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    • 专利摘要:
    The present invention recommends a process for obtaining monolayer carboxylated graphene oxide, without ordered stacking, which presents a selective functionalization of oxygenated groups through a consecutive oxidation-exfoliation-oxidation process. In this way, the graphene oxide obtained presents a laminar structure functionalized with selectively oxygenated groups, which allows greater chemical interaction and compatibility with the polar groups of a polymeric matrix and a fiber. The monolayer carboxylated graphene oxide obtained by means of the described procedure is also an object of the present invention, which has a high application in the field of nanocomposites as it allows compatibilization with a greater number of polymeric matrices. (Machine-translation by Google Translate, not legally binding)
    公开号:ES2787504A1
    申请号:ES202030813
    申请日:2020-07-30
    公开日:2020-10-16
    发明作者:Pastor Iluminada Rodríguez
    申请人:Applynano Solutions S L；
    IPC主号:
    专利说明:

    [0004] TECHNICAL SECTOR
    [0006] The present invention relates to a process for the synthesis of graphene oxide with specific properties for its use, among other uses, as a reinforcing material in composite materials of polymeric matrices and for the formation of membranes. Specifically, the graphene oxide obtained is monolayer, so that each of the layers is functionalized with selective oxygen groups by the oxidation process carried out on previously exfoliated monolayers, and not on stacked layers, unlike the usual processes of synthesis of graphene oxide.
    [0008] The object of the invention is to make it possible to obtain an exfoliated graphene oxide with a size and degree of functionalization that can be adjusted to the needs of the application and the matrix where it is going to be incorporated, the membrane that is going to form, or simply be joined. through functionalization with any other entity.
    [0010] Advantageously, the graphene oxide obtained by the process of the present invention has suitable surface properties to achieve an adequate dispersion in polymeric matrices, together with a greater control of the dimensions and number of layers of the graphene oxide.
    [0012] BACKGROUND OF THE INVENTION
    [0014] Graphene oxide is obtained by exfoliation of an intermediate product called graphite oxide, which comes from an intercalation compound of materials with a graphite structure, mainly graphite with acids and oxysalts, which is unstable and decomposes into graphite oxide. Thus, a large number of functional groups are formed between the graphitic stacked planes, adding water sandwiched between the oxygenated layers to produce the separation between the layers that in graphite have a separation of 0.34 nm and in graphite oxide have a separation of 0.9 nm as disclosed in the JEONG, HK et al. Evidence of graphitic AB stacking order of graphite oxides, J. Am. Chem. Soc. 130 (2008) 1362-1366. ISSN 0002-7863. This separation in the Graphite oxide layers allow its exfoliation more easily through both solution and thermal processes, with a high content of monolayers.
    [0016] Among the known synthesis methods for graphene oxide, the Hummers and Offeman method is the chemical exfoliation method that allows obtaining a high degree of intercalation and oxidation between the layers of the prepared graphite oxide, obtaining a graphene oxide with a higher proportion of monolayers, as disclosed in the publication of BOTAS, C. et al. Graphene materials with different structures prepared from the same graphite by the Hummers and Brodie methods. Carbon 65 (2013) 156-164. ISSN 0008-6223.
    [0018] In this sense, modifications of the Hummers and Offeman method are known. The international patent application PCT no. WO2010042912 which discloses a method for preparing graphite oxide in which a potassium permanganate salt is used in a solution of sodium nitrate and sulfuric acid in water at temperatures up to 100 ° C. By means of said invention, graphene oxide sheets are obtained by exfoliation. Additionally, graphite oxide can be chemically reduced by hydrazine, hydroquinone, plasma, etc. However, the aforementioned patent application does not disclose data on the type and properties of the synthesized graphene oxide.
    [0020] Additionally, the international patent application PCT no. WO2011016889 discloses a method for the production of highly oxidized graphene oxide of high structural quality, with a proportion of rings and aromatic domains higher than that presented by graphene oxide, where the presence of at least one protective agent is added. They are based on the Hummers-Offeman method using potassium permanganate as oxidant, sulfuric acid reaction medium, and different non-aqueous weak acids (eg phosphoric acid and its related, trifluoroacetic acid, boric acid) as protective agent, to avoid the formation of defects in the graphene sheets that occur during the oxidation process.
    [0022] Also patent no. US10336619B2 discloses a modification of the Hummers and Offeman method by which graphene oxide is obtained with a single layer or with few layers, where after the reaction of KMnO 4 and graphite in sulfuric acid medium, quenching is carried out by dumping the mixture into aqueous hydrogen peroxide solution. The invention does not use NaNO 3 or H 3 PO 4 as a protective agent for graphene oxide. The patent discloses that the intercalation process in the graphite sheets occurs completely only with the presence of H 2 SO 4 and KMnÜ 4 . The graphene oxide obtained in this way has high solubility both in aqueous medium and in polar organic solvents.
