Preparation method of micro-liquid assisted grinding and eutectic template strategy assisted synthesis of chitosan-covalent organic framework aerogel and application thereof in oil-water separation

Abstract

The application discloses a preparation method of micro-liquid assisted grinding and eutectic template strategy assisted synthesis of chitosan (CS)-covalent organic framework (COF) aerogel and application of the CS-COF aerogel in oil-water separation. The preparation method is as follows: 1) dissolving CS in an acidic aqueous solution, adding TA for crosslinking reaction, adding APTES for hydrophobation and amination reaction, and finally adding TA to obtain CTAT under the assistance of micro-liquid; 2) using a mechanical chemical method to perform eutectic on TAPT and PTSA to obtain eutectic product TAPT-PTSA; and 3) placing CTAT, TAPT-PTSA and TA in a mortar, using an eutectic template strategy to promote in-situ growth of COF, and finally obtaining CTAT-COF aerogel through mechanical grinding. The CTAT-COF aerogel prepared by the application has the characteristics of light weight, high porosity and strong hydrophobicity, and can significantly improve the oil-water separation efficiency and oil adsorption capacity. Therefore, the application has wide application prospects in the field of treating oily wastewater and the like, and has very important significance for effectively solving the problem of oil pollution.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of application of aerogel in oil-water separation, and relates to a preparation method of a chitosan (CS)-covalent organic framework (COF) aerogel and application thereof in oil-water separation, in particular to a mechanical-chemical method without inert gas protection, which is simple to operate and friendly to the environment, and a eutectic template strategy is used to promote in-situ growth of COF, so that a CTAT-COF aerogel with strong hydrophobicity is prepared. BACKGROUND

[0002] In order to solve the leakage of organic solvents and the harm caused by oil exploitation to water environment, it is urgent to clean and recover the oil substances retained in the water body, and avoid further spread of harmful oil substances. Traditional oil-water separation methods include gravity separation, centrifugation, flotation, bioremediation, in-situ combustion and electrochemical method. However, these conventional methods have the limitations of low separation efficiency, secondary pollution and high cost, and have poor actual performance in the field of oil-water separation.

[0003] Covalent organic framework material (COF) is a kind of crystalline porous material. Due to its large specific surface area, high porosity, easy modification, low density, strong chemical stability and thermal stability, COF has broad application prospects in the field of oil-water separation. However, COF is usually obtained in the form of powder, and the difficulty in maintaining the plasticity of the material hinders the effective recovery and regeneration of the material. In order to solve this problem, molding COF particles into layered porous aerogel is a promising strategy, which can overcome the shortcomings of powder form COF and realize higher efficient recovery and regeneration capacity.

[0004] Chitosan-based oil-water separation material mainly uses adsorbents to physically adsorb oil pollution for treatment, which is one of the most promising wastewater treatment methods at present. However, CS alone as an adsorbent is easy to dissolve under acidic conditions, and CS has the disadvantages of strong hydrophilicity, poor thermal stability and low specific surface area, which limits the application of CS in oil-water separation. However, COF powder with hydrophobicity and CS are molded into a three-dimensional network structure to form CS-COF aerogel, which not only improves the plasticity and mechanical properties of COF, but also endows the aerogel material with a layered porous structure to enhance the transport of pollutants, thereby having excellent oil-water separation selectivity. At the same time, after modification by silane reagent and the hydrophobic property of COF itself, the aerogel material has strong hydrophobicity and excellent oil absorption capacity, which has broad application prospects in the field of oil-water separation.

[0005] However, most of the COF-containing aerogel preparation requires harsh reaction conditions, such as long-time high-temperature reflux, inert gas protection or high pressure, which limits its large-scale rapid preparation in industrial environment, so it is necessary to use a green synthesis method that can improve efficiency and reduce pollution. Mechanical chemical method is a green synthesis method that induces chemical reaction, physical and chemical properties or internal microstructure change of substances by mechanical force, which is widely used in synthesis, catalysis and self-assembly. Therefore, not only the excessive use of toxic and harmful solvents is avoided, but also the experimental process is greatly simplified, the reaction rate is improved and the reaction time is greatly shortened.

