of the porous organic polymer LNU-81 synthesized in the present invention for MG under different pH conditions. 4 mg of LNU-81 was selected as the solid adsorbent, and 10 mL of an aqueous solution of malachite green with a concentration of 400 ppm in the pH range of 2 - 10 was used to study the adsorption performance of malachite green (MG). It can be seen that the adsorption capacity of the material for the cationic dye malachite green increases with the increase of pH and reaches the best value of the adsorption effect at pH = 10. This difference may be due to the surface charge of the adsorbent. However, considering that most sewage treatment conditions are neutral, subsequent experiments were carried out under the condition of pH = 7.

[0041] Figure 6 This is the adsorption isotherm of the porous organic polymer LNU-81 for malachite green. It can be seen from the figure that the Langmuir model is more suitable for describing the adsorption behavior of the polymer for the dye. According to the Langmuir model calculation, the maximum adsorption capacity of LNU-81 for malachite green can reach 1945.36 mg g -1 , and its adsorption performance is much higher than that of the reported porous materials at present

[0042] Example 3 Selective adsorption of malachite green by carboxylic acid-functionalized porous organic polymer LNU-81

[0043] Figure 7The UV-visible spectra of the porous organic polymer LNU-81 synthesized in the present invention before and after adsorbing a mixed dye solution of malachite green and methyl orange. LNU-81 was selected as the solid adsorbent, and methyl orange (an anionic dye) was used as the charge dye model. Methyl orange and malachite green (each 100 ppm) were blended as the mixed solution. Then, 4 mg of the adsorbent material was weighed and added to the above mixed solution. Samples were collected within different time ranges, photographed, and the adsorption process of the mixed dye was further recorded by observing the UV-visible spectra. For the mixed solution of malachite green (cationic dye) and methyl orange (anionic dye), the absorbance of malachite green decreased significantly after adsorption, and the removal efficiency reached 98.5%. Correspondingly, the removal efficiency of methyl orange was only 2.1%. The above results indicate that the material has good adsorption selectivity for anionic dyes.

[0044] Figure 8 The UV-visible spectra of the porous organic polymer LNU-81 synthesized in the present invention before and after adsorbing a mixed dye solution of malachite green and calcein. LNU-81 was selected as the solid adsorbent, and calcein (a neutral dye) was used as the charge dye model. Calcein and malachite green (each 100 ppm) were blended as the mixed solution. Then, 4 mg of the adsorbent material was weighed and added to the above mixed solution. Samples were collected within different time ranges, photographed, and the adsorption process of the mixed dye was further recorded by observing the UV-visible spectra. For the mixed solution of malachite green (cationic dye) and calcein (neutral dye), LNU-81 also had good adsorption selectivity, and the removal efficiency of malachite green after adsorption was 97.3%. Correspondingly, the removal efficiency of calcein was only 12.2%.

[0045] Example 4 Influence of the carboxylic acid-functionalized porous organic polymer LNU-81 on the adsorption efficiency of malachite green in different water quality environments

[0046] Figure 9 The influence of the porous organic polymer LNU-81 synthesized in the present invention on the adsorption efficiency of malachite green in different water quality environments. 4 mg of LNU-81 was selected as the solid adsorbent, and 10 mL of lake water, rainwater, tap water, and domestic sewage were respectively taken to prepare an aqueous solution of malachite green with a concentration of 400 ppm, and then a dynamic adsorption experiment was carried out. As shown in the figure, in different water quality environments, the adsorption efficiency of LNU-81 for malachite green did not change significantly, and the removal efficiency remained almost unchanged. Although the removal rate decreased slightly when rainwater was present, the adsorption efficiency still remained above 80%. The experimental results show that LNU-81 still has good adsorption performance for dyes in different water quality environments.

[0047] Example 4 Recycling performance of the carboxylic acid-functionalized porous organic polymer LNU-81 for adsorbing malachite green

[0048] Figure 10 The cyclic performance of the porous organic polymer LNU-81 synthesized in the present invention for adsorbing malachite green. Since the recyclability of the adsorbent in industry is a crucial factor, the cyclic performance of LNU-81 for adsorbing malachite green was studied. We used acidic methanol as the eluent to conduct a regeneration experiment on LNU-81. Using LNU-81 as the solid adsorbent to adsorb malachite green, after adsorption, the adsorbent was immersed in a methanol solution containing hydrochloric acid (0.1 mol L -1 ) to release the adsorbed malachite green. It is worth noting that LNU-81 still maintained good adsorption efficiency after 5 regeneration cycles, indicating that LNU-81 has high efficiency in removing malachite green, is easy to regenerate, and can be used in the field of sewage treatment. The above results show that a carboxylic acid-functionalized porous organic polymer prepared in the present invention has good application prospects in the field of dye adsorption.

Claims

1. A carboxylic acid-functionalized porous organic polymer for adsorbing cationic dyes, characterized in that, The preparation method is as follows: Mix the catalyst aluminum trichloride with the dichloroethane solvent and then activate it. Dissolve the mixture of the reaction monomers octaphenyl-POSS and pyromellitic dianhydride in dichloroethane and stir, add it to the catalyst solution for reaction, wash the precipitate obtained by suction filtration, perform Soxhlet extraction, and dry to obtain the red powder LNU-81.

2. The carboxylic acid-functionalized porous organic polymer for adsorbing cationic dyes according to claim 1, wherein The activation is carried out at 70 °C for 3 hours.

3. The carboxylic acid-functionalized porous organic polymer for adsorbing cationic dyes according to claim 1, wherein The reaction is carried out at 80 °C for 24 hours.

4. Use of the carboxylic acid-functionalized porous organic polymer for adsorbing cationic dyes as described in any one of claims 1-3 in the adsorption of organic dyes.

5. The application according to claim 4, wherein The organic pollutant is malachite green.

6. The application according to claim 5, characterized in that, The method is as follows: Add LNU-81 to the aqueous solution of malachite green with a pH value of 2-10 to adsorb malachite green.

7. The application according to claim 6, characterized in that, The concentration of the malachite green aqueous solution is 100 - 400 ppm.

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