CN103492317B - The method preparing Graphene - Google Patents

Abstract

A kind of method that the invention provides graphene-like fragment preparing Graphene or another layer structure, described method includes graphite or another layer structure being mixed with at least one ionic liquid and grinding.Present invention also offers the purposes ground in ionic liquid in the method and formed the product that maybe can be formed by the method.

Description

The method preparing Graphene

Technical field

The method that the present invention relates to prepare Graphene and graphene-like structure.Particularly, the present invention relates to there is not oxygen The method preparing Graphene in the case of changing reducing agents, and particularly relate to physical preparation method.The invention still further relates to The Graphene prepared by the method and the method purposes in preparing Graphene.

Background technology

Graphene is the sp being positioned in honeycomb lattice²The plane lamina of the monoatomic thickness of bonding carbon atom.Term " stone Ink alkene " it is also used for representing the structure with a small amount of graphene layer and similar performance.Except in other material from undiscovered amount Outside sub-effect, the distinguished structure of Graphene gives its a lot of unique machinery, electronics, calorifics, optics and magnetic properties.Example As, the charge carrier in Graphene is equivalent to the dirac fermion without quality and presents ambipolar field effect and room-temperature quantum suddenly That effect.

Graphene has at a relatively high electron mobility, is up to 2 × 10 under room temperature⁵cm²V^-1s^-1.This is owing to it does not exists Defect and hetero atom, electronics facilitates penetration of lattice.Its heat conductivity also significantly improves and nearest measurement is up to 3000wm^-1k^-1, more than measured CNT and the value of diamond.The combination of these performances make Graphene become be hopeful replace Si make A kind of a new generation candidate material for semi-conductor industry material.Graphene can also be at electricity and photoelectricity such as field effect transistor Pipe, light emitting diode, solaode, sensor and flat faced display have the most potential application.

Predicting the most in theory and be experimentally confirmed, the size of Graphene, composition and edge geometry are all weights The factor wanted, owing to strong quantum limits and edge effect, these factors decide the total electricity of Graphene, magnetic, optics and urge Change performance.Such as, by graphene platelet being cut into long and narrow ribbon (GNR) (width is less than 10nm), it is possible to Graphene introduces direct band gap, this make GNR present characteristic of semiconductor (M.Y.Han, et al.Phys.Rev.Lett., 2007,98,206805-2066808).Limiting further in base plane (overall size is less than 100nm) causes having zero dimension Quantum dot (GQD).Repressed hyperfine interaction and weak Quantum geometrical phase make GQD become for following amount Candidate (the A.Donarini et of the spin quantum with long coherence time attracted people's attention for sub-information technology Al.Nano Lett., 2009,9,2897-2902).Therefore the stone that the lateral dimension of nano strip thing or quantum dot form reduces Ink alkene thin slice can effectively adjust the band gap of Graphene and promote the horizontal scaling of Graphene in nano electron device.At this In the case of Zhong, in the urgent need to being developed for adjusting effective way (J.Lu, the et al.Nat of graphene-structured Nanotechnol.2011,6,247-252, L.A Ponomarenko, et al.Science, 2008,320,356-358).

At present, having many possible methods, can manufacture graphene platelet by these methods, it includes that chemical vapor is sunk Long-pending (CVD), micromechanics stripping, epitaxial growth and chemistry peel off.With other Technical comparing, chemistry peeling relates to various solid and initiates Directly peeling off of material such as graphite oxide, expanded graphite and native graphite, it is in terms of simplification, cost and high-volume production It is favourable.But, there is the shortcoming much needing to overcome in the chemical solution exfoliating method of exploitation at present.

Most-often used chemical exfoliating method uses chemical oxidation that Graphene is oxidized to electronegative graphene oxide Thin slice, it easily can be peeled off as single graphene oxide thin slice by supersound process in water.In order to recover Graphene Special performance, remove oxy radical by electronation；But, when neutral, between the graphene platelet of reduction Strong Van der Waals interaction can cause them assemble immediately and again stack.Latest find, due to from staying on sheet surface The Coulomb repulsion of electronegative hydroxy-acid group, add ammonia in aqueous and may result in the stable aqueous dispersion of Graphene Body.Other trial preventing Graphene from assembling is concentrated mainly on the surface with the mutually graphene coated oxide of dispersant, dispersant Usually produce surfactant or the polymer of the internal repulsion of weak nano flake.

