Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B1/00—Electrolytic production of inorganic compounds or non-metals
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y40/00—Manufacture or treatment of nanostructures
• • 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
  • C01B32/15—Nano-sized carbon materials
  • C01B32/182—Graphene
  • C01B32/184—Preparation
• • 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
  • C01B32/15—Nano-sized carbon materials
  • C01B32/182—Graphene
  • C01B32/184—Preparation
  • C01B32/19—Preparation by exfoliation
  • C01B32/192—Preparation by exfoliation starting from graphitic oxides
• • 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
  • C01B32/15—Nano-sized carbon materials
  • C01B32/182—Graphene
  • C01B32/194—After-treatment
  • C01B32/196—Purification

Definitions

• the present invention relates to a process for the preparation of graphene substantially free from contamination by metallic, magnetic, organic and inorganic impurities and the use of graphene obtained by this process for producing transparent electrodes, batteries, acceptor materials or electron donors especially in photovoltaics, photovoltaic panels, transistors channels in particular in electronics, nonlinear emitters or absorbers of infrared photons, current-conducting electrodes, antistatic coatings, chemical detectors, vias and interconnections in electronics, current conduction cables, and solar cells.
• Graphene is a two-dimensional crystal (monoplane) of carbon whose stack constitutes graphite. Graphene is found naturally in graphite crystals, where it is in the form of a stack of leaves. Several processes for the preparation of graphene from graphene oxide have emerged in recent years.
• Graphene oxide also known as graphitic acid or graphite oxide, is an oxygenated graphite compound that contains about 50% by weight of oxygen. Its reduction in graphene is generally by the use of hydrazine or transition metal compounds such as iron.
• OC Compton ST Nguyen, Small, 2010, 6, p.711-723, describes the reduction of an aqueous dispersion of graphene oxide with hydrazine hydrate in the presence of poly (4- sodium).
• PS S styrenesulfonate
• This type of graphene-tin oxide composite material was also synthesized by homogenous precipitation of SnCl 4 in a suspension of graphene oxide using urea followed by reduction of graphene oxide with hydrazine under microwave irradiation (X. Zhu, Y. Zhu, S. Murali, M, D. Stoller, RS Ruoff, Journal of Power Sources, 2011, 196, pp. 6473-6477).
• the graphene obtained is a composite material in the form of platelets decorated on the surface with tin oxide (SnO 2 ).
• the graphene obtained always contains traces of metallic or magnetic elements or organic or inorganic compounds adsorbed on its surface. These impurities modify or at best completely disturb the intrinsic properties of the material: reduction of the electrical conductivity, modification of the nature of the electron transport mode, modification of the magnetic properties.
• impurities for example silicon, may be beneficial. However, this doping is only possible if the starting graphene is free of contamination.
• the graphene which will serve as a catalyst support is free of any metallic, magnetic, organic or inorganic impurities.
• impurities may have intrinsic catalytic properties, and their presence in graphene may degrade the selectivity of the catalyst by catalyzing, for example, parasitic reactions.
• the present invention is specifically intended to meet these needs by providing a method of preparing graphene substantially free of contamination by metallic, magnetic, organic and inorganic impurities, that is to say a graphene whose contamination rate by metal, magnetic, organic and inorganic impurities is at most 0.01% by weight, preferably at most 0.001% by weight, more preferably at most 0.0001% by weight, relative to the mass graphene, characterized in that
• a graphene oxide (OG) dispersion is reacted in a solvent or a mixture of solvent (s) with at least one tin compound and at least one acidic compound, the pH of the dispersion being less than 7
• step b) the graphene obtained in step a) is subjected to at least one acidic washing step carried out at a pH ⁇ 5.
• the method of the invention thus makes it possible to prepare a graphene substantially free of contamination by metallic, magnetic, organic and inorganic impurities.
• Graphene substantially free from contamination by metallic, magnetic, organic and inorganic impurities means a graphene the degree of contamination by metallic, magnetic, organic and inorganic impurities is not more than 0,01% by mass, preferably, the process of the invention makes it possible to prepare a graphene whose graphene content is at most 0.001% by weight, more preferably at most 0.0001% by weight, relative to the total mass of graphene .
• the impurities can come from the starting material (graphite or graphite oxide) or from the graphene synthesis process. Their nature varies.
• the inorganic impurities may be metal ions (transitions or other) optionally in oxide form or attached to the graphene surface.
• Organic impurities can be small molecules capable of interacting (by hydrophobic bond for example) with the graphene surface. In this respect, mention may be made of aromatic compounds.
