CN111569797B - Inverse opal type macroporous/mesoporous nitrogen-doped carbon microsphere and preparation method thereof - Google Patents

Inverse opal type macroporous/mesoporous nitrogen-doped carbon microsphere and preparation method thereof Download PDF

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CN111569797B
CN111569797B CN202010455942.4A CN202010455942A CN111569797B CN 111569797 B CN111569797 B CN 111569797B CN 202010455942 A CN202010455942 A CN 202010455942A CN 111569797 B CN111569797 B CN 111569797B
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汪谟贞
杨文秀
葛学武
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University of Science and Technology of China USTC
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Abstract

The invention provides a preparation method of inverse opal type macroporous/mesoporous nitrogen-doped carbon microspheres, which comprises the following steps: A) F-SiO2Washing the nano particles, and washing the F-SiO2Mixing the nano particles, water, a non-polar solvent and an emulsifier to obtain an inverse emulsion; standing the inverse emulsion to obtain F-SiO2Colloidal crystal microspheres; B) injecting one of acrylonitrile and acrylonitrile/initiator mixed solution into F-SiO2Colloidal crystal microsphere and initiating acrylonitrile to polymerize to obtain polyacrylonitrile/F-SiO2Compounding the microspheres; C) subjecting the polyacrylonitrile/F-SiO2And sequentially carbonizing and etching the composite microspheres to obtain the inverse opal type macroporous/mesoporous nitrogen-doped carbon microspheres. The inverse opal type macroporous/mesoporous nitrogen-doped carbon microsphere prepared by the method has rich mesopores, macropore pores and more N active sites, and has potential application in the aspects of adsorption separation, new energy technology, environmental pollution treatment and the like.

Description

Inverse opal type macroporous/mesoporous nitrogen-doped carbon microsphere and preparation method thereof
Technical Field
The invention relates to the technical field of inorganic non-metallic material synthesis, in particular to an inverse opal type macroporous/mesoporous nitrogen-doped carbon microsphere and a preparation method thereof.
Background
The porous carbon material has the advantages of high chemical stability, good conductivity, low price and the like, is widely concerned, and can be applied to a plurality of fields of adsorption separation, catalysis, carriers, electrochemical energy storage and the like.
Researchers have conducted many studies on the preparation of porous carbon materials. Related literature (Lee J, Kim J, Hyeon T. advanced Materials,2006,18(16):2073-Hong K, Burke N.catalysis Today,2011,178(1):197-205.) reports that introduction of porous structures into carbon matrices often requires the use of specific templates. Depending on the phase of the template, a non-solid soft template and a solid hard template can be distinguished. Soft template methods generally use micelles formed by surfactants as pore-forming units to directly synthesize ordered mesoporous carbon-carbon materials (Liang C, Hong K, Guiochon G A, et al. Angewandte chemical International Edition,2004,43(43): 5785-5789.). The hard template method is that a carbon precursor is combined with a solid hard template with a special structure, the carbon precursor is carbonized to form a carbon substrate, and then the hard template is removed, so that the porous carbon material with the corresponding pore structure is obtained; for example: 200nm solid SiO2The nano particles are assembled into a colloidal crystal block by a natural sedimentation method, phenol and formaldehyde are filled into the colloidal crystal block as a template to initiate the phenol and the formaldehyde to polymerize to form a crosslinked phenolic aldehyde polymer as a carbon source, and then the crosslinked phenolic aldehyde polymer is carbonized and etched to form SiO2The process of nanoparticles produces carbon materials having a continuous uniform macropore throughout (Yu J S, Kang S, Yoon S B, et al. journal of the American Chemical Society,2002,124(32): 9382-.
In the soft template method, the formation of the soft template generally needs to be generated in situ in a carbon material synthesis system, and the formation conditions and the type of the pore structure are very limited; the hard template method can independently synthesize the hard template in advance according to needs, and has great advantages compared with the soft template method in variety of type and structural design and convenience in preparation, so that the hard template method is widely used in preparation of the porous carbon material. According to the principle of pore-forming by a template, the pore structure of the porous carbon material prepared by the template method completely depends on the structure of the template, so that the design and preparation of the hard template with a novel structure are the key for developing the porous carbon material.
According to the definition of the International Union of Pure and Applied Chemistry (IUPAC), porous materials can be divided into three types according to pore size: macropores (>50nm), mesopores (2-50 nm) and micropores (<2 nm). Limited by the structural design of the template, most of the current porous carbon materials are in a single-aperture structure. For example, in the micelle soft template method, the size of the micelle is generally 50nm or less, and thus the pore structure formed is generally a dispersed uniform mesoporous structure. The size of the solid hard template is generally larger than 50nm, so that the obtained carbon material is mostly macroporous carbon material. A single pore size sometimes imposes certain limitations on the application of porous materials. In order to make the porous material have good permeability, large pore volume and high specific surface area, multi-level pore structures such as macropores and mesopores are often required to be introduced into the carbon material, which puts new requirements on the design of the template material.