But, it is undesirable for being joined in Graphene by foreign molecules in numerous applications, and causes by this The Graphene that a little chemistry exfoliating method produce is compared to the Graphene poor quality manufactured by CVD and micromechanics stripping method.This The various the chemical substances such as solvent, Oxidizing and Reducing Agents that are primarily due to be used in processes may corrosion Graphene crystalline substances Lattice or be difficult to remove, thus inevitably lead to remaining surface material.Generally speaking, these are chemically incorporated into various shape The surface defect of formula, it destroys the band structure of Graphene and limits the electric conductivity of the graphene platelet obtained.Need New method produces substantial amounts of relative clean and keeps the graphene platelet of its single separation simultaneously.

Another shortcoming of known chemistry exfoliating method is, a lot of chemicals of being used otherwise expensive otherwise poisonous And needing handled, it is unfriendly and unsustainable that this causes environment.And, most of chemical solution exfoliating method The most time-consuming multiple steps taken several days when including.For example, it is possible to by heat or chemicals and hot combination, or Processing procedure increases the most original of another step and removes defect oxide present in graphene oxide.In addition, about Carry out thermal reduction at 1000 DEG C the most effective, but this temperature is not suitable for much applying.

Therefore, studying always can overcome above-mentioned obstacle and allow formed high-quality graphene alternative.So far Till, progressive achieved with some.

Coleman and his colleague from Trinity College Dublin prove (Nature recently Nanotechnology3563,2008), select a kind of strong interaction guaranteed between solvent and graphenic surface advisably Graphene may be peeled off thus produce monolayer and a few layer graphene by solvent.But, the yield of the Graphene that the method produces is very Little and be unsuitable for large-scale production.In organic solution, directly peeling off of Graphene can increase yield, but this can only be super Speed centrifugation during or extended period chien shih extend sonication treatment time realized close to 3 weeks.

Liu et al., at Chem.Commun., reports in 2010,46,2844-2846, in the presence of single stranded DNA, Use simple sonicated can produce single-layer graphene thin slice and bilayer graphene by directly peeling off from graphite flake Thin slice.To produce graphene platelet from graphite the most by Wang et al. (Chem by carrying out sonicated in ionic liquid Commun., 2010,46,2844-2846), Nuvoli et al. (J.Mater.Chem., 2010) and WO2010/065346 report Road.But, the graphene platelet produced by these simple methods still contains a small amount of impurity (such as fluorine, sulfur etc.), and class It is similar to reduce the most oxygen (more than 10at%) in the presence of the Graphene obtained from graphene oxide.In Graphene Oxygen be difficult to remove and may interfere significantly on performance and the purposes of Graphene.Therefore, it is possible to manufacture for production in enormous quantities The optional method of the graphene platelet of high-quality and high concentration is the most desired.

Accordingly, it would be desirable to new solution-phase processes produce a large amount of high-quality (defect is few or zero defect, and/or do not aoxidize or The most non-functionalization) Graphene.Particularly, need improve cost and efficiency and/or can produce than in prior art more The more high-quality known or the new method of higher yield Graphene.Expect to have many improvement.Finally, it is desirable to one can be used in The business method of large-scale production Graphene.The present inventor determines surprisingly, uses one to relate to native graphite and Plant or the method for the mixing of different kinds of ions liquid and grinding can produce high-quality Graphene.With expanded graphite or graphene oxide Comparing, the use of native graphite not only can reduce cost, and owing to low oxygen content can improve the quality of the Graphene obtained. The method can be more possible than former method yield higher yield production Graphene, during therefore the method becomes prior art The alternative method likely of known method.Particularly, the method for the present invention provides impurity Graphene solvent-free, low and permissible Be suitable to large-scale use.Additionally, the use of ionic liquid is more possible than the replacement scheme researched and developed in the past less expensive and is easier to by ring Border accepts.

Summary of the invention

The present invention relates to the new method manufacturing Graphene of inventor's research and development.

From the point of view of in terms of first, the invention provides a kind of method preparing Graphene, the method include by graphite with The mixing of at least one ionic liquid and the step ground.Optionally and preferably, the method for the present invention does not include sonicating step.

From the point of view of in terms of another, the invention provides a kind of method herein limited, wherein Graphene is that Graphene is received Rice sheet or the form of graphene nano point.

From the point of view of in terms of another, the invention provides the device used in the method for above-mentioned restriction, it includes and stone The grinding mechanism (grinding mechanism) that ink contacts with one or more ionic liquid.

From the point of view of in terms of another, the invention provides and in one or more ionic liquid, grind graphite at formation Graphene In purposes.

From the point of view of in terms of another, the invention provides and form, by method as described above, the Graphene that maybe can be formed.

From the point of view of in terms of another, the invention provides the height graphene nano point for 1-3nm.Alternatively and preferably Ground, the diameter of these graphene nano points is less than 10nm.Can be formed by method as described above and maybe can form the present invention's Graphene nano point.