    [0024] On the other hand, the incorporation of graphene oxide into polymeric matrices is one of the current challenges in the field of composite materials in order to obtain materials with improved properties, such as fiberglass or carbon fiber. which use thermosetting resins as matrix. In particular, it should be noted that in order to achieve a high interaction between the polymeric matrix, the graphene oxide and the fiber, it is necessary for the graphene oxide to present a controlled size and number of planes, as well as the selective type of oxygenated groups.
    [0026] In this way, the incorporation of nanomaterials is essential to obtain materials with improved properties (such as mechanical properties, thermal and electrical conductivity, anti-corrosion, etc.) but whose limitation lies in the difficulty of obtaining homogeneous dispersions of the nanomaterials in said matrices.
    [0028] For example, in the synthesis of resins, the use of graphene oxide as a second reinforcing filler - in addition to the fiber - improves the mechanical properties of the material. However, the selection of the filler and resin is essential to avoid problems in the processing, such as premature curing of the resin or failure to fill the mold during the infusion process.
    [0030] The addition of graphene oxide in carbon fibers has also been studied, verifying the influence of the functional groups of graphene oxide on the reinforcement capacity of epoxy resin composite materials processed by vacuum infusion, concluding that graphene oxide increases the toughness of epoxy resin laminates with carbon fiber.
    [0031] On the other hand, in recent years, graphene-based membranes have been developed for water treatment, where the membranes are produced by layer by layer stacking of functionalized graphene oxide sheets, where the distance between the different planes or layers of the oxide graphene is small and makes effective dispersion difficult.
    [0033] It should be noted that graphene oxide mainly has hydroxyl, etherpoxy, quinone and lactol groups as detailed in the disclosure by MARTIN GULLON, I. et al. New insights into oxygen surface coverage and the resulting two-component structure of graphene oxide. Carbon 158 (2020) 406-417. ISSN 0008-6223. However, for many of the functionalization reactions the presence of carboxyl and carboxylate groups is necessary, so it is necessary to previously anchor the carboxyl groups to the graphene surface.
    [0035] That is why the applicant of the present patent application detects the need to develop a process to obtain graphene oxide with a low number of planes or stacked layers and with the majority or selective presence of carboxylic groups, so that the oxide The graphene obtained has characteristics that favor its effective dispersion in a polymeric matrix, improving its compatibility and better fiber-resin interfacial interaction.
    [0037] DESCRIPTION OF THE INVENTION
    [0039] The present invention recommends a process for obtaining monolayer carboxylated graphene oxide whose majority presence of selective functional groups such as carboxyl, carboxylate, lactone and anhydride allow an exhaustive control of the resin-graphene oxide interface through an interlaminar functionalization with oxygenated groups that enables the best dispersion of the graphene oxide sheets in the resin.
    [0041] Thus, it is proposed to obtain monolayer carboxylated graphene oxide that presents a selective functionalization of oxygenated groups by means of a consecutive oxidation-exfoliation-oxidation process, as detailed below.
    [0043] Specifically, the process for obtaining monolayer carboxylated graphene oxide is made up of at least the following steps:
    [0045] - Oxidation of a material with a crystalline graphite structure by oxo acids and oxysalts that are intercalated between the layers of the material with a graphitic structure at temperatures between 5 ° C and 20 ° C, forming the graphite intercalation compound, which decomposes at temperatures between 25 and 100 ° C, oxidizing the graphite layers to obtain graphite oxide,
    [0046] - Thermal exfoliation of the graphite oxide by thermal shock, removing part of the oxygen from the oxygenated groups and generating the separation into hydrophobic sheets of chemically exfoliated graphene in a single layer, without orderly stacking, and - Oxidation of the hydrophobic sheets of chemically exfoliated graphene for obtaining monolayer carboxylated graphene oxide sheets.
    [0048] Preferably, the crystalline graphitic structure material is natural graphite, synthetic graphite, carbon nanotubes, helical ribbon carbon nanofibers, carbon fiber and / or carbon black.
    [0050] Advantageously, the monolayer carboxylated graphene oxide sheets formed are constituted by a sheet where the functional groups formed are mostly selective of the carboxyl, carboxylate, lactone and anhydride type, which are located on the edges of the sheets of carboxylated graphene oxide. monolayer and in the structural defects of its interior, that is to say, located in defects such as the holes located in the sheets.
    [0052] In the first stage, the precursor material - the material with a crystalline graphitic structure - is oxidized to obtain the graphite oxide and in it, oxo acids such as sulfuric acid or nitric acid are preferably used, while the oxysalts used are, preferably potassium permanganate or potassium chlorate.
    [0054] In this way, when the oxidation of the precursor material is carried out by the Brodie method, the oxidation is carried out using potassium chlorate in a fuming nitric acid medium.
    [0056] If the oxidation of the precursor material is carried out by the Staudenmeier method, the oxidation of the precursor material is carried out using potassium chlorate in nitric and sulfuric acid medium.
