Nitrogen-doped hierarchical pore hollow carbon sphere as well as preparation method and application thereof

Abstract

The invention discloses a preparation method of nitrogen-doped hierarchical pore hollow carbon spheres, and relates to the technical field of electrochemical desalination, the preparation method comprises the following steps: carrying out polycondensation on melamine and formaldehyde in the presence of PVP to form a spherical template; resorcinol and HMTA form a phenolic resin coating layer on the surface of the template; calcining at high temperature to realize decomposition and carbonization of the template, and introducing double bonds through a silane coupling agent; introducing a phosphoryl chloride group through free radical polymerization; finally, grafting a sulfonic acid group through nucleophilic substitution to obtain a final product. The nitrogen-doped hollow carbon spheres with a hierarchical pore structure are prepared through a hollowing strategy and surface modification, and N, P and S ternary heteroatom synergy is realized through introduction of a phosphoryl chloride group and a sulfonic acid group, so that the material has high specific surface area, optimized pore structure and strong ion exchange capacity; the composite material shows excellent ion adsorption performance and cycling stability, and has a good application prospect in the field of capacitive deionization.

Description

Technical Field

[0001] The present invention relates to the technical field of electrochemical desalination, and particularly relates to a nitrogen-doped hierarchical porous hollow carbon sphere, a preparation method thereof, and an application thereof. Background Art

[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) refer to carbon particles with a hollow structure, whose sizes can range from millimeters to nanometers, and have a unique thin-shell structure. Due to possessing the properties of both internal and external materials, as well as excellent chemical and thermal stabilities, hollow carbon spheres exhibit broad application prospects in fields such as fuel cells, supercapacitors, and hydrogen storage.

[0003] Currently, the world is facing a severe water resource crisis. Factors such as economic development, population growth, and water pollution have led to the increasing scarcity of fresh water resources, and the supply of clean water has become one of the major challenges faced by human society in the 21st century. Given the abundant reserves of seawater and brackish water globally, the development of efficient desalination technologies is of great significance for ensuring the sustainable development of human society.

[0004] Among various seawater desalination technologies, capacitive deionization (CDI) technology has received increasing attention in recent years due to its advantages such as low cost, low energy consumption, and environmental friendliness. The core of this technology lies in the performance of the electrode material, and an ideal electrode material should possess characteristics such as a high specific surface area, excellent chemical stability, and good electrical conductivity. Due to its unique structural characteristics, hollow carbon spheres exhibit great application potential in CDI applications.

[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 for condensation reflux and then soaking, washing the YSPCs material until the waste liquid is neutral, vacuum drying and then grinding for standby, adding the pretreated YSPCs material into deionized water containing polyvinylpyrrolidone, forming a uniform suspension after ultrasonic dispersion, slowly adding a Na4Fe(CN)6 solution to the suspension, heating and stirring the mixture to generate a blue-black precipitate, washing the blue-black precipitate product, vacuum drying and then grinding to obtain composite nanoparticles, mixing the composite nanoparticles, carbon black, and polytetrafluoroethylene in alcohol, and coating on graphite paper to prepare the positive and negative electrodes of a CDI desalination device.

[0006] However, the existing hollow carbon sphere preparation technologies still have the following problems: 1. Additional substances need to be introduced during the preparation process, increasing the process complexity; 2. The preparation process is cumbersome and energy-consuming; 3. The production cost is relatively high, which is not conducive to large-scale application; 4. The environmental performance needs to be improved.

[0007] Therefore, developing a preparation method of hollow carbon spheres with energy conservation, high efficiency, environmental friendliness and low cost has important practical significance for promoting the practical application of CDI technology. The nitrogen-doped hierarchical porous hollow carbon spheres and the preparation method provided by the present invention not only solve the problems in the prior art, but also further improve the performance of the material in CDI applications through the design of nitrogen doping and hierarchical pore structure. Summary of the Invention

[0008] In order to solve the deficiencies of the prior art, the purpose of the present invention is to provide a nitrogen-doped hierarchical porous hollow carbon sphere, its preparation method and application. The present invention prepares a nitrogen-doped hollow carbon sphere with a hierarchical pore structure through a hollowing strategy and surface modification, and realizes the synergy of N, P, and S ternary heteroatoms through the introduction of phosphoryl chloride groups and sulfonic acid groups, so that the material has a high specific surface area, an optimized pore structure and strong ion exchange ability, showing excellent ion adsorption performance and cycle stability, and having good application prospects in the field of capacitive deionization.

