CN111883745A - MOF/MXene/CF composite nanosheet and synthesis method thereof - Google Patents

Abstract

The invention relates to a MOF/MXene/CF composite nanosheet. The MOF/MXene composite nanomaterial is electrostatically self-assembled on the surface of a carbon fiber cloth by a liquid deposition method to obtain a composite nanosheet with a self-supporting structure. MAX material treatment removes the metal atoms of the material to obtain MXene material, MOF material decomposes to obtain metal atoms and organic ligands, the metal atoms in MOF enter the MXene material, and the organic ligands also enter the MXene material along with the metal atoms, MOF/MXene The composite structure was electrostatically self-assembled on carbon fiber cloth by liquid deposition method to form MOF/MXene/CF composite nanosheets. The composite nanosheet of the invention is that the secondary generated MOF material is interspersed in the MXene layered structure obtained by etching the MAX material and attached to the surface of the layered structure; the secondary generated MOF material is the organic ligand obtained after the original MOF is decomposed. The free metal atoms A and organic ligands, free metal nodes and organic ligands are self-assembled by complexation.

Description

A kind of MOF/MXene/CF composite nanosheet and its synthesis method

technical field

The invention relates to the technical field of composite materials, in particular to a method for synthesizing MOF/MXene/CF composite nanosheets.

Background technique

At present, the anode materials in lithium-ion batteries are mainly carbons, such as graphite, soft and hard carbon, etc., or new electrode materials, such as silicon carbon anodes or transition metal oxides. With the exhaustion of petroleum energy, the problem of environmental pollution, and the gradual increase in the market's requirements for battery capacity, traditional lithium-ion batteries with negative electrodes can no longer be satisfied with the status quo. In this case, the composite preparation of new materials and their application in lithium-ion batteries have become a research hotspot.

As a new material, MXene is a two-dimensional material with a structure similar to graphene. The chemical formula is denoted as M _n+1 X _n T _x , where M represents the former transition group metal, such as Ti, V, Zr, Mn, etc., and X is carbon. element or nitrogen element, T is the surface functional group. The MXene layered structure is obtained by etching away the intermediate layer from the precursor MAX phase (a ternary layered compound, A is a III or IV main group element), but the lamellae are prone to self-stacking, which hinders the electrolyte interaction in lithium battery applications. Its wetting and fast transport of lithium ions between layers. MOF material is a kind of porous material with regular pore structure, which is composed of metal ions and organic ligands combined by covalent bonds, coordination bonds and intermolecular forces. MOF materials have a regular and controllable three-dimensional channel structure, which is beneficial for lithium ion storage and transport. CF (carbon fiber) material has high strength, low density, high durability and stable structure, and is suitable for use in high acid, alkali, salt and atmospheric corrosion environments.

At this stage, the application of composite materials in the field of supercapacitors such as lithium batteries is in a period of rapid development, and the electrode as an important part of the capacitor's energy storage has always been the focus of research. MXene is a graphene-like two-dimensional material discovered in recent years. It has ultra-high volume specific capacity, metal-level conductivity, good hydrophilicity and rich surface chemistry, so it has a wide range of applications in flexible energy storage electrode materials. . In the patent published by Hubei Institute of Automotive Industry (publication number: 109003836B), a preparation method and application of a flexible fabric electrode based on MXene are disclosed. Synthesis of MXene flexible fabric electrodes by electroplating: sintering TiH ₂ , A1 and C powders in proportion to obtain MAX phase powder, chemically etch the MAX phase powder to obtain MXene material, and then obtain Ti ₃ C by low-temperature ultrasonication and centrifugation ₂ MXene colloidal solution, and finally the cleaned fabric was soaked in the diluted MXene solution and vacuum-dried. In the process, the oxidation of Ti ₃ C ₂ to TiO ₂ can be effectively avoided, the capacitance performance can be significantly improved, the cost is low, and it is non-toxic and non-polluting, and can be applied to the field of super capacitors. MXene has been widely concerned for its high specific capacity. However, its severe layer-by-layer stacking phenomenon is not conducive to the rapid diffusion of ions in the vertical direction, which affects its specific capacity at large current densities, and MXene has poor oxidation resistance. The performance seriously affects its electrical conductivity and cycling stability, so it is particularly important to compound MXene with high specific capacity active materials to improve the layer stacking phenomenon of MXene and enhance the oxidation resistance.

