WO2023194683A1 - Solid-state fluorescent graphene-based quantum dots - Google Patents
Solid-state fluorescent graphene-based quantum dots Download PDFInfo
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- WO2023194683A1 WO2023194683A1 PCT/FR2023/050480 FR2023050480W WO2023194683A1 WO 2023194683 A1 WO2023194683 A1 WO 2023194683A1 FR 2023050480 W FR2023050480 W FR 2023050480W WO 2023194683 A1 WO2023194683 A1 WO 2023194683A1
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Classifications
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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
- C01B32/15—Nano-sized carbon materials
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- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
- C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
- C09K11/65—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing carbon
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2002/00—Crystal-structural characteristics
- C01P2002/80—Crystal-structural characteristics defined by measured data other than those specified in group C01P2002/70
- C01P2002/82—Crystal-structural characteristics defined by measured data other than those specified in group C01P2002/70 by IR- or Raman-data
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2002/00—Crystal-structural characteristics
- C01P2002/80—Crystal-structural characteristics defined by measured data other than those specified in group C01P2002/70
- C01P2002/85—Crystal-structural characteristics defined by measured data other than those specified in group C01P2002/70 by XPS, EDX or EDAX data
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2004/00—Particle morphology
- C01P2004/51—Particles with a specific particle size distribution
- C01P2004/52—Particles with a specific particle size distribution highly monodisperse size distribution
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2004/00—Particle morphology
- C01P2004/60—Particles characterised by their size
- C01P2004/64—Nanometer sized, i.e. from 1-100 nanometer
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/90—Other properties not specified above
Definitions
- the present invention relates to a process for preparing graphene quantum dots (GQDs), the graphene quantum dots capable of being obtained according to this process, and their use, in particular in energy production devices such as light-emitting diodes, batteries, or solar cells.
- GQDs graphene quantum dots
- Graphene corresponds to an infinite 2D monolayer of sp 2 bonded hexagonal carbon lattice that exhibits interesting zero band gap properties due to electron delocalization.
- GQDs are functionalized graphene nanofragments with a lateral size typically less than 10 nm. Their anisotropic morphology comes from the lateral dimension which is greater than their height. GQDs systematically possess graphitic networks within their structures, as evidenced by high-resolution microscopy images of their structures (HR-TEM). Their height is generally between 0.4 and 4 nm, as shown by statistical AFM analysis, which corresponds to a few GQDs (from 1 to 10) stacked on top of each other.
- GQDs can be considered as polycyclic aromatic hydrocarbons (PAH) with a size greater than 1 nm.
- GQDs are composed of many fused aromatic rings, their synthesis generally involves one or more key intramolecular cyclization steps. Although difficult to transpose to the industrial scale, this step-by-step approach has the notable advantage of producing atomically precise nanographene structures, in terms of size and doping of the heteroatoms (nature, position and concentration of the heteroatom).
- chemists have also developed approaches to the synthesis of GQDs (bottom-up or top-down method), in most cases, in a single step, which result in the preparation of a mixture of GQDs presenting a statistical distribution in terms of size and chemistry. Consequently, the macroscopic properties arise from those of the total population of GQDs.
- Top-down synthesis consists of the chemical decomposition of large carbon-based materials (carbon fibers, graphene oxide GO, carbon, fullerenes, graphite, etc.) into small fragments with concentrated acids.
- Graphene oxide is typically the ideal starting material due to the presence of numerous functional groups containing oxygen which facilitate chemical cleavage towards nanometer-sized GQDs. Nevertheless, graphene oxide does not exist naturally and therefore must be prepared from various materials such as coal or anthracite by Hummers' complex chemical approach. In this context, the use of graphite as a natural source has been evaluated as a substitute for graphene oxide, with less success to date due to lower synthetic yields. Top-down syntheses are possible through hydrothermal or solvothermal cutting, microwave-assisted exfoliation, electrochemical methods, and oxidation.
- the one-step bottom-up synthesis consists of carbonizing organic precursors (citric acid, glucose, glutamic acid, hexa-perihexabenzocoronene, etc.) by microwave-assisted pyrolysis, solvothermal heating or under pulsed laser irradiation.
- organic precursors citric acid, glucose, glutamic acid, hexa-perihexabenzocoronene, etc.
- bottom-up approaches generally suffer from lower yields associated with purification issues to remove small, unreacted organic materials.
- the invention firstly relates to a process for preparing quantum dots based on graphene (GQDs) comprising the steps of: i) Suspending a carbon source in a mixture of water and sulfuric acid; ii) Microwave heating of the suspension obtained at a temperature between 20°C and 200°C, in particular between 100°C and 180°C, iii) Recovery and possibly washing and/or drying of the carbonaceous residue obtained; iv) Suspending the residue obtained in nitric acid; v) Microwave heating of the suspension obtained at a temperature between 20°C and 200°C, in particular between 100°C and 180°C, and vi) Recovery of the graphene-based quantum dots (GQDs) obtained.
- GQDs graphene
- the inventors were able to show that by carrying out, in a first phase, a treatment of a carbon source in sulfuric acid, followed by a second phase of treatment in nitric acid, the two stages being made by microwave heating, it was possible to obtain GQDs in a very rapid time, notably in around ten minutes, at lower cost, and in a very reproducible manner.
- the GQDs obtained at the end of these two phases are relatively homogeneous and very easy to purify by simple extraction with an organic solvent.
- it is not necessary to resort to heavy and costly extraction methods such as dialysis or chromatography methods commonly used in the field.
- the carbon source used in this process can be a source of organic carbon, in particular renewable, in particular organic waste such as plant waste, which further reduces the ecological impact of the process.
- this process makes it possible to access GQDs having very advantageous characteristics, in particular a very homogeneous size distribution, in particular monomodal, and very good solubility in aqueous or organic solvents. Furthermore, unexpectedly, the inventors were able to demonstrate that these GQDs exhibited white fluorescence in the solid state, that is to say that when the material is irradiated in the solid state, we obtain the spectrum of white light, without the need to use a polymer matrix such as PMMA, as a diluent. This property is particularly advantageous for certain applications such as OLED devices, white light emitters, organic transistors (OFET), fluorescent sensors, optical sensors and the field of anti-counterfeiting.
- OLED devices white light emitters
- OFET organic transistors
- fluorescent sensors optical sensors and the field of anti-counterfeiting.
- the method according to the invention further comprises one or more of the following characteristics:
- the carbon source is a renewable organic material, particularly plant material
- the carbon source is in powder form
- step i) the proportion of water by volume in the water/sulfuric acid mixture used in step i) varies between 0 and 50% of the total volume;
- the concentration by weight of the carbon source relative to the volume of the water/sulfuric acid mixture used in step i) is between 0.1 and 100 g/L, in particular between 1 and 30 g/L;
- step ii) and/or v) is carried out at a pressure of between 5 and 50 bars;
- - recovery step iii) includes the steps of:
- the concentration of the carbon residue in the nitric acid in step iv) is between 1 and 40 g/L, in particular between 5 and 25 g/L;
- the recovery of GQDs includes an extraction step with an organic solvent
- the recovery stage includes the stages of:
- the inventors were able to characterize the GQDs obtained according to the process of the invention according to different methods, in particular spectrophotometry of photoelectrons induced by X-rays (XPS), and infrared (IR).
- XPS X-rays
- IR infrared
- the invention relates to graphene quantum dots capable of being obtained according to the method of the invention.
- quantum dots are notably obtained by the process according to the invention.
- the graphene quantum dots according to the invention comprise one or more of the following characteristics:
- XPS X-ray induced photoelectron spectrometry
- XPS X-ray induced photoelectron spectrometry
- the number mode is between 1 and 10 nm, in particular between 1 and 5 nm;
- the median D50 is between 1 and 5 nm, in particular between 2 and 4 nm;
- the standard deviation is between 1 and 20%, notably between 6 and 12%;
- the invention relates to the use of graphene quantum dots according to the invention, in imaging, detection, optoelectronic, energy production and storage devices. energy (batteries and supercapacitors), photocatalytic, as well as within conductive or composite materials.
- the graphene quantum dots according to the invention are used in energy production devices such as light-emitting diodes, batteries, or solar cells.
- Figure 1 represents the XPS 01s spectrum of the graphene quantum dots according to the invention.
- Figure 2 represents the XPS C1s spectrum of the graphene quantum dots according to the invention.
- Figure 3 represents the XPS N1s spectrum of the graphene quantum dots according to the invention.
- Figure 4 represents the FT-IR spectrum of the graphene quantum dots according to the invention.
- Figure 5 represents the fluorescence spectrum of graphene quantum dots according to the invention in ultrapure water, as a function of the excitation wavelength (values indicated by an arrow)
- Figure 6 represents the fluorescence spectrum of graphene quantum dots according to the invention in the solid state.
- Figure 7 represents an image of the GQDs according to the invention obtained by transmission electron microscopy (TEM).
- the invention relates to a process for preparing quantum dots based on graphene (GQDs) comprising the steps of: i) Suspending a carbon source in a mixture of water and sulfuric acid ; ii) Microwave heating of the suspension obtained at a temperature between 20°C and 200°C, in particular between 100°C and 180°C, iii) Recovery and possibly drying of the carbonaceous residue obtained; iv) Suspending the residue obtained in nitric acid; v) Microwave heating of the suspension obtained at a temperature between 20°C and 200°C, in particular between 100°C and 180°C, and vi) Recovery of the graphene-based quantum dots (GQDs) obtained.
- GQDs graphene
- graphene-based quantum dots also herein referred to as “GQDs” refers to any nanoparticle composed mainly of carbon atoms, in particular carbon, fused and aromatic rings. It mainly designates anisotropic nanoobjects, that is to say planar, (wider than tall) and crystallized, in particular exclusively crystallized.
- this term also includes “carbon nanodots” (also called “carbon dots”) which are spherical carbon particles which may have crystallized parts.
- the term “graphene-based quantum dots”, or GQDs refers to anisotropic and crystallized nanoobjects.
- Step i) consists of suspending a carbon source, more particularly a renewable organic material, in a mixture of water and sulfuric acid.
- renewable organic matter we mean material coming from living nature and including animal and plant materials, which are generally produced by agriculture, forestry or fishing. They regenerate constantly in relatively short cycles (from a few days to a few decades).
- animal material we can cite for example wool, animal fats, etc.
- plant materials include cereals, wood, rubber, cotton, algae, vegetable fats, fruits and vegetables.
- the plant material used in step i) may be dehydrated or dried plant material.
- it does not include plant carbons, that is to say carbons obtained in particular by pyrolysis of plant material.
- the carbon source is plant material.
- the plant organic matter consists of plant waste. This embodiment is particularly advantageous since it makes it possible to recycle waste and prepare graphene quantum dots from an abundant, renewable and inexpensive raw material.
- the carbon source can be used in the form of a powder. This advantageously makes it possible to obtain a homogeneous dispersion in the water/sulfuric acid mixture, and therefore a homogeneous reactivity of all of the material involved in steps i) and ii) of the process.
- the plant waste powder can for example be obtained by drying in an oven at a temperature between 60°C and 100°C, then grinding.
- This carbon source is then suspended in a water/sulfuric acid (H2SO4) mixture.
- Sulfuric acid is notably sulfuric acid in concentrated form.
- the proportion of water by volume in the water/sulfuric acid mixture used in step i) can vary to a large extent. It may in particular be between 0 and 50% of the total volume of the mixture.
