Preparation method of Fe3O4@CD-MOF and porous carbon derived therefrom

Abstract

The application discloses a preparation method of Fe3O4@CD-MOF and porous carbon derived therefrom, and is prepared through the following steps: step one, condensation of carboxyl-functionalized Fe3O4 magnetic nanoparticles and amino-modified cyclodextrin to obtain Fe3O4-CD; step two, mixing of potassium hydroxide, cyclodextrin, Fe3O4-CD and an alcohol-water mixed solution; step three, microwave treatment of the mixed solution, mechanical stirring in an alcohol solvent or in an alcohol gas atmosphere, separation, cleaning, vacuum drying, and obtaining of the Fe3O4@CD-MOF material with a core-shell structure. The Fe3O4@CD-MOF material with a core-shell structure is formed by means of microwave through layer-by-layer wrapping and assembly, the preparation method is simple in process, mild in reaction condition, low in cost, friendly to the environment, and free of toxic and harmful substances, and the Fe3O4@CD-MOF material can be recycled and reused through an external magnetic field.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of new material production, in particular to a preparation method of Fe3O4@CD-MOF and derived porous carbon. BACKGROUND

[0002] With the rapid development of industry, heavy metals and dyes cause serious pollution to water resources. Especially heavy metals, they are easy to accumulate in the environment and organisms, and have high toxicity even at low concentrations. Therefore, it is essential to develop effective and feasible methods to remove these toxic pollutants in water, and the adsorption method is one of the simple, economical and environmentally friendly treatment methods. The adsorbent material with high and accurate adsorption capacity and without secondary pollution to the environment is a widely studied direction.

[0003] Metal-organic framework (MOFs) is a new material developed rapidly in recent years, which is a kind of porous organic-inorganic hybrid material with metal ions or metal clusters as ligand center, and oxygen-containing or nitrogen-containing organic ligand through forming a strong chemical bond. Due to the advantages of large specific surface area, structural diversity, adjustable pore size and skeleton modification, it becomes an excellent adsorbent material. In sample separation and analysis, magnetic MOFs material does not need high-speed centrifugation or membrane filtration, and is favored because of its magnetic response characteristics of magnetic particles and excellent adsorption performance of MOFs material. It shows great potential in sample pre-concentration and environmental pollutant separation and analysis.

[0004] CD-MOF (cyclodextrin-metal organic framework) is a MOF with high biocompatibility, which is synthesized by edible cyclodextrin and potassium ions, and is a kind of environment-friendly and renewable MOF material. SUMMARY

[0005] The purpose of the application is to provide a preparation method of Fe3O4@CD-MOF and derived porous carbon. The Fe3O4@CD-MOF material with core-shell structure is formed by means of microwave-assisted nucleation assembly through layer-by-layer wrapping assembly, and the derived porous carbon material of Fe3O4@CD-MOF is obtained by carbonization. The material has the characteristics of high-efficiency adsorption of heavy metals, reusability and wide pH range. The preparation method is simple in process, mild in reaction condition, low in cost, environment-friendly and does not produce toxic substances, and can be recycled by external magnetic field.

[0006] The technical scheme adopted by the application to solve the technical problems is:

[0007] A preparation method of Fe3O4@CD-MOF is prepared by the following steps:

[0008] Step one, the carboxyl functionalized Fe3O4 magnetic nanoparticles (Fe3O4-COOH) are dissolved in water and uniformly dispersed, then the amino modified cyclodextrin (CD-NH2) is added, after ultrasonic mixing, the condensing agent is added for condensation, after the reaction is completed, it is taken out by magnetic separation, washed, and the intermediate product Fe3O4-CD is obtained;

[0009] Step two, potassium hydroxide and cyclodextrin are dissolved in an alcohol-water mixed solution, then Fe3O4-CD is added, after ultrasonic dispersion, a mixed solution is obtained;

[0010] Step three, the mixed solution is treated by microwave, after re-ultrasonic dispersion, alcohol solvent is directly added or placed in an alcohol gas atmosphere for continuous mechanical stirring until gray crystal particle materials grow, the product is separated by a magnet, washed with alcohol (methanol or ethanol) for several times, and vacuum dried, to obtain the Fe3O4@CD-MOF material with a core-shell structure.