Metal-organic frameworks (MOFs) are crystal framework materials with intramolecular pores formed by self-assembly of metal ions or clusters and organic ligands through coordination bonds under certain conditions. Such materials have large specific surface area, adjustable pore size and shape, and are easy to be modified. The proton-conducting and electronic-conducting MOF materials show potential application value in the fields of fuel cells, electrocatalysis, lithium-ion batteries, and supercapacitors. The introduction of other components into the MOF structure can fine-tune the structure of the MOF, improve the adsorption performance, catalytic activity, and electrical conductivity, and even enable the MOF to have properties that it did not have before. In the patent published by Nanjing University of Posts and Telecommunications (Publication No.: 106611653A), a "one-step" method for preparing a new MOF composite material is disclosed: MAX material is etched to obtain MXene material and free A ions, and organic Ligand molecules, the organic ligand molecules react with the above-mentioned A ions on the surface of the MXene material to form MOF crystals, so that a MOF/MXene composite material in which the MOF and the MXene material are superimposed in a layered structure can be formed. In the patent (publication number: 105047435B) published by Shanghai University of Engineering and Technology, a method and application for synthesizing manganese metal organic framework electrode materials by hydrothermal method are disclosed: the soluble salt, organic acid and bidentate containing Mn ²⁺ The nitrogen ligand is added to deionized water, stirred and mixed evenly, and reacted in a reaction kettle at 120-200 ° C for 48-96 hours. After the reaction is completed, the manganese metal organic framework electrode material can be obtained by cooling, filtering, washing, drying and other steps. , the specific capacitance can reach 242F/g, which can be used in high power density power supply occasions.

MOF has attracted widespread attention due to its unique pore structure and the characteristics of containing transition metal elements. MOFs have been successfully prepared as active materials or electrodes as active material carriers, and MOFs have also been prepared as precursors to form active materials or active materials. The electrode of the material carrier, but the conductivity of MOF as an electrode is slightly worse than that of other electrode materials, and the maximum storage performance of the capacitor with MOF material as the electrode cannot be maximized. Secondly, the preparation process of MOF itself is relatively complex, which affects the controllability of its morphology, which makes the stability of the preparation layers poor, which limits the wide application of MOF in electrode materials. Therefore, it is of great significance to find a composite material with stable structure, large specific surface area, wider application range, and greatly improved charge-discharge Coulombic efficiency and cyclability.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide a method for synthesizing MOF/MXene/CF composite nanosheets, which overcomes the shortcomings of traditional MXene composite materials such as small interlayer spacing and easy stacking between layers.

To achieve the above object, the present invention adopts the following technical solutions to realize:

A MOF/MXene/CF composite nanosheet, the MOF/MXene composite nanomaterial is electrostatically self-assembled on the surface of a carbon fiber cloth by a liquid deposition method to obtain a composite nanosheet with a self-supporting structure.

A method for synthesizing MOF/MXene/CF composite nanosheets, the specific steps are as follows:

Step 1, MAX material etching: ball milling the MAX phase material in an organic solvent or water, vacuum drying and then ball milling and sieving to obtain submicron-sized powder; the powder is immersed in hydrofluoric acid and magnetically stirred at room temperature for 10 to 40 hours , washed with deionized water to remove excess acid solution, and dried at room temperature overnight to obtain MXene powder;

Step 2, decompose the MOF material: the MOF material uses a mixture of carbonate and bicarbonate, decomposed at room temperature for 2-5 hours in an argon-filled environment, fully washed with deionized water to remove excess salt solution, and dried at room temperature overnight to obtain a decomposed state MOF powder;

Step 3: Synthesize MOF/MXene nanomaterials: add the MXene powder obtained in step 1, the decomposed MOF powder obtained in step 2, and the alcohol solution for synthesis reaction, and the molar ratio of MXene powder to decomposed MOF powder is (0.8～1.55). ): 1; hydrothermally heated at 150～165℃ for 5～7 hours to obtain a MOF/MXene suspension with charge;

Step 4, the MOF/MXene suspension is purified to remove unreacted ions and organic matter to obtain MOF/MXene precipitate;

In step 5, the MOF/MXene precipitate is added to an alcohol solution, and the surface of the impurity-removed carbon fiber cloth is electrostatically self-assembled by a liquid deposition method to obtain a MOF/MXene/CF composite nanosheet.

In the first step, the MAX material is selected from one of Mn ₄ AlC ₃ and V ₄ AlC ₃ ; the organic solvent is an ethanol solution with a concentration of 50%; the magnetic stirring speed is 1200rmp; the pH value after washing with deionized water is 6.5-8.5 between.