- the concentration by weight of the carbon source relative to the volume of the water/sulfuric acid mixture used in step i) may vary. It may in particular be between 0.1 and 100 g/L, in particular between 1 and 30 g/L.
- Step ii) consists of heating the suspension obtained in step i) by microwave to a temperature between 20°C and 200°C, in particular between 100°C and 180°C, in particular at approximately 150°C. This heating is generally carried out at a pressure of between 1 and 10 bars, in particular between 2 and 5 bars.
- step iii) can be carried out in less than 10 minutes, in particular in 5 minutes.
- steps i) and ii) would make it possible to promote dehydration reactions of the plant material to form an oxygenated carbon material.
- this step is not carried out under an inert atmosphere, so as to promote the incorporation of oxygen into the carbon residue.
- Step iii) consists of recovering and possibly washing and/or drying the carbonaceous residue obtained in step ii).
- This step iii), may in particular include the recovery and washing of the carbon residue according to the steps of:
- This step makes it possible in particular to reduce or even substantially eliminate the presence of sulfuric acid in the carbon residue.
- the carbonaceous residue recovered and washed can then be dried, for example in an oven at a temperature between 60°C and 90°C for several hours.
- Step iv) consists of treating the carbon residue in nitric acid.
- concentration of the carbon residue in the nitric acid in step iv) can be between 1 and 40 g/L, in particular between 5 and 25 g/L.
- Step v) consists of heating the suspension obtained by microwave to a temperature between 20°C and 200°C, in particular between 100°C and 180°C, and in particular at approximately 150°C. This step is preferably carried out with stirring.
- Heating by microwave in step v) can be carried out at a pressure of between 5 and 60 bars, in particular between 10 and 40 bars.
- step v) can be carried out in less than 10 minutes, particularly in 5 minutes.
- the conversion rate of the carbon residue used in step v) into quantum dots of graphene at the end of step v) is generally 100%.
- the progress of the conversion reaction can be easily followed: start of the reaction in step v), the carbon residue is not soluble in the reaction medium and becomes soluble as it is converted.
- the reaction is generally completed when the initial carbon residue has completely disappeared, i.e. is completely solubilized in the form of GQDs.
- steps iv) and v) would make it possible to chemically cut fragile chemical bonds in order to lead to the formation of functionalized fragments, called GQDs.
- Step vi) consists of the recovery of graphene-based quantum dots (GQDs) obtained in step iv).
- This step can be carried out using conventional methods such as chromatography, extraction, dialysis and/or ultracentrifugation.
- this step is carried out by extracting the reaction medium with an organic solvent, in particular a polar organic solvent, in particular a polar protic solvent, such as an alcohol, more particularly an aliphatic alcohol.
- an organic solvent in particular a polar organic solvent, in particular a polar protic solvent, such as an alcohol, more particularly an aliphatic alcohol.
- the graphene quantum dots are recovered in the organic phase which can be washed and concentrated under reduced pressure.
- the residue obtained can be dried under vacuum, at a temperature of around 80°C, typically for 2 hours.
- the process of the invention makes it possible to obtain quantum dots of graphene with good yields, in particular between 15 and 70%, in particular between 20 and 60%, this yield being calculated by making the ratio between the mass of GQDs recovered and the mass of hydrocarbon material used in step i).
- the invention relates to graphene quantum dots capable of being obtained according to the process as defined above.
- the subject of the invention is graphene quantum dots characterized in that their spectrum obtained by X-ray induced photoelectron spectrometry (XPS) N1 s comprises the following energy bands:
- relative intensity is understood to mean the value of the area under the curve of one of the bands relative to the sum of the area under the curve of the two bands.
- the N1 s spectrum of the quantum dots according to the invention obtained by X-ray induced photoelectron spectrometry (XPS), comprises two energy bands:
- the other being characterized by a binding energy of between 404 eV and 406 eV, and a relative intensity of between 40% and 70%.
- the sum of the relative intensities of these two energy bands is equal to 100%.
- X-ray induced photoelectron spectrometry can be carried out with a Kratos Axis Ultra spectrometer (Kratos Analytical, U.K.) notably equipped with a monochromatic Al Ka source (1486.6 eV).
- the spectra are notably recorded at an elevation angle of 90° over an area 0.7 x 0.3 mm.
- the high resolution spectra are notably measured with a step of 0.1 eV.
- the XPS N1 s spectrum of the graphene quantum dots according to the invention can include the following energy bands (eV): 401.5 and 405.8.
- the XPS N1 s spectrum of the graphene quantum dots according to the invention can comprise the following two energy bands:
- the N1 s spectrum of the quantum dots according to the invention obtained by X-ray induced photoelectron spectrometry (XPS), comprises two energy bands:
- the graphene quantum dots according to the invention can be further characterized in that their spectrum obtained by X-ray induced photoelectron spectrometry (XPS) of C1 s comprises 4 energy bands whose binding energies are between 282 and 290 eV.
- XPS X-ray induced photoelectron spectrometry
- the graphene quantum dots according to the invention can be further characterized by an XPS spectrum of C1 s comprising the energy bands characterized by the following binding energies (in eV): 284.6; 286; 287.4; and 288.8.
- This spectrum is notably measured with a Kratos Axis Ultra spectrometer (Kratos Analytical, U.K.), notably equipped with a monochromatic Al Ka source (1486.6 eV).
- the spectra are notably recorded at an elevation angle of 90° over an area 0.7 x 0.3 mm.
- the high resolution spectra are notably measured with a step of 0.1 eV.
- the graphene quantum dots according to the invention can be further characterized by an XPS spectrum of C1 s comprising the following energy bands:
- the graphene quantum dots according to the invention can be further characterized in that their O1 s spectrum obtained by X-ray induced photoelectron spectrometry (XPS) comprises 3 energy bands whose binding energies are between 530 and 536 eV.
- XPS X-ray induced photoelectron spectrometry
- graphene quantum dots according to the invention can be further characterized in that their XPS O1 s spectrum comprises the following energy bands (in eV):
- the quantum dots according to the invention can be characterized in that they have a monomodal particle size distribution in number.
- the particle size distribution of graphene quantum dots can be measured in number using the dynamic light scattering (DLS) method on VASCO KIN equipment (Cordouan Technologies, Pessac, France). The measurements were carried out on suspensions freshly prepared in ultrapure water at 25°C and in triplicate. The data were analyzed by Data Nano Kin® software in multimodal number determination mode.
- DLS dynamic light scattering
- the number mode can be between 1 and 10 nm, in particular between 1 and 5 nm.
- the median D50 in number can be between 1 and 5 nm, in particular between 2 and 4 nm.
- the standard deviation can be between 1 and 20%, especially between 6 and 12%.
- the graphene quantum dots according to the invention can be characterized in that they exhibit white luminescence in the solid state.
- the graphene quantum dots according to the invention can be further characterized in that they exhibit luminescence in water. More particularly, this luminescence is characterized in that the emission wavelength varies as a function of the excitation wavelength. More particularly, for an excitation wavelength varying from 300 nm to 420 nm, the emission wavelength of the GQDs according to the invention varies from 430 nm to 510 nm.
- GQDs are characterized by a high solubility, of more than 500 g/L in aliphatic alcohols, including ethanol in particular. This solubility is particularly advantageous in the field of ink formulation, particularly for inkjet printing, which are generally composed of an aliphatic alcohol solvent.
- the GQDs according to the invention can therefore be advantageously incorporated into inks, used in the field of electronics in particular.
- GQDs are characterized by an interesting solubility of 10g/L in water, which allows their use in the field of biology, particularly in the field of imaging, or diagnosis.
- the invention relates to the use of graphene quantum dots according to the invention, in imaging, detection, optoelectronic, energy production, energy storage devices, in particular batteries and/or or supercapacitors, photocatalytic, as well as within conductive or composite materials.
- the graphene quantum dots according to the invention can be used in energy production devices such as light-emitting diodes, batteries, or solar cells.
- the invention relates to a method for preparing graphene quantum dots (GQDs) comprising the steps of: a. Suspending a carbon source in nitric acid, the carbon source being chosen from coal, coal coke, biochar, asphalt and mixtures thereof; b. Microwave heating of the suspension obtained at a temperature between 20°C and 200°C, in particular between 100°C and 180°C, at a pressure between 5 and 50 bars; etc. Recovery of the graphene-based quantum dots (GQDs) obtained.
- the carbon source used in step a) can be prepared according to steps i) to ill) of process (A), as defined above.
- steps a), b) and c) are identical to steps iv), v) and vi) respectively, defined above.
- All chemicals used (reagents and solvents) in the method are of reagent grade and are used directly.
- the water used is ultrapure water, that is, with a resistivity of 18.2 m ⁇ . cm at 25°C.
- Step 1 of the synthesis is carried out in a Masterwave BTR microwave reactor from the Anton Paar brand.
- Step 2 of the synthesis is carried out in a Multiwave 5000 microwave reactor from the Anton brand Paar.
- the FT-IR spectra are carried out on a Nicolet iS5 instrument.
- the VASCO KIN device from the Cordouan Technologies brand. All measurements were carried out on suspensions freshly prepared in ultrapure water, at 25°C and in triplicate.
- the data were analyzed using the Nano Kin software using a distribution multimodal in number and expressed as an average ( ⁇ the standard deviation).
- the transmission electron microscopy analyzes were carried out on a JEM - ARM 200F Cold FEG TEM/STEM device operating at 200 kV.
- the grids were prepared by depositing a drop of GQDs solution (1 mg/mL in water) on a carbon-coated copper grid for 4 minutes. The drop was then removed with blotting paper, the grid was then dried at 80°C for 20 minutes.
- the UV-vis spectra were measured on a Cary® spectrophotometer from Varian.
- the fluorescence emission spectra were measured on a Horiba Jobin Yvon brand FluoroMax-3 spectrofluorometer at 25°C.
- XPS analyzes were carried out with a Ka monochromatized Al source.
- Step 0 The banana skins are dried in an oven at 75°C for
- the reaction medium is diluted in water (1.5 L).
- the aqueous medium is extracted with an aliphatic alcohol (2 x 800 mL).
- the organic phases are washed with water (2 x 400 mL) then with 1 M HCl (3 x 600 mL).
- the organic phase is then concentrated under reduced pressure.
- the residue is dried under vacuum at 80°C for 2 hours.
- the final yield is 22%.
- the obtained GQDs were characterized by N1 s, O1 s and C1 s X-ray induced photoelectron spectroscopy (XPS), FT-IR and spectrofluorometry.
- XPS X-ray induced photoelectron spectroscopy
- the same protocol was implemented using olive pits, orange peels and oak acorns.
- the obtained GQDs were characterized by N1s, O1s and C1s X-ray induced photoelectron spectroscopy (XPS), FT-IR and spectrofluorometry.
- XPS X-ray induced photoelectron spectroscopy
- FT-IR FT-IR spectrofluorometry
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Abstract
The invention relates to a method for preparing graphene quantum dots (GQDs), the method comprising the steps of: i) suspending a carbon source in a mixture of water and sulphuric acid; ii) microwaving the obtained suspension to a temperature of between 20°C and 200°C, in particular between 100°C and 180°C; iii) recovering and optionally washing and/or drying the obtained carbonaceous residue; iv) suspending the obtained residue in nitric acid; v) microwaving the obtained suspension to a temperature of between 20°C and 200°C, in particular between 100°C and 180°C; and vi) recovering the obtained graphene-based quantum dots (GQDs).