[0009] In order to achieve the above purpose, the present invention adopts the following technical solutions:

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

[0011] (1) Dissolve melamine and polyvinylpyrrolidone in deionized water, heat to form a transparent solution, add an aqueous formaldehyde solution and mix evenly, add glacial acetic acid to the mixed solution and continue stirring, and after stirring is completed, centrifuge, wash and dry to obtain a template;

[0012] Melamine and formaldehyde undergo a polycondensation reaction to form a three-dimensional network structure under acidic conditions. Polyvinylpyrrolidone (PVP) acts as a dispersant and stabilizer, and controls the polycondensation process through hydrogen bond action, 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 aqueous formaldehyde solution is 30-40 wt%; the heating condition is stirring at 70-90 °C and 100-300 r / min for 5-15 min; the mixing condition is stirring at 100-300 r / min for 30-60 min; after adding glacial acetic acid, continue stirring at 200-500 r / min and 70-90 °C for 1-5 h.

[0014] (2) Disperse the template in deionized water, add polyvinylpyrrolidone and stir evenly, then add resorcinol, hexamethylenetetramine and ammonia water and continue stirring, and after stirring is completed, centrifuge, wash and dry to obtain a precursor;

[0015] Hexamethylenetetramine (HMTA) slowly decomposes under heating conditions to release formaldehyde, which undergoes a Mannich reaction with resorcinol to form phenolic resin and provides part of the nitrogen source; ammonia water provides a stable alkaline environment to control the reaction rate. PVP guides the directional growth of monomers on the template surface through π-π interactions and hydrogen bonding. The phenolic resin generated under alkaline conditions uniformly coats 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 water is 0.2 - 1 g : 2 - 5 g : 0.4 - 1.2 g : 1 - 3 g : 10 - 30 μL; after adding polyvinylpyrrolidone, stir at 100 - 300 r / min for 1 - 5 h, after adding ammonia water, stir at 30 - 50 °C and 100 - 300 r / min for 1 - 5 h, and then raise the temperature to 70 - 90 °C and react at 100 - 300 r / min for 20 - 30 h.

[0017] (3) Place the precursor in a nitrogen atmosphere, heat up and calcine to obtain hollow carbon spheres; add the hollow carbon spheres and glacial acetic acid to anhydrous tetrahydrofuran, ultrasonically disperse evenly, then add KH570, carry out a reflux reaction, centrifuge, wash, and dry the product to obtain vinylated carbon spheres;

[0018] The precursor is calcined at high temperature in a nitrogen atmosphere. The template decomposes while the phenolic resin carbonizes to form a nitrogen-containing hollow carbon sphere structure. Subsequently, surface modification is carried out: KH570 first hydrolyzes under acid catalysis to generate silanol, and forms a Si - O - C covalent bond with the hydroxyl groups on the carbon sphere surface through a condensation reaction, introducing a double bond functional group on the surface.

[0019] Preferably, in step (3), heat up to 700 - 900 °C at a heating rate of 2 °C / min and calcine for 1 h.

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

[0021] Preferably, in step (3), ultrasonically disperse for 15 - 30 min; the reflux reaction conditions are reflux reaction at 55 - 70 °C for 6 - 12 h.

[0022] (4) Add the vinylated carbon spheres and AIBN to anhydrous tetrahydrofuran, ultrasonically disperse under a nitrogen atmosphere and in the dark, slowly dropwise add vinylphosphoryl chloride, stir and react, centrifuge, wash, and dry the product to obtain acyl chloride functionalized carbon spheres;

[0023] AIBN decomposes under heating conditions to generate free radicals, which initiate the free radical graft polymerization of the double bonds on the carbon sphere surface with vinylphosphoryl chloride, forming grafted phosphoryl chloride groups on the carbon sphere surface.