• magnetic impurities The nature of magnetic impurities is diverse. However, they can be classified as inorganic and organic magnetic impurities.
• defects related to the graphene structure may be defects related to the graphene structure (broken C-C bond, etc.).
• it is a radical type C ° where the single electron can be relocated (or not) over the entire graphene structure.
• the origin of the defects is multiple.
• these defects can be associated with all the carbonaceous materials (coal, graphite).
• the defects can also result from the graphene synthesis process, for example, in the case where the reduction of the GO is not complete.
• the material is dispersed in a solvent by sonication, it can induce, if no precaution is taken, a C-C bond cleavage and the formation of associated radicals;
• graphene designates a graphene possessing a sheet with a stack of ten sheets of graphite, preferably a sheet with a stack of five sheets of graphite.
• the graphene obtained by the process of the invention is of high quality sp. Indeed, graphene owes its electrical and mechanical properties to the existence of hybridized carbon atoms sp. The more the material has sp hybridized carbons, the more its properties are degraded. These sp 3 carbons come either from the synthesis of graphene or from its degradation.
• the term "dispersion” means a suspension or dispersion of two distinct phases: a dispersion medium (a solvent or a mixture of solvents) and a dispersed phase (graphene oxide), dispersion or suspension is said to be stable when the dispersed phase (graphene oxide) does not sediment.
• the dispersion is said to be homogeneous when the dispersed phase in the dispersion medium is not visible to the naked eye or to the optical microscope. When the dispersion is homogeneous, it can also be considered as a "solution”. Thus, the term “dispersion” encompasses both dispersions, suspensions, and solutions.
• alkyl means a linear, branched or cyclic, saturated or unsaturated, optionally substituted carbon radical comprising 1 to 12 carbon atoms.
• linear or branched saturated alkyl there may be mentioned, for example, the methyl, ethyl, propyl, butyl, pentyl, hexyl, octyl, nonyl, decyl, undecyl and dodecanyl radicals and their branched isomers.
• cyclic alkyl there may be mentioned cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, bicylco [2,1,1] hexyl, bicyclo [2,2,1] heptyl radicals.
• Unsaturated cyclic alkyls include, for example, cyclopentenyl and cyclohexenyl.
• Unsaturated alkyls also referred to as "alkenyl” or "alkynyl” respectively contain at least one double or one triple bond.
• the alkyl group within the meaning of the invention including the alkenyl and alkynyl groups, may be optionally substituted by one or more hydroxyl groups; one or more alkoxyl groups; one or more halogen atoms selected from fluorine, chlorine, bromine and iodine atoms; one or more nitro groups (-NO 2 ); one or more nitrile groups (-CN); one or more aryl groups, with the alkoxy and aryl groups as defined in the context of the present invention.
• aryl generally refers to a cyclic aromatic substituent having from 6 to 20 carbon atoms.
• the aryl group may be mono- or polycyclic.
• the aryl group may be optionally substituted by one or more hydroxyl groups, one or more alkoxyl groups, one or more halogen atoms selected from fluorine, chlorine, bromine and iodine atoms, one or more nitro groups (-NO 2 ) , one or more nitrile groups (-CN), one or more groups alkyl, with the alkoxyl and alkyl groups as defined in the context of the present invention.
• alkoxyl means an alkyl group, as defined above, bonded through an oxygen atom (-O-alkyl).
• the dispersion may comprise a solvent or a mixture of solvents chosen from:
• solvents having a non-zero dipole moment that is to say a dipole moment of at least 6 Debye, chosen from water, pyrrolidinone; a Ci-C
• inorganic acids chosen from hydrochloric acid; sulfuric acid; nitric acid; perchloric acid;
• organic acids chosen from formic acid; lactic acid; benzoic acid; methanesulfonic acid, para-toluenesulfonic acid (APTS); trifluoroacetic acid; trichloroacetic acid; alpha naphthol; picric acid;
• the dispersion or the solution is called aqueous.
• the dispersion of the graphene oxide in step a) is aqueous.
• the dispersion medium is water.
• the graphene oxide used as raw material in the process of the invention can be synthesized from natural graphite powder (such as, for example, that marketed by Bay Carbon Inc.) or synthetic graphite (such as for example, that marketed by Nano Armor), according to the modified Hummer procedure as described by OC Compton, ST Nguyen, Small, 2010, 6, 711-723.
• the origin of graphite affects the final size of graphene sheets but not the progress of the graphene preparation process.