Description
Quantum dots à base de graphene fluorescents à l’état solide Quantum dots based on solid-state fluorescent graphene
Domaine de l’invention Field of the invention
La présente invention concerne un procédé de préparation de quantum dots de graphène (GQDs), les quantum dots de graphène susceptibles d’être obtenus selon ce procédé, et leur utilisation, notamment dans des dispositifs de production d’énergie tels que les diodes électroluminescentes, les batteries, ou les cellules solaires. The present invention relates to a process for preparing graphene quantum dots (GQDs), the graphene quantum dots capable of being obtained according to this process, and their use, in particular in energy production devices such as light-emitting diodes, batteries, or solar cells.
Arrière-plan technique Technical background
Le graphène correspond à une monocouche infinie en 2D de réseau de carbone hexagonal à liaison sp2 qui présente d'intéressantes propriétés de bande interdite nulle (« zero band gap ») en raison de la délocalisation des électrons. Graphene corresponds to an infinite 2D monolayer of sp 2 bonded hexagonal carbon lattice that exhibits interesting zero band gap properties due to electron delocalization.
En conséquence, cela donne un comportement semi-métallique au graphène. Ainsi, les électrons se déplacent à travers le graphène avec pratiquement aucune résistance, ce qui conduit à une conductivité électrique élevée. Grâce à d'autres propriétés remarquables comme la résistance, la légèreté, la conductivité thermique et la transparence, le graphène est très prometteur dans les domaines suivants : semi-conducteurs, l'électronique et les applications de stockage d'énergie. As a result, this gives semi-metallic behavior to graphene. Thus, electrons move through graphene with virtually no resistance, leading to high electrical conductivity. Thanks to other remarkable properties such as strength, lightness, thermal conductivity and transparency, graphene holds great promise in the following areas: semiconductors, electronics and energy storage applications.
Toutefois la production, à grande échelle de graphène, de haute qualité et sa faible capacité de transformation constituent encore des obstacles techniques à surmonter pour permettre au graphène d'atteindre l'échelle industrielle. En outre, la mise au point de dispersions stables et homogènes de graphène, sans agglomération, constitue encore aujourd’hui un défi de taille. Par ailleurs, la bande interdite nulle du graphène entrave leur mise en œuvre dans les dispositifs optoélectroniques ainsi que dans les transistors à effet de champ (FET). However, the large-scale production of high-quality graphene and its low processing capacity still constitute technical obstacles to overcome to allow graphene to reach the industrial scale. In addition, the development of stable and homogeneous dispersions of graphene, without agglomeration, still constitutes a major challenge today. Furthermore, the zero bandgap of graphene hinders their implementation in optoelectronic devices as well as in field effect transistors (FETs).
Dans ce contexte, la découverte récente des points quantiques de graphène, encore dénommés « graphene quantum dots » (GQDs) en anglais, et les progrès rapides dans leur préparation synthétique offrent une possibilité d'amélioration de l'efficacité des dispositifs optoélectroniques. In this context, the recent discovery of graphene quantum dots, also called “graphene quantum dots” (GQDs) in English, and the rapid progress in their synthetic preparation offer a possibility of improving the efficiency of optoelectronic devices.
L'intérêt majeur de ces nanoparticules réside en leur photoluminescence, à l'origine de diverses applications, notamment dans le domaine de l'énergie (photocatalyse hétérogène, dispositifs photovoltaïques, LED ... ) et également à l'interface de la biologie pour l'imagerie.
Ces points quantiques carbonés (GQDs) combinent plusieurs attributs favorables des points quantiques traditionnels à base de semi-conducteurs (à savoir, une taille nanométrique, émission de luminescence dépendant de la taille et de la longueur d'onde, la résistance au photoblanchiment, la facilité de bioconjugaison) sans pour autant impliquer une toxicité intrinsèque ou une rareté des éléments, ou encore d'étapes de préparation rigoureuses, coûteuses ou inefficaces. The major interest of these nanoparticles lies in their photoluminescence, at the origin of various applications, notably in the field of energy (heterogeneous photocatalysis, photovoltaic devices, LEDs, etc.) and also at the interface of biology for imagery. These carbon quantum dots (GQDs) combine several favorable attributes of traditional semiconductor-based quantum dots (i.e., nanometer size, size- and wavelength-dependent luminescence emission, resistance to photobleaching, ease of bioconjugation) without implying intrinsic toxicity or rarity of the elements, or even rigorous, costly or ineffective preparation steps.
Les GQDs sont des nanofragments de graphène fonctionnalisés avec une taille latérale généralement inférieure à 10 nm. Leur morphologie anisotrope provient de la dimension latérale qui est plus grande que leur hauteur. Les GQDs possèdent systématiquement des réseaux graphitiques au sein de leurs structures, comme en témoignent les images de microscopie à haute résolution de leurs structures (HR-TEM). Leur hauteur est généralement comprise entre 0,4 et 4 nm, comme le montre l'analyse AFM statistique, ce qui correspond à quelques GQDs (de 1 à 10) empilés les uns sur les autres. GQDs are functionalized graphene nanofragments with a lateral size typically less than 10 nm. Their anisotropic morphology comes from the lateral dimension which is greater than their height. GQDs systematically possess graphitic networks within their structures, as evidenced by high-resolution microscopy images of their structures (HR-TEM). Their height is generally between 0.4 and 4 nm, as shown by statistical AFM analysis, which corresponds to a few GQDs (from 1 to 10) stacked on top of each other.
Les GQDs peuvent être considérés comme des hydrocarbures aromatiques polycycliques (PAH) de taille supérieure à 1 nm. GQDs can be considered as polycyclic aromatic hydrocarbons (PAH) with a size greater than 1 nm.
La synthèse organique en plusieurs étapes des GQDs est très difficile, impliquant généralement de nombreuses transformations chimiques successives à partir d'un produit chimique disponible dans le commerce. Comme les GQDs sont composés de nombreux cycles aromatiques fusionnés, leur synthèse implique généralement une ou plusieurs étapes clés de cyclisation intramoléculaire. Bien que difficilement transposable à l'échelle industrielle, cette approche par étapes présente l'avantage notable de produire des structures de nanographène atomiquement précises, en termes de taille et de dopage des hétéroatomes (nature, position et concentration de l'hétéroatome). D'autre part, les chimistes ont également développé des approches de synthèse des GQDs (méthode ascendante ou descendante, dites « bottom-up » ou « top-down » en anglais), dans la plupart des cas, en une seule étape, qui aboutissent à la préparation d'un mélange de GQDs présentant une distribution statistique en termes de taille et de chimie. En conséquence, les propriétés macroscopiques découlent de celles de la population totale des GQDs. The multistep organic synthesis of GQDs is very difficult, typically involving many successive chemical transformations from a commercially available chemical. As GQDs are composed of many fused aromatic rings, their synthesis generally involves one or more key intramolecular cyclization steps. Although difficult to transpose to the industrial scale, this step-by-step approach has the notable advantage of producing atomically precise nanographene structures, in terms of size and doping of the heteroatoms (nature, position and concentration of the heteroatom). On the other hand, chemists have also developed approaches to the synthesis of GQDs (bottom-up or top-down method), in most cases, in a single step, which result in the preparation of a mixture of GQDs presenting a statistical distribution in terms of size and chemistry. Consequently, the macroscopic properties arise from those of the total population of GQDs.
La synthèse descendante consiste en la décomposition chimique de matériaux de grande taille à base de carbone (fibres de carbone, oxyde de graphène GO, charbon, fullerènes, graphite,...) en petits fragments avec des acides concentrés. L’oxyde de graphène est typiquement le matériau de départ idéal en raison de la présence de nombreux groupes fonctionnels
contenant de l'oxygène qui facilitent le clivage chimique vers des GQDs de taille nanométrique. Néanmoins, l’oxyde de graphène n'existe pas à l'état naturel et doit donc être préparé à partir de divers matériaux tels que le charbon ou l'anthracite par l'approche chimique complexe de Hummers. Dans ce contexte, l'utilisation du graphite comme source naturelle a été évaluée en tant que substitut de l’oxyde de graphène, avec un succès moindre à ce jour en raison de rendements synthétiques plus faibles. Des synthèses descendantes sont possibles grâce à un découpage hydrothermique ou solvothermique, exfoliation assistée par micro-ondes, méthodes électrochimiques et oxydation. Top-down synthesis consists of the chemical decomposition of large carbon-based materials (carbon fibers, graphene oxide GO, carbon, fullerenes, graphite, etc.) into small fragments with concentrated acids. Graphene oxide is typically the ideal starting material due to the presence of numerous functional groups containing oxygen which facilitate chemical cleavage towards nanometer-sized GQDs. Nevertheless, graphene oxide does not exist naturally and therefore must be prepared from various materials such as coal or anthracite by Hummers' complex chemical approach. In this context, the use of graphite as a natural source has been evaluated as a substitute for graphene oxide, with less success to date due to lower synthetic yields. Top-down syntheses are possible through hydrothermal or solvothermal cutting, microwave-assisted exfoliation, electrochemical methods, and oxidation.
D'autre part, la synthèse ascendante en une étape consiste à carboniser des précurseurs organiques (acide citrique, glucose, acide glutamique, hexa-perihexabenzocoronène, ...) par pyrolyse assistée par micro-ondes, chauffage solvothermique ou sous irradiation laser pulsée. Cependant, les approches ascendantes souffrent généralement de rendements plus faibles associés à des problèmes de purification pour éliminer les matériaux organiques de petite taille qui n'ont pas réagi. On the other hand, the one-step bottom-up synthesis consists of carbonizing organic precursors (citric acid, glucose, glutamic acid, hexa-perihexabenzocoronene, etc.) by microwave-assisted pyrolysis, solvothermal heating or under pulsed laser irradiation. However, bottom-up approaches generally suffer from lower yields associated with purification issues to remove small, unreacted organic materials.
Les synthèses actuelles décrites dans la littérature reposent principalement sur des techniques de réactions hydrothermiques qui requièrent des intervalles de temps de plusieurs heures. Ainsi, les techniques de fabrication (ablation laser, lithographie par faisceau d'électrons, synthèses par voies électrochimique) restent sur des niveaux faibles en rendement pour des coûts élevés ayant pour conséquence qu'une production pour des applications commerciales reste difficile à envisager. Current syntheses described in the literature are mainly based on hydrothermal reaction techniques which require time intervals of several hours. Thus, manufacturing techniques (laser ablation, electron beam lithography, electrochemical syntheses) remain at low levels of yield for high costs with the consequence that production for commercial applications remains difficult to envisage.
Il existe donc aujourd’hui un réel besoin de pouvoir disposer d’un procédé de synthèse de GQDs rapide, facile à mettre en œuvre et permettant d’isoler les GQDs avec de bons rendements. There is therefore today a real need to have a process for synthesizing GQDs that is fast, easy to implement and allows GQDs to be isolated with good yields.
Résumé de l’invention Summary of the invention
Il a maintenant été mis au point un procédé simple, rapide et efficace permettant d’accéder à des GQDs avec de bons rendements. A simple, rapid and efficient process has now been developed allowing access to GQDs with good yields.