In the step 2, the MOF material is selected from one of (C ₅ H ₅ )Mn(CO) ₃ and (C ₅ H ₅ )V(CO) ₃ ; the mixed solution of carbonate and bicarbonate is NaCO ₃ For the mixed solution with NaHCO ₃ , the molar ratio of NaCO ₃ and NaHCO ₃ is (0.3-0.5): (0.8-1.1), and the concentration of the mixed solution is (0.8-1.2) mol/L.

The alcohol solution in the third step is an ethanol solution with a concentration of 10%, and the pressure in the reaction kettle is 8MPa during the synthesis process.

In the fourth step, use a centrifuge to remove impurities, and the centrifugal speed is 3000 rmp.

The carbon fiber cloth impurity removal method in step 5: carry out impurity removal with 60% nitric acid, ultrasonic power 1000W, ultrasonic for 45 minutes.

In step 5, the alcohol solution concentration is 10% ethanol solution,

The operation of the liquid deposition method in step 5: the impurity-removed carbon fiber cloth is immersed in the alcohol solution of the MOF/MXene precipitate for more than 35 minutes, and then the carbon fiber cloth is poured into the 2-methylimidazole solution with the solution and allowed to stand for 2 to 3 hours. Finally, rinsed with deionized water and dried to obtain MOF/MXene composite nanosheets.

The MOF/MXene/CF composite nanosheets are used as negative electrode materials for lithium batteries.

In the first step, the processing of the MAX material is to remove the metal atoms of the material to obtain the MXene material. In the second step, the MOF material is decomposed to obtain metal atoms and organic ligands. The metal atoms in the MOF material enter the MXene material, and the organic ligands follow the MXene material. The metal atoms also enter the MXene material, so that the MOF/MXene composite structure is negatively charged, and there is a positive charge on the surface of the carbon fiber cloth after impurity removal. The place where the negative charge exists in the MOF/MXene composite structure provides electrostatic adsorption for the positive charge of the carbon fiber cloth. site. After fully soaking the carbon fiber cloth and the alcohol solution of the MOF/MXene composite nanomaterial, the MOF/MXene/CF composite nanosheets were formed by electrostatic self-assembly on the carbon fiber cloth by the liquid deposition method.

Compared with the prior art, the beneficial effects of the present invention are:

The composite nanosheet of the invention is that the secondary generated MOF material is interspersed in the MXene layered structure obtained by etching the MAX material and attached to the surface of the layered structure; the secondary generated MOF material is the organic ligand obtained after the original MOF is decomposed. The free metal atoms A and organic ligands, free metal nodes and organic ligands are self-assembled by complexation.

MXene materials are combined with MOF materials to form nano-layered materials with a "sandwich" structure in which MXene materials and MOF materials are alternately stacked. On the basis of exerting the excellent performance of MXene's high volume specific capacity, the stability and microscopic structure of MOF materials are utilized. Structural controllability, inserted between the soft layers of MXene, acts like a "support column", forming channels and spaces that can provide diffusion and storage for ions to the greatest extent, and form a stable layered structure, Thereby, the scope of application is further expanded, and the charge-discharge Coulomb efficiency and cycle performance of the material are improved.

On the basis of MOF/MXene composites, carbon fiber cloth (CF) was introduced, and the MOF/MXene composites were in-situ synthesized on CF to form structurally stable MOF/MXene/CF composite nanosheets. Secondly, CF itself has electrical conductivity and large specific surface area, which further increases the storage capacity of MOF/MXene/CF composite nanosheets for ion pairs while improving the material stability.

Novel MOF/MXene/CF composite nanosheets are prepared based on the process of decomposing MAX materials and MOF materials and synthesizing them on the surface of CF, that is, using the controllability of MXene structure to obtain MOF composite nanosheets with uniform structure, which overcomes the traditional MXene. The composite materials have shortcomings such as small interlayer spacing and easy stacking between layers, and MOF/MXene/CF composite nanosheets have great application prospects as energy storage materials in supercapacitors, which can be directly used as new binder-free electrodes. , the preparation of electrode sheets is omitted, the electrode volume is reduced, and it can exist as a flexible electrode. As a negative electrode material for lithium batteries, it can improve the stability, energy storage and utilization efficiency of devices.

Detailed ways

Below in conjunction with embodiment, the present invention is further described:

The following examples illustrate the invention in detail. These examples merely describe the best embodiments of the present invention and do not limit the scope of the present invention.