• the so-called modified Hummer procedure is usable both with the GOs whose sheets have a size of the order of a centimeter than with the GOs whose particle size is of the order of ten nanometers. means the length and width of the leaflets.
• Graphene oxide when obtained in powder form, can be directly dispersed in the reaction solvent.
• the dispersion is used as such in the process.
• the concentration of the graphene oxide (OG) dispersion in step a) depends on the ability of the reaction solvent to separate the GO sheets well. It can vary, for example, from a few milligrams per liter to several hundred grams per liter.
• the concentration of graphene oxide (GO) in the dispersion may be between 1.10 "4 to 1.10 3 g / L, preferably between 1.10" 3 and 9.10 to 2 g / L, and more preferably between 1.10 "3 and 1.10 2 g / L, terminals included.
• the dispersion of the graphene oxide can react with at least one compound comprising an element chosen from tin or zinc.
• the element may be, for example, in metallic form, in salt form or in oxide form.
• the process of the invention is carried out with a tin compound.
• the tin compound can be selected from:
• tin salts (II) chosen from tin chloride; tin sulfate; tin nitrate; tin perchlorate; tin tetraphenylborate; tin phosphate; tin acetate; tin oxalate;
• Tin Metal tin or its salts (tin (II)) is used as a reducing agent.
• Tin has several advantages: the tin salts (IV) generated by the reaction are well soluble, for example in concentrated acids (hydrochloric acids in particular), the tin (II) ion plays a catalytic role for the reduction. graphene oxide (GO). Finally, the tin (II) salts are sufficiently reducing to reduce the OG without the need for a co-reducer such as for example hydrazine. This is an important advantage of the process of the invention since the elimination of the co-reducer at the end of the process is difficult, it is likely to pollute the graphene irreversibly.
• the amount of the tin compound used in the process of the invention is from 0.1 to 5 equivalents, preferably from 1 to 5 equivalents, more preferably from 1 to 2 equivalents, inclusive, with respect to the amount of oxygen to remove from graphene oxide.
• at least one acid compound is used in the process of the invention.
• the acidic compound may be the same as the solvent (s) or different. It is preferably chosen from:
• inorganic acids chosen from hydrochloric acid; sulfuric acid; nitric acid; perchloric acid; Phosphoric acid ;
• organic acids chosen from formic acid; lactic acid; benzoic acid; methanesulfonic acid, para-toluenesulfonic acid (APTS); trifluoroacetic acid; trichloroacetic acid; alpha naphthol; picric acid;
• the acidic compound can be used pure or diluted in aqueous solution to a concentration of at least 0.1 mMl- 1 .
• the addition of the acidic compound can be either anterior, simultaneous or subsequent to the addition of the compound of the invention. 'tin.
• step a) when the pH of the dispersion in step a) is maintained at a pH ⁇ 7, in particular at a pH ⁇ 5, and / or that the washing (s) ( s) acid (s) of step b) is (are) also carried out at a pH ⁇ 5, in particular at a pH ⁇ 3, more particularly at a pH ⁇ 1, the contamination of graphene by impurities metallic, magnetic, organic and inorganic, is substantially reduced or eliminated.
• step a) the pH of the dispersion is, in particular, less than 5, more particularly less than 3.
• step b) the washing (s) is (are) carried out ( s), in particular, at a pH ⁇ 3, more particularly at pH ⁇ 1.
• the reaction can take place at a temperature between 0 ° C and the reflux temperature of the solvent.
• the reaction takes place at a temperature of between 15 and 40 ° C. More preferably, the reaction takes place at ambient temperature, that is to say at a temperature of 20 ° C. ⁇ 5 ° C.
• step a) the reaction can take place under manual, mechanical, magnetic and / or ultrasonic agitation.
• Other stirring means may also be suitable.
• the duration of the reaction in step a) depends on the conversion rate of graphene oxide to graphene.
• the reaction is advantageously maintained until the total conversion of graphene oxide to graphene.
• the reaction in step a) is carried out during a duration of 1 minute to 72 hours, for example from 30 minutes to 48 hours, for example from 1 to 24 hours, limits included.
• Step a) of the process can be carried out chemically or electro-chemically.
• the evolution of the reaction can be followed by the color change of the reaction medium: the color of the reaction medium changes from yellow brown (color of graphene oxide) to black (color of the reaction medium). graphene.
• one of the electrodes may be in a member selected from tin or zinc, preferably a tin compound, more preferably tin metal.
