CN102167309A - Preparation method of shape-controllable hollow carbon microsphere - Google Patents

Abstract

The invention discloses a method for preparing hollow carbon microspheres with controllable morphology, which belongs to the technical field of energy materials. Acidification treatment with concentrated sulfuric acid, modification treatment on its surface, so that the surface is equipped with sulfonate groups (-SO ₃ H ^- ) with initiation activity of p-resole phenolic resin, and then dispersed modified polystyrene microspheres Add the ethanol solution of resole phenolic resin dropwise to the absolute ethanol to make it cross-linked on the surface of the microspheres to prepare composite microspheres with core-shell structure, and finally place the composite microspheres in an inert gas protection environment Carry out carbonization. The invention can effectively control the particle size of hollow microspheres by changing the particle size of the microspheres, avoid the operation process of removing the template, effectively reduce the preparation process, and realize the hollow microspheres in the same system only by changing one variable. Control of carbon microsphere morphology.

Description

A method for preparing hollow carbon microspheres with controllable morphology

technical field

The invention belongs to the technical field of energy materials, and relates to a method for preparing a novel carbon carrier used as a direct methanol fuel cell, in particular to a method for preparing hollow carbon microspheres with controllable morphology.

Background technique

In recent years, direct methanol fuel cells have attracted more and more attention due to their excellent performance in many aspects, such as high energy density, simple operation, low reaction temperature, and broad application prospects in transportation and portable electronic devices. Whether it has high activity catalytic performance is the criterion for judging the performance of direct methanol fuel cells. Precious metals such as Pt and Pt-Ru alloys are often used to prepare anode catalysts for methanol oxidation, but due to their high prices, they are not used as anode catalysts in practical applications. Very restrictive. Therefore, people hope to develop more economical and effective catalysts, which requires reducing the amount of precious metals as much as possible, which not only improves the catalytic efficiency of the catalyst. Usually, noble metal particles are supported on a carrier with high specific surface area and excellent conductivity, such as carbon black or carbon nanotubes. After research, it is found that the carbon support plays an important role in the morphology and dispersion of Pt nanoparticles, which in turn affects the catalytic performance of the catalyst. So that researchers hope to take advantage of the porous and high specific surface area of the carrier, and use appropriate methods to load the catalytically active components on the carrier to obtain a supported catalyst with fine grains, highly dispersed, and large catalytically active surface. To improve the utilization rate of the catalyst and reduce its dosage, the selection of a suitable carrier is also crucial to the development of fuel cell catalysts.

Due to the unique properties of hollow carbon microspheres, it has aroused the interest of extensive researchers, such as its structure tunability, low density, high specific surface area, and high conductivity. Therefore, many scientific researchers have conducted a lot of research on the application of hollow carbon microspheres in aspects such as lithium batteries, gas storage materials, catalyst supports, drug delivery, adsorbents, and lubricants. According to recent literature, the application of highly graphitized hollow graphite microspheres (diameter: 30-40nm) as a catalyst carrier in direct methanol fuel cells has been studied. The electrode prepared by heat treatment of the salt mixture exhibited higher current density and energy density than the commercial electrode in the methanol oxidation catalysis, which indicated that the hollow carbon microspheres played an important role in it. Therefore, it is necessary to study a new type of carbon material as a catalyst support to achieve the purpose of low Pt loading and high catalytic activity.

At present, there are mainly the following methods for preparing hollow carbon microspheres: metal reduction method, supercritical method, chemical vapor deposition method, template method, and dispersion polymerization method. However, as far as the current experimental technology is concerned, different experimental methods have their own advantages and disadvantages. It is not fully applicable to the requirements of industrialized production. As far as the metal reduction method is concerned: due to the reducibility and dechlorination of metals, the preparation of carbon spheres and hollow carbon spheres by metal reduction can be carried out at relatively low temperatures. Especially when Na or _NaNH2 is used as the reducing agent, the reaction can be carried out below 200 °C to form hollow carbon spheres. However, Na and NaNH: have strong reactivity, and at the same time, the halides in the reactants are more toxic and have greater danger in industrial production. When Fe(CSH slurry or Mg/AlCl ₃ is used as reducing agent, although the danger of reaction is reduced to some extent, the diameter dispersion of the product generated is not uniform. Since the hollow carbon spheres prepared by metal reduction method involve self-assembly process, so It is impossible to prepare hollow carbon spheres of different sizes by changing some simple conditions under the same raw material. In the supercritical state, the substance will show special physical and chemical properties different from the normal state, so academia and industry have given great attention Great concern. However, as far as the current literature is concerned, it is difficult to generate hollow carbon spheres by a single supercritical method. Chemical vapor deposition (CVD) is similar to a supercritical method. Although it is relatively easy to industrialize, it is difficult to change the temperature alone and other simple process conditions directly form hollow carbon spheres. At the same time, compared with other methods, the energy consumption of the CVD method is relatively large, and the cost in industrial production is relatively high. Through research, it has been found that the above several methods have great influence on the shape of the prepared hollow carbon microspheres. The shape can not be controlled and the yield is low. The template method is a simple method for preparing substances with a controllable shape. When preparing hollow carbon spheres, the size and pore size of the product can be controlled only by changing the size of the template At present, when the template method is used to prepare hollow carbon spheres, Si and other inorganic particle templates are mainly used. When inorganic particles are used as templates, due to their high temperature stability, it is easier to obtain hollow carbon with complete size and shape. However, with this method, after forming the carbon/inorganic particle composite sphere, the template must be removed through a subsequent step, thereby prolonging the production period.

