CN108465489B - Fe3O4@ ZIF-8 core-shell composite material and preparation method and catalytic application thereof - Google Patents

Fe3O4@ ZIF-8 core-shell composite material and preparation method and catalytic application thereof Download PDF

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CN108465489B
CN108465489B CN201810188441.7A CN201810188441A CN108465489B CN 108465489 B CN108465489 B CN 108465489B CN 201810188441 A CN201810188441 A CN 201810188441A CN 108465489 B CN108465489 B CN 108465489B
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zif
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CN108465489A (en
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王光明
张攀
蔡坊林
公艳艳
陈宬
沙南
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Wuhan University of Technology WUT
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    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J31/00—Catalysts comprising hydrides, coordination complexes or organic compounds
    • B01J31/16—Catalysts comprising hydrides, coordination complexes or organic compounds containing coordination complexes
    • B01J31/1691—Coordination polymers, e.g. metal-organic frameworks [MOF]
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    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J31/00—Catalysts comprising hydrides, coordination complexes or organic compounds
    • B01J31/16—Catalysts comprising hydrides, coordination complexes or organic compounds containing coordination complexes
    • B01J31/18—Catalysts comprising hydrides, coordination complexes or organic compounds containing coordination complexes containing nitrogen, phosphorus, arsenic or antimony as complexing atoms, e.g. in pyridine ligands, or in resonance therewith, e.g. in isocyanide ligands C=N-R or as complexed central atoms
    • B01J31/1805—Catalysts comprising hydrides, coordination complexes or organic compounds containing coordination complexes containing nitrogen, phosphorus, arsenic or antimony as complexing atoms, e.g. in pyridine ligands, or in resonance therewith, e.g. in isocyanide ligands C=N-R or as complexed central atoms the ligands containing nitrogen
    • B01J31/181—Cyclic ligands, including e.g. non-condensed polycyclic ligands, comprising at least one complexing nitrogen atom as ring member, e.g. pyridine
    • B01J31/1815—Cyclic ligands, including e.g. non-condensed polycyclic ligands, comprising at least one complexing nitrogen atom as ring member, e.g. pyridine with more than one complexing nitrogen atom, e.g. bipyridyl, 2-aminopyridine
    • B—PERFORMING OPERATIONS; TRANSPORTING
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    • B01J31/00—Catalysts comprising hydrides, coordination complexes or organic compounds
    • B01J31/26—Catalysts comprising hydrides, coordination complexes or organic compounds containing in addition, inorganic metal compounds not provided for in groups B01J31/02 - B01J31/24
    • B01J31/28—Catalysts comprising hydrides, coordination complexes or organic compounds containing in addition, inorganic metal compounds not provided for in groups B01J31/02 - B01J31/24 of the platinum group metals, iron group metals or copper
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    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/0009—Use of binding agents; Moulding; Pressing; Powdering; Granulating; Addition of materials ameliorating the mechanical properties of the product catalyst
    • B01J37/0027—Powdering
    • B01J37/0045—Drying a slurry, e.g. spray drying
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/02—Impregnation, coating or precipitation
    • B01J37/0234—Impregnation and coating simultaneously
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C253/00—Preparation of carboxylic acid nitriles
    • C07C253/30—Preparation of carboxylic acid nitriles by reactions not involving the formation of cyano groups
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2231/00—Catalytic reactions performed with catalysts classified in B01J31/00
    • B01J2231/40—Substitution reactions at carbon centres, e.g. C-C or C-X, i.e. carbon-hetero atom, cross-coupling, C-H activation or ring-opening reactions
