CN112279236A - Nitrogen-doped hollow carbon sphere and preparation method and application thereof - Google Patents
Nitrogen-doped hollow carbon sphere and preparation method and application thereof Download PDFInfo
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Abstract
The invention relates to a nitrogen-doped hollow carbon sphere and a preparation method and application thereof, belonging to the technical field of organic/inorganic hybrid materials. Solves the technical problems of high cost, complex synthesis process and limited application of the carbon dioxide capturing solid adsorbent in the prior art. The nitrogen-doped hollow carbon sphere is prepared by coating a silicon dioxide nanosphere with nitrogen-containing resorcinol formaldehyde resin, carbonizing to obtain a silicon dioxide core carbon sphere, and performing KOH and g-C3N4Enhancing porosity and nitrogen doping activation to obtain activated silicon dioxide core carbon spheres, and removing silicon cores by using HF. The nitrogen-doped hollow carbon sphere has uniform particle size, unique hollow structure, larger BET surface area and hierarchical porosity, and rich pyridine N sites exposed on the carbon shell can enhance the accessibility of the nitrogen site, facilitate the mass transfer of an object and the CO2Interaction between gases to CO in multi-component gases2With high efficiency of selective captureAnd (4) collecting.
Description
Technical Field
The invention belongs to the technical field of organic/inorganic hybrid materials, and particularly relates to a nitrogen-doped hollow carbon sphere and a preparation method and application thereof.
Background
With the continuous development of national science and technology and the continuous improvement of environmental protection requirements, carbon dioxide (CO)2) The control of emissions has become an inevitable problem in industrial processes and global energy utilization. The greenhouse effect is one of the most serious problems facing human beings at present, and is a pair of ringsEnvironmental effects are potentially damaging. Carbon dioxide, which is constantly accumulating in the atmosphere, is a major "contributor" to the greenhouse effect. The emission of carbon dioxide is inevitably generated mainly by the combustion of fossil fuels in the industry, and thus the control and reduction of the emission of carbon dioxide becomes a vital task in academia and industry. To this end, carbon capture and fixation (CCS) is proposed as a solution, and as a first step of CCS, CO is widely achieved by a wet scrubbing process2In this process, aqueous organic amines (e.g. monoethanolamine, methyldiethanolamine and piperazine) are typically used as liquid absorbents. However, amine scrubbing methods are not widely recognized due to the high volatility and strong corrosivity of the liquid absorbents used. In addition, the heat capacity of the liquid solvent is high, and the energy consumed during regeneration is also high. Therefore, new materials or process strategies are sought to replace liquid adsorbents or amine purification processes to capture CO2It is of great importance.
In the current options, the adsorption capacity of porous materials is well documented, while porous materials do not have volatility and corrosion problems and are relatively easy to regenerate. In recent years, efforts have been made to develop better carbon dioxide capturing solid adsorbents as ideal alternatives to amine-based adsorbents. The solid adsorbent must have the characteristics of high specific surface area, good thermal stability, pore structure and controllable adsorption position. A number of academic workers have characterized solid porous materials such as porous polymers, zeolites, and crystalline metal-organic frameworks, and their CO2Test study of adsorption properties of (1). However, we have found that the development and use of these adsorbents is limited due to the high cost and complexity of the synthesis process. Therefore, there is an urgent need to search a low-cost and easily-industrialized solid adsorbent for high-efficiency selective capture of carbon dioxide to replace the original liquid absorbent and amine-impregnated material.
In previous studies, there has been a "contradiction" that a three-dimensional hollow structure can significantly improve a specific region and promote mass transport of reactants, but is not favorable for exposure of active sites, and a microporous structure has an opposite effect on the same. Thus, optimizing a suitable carbon-based structure can increase the exposure of specific active sites while reducing mass diffusion barriers. In addition, controlling the content and configuration of nitrogen doping in different carbon materials is still a great challenge, and in various research fields, nitrogen doping plays a crucial role in improving the performance of the carbon materials.