But at present, the preparation of hollow carbon microspheres by the template method also has the following problems: 1) modification treatment of polystyrene microspheres, mainly utilizes concentrated sulfuric acid to carry out acidification treatment to self-prepared polystyrene microspheres in the present invention, so that There are sulfonate groups on its surface to achieve the purpose of modification. It has been proved by experiments that after the modification treatment of small-sized polystyrene microspheres (<300nm), due to the hydrophilic sulfonate groups on the surface , and its dispersibility in water is very good, which makes the separation process more difficult and requires higher centrifugal equipment. 2) The effect of carbonization rate and temperature on the morphology and structure of hollow carbon microspheres. Excessive heating rate during carbonization will cause damage to hollow carbon microspheres, making it difficult to maintain a hollow structure, and the degree of graphitization depends on carbonization Temperature, which must be controlled according to the application requirements.

Contents of the invention

The purpose of the present invention is to solve the problems in the prior art, and provide a method for preparing hollow carbon microspheres with controllable morphology. The hollow carbon microspheres are prepared by the template method, in which polystyrene microspheres with a low residual carbon content are used as templates, and the particle size and hollow particle size of the prepared hollow carbon microspheres are controlled by controlling the particle size of the microspheres. The controllability of the particle size of the hollow carbon microspheres is realized, and because of its low carbon residue, the procedure of removing the template in the follow-up work is avoided, and the production cycle is greatly shortened. The process of this method is simple and the cost is low, which provides the possibility for realizing industrialized production.

The present invention prepares shape-controllable hollow carbon microspheres through the following technical scheme: First, monodisperse polystyrene microspheres are prepared by soap-free emulsion polymerization, and the surface is modified by acidification treatment with concentrated sulfuric acid , so that the surface of the p-resole phenolic resin has an initiating sulfonate group (-SO ₃ H ^- ), and then the resole phenolic resin ethanol is added dropwise in the absolute ethanol in which the modified polystyrene microspheres are dispersed. Solution, make it carry out cross-linking reaction on the surface of the microsphere, prepare the composite microsphere of the core-shell structure, and finally place the composite microsphere in an inert gas protection environment for carbonization. Specific steps are as follows:

1) Prepare polystyrene microspheres as a template by soap-free emulsion polymerization: add potassium persulfate (KPS) as an initiator in deionized water with a concentration of 0.0028-0.0103 mol/L, charge at room temperature Deoxygenate with nitrogen for 30 minutes, then add styrene, potassium persulfate is 1-4% of the mass of styrene, and mechanically stir in a water bath at 70°C for 12 hours to prepare monodisperse polystyrene microspheres;

2) Preparation of sulfonated polystyrene microspheres (SPS): add the polystyrene microspheres (preferably 40g/L) prepared in step 1) to 98% concentrated sulfuric acid at a mass concentration, acidify at 30°C 1-3h, then wash and separate with water;

3) Preparation of core-shell structure phenolic resin/sulfonated polystyrene microspheres (PF/SPS) composite microspheres: add the SPS (preferred concentration 8.33g/L) prepared in step 2) to absolute ethanol, and heat in a water bath After reaching 40°C, dropwise add the resole phenolic resin ethanol solution (the concentration of the resole phenolic resin ethanol solution is preferably 0.025-0.2g/L), the mass ratio of the resole phenolic resin to the modified polystyrene microspheres is 0.5-6, The dropwise addition was completed within 1 hour, and then reacted for 6 hours to obtain PF/SPS composite microspheres with different particle sizes;

4) Preparation of hollow carbon microspheres: under the protection of argon or nitrogen, the PF/SPS composite microspheres were carbonized at 900° C. to obtain hollow carbon microspheres.

