Preparation method and application of polydopamine-mediated uniformly phosphorylated nano onion carbon

Abstract

The invention discloses a preparation method and application of polydopamine-mediated uniformly phosphorylated nano onion carbon, nano onion carbon prepared in a laboratory is used as a raw material, and carboxylated nano onion carbon (C-CNOs) is generated by a concentrated nitric acid / sulfuric acid mixed acid oxidation reaction; the preparation method comprises the following steps: obtaining nano onion carbon (D-CNOs) uniformly wrapped by polydopamine by adopting a dopamine polymerization deposition method; then, alendronic acid and D-CNOs are subjected to a Michael addition reaction, and uniformly phosphorylated CNOs (PD-CNOs) are prepared; the preparation process is simple, and the obtained product has a typical onion-like layered structure, is uniform in size, can be widely applied to the field of ion exchange materials as a functional nanofiller, and is particularly suitable for modification and enhancement of polymer electrolyte membranes.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of new energy and environmental functional materials, and particularly relates to a preparation method and application of polydopamine-mediated uniformly phosphonated nano-onion carbon. BACKGROUND

[0002] Carbon-based nanomaterials, with diversified dimensional structures (zero-dimensional nanospheres, one-dimensional nanotubes, and two-dimensional nanosheets) and unique properties, exhibit significant advantages in improving the mechanical integrity and proton conductivity of membrane materials, and have become a current research hotspot. Zero-dimensional nanomaterials can effectively improve the compatibility of organic-inorganic phase interfaces due to their high active edge sites, ultra-small size, and excellent specific surface area characteristics, and are widely used in the development of new composite membrane materials.

[0003] As a typical zero-dimensional carbon-based material, nano-onion carbon (CNOs) is composed of multiple concentric graphite shell layers with a diameter of 5-7 nm. This unique cage-like nanostructure endows CNOs with ultra-small particle size, high reactivity, excellent electrical conductivity, and mechanical chemical stability, as well as the characteristic of easy surface functionalization, making it have wide application potential in energy storage, catalysis, sensing, and water purification. In particular, by introducing rich functional groups on the surface of CNOs, the problem of nanoparticle agglomeration can be effectively inhibited, and it is expected to break through the performance bottleneck of proton conductivity-stability of membrane materials, providing a new solution for the design of high-performance composite membrane materials. According to the literature (Journal of Membrane Science 660 (2022) 120774), on the basis of synthesizing CNOs, phosphonated CNOs (P-CNOs) were successfully prepared through oxidation and hydrothermal reaction, and then ATP was introduced into the SPAES matrix together with P-CNOs to prepare a series of SPAES / ATP / P-CNOs composite membranes. The membrane has good stability and battery performance. However, due to the easy solubility of ATP in water, it will be lost during the actual operation of the fuel cell. If P-CNOs is simply doped into SPAES, it is easy to agglomerate, which is due to the poor compatibility of SPAES and P-CNOs, to some extent, limiting the performance of the proton exchange membrane. Therefore, a simple, efficient, and mild method is needed to prepare phosphonated inorganic nanomaterials with higher water retention capacity and more uniform surface functional groups. SUMMARY

[0004] The purpose of the present application is to design a preparation method and application of polydopamine-mediated uniformly phosphonated nano-onion carbon, which is used as an inorganic filler in a proton exchange membrane, to prepare a composite membrane with better comprehensive performance.

[0005] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: The technical scheme for realizing the purpose of the present application with CNOs as raw materials is as follows: (1) Preparation of carboxylated nano-onion carbon (C-CNOs): CNOs and a certain amount of concentrated sulfuric acid are added into a reaction container, and stirred at room temperature overnight. Concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 1:1 are mixed and slowly dripped into the reaction container. After the liquid is completely dripped, the solution is gradually heated and stirred. After the reaction is completed, the solution in the container is poured into cooled pure water, and then precipitated, centrifuged, washed with water and dried to obtain sample C-CNOs. (2) Preparation of polydopamine modified nano-onion carbon (D-CNOs): C-CNOs powder is dispersed into a certain concentration of dopamine+Tris solution and ultrasonically treated, and then the mixture is added into a reaction container and heated and stirred. After the reaction is completed, the mixture is centrifuged, washed with water and dried to obtain sample D-CNOs. (3) Preparation of polydopamine-mediated uniformly phosphated CNOs (PD-CNOs): A certain amount of D-CNOs powder and alendronate are added into a Tris solution and ultrasonically treated, and then the mixture is added into a reaction container and heated and stirred. After the reaction is completed, the mixture is centrifuged, washed with water and dried to obtain sample PD-CNOs.

