CN108539144A - A kind of extra small metal organic frame is nanocrystalline and preparation method and application - Google Patents

Abstract

The invention belongs to field of material preparation, specially a kind of extra small metal organic frame is nanocrystalline and preparation method and application.Step of the present invention is：The first homoepitaxial large scale metal-organic framework material in graphene oxide layer, then polymer wraps up metal-organic framework material by in-situ polymerization, it calcines in air, it is nanocrystalline to obtain super-small metal-organic framework material by the atomizing of heat auxiliary.Advantage of the present invention：Preparation method is simple, and raw material is cheap and easy to get, and low energy consumption for preparation process, the nanocrystalline size uniformity of metal-organic framework material of preparation（~5 nm）.When the material may be directly applied to lithium ion battery negative material, active material utilization is high, and the specific capacity based on entire electrode is big（1301 mAh g^‑1）, have extended cycle life（Capacity retention ratio has 98.6% after 1000 circles）, it is expected to become next-generation lithium ion battery material.

Description

A kind of ultra-small metal-organic framework nanocrystal and its preparation method and application

technical field

The invention belongs to the technical field of material preparation, and in particular relates to an ultra-small metal organic framework nanocrystal, a preparation method and an application.

Background technique

Metal-organic frameworks can be widely used in gas separation and storage, catalysts and catalyst supports, light absorption and conversion, supercapacitors, secondary batteries, Drug carrier and many other fields. At the same time, when the size of a material is reduced to the nanoscale, its physical and chemical properties will change significantly, so people have invented many methods to prepare ultra-small nanomaterials. These traditional methods include: laser synthesis processing, ultrasonic or microwave treatment, rapid heating , atomic or molecular layer deposition, etc. However, on the one hand, these methods are not suitable for the preparation of ultra-small metal-organic framework materials, because of the instability of metal-organic framework materials under some extreme conditions; Scale preparation. Therefore, it is particularly important to develop a low-cost method for large-scale preparation of ultra-small metal-organic framework nanocrystals.

Contents of the invention

The purpose of the present invention is to provide a simple, quick and safe ultra-small metal organic framework nanocrystal and its preparation method and application.

The method for preparing ultra-small metal-organic framework nanocrystals provided by the present invention, the specific steps are as follows:

(1) Preparation of graphene oxide precursor:

Prepared by the improved Hummers method, that is, take 1~3g of 325 mesh graphite powder, add 1~2g of sodium nitrate powder and 40~120ml of concentrated sulfuric acid, slowly add 3~9 g of potassium permanganate in a cold water bath, at 30~40 Stir in a water bath at ℃ for 0.5 h, then add 50-100 ml of water, continue to react for 10-30 min, then add 200-400 ml of water, react for 5-20 min, then add 10-30 ml of 3% hydrogen peroxide until the solution becomes is golden yellow;

After the solution was left to settle, decant to remove the supernatant, add hydrochloric acid with a mass concentration of 10%, put it into centrifuge tubes and discard the supernatant by high-speed centrifugation at a speed of 10000-12000 r/min, and then use deionized Wash with water until neutral, collect the product after washing with water, add deionized water for ultrasonic dispersion, and centrifuge at low speed to take the supernatant to obtain a graphene oxide (GO) aqueous solution.

(2) Preparation of graphene oxide/metal organic framework/polymer composites:

First configure cobalt chloride and sodium ferricyanide solution; add cobalt chloride solution to 0.4-2 mg/mL graphene oxide aqueous solution, stir and ultrasonically; add sodium ferricyanide solution to the above solution, stir for 0.5-1.5h, Obtain the graphene oxide/metal organic framework composite; then add ammonium persulfate and pyrrole monomer in turn, continue to stir for 8 to 12 hours, centrifuge and wash to obtain the graphene oxide/metal organic framework/polymer composite; after Freeze-drying, the composite airgel can be obtained;

(3) Preparation of ultra-small metal-organic framework nanocrystals

The composite airgel obtained in the step (2) is calcined in the air atmosphere to obtain the carbon-coated ultra-small metal-organic framework nanocrystal aerogel.