L’invention concerne en premier lieu un procédé de préparation de quantum dots à base de graphène (GQDs) comprenant les étapes de : i) Mise en suspension d’une source de carbone dans un mélange d’eau et d’acide sulfurique ;
ii) Chauffage par microonde de la suspension obtenue à une température comprise entre 20°C et 200°C, notamment entre 100°C et 180 °C, iii) Récupération et éventuellement lavage et/ou séchage du résidu carboné obtenu ; iv) Mise en suspension du résidu obtenu dans de l’acide nitrique ; v) Chauffage par microonde de la suspension obtenue à une température comprise entre 20°C et 200°C, notamment entre 100°C et 180 °C, et vi) Récupération des quantum dots à base de graphène (GQDs) obtenus. The invention firstly relates to a process for preparing quantum dots based on graphene (GQDs) comprising the steps of: i) Suspending a carbon source in a mixture of water and sulfuric acid; ii) Microwave heating of the suspension obtained at a temperature between 20°C and 200°C, in particular between 100°C and 180°C, iii) Recovery and possibly washing and/or drying of the carbonaceous residue obtained; iv) Suspending the residue obtained in nitric acid; v) Microwave heating of the suspension obtained at a temperature between 20°C and 200°C, in particular between 100°C and 180°C, and vi) Recovery of the graphene-based quantum dots (GQDs) obtained.
Plus particulièrement, les inventeurs ont pu montrer qu’en réalisant, dans une première phase, un traitement d’une source de carbone dans l’acide sulfurique, suivi d’une deuxième phase de traitement dans l’acide nitrique, les deux étapes étant réalisées par chauffage microonde, il était possible d’obtenir des GQDs en un temps très rapide, notamment en une dizaine de minutes, à moindre coût, et ce, de façon très reproductible. More particularly, the inventors were able to show that by carrying out, in a first phase, a treatment of a carbon source in sulfuric acid, followed by a second phase of treatment in nitric acid, the two stages being made by microwave heating, it was possible to obtain GQDs in a very rapid time, notably in around ten minutes, at lower cost, and in a very reproducible manner.
Avantageusement, les GQDs obtenus à l’issue de ces deux phases sont relativement homogènes et très faciles à purifier par simple extraction avec un solvant organique. Ainsi, il n’est pas nécessaire de recourir à des méthodes d’extractions lourdes et coûteuses à mettre en œuvre telles que méthodes de dialyse ou de chromatographie couramment utilisées dans le domaine. Advantageously, the GQDs obtained at the end of these two phases are relatively homogeneous and very easy to purify by simple extraction with an organic solvent. Thus, it is not necessary to resort to heavy and costly extraction methods such as dialysis or chromatography methods commonly used in the field.
Selon un autre avantage, la source de carbone mise en œuvre dans ce procédé peut être une source de carbone organique, notamment renouvelable, en particuliers des déchets organiques tels que des déchets végétaux, ce qui réduit d’autant l’impact écologique du procédé. According to another advantage, the carbon source used in this process can be a source of organic carbon, in particular renewable, in particular organic waste such as plant waste, which further reduces the ecological impact of the process.
Selon encore un autre avantage, ce procédé permet d’accéder à des GQDs présentant des caractéristiques très avantageuses, en particulier une distribution de taille très homogène, notamment monomodale, et une très bonne solubilité dans les solvants aqueux ou organiques. Par ailleurs, de façon inattendue, les inventeurs ont pu mettre en évidence que ces GQDs présentaient une fluorescence blanche à l’état solide, c’est-à-dire que lorsque l’on irradie le matériau à l’état solide, on obtient le spectre de la lumière blanche, et ce, sans qu’il soit nécessaire d’utiliser une matrice polymérique tel que le PMMA, comme diluant. Cette propriété est particulièrement avantageuse pour certaines applications telles que les dispositifs OLED, les
émetteurs de lumière blanche, les transistors organiques (OFET), les capteurs fluorescents, les capteurs optiques et le domaine de l'anticontrefaçon. According to yet another advantage, this process makes it possible to access GQDs having very advantageous characteristics, in particular a very homogeneous size distribution, in particular monomodal, and very good solubility in aqueous or organic solvents. Furthermore, unexpectedly, the inventors were able to demonstrate that these GQDs exhibited white fluorescence in the solid state, that is to say that when the material is irradiated in the solid state, we obtain the spectrum of white light, without the need to use a polymer matrix such as PMMA, as a diluent. This property is particularly advantageous for certain applications such as OLED devices, white light emitters, organic transistors (OFET), fluorescent sensors, optical sensors and the field of anti-counterfeiting.
Selon des modes de réalisation, le procédé selon l’invention comprend en outre une ou plusieurs des caractéristiques ci-après : According to embodiments, the method according to the invention further comprises one or more of the following characteristics:
- la source de carbone est une matière organique renouvelable, notamment végétale ; - the carbon source is a renewable organic material, particularly plant material;
- la matière organique végétale est constituée de déchets végétaux ;- plant organic matter is made up of plant waste;
- la source de carbone est sous forme de poudre ; - the carbon source is in powder form;
- la proportion d’eau en volume, dans le mélange eau/acide sulfurique mis en œuvre à l’étape i) varie entre 0 et 50 % du volume total ;- the proportion of water by volume in the water/sulfuric acid mixture used in step i) varies between 0 and 50% of the total volume;
- la concentration en poids de la source de carbone rapportée au volume du mélange eau/acide sulfurique mise en œuvre à l’étape i) est comprise entre 0,1 et 100 g/L, notamment entre 1 et 30 g/L ;- the concentration by weight of the carbon source relative to the volume of the water/sulfuric acid mixture used in step i) is between 0.1 and 100 g/L, in particular between 1 and 30 g/L;
- le chauffage par microonde à l’étape ii) et/ou v) est réalisé à une pression comprise entre 5 et 50 bars ; - microwave heating in step ii) and/or v) is carried out at a pressure of between 5 and 50 bars;
- l’étape iii) de récupération comprend les étapes de : - recovery step iii) includes the steps of:
- dilution du mélange réactionnel obtenu à l’étape ii) dans l’eau ;- dilution of the reaction mixture obtained in step ii) in water;
- récupération du résidu carboné obtenu, notamment par centrifugation, et élimination du surnageant ; et éventuellement- recovery of the carbonaceous residue obtained, in particular by centrifugation, and elimination of the supernatant; and eventually
- répétition des étapes de dilution et de récupération précédentes jusqu’à ce que le surnageant ait un pH neutre, notamment compris entre 6,5 et 7,5 ; - repetition of the previous dilution and recovery steps until the supernatant has a neutral pH, in particular between 6.5 and 7.5;
- la concentration du résidu carboné dans l’acide nitrique à l’étape iv) est comprise entre 1 et 40 g/L, notamment entre 5 et 25 g/L ; - the concentration of the carbon residue in the nitric acid in step iv) is between 1 and 40 g/L, in particular between 5 and 25 g/L;
- la récupération des GQDs comprend une étape d’extraction avec un solvant organique ; - the recovery of GQDs includes an extraction step with an organic solvent;
- l’étape de récupération comprend les étapes de : - the recovery stage includes the stages of:
- dilution du mélange réactionnel obtenu à l’étape v) dans l’eau ;- dilution of the reaction mixture obtained in step v) in water;
- extraction de la phase aqueuse avec un solvant organique ;- extraction of the aqueous phase with an organic solvent;
- lavage de la phase organique avec de l’eau et/ou une solution acide ; - washing the organic phase with water and/or an acid solution;
- récupération de la phase organique et élimination du solvant d’extraction, ce par quoi on obtient des GQDs. - recovery of the organic phase and elimination of the extraction solvent, whereby GQDs are obtained.
Les inventeurs ont pu caractériser les GQDs obtenus selon le procédé de l’invention selon différentes méthodes, notamment spectrophotométrie de photoélectrons induits par rayons X (XPS), et infrarouge (IR).
Ainsi, selon un deuxième aspect, l’invention concerne des quantum dots de graphène susceptibles d’être obtenus selon le procédé de l’invention. The inventors were able to characterize the GQDs obtained according to the process of the invention according to different methods, in particular spectrophotometry of photoelectrons induced by X-rays (XPS), and infrared (IR). Thus, according to a second aspect, the invention relates to graphene quantum dots capable of being obtained according to the method of the invention.
Elle concerne également les quantum dots de graphène caractérisés en ce que leur spectre obtenu par spectrométrie de photoélectrons induits par rayons X (XPS) N1s comprend les bandes énergétiques suivantes :
It also concerns graphene quantum dots characterized in that their spectrum obtained by X-ray induced photoelectron spectrometry (XPS) N1s includes the following energy bands:
Ces quantum dots sont notamment obtenus par le procédé selon l’invention. These quantum dots are notably obtained by the process according to the invention.
Selon des modes de réalisation, les quantum dots de graphène selon l’invention comprennent une ou plusieurs des caractéristiques ci-après : According to embodiments, the graphene quantum dots according to the invention comprise one or more of the following characteristics:
- leur spectre obtenu par spectrométrie de photoélectrons induits par rayons X (XPS) du C1s comprend en outre 4 bandes énergétiques comprises entre 282 et 290 eV., en particulier les bandes suivantes (en eV) : 284,6 ; 286 ; 287,4 ; et 288,8 ; - their spectrum obtained by X-ray induced photoelectron spectrometry (XPS) of C1s also includes 4 energy bands between 282 and 290 eV., in particular the following bands (in eV): 284.6; 286; 287.4; and 288.8;
- leur spectre 01 s obtenu par spectrométrie de photoélectrons induits par rayons X (XPS) comprend en outre 3 bandes énergétiques comprises entre 530 et 536 eV ; - their 01 s spectrum obtained by X-ray induced photoelectron spectrometry (XPS) also includes 3 energy bands between 530 and 536 eV;
- leur spectre infra-rouge comprend en outre les bandes d’absorption suivantes (en cm-1) : 3000 ,1695 ,1574, 1123 et 1021 ; - their infrared spectrum also includes the following absorption bands (in cm -1 ): 3000, 1695, 1574, 1123 and 1021;
- Ils présentent une distribution de taille de particules en nombre, monomodale ; - They have a monomodal particle size distribution;
- le mode en nombre est compris entre 1 et 10 nm, notamment entre 1 et 5 nm ; - the number mode is between 1 and 10 nm, in particular between 1 and 5 nm;
- la médiane D50 est comprise entre 1 et 5 nm, notamment entre 2 et 4 nm ; - the median D50 is between 1 and 5 nm, in particular between 2 and 4 nm;
- la déviation standard est comprise entre 1 et 20 %, notamment entre 6 et 12 % ; - the standard deviation is between 1 and 20%, notably between 6 and 12%;
- ils présentent une luminescence blanche à l’état solide ; - they exhibit white luminescence in the solid state;
Selon un dernier aspect, l’invention a pour objet l’utilisation des quantum dots de graphène selon l’invention, dans des dispositifs d’imagerie, de détection, optoélectroniques, de production d’énergie, de stockage
d’énergie (batteries et supercondensateurs), photocatalytiques, ainsi qu’au sein de matériaux conducteurs ou composites. According to a final aspect, the invention relates to the use of graphene quantum dots according to the invention, in imaging, detection, optoelectronic, energy production and storage devices. energy (batteries and supercapacitors), photocatalytic, as well as within conductive or composite materials.
Selon des modes de réalisation, les quantum dots de graphène selon l’invention sont utilisés dans des dispositifs de production d’énergie tels que les diodes électroluminescentes, les batteries, ou les cellules solaires. According to embodiments, the graphene quantum dots according to the invention are used in energy production devices such as light-emitting diodes, batteries, or solar cells.
Brève description des figures Brief description of the figures
La figure 1 représente le spectre XPS 01s des quantum dots de graphène selon l’invention. Figure 1 represents the XPS 01s spectrum of the graphene quantum dots according to the invention.
