1. An amino functionalized metal organic framework/graphene porous composite aerogel and a preparation method thereof are characterized in that the preparation method comprises the following steps:

(1) putting the MOF crystal powder into a vacuum drying oven at 150 ℃ for activation to generate Coordination Unsaturated Sites (CUSs), adding the activated MOF crystal powder and an amino functional reagent into a solvent together, and condensing and refluxing for a certain time to obtain NH₂-MOF；

(2) Preparing a graphene oxide stock solution by a modified Hummers method, and diluting the graphene oxide stock solution by a stirring and ultrasonic dispersion method to obtain a graphene oxide dispersion solution with a certain concentration;

(3) NH obtained in the step (1)₂Adding MOF crystal powder into graphene oxide dispersion liquid, closing the container, and oscillating, ultrasonically treating or stirring to enable NH₂-the MOF crystal powder is homogeneously dispersed in the graphene oxide dispersion;

(4) sealing the dispersed mixed solution, and placing the mixed solution in a blast drying oven for heat treatment to promote the graphene oxide lamella to be heated and NH₂-reduction and self-assembly by the combined action of MOF crystal powders and formation of stable composite porous hydrogels;

(5) and (4) freezing and drying the hydrogel obtained in the step (4) to obtain the stable amino functionalized metal organic framework/graphene porous composite aerogel.

2. The method of claim 1, wherein: in the step (1), the amino-functional reagent of the MOFs crystal powder is preferably one of ethylenediamine, triethylamine, ammonia water, polyacrylamide or triethylenediamine.

3. The preparation method of the amino-functionalized metal organic framework/graphene porous composite aerogel according to claim 1, wherein the preparation method comprises the following steps: in the step (1), the mass ratio of the added amino functional reagent to the MOFs crystal powder is 1: 5-1: 1.

4. The method of claim 1, wherein: in the step (1), the condensation reflux temperature of the amino functionalization reaction is controlled to be 120-150 ℃, and the reaction time is 6-18 h.

5. The preparation method of the amino-functionalized metal organic framework/graphene porous composite aerogel according to claim 1, wherein the preparation method comprises the following steps: in the step (2), the concentration of the graphene oxide dispersion liquid is controlled to be 3 mg/mL-10 mg/mL.

6. The preparation method of the amino-functionalized metal organic framework/graphene porous composite aerogel according to claim 1, wherein the preparation method comprises the following steps: in the step (3), NH is added₂The mass ratio of MOF crystal powder to graphene oxide is preferably 1: 5-1: 1; more preferably 2: 5-4: 5.

7. the preparation method of the amino-functionalized metal organic framework/graphene porous composite aerogel according to claim 1, wherein the preparation method comprises the following steps: in step (3), NH₂The MOF crystal powder and the graphene oxide dispersion liquid can be uniformly mixed in a mode of oscillating, ultrasonic or stirring for 0.5-2 h.

8. The preparation method of the amino-functionalized metal organic framework/graphene porous composite aerogel according to claim 1, wherein the preparation method comprises the following steps: in the step (4), the temperature of the heat treatment is preferably 50 to 100 ℃ and more preferably 60 to 80 ℃.

9. The method according to any one of claims 1 to 8, wherein: NH (NH)₂The MOF crystal powder can be used as a modification structure and has certain reducibility, and the MOF crystal powder is compounded with the surface of a graphene oxide sheet layer by one or more of the following modes: NH (NH)₂The MOF crystal powder is uniformly attached to the graphene sheet layer after interacting with the oxygen-containing functional group of the graphene sheet layer in the modes of hydrogen bond acting force, pi-pi interaction, covalent complexation and the like; the graphene oxide sheets are gradually arranged by the low-temperature heat treatment processGradually reduced by MOFs powder, the pi-pi interaction between the sheet layers is strengthened, and NH is simultaneously generated₂-the MOF crystal powder is stably immobilized inside the gel.

