Synthetic method of acryloyloxyethyl trimethyl ammonium chloride

Abstract

The invention relates to the technical field of synthesis of chemical products, in particular to a synthesis method of acryloyloxyethyl trimethyl ammonium chloride. According to the method, a one-pot reaction system is adopted, ethyl acrylate and N, N-dimethylaminoethanol are taken as raw materials and are subjected to quaternization reaction with chloromethane under an alkaline condition, and efficient conversion is realized through the synergistic effect of a composite catalytic system and a polymerization inhibitor. The composite catalyst is constructed by compounding magnetic nanoparticles and a metal organic framework material, forms a multilevel structure through titanate crosslinking, and has high catalytic activity and magnetic separation and recovery characteristics. The method simplifies the traditional step-by-step process, has the advantages of simple and convenient one-pot operation, recyclable catalyst, high raw material utilization rate, environmental friendliness and the like, and is suitable for large-scale preparation of acryloyloxyethyl trimethyl ammonium chloride.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of chemical product synthesis, more particularly, it relates to a synthesis method of acryloyloxyethyl trimethyl ammonium chloride. BACKGROUND

[0002] As an important cationic monomer, acryloyloxyethyl trimethyl ammonium chloride is widely used in water treatment, papermaking aids, oil field chemicals and polymer material modification. Its molecular structure contains both polymerizable acryloyloxy group and quaternary ammonium salt group, which endows it with excellent charge density and reactivity, especially suitable for preparing polymer materials with antibacterial, antistatic and flocculation functions. In recent years, with the tightening of environmental regulations and the upgrading of industrial application requirements, the development of efficient, green and suitable for large-scale production synthesis process has become a research hotspot in this field.

[0003] The traditional synthesis process usually adopts a step-by-step route: first, an ester exchange reaction of ethyl acrylate and N,N-dimethylaminoethanol is carried out to generate an acryloyloxyethyl dimethylamine intermediate, and then a quaternary ammonium reaction is carried out with methyl chloride under alkaline conditions to generate the target product. However, such process has many technical bottlenecks. Firstly, the step-by-step operation requires multiple separations and purifications of the intermediate, resulting in a long process flow, increased energy consumption, and limited production efficiency; secondly, the commonly used homogeneous catalysts such as potassium iodide or tetrabutylammonium bromide in the quaternary ammonium reaction cause waste of catalyst and environmental pollution due to their difficulty in recovery; thirdly, the methyl chloride gas is easy to escape in the reaction system, not only with low utilization rate, but also with the safety hazard of flammability and explosiveness; fourthly, the high polymerization activity of acrylate monomers leads to the occurrence of side reactions in the reaction process, and the traditional single polymerization inhibitor system cannot effectively inhibit the free radical polymerization, thereby affecting the purity of the product. In addition, the separation of the catalyst in the prior art relies on centrifugation or filtration, which is complex and difficult to realize continuous production, further restricting the economy of the process. Therefore, the present application provides a synthesis method of acryloyloxyethyl trimethyl ammonium chloride to solve the above technical problems. SUMMARY

[0004] In order to solve the above problems, the present application provides a synthesis method of acryloyloxyethyl trimethyl ammonium chloride, which simplifies the traditional step-by-step process, has the advantages of one-pot operation, recyclable catalyst, high raw material utilization rate and environmental friendliness, and is suitable for large-scale preparation of acryloyloxyethyl trimethyl ammonium chloride.

[0005] To achieve the above purpose, the present application provides the following technical solutions:

[0006] A synthesis method of acryloyloxyethyl trimethyl ammonium chloride, comprising the following steps:

[0007] (1) mixing ethyl acrylate, N,N-dimethylaminoethanol and potassium carbonate, adding composite catalyst and polymerization inhibitor, heating to 70-75℃ under nitrogen protection, continuously passing in chloromethane gas at a rate of 0.5-1.5L / min, maintaining the pH of the system at 7-8, and reacting for 6-8h;

[0008] (2) after the reaction is completed, the composite catalyst is recovered by magnetic separation, the filtrate is condensed to recover unreacted chloromethane gas and recycled, the mother liquor is decolorized by adding activated carbon for 20-30min, filtered, recrystallized at 5-15℃, and vacuum dried to obtain white crystalline acryloyloxyethyl trimethyl ammonium chloride.