La figure 2 représente le spectre XPS C1s des quantum dots de graphène selon l’invention. Figure 2 represents the XPS C1s spectrum of the graphene quantum dots according to the invention.
La figure 3 représente le spectre XPS N1s des quantum dots de graphène selon l’invention. Figure 3 represents the XPS N1s spectrum of the graphene quantum dots according to the invention.
La figure 4 représente le spectre FT-IR des quantum dots de graphène selon l’invention. Figure 4 represents the FT-IR spectrum of the graphene quantum dots according to the invention.
La figure 5 représente le spectre de fluorescence des quantum dots de graphène selon l’invention dans l’eau ultrapure, en fonction de la longueur d’onde d’excitation (valeurs indiquées par une flèche) Figure 5 represents the fluorescence spectrum of graphene quantum dots according to the invention in ultrapure water, as a function of the excitation wavelength (values indicated by an arrow)
La figure 6 représente le spectre de fluorescence des quantum dots de graphène selon l’invention à l’état solide. Figure 6 represents the fluorescence spectrum of graphene quantum dots according to the invention in the solid state.
La figure 7 représente une image des GQDs selon l’invention obtenue par microscopie électronique à transmission (TEM).
détaillée Figure 7 represents an image of the GQDs according to the invention obtained by transmission electron microscopy (TEM). detailed
L’invention est maintenant décrite plus en détail et de façon non limitative dans la description qui suit. The invention is now described in more detail and in a non-limiting manner in the description which follows.
Procédé (A) de préparation des GQDs Process (A) for preparing GQDs
Selon un premier aspect, l’invention concerne un procédé de préparation de quantum dots à base de graphène (GQDs) comprenant les étapes de : i) Mise en suspension d’une source de carbone dans un mélange d’eau et d’acide sulfurique ; ii) Chauffage par microonde de la suspension obtenue à une température comprise entre 20°C et 200°C, notamment entre 100°C et 180 °C, iii) Récupération et éventuellement séchage du résidu carboné obtenu ;
iv) Mise en suspension du résidu obtenu dans de l’acide nitrique ; v) Chauffage par microonde de la suspension obtenue à une température comprise entre 20°C et 200°C, notamment entre 100°C et 180 °C, et vi) Récupération des quantum dots à base de graphène (GQDs) obtenus. According to a first aspect, the invention relates to a process for preparing quantum dots based on graphene (GQDs) comprising the steps of: i) Suspending a carbon source in a mixture of water and sulfuric acid ; ii) Microwave heating of the suspension obtained at a temperature between 20°C and 200°C, in particular between 100°C and 180°C, iii) Recovery and possibly drying of the carbonaceous residue obtained; iv) Suspending the residue obtained in nitric acid; v) Microwave heating of the suspension obtained at a temperature between 20°C and 200°C, in particular between 100°C and 180°C, and vi) Recovery of the graphene-based quantum dots (GQDs) obtained.
Au sens de la présente description, le terme « quantum dots à base de graphène », également ci-désigné « GQDs », se réfère à toute nanoparticule composée principalement d’atomes de carbone, notamment de cycles carbonés, fusionnés et aromatiques. Il désigne principalement des nanoobjets anisotropes, c’est-à-dire plans, (plus larges que hauts) et cristallisés, notamment exclusivement cristallisés. Par extension, au sens de la présente demande, ce terme inclut également les « carbon nanodots » (appelés aussi « carbon dots ») qui sont des particules carbonées sphériques qui peuvent présenter des parties cristallisées. De préférence, le terme « quantum dots à base de graphène »,ou GQDs, désigne des nanoobjets anisotropes et cristallisés. For the purposes of this description, the term “graphene-based quantum dots”, also herein referred to as “GQDs”, refers to any nanoparticle composed mainly of carbon atoms, in particular carbon, fused and aromatic rings. It mainly designates anisotropic nanoobjects, that is to say planar, (wider than tall) and crystallized, in particular exclusively crystallized. By extension, for the purposes of the present application, this term also includes “carbon nanodots” (also called “carbon dots”) which are spherical carbon particles which may have crystallized parts. Preferably, the term “graphene-based quantum dots”, or GQDs, refers to anisotropic and crystallized nanoobjects.
[Etape i)] [Step i)]
L’étape i) consiste en la mise en suspension d’une source de carbone, plus particulièrement d’une matière organique renouvelable, dans un mélange d’eau et d’acide sulfurique. Step i) consists of suspending a carbon source, more particularly a renewable organic material, in a mixture of water and sulfuric acid.
Par « matière organique renouvelable » on entend une matière provenant de la nature vivante et comprenant les matières animales et végétales, qui sont généralement produites par l’agriculture, la sylviculture ou la pêche. Elles se régénèrent sans cesse dans des cycles relativement courts (de quelques jours à quelques dizaines d’années). By “renewable organic matter” we mean material coming from living nature and including animal and plant materials, which are generally produced by agriculture, forestry or fishing. They regenerate constantly in relatively short cycles (from a few days to a few decades).
Comme exemples de matière animale, on peut citer par exemple la laine, les graisses animales... As examples of animal material, we can cite for example wool, animal fats, etc.
Comme exemples de matières végétales, on peut citer les céréales, le bois, le caoutchouc, le coton, les algues, les graisses végétale, les fruits et légumes. Examples of plant materials include cereals, wood, rubber, cotton, algae, vegetable fats, fruits and vegetables.
Au sens de l’invention, la matière végétale mise en œuvre à l’étape i) peut être une matière végétale déshydratée ou séchée. En revanche, elle n’inclut pas les charbons végétaux, c’est-à-dire les charbons obtenus notamment par pyrolyse de matière végétale. For the purposes of the invention, the plant material used in step i) may be dehydrated or dried plant material. On the other hand, it does not include plant carbons, that is to say carbons obtained in particular by pyrolysis of plant material.
De préférence, la source de carbone est une matière végétale.
Selon un mode de réalisation préféré, la matière organique végétale est constituée de déchets végétaux. Ce mode de réalisation est particulièrement avantageux puisqu’il permet de valoriser les déchets et de préparer les quantum dots de graphène à partir d’une matière première abondante, renouvelable et peu coûteuse. Preferably, the carbon source is plant material. According to a preferred embodiment, the plant organic matter consists of plant waste. This embodiment is particularly advantageous since it makes it possible to recycle waste and prepare graphene quantum dots from an abundant, renewable and inexpensive raw material.
La source de carbone peut être mise en œuvre sous la forme d’une poudre. Cela permet avantageusement d’obtenir une dispersion homogène dans le mélange eau/acide sulfurique, et donc une réactivité homogène de l’ensemble de la matière mise en jeu dans les étapes i) et ii) du procédé. La poudre de déchets végétaux peut par exemple être obtenue par séchage dans une étuve à une température comprise entre 60°C et 100°C, puis broyage. The carbon source can be used in the form of a powder. This advantageously makes it possible to obtain a homogeneous dispersion in the water/sulfuric acid mixture, and therefore a homogeneous reactivity of all of the material involved in steps i) and ii) of the process. The plant waste powder can for example be obtained by drying in an oven at a temperature between 60°C and 100°C, then grinding.
Cette source de carbone est ensuite mise en suspension dans un mélange eau/acide sulfurique (H2SO4). L’acide sulfurique est notamment de l’acide sulfurique sous forme concentré. This carbon source is then suspended in a water/sulfuric acid (H2SO4) mixture. Sulfuric acid is notably sulfuric acid in concentrated form.
La proportion d’eau en volume, dans le mélange eau/acide sulfurique mis en œuvre à l’étape i) peut varier dans une large mesure. Elle peut être notamment comprise entre 0 et 50 % du volume total du mélange. The proportion of water by volume in the water/sulfuric acid mixture used in step i) can vary to a large extent. It may in particular be between 0 and 50% of the total volume of the mixture.
La concentration en poids de la source de carbone rapportée au volume du mélange eau/acide sulfurique mise en œuvre à l’étape i) peut varier. Elle peut être notamment comprise entre 0,1 et 100 g/L, notamment entre 1 et 30 g/L. The concentration by weight of the carbon source relative to the volume of the water/sulfuric acid mixture used in step i) may vary. It may in particular be between 0.1 and 100 g/L, in particular between 1 and 30 g/L.
[Etape ii)] [Step (ii)]
L’étape ii) consiste à chauffer par microonde la suspension obtenue à l’étape i) à une température comprise entre 20°C et 200°C, notamment entre 100°C et 180°C, en particulier à environ 150°C. Ce chauffage est généralement réalisé à une pression comprise entre 1 et 10 bars, notamment entre 2 et 5 bars. Step ii) consists of heating the suspension obtained in step i) by microwave to a temperature between 20°C and 200°C, in particular between 100°C and 180°C, in particular at approximately 150°C. This heating is generally carried out at a pressure of between 1 and 10 bars, in particular between 2 and 5 bars.
Avantageusement, à une température de 150°C et une pression de 4 bars, l’étape iii) peut être réalisée en moins de 10 minutes notamment en 5 minutes. Advantageously, at a temperature of 150°C and a pressure of 4 bars, step iii) can be carried out in less than 10 minutes, in particular in 5 minutes.
Sans vouloir se limiter à une théorie particulière, les étapes i) et ii) permettraient de promouvoir des réactions de déshydratation de la matière végétale pour former un matériau charbonneux oxygéné. Without wishing to be limited to a particular theory, steps i) and ii) would make it possible to promote dehydration reactions of the plant material to form an oxygenated carbon material.
De préférence, cette étape n’est pas réalisée sous atmosphère inerte, de manière à favoriser l’incorporation d’oxygène dans le résidu carboné. Preferably, this step is not carried out under an inert atmosphere, so as to promote the incorporation of oxygen into the carbon residue.
[Etape iii)] [Step (iii)]
L’étape iii) consiste à récupérer et éventuellement laver et/ou sécher le résidu carboné obtenu à l’étape ii).
Cette étape iii), peut notamment comprendre la récupération et le lavage du résidu carboné selon les étapes de : Step iii) consists of recovering and possibly washing and/or drying the carbonaceous residue obtained in step ii). This step iii), may in particular include the recovery and washing of the carbon residue according to the steps of:
- dilution du mélange réactionnel obtenu à l’étape ii) dans l’eau ;- dilution of the reaction mixture obtained in step ii) in water;
- récupération du résidu carboné obtenu, notamment par centrifugation, et élimination du surnageant ; et éventuellement- recovery of the carbonaceous residue obtained, in particular by centrifugation, and elimination of the supernatant; and eventually
- répétition des étapes de dilution et de récupération précédentes jusqu’à ce que le surnageant ait un pH neutre, notamment compris entre 6,5 et 7,5. - repetition of the previous dilution and recovery steps until the supernatant has a neutral pH, in particular between 6.5 and 7.5.
Cette étape permet notamment de réduire, voire d’éliminer substantiellement la présence d’acide sulfurique dans le résidu carboné. This step makes it possible in particular to reduce or even substantially eliminate the presence of sulfuric acid in the carbon residue.
Le résidu carboné récupéré, et lavé peut être ensuite séché, par exemple dans une étuve à une température comprise entre 60°C et 90°C pendant plusieurs heures. The carbonaceous residue recovered and washed can then be dried, for example in an oven at a temperature between 60°C and 90°C for several hours.