10. The amino-functionalized metal organic framework/graphene porous composite aerogel obtained by the preparation method according to claims 1 to 9, simultaneously retains the respective excellent characteristics of the two materials, and has good water stability.

Background

Graphene (Graphene) is a single atom thick nanosheet with a two-dimensional planar periodic honeycomb lattice structure composed of six-membered rings. Since the existence of graphene was found by Geim and Novoseov in 2004 through mechanical stripping of adhesive tapes, a great deal of research proves that the unique atomic arrangement structure and the good thermodynamic stability, mechanical properties and electrical properties caused by the structure are widely applied to the fields of electronic devices, energy storage, environmental catalysis, environmental adsorption and the like, and show great application prospects. Graphene Oxide (GO) is an oxidation state of graphene, and is usually prepared by oxidizing graphite powder by a Hummers method, oxygen-containing functional groups including hydroxyl, carboxyl, carbonyl and epoxy are introduced on the surface and at the edge of a lamella in the oxidation process, and the existence of the functional groups enables the graphene oxide to have good hydrophilicity and to be more easily modified, so that the graphene oxide is widely applied to composite material synthesis. In addition, GO can be converted into reduced graphene (rG), reduced graphene oxide (rGO), Graphene Aerogel (GA) through heat treatment or reduction or partial reduction by a reducing agent, further widening the application field of graphene-based materials.

Metal-organic frameworks (MOFs) are porous materials formed by self-assembly of Metal ions or Metal clusters and oxygen-containing organic ligands through coordination and complexation. From the 1995 Yaghi reports that Co-based MOFs they synthesized have so far been synthesized by tens of thousands of MOFs materials containing different metal centers by hydrothermal or solvothermal methods. The MOFs have the characteristics of simple synthesis process, large specific surface area, special pore structure, adjustable pore size, easiness in modification and design and the like, are widely researched and are applied to the fields of gas storage separation, environmental adsorption and catalysis, drug delivery, optoelectronics and the like. However, the MOFs is in a superfine powder state, and is difficult to separate from the environment, and the water stability and acid-base stability of the MOFs are relatively poor, which limits the further application of the material.

In recent years, two materials with excellent performance, namely graphene and MOFs, are compounded, so that the defect of the single action of the two materials is overcome, the two materials can generate a synergistic effect at an interface, and the application prospect of the materials is further enhanced, and therefore the method is paid attention to by researchers. Firstly, the oxygen-containing functional group of the graphene oxide can be used as a nucleation site of the MOFs crystal to form different structures and geometrical forms, so that the compound has more active sites and higher specific surface area. Secondly, the graphene oxide material with the introduced atomic layer density can protect MOFs pore channels from being blocked to cause poisoning. Thirdly, the MOFs crystal is coated in the inner space by the graphene oxide material with good hydrophilicity, so that the water stability and the acid-base stability of the MOFs are enhanced. The MOFs/graphene-based composite material is mainly synthesized by an in-situ method and an ex-situ method.

The most common in-situ synthesis method is a hydrothermal/solvothermal method, which comprises the steps of directly dispersing metal salt, an organic ligand, a solvent and graphene oxide uniformly, packaging the uniformly dispersed metal salt, organic ligand, solvent and graphene oxide into a stainless steel reaction kettle with a polytetrafluoroethylene lining, sealing the stainless steel reaction kettle, placing the stainless steel reaction kettle into a heating device, reacting for a certain time at a set temperature, washing and drying to obtain the required composite material. In the process, oxygen-containing functional groups of the GO sheet layer are firstly used as nucleation sites of MOFs to be combined with precursor metal ions, and then the MOFs crystals are promoted to grow through the coordination effect between the metal ions and the organic solvent, and finally the MOFs/graphene-based composite material is obtained. The method can obtain the composite material only by one-step operation, so that the intermediate operation step is avoided, and the method is a synthetic method which saves time and raw materials. However, because the yields of different MOFs powders are different, the addition amounts and proportions of the MOFs precursor and the graphene are difficult to control, and the method has the defects of uncontrollable product morphology, easy agglomeration of graphene sheet layers, large energy consumption in the preparation process and the like [ Coordination Chemistry Reviews 387 (2019) 262-272 ].

