CN116161657A - Spheroid hollow graphite and preparation method and application thereof - Google Patents
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims abstract description 165
- 229910002804 graphite Inorganic materials 0.000 title claims abstract description 153
- 239000010439 graphite Substances 0.000 title claims abstract description 153
- 238000002360 preparation method Methods 0.000 title claims abstract description 24
- AKEJUJNQAAGONA-UHFFFAOYSA-N sulfur trioxide Chemical group O=S(=O)=O AKEJUJNQAAGONA-UHFFFAOYSA-N 0.000 claims abstract description 53
- 239000007770 graphite material Substances 0.000 claims abstract description 48
- 238000000034 method Methods 0.000 claims abstract description 40
- 238000009830 intercalation Methods 0.000 claims abstract description 39
- 230000002687 intercalation Effects 0.000 claims abstract description 39
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- 239000003795 chemical substances by application Substances 0.000 claims abstract description 22
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- HIFJUMGIHIZEPX-UHFFFAOYSA-N sulfuric acid;sulfur trioxide Chemical compound O=S(=O)=O.OS(O)(=O)=O HIFJUMGIHIZEPX-UHFFFAOYSA-N 0.000 claims abstract description 16
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- ROOXNKNUYICQNP-UHFFFAOYSA-N ammonium persulfate Chemical compound [NH4+].[NH4+].[O-]S(=O)(=O)OOS([O-])(=O)=O ROOXNKNUYICQNP-UHFFFAOYSA-N 0.000 claims description 66
- QAOWNCQODCNURD-UHFFFAOYSA-N sulfuric acid Substances OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims description 46
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- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
- H01B1/04—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors mainly consisting of carbon-silicon compounds, carbon or silicon
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B32/00—Carbon; Compounds thereof
- C01B32/20—Graphite
- C01B32/21—After-treatment
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B32/00—Carbon; Compounds thereof
- C01B32/20—Graphite
- C01B32/21—After-treatment
- C01B32/22—Intercalation
- C01B32/225—Expansion; Exfoliation
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Abstract
The invention belongs to the technical field of materials, and particularly relates to a spheroidal hollow graphite material, and a preparation method and application thereof. The invention provides a preparation method of spheroidal hollow graphite, which comprises the following steps: firstly, fuming sulfuric acid and sulfur trioxide form an anhydrous environment; adding flake graphite, an intercalation agent and an expanding agent to perform intercalation reaction; then adding aqueous solution to promote the flake graphite to expand uniformly; finally, diluting, washing and drying the product to obtain a spheroidal hollow graphite material; wherein, the flake size of the flake graphite is 100 um-500 um. The invention avoids using graphite oxide in the preparation process of the spheroidal hollow graphite material, and provides a new method for preparing spheroidal hollow graphite from natural raw material flake graphite by a one-step method.
Description
Technical Field
The invention belongs to the technical field of materials, and particularly relates to a spheroidal hollow graphite material, and a preparation method and application thereof.
Background
The flake graphite is a lamellar structure formed by lamellar arrangement of graphite molecules, sheets are connected by pi-pi acting force, the bonding force between carbon layers is weak, the interlayer spacing is large, various chemical substances can be intercalated between the layers, and the chemical substances are further peeled into lamellar graphite materials.
The intercalation of the flake graphite endows the material with new properties such as high conductivity, hydrogen storage property, catalytic effect and sealing property, and the material has wide application prospect as a novel nanoscale composite material.
The spheroidal graphite is a graphite material prepared from flake graphite or graphite oxide through special process treatment, has excellent performances in self-lubricating property, flexibility, heat conductivity and corrosion resistance, and is widely applied to the fields of electrodes, energy storage, flame retardance and the like.