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

[0025] Preferably, in step (4), ultrasonic dispersion is carried out for 10 - 20 min; the stirring reaction conditions are reaction at 45 - 60 °C for 6 - 18 h.

[0026] (5) Add the carbon spheres with acyl chloride groups and DMAP to DMF, disperse them evenly by ultrasonic treatment, add sulfanilic acid and triethylamine, stir and react, and centrifuge, wash, and dry the product to obtain the nitrogen-doped hierarchical porous hollow carbon spheres.

[0027] The acyl chloride groups on the surface of the carbon spheres with acyl chloride groups undergo a nucleophilic substitution reaction with sulfanilic acid. DMAP serves as a catalyst, and triethylamine serves as a basic 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, nitrogen-doped hierarchical porous hollow carbon spheres with sulfonic acid functional groups are obtained.

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

[0029] Preferably, in step (5), ultrasonic dispersion is carried out for 10 - 20 min; the stirring reaction conditions are reaction at 20 - 45 °C for 4 - 12 h.

[0030] The present invention also claims to protect a nitrogen-doped hierarchical porous hollow carbon sphere prepared by the above preparation method.

[0031] The present invention also claims to protect an application of the above-mentioned nitrogen-doped hierarchical porous hollow carbon sphere in capacitive deionization.

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

[0033] 1. The present invention provides a method for preparing nitrogen-doped hierarchical porous hollow carbon spheres. Using melamine-formaldehyde resin spheres as templates, a uniform and controllable spherical structure is achieved in the presence of PVP. During the coating process of phenolic resin on the template surface, 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 prepares hierarchical porous hollow carbon spheres with a high specific surface area and optimized pore volume, but also the doping of nitrogen atoms enhances the hydrophilicity of the pore surface, providing more active sites for ion adsorption, thus showing excellent NaCl adsorption performance. The whole 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 present invention provides a method for preparing nitrogen-doped hierarchical porous hollow carbon spheres. Through subsequent introduction of phosphoryl chloride groups and modification of sulfonic acid groups, the material properties are further optimized: First, phosphorus-containing groups are introduced on the carbon sphere surface through controllable radical polymerization, enhancing the electron conduction ability and surface polarity of the material; Subsequently, sulfonic acid groups are grafted on the surface through a mild nucleophilic substitution reaction, providing strong ion exchange sites. The synergistic effect of these three heteroatoms of N, P, and S significantly improves the ion adsorption ability and transport efficiency of the material, while maintaining the original hierarchical 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, making it show fast ion transport kinetics and excellent cycle stability during the capacitive deionization process, and is particularly suitable for applications in water desalination and heavy metal ion removal. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some schematic diagrams of certain embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0036] Figure 1 It is a scanning electron microscope picture of the nitrogen-doped hollow carbon spheres in Embodiment 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0037] In order to make the objectives, technical solutions and advantages of the present invention clearer, the following will further elaborate on the present invention in conjunction with embodiments. Of course, the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0038] Unless otherwise specified, the chemical reagents and materials in the present invention are all purchased through the market or synthesized from raw materials purchased through the market.

[0039] A preparation method of nitrogen-doped hierarchical porous hollow carbon spheres includes the following steps:

[0040] (1) Dissolve 1-2 g of melamine and 1-2 g of polyvinylpyrrolidone in 100 mL of deionized water, stir at 70-90 °C and 100-300 r / min for 5-15 min to form a transparent solution, add 5-10 mL of 30-40 wt% formaldehyde aqueous solution and stir at 100-300 r / min for 30-60 min to mix evenly. Add 0.3-1.2 mL of glacial acetic acid to the mixed solution and continue to stir at 200-500 r / min and 70-90 °C for 1-5 h. After stirring, centrifuge, wash, and dry to obtain a template.