    • B01J2231/42—Catalytic cross-coupling, i.e. connection of previously not connected C-atoms or C- and X-atoms without rearrangement
    • B01J2231/4205—C-C cross-coupling, e.g. metal catalyzed or Friedel-Crafts type
    • B—PERFORMING OPERATIONS; TRANSPORTING
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    • B01J2531/00—Additional information regarding catalytic systems classified in B01J31/00
    • B01J2531/20—Complexes comprising metals of Group II (IIA or IIB) as the central metal
    • B01J2531/26—Zinc

Abstract

The invention provides Fe3O4The high-efficiency preparation method of @ ZIF-8 core-shell composite material is characterized by firstly adopting spray drying method to quickly prepare pre-crystallized ZIF-8, then soaking it in Fe3O4In the solution of (4), pre-crystallized ZIF-8 is crystallized and coated with Fe3O4To obtain Fe3O4@ ZIF-8 composite material. According to the invention, the spray drying method is adopted, so that the crystallization rate of the ZIF-8 can be remarkably improved, and the defects of partial metal ions and organic ligands in the ZIF-8 crystallization process are caused, so that the defects are generated on the surface of the ZIF-8, and the activity of the ZIF-8 in a catalytic reaction is effectively improved; meanwhile, ZIF-8 can be coated with magnetic Fe in the crystallization process3O4The nano particles can effectively improve the cycle performance and the stability of the obtained composite material on the basis of ensuring the excellent catalytic performance, and are Fe3O4The preparation of the @ ZIF-8 composite material provides a new idea.

Description

Fe3O4@ ZIF-8 core-shell composite material and preparation method and catalytic application thereof
Technical Field
The invention belongs to the field of application of novel magnetic-metal organic frameworks (MMOFs) materials, and particularly relates to Fe3O4@ ZIF-8 core-shell composite material and preparation method and catalytic application thereof.
Background
Metal-Organic Frameworks (MOFs) are a kind of reticular polymer with an infinite topological structure formed by combining Metal ions or Metal ion clusters with Organic bridging ligands through coordination bonds, wherein ZIFs is another series of MOFs materials, namely zeolite-like imidazolate framework materials, and the MOFs materials with a zeolite-like structure are synthesized by utilizing Zn (II) or Co (II) to react with imidazole ligands. Compared with the traditional porous organic and inorganic materials, in terms of physical properties, ZIFs have high specific surface area, adjustable pore size and good thermal stability; in the aspect of chemical properties, ZIFs have uniformly distributed catalytic active sites, and the excellent performances in two aspects promote that the ZIFs have huge application potential in the field of catalysis.
Fe3O4@ ZIF-8 core-shell type composite material integrated with magnetic functional particles Fe3O4The composite material has the advantages of easy separation, easy dispersion and reusability, and the high catalytic activity of ZIF-8, and can simultaneously ensure the high efficiency of a homogeneous catalyst and the recyclability of a heterogeneous catalyst. But Fe3O4The @ ZIF-8 core-shell type composite catalysts also face many challenges: first, Fe3O4The conventional preparation method of @ ZIF-8 is to use a surfactant for Fe3O4Surface modification is carried out, and then modified Fe3O4Repeatedly soaking in metal ion and organic ligand solution to attach ZIF-8 crystal grains to large-size Fe3O4The surface is formed, but the method is tedious and time-consuming, has higher cost and large energy consumption, and is not suitable for industrial production; secondly, the surfactant has potential influence on the structure and the appearance of the ZIF-8, so that the catalytic activity of the ZIF-8 is influenced, and meanwhile, the ZIF-8 and the Fe have potential influence3O4Has a weak bonding degree and is liable to adhere to Fe3O4The problem of falling of ZIF-8 crystal grains on the surface influences the cyclic usability of the catalyst; third, Fe3O4The nanometer particles are easy to block ZIF-8 pore channels, and the porosity and the specific surface area of the nanometer particles are reduced.
