Preparation method and application of phenolic aldehyde-based hollow mesoporous carbon microspheres and silicon dioxide microspheres

Abstract

The invention relates to the technical field of microsphere materials, in particular to microspheres and derivatives thereof, including phenolic resin-based hollow mesoporous carbon materials (hollow mesoporous carbon microspheres) and core-shell silicon dioxide microspheres as well as a preparation method and application thereof. The preparation method of the microspheres comprises the step of reacting resorcinol and aldehyde in a solvent in the absence of a surfactant in a system by taking ammonia water as a basic catalyst, when the molar ratio of the reaction amount of the aldehyde to the resorcinol is (0.5-1): 1, adding tetraethyl silicate to obtain microspheres; and carbonizing the microspheres and removing the silicon dioxide to obtain the phenolic aldehyde-based hollow mesoporous carbon microspheres. The preparation method provided by the invention can be used for preparing the hollow large mesoporous carbon microspheres under the reaction condition of no surfactant.

Description

Technical Field

[0001] The present invention relates to the technical field of microsphere materials, and in particular to a microsphere and its derivatives, including phenolic resin-based hollow mesoporous carbon materials (hollow mesoporous carbon microspheres), core-shell silica microspheres, and preparation methods and applications thereof. Background Art

[0002] Resource shortage and environmental pollution are two major challenges facing mankind. In order to solve the problem of environmental pollution and achieve the goals of carbon peak and carbon neutrality, the development of renewable energy is an important way, and the storage of renewable energy is crucial. Current energy storage devices include supercapacitors, lithium-ion batteries, etc. Carbon materials have a great influence on the performance of energy storage devices, and carbon microspheres have rich surface and internal structures and large specific surface area, and are a kind of carbon material with excellent performance. Phenolic resin is simple to prepare, easy to carbonize, and has a high carbonization yield. It is an ideal material for preparing carbon materials. The existing carbon microspheres prepared with phenolic resin as raw material are mainly microporous structures. When used as electrodes, they have the disadvantages of large ion transmission resistance, large impedance and low capacity. The introduction of mesopores can improve the above shortcomings. The existing hard template method is difficult to prepare carbon microspheres with large mesopores, and the soft template method requires the assistance of surfactants. The preparation of hollow mesoporous carbon microspheres based on surfactant-free has become a huge challenge. Zhang et al. (Chemistry of Materials, 2015, 27: 6297–304) obtained multi-shell hollow mesoporous (depressed) carbon microspheres by adding TEOS twice at the right time. The silicon dioxide produced by the hydrolysis of high-concentration TEOS played an important role in the generation of mesopores. However, this method has many steps, the process requires precise control, and the raw material consumption is large.

[0003] Silica is an important industrial inorganic material. Silica prepared by traditional methods is mostly irregular or solid structure. Spherical silica has a high specific surface area and good surface properties, while silica prepared by existing methods is mostly single-layer and single-pore structure. The development of silica with rich morphology and pore structure will enable it to achieve better applications in the fields of medicine, food, electronics, etc. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a microsphere and its derivatives, including phenolic resin-based hollow mesoporous carbon materials (hollow mesoporous carbon microspheres), core-shell silica microspheres and their preparation methods and applications. The preparation method provided by the present application can be used to prepare hollow large mesoporous carbon microspheres and core-shell multi-level structured silica microspheres under surfactant-free reaction conditions, which have great potential in the fields of catalytic materials, electrode materials, molding materials, adsorption materials or drug loading materials.

[0005] In order to solve the above technical problems, the present invention provides a method for preparing phenolic hollow mesoporous carbon microspheres, comprising the steps of reacting resorcinol with aldehyde in a solvent with ammonia water as an alkaline catalyst in the absence of a surfactant in the system;

[0006] and adding tetraethyl silicate when the molar ratio of the reaction amount of the aldehyde to the resorcinol is (0.5-1):1 to obtain microspheres;

[0007] And the step of carbonizing the microspheres and removing silicon dioxide to obtain phenolic hollow mesoporous carbon microspheres.

[0008] Furthermore, the tetraethyl silicate is added to the solvent before the system becomes turbid.

