Nitrogen-doped hierarchical porous hollow carbon spheres, and preparation method and application thereof

Abstract

The application discloses a preparation method of nitrogen-doped multi-level hole hollow carbon spheres, and relates to the technical field of electrochemical desalination. The preparation method is as follows: melamine and formaldehyde are condensed to form a spherical template in the presence of PVP; resorcinol and HMTA form a phenolic resin coating layer on the surface of the template; high-temperature calcination is performed to realize template decomposition and carbonization, and a double bond is introduced through a silane coupling agent; a phosphoryl chloride group is introduced through free radical polymerization; finally, a sulfonic acid group is grafted through nucleophilic substitution to obtain the final product; through a hollowing strategy and surface modification, the nitrogen-doped hollow carbon spheres with multi-level hole structure are prepared, and the introduction of the phosphoryl chloride group and the sulfonic acid group realizes the synergy of N, P and S ternary heteroatoms, so that the material has a high specific surface area, an optimized pore structure and a strong ion exchange capacity, exhibits excellent ion adsorption performance and cycle stability, and has a good application prospect in the field of capacitive deionization.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrochemical desalination, in particular to a nitrogen-doped multi-level porous hollow carbon sphere, a preparation method and application thereof. BACKGROUND

[0002] With the rapid development of science and technology, hollow carbon spheres have attracted increasing attention in the field of advanced nanocomposites due to their unique structural characteristics. Hollow carbon spheres, also known as carbon capsules, are carbon particles with hollow structures, ranging in size from millimeters to nanometers, and have a unique thin shell structure. Due to the combination of the properties of internal and external materials, as well as excellent chemical stability and thermal stability, hollow carbon spheres have shown great application potential in fuel cells, supercapacitors, and hydrogen storage.

[0003] Currently, the world is facing a severe water resource crisis. Economic development, population growth, and water pollution have led to a growing scarcity of freshwater resources, and the supply of clean water resources has become one of the major challenges facing human society in the 21st century. Given the abundant reserves of seawater and brackish water worldwide, developing efficient seawater desalination technology is of great significance to ensuring the sustainable development of human society.

[0004] Among the various seawater desalination technologies, capacitive deionization technology (CDI) has received increasing attention in recent years due to its low cost, low energy consumption, and environmental friendliness. The core of this technology lies in the performance of electrode materials, and ideal electrode materials should have high specific surface area, excellent chemical stability, and good electrical conductivity. Hollow carbon spheres have shown great application potential in CDI due to their unique structural characteristics.

[0005] CN118398389A discloses a preparation and application of a Prussian blue analogue anchored porous carbon sphere electrode material, including the following steps: placing the prepared porous carbon sphere material in a mixed acid solution, condensing and refluxing, then soaking, washing the YSPCs material until the waste liquid is neutral, vacuum drying, and grinding for use. The pretreated YSPCs material is added to deionized water containing polyvinylpyrrolidone, ultrasonic dispersion is performed to form a uniform suspension, Na4Fe(CN)6 solution is slowly added to the suspension, the mixture is heated and stirred to generate a blue-black precipitate, the blue-black precipitate product is washed, vacuum dried, and ground to obtain composite nanoparticles. The composite nanoparticles, carbon black, and polytetrafluoroethylene are mixed in alcohol, coated on graphite paper to prepare the positive and negative electrodes of a CDI desalination device.

[0006] However, the existing hollow carbon sphere preparation technology still has the following problems: 1. The preparation process requires the introduction of additional substances, increasing the process complexity; 2. The preparation process is complicated and energy-intensive; 3. The production cost is high, which is not conducive to large-scale application; 4. The environmental performance needs to be improved.

[0007] Therefore, developing an energy-saving, environment-friendly, low-cost preparation method of hollow carbon spheres has important practical significance for promoting the practical application of CDI technology. The nitrogen-doped multi-level pore hollow carbon sphere and the preparation method thereof provided by the application not only solve the problems in the prior art, but also further improve the performance of the material in the application of CDI through the design of nitrogen doping and multi-level pore structure. SUMMARY

[0008] In order to solve the problems in the prior art, the purpose of the present application is to provide a nitrogen-doped multi-level pore hollow carbon sphere and a preparation method and application thereof. The nitrogen-doped multi-level pore hollow carbon sphere is prepared by hollowing strategy and surface modification, and the N, P and S ternary heteroatom synergy is realized by introducing phosphoryl chloride groups and sulfonic acid groups, so that the material has high specific surface area, optimized pore structure and strong ion exchange capacity, exhibits excellent ion adsorption performance and cycle stability, and has good application prospect in the field of capacitive deionization.

[0009] In order to achieve the above purpose, the application adopts the following technical scheme:

[0010] A preparation method of a nitrogen-doped multi-level pore hollow carbon sphere, comprising the following steps:

[0011] (1) Dissolve melamine and polyvinylpyrrolidone in deionized water, heat to form a transparent solution, and uniformly mix with a formaldehyde aqueous solution. After adding glacial acetic acid to the mixed solution, continue to stir, centrifuge, wash and dry to obtain a template.