Disclosure of Invention
The invention aims to provide Fe3O4The method for efficiently preparing the @ ZIF-8 core-shell composite material adopts a spray drying method to accelerate the crystallization rate of ZIF-8 and prepare pre-crystallized ZIF-8; then placing in Fe3O4In the solution, ZIF-8 is coated with magnetic Fe in the crystallization process3O4Nano particles to prepare Fe3O4@ ZIF-8 core-shell composites; obtained byFe3O4The @ ZIF-8 core-shell composite material has excellent catalytic activity and circulation stability, and the related preparation method is simple and suitable for popularization and application.
In order to achieve the purpose, the invention adopts the technical scheme that:
fe3O4The preparation method of the @ ZIF-8 core-shell composite material comprises the following steps:
1) mixing 2-methylimidazole and zinc salt in water to obtain a mixed solution I, and then carrying out spray drying to prepare pre-crystallized ZIF-8;
2) magnetic Fe3O4The nano microsphere particles are placed in methanol solution for ultrasonic stirring to obtain Fe3O4Suspending liquid;
3) adding the pre-crystallized ZIF-8 white powder obtained in the step 1) into the Fe obtained in the step 2)3O4Soaking the suspension, filtering, washing with methanol, and drying to obtain Fe3O4@ ZIF-8 core-shell composite material.
In the scheme, the molar ratio of the 2-methylimidazole to the zinc salt is 1: 1.
In the scheme, the concentration of the zinc salt in the mixed solution I is 0.1-0.5 mol/L.
In the scheme, in the spray drying process, the feeding speed is 300-320 ml/h, the temperature of hot air is 180-200 ℃, and the flow speed is 160-180 m3/h。
In the above scheme, the magnetic Fe3O4The particle size of the nano microsphere particles is 100-200 nm; the preparation method comprises the following steps: mixing anhydrous ferric chloride and sodium citrate in ethylene glycol, stirring and performing ultrasonic treatment to obtain a mixed solution I; then adding sodium acetate under the condition of stirring, heating, carrying out heat preservation reaction to obtain black powder, washing and drying to obtain magnetic Fe3O4Nano-microsphere particles;
in the scheme, the mass ratio of the anhydrous ferric chloride to the sodium citrate to the sodium acetate is 13 (4-6) to (24-26), and the concentration range of the anhydrous ferric chloride in the mixed solution I is 0.1-0.3 mmol/ml.
In the scheme, the drying step adopts a vacuum drying process, the drying temperature is 80-100 ℃, and the drying time is 6-12 hours.
In the scheme, the temperature of the heat preservation reaction is 150-250 ℃.
In the above scheme, the Fe3O4Fe in suspension3O4The concentration of (b) is 0.5-8 mg/ml.
In the scheme, the addition amount of the pre-crystallized ZIF-8 in the step 3) and the Fe in the step 2)3O4The mass ratio of (1) - (15) is 20.
In the scheme, the soaking treatment time is 6-12 hours.
Fe prepared according to the above scheme3O4@ ZIF-8 core-shell composite material comprising magnetic Fe3O4Nanoparticle and ZIF-8, and Fe3O4The nanoparticles are encapsulated in a single ZIF-8 crystal, Fe3O4The diameter of the microsphere is 100-200 nm, and the size of the ZIF-8 crystal is 300-500 nm.
Fe obtained by the above scheme3O4The application of the @ ZIF-8 core-shell composite material in catalyzing Knoevenagel condensation reaction comprises the following steps: mixing Fe3O4Mixing the @ ZIF-8 core-shell composite material with malononitrile and 4-bromobenzaldehyde, adding a methanol solution, stirring at room temperature, and sampling at intervals to perform nuclear magnetic detection on the conversion rate.
In the scheme, the molar ratio of the 4-bromobenzaldehyde to the malononitrile is 1: 1; fe3O4The mass ratio of the addition amount of the @ ZIF-8 core-shell composite material to 4-bromobenzaldehyde is 1: 37-1: 4.