A method for synthesizing MOF/MXene/CF composite nanosheets. MOF/MXene composite nanomaterials are electrostatically self-assembled on the surface of carbon fiber cloth by a liquid deposition method to obtain MOF/MXene/CF composite nanosheets with a self-supporting structure; the specific steps are as follows:

Step 1, MAX material etching: use a ball mill to grind the MAX material into a sub-micron-sized MAX material, and etch the sub-micron-sized MAX material to obtain free metal atoms A and MXene layered structures; Or ball-milling in water, vacuum-drying, ball-milling and sieving to obtain sub-micron-sized powder; the powder is immersed in hydrofluoric acid, magnetically stirred at room temperature for 10-40 hours, washed with deionized water to remove excess acid solution, and dried at room temperature overnight to obtain MXene powder;

Step 2, decompose the MOF material: use carbonate and bicarbonate aqueous solutions to decompose the MOF material into metal nodes and organic ligands; the MOF material uses a mixture of carbonate and bicarbonate at room temperature in an argon-filled environment Decompose for 2 to 5 hours, fully wash with deionized water to remove excess salt solution, and dry at room temperature overnight to obtain decomposed MOF powder;

Step 3: Synthesize MOF/MXene composite nanomaterials: add the MXene powder obtained in step 1, the decomposed MOF powder obtained in step 2, and the alcohol solution for synthesis reaction, and the molar ratio of MXene powder and decomposed MOF powder is (0.8～ 1.55): 1; 150～165 ℃ of water heat for 5～7 hours to obtain the MOF/MXene suspension with charge;

Step 4, the MOF/MXene suspension is purified to remove unreacted ions and organic matter to obtain MOF/MXene precipitate;

In step 5, the MOF/MXene precipitate is added to an alcohol solution, and the surface of the impurity-removed carbon fiber cloth is electrostatically self-assembled by a liquid deposition method to obtain a MOF/MXene/CF composite nanosheet.

Example 1

A method for synthesizing MOF/MXene/CF composite nanosheets, using Mn ₄ AlC ₃ and (C ₅ H ₅ )Mn(CO) ₃ as MAX material and MOF material, including MXene material Mn ₄ C ₃ with a layered structure , the free metal node V, the MOF crystal interspersed in the layered structure and the surface of the material with Al as the node and cyclopentadiene as the organic ligand, and carbon cloth as the carrier.

Specific steps are as follows:

Step 1, MAX material etching: Select 20 mL of 50% ethanol solution as a dispersant, take 1.2 g of Mn ₄ AlC ₃ and perform ball milling in ethanol for 30 hours, vacuum dry and then ball mill and sieve to obtain sub-micron Mn ₄ AlC ₃ powder. The submicron Mn ₄ AlC ₃ powder was immersed in 300 mL of hydrofluoric acid with a concentration of 49%, and after magnetic stirring for 20 h at room temperature at a speed of 1200 rmp, the solution was fully washed with deionized water to remove excess acid solution. Between 6.5 and 8.5, dry at room temperature overnight to obtain Mn ₄ C ₃ powder.

Step 2, decompose the MOF material: take 1.5g (C ₅ H ₅ )Mn(CO) ₃ , dissolve (C ₅ H ₅ )Mn(CO) ₃ in 200mL NaCO ₃ and In the mixed solution of NaHCO ₃ , the molar ratio of the mixed solution of NaCO ₃ and NaHCO ₃ is 0.3:0.8, the concentration of the mixed solution is 1.2mol/L, and the reaction time is 2.5h, so that (C ₅ H ₅ )Mn(CO) ₃ is fully decomposed , fully washed with deionized water to remove excess salt solution, and dried at room temperature overnight to obtain Mn-MOFs powder in a decomposed state.

Step 3: Synthesize MOF/MXene composite nanomaterials: add the powders dried in steps 1 and 2 into a stainless steel reaction kettle lined with PTFE, take 0.8 g of MXene powder in step 1, and decompose in step 2. 1 g of the powder was added, and 30 mL of an ethanol solution with a concentration of 10% was added, and the mixture was heated in a reaction kettle at a pressure of 8 Mpa and 155 ° C for 5 hours to obtain a MOF/MXene composite nanosheet suspension.

Step 4: Purify and remove unreacted ions and organic matter. The MOF/MXene composite nanosheet suspension was centrifuged at 3000 rmp for 5 minutes, washed with deionized water three times, and the solid precipitate was vacuum dried at 65°C overnight.

Step 5: Ultrasonic the carbon fiber cloth with a side length of 5 mm in 20 mL of absolute ethanol and 100 mL of deionized water, respectively, with a power of 1000w for 45 min to remove impurities on the surface of the carbon fiber cloth. The cleaned carbon fibers are arranged in 10 mL with a concentration of 60%. Treated in nitric acid for 10h, washed and dried for later use. Dissolve the solid precipitate obtained in step 4 in deionized water, and immerse the treated carbon fiber cloth in the solution for more than 30 minutes, then quickly pour the carbon fiber cloth into the 2-methylimidazole solution with the solution, and let stand for 2 hours . Finally rinsed with deionized water and dried in a drying oven at 65°C. MOF/MXene/CF composite nanosheets were obtained.