[0006] Finally, the CTAT-COF aerogel improves the adsorption performance of oil materials, solves the problems of COF recovery difficulty and secondary pollution. Due to the layered porous structure and high porosity of the aerogel, the aerogel has excellent adsorption capacity for carbon tetrachloride in water, reaching 14130mg / g. In addition, the aerogel shows excellent recyclability, and the adsorption capacity still maintains 95.73% after five cycles. Therefore, it is of great industrial value to develop a green synthesis, simple process, low cost, high porosity and hydrophobic aerogel material. SUMMARY

[0007] In view of the lack of high-strength oil-water separation aerogel materials applied to complex environments and the broad application prospect thereof, the application discloses a preparation method of CTAT-COF aerogel for efficient oil-water separation.

[0008] To achieve the above-mentioned purpose, the application realizes the technical scheme as follows.

[0009] A preparation method of a chitosan-covalent organic framework aerogel, comprising the following steps:

[0010] 1) First, chitosan is dissolved in an acidic aqueous solution to obtain a clear transparent liquid in a viscous state, and then p-xylylene glycol dissolved in DMSO is added for crosslinking reaction; after the reaction is completed, 3-aminopropyl triethoxysilane is added for hydrophobization and amination reaction; after the reaction is completed, impurities are removed by suction filtration, washing and drying to obtain CTA solid;

[0011] 2) p-xylylene glycol is added to the CTA solid obtained in step 1), and glacial acetic acid is used as a catalyst and grinding agent to grind under the assistance of a small amount of liquid to obtain a CTAT base, which is dried for standby;

[0012] 3) 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and p-toluenesulfonic acid are placed in a mortar, and a eutectic product TAPT-PTSA is formed by mechanical grinding;

[0013] 4) Put the CTAT base obtained in step 2) and the co-crystal product TAPT-PTSA obtained in step 3) into a mortar, mix them, add p-xylylene glycol, and mechanically grind them with 1,4-dioxane as a grinding agent and a catalyst. After grinding, the sample is cleaned with a solvent, and the sample after removing impurities is placed in a mold and freeze-dried to obtain a CTAT-COF aerogel.

[0014] Further, in step 1) of the preparation method, the acid aqueous solution is hydrochloric acid aqueous solution or acetic acid aqueous solution, the volume concentration of the acid aqueous solution is 1-3%, and the volume of the acid aqueous solution is 15-20 mL.

[0015] Preferably, the acid aqueous solution is acetic acid aqueous solution, the volume concentration of the acetic acid aqueous solution is 3%, and the volume of the acetic acid aqueous solution is 20 mL.

[0016] Further, in step 1) of the preparation method, the volume of the DMSO is 3-5 mL.

[0017] Preferably, the volume of the DMSO is 5 mL.

[0018] Further, in step 1) of the preparation method, the 3-aminopropyl triethoxysilane is dissolved in a mixed solution of anhydrous ethanol and distilled water in a volume ratio of 1:1, and the volume concentration of the 3-aminopropyl triethoxysilane is 8-10%.

[0019] Preferably, the volume concentration of the 3-aminopropyl triethoxysilane is 10%.

[0020] Further, in step 1) of the preparation method, the temperature for dissolving the chitosan in the acid aqueous solution is 50-60°C, and the time is 4-5 hours.

[0021] Preferably, the temperature for dissolving the chitosan in the acid aqueous solution is 60°C, and the time is 5 hours.

[0022] Further, in step 1) of the preparation method, the temperature for the cross-linking reaction is 50-60°C, and the reaction time is 4-5 hours.

[0023] Preferably, the temperature for the cross-linking reaction is 60°C, and the reaction time is 5 hours.

[0024] Further, in step 1) of the preparation method, the temperature for the hydrophobation and amination reaction is 50-60°C, and the reaction time is 10-12 hours.

[0025] Preferably, the temperature for the hydrophobation and amination reaction is 60°C, and the reaction time is 12 hours.