In the step (1) of the present invention, the concentration of the graphene oxide aqueous solution is 0.4-2 mg/mL.

In step (2) of the present invention, the concentrations of sodium ferricyanide and cobalt chloride are both 0.1-1 mol/ml.

In the step (2) of the present invention, the freeze-drying of the composite of graphene oxide/metal organic framework/polymer uses a freeze dryer, and puts it in a refrigerator at -20-0°C for 1-3 hours before putting it into the freeze-dryer. The freeze-drying time is 16~24h.

In step (3) of the present invention, the calcination temperature is controlled at 150-400°C.

The carbon-coated ultra-small metal organic framework nanocrystalline airgel of the present invention can be directly used as a negative electrode material without adding additional conductive additives and binders.

The invention has the advantages that metal ions can be closely adsorbed on the surface of graphene oxide due to positive charge, and then organic ligands can be added to obtain metal-organic framework particles with uniform size distribution. Then polymer-coated metal-organic framework particles can be obtained by in-situ polymerization; calcined in air, and ultra-small-sized metal-organic framework material nanocrystals can be obtained through a heat-assisted pulverization process. At the same time, the preparation method of the present invention is simple, the raw materials are cheap and easy to obtain, and the nanocrystals of the prepared metal frame material are small in size and evenly distributed (~5 nm). As an anode material for lithium-ion batteries, it has a high utilization rate of active materials, a large specific capacity based on the entire electrode (1301 mAh g ^-1 ), and a long cycle life (98.6% capacity retention after 1000 cycles), and is expected to become the next generation of lithium-ion batteries Material.

Description of drawings

Figure 1 is a transmission electron microscope image of a composite of graphene oxide/metal organic framework/polymer.

Fig. 2 is a transmission electron microscope image of carbon-coated ultra-small metal organic framework nanocrystals formed after the composite in Fig. 1 is calcined.

Fig. 3 is the Fourier transform infrared spectrum of the carbon-coated ultra-small organometallic framework nanocrystal formed after calcination.

Figure 4 shows the charge and discharge curves of carbon-coated ultra-small metal-organic framework nanocrystalline composites and lithium sheets assembled into a half-cell at different current densities, and the specific capacity is calculated based on the mass of the entire electrode.

Figure 5 shows the cycle charge-discharge capacity retention curves of carbon-coated ultra-small metal-organic framework nanocrystals and lithium sheets assembled into a half-cell at 5 and 10 A g ^-1 , and the specific capacity is calculated based on the mass of the entire electrode.

Detailed ways

The technical solution of the present invention will be further described below in conjunction with the examples, but it is not limited to the following examples. Any modification or equivalent replacement of the technical solution of the present invention without departing from the scope of the technical solution of the present invention belongs to the protection scope of the present invention .

A method for preparing ultra-small metal-organic framework nanocrystals uniformly grows metal-organic framework particles on the surface of graphene oxide through electrostatic adsorption and coordination, and then uniformly wraps polymer materials on the surface of metal-organic framework particles by in-situ polymerization. Graphene oxide/metal organic framework/polymer airgel obtained by freeze-drying. Finally, the above airgel is calcined in the air atmosphere to obtain carbon-coated ultra-small metal-organic framework nanocrystals.

Example 1:

(1) Preparation of graphene oxide precursor:

Prepared by the improved Hummers method, that is, take 3g of 325 mesh graphite powder, add 2g of sodium nitrate powder and 120 ml of concentrated sulfuric acid, slowly add 9 g of potassium permanganate in a cold water bath, stir in a water bath at 30-40 °C for 0.5 h, Then add 100ml of water, continue to react for 30 minutes, then add 400ml of deionized water, react for 5~20 minutes, then add 30 ml of 3% hydrogen peroxide until the solution turns golden yellow.