[0009] Furthermore, the solvent includes water and alcohol, and the alcohol is selected from at least one of methanol, ethanol, propanol, butanol, octanol, pentanol, hexanol, heptanol, hemptanol, ethylene glycol, glycerol, propylene glycol, and pentaerythritol.

[0010] Furthermore, the volume ratio of the water to the alcohol is 1:(1-10).

[0011] Furthermore, the aldehyde is selected from paraformaldehyde or formaldehyde.

[0012] Furthermore, the molar ratio of the ammonia water to resorcinol is (1-20):1;

[0013] The molar ratio of the added amount of the aldehyde to resorcinol is (1.5-3):1;

[0014] The molar ratio of tetraethyl silicate to resorcinol is (0.5-20):1;

[0015] The concentration of the resorcinol in the solvent is 1 to 100 mg / mL.

[0016] Further provided is a phenolic-based hollow mesoporous carbon microsphere prepared by the above-mentioned preparation method.

[0017] Further provided is a core-shell silica microsphere, which is obtained by removing the phenolic resin from the microsphere prepared by the above preparation method.

[0018] Furthermore, the core-shell silica microspheres have an outer pore structure and an inner pore structure, and the pore diameter of the outer pore structure is larger than the pore diameter of the inner pore structure.

[0019] Further provided is the use of the aforementioned phenolic hollow mesoporous carbon microspheres in the preparation of catalytic materials, electrode materials, molding materials, adsorption materials or drug-loaded materials.

[0020] The beneficial effects of the present invention are as follows: the preparation method provided by the present invention is easy to operate, a variety of derivatives can be obtained based on the microspheres, and the derivatives have large mesoporous structures and void structures, are particularly suitable for applications in electrode materials, etc., and have good electrochemical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a SEM image of the carbon microspheres prepared in Example 1 of the specific implementation manner of the present invention;

[0022] Figure 2 TEM image of the carbon microspheres prepared in Example 1 of the specific embodiment of the present invention;

[0023] Figure 3 This is a TEM image of the silica microspheres prepared in Example 1 of the specific implementation mode of the present invention;

[0024] Figure 4 This is a TEM image of the carbon microspheres prepared in Comparative Example 1 in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0025] In order to explain the technical content, achieved objectives and effects of the present invention in detail, the following is an explanation in conjunction with the implementation modes and the accompanying drawings.

[0026] In the present invention, resorcinol and formaldehyde are preferentially reacted to a certain extent under the catalytic action of water / alcohol system and ammonia water to form a soluble phenolic resin with a certain molecular weight, and then tetraethyl silicate is added. Tetraethyl silicate is first rapidly hydrolyzed and condensed to form silicon dioxide and become a core under the catalytic action of water / alcohol system and ammonia water. In the process of hydrolysis and condensation of tetraethyl silicate to form silicon dioxide, the condensation reaction of resorcinol and formaldehyde is also continued. When the reaction reaches a certain extent, the molecular weight of the phenolic resin reaches a sufficiently large level, and microparticles will also be precipitated. At this time, the phenolic resin microparticles will be coated on the surface of the silicon dioxide core together with the silicon dioxide microparticles to form a phenolic resin / silicon dioxide composite shell layer, and finally form silicon dioxide coated phenolic resin / silicon dioxide shell core microspheres. Since the hydrolysis and condensation of tetraethyl silicate is delayed, when resorcinol and formaldehyde react to precipitate microparticles, a certain amount of tetraethyl silicate and its soluble condensation products still exist in the system, and the silica produced by its hydrolysis and condensation will be assembled together with the phenolic resin microparticles. Therefore, the preferential condensation of resorcinol and formaldehyde significantly increases the concentration of tetraethyl silicate and its soluble condensation products in the later system, so that more silica and phenolic resin are co-coated / assembled, and the amount of silica in the composite shell is increased. After carbonization, silica-coated carbon / silicon dioxide shell core microspheres are obtained, and hollow structure mesoporous carbon microspheres are obtained after removing the silica in the core and the composite shell. The silica produced by the early hydrolysis and condensation of tetraethyl silicate serves as a hollow template, while the silica produced by the later hydrolysis and condensation becomes a pore-forming agent, and mesopores are obtained after etching, that is, the outer layer pore structure and the inner layer pore structure are formed respectively. Based on the above process, phenolic resin is used as a template for silica, and after removing the phenolic resin from the silica-coated phenolic resin / silica core-shell microspheres, a core-shell structured silica is obtained, in which the pore size of the outer pore structure is larger than that of the inner pore structure.