The principle of the invention is as follows: the method adopts a spray drying method to quickly prepare the pre-crystallized ZIF-8, and the high crystallization rate causes the deletion of partial metal ions and organic ligands on the surface of the ZIF-8 crystal to further generate defects and increase the catalytic activity of the crystal; meanwhile, the pre-crystallized ZIF-8 can effectively coat magnetic Fe in the crystallization process3O4Nanoparticles, fast formation of Fe3O4@ ZIF-8 core-shell type magnetic composite material with excellent catalysisOn the basis of the performance, the cycle performance and the stability of the obtained composite material can be effectively improved.
The invention has the beneficial effects that:
1) the invention firstly proposes that the spray drying method is adopted to prepare the pre-crystallized ZIF-8, and then the pre-crystallized ZIF-8 is dipped in the Fe3O4In the mixed solution, magnetic Fe is coated in the crystallization process3O4Nanoparticles of Fe3O4The @ ZIF-8 core-shell type magnetic composite material has the advantages of simple preparation process, low cost and good composite effect, and provides a new idea for the preparation of ZIFs composite materials.
2) The ZIF-8 crystal prepared by the spray drying method has defects on the surface, and compared with the traditional preparation method, the catalytic activity of the ZIF-8 crystal is greatly improved.
3) The invention omits expensive surface active agent used in the traditional preparation method, uses a spray drying method to quickly prepare the pre-crystallized ZIF-8, and utilizes the pre-crystallized ZIF-8 to carry out Fe crystallization3O4Coating of nanoparticles to prepare Fe3O4The @ ZIF-8 core-shell type magnetic composite material avoids the influence of a surfactant on the shape and structure of the ZIF-8 crystal, greatly saves the cost and time, and can realize industrial production.
4) The invention firstly uses the nanoscale Fe3O4The particles are coated inside the single ZIF-8 crystal, so that the ZIF-8 crystal can be effectively prevented from falling off in the catalytic reaction, and the Fe content is improved3O4@ ZIF-8 cyclability.
Drawings
FIG. 1 shows Fe according to the invention3O4A process flow chart of a preparation method of the @ ZIF-8 core-shell composite material.
FIG. 2 shows magnetic Fe obtained in example 1 of the present invention3O4Scanning electron micrographs at different magnifications.
FIG. 3 shows Fe obtained in example 1 of the present invention3O4And a transmission electron microscope image of the @ ZIF-8 core-shell type magnetic composite material under different magnifications.
FIG. 4 shows Fe obtained in example 1 of the present invention3O4@ ZIF-8 core-shellScanning electron micrographs of the magnetic composite material under different magnifications.
FIG. 5 shows Fe obtained in example 1 of the present invention3O4The infrared analysis pattern and wide-angle XRD diffraction pattern of the @ ZIF-8 core-shell type magnetic composite material.
FIG. 6 shows Fe contents obtained in examples 1 and 2, comparative examples 1 and 2 of the present invention3O4Fe with different mass fractions3O4@ ZIF-8 core-shell magnetic composite nitrogen adsorption curve.
FIG. 7 shows Fe obtained in example 1 of the present invention3O4The change graph of the conversion rate of the @ ZIF-8 core-shell type magnetic composite material in the Knoevenagel condensation reaction along with time and the recycling performance.
FIG. 8 shows Fe obtained in example 1 of the present invention3O4And (3) a real object diagram of the @ ZIF-8 core-shell type magnetic composite material recovered under a magnet after catalytic reaction.
Detailed Description
For a better understanding of the present invention, the following further illustrates the present invention with reference to specific examples and drawings, but the present invention is not limited to the following examples.
In the following examples, a spray dryer having a spray nozzle length of 8mm was used.