Disclosure of Invention
The invention provides a nitrogen-doped hollow carbon sphere and a preparation method and application thereof, aiming at solving the technical problems of high cost, complex synthesis process and limited application of a carbon dioxide capture solid adsorbent in the prior art.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
the invention provides a preparation method of a nitrogen-doped hollow carbon sphere, which comprises the following steps:
adding ammonia water into a mixed solvent of ethanol and deionized water, and uniformly stirring to obtain a mixed solution;
step two, adding tetraethyl orthosilicate (TBOT) into the mixed solution under continuous stirring, adding resorcinol after 5-15min, adding formaldehyde after 5-15min, adding urotropine (HMTA) after 5-15min, stirring uniformly, curing, centrifuging, washing, and drying in vacuum to obtain a brown polymer (SiO)2@RF)；
Carbonizing the brown polymer under the protection of inert gas to obtain silicon dioxide core carbon spheres;
mixing the silicon dioxide core carbon spheres with potassium hydroxide under the protection of inert gas, etching, pickling, washing with water, and drying in vacuum to obtain etched silicon dioxide core carbon spheres;
step five, using g-C3N4Activating the etched silicon dioxide core carbon spheres, and cooling to room temperature to obtain activated silicon dioxide core carbon spheres;
and step six, mixing the etched silicon dioxide core carbon spheres or the activated silicon dioxide core carbon spheres with hydrofluoric acid, etching, washing and drying to obtain the nitrogen-doped hollow carbon spheres (NHCN-Ts or A-NHCN-Ts).
Preferably, in the first step, the concentration of the ammonia water is 20-30 wt%; the volume ratio of the ethanol to the deionized water is (2-3) to 1; the stirring temperature is 25-35 ℃, the stirring speed is 400-800rpm, and the stirring time is 10-60 min.
Preferably, in the second step, based on the concentration of the ammonia water in the first step being 20-30 wt% and the volume being 1-2mL, the addition amount of tetraethyl orthosilicate is 1-1.5mL, the addition amount of resorcinol is 0.1-0.3g, the addition amount of formaldehyde is 0.25-0.3mL, and the addition amount of urotropine is 0.06-0.08 g; the stirring speed is 400-800 rpm; the curing temperature is 80-150 ℃, and the curing time is 12-36 h; washing is to wash with ethanol and then with deionized water to be neutral; the vacuum drying temperature was 80 ℃.
Preferably, in the third step, the carbonization process is as follows: heating the brown polymer to 700-800 ℃ at the heating rate of 5-10 ℃/min for carbonization for 1 h.
Preferably, in the fourth step, the mass ratio of the potassium hydroxide to the silicon dioxide core carbon spheres is 1: 1; the etching process comprises the following steps: heating the mixture of potassium hydroxide and silicon dioxide core carbon spheres to 800-900 ℃ at the heating rate of 1-2 ℃/min for carbonization for 1 h; the acid adopted in the acid washing is H2SO4Or HCl with a concentration of 0.2-2M; the vacuum drying temperature was 100 ℃.
Preferably, in the fifth step, the etched silicon dioxide core carbon spheres and the g-C3N4The mass ratio of (A) to (B) is 1: 1; the activation process comprises the following steps: mixing the etched silicon dioxide core carbon spheres with g-C3N4The mixture is heated to 600 ℃ at the heating rate of 2-5 ℃/min and is kept for 10-30min, and then heated to 900 ℃ within 5min and is kept for 10-30 min.
Preferably, in the sixth step, the concentration of the hydrofluoric acid is 15-25 wt%; the mass ratio of the etched silicon dioxide core carbon spheres to the hydrofluoric acid is 1 (4-10); the mass ratio of the activated silicon dioxide core carbon spheres to the hydrofluoric acid is 1 (4-10); the etching process comprises the following steps: stirring at the stirring speed of 400-800rpm for more than 12 h; the washing is that ethanol is used for washing firstly, and then deionized water is used for washing until the solution is neutral.
The invention also provides the nitrogen-doped hollow carbon sphere prepared by the preparation method of the nitrogen-doped hollow carbon sphere.
The invention also provides application of the nitrogen-doped hollow carbon sphere in capturing carbon dioxide.
Preferably, the dosage of the nitrogen-doped hollow carbon spheres in the process of capturing carbon dioxide is 4.8mmol/g CO2。
Compared with the prior art, the invention has the beneficial effects that:
the preparation method of the nitrogen-doped hollow carbon sphere is convenient to operate and low in cost.