[0012] Melamine and formaldehyde undergo condensation reaction to form a three-dimensional network structure under acidic conditions. Polyvinylpyrrolidone (PVP) acts as a dispersant and stabilizer to control the condensation process through hydrogen bonding, so that the reaction product forms a uniform spherical structure.

[0013] Preferably, in step (1), the mass-volume ratio of melamine, polyvinylpyrrolidone, formaldehyde solution and glacial acetic acid is 1-2 g: 1-2 g: 5-10 mL: 0.3-1.2 mL, and the concentration of the formaldehyde aqueous solution is 30-40 wt%. The heating condition is 70-90℃, 100-300r / min stirring for 5-15min; the mixing condition is 100-300r / min stirring for 30-60min; after adding glacial acetic acid, continue to stir at 200-500r / min, 70-90℃ for 1-5h.

[0014] (2) Disperse the template in deionized water, add polyvinylpyrrolidone and stir uniformly, then add resorcinol, hexamethylenetetramine and ammonia water and continue to stir. After stirring, centrifuge, wash and dry to obtain a precursor.

[0015] Hexamethylenetetramine (HMTA) slowly decomposes to release formaldehyde under heating condition, which reacts with resorcinol to form phenolic resin and provides part of nitrogen source; ammonia provides stable alkaline environment and controls the reaction rate. PVP guides the monomer to grow on the template surface by π-π interaction and hydrogen bonding. The phenolic resin generated under alkaline condition uniformly coats on the template surface to form a nitrogen-containing core-shell structure precursor.

[0016] Preferably, in step (2), the mass-volume ratio of the template, polyvinylpyrrolidone, resorcinol, hexamethylenetetramine and ammonia is 0.2-1 g:2-5 g:0.4-1.2 g:1-3 g:10-30 μL; after adding polyvinylpyrrolidone, stirring at 100-300 r / min for 1-5 h, after adding ammonia, stirring at 100-300 r / min at 30-50 ℃ for 1-5 h, and then heating to 70-90 ℃ for 20-30 h.

[0017] (3) The precursor is placed in a nitrogen atmosphere, heated and calcined to obtain hollow carbon spheres; the hollow carbon spheres and glacial acetic acid are added to anhydrous tetrahydrofuran, ultrasonically dispersed uniformly, then KH570 is added, refluxed, the product is centrifuged, washed and dried to obtain alkenyl carbon spheres;

[0018] The precursor is calcined at high temperature in a nitrogen atmosphere, the template is decomposed and the phenolic resin is carbonized to form a nitrogen-containing hollow carbon sphere structure. Subsequent surface modification: KH570 is first hydrolyzed to generate silanol under acid catalysis, and forms Si-O-C covalent bond with the hydroxyl group on the surface of the carbon sphere by condensation reaction, introducing double bond functional groups on the surface.

[0019] Preferably, in step (3), the temperature is raised to 700-900 ℃ at a rate of 2 ℃ / min and calcined for 1 h.

[0020] Preferably, in step (3), the hollow carbon spheres, glacial acetic acid, anhydrous tetrahydrofuran and KH570 are used in a ratio of 10 g:1-2 mL:80-120 mL:3-8 mL.

[0021] Preferably, in step (3), ultrasonic dispersion is performed for 15-30 min; the reflux reaction conditions are refluxing at 55-70 ℃ for 6-12 h.

[0022] (4) The alkenyl carbon spheres and AIBN are added to anhydrous tetrahydrofuran, ultrasonically dispersed in a nitrogen atmosphere and in the dark, and vinyl phosphonic dichloride is slowly added dropwise, and the product is centrifuged, washed and dried to obtain acyl chloride carbon spheres;

[0023] AIBN decomposes to generate free radicals under heating condition, which initiates free radical graft polymerization of the double bond on the surface of the carbon sphere with vinyl phosphonic dichloride to form grafted phosphonyl chloride groups on the surface of the carbon sphere.

[0024] Preferably, in step (4), the amount ratio of alkenylized carbon spheres, AIBN, anhydrous tetrahydrofuran and vinyl phosphonic chloride is 10g: 0.5-1.5g: 80-120mL: 5-10mL.

[0025] Preferably, in step (4), the ultrasonic dispersion is performed for 10-20min; and the stirring reaction is performed at 45-60℃ for 6-18h.

[0026] (5) adding acyl chloride carbon spheres and DMAP into DMF, ultrasonic dispersion, adding p-aminobenzenesulfonic acid and triethylamine, stirring reaction, centrifugation, washing and drying the product to obtain the nitrogen-doped multi-level porous hollow carbon spheres.

[0027] The acyl chloride groups on the surface of the acyl chloride carbon spheres undergo nucleophilic substitution reaction with p-aminobenzenesulfonic acid, DMAP acts as a catalyst, and triethylamine acts as an alkaline reagent to capture the generated HCl. The reaction connects the sulfonic acid groups to the surface of the carbon spheres through amide bonds, and finally obtains the nitrogen-doped multi-level porous hollow carbon spheres with sulfonic acid functional groups.

