RU2709594C1 - Graphene oxide production method - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to chemical industry and nanotechnology. First, graphite is treated with hydrogen peroxide solution in sulphuric acid, wherein amount of hydrogen peroxide is from 0.15 to 0.30 pts.wt. by 1 pts.wt. graphite in conversion to 100 % hydrogen peroxide with total concentration of free water in reaction mixture, not exceeding 0.5 % taking into account water formed in reaction H₂O₂+ H₂SO₄= H₂SO₅+ H₂O. Further, water is added to the reaction mixture in such an amount that free water concentration is close to 2 %. Then potassium permanganate is added while maintaining free water concentration. Water is added to the obtained reaction mixture in an amount which provides concentration of free water close to 5 %, and hydrogen peroxide is added again. Obtained carbon-containing oxidation product is washed with an acid solution, then with water.

EFFECT: method of producing graphene oxide is environmentally friendly and is suitable for industrial production.

1 cl, 1 dwg, 1 tbl, 1 ex

Description

The invention relates to the technology of graphene materials, specifically, to a technology for producing graphene oxide by oxidation of graphite.

Graphene oxide (GH) is a graphene derivative that is widely used in science and technology. However, to date, this substance remains very expensive, from $ 100 to $ 400 per 1 gram of dry matter. The high cost is associated with the complexity of the exhaust gas synthesis technology and the complexity of its scaling.

It should be noted that before the boom in research on graphene materials began, graphene oxide was called (and sometimes is now called) graphite oxide. The name graphene oxide is a tribute to fashion. Graphene oxide and graphite oxide are one and the same substance.

Currently, the most commonly used method for obtaining exhaust gas is the method described in 1958 by Hammers and Offeman [W.S. Hummers Jr., R.E. Offeman. Preparation of Graphitic Oxide // Journal of American Chemical Society, 1958, Volume 80, Issue 6, p. 1339]. One of the modern versions of this method is described in the book [Guide to inorganic synthesis. T. 3. Ed. G. Brauer. - M., Mir, 1985, 392 p. - S. 675-677]. This method involves the oxidation of natural graphite with potassium permanganate with the addition of sodium nitrate in concentrated (95-98%) sulfuric acid. Currently, there are many modifications of this method relating to the preparation of the starting components and their mass ratio, process conditions, and product cleaning methods. A review of known methods for the synthesis of graphene oxide is given in [S. Shamaila, A.K.L. Sajjad, I. Anum. Modifications in development of grapheme oxide synthetic routes. Chemical Engineering Journal (2016), doi: http://dx.doi.org/10.1016/j.cej.2016.02.02.109].

Despite numerous attempts to improve the method of synthesis of exhaust gas according to Hammers-Offeman [W.S. Hummers Jr., R.E. Offeman. Preparation of Graphitic Oxide // Journal of American Chemical Society, 1958, Volume 80, Issue 6, p. 1339], it remains difficult in terms of control of technological conditions and takes a lot of time (especially for cleaning the final product). This method includes the following process steps:

- mixing crystalline graphite, sodium nitrate and concentrated (66 ° Be≈95%) sulfuric acid while cooling the reactor in an ice bath;

- adding to the reaction mixture with vigorous stirring solid potassium permanganate (3 parts by weight per 1 part by weight of graphite) at such a rate that the temperature of the reaction mixture does not exceed 20 ° C;

- after adding all the potassium permanganate, heating the reaction mixture to 35 ° C and half an hour exposure at this temperature;

- dilution of the reaction mixture with water, washing with water, then with ion exchange resins to remove electrolyte residues (salts).

The role of sodium nitrate in this method is not entirely clear. It can be assumed that in a medium of concentrated sulfuric acid, nitrate gives a nitronium cation, which, being a strong oxidizing agent, initiates the oxidative intercalation of graphite and thereby contributes to its exfoliation, which in turn accelerates the oxidation of permanganate. It was experimentally established that without the addition of nitrate, the admixture of underoxidized graphite in the final product is much greater.

Common essential features of the claimed invention and the classical method of obtaining exhaust gas according to Hammers-Offeman are the following:

- Treatment of graphite suspended in concentrated sulfuric acid with potassium permanganate.

- Dilution of the reaction mixture with water.

- Adding hydrogen peroxide to the reaction mixture to reduce manganese compounds of higher oxidation states to divalent manganese sulfate.

- The use of ion exchange resins to remove electrolytes from an aqueous dispersion of graphene oxide.

This method has the following disadvantages:

- The use of sodium nitrate in the process of graphite oxidation, which entails the need to purify wash water from nitrate ion. In addition, the use of nitrate in concentrated sulfuric acid gives the vapor of nitric acid, and the reaction with graphite produces toxic nitrogen oxides.