The nitrogen-doped hollow carbon sphere has uniform particle size, unique hollow structure and larger BET surface area (704-2The/g) and the fractional porosity, and abundant pyridine N sites (55-70 wt%) and nitrogen sites (11.6-14.8 wt%) are exposed on the carbon shell, so that the accessibility of the nitrogen sites can be enhanced, the mass transfer of objects is facilitated, the carbon shell has excellent performance and good stability in acid gas capture, and the carbon shell is beneficial to CO and CO2Interaction between gases to CO in multi-component gases2Has high-efficiency selective capture, and can reach about 4.8mmol/g CO at the temperature of 25 ℃ through experimental detection2Is suitable for low-medium temperature CO2Selective adsorption of (3). Has important application potential in the field of carbon nano tubes.
The nitrogen-doped hollow carbon spheres have low corrosion to equipment, are easily separated from the reaction medium, are convenient to recycle, and are convenient to transport on a large scale.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.
Fig. 1 is an XRD spectrum of nitrogen-doped hollow carbon spheres prepared in examples 1 and 3 of the present invention;
FIG. 2 is a Raman spectrum of nitrogen-doped hollow carbon spheres prepared in examples 1 to 4 of the present invention;
FIG. 3 shows N of N-doped hollow carbon spheres prepared in examples 1 to 4 of the present invention2Adsorption-desorption isotherms;
FIG. 4 is a graph showing pore size distributions of nitrogen-doped hollow carbon spheres prepared in examples 1 to 4 of the present invention;
FIG. 5 is an SEM image of nitrogen-doped hollow carbon spheres prepared in examples 1-4 of the present invention;
FIG. 6 shows CO of nitrogen-doped hollow carbon spheres prepared in examples 1 and 3 of the present invention2And N2Adsorption isotherm and CO for the adsorbents of comparative example 1 and comparative example 22Adsorption isotherms.
Detailed Description
For a further understanding of the invention, preferred embodiments of the invention are described below in conjunction with the detailed description, but it is to be understood that the description is intended to further illustrate the features and advantages of the invention and not to limit the claims to the invention.
The nitrogen-doped hollow carbon spheres (NHCN-Ts or A-NHCN-Ts) are prepared by coating silica nanospheres with resorcinol formaldehyde resin in the presence of urotropine (HMTA) to synthesize a silica-resorcinol formaldehyde core-shell composite material (SiO)2@ RF), and then mixing the resultant SiO2The @ RF core-shell composite is carbonized, etched with KOH to obtain rich microporosity, preferably with g-C3N4Rapid activation increases nitrogen doping and finally HF etching is used to remove the silicon dioxide core.
The preparation method of the nitrogen-doped hollow carbon sphere comprises the following steps:
adding ammonia water into a mixed solvent of ethanol and deionized water, and uniformly stirring to obtain a mixed solution;
step two, adding tetraethyl orthosilicate into the mixed solution under continuous stirring, adding resorcinol after 5-15min, adding formaldehyde after 5-15min, adding urotropine after 5-15min, uniformly stirring, curing, centrifuging, washing, and drying in vacuum to obtain a brown polymer;
carbonizing the brown polymer under the protection of inert gas to obtain silicon dioxide core carbon spheres;
mixing the silicon dioxide core carbon spheres with potassium hydroxide under the protection of inert gas, etching, pickling, washing with water, and drying in vacuum to obtain etched silicon dioxide core carbon spheres;
step five, using g-C3N4Activating the etched silicon dioxide core carbon spheres, and cooling to room temperature to obtain activated silicon dioxide core carbon spheres;
and step six, mixing the etched silicon dioxide core carbon spheres or the activated silicon dioxide core carbon spheres with hydrofluoric acid, etching, washing and drying to obtain the nitrogen-doped hollow carbon spheres.
In the technical scheme, in the step one, the concentration of the ammonia water is 20-30 wt%; the mass ratio of the ammonia water to the mixed solvent is 1 (1-10); the volume ratio of the ethanol to the deionized water is (2-3) to 1; the stirring temperature is 25-35 ℃, the stirring speed is 400-800rpm, preferably 600rpm, and the stirring time is 10-60 min.
In the technical scheme, in the second step, by taking the ammonia water concentration of 20-30 wt% in the first step and the volume of 1-2mL, the addition amount of tetraethyl orthosilicate is 1-1.5mL, the addition amount of resorcinol is 0.1-0.3g, the addition amount of formaldehyde is 0.25-0.3mL, and the addition amount of urotropine is 0.06-0.08 g; the stirring rate is 400-800rpm, preferably 600 rpm; the curing temperature is 80-150 ℃, and the curing time is 12-36 h; washing is to wash with ethanol and then with deionized water to be neutral; the vacuum drying temperature was 80 ℃.