The ectopic self-assembly strategy requires that GO dispersion liquid and MOFs crystals are prepared respectively; then mixing the MOFs crystal powder and the graphene dispersion liquid according to a certain proportion, and enabling the two materials to react under the actions of electrostatic attraction, pi-pi stacking, hydrogen bonds and the like through stirring, ultrasound, oscillation and the like to form different composite materials. The ectopic self-assembly method has the advantages of simple operation, easy realization of large scale, contribution to controlling the proportion of different materials and the like, thereby being widely applied. However, because the interaction force between the MOFs crystal powder and the graphene is weak, a long mixing time or a certain other external force is required, and a part of the MOFs powder may fall off from the surface of the graphene sheet layer during subsequent operations such as washing, centrifugation and the like, so that the distribution of the components, the morphology and the like of the composite material may be uneven.

In summary, how to prepare the MOFs/graphene porous composite three-dimensional gel material with controllable structure, strong stability and uniform component distribution by compounding the MOFs crystal powder and the graphene nanosheet layer through a proper method under a relatively mild condition is an urgent problem in the field, while the respective excellent performances of the two nanomaterials are maintained, a synergistic effect is formed to further improve the application of the materials.

Disclosure of Invention

The invention provides an amino-functionalized metal organic framework structure/graphene composite aerogel which is controllable in appearance and structure, uniform in component distribution and provided with multistage pores, and is prepared by a simple mixing and low-temperature heat treatment combined method. The preparation method is mild in condition and simple to operate, the prepared composite aerogel has a stable three-dimensional frame structure and an adjustable pore size, and the graphene oxide and NH are reserved₂Structural integrity of MOF crystals and effective inhibition of self-stacking between graphene oxide sheets and NH₂-self-agglomeration of MOF nanocrystal powders.

In order to achieve the purpose, the invention adopts the following technical scheme:

an amino functionalized metal organic framework/graphene porous composite aerogel and a preparation method thereof comprise the following steps:

(1) putting the MOF crystal powder into a vacuum drying oven at 150 ℃ for activation to generate Coordination Unsaturated Sites (CUSs), adding the activated MOF crystal powder and an amino functional reagent into a solvent together, and condensing and refluxing for a certain time to obtain NH₂-MOF；

(2) Preparing a graphene oxide stock solution by a modified Hummers method, and diluting the graphene oxide stock solution by a stirring and ultrasonic dispersion method to obtain a graphene oxide dispersion solution with a certain concentration;

(3) will be described in detail(1) Obtained NH₂Adding MOF crystal powder into graphene oxide dispersion liquid, closing the container, and oscillating, ultrasonically treating or stirring to enable NH₂-the MOF crystal powder is homogeneously dispersed in the graphene oxide dispersion;

(4) sealing the dispersed mixed solution, and placing the mixed solution in a blast drying oven for heat treatment to promote the graphene oxide lamella to be heated and NH₂-reduction and self-assembly by the combined action of MOF crystal powders and formation of stable composite porous hydrogels;

(5) and (4) freezing and drying the hydrogel obtained in the step (4) to obtain the stable amino functionalized metal organic framework/graphene porous composite aerogel.

According to the scheme, the amino functional reagent of the MOFs crystal powder in the step (1) is preferably one of ethylenediamine, triethylamine, ammonia water, polyacrylamide or triethylene diamine, and the mass ratio of the added amino functional reagent to the MOFs crystal powder is 1: 5-3: 5.

According to the scheme, in the step (1), the condensation reflux temperature of the amino functionalization reaction is controlled to be 120-150 ℃, and the time is 6-18 h.

According to the scheme, in the step (2), the concentration of the graphene oxide dispersion liquid is 3 mg/mL-10 mg/mL.