[0028] Preferably, in step (5), the amount ratio of acyl chloride carbon spheres, DMAP, DMF, p-aminobenzenesulfonic acid and triethylamine is 10g: 0.2-0.6g: 80-120mL: 3-6g: 2-4mL.

[0029] Preferably, in step (5), the ultrasonic dispersion is performed for 10-20min; and the stirring reaction is performed at 20-45℃ for 4-12h.

[0030] The application also claims a nitrogen-doped multi-level porous hollow carbon sphere prepared by the preparation method.

[0031] The application also claims the application of the nitrogen-doped multi-level porous hollow carbon sphere in capacitive deionization.

[0032] Compared with the prior art, the application has the following beneficial effects:

[0033] 1. The application provides a preparation method of nitrogen-doped multi-level porous hollow carbon spheres, which uses melamine-formaldehyde resin spheres as a template to realize uniform and controllable spherical structure in the presence of PVP; in the coating process of the template surface phenolic resin, the synergistic effect of HMTA and ammonia ensures the uniformity of the coating; in the subsequent pyrolysis process, the template can be automatically degraded without additional acid-base treatment, while carbonization and nitrogen doping are realized, greatly simplifying the preparation process. This method not only produces multi-level porous hollow carbon spheres with high specific surface area and optimized pore volume, but also enhances the hydrophilicity of the pore surface through the doping of nitrogen atoms, providing more active sites for ion adsorption, thereby exhibiting excellent NaCl adsorption performance. The entire preparation process is simple to operate, the process parameters are controllable, the product quality is stable, and it has good reproducibility and industrialization potential.

[0034] 2. The application provides a preparation method of nitrogen-doped multi-level porous hollow carbon spheres, which realizes further optimization of material performance through subsequent introduction of phosphoryl chloride groups and modification of sulfonic acid groups: first, the introduction of phosphorus-containing groups on the surface of the carbon spheres through controlled radical polymerization enhances the electronic conductivity and surface polarity of the material; then, the sulfonic acid groups are grafted on the surface through a mild nucleophilic substitution reaction, providing efficient ion exchange sites. The synergistic effect of the three heteroatoms N, P and S significantly improves the ion adsorption capacity and transmission efficiency of the material, while maintaining the original multi-level pore structure and high specific surface area characteristics of the material. The introduction of sulfonic acid groups also endows the material with excellent ion selectivity, enabling it to exhibit fast ion transport kinetics and excellent cycle stability during capacitive deionization, making it particularly suitable for application in water desalination and heavy metal ion removal. BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the application, the following will briefly introduce the drawings needed to be used in the embodiments, and it should be understood that the following drawings only show some embodiment schematic diagrams of the application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0036] Figure 1 The scanning electron microscope picture of the nitrogen-doped hollow carbon spheres in Example 1 of the application. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of the application more clear, the following will further describe the application in combination with embodiments. Of course, the specific embodiments described here are only used to explain the application, and are not used to limit the application.

[0038] Unless otherwise specified, the chemicals and materials in the present application are purchased through market channels or synthesized from raw materials purchased through market channels.

[0039] A preparation method of a nitrogen-doped multi-level pore hollow carbon sphere, comprising the following steps:

[0040] (1) 1-2 g of melamine and 1-2 g of polyvinylpyrrolidone are dissolved in 100 mL of deionized water, stirred at 70-90 °C and 100-300 r / min for 5-15 min to form a transparent solution, and 5-10 mL of 30-40 wt% formaldehyde aqueous solution is added and stirred at 100-300 r / min for 30-60 min to mix uniformly, 0.3-1.2 mL of glacial acetic acid is added to the mixed solution, and stirring is continued at 200-500 r / min and 70-90 °C for 1-5 h, after stirring is completed, centrifugation, washing, and drying are performed to prepare a template;

[0041] (2) 0.2-1 g of the template is dispersed in 40-80 mL of deionized water, 2-5 g of polyvinylpyrrolidone is added and stirred at 100-300 r / min for 1-5 h, 0.4-1.2 g of resorcinol, 1-3 g of hexamethylenetetramine, and 10-30 μL of 10 wt% ammonia water are added, stirring is performed at 30-50 °C and 100-300 r / min for 1-5 h, then the temperature is increased to 70-90 °C, and stirring is performed at 100-300 r / min for 20-30 h, after stirring is completed, centrifugation, washing, and drying are performed to prepare a precursor;

[0042] (3) the precursor is placed in a nitrogen atmosphere, heated to 700-900 °C at a heating rate of 2 °C / min, and calcined for 1 h to prepare a hollow carbon sphere; 10 g of the hollow carbon sphere and 1-2 mL of glacial acetic acid are added to 80-120 mL of anhydrous tetrahydrofuran, ultrasonic dispersion is performed for 15-30 min, then 3-8 mL of KH570 is added, reflux reaction is performed at 55-70 °C for 6-12 h, the product is centrifuged, washed, and dried to obtain an alkenylated carbon sphere;