In the above technical scheme, in the third step, the carbonization process is as follows: heating the brown polymer to 700-800 ℃ at the heating rate of 5-10 ℃/min for carbonization for 1 h.
In the fourth step, the mass ratio of potassium hydroxide to the silicon dioxide core carbon spheres is 1: 1; the etching process comprises the following steps: heating the mixture of potassium hydroxide and silicon dioxide core carbon spheres to 800-900 ℃ at the heating rate of 1-2 ℃/min for carbonization for 1 h; the acid adopted in the acid washing is H2SO4Or HCl with a concentration of 0.2-2M; the vacuum drying temperature was 100 ℃.
In the fifth step, the etched silicon dioxide core carbon spheres and g-C3N4Quality of (1)The quantity ratio is 1: 1; the activation process comprises the following steps: mixing the etched silicon dioxide core carbon spheres with g-C3N4The mixture is heated to 600 ℃ at the heating rate of 2-5 ℃/min and is kept for 10-30min, and then heated to 900 ℃ within 5min and is kept for 10-30 min.
In the sixth step, the concentration of the hydrofluoric acid is 15-25%; the mass ratio of the etched silicon dioxide core carbon spheres to the hydrofluoric acid is 1 (4-10); the mass ratio of the activated silicon dioxide core carbon spheres to the hydrofluoric acid is 1 (4-10); the etching process comprises the following steps: stirring at the stirring speed of 400-800rpm for more than 12h, preferably 600 rpm; the washing is that ethanol is used for washing firstly, and then deionized water is used for washing until the solution is neutral.
The invention also provides the nitrogen-doped hollow carbon sphere prepared by the preparation method of the nitrogen-doped hollow carbon sphere.
The invention also provides application of the nitrogen-doped hollow carbon sphere in capturing carbon dioxide. Preferably, the dosage of the nitrogen-doped hollow carbon spheres in the carbon dioxide capture is 4.8mmol/g CO2。
The terms used in the present invention generally have meanings commonly understood by those of ordinary skill in the art, unless otherwise specified.
In order to make those skilled in the art better understand the technical solution of the present invention, the present invention will be further described in detail with reference to the following embodiments.
In the following examples, various procedures and methods not described in detail are conventional methods well known in the art. Materials, reagents, devices, instruments, apparatuses and the like used in the following examples are commercially available unless otherwise specified.
Example 1
1.6mL of an aqueous ammonia solution (25 wt%) was added to a mixed solvent of ethanol (26.6mL) and deionized water (13.3mL), and the mixture was stirred at 600rpm at 30 ℃ for 30 minutes to obtain a mixed solution.
1.4mL of TBOT was added to the mixture with constant stirring at 600rpm, after 10min 0.2g resorcinol was added, after 10min 0.28mL formaldehyde was added, after 10min 0.075g HMTA was added, magnetic stirring at 600rpm for 24h at 30 ℃ was transferred to the autoclave,hydrothermal treatment at 100 deg.C for 24h, centrifuging to collect the product, washing with large amount of ethanol and deionized water to neutrality, and drying at 80 deg.C under vacuum overnight to obtain brown polymer (SiO) with silica core and polymer shell structure2@RF)。
Under the protection of nitrogen, SiO2And heating up to 700 ℃ at the heating rate of 5 ℃/min and carbonizing for 1h to obtain the silicon dioxide @ carbon core-shell nano structure.
Fully mixing the silicon dioxide @ carbon sphere-shell nano structure with anhydrous KOH according to the mass ratio of 1:1, heating to 800 ℃ at the heating rate of 1 ℃/min under the protection of nitrogen, carbonizing for 1h, washing with 1M HCl to remove all inorganic salts, washing to be neutral with deionized water, and drying for 12h at the temperature of 100 ℃ to obtain the etched silicon dioxide @ carbon core-shell nano structure.
Mixing the etched silicon dioxide @ carbon core-shell nano structure with g-C3N4Fully mixing according to the mass ratio of 1:1, transferring the obtained mixture into a tube furnace, heating to 550 ℃ at the heating rate of 3 ℃/min under the protection of nitrogen, keeping for 20min, heating the generated substance to 800 ℃ within 5min, keeping for 20min, cooling to room temperature, finally mixing with HF (15 wt%) (according to the mass ratio of 1 (4-10)), stirring for 12h at the stirring speed of 600rpm, removing silicon dioxide nuclei, washing with ethanol, washing with deionized water to be neutral, and drying to obtain hollow nitrogen-doped carbon spheres, namely A-NHCN-800, which is marked as adsorbent A.