According to the scheme, in the step (3), NH is added₂-the mass ratio of MOF crystal powder to graphene oxide is controlled to be 1: 5-1: 1; more preferably 2: 5-4: 5.

according to the above scheme, in the step (3), NH₂The MOF crystal powder and the graphene oxide dispersion liquid can be uniformly mixed in a mode of oscillating, ultrasonic or stirring for 0.5-2 h.

According to the above-mentioned aspect, in the step (4), the temperature of the heat treatment is preferably 50 to 100 ℃, and more preferably 60 to 80 ℃.

NH in the invention₂The MOF crystal powder can be used as a modification structure and has certain reducibility, and the MOF crystal powder is compounded with the surface of a graphene oxide sheet layer by one or more of the following modes: NH (NH)₂-MOF crystal powders, pi-pi to each other by hydrogen bonding forcesThe graphene sheet layer is uniformly attached after interaction with oxygen-containing functional groups of the graphene sheet layer in modes of action, covalent complexation and the like; the compound mode can exist singly or in combination, and is determined by the self properties and the feeding mass ratio of the amino functionalized MOFs crystal and the graphene oxide. During low temperature heat treatment, graphene oxide lamellae are NH coated₂Partial reduction of the MOF powder, strengthening of pi-pi interaction between graphene sheets to enable stable connection of graphene oxide sheets to form composite hydrogel, freeze drying to form composite aerogel, and simultaneously adding NH₂-the MOF crystal powder is stably immobilized inside the gel.

The amino-functionalized metal organic framework/graphene porous composite aerogel prepared by the invention has a self-supporting multi-level pore structure and relatively mild synthesis conditions, the structural integrity of two parent materials is kept in the synthesis process, the excellent performances of graphene and MOFs can be simultaneously exerted in the fields of energy storage, adsorption, catalysis, sensing and the like, and the application potential is relatively high.

The invention has the following outstanding advantages and characteristics with respect to the prior art:

firstly, reagents such as ethylenediamine are used for functionalizing MOFs crystal powder, the interaction between MOFs crystal particles and graphene oxide lamellar layers is enhanced, and then the MOFs crystal powder can be uniformly dispersed in graphene oxide dispersion liquid by means of methods such as ultrasound and stirring.

Secondly, the method is based on the principle of sol-gel, partial reduction of graphene oxide nanosheets is realized by using MOFs powder under the condition of low-temperature heat treatment, the inter-slice connection inside the gel is strengthened, and graphene sheets are mutually stacked to form hydrogel. According to the method, an additional reducing agent is not required, and the amino-functionalized MOF and the graphene oxide lamella are crosslinked, so that the lamella is mildly reduced, and self-stacking of the nanosheet layer in the self-assembly process of the lamella in the gel is effectively avoided. Compared with the traditional high-temperature hydrothermal reduction and reducing agent reduction, the structural integrity of the graphene oxide and the amino functionalized MOFs crystal powder can be retained to a greater extent, meanwhile, the porous composite aerogel has good hydrophilicity, the defect of poor stability of MOFs crystal particle water is overcome, and the porous composite aerogel can be better suitable for the application field of water environments.

Third, the method of the present invention has extrapolation applicability other than the NH of the present invention₂Besides MOF, the method is also suitable for other MOFs crystal powder functionalized by reducing groups, and the pore structure and the pore size of the prepared composite graphene aerogel can be simply adjusted by adjusting the mass ratio of the added functionalized MOFs crystal powder to the graphene oxide.

Fourthly, the synthesis method of the invention is convenient for batch production or industrial production. The method adopted by the invention is a method of mixing and low-temperature heat treatment, has the characteristics of simple instrument and equipment, convenience in operation, low energy consumption and the like, meets the requirements of industrial production, and the synthesized composite material has relatively complete graphene oxide and amino functionalized MOFs crystal structures.

Drawings

FIG. 1: a preparation flow chart of graphite, graphene oxide and graphene aerogel.