[Etape iv)] [Step (iv)]
L’étape iv) consiste à traiter le résidu carboné dans l’acide nitrique. La concentration du résidu carboné dans l’acide nitrique à l’étape iv) peut être comprise entre 1 et 40 g/L, notamment entre 5 et 25 g/L. Step iv) consists of treating the carbon residue in nitric acid. The concentration of the carbon residue in the nitric acid in step iv) can be between 1 and 40 g/L, in particular between 5 and 25 g/L.
[Etape v)] [Step v)]
L’étape v) consiste à chauffer par microonde la suspension obtenue à une température comprise entre 20°C et 200°C, notamment entre 100°C et 180°C, et en particulier à environ 150°C. Cette étape est de préférence réalisée sous agitation. Step v) consists of heating the suspension obtained by microwave to a temperature between 20°C and 200°C, in particular between 100°C and 180°C, and in particular at approximately 150°C. This step is preferably carried out with stirring.
Le chauffage par microonde à l’étape v) peut être réalisé par à une pression comprise entre 5 et 60 bars, notamment entre 10 et 40 bars. Heating by microwave in step v) can be carried out at a pressure of between 5 and 60 bars, in particular between 10 and 40 bars.
Avantageusement, à une température de 150°C et une pression de 35 bars, l’étape v) peut être réalisée en moins de 10 minutes notamment en 5 minutes. Advantageously, at a temperature of 150°C and a pressure of 35 bars, step v) can be carried out in less than 10 minutes, particularly in 5 minutes.
Le taux de conversion du résidu carboné mis en œuvre à l’étape v) en quantum dots de graphène à l’issue de l’étape v) est généralement de 100% L’avancement de la réaction de conversion peut être aisément suivi : au début de la réaction à l’étape v), le résidu carboné n’est pas soluble dans le milieu réactionnel et devient soluble au fur et à mesure de sa conversion. La réaction est généralement terminée lorsque le résidu carboné initial a totalement disparu, c’est-à-dire est totalement solubilisé sous la forme de GQDs. The conversion rate of the carbon residue used in step v) into quantum dots of graphene at the end of step v) is generally 100%. The progress of the conversion reaction can be easily followed: start of the reaction in step v), the carbon residue is not soluble in the reaction medium and becomes soluble as it is converted. The reaction is generally completed when the initial carbon residue has completely disappeared, i.e. is completely solubilized in the form of GQDs.
Sans vouloir se limiter à une théorie particulière, les étapes iv) et v) permettraient de couper chimiquement des liaisons chimiques fragiles afin de conduire à la formation de fragments fonctionnalisés, appelés GQDs. Without wishing to be limited to a particular theory, steps iv) and v) would make it possible to chemically cut fragile chemical bonds in order to lead to the formation of functionalized fragments, called GQDs.
[Etape vi)]
L’étape vi) consiste en la récupération des quantum dots à base de graphène (GQDs) obtenus à l’étape iv). [Step vi)] Step vi) consists of the recovery of graphene-based quantum dots (GQDs) obtained in step iv).
Cette étape peut être réalisée selon des méthodes conventionnelles telles que par chromatographie, extraction, dialyse et/ou ultracentrifugation. This step can be carried out using conventional methods such as chromatography, extraction, dialysis and/or ultracentrifugation.
De préférence, cette étape est réalisée par extraction du milieu réactionnel avec un solvant organique, en particulier un solvant organique polaire, notamment polaire protique, tel qu’un alcool, plus particulièrement un alcool aliphatique. Preferably, this step is carried out by extracting the reaction medium with an organic solvent, in particular a polar organic solvent, in particular a polar protic solvent, such as an alcohol, more particularly an aliphatic alcohol.
De façon avantageuse, les quantum dots de graphène sont récupérés dans la phase organique qui peut être lavée et concentrée sous pression réduite. Le résidu obtenu peut être séché sous vide, à une température de l’ordre de 80°C, typiquement pendant 2 heures. Advantageously, the graphene quantum dots are recovered in the organic phase which can be washed and concentrated under reduced pressure. The residue obtained can be dried under vacuum, at a temperature of around 80°C, typically for 2 hours.
Avantageusement, le procédé de l’invention permet d’obtenir des quantum dots de graphène avec de bons rendements, notamment compris entre 15 et 70%, en particulier entre 20 et 60%, ce rendement étant calculé en faisant le ratio entre la masse de GQDs récupérés et la masse de matière hydrocarbonée mise en œuvre à l’étape i). Advantageously, the process of the invention makes it possible to obtain quantum dots of graphene with good yields, in particular between 15 and 70%, in particular between 20 and 60%, this yield being calculated by making the ratio between the mass of GQDs recovered and the mass of hydrocarbon material used in step i).
GQDs GQDs
Selon un deuxième aspect, l’invention concerne des quantum dots de graphène susceptibles d’être obtenus selon le procédé tel que défini ci- dessus. According to a second aspect, the invention relates to graphene quantum dots capable of being obtained according to the process as defined above.
Selon un troisième aspect, l’invention a pour objet des quantum dots de graphène caractérisés en ce que leur spectre obtenu par spectrométrie de photoélectrons induits par rayons X (XPS) N1 s comprend les bandes énergétiques suivantes :
According to a third aspect, the subject of the invention is graphene quantum dots characterized in that their spectrum obtained by X-ray induced photoelectron spectrometry (XPS) N1 s comprises the following energy bands:
Dans le cadre de la présente invention on entend par intensité relative la valeur de l’aire sous la courbe de l’une des bandes par rapport à la somme de l’aire sous la courbe des deux bandes.
Plus particulièrement, le spectre N1 s des quantum dots selon l’invention, obtenu par spectrométrie de photoélectrons induits par rayons X (XPS), comprend deux bandes énergétiques : In the context of the present invention, relative intensity is understood to mean the value of the area under the curve of one of the bands relative to the sum of the area under the curve of the two bands. More particularly, the N1 s spectrum of the quantum dots according to the invention, obtained by X-ray induced photoelectron spectrometry (XPS), comprises two energy bands:
- l’une étant caractérisée par une énergie de liaison comprise entre 400 eV et 403 eV, et une intensité relative comprise entre 30% et 60%, et - one being characterized by a binding energy of between 400 eV and 403 eV, and a relative intensity of between 30% and 60%, and
- l’autre étant caractérisée par une énergie de liaison comprise entre 404 eV et 406 eV, et une intensité relative comprise entre 40% et 70%. - the other being characterized by a binding energy of between 404 eV and 406 eV, and a relative intensity of between 40% and 70%.
De préférence, la somme des intensités relatives de ces deux bandes énergétiques est égale à 100%. Preferably, the sum of the relative intensities of these two energy bands is equal to 100%.
La spectrométrie de photoélectrons induits par rayons X (XPS) peut être réalisée avec un spectromètre Kratos Axis Ultra (Kratos Analytical, U.K.) notamment équipé avec une source monochromatique Al Ka source (1486,6 eV). Les spectres sont notamment enregistrés à un angle de site de 90° sur une aire 0,7 x 0,3 mm. Les spectres de haute résolution sont notamment mesurés avec un pas de 0,1 eV. X-ray induced photoelectron spectrometry (XPS) can be carried out with a Kratos Axis Ultra spectrometer (Kratos Analytical, U.K.) notably equipped with a monochromatic Al Ka source (1486.6 eV). The spectra are notably recorded at an elevation angle of 90° over an area 0.7 x 0.3 mm. The high resolution spectra are notably measured with a step of 0.1 eV.
Le spectre XPS N1 s des quantum dots de graphène selon l’invention peut comprendre les bandes énergétiques suivantes (eV) : 401 ,5 et 405, 8. The XPS N1 s spectrum of the graphene quantum dots according to the invention can include the following energy bands (eV): 401.5 and 405.8.
Plus particulièrement, le spectre XPS N1 s des quantum dots de graphène selon l’invention peut comprendre les deux bandes énergétiques suivantes :
More particularly, the XPS N1 s spectrum of the graphene quantum dots according to the invention can comprise the following two energy bands:
Ainsi, le spectre N1 s des quantum dots selon l’invention, obtenu par spectrométrie de photoélectrons induits par rayons X (XPS), comprend deux bandes énergétiques : Thus, the N1 s spectrum of the quantum dots according to the invention, obtained by X-ray induced photoelectron spectrometry (XPS), comprises two energy bands:
- l’une étant caractérisée par une énergie de liaison comprise de 401 ,5 eV, et une intensité relative de 55,4%, et - one being characterized by a binding energy of 401.5 eV, and a relative intensity of 55.4%, and
- l’autre étant caractérisée par une énergie de liaison de 405,8 eV, et une intensité relative de 44,6%. - the other being characterized by a binding energy of 405.8 eV, and a relative intensity of 44.6%.
Les quantum dots de graphène selon l’invention peuvent se caractériser en outre en ce que leur spectre obtenu par spectrométrie de photoélectrons induits par rayons X (XPS) du C1 s comprend 4 bandes énergétiques comprises dont les énergies de liaison sont comprises entre 282 et 290 eV.
En particulier, les quantum dots de graphène selon l’invention peuvent se caractériser en outre par un spectre XPS du C1 s comprenant les bandes énergétiques caractérisées par les énergies de liaison suivantes (en eV) : 284,6 ; 286 ; 287,4 ; et 288,8. The graphene quantum dots according to the invention can be further characterized in that their spectrum obtained by X-ray induced photoelectron spectrometry (XPS) of C1 s comprises 4 energy bands whose binding energies are between 282 and 290 eV. In particular, the graphene quantum dots according to the invention can be further characterized by an XPS spectrum of C1 s comprising the energy bands characterized by the following binding energies (in eV): 284.6; 286; 287.4; and 288.8.
Ce spectre est notamment mesuré avec un spectromètre Kratos Axis Ultra (Kratos Analytical, U.K.), notamment équipé avec une source monochromatique Al Ka source (1486,6 eV). Les spectres sont notamment enregistrés à un angle de site de 90° sur une aire 0,7 x 0,3 mm. Les spectres de haute résolution sont notamment mesurés avec un pas de 0,1 eV. This spectrum is notably measured with a Kratos Axis Ultra spectrometer (Kratos Analytical, U.K.), notably equipped with a monochromatic Al Ka source (1486.6 eV). The spectra are notably recorded at an elevation angle of 90° over an area 0.7 x 0.3 mm. The high resolution spectra are notably measured with a step of 0.1 eV.
Plus spécifiquement, les quantum dots de graphène selon l’invention peuvent se caractériser en outre par un spectre XPS du C1 s comprenant les bandes énergétiques suivantes :
More specifically, the graphene quantum dots according to the invention can be further characterized by an XPS spectrum of C1 s comprising the following energy bands:
Ces bandes peuvent être mesurées avec un spectromètre Kratos Axis Ultra (Kratos Analytical, U.K.), notamment équipé avec une source monochromatique Al Ka source (1486,6 eV). Les spectres sont notamment enregistrés à un angle de site de 90° sur une aire 0,7 x 0,3 mm. Les spectres de haute résolution sont notamment mesurés avec un pas de 0,1 eV. These bands can be measured with a Kratos Axis Ultra spectrometer (Kratos Analytical, U.K.), notably equipped with a monochromatic Al Ka source (1486.6 eV). The spectra are notably recorded at an elevation angle of 90° over an area 0.7 x 0.3 mm. The high resolution spectra are notably measured with a step of 0.1 eV.