The preparation methods of spheroidal graphite materials are mainly divided into two categories: hard template methods and soft template methods. The hard template method is to use silicon dioxide and metal oxide as basic templates and to prepare microspheres by using preformed pore structures; the soft template method adopts polymer, surfactant or other non-inorganic matters as a basic template, and then the template is washed out by acid or strong alkali; typically, a carbon precursor (e.g., glucose, sucrose, or monomer) is impregnated into the porous template and fills the pores. The impregnated structure may be subjected to a gel polymerization process or direct carbonization to produce a silica-carbon composite material, wherein the silica is typically removed by acid etching to produce a porous carbon material; also, the scholars have used Metal Organic Frameworks (MOFs) as templates for the production of porous carbon materials 1 MOFs are crystalline porous materials formed by the attachment of metal ions to organic ligands, and there is a great opportunity to produce MOFs with desirable properties due to the large number of metal ions and the virtually unlimited types of organic ligands available; although a large number of MOFs are available, only a small fraction of MOFs (mainly Zn-based and Al-based MOFs) have been used so far to produce templates for porous carbon materials, unlike zeolites, MOFs contain organic ligands, and many ligands are aromatic polycarboxylic acids, carbon-rich precursors. By virtue of its inherent crystalline microporosity, MOFs can be carbonized directly to produce nanoporous carbon materials. In addition, anotherThere are research teams that use chemical vapor deposition to prepare microspheres: the gaseous precursor is decomposed and aggregated, and the gaseous precursor is continuously deposited and grown into carbon microspheres; catalysts may also be used as nucleation sites for the microspheres; for example, siO 2 As a CVD template, siO is subsequently removed by HF etching 2 Obtaining hollow microspheres; hydrothermal carbonization has also been used to convert carbohydrates or lignocellulose into carbonaceous materials at sealed high pressures using mild temperatures; for example, treating glucose at 160-180℃produces microspheres with high dispersibility. A template may be introduced into the precursor solution prior to the hydrothermal treatment to produce composite spheres or hollow spheres, forming a uniform carbon layer on the template while maintaining discrete sphere morphology during the hydrothermal treatment 2 。
In contrast to hard templates, polymer gels in soft templates have been widely used to produce porous carbon microspheres, polymethyl methacrylate (PMMA) and Polystyrene (PS) colloids are most commonly used, which can be removed by washing with a suitable solvent (e.g., toluene, tetrahydrofuran) or by decomposition during heat treatment; in addition, the surfactant is used as a product commonly used in life, plays a unique role in preparing porous microspheres, and the cationic surfactant (cetyl trimethyl ammonium bromide) is usually used as a soft template and can be removed through carbonization or solvent exchange so as to form a mesoporous carbon material; both emulsion templates and ice templates can be regarded as soft template methods, the types of emulsion templates being divided into two categories: oil-in-water (O/W) emulsions and water-in-oil (W/O) emulsions, in order to prepare porous polymers using the emulsion as a template, monomers and initiators need to be dissolved in a continuous phase and then polymerized while maintaining the emulsion structure; removal of solvent from the continuous and droplet phases can produce emulsion templated porous materials, both O/W and W/O emulsions have been used to produce a range of porous polymers and porous inorganic materials; the ice template method is to remove a freezing solvent by freeze-drying (also called freeze-drying) to generate a highly interconnected macroporous structure, and control the size and growth direction of ice crystals to regulate the structure of the pores; in general, higher temperature gradients and faster freezing rates can produce samples with smaller ice crystal sizes, and the addition of some inorganic salts can also alter the size distribution of the crystals.
The 2018 research team proposes a template-free method 3 Preparing porous carbon microspheres, forming GO aqueous solution into small liquid drops through a nozzle by utilizing a spray drying technology under the action of air pressure, rapidly drying, shrinking GO sheets into folded microspheres by utilizing the capillary action caused by water evaporation, and decomposing oxygen-containing functional groups on the GO surfaces to release gas by high-temperature treatment to expand the folded microspheres to form the hollow microsphere carbonaceous material.
The porous carbon microsphere structure has hydrophobicity and lipophilicity, and can selectively remove non-aqueous solution in water, such as floating oil from sea, river and lake 4 The method comprises the steps of carrying out a first treatment on the surface of the After absorbing a large amount of oil, the oil can be gathered into blocks, float on the liquid surface, is convenient to collect, can be subjected to regeneration treatment and can be recycled; since the porous carbon material is composed of substantially pure carbon, is nontoxic and chemically inert, it does not cause secondary pollution in water. Secondly, the porous carbon microsphere can also be used for anodes in high-performance battery materials, enhancing the conductivity of the electrodes, inhibiting dendrite formation, reducing polarization during anode charging, and prolonging the service life of the battery 5 The method comprises the steps of carrying out a first treatment on the surface of the The porous carbon material has rich pore structure and high heat conductivity, so that the problems of poor heat conductivity, poor heat exchange performance and the like of the phase change heat storage material can be solved 6 The method comprises the steps of carrying out a first treatment on the surface of the In addition, the porous carbon material can also be used in the fields of flame retardance, infrared shielding, electromagnetic shielding, sound insulation, catalysis and the like 7 。
1.Chaudhari,S.；Kwon,S.Y.；Yu,J.-S.,Ordered multimodal porous carbon with hierarchical nanostructure as high performance electrode material for supercapacitors.RSC Adv.2014,4(73),38931-38938.
2.Roberts,A.D.；Li,X.；Zhang,H.,Porous carbon spheres and monoliths:morphology control,pore size tuning and their applications as Li-ion battery anode materials.Chem.Soc.Rev.2014,43(13),4341-4356.
3.Chen,C.；Xi,J.；Han,Y.；Peng,L.；Gao,W.；Xu,Z.；Gao,C.,Ultralight graphene micro-popcorns for multifunctional composite applications.Carbon 2018,139,545-555.