FIG. 2: 5 mg/mL graphene oxide dispersion prepared composite aerogels in different proportions: graphene aerogel (a); NH (NH)₂-MOF: GO = 1:5 (b); NH₂-MOF : GO = 2:5 (c); NH₂-MOF : GO = 3:5 (d); NH₂-MOF: GO = 4:5 (e); NH₂-MOF: GO = 1:1 (f)。

FIG. 3: pure graphene aerogel, NH₂Scanning electron micrographs of MOF and composite aerogels in different proportions: NH (NH)₂MOF crystal powder (a, b), pure graphene aerogel (c, d), NH₂-MOF: GO = 3:5 (e, f); NH₂-MOF : GO = 4:5 (g, h)。

FIG. 4: NH (NH)₂-EMAX swept area and individual element profiles of composite aerogel with MOF: GO = 3: 5: (a) scanning the area; (b) c element distribution diagram; (c) an O element distribution diagram; (d) distribution diagram of Cr element.

FIG. 5: pure graphene aerogel, NH₂-mof (cr) and a mass ratio of 3:5, an XRD spectrum (a) and an FTIR spectrum (b).

FIG. 6: different graphene oxide concentrationsNH in different proportions₂-photographs of water stability tests of composite aerogels of MOF to graphene oxide mass ratio:

5 mg/mL GO: NH₂-MOF: GO = 3:5 to 5:5; adding water to the mixture (a); standing for 48h, (d) oscillating for 1h, (e);

8 mg/mL GO, NH₂MOF GO = 1:5; 2: 5; after addition of water (b), after standing for 48h (f), after shaking for 1h (g)

10 mg/mL GO, NH₂-MOF GO = 3: 5; 5:5; after addition of water (c); standing for 48h (h);

FIG. 7: photograph of water stability test of pure graphene aerogel: adding water to the mixture (a); after standing for 48h (b).

Detailed Description

The present invention will now be described in further detail with reference to the following detailed description and the accompanying drawings, but the embodiments of the invention are not limited thereto.

Comparative example 1

The preparation methods of the graphene oxide stock solution and the pure graphene aerogel prepared by using the modified Hummers method are as follows:

(1) in an ice water bath, mixing a mixture of 2: adding 1 of pre-oxidized graphite powder and sodium nitrate into concentrated sulfuric acid, and then slowly adding a certain amount of potassium permanganate into an ice water bath at the temperature of less than 4 ℃, wherein the mass ratio of the potassium permanganate to the graphite powder is 3: 1; heating to 35 deg.C for 4 hr, heating to 98 deg.C, adding deionized water, heating to 98 deg.C, maintaining for 15min, stopping heating, adding deionized water and 30% H₂O₂Reducing the residual potassium permanganate by using the solution; and after centrifugation, washing by using 1mol/L hydrochloric acid solution until no sulfate radical is detected in the supernatant, finally ultrasonically dispersing the obtained suspension into deionized water, filling into a dialysis bag, and dialyzing until the pH value of the solution is neutral to obtain brown graphene oxide dispersion liquid.

(2) Adding a certain amount of concentrated GO dispersion liquid into a proper amount of deionized water, carrying out magnetic stirring for 12 hours, then carrying out ultrasonic treatment for 15min, diluting the dispersion liquid until the solid concentration of GO in the dispersion liquid is 5 mg/mL, adding 4 mL of GO dispersion liquid into a 5 mL freeze-drying tube, carrying out oscillation treatment for 1 hour by using a Votex-3 vortex oscillator, and then placing the freeze-drying tube into a blast drying oven at 80 ℃ for heat treatment for 12 hours; and after cooling to room temperature, putting the graphene aerogel into liquid nitrogen for freezing for 5min, then putting the graphene aerogel into a refrigerator with the temperature of 18 ℃ below zero for freezing for 2h, and finally carrying out freeze drying for 48h to remove water to form the pure graphene aerogel.