[0043] (4) 10 g of the alkenylated carbon sphere and 0.5-1.5 g of AIBN are added to 80-120 mL of anhydrous tetrahydrofuran, ultrasonic dispersion is performed for 10-20 min in a nitrogen atmosphere and in the dark, 5-10 mL of vinyl phosphonic dichloride is slowly added dropwise, stirring is performed at 45-60 °C for 6-18 h, the product is centrifuged, washed, and dried to obtain an acyl chloride carbon sphere;

[0044] (5) 10 g of the acyl chloride carbon sphere and 0.2-0.6 g of DMAP are added to 80-120 mL of DMF, ultrasonic dispersion is performed for 10-20 min, 3-6 g of p-aminobenzenesulfonic acid and 2-4 mL of triethylamine are added, stirring is performed at 20-45 °C for 4-12 h, the product is centrifuged, washed, and dried to obtain the nitrogen-doped multi-level pore hollow carbon sphere.

[0045] The application will be further described below by specific examples.

[0046] Example 1

[0047] A preparation method of nitrogen-doped multi-level porous hollow carbon spheres, comprising the following steps:

[0048] (1) 1.26 g of melamine and 1.2 g of F127 are dissolved in 100 mL of deionized water, heated to 80°C to form a transparent solution, then stirred at a speed of 100 r / min for 5 min; then 5 mL (37 wt% aqueous solution) of formaldehyde solution is added, and stirring is continued for 30 min; then 0.5 mL of glacial acetic acid is added, and stirring is carried out at 80°C at a speed of 350 rpm for 2 h; finally, the melamine-formaldehyde resin sphere template is collected by centrifugation at a speed of 4000 rpm, and washed with water and ethanol to remove residual impurities, and dried at 80°C to obtain the melamine-formaldehyde resin sphere template;

[0049] (2) 0.5 g of the melamine-formaldehyde resin sphere template is dispersed in 40 mL of deionized water, and a uniform suspension is formed by ultrasonic treatment for 30 min; then 3.0 g of F127 is added, and stirring is carried out for 2 h; then 0.4 g of resorcinol and 1.0 g of hexamethylenetetramine, 20 μL of ammonia water are added, and the reaction is carried out at 35°C for 1 h; then the temperature is increased to 80°C, and the reaction is carried out for 24 h, after which the precipitate is collected by centrifugation, and washed with water and ethanol to remove unreacted components, to obtain a brown powder of nitrogen-doped precursor;

[0050] (3) 0.1 g of the nitrogen-doped precursor powder is calcined at 800°C for 1 h at a temperature increasing rate of 2°C / min in a nitrogen atmosphere, and the obtained black powder is nitrogen-doped multi-level porous hollow carbon spheres; 10 g of the hollow carbon spheres and 2 mL of glacial acetic acid are added to 100 mL of anhydrous tetrahydrofuran, ultrasonic dispersion is carried out for 30 min, then 8 mL of KH570 is added, and reflux reaction is carried out at 70°C for 6 h, after which the product is centrifuged, washed, and dried to obtain alkenylated carbon spheres;

[0051] (4) 10 g of the alkenylated carbon spheres and 1.5 g of AIBN are added to 100 mL of anhydrous tetrahydrofuran, ultrasonic dispersion is carried out for 20 min in a nitrogen atmosphere and in the dark, 10 mL of vinyl phosphonic dichloride is slowly added dropwise, and stirring reaction is carried out at 60°C for 6 h, after which the product is centrifuged, washed, and dried to obtain acyl chloride carbon spheres;

[0052] (5) 10 g of the acyl chloride carbon spheres and 0.6 g of DMAP are added to 100 mL of DMF, ultrasonic dispersion is carried out for 20 min, 6 g of p-aminobenzenesulfonic acid and 4 mL of triethylamine are added, and stirring reaction is carried out at 45°C for 4 h, after which the product is centrifuged, washed, and dried to obtain the nitrogen-doped multi-level porous hollow carbon spheres.

[0053] Example 2

[0054] A preparation method of nitrogen-doped multi-level porous hollow carbon spheres, comprising the following steps:

[0055] (1) 1.26 g of melamine and 1.2 g of F127 are dissolved in 100 mL of deionized water, heated to 80°C to form a transparent solution, then stirred at a speed of 100 r / min for 5 min; then 5 mL (37 wt% aqueous solution) of formaldehyde solution is added, and stirring is continued for 30 min; then 0.5 mL of glacial acetic acid is added, and stirring is carried out at 80°C at a speed of 350 rpm for 2 h; finally, the melamine-formaldehyde resin sphere template is collected by centrifugation at a speed of 4000 rpm, and washed with water and ethanol to remove residual impurities, and dried at 80°C to obtain melamine-formaldehyde resin spheres;