In the following examples, magnetic Fe was used3O4The preparation method of the nano microsphere particles comprises the following steps: 1) weighing 0.65g of anhydrous ferric chloride and 0.2g of sodium citrate, adding into a 50ml beaker, adding 20ml of ethylene glycol, stirring and dissolving, and performing ultrasonic treatment for 15min to obtain a mixed solution I; adding 1.2g of sodium acetate into the obtained mixed solution I while stirring, and continuously stirring for 30 min; placing the obtained black mixed solution in an incubator, carrying out heat preservation reaction for 10 hours at the temperature of 200 ℃, and naturally cooling to room temperature; then centrifuging (the rotating speed of the centrifuge is 8000rmp), washing with 20ml of ethanol solution for three times, and vacuum drying at 80 ℃ for 12 hours to obtain 150mg of magnetic Fe with the particle size of 100-200 nm3O4Nanoparticle.
Example 1
Fe3O4@ ZIF-8 core-shell type composite material and its preparation methodThe process flow chart is shown in figure 1, and the specific preparation steps are as follows:
1) weighing 2.38g of zinc nitrate hexahydrate and 0.66g of 2-methylimidazole, adding into a 50ml beaker, adding 25ml of deionized water, stirring and dissolving to obtain a raw material of a spray dryer, and performing a spray drying method to prepare 200mg of pre-crystallized ZIF-8 white powder, wherein the feeding speed adopted in the spray drying process is 300ml/h, the hot air temperature is 180 ℃, and the flow rate is 160m3/h；
2) Taking magnetic Fe3O4Putting 22mg of nano microsphere particles into a 50ml beaker, adding 20ml of methanol, and carrying out ultrasonic treatment for 30min to obtain Fe3O4Suspending liquid;
3) adding the white powder obtained in the step 1) into the Fe obtained in the step 2)3O4Pre-crystallizing ZIF-8 and Fe in suspension3O4The mass ratio of the components is 9:1, and the components are soaked for 12 hours at room temperature; after the soaking treatment is finished, filtering the obtained solution, washing the solution for three times by using methanol, and placing the solution in a vacuum drying oven at the temperature of 80 ℃ for 12 hours to obtain the Fe3O4@ ZIF-8 core-shell composite (10 wt% Fe)3O4@ ZIF-8 composite).
FIG. 2 shows the magnetic Fe obtained in this example3O4The scanning electron microscope images of the nano-microspheres under different magnifications show that Fe can be seen in the images3O4The microspheres are regular in shape and uniform in size, and the diameter of the microspheres is 100-200 nnm.
FIG. 3 shows 10 wt% Fe obtained in this example3O4In a transmission electron microscope image of the @ ZIF-8 composite material under different magnifications, a dark part (Fe) can be obviously observed from the image (a)3O4) Located inside the light-colored part (ZIF-8), while FIG. (b) shows Fe3O4And a clear lattice fringe of ZIF-8 crystal, proving Fe3O4The nanoparticles were successfully encapsulated in ZIF-8 crystals.
FIG. 4 shows 10 wt% Fe obtained in this example3O4Scanning electron microscope images of the @ ZIF-8 composite material under different multiples. From the graph, it can be found that Fe is hardly present3O4Microspheres, mostly crystals of ZIF-8, indicate a majority of Fe3O4The nanoparticles are coated with ZIF-8 crystals.
FIG. 5(a) shows 10 wt% Fe obtained in this example3O4The infrared spectral analysis of the @ ZIF-8 composite material and the ZIF-8 shows that the two materials have no obvious difference from the figure, which indicates that the Fe3O4No valence bond is formed between the zinc oxide and the ZIF-8, and the structure of the ZIF-8 is not influenced; FIG. 5(b) shows 10 wt% Fe obtained in this example3O4@ ZIF-8 composite and ZIF-8 Wide-Angle XRD diffractogram, from which it is known that the composite contains almost no Fe3O4Peak of (2), indicates Fe3O4The nanoparticles are mostly encapsulated in the ZIF-8 crystals.