• the evolution of the reaction is then monitored as a function of the intensity of the current flowing between the electrodes. When the intensity of the circulating current becomes zero, the reaction is complete.
• Step a) of the electrochemical process can be carried out using an acid or an acidic solution as described above, as conducting medium.
• an acid or an acidic solution as described above, as conducting medium.
• the potential of said tin electrode is maintained at a negative value with respect to the normal hydrogen electrode (ENH), so that all the metal element selected from tin or zinc, in particular, tin which can pass into solution in the form of metal ion is redeposited in the form of metal to the electrode.
• ENH normal hydrogen electrode
• concentrations of OG are the same as those previously described for the chemical route.
• the end of the reaction is indicated by the color changes of the medium (it becomes black, for example), and the decrease of the current flowing between the electrodes.
• step a) When step a) is carried out electrochemically, the tin or zinc compound, preferably the tin compound, may be recycled, for example by reducing it to the metallic state or, alternatively, using it as an electrode for electrochemically converting graphene oxide to graphene.
• tin or its salts act as an electrocatalyst.
• This last variant can make it possible to better control the kinetics of conversion of graphene oxide to graphene and, consequently, to avoid too great a release of heat which could damage the equipment or injure the operator. This is particularly relevant in the case of a process carried out with large amounts (several kilograms) of graphene oxide.
• the graphene At the end of step a), the graphene can be kept dispersed or separated before being subjected to the acid washing (s) of step b).
• the acidic washing of step b) is advantageously carried out with an inorganic acid chosen from hydrochloric acid; sulfuric acid; nitric acid; perchloric acid, or phosphoric acid.
• the acid is, in general, in the form of an aqueous solution whose acid concentration is between pure acid and 0.1 mol.L -1 .
• the acid washes of step b) of the process of the invention may optionally be followed by one or more washings with water to a pH of 6.5 and 7.5.
• the graphene obtained can be used as it is. It can optionally be separated and / or dried.
• stirring means include manual stirring, ultrasonic treatment, mechanical stirring or a combination of such techniques. These techniques may require the use of a magnetic stirrer, a magnetic bar, an ultrasonic bath, a mechanical stirrer with rods, blades, propellers, etc. Those skilled in the art will know how to choose the means of agitation adapted to each case.
• the graphene can be separated and / or dried.
• Separation can be done by any known separation technique in this field, such as, for example, filtration and / or centrifugation.
• the drying can be carried out by any means known in this field, for example:
• the drying can be done by one of the above-mentioned operations or by a combination of two or more of these operations.
• the drying temperature can range from 20 ° C. to 1000 ° C., for example from 30 ° to 80 ° C., for example from 40 ° to 60 ° C., limits included.
• the drying time can be from 1 to 72 hours, preferably from 1 to 24 hours.
• the graphene obtained by the process of the invention is in the form of a powder, in particular a very sparse powder (density ⁇ 100 mg.mL -1 )
• the graphene obtained by the process of the invention is in the form of a very low density black powder (density ⁇ 100 mg.mL "1 ).
• the process of the invention is reproducible and allows the preparation of graphene in large quantities (on a scale of several kilograms);
• Another object of the present invention is the use of graphene substantially free from contamination by metallic impurities, that is to say a graphene whose contamination rate by metallic, magnetic, organic and inorganic impurities is from more than 0.01% by weight, preferably not more than 0.001% by weight, more preferably not more than 0.0001% by mass, relative to the total mass of graphene, magnetic, organic and inorganic, obtained by the method of the invention, for the production of catalysts, catalyst supports, transparent electrodes, batteries (either for storing lithium or the alkali metal used, or as conductive adjuvant), acceptor or electron donor materials especially in photovoltaics, photovoltaic panels, transistors channels in particular in electronics, spintronic materials, nonlinear emitters or absorbers of infrared photons, electrons current conducting rodes, antistatic coatings, chemical detectors, vias and interconnections in electronics, current conduction cables, and solar cells.
• the invention furthermore relates to a process for producing catalysts, catalyst supports, transparent electrodes, batteries (either for storing lithium or the alkali metal used, or as a conductive adjuvant), acceptor materials of electrons, in particular in photovoltaics, photovoltaic panels, transistor channels in particular in electronics, spintronic materials, nonlinear emitters or absorbers of infrared photons, conductive electrodes of current, antistatic coatings, chemical detectors, vias and interconnections in electronics, current conduction cables, and solar cells, characterized in that it implements the graphene preparation process according to the invention, said graphene being substantially free from contamination by metallic, magnetic, organic and inorganic impurities, i.e. a graphene whose contamination rate by metallic, magnetic, organic and inorganic impurities is at most 0.01 % by weight, preferably at most 0.001% by weight, more preferably at most 0.0001% by weight, relative to the total weight of graphene.