Example 2
0.8mL of an aqueous ammonia solution (25 wt%) was added to a mixed solvent of ethanol (13.3mL) and deionized water (6.65mL), and after stirring at 600rpm for 20min at 30 ℃, a mixture was obtained.
Adding 0.7mL of TBOT to the mixed solution under continuous stirring, adding 0.1g of resorcinol after 10min, adding 0.14mL of formaldehyde after 10min, adding 0.037g of HMTA after 10min, magnetically stirring at 30 ℃ at 600rpm for 24h, transferring to an autoclave, performing hydrothermal treatment at 100 ℃ for 24h, centrifuging to collect the product, washing with ethanol and deionized water to neutrality, and drying at 80 ℃ under vacuum conditions overnight to obtain a brown polymer (SiO) with a silica core and polymer shell structure2@RF)。
Under the protection of nitrogen, SiO2And heating up to 700 ℃ at the heating rate of 5 ℃/min and carbonizing for 1h to obtain the silicon dioxide @ carbon core-shell nano structure.
Fully mixing silicon dioxide @ carbon spheres and anhydrous KOH according to the mass ratio of 1:1, heating to 900 ℃ at the speed of 1 ℃/min under the protection of nitrogen, carbonizing for 1h, washing with 1M HCl to remove all inorganic salts, washing to neutrality with deionized water, and drying for 6h at the temperature of 100 ℃ to obtain the etched silicon dioxide @ carbon core-shell nano structure.
Mixing the etched silicon dioxide @ carbon core-shell nano structure with g-C3N4Fully mixing the raw materials according to the mass ratio of 1:1, transferring the obtained mixture into a tubular furnace, under the protection of nitrogen, heating to 550 ℃ at the heating rate of 3 ℃/min, keeping the temperature for 20min, heating to 900 ℃ within 5min, keeping the temperature for 20min, cooling to room temperature, finally mixing with HF (15 wt%) (according to the mass ratio of 1 (4-10)), stirring at the stirring speed of 600rpm for 12h, removing silicon dioxide nuclei, washing with ethanol, washing with deionized water to be neutral, and drying to obtain hollow nitrogen-doped carbon spheres, namely A-NHCN-900, which is marked as an adsorbent B.
Example 3
1.6mL of an aqueous ammonia solution (25 wt%) was added to a mixed solvent of ethanol (26.6mL) and deionized water (13.3mL), and after stirring at 600rpm for 30min at 30 ℃, a mixed solution was obtained.
Adding 1.4mL of TBOT to the mixture under constant stirring, adding 0.2g of resorcinol after 10min, adding 0.28mL of formaldehyde after 10min, adding 0.075g of HMTA after 10min, magnetically stirring at 600rpm for 24h at 30 ℃, transferring to an autoclave, performing hydrothermal treatment at 100 ℃ for 24h, centrifuging to collect the product, washing with a large amount of ethanol and deionized water to neutrality, and drying at 80 ℃ overnight under vacuum to obtain a brown polymer (SiO) with a silica core and polymer shell structure (i.e., a polymer with a silica core and a polymer shell structure)2@RF)。
Under the protection of nitrogen, SiO2And heating up to 700 ℃ at the heating rate of 5 ℃/min and carbonizing for 1h to obtain the silicon dioxide @ carbon core-shell nano structure.
Fully mixing silicon dioxide @ carbon spheres and anhydrous KOH according to the mass ratio of 1:1, heating to 800 ℃ at the heating rate of 1 ℃/min under the protection of nitrogen, carbonizing for 1h, washing the obtained solid with 1M HCl to remove all inorganic salts, washing with deionized water to be neutral, and drying at 100 ℃ for 12h to obtain the etched silicon dioxide @ carbon core-shell nano structure.
And cooling the etched silicon dioxide @ carbon core-shell nano structure to room temperature, mixing the silicon dioxide @ carbon core-shell nano structure with HF (15 wt%) (mass ratio is 1 (4-10)), stirring the mixture for 12 hours at a stirring speed of 600rpm, removing the silicon dioxide core, washing the silicon dioxide core with ethanol, then washing the silicon dioxide core with deionized water to be neutral, and drying the silicon dioxide core to obtain a hollow nitrogen-doped carbon sphere, namely NHCN-800, which is marked as an adsorbent C.