Mn ₄ AlC ₃ and (C ₅ H ₅ )Mn(CO) ₃ are used as MAX materials and MOF materials, and Mn ₄ AlC ₃ is etched to separate Al ions to obtain MXene material Mn ₄ C ₃ and free Al, which are decomposed while etching (C ₅ H ₅ )Mn(CO) ₃ obtains free metal nodes Mn, cyclopentadiene and carboxyl groups. Cyclopentadiene and the above-mentioned Al self-assemble in the interlayer of Mn ₄ C ₃ to form Al as the node and cyclopentadiene In the MOF crystal with alkene as the ligand, the metal node Mn enters the surface void of Mn ₄ C ₃ , and the MOF crystal with Mn as the node and cyclopentadiene and free carboxyl group as the ligand is re-formed on the surface of Mn ₄ C ₃ , and finally MOF/ For the MXene composite material, the MOF/MXene composite material was immersed in an ethanol solution and the treated CF was co-soaked and static, and finally MOF/MXene/CF composite nanosheets were obtained.

The above-mentioned composite nanosheets have a specific capacity of 252F g ^-1 under the condition of a cyclic voltammetry scan rate of 2mVs ^-1 , and can be cycled 3000 times at a large scan rate with a high specific capacitance such as a current density of 5A g ^-1 , and the capacitance retention rate is up to 3000 times. 99%.

Example 2

A method for synthesizing MOF/MXene/CF composite nanosheets, using Mn ₄ AlC ₃ and (C ₅ H ₅ )Mn(CO) ₃ as MAX material and MOF material, including MXene material Mn ₄ C ₃ with a layered structure , the free metal node V, the MOF crystal interspersed in the layered structure and the surface of the material with Al as the node and cyclopentadiene as the organic ligand, and carbon cloth as the carrier.

Specific steps are as follows:

Step 1, MAX material treatment: choose 20 mL of ethanol solution with a concentration of 50% as a dispersant, take 1.2 g of Mn ₄ AlC ₃ for ball milling in ethanol for 30 hours, vacuum dry and then ball mill and sieve to obtain sub-micron Mn ₄ AlC ₃ powder . The submicron Mn ₄ AlC ₃ powder was immersed in 300 mL of hydrofluoric acid with a concentration of 49%, and after magnetic stirring at room temperature for 25 hours at a rotational speed of 1200 rmp, the solution was fully washed with deionized water to remove excess acid solution. Between 6.5 and 8.5, dry overnight at room temperature. Mn ₄ C ₃ powder was obtained.

Step 2, decompose the MOF material: take 1.5g (C ₅ H ₅ )Mn(CO) ₃ , dissolve (C ₅ H ₅ )Mn(CO) ₃ in 200mL NaCO ₃ and In the mixed solution of NaHCO ₃ , the reaction time was 3.5h, (C ₅ H ₅ )Mn(CO) ₃ was fully decomposed, washed with deionized water to remove excess salt solution, and dried at room temperature overnight to obtain Mn-MOFs powder.

Step 3, synthesizing MOF/MXene composite nanomaterials, adding the powders dried in steps 1 and 2 into a stainless steel reaction kettle lined with polytetrafluoroethylene, wherein 0.8 g of MXene powder in step 1 is taken and decomposed in step 2. 1 g of the powder was added, and 30 mL of an ethanol solution with a concentration of 10% was added, and the mixture was heated for 6 hours in a reaction kettle at a pressure of 8 Mpa and 160° C. to obtain a MOF/MXene composite nano-suspension.

Step 4: Purify and remove unreacted ions and organic matter. The MOF/MXene composite nanosheet suspension was centrifuged at 3000 rmp for 5 minutes, washed with deionized water three times, and the solid precipitate was vacuum dried at 65°C overnight.

Step 5: Ultrasonic the carbon cloth with a side length of 5 mm in 20 mL of absolute ethanol and 100 mL of deionized water, respectively, with a power of 1000 w for 45 min to remove impurities on the surface of the carbon cloth, and the cleaned carbon is arranged in 10 mL with a concentration of 60%. Treated in nitric acid for 10h, washed and dried for later use. The MOF/MXene composite nano-solid precipitate was dissolved in deionized water, and the pretreated carbon cloth was immersed in the solution for more than 30 minutes, and then the carbon cloth was quickly poured into the 2-methylimidazole solution with the solution, and allowed to stand. 2h. Finally, rinse with deionized water and dry in a drying oven at 65°C to obtain the finished product.