- As a rule, this method gives an incompletely oxidized product, that is, graphene oxide flakes, in the center of which are dark inclusions of underoxidized graphite. The completeness of oxidation strongly depends on the quality of the initial graphite and the temperature-time regime of the process; with very high quality graphite (with perfect crystalline structure), the admixture of underoxidized graphite is minimal. But with the commonly used grades of graphite available on the market, graphene oxide obtained by the method under consideration contains a significant admixture of unoxidized graphite.

To eliminate these shortcomings in various studies, attempts have been made to improve the Hammers-Offeman method, which mainly boiled down to the preliminary preparation of the initial graphite by preliminary intercalation and exfoliation, which accelerated the subsequent oxidation reaction of potassium permanganate.

So, in [Ling Sun, Bunshi Fugetsu. Mass production of graphene oxide from expanded graphite // Materials Letters, 2013, vol. 109, p. 207-210], thermally expanded graphite was used as initial graphite, and the order of mixing of the components was modified. First, thermally expanded graphite was mixed with finely ground potassium permanganate powder, then 98% sulfuric acid was added to this mixture while cooling in an ice bath with stirring. A thick paste formed. Then the cooling bath was removed and stirring was continued; as a result, oxidation proceeded with foaming of the reaction mixture. Further processing of the product is common.

The disadvantage of this method, firstly, is the need to obtain thermally expanded graphite. Secondly, the addition of concentrated sulfuric acid immediately to a mixture of thermally expanded graphite and solid finely ground potassium permanganate is very dangerous, because under these conditions, in violation of the mixing or temperature conditions, explosive heptavalent manganese oxide can be obtained. Obviously, this method is not only dangerous, but also not very suitable for scaling, despite the declaration of mass production of graphene oxide in the title of the article.

In the patent [United States Patent 9,428,394. Highly oxidized graphene oxide and methods for production thereof. Tour J.M., Kosynkin, D.V. August 30, 2016] in order to exclude the use of nitrate and at the same time ensure complete oxidation of graphite, we increased the mass ratio of potassium permanganate to graphite and carried out the process in a mixture of sulfuric and phosphoric acids. However, this method leads to an unreasonably high consumption of potassium permanganate and according to the cost of cleaning or recovering the waste.

A known method for producing exhaust gas is described in [Nina I. Kovtyukhova, Patricia J. Ollivier, Benjamin R. Martin, Thomas E. Mallouk, Sergey A. Chizhik, Eugenia V. Buzaneva, and Alexandr D. Gorchinskiy. Layer-by-Layer Assembly of Ultrathin Composite Films from Micron-Sized Graphite Oxide Sheets and Polycations // Chemistry of Materials, 1999, vol. 11, No. 3, p. 771-778] (prototype). In this paper, attention is drawn to the fact that usually the Hammers-Offeman method gives an under-oxidized product, that is, flakes with dark inclusions of the original graphite in the center. To eliminate this drawback, graphite was subjected to preliminary oxidative intercalation in a solution containing concentrated sulfuric acid, phosphorus pentoxide, and potassium persulfate. In this case, a dark blue intercalated graphite compound was obtained, which, obviously, is nothing but graphite bisulfate of the first intercalation step.

Note: it is obvious that phosphorus pentoxide in this work was used to bind free water in concentrated sulfuric acid. As our experience with this and similar systems shows, oxidative intercalation of graphite with potassium or ammonium persulfates to a blue intercalated compound of stage I graphite occurs only in anhydrous sulfuric acid. In ordinary concentrated sulfuric acid containing about 5% water, the blue compound of graphite does not form under the action of persulfates on graphite; intercalation does not occur completely.

After oxidative intercalation under the indicated conditions, the reaction mixture was diluted with water, the graphite was filtered off, washed with water to a neutral pH and dried. Then, the usual synthesis of exhaust gas was carried out according to Hammers, as a result of which exhaust gas was obtained without dark inclusions. The resulting product after reduction of manganese dioxide with hydrogen peroxide was filtered off, washed first with dilute (1:10) hydrochloric acid to remove metal salts, then the product was washed with dialysis to remove hydrochloric acid. Received an aqueous dispersion of graphene oxide, not containing inclusions of underoxidized graphite.

As is known from the prior art, the oxidative intercalation of graphite to blue graphite bisulfate of the first stage, followed by hydrolysis, leads to partial exfoliation of the graphite crystals on thin flakes, and exfoliation occurs at the hydrolysis stage. Thus, permanganate access to the inner zones of graphite flakes is accelerated, which ultimately leads to a more complete oxidation of graphite to graphene oxide. It is likely that the effect of exfoliation of graphite ensures the complete oxidation of graphite with potassium permanganate under these conditions.