• FIG. 1 shows the Raman spectrum recorded on the graphene prepared according to Example 1 of the invention.
• the Raman displacement, in cm “1 , is indicated on the abscissa and the intensity of the Raman lines is given on the ordinate.
• This spectrum shows the presence of so-called D, G and 2D bands. These bands are characteristic of graphene with a low number of leaflet (between 1 and 10), good crystalline quality, and few structural defects.
• FIG. 2 represents the characterization of graphene prepared according to the method of example 1 of the invention by Fourier transform infrared spectroscopy.
• the absorption wavelengths, in cm -1 are indicated on the abscissa and the absorbance or the transmittance on the ordinate.
• the infrared spectrum shows the disappearance of the bands linked to the oxygen functions present in the OG, namely essentially the acid functions ( v ⁇ 1740 cm "1 ).
• the bands marked OH and C0 2 are related to the experimental conditions and do not belong to the final graphene.
• FIG. 3 shows the characterization of graphene prepared according to the method of Example 1 of the invention by X-ray diffraction performed on powder.
• the position of the peaks 2 ⁇ , in degree, is indicated on the abscissa and the intensity of the X-rays on the ordinate.
• the recorded powder diffractogram clearly shows the disappearance of the original graphite or graphite oxide. No diffraction peak belonging to salts or tin oxides is present.
• FIGS. 4a-4c show the characterization of graphene prepared according to the method of example 1 of the invention by electronic photo spectrometry X (in English, X-Ray photoelectron spectrometry or XPS).
• the intensity of the radiation (ordinate) is plotted as a function of the energy (abscissa) expressed in electron volts (eV).
• the XPS spectrum shown in Figure 4a shows the presence of two elements within the sample: carbon (strongly majority) and oxygen (residual).
• the oxygen signal is attributed to the presence of water or atmospheric oxygen adsorbed on the surface of graphene.
• the XPS spectrum shown in FIG. 4b is the signal recorded in the region of the carbon which is representative of the hybridized carbons constituting the graphene obtained.
• the XPS spectrum shown in Figure 4c is the enlargement of the area of the tin signature. It does not show the presence of any peak, attesting to the absence of tin compounds adsorbed or bound within the final graphene.
• FIG. 5a and 5b show the characterization of graphene prepared according to the method of Example 1 of the invention by transmission electron microscopy (TEM or TEM for Transmission Electron Microscopy).
• the TEM images show that the size of the sheets of the final graphene corresponds to the average size of the graphite grains used for the synthesis of the starting graphite oxide.
• the inset in the image shows an electronic diffractogram representative of those recorded on several samples at different leaflet locations of the final graphene.
• These diffractograms show graphene perfectly well crystallized and having few defects such as, for example, dangling bonds, holes in the structure, or lack of order. This enlargement makes it possible to count the number of layers of graphene constituting the sheets, this number is between 1 and 5 for all the samples made with graphene prepared according to the method of the invention.
• FIG. 6 shows the evolution / conversion of graphene oxide to graphene by gravimetric thermal analysis (ATG).
• the mass variation of the sample expressed in% (ordinate), is measured as a function of its heating temperature expressed in degrees Celsius (abscissa).
• the gravimetric thermal analysis recorded under a nitrogen atmosphere shows a progressive mass loss of about 12% at 800 ° C, which is the loss of water or oxygen adsorbed on the surface of graphene .
• FIG. 7 represents the characterization of graphene prepared according to the method of example 1 of the invention by magnetic analysis - Paramagnetic Resonance Electronics (RPE).
• EPR allows to know and analyze the paramagnetic species present within a sample.
• Graphene samples prepared according to the process of the invention were compared with samples obtained according to the "conventional" procedures using hydrazine or iron. The spectra were recorded at 4 Kelvin on an X-band EPR spectrometer. The magnetic field in Gauss is indicated on the abscissa.
• Graphene prepared according to the method of the invention has no trace of paramagnetic metal ions, while the spectrum shown has been amplified along the ordinate axis. The only signal observed corresponds to the carbonaceous paramagnetic species and probably to the conduction electrons of graphene.