MXene material Mn ₄ C ₃ with layered structure, free metal node V, MOF crystal with Al as node and cyclopentadiene as organic ligand interspersed in the layered structure and the surface of the material, and carbon cloth as the carrier.

The above-mentioned composite nanosheets have a specific capacity of 246F g ^-1 under the condition of a cyclic voltammetry scan rate of 2mVs ^-1 , and can be cycled 3000 times at a large scan rate with a high specific capacitance such as a current density of 5A g ^-1 , and the capacitance retention rate reaches 246F g -1 . 97%.

Example 3

A method for synthesizing MOF/MXene/CF composite nanosheets, selecting V ₄ AlC ₃ and (C ₅ H ₅ )V(CO) ₃ as MAX material and MOF material, including MXene material V ₄ C ₃ with layered structure , free metal node Mn, MOF crystals interspersed in the layered structure and the surface of the material with Al as the node and cyclopentadiene as the organic ligand, and carbon cloth as the carrier. Specific steps are as follows:

Step 1, MAX material treatment: choose 20 mL of 50% ethanol solution as the dispersant, take 1.2 g of V ₄ AlC ₃ for ball milling in ethanol for 20 hours, vacuum dry and then ball mill and sieve to obtain sub-micron V ₄ AlC ₃ powder . The submicron V ₄ AlC ₃ powder was immersed in 300 mL of hydrofluoric acid with a concentration of 49%, and after magnetic stirring for 20 h at room temperature at a rotational speed of 1200 rmp, the solution was fully washed with deionized water to remove excess acid solution. Between 6.5 and 8.5, dry at room temperature overnight to obtain V ₄ C ₃ powder.

Step 2, decompose the MOF material: take 1.5g (C ₅ H ₅ )V(CO) ₃ , dissolve (C ₅ H ₅ )V(CO) ₃ in 200mL NaCO ₃ and In the mixed solution of NaHCO ₃ , the reaction time was 2.5h, the (C ₅ H ₅ )V(CO) ₃ was fully decomposed, the excess salt solution was removed by washing with deionized water, and the V-MOFs powder was obtained by drying at room temperature overnight.

Step 3: Synthesize MOF/MXene composite nanomaterials: add the powders dried in steps 1 and 2 into a stainless steel reaction kettle lined with PTFE, take 0.8 g of MXene powder in step 1, and decompose in step 2. 1 g of the powder was added, and 30 mL of an ethanol solution with an excess concentration of 10% was added, and the mixture was heated for 5 hours in a reaction kettle at a pressure of 8 Mpa and 155° C. to obtain a MOF/MXene composite nano-suspension.

Step 4: Purify and remove unreacted ions and organic matter. The MOF/MXene composite nanosheet suspension was centrifuged at 3000 rmp for 5 minutes, washed with deionized water three times, and the solid precipitate was vacuum dried at 65°C overnight.

Step 5: Ultrasonic the carbon cloth with a side length of 5 mm in 20 mL of absolute ethanol and 100 mL of deionized water, respectively, with a power of 1000 w for 45 min to remove impurities on the surface of the carbon cloth, and the cleaned carbon is arranged in 10 mL with a concentration of 60%. Treated in nitric acid for 10h, washed and dried for later use. The solid precipitate of MOF/MXene composite nanosheets was dissolved in deionized water, and the pretreated carbon cloth was immersed in the solution for more than 30 minutes, and then the carbon cloth was quickly poured into the 2-methylimidazole solution along with the solution. Set 2h. Finally, rinse with deionized water and dry in a drying oven at 65°C to obtain the finished product.

The above-mentioned composite nanosheets have a specific capacity of 242F g ^-1 under the condition of a cyclic voltammetry scan rate of 2mVs ^-1 , and can be cycled 3000 times at a high specific capacitance such as a current density of 5A g ^-1 , and the capacitance retention rate is up to 3000 times. 99%.