Hollow carbon microspheres with different shapes can be prepared according to the quality of PF and SPS. When the quality is relatively low (0.5-2), hemispherical hollow carbon microspheres with a particle size of about 400nm will be obtained. When the mass ratio is ( 2-3), a mixture of hemispherical and spherical hollow carbon microspheres with a particle diameter of about 415nm will be obtained. When its quality is relatively low (3-6), a complete spherical hollow carbon microsphere with a particle size of about 430 nm will be obtained. In step 4), heat to 900° C. at a heating rate of 5 K/min.

Compared with the prior art, the inventive method has the following beneficial effects:

1) The present invention uses resole phenolic resin with higher carbon residue as a carbon source, and polystyrene microspheres with low carbon residue as a template for preparing hollow microspheres. By changing the particle size of the microspheres, the hollow microspheres can be effectively The spherical particle size is controlled, and at the same time, the operation process of removing the template in the previous preparation method is avoided, which effectively reduces the complexity of the preparation process.

2) In the present invention, by adjusting the mass ratio of resole phenolic resin and polystyrene microspheres, the control of the shape of hollow carbon microspheres can be realized for the first time in the same system by only changing one variable, and the hemispheres are prepared. hollow carbon microspheres and spherical hollow carbon microspheres.

Description of drawings

Fig. 1, scanning electron micrograph (a) and transmission electron micrograph (b) of hemispherical hollow carbon microsphere prepared in embodiment 1.

Fig. 2, the scanning electron micrograph of the hollow carbon microsphere prepared in embodiment 2.

Fig. 3, scanning electron micrograph (a) and transmission electron micrograph (b) of the spherical carbon microsphere prepared in embodiment 3.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

Polystyrene microspheres as templates were prepared by soap-free emulsion polymerization: potassium persulfate (concentration: 3.33×10 ^-3 mol/L) was added to 100 ml of deionized water as an initiator, and charged at room temperature Nitrogen deoxygenated for 30 minutes, then added 5ml of styrene and reacted with mechanical stirring at 70°C for 12 hours in a water bath to prepare monodisperse polystyrene microspheres. Since different initiator additions will affect the particle size and dispersibility of polystyrene microspheres, in this embodiment, monodisperse polystyrene particles with a particle size of 500 nm can be prepared by adding an appropriate amount of initiator. Styrene microspheres.

Preparation of sulfonated polystyrene microspheres (SPS): add an appropriate amount of the above-prepared polystyrene microspheres to 50ml of concentrated sulfuric acid at a concentration of 40g/L, acidify at 30°C for 0.5-4h, then wash and separate and dry.

Example 1

1) Preparation of core-shell structure phenolic resin/sulfonated polystyrene microspheres (PF/SPS) composite microspheres: add prepared SPS (8.33g/L) to 60ml of absolute ethanol, and heat in a water bath to After 40°C, 20ml of ethanol solution of resole phenolic resin was added dropwise, the mass ratio of resole phenolic resin to sulfonated polystyrene microspheres was 1.5:1, the dropwise addition was completed within 1 hour, reacted for 6h under mechanical stirring conditions, and separated And drying, the obtained particle size is 465nm and shows monodisperse PF/SPS composite microsphere;

2) Preparation of hollow carbon microspheres: Under the protection of argon or nitrogen, the PF/SPS composite microspheres were carbonized at 900°C, and the heating rate was 5K/min to obtain hemispherical hollow carbon microspheres.

The scanning electron microscope photos and transmission electron microscope photos are shown in (a) and (b) in Figure 1. It can be seen from these two photos that the prepared hollow microspheres have a particle size of ~400nm and are monodisperse. Hemispherical morphology, and there is no bonding phenomenon between the microspheres.

Example 2

1) Preparation of core-shell structure phenolic resin/sulfonated polystyrene microspheres (PF/SPS) composite microspheres: add prepared SPS (8.33g/L) to 60ml of absolute ethanol, and heat in a water bath to After 40°C, 20ml of ethanol solution of resole phenolic resin was added dropwise, the mass ratio of resole phenolic resin to sulfonated polystyrene microspheres was 2.5:1, the dropwise addition was completed within 1 hour, reacted for 6h under mechanical stirring conditions, and separated And drying, the obtained particle size is 480nm and shows monodisperse PF/SPS composite microsphere;

2) Preparation of hollow carbon microspheres: Under the protection of argon or nitrogen, the PF/SPS composite microspheres were carbonized at 900 °C, and the heating rate was 5K/min to obtain hemispherical hollow carbon microspheres and complete Spherical hollow carbon microsphere mixture.