[0009] Preferably, in step (1), the amounts by weight are ethyl acrylate 40-50 parts, N,N-dimethylaminoethanol 28-35 parts, potassium carbonate 10-15 parts, composite catalyst 1-3 parts, and polymerization inhibitor 0.1-0.3 parts.

[0010] Preferably, in step (1), the polymerization inhibitor is composed of hydroquinone and phenothiazine in a molar ratio of 1:1-3.

[0011] Preferably, in step (1), the composite catalyst is prepared by the following method:

[0012] S1. dispersing MIL-101(Fe) in ethanol, adding triethylamine and an ethanol solution of -N,N,N-trimethyl-1-dodecylammonium chloride, refluxing and stirring at 60-65℃ for 18-24h, centrifuging, washing, and drying to obtain MIL-101(Fe) precursor;

[0013] S2. dissolving CoCl2•6H2O and FeCl3•6H2O in deionized water, adjusting the pH with ammonia water under nitrogen protection, heating to 130-140℃, continuously stirring for 3-6h, and then separating, washing, and drying to obtain CoFe2O4 nanoparticles;

[0014] S3. dispersing CoFe2O4 nanoparticles in toluene, adding MIL-101(Fe) precursor and tetrabutyl titanate, reacting at 60-70℃ for 2-4h, and then separating, washing, and drying to obtain the composite catalyst.

[0015] Preferably, in step S1, the concentration of the ethanol solution of -N,N,N-trimethyl-1-dodecylammonium chloride is 15-20wt%.

[0016] Preferably, in step S1, the amounts by weight are 30-35 parts of MIL-101(Fe), 80-90 parts of ethanol, 5-10 parts of triethylamine, and 80-100 parts of the ethanol solution of -N,N,N-trimethyl-1-dodecylammonium chloride.

[0017] Preferably, the mass ratio of CoCl2 6H2O and FeCl3 6H2O in step S2 is 1:2-3.

[0018] Preferably, the pH is adjusted to 7-8 in step S2.

[0019] Preferably, the amount of CoFe2O4 nanoparticles, toluene, MIL-101(Fe) precursor and tetrabutyl titanate in step S3 is 20-25 parts, 100-120 parts, 30-35 parts and 1-5 parts by weight, respectively.

[0020] Compared with the prior art, the present application has the following beneficial effects:

[0021] The present application avoids the cumbersome operation of multiple separation and purification in the traditional process through the coupling design of quaternization and esterification reaction, greatly shortens the reaction period. With magnetic nanoparticles as the core, combined with the porous characteristics and surface functionalization modification of metal organic framework materials, a composite catalyst system with high activity and stability is formed. The mass transfer efficiency is strengthened by the multi-level pore structure constructed by titanate crosslinking, and the catalyst has fast separation capacity due to the magnetic core, which significantly improves the reaction efficiency and simplifies the recovery process. A composite polymerization inhibitor system is used, which effectively inhibits the self-polymerization and thermal polymerization side reactions of acryloyloxy groups through the dual action mechanism of free radical capture and chain transfer, ensuring that the product purity is significantly improved. The composite catalyst maintains excellent chemical stability in the alkaline reaction environment through interface crosslinking and structure optimization, the dissolution rate of active components is very low, and the catalyst still maintains high catalytic activity after multiple cycles, which significantly reduces the process cost.

[0022] In summary, through the combination of process innovation and functionalization design of catalyst, the present application solves the problems of low efficiency, multiple by-products and non-recyclable catalysts in traditional methods, and provides an efficient, economic and environmentally friendly technical solution for the large-scale clean production of acryloyloxyethyl trimethyl ammonium chloride. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of the present application.

[0024] In the following examples, the experimental methods are conventional methods unless otherwise specified, and the test materials used are commercially available from conventional biochemical reagent stores unless otherwise specified. In the quantitative tests in the following examples, three repeated experiments were set, and the data were the average value or average value ± standard deviation of the three repeated experiments.

[0025] MIL-101(Fe): Purchased from Xi'an Qiyue Biotechnology Co., Ltd., CAS No. 1189182-67-9.