[0026] Further, in the preparation method, the temperature of the drying in step 1) is 80-100℃, and the time is 50-60 minutes.

[0027] Preferably, the temperature of the drying is 90℃, and the time is 60 minutes.

[0028] Further, in the preparation method, the solvent used for the washing in step 1) is anhydrous ethanol and water.

[0029] Further, in the preparation method, the temperature of the grinding in step 2) is 25℃, and the time is 15-20 minutes.

[0030] Preferably, the time of the grinding is 20 minutes.

[0031] Further, in the preparation method, the temperature of the drying in step 2) is 80-100℃, and the time is 50-60 minutes.

[0032] Preferably, the temperature of the drying is 90℃, and the time is 60 minutes.

[0033] Further, in the preparation method, the temperature of the mechanical grinding in step 3) is 25℃, and the time is 10-15 minutes.

[0034] Preferably, the time of the grinding is 15 minutes.

[0035] Further, in the preparation method, the temperature of the mechanical grinding in step 4) is 25℃, and the time is 50-60 minutes.

[0036] Preferably, the time of the grinding is 60 minutes.

[0037] Further, in the preparation method, the temperature of the freeze-drying in step 4) is -60℃, and the time is 24-48 hours.

[0038] Preferably, the time of the freeze-drying is 48 hours.

[0039] Further, in the preparation method, the solvent used for the washing in step 4) is methanol, tetrahydrofuran, N,N-dimethylformamide, and dichloromethane.

[0040] The CTAT-COF aerogel prepared by the preparation method of any one of the above-mentioned applications is used in oil-water separation.

[0041] Further, in the application, the oil is light oil or heavy oil.

[0042] Preferably, the light oil is n-hexane, N,N-dimethylformamide or ethyl acetate; the heavy oil is dichloromethane, trichloromethane or carbon tetrachloride.

[0043] The beneficial effects of the present application are:

[0044] 1、The present application uses chitosan as a base material to prepare aerogels, which has a wide source and low price. Through a green and environmentally friendly mechanochemical method, the in-situ growth of COF is promoted by using a co-crystal template strategy. The CTAT-COF aerogel has the advantages of light weight, high porosity, strong hydrophobicity, and high oil-water separation efficiency.

[0045] 2、The preparation method provided by the present application is fast, environmentally friendly, and simple to operate; the mechanical force method is carried out under normal conditions, without the need for high temperature and pressure or inert gas protection, simplifying the experimental steps; only a small amount of liquid is used for grinding, eliminating the use of a large amount of organic solvent, reducing the reaction cost while minimizing the harm to the environment.

[0046] 3、Through a simple process of mechanochemical method, the hydrophobic aerogel is rapidly prepared, and the application potential of aerogel materials in the field of oil-water separation is expanded. The key to oil-water separation performance lies in the internal structure and surface properties, and the porous structure provides a longer penetration channel for oil or water in oil-containing wastewater, and the higher porosity can improve the separation flux of the separation material for oil-containing wastewater. The prepared aerogel material is used as a filter layer, and organic solvent and water are poured into a designed oil-water separation device, so that oil with a density greater than water can pass through the aerogel channel and be filtered out from the lower end of the device, and water is blocked outside the aerogel and cannot penetrate into the aerogel, thereby realizing the oil-water separation effect. The water contact angle of the prepared CTAT-COF aerogel can reach 141.6°, the oil-water separation efficiency of chloroform / water can reach 99.62%, the oil-water separation efficiency of n-hexane / water can reach 99.76%, and the oil adsorption capacity of carbon tetrachloride can reach 14130mg / g. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 is a process diagram for preparing CTAT-COF aerogel in Example 1.

[0048] Figure 2 is a water contact angle diagram of the CTAT-COF aerogel prepared in Example 1.

[0049] Figure 3 is an infrared spectrum diagram of the CTAT-COF aerogel prepared in Example 1.

[0050] Figure 4 is an X-ray diffraction diagram of the CTAT-COF aerogel prepared in Example 1.

[0051] Figure 5 is a plot of oil adsorption capacity of the CTAT-COF aerogel prepared in Example 1.