[0011] The Fe3O4@CD-MOF material is formed by the layer-by-layer assembly method, the carboxyl functional group is modified on the Fe3O4, then the CD-MOF is grown, and then modified and grown again, so that the MOF is wrapped on the core-shell structure of the Fe3O4, thereby realizing the in-situ growth of the CD-MOF on the surface of the magnetic Fe3O4. The conventional layer-by-layer assembly method is difficult to grow the CD-MOF on the surface of the Fe3O4, and it is difficult to form the Fe3O4@CD-MOF material with a core-shell structure. In the process of improving the layer-by-layer assembly method, the microwave treatment is used, the microwave is used to promote the nucleation assembly, thereby realizing the in-situ growth of the CD-MOF on the surface of the Fe3O4, and forming the Fe3O4@CD-MOF material with a core-shell structure. The core-shell structure has the advantages of firm combination, easy recovery of the Fe3O4, large specific surface area of the CD-MOF and good adsorption.

[0012] Preferably, in step one, the amino modified cyclodextrin is selected from one of six (6-amino-6-deoxy)-alpha-cyclodextrin, single (6-amino-6-deoxy)-beta-cyclodextrin, seven (6-amino-6-deoxy)-beta-cyclodextrin, and eight (6-amino-6-deoxy)-gamma-cyclodextrin.

[0013] Preferably, in step one, the condensing agent is selected from one or more of dicyclohexyl carbodiimide, 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride, and 4-dimethylamino pyridine; the condensation reaction temperature is controlled at 0-25 DEG C, and the reaction time is 2-24 h.

[0014] As preferred, in step one, the mass ratio of carboxyl functionalized Fe3O4 magnetic nanoparticles and amino modified cyclodextrin is 1:65-1:200, and the molar ratio of amino modified cyclodextrin and condensing agent is 1:1-1:2.

[0015] As preferred, in step two, the concentration of Fe3O4-CD in the mixed solution is 0.25-10 mg / mL, the concentration of potassium hydroxide is 0.1-0.4 mol / L, and the molar ratio of cyclodextrin to potassium hydroxide is 1:8, wherein the cyclodextrin is selected from one or more of α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin.

[0016] As preferred, in step two, the concentration of alcohol in the alcohol-water mixed solution is less than or equal to 50%, and the alcohol is selected from one or both of methanol and ethanol.

[0017] As preferred, in step three, the microwave power for microwave treatment is 400-1000 W, the microwave time is 3-10 min, and the microwave treatment temperature is controlled at 50-90℃.

[0018] As preferred, in step three, the alcohol of the alcohol solvent or alcohol gas is selected from one or both of methanol and ethanol; after the mixed solution is added to the alcohol solvent to form an alcohol-mixed solution, the volume concentration of alcohol in the alcohol-mixed solution is 30-40%.

[0019] A preparation method of Fe3O4@CD-MOF derived porous carbon, wherein the Fe3O4@CD-MOF material is calcined for carbonization in nitrogen to obtain a Fe3O4@CD-MOF derived porous carbon material, and the calcination condition is to heat at a speed of 2-8℃ / min to 200-300℃ and calcine for 2-5 h. The conventional Fe3O4@CD-MOF is easily decomposed in aqueous solution, but the porous morphology is fixed by carbonization, and the performance is stable.

[0020] The Fe3O4@CD-MOF derived porous carbon is used as a heavy metal adsorbent, and the addition amount in the aqueous phase is 0.1-2 g / L.

[0021] The present application has the following beneficial effects: through layer-by-layer wrapping assembly, the Fe3O4@CD-MOF material with core-shell structure is formed by means of microwave-assisted nucleation assembly, and the Fe3O4@CD-MOF derived porous carbon material is derived by carbonization, which has the characteristics of high-efficiency adsorption of heavy metals, reusability, and wide pH range, and the preparation method has the advantages of simple process, mild reaction conditions, low cost, environmental friendliness, and no toxic and harmful substances, and can be recycled by external magnetic field. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1is the SEM electron micrograph of Fe3O4@ β-CD-MOF material in Example 1 of the present application.