    [0058] Whereas, if the oxidation of the precursor material is carried out by the Hummers and Offeman method, potassium permanganate is used in sulfuric acid medium, with the presence or not of sodium nitrate.
    [0060] Preferably, the oxidation of the material with a crystalline graphitic structure is carried out using the Hummers and Offeman method, being formed by, at least, the following stages:
    [0062] - The material with a crystalline graphical structure (precursor) is suspended in a sulfuric acid medium or in a sulfuric acid-sodium nitrate medium with a ratio (mass of the precursor: volume) between 1:20 and 1: 150 (g graphite: ml of H 2 SO 4 ), performing mechanical stirring for at least 15 minutes at room temperature.
    [0063] - A graphite: sulfuric acid intercalation compound is generated, separating the graphite layers.
    [0064] - Addition of potassium permanganate in a mass ratio KMnO 4 : precursor of between 7: 1 and 1: 1 at a temperature below 25 ° C.
    [0065] - Stirring maintaining a temperature between 25 ° C and 70 ° C for at least 15 minutes, where the penetration of permanganate between the layers is favored.
    [0066] - A preliminary graphite oxide reaction mixture is generated, which presents functional groups on the structural defects of the graphical structure (basal planes and edges) when decomposing the intercalation compound formed.
    [0067] - Pouring the reaction mixture onto water in a volumetric ratio of sulfuric acid: water between 1: 1 and 1:10, generating heat and an oxidation-hydrolyzation chain reaction caused by the presence of potassium permanganate, generating MnO 2 (insoluble ), multiplying the presence of oxygenated functional groups by this chain reaction that cuts the graphite layers, reducing their size. These functional groups formed are, for the most part, hydroxyl, lactol, ether-epoxy, quinones, and to a lesser extent, carboxyl. The speed and intensity of the reaction in this stage is controlled by acting on the temperature, by means of the extraction of part of the heat generated, in order to preferably keep below 60 ° C.
    [0068] - Addition, applying stirring, of an aqueous solution of hydrogen peroxide, with a volumetric proportion of hydrogen peroxide and the previous mixture of between 1:20 and 1:50, converting all the manganese species present, the MnO 2 formed (insoluble ) and the remaining permanganate to manganese (II) (soluble).
    [0069] - Separation of the liquid phase and the solid phase by centrifugation or filtration processes, discarding the clear liquid phase.
    [0070] - Washing the solid with water, preferably at a pH greater than 2.
    [0071] - Separation.
    [0072] - Washing with water.
    [0073] - Drying of the wet solid phase by convection at temperatures between 50 ° C and 95 ° C to obtain graphite oxide in a dry and powder state.
    [0075] As mentioned previously, in the first stage of oxidation of the material with a crystalline graphitic structure, it is suspended in a sulfuric acid medium or in a sulfuric acid-sodium nitrate medium. In this sense, when the suspension of the precursor material is carried out on the sulfuric acid-sodium nitrate medium, it will be necessary to prepare a suspension of sodium nitrate in sulfuric acid in a mass ratio preferably between 1: 1 and 1: 2 (NaNO 3 : precursor) .
    [0077] On the other hand, the second stage of the process for obtaining monolayer carboxylated graphene oxide refers to the thermal exfoliation of the graphite oxide obtained in the first oxidation, the thermal exfoliation being formed by, at least, the following stages:
    [0079] - Increase in temperature between 90 ° C and 250 ° C, producing the violent exit of the water interspersed between the layers, both physisorbed and chemisorbed, exfoliating the material.
    [0080] - Drag of existing functional groups in the graphite oxide, together with the exit of chemisorbed water, reaching pressures that exceed the Van der Waals forces that bind the graphite sheets. The entrained / removed functional groups are hydroxyl, ether, epoxy, lactol, anhydride, quinones and carboxyls.
    [0081] - Obtaining hydrophobic sheets of reduced graphene oxide (also called chemically exfoliated graphene) that are separated and do not present an ordered graphical stacking.
    [0083] In this way, the functional groups entrained and eliminated in the thermal exfoliation stage of the graphite oxide are those that were formed in the defects generated, and subsequent propagation, during the oxidation of the crystalline graphite structure.
    [0085] Optionally, and preferably, the increase in temperature in the thermal exfoliation stage is generated by microwave irradiation, since it is a much more efficient heating process on materials rich in carbon and water than convective heating by temperature gradient. .
    [0086] Finally, the next and last stage is a second oxidation of the hydrophobic sheets of chemically exfoliated graphene, which is formed by the following stages:
    [0088] - The hydrophobic sheets of chemically exfoliated graphene are suspended in a sulfuric acid medium or in a sulfuric acid-sodium nitrate medium with a mass ratio of hydrophobic films: volume between 1:20 and 1: 150 (g of hydrophobic film: ml of H 2 SO 4 ), performing mechanical stirring for at least 15 minutes at room temperature. In this case, no intercalation compound is formed since the sheets do not have crystalline stacking, so their solvation by the acid is lower.