Detailed description of the invention

The present invention relates to prepare the method for Graphene, the Graphene that produced by the method and be adapted for carrying out the method Device.Terms used herein " Graphene " refers to the sp being positioned in honeycomb lattice^-2The single atom thick that bonding carbon atom is constituted The planar lamina of degree.In the background of the invention, term " Graphene " be also used to refer to be arranged in layer structure more than one layer but It is not more than these single sheets of 10 layers.Therefore, the quantity of layer is preferably 1-10, preferably 1-8, more preferably 1-5(such as 2- 10 or 2-5).When the surface area of Graphene is more than 0.005 μm²(it is greater than 0.08 μm²), preferably 0.006-0.038 μm² (it can be 0.5 μm²(such as 0.45 μm²) or bigger) time, no matter it is single sheet or the multi-layer thin being arranged in layer structure Sheet, Graphene can be the form of " nanometer sheet " in the present invention.But, if the surface area of Graphene is less (such as Surface area is less than 0.5 μm², such as less than 0.08 μm²), it can be the form of " nano dot ".In the background of the invention, art Language " nano dot " is for referring to single sheet or the multilamellar of Graphene, and its diameter is less than 20nm, such as 10nm or less.

Known to term " graphite " is to those skilled in the art, and graphite is used for representing stratiform in this article The usual implication of planar structure, each layer includes one layer of sp^-2Bonding carbon atom thin slice.Graphite as referred to herein has at least 11 layers Such hexagon carbon, it is combined by weak Van der Waals force.In all embodiments of the present invention, graphite can be Any type in any source, it is preferred that graphite is native graphite, the most unprocessed material.

The method of the present invention includes the step being mixed with at least one ionic liquid by graphite and grinding.Graphite can be any Form, but preferably native graphite.The method using native graphite to not only facilitate the reduction present invention as parent material is relative In use expanded graphite as known in the art or the cost of the method for graphene oxide, and contribute to making end-product contains Oxygen groups is minimum.

Ionic liquid relatively easily can make the method for the present invention be well suited for continuous operation with other material separation.

In all embodiments of the present invention, the method can include the step of extra deionizing liquid.This is permissible By any suitable method, preferably by using one or more solvents.Preferably this solvent is polar solvent, such as diformazan Base Methanamide (DMF) or acetone.In one embodiment, this solvent is the mixture of DMF and acetone.The method can also be wrapped Include the step of extra separating step and recycling design alternatively.Then can reclaim in batch or Continuous maching (or part Reclaim) and utilize this solvent.This makes the cost of the inventive method and impact on environment the most minimum so that the method is suitable to advise greatly Mould produces Graphene.Thus the method for the present invention can be batch machining or Continuous maching, although Continuous maching is preferred, special It not in larger-scale produces.

In all embodiments, the method for the present invention does not the most include sonicating step.Sonicated method exists Known in this area being, and it is relevant to the response time extended and high-energy input in the production of Graphene.Therefore, Sonicated method is not particularly suitable for large-scale production and/or commercial production.For using any sonicated, it is preferably such as Sonicated is less than 60 minutes.This is formed with the method using sonicated a couple of days in the past and compares.

The grinding of the method for the present invention can be carried out by any Ginding process known in the art.Preferably, the present invention Method in mixing and grind occur simultaneously, although be also possible to one occur before another.All of embodiment party In case, graphite and the mixing of one or more ionic liquid and the total time (such as 0.3-4) in the range of 0.1-4 hour ground, It is preferably 10 minutes to 2 hours (such as 0.5 to 2).Generally use manpower and pestle hand-ground reaches 1 hour or less (the most such as 30 minutes or less, such as 10-30 minute) produce graphene nanometer sheet.Grinding more than 30 minutes, especially more than one hour The increasing number of the graphene nano point that (such as 2-4 hour) produces.The diameter of nano dot is typically smaller than 40nm, such as average straight Footpath is 35nm or less.This will reduce further grinding.The thickness of graphene nano point of the present invention is averagely less than 20nm(such as 16nm or less).This also will reduce along with further grinding, and along with the increase of milling time may be typically less than 5nm Or less than 1nm.The grinding (such as 30 minutes to 4 hours) of typically for up to about 4 hours may be used for nano dot.It is alternatively possible to Use plane lapping or ball milling, pressurized fluid grinding and the airflow milling in liquid mixture.Mechanical grinding method allows grinding Mill uses bigger energy, therefore skilled artisan recognize that shorter milling time is suitable.These will Optimized by conventional method.

In all respects, the method for the present invention preferably relative to the weight of graphite starting materials with at least 10wt%, preferably The productivity of ground at least 15wt% or at least 20wt% produces Graphene.