The experimental part of this work does not say whether the authors added sodium nitrate to the reaction mixture or not. It is only written that the oxidized graphite pretreated, as described above, was carried out by the Hammers method and they briefly described the procedure. Perhaps they forgot to mention sodium nitrate.

Common essential features of the claimed invention and the prototype method are the following:

- Treatment of graphite with a peroxide reagent in sulfuric acid.

- Processing of graphite under conditions causing exfoliation of graphite.

- Treatment of pre-exfoliated graphite suspended in concentrated sulfuric acid with potassium permanganate.

- Dilution of the reaction mixture with water.

- Adding hydrogen peroxide to the diluted reaction mixture to reduce manganese compounds of higher oxidation states to divalent manganese sulfate.

- Washing the product with an acid solution.

- Alternatively, flushing the product with dialysis.

The disadvantages of the prototype method are as follows:

- The process of graphite pretreatment, including oxidative intercalation of graphite with potassium persulfate in a solution of sulfuric acid with phosphorus pentoxide, dilution, washing with water and drying, is a multi-stage process and requires additional equipment for its implementation. Also, new production wastes appear, which entails additional costs for their disposal or disposal. This complicates and increases the cost of technology.

- Since the authors of the prototype method write about the application of the classical Hammers method, sodium nitrate was probably used, which leads to the appearance of hard-to-catch waste nitrates in production waste, as well as the above problems associated with the appearance of toxic fumes of nitric acid and nitrogen dioxide.

Closest to the claimed invention (prototype) is a method for producing reduced graphene oxide described in US patent [United States Patent 9815701. Synthesis of reduced graphene oxide nanoparticles. Nov. 14, 2017]. According to the prototype, the synthesis of nanoparticles of reduced graphene oxide includes the following stages:

- mixing carbon black with acid;

- the gradual addition of the first oxidizing agent to this solution to oxidize the starting carbon material to form a suspension;

- stirring the suspension at a temperature of 35 ° C followed by a rise in temperature to approximately 60 ° C;

- adding to the resulting solution (suspension) of water;

- adding a second oxidizing agent to the suspension with stirring, resulting in the formation of reduced graphene oxide nanoparticles.

Sulfuric acid with the addition of phosphoric acid is used as the acid. Potassium permanganate and hydrogen peroxide are used respectively as the first and second oxidizing agents.

From the description of example 1 of the prototype method, it follows that in fact the technological process according to the prototype method is no different from one of the known variants of the Hammers method, except that carbon black instead of graphite is used as the starting carbon material. It should be noted that hydrogen peroxide, which is introduced into the reaction mixture after oxidation of the starting carbon material with potassium permanganate in an acid medium, after dilution of the reaction mixture with water, is not an oxidizing agent, as the authors of the prototype invention erroneously claim. In this case, hydrogen peroxide is added to reduce manganese dioxide to sulphate of divalent manganese. In this case, hydrogen peroxide is oxidized by manganese dioxide with the release of molecular oxygen.

The disadvantages of this method are as follows.

The use of carbon black instead of graphite does not allow to obtain high-quality graphene oxide, since the soot is not able to intercalate and separate into layers of oxidized graphene. In fact, from the x-ray diffraction pattern of the product described in the description of the prototype method, it follows that the obtained product is an oxidized form of low-order carbon, and not graphene oxide at all. Indeed, if we look at the X-ray diffraction pattern shown in this patent, then the maximum at 2 Θ = 25 degrees and at the radiation wavelength λ = 0.154060 nm indicated in the figure corresponds, according to the well-known Wulf-Bragg formula (2dsinΘ = nλ), interlayer distance d = 0.3948 nm. This is slightly larger than the interlayer distance in graphite (d = 0.3354 nm), and indicates a very imperfect structure of the carbon skeleton with graphene-like fragments. In high-quality graphene oxide, this interlayer distance is much larger, usually within d = 0.9-1.4 nm, because the oxidized graphene layers in graphene oxide are easily separated in water and polar solvents. Nothing like the product obtained by the patent prototype, is not available.

It is also obvious that, with the exception of the starting carbon material used, the prototype method is identical to the well-known Hammers method, with all its disadvantages. In particular, even when using crystalline graphite as the starting carbon material, the known method provides a product containing a significant admixture of under-oxidized graphite.

The basis of the claimed invention is the task, by changing the reagents used and the choice of technological modes, to create an environmentally friendly technology for the production of high-quality graphene oxide, suitable for industrial production with minimal cost.