On the other hand, in the development of carbon material applications, it is desirable that the carbon material matrix have sufficient active sites to impart desired properties and functions thereto. Research shows that nitrogen atom doping can regulate electronic structure, change some physical and chemical properties of carbon material and improve its performance. For example, polyacrylonitrile is used as carbon source and coated on mesoporous SiO2And carbonizing and removing the template on the microsphere template to obtain the N-doped porous carbon spheres. Due to the introduction of N element, the dispersibility of the porous carbon microsphere in polar solvent (such as water) and the adsorption performance of small molecules can be improved (Xie Y, Yang W, Wang M, et al, chemical Engineering Journal,2017,323, 224-232.). Therefore, introduction of N element into the porous carbon material in order to achieve further improvement in performance is an important point currently demanded by researchers.
Disclosure of Invention
The invention aims to provide a preparation method of an inverse opal type macroporous/mesoporous nitrogen-doped carbon microsphere, and the inverse opal type macroporous/mesoporous nitrogen-doped carbon microsphere prepared by the method has rich mesopores, macropore pores and more N active sites.
In view of the above, the application provides a preparation method of an inverse opal type macroporous/mesoporous nitrogen-doped carbon microsphere, which is characterized by comprising the following steps:
A) F-SiO2Washing the nano particles, and washing the F-SiO2Mixing the nano particles, water, a non-polar solvent and an emulsifier to obtain an inverse emulsion; standing the inverse emulsion to obtain F-SiO2Colloidal crystal microspheres;
B) adding acrylonitrile and acrylonitrile/initiator mixed solutionIs implanted into the F-SiO2Colloidal crystal microsphere and initiating acrylonitrile to polymerize to obtain polyacrylonitrile/F-SiO2Compounding the microspheres;
C) subjecting the polyacrylonitrile/F-SiO2Carbonizing the composite microspheres to obtain the nitrogen-doped C/F-SiO2Compounding the microspheres;
D) doping the nitrogen with C/F-SiO2And etching the composite microspheres to obtain the inverse opal type macroporous/mesoporous nitrogen-doped carbon microspheres.
Preferably, the F-SiO2The preparation method of the nano particles comprises the following steps:
mixing an emulsifier, a catalyst, a water phase, an oil phase and a cosolvent, and then reacting with alkyl orthosilicate;
the volume ratio of the water phase to the oil phase is 1:1, the oil phase is one or more of cyclohexane, normal hexane, normal heptane and normal octane, the emulsifier is cetyl trimethyl ammonium bromide, the cosolvent is isopropanol, and the catalyst is urea.
Preferably, the F-SiO2The particle size of the nanoparticles is 50-500 nm.
Preferably, the F-SiO2Washing the nano particles by alternately washing with ethanol and water until the F-SiO is washed2The Zeta potential of the nano particles dispersed in water is-25 to-5 mV.
Preferably, in step A), in the inverse emulsion, the F-SiO2The content of the nano particles is 3-20 wt%; the emulsifier is one or two of Span80 and Hypermer2296, and the nonpolar solvent is one or two of kerosene and n-hexadecane; the standing temperature is 20-50 ℃.
Preferably, in step B), the polymerization is initiated by radiation or heat; the radiation-initiated polymerization employs60Introducing nitrogen to remove oxygen before irradiation by using Co gamma rays, wherein the absorption dose rate is 70-100 Gy/min, the irradiation time is 17-96 h, and the corresponding absorption dose is 100-400 kGy; the temperature for heating to initiate polymerization is 40-50 ℃, and the reaction time is 12-24 h.
Preferably, in the step C), the carbonization is carried out in an inert atmosphere, the temperature rise rate of the carbonization is 1-20 ℃/min, the temperature is 500-700 ℃, and the time is 60-180 min.
Preferably, in the step D), the etching is carried out in a hydrofluoric acid solution, the etching temperature is 40-60 ℃, and the etching time is 8-12 hours.
The application also provides the inverse opal type macroporous/mesoporous nitrogen-doped carbon microsphere prepared by the preparation method, which has a cage-shaped structure formed by three-dimensional through macropores formed by a nitrogen-carbon framework, wherein the inner wall of each macropore is a fibrous porous surface.
Preferably, the size of the macropores in the cage-pore structure is 50-250 nm.