[0026] Example 1

[0027] A method for synthesizing acryloyloxyethyltrimethylammonium chloride includes the following steps:

[0028] By weight, 40 parts of ethyl acrylate, 28 parts of N,N-dimethylaminoethanol, and 10 parts of potassium carbonate were added to a reactor, along with 1 part of a composite catalyst and 0.1 part of a polymerization inhibitor. After nitrogen purging, the mixture was heated to 70°C, and chloromethane gas was continuously introduced at a rate of 0.5 L / min to maintain the pH of the system at 7. The reaction was stirred at 300 rpm for 8 hours. The polymerization inhibitor consisted of hydroquinone and phenothiazine in a molar ratio of 1:1. The composite catalyst was recovered by magnetic separation. The filtrate was condensed at -3°C to recover chloromethane. The mother liquor was decolorized by adding 1 part of activated carbon for 30 min, filtered, and recrystallized at 15°C. After vacuum drying, white crystalline acryloyloxyethyltrimethylammonium chloride was obtained.

[0029] The composite catalyst in the aforementioned step is prepared by the following method:

[0030] S1. Disperse 30 parts of MIL-101(Fe) in 80 parts of ethanol, add 5 parts of triethylamine and 80 parts of 15wt% ethanol solution of N,N,N-trimethyl-1-dodecylammonium chloride, control the stirring speed at 300 rpm, reflux and stir at 60℃ for 24 h, centrifuge, wash and dry to obtain MIL-101(Fe) precursor;

[0031] S2. Dissolve 1 part CoCl2•6H2O and 2 parts FeCl3•6H2O in 20 parts deionized water, adjust the pH to 7 with ammonia water under nitrogen protection, raise the temperature to 130℃, stir continuously for 6 hours, and then separate, wash and dry to obtain CoFe2O4 nanoparticles.

[0032] S3. Disperse 20 parts of CoFe2O4 nanoparticles in 100 parts of toluene, add 30 parts of MIL-101(Fe) precursor and 1 part of tetrabutyl titanate, react at 60℃ for 4 h, centrifuge, wash and dry to obtain composite catalyst.

[0033] Example 2

[0034] A method for synthesizing acryloyloxyethyltrimethylammonium chloride includes the following steps:

[0035] Into a reactor, 41 parts of ethyl acrylate, 29 parts of N,N-dimethylaminoethanol and 12 parts of potassium carbonate were mixed, 2 parts of composite catalyst and 0.18 parts of polymerization inhibitor were added, and after nitrogen replacement, the temperature was raised to 72°C. Chloromethane gas was continuously introduced at a rate of 0.6 L / min, the pH of the system was maintained at 7.2, and the reaction was stirred at 320 rpm for 7.7 h. The polymerization inhibitor was composed of molar ratio 1:1.8 of hydroquinone and phenothiazine. The composite catalyst was recovered by magnetic separation, the filtrate was condensed at -5°C to recover chloromethane, the mother liquor was decolorized with 1.3 parts of activated carbon for 28 min, filtered, recrystallized at 13°C, and vacuum dried to obtain white crystalline acryloyloxyethyl trimethyl ammonium chloride.

[0036] The composite catalyst in the step is prepared by the following method:

[0037] S1. 31 parts of MIL-101(Fe) were dispersed in 82 parts of ethanol, 6 parts of triethylamine and 82 parts of 16wt% N,N,N-trimethyl-1-dodecylammonium chloride ethanol solution were added, the stirring rate was controlled at 320 rpm, and reflux stirring was carried out at 61°C for 23 h. After centrifugal washing and drying, MIL-101(Fe) precursor was obtained.

[0038] S2. 1 part of CoCl2·6H2O and 2.2 parts of FeCl3·6H2O were dissolved in 22 parts of deionized water. After adjusting the pH to 7.2 with ammonia water under nitrogen protection, the temperature was raised to 132°C, and stirring was continued for 5.8 h. After separation, washing and drying, CoFe2O4 nanoparticles were obtained.

[0039] S3. 22 parts of CoFe2O4 nanoparticles were dispersed in 105 parts of toluene, 31 parts of MIL-101(Fe) precursor and 2 parts of tetrabutyl titanate were added, and reaction was carried out at 62°C for 3.8 h. After centrifugal washing and drying, the composite catalyst was obtained.