    [0089] - Adding potassium permanganate in a mass ratio KMnO 4 : hydrophobic sheets of between 7: 1 and 1: 1 at a temperature below 25 ° C.
    [0090] - Stirring maintaining a temperature between 25 ° C and 70 ° C for at least 15 minutes.
    [0091] - Pre-oxidation of the defects present in the hydrophobic sheets by the generation of an intermediate structure between the hydrophobic sheets. In this case, as an intercalation compound has not been formed, the pre-oxidation is weaker (forming hydroxyl groups) and located in the major defects, mainly edges.
    [0092] - Pouring the reaction mixture over water in a volumetric ratio of sulfuric acid: water between 1: 1 and 1:10, generating a heat of dilution that controls the temperature to be less than 100 ° C. Optionally, the heat of dilution produced by pouring the reaction mixture into water is removed to keep the mixture below 60 ° C.
    [0093] - Oxidation-hydrolyzation reaction generated by the presence of potassium permanganate combined with the heat of dilution, where potassium permanganate (transforming to insoluble MnO 2 ) completes the oxidation of the defects of the hydrophobic sheets of chemically exfoliated graphene to preferably mainly carboxylic groups , carboxylate and anhydride, on the edges of these, without in this case there being a chain propagation reaction that cuts the sheets, as they are not stacked.
    [0094] - Addition, applying stirring, of an aqueous solution of hydrogen peroxide, with a volumetric proportion of hydrogen peroxide: mixture of between 1:20 and 1:50, producing the reduction of the manganese species present (manganese (IV) of MnO 2 (insoluble) and manganese (VII) from permanganate) to manganese (II) (soluble), passing into aqueous solution.
    [0095] - Separation of the liquid phase and the solid phase by centrifugation or filtration processes, discarding the clear liquid phase.
    [0096] - Washing the solid with water, preferably at a pH greater than 2.
    [0097] - Separation.
    [0098] - Washing with water.
    [0099] - Drying of the wet solid phase by convection at temperatures between 50 and 95 ° C to obtain graphite oxide in a dry and powder state functionalized with carboxylic, carboxylate and anhydride groups.
    [0101] As mentioned above, in the first stage of oxidation of the hydrophobic sheets of chemically exfoliated graphene, they are suspended in a sulfuric acid medium or in a sulfuric acid-sodium nitrate medium. In this sense, when the suspension of the hydrophobic sheets of chemically exfoliated graphene is carried out on the sulfuric acid-sodium nitrate medium, it will be necessary to prepare a suspension of sodium nitrate in sulfuric acid in a mass ratio preferably between 1: 1 and 1: 2.
    [0103] The recommended procedure makes it possible to obtain a monolayer carboxylated graphene oxide that offers the following advantages:
    [0105] - The graphene oxide obtained has a controlled plane size, uniform and smaller than that obtained with the conventional process of Hummers and Offeman. Advantageously, the exfoliation and subsequent oxidation stages make it possible to obtain a graphene oxide with a high monolayer rate without ordered stacking.
    [0107] - The graphene oxide obtained presents a laminar structure functionalized with selectively oxygenated groups (carboxylates, carboxylics, alkoxy, etc.), which allows greater chemical interaction and compatibility with the polar groups of a polymeric matrix and the fiber. Advantageously, the oxygenated groups present in the sheets of the synthesized graphene oxide also present the possibility of surface functionalization, offering a high application in the field of nanocomposites by allowing compatibility with a greater number of polymeric matrices and even providing special properties. .
    [0110] For all the above, the characteristics of the monolayer carboxylated graphene oxide obtained allow its use as a reinforcing material in composite materials of thermosetting polymeric matrices (epoxy resins, polyester, vinyl ester) reinforced with fiber (for example, fiberglass, .de carbon, from aramid) in order to obtain materials with improved mechanical properties, where the matrix phase is dominant.
    [0112] Specifically, in the manufacture by vacuum infusion of composite materials with resins - where the interface between the fiber and the matrix is weak - the addition of monolayer carboxylated graphene oxide sheets of the present invention allow an exhaustive control of the resin-interface. oxide. In this way, the monolayer carboxylated graphene oxide has a selectivity of oxygenated functional groups and, consequently, its presence in the mixture with fibers and / or resins favors the dispersion of the graphene oxide sheets in the resin and / or fiber. and an increase in the mechanical properties of the composite materials obtained.
    [0114] Likewise, the incorporation of the monolayer carboxylated graphene oxide of the present invention in the thermoplastic sector allows the production of mechanically reinforced plastics and polymers with antibacterial properties, a decrease in permeability due to the barrier effect, etc., with innovative applications in the packaging or 3D printing industry. Thus, the monolayer carboxylated graphene oxide allows subsequent functionalization processes for use in other matrices (for example, amine groups, silanes, etc.) and applications in the formation of graphene-based membranes for water treatment, in microfiltration, ultrafiltration , nanofiltration and desalination.