4.Takeuchi,K.；Kitazawa,H.；Fujishige,M.；Akuzawa,N.；Ortiz-Medina,J.；Morelos-Gomez,A.；Cruz-Silva,R.；Araki,T.；Hayashi,T.；Endo,M.,Oil removing properties of exfoliated graphite in actual produced water treatment.Journal of Water Process Engineering 2017,20,226-231.
5.Tu,J.；Tong,H.；Zeng,X.；Chen,S.；Wang,C.；Zheng,W.；Wang,H.；Chen,Q.,Modification of Porous N-Doped Carbon with Sulfonic Acid toward High-ICE/Capacity Anode Material for Potassium-Ion Batteries.Advanced Functional Materials 2022,32(34).
6.Yadav,M.；Pasarkar,N.；Naikwadi,A.；Mahanwar,P.,Areview on microencapsulation,thermal energy storage applications,thermal conductivity and modification of polymeric phase change material for thermal energy storage applications.Polymer Bulletin 2022.
7.Murugan,P.；Nagarajan,R.D.；Shetty,B.H.；Govindasamy,M.；Sundramoorthy,A.K.,Recent trends in the applications of thermally expanded graphite for energy storage and sensors-a review.Nanoscale Adv 2021,3(22),6294-6309.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, avoid using graphite oxide in the preparation process of a spheroidal hollow graphite material, and provide a novel method for preparing spheroidal hollow graphite from natural raw materials (flake graphite) by a one-step method.
The technical scheme of the invention is as follows:
the first technical problem to be solved by the invention is to provide a preparation method of spheroidal hollow graphite, which comprises the following steps: firstly, fuming sulfuric acid and sulfur trioxide form an anhydrous environment; adding flake graphite, an intercalation agent and an expanding agent to perform intercalation reaction; then adding aqueous solution to promote the flake graphite to expand uniformly; finally, diluting, washing and drying the product to obtain a spheroidal hollow graphite material; wherein, the flake size of the flake graphite is 100 um-500 um. The sheet size of the flake graphite refers to the average value of the maximum transverse size of each sheet in the irregularly-shaped material after screening by the screen.
Further, the intercalating agent and the expanding agent are selected from substances capable of generating gas at a temperature below 35 ℃; ammonium persulfate is preferred.
Further, the aqueous solution is hydrogen peroxide aqueous solution or deionized water.
Further, the volume ratio of fuming sulfuric acid to concentrated sulfuric acid is 1:1 to 1:3.
further, the mass volume ratio of the crystalline flake graphite to the fuming sulfuric acid is as follows: 1-3 g: 30-80 mL.
Further, the mass ratio of the total mass of the intercalation agent and the expanding agent to the crystalline flake graphite is 10-30: 1 to 5.
Further, the volume mass ratio of the aqueous solution to the crystalline flake graphite is 10-20 ml: 1-2 g.
Further, the method for forming the anhydrous environment comprises the following steps: adding fuming sulfuric acid (containing 50wt% of sulfur trioxide) and concentrated sulfuric acid (containing 98wt% of sulfuric acid and 2wt% of water) into a reactor together, and stirring to ensure that the sulfur trioxide in the system consumes water to form an anhydrous environment; wherein, the volume ratio of fuming sulfuric acid to concentrated sulfuric acid is 1:1 to 1:3.
further, the intercalation reaction refers to: reacting at 25-45 deg.c, preferably 35 deg.c for 0.5-1 hr, preferably 1 hr; wherein the mass ratio of the total mass of the intercalation agent and the expanding agent to the crystalline flake graphite is 10-30: 1 to 5.
Further, in the method, the process of adding the aqueous solution to promote the uniform expansion of the crystalline flake graphite comprises the following steps: adding an aqueous solution into the system to enable the system to be in a humid environment, decomposing an expanding agent in the humid environment to release gas (such as oxygen and nitrogen), simultaneously instantaneously gasifying sulfur trioxide, enabling the pressure caused by gas release to exceed pi-pi acting force among flake graphite sheets, and uniformly expanding flake graphite; wherein, the volume mass ratio of the aqueous solution to the crystalline flake graphite is 10-20 ml: 1-2 g.
In the method, deionized water is added into the product to dilute and wash the product to remove concentrated sulfuric acid.
Further, in the method, the suction filtration bottle is used for washing, concentrated sulfuric acid on the surface of the material is removed, and the washing process is repeated for 4-5 times until the liquid in the suction filtration bottle below is neutral, and the suction filtration is finished.
The second technical problem to be solved by the invention is to provide spheroidal graphite which is prepared by the method.
Further, the spheroidal graphite is of a hollow structure.
Further, the pore size distribution of the spheroidal graphite is 10-120 um.