One aspect of the present invention is included in one or more ionic liquid the purposes ground in forming Graphene.Preferably Ground grinds graphite starting materials.In such an application, Graphene can be produced by any method mentioned above.

The method of the present invention can use the device of any suitable form to implement, and this device includes and graphite and one or many Plant the grinding mechanism of ionic liquid contact.Typical grinding mechanism is well known to those skilled in the art, and it includes example Such as the airflow milling in employment and the grinding of pestle, ball milling, plane lapping, pressurized fluid grinding and liquid mixture.All of In embodiment, the mixing of the inventive method and grinding stage can be carried out in a container or multiple container.For example, it is possible to In the first container, admixed graphite and one or more ionic liquid, be then transferred in second container being ground.Excellent at one The aspect of choosing, mixes graphite with ionic liquid and grinds, subsequently by carrying out in solvent (mixture of such as DMF and acetone) It is centrifuged off ionic liquid.Further separating step can be carried out subsequently, such as, (such as only exist in other solvent or mixture In DMF) centrifugation further.Solvent such as DMF can be separated alternatively recycle for optional, and can be continuously Processing separates Graphene.Similarly, graphite can be fed simultaneously into one or more grinding with some or all of ionic liquid Mill station, and in Continuous maching, pass through other optional grinding stations as required, then arrive the separation for deionizing liquid Device.The modification of the method will be readily apparent to one having ordinary skill.In all methods of the present invention, can be by remaining Graphite starting materials separate with graphene product.In the method for the invention, after isolation, can be remaining by recycling recovery The graphite stayed.

The method of the present invention may be used for producing and has the covalency of low-level organic solvent and/or low relative levels and non- The Graphene being of high quality of covalent bond impurity.This can be by the condition being substantially absent from redox reaction reagent Lower enforcement the method realizes and/or improves.In one embodiment, can be real under conditions of there is not any oxidant Execute all aspects of the invention.Similarly, in another embodiment, can be real under conditions of there is not any reducing agent Execute all aspects of the invention.In this article, it is clear that oxidant is to aoxidize the carbon-carbon bond in carbon-carbon bond such as Graphene Reagent, and reducing agent is to reduce the examination of carbon-heteroatom bond such as carbon-oxygen bond (such as in graphene oxide) Agent.

In all embodiments of the present invention, Graphene can be any form, although being preferably graphene nano Sheet or the form of graphene nano point.

When the form that Graphene is nanometer sheet, these nanometer sheet can include multiple layer.The quantity of layer is preferably less than 10 Scope, more preferably 1-5.The quantity of layer is very preferably 2.

When the form that Graphene is nano dot, these nano dots are preferably essentially uniform.Owning in the present invention In embodiment, the diameter of nano dot is preferably less than 20nm, in the range of even more preferably less than 10nm.Nano dot of the present invention Highly preferred for 1-3nm.

Without being constrained by theory, it is believed that change the milling time used by method of the present invention and ionic liquid Volume allows to control to a certain extent the performance of the Graphene thus produced.Longer milling time such as more than 1 hour, and The such as every 50mg Graphene of the ionic liquid of smaller volume is less than 0.3mL, and the bigger distribution to the Graphene of nano dot form is relevant. Shorter milling time e.g., less than 1 hour, and higher volume of ionic liquid such as every 50mg Graphene 0.4mL or bigger, lead Cause primarily forms graphene nanometer sheet.

It is preferably smaller than 5at% by the oxygen content of the Graphene of the method production of the present invention, more preferably less than 4at%, even More preferably less than 3at%.Without being constrained by theory, it is believed that be present in the Graphene produced by the method for the present invention In any oxygen, be that in Graphene parent material, already present oxygen causes, and mixing and process of lapping in do not absorbed.

Despite the presence of oxygen, but preferably, there is no other impurity by the Graphene that the method for the present invention produces, Including impurity chemically combined with Graphene.Particularly, impurity such as fluorine, nitrogen, p and s is preferably substantially not present in being given birth to In the Graphene produced." it is substantially absent from " expression impurity level herein and is near or below x-ray photoelectron spectroscopy method (XPS) measuring limit.Generally, such level will be less than 1at%, i.e. the true resolution limit of XPS.Do not exist such Impurity means that the method for the present invention provides relative to other method (such as chemistry) producing Graphene as known in the art Qualitative improvement.The Graphene obtained by the method for the present invention does not exists or is substantially absent from structure and lacks Fall into.

The method of the present invention all includes with at least one, graphite is preferably the pass that only a kind of ionic liquid mixes and grinds Key step.