The application provides a preparation method of inverse opal type macroporous/mesoporous nitrogen-doped carbon microspheres, which utilizes narrow-distribution fibrous silicon dioxide nanoparticles (F-SiO)2) F-SiO formed by inducing self-assembly thereof in inverse emulsion through water evaporation2Using colloid crystal microsphere as template, infiltrating Acrylonitrile (AN) into the pores of the template microsphere, polymerizing to form Polyacrylonitrile (PAN), carbonizing PAN, and etching to remove F-SiO2And (3) obtaining the novel inverse opal type macroporous/mesoporous nitrogen-doped carbon microsphere by using the colloidal crystal template microsphere. The microsphere has rich mesopores and macropores and more N active sites, and has potential application in the aspects of adsorption separation, new energy technology, environmental pollution treatment and the like.
Drawings
FIG. 1 shows F-SiO prepared in example 1 of the present invention2TEM photographs of the nanoparticles at different magnifications;
FIG. 2 shows F-SiO prepared in example 1 of the present invention2An infrared spectrum of the nanoparticles;
FIG. 3 shows a composition containing F-SiO in example 1 of the present invention2The reverse phase emulsion optical microscope photograph of (1);
FIG. 4 shows porous F-SiO prepared according to example 1 of the present invention with different magnifications2SEM photograph of colloid crystal microsphere;
fig. 5 is SEM photographs of inverse opal-type macroporous/mesoporous nitrogen-doped carbon microspheres prepared in example 1 of the present invention at different magnifications;
fig. 6 is a nitrogen adsorption-desorption isotherm of the inverse opal-type macroporous/mesoporous nitrogen-doped carbon microsphere prepared in example 1 of the present invention;
FIG. 7 shows F-SiO at different magnifications prepared in example 2 of the invention2TEM photograph of the nanoparticles;
FIG. 8 shows porous F-SiO prepared in example 2 of the present invention2A colloidal crystal microsphere SEM photo and an inverse opal type macroporous/mesoporous nitrogen-doped carbon microsphere SEM photo;
FIG. 9 shows F-SiO with different Zeta potentials2Scanning electron microscope photographs of the assembly formed by the nanoparticles before and after the evaporation of the inverse emulsion solvent;
fig. 10 shows the ultraviolet-visible absorption spectrum change of the solution after the inverse opal-type macroporous/mesoporous nitrogen-doped carbon microsphere prepared in example 1 of the present invention is added into RhB aqueous solutions with different concentrations for a specific time.
Detailed Description
For a further understanding of the invention, reference will now be made to the preferred embodiments of the invention by way of example, and it is to be understood that the description is intended to further illustrate features and advantages of the invention, and not to limit the scope of the claims.
Aiming at the preparation current situation and performance requirement of a nitrogen-doped carbon material, the application firstly utilizes a fibrous SiO with the particle size of 50-500 nm and containing mesopores2Nanoparticles (F-SiO)2) Controlling conditions in the inverse emulsion as a self-assembly unit to enable the inverse emulsion to be self-assembled to form a novel micron-sized colloidal crystal microsphere with a mesoporous-macroporous multi-layered structure, taking the colloidal crystal microsphere as a template for preparing a porous carbon microsphere material, pouring Acrylonitrile (AN) into the template to initiate in-situ polymerization of the acrylonitrile to form Polyacrylonitrile (PAN) as a carbon source, carbonizing the polyacrylonitrile to form a carbon matrix containing N, and finally removing the template microsphere to obtain the micron-sized inverse opal type nitrogen-doped carbon microsphere with the multi-layered porous structure. The porous carbon microsphere is superposed with a mesoporous structure in a continuous macroporous skeleton, contains rich N active sites, and is expected to be widely applied in the fields of adsorption separation and electrochemistry. In particular, the method comprises the following steps of,the application provides a preparation method of an inverse opal type macroporous/mesoporous nitrogen-doped carbon microsphere, which is characterized by comprising the following steps:
A) F-SiO2Washing the nano particles, and washing the F-SiO2Mixing the nano particles, water, a non-polar solvent and an emulsifier to obtain an inverse emulsion; standing the inverse emulsion to obtain F-SiO2Colloidal crystal microspheres;
B) injecting one of acrylonitrile and acrylonitrile/initiator mixed solution into F-SiO2Colloidal crystal microsphere and initiating acrylonitrile to polymerize to obtain polyacrylonitrile/F-SiO2Compounding the microspheres;
C) subjecting the polyacrylonitrile/F-SiO2Carbonizing the composite microspheres to obtain the nitrogen-doped C/F-SiO2Compounding the microspheres;
D) doping the nitrogen with C/F-SiO2And etching the composite microspheres to obtain the inverse opal type macroporous/mesoporous nitrogen-doped carbon microspheres.