The scanning electron microscope photo is shown in Figure 2. The hollow carbon microspheres thus prepared are monodisperse, and there is no bonding between the microspheres, but there are two different shapes of hollow carbon microspheres: hemispherical and spherical. mixture, the prepared hollow microspheres have a particle size of about 415nm.

Example 3

1) Preparation of core-shell structure phenolic resin/polystyrene microspheres (PF/SPS) composite microspheres: add the prepared SPS (8.33g/L) to 60ml of absolute ethanol, and heat to 40°C in a water bath Finally, 20ml of ethanol solution of resole phenolic resin was added dropwise, the mass ratio of resole phenolic resin to modified polystyrene microspheres was 4:1, the dropwise addition was completed within 1 hour, reacted for 6h under mechanical stirring conditions, separated and dried , the obtained particle diameter is 515nm and shows monodisperse PF/SPS composite microsphere;

2) Preparation of hollow carbon microspheres: Under the protection of argon or nitrogen, the PF/SPS composite microspheres were carbonized at 900°C, and the heating rate was 5K/min to obtain complete spherical hollow carbon microspheres

The scanning electron micrographs and transmission electron micrographs are shown in (a) and (b) in Figure 3. The spherical hollow carbon microspheres thus prepared are monodisperse, and there is no bonding between the microspheres, and The hollow carbon microspheres have a complete spherical shape, and the particle size of the hollow carbon microspheres is about 430nm and exhibits monodispersity.

Claims (7)

1. the preparation method of the controlled hollow carbon microballoon of pattern; it is characterized in that; at first; prepare the polystyrene microsphere of monodispersity by the method for emulsifier-free emulsion polymerization; by vitriol oil acidification; modification is carried out on its surface to be handled; make its surface have the sulfonate group of initiating activity to resole with going up; in the dehydrated alcohol that has disperseed the modified polystyrene microballoon, drip the resole ethanolic soln then; make it carry out crosslinking reaction at microsphere surface; prepare the mixture microballoon of nucleocapsid structure, place the protection of inert gas environment to carry out carbonization this mixture microballoon at last, concrete steps are as follows:

1) method by emulsifier-free emulsion polymerization is prepared the polystyrene microsphere as template: add Potassium Persulphate (KPS) as initiator in deionized water, its concentration is 0.0028-0.0103mol/L, the 30min of inflated with nitrogen deoxygenation at normal temperatures, then add vinylbenzene, Potassium Persulphate is the 1-4% of vinylbenzene quality, and 70 ℃ of mechanical stirring are reacted 12h in water-bath, prepare the polystyrene microsphere of monodispersity;

2) preparation of sulfonated polystyrene microballoon (SPS): in mass concentration is to add the polystyrene microsphere for preparing in the step 1) in 98% the vitriol oil, acidifying 1-3h under 30 ℃ of conditions, and after washing separates;

3) preparation of nucleocapsid structure resol/sulfonated polystyrene microballoon (PF/SPS) mixture microballoon: in dehydrated alcohol, the add step 2) SPS of preparation, behind the heating in water bath to 40 ℃, drip the resole ethanolic soln, the mass ratio of resole and modified polystyrene microballoon is 0.5-6, dropwise in 1 hour, afterreaction 6h makes PF/SPS mixture microballoon;

4) preparation of hollow carbon microballoon: under argon gas or nitrogen protection condition, PF/SPS mixture microballoon is carried out carbonization under 900 ℃, obtain the hollow carbon microballoon.

2. according to the method for claim 1, it is characterized in that step 2) the preferred 40g/L of polystyrene microsphere concentration.

3. according to the method for claim 1, it is characterized in that step 3) sulfonated polystyrene microballoon is at the preferred 8.33g/L of the concentration in dehydrated alcohol.

4. according to the method for claim 1, it is characterized in that the preferred 0.025-0.2g/L of step 3) resole ethanolic soln concentration.

5. according to the method for claim 1, it is characterized in that when the mass ratio of resole and modified polystyrene microballoon was 0.5-2 in the step 3), the product of step 4) was the hemispherical hollow carbosphere.

6. according to the method for claim 1, it is characterized in that when the mass ratio of resole and modified polystyrene microballoon was 2-3 in the step 3), the product of step 4) was hemispherical and globular hollow carbon mixture of microspheres.

7. according to the method for claim 1, it is characterized in that when the mass ratio of resole and modified polystyrene microballoon was 3-6 in the step 3), the product of step 4) was a full spherical hollow carbon microballoon.

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