[0041] (2) Disperse 0.2-1 g of the template in 40-80 mL of deionized water, add 2-5 g of polyvinylpyrrolidone and stir at 100-300 r / min for 1-5 h. Then add 0.4-1.2 g of resorcinol, 1-3 g of hexamethylenetetramine, and 10-30 μL of 10 wt% ammonia water, and stir at 30-50 °C and 100-300 r / min for 1-5 h. Subsequently, raise the temperature to 70-90 °C and react at 100-300 r / min for 20-30 h. After stirring, centrifuge, wash, and dry to obtain a precursor.

[0042] (3) Place the precursor in a nitrogen atmosphere and heat it to 700-900 °C at a heating rate of 2 °C / min, and calcine for 1 h to obtain hollow carbon spheres. Add 10 g of hollow carbon spheres and 1-2 mL of glacial acetic acid to 80-120 mL of anhydrous tetrahydrofuran, ultrasonically disperse for 15-30 min, then add 3-8 mL of KH570, and reflux and react at 55-70 °C for 6-12 h. Centrifuge, wash, and dry the product to obtain vinylated carbon spheres.

[0043] (4) Add 10 g of vinylated carbon spheres and 0.5-1.5 g of AIBN to 80-120 mL of anhydrous tetrahydrofuran, ultrasonically disperse in a nitrogen atmosphere and under light protection for 10-20 min, slowly dropwise add 5-10 mL of vinylphosphonyl chloride, and stir and react at 45-60 °C for 6-18 h. Centrifuge, wash, and dry the product to obtain acyl chloride carbon spheres.

[0044] (5) Add 10 g of acyl chloride carbon spheres and 0.2-0.6 g of DMAP to 80-120 mL of DMF, ultrasonically disperse for 10-20 min, add 3-6 g of p-aminobenzenesulfonic acid and 2-4 mL of triethylamine, and stir and react at 20-45 °C for 4-12 h. Centrifuge, wash, and dry the product to obtain the nitrogen-doped hierarchical porous hollow carbon spheres.

[0045] The present invention will be further described below through specific embodiments.

[0046] Example 1

[0047] A method for preparing nitrogen-doped hierarchical porous hollow carbon spheres includes the following steps:

[0048] (1) Dissolve 1.26 g of melamine and 1.2 g of F127 in 100 mL of deionized water, heat to 80 °C to form a transparent solution, and then stir at a speed of 100 r / min for 5 min; then add 5 mL (37 wt% aqueous solution) of formaldehyde solution and continue stirring for 30 min; then add 0.5 mL of glacial acetic acid and stir at 80 °C at a speed of 350 rpm for 2 h; finally, collect the melamine-formaldehyde resin sphere template by centrifugation at a speed of 4000 rpm, and wash with water and ethanol to remove residual impurities, and dry at 80 °C to obtain the melamine-formaldehyde resin sphere template;

[0049] (2) Disperse 0.5 g of the melamine-formaldehyde resin sphere template in 40 mL of deionized water, and form a uniform suspension by ultrasonic treatment for 30 min; then add 3.0 g of F127 and stir for 2 h; then add 0.4 g of resorcinol, 1.0 g of hexamethylenetetramine, and 20 μL of ammonia water, and keep the reaction at 35 °C for 1 h; then raise the temperature to 80 °C and react for 24 h, and collect the precipitate by centrifugation, and wash with water and ethanol to remove unreacted components to obtain a brown powder of nitrogen-doped precursor;

[0050] (3) In a nitrogen atmosphere, calcine 0.1 g of the nitrogen-doped precursor powder at 800 °C for 1 h at a heating rate of 2 °C / min, and the obtained black powder is nitrogen-doped hierarchical porous hollow carbon spheres; add 10 g of hollow carbon spheres and 2 mL of glacial acetic acid to 100 mL of anhydrous tetrahydrofuran, ultrasonically disperse for 30 min, then add 8 mL of KH570, and reflux and react at 70 °C for 6 h, centrifuge, wash, and dry the product to obtain vinylated carbon spheres;

[0051] (4) Add 10 g of vinylated carbon spheres and 1.5 g of AIBN to 100 mL of anhydrous tetrahydrofuran, ultrasonically disperse under a nitrogen atmosphere and in the dark for 20 min, slowly dropwise add 10 mL of vinylphosphoryl chloride, and stir and react at 60 °C for 6 h, centrifuge, wash, and dry the product to obtain acyl chloride carbon spheres;

[0052] (5) Add 10 g of acyl chloride carbon spheres and 0.6 g of DMAP to 100 mL of DMF, ultrasonically disperse for 20 min, add 6 g of p-aminobenzenesulfonic acid and 4 mL of triethylamine, and stir and react at 45 °C for 4 h, centrifuge, wash, and dry the product to obtain the nitrogen-doped hierarchical porous hollow carbon spheres.