In the process of preparing the inverse opal type macroporous/mesoporous nitrogen-doped carbon microspheres, the application firstly utilizes narrow-distribution fibrous silicon dioxide nano particles (F-SiO)2) Self-assembly to form F-SiO2Colloidal crystal microspheres; in this process, F-SiO is first prepared2The specific preparation process of the nano particles is as follows: mixing an emulsifier, a catalyst, a water phase, an oil phase and a cosolvent, and then reacting with alkyl orthosilicate; wherein the volume ratio of the water phase to the oil phase is 1:1, the oil phase is one or more of cyclohexane, n-hexane, n-heptane and n-octane, the emulsifier is cetyl trimethyl ammonium bromide, the cosolvent is isopropanol, and the catalyst is urea; the emulsifier accounts for 3-5 wt% of the water phase, the cosolvent accounts for 3-5 wt% of the water phase, the catalyst accounts for 1-3 wt% of the water phase, and the alkyl orthosilicate accounts for 0.8-20 vol% of the water phase. The F-SiO2The preparation process of the nano particles is more specifically as follows: dissolving Cetyl Trimethyl Ammonium Bromide (CTAB) and urea in water, adding cyclohexane and isopropanol to prepare emulsion, adding a certain amount of alkyl orthosilicate, and reacting to obtain narrow-distribution fibrous SiO2Nanoparticles of (A), (B)F-SiO2) The reaction temperature is 50-80 ℃, and the reaction time is 12-24 h. The F-SiO2The particle size of the nanoparticles is 50-500 nm. In the process, tetraethyl orthosilicate (TEOS) at the outer layer of the oil phase liquid drop of the emulsion system is hydrolyzed and condensed under alkaline conditions, and shrinkage is generated on the surface of the liquid drop, so that a fibrous structure F-SiO is formed2Nanoparticles.
To obtain F-SiO2After the nanoparticles, washing the nanoparticles, wherein the washing is used for enabling the nanoparticles to have a proper Zeta potential in water so as to ensure that the nanoparticles can be self-assembled into spherical particles; for example for 230nm F-SiO2The microsphere F-SiO can be prepared only when the Zeta potential is washed to-25 to-15 mV2A colloidal crystal template. FIG. 9 is a graph of F-SiO at different Zeta potentials as shown in FIG. 9 below2Scanning electron micrographs of assemblies of nanoparticles formed before and after evaporation of the inverse emulsion solvent: (a) -3.53 mV; (b) -20.49 mV; (c) -21.63 mV; (d) -24.07 mV; (e) 30.59 mV; as can be seen, no assembled colloidal crystal microsphere template was obtained at potentials outside the above ranges. The washing is carried out by mixing F-SiO2The nano particles are washed in ethanol and water for multiple times until the F-SiO2The Zeta potential is-25 to-5 mV when the nano particles are dispersed in water.
In F-SiO2After the nano particles are washed, the nano particles are mixed with water, a nonpolar solvent and an emulsifier to obtain an inverse emulsion, and the inverse emulsion is heated to volatilize water, so that the self-assembled F-SiO is obtained2Colloidal crystal microspheres; in this process, the inverse emulsion is actually F-SiO dispersed and stabilized by an emulsifier2Consists of water droplets with a continuous phase of a non-polar solvent. As the water evaporates, the volume of the water drops gradually decreases, and the F-SiO in the water drops2The nano particles are gradually gathered and then regularly arranged under the action of van der Waals force, so that the energy of the system is lowest. After the water is completely evaporated, F-SiO is formed2Colloidal crystal microspheres. In inverse emulsion, the F-SiO2The content of the nano particles is 3-20 wt%; the emulsifier is one or two of Span80 and Hypermer2296, and the nonpolar solvent is kerosene and n-decamethyleneOne or two kinds of hexaalkane; the standing temperature is 20-50 ℃; the inverse emulsion can be formed by using a high-speed homogenizer with a speed of 8000-12000 rpm for 1-3 min or by manual shaking. The standing temperature is controlled within the range, and the self-assembly to the colloidal crystal microspheres with regular arrangement can be ensured. The standing temperature is less than or equal to 50 ℃, and F-SiO2The concentration of the aqueous dispersion (. ltoreq.20%), the type of oil phase (kerosene or n-hexadecane) and emulsifier (Span 80 or Hypermer 2296) also influence the F-SiO2And (3) forming a colloidal crystal microsphere template.