[0023] Figure 2 is the TEM electron micrograph of Fe3O4@ γ-CD-MOF material in Example 2 and Comparative Example 1 of the present application.

[0024] Figure 3 is the SEM electron micrograph of Fe3O4@ β-CD-MOF derived porous carbon material in Example 5 of the present application.

[0025] Figure 4 is the comparison chart of the adsorption efficiency of cadmium ions of Fe3O4@ β-CD-MOF derived porous carbon material and CD-MOF derived porous carbon material under a series of concentrations of cadmium-containing aqueous solution of the porous carbon material in Example 5 and Comparative Example 2 of the present application.

[0026] Figure 5 is the comparison chart of the cadmium ion adsorption capacity of Fe3O4@ β-CD-MOF derived porous carbon material and CD-MOF derived porous carbon material at different times when the same concentration of cadmium-containing aqueous solution is adsorbed by the porous carbon material in Example 5 and Comparative Example 2 of the present application.

[0027] Figure 6 is a process flow chart of the present application. DETAILED DESCRIPTION

[0028] The technical solutions of the present application will be further described in detail below through specific examples.

[0029] In the present application, unless specified, the raw materials and equipment used can be purchased from the market or commonly used in the art. The methods in the following examples are all conventional methods in the art, unless otherwise specified.

[0030] Preparation of Fe3O4-COOH: 6 mmol of FeCl3·6H2O, 1 mmol of sodium citrate dihydrate and 36 mmol of anhydrous sodium acetate were added to 30 mL of ethylene glycol, stirred, ultrasonically dispersed, transferred to a reaction kettle, solvent thermal reaction at 200℃ for 12 h, cooled to room temperature, the black magnetic nanoparticles were collected with a magnet, and then washed with ethanol and deionized water for three times each to obtain.

[0031] The process flow of the present application is shown in Figure 6 .

[0032] Example 1:

[0033] Preparation of Fe3O4@ β-CD-MOF material

[0034] Take 20 mg of carboxyl functionalized Fe3O4 magnetic nanoparticles dissolved in 20 mL of deionized water, add 3 g of mono (6-amino-6-deoxy) -β-cyclodextrin (commercially available), ultrasonic dispersion, then add 70 mg of 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride (commercially available), continuously mechanical stirring at room temperature for 6 h, magnetic separation of the product, deionized water washing 5 times, 60 ℃ vacuum drying for 6 h to obtain Fe3O4-β-CD. Weigh 225 mg of KOH and 570 mg of β-CD dissolved in 30 mL of 10% methanol aqueous solution, then add 30 mg of Fe3O4-β-CD, ultrasonic dispersion, microwave treatment at 500 W, 65 ℃ for 5 min, disperse for 1 min under 65 ℃ ultrasonic, immediately continuous mechanical stirring, slowly add 20 mL of methanol and keep sealed, continuous stirring for 2 h, then separate the gray product with a magnet, wash with 50 mL of methanol for three times, and place in 60 ℃ vacuum drying for 12 h to obtain gray Fe3O4@β-CD-MOF material. Figure 1 ).

[0035] Example 2:

[0036] Preparation of Fe3O4@γ-CD-MOF material

[0037] Take 20 mg of carboxyl functionalized Fe3O4 magnetic nanoparticles dissolved in 20 mL of deionized water, add 3.2 g of octa (6-amino-6-deoxy) -γ-cyclodextrin (commercially available), ultrasonic dispersion, then add 70 mg of 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride, continuously mechanical stirring at room temperature for 6 h, magnetic separation of the product, and deionized water washing 5 times, 60 ℃ vacuum drying for 6 h to obtain Fe3O4-γ-CD. Weigh 225 mg of KOH and 650 mg of γ-CD dissolved in 30 mL of 10% methanol aqueous solution, then add 30 mg of Fe3O4-γ-CD, ultrasonic dispersion, microwave treatment at 500 W, 65 ℃ for 3 min, disperse for 1 min under 65 ℃ ultrasonic, immediately continuous mechanical stirring, slowly add 20 mL of methanol and keep sealed, continuous stirring for 2 h, then separate the gray product with a magnet, wash with 50 mL of methanol for three times, and place in 60 ℃ vacuum drying for 12 h to obtain gray Fe3O4@γ-CD-MOF material.