[0052] Figure 6 is a plot of oil-water separation cycle efficiency of the CTAT-COF aerogel prepared in Example 1, where (a) is n-hexane and (b) is chloroform. DETAILED DESCRIPTION

[0053] The application will be further described in conjunction with the drawings and specific embodiments of the application. Obviously, the described embodiments are part of the application, but not all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of the application.

[0054] Example 1

[0055] The application provides a hydrophobic, high adsorption capacity and high efficiency oil-water separation CTAT-COF aerogel and a preparation method thereof. The application crosslinks CS and TA to lay a foundation for improving the stability of the CTAT-COF aerogel, then adds APTES and -OH on the CS to perform silanization reaction, thereby realizing the first step of hydrophobic modification. After the silanization reaction, there are exposed -NH2, which can provide aldehyde group sites for in-situ growth of COF after reacting with TA by a mechanical method. Finally, the CTAT-COF aerogel is prepared by using a co-crystal template strategy to promote in-situ growth of COF and a freeze-drying method.

[0056] The application provides a preparation method of a hydrophobic and high-efficiency oil-water separation CTAT-COF aerogel (as shown in Figure 1 ), which comprises the following steps.

[0057] 1) 322.32 mg of chitosan (CS) is dissolved in 20 mL of 3% acetic acid aqueous solution, and reacted in a 60°C electric heating plate for 5 hours. Then 134.13 mg of terephthaldehyde (TA) is added and dissolved in 5 mL of DMSO, and the reaction is continued at 60°C for 5 hours. After the reaction is completed, 100 mL of anhydrous ethanol / distilled water mixed solution with a volume ratio of 1:1 and 10 mL of 3-aminopropyltriethoxysilane (APTES) are added, and the reaction is carried out at 60°C for 12 hours. After the reaction is completed, the mixture is suction filtered, washed with ethanol and water for multiple times to remove impurities, and then dried in a 90°C oven for 60 minutes. The obtained CS-TA-APTES (CTA) solid is taken out and reserved for use.

[0058] 2) Put the CTA solid obtained in step 1) and 134.13 mg of p-xylylene diamine into a mortar, acetic acid as grinding agent and catalyst, mechanical force, grinding at room temperature for 20 minutes, to provide sites for COF in-situ growth, drying in an oven at 90 °C for 60 minutes, take out, get the CTAT substrate, ready for use.

[0059] 3) Put 126 mg of 2,4,6-tris (4-aminophenyl) -1,3,5-triazine (TAPT) and 101 mg of p-toluenesulfonic acid (PTSA) into a mortar and mix well, grind at room temperature for 15 minutes until the sample is dry, to prepare the eutectic product TAPT-PTSA.

[0060] 4) Put the CTAT substrate obtained in step 2) and the eutectic product TAPT-PTSA obtained in step 3) into a mortar and mix well, add 73.1 mg of p-xylylene diamine, 1,4-dioxane as grinding agent and catalyst, mechanical force, grinding at room temperature for 60 minutes; after the reaction is complete, sequentially wash with methanol, tetrahydrofuran, N, N-dimethylformamide, dichloromethane solvents to remove PTSA and polymer impurities, after removing the impurities, place in a mold and freeze dry at -60 °C for 48 hours, finally synthesize the CTAT-COF aerogel with light weight, high porosity and high hydrophobicity.

[0061] Figure 2 is the water contact angle diagram of the CTAT-COF aerogel prepared in Example 1, the CTAT-COF aerogel after silanization reaction and COF in-situ growth, the hydrophobicity is obviously increased, the water contact angle is 141.9°. Therefore, the results of the water contact angle prove that the CTAT-COF aerogel has good hydrophobic performance.

[0062] Figure 3 is the infrared spectrum of the CTAT-COF aerogel prepared in Example 1, the COF and the CTAT-COF aerogel both appear the stretching vibration peak of the -C=N bond at 1508.08 cm -1 -1, the CTAT-COF aerogel appears the stretching vibration peak of the -Si-O-Si bond at 1012.46 cm -1 -1. Therefore, the results of the infrared prove the successful modification of the silanization reaction and the successful in-situ growth of the COF.