This application then injects one of the acrylonitrile and acrylonitrile/initiator mixtures into the F-SiO2In the colloidal crystal microsphere, acrylonitrile is initiated to polymerize to obtain polyacrylonitrile/F-SiO2Compounding the microspheres; in this process, F-SiO2Immersing the colloidal crystal microspheres in AN Acrylonitrile (AN) or AN/initiator mixed liquid system to allow AN or AN and initiator to naturally diffuse to F-SiO2Absorbing excessive monomers in gaps of the colloidal crystal template microspheres, and initiating acrylonitrile polymerization by radiation or heating to obtain polyacrylonitrile/F-SiO2Composite microsphere (PAN/F-SiO)2) (ii) a The radiation-initiated polymerization employs60Introducing nitrogen to remove oxygen before irradiation by using Co gamma rays, wherein the absorption dose rate is 70-100 Gy/min, the irradiation time is 17-96 h, the corresponding absorption dose is 100-400 kGy, and the radiation-initiated polymerization is carried out at room temperature, so that the stability of the morphology of the template microspheres can be maintained; the temperature for heating to initiate polymerization is 40-50 ℃, the reaction time is 12-24 hours, and when the temperature is too high, the self-assembled template is disassembled. The initiator is selected from one or more of azobisisoheptonitrile, azobisisobutyronitrile and ammonium persulfate.
The application finally relates to the polyacrylonitrile/F-SiO2Carbonizing the composite microspheres to obtain the nitrogen-doped C/F-SiO2Compounding the microspheres; doping the nitrogen with C/F-SiO2And etching the composite microspheres to obtain the inverse opal type macroporous/mesoporous nitrogen-doped carbon microspheres. The carbonization is carried out in an inert atmosphere, the temperature rise rate of the carbonization is 1-20 ℃/min, the temperature is 500-700 ℃, and the time is 60-180 min; the etching concentration is 20-40%The etching is carried out in the hydrofluoric acid solution, the etching temperature is 40-60 ℃, and the etching time is 8-12 hours.
The application provides the inverse opal type macroporous/mesoporous nitrogen-doped carbon microsphere prepared by the method, which has a cage-shaped structure formed by three-dimensional through macropores formed by a nitrogen-carbon framework, wherein the inner wall of each macropore is a fibrous porous surface.
The particle size of the inverse opal type macroporous/mesoporous nitrogen-doped carbon microsphere is 1-25 micrometers, wherein the size of macropores is 50-250 nm; the inner wall of the macropore is a fibrous porous surface and is also a surface formed by macropores/mesopores.
In order to further understand the present invention, the inverse opal-type macroporous/mesoporous nitrogen-doped carbon microsphere and the preparation method thereof provided by the present invention are described in detail below with reference to the following examples, and the scope of the present invention is not limited by the following examples.
Example 1
1) Fibrous porous SiO2Nanoparticles (F-SiO)2) Preparation of
2.0g of cetyltrimethylammonium bromide (CTAB), 1.2g of urea and 60.0mL of distilled water were sequentially added to a 250mL three-necked flask, the solid was completely dissolved by ultrasonic dispersion, and 60.0mL of cyclohexane and 1.84mL of isopropanol were sequentially added to the above system under mechanical stirring (250 rpm); dropwise adding 5.0mL of tetraethyl orthosilicate (TEOS) into the system, mechanically stirring the system at room temperature for 30min, heating to 70 ℃ and reacting for 16h to obtain F-SiO2A product; centrifuging (HC-2518ZONKIA, 8000r/min), ultrasonic dispersing with ethanol and water alternately, centrifuging and washing 3 times respectively until F-SiO2Zeta potential in water is-21.63 mV; washing the F-SiO2Drying at 50 deg.C in an electrothermal blowing drying oven;
synthesized F-SiO2The morphology (TEM, Hitachi H7650, 100kV) and the infrared spectrum (Bruker VECTOR-22) are shown in FIGS. 1 and 2, respectively, and FIG. 1 shows F-SiO prepared in this example2TEM photographs of nanoparticles at different magnifications are shown in FIG. 2, which is F-SiO prepared in this example2An infrared spectrum of the nanoparticles; FIG. 1 shows F-SiO2Is a fibrous nanoparticle with particle diameter of 230 + -50 nm and 1090cm in infrared spectrum of FIG. 2-1The strong and wide nearby absorption peak is the Si-O-Si antisymmetric stretching vibration peak, 805cm-1And 466cm-1The absorption peak is generated by Si-O-Si symmetric stretching vibration and bending vibration; 1635cm-1And 3500cm-1The peaks are respectively bending vibration peaks and stretching vibration peaks of the absorbed water; 962cm-1The peak belongs to the in-plane stretching vibration of Si-O in Si-OH; 2858cm-1And 2930cm-1And 1382cm-1And 1473cm-1Mainly comprises stretching and bending vibration peaks of saturated C-H on residual CTAB molecules;