[0027] Specifically, the present invention provides a method for preparing microspheres, including the steps of reacting resorcinol and aldehyde in a solvent with ammonia water as an alkaline catalyst in the absence of a surfactant in the system; adding tetraethyl silicate when the molar ratio of the reaction amount of the aldehyde to the resorcinol is (0.5-1):1 to obtain microspheres; and obtaining phenolic hollow mesoporous carbon microspheres after carbonizing the microspheres and removing silicon dioxide.

[0028] Specifically, in the absence of a surfactant, resorcinol and aldehyde (such as formaldehyde) are in water / alcohol, and resorcinol and formaldehyde preferentially condense under the catalytic action of ammonia water. When the molar ratio of the reaction amount of formaldehyde to resorcinol reaches (0.5-1):1 and before the system becomes turbid, tetraethyl silicate is added, and the reaction is continued to obtain silica-coated phenolic resin / silicon dioxide microspheres, i.e., the aforementioned microspheres.

[0029] In the water / alcohol / ammonia system, the hydrolysis and condensation rate of tetraethyl silicate is significantly greater than the condensation rate of resorcinol-formaldehyde. Therefore, if tetraethyl silicate and resorcinol / formaldehyde are added to the water / alcohol / ammonia system, tetraethyl silicate will be rapidly hydrolyzed and condensed to form silica microspheres. When resorcinol / formaldehyde condenses to a degree sufficient to precipitate phenolic resin microparticles, the tetraethyl silicate in the system has basically reacted to form silica microspheres. Therefore, the phenolic resin microparticles can only be coated on the surface of silica alone to form silica-coated phenolic resin microspheres. After carbonizing and removing the silica in the inner core, only hollow microporous carbon microspheres can be obtained (see Comparative Example 1). After removing the phenolic resin from the silica-coated phenolic resin microspheres, only single-layer and densely structured silica microspheres can be obtained. Therefore, in the absence of a surfactant, resorcinol and formaldehyde are preferentially condensed in water / alcohol under the catalytic action of ammonia water. When the molar ratio of the reaction amount of formaldehyde to resorcinol reaches (0.5-1):1 and before the system becomes turbid, tetraethyl silicate is added. This is the key technical concept for obtaining the patented hollow structure carbon microspheres of the present invention. When the molar ratio of the reaction amount of formaldehyde to resorcinol reaches (0.5-1):1 and before the system becomes turbid, resorcinol and formaldehyde have condensed to a certain extent. At this time, adding tetraethyl silicate can just make resorcinol / formaldehyde condense to precipitate particles. There is still enough tetraethyl silicate and its soluble condensation product in the system. The silicon dioxide produced by the hydrolysis of tetraethyl silicate and its soluble condensation product will be co-coated with the phenolic resin particles to form a phenolic resin / silicon dioxide composite shell layer. After carbonizing and removing the silicon dioxide of the shell layer, a carbon shell layer with mesopores can be obtained. If the phenolic resin is removed, a silicon dioxide shell layer with a loose structure will be obtained. It is understandable that the timing of adding tetraethyl silicate is very critical. If it is added earlier, the hydrolysis and condensation of tetraethyl silicate will be more thorough, and there will not be enough silica in the later system to achieve co-assembly, making it difficult to form a phenolic resin / silicon dioxide composite shell and the subsequent mesopores, and what is obtained is a microporous carbon microsphere with a hollow structure and a single-layer dense silica microsphere with a solid structure. If the addition is delayed for a longer time, resorcinol and formaldehyde will undergo a deeper condensation to form phenolic resin particles. The formed phenolic resin particles will become the core, and the hollow structure cannot be obtained. What is obtained is a carbon microsphere with a core-shell structure and a single-layer silica microsphere with a hollow structure.