Comparative example 2

Amino-functionalized metal organic framework structure NH₂The preparation method of mof (cr) is as follows:

(1) weigh 4 g Cr (NO)₃)₂.9H₂Dissolving O and 1.66 g of terephthalic acid into 50mL of deionized water, slowly adding 0.5 mL of HF in the stirring process, transferring the mixed solution into a polytetrafluoroethylene lining, packaging in a stainless steel reaction kettle sleeve, and carrying out hydrothermal treatment at 220 ℃ for 8 hours; after cooling to room temperature, centrifuging to remove supernatant, washing the obtained green crystals for three times by using N, N-dimethylformamide and absolute ethyl alcohol respectively, and carrying out vacuum drying on the product at 60 ℃ for 12 hours to obtain Cr-MOF crystal powder;

(2) before functionalization, the obtained solid powder is placed in a vacuum drying oven at 150 ℃ to be treated for 12h to activate a sample to generate coordinated unsaturated metal Centers (CUSs);

(3) 30 ml of anhydrous toluene was added to a three-necked flask, and then 300 mg of Cr-MOF and 1 mmol of ethylenediamine were added thereto, followed by reaction at 120 ℃ under reflux condensation for 12 hours. After the reaction is finished, washing the reaction product for 3 times by using deionized water, and then placing the reaction product in a fume hood at normal temperature until the reaction product is dried to finally obtain NH₂-MOF(Cr)。

Example 1

The preparation method of the amino functionalized metal organic framework/graphene porous composite aerogel comprises the following steps:

weigh 8 mg NH₂-adding mof (cr) crystal powder to a 5 mL freeze-dried tube, adding 4 mL GO dispersion with a concentration of 5 mg/mL thereto, shaking for 1h using a Votex-3 vortex shaker, and then heat treating the resulting mixture in a forced air drying oven at 80 ℃ for 12 h; after cooling to room temperature, putting the hydrogel into liquid nitrogen for freezing for 5min, then putting the hydrogel into a refrigerator at the temperature of 18 ℃ below zero for freezing for 2h, and finally, carrying out freeze drying for 48h to remove water, thus obtaining the hydrogel with the mass ratio of 2: 5 of the three-dimensional porous composite aerogel.

Example 2

The preparation method of the amino functionalized metal organic framework/graphene porous composite aerogel comprises the following steps:

weigh 12 mg NH₂-adding mof (cr) crystal powder to a 5 mL freeze-dried tube, adding 4 mL GO dispersion with a concentration of 5 mg/mL thereto, shaking for 1h using a Votex-3 vortex shaker, and then heat treating the resulting mixture in a forced air drying oven at 80 ℃ for 12 h; after cooling to room temperature, putting the hydrogel into liquid nitrogen for freezing for 5min, then putting the hydrogel into a refrigerator at the temperature of 18 ℃ below zero for freezing for 2h, and finally, carrying out freeze drying for 48h to remove water, thus obtaining the hydrogel with the mass ratio of 3:5 of the three-dimensional porous composite aerogel.

Example 3

The preparation method of the amino functionalized metal organic framework/graphene porous composite aerogel comprises the following steps:

weigh 16 mg NH₂-adding mof (cr) crystal powder to a 5 mL freeze-dried tube, adding 4 mL GO dispersion with a concentration of 5 mg/mL thereto, shaking for 1h using a Votex-3 vortex shaker, and then heat treating the resulting mixture in a forced air drying oven at 80 ℃ for 12 h; after cooling to room temperature, putting the hydrogel into liquid nitrogen for freezing for 5min, then putting the hydrogel into a refrigerator at the temperature of 18 ℃ below zero for freezing for 2h, and finally, carrying out freeze drying for 48h to remove water, thus obtaining the hydrogel with the mass ratio of 4: 5 of the three-dimensional porous composite aerogel.