2)F-SiO2preparation of colloidal crystal microsphere template
Weighing 0.09g of the dried F-SiO prepared in 1)2Placing the mixture into a centrifuge tube, measuring 0.6mL of water, pouring the water into the centrifuge tube, and ultrasonically dispersing the water into uniform dispersion liquid; 0.18g of emulsifier Hypermer2296 was additionally weighed and dissolved in another centrifuge tube containing 6mL of kerosene; using a pipette to mix the F-SiO2The nanoparticle aqueous dispersion was added dropwise thereto, and the system was homogenized with a high speed homogenizer (10000rpm, 2min) to form a stable white inverse emulsion as shown in the optical microscope photograph of FIG. 3; pouring the inverse emulsion into a culture dish, putting the culture dish into a far infrared rapid constant temperature drying oven, keeping the temperature at 46 ℃, and standing for 24 hours to completely volatilize water; washing the product with n-hexane to remove kerosene and emulsifier, and oven-drying in a far infrared rapid constant temperature drying oven at 50 deg.C to obtain F-SiO2Colloidal crystal microspheres, FIG. 4 shows porous F-SiO prepared in this example at different magnifications2SEM photograph of colloidal crystal microspheres: (a)500 x; (b) 3500X; (c)20000 XF-SiO, as shown in FIG. 4(SEM, JEOL JSM 67005 kV)2The grain size of the colloidal crystal microspheres is 2-25 mu m, and the enlarged surface of the microspheres can show that F-SiO2The colloidal crystal microsphere is prepared from F-SiO2Is formed by close packing;
3) preparation of inverse opal type macroporous/mesoporous nitrogen-doped carbon microsphere
Weighing 50mg of the F-SiO2Placing the colloidal crystal microsphere powder in a sample bottle, and dropwise adding Acrylonitrile (AN) until the white powder is submergedStanding for 2h to enable the monomer to completely penetrate into the colloidal crystal microspheres; sucking away the excessive liquid with a dropper, introducing nitrogen for 2min to remove oxygen in the system, sealing the sample bottle, and placing in a container60The radiation time is 27h in a Co gamma ray radiation field, the dosage rate is 81.83Gy/min, and the absorbed dose is 132.56 kGy; taking out the sample after irradiation, washing the sample with ethanol, and drying the sample in a forced air drying oven at 40 ℃ for 12 hours to obtain light yellow microsphere powder;
putting the dried powder into a quartz boat, and then putting the quartz boat into a horizontal tube furnace for carbonization; introducing argon in advance for 30min before carbonization, heating the tube furnace to 600 ℃ at the heating rate of 6 ℃/min under the protection of argon, keeping the temperature for 120min to fully carbonize the tube furnace, naturally cooling the tube furnace to room temperature, and taking out the tube furnace to obtain the nitrogen-doped C/F-SiO2Compounding microsphere powder; dispersing the mixture into 8mL of hydrofluoric acid solution (HF is more than or equal to 40%), treating the mixture in an oil bath at 40 ℃ for 10 hours, naturally cooling the system, centrifugally separating the reaction solution, washing the lower-layer precipitate with deionized water for 3 times, and drying the lower-layer precipitate in a forced air drying oven at 40 ℃ for 12 hours to obtain the inverse opal macroporous/mesoporous nitrogen-doped carbon microspheres, as shown in FIG. 5, wherein FIG. 5 is SEM photographs of the inverse opal macroporous/mesoporous nitrogen-doped carbon microspheres prepared in the embodiment with different magnifications: (a) 2000X; (b)80000 × (magnified surface of microsphere part showing that carbon microspheres are formed by packing nanoparticles around 300 nm); (c)35000 × (enlarged cross-sectional view of ruptured microspheres, showing that the interior of the nanoparticles constituting the carbon microspheres is of a hollow macroporous structure and the inner wall of the pores is of a fibrous porous surface).
The nitrogen adsorption-desorption isotherm of the inverse opal-type macroporous/mesoporous nitrogen-doped carbon microsphere prepared as described above is shown in fig. 6a, belongs to a type iv isotherm, and has a typical H3 hysteresis loop, indicating that a large number of mesopores exist in the microsphere, and the specific surface area and the pore volume of the mesopores are 266.4m2G and 0.62cm2(ii)/g; the pore size distribution calculated by the BJH method is shown in fig. 6b, and the mode pore size is in the mesoporous range of less than 50 nm. The composition was further characterized using an elemental analyzer (Elementarvariato EL cube), and the results are shown in Table 1, and the C/N molar ratio was calculated to be 5.