[0056] (2) 0.5 g of MF spheres are dispersed in 40 mL of deionized water, and a uniform suspension is formed by ultrasonic treatment for 30 min; then 3.0 g of F127 is added and stirred for 2 h; then 0.8 g of resorcinol and 1.0 g of hexamethylenetetramine are added, and 20 μL of ammonia water is added after 30 min, and the reaction is maintained at 35°C for 1 h; then the temperature is increased to 80°C, and after 24 h of reaction, the precipitate is collected by centrifugation, and washed with water and ethanol to remove unreacted components, to obtain a brown powder of nitrogen-doped precursor;

[0057] (3) 0.1 g of the nitrogen-doped precursor powder is calcined at 800°C for 1 h at a temperature increasing rate of 2°C / min in a nitrogen atmosphere, and the obtained black powder is nitrogen-doped multi-level porous hollow carbon spheres; 10 g of hollow carbon spheres and 1.5 mL of glacial acetic acid are added to 100 mL of anhydrous tetrahydrofuran, ultrasonically dispersed for 30 min, then 6 mL of KH570 is added, and refluxed at 65°C for 8 h; the product is centrifuged, washed, and dried to obtain alkenylated carbon spheres;

[0058] (4) 10 g of alkenylated carbon spheres and 1.2 g of AIBN are added to 100 mL of anhydrous tetrahydrofuran, ultrasonically dispersed for 20 min in a nitrogen atmosphere and in the dark, 8 mL of vinyl phosphonic dichloride is slowly added dropwise, and stirred at 55°C for 10 h; the product is centrifuged, washed, and dried to obtain acyl chloride carbon spheres;

[0059] (5) 10 g of acyl chloride carbon spheres and 0.4 g of DMAP are added to 100 mL of DMF, ultrasonically dispersed for 20 min, 5 g of p-aminobenzenesulfonic acid and 3 mL of triethylamine are added, and stirred at 40°C for 6 h; the product is centrifuged, washed, and dried to obtain the nitrogen-doped multi-level porous hollow carbon spheres.

[0060] Example 3

[0061] A preparation method of nitrogen-doped multi-level porous hollow carbon spheres, comprising the following steps:

[0062] (1) 1.26 g of melamine and 1.2 g of F127 were dissolved in 100 mL of deionized water, heated to 80°C to form a transparent solution, and then stirred at a speed of 100 r / min for 5 min; then 5 mL (37 wt% aqueous solution) of formaldehyde solution was added, and stirring was continued for 30 min; then 0.5 mL of glacial acetic acid was added, and stirring was carried out at 80°C at a speed of 350 rpm for 2 h; finally, the melamine-formaldehyde resin sphere template was collected by centrifugation at a speed of 4000 rpm, and washed with water and ethanol to remove residual impurities, and dried at 80°C to obtain melamine-formaldehyde resin spheres;

[0063] (2) 0.5 g of MF spheres were dispersed in 40 mL of deionized water, and a uniform suspension was formed by ultrasonic treatment for 30 min; then 3.0 g of F127 was added and stirred for 2 h; then 1.2 g of resorcinol and 1.0 g of hexamethylenetetramine were added, and 20 μL of ammonia water was added after 30 min, and the reaction was maintained at 35°C for 1 h; then the temperature was increased to 80°C, and after 24 h of reaction, the precipitate was collected by centrifugation, and washed with water and ethanol to remove unreacted components, to obtain a brown powder of nitrogen-doped precursor;

[0064] (3) 0.1 g of the nitrogen-doped precursor powder was calcined at 800°C for 1 h at a temperature increasing rate of 2°C / min in a nitrogen atmosphere, and the obtained black powder was nitrogen-doped multi-level porous hollow carbon spheres; 10 g of hollow carbon spheres and 1.5 mL of glacial acetic acid were added to 100 mL of anhydrous tetrahydrofuran, and ultrasonic dispersion was carried out for 30 min, then 5 mL of KH570 was added, and reflux reaction was carried out at 60°C for 10 h, and the product was centrifuged, washed, and dried to obtain alkenylated carbon spheres;

[0065] (4) 10 g of alkenylated carbon spheres and 0.8 g of AIBN were added to 100 mL of anhydrous tetrahydrofuran, and ultrasonic dispersion was carried out for 20 min in a nitrogen atmosphere and in the dark, 6 mL of vinyl phosphonic dichloride was slowly added dropwise, and stirring reaction was carried out at 50°C for 14 h, and the product was centrifuged, washed, and dried to obtain acyl chloride carbon spheres;

[0066] (5) 10 g of acyl chloride carbon spheres and 0.4 g of DMAP were added to 100 mL of DMF, and ultrasonic dispersion was carried out for 20 min, 4 g of p-aminobenzenesulfonic acid and 3 mL of triethylamine were added, and stirring reaction was carried out at 35°C for 10 h, and the product was centrifuged, washed, and dried to obtain the nitrogen-doped multi-level porous hollow carbon spheres.