Example 4

A method for synthesizing MOF/MXene/CF composite nanosheets, selecting V ₄ AlC ₃ and (C ₅ H ₅ )V(CO) ₃ as MAX material and MOF material, including MXene material V ₄ C ₃ with layered structure , free metal node Mn, MOF crystals interspersed in the layered structure and the surface of the material with Al as the node and cyclopentadiene as the organic ligand, and carbon cloth as the carrier. Specific steps are as follows:

Step 1, MAX material treatment: choose 20 mL of ethanol solution with a concentration of 50% as a dispersant, take 1.2 g of V ₄ AlC ₃ and carry out ball milling in ethanol for 30 hours, vacuum dry and then ball mill and sieve to obtain sub-micron V ₄ AlC ₃ powder . The submicron V ₄ AlC ₃ powder was immersed in 300 mL of hydrofluoric acid with a concentration of 49%, and after magnetic stirring at room temperature for 25 hours at a speed of 1200 rmp, the solution was fully washed with deionized water to remove excess acid solution. Between 6.5 and 8.5, dry at room temperature overnight to obtain V ₄ C ₃ powder.

Step 2, decompose the MOF material: take 1.5g (C ₅ H ₅ )V(CO) ₃ , dissolve (C ₅ H ₅ )V(CO) ₃ in 200mL NaCO ₃ and In the mixed solution of NaHCO ₃ , the reaction time was 2.5h, the (C ₅ H ₅ )V(CO) ₃ was fully decomposed, the excess salt solution was removed by washing with deionized water, and the V-MOFs powder was obtained by drying at room temperature overnight.

Step 3: Synthesize MOF/MXene composite nanomaterials: add the powders dried in steps 1 and 2 into a stainless steel reaction kettle lined with PTFE, take 0.8 g of MXene powder in step 1, and decompose in step 2. 1 g of the powder was added, and 30 mL of an ethanol solution with an excess concentration of 10% was added, and the mixture was heated with water for 6 hours in a reaction kettle at a pressure of 8 Mpa and 160° C. to obtain a MOF/MXene composite nano-suspension.

Step 4: Purify and remove unreacted ions and organic matter. The MOF/MXene composite nanosheet suspension was centrifuged at 3000 rmp for 5 minutes, washed with deionized water three times, and the solid precipitate was vacuum dried at 65°C overnight.

Step 5. Synthesis on CF: ultrasonically sonicate the carbon cloth with a side length of 5 mm in 20 mL of absolute ethanol and 100 mL of deionized water, and the power is 1000w for 45 minutes to remove impurities on the surface of the carbon cloth, and the carbon layout after cleaning Treated in 10 mL of 60% nitric acid for 10 h, washed and dried for later use. The solid precipitate of MOF/MXene composite nanosheets was dissolved in deionized water, and the pretreated carbon cloth was immersed in the solution for more than 30 minutes, and then the carbon cloth was quickly poured into the 2-methylimidazole solution along with the solution. Set 2h. Finally, rinse with deionized water and dry in a drying oven at 65°C to obtain the finished product.

The above-mentioned composite nanosheets have a specific capacity of 242F g ^-1 under the condition of a cyclic voltammetry scan rate of 2mVs ^-1 , and can be cycled 3000 times at a high specific capacitance such as a current density of 5A g ^-1 , and the capacitance retention rate is up to 3000 times. 97%.

The invention etches the MAX material, decomposes the MAX material to obtain the MXene layered material and free metal ions A, separates the MOF material while etching, and obtains the same free metal nodes and organic complexes as the metal ions in the layered structure. In this way, MOF/MXene composite nanomaterials can be formed in which MOF and MXene materials are superimposed on each other in a layered structure.

Due to the structural characteristics of MAX materials, the obtained MXene layered structure has the characteristics of uniform interlayer spacing distribution and high structural controllability, which provides conditions for the insertion and attachment of MOFs. MOF crystals based on MXene layered structure are also more uniform and controllable in structure than traditional MOF materials. MOF/MXene composite nanomaterials with different interlayer spacings can be obtained according to the microscopic radii of metal nodes, which expands its application in lithium batteries and other storage. applications in the energy field. By selecting MAX materials, the layer thickness, interlayer spacing and other structural features of the MXene layered structure can be adjusted, thereby realizing the structural diversity and controllability of MOF/MXene composite nanomaterials; by selecting CF materials, a self-supporting structure can be formed. MOF/MXene/CF composite nanosheets not only improve the stability of the material, but also have strong electron accepting and transfer properties of CF itself, which will improve the storage and lithium ion transport performance of the composite nanosheets, and can be directly used as a new type of binderless electrode.

MOF/MXene/CF composite nanosheets combine three structures, which increase the specific surface area and porosity of the material, the controllability of the structure improves the utilization rate of the material, and the structure is more stable and can be directly used as a new type of binderless electrode, thus making the Composite nanosheets improve energy storage and utilization efficiency.