TABLE 1 elemental analysis data sheet for carbon microspheres of this example
Element(s) O C H N
Content (wt%) 15.34 64.75 2.62 15.04
An organic dye rhodamine b (RhB) is used as a model molecule to characterize the adsorption performance of the inverse opal macroporous/mesoporous nitrogen-doped microspheres prepared in the embodiment on small molecules, as shown in fig. 10, fig. 10 shows that micron-sized inverse opal macroporous/mesoporous nitrogen-doped carbon microspheres are added with RhB aqueous solutions [ (a)5mg/L at different concentrations; (b)10mg/L ], the ultraviolet-visible absorption spectrum of the solution changes (the concentration of the microspheres is 0.2 mg/mL); as can be seen from FIG. 10, when 4mg of the microspheres were dispersed in 20mL of 5mg/L RhB aqueous solution, all RhB molecules in the solution could be adsorbed into the microspheres after 12 hours; when the concentration of the RhB is 10mg/L, the adsorption amount of the microspheres to the RhB within 12h is 41.53mg/(g of microspheres), and only a small amount of dye molecules in the solution are remained.
Example 2
1) Fibrous porous SiO2Nanoparticles (F-SiO)2) Preparation of
2.0g of ten are added in sequenceHexaalkyltrimethylammonium bromide (CTAB), 1.2g of urea and 60.0mL of distilled water were added to a 250mL three-necked flask, the solid was completely dissolved by ultrasonic dispersion, 60.0mL of cyclohexane and 1.84mL of isopropanol were added to the above system in this order under mechanical stirring (250rpm), and 1.0mL of Tetraethylorthosilicate (TEOS) was added dropwise to the above system; mechanically stirring the system at room temperature for 30min, heating to 70 ℃ and reacting for 14h to obtain F-SiO2A product; centrifuging (HC-2518ZONKIA, 8000r/min), ultrasonic dispersing with ethanol and water alternately, centrifuging and washing 3 times respectively until F-SiO2Zeta potential in water is-20.84 mV; washing the F-SiO2Drying at 40 deg.C in electrothermal blowing dry box to obtain F-SiO2The morphology (TEM, Hitachi H7650, 100kV) is shown in FIG. 7, and FIG. 7 is F-SiO under different magnifications in this example2TEM photograph of nanoparticles, (a)60000 ×; (b) 600000X, FIG. 7 shows F-SiO2Is a fibrous nano particle with the particle diameter of 60 +/-8 nm;
2)F-SiO2preparation of colloidal crystal microsphere template
Weighing the dried F-SiO prepared in 0.045g 1)2Placing in a centrifuge tube, measuring 0.6mL water, pouring into the centrifuge tube, ultrasonically dispersing into uniform dispersion, dissolving 0.18g emulsifier Hypermer2296 in another centrifuge tube containing 6mL kerosene, and transferring to liquid gun2Dropwise adding the nanoparticle aqueous dispersion into the solution, and manually shaking the mixed system until a stable white emulsion is formed; pouring the inverse emulsion into a culture dish, putting the culture dish into a far infrared rapid constant temperature drying oven, keeping the temperature at 30 ℃, and standing for 48 hours to completely volatilize water; washing the product with n-hexane to remove kerosene and emulsifier, and oven-drying in a far infrared rapid constant temperature drying oven at 50 deg.C to obtain F-SiO2Colloidal crystal microspheres, FIG. 8 is F-SiO prepared in this example2SEM (SEM, JEOL JSM 67005 kV) photographs of colloidal crystal microspheres at different magnifications: FIGS. 8a and 8b (enlarged views of the surface) show that, in FIG. 8, F-SiO2The particle size of the colloidal crystal microspheres is 1-10 mu m;
3) preparation of inverse opal type macroporous/mesoporous nitrogen-doped carbon microsphere
Weighing 50mg of the F-SiO2Putting the colloidal crystal microsphere powder into a sample bottle, dropwise adding AN AN monomer (ABVN content is 0.3% of monomer mass) containing Azobisisoheptonitrile (ABVN) until the monomer is submerged to white powder, standing for 2h to enable the monomer and the initiator to completely permeate into the colloidal crystal microsphere, and then sucking away the redundant liquid by using a dropper; sealing the sample bottle, placing the sealed sample bottle in an oil bath, heating to 50 ℃ for reaction for 16h, washing with ethanol, and then placing the sample bottle in a 40 ℃ forced air drying oven for drying for 12h to obtain light yellow microsphere powder; placing the dried powder in a quartz boat, placing in a horizontal tube furnace for carbonization, introducing argon gas for 30min before carbonization, heating the tube furnace to 600 ℃ at a heating rate of 6 ℃/min under the protection of argon gas, keeping the temperature for 120min to fully carbonize, naturally cooling to room temperature, and taking out to obtain the nitrogen-doped C/F-SiO2Compounding microsphere powder; dispersing the solution into 8mL of hydrofluoric acid solution (HF is more than or equal to 40 percent), placing the solution in an oil bath at 40 ℃ for treatment for 10 hours, and naturally cooling the system; and (3) centrifugally separating the reaction liquid, washing the lower-layer precipitate with deionized water for 3 times, and then placing the lower-layer precipitate in a 40 ℃ blast drying oven to dry for 12 hours to obtain a final product, namely the inverse opal macroporous/mesoporous nitrogen-doped carbon microsphere, as shown in figures 8c and 8d (enlarged surface images).