Les quantum dots de graphène selon l’invention peuvent se caractériser en outre en ce que leur spectre O1 s obtenu par spectrométrie de photoélectrons induits par rayons X (XPS) comprend 3 bandes énergétiques dont les énergies de liaison sont comprises entre 530 et 536 eV. The graphene quantum dots according to the invention can be further characterized in that their O1 s spectrum obtained by X-ray induced photoelectron spectrometry (XPS) comprises 3 energy bands whose binding energies are between 530 and 536 eV.
Plus particulièrement, les quantum dots de graphène selon l’invention peuvent se caractériser en outre en ce que leur spectre XPS O1 s comprend les bandes énergétiques suivantes (en eV) :
More particularly, the graphene quantum dots according to the invention can be further characterized in that their XPS O1 s spectrum comprises the following energy bands (in eV):
Ces bandes peuvent être mesurées avec un spectromètre Kratos Axis Ultra (Kratos Analytical, U.K.), notamment équipé avec une source
monochromatique Al Ka source (1486,6 eV). Les spectres sont notamment enregistrés à un angle de site de 90° sur une aire 0,7 x 0,3 mm. Les spectres de haute résolution sont notamment mesurés avec un pas de 0,1 eV. These bands can be measured with a Kratos Axis Ultra spectrometer (Kratos Analytical, UK), in particular equipped with a source monochromatic Al Ka source (1486.6 eV). The spectra are notably recorded at an elevation angle of 90° over an area 0.7 x 0.3 mm. The high resolution spectra are notably measured with a step of 0.1 eV.
Les quantum dots selon l’invention peuvent se caractériser en outre en ce que leur spectre infra-rouge comprend les bandes d’absorption suivantes (en cm’1) : 3000 (bande large COOH), 1695 (bande C=O), 1574, en particulier les bandes 3000, 1695, 1574, 1123 et 1021 . The quantum dots according to the invention can be further characterized in that their infrared spectrum comprises the following absorption bands (in cm' 1 ): 3000 (COOH wide band), 1695 (C=O band), 1574 , in particular bands 3000, 1695, 1574, 1123 and 1021.
Les quantum dots de graphène selon l’invention peuvent se caractériser en ce qu’ils présentent : The graphene quantum dots according to the invention can be characterized in that they present:
- Un spectre XPS N1 s comprenant les bandes énergétiques suivantes (en eV) : 401 ,5 et 405, 8 ; et - An XPS N1 s spectrum including the following energy bands (in eV): 401.5 and 405.8; And
- Un spectre infra-rouge comprenant les bandes d’absorption suivantes (en cm’1) : 3000 ; 1695 ;1574 ;1123 et 1021 . - An infrared spectrum including the following absorption bands (in cm' 1 ): 3000; 1695;1574;1123 and 1021.
Par ailleurs, les quantum dots selon l’invention peuvent se caractériser en ce qu’ils présentent une distribution de taille de particules en nombre, monomodale. Furthermore, the quantum dots according to the invention can be characterized in that they have a monomodal particle size distribution in number.
La répartition granulométrique des quantum dots de graphène peut être mesurée en nombre via la méthode de diffusion dynamique de la lumière (DLS en anglais) sur un appareillage VASCO KIN (Cordouan Technologies, Pessac, France). Les mesures ont été réalisées sur des suspensions fraîchement préparées dans l’eau ultrapure à 25°C et en triplicata. Les données ont été analysées par le logiciel Data Nano Kin® en mode de détermination multimodale en nombre. The particle size distribution of graphene quantum dots can be measured in number using the dynamic light scattering (DLS) method on VASCO KIN equipment (Cordouan Technologies, Pessac, France). The measurements were carried out on suspensions freshly prepared in ultrapure water at 25°C and in triplicate. The data were analyzed by Data Nano Kin® software in multimodal number determination mode.
En particulier, le mode en nombre peut être compris entre 1 et 10 nm, notamment entre 1 et 5 nm. In particular, the number mode can be between 1 and 10 nm, in particular between 1 and 5 nm.
La médiane D50 en nombre peut être comprise entre 1 et 5 nm, notamment entre 2 et 4 nm. The median D50 in number can be between 1 and 5 nm, in particular between 2 and 4 nm.
La déviation standard peut être comprise entre 1 et 20 %, notamment entre 6 et 12 %. The standard deviation can be between 1 and 20%, especially between 6 and 12%.
De façon très avantageuse, les quantum dots de graphène selon l’invention peuvent se caractériser en ce qu’ils présentent une luminescence blanche à l’état solide. Very advantageously, the graphene quantum dots according to the invention can be characterized in that they exhibit white luminescence in the solid state.
Les quantum dots de graphène selon l’invention peuvent se caractériser en outre en ce qu’ils présentent une luminescence dans l’eau. Plus particulièrement, cette luminescence se caractérise en ce que la longueur d’onde d’émission varie en fonction de la longueur d’onde d’excitation. Plus particulièrement, pour une longueur d’onde d’excitation variant de 300 nm à
420 nm, la longueur d’onde d’émission des GQDs selon l’invention varie de 430 nm à 510 nm. The graphene quantum dots according to the invention can be further characterized in that they exhibit luminescence in water. More particularly, this luminescence is characterized in that the emission wavelength varies as a function of the excitation wavelength. More particularly, for an excitation wavelength varying from 300 nm to 420 nm, the emission wavelength of the GQDs according to the invention varies from 430 nm to 510 nm.
Par ailleurs, les GQDs se caractérisent par une solubilité élevée, de plus de 500 g/L dans les alcools aliphatiques, dont notamment l’éthanol. Cette solubilité est particulièrement avantageuse dans le domaine de la formulation d’encres, en particulier pour l’impression jet d’encres, qui sont généralement composées d’un solvant alcool aliphatique. Les GQDs selon l’invention peuvent donc être avantageusement incorporés dans des encres, utilisées dans le domaine de l’électronique notamment. Furthermore, GQDs are characterized by a high solubility, of more than 500 g/L in aliphatic alcohols, including ethanol in particular. This solubility is particularly advantageous in the field of ink formulation, particularly for inkjet printing, which are generally composed of an aliphatic alcohol solvent. The GQDs according to the invention can therefore be advantageously incorporated into inks, used in the field of electronics in particular.
En outre, les GQDs se caractérisent par une solubilité intéressante, de 10g/L dans l’eau, ce qui permet leur utilisation dans le domaine de la biologie, notamment dans le domaine de l’imagerie, ou du diagnostic. In addition, GQDs are characterized by an interesting solubility of 10g/L in water, which allows their use in the field of biology, particularly in the field of imaging, or diagnosis.
Utilisation des GQDs Use of GQDs
Selon un quatrième aspect, l’invention concerne l’utilisation des quantum dots de graphène selon l’invention, dans des dispositifs d’imagerie, de détection, optoélectroniques, de production d’énergie, de stockage d’énergie, notamment batteries et/ou supercondensateurs, photocatalytiques, ainsi qu’au sein de matériaux conducteurs ou composites. According to a fourth aspect, the invention relates to the use of graphene quantum dots according to the invention, in imaging, detection, optoelectronic, energy production, energy storage devices, in particular batteries and/or or supercapacitors, photocatalytic, as well as within conductive or composite materials.
Les quantum dots de graphène selon l’invention peuvent être utilisés dans des dispositifs de production d’énergie tels que les diodes électroluminescentes, les batteries, ou les cellules solaires. The graphene quantum dots according to the invention can be used in energy production devices such as light-emitting diodes, batteries, or solar cells.
Procédé (B) de préparation des GQDs Process (B) for preparing GQDs
Selon encore un autre aspect, l’invention concerne un procédé de préparation de quantum dots de graphène (GQDs) comprenant les étapes de : a. Mise en suspension d’une source de carbone dans de l’acide nitrique, la source de carbone étant choisie parmi le charbon, le coke de charbon, le biochar, l'asphalte et les mélanges de ceux-ci ; b. Chauffage par microonde de la suspension obtenue à une température comprise entre 20°C et 200°C, notamment entre 100°C et 180 °C, à une pression comprise entre 5 et 50 bars ; et c. Récupération des quantum dots à base de graphène (GQDs) obtenus.
La source de carbone mise en œuvre à l’étape a) peut être préparée selon les étapes i) à ill) du procédé (A), telles que définies ci-dessus. According to yet another aspect, the invention relates to a method for preparing graphene quantum dots (GQDs) comprising the steps of: a. Suspending a carbon source in nitric acid, the carbon source being chosen from coal, coal coke, biochar, asphalt and mixtures thereof; b. Microwave heating of the suspension obtained at a temperature between 20°C and 200°C, in particular between 100°C and 180°C, at a pressure between 5 and 50 bars; etc. Recovery of the graphene-based quantum dots (GQDs) obtained. The carbon source used in step a) can be prepared according to steps i) to ill) of process (A), as defined above.
Par ailleurs, les étapes a), b) et c) sont identiques aux étapes iv), v) et vi) respectivement, définies ci-dessus. Furthermore, steps a), b) and c) are identical to steps iv), v) and vi) respectively, defined above.
Exemples Examples
Matériels et méthodes Materials and methods
Tous les produits chimiques utilisés (réactifs et solvants) dans la méthode sont de qualité "réactif et sont utilisés directement. L’eau utilisée est de l’eau ultrapure, c’est-à-dire avec une résistivité de 18,2 mQ.cm at 25°C. L’étape 1 de la synthèse est réalisée dans un réacteur micro-ondes Masterwave BTR de la marque Anton Paar. L’étape 2 de la synthèse est réalisée dans un réacteur micro-ondes Multiwave 5000 de la marque Anton Paar. Les spectres FT-IR sont réalisés sur un appareil Nicolet iS5. Les spectres XPS sont réalisés sur un appareil Kratos Axis Ultra (Kratos Analytical, U.K.). La taille des particules de GQDs a été déterminée par diffusion dynamique de la lumière sur un appareil VASCO KIN de la marque Cordouan Technologies. Toutes les mesures ont été réalisées sur des suspensions fraîchement préparées dans de l’eau ultrapure, à 25°C et en triplica. Les données ont été analysées en utilisant le logiciel Nano Kin en utilisant une distribution multimodale en nombre et exprimées sous la forme d’une moyenne (± la déviation standard). Les analyses par microscopie électronique à transmission ont été réalisées sur un appareil JEM - ARM 200F Cold FEG TEM/STEM fonctionnant à 200 kV. Les grilles ont été préparées en déposant une goutte de solution de GQDs (1 mg/mL dans l’eau) sur une grille de cuivre recouverte de carbone pendant 4 minutes. La goutte a ensuite été retirée avec un papier buvard, la grille a ensuite été séchée à 80°C pendant 20 minutes. Les spectres UV-vis ont été mesurés sur un spectrophotomètre Cary® de la marque Varian. Les spectres d’émission de fluorescence ont été mesurés sur un spectrofluorimètre FluoroMax-3 de marque Horiba Jobin Yvon à 25°C. Les analyses XPS ont été réalisées avec une source Al monochromatisée Ka. All chemicals used (reagents and solvents) in the method are of reagent grade and are used directly. The water used is ultrapure water, that is, with a resistivity of 18.2 mΩ. cm at 25°C. Step 1 of the synthesis is carried out in a Masterwave BTR microwave reactor from the Anton Paar brand. Step 2 of the synthesis is carried out in a Multiwave 5000 microwave reactor from the Anton brand Paar. The FT-IR spectra are carried out on a Nicolet iS5 instrument. The VASCO KIN device from the Cordouan Technologies brand. All measurements were carried out on suspensions freshly prepared in ultrapure water, at 25°C and in triplicate. The data were analyzed using the Nano Kin software using a distribution multimodal in number and expressed as an average (± the standard deviation). The transmission electron microscopy analyzes were carried out on a JEM - ARM 200F Cold FEG TEM/STEM device operating at 200 kV. The grids were prepared by depositing a drop of GQDs solution (1 mg/mL in water) on a carbon-coated copper grid for 4 minutes. The drop was then removed with blotting paper, the grid was then dried at 80°C for 20 minutes. The UV-vis spectra were measured on a Cary® spectrophotometer from Varian. The fluorescence emission spectra were measured on a Horiba Jobin Yvon brand FluoroMax-3 spectrofluorometer at 25°C. XPS analyzes were carried out with a Ka monochromatized Al source.