[0006] The specific preparation method is as follows: Step 1, preparation of carboxylated nano-onion carbon (C-CNOs) CNOs and a certain amount of concentrated sulfuric acid are added into a three-necked flask, and then the three-necked flask is placed into a magnetic stirrer, wherein the speed of the magnetic stirrer is set to 100 r / min and stirring is performed for 12 h. Concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 1:1 are mixed and poured into a constant-pressure dropping funnel, and then dripped into the three-necked flask. A condenser tube is placed above the three-necked flask, and the temperature of the magnetic stirrer is controlled to 40℃. After the liquid in the constant-pressure dropping funnel is dripped, the magnetic stirrer is heated at a heating rate of 5℃ / min to 60-75℃, and stirring is performed at the temperature for 0.5-2 h. After the reaction is completed, the solution in the flask is poured into cooled pure water, and then precipitated, washed with water, centrifuged and dried to obtain sample C-CNOs.

[0007] Step 2, preparation of polydopamine modified nano-onion carbon (D-CNOs) C-CNOs powder is dispersed into a certain concentration of dopamine+Tris solution, the pH of the Tris solution is 8.5, and ultrasonic treatment is performed for 0.5-1 h. The mixture is added into a reaction container, the rotation speed is 100 r / min, and the reaction is performed at 25-35℃ for 24 h. After the reaction is completed, the mixture is washed with water several times, centrifuged and dried for standby use.

[0008] Step 3, preparation of polydopamine-mediated homogeneous phosphonated CNOs (PD-CNOs) D-CNOs powder and alendronate in a mass ratio of 1:3 were dispersed into a certain amount of Tris solution with a pH of 8.5, and ultrasonic treatment was performed for 0.5-1 h, the mixture was added into a reaction container at a rotation speed of 100 r / min, and reaction was performed at 25-35 DEG C for 24 h. After the reaction was completed, the mixture was washed with ethanol and water each once, and was dried after centrifugation for standby use.

[0009] Further, the volume ratio of the certain amount of concentrated sulfuric acid to the mixed acid of concentrated sulfuric acid / concentrated nitric acid in step 1 is 1-1.5:2.

[0010] Further, the C-CNOs powder in step 2 is dispersed into a certain concentration of dopamine+Tris solution, the dopamine and Tris solution are configured into a dopamine aqueous solution with a concentration of 1.0-3.0 mg / mL, and the mass ratio of the C-CNOs powder to the dopamine is 1:1-1.5.

[0011] Further, the solid-liquid ratio of the mixed amount of D-CNOs / alendronate in step 3 to the Tris solution is 1:0.25-0.5 mg / mL.

[0012] The application of the polydopamine-mediated homogeneous phosphonated nano-onion carbon, as a filler, for preparing a polymer electrolyte membrane, the composite membrane has a proton conductivity as high as 88.1-222.1 mS / cm at 30-90 DEG C, and after Fenton treatment, the mass loss of the membrane is only 2.8%.

[0013] The following beneficial effects can be obtained through the above technical solution: The present application adopts a three-step method of "oxidation reaction-dopamine self-polymerization-Michael addition" to synthesize the homogeneous phosphonated nano-onion carbon (PD-CNOs), and the preparation process is simple and does not require complex conditions, and the operation is controllable; The PD-CNOs have a uniform onion-like ring structure, the uniform polydopamine coating ensures the interface stability and reactivity, and the phosphonated modification endows it with strong ion exchange capacity. As a nano filler, it can effectively improve the proton conductivity and stability of the polymer electrolyte membrane, and especially improve the fuel cell performance of the membrane under low humidity. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 The HRTEM image and the EDS image of the PD-CNOs of Example 1.

[0015] Figure 2 The XPS spectrum of the PD-CNOs of Example 1.

[0016] Figure 3 Infrared spectra of CNOs, C-CNOs, D-CNOs and PD-CNOs of Example 1.

[0017] Figure 4 Schematic diagram of phosphated carbon nano-onion carbon (P-CNOs).