Further, the surface structure defect of the spheroidal graphite is smaller, the ID/IG value in the Raman spectrum is between 0.2 and 0.85, and the C/O in the XPS spectrum is 7.758.
The third technical problem to be solved by the invention is to indicate the use of the spheroidal graphite in heat conduction, electric conduction and electromagnetic shielding.
The invention has the beneficial effects that:
compared with the preparation method of a template method and a non-template method, the preparation method is simple and efficient, and graphite oxide is avoided; because the preparation method of the graphite oxide is complex, the flake graphite is firstly intercalated and expanded to form Expanded Graphite (EG), and then the graphite oxide is prepared under the reaction conditions of concentrated sulfuric acid, sodium nitrate, potassium permanganate and hydrogen peroxide, and the addition of the potassium permanganate has an explosive risk; the final product, namely graphene oxide, can be obtained after the obtained graphite oxide is subjected to long-time centrifugal water washing; it can be seen that the process of preparing graphite oxide is dangerous and tedious. The spherical hollow graphite material is prepared by the flake graphite one-step method, and the preparation method is simple, efficient, low in cost and low in risk; the prepared spheroidal graphite material has low oxidation degree, less damage to lamellar layers and no need of high-temperature graphitization or chemical reduction to recover the SP of lamellar layers 2 The structure has small influence on the electric conduction and heat conduction properties of the material.
Drawings
FIG. 1 is a flow chart of a method of preparing spheroidal hollow graphite according to the present invention.
Fig. 2 is a graph showing the change in phenomenon during the preparation of the spheroidal hollow graphite according to example 1: fig. 2a is a digital photograph, and fig. 2b is a polarized photograph.
FIG. 3 is a graph showing the change in expansion volume during the preparation of spheroidal hollow graphite according to example 1 (digital photograph).
FIGS. 4 a1 and a2 are XRD and Raman spectra of a black material during the preparation of the spheroidal hollow graphite of example 1; b1 and b2 are XRD and Raman spectra of yellow substances in the preparation process respectively; and c, a Raman spectrum of the concentrated sulfuric acid.
FIG. 5 a is a scanning electron microscope image of the crystalline flake graphite used in example 1; b1 and b2 are scanning electron microscope pictures of spheroidal hollow graphite obtained by intercalation expansion in example 1; and c, a partial scanning electron microscope picture of the spheroidal hollow graphite in the embodiment 1.
Fig. 6 is an XRD spectrum of the crystalline flake graphite (a-plot) used in example 1 and the spheroidal hollow graphite (b-plot) obtained by intercalation expansion.
FIG. 7 is a Raman spectrum of spheroidal hollow graphite and flake graphite of example 1.
FIGS. 8A 1 and B1 are XPS spectra of crystalline flake graphite and spheroidal hollow graphite, respectively, of example 1; FIGS. a2 and b2 are C1s spectra of the crystalline flake graphite and spheroidal hollow graphite, respectively, of example 1.
FIG. 9 a is a graph of pressure-mercury intrusion/pore size for the spheroidal hollow graphite material of example 1; and b, the pore diameter distribution diagram of the spheroidal hollow graphite material.
FIG. 10 a is an XRD spectrum of the material obtained after intercalation expansion using small-sized crystalline flake graphite (20 um) of comparative example 1 and crystalline flake graphite; panel b shows the Raman spectrum of the material obtained after intercalation expansion of small-size crystalline flake graphite (20 um) in comparative example 1 and crystalline flake graphite.
FIG. 11 is a scanning electron microscope image of the material obtained after intercalation expansion using small-sized crystalline graphite (20 um) in comparative example 1.
Detailed Description
The invention provides a preparation method of a spherical hollow graphite material, which can be prepared by adopting the following specific modes:
firstly, constructing an anhydrous environment, avoiding the rapid decomposition of ammonium persulfate, and realizing the pre-intercalation of sulfur trioxide and ammonium persulfate; 60ml of fuming sulfuric acid (containing 50wt% of sulfur trioxide) and 100ml of concentrated sulfuric acid (containing 98wt% of sulfuric acid and 2wt% of water) are added into a 500ml beaker together, and stirred at a constant speed for 5 minutes under the action of a polytetrafluoroethylene stirring rod, so that the sulfur trioxide in the system consumes water to form an anhydrous environment;
step two, adding 2g of large-sheet-layer crystalline flake graphite into an anhydrous environment, wherein the sheet size of the crystalline flake graphite is 400-500 um; in the invention, if the size of the flake graphite is too small and is smaller than 100um, for example, when the size of the flake graphite is 20um, the flakes cannot expand, because the gas generated by the expanding agent easily escapes from the edges of the flakes, and the effect of stripping the flakes cannot be achieved; if the size of the flake graphite is too large and is larger than 500um, pi-pi acting force between flake graphite flakes is large, and an intercalation agent and an expanding agent are difficult to enter the middle of the flakes, so that the expansion is insufficient, and a complete spheroidal graphite material is not obtained;
step three, adding 20g of ammonium persulfate into the system, stirring the mixture at a constant speed by a stirring rod, wherein the rotating speed is 200r/min, the reaction temperature is 35 ℃, and the reaction duration is 1h;
step four, after the reaction is finished for 1 hour, adding 15ml of hydrogen peroxide into the system to enable the system to be in a humid environment, decomposing ammonium persulfate in the humid environment to release gas (oxygen and nitrogen), simultaneously instantaneously gasifying sulfur trioxide, enabling the pressure caused by gas release to exceed pi-pi acting force between flake graphite sheets, and enabling flake graphite to uniformly expand, wherein the process is continuous for 1 hour;
step five, adding deionized water for dilution after the reaction is finished, washing by using a suction filtration bottle, removing concentrated sulfuric acid on the surface of the material, and repeating the washing process for 4-5 times until the liquid in the suction filtration bottle below is neutral, and finishing suction filtration;
step six, transferring the product into a surface dish, and putting the surface dish into a blast oven to dry for 12 hours at 70 ℃; and (5) drying to obtain the spheroidal hollow graphite material.