[0030] More specifically, the method for preparing the microspheres comprises the following steps:

[0031] 1) Add resorcinol to water / alcohol, add ammonia water, and stir evenly;

[0032] 2) adding aldehyde to cause formaldehyde and resorcinol to preferentially undergo condensation reaction;

[0033] 3) When the molar ratio of the reaction amount of aldehyde to resorcinol reaches (0.5-1):1 and before the system becomes turbid, tetraethyl silicate is added;

[0034] 4) After continuing the reaction, a turbid solution is obtained;

[0035] 5) The turbid liquid is centrifuged, washed and dried to obtain silica-coated phenolic resin / silica microspheres.

[0036] In one embodiment, the solvent includes water and alcohol, and the alcohol is selected from one or two of methanol, ethanol, propanol, butanol, octanol, pentanol, hexanol, heptanol, heptyl alcohol, ethylene glycol, glycerol, propylene glycol, and pentaerythritol, or a combination of two or more thereof, and the volume ratio of the water to the alcohol is 1: (1 to 10).

[0037] In one embodiment, the concentration of resorcinol in the solvent is 1-100 mg / mL, and the molar ratio of ammonia water to resorcinol is (1-20): 1. In this embodiment, ammonia water as an alkaline catalyst can promote the reaction of tetraethyl silicate and resorcinol / aldehyde (such as formaldehyde), and its ammonium ions can also promote the co-assembly and coating of phenolic resin and silica on the surface of the silica core.

[0038] In one embodiment, the aldehyde is selected from paraformaldehyde, formaldehyde or formaldehyde solution, and the molar ratio of the aldehyde to resorcinol is (1.5-3):1. In this embodiment, formaldehyde is used as a carbon source to react with resorcinol to form a phenolic resin. In an alternative embodiment, the ammonia water and formaldehyde are replaced by the aforementioned hexamethylenetetramine, and reacted with resorcinol in the solvent.

[0039] In one embodiment, the molar ratio of tetraethyl silicate to resorcinol is (0.5-20):1.

[0040] It should be noted that, in this article, unless otherwise specified, the molar ratio, mass ratio, volume ratio, etc. of each raw material are calculated based on their added amount.

[0041] A phenolic hollow mesoporous carbon microsphere is prepared by the above-mentioned preparation method. The method of removing silicon dioxide is a conventional technical means in the art, such as solvent etching, and the solvent can be hydrofluoric acid.

[0042] A core-shell silica microsphere is obtained by removing the phenolic resin from the microsphere prepared by the above preparation method. Based on the above, it can be known that the phenolic resin is formed inside the microsphere, so the phenolic resin can be removed by solvent dissolution or high-temperature burning.

[0043] An application of the above-mentioned phenolic hollow mesoporous carbon microspheres in the preparation of catalytic materials, electrode materials, molding materials, adsorption materials or drug-loaded materials.

[0044] Example 1

[0045] A method for preparing microspheres comprises the following steps:

[0046] 1) Add resorcinol to water / ethanol, add ammonia water, and stir evenly;

[0047] 2) adding formaldehyde aqueous solution to allow formaldehyde and resorcinol to preferentially undergo condensation reaction;

[0048] 3) When the molar ratio of the reaction amount of formaldehyde to resorcinol reaches 0.6:1, tetraethyl silicate is added;

[0049] 4) After continuing the reaction, a turbid solution is obtained;

[0050] 5) centrifuging, washing and drying the turbid liquid to obtain silica-coated phenolic resin / silica microspheres;

[0051] 6) The microspheres were carbonized at 700 °C for 4 h and the silicon dioxide was removed by hydrofluoric acid to obtain hollow mesoporous carbon microspheres HMCS1 (such as Figure 1 and 2 shown);

[0052] The volume ratio of water to alcohol is 1:7;

[0053] The molar ratio of ammonia water to resorcinol is 11:1;

[0054] The concentration of resorcinol in the solution is 5 mg / mL;

[0055] The molar ratio of formaldehyde to resorcinol is 2:1;

[0056] The molar ratio of tetraethyl silicate to resorcinol is 3.4:1;

[0057] The pore size of the carbon microspheres was found to be about 12 nm, which resulted in large mesopores in the carbon microspheres. The BET specific surface area and pore volume were 675.8 m 2 ·g -1 and 1.1cm 3 ·g -1 .