Ionic liquid is organic salt known in the art or part inorganic salt, its at a temperature of 100 DEG C be liquid and Its uniquely (or major part) include ion and/or of short duration ion pair.Except many polarity and non-polar compound are had Outside favourable solvate performance, ionic liquid also has many attractive performances, such as low volatility and low flammability. Without being constrained by theory, ionic liquid is considered to be very suitable for the method for the present invention, because its surface tension is similar to The surface energy of graphite.And, its ionic nature means that they can stablize Graphene by Coulomb interactions.

Any of ionic liquid kind of this area is suitable in the method for the present invention.Particularly preferred ionic liquid is Comprising the ionic liquid of organic salt, wherein organic salt contains the free ammonium ion of choosing, imidazol ion (imidazolium ion) and pyridine One or more cationes in molecular group.Preferably organic salt is the organic salt containing imidazol ion.Very preferably Ionic liquid be 1-butyl-3-methyl-imidazoles hexafluorophosphate, i.e. BMIMPF₆。

The Graphene produced by the method for the present invention is suitable for use in appointing of employing Graphene currently known in the art In what application.Specifically, it is very suitable for for preparing composite or transparent membrane.Alternatively, should in electronic energy Itself and suitable ink material can be mixed for ink jet printing in.Graphene conductive ink may be used for manufacturing printing electricity Conducting element in road and sensor electrode.Other staple market of electrically conductive ink includes display, RF identification, solar energy Electroplax, illumination, disposable electric product and storage sensor and wherein at printed circuit board (PCB), auto heater and electromagnetic shielding Deng manufacture in use traditional thick film of silk screen printing to apply.

IL is low temperature molten salt, as its name implies, for the liquid being made up of ion completely.IL has been proposed as novel " green " organic solvent, because it can not only make various organic compound and inorganic compound (polarity or nonpolar) become molten Agent compound, and it has high thermo-chemical stability, high ion conductivity, wide electrochemical window and negligible vapour pressure Power.Mix a small amount of IL and graphite flake forms colloidal complex.When graphite flake is ground with ionic liquid, shearing force Graphene layer will be separated from graphite flake.Ionic liquid can surround each layer effectively, to prevent the Graphene of separation again Stacking.According to the simulation and experimental study, the electricity of the graphene layer in hard fragility colloid that process CNT with the IL of imidazole radicals Minor structure keeps constant, and does not has electric charge to shift between Graphene and glyoxaline cation.

The most favourable formation that application is fluorescence graphene nano point of the graphene nano point of the present invention, such as, make It is used in bio-imaging application.Such fluorescence graphene nano point can be by making nano dot through peroxidation step by the present invention Nano dot (nano dot such as produced by any method of the present invention) formed.Therefore the method for the present invention, the most raw The method producing nano dot can include, by the additional step of graphene product oxidation, being preferably and providing fluorescence graphene nano point.

It will be apparent to one skilled in the art that in the case of there is ionic liquid, the pinch spalling of the present invention Method, in addition to being used for forming Graphene, will also apply to form other " 2D " type structure.The peeling of other stratified material exists Correlation technique is known (such as Coleman et al.Science331 (2011) p568-571), and the present invention's Any stratified material of all aspects can replace graphite to use effectively, thus provides thin slice and/or the nano dot of respective material. " stratified material " represents have strong bonding effect (such as covalent bond) between the atom in structure sheaf and have relatively at interlayer Any material that weak (the most non-covalent, such as coulomb and Van der Waals) interacts.It is known in the art many materials to use Such structure, including graphite, magnesium-yttrium-transition metal two chalkogenide (TMD), transition group metallic oxide (TMO) and include BN、Bi₂Te₃And Bi₂Se₃Other material.Preferably stratified material includes graphite, MoS₂、WS₂、MoSe₂、MoTe₂、TaSe₂、 NbSe₂、NiTe₂、BN、Bi₂Se₃And Bi₂Te₃。

In another aspect of the present invention, all " graphite " referred to herein can be considered as representing layer as defined herein Shape structure, and any " Graphene " of indication can be considered as representing the monolayer of " graphene-like " or which floor (example of respective material Such as 1 to 10 layer, such as description to Graphene herein) fragment.Such fragment is usually corresponding to describing Graphene herein Form, and all aspects of the invention are applicable to stratified material and are consequently formed corresponding " graphene-like structure ", and Corresponding purposes and be consequently formed the product that maybe can be formed.Any advantage such as high-purity, structural intergrity and be readily produced can To be equally applicable to other structural material, make these materials just be similar to as the principle example of this paper layer structure and retouch The graphite stated and Graphene.