[0067] Example 4

[0068] A preparation method of nitrogen-doped multi-level porous hollow carbon spheres, comprising the following steps:

[0069] (1) 1.26 g melamine and 1.2 g F127 were dissolved in 100 mL deionized water, heated to 80 °C to form a transparent solution, then stirred at a speed of 100 r / min for 5 min; then 5 mL (37 wt% aqueous solution) formaldehyde solution was added, and stirring was continued for 30 min; then 0.5 mL glacial acetic acid was added, and stirring was carried out at 80 °C at a speed of 350 rpm for 2 h; finally, the melamine-formaldehyde resin sphere template was collected by centrifugation at a speed of 4000 rpm, and washed with water and ethanol to remove residual impurities, and dried at 80 °C to obtain melamine-formaldehyde resin spheres;

[0070] (2) 0.5 g MF spheres were dispersed in 40 mL deionized water, and a uniform suspension was formed by ultrasonic treatment for 30 min; then 3.0 g F127 was added, and stirred for 2 h; then 1.2 g resorcinol and 1.0 g hexamethylenetetramine were added, and 20 μL ammonia water was added after 30 min, and the reaction was maintained at 35 °C for 1 h; then the temperature was increased to 80 °C, and after 24 h of reaction, the precipitate was collected by centrifugation, and washed with water and ethanol to remove unreacted components, to obtain a brown powder nitrogen-doped precursor;

[0071] (3) 0.1 g of the nitrogen-doped precursor powder was calcined at 800 °C for 1 h under a nitrogen atmosphere at a temperature increase rate of 2 °C / min, and the obtained black powder was a nitrogen-doped multi-level porous hollow carbon sphere; 10 g of the hollow carbon sphere, 1 mL of glacial acetic acid were added to 100 mL of anhydrous tetrahydrofuran, and ultrasonic dispersion was carried out for 30 min, then 3 mL of KH570 was added, and reflux reaction was carried out at 55 °C for 12 h, and the product was centrifuged, washed, and dried to obtain an alkenylated carbon sphere;

[0072] (4) 10 g of the alkenylated carbon sphere, 0.5 g of AIBN were added to 100 mL of anhydrous tetrahydrofuran, and ultrasonic dispersion was carried out for 20 min under a nitrogen atmosphere and in the dark, 5 mL of vinyl phosphonic dichloride was slowly added dropwise, and stirring reaction was carried out at 45 °C for 18 h, and the product was centrifuged, washed, and dried to obtain an acyl chloride carbon sphere;

[0073] (5) 10 g of the acyl chloride carbon sphere, 0.2 g of DMAP were added to 100 mL of DMF, and ultrasonic dispersion was carried out for 20 min, 3 g of p-aminobenzenesulfonic acid and 2 mL of triethylamine were added, and stirring reaction was carried out at 20 °C for 12 h, and the product was centrifuged, washed, and dried to obtain the nitrogen-doped multi-level porous hollow carbon sphere.

[0074] Comparative Example 1

[0075] A method for preparing a carbon sphere, comprising the following steps:

[0076] (1) 1.26 g melamine and 1.2 g F127 were dissolved in 100 mL deionized water, heated to 80 °C to form a transparent solution, then stirred at 100 r / min for 5 min; then 5 mL (37 wt% aqueous solution) formaldehyde solution was added, and stirring was continued for 30 min; then 0.5 mL glacial acetic acid was added, and stirring was carried out at 80 °C at a speed of 350 rpm for 2 h; finally, the melamine-formaldehyde resin sphere template was collected by centrifugation at a speed of 4000 rpm, and washed with water and ethanol to remove residual impurities, and dried at 80 °C to obtain the melamine-formaldehyde resin sphere template;

[0077] (2) 0.5 g melamine-formaldehyde resin sphere template was dispersed in 40 mL deionized water, and a uniform suspension was formed by ultrasonic treatment for 30 min; then 3.0 g F127 was added and stirred for 2 h; then 0.4 g resorcinol and 1.0 g hexamethylenetetramine, 20 μL ammonia water were added, and the reaction was carried out at 35 °C for 1 h; then the temperature was increased to 80 °C, and after 24 h of reaction, the precipitate was collected by centrifugation, and washed with water and ethanol to remove unreacted components, to obtain a brown powder of nitrogen-doped precursor;

[0078] (3) 0.1 g of the nitrogen-doped precursor powder was calcined at 800 °C for 1 h at a temperature increasing rate of 2 °C / min under a nitrogen atmosphere, and the obtained black powder was nitrogen-doped multi-level porous hollow carbon spheres; 10 g of the hollow carbon spheres and 2 mL of glacial acetic acid were added to 100 mL of anhydrous tetrahydrofuran, and ultrasonic dispersion was carried out for 30 min, then 8 mL of KH570 was added, and reflux reaction was carried out at 70 °C for 6 h, the product was centrifuged, washed, and dried to obtain alkenylated carbon spheres;

[0079] (4) 10 g of the alkenylated carbon spheres and 1.5 g of AIBN were added to 100 mL of anhydrous tetrahydrofuran, and ultrasonic dispersion was carried out for 20 min under a nitrogen atmosphere and in the dark, 10 mL of vinyl phosphonic dichloride was slowly added dropwise, and stirring reaction was carried out at 60 °C for 6 h, the product was centrifuged, washed, and dried to obtain acyl chloride carbon spheres.