[0053] Example 2

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

[0055] (1) Dissolve 1.26 g of melamine and 1.2 g of F127 in 100 mL of deionized water, heat to 80 °C to form a transparent solution, and then stir at a speed of 100 r / min for 5 min; then add 5 mL (37 wt% aqueous solution) of formaldehyde solution and continue stirring for 30 min; then add 0.5 mL of glacial acetic acid and stir at 80 °C at a speed of 350 rpm for 2 h; finally, collect the melamine-formaldehyde resin sphere template by centrifugation at a speed of 4000 rpm, and wash with water and ethanol to remove residual impurities, and dry at 80 °C to obtain melamine-formaldehyde resin spheres;

[0056] (2) Disperse 0.5 g of MF spheres in 40 mL of deionized water, and form a uniform suspension by ultrasonic treatment for 30 min; then add 3.0 g of F127 and stir for 2 h; then add 0.8 g of resorcinol and 1.0 g of hexamethylenetetramine, add 20 μL of ammonia water after 30 min, and react at 35 °C for 1 h; then raise the temperature to 80 °C and react for 24 h, and collect the precipitate by centrifugation, and wash with water and ethanol to remove unreacted components to obtain a brown powder of nitrogen-doped precursor;

[0057] (3) In a nitrogen atmosphere, calcine 0.1 g of the nitrogen-doped precursor powder at 800 °C for 1 h at a heating rate of 2 °C / min, and the obtained black powder is nitrogen-doped hierarchical porous hollow carbon spheres; add 10 g of hollow carbon spheres and 1.5 mL of glacial acetic acid to 100 mL of anhydrous tetrahydrofuran, ultrasonically disperse for 30 min, then add 6 mL of KH570, and reflux and react at 65 °C for 8 h, and centrifuge, wash and dry the product to obtain vinylated carbon spheres;

[0058] (4) Add 10 g of vinylated carbon spheres and 1.2 g of AIBN to 100 mL of anhydrous tetrahydrofuran, ultrasonically disperse under a nitrogen atmosphere and in the dark for 20 min, slowly dropwise add 8 mL of vinylphosphoryl chloride, and stir and react at 55 °C for 10 h, and centrifuge, wash and dry the product to obtain acyl chloride carbon spheres;

[0059] (5) Add 10 g of acyl chloride carbon spheres and 0.4 g of DMAP to 100 mL of DMF, ultrasonically disperse for 20 min, add 5 g of p-aminobenzenesulfonic acid and 3 mL of triethylamine, and stir and react at 40 °C for 6 h, and centrifuge, wash and dry the product to obtain the nitrogen-doped hierarchical porous hollow carbon spheres.

[0060] Example 3

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

[0062] (1) Dissolve 1.26 g of melamine and 1.2 g of F127 in 100 mL of deionized water, heat to 80 °C to form a transparent solution, and then stir at a speed of 100 r / min for 5 min; then add 5 mL (37 wt% aqueous solution) of formaldehyde solution and continue stirring for 30 min; then add 0.5 mL of glacial acetic acid and stir at 80 °C at a speed of 350 rpm for 2 h; finally, collect the melamine-formaldehyde resin sphere template by centrifugation at a speed of 4000 rpm, and wash with water and ethanol to remove residual impurities, and dry at 80 °C to obtain melamine-formaldehyde resin spheres;