[0038] Example 3:

[0039] The difference between this embodiment and Example 1 is that the microwave condition is: microwave treatment at 400 W, 50 ℃ for 10 min.

[0040] Example 4:

[0041] The difference between this example and Example 2 is that the microwave conditions are: 1000W, 90℃ for 3min.

[0042] Example 5:

[0043] Preparation of Fe3O4@β-CD-MOF derived porous carbon material

[0044] The dried Fe3O4@β-CD-MOF material of Example 1 was placed in a tube furnace, and heated to 300℃ at a heating rate of 2℃ / min under a nitrogen atmosphere and calcined for 2h, and then removed after cooling to room temperature. The entire heating and cooling process was carried out under nitrogen protection. After cooling, the Fe3O4@β-CD-MOF derived porous carbon material was obtained. Figure 3

[0045] Example 6:

[0046] Preparation of Fe3O4@γ-CD-MOF derived porous carbon material

[0047] The dried Fe3O4@γ-CD-MOF material of Example 2 was placed in a tube furnace, and heated to 200℃ at a heating rate of 4℃ / min under a nitrogen atmosphere and calcined for 5h, and then removed after cooling to room temperature. The entire heating and cooling process was carried out under nitrogen protection. After cooling, the Fe3O4@γ-CD-MOF derived porous carbon material was obtained.

[0048] Example 7:

[0049] Preparation of Fe3O4@β-CD-MOF derived porous carbon material

[0050] The dried Fe3O4@β-CD-MOF material of Example 1 was placed in a tube furnace, and heated to 240℃ at a heating rate of 8℃ / min under a nitrogen atmosphere and calcined for 3.5h, and then removed after cooling to room temperature. The entire heating and cooling process was carried out under nitrogen protection. After cooling, the Fe3O4@β-CD-MOF derived porous carbon material was obtained.

[0051] Comparative Example 1

[0052] Preparation of Fe3O4@γ-CD-MOF (without microwave)

[0053] ​20 mg of carboxyl-functionalized Fe3O4 magnetic nanoparticles were dissolved in 20 mL of deionized water. 3.2 g of octa(6-amino-6-deoxy)-γ-cyclodextrin was added, and the mixture was ultrasonically dispersed. Then, 70 mg of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride was added. The mixture was mechanically stirred at 250 rpm for 6 h at room temperature. The product was magnetically separated, washed five times with deionized water, and then vacuum-dried at 60 °C for 6 h to obtain Fe3O4-γ-CD. 225 mg of KOH and 650 mg of γ-CD were dissolved in 30 mL of an aqueous solution containing 10% methanol. 30 mg of Fe3O4-γ-CD was added, and the mixture was ultrasonically dispersed. Continuous mechanical stirring was performed, and 20 mL of methanol was slowly added while maintaining a sealed environment. After stirring for 2 h, the gray product was separated using a magnet and washed three times with 50 mL of methanol. The product was then vacuum-dried at 60 °C for 12 h to obtain gray Fe3O4@γ-CD-MOF material.

[0054] like Figure 2 As shown, comparing the TEM images of Fe3O4@γ-CD-MOF materials in Example 2 and Comparative Example 1, the Fe3O4@γ-CD-MOF material without microwave treatment did not form a core-shell structure, and CD-MOF was difficult to nucleate and grow on Fe3O4.

[0055] Comparative Example 2

[0056] β-CD-MOF-derived porous carbon materials

[0057] Weigh 225 mg of KOH and dissolve it in 40 mL of an aqueous solution containing 30% methanol to obtain mixed solution A. Separately, weigh 570 mg of β-CD and dissolve it in 30 mL of an aqueous solution containing 10% methanol. After microwave treatment at 500 W and 65 °C for 5 min, slowly add 20 mL of methanol, mix well, and keep the solution sealed. After standing for 2 h, filter and collect the white product, wash it three times with 50 mL of methanol, and dry it under vacuum at 60 °C for 12 h to obtain white β-CD-MOF material.