[0063] Figure 4is the X-ray diffraction pattern of the CTAT-COF aerogel prepared in Example 1. The crystalline properties of the CS aerogel show two broad peaks at 2Q = 12.05° and 20.03°, respectively, which are due to the hydrogen bonds formed between the amino and hydroxyl groups of CS. The CTAT-COF aerogel shows a typical peak of the synthesized COF at 2Q = 2.91°, which is consistent with the simulated COF peak in Materials Studio. The clear and identifiable COF peak present in the CTAT-COF aerogel spectrum indicates the presence of an intact crystal structure within the CTAT-COF aerogel. Thus, the XRD results establish the successful preparation of the CTAT-COF aerogel.

[0064] Example 2

[0065] The absorption capacity of the CTAT-COF aerogel was determined for different organic solvents (n-hexane, N,N-dimethylformamide, ethyl acetate, dichloromethane, trichloromethane, carbon tetrachloride). The absorption capacity of the CTAT-COF aerogel was calculated over a certain period of time in which the CTAT-COF aerogel was immersed in different oils. At the same time, in order to evaluate the recyclability of the CTAT-COF aerogel, after the CTAT-COF aerogel reached saturation, it was washed with anhydrous ethanol and vacuum dried to facilitate the desorption process. Subsequently, the cycle could be repeated five times, thus achieving the recycling goal. As shown in Figure 5 Figure 2, the adsorption capacity of n-hexane was 6729 mg / g, the adsorption capacity of N,N-dimethylformamide was 7223 mg / g, the adsorption capacity of ethyl acetate was 8340 mg / g, the adsorption capacity of dichloromethane was 12163 mg / g, the adsorption capacity of trichloromethane was 14060 mg / g, and the adsorption capacity of carbon tetrachloride was 14130 mg / g. In addition, the aerogel also showed excellent recyclability, with an adsorption capacity of more than 95% after five cycles.

[0066] Figure 6A continuous gravity-driven process of CTAT-COF aerogel was depicted, chloroform and n-hexane were dyed with oil red o, and water was dyed with methylene blue. For the oil-water separation efficiency of chloroform / water, first, water (blue) was poured into the funnel, and no water seepage from the aerogel was observed, then chloroform (red) was poured, and chloroform was quickly absorbed after contacting with the CTAT-COF aerogel to form an oil film, which could significantly reduce the contact area between water and the aerogel, thereby promoting oil-water separation. As it approached its absorption limit, chloroform (red) was gradually poured into the beaker, while water (blue) remained in the funnel. After 5 minutes of complete separation, no water seepage from the aerogel was observed. For the oil-water separation efficiency of n-hexane / water, first, n-hexane (red) was poured into the funnel, and n-hexane was quickly absorbed after contacting with the CTAT-COF aerogel, then water (blue) was poured, and n-hexane (red) was completely poured into the beaker, while water (blue) remained in the funnel. After 5 minutes of separation, no water seepage from the aerogel was observed, and the CTAT-COF aerogel showed good oil / water separation capacity. As shown in (a) and (b), the oil-water separation efficiency of chloroform / water was 99.62%, and the oil-water separation efficiency of n-hexane / water was 99.76%. After ten oil / water mixture separations, the aerogel still maintained its porous structure and morphology, indicating that it had good stability and durability and could be used for long-term continuous oil / water separation without changing its original properties or structure. Figure 6 (a) and (b) show that the oil-water separation efficiency of chloroform / water is 99.62%, and the oil-water separation efficiency of n-hexane / water is 99.76%. After ten oil / water mixture separations, the aerogel still maintains its porous structure and morphology, indicating that it has good stability and durability and can be used for long-term continuous oil / water separation without changing its original properties or structure.