FIG. 6(c) shows 10 wt% Fe obtained in this example3O4@ ZIF-8 nitrogen adsorption Curve having a specific surface area of 1012.92m2Per g, pore volume of 0.39cm3(ii)/g, pore diameter of 1.01nm, and a small reduction in comparison with ZIF-8 (FIG. 6(a)), because of Fe3O4The nano particles slightly block the ZIF-8 pore channels, but the composite material still has higher specific surface area and porosity, and simultaneously has stronger magnetism and excellent catalytic activity.
Application example
The product obtained in the example 1 is applied to the catalysis of Knoevenagel condensation reaction, and the specific steps are as follows:
5mg of 10 wt% Fe obtained3O4Mixing the @ ZIF-8 composite material with 0.32g of malononitrile and 0.92g of 4-bromobenzaldehyde, adding 5ml of methanol solution, stirring at room temperature, sampling every 10min for nuclear magnetic detection of conversion rate until the reaction is finished, then recovering the catalyst by using a magnet, washing the catalyst by using methanol three times, placing the washed catalyst in a vacuum drying oven at 80 ℃, keeping the temperature for 12 hours, and repeatedly using the catalyst for five times.
FIG. 7(a) shows 10 wt% Fe obtained in this example3O4Compared with a blank control, the conversion rate of @ ZIF-8 in Knoevenagel condensation reaction every 10min is improved, and meanwhile, no loss of catalytic activity is found in three circulation experiments; FIG. 7(b) is 10 wt% Fe3O4Results of the experiment of @ ZIF-8 in 5 cycles, it was found from the figure that the catalyst was used in the present inventionThe conversion rate of the reaction after 2 hours can reach more than 95 percent, and the high efficiency and the cyclic usability of the composite catalyst are proved;
FIG. 8 shows 10 wt% Fe obtained in this example3O4The graph shows that the composite material still has strong magnetism after multiple circulation experiments.
Example 2
Fe3O4The preparation method of the @ ZIF-8 core-shell composite material comprises the following steps:
1) weighing 2.38g of zinc nitrate hexahydrate and 0.66g of 2-methylimidazole, adding into a 50ml beaker, adding 25ml of deionized water, stirring and dissolving to obtain a raw material of a spray dryer, and performing a spray drying method to prepare 200mg of pre-crystallized ZIF-8 white powder, wherein the feeding speed adopted in the spray drying process is 300ml/h, the hot air temperature is 180 ℃, and the flow rate is 160m3/h；
2) Taking magnetic Fe3O4Putting 50mg of nano microsphere particles into a 50ml beaker, adding 20ml of methanol, and carrying out ultrasonic treatment for 30min to obtain Fe3O4Suspending liquid;
3) adding the white powder obtained in the step 1) into the Fe obtained in the step 2)3O4Pre-crystallizing ZIF-8 and Fe in suspension3O4The mass ratio of the components is 4:1, and the components are soaked for 12 hours at room temperature; after the soaking treatment is finished, filtering the obtained solution, washing the solution for three times by using methanol, and placing the solution in a vacuum drying oven at the temperature of 80 ℃ for 12 hours to obtain the Fe3O4@ ZIF-8 core-shell composite (20 wt% Fe)3O4@ ZIF-8 composite).
FIG. 6(d) shows 20 wt% Fe obtained in this example3O4@ ZIF-8 nitrogen adsorption Curve having a specific surface area of 850.85m2Per g, pore volume 0.33cm3(ii)/g, pore diameter of 0.89nm, was partially reduced compared with ZIF-8 (FIG. 6(a)), because of Fe3O4The nanoparticles partially plugged the ZIF-8 channels.