Example 4

The preparation method of the amino functionalized metal organic framework/graphene porous composite aerogel comprises the following steps:

weigh 20 mg NH₂-adding mof (cr) crystal powder to a 5 mL freeze-dried tube, adding 4 mL GO dispersion with a concentration of 5 mg/mL thereto, shaking for 1h using a Votex-3 vortex shaker, and then heat treating the resulting mixture in a forced air drying oven at 80 ℃ for 12 h; after cooling to room temperature, putting the hydrogel into liquid nitrogen for freezing for 5min, then putting the hydrogel into a refrigerator at the temperature of 18 ℃ below zero for freezing for 2h, and finally, carrying out freeze drying for 48h to remove water, thus obtaining the hydrogel with the mass ratio of 1:1 of a three-dimensional porous composite aerogel.

Example 5

The preparation method of the amino functionalized metal organic framework/graphene porous composite aerogel comprises the following steps:

weigh 6.4 mg NH₂-putting MOF (Cr) crystal powder into a 5 mL freeze-dried tube, adding 4 mL GO dispersion with a concentration of 8 mg/mL, shaking for 1h by using a Votex-3 vortex shaker, and then putting the obtained mixture into a forced air drying oven at 80 ℃ for heat treatment for 12 h; after cooling to room temperature, putting the hydrogel into liquid nitrogen for freezing for 5min, then putting the hydrogel into a refrigerator at the temperature of 18 ℃ below zero for freezing for 2h, and finally, carrying out freeze drying for 48h to remove water, thus obtaining the hydrogel with the mass ratio of 1:5 of the three-dimensional porous composite aerogel.

Example 6

The preparation method of the amino functionalized metal organic framework/graphene porous composite aerogel comprises the following steps:

weigh 12.8 mg NH₂-putting MOF (Cr) crystal powder into a 5 mL freeze-dried tube, adding 4 mL GO dispersion with a concentration of 8 mg/mL, shaking for 1h by using a Votex-3 vortex shaker, and then putting the obtained mixture into a forced air drying oven at 80 ℃ for heat treatment for 12 h; after cooling to room temperature, putting the hydrogel into liquid nitrogen for freezing for 5min, then putting the hydrogel into a refrigerator at the temperature of 18 ℃ below zero for freezing for 2h, and finally, carrying out freeze drying for 48h to remove water, thus obtaining the hydrogel with the mass ratio of 2: 5 of the three-dimensional porous composite aerogel.

Example 7

The preparation method of the amino functionalized metal organic framework/graphene porous composite aerogel comprises the following steps:

weigh 24 mg NH₂-putting MOF (Cr) crystal powder into a 5 mL freeze-dried tube, adding 4 mL GO dispersion with a concentration of 10 mg/mL, shaking for 1h by using a Votex-3 vortex shaker, and then putting the obtained mixture into a forced air drying oven at 80 ℃ for heat treatment for 12 h; after cooling to room temperature, putting the hydrogel into liquid nitrogen for freezing for 5min, then putting the hydrogel into a refrigerator at the temperature of 18 ℃ below zero for freezing for 2h, and finally, carrying out freeze drying for 48h to remove water, thus obtaining the hydrogel with the mass ratio of 3:5 of the three-dimensional porous composite aerogel.

Example 8

The preparation method of the amino functionalized metal organic framework/graphene porous composite aerogel comprises the following steps:

weigh 40 mgNH₂-putting MOF (Cr) crystal powder into a 5 mL freeze-dried tube, adding 4 mL GO dispersion with a concentration of 10 mg/mL, shaking for 1h by using a Votex-3 vortex shaker, and then putting the obtained mixture into a forced air drying oven at 80 ℃ for heat treatment for 12 h; after cooling to room temperature, putting the hydrogel into liquid nitrogen for freezing for 5min, then putting the hydrogel into a refrigerator at the temperature of 18 ℃ below zero for freezing for 2h, and finally, carrying out freeze drying for 48h to remove water, thus obtaining the hydrogel with the mass ratio of 1:1 of a three-dimensional porous composite aerogel.