According to the invention, the edges of the flake graphite sheets are opened through weak oxidation of sulfuric acid and sulfur trioxide, so that ammonium persulfate can well enter the middle of the flake graphite sheets; the system is in an anhydrous environment due to the existence of sulfur trioxide, and ammonium persulfate can be decomposed in the presence of water, so that the ammonium persulfate firstly realizes the pre-intercalation of graphite sheets into the middle of the sheets of crystalline flake graphite in the anhydrous system; the hydrogen peroxide aqueous solution or water added later can induce the decomposition of ammonium persulfate to release gas, and the heat released by the reaction of deionized water and sulfuric acid releases sulfur trioxide in the lamellar layers, so that the lamellar graphite lamellar layers are uniformly expanded under the dual action of the two gases; in addition, the oxidation effect of sulfur trioxide and ammonium persulfate is weak, and the damage of a lamellar structure is small; when the final water dilution is carried out, sulfuric acid molecules among the lamellar layers are removed, and unlike graphene oxide, the lamellar layers are mutually isolated by electrostatic repulsion under the action of oxygen-containing functional groups which are dissociated to form oxygen anions; the graphite sheet formed in the method has no strong oxidation effect, has fewer oxygen-containing functional groups on the surface, can be gradually washed away along with the dilution of water, gradually recovers pi-pi effect among the sheet layers, and is stacked to form the spheroidal graphite material. The invention adopts an intercalation expansion method to obtain inspiration from the stripping of a graphite intercalation compound, and the key idea is to overcome the strong pi-pi acting force between flake graphite, weaken the attractive force between flake graphite layers and reduce stripping energy.
In the invention, the ammonium persulfate decomposition mechanism in the preparation process of the spheroidal hollow graphite material is as follows:
the following describes the invention in further detail with reference to examples, which are not intended to limit the invention thereto.
In the embodiment of the invention, fuming sulfuric acid refers to sulfuric acid containing 50 weight percent of sulfur trioxide and 50 weight percent of concentrated sulfuric acid, the concentrated sulfuric acid refers to sulfuric acid containing 98 weight percent of sulfuric acid and 2 weight percent of water, and a hydrogen peroxide solution is a mixed solution of 30 weight percent of hydrogen peroxide and 70 weight percent of water, and the preparation method is carried out in a liquid phase and is used for carrying out synchronous intercalation expansion and oxidation on crystalline flake graphite; in the reaction process, sulfuric acid and sulfur trioxide play a role in pre-intercalation, and ammonium persulfate plays a role in intercalation and expansion.
Example 1
Firstly, 60ml of fuming sulfuric acid and 100ml of 98% concentrated sulfuric acid are added into a 500ml beaker, and then a polytetrafluoroethylene stirring rod is adopted for stirring for 5min, so that the system is in an anhydrous environment; then adding 2g of crystalline flake graphite (the lamellar size of the crystalline flake graphite is 400 um) and 20g of ammonium persulfate, and reacting for 1h; along with the progress of the reaction, ammonium persulfate is gradually brought into the middle of the flake graphite sheet layer by sulfuric acid, but the system is in an anhydrous environment, so that the ammonium persulfate cannot be instantaneously expanded, the pre-intercalation of ammonium persulfate and sulfur trioxide firstly occurs, the intercalation is gradually complete, and a foundation is laid for the effective expansion of the flake graphite; after the reaction is finished for 1h, 15ml of hydrogen peroxide is added into the system for reaction for 1h, the decomposition of ammonium persulfate is induced and gas is released, and in addition, the water in the hydrogen peroxide is dissolved in concentrated sulfuric acid to release a large amount of heat, so that sulfur trioxide in the system is gasified instantaneously; under the combined action of the gas released by the decomposition of ammonium persulfate and the instantaneous gasification of sulfur trioxide, the pressure brought by the gas release exceeds pi-pi acting force among flake graphite sheets, and flake graphite is uniformly expanded; after expansion for 1h, adding deionized water for dilution, suction filtration and drying; as the gas between the sheets is gradually released, the distance between the layers is gradually reduced, and the pi-pi acting force between the layers is also gradually recovered, so that the assembly of the sheets occurs, and the assembly tends to minimize the surface energy, so that the spheroidal hollow graphite material is formed. Table 1 shows pore size data of spheroidal hollow graphite materials according to the present invention.