    [0116] BRIEF DESCRIPTION OF THE DRAWINGS
    [0118] To complement the description that is going to be made below and with the aim of helping to better understand the characteristics of the invention, according to a preferred example of a practical embodiment thereof, a set of figures is attached as an integral part of said description. where, for illustrative and non-limiting purposes, the following has been represented:
    [0120] Figure 1.- Shows a representation of an X-ray photoelectronic spectrometry of the material with a crystalline graphitic structure to be oxidized.
    [0121] Figure 2.- Shows a representation of an X-ray photoelectron spectrometry of the graphite oxide obtained after the first oxidation.
    [0123] Figure 3.- Shows a representation of an X-ray photoelectron spectrometry of the exfoliated graphene oxide.
    [0125] Figure 4.- Shows a representation of an X-ray photoelectronic spectrometry of the monolayer carboxylated graphene oxide obtained after the second oxidation.
    [0127] Figure 5.- Shows a representation of the X-ray diffractogram of graphite oxide, exfoliated graphene oxide and monolayer carboxylated graphene oxide.
    [0129] Figure 6. Shows a transmission electron microscopy image of different sheets of the monolayer carboxylated graphene oxide, where it is observed that they have a very similar size.
    [0131] PREFERRED EMBODIMENT OF THE INVENTION
    [0133] In the preferred embodiment of the process for obtaining the monolayer carboxylated graphene oxide of the present invention, the oxidation step of the material with a crystalline graphitic structure is carried out using the Hummers and Offeman method, as it is the most efficient in the intercalation of anhydrous sulfuric acid between each and every one of the layers, and subsequently oxidize the interior by the action of permanganate.
    [0135] Advantageously, the presence of sodium nitrate during the first and second oxidation helps the sulfuric acid and potassium permanganate to penetrate into the galleries or structural defects both of the material with a crystalline graphite structure and in the galleries or structural defects of the graphene oxide.
    [0137] Preferably, the crystalline structure material used as a precursor is natural graphite.
    [0139] Thus, in a preferred embodiment of the invention, the oxidation of the precursor material is carried out by the Hummers and Offeman method, as it is the most efficient in the intercalation of anhydrous sulfuric acid between each and every one of the layers, and subsequently oxidizing the interior of the layers by the action of permanganate. The presence of sodium nitrate promotes the penetration of sulfuric acid and sodium permanganate in the galleries or defects present in the graphite layers.
    [0141] Preferably, natural graphite and sodium nitrate are suspended, in a 1: 1 mass ratio, in sulfuric acid (preferably 98%) with a precursor mass: sulfuric acid volume ratio of 1:50 (g graphite: ml of H 2 SO 4 ), of 70 ml of sulfuric acid and mixed with mechanical stirring for several hours, at room temperature. In this process, a graphite: sulfuric acid intercalation compound is generated, separating the graphite layers.
    [0143] The corresponding amount of potassium permanganate (mass ratio KMnO 4 : precursor 4: 1) is slowly added while controlling the temperature below 25 ° C. Then, stirring is maintained at a temperature of 35-55 ° C for one or two hours.
    [0145] In this stage the preliminary graphite oxide is generated, as the potassium permanganate acts in the galleries, with the sulfuric acid, generating functional groups on the structural defects of the graphical structure. After the reaction time has elapsed, the reaction mixture is poured onto water ( quenching) in a relative volumetric ratio of sulfuric acid: water of 1: 1.8. This process can produce up to 100 ° C, so it is advisable to extract heat and keep the mixture at 60 ° C.
    [0147] In this process, the presence of water together with the heat of dilution, trigger the action of potassium permanganate in the graphical galleries through the oxidation-hydrolyzation chain reaction, also generating MnO 2 (insoluble), being a very fast reaction and cutting the graphitic sheets.
    [0149] An aqueous hydrogen peroxide solution (preferably 30% v / v) is then added with stirring, with a volumetric ratio of hydrogen peroxide: quenching mixture of 1:30. In this way, manganese is reduced to manganese (II), the action of unreacted manganese (VII) is stopped and the manganese (IV) formed is solubilized.
    [0151] Finally, the liquid phase is separated from the solid phase by centrifugation or filtration processes, discarding the clear liquid phase. The solid is washed with water at pH 2 and separated again, and finally washed with water. The wet solid phase is then dried by
    [0154] convection at temperatures between 60 and 70 ° C. The product thus obtained corresponds to graphite oxide, which is a dry, powdery material.
    [0156] The graphite oxide obtained is subjected to a thermal exfoliation treatment. This process takes place at a temperature between 140 ° and 200 ° C. The increase in temperature of the particle produces the violent exit of the large quantity of water sandwiched between the layers, both physisorbed and chemisorbed, exfoliating the material.
    [0158] Simultaneously, this chemisorbed water outlet drags functional groups existing in the graphite oxide, reaching pressures that exceed the Van der Waals forces that bind the graphite sheets. The entrained functional groups are hydroxyl, ether, lactol, and quinones and, to a lesser extent, carboxyl, which are preferably located in the large number of defects produced during the generation of graphite oxide, leaving as CO, CO 2 and H 2 O in the space between the sheets. This results in the exfoliation of the graphene oxide and its reduction, since it loses most of the oxygen content.