Example 3
Fe3O4@ZIF-The preparation method of the 8-core-shell composite material comprises the following steps:
1) weighing 3.57g of zinc nitrate hexahydrate and 0.98g of 2-methylimidazole, adding into a 50ml beaker, adding 25ml of deionized water, stirring and dissolving to be used as a raw material of a spray dryer, and performing spray drying to prepare 260mg of pre-crystallized ZIF-8 white powder, wherein the feeding speed adopted in the spray drying process is 320ml/h, the hot air temperature is 200 ℃, and the flow speed is 180m3/h；
2) Taking magnetic Fe3O4Putting 100mg of nano microsphere particles into a 50ml beaker, adding 20ml of methanol, and carrying out ultrasonic treatment for 30min to obtain Fe3O4Suspending liquid;
3) adding the white powder obtained in the step 1) into the Fe obtained in the step 2)3O4Soaking in the suspension at room temperature for 6 h; after the soaking treatment is finished, filtering the obtained solution, washing the solution for three times by using methanol, and placing the solution in a vacuum drying oven at the temperature of 100 ℃ for 6 hours to obtain the Fe3O4@ ZIF-8 core-shell composite material.
Example 4
Fe3O4The preparation method of the @ ZIF-8 core-shell composite material comprises the following steps:
1) 0.74g of zinc nitrate hexahydrate and 0.21g of 2-methylimidazole are weighed and added into a 50ml beaker, 25ml of deionized water is added, the mixture is stirred and dissolved to be used as a raw material of a spray dryer, and spray drying treatment is carried out to prepare 150mg of pre-crystallized ZIF-8 white powder, wherein the feeding speed adopted in the spray drying process is 320ml/h, the hot air temperature is 200 ℃, and the flow speed is 180m3/h；
2) Taking magnetic Fe3O4Putting 80mg of nano microsphere particles into a 50ml beaker, adding 20ml of methanol, and carrying out ultrasonic treatment for 30min to obtain Fe3O4Suspending liquid;
3) adding the white powder obtained in the step 1) into the Fe obtained in the step 2)3O4Soaking in the suspension at room temperature for 6 h; after the soaking treatment is finished, filtering the obtained solution, washing the solution for three times by using methanol, and placing the solution in a vacuum drying oven at the temperature of 100 ℃ for 6 hours to obtain the Fe3O4@ ZIF-8 core-shell composite material.
Comparative example 1
Fe3O4The preparation method of the @ ZIF-8 core-shell composite material is substantially the same as that of the embodiment 1, and the difference is that the magnetic Fe in the step 4) is adopted3O4The addition amount of the nano microsphere particles is 10mg, and the pre-crystallization is ZIF-8 and Fe3O4In a mass ratio of 19:1(5 wt% Fe)3O4@ ZIF-8 composite).
Comparative example 5 wt% Fe3O4FIG. 6(b) for nitrogen adsorption of @ ZIF-8, which shows that the specific surface area of the resulting product is 1303m2Per g, pore volume 0.49cm3(ii)/g, pore diameter of 1.04nm, which is not much changed from ZIF-8 (FIG. 6(a)), indicating that Fe3O4The nanometer particles have little influence on the properties of the ZIF-8 crystal, but the composite material has weak magnetism and is not beneficial to the recycling of the catalyst.
Comparative example 2
Fe3O4The preparation method of the @ ZIF-8 core-shell composite material is substantially the same as that of the embodiment 1, and the difference is that the magnetic Fe in the step 4) is adopted3O4The addition amount of the nano microsphere particles is 133mg, and the pre-crystallization is ZIF-8 and Fe3O4In a mass ratio of 3:2(40 wt% Fe)3O4@ ZIF-8 composite).
40 wt% Fe obtained in this comparative example3O4@ ZIF-8 Nitrogen adsorption Curve 6(e) showing specific surface area 285.79m in the resulting product2Per g, pore volume of 0.20cm3The pore diameter was 0.54nm, which is greatly reduced as compared with ZIF-8 (FIG. 6(a)), indicating that Fe3O4The nano particles seriously block the ZIF-8 pore channels, and the activity of the catalyst is seriously influenced.
Examples 1 and 2 and comparative examples 1 and 2 containing different Fe3O4The specific surface area, Langmuir specific surface area, pore volume and pore diameter data of the core-shell type magnetic composite material with mass fraction are shown in Table 1.