[0058] Preparation method of core-shell silica microspheres: The silica-coated phenolic resin / silica microspheres of step 5) are calcined in air at 600°C for 2h to remove the phenolic resin of the shell layer, thereby obtaining core-shell silica microspheres (such as Figure 3 shown).

[0059] Comparative Example 1

[0060] A method for preparing microspheres comprises the following steps:

[0061] 1) Add resorcinol to water / ethanol, add ammonia water, and stir evenly;

[0062] 2) adding formaldehyde aqueous solution and tetraethyl silicate to obtain a turbid liquid after reaction;

[0063] 3) centrifuging, washing and drying the turbid liquid to obtain silica-coated phenolic resin microspheres;

[0064] 4) The microspheres were carbonized at 700 °C for 4 h and the silicon dioxide was removed by hydrofluoric acid to obtain hollow carbon microspheres HCS (such as Figure 4 shown);

[0065] The volume ratio of water to alcohol is 1:7;

[0066] The molar ratio of ammonia water to resorcinol is 11:1;

[0067] The concentration of resorcinol in the solution is 5 mg / mL;

[0068] The molar ratio of formaldehyde to resorcinol is 2:1;

[0069] The molar ratio of tetraethyl silicate to resorcinol is 3.4:1;

[0070] After testing, the pore size of the carbon microspheres is less than 2nm, so there is no mesopore, and the main structure is microporous (when the pore size is less than 2nm, the main structure in the carbon microspheres is microporous structure). The BET specific surface area and pore volume are 514.3m 2 ·g -1 and 1.2cm 3 ·g -1 .

[0071] Preparation method of silica microspheres: calcining the silica-coated phenolic resin microspheres in step 3) at 700° C. for 4 hours in air to remove the phenolic resin in the shell layer to obtain solid silica microspheres.

[0072] Example 2

[0073] 1) Add resorcinol to water / ethanol, add ammonia water, and stir evenly;

[0074] 2) adding formaldehyde aqueous solution to allow formaldehyde and resorcinol to preferentially undergo condensation reaction;

[0075] 3) When the molar ratio of the reaction amount of formaldehyde to resorcinol reaches 0.725:1, tetraethyl silicate is added;

[0076] 4) After continuing the reaction, a turbid solution is obtained;

[0077] 5) centrifuging, washing and drying the turbid liquid to obtain silica-coated phenolic resin / silica microspheres;

[0078] 6) The microspheres were carbonized at 700°C for 4 h and the silicon dioxide was removed by hydrofluoric acid to obtain hollow mesoporous carbon microspheres HMCS2;

[0079] The volume ratio of water to alcohol is 1:7;

[0080] The molar ratio of ammonia water to resorcinol is 11:1;

[0081] The concentration of resorcinol in the solution is 5 mg / mL;

[0082] The molar ratio of formaldehyde to resorcinol is 2:1;

[0083] The molar ratio of tetraethyl silicate to resorcinol is 3.4:1;

[0084] The pore size of the carbon microspheres was found to be about 13.4 nm, and the BET specific surface area and pore volume were 772.2 m 2 ·g -1 and 1.698cm 3 ·g -1 .

[0085] Preparation method of core-shell silica microspheres: calcine the silica-coated phenolic resin / silica microspheres in step 5) at 600° C. in air for 2 h to remove the phenolic resin in the shell layer, thereby obtaining core-shell silica microspheres.