[0063] (2) Disperse 0.5 g of MF spheres in 40 mL of deionized water, and form a uniform suspension by ultrasonic treatment for 30 min; then add 3.0 g of F127 and stir for 2 h; then add 1.2 g of resorcinol and 1.0 g of hexamethylenetetramine, add 20 μL of ammonia water after 30 min, and react at 35 °C for 1 h; then raise the temperature to 80 °C, after reacting for 24 h, collect the precipitate by centrifugation, and wash with water and ethanol to remove unreacted components to obtain a brown powder of nitrogen-doped precursor;

[0064] (3) In a nitrogen atmosphere, calcine 0.1 g of the nitrogen-doped precursor powder at 800 °C for 1 h at a heating rate of 2 °C / min, and the obtained black powder is nitrogen-doped hierarchical porous hollow carbon spheres; add 10 g of hollow carbon spheres and 1.5 mL of glacial acetic acid to 100 mL of anhydrous tetrahydrofuran, ultrasonically disperse for 30 min, then add 5 mL of KH570, and reflux and react at 60 °C for 10 h, centrifuge, wash and dry the product to obtain vinylated carbon spheres;

[0065] (4) Add 10 g of vinylated carbon spheres and 0.8 g of AIBN to 100 mL of anhydrous tetrahydrofuran, ultrasonically disperse under a nitrogen atmosphere and in the dark for 20 min, slowly dropwise add 6 mL of vinylphosphoryl chloride, and stir and react at 50 °C for 14 h, centrifuge, wash and dry the product to obtain acyl chloride carbon spheres;

[0066] (5) Add 10 g of acyl chloride carbon spheres and 0.4 g of DMAP to 100 mL of DMF, ultrasonically disperse for 20 min, add 4 g of p-aminobenzenesulfonic acid and 3 mL of triethylamine, and stir and react at 35 °C for 10 h, centrifuge, wash and dry the product to obtain the nitrogen-doped hierarchical porous hollow carbon spheres.

[0067] Example 4

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

[0069] (1) Dissolve 1.26 g of melamine and 1.2 g of F127 in 100 mL of deionized water, heat to 80 °C to form a transparent solution, and then stir at a speed of 100 r / min for 5 min; then add 5 mL (37 wt% aqueous solution) of formaldehyde solution and continue stirring for 30 min; then add 0.5 mL of glacial acetic acid and stir at 80 °C at a speed of 350 rpm for 2 h; finally, collect the melamine-formaldehyde resin sphere template by centrifugation at a speed of 4000 rpm, and wash with water and ethanol to remove residual impurities, and obtain melamine-formaldehyde resin spheres after drying at 80 °C;

[0070] (2) Disperse 0.5 g of MF spheres in 40 mL of deionized water and form a uniform suspension by ultrasonic treatment for 30 min; then add 3.0 g of F127 and stir for 2 h; then add 1.2 g of resorcinol and 1.0 g of hexamethylenetetramine, add 20 μL of ammonia water after 30 min, and keep reacting at 35 °C for 1 h; then raise the temperature to 80 °C, after reacting for 24 h, collect the precipitate by centrifugation, and wash with water and ethanol to remove unreacted components to obtain a brown powder nitrogen-doped precursor;

[0071] (3) In a nitrogen atmosphere, calcine 0.1 g of the nitrogen-doped precursor powder at 800 °C for 1 h at a heating rate of 2 °C / min, and the obtained black powder is nitrogen-doped hierarchical porous hollow carbon spheres; add 10 g of hollow carbon spheres and 1 mL of glacial acetic acid to 100 mL of anhydrous tetrahydrofuran, ultrasonically disperse for 30 min, then add 3 mL of KH570, and reflux and react at 55 °C for 12 h, centrifuge, wash, and dry the product to obtain vinylated carbon spheres;

[0072] (4) Add 10 g of vinylated carbon spheres and 0.5 g of AIBN to 100 mL of anhydrous tetrahydrofuran, ultrasonically disperse in a nitrogen atmosphere and under light shielding for 20 min, slowly dropwise add 5 mL of vinylphosphoryl chloride, and stir and react at 45 °C for 18 h, centrifuge, wash, and dry the product to obtain acyl chloride carbon spheres;

[0073] (5) Add 10 g of acyl chloride carbon spheres and 0.2 g of DMAP to 100 mL of DMF, ultrasonically disperse for 20 min, add 3 g of p-aminobenzenesulfonic acid and 2 mL of triethylamine, and stir and react at 20 °C for 12 h, centrifuge, wash, and dry the product to obtain the nitrogen-doped hierarchical porous hollow carbon spheres.