    [0160] The reduced graphene oxide sheets are separate and do not exhibit graphical stacking. Likewise, the graphene oxide sheets are smaller in size than the starting graphite, since the original graphite planes were largely cut with the generation of functional groups and subsequent breaking of these bonds in thermal exfoliation. Therefore, the result of the thermal exfoliation of graphite oxide by thermal shock is a plurality of sheets of chemically exfoliated graphene, without ordered stacking and hydrophobic, as a part of the oxygen is removed by the thermal decomposition of the oxygenated groups. Hydrophobic sheets of a similar size and smaller than that of the starting graphite oxide are generated.
    [0162] A second oxidation is performed from the chemically exfoliated graphene oxide sheets by the same modified Hummers-Offeman chemical method described above. 1g of the exfoliated graphene oxide is suspended in 70 ml of H 2 SO 4 together with 1 g of NaNO 3 and stirred on a magnetic heating plate for three hours at room temperature. Potassium permanganate is added in a 3: 1 ratio and stirred for two hours at 35 ° C. The mixture is then heated to 55 ° C and allowed to stabilize. It is allowed to cool and is poured onto about 160 ml of ice water, stirred and 8 ml of hydrogen peroxide are added. The solution is filtered and the solid is washed with water for 30 min, filtered again and the product is dried in the oven at 65 ° C. Finally, the product thus obtained is monolayer carboxylated graphene oxide that presents a selective functionalization with carboxylic groups, carboxylate, without hardly changing the size of the sheets in this last stage, but with a hydrophilic character, resulting in a very fine and dry black powder. .
    [0164] Figures 1, 2, 3 and 4 are attached which correspond, respectively, to the representations of the X-Ray Photoelectronic Spectrometries for the material with a crystalline graphitic structure to be oxidized, the graphite oxide, the chemically exfoliated graphene and the graphene oxide. monolayer carboxylate obtained, the bond energy (eV) being represented on the abscissa axis and the intensity on the ordinate axis. Each letter of those represented in figures 1, 2, 3 and 4 to which they correspond is indicated below:
    [0166] A corresponds to the data
    [0167] B corresponds to the global adjustment
    [0168] C corresponds to deconvolution by sp2C = sp2C
    [0169] D corresponds to deconvolution sp3C - OH / sp3C - sp3C
    [0170] E corresponds to sp3C - O - sp3C
    [0171] F corresponds to O - sp2C = O
    [0173] The graphite oxide obtained in the first stage (figure 2) has a higher percentage of oxygen than the graphene oxide obtained after the second stage (figure 4). In this sense, the C / O atomic ratio is higher in the monolayer carboxylated graphene oxide (figure 4) obtained after the second oxidation than in the conventional graphite oxide (figure 2) obtained in the first oxidation.
    [0175] The following table shows the evolution of the carbon-oxygen (C / O) ratio for each of the compounds involved in the steps of the process object of the present invention, measured by X-ray Photoelectron Spectroscopy.
    [0177]
    [0181] However, despite the fact that monolayer carboxylated graphene oxide has less oxygen than conventional graphite oxide, it shows greater functionalization of carboxylic, anhydride, carboxylate and / or lactone groups, as observed in the comparison of figures 2 and Four.
    [0183] In this way, it is confirmed that with the first oxidation stage, the material with a crystalline graphitic structure introduces a high percentage of ether, epoxy, lactol and quinone groups (51% of the total C bonds, 286.7 eV, even more than sp2C = sp2C bonds), as well as 10% COOH groups (289.0 eV). The exfoliation process - second stage of the process of the invention - removes oxygenated groups, obtaining a reduced graphene oxide with a surface composition similar to that of the initial crystalline graphite structure material. Additionally, exfoliation allows the separation of the graphite layers, which in the next oxidation stage enables the introduction of new oxygenated groups, in this case with a higher degree of oxidation, in the form of anhydrides, lactones and / or carboxylates (15% , 289.0 eV), surpassing the peak of 286.7 eV, different from the oxygenated groups obtained in the conventional graphite oxide obtained with the first oxidation stage.
    [0185] The aforementioned effect is consistent with the measurements made by zeta potential at 0.1 mg / mL aqueous suspensions of conventional graphite oxide and monolayer carboxylated graphene oxide. The first has a value of -33.3 mV, while the second -48.1 mV, indicative that the monolayer carboxylated graphene oxide has more polarity, and more stability in water, because its functional groups are preferentially carboxyl and carboxylate, even when the oxygen content is lower than conventional graphite oxide.