The test results of the comparative example and the example were compared and analyzed as follows:

fig. 2 shows photographs of the pure graphene aerogel prepared in comparative example 1 and the composite aerogels with GO concentration of 5 mg/mL in different proportions in examples 1 to 4, and the pictures show that the composite aerogels with different proportions prepared by the mixing and heat treatment method have stable appearance.

Fig. 3 shows the pure graphene aerogel prepared in comparative example 1 and the NH prepared in comparative example 2₂SEM photographs of the porous composite aerogels prepared by mof (cr) and examples 3 and 4, reflecting the structure and morphology of the material. Wherein FIG. 3(a, b) is NH synthesized in comparative example 2₂SEM photograph of MOF (Cr) crystals, from which NH can be inversely seen₂-MOF (Cr) is an octahedral three-dimensional framework structure with the particle size of 2-10 mu m; SEM photographs of pure graphene aerogel at different magnifications fig. 3(c, d) show that graphene aerogel is formed by stacking a large number of GO sheets, and the surface wrinkle structure indicates that thermal treatment may cause partial stacking of GO sheets; FIG. 3 (e-g) is SEM photographs of composite aerogels prepared in examples 3 and 4 in different proportions, compared with pure graphene aerogel with relatively flat surface due to NH₂The MOF (Cr) crystal particles are internally coated by graphene platelets, forming a large number of "bulge" structures on the GO surface, the size NH of which₂The crystal size of-MOF (Cr) is consistent, demonstrating NH₂The MOF (Cr) crystal powder and GO sheets are compounded, crystal particles are well fixed on the surfaces of the nanosheet layers, and a three-dimensional framework structure of the composite aerogel is successfully obtained.

FIG. 4 shows the EMAX swept area and elements of the composite aerogel of example 3Distribution profile, as can be seen from the figure, due to NH₂The MOF (Cr) is wrapped inside the GO sheet layer, so that the obvious Cr element distribution is formed at the position of the bulge, but the content of the characterized Cr element can be relatively low due to the limitations of the penetration force of an electron microscope and the like.

FIGS. 5(a, b) show XRD and FTIR spectra of samples prepared in comparative examples 1 and 2 and example 2, and the peak existing in example 2 shown in FIG. 5a can be found in the sample of example 4, indicating that the composite aerogel obtained in example 4 contains NH in example 2₂-MOF (Cr), but due to NH₂The combined action of the mof (cr) crystals and the heating treatment allows the graphene oxide sheets to be reduced to a greater extent than with a simple heat treatment, and therefore no diffraction peak at 11 ° is found in the composite aerogel, representing the (002 crystal planes) of GO, further demonstrating the NH at₂The combined action of the mof (cr) crystalline powder and the heat treatment promotes the mild reduction of GO sheets and their progressive stacking to form a composite porous aerogel. Fig. 5b is FTIR spectra of samples prepared in comparative examples 1 and 2 and example 2, and FTIR peaks of the composite aerogel prepared in example 2 almost coincide with absorption peaks of samples in comparative examples 1 and 2, indicating that samples of example 2 simultaneously include samples of examples 1 and 2. In conclusion, the composite aerogel with uniformly distributed components and controllable morphology is successfully prepared by the method combining mixing and heat treatment.

Fig. 6 is a photograph of water stability tests of composite aerogels prepared in examples 1 to 8 in different concentrations and proportions, from this group of photographs, it can be seen that the composite aerogels just added to water in different proportions, fig. 6(a to c), the graph (d, f, h) after being soaked in water for 48 hours, and the graph (e, g) after being shaken in a shaker for 1 hour, all present stable three-dimensional structures, and in contrast, fig. 7 (a, b) can be seen that the pure graphene aerogel immediately disperses into floccules in water and completely precipitates to the bottom after standing for a while, which indicates that the composite aerogels with good water stability in different proportions can be successfully prepared by the method of combining "mixing and low temperature heat treatment".