[0080] Comparative Example 2

[0081] A method for preparing carbon spheres, comprising the following steps:

[0082] (1) 1.26 g of melamine and 1.2 g of F127 were dissolved in 100 mL of deionized water, heated to 80° C. to form a transparent solution, and then stirred at a speed of 100 r / min for 5 min; then 5 mL of formaldehyde solution (37 wt% aqueous solution) was added and stirred for 30 min; then 0.5 mL of glacial acetic acid was added and stirred at a speed of 350 rpm at 80° C. for 2 h; finally, the melamine-formaldehyde resin ball template was collected by centrifugation at a speed of 4000 rpm, washed with water and ethanol to remove residual impurities, and dried at 80° C. to obtain the melamine-formaldehyde resin ball template;

[0083] (2) 0.5 g of melamine-formaldehyde resin sphere template was dispersed in 40 mL of deionized water and ultrasonically treated for 30 min to form a uniform suspension; then 3.0 g of F127 was added and stirred for 2 h; then 0.4 g of resorcinol, 1.0 g of hexamethylenetetramine, and 20 μL of ammonia water were added and the reaction was maintained at 35 ° C for 1 h; then the temperature was increased to 80 ° C, and after the reaction for 24 h, the precipitate was collected by centrifugation and washed with water and ethanol to remove the unreacted components to obtain a brown powder nitrogen-doped precursor;

[0084] (3) In a nitrogen atmosphere, 0.1 g of nitrogen-doped precursor powder was calcined at 800 °C for 1 h at a heating rate of 2 °C / min to obtain black powder, which was nitrogen-doped hierarchical hollow carbon spheres. 10 g of hollow carbon spheres and 2 mL of glacial acetic acid were added to 100 mL of anhydrous tetrahydrofuran and ultrasonically dispersed for 30 min. Then, 8 mL of KH570 was added and refluxed at 70 °C for 6 h. The product was centrifuged, washed, and dried to obtain olefinated carbon spheres.

[0085] The hollow carbon spheres prepared in Examples 1 to 4 and Comparative Examples 1 to 2 were subjected to performance tests, wherein the specific surface area, pore volume and average pore diameter of the samples were tested using a TriStarII 3020 fully automatic specific surface and pore analyzer.

[0086] The electrochemical tests were carried out on an electrochemical workstation (Wuhan Coster). All tests used a three-electrode system. The working electrode preparation process was as follows: the prepared hollow carbon spheres were mixed with a conductive agent (acetylene black) and a binder (polytetrafluoroethylene) in a mass ratio of 8:1:1, and an appropriate amount of NMP (N-methylpyrrolidone) was added. The mixture was stirred for 12 h and applied to a conductive graphite paper with an application area of ​​1 cm. 2 . Platinum sheet was used as counter electrode, Ag / AgCl reference electrode, and the prepared electrode sheet was used as working electrode, and the capacitance performance test was carried out in 1 mol / L sodium chloride solution. The test results are shown in Table 1. Example 1 showed a higher specific capacitance (the capacitance value was 236.6 F / g when the current density was 0.5 A / g). 16 mg of hollow carbon spheres were used as electrode materials and evenly coated on 2×2 cm2 The conductive graphite paper was used as the CDI cathode, and the CDI anode was prepared by the same method. The symmetric capacitive deionization device was assembled for performance test, and the test results are shown in Table 1. The material has the best desalination effect in the 500 mg / L sodium chloride solution at 1.2 V voltage, and the salt adsorption capacity is 25.21 mg / g.

[0087] Table 1 Performance test results

[0088]

[0089] As can be seen from Examples 1-4 and Comparative Examples 1-2, the material with a hollow structure prepared by the present application is characterized by high specific surface area and excellent pore volume, which ensures the accessibility of the electric adsorption interface, thereby effectively promoting the ion diffusion. This structural design not only improves the electrochemical performance of the material, but also enhances the efficiency and stability of the material in the electric adsorption process. The synergistic effect of N, P and S ternary heteroatoms greatly enhances the ion exchange capacity of the material and exhibits excellent ion adsorption performance. Comprehensive analysis shows that the technical solution of the present application effectively overcomes many challenges in the prior art. Through the innovative design of nitrogen doping and hierarchical pore structure, the performance of the material in the application of capacitive deionization is significantly improved, which has significant practical application value and broad market prospect.