[0018] Figure 5 Schematic diagram of uniform phosphating of the present application. DETAILED DESCRIPTION

[0019] The present application will be further described below in conjunction with the accompanying Figures 1-3 and examples: A preparation method of polydopamine-mediated uniform phosphated nano-onion carbon, taking laboratory-made CNOs as raw material, first performing oxidation reaction with mixed acid of nitric acid / sulfuric acid to generate C-CNOs, then adopting dopamine polymerization deposition method to obtain D-CNOs uniformly coated with polydopamine; finally, performing Michael addition reaction with alendronate and D-CNOs to prepare PD-CNOs. The ion exchange capacity of the prepared PD-CNOs is 1.76-1.95 mmol / g, which is added to sulfonated polyaryl ether sulfone polymer to prepare a composite membrane. In the polymer membrane, on the one hand, the introduced PD-CNOs have rich functional groups (such as -COOH, -NH- / -NH2 and -PO3H2), which endow the particles with good hydrophilicity and dispersity, and improve the compatibility of the organic-inorganic composite membrane; on the other hand, the -PO3H2 group has low zero-point energy, high hydration energy and amphoteric characteristics, which can easily construct low-energy barrier channels and hydrogen bond water bridges, and is conducive to the rapid hopping / diffusion of protons at low relative humidity (RH), so that the composite membrane exhibits superior proton conductivity and durability. Example 1

[0020] Step 1, preparation of carboxylated nano-onion carbon (C-CNOs) Put 0.4 g of CNOs and 25 mL of concentrated sulfuric acid into a 100 mL three-necked flask, and then put the three-necked flask into a magnetic stirrer, at this time the speed of the magnetic stirrer is set to 100 r / min, and stirring is performed for 12 h. After mixing 25 mL of concentrated sulfuric acid and 25 mL of concentrated nitric acid, pour them into a constant pressure dropping funnel, and then drop them into the three-necked flask. A condenser tube is placed above the three-necked flask, and at this time the temperature of the magnetic stirrer is controlled to 40℃. After the liquid in the constant pressure funnel is dropped, the magnetic stirrer is heated to 60℃ at a heating rate of 5℃ / min, and stirring is performed at this temperature for 2 h. After the reaction is completed, pour the solution in the flask into cooled pure water, stand for precipitation, and then wash with water, centrifuge and dry to obtain sample C-CNOs.

[0021] Step 2, preparation of polydopamine-modified nano-onion carbon (D-CNOs) Place 150 mg of C-CNOs powder, 0.2 g of dopamine, and 100 mL of Tris solution (pH 8.5) in a 250 mL flask. Cool and sonicate the solution for 0.5–1 h. Stir the flask in a magnetic stirrer at 100 rpm for 24 h at 25°C. After the reaction, rinse the mixture several times with water, centrifuge, and dry to obtain the D-CNOs sample.

[0022] Step 3. Preparation of polydopamine-mediated uniformly phosphorylated CNOs (PD-CNOs) Place 0.1 g of D-CNOs powder and 0.3 g of alendronate in a 250 mL flask. Add 150 mL of Tris solution (pH 8.5) and sonicate for 0.5–1 h. Place the flask in a reaction vessel, rotate at 100 rpm, and allow the reaction to continue at 25°C for 24 h. After the reaction, rinse the mixture once with ethanol and once with water, then centrifuge and dry to obtain the PD-CNOs sample.

[0023] Figure 1 HRTEM images and EDS images of PD-CNOs; Figure 2 is the XPS spectrum of PD-CNOs; Figure 3 Contains infrared spectra of CNOs, C-CNOs, D-CNOs and PD-CNOs. Example 2

[0024] Step 1, Preparation of Carboxylated Nano-onion Carbons (C-CNOs) Place 0.4 g of CNOs and 30 mL of concentrated sulfuric acid in a 100 mL three-necked flask. Stir the flask at 100 rpm for 12 hours. Then, pour a mixture of 25 mL of concentrated sulfuric acid and 25 mL of concentrated nitric acid into a constant-pressure dropping funnel and drip it dropwise into the flask. A condenser should be placed above the flask, and the magnetic stirrer should be maintained at 40°C. After the addition of the liquid to the constant-pressure funnel, heat the magnetic stirrer at a rate of 5°C / min to 70°C and stir at this temperature for 1.5 hours. After the reaction, pour the solution into cooled pure water, let it settle, then rinse, centrifuge, and dry to obtain the C-CNOs sample.

[0025] Step 2, Preparation of polydopamine-modified nanocarbon onions (D-CNOs) Put 200 mg C-CNOs powder, 0.2 g dopamine and 200 mL Tris solution into a 250 mL flask, the pH of the Tris solution is 8.5, and the cooling ultrasonic treatment is 0.5-1 h. Put the flask into the magnetic stirrer and stir for 24 h at 100 r / min, and react at 30℃ for 24 h. After the reaction is completed, wash the mixture with water several times, then centrifuge, dry and obtain sample D-CNOs.