    [0187] Figure 5 is attached, which shows the X-ray diffraction diffractograms (XRD) of graphite oxide (corresponds to line I), chemically exfoliated graphene (or reduced graphene oxide) (corresponds to line J) and oxide of carboxylated graphene (corresponds to line K), inventive product of this patent. The abscissa axis represents the angle 20 and the ordinate axis the intensity. It is observed that the graphite oxide exhibits stacking, given the prominence of the 002 peak around 10 ° of the diffraction angle. Thermal peel removes such stacking, since no peaks occur in the range, as well as in carboxylated graphene oxide. It is proven that the product of the third stage, the oxidation of the hydrophobic sheets of chemically exfoliated graphene, gives a
    [0190] product very different from that of stage 1, consisting of monolayers.
    [0192] Figure 6 shows an image obtained by Transmission Electron Microscopy (TEM) on a grid support in which a strip (2) corresponding to 2 micrometers is represented. In this way, it is observed that the sheets (1) of carboxylated graphene oxide obtained according to the process of the invention have a more homogeneous size between them.
    [0194] The homogeneity between sheets (1) is due to the fact that the second oxidation, as it does not take place between the layers, is not the result of a chain reaction that leads to the sheets being cut, but rather acts punctually, only on the defects and previously formed edges, resulting in planes of similar sizes.
    [0196] With the thermal exfoliation process, the plane size decreases and they become similar, and after the second oxidation, the same size as before, but flat due to the hydrophilic character acquired.
    [0198] Therefore, the monolayer carboxylated graphene oxide obtained from the second oxidation exhibits three key characteristics:
    [0199] - It is specifically functionalized with carboxylate oxygenated groups, lactones and / or anhydrides;
    [0200] - The functionalization takes place in the separated monolayers during the exfoliation process.
    [0201] - Smaller plane size and more homogeneous.
    [0203] The monolayer carboxylated graphene oxide obtained being a suitable nanomaterial for its incorporation into composite materials of thermosetting polymeric matrices to obtain materials with improved mechanical properties.
    权利要求:
    Claims (9)
    [1]
    1§.- Procedure for obtaining monolayer carboxylated graphene oxide that comprises the following steps:
    - Oxidation of a material with a crystalline graphitic structure - precursor - by oxo acids and oxysalts that are intercalated between the layers of the graphitic structure material at temperatures between 5 ° C and 20 ° C, forming the graphite intercalation compound, which is decomposes at temperatures between 25 and 100 ° C, oxidizing the graphite layers to obtain graphite oxide,
    - Thermal exfoliation of the graphite oxide by thermal shock, removing part of the oxygen from the oxygenated groups and generating the separation into hydrophobic sheets of chemically exfoliated graphene in a single layer, without orderly stacking, and - Oxidation of the hydrophobic sheets of chemically exfoliated graphene to obtain monolayer carboxylated graphene oxide sheets,
    characterized in that the monolayer carboxylated graphene oxide sheets formed are constituted by a sheet where the functional groups formed are mostly selective of the carboxyl, carboxylate, lactone and anhydride type, which are located at the edges of the carboxylated graphene oxide sheets monolayer and in the structural defects of its interior.
    [2]
    2§.- Procedure for obtaining monolayer carboxylated graphene oxide, according to claim 1§, characterized in that oxo acids such as sulfuric acid or nitric acid are used in the oxidation of the crystalline graphite structure material to obtain graphite oxide. while the oxysalts used are potassium permanganate or potassium chlorate.
    [3]
    3§.- Procedure for obtaining monolayer carboxylated graphene oxide, according to claim 1§ or 2§, characterized in that the oxidation of the material with a crystalline graphitic structure comprises the following stages:
    - The material with a crystalline graphitic structure - precursor - is suspended in a sulfuric acid medium or in a sulfuric acid-sodium nitrate medium with a g ratio graphite: ml of H 2 SO 4 between 1:20 and 1: 150, with mechanical stirring for at least 15 minutes, at room temperature,
    - A graphite intercalation compound is generated: sulfuric acid, separating the graphite layers,
    - Adding potassium permanganate in a mass ratio KMnO 4 : precursor between 7: 1 and 1: 1 at a temperature below 25 ° C,
    - Stirring maintaining a temperature between 25 ° C and 70 ° C for at least 15 minutes,
    - A preliminary graphite oxide reaction mixture is generated that presents functional groups on the structural defects of the graphite structure.
    - Pouring the reaction mixture over water in a volumetric ratio of sulfuric acid: water between 1: 1 and 1:10, generating heat and an oxidation-hydrolyzation chain reaction caused by the presence of potassium permanganate, generating MnO 2 and originating the cutting of the graphical layers, with a multitude of oxygenated functional groups.
    - Addition, applying stirring, of an aqueous solution of hydrogen peroxide, with a volumetric proportion of hydrogen peroxide and the previous mixture between 1:20 and 1:50, converting the insoluble species of MnO 2 and the remaining permanganate to manganese ( II) which is soluble.
    - Separation of the liquid phase and the solid phase by centrifugation or filtration processes, discarding the clear liquid phase.
    - Washing of the solid with water at a pH greater than 2.