[0058] The dried β-CD-MOF material was placed in a tube furnace and heated to 300°C at a heating rate of 2°C / min in a nitrogen atmosphere and fired for 2 hours. After cooling to room temperature, the material was removed. The entire heating and cooling process was carried out under nitrogen protection. After cooling, β-CD-MOF-derived porous carbon material was obtained.

[0059] Experimental Example 1:

[0060] Fe3O4@β-CD-MOF-derived porous carbon materials and β-CD-MOF-derived porous carbon materials adsorb cadmium ions in water.

[0061] The Fe3O4@β-CD-MOF derived porous carbon material prepared in Example 5 was used as an adsorbent. 20 mg of the carbon material was added to 20 mL of a cadmium (II) ion aqueous solution with a cadmium concentration of 5, 10, 25, 50, 100, 150, 200, 300, or 500 mg / L, respectively. Each group included three parallel samples and one control sample (the control sample did not contain the carbon material). After magnetic stirring at 25°C and 300 rpm for 1 h, the porous carbon material was separated by magnetism. The supernatant was taken and the cadmium content was determined by inductively coupled plasma atomic emission spectrometry. The results are shown in Table 1. Figure 4

[0062] The β-CD-MOF derived porous carbon material prepared in Comparative Example 2 was used as an adsorbent. 20 mg of the carbon material was added to 20 mL of a cadmium (II) ion aqueous solution with a cadmium concentration of 5, 10, 25, 50, 100, 150, 200, 300, or 500 mg / L, respectively. Each group included three parallel samples and one control sample (the control sample did not contain the carbon material). After magnetic stirring at 25°C and 300 rpm for 1 h, the carbon material was separated by centrifugation. The supernatant was filtered through a 0.45 μm membrane, and the cadmium content was determined by inductively coupled plasma atomic emission spectrometry. The results are shown in Table 2. Figure 4

[0063] The results show that, for the same amount of adsorbent, the Fe3O4@β-CD-MOF derived porous carbon material containing less β-CD-MOF structure than the β-CD-MOF derived porous carbon material has basically the same adsorption effect on cadmium ions with different concentrations, and nearly 98% of cadmium ions are removed from a low-concentration cadmium solution.

[0064] Test Example 2

[0065] Adsorption of cadmium ions in water by Fe3O4@β-CD-MOF derived porous carbon material and β-CD-MOF derived porous carbon material

[0066] The Fe3O4@β-CD-MOF derived porous carbon material prepared in Example 5 was used as an adsorbent. 10 mg of the carbon material was added to 10 mL of a cadmium (II) ion aqueous solution (containing 100 mg / L of cadmium). The adsorption end time was set to 5, 10, 15, 30, 60, or 120 min, respectively. Each group included three parallel samples and one control sample (the control sample did not contain the carbon material, and the adsorption time was 0). The reaction was carried out by stirring at 20°C and 300 rpm. After the reaction time, the carbon material was separated by magnetism. The supernatant was taken and the cadmium content was determined by inductively coupled plasma atomic emission spectrometry. The results are shown in Table 3. Figure 5 ​​The results show that the adsorption capacity of the Fe3O4 β-CD-MOF derived carbon material is higher than that of the β-CD-MOF derived carbon material, and the adsorption rate of the Fe3O4 β-CD-MOF derived carbon material is slightly faster than that of the β-CD-MOF derived carbon material, and the trend of reaching adsorption equilibrium of the two is basically the same.

[0067] The β-CD-MOF derived porous carbon material prepared in Comparative Example 2 was used as an adsorbent, 10 mg of the carbon material was added into 10 mL of a cadmium (II) ion aqueous solution (containing 100 mg / L of cadmium), and adsorption end point times of 5, 10, 15, 30, 60 and 120 min were set, respectively, each group having three parallel samples and one control sample (the control sample was not added with the carbon material, and the adsorption time was 0). The reaction was carried out under stirring at 20°C and 300 rpm, after the reaction time, the carbon material was centrifuged and separated, the supernatant was taken, filtered through a 0.45 μm membrane, and the cadmium content after treatment was determined by inductively coupled plasma atomic emission spectrometry, and the results are shown in Table 2. Figure 5

[0068] The results show that the adsorption capacity of the Fe3O4 β-CD-MOF derived carbon material is higher than that of the β-CD-MOF derived carbon material, and the adsorption rate of the Fe3O4 β-CD-MOF derived carbon material is slightly faster than that of the β-CD-MOF derived carbon material, and the trend of reaching adsorption equilibrium of the two is basically the same.