From above-mentioned it is readily apparent that as used herein, term " graphene-like " represent can be from any stratiform Crystalline material forms the flake-like crystals structure of the substantially two dimension that maybe can be formed, such as structures described herein.This term It is not limited to the lattice of carbon, is also not necessarily limited to hexagonal array, although both of which constitutes preferred embodiment.

Accompanying drawing explanation

Fig. 1: the optical imagery of graphene platelet solution.

The XPS measuring scanning of Fig. 2: graphene platelet and initial graphite flake；Elements C 1s(d on graphene platelet) and O1s(e) narrow scan.

Fig. 3 (a) and (c): single graphene platelet and the typical afm image of nano dot；(b) and (d): be respectively (a) (c) altitude information of corresponding cross-section analysis, and (e) be the relatedness between Graphene size and milling time.

Fig. 4 (a): the high-resolution TEM image of single graphene platelet；(b): the corresponding electronogram of (a).

The typical Raman spectrum of Fig. 5: graphene platelet.

The TGA spectrum of Fig. 6: graphene platelet and parent material.

Fig. 7: graphene platelet film is as the resistivity of annealing temperature function.

The TEM image that the typical low power of Fig. 8 (a) graphene platelet is amplified；(b): the corresponding electronogram of (a)；(c) The distribution of sizes of graphene platelet；The HRTEM image of (d) bilayer graphene thin slice；The HRTEM figure of (e) three layer graphene thin slice Picture；(f) the HRTEM image of 4-5 layer graphene thin slice.

Embodiment

Synthesis

The 50mg powdered graphite (99.0% purity, come from Sigma-Aldrich) of 20 μm (usual 50mg) will be smaller in size than Ionic liquid (1-butyl-3-methyl-imidazoles hexafluorophosphate, BMIMPF with 0.1-0.5mL₆, come from Sigma-Aldrich) Mixing and grinding reach 0.5-4 hour.Then N,N-dimethylformamide (DMF) and the acetone of 15mL of 15mL are fed the mixture into Solution in, and with the centrifugation 30 minutes of 3000rpm with deionizing liquid.After repeating this cleaning step three times, at 1L DMF in dilute the precipitate (seeing Fig. 1) obtained.After precipitation one day, big/thick graphite flake is deposited at the bottom of bottle completely Portion.Being dried supernatant and to calculate productivity be 20wt%, this productivity reported much larger than other method, such as Coleman et al. exists Report in Nature Nanotechnology2008 the 3rd phase the 563-568 page.Collect supernatant and be centrifuged, dense to obtain Suspension, uses this suspension to prepare Graphene sample, for being used for studying its microstructure and Electronic Performance.Dilute suspension liquid is also Dropped on the Cu grid of silk ribbon carbon cladding, for tem observation, drop on the Si wafer of cleaning or on splitting, be used for XPS, Raman and AFM research, and drop in 300nm and be coated with SiO₂Si wafer on, for Electronic Performance study.Note, for The uniform large-area graphene film of acquisition, by 3-triethoxysilylpropylamine (APTES) aqueous solution pair of 5% 300nm is coated with SiO₂Si wafer functionalization 30 minutes.Before measuring, by all samples under infrared ray or on electric hot plate It is completely dried.

XPS analysis

Fig. 2 (a) shows the typical XPS measuring scanning optical spectrum of graphene nanometer sheet, it is shown that be in the strong of 284.5eV C1s peak, is in the little O1s peak of 532.6eV and the weak O KLL Auger between 955-985eV can carry.Except deriving from stone Outside some oxygen of ink alkene thin slice and carbon, the most do not find other element such as F, N and P from ionic liquid or DMF. In sample, the concentration of Elements C and O is computed being about respectively 96.55 and 3.4at%.It should be noted that present in graphene product The oxygen of 3.4at% derives from initial graphite flake powder (Fig. 2 b) rather than the product of the method for use.Fig. 2 (c) and (d) point The XPS spectrum of asymmetrical C1s and O1s of high-resolution of graphene platelet is not shown.Use subsequently deducting Shirley background After Lorentzian and Gaussian function is fitted, C1s peak can mainly be distributed as being in 284.4,284.9,285.5 With the four of 288.9eV sub-peaks, it has been respectively allocated to C-C (sp2), " defect peak ", C-O and COOC/COOH key, and O1s peak can by corresponding to C-O and COOH key be in 532.1 and 534.7eV two Gaussian peak matchings.This table Bright, graphene platelet is cleaning and in addition to its source a small amount of oxygen for initial graphite material, it does not exist and comes from Any impurity of chemicals used and pollutant.