[0090] The above is only the preferred specific implementation of the present application, but the protection scope of the present application is not limited to this. Any skilled person in the art, according to the technical solution and the inventive concept of the present application, makes equivalent replacement or change within the technical range disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A method for preparing nitrogen-doped hierarchically porous hollow carbon spheres, characterized in that: The steps include: (1) Melamine and polyvinyl pyrrolidone are dissolved in deionized water, heated to form a transparent solution, and a formaldehyde solution is added and mixed evenly. Glacial acetic acid is added to the mixed solution and stirred continuously. After stirring, the mixture is centrifuged, washed, and dried to obtain a template; (2) dispersing the template in deionized water, adding polyvinyl pyrrolidone and stirring evenly, then adding resorcinol, hexamethylenetetramine and ammonia water and continuing to stir, centrifuging, washing and drying after the stirring is completed to obtain a precursor; (3) placing the precursor in a nitrogen atmosphere, heating, and calcining to obtain hollow carbon spheres; adding the hollow carbon spheres and glacial acetic acid to anhydrous tetrahydrofuran, ultrasonically dispersing them uniformly, then adding KH570, reflux reaction, centrifuging, washing, and drying the product to obtain olefinated carbon spheres; (4) Adding olefinated carbon spheres and AIBN to anhydrous tetrahydrofuran, ultrasonically dispersing under a nitrogen atmosphere and in the dark, slowly adding vinylphosphonyl chloride dropwise, stirring to react, centrifuging, washing, and drying the product to obtain acyl chloride carbon spheres; (5) Adding acyl chloride carbon spheres and DMAP into DMF, uniformly dispersing by ultrasonication, adding p-aminobenzenesulfonic acid and triethylamine, stirring for reaction, centrifuging, washing, and drying the product to obtain the nitrogen-doped multi-level porous hollow carbon spheres.

2. The method for preparing nitrogen-doped multi-level porous hollow carbon spheres according to claim 1, characterized in that: In step (1), the mass volume ratio of the melamine, polyvinyl pyrrolidone, formaldehyde solution and glacial acetic acid is 1-2 g: 1-2 g: 5-10 mL: 0.3-1.2 mL, and the concentration of the formaldehyde aqueous solution is 30-40 wt%; The heating conditions are 70-90°C, stirring at 100-300 r / min for 5-15 minutes; the mixing conditions are stirring at 100-300 r / min for 30-60 minutes; after adding glacial acetic acid, stirring is continued at 200-500 r / min and 70-90°C for 1-5 hours.

3. The method for preparing nitrogen-doped hierarchically porous hollow carbon spheres according to claim 1, wherein: In step (2), the mass volume ratio of the template, polyvinyl pyrrolidone, resorcinol, hexamethylenetetramine and ammonia water is 0.2-1g:2-5g:0.4-1.2g:1-3g:10-30μL; after adding polyvinyl pyrrolidone, stirring is carried out at 100-300r / min for 1-5h, and after adding ammonia water, stirring is carried out at 30-50°C and 100-300r / min for 1-5h, and then the temperature is raised to 70-90°C and 100-300r / min for reaction for 20-30h.

4. The method for preparing nitrogen-doped hierarchically porous hollow carbon spheres according to claim 1, wherein: In step (3), the temperature is raised to 700-900°C at a heating rate of 2°C / min and calcined for 1 hour.

5. The method for preparing nitrogen-doped hierarchically porous hollow carbon spheres according to claim 1, wherein: In step (3), the ratio of hollow carbon spheres, glacial acetic acid, anhydrous tetrahydrofuran, and KH570 is 10 g: 1-2 mL: 80-120 mL: 3-8 mL; ultrasonic dispersion is performed for 15-30 min; and the reflux reaction conditions are reflux reaction at 55-70° C. for 6-12 h.

6. The method for preparing nitrogen-doped hierarchically porous hollow carbon spheres according to claim 1, wherein: In step (4), the ratio of the olefinated carbon spheres, AIBN, anhydrous tetrahydrofuran, and vinylphosphonyl chloride is 10 g: 0.5-1.5 g: 80-120 mL: 5-10 mL; ultrasonic dispersion is performed for 10-20 min; and the stirring reaction conditions are 45-60° C. and the reaction is carried out for 6-18 h.

7. The method for preparing nitrogen-doped hierarchically porous hollow carbon spheres according to claim 1, wherein: In step (5), the usage ratio of carbon acyl chloride spheres, DMAP, DMF, p-aminobenzenesulfonic acid, and triethylamine is 10 g: 0.2-0.6 g: 80-120 mL: 3-6 g: 2-4 mL.

8. The method for preparing nitrogen-doped hierarchically porous hollow carbon spheres according to claim 1, wherein: In step (5), ultrasonic dispersion is performed for 10 to 20 minutes; and the stirring reaction conditions are 20 to 45° C. and the reaction is performed for 4 to 12 hours.

9. Nitrogen-doped multi-level porous hollow carbon spheres prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the nitrogen-doped multi-level porous hollow carbon spheres as claimed in claim 9 in capacitive deionization.

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