Example 4
0.8mL of an aqueous ammonia solution (25 wt%) was added to a mixed solvent of ethanol (13.3mL) and deionized water (6.65mL), and after stirring at 600rpm for 30min at 30 ℃, a mixed solution was obtained.
Adding 0.7mL of TBOT into the mixed solution under continuous stirring, adding 0.21g of resorcinol after 10min, adding 0.14mL of formaldehyde after 10min, adding 0.037g of HMTA after 10min, magnetically stirring at 600rpm for 24h at 30 ℃, transferring to an autoclave, performing hydrothermal treatment at 100 ℃ for 24h, centrifuging to collect the product, washing with ethanol and deionized water to neutrality, and drying at 80 ℃ under vacuum condition overnight to obtain a brown polymer (SiO) with a silicon dioxide core and polymer shell structure2@RF)。
Under the protection of nitrogen, SiO2And heating up to 700 ℃ at the heating rate of 5 ℃/min and carbonizing for 1h to obtain the silicon dioxide @ carbon core-shell nano structure.
Fully mixing silicon dioxide @ carbon spheres and anhydrous KOH according to the mass ratio of 1:1, heating to 900 ℃ at the heating rate of 1 ℃/min under the protection of nitrogen, carbonizing for 1h, washing the obtained solid with 1M HCl to remove all inorganic salts, washing with deionized water to be neutral, and drying at 100 ℃ for 12h to obtain the etched silicon dioxide @ carbon core-shell nano structure.
And cooling the etched silicon dioxide @ carbon core-shell nano structure to room temperature, mixing the silicon dioxide @ carbon core-shell nano structure with HF (15 wt%) (mass ratio is 1 (4-10)), stirring at a stirring speed of 600rpm for 12 hours, removing the silicon dioxide core, washing with ethanol, washing with deionized water to be neutral, and drying to obtain a hollow nitrogen-doped carbon sphere, namely NHCN-900, which is marked as an adsorbent D.
Comparative example 1
Pouring 20g of anhydrous ethanol and 0.5-2g of ethylenediamine (used as an alkaline modifier) into a beaker, standing for 30min, then putting into a three-neck flask, weighing 5g of activated carbon after alkaline cleaning, pouring into the three-neck flask, putting the three-neck flask into a constant-temperature water bath kettle, sealing and stirring for 24h at 80 ℃, and after the reaction is finished, drying at 120 ℃ for later use, and marking as an adsorbent E.
Comparative example 2
0.9g of F127 is added into a mixed solvent of 10g of ethanol and 9g of water to be stirred and dissolved, then 1.25g of phloroglucinol is added, and stirring is carried out for 0.5h at room temperature to realize self-assembly between the template and the phloroglucinol. And then adding 2.0g of formaldehyde into the system, stirring for 1h at room temperature, uncovering the cover, volatilizing the solvent for about 24h at room temperature, and thermally curing the solid for 24h at 150 ℃ to obtain a mesoporous phenolic resin primary product. Dispersing the primary product in 50ml of ethanol and 7ml of concentrated hydrochloric acid mixed solution, and refluxing for 24 hours at 90 ℃ to obtain the mesoporous phenolic resin material with open pore channels, which is marked as an adsorbent F.
The resulting adsorbent was analyzed and tested accordingly.
Figure 1 is the XRD pattern of a-NHCN-800 of example 1 and NHCN-800 of example 3. For the a-NHCN-800 and NHCN-800 samples, two broad peaks can be observed around 2 θ ═ 24 and 43 °, which can be labeled as (002) and (100) reflections, indicating their amorphous nature. They showed similar peaks around 24 and 43 °, indicating that they all have good graphitization and amorphous network structures.
FIG. 2 is a Raman spectrum of nitrogen-doped hollow carbon spheres prepared in examples 1 to 4, all of which showed two broad peaks associated with D-band and G-band, respectively at 1350 and 1580cm-1Left and right. In these samples, the D band represents the Sp3 carbon atoms in the sample network, while the G band correlates with the Sp2 carbon atoms in the sample two-dimensional graphite hexagonal lattice. On the other hand, ID/IGIs a measure of the extent of defects in the synthesized sample. As shown in FIG. 2, in the case of etching with KOH and g-C3N4Sample after activation, ID/IGAnd increasing, which also indicates that a large number of micro-nano defects and nitrogen sites exist in the activated sample.