[0040] Example 3

[0041] A method for synthesizing acryloyloxyethyl trimethyl ammonium chloride, comprising the following steps:

[0042] Into a reactor, 43 parts of ethyl acrylate, 30 parts of N,N-dimethylaminoethanol and 12 parts of potassium carbonate were mixed, 2 parts of composite catalyst and 0.16 parts of polymerization inhibitor were added, and after nitrogen replacement, the temperature was raised to 73°C. Chloromethane gas was continuously introduced at a rate of 0.8 L / min, the pH of the system was maintained at 7.4, and the reaction was stirred at 350 rpm for 7 h. The polymerization inhibitor was composed of molar ratio 1:2.5 of hydroquinone and phenothiazine. The composite catalyst was recovered by magnetic separation, the filtrate was condensed at -6°C to recover chloromethane, the mother liquor was decolorized with 1.5 parts of activated carbon for 25 min, filtered, recrystallized at 10°C, and vacuum dried to obtain white crystalline acryloyloxyethyl trimethyl ammonium chloride.

[0043] The composite catalyst in the step is prepared by the following method:

[0044] S1. 33 parts of MIL-101(Fe) were dispersed in 84 parts of ethanol, 8 parts of triethylamine and 90 parts of 18wt% N,N,N-trimethyl-1-dodecylammonium chloride ethanol solution were added, the stirring rate was controlled at 360 rpm, and stirring was carried out at 63℃ for 22 h, and then centrifugal washing and drying were performed to obtain a MIL-101(Fe) precursor;

[0045] S2. 1 part of CoCl2·6H2O and 2.4 parts of FeCl3·6H2O were dissolved in 23 parts of deionized water, and after the pH was adjusted to 7.5 by ammonia water under nitrogen protection, the temperature was increased to 136℃, and stirring was continued for 5 h, and then separation, washing and drying were performed to obtain CoFe2O4 nanoparticles;

[0046] S3. 24 parts of CoFe2O4 nanoparticles were dispersed in 110 parts of toluene, 33 parts of MIL-101(Fe) precursor and 3 parts of tetrabutyl titanate were added, and reaction was carried out at 65℃ for 3.5 h, and then centrifugal washing and drying were performed to obtain a composite catalyst.

[0047] Example 4

[0048] A synthesis method of acryloyloxyethyl trimethyl ammonium chloride, comprising the following steps:

[0049] According to parts by weight, 50 parts of ethyl acrylate, 35 parts of N,N-dimethylaminoethanol and 15 parts of potassium carbonate were mixed and added to a reaction kettle, 3 parts of composite catalyst and 0.3 parts of polymerization inhibitor were added, and after nitrogen replacement, the temperature was increased to 75℃, chloromethane gas was continuously introduced at a rate of 1.5 L / min, the pH of the system was maintained at 8, and stirring was carried out at 500 rpm for 6 h, wherein the polymerization inhibitor was composed of molar ratio 1:3 of hydroquinone and phenothiazine. The composite catalyst was recovered by magnetic separation, the filtrate was condensed at-10℃ to recover chloromethane, 2 parts of activated carbon was added to the mother liquor for decolorization for 30 min, and then filtration was carried out, and recrystallization was carried out at 5℃, and vacuum drying was carried out to obtain white crystal acryloyloxyethyl trimethyl ammonium chloride.

[0050] The composite catalyst in the step is prepared by the following method:

[0051] S1. 35 parts of MIL-101(Fe) were dispersed in 90 parts of ethanol, 10 parts of triethylamine and 100 parts of 20wt% N,N,N-trimethyl-1-dodecylammonium chloride ethanol solution were added, the stirring rate was controlled at 500 rpm, and stirring was carried out at 65℃ for 18 h, and then centrifugal washing and drying were performed to obtain a MIL-101(Fe) precursor;

[0052] S2. Dissolve 1 part of CoCl2•6H2O and 3 parts of FeCl3•6H2O in 25 parts of deionized water, adjust the pH to 8 with ammonia under nitrogen protection, and then heat to 140℃. Stir for 3h, then separate, wash and dry to obtain CoFe2O4 nanoparticles;

[0053] S3. Disperse 25 parts of CoFe2O4 nanoparticles in 120 parts of toluene, add 35 parts of MIL-101(Fe) precursor and 5 parts of tetrabutyl titanate, react at 70℃ for 2h, centrifugal wash and dry to obtain a composite catalyst.