TABLE 1
Figure BDA0001591006900000071
Comparative example 3
Fe3O4The traditional preparation method of the @ ZIF-8 core-shell composite material comprises the following steps: firstly, preparing 30ml of surfactant styrene sulfonic acid sodium salt aqueous solution with the mass fraction of 0.3 percent, and taking 0.01g of Fe3O4Adding into water solution, ultrasonic treating for 20 min, and recovering Fe modified by surfactant via external magnetic field3O4Washing with distilled water for three times, drying, dispersing in 30ml methanol solution, adding 0.025g zinc nitrate hexahydrate, stirring for 3 hr, adding 0.622g dimethyl imidazole, reacting in 323K incubator for 12 hr, filtering to obtain solid material, and repeating the above steps for three times to obtain Fe3O4The whole preparation process of the @ ZIF-8 core-shell composite material lasts for 45 hours, and simultaneously Fe3O4The accumulation of the ZIF-8 crystal layer on the surface causes the contact area between the substrate and the catalyst to be reduced in the reaction process, and the catalytic activity of the catalyst is reduced.
Compared with the traditional preparation process, the preparation method disclosed by the invention has the advantages that on one hand, the complicated repeated steps are avoided, the workload is reduced, and the efficiency of preparing the composite MOFs material is improved by adopting a spray drying method; on the other hand, the surfactant is avoided, and the potential influence of the surfactant on the structure and the property of the ZIF-8 is reduced.
The above embodiments are merely examples for clearly illustrating the present invention and do not limit the present invention. Other variants and modifications of the invention, which are obvious to those skilled in the art and can be made on the basis of the above description, are not necessary or exhaustive for all embodiments, and are therefore within the scope of the invention.

Claims (10)

1. Fe3O4A process for the preparation of @ ZIF-8 core-shell composites, comprisingThe following steps:
1) mixing 2-methylimidazole and zinc salt in water to obtain a mixed solution I, and then carrying out spray drying to prepare pre-crystallized ZIF-8;
2) magnetic Fe3O4The nano microsphere particles are placed in methanol solution for ultrasonic stirring to obtain Fe3O4Suspending liquid;
3) adding the pre-crystallized ZIF-8 white powder obtained in the step 1) into the Fe obtained in the step 2)3O4Soaking the suspension, filtering, washing with methanol, and drying to obtain Fe3O4@ ZIF-8 core-shell composite material.
2. The method according to claim 1, wherein the molar ratio of the 2-methylimidazole to the zinc salt is 1: 1.
3. The preparation method according to claim 1, wherein the concentration of the zinc salt in the mixed solution I is 0.1-0.5 mol/L.
4. The preparation method according to claim 1, wherein the spray drying process uses a feed rate of 300-320 ml/h, a hot air temperature of 180-200 ℃, and a flow rate of 160-180 m3/h。
5. The method according to claim 1, wherein the magnetic Fe is Fe3O4The particle size of the nano microsphere particles is 100-200 nm.
6. The method of claim 1, wherein the Fe is3O4Fe in suspension3O4The concentration of (b) is 0.5-8 mg/ml.
7. The method of claim 1, wherein the amount of ZIF-8 pre-crystallized in step 3) is the same as the amount of Fe added in step 2)3O4The mass ratio of (1) - (15) is 20.
8. The preparation method according to claim 1, wherein the soaking time is 6-12 hours.
9. Fe produced by the production method according to any one of claims 1 to 83O4@ ZIF-8 core-shell composite material comprising magnetic Fe3O4Nanoparticle and ZIF-8, and Fe3O4The nanoparticles are encapsulated in a single ZIF-8 grain, Fe3O4The particle size of the microsphere is 100-200 nm, and the size of the ZIF-8 crystal is 300-500 nm.
10. Fe as recited in claim 93O4Application of @ ZIF-8 core-shell type composite material in catalysis of Knoevenagel condensation reaction.
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