[0074] Comparative Example 1

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

[0076] (1) Dissolve 1.26 g of melamine and 1.2 g of F127 in 100 mL of deionized water, heat to 80 °C to form a transparent solution, and then stir at a speed of 100 r / min for 5 min; then add 5 mL (37 wt% aqueous solution) of formaldehyde solution and continue to stir for 30 min; then add 0.5 mL of glacial acetic acid and stir at 80 °C at a speed of 350 rpm for 2 h; finally, collect the melamine-formaldehyde resin sphere template by centrifugation at a speed of 4000 rpm, and wash with water and ethanol to remove residual impurities. After drying at 80 °C, the melamine-formaldehyde resin sphere template is obtained;

[0077] (2) Disperse 0.5 g of the melamine-formaldehyde resin sphere template in 40 mL of deionized water, and form a uniform suspension by ultrasonic treatment for 30 min; then add 3.0 g of F127 and stir for 2 h; then add 0.4 g of resorcinol, 1.0 g of hexamethylenetetramine, and 20 μL of ammonia water, and react at 35 °C for 1 h; then raise the temperature to 80 °C and react for 24 h. After centrifuging to collect the precipitate, wash with water and ethanol to remove unreacted components, and obtain the brown powder of the nitrogen-doped precursor;

[0078] (3) In a nitrogen atmosphere, calcine 0.1 g of the nitrogen-doped precursor powder at 800 °C for 1 h at a heating rate of 2 °C / min. The obtained black powder is the nitrogen-doped hierarchical porous hollow carbon spheres; add 10 g of the hollow carbon spheres and 2 mL of glacial acetic acid to 100 mL of anhydrous tetrahydrofuran, ultrasonically disperse for 30 min, then add 8 mL of KH570, and reflux and react at 70 °C for 6 h. Centrifuge, wash, and dry the product to obtain the vinylated carbon spheres;

[0079] (4) Add 10 g of the vinylated carbon spheres and 1.5 g of AIBN to 100 mL of anhydrous tetrahydrofuran, ultrasonically disperse in a nitrogen atmosphere and under light protection for 20 min, slowly dropwise add 10 mL of vinylphosphoryl chloride, and stir and react at 60 °C for 6 h. Centrifuge, wash, and dry the product to obtain the acyl chloride carbon spheres.

[0080] Comparative Example 2

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

[0082] (1) Dissolve 1.26 g of melamine and 1.2 g of F127 in 100 mL of deionized water, heat to 80 °C to form a transparent solution, and then stir at a speed of 100 r / min for 5 min; then add 5 mL (37 wt% aqueous solution) of formaldehyde solution and continue stirring for 30 min; after that, add 0.5 mL of glacial acetic acid and stir at 80 °C at a speed of 350 rpm for 2 h; finally, collect the melamine-formaldehyde resin sphere template by centrifugation at a speed of 4000 rpm, wash with water and ethanol to remove residual impurities, and obtain the melamine-formaldehyde resin sphere template after drying at 80 °C;

[0083] (2) Disperse 0.5 g of the melamine-formaldehyde resin sphere template in 40 mL of deionized water, and form a homogeneous suspension by ultrasonic treatment for 30 min; then add 3.0 g of F127 and stir for 2 h; then add 0.4 g of resorcinol, 1.0 g of hexamethylenetetramine, and 20 μL of ammonia water, and keep the reaction at 35 °C for 1 h; then raise the temperature to 80 °C, after reacting for 24 h, collect the precipitate by centrifugation, and wash with water and ethanol to remove unreacted components to obtain a brown powder of nitrogen-doped precursor;

[0084] (3) In a nitrogen atmosphere, calcine 0.1 g of the nitrogen-doped precursor powder at 800 °C for 1 h at a heating rate of 2 °C / min, and the obtained black powder is nitrogen-doped hierarchical porous hollow carbon spheres; add 10 g of hollow carbon spheres and 2 mL of glacial acetic acid to 100 mL of anhydrous tetrahydrofuran, ultrasonically disperse for 30 min, then add 8 mL of KH570, and reflux and react at 70 °C for 6 h. Centrifuge, wash, and dry the product to obtain vinyl-functionalized carbon spheres.