    - Separation.
    - Washing with water.
    - Drying of the wet solid phase by convection at temperatures between 50 ° C and 95 ° C to obtain the graphite oxide in a dry and powder state.
    [4]
    4§.- Procedure for obtaining monolayer carboxylated graphene oxide, according to claim 3§, characterized in that the sulfuric acid - sodium nitrate medium is prepared by suspending sodium nitrate in sulfuric acid, in a mass ratio between 1: 1 and 1 : 2 sodium nitrate: precursor.
    [5]
    5§.- Procedure for obtaining monolayer carboxylated graphene oxide, according to claim 1§, characterized in that the thermal exfoliation of the graphite oxide comprises the following stages:
    1
    - Increase in temperature between 90 ° C and 250 ° C, producing the exit of the water interspersed between the layers, both physisorbed and chemisorbed, exfoliating the material.
    - Drag of functional groups existing in graphite oxide, together with the exit of chemisorbed water, reaching pressures that exceed the Van der Waals forces that bind the graphite sheets, so that the functional groups dragged and eliminated are hydroxyl, ether, epoxy, lactol, anhydride, quinones and carboxyls,
    - Obtaining sheets of reduced graphene oxide that are separated without graphical stacking.
    [6]
    6§.- Procedure for obtaining monolayer carboxylated graphene oxide, according to claim 5§, characterized in that the temperature increase is generated by microwave irradiation.
    [7]
    7§.- Procedure for obtaining monolayer carboxylated graphene oxide, according to claim 1§, characterized in that the oxidation of the hydrophobic sheets of chemically exfoliated graphene comprises the following steps:
    - The hydrophobic sheets of chemically exfoliated graphene are suspended in a sulfuric acid medium or in a sulfuric acid-sodium nitrate medium with a g ratio of hydrophobic film: ml of H 2 SO 4 of between 1:20 and 1: 150, with stirring mechanical for at least 15 minutes, at room temperature,
    - Addition of potassium permanganate in a mass ratio KMnO 4 : hydrophobic sheets between 7: 1 and 1: 1 at a temperature below 25 ° C,
    - Stirring maintaining a temperature between 25 ° C and 70 ° C for at least 15 minutes,
    - Pre-oxidation of the defects present in the hydrophobic sheets of chemically exfoliated graphene by the generation of an intermediate structure between the hydrophobic sheets of chemically exfoliated graphene.
    - Pouring the reaction mixture over water in a volumetric ratio of sulfuric acid: water between 1: 1 and 1:10, generating a heat of dilution that controls the temperature to be less than 100 ° C.
    - Oxidation-hydrolyzation reaction generated by the presence of permanganate
    2
    potassium combined with the heat of dilution, generating insoluble MnU 2 , so that potassium permanganate preferentially oxidizes and forms carboxylic groups in the defects of the hydrophobic sheets of chemically exfoliated graphene.
    - Addition, applying stirring, of an aqueous solution of hydrogen peroxide, with a volumetric proportion of hydrogen peroxide: mixture of between 1:20 and 1:50, producing the reduction of the manganese (IV) species, of the insoluble MnÜ 2 and manganese (VII) from permanganate to soluble manganese (II), passing into aqueous solution.
    - Separation of the liquid phase and the solid phase by centrifugation or filtration processes, discarding the clear liquid phase.
    - Washing of the solid with water at a pH greater than 2.
    - Separation.
    - Washing with water.
    - Drying of the wet solid phase by convection at temperatures between 50 and 95 ° C to obtain graphite oxide in a dry and powder state functionalized with carboxylic, carboxylate and anhydride groups.
    [8]
    8§.- Procedure for obtaining monolayer carboxylated graphene oxide, according to claim 7§, characterized in that the sulfuric acid - sodium nitrate medium is prepared by suspending the sodium nitrate in the sulfuric acid, in a mass ratio between 1: 1 and 1: 2 sodium nitrate: precursor.
    [9]
    9§.- Process for obtaining monolayer carboxylated graphene oxide, according to claim 7§, characterized in that the heat of dilution produced by pouring the reaction mixture over water is extracted to keep the mixture below 60 ° C.
    10 ".- Procedure for obtaining monolayer carboxylated graphene oxide, according to any of the preceding claims, characterized in that the material with a crystalline graphite structure is natural graphite, synthetic graphite, carbon nanotubes, helical ribbon carbon nanofibers, carbon fiber and / or carbon black,
    11 ".- Monolayer carboxylated graphene oxide obtained according to the procedure detailed in any of the preceding claims.
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    同族专利:
    公开号 | 公开日
    WO2022023600A1|2022-02-03|
    ES2787504B2|2021-03-15|
    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    US20150274531A1|2012-10-09|2015-10-01|Grapheneall Co., Ltd.|Method for Forming Graphene Oxide|
    US20190218102A1|2016-06-24|2019-07-18|Instituto Presbiteriano Mackenzie|Process for obtaining graphene oxide|
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