FIG. 2 is a graph showing the change of the phenomenon during the preparation of the spheroidal hollow graphite material according to example 1; as can be seen from the figure: under the anhydrous environment, the crystalline flake graphite is not expanded and the solution is black in color, and when the aqueous solution is added, the ammonium persulfate is induced to release gas, so that the crystalline flake graphite is expanded and the solution is yellow in color; the resulting yellow material was observed under a polarizing microscope, and it was found that the color gradually changed from yellow to green to black over time.
FIG. 3 is a graph showing the change in expansion volume during the preparation of the spheroidal hollow graphite material according to example 1; as can be seen from the figure: when the aqueous solution is added, the crystalline flake graphite expands rapidly, and the volume of the system is changed from 200ml to 600ml.
FIG. 4 is an in situ XRD and in situ Raman chart of the spheroidal hollow graphite material of example 1; as can be seen from the figure: in-situ Raman test chart, the yellow substance and the black substance have no G peak (1580-1610 cm) -1 ) And D peak (1340-1360 cm) -1 ) Other peaks (at 900-1100cm -1 Diffraction peak for concentrated sulfuric acid), demonstrating that the yellow material is not caused by a chemical structure change; in the XRD spectrum, a weak peak was found in the effect of yellow substance at 10 °, whereas no peak was observed in the spectrum of black substance, thus proving to be caused by the process of changing black to yellow as a structural change.
FIG. 5 is a scanning electron microscope image of a spheroidal hollow graphite material according to example 1; as can be seen from the figure: the spheroidal hollow graphite material is obtained through the expansion action of ammonium persulfate and sulfur trioxide.
Fig. 6 a shows the XRD spectrum of the crystalline flake graphite used in example 1, as follows: the 2 theta angle of the crystalline flake graphite is 26.6 DEG, and the interplanar spacing is obtained by the Bragg formula (nλ=2dsinθ)
Graph b shows the XRD spectrum of the spheroidal hollow graphite material of example 1, as follows: the spheroidal hollow graphite material has a peak at 8.383 ° compared to the flake graphite, and the (002) peak (26.6 °) of the graphite characteristic moves to the left to 26.4 °, and the interplanar spacing thereof is ± as obtainable by the bragg formula (nλ=2dsinθ)>
Proving that the sheets of the flake graphite are expanded open.
FIG. 7 is a Raman spectrum of a spheroidal hollow graphite material according to example 1; as can be seen from the figure: the ID/IG of the spheroidal graphite material is 0.592, and the sheet defect degree is smaller than that of graphite oxide (ID/IG > 1), so that the method can not cause larger damage to the sheet.
FIGS. 8 a1 and b1 are XPS spectra of spheroidal hollow graphite materials according to example 1; as can be seen from the figure: the C/O of the flake graphite is 28.8, the C/O of the spheroidal graphite material is 7.758, and the smaller the C/O is, the higher the oxidation degree of the carbon material is; it can also be seen from the carbon spectra (a 2 and b 2) that spheroidal graphite materials oxidize to some extent, but not to a high extent, compared to flake graphite.
FIG. 9 is a graph of mercury intrusion aperture of a spheroidal hollow graphite material according to example 1; as can be seen from the figure: along with the gradual increase of the pressure, the amount of mercury pressed in is continuously increased, the pore diameter of the material is continuously reduced, and the pore diameter of the spheroidal graphite material is distributed between 10 and 120 mu m.