FIG. 3 shows the N of NHCN-800, NHCN-900, A-NHCN-800 and A-NHCN-9002Adsorption-desorption isotherms of (a). FIG. 4 shows the N of NHCN-800, NHCN-900, A-NHCN-800 and A-NHCN-9002Pore size distribution of (2). The results show that all samples show similar isotherms at relative pressure P/P0The adsorption capacity is obvious under 0.15, and the product is equivalent to a typical microporous structure. Capillary condensation occurs at a relatively high relative pressure (P/P)00.9-1.0), a large number of large pores are provided due to aggregation of the hollow carbon nanoball. In addition, the structural parameters of the synthesized samples are summarized in table 1. The BET surface area and total pore volume of the NHCN sample are respectively 320-1032m2G and 0.35-0.79cm3In the range of/g. It was found that the BET surface area and total pore volume of the synthesized samples decreased with increasing pyrolysis temperature, and similar results were observed in A-NHCN-800 and A-NHCN-900. This phenomenon can be explained by the increase in graphitization and the partial destruction of microporosity at high temperatures. Furthermore, all samples showed hierarchical nanopores distributed in micro-meso pore size (0.5-10nm) and macro-pore size (20-150 nm). The presence of abundant bimodal nanopores increases the degree of internal connectivity in the samples, which facilitates rapid diffusion of the reaction medium in these samples. Compared to NHCN-800 and NHCN-900, the activated samples of A-NHCN-800 and A-NHCN-900 have greatly enhanced volume adsorption and increased pore size due to the enhanced microporosity and large number of structural defects present in the activated samples (FIG. 4). Due to the strong corrosiveness of KOH at high temperatures, a large number of micropores are created in the a-NHCN sample after etching. In addition, the nitrogen content determined by elemental analysis is also summarized in table 1. It is clearly found that NHCN is g-C at high pyrolysis temperature3N4The nitrogen content in the activated sample is greatly increased, and the nitrogen content of the adsorbent is in the range of 2.9-14.8 wt%.
Table 1 structural parameters of nitrogen-doped hollow carbon spheres prepared in examples 1 to 4
FIG. 5 shows SEM images of NHCN-800(A), NHCN-900(B), A-NHCN-800(C) and A-NHCN-900 (D). As shown in fig. 5, NHCN-800 and NHCN-900 have a uniform spherical morphology, have smooth surface features and hollow nanostructures, and their diameter is 150nm to 200 nm. While similar hollow structures can be observed in A-NHCN-800 and A-NHCN-900.
FIG. 6 shows CO for adsorbents A-NHCN-800, comparative example 1, and comparative example 2 at 0 deg.C2And N2Adsorption isotherms. The results show that CO2The adsorption is due to the combined results of nitrogen functionality and nanoporosity, and the CO of A-NHCN-8002The capacity is much higher than NHCN-800. As shown in FIG. 6, A-NHCN-800 has its CO at 0 ℃ and 1bar2The capacity was as high as 4.94mmol/g, which is much higher than that of NHCN-800(3.12mmol/g) which is not activated, and is significantly higher than that of the adsorbent E, F. With CO2Both A-NHCN-800 and NHCN-800 show quite limited N in comparison to adsorption2Adsorption capacity to CO2The adsorption amount of (A) is two orders of magnitude lower. The A-NHCN-800 and NHCN-800 synthesized were then estimated to be at 1.0bar for CO based on the Ideal Adsorption Solution Theory (IAST)2And N2Mixture (0.10/0.90v/v) of (A) with corresponding CO2/N2And (4) selectivity. The measurement result range is 31.5 to 46.0, and the carbon-containing material has certain superiority compared with most reported carbon-containing materials, namely CO2The selective capture has a profound application prospect.
It should be understood that the above embodiments are only examples for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither necessary nor exhaustive of all embodiments. And obvious variations or modifications of the invention may be made without departing from the spirit or scope of the invention.