[0026] Step 3, preparation of polydopamine-mediated homogeneously phosphorylated CNOs (PD-CNOs) Put 0.1 g D-CNOs powder and 0.3 g alendronate into a 250 mL flask, then add 100 mL Tris solution, the pH of the Tris solution is 8.5, and ultrasonic treatment is 0.5-1 h. Put the flask into the reaction container, stir at 100 r / min, and react at 30℃ for 24 h. After the reaction is completed, wash the mixture with ethanol and water each once, then centrifuge, dry and obtain sample PD-CNOs. Example 3

[0027] Step 1, preparation of carboxylated nano-onion carbon (C-CNOs) Put 0.4 g CNOs and 40 mL concentrated sulfuric acid into a 250 mL three-necked flask, then put the three-necked flask into a magnetic stirrer, at this time the magnetic stirrer is set to 100 r / min, and stir for 12 h. Mix 30 mL concentrated sulfuric acid and 30 mL concentrated nitric acid, then pour them into a constant pressure dropping funnel and drop them into the three-necked flask. A condenser tube is placed above the three-necked flask, at this time the temperature of the magnetic stirrer is controlled to 40℃. After the liquid in the constant pressure funnel is dropped, the magnetic stirrer is heated to 75℃ at a heating rate of 5℃ / min, and stirred at this temperature for 1 h. After the reaction is completed, pour the solution in the flask into cooled pure water, stand for precipitation, then wash with water, centrifuge and dry to obtain sample C-CNOs.

[0028] Step 2, preparation of polydopamine-modified nano-onion carbon (D-CNOs) Put 200 mg C-CNOs powder, 0.3 g dopamine and 100 mL Tris solution into a 250 mL flask, the pH of the Tris solution is 8.5, and the cooling ultrasonic treatment is 0.5-1 h. Put the flask into the magnetic stirrer and stir for 24 h at 100 r / min, and react at 35℃ for 24 h. After the reaction is completed, wash the mixture with water several times, then centrifuge, dry and obtain sample D-CNOs.

[0029] Step 3, preparation of polydopamine-mediated homogeneously phosphorylated CNOs (PD-CNOs) Put 0.1 g of D-CNOs powder and 0.3 g of alendronate into a 250 mL flask, then add 200 mL of Tris solution with pH 8.5, and ultrasonic treatment for 0.5-1 h. Put the flask into the reaction container with a rotation speed of 100 r / min, and react at 35℃ for 24 h. After the reaction is completed, wash the mixture with ethanol and water each once, then centrifuge, dry, and obtain sample PD-CNOs. Example 4

[0030] Preparation of PD-CNOs doped polymer electrolyte membrane (SPAES-1.5wt%PD-CNOs) and fuel cell performance: Put 0.5 g of sulfonated polyarylether sulfone SPAES with a sulfonation degree of 45% into 8 mL of N,N-dimethylformamide (DMAc), and stir at room temperature for 48 h to obtain mixed solution A, and meanwhile, dissolve 75 mg of PD-CNOs powder prepared in Example 1 in 3 mL of DMAc, ultrasonic treatment for 1 h, and stir at room temperature for 12 h to obtain solution B. Blend solution A and B, and stir at room temperature for 24 h to obtain a mixed casting solution. Slowly pour the mixed casting solution into a super-horizon film pouring plate, and the casting oven is programmed to increase the temperature as follows: 50℃, 6 h→80℃, 10 h→120℃, 2 h. After the composite membrane is taken out, immerse it in 1 M HCl solution for 72 h, then wash with deionized water until neutral, and obtain the composite membrane SPAES-1.5wt%PD-CNOs.

[0031] Test the performance of the prepared composite membrane: the IEC of the composite membrane SPAES-1.5wt%PD-CNOs reaches 1.72 mmol / g, and the conductivity in water at 90℃ is as high as 222.1 mS / cm. In the H2 / O2 fuel cell test, the maximum output power of the cell is 550 mW / cm under the condition of 80℃@60%RH, which is 150% higher than that of the undoped SPAES membrane.