• the graphene samples obtained by reaction with hydrazine both have signals: one corresponding to the carbonaceous paramagnetic species (fine signal at 3440 Gauss) and a larger one (approximately 1000 to 6000 Gauss) corresponding to manganese ions.
• These manganese ions come from the synthesis of graphite oxide, and the reduction with hydrazine does not manage to eliminate them.
• the graphene samples obtained by reaction with iron have, in addition to the signal corresponding to the carbonaceous paramagnetic species, a wider signal (around 1500 Gauss) characteristic of iron compounds.
• FIG. 8 represents the characterization of graphene prepared according to the method of example 1 of the invention by magnetic analysis - measurement of magnetic mass moments by SQUID magnetometer.
• the mass magnetic moment (or magnetic susceptibility) expressed in emu / g of several types of samples at 1.8 Kelvin (ordinate) is represented as a function of the magnetic field expressed in Gauss (abscissa).
• the graphene samples obtained by the "conventional" processes with hydrazine all show a large magnetic moment corresponding to the presence of manganese (II) ions within the samples. It is possible to quantify these impurities at a level of about one manganese (II) ion per 1400 carbon atoms.
• the samples obtained by reaction with iron are about 5 times less magnetic than the previous ones, which corresponds to about one iron (III) ion per 7000 carbon atoms.
• the measurements made with the graphene obtained according to the process of the invention show a magnetism approximately one hundred times lower than the samples of the process with hydrazine.
• the study of the curves shows that in this case, the measured magnetic moment corresponds to 1 ⁇ 2 spins, or to paramagnetic carbon species at a rate of about 1 spin 1 ⁇ 2 for 16,000 carbon atoms.
• the carbonaceous paramagnetic species encountered in the graphene samples prepared according to the method of the invention probably correspond to the conduction electrons of graphene.
• the graphene samples obtained according to the method of the invention do not contain any trace of paramagnetic metal elements. Also, they are particularly suitable for magnetism studies or magnetic doping of graphene.
• the graphene oxide (OG) used is synthesized from natural graphite powder (Bay Carbon) or synthetic (Nano Armor) according to the modified Hummer procedure described by OC Compton, ST Nguyen, Small 2010, 6, 711 -723.
• Hydrochloric acid and the chemicals necessary for carrying out this process were purchased from Sigma Aldrich and used as is.
• the apparatus used for the ultrasonic dispersion steps is provided by Branson (Model 2210).
• the reactions are carried out at ambient temperature, that is to say at 20 ⁇ 5 ° C.
• the XPS spectra were recorded on a device supplied by Surface Science Instruments, the infrared spectra were made on a Spectrum GX spectrometer (USA), the Raman spectrometer was supplied by the Reinshaw company, the X-ray diffraction spectra on powder were obtained on an apparatus X'Pert (PANalytical).
• the MET images were made using a JO ⁇ L 3010 microscope.
• the EPR spectra were made on an X-band Brucker EMX spectrometer equipped with an Oxford Instrument ESR900 cryostat. Magnetic measurements were performed using a SQUID MPMS magnetometer supplied by Qantum Design.
• 300 mg of OG are dispersed in 300 ml of distilled water (milliQ type) and sonicated for about one hour. 3 grams of tin (II) chloride are then added and the reaction mixture is sonicated for 30 minutes, then 60 ml of concentrated hydrochloric acid (37% by weight) are added with stirring (without sonication). The The dispersion is stirred for one hour and then allowed to stand for six hours. After the addition of hydrochloric acid, the solution turns black indicating the conversion of OG to graphene. 60 ml of concentrated hydrochloric acid (37% mass) are again added to facilitate the removal of tin salts.
• the graphene is separated by filtration, then washed several times with concentrated hydrochloric acid (37% mass) (3 times 60 ml), then with water (approximately 1.5 L) until this becomes neutral from a pH point of view (6.5 ⁇ pH ⁇ 7.5).
• the graphene obtained is either redispersed in a suitable solvent such as pyrrolidinone by sonication, or dried under vacuum (paddle pump at 10 -4 mmHg).
• the graphene thus prepared was characterized by a set of techniques aimed at showing the quality of the final graphene and its main characteristics as shown in FIGS. 1 to 6.
• a comparison of the magnetic properties with syntheses carried out according to the procedures previously described was performed as shown in Figures 7 and 8.
• graphene prepared according to the process of the invention shows no trace of impurities, in particular metal ions, (para) magnetic ions or organic or inorganic impurities. , which is never observed with graphenes prepared according to the known methods.

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