Microscopic analysis (HR-TEM and AFM)

Two kinds of graphene-structured can be formed in supernatant: submicron number layer thin slice and nano dot by prior art, This depends greatly on preparation parameter.Fig. 3 a illustrates the typical afm image of single submicron graphite alkene thin slice, shorter when using Milling time (< 30min (minute)) and during a large amount of ionic liquid (0.5mL), this submicron graphite alkene thin slice accounts in supernatant Advantage.Use tapping-mode to implement AFM to measure.Graphene platelet is straight, has slight curving edge.Graphene platelet There is about 0.6 × 1.5 μm²Size and the thickness (Fig. 3 c) of 1.2-1.5nm, this is the height of typical bilayer graphene.Figure 3b shows the typical afm image of the point of nanosized, when using longer milling time (> 1 hour) and small amount ionic liquid (< 0.5mL) time, this nano-scale point is preponderated in supernatant.Graphene nano point is uniform, its a diameter of 20-40nm, It is highly 1-3nm(Fig. 3 d).By considering that AFM tip, in " extension " effect of lateral dimension and the spherical characteristic of nano dot, is recognized Actual diameter for this graphene nano point is less than 5nm.Fig. 4 shows typical high-resolution TEM of single graphene platelet Image.It can be seen that graphene platelet is made up of the Graphene that 3-4 layer spacing of lattice is 0.342nm.At graphene platelet Edge does not find other carbon such as amorphous carbon and fullerene etc. mutually.Corresponding electron diffraction pattern have typical six-times Symmetry, thus confirm that graphene platelet has high-quality monocrystal character.Therefore, these discoveries are unequivocally demonstrated that, pass through This simple method produces high-quality several layer graphene thin slices.

Raman scattering

Raman scattering is for characterizing the convenience of Graphene and powerful macro tool.Spectral intensity, frequency can be passed through The number of plies and the quality of the Graphene manufactured by micromechanics stripping means is distinguished in analysis with live width etc. well.Fig. 5 shows stone The typical Raman spectrum of ink alkene sample.In back scattering solid, at room temperature use and there is 1-2 μm spot size The laser excitation of 514nm carries out Raman Measurement.There are three strong peaks at 1348,1571 and 2711cm-1, it is attributed to respectively D, G of graphite material and G ' can carry.Sample does not has find the broad peak relevant to amorphous carbon.The existence at D peak be attributable to (1-2 μm) laser facula is in a ratio of undersized graphene platelet, the defect on this laser acquisition graphene platelet edge.D energy The bulk strength ratio only 0.23 that band can carry with G, owing to D can band be the instruction of defect in graphite material, this meanS that produce Graphene there is high quality.G ' energy band is the instruction of Graphene, and G ' energy band is very strong, and but it can carry in intensity much larger than D On be slightly lower than G and can carry.The bulk strength ratio about 0.61 that G ' and G can carry, there is 3-4 layer graphene in display, this and the sight of TEM Examine consistent.Note, at present by Raman spectrum and the graphite produced by other method of the Graphene of method manufacture based on solution The Raman spectrum of alkene is dissimilar.Due to the sensitivity to chemicals, they do not show identical spectroscopic properties, and They depend greatly on used manufacture method and chemicals.But, all being found to proposed here determines, we The crystal mass of the Graphene produced is better than the crystal of the Graphene manufactured by the solution methods in other groups reported Quality, such as Qian et al.Nano Res., 2009,2,706-712, but, but it is inferior to be by mechanically pulling off highly directional heat Solve graphite (HOPG) method and can high temperature CVD side on the metal surface of band defect by being not detected by the D that is correlated with wherein The crystal mass of the Graphene that method produces.The quality of graphene platelet relative mistake is considered as owing to comparing low-quality of HOPG Caused by beginning material (native graphite) rather than caused by milled processed.

Thermogravimetric analysis

Pollutant and knot is determined by TGA methods based on a large amount of (magnitudes of several mg) graphene platelets and nano dot Lacking of structure defect.Fig. 6 shows the TGA spectrum obtained from graphene platelet and parent material.Spreading with 1 DEG C/min 50%N₂And 50%O₂Mixture ambient in implement measure.It can be seen that graphene platelet shows almost identical with parent material Hot property.They start simultaneously at oxidation and burnout completely at 700 DEG C when about 500 DEG C.This explanation is identical in quality, thus table Bright the most do not introduce high/low melting material.