[0054] Example 5

[0055] A method for synthesizing acryloyloxyethyl trimethyl ammonium chloride, comprising the following steps:

[0056] According to parts by weight, 50 parts of ethyl acrylate, 35 parts of N,N- dimethylamino ethanol and 14 parts of potassium carbonate are mixed in a reaction kettle, 3 parts of composite catalyst and 0.3 parts of polymerization inhibitor are added, nitrogen is replaced, heated to 75℃, chloromethane gas is continuously introduced at a rate of 1.5L / min, the pH of the system is maintained at 7.5, and the stirring speed is 400rpm. React for 7h, wherein the polymerization inhibitor is composed of hydroquinone and phenothiazine in a molar ratio of 1:3. The composite catalyst is recovered by magnetic separation, the filtrate is condensed at-10℃ to recover chloromethane, 1.8 parts of activated carbon is added to the mother liquor to decolorize for 25min, filtered and recrystallized at 5℃ to obtain white crystal acryloyloxyethyl trimethyl ammonium chloride.

[0057] The composite catalyst in the step is prepared by the following method:

[0058] S1. Disperse 35 parts of MIL-101(Fe) in 90 parts of ethanol, add 8 parts of triethylamine and 100 parts of 18wt% N,N,N-trimethyl-1-dodecylammonium chloride ethanol solution, control the stirring speed at 400rpm, reflux and stir at 65℃ for 20h, centrifugal wash and dry to obtain MIL-101(Fe) precursor;

[0059] S2. Dissolve 1 part of CoCl2•6H2O and 2.8 parts of FeCl3•6H2O in 25 parts of deionized water, adjust the pH to 7.8 with ammonia under nitrogen protection, and then heat to 140℃. Stir for 3h, then separate, wash and dry to obtain CoFe2O4 nanoparticles;

[0060] S3. Disperse 25 parts of CoFe2O4 nanoparticles in 120 parts of toluene, add 35 parts of MIL-101(Fe) precursor and 4 parts of tetrabutyl titanate, react at 70℃ for 2.5h, centrifugal wash and dry to obtain a composite catalyst.

[0061] Comparative Example 1

[0062] A synthesis method of acryloyloxyethyl trimethyl ammonium chloride, which is different from example 5 in that the catalyst is replaced by a homogeneous catalyst, i.e. tetrabutylammonium bromide is used instead of a composite catalyst, and other conditions are the same as example 5.

[0063] Comparative example 2

[0064] A synthesis method of acryloyloxyethyl trimethyl ammonium chloride, which is different from example 5 in that the polymerization inhibitor is replaced by a single polymerization inhibitor, i.e. only hydroquinone is used instead of a polymerization inhibitor, and other conditions are the same as example 5.

[0065] Comparative example 3

[0066] A synthesis method of acryloyloxyethyl trimethyl ammonium chloride, which is different from example 5 in that a traditional step-by-step process is used, i.e. the intermediate acryloyloxyethyl dimethyl amine is first generated by ester exchange reaction of ethyl acrylate and N,N-dimethylamino ethanol, and then quaternary ammonium reaction is carried out with methyl chloride under alkaline conditions, and other conditions are the same as example 5.

[0067] Comparative example 4

[0068] A synthesis method of acryloyloxyethyl trimethyl ammonium chloride, which is different from example 5 in that the catalyst carrier is replaced by a non-magnetic carrier, i.e. silica nanoparticles are used instead of CoFe2O4 nanoparticles as catalyst carrier, and other conditions are the same as example 5.

[0069] Comparative example 5

[0070] A synthesis method of acryloyloxyethyl trimethyl ammonium chloride, which is different from example 5 in that the metal organic framework material is replaced by other materials, i.e. UiO-66 is used instead of MIL-101(Fe) as metal organic framework material, and other conditions are the same as example 5.

[0071] Performance test

[0072] The yield (%), product purity (%), catalyst recovery rate (%) and catalyst cycle 5 times yield (%) of the synthesis method of acryloyloxyethyl trimethyl ammonium chloride in examples 1-5 and comparative examples 1-4 were calculated, and the test results are shown in table 1.