Protocole expérimental Experimental protocol
Etape 0: Les peaux de bananes sont séchées à l’étuve à 75°C pendantStep 0: The banana skins are dried in an oven at 75°C for
48h puis broyées.
Etape i) à iii): 5g de de matière organique sèche est traitée dans le micro-onde monowave BTR avec 160 mL H2SO4 et 40 ml d’FW dans un tube téflon de 1 L à 150°C pendant 5’. Dilution dans l’eau (700 mL), centrifugé et lavé avec de l’eau. Séchage du résidu une nuit à 75°C. Obtention de 4,6g (92%) 48 hours then crushed. Step i) to iii): 5g of dry organic matter is treated in the BTR monowave microwave with 160 mL H2SO4 and 40 ml of FW in a 1 L Teflon tube at 150°C for 5'. Diluted in water (700 mL), centrifuged and washed with water. Drying of the residue overnight at 75°C. Obtaining 4.6g (92%)
Etape iv) à vi): 3,2 g de charbon (obtenu à l’étape 1 ) sont répartis dans 8 tubes et sont traités par HNO3 conc. (40 mL/par tube) dans le micro-onde Multiwave à 150°C pendant 5’. Le milieu réactionnel est dilué dans l’eau (1 ,5 L). Le milieu aqueux est extrait avec un alcool aliphatique (2 x 800 mL). Les phases organiques sont lavées avec de l’eau (2 x 400 mL) puis avec HCl 1 M (3 x 600 mL). La phase organique est ensuite concentrée sous pression réduite. Le résidu est séché sous vide à 80°C pendant 2h. Le rendement final est de 22% On obtient 700 mg de GQDs (22%) Step iv) to vi): 3.2 g of coal (obtained in step 1) are distributed in 8 tubes and are treated with HNO3 conc. (40 mL/per tube) in the Multiwave microwave at 150°C for 5’. The reaction medium is diluted in water (1.5 L). The aqueous medium is extracted with an aliphatic alcohol (2 x 800 mL). The organic phases are washed with water (2 x 400 mL) then with 1 M HCl (3 x 600 mL). The organic phase is then concentrated under reduced pressure. The residue is dried under vacuum at 80°C for 2 hours. The final yield is 22%. We obtain 700 mg of GQDs (22%).
Les GQDs obtenus ont été caractérisés par spectrométrie de photoélectrons induits par rayons X (XPS) N1 s, O1 s et C1 s, FT-IR et spectrofluorométrie. The obtained GQDs were characterized by N1 s, O1 s and C1 s X-ray induced photoelectron spectroscopy (XPS), FT-IR and spectrofluorometry.
Le même protocole a été mis en œuvre à partir de noyaux d’olives, de peaux d’oranges et de glands de chêne. Les GQDs obtenus ont été caractérisés par spectrométrie de photoélectrons induits par rayons X (XPS) N1s, O1 s et C1s, FT-IR et spectrofluorométrie. Les spectres obtenus sont similaires à ceux obtenus avec les peaux de bananes.
The same protocol was implemented using olive pits, orange peels and oak acorns. The obtained GQDs were characterized by N1s, O1s and C1s X-ray induced photoelectron spectroscopy (XPS), FT-IR and spectrofluorometry. The spectra obtained are similar to those obtained with banana peels.
Claims
1. Procédé de préparation de quantum dots de graphène (GQDs) comprenant les étapes de : i) Mise en suspension d’une source de carbone dans un mélange d’eau et d’acide sulfurique, ladite source de carbone étant une matière organique renouvelable ; ii) Chauffage par microonde de la suspension obtenue à une température comprise entre 20°C et 200°C, notamment entre 100°C et 180 °C, iii) Récupération et éventuellement lavage et/ou séchage du résidu carboné obtenu ; iv) Mise en suspension du résidu obtenu dans de l’acide nitrique ; v) Chauffage par microonde de la suspension obtenue à une température comprise entre 20°C et 200°C, notamment entre 100°C et 180 °C, et vi) Récupération des quantum dots à base de graphène (GQDs) obtenus. 1. Process for preparing graphene quantum dots (GQDs) comprising the steps of: i) Suspending a carbon source in a mixture of water and sulfuric acid, said carbon source being a renewable organic material ; ii) Microwave heating of the suspension obtained at a temperature between 20°C and 200°C, in particular between 100°C and 180°C, iii) Recovery and possibly washing and/or drying of the carbonaceous residue obtained; iv) Suspending the residue obtained in nitric acid; v) Microwave heating of the suspension obtained at a temperature between 20°C and 200°C, in particular between 100°C and 180°C, and vi) Recovery of the graphene-based quantum dots (GQDs) obtained.
2. Procédé selon la revendication 1 , dans lequel la source de carbone est une matière organique renouvelable végétale. 2. Method according to claim 1, wherein the carbon source is a renewable organic plant material.
3. Procédé selon l’une quelconque des revendications précédentes, dans lequel le chauffage par microonde à l’étape ii) et/ou v) est réalisé à une pression comprise entre 5 et 50 bars. 3. Method according to any one of the preceding claims, in which the microwave heating in step ii) and/or v) is carried out at a pressure of between 5 and 50 bars.
4. Procédé selon l’une quelconque des revendications précédentes, dans lequel la concentration du résidu carboné dans l’acide nitrique à l’étape iv) est comprise entre 1 et 40 g/L, notamment entre 5 et 25 g/L. 4. Method according to any one of the preceding claims, in which the concentration of the carbon residue in the nitric acid in step iv) is between 1 and 40 g/L, in particular between 5 and 25 g/L.
5. Quantum dots de graphène susceptibles d’être obtenus selon le procédé tel que défini selon l’une quelconque des revendications 1 à 4.
5. Quantum dots of graphene capable of being obtained according to the process as defined according to any one of claims 1 to 4.
6. Quantum dots de graphène caractérisés en ce que leur spectre obtenu par spectrométrie de photoélectrons induits par rayons X (XPS) N1 s comprend les bandes énergétiques suivantes :
6. Quantum dots of graphene characterized in that their spectrum obtained by X-ray induced photoelectron spectrometry (XPS) N1 s includes the following energy bands:
7. Quantum dots selon la revendication 6, caractérisés en outre en ce que leur spectre obtenu par spectrométrie de photoélectrons induits par rayons X (XPS) du C1 s comprend 4 bandes énergétiques comprises entre 282 et 290 eV., en particulier les bandes suivantes (en eV) : 284,6 ; 286 ; 287,4 ; et 288,8. 7. Quantum dots according to claim 6, further characterized in that their spectrum obtained by X-ray induced photoelectron spectrometry (XPS) of C1 s comprises 4 energy bands between 282 and 290 eV., in particular the following bands ( in eV): 284.6; 286; 287.4; and 288.8.
8. Quantum dots selon la revendication 6 ou 7, caractérisés en outre en ce que leur spectre O1 s obtenu par spectrométrie de photoélectrons induits par rayons X (XPS) comprend 3 bandes énergétiques comprises entre 530 et 536 eV. 8. Quantum dots according to claim 6 or 7, further characterized in that their O1 s spectrum obtained by X-ray induced photoelectron spectrometry (XPS) comprises 3 energy bands between 530 and 536 eV.
9. Quantum dots selon la revendication 6 à 8, caractérisés en ce que leur spectre infra-rouge comprend les bandes d’absorption suivantes (en cm-1) : 3000 ,1695 ,1574, 1123 et 1021 . 9. Quantum dots according to claim 6 to 8, characterized in that their infrared spectrum comprises the following absorption bands (in cm -1 ): 3000, 1695, 1574, 1123 and 1021.
10. Quantum dots selon l’une quelconque des revendications 6 à 9, caractérisés en ce qu’ils présentent une distribution de taille de particules en nombre, monomodale. 10. Quantum dots according to any one of claims 6 to 9, characterized in that they have a monomodal particle size distribution in number.
11. Quantum dots selon la revendication 10, caractérisés en ce que le mode en nombre est compris entre 1 et 10 nm, notamment entre 1 et 5 nm. 11. Quantum dots according to claim 10, characterized in that the number mode is between 1 and 10 nm, in particular between 1 and 5 nm.
12. Quantum dots selon l’une quelconque des revendications 10 et 11 , caractérisés en ce que la médiane D50 est comprise entre 1 et 5 nm, notamment entre 2 et 4 nm. 12. Quantum dots according to any one of claims 10 and 11, characterized in that the median D50 is between 1 and 5 nm, in particular between 2 and 4 nm.
13. Quantum dots selon l’une quelconque des revendications 6 à 12, caractérisés en ce qu’ils présentent une luminescence blanche à l’état solide
13. Quantum dots according to any one of claims 6 to 12, characterized in that they exhibit white luminescence in the solid state
14. Utilisation des quantum dots de graphène selon l’une quelconque des revendications 6 à 13, dans des dispositifs d’imagerie, de détection, optoélectroniques, de production d’énergie, de stockage d’énergie, notamment des batteries et/ou supercondensateurs, photocatalytiques, ainsi qu’au sein de matériaux conducteurs ou composites. 14. Use of graphene quantum dots according to any one of claims 6 to 13, in imaging, detection, optoelectronic, energy production, energy storage devices, in particular batteries and/or supercapacitors , photocatalytic, as well as within conductive or composite materials.
15. Utilisation selon la revendication 14, dans des dispositifs de production d’énergie tels que les diodes électroluminescentes, les batteries, ou les cellules solaires.
15. Use according to claim 14, in energy production devices such as light-emitting diodes, batteries, or solar cells.
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| CN108455578A (en) * | 2018-03-17 | 2018-08-28 | 宁夏大学 | Graphene quantum dot and preparation method and application |
| CN111634905A (en) * | 2020-05-19 | 2020-09-08 | 湖南科技学院 | Method for preparing graphene quantum dots under coupling effect of magnetic field and ultrasonic field |
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| CN105502340A (en) * | 2015-12-30 | 2016-04-20 | 哈尔滨工业大学 | Preparation method of fluorescent carbon dots |
| CN108455578A (en) * | 2018-03-17 | 2018-08-28 | 宁夏大学 | Graphene quantum dot and preparation method and application |
| CN111634905A (en) * | 2020-05-19 | 2020-09-08 | 湖南科技学院 | Method for preparing graphene quantum dots under coupling effect of magnetic field and ultrasonic field |
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| ATCHUDAN RAJI ET AL: "Sustainable synthesis of carbon quantum dots from banana peel waste using hydrothermal process for in vivo bioimaging", PHYSICA E: LOW-DIMENSIONAL SYSTEMS AND NANOSTRUCTURES, ELSEVIER SCIENCE BV, NL, vol. 126, 6 September 2020 (2020-09-06), XP086378991, ISSN: 1386-9477, [retrieved on 20200906], DOI: 10.1016/J.PHYSE.2020.114417 * |
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