After the solution was left to settle, decant to remove the supernatant, add 10% hydrochloric acid, divide into centrifuge tubes and discard the supernatant by high-speed centrifugation at a speed of 10,000~12,000 r/min, and then wash with deionized water to medium. properties, the product was collected after washing with water, ultrasonically dispersed by adding deionized water, and the supernatant was obtained by low-speed centrifugation to obtain a graphene oxide aqueous solution. The low-speed centrifugation speed was 2000-5000 r/min.

(2) Preparation of composites of polymer/metal organic framework/graphene oxide:

First configure 1 mol/L cobalt chloride and sodium ferricyanide solution. Add 0.2 ml of cobalt chloride solution to 0.4~2 mg/mL graphene oxide aqueous solution, stir and sonicate; continue to add 2 ml of sodium ferricyanide solution, and stir for 1 hour to obtain a metal organic framework/graphene oxide composite. Then add Ammonium persulfate and pyrrole monomer, continue to stir for 8 to 12 hours, centrifuge and wash to obtain a composite of polymer/metal organic framework/graphene oxide. The composite airgel can be obtained after freeze-drying.

Figure 1 is a transmission electron microscope picture of the composite of graphene oxide/metal organic framework/polymer, which shows that the metal organic framework material is well encapsulated in graphene oxide/polymer.

(3) Preparation of ultra-small metal-organic framework nanocrystals

The airgel obtained in (2) was calcined at 350 °C for 2 h in an air atmosphere to obtain carbon-coated ultra-small metal-organic framework nanocrystalline airgel.

Figure 2 is a transmission electron microscope image of carbon-coated ultra-small metal-organic framework nanocrystals formed after calcination, indicating that the metal-organic framework material is differentiated into uniformly distributed ultra-small metal-organic framework nanocrystals. Figure 3 is the Fourier transform infrared spectrum of carbon-coated ultra-small metal-organic framework nanocrystals, which shows that the composition of ultra-small metal-organic framework nanocrystals formed by calcination in air has not changed and has not been oxidized.

(4) The obtained carbon-coated ultra-small metal-organic framework nanocrystalline airgel was used as the negative electrode material and the lithium sheet was assembled into a half-cell in a glove box, the separator was polypropylene (Celgard 2400), and the electrolyte was 1 M LiPF ₆ was dissolved in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DME) (volume ratio 1:1). The charge and discharge test was carried out after the battery was left to stand for 12 hours. The voltage range was 0.01~3V, and the specific capacity was calculated according to the mass of the entire positive electrode.

Figure 4 shows the galvanostatic charge and discharge curves of the half-cell at different current densities (0.1-40 A g ^-1 ), and the discharge specific capacity at 0.1 A g ^-1 reaches 1301 mAh g ^-1 . Figure 5 shows the cycle charge-discharge capacity retention curves of the half-cell at 5 and 10 A g ^-1 , and the specific capacity retention rates after 500 cycles are 92.9% and 98.6%, respectively.

Example 2:

Obtain a 1 mg/mL graphene oxide aqueous solution according to the method in Example 1 above, and add 0.2 ml of cobalt chloride (0.5 mol/L) and 2 ml of sodium ferricyanide solution (0.5 mol/L) into the oxidation In the graphene aqueous solution, after stirring for 30 min, let it stand for 30 min, centrifuge to remove the supernatant, and disperse the remaining solid in deionized water. 120 microliters of pyrrole was added to the above solution for in-situ polymerization, then the supernatant was removed by centrifugation, and the remaining solid was dispersed in deionized water.

The above solution was freeze-dried for 24 hours to obtain a self-supporting graphene oxide/metal organic framework/polymer aerogel. The airgel is calcined at 300° C. for 2 h in an air atmosphere to obtain a carbon-coated ultra-small metal-organic framework nanocrystalline material.