[0073] Table 1:

[0074] Test item Yield / % Product purity / % Catalyst recovery / % Yield / % after 5 cycles Example 1 92.3 92.8 93.1 86.5 Example 2 93.1 93.6 95.2 86.3 Example 3 94.5 94.1 96.2 87.1 Example 4 95.2 94.7 97.9 87.5 Example 5 96.8 95.3 98.7 88.3 Comparative Example 1 78.2 85.5 0 65.3 Comparative Example 2 85.1 80.7 95.5 80.4 Comparative Example 3 73.6 83.4 88.1 69.8 Comparative Example 4 88.4 86.1 62.3 63.2 Comparative Example 5 83.7 88.2 75.6 68.9

[0075] The embodiments 1-5 have significantly better comprehensive performance than the comparative examples 1-5 by the one-pot process, the optimization of the magnetic composite catalyst and the synergistic polymerization inhibitor system. The present application solves the problems of low efficiency, many by-products and non-recyclable catalysts of the traditional method by the synergistic effect of process innovation and catalyst design, and provides an efficient scheme for large-scale clean production.

[0076] The above is only an example and description of the present application. Those skilled in the art can make various modifications or supplements to the described specific embodiments or use similar ways to replace, as long as they do not deviate from the invention or exceed the scope defined by the present claims, which shall belong to the protection scope of the present application.

Claims

1. A method for the synthesis of acryloyloxyethyltrimethylammonium chloride, characterized in that, It comprises the following steps: (1) mixing ethyl acrylate, N, N-dimethylaminoethanol and potassium carbonate, adding composite catalyst and polymerization inhibitor, heating to 70-75 DEG C under nitrogen protection, continuously passing in chloromethane gas at a rate of 0.5-1.5 L / min, maintaining the pH of the system at 7-8, and reacting for 6-8 h; (2) after the reaction is completed, the composite catalyst is recovered by magnetic separation, the filtrate is condensed to recover unreacted chloromethane gas and recycled, the mother liquor is decolorized by adding activated carbon for 20-30 min, filtered, recrystallized at 5-15 DEG C, and vacuum dried to obtain white crystalline acryloyloxyethyl trimethyl ammonium chloride.

2. The method of claim 1, wherein, In step (1), the ethyl acrylate is 40-50 parts by weight, the N, N-dimethylaminoethanol is 28-35 parts by weight, the potassium carbonate is 10-15 parts by weight, the composite catalyst is 1-3 parts by weight, and the polymerization inhibitor is 0.1-0.3 parts by weight.

3. The method of claim 1, wherein, In step (1), the polymerization inhibitor is composed of hydroquinone and phenothiazine in a molar ratio of 1:1-3.

4. The method of claim 1, wherein, The composite catalyst in step (1) is prepared by the following method: S1. dispersing MIL-101(Fe) in ethanol, adding triethylamine and an ethanol solution of -N, N, N-trimethyl-1-dodecylammonium chloride, refluxing and stirring at 60-65 DEG C for 18-24 h, centrifuging, washing and drying to obtain MIL-101(Fe) precursor; S2. dissolving CoCl2•6H2O and FeCl3•6H2O in deionized water, adjusting the pH with ammonia water under nitrogen protection, heating to 130-140 DEG C, continuously stirring for 3-6 h, and then separating, washing and drying to obtain CoFe2O4 nanoparticles; S3. dispersing CoFe2O4 nanoparticles in toluene, adding MIL-101(Fe) precursor and tetrabutyl titanate, and reacting at 60-70 DEG C for 2-4 h, and then separating, washing and drying to obtain the composite catalyst.

5. The method of claim 4, wherein, In step S1, the concentration of the ethanol solution of -N, N, N-trimethyl-1-dodecylammonium chloride is 15-20 wt%.

6. The method of claim 4, wherein, In step S1, 30-35 parts by weight of MIL-101(Fe), 5-10 parts by weight of triethylamine, and 80-100 parts by weight of the ethanol solution of -N, N, N-trimethyl-1-dodecylammonium chloride are used.

7. The method of claim 4, wherein, In step S2, the mass ratio of CoCl2•6H2O to FeCl3•6H2O is 1:2.3-2.

8.

8. The method of claim 4, wherein, In step S2, the pH is adjusted to 7-8.

9. The method of claim 4, wherein, In step S3, 20-25 parts by weight of CoFe2O4 nanoparticles, 100-120 parts by weight of toluene, 30-35 parts by weight of MIL-101(Fe) precursor, and 1-5 parts by weight of tetrabutyl titanate are used.