[0086] Example 3

[0087] 1) Add resorcinol to water / ethanol, add ammonia water, and stir evenly;

[0088] 2) adding formaldehyde aqueous solution to allow formaldehyde and resorcinol to preferentially undergo condensation reaction;

[0089] 3) When the molar ratio of the reaction amount of formaldehyde to resorcinol reaches 0.85:1, tetraethyl silicate is added;

[0090] 4) After continuing the reaction, a turbid solution is obtained;

[0091] 5) centrifuging, washing and drying the turbid liquid to obtain silica-coated phenolic resin / silica microspheres;

[0092] 6) Carbonizing the microspheres and removing silicon dioxide to obtain hollow mesoporous carbon microspheres HMCS3;

[0093] The volume ratio of water to alcohol is 1:7;

[0094] The molar ratio of ammonia water to resorcinol is 11:1;

[0095] The concentration of resorcinol in the solution is 5 mg / mL;

[0096] The molar ratio of formaldehyde to resorcinol is 2:1;

[0097] The molar ratio of tetraethyl silicate to resorcinol is 3.4:1;

[0098] The pore size of the carbon microspheres was found to be about 12.8 nm, and the BET specific surface area and pore volume were 786.2 m 2 ·g -1 and 2.001cm 3 ·g -1 .

[0099] Preparation method of core-shell silica microspheres: calcine the silica-coated phenolic resin / silica microspheres in step 5) at 600° C. in air for 1 h to remove the phenolic resin in the shell layer, thereby obtaining core-shell silica microspheres.

[0100] Test example

[0101] The hollow mesoporous carbon microspheres prepared in Examples 1 to 3 and Comparative Example 1 were respectively tested for supercapacitor performance, and the results are shown in Table 1.

[0102] Supercapacitor performance test: The prepared carbon microspheres were mixed with binder PVDF and carbon black in a mass ratio of 8:1:1 and coated on an electrode sheet to obtain a working electrode. The performance was tested in the following way: On a CHI760E electrochemical workstation, a constant current charge and discharge test was performed using a 6M KOH electrolyte and a three-electrode system. The electrodes of the three-electrode system included a reference electrode (Hg / HgO), a counter electrode (Pt sheet) and a working electrode.

[0103] Table 1

[0104]

[0105] It can be seen from Table 1 that the electrode prepared using the phenolic hollow mesoporous carbon microspheres obtained in the present invention as the material has a high capacity and capacity retention rate.

[0106] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent transformations made using the contents of the present invention's specification and drawings, or directly or indirectly applied in related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for preparing phenolic hollow mesoporous carbon microspheres, characterized in that: The method comprises the steps of reacting resorcinol with aldehyde in a solvent with ammonia water as a basic catalyst in the absence of a surfactant in the system; When the molar ratio of the reaction amount of the aldehyde to the resorcinol is (0.5-1):1, tetraethyl silicate is added to obtain microspheres; And the step of carbonizing the microspheres and removing silicon dioxide to obtain phenolic hollow mesoporous carbon microspheres.

2. The preparation method according to claim 1, characterized in that: The tetraethyl silicate is added into the solvent before the system becomes turbid.

3. The preparation method according to claim 1, characterized in that: The solvent comprises water and alcohol, and the alcohol is selected from at least one of methanol, ethanol, propanol, butanol, octanol, pentanol, hexanol, heptanol, hemptanol, ethylene glycol, glycerol, propylene glycol, and pentaerythritol.

4. The preparation method according to claim 3, characterized in that: The volume ratio of the water to the alcohol is 1:(1-10).

5. The preparation method according to claim 1, characterized in that: The aldehyde is selected from paraformaldehyde or formaldehyde.

6. The preparation method according to claim 1, characterized in that: The molar ratio of the ammonia water to the resorcinol is (1-20):1; The molar ratio of the added amount of the aldehyde to resorcinol is (1.5-3):1; The molar ratio of tetraethyl silicate to resorcinol is (0.5-20):1; The concentration of the resorcinol in the solvent is 1 to 100 mg / mL.

7. A core-shell silica microsphere, characterized in that: The microspheres prepared by the preparation method according to any one of claims 1 to 6 are obtained by removing the phenolic resin.

8. The core-shell silica microsphere according to claim 7, characterized in that: The core-shell silica microspheres have an outer pore structure and an inner pore structure, and the pore diameter of the outer pore structure is larger than that of the inner pore structure.

9. Phenolic hollow mesoporous carbon microspheres prepared by the preparation method according to any one of claims 1 to 6.

10. Use of the phenolic hollow mesoporous carbon microspheres as claimed in claim 9 in preparing catalytic materials, electrode materials, molding materials, adsorption materials or drug-loaded materials.

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