Example 3:

Obtain a 0.5 mg/mL GO aqueous solution according to the method in the above-mentioned Example 1, and add 0.2 ml of cobalt chloride (0.5 mol/L) and 2 ml of sodium ferricyanide solution (0.5 mol/L) into the GO aqueous solution under stirring , continue to stir for 30 minutes and then stand still for 30 minutes, centrifuge to remove the supernatant, and disperse the remaining solids in deionized water, and disperse evenly. 60 microliters of pyrrole was added to the above solution for in-situ polymerization, then the supernatant was removed by centrifugation, and the remaining solid was dispersed in deionized water.

The above solution was freeze-dried for 16-24 hours to obtain a self-supporting graphene oxide/metal organic framework/polymer aerogel. The airgel is calcined at 350° C. for 2 h in an air atmosphere to obtain a carbon-coated ultra-small metal-organic framework nanocrystalline material.

Claims (7)

1. A method for preparing ultra-small metal-organic framework nanocrystals, characterized in that, the specific steps are as follows: (1) Preparation of graphene oxide precursor: Prepared by the improved Hummers method, that is, take 1~3g of 325 mesh graphite powder, add 1~2g of sodium nitrate powder and 40~120ml of concentrated sulfuric acid, slowly add 3~9 g of potassium permanganate in a cold water bath, at 30~40 Stir in a water bath at ℃ for 0.5 h, then add 50-100 ml of water, continue to react for 10-30 min, then add 200-400 ml of water, react for 5-20 min, then add 10-30 ml of 3% hydrogen peroxide until the solution becomes is golden yellow; After the solution was left to settle, decant to remove the supernatant, add hydrochloric acid with a mass concentration of 10%, put it into centrifuge tubes and discard the supernatant by high-speed centrifugation at a speed of 10,000-12,000 r/min, and then wash with deionized water To neutrality, collect the product after washing with water, add deionized water to ultrasonically disperse, and centrifuge at a low speed to take the supernatant to obtain a graphene oxide (GO) aqueous solution. (2) Preparation of graphene oxide/metal organic framework/polymer composites: First prepare cobalt chloride and sodium ferricyanide solution; add cobalt chloride solution to 0.4~2 mg/mL graphene oxide aqueous solution, stir and sonicate; add sodium ferricyanide solution to the above solution, and stir for 1 hour to obtain graphite oxide Then add ammonium persulfate and pyrrole monomer in sequence, continue to stir for 8-12 hours, centrifuge and wash to obtain the composite of graphene oxide/metal organic framework/polymer; after freeze-drying, Obtain composite airgel; (3) Preparation of ultra-small metal-organic framework nanocrystals The composite airgel obtained in the step (2) is calcined in the air atmosphere to obtain the carbon-coated ultra-small metal-organic framework nanocrystal aerogel. 2. The method for preparing ultra-small metal-organic framework nanocrystals according to claim 1, wherein in step (1), the concentration of the graphene oxide aqueous solution is 0.4-2 mg/mL. 3. The method for preparing ultra-small metal-organic framework nanocrystals according to claim 1, characterized in that, in step (2), the concentrations of sodium ferricyanide and cobalt chloride are both 0.1-1 mol/ml. 4. The method for preparing ultra-small metal-organic framework nanocrystals as claimed in claim 1, characterized in that in step (2), the freeze-drying of graphene oxide/metal-organic framework/polymer composites uses a freeze dryer , Before putting into the freeze dryer, put it in the refrigerator at -20~0℃ for 1~3h, and then freeze dry for 16~24h. 5. The method for preparing ultra-small metal organic framework nanocrystals according to claim 1, characterized in that, in step (3), the calcination temperature is 150-400°C. 6. The ultra-small metal-organic framework nanocrystal prepared according to the preparation method described in claims 1-5. 7. the application of ultra-small metal organic framework nanocrystal as claimed in claim 6 in lithium ion battery electrode material.