[0085] Perform performance tests on the hollow carbon spheres prepared in Examples 1-4 and Comparative Examples 1-2. Among them, use a TriStarII 3020 type automatic specific surface and pore size analyzer to test the specific surface area, pore volume, and average pore diameter of the samples.

[0086] Electrochemical tests were carried out on an electrochemical workstation (Wuhan Koster). All tests used a three-electrode system. The preparation process of the working electrode is as follows: Mix the prepared hollow carbon spheres, conductive agent (acetylene black), and binder (polytetrafluoroethylene) in a mass ratio of 8:1:1, add an appropriate amount of NMP (N-methylpyrrolidone), stir for 12 h, and apply it on conductive graphite paper. The application area is 1 cm 2 . Use a platinum sheet as the counter electrode and an Ag / AgCl reference electrode, and the prepared electrode sheet as the working electrode, and perform capacitance performance tests in a 1 mol / L sodium chloride solution. The test results are shown in Table 1. Example 1 showed a relatively high specific capacitance (when the current density was 0.5 A / g, the capacitance value was 236.6 F / g). Use 16 mg of hollow carbon spheres as the electrode material and uniformly coat it on 2×2 cm2 It was used as the CDI cathode on the conductive graphite paper, and the CDI anode was prepared by the same method. A symmetric capacitive deionization device was assembled for performance testing, and the test results are shown in Table 1. The desalination effect of Example 1 was the best in a sodium chloride solution of 500 mg / L at a voltage of 1.2 V, and its salt adsorption capacity was 25.21 mg / g.

[0087] Table 1 Performance test results

[0088]

[0089] It can be seen from Examples 1 to 4 and Comparative Examples 1 to 2 that the hollow-structured materials prepared by the present invention are characterized by their high specific surface area and excellent pore volume, ensuring the accessibility of the electroadsorption interface, thus effectively promoting ion diffusion. This structural design not only improves the electrochemical performance of the material but also enhances its efficiency and stability in the electroadsorption process. Moreover, the synergistic effect of N, P, and S ternary heteroatoms greatly enhances the ion exchange ability of the material and exhibits excellent ion adsorption performance. Through comprehensive analysis, the technical solution of the present invention effectively overcomes multiple challenges in the prior art. Through the innovative design of nitrogen doping and hierarchical pore structure, the performance of the material in capacitive deionization applications is significantly improved, having significant practical application value and broad market prospects.

[0090] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and all should be covered within the protection scope of the present invention.

Claims

1. A method for preparing nitrogen-doped multi-level porous hollow carbon spheres, characterized in that: The steps include: (1) dissolving melamine and polyvinyl pyrrolidone in deionized water, heating to form a transparent solution, adding formaldehyde aqueous solution and mixing evenly, adding glacial acetic acid to the mixed solution and continuing to stir, centrifuging, washing, and drying after the stirring is completed 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 olefinic carbon spheres and AIBN to anhydrous tetrahydrofuran, dispersing by ultrasonication 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 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 and stirring at 100-300 r / min for 5-15 min. The mixing conditions are stirring at 100-300 r / min for 30-60 min. After adding glacial acetic acid, continue stirring at 200-500 r / min and 70-90°C for 1-5 h.

3. The method for preparing nitrogen-doped multi-level porous hollow carbon spheres according to claim 1, characterized in that: 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, characterized in that: 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, characterized in that: In step (3), the amount 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, characterized in that: In step (4), the amount ratio of olefinic 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, characterized in that: In step (5), the usage ratio of carbon 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, characterized in that: 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. A nitrogen-doped multi-level porous hollow carbon sphere 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 sphere as claimed in claim 9 in capacitive deionization.

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