TABLE 1 pore size data for spheroidal hollow graphite materials
Example 2
Firstly, adding 50ml of fuming sulfuric acid and 110ml of 98% concentrated sulfuric acid into a 500ml beaker, and then stirring for 5min by adopting a polytetrafluoroethylene stirring rod to enable the system to be in an anhydrous environment; then adding 2g of crystalline flake graphite (the size of the crystalline flake graphite is 400 um) and 20g of ammonium persulfate, and reacting for 1h; along with the progress of the reaction, ammonium persulfate is gradually brought into the middle of the flake graphite sheet layer by sulfuric acid, but the system is in an anhydrous environment, so that the ammonium persulfate cannot be instantaneously expanded, the pre-intercalation of ammonium persulfate and sulfur trioxide firstly occurs, the intercalation is gradually complete, and a foundation is laid for the effective expansion of the flake graphite; after the reaction is finished for 1h, 15ml of hydrogen peroxide is added into the system for reaction for 1h, the decomposition of ammonium persulfate is induced and gas is released, and in addition, the water in the hydrogen peroxide is dissolved in concentrated sulfuric acid to release a large amount of heat, so that sulfur trioxide in the system is gasified instantaneously; under the combined action of the gas released by the decomposition of ammonium persulfate and the instantaneous gasification of sulfur trioxide, the pressure brought by the gas release exceeds pi-pi acting force among flake graphite sheets, and flake graphite is uniformly expanded; after expansion for 1h, adding deionized water for dilution, suction filtration and drying; as the gas between the sheets is gradually released, the distance between the layers is gradually reduced, and the pi-pi acting force between the layers is also gradually recovered, so that the assembly of the sheets occurs, and the assembly tends to minimize the surface energy, so that the spheroidal hollow graphite material is formed. Table 2 shows XRD/Raman data of the spheroidal hollow graphite material obtained in example 2; table 3 shows pore diameter data of spheroidal hollow graphite materials obtained in example 2;
as can be seen from table 2: i of the spheroidal graphite material obtained in example 2 D /I G 0.2132, the sheet layer defect degree is smaller than that of graphite oxide (ID/IG > 1), and the method is proved to not cause larger damage to the sheet layer; and from XRD data it is known that: the (002) peak of the spheroidal hollow graphite was also changed from 26.6 ° (flake graphite) to 26.32 °, shifted to the left by 0.28 °, and the interlayer spacing was increased
Proving that the sheets of the flake graphite are expanded open.
As can be seen from table 3: the specific surface area of the spheroidal hollow graphite material obtained in example 2 was 11.44m 2 Per g, porosity of 85.99% and density of 0.0573g/cm 3 The most probable pore size is 40.36um.
TABLE 2 XRD/Raman data of spheroidal hollow graphite materials and flake graphite obtained in EXAMPLE 2
TABLE 3 pore size data for materials obtained by intercalation expansion of 50ml oleum
Example 3
Firstly, 60ml of fuming sulfuric acid and 100ml of 98% concentrated sulfuric acid are added into a 500ml beaker, and then a polytetrafluoroethylene stirring rod is adopted for stirring for 5min, so that the system is in an anhydrous environment; then adding 1g of crystalline flake graphite (the size of the crystalline flake graphite is 400 um) and 20g of ammonium persulfate, and reacting for 1h; along with the progress of the reaction, ammonium persulfate is gradually brought into the middle of the flake graphite sheet layer by sulfuric acid, but the system is in an anhydrous environment, so that the ammonium persulfate cannot be instantaneously expanded, the pre-intercalation of ammonium persulfate and sulfur trioxide firstly occurs, the intercalation is gradually complete, and a foundation is laid for the effective expansion of the flake graphite; after the reaction is finished for 1h, 15ml of hydrogen peroxide is added into the system for reaction for 1h, the decomposition of ammonium persulfate is induced and gas is released, and in addition, the water in the hydrogen peroxide is dissolved in concentrated sulfuric acid to release a large amount of heat, so that sulfur trioxide in the system is gasified instantaneously; under the combined action of the gas released by the decomposition of ammonium persulfate and the instantaneous gasification of sulfur trioxide, the pressure brought by the gas release exceeds pi-pi acting force among flake graphite sheets, and flake graphite is uniformly expanded; after expansion for 1h, adding deionized water for dilution, suction filtration and drying; as the gas between the sheets is gradually released, the distance between the layers is gradually reduced, and the pi-pi acting force between the layers is also gradually recovered, so that the assembly of the sheets occurs, and the assembly tends to minimize the surface energy, so that the spheroidal hollow graphite material is formed. Table 4 shows XRD and Raman data for the spheroidal hollow graphite material obtained in example 3; table 5 shows pore diameter data of spheroidal hollow graphite materials obtained in example 3;
as can be seen from table 4: i of the spheroidal graphite material obtained in example 3 D /I G 0.2132 the degree of lamellar defects is smaller than that of graphite oxide (I D /I G > 1), it is demonstrated that this method does not introduce significant damage to the lamellae; and from XRD data it is known that: the (002) peak of the spheroidal hollow graphite was also changed from 26.6 ° (flake graphite) to 26.33 °, shifted to the left by 0.27 °, and the interlayer spacing was increased
Proving that the sheets of the flake graphite are expanded open.
As can be seen from table 5: the specific surface area of the spheroidal hollow graphite material obtained in example 3 was 11.66m 2 Per g, porosity of 89.58% and density of 0.0562g/cm 3 The most probable pore size is 46.26um.