[0032] The present application and patent publication No. CN113979426B, entitled "Phosphoric acid grafted nano-onion carbon and preparation method and application thereof" (hereinafter referred to as the comparative example), use two completely different modification methods and modification materials for nano-onion carbon, and the final products are also different (as shown in Figure 4 and 5 ), and the specific differences are as follows: 1. The preparation methods of C-CNOs in the present application and the comparative example are different, and the proportions of mixed acids and the synthesis methods (heating temperature, time, and heating rate, etc.) are also different. The carboxylic acid content obtained by the present application is 20-30%, and the carboxylic acid content of the comparative example is ~40%. However, too high carboxylic acid content will cause the nano-particles to absorb water and agglomerate, which is not conducive to further modification. 2、The PD-CNOs of the application and the P-CNOs of the comparative example use completely different materials. The performance of the application applied to the polymer electrolyte membrane is also greatly improved. The application is to modify the C-CNOs with polydopamine (DPA) first. DPA can not only provide more functional groups (-NH2 and -NH-), but also facilitate the uniform grafting of alendronate to the particle surface in the later stage. Both can synergistically promote the compatibility between nanoparticles and polymers, and also provide additional proton transfer sites. The P-CNOs of the comparative example only graft phytic acid directly on the basis of C-CNOs. Phosphoric acid is non-uniformly grafted on the surface of the particles. At the same time, the surface of the particles has no basic groups. The P-CNO particles are prone to agglomeration in the polymer, and the proton transfer sites are few and single.

[0033] The performance comparison of the PD-CNOs of the application and the P-CNOs of the comparative example applied to the polymer membrane is shown in the following table: The above are preferred embodiments of the application. For those skilled in the art, various equivalent modifications of the application without departing from the principles of the application are within the scope of protection of the appended claims. The above are preferred embodiments of the application. For those skilled in the art, various equivalent modifications of the application without departing from the principles of the application are within the scope of protection of the appended claims.

Claims

1. A method for preparing uniformly phosphorylated nano-onion carbon mediated by polydopamine, characterized in that: The method is as follows Step (1): preparation of carboxylated nano-onion carbon C-CNOs: CNOs and a certain amount of concentrated sulfuric acid were added to a reaction vessel, stirred at room temperature overnight, and then mixed with concentrated nitric acid at a volume ratio of 1:1 and slowly dropped into the reaction vessel. After the liquid was completely dropped, the temperature was gradually increased and heated and stirred. After the reaction was completed, the solution in the vessel was poured into cooled pure water, allowed to stand and precipitate, and then centrifuged, washed with water, and dried to obtain sample C-CNOs. Step (2): preparation of polydopamine-modified nano-onion carbon D-CNOs: The C-CNOs powder obtained in step (1) was dispersed in a dopamine+Tris solution of a certain concentration and ultrasonically treated, and then the mixture was added to a reaction vessel and heated and stirred. After the reaction was completed, the sample D-CNOs was obtained by centrifugation, water washing, and drying. Step (3): preparation of polydopamine-mediated uniformly phosphated CNOs PD-CNOs: A certain amount of D-CNOs powder obtained in step (2) and alendronate were placed in a Tris solution and ultrasonically treated, and then the mixture was added to a reaction vessel and heated and stirred. After the reaction was completed, the sample PD-CNOs was obtained by centrifugation, water washing, and drying.

2. The method of claim 1, wherein the method is characterized by: In step (1), the volume ratio of the certain amount of concentrated sulfuric acid to the mixed acid of concentrated sulfuric acid / concentrated nitric acid is 1-1.5:

2.

3. The method of claim 1, wherein the method is characterized by: In step (1), the magnetic stirrer is used to realize the gradual heating and stirring, and the temperature is increased to 60-75℃ at a rate of 5℃ / min, and the stirring is continued at this temperature for 0.5-2 h.

4. The method of claim 1, wherein the method is characterized by: In step (2), the C-CNOs powder is dispersed in a dopamine+Tris solution of a certain concentration, and the dopamine and Tris solution are configured into a dopamine aqueous solution with a concentration of 1.0-3.0 mg / mL. The mass ratio of C-CNOs powder to dopamine is 1:1-1.

5.

5. The method of claim 1, wherein the method is characterized by: In steps (2) and (3), the stirring speed is 100 r / min, the temperature is heated to 25-35℃, and the reaction is carried out for 24 h.

6. The method of claim 1, wherein the method is characterized by: In step (3), the mass ratio of D-CNOs powder to alendronate is 1:3, the solid-liquid ratio of the mixture of D-CNOs and alendronate to Tris solution is 1:0.25-0.5 mg / mL, and the pH of the Tris solution is 8.

5.

7. A polydopamine-mediated uniformly phosphated nano-onion carbon obtained according to any one of claims 1-6.

8. Use of polydopamine-mediated homogeneously phosphorylated nano-onion carbon, characterized in that, As a filler, used for preparing a polymer electrolyte membrane.

9. The use according to claim 1, characterized in that, The polymer electrolyte membrane has a proton conductivity of 88.1-222.1 mS / cm at 30-90℃, and after Fenton treatment, the mass loss of the membrane is only 2.8%.

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