Claims (10)
1. The preparation method of the nitrogen-doped hollow carbon sphere is characterized by comprising the following steps of:
adding ammonia water into a mixed solvent of ethanol and deionized water, and uniformly stirring to obtain a mixed solution;
step two, adding tetraethyl orthosilicate into the mixed solution under continuous stirring, adding resorcinol after 5-15min, adding formaldehyde after 5-15min, adding urotropine after 5-15min, uniformly stirring, curing, centrifuging, washing, and drying in vacuum to obtain a brown polymer;
carbonizing the brown polymer under the protection of inert gas to obtain silicon dioxide core carbon spheres;
mixing the silicon dioxide core carbon spheres with potassium hydroxide under the protection of inert gas, etching, pickling, washing with water, and drying in vacuum to obtain etched silicon dioxide core carbon spheres;
step five, using g-C3N4Activating the etched silicon dioxide core carbon spheres, and cooling to room temperature to obtain activated silicon dioxide core carbon spheres;
and step six, mixing the etched silicon dioxide core carbon spheres or the activated silicon dioxide core carbon spheres with hydrofluoric acid, etching, washing and drying to obtain the nitrogen-doped hollow carbon spheres.
2. The method for preparing nitrogen-doped hollow carbon spheres according to claim 1,
in the first step, the first step is carried out,
the concentration of the ammonia water is 20-30 wt%;
the mass ratio of the ammonia water to the mixed solvent is 1 (1-10);
the volume ratio of the ethanol to the deionized water is (2-3) to 1;
the stirring temperature is 25-35 ℃, the stirring speed is 400-800rpm, and the stirring time is 10-60 min.
3. The method for preparing nitrogen-doped hollow carbon spheres according to claim 1,
in the second step, the first step is carried out,
based on the concentration of the ammonia water in the first step being 20-30 wt% and the volume being 1-2mL, the addition amount of tetraethyl orthosilicate is 1-1.5mL, the addition amount of resorcinol is 0.1-0.3g, the addition amount of formaldehyde is 0.25-0.3mL, and the addition amount of urotropine is 0.06-0.08 g;
the stirring speed is 400-800 rpm;
the curing temperature is 80-150 ℃, and the curing time is 12-36 h;
washing is to wash with ethanol and then with deionized water to be neutral;
the vacuum drying temperature was 80 ℃.
4. The method for preparing nitrogen-doped hollow carbon spheres according to claim 1, wherein in the third step, the carbonization process comprises: heating the brown polymer to 700-800 ℃ at the heating rate of 5-10 ℃/min for carbonization for 1 h.
5. The method for preparing nitrogen-doped hollow carbon spheres according to claim 1,
in the fourth step of the method, the first step of the method,
the mass ratio of the potassium hydroxide to the silicon dioxide core carbon spheres is 1: 1;
the etching process comprises the following steps: heating the mixture of potassium hydroxide and silicon dioxide core carbon spheres to 800-900 ℃ at the heating rate of 1-2 ℃/min for carbonization for 1 h;
the acid adopted in the acid washing is H2SO4Or HCl with a concentration of 0.2-2M;
the vacuum drying temperature was 100 ℃.
6. The method for preparing nitrogen-doped hollow carbon spheres according to claim 1,
in the fifth step, the process is carried out,
etched silica core carbon spheres with g-C3N4The mass ratio of (A) to (B) is 1: 1;
the activation process comprises the following steps: mixing the etched silicon dioxide core carbon spheres with g-C3N4The mixture is heated to 600 ℃ at the heating rate of 2-5 ℃/min and is kept for 10-30min, and then heated to 900 ℃ within 5min and is kept for 10-30 min.
7. The method for preparing nitrogen-doped hollow carbon spheres according to claim 1,
in the sixth step, in the step III,
the concentration of hydrofluoric acid is 15-25 wt%;
the mass ratio of the etched silicon dioxide core carbon spheres to the hydrofluoric acid is 1 (4-10);
the mass ratio of the activated silicon dioxide core carbon spheres to the hydrofluoric acid is 1 (4-10);
the etching process comprises the following steps: stirring at the stirring speed of 400-800rpm for more than 12 h;
the washing is that ethanol is used for washing firstly, and then deionized water is used for washing until the solution is neutral.
8. The nitrogen-doped hollow carbon sphere prepared by the method for preparing a nitrogen-doped hollow carbon sphere according to any one of claims 1 to 7.
9. Use of the nitrogen-doped hollow carbon spheres of claim 8 to capture carbon dioxide.
10. Use of nitrogen-doped hollow carbon spheres in carbon dioxide capture according to claim 9, wherein the amount of nitrogen-doped hollow carbon spheres used in carbon dioxide capture is 4.8mmol/g CO2。
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