Resistivity

Fig. 7 shows the resistivity function as annealing temperature of graphene film.Coated by drippage big and be coated with There is SiO₂Si wafer on manufacture there is the graphene film of about 12.8 μ m thick, then graphene film is cut into several 10 ×20mm²The block of size, within the temperature range of 200-600 DEG C in vacuum (less than 8 × 10^-5Torr) annealing 1 hour in. Resistance (resistivity test equipment, Model B, A&M Fell LTD, Britain) is at room temperature measured by four-probe technique.Original The resistivity of graphene film is about 1 × 10^-2Ω·m.Along with the rising of annealing temperature, resistivity in the range of 200-400 DEG C Drop to 8 × 10^-3Ω·m.When annealing temperature is increased to 500-600 DEG C, resistivity significantly reduces to 2 × 10^-3Ω·m.So And, this value is still above resistivity (0.07-0.11 × 10 of the graphene film produced by other chemical solution method^-3 Ω m).It is less or there is a large amount of space and cause existing in thin film that it is primarily due to the size of single graphene platelet A lot of nodes.Original graphene film and the graphene film of annealing standard deviation at low temperatures are very big, and this shows graphite Alkene thin film is likely to be of different thickness and inside exists substantial amounts of structural void.Obviously, the change of Graphene resistivity is sent out In two steps, this shows that graphene film experienced by two kinds of structural transformations during annealing in life.According to estimates, first step It is owing to going to inhale to adsorbent such as water, C-H and COOH group from the inner surface on graphene film surface and structural void Attached.Second step can be owing to the contraction in space or avalanche, and this causes the graphene platelet weight of at high temperature all components New definition and dense uniform thin film are formed, and this is proven by the standard deviation of smaller value.

The synthesis of other " graphene-like " material

Will be selected from MoS₂、WS₂、MoSe₂、MoTe₂、TaSe₂、NbSe₂、NiTe₂、BN、Bi₂Se₃And Bi₂Te₃(50mg) and chi The very little material powder being less than 20 μm (typically 50mg) and the ionic liquid (1-butyl-3-methyl-imidazoles hexafluoro phosphorus of 0.1-0.5mL Hydrochlorate, BMIMPF₆, derive from Sigma-Aldrich) mix and grinding reaches 0.5-4 hour.Then 15mL is added the mixture to N,N-dimethylformamide (DMF) and the acetone soln of 15mL in and with the centrifugation 30 minutes of 3000rpm with remove from Sub-liquid.After repeating this cleaning step three times, the DMF of 1L dilutes the precipitate obtained.After precipitation one day, residue is initial Big/thick graphite flake of material is deposited in bottle bottom completely.Then dry supernatant calculates productivity.Collect supernatant and from The heart, to obtain dense suspension, is prepared " graphene-like " sample by this suspension, for or for further study.

Claims (20)

1. the method preparing the graphene-like fragment of Graphene or another kind of layer structure, described method include graphite or Another layer structure described mixes with at least one ionic liquid and grinds, and wherein said method does not include sonicating step.

The most the method for claim 1, wherein mix and grind and carry out the time between 0.5 to 4 hour.

3. method as claimed in claim 1 or 2, wherein, described graphite is native graphite.

The most described graphite is graphene nanometer sheet or the form of graphene nano point.

5. method as claimed in claim 4, wherein, described graphene nanometer sheet includes 2 to 4 layer graphenes.

6. method as claimed in claim 4, wherein, the height of described graphene nano point is 1-3nm.

7. method as claimed in claim 4, wherein, the diameter of described graphene nano point is less than 10nm.

The most described ionic liquid includes that organic salt, described organic salt contain the free ammonium of choosing One or more cationes in the group of ion, imidazol ion and pyridinium ion composition.

9. method as claimed in claim 8, wherein, described organic salt contains imidazol ion.

10. method as claimed in claim 8, wherein, described ionic liquid is 1-butyl-3-methyl-imidazoles hexafluorophosphate.

The oxygen content of 11. the most described Graphenes is less than 5at%.

The oxygen content of 12. the most described Graphenes is less than 4at%.

13. the method for claim 1, do not include any use reducing agent and/or oxidant.

14. the method for claim 1, also include separating described ionic liquid with described Graphene.

15. methods as claimed in claim 14, including making described ionic liquid and described stone by adding solvent to be then centrifuged for Ink alkene separates.

16. methods as claimed in claim 4, the yield of graphene nanometer sheet and/or graphene nano point than graphite or other The starting weight big 10% of stratified material.

17. Graphenes that maybe can be formed formed by method according to any one of claim 1-16.

18. in the method according to any one of claim 1-16 use devices, including with graphite and one or more from The grinding mechanism of sub-liquid contact.

19. are forming Graphene or the stone of another stratified material without grinding graphite under sonicated in one or more ionic liquid Purposes in ink alkene shape fragment.

20. purposes as claimed in claim 19, wherein, form Graphene by method described in claim 1.