The method is simple and safe to operate, and solves the problem of introducing an acid solution to react with the MAX material in the early stage, resulting in high yield and purity, no introduction of new impurities and basically no by-products, and at the same time solving the problem of poor stability of the composite structure of the two materials.

Claims (10)

1. An MOF/MXene/CF composite nanosheet is characterized in that the MOF/MXene composite nanomaterial is subjected to electrostatic self-assembly on the surface of carbon fiber cloth by a liquid phase deposition method to obtain the composite nanosheet with a self-supporting structure.

2. A synthesis method of MOF/MXene/CF composite nanosheets is characterized in that the MOF/MXene composite nanomaterial is subjected to electrostatic self-assembly on the surface of carbon fiber cloth by a liquid phase deposition method to obtain the MOF/MXene/CF composite nanosheets with self-supporting structures; the method comprises the following specific steps:

step one, etching an MAX material: ball-milling MAX phase materials in an organic solvent or water, carrying out vacuum drying, and then carrying out ball-milling and sieving to obtain submicron-sized powder; immersing the powder in hydrofluoric acid, magnetically stirring for 10-40 h at room temperature, washing with deionized water to remove redundant acid solution, and drying overnight at room temperature to obtain MXene powder;

step two, decomposing the MOF material: decomposing the MOF material at room temperature for 2-5 h in an argon-filled environment by using a mixed solution of carbonate and bicarbonate, fully washing with deionized water to remove redundant salt solution, and drying at room temperature overnight to obtain decomposed MOF powder;

step three, synthesizing the MOF/MXene nano material: adding MXene powder obtained in the first step, decomposed MOF powder obtained in the second step and an alcohol solution into a reaction kettle for synthesis reaction, wherein the molar ratio of the MXene powder to the decomposed MOF powder is (0.8-1.55): 1; carrying out hydrothermal treatment at 150-165 ℃ for 5-7 hours to obtain an MOF/MXene turbid liquid with charges;

purifying the MOF/MXene suspension to remove unreacted ions and organic matters to obtain an MOF/MXene precipitate;

and fifthly, adding an alcoholic solution into the MOF/MXene precipitate, and performing electrostatic self-assembly on the surface of the carbon fiber cloth subjected to impurity removal by using a liquid phase deposition method to obtain the MOF/MXene/CF composite nanosheet.

3. The method for synthesizing MOF/MXene/CF composite nanosheets of claim 2, wherein in the first step, the MAX material is selected from Mn₄AlC₃、V₄AlC₃One of (1); the organic solvent is ethanol solution with the concentration of 50 percent; the magnetic stirring speed is 1200 rmp; the pH value of the deionized water after washing is 6.5-8.5.

4. The synthesis method of MOF/MXene/CF composite nanosheets of claim 2, wherein in step two the MOF material is selected from (C)₅H₅)Mn(CO)₃、(C₅H₅)V(CO)₃One of (1); the mixed solution of carbonate and bicarbonate is NaCO₃And NaHCO₃Mixed liquor of (1), NaCO₃And NaHCO₃The molar ratio is (0.3-0.5): (0.8-1.1), the concentration of the mixed liquid is 0.8-1.2 mol/L.

5. The synthesis method of the MOF/MXene/CF composite nanosheet according to claim 2, wherein the alcohol solution in the third step is a 10% ethanol solution, and the pressure in the reaction kettle during the synthesis process is 8 MPa.

6. The synthesis method of MOF/MXene/CF composite nanosheets of claim 2, wherein in step four, impurity removal is performed by a centrifuge at a centrifugation rate of 3000 rmp.

7. The synthesis method of the MOF/MXene/CF composite nanosheet according to claim 2, wherein in step five, the carbon fiber cloth impurity removal method comprises: removing impurities by using nitric acid with the concentration of 60%, and carrying out ultrasonic treatment for 45 minutes at the ultrasonic power of 1000W.

8. The synthesis method of MOF/MXene/CF composite nanosheets of claim 2, wherein the alcohol solution concentration in step five is a 10% ethanol solution.

9. The synthesis method of MOF/MXene/CF composite nanosheets according to claim 2, wherein the liquid phase deposition method operates in step five: and immersing the carbon fiber cloth subjected to impurity removal into an alcoholic solution of the MOF/MXene precipitate for more than 35 minutes, pouring the carbon fiber cloth into a 2-methylimidazole solution along with the solution, standing for 2-3 hours, finally washing with deionized water, and drying to obtain the MOF/MXene composite nanosheet.

10. The MOF/MXene/CF composite nanosheet produced by the synthesis method according to claim 2, being used as a lithium battery anode material.