[0067] In summary, the present application provides a green micro-liquid assisted grinding (LAG) technique for synthesizing CTAT-COF aerogel with strong hydrophobicity and high-efficiency oil-water separation and a preparation method thereof. The method includes crosslinking chitosan and p-phenylenediamine, performing silanization and amination reactions on the crosslinked product with APTES, providing sites for in-situ growth of COF by reacting with p-phenylenediamine, in-situ growing COF by adopting a TAPT and PTSA co-crystal method, and finally obtaining CTAT-COF aerogel with strong hydrophobicity and high-efficiency oil-water separation. The crosslinking of the aerogel enhances the stability of the aerogel, and the modification of the aerogel with APTES silane reagent and the hydrophobic properties of COF itself can endow the aerogel with strong hydrophobic properties and excellent oil absorption capacity, achieving high-efficiency oil-water separation and making it have broad application prospects in the field of oil-water separation.

Claims

1. A method for preparing a chitosan-covalent organic framework aerogel, characterized in that, The preparation method comprises the following steps: 1) dissolving chitosan in an acidic aqueous solution to obtain a clear transparent liquid in a viscous state, and then adding p-xylylene glycol dissolved in DMSO to perform a cross-linking reaction; after the reaction is completed, 3-aminopropyl triethoxysilane is added to perform a hydrophobization and amination reaction; after the reaction is completed, impurities are removed by suction filtration, washing, and drying to obtain CTA solid; 2) adding p-xylylene glycol to the CTA solid obtained in step 1), using glacial acetic acid as a catalyst and a grinding agent, and grinding under the assistance of a trace amount of liquid to obtain a CTAT base, which is dried and reserved; 3) placing 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and p-toluenesulfonic acid in a mortar, and performing mechanical grinding to form a co-crystal product TAPT-PTSA; 4) placing the CTAT base obtained in step 2) and the co-crystal product TAPT-PTSA obtained in step 3) in a mortar, mixing, adding p-xylylene glycol, and performing mechanical grinding with 1,4-dioxane as a grinding agent and a catalyst; after the grinding is completed, the sample after removing impurities is placed in a mold and freeze-dried to finally obtain CTAT-COF aerogel.

2. The production method according to claim 1, characterized by, In step 1), the acidic aqueous solution is hydrochloric acid or acetic acid, the volume concentration of the acidic aqueous solution is 1-3%, and the volume of the acidic aqueous solution is 15-20 mL; the volume of DMSO is 3-5 mL.

3. The preparation method according to claim 1, characterized in that, In step 1), the 3-aminopropyl triethoxysilane is dissolved in a mixed solution of anhydrous ethanol and distilled water in a volume ratio of 1:1, and the volume concentration of the 3-aminopropyl triethoxysilane is 8-10%.

4. The method of claim 1, wherein, In step 1), the temperature for dissolving chitosan in the acidic aqueous solution is 50-60℃, the time is 4-5 hours; the temperature for the cross-linking reaction is 50-60℃, and the reaction time is 4-5 hours; the temperature for the hydrophobization and amination reaction is 50-60℃, and the reaction time is 10-12 hours; the temperature for drying is 80-100℃, and the time is 50-60 minutes.

5. The preparation method according to claim 1, characterized in that, In step 2), the grinding temperature is 25℃, the grinding time is 15-20 minutes; and the drying temperature is 80-100℃, and the time is 50-60 minutes.

6. The method of claim 1, wherein, In step 3), the mechanical grinding temperature is 25℃, and the grinding time is 10-15 minutes.

7. The preparation method according to claim 1, characterized in that, In step 4), the mechanical grinding temperature is 25℃, the grinding time is 50-60 minutes; the freeze-drying temperature is -60℃, and the time is 24-48 hours.

8. The method of claim 1, wherein, In step 4), the method for cleaning with a solvent is: sequentially using methanol, tetrahydrofuran, N,N-dimethylformamide, and dichloromethane for cleaning.

9. The application of the CTAT-COF aerogel prepared by the preparation method in any one of claims 1-8 in oil-water separation.

10. Use according to claim 9, characterized in that, The oil is light oil or heavy oil, the light oil is n-hexane, N,N-dimethylformamide or ethyl acetate; and the heavy oil is dichloromethane, trichloromethane or carbon tetrachloride.

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