TABLE 4 XRD/Raman data for the spheroidal hollow graphite material obtained in example 3 and the flake graphite
TABLE 5.1 pore size data for materials obtained by intercalation expansion of crystalline flake graphite
Comparative example 1
The preparation process was the same as in example 1, except that the flake graphite used was 20um in size; because the flake graphite is too small in flake layers, the gas escape speed between the flake layers is too high, the expansion effect cannot be generated, and the finally prepared product is the flake graphite with weak oxidation degree, and the structure is lamellar.
FIG. 10 a is an XRD spectrum of a material obtained after intercalation expansion of small-sized crystalline graphite (20 um) in comparative example 1; as can be seen from XRD spectra, the peak positions before and after the reaction are not changed, and only the peak intensity is reduced, so that the material obtained after the reaction is proved to have no intercalation expansion. b graph is Raman spectrum of the material obtained after intercalation expansion of small-size crystalline flake graphite (20 um) in comparative example 1; as can be seen from a Raman spectrum, the ID/IG value of the material obtained after the reaction is increased, but the increase amplitude is smaller, and the lamellar structure of the obtained material is proved to be little damaged.
FIG. 11 is a Scanning Electron Microscope (SEM) image of the material obtained after intercalation expansion of small-sized crystalline graphite (20 um) in comparative example 1; as can be seen from SEM images, the surface of the obtained material contains more folds, the structure is flaky, the thickness of the flaky graphite is similar to that of the flaky graphite, and the small-size flaky graphite cannot be fully expanded.
Claims (10)
1. The preparation method of the spheroidal hollow graphite is characterized by comprising the following steps: firstly, fuming sulfuric acid and sulfur trioxide form an anhydrous environment; adding flake graphite, an intercalation agent and an expanding agent to perform intercalation reaction; then adding aqueous solution to promote the flake graphite to expand uniformly; finally, diluting, washing and drying the product to obtain a spheroidal hollow graphite material; wherein, the flake size of the flake graphite is 100 um-500 um.
2. The method of claim 1, wherein the intercalation agent and the expanding agent are selected from substances capable of generating gas at a temperature below 35 ℃; preferably ammonium persulfate; and/or:
the aqueous solution is hydrogen peroxide aqueous solution or deionized water.
3. A process for preparing spheroidal hollow graphite according to claim 1 or 2, wherein,
the volume ratio of fuming sulfuric acid to concentrated sulfuric acid is 1:1 to 1:3, a step of; and/or:
the mass volume ratio of the crystalline flake graphite to the fuming sulfuric acid is as follows: 1-3 g: 30-80 mL; and/or:
the mass ratio of the total mass of the intercalation agent and the expanding agent to the crystalline flake graphite is 10-30: 1 to 5; and/or:
the volume mass ratio of the aqueous solution to the crystalline flake graphite is 10-20 ml: 1-2 g.
4. A method for producing spheroidal hollow graphite according to any one of claims 1 to 3, wherein the method for forming an anhydrous environment comprises: adding fuming sulfuric acid and concentrated sulfuric acid into a reactor together, and stirring to enable sulfur trioxide in the system to consume water to form an anhydrous environment; wherein, the volume ratio of fuming sulfuric acid to concentrated sulfuric acid is 1:1 to 1:3.
5. the method for preparing spheroidal hollow graphite according to any one of claims 1 to 4, wherein the intercalation reaction is: reacting for 0.5-1 h at 25-45 ℃; wherein the mass ratio of the total mass of the intercalation agent and the expanding agent to the crystalline flake graphite is 10-30: 1 to 5.
6. The method for preparing spheroidal hollow graphite according to any one of claims 1 to 5, wherein the step of adding the aqueous solution to promote uniform expansion of the flake graphite comprises: adding an aqueous solution into the system to enable the system to be in a humid environment, decomposing an expanding agent in the humid environment to release gas, simultaneously instantaneously gasifying sulfur trioxide, enabling the pressure caused by gas release to exceed pi-pi acting force among flake graphite sheets, and uniformly expanding flake graphite; wherein, the volume mass ratio of the aqueous solution to the crystalline flake graphite is 10-20 ml: 1-2 g.
7. The method for preparing spheroidal hollow graphite according to any one of claims 1 to 6, wherein deionized water is added to the product to dilute and wash the product to remove concentrated sulfuric acid.
8. A spheroidal graphite prepared by the method of any one of claims 1 to 7.
9. A spheroidal graphite according to claim 8 wherein the spheroidal graphite is hollow; and/or:
the pore diameter of the spheroidal graphite is distributed between 10 and 120 mu m.
10. Use of spheroidal graphite produced by the method according to any one of claims 1 to 7 for heat conduction, electrical conduction and electromagnetic shielding.
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