[0069] The above-described embodiments are only a preferred scheme of the present application, and do not limit the present application in any form, and other variants and modifications can be made without departing from the technical scheme recited in the claims.​

Claims

1. A method for preparing Fe3O4@CD-MOF, characterized in that, It is prepared through the following steps: Step 1: Dissolve carboxyl-functionalized Fe3O4 magnetic nanoparticles in water and disperse them evenly. Then add amino-modified cyclodextrin, mix with sonication, add a condensing agent to condense, and after the reaction is complete, remove them by magnetic selection, wash them, and obtain the intermediate product Fe3O4-CD. Step 2: Dissolve potassium hydroxide and cyclodextrin in an alcohol-water mixed solution, then add Fe3O4-CD to the solution, and disperse by ultrasonication to obtain a mixed solution; Step 3: After microwave treatment and ultrasonic re-dispersion of the mixed solution, add alcohol solvent directly or place it in an alcohol gas atmosphere for continuous mechanical stirring until gray crystalline particles grow. Separate the product with a magnet, wash it several times with alcohol, and then vacuum dry it to obtain Fe3O4@CD-MOF material with a core-shell structure.

2. The preparation method according to claim 1, characterized in that, In step one, the amino-modified cyclodextrin is selected from one of hexa(6-amino-6-deoxy)-α-cyclodextrin, mono(6-amino-6-deoxy)-β-cyclodextrin, hepta(6-amino-6-deoxy)-β-cyclodextrin, and octa(6-amino-6-deoxy)-γ-cyclodextrin.

3. The preparation method according to claim 1, characterized in that, In step one, the condensing agent is selected from one or more of dicyclohexylcarbodiimide, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, and 4-dimethylaminopyridine; the condensation reaction temperature is controlled at 0~25℃, and the reaction time is 2-24h.

4. The preparation method according to claim 1, characterized in that, In step one, the mass ratio of carboxyl-functionalized Fe3O4 magnetic nanoparticles to amino-modified cyclodextrin is 1:65-1:200, and the molar ratio of amino-modified cyclodextrin to condensing agent is 1:1-1:

2.

5. The preparation method according to claim 1, characterized in that, In step two, the concentration of Fe3O4-CD in the mixed solution is 0.25-10 mg / mL, the concentration of potassium hydroxide is 0.1-0.4 mol / L, and the molar ratio of cyclodextrin to potassium hydroxide is 1:

8. The cyclodextrin is selected from one or more of α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin.

6. The preparation method according to claim 1, characterized in that, In step two, the concentration of alcohol in the alcohol-water mixed solution is less than or equal to 50%, and the alcohol is selected from one or both of methanol and ethanol.

7. The preparation method according to claim 1, characterized in that, In step three, the microwave power of the microwave treatment is 400-1000W, the microwave time is 3-10min, and the microwave treatment temperature is controlled at 50-90℃.

8. The preparation method according to claim 1, characterized in that, In step three, the alcohol in the alcohol solvent or alcohol gas is selected from one or two of methanol and ethanol; when the mixed solution is added to the alcohol solvent to form an alcohol-mixed solution, the volume concentration of alcohol in the alcohol-mixed solution is 30-40%.

9. A method for preparing Fe3O4@CD-MOF derived porous carbon, characterized in that, The Fe3O4@CD-MOF material of claim 1 is carbonized by calcination in nitrogen to obtain Fe3O4@CD-MOF-derived porous carbon material. The calcination conditions are: heating to 200-300℃ at a rate of 2-8℃ / min and calcining for 2-5 hours.

10. The use of Fe3O4@CD-MOF derived porous carbon prepared by the method described in claim 9 as a heavy metal adsorbent, characterized in that, The dosage added to the aqueous phase is 0.1-2 g / L.

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