The above description of the embodiments is only intended to facilitate the understanding of the method of the invention and its core idea. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (9)

1. A preparation method of inverse opal type macroporous/mesoporous nitrogen-doped carbon microspheres is characterized by comprising the following steps:
A) F-SiO2Washing the nano particles, and washing the F-SiO2Mixing the nano particles, water, a non-polar solvent and an emulsifier to obtain an inverse emulsion; standing the inverse emulsion to obtain F-SiO2Colloidal crystal microspheres;
B) injecting one of acrylonitrile and acrylonitrile/initiator mixed solution into the F-SiO2Colloidal crystal microsphere and initiating acrylonitrile to polymerize to obtain polyacrylonitrile/F-SiO2Compounding the microspheres;
C) subjecting the polyacrylonitrile/F-SiO2Carbonizing the composite microspheres to obtain the nitrogen-doped C/F-SiO2Compounding the microspheres;
D) doping the nitrogen with C/F-SiO2Etching the composite microspheres to obtain inverse opal type macroporous/mesoporous nitrogen-doped carbon microspheres;
the F-SiO2The preparation method of the nano particles comprises the following steps:
mixing an emulsifier, a catalyst, a water phase, an oil phase and a cosolvent, and then reacting with alkyl orthosilicate;
the volume ratio of the water phase to the oil phase is 1:1, the oil phase is one or more of cyclohexane, normal hexane, normal heptane and normal octane, the emulsifier is cetyl trimethyl ammonium bromide, the cosolvent is isopropanol, and the catalyst is urea.
2. The method of claim 1, wherein the F-SiO is present in a gas phase2The particle size of the nanoparticles is 50-500 nm.
3. The method of claim 1, wherein the F-SiO is present in a gas phase2Washing the nano particles by alternately washing with ethanol and water until the F-SiO is washed2The Zeta potential of the nano particles dispersed in water is-25 to-5 mV.
4. According to claimThe process according to claim 1, wherein in step A), the F-SiO is present in an inverse emulsion2The content of the nano particles is 3-20 wt%; the emulsifier is one or two of Span80 and Hypermer2296, and the nonpolar solvent is one or two of kerosene and n-hexadecane; the standing temperature is 20-50 ℃.
5. The method according to claim 1, wherein in step B), the polymerization is initiated by radiation-initiated polymerization or heat-initiated polymerization; the radiation-initiated polymerization employs60Introducing nitrogen to remove oxygen before irradiation by using Co gamma rays, wherein the absorption dose rate is 70-100 Gy/min, the irradiation time is 17-96 h, and the corresponding absorption dose is 100-400 kGy; the temperature for heating to initiate polymerization is 40-50 ℃, and the reaction time is 12-24 h.
6. The method according to claim 1, wherein the carbonization is performed under an inert atmosphere in step C), and the temperature of the carbonization is increased at a rate of 1 to 20 ℃/min and at a temperature of 500 to 700 ℃ for 60 to 180 min.
7. The preparation method according to claim 1, wherein in the step D), the etching is carried out in a hydrofluoric acid solution, and the etching temperature is 40-60 ℃ and the etching time is 8-12 h.
8. The inverse opal-type macroporous/mesoporous nitrogen-doped carbon microsphere prepared by the preparation method of claim 1 has a cage-pore structure formed by three-dimensionally through macropores formed by a nitrogen-carbon skeleton, and the inner wall of each macropore is a fibrous porous surface.
9. The inverse opal-type macroporous/mesoporous nitrogen-doped carbon microsphere according to claim 8, wherein the size of macropores in the cage-like structure is 50-250 nm.
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