The problem is solved in that in a method for producing graphene oxide, comprising treating a carbon material with a first oxidizing agent (potassium permanganate) in a concentrated sulfuric acid medium, diluting the reaction mixture with water, then treating with a second oxidizing agent (hydrogen peroxide) and washing the obtained carbon-containing oxidation product with an acid solution, then with water, in the inventive method, graphite is used as a carbon material, and before treatment with potassium permanganate, graphite is additionally treated with thief hydrogen peroxide in sulfuric acid, the amount of hydrogen peroxide charge of from 0.15 to 0.30 phr for 1 mass.h. graphite in terms of 100% hydrogen peroxide.

In this case, it is optimal to carry out the process at a controlled water content in the reaction mixture in stages in accordance with the following scheme:

- at the first stage of processing graphite with hydrogen peroxide, the amounts of reagents are calculated so that the total concentration of free water in the reaction mixture does not exceed 0.5%, taking into account the water formed in the reaction H ₂ O ₂ + H ₂ SO ₄ = H ₂ SO ₅ + H ₂ O;

- in the second stage, water is added to the reaction mixture in such an amount that the concentration of free water becomes close to 2%;

- at the third stage, potassium permanganate is added to the system while maintaining the concentration of free water of the second stage;

- in the fourth stage, water is added to the reaction mixture in an amount providing a concentration of free water close to 5%.

An explanation is needed here regarding the proposed mechanisms of the reactions. It is known from the prior art that the reaction of graphite with peroxomonosulfuric acid, H ₂ SO ₅ , taken as a solution in sulfuric acid, leads to rapid exfoliation of graphite with a significant increase in apparent volume. Peroxodisulfuric acid also reacts with graphite with its exfoliation, however, the process of exfoliation with peroxodisulfuric acid is much slower. For the first time, these effects were described in [Melezhik A.V., Chuyko A.A. Cold expansion of graphite - the path to new technologies // Chemical Technology (Kiev), 1992, No. 2, p. 3-11]. Hydrogen peroxide itself does not react with graphite. Therefore, for the fast and efficient exfoliation of graphite in the first stage, it is necessary to create conditions under which hydrogen peroxide added to sulfuric acid is converted to peroxonosulfuric acid according to the reaction equation:

It was experimentally established that the equilibrium of reaction (1) is shifted to the right if sulfuric acid is present in excess and the content of free water in it is less than 0.5%. For this, it is necessary to take a sufficiently concentrated hydrogen peroxide (at least 50%, preferably 60%, hydrogen peroxide with a higher concentration is not commercially available) and a sufficiently large excess of anhydrous sulfuric acid.

So, when using 60% hydrogen peroxide in the claimed range of the mass ratio of H ₂ O ₂ to graphite, the use of anhydrous (100%) sulfuric acid in the amount indicated below in the examples of the invention provides almost complete conversion of hydrogen peroxide to peroxomonosulfuric acid and effective exfoliation of graphite. To implement the claimed invention, it is possible to use a more dilute hydrogen peroxide, for example, 30-50%, but at the same time, a certain amount of oleum will need to be added to 100% sulfuric acid to bind excess water. The required amount of oleum can be calculated according to the reaction equation:

The calculation of the required number of components according to the equations of reactions (1) and (2) can be performed by any chemist with a secondary education. However, in practice, given the availability of 60% hydrogen peroxide on the market, it is advisable to use it, with no need to add oleum or calculate its amount. Hydrogen peroxide of higher concentration can also be used, however, it is dangerous to handle and does not go on sale.

Further, in the examples of the invention, the amounts of reagents used are given based on the use of 60% hydrogen peroxide. If hydrogen peroxide of a different concentration is used, the amount of water added at different stages should be recalculated, which can be easily done by any specialist chemist.

The following are data proving the feasibility of the proposed method and its effectiveness.

The following starting materials were used to carry out the invention.

Graphite

The quality of the graphene oxide obtained largely depends on the quality of the starting graphite. It is preferable to use high-purity graphite with a good crystalline structure, preferably not fine dust, but possibly large flakes, of the order of 0.1-0.5 mm. Graphite proved to be very good in special low-ash Soviet-made fuel grade GSM-1 (99.9% carbon). However, it is not being released now. It is preferable that the graphite contains as little as possible fine (pulverulent) fraction, which may have a defective crystalline structure and poorly intercalate. Our experiments have shown that for the implementation of the claimed invention graphite special low-ash fuel and lubricants GSM-2 according to GOST 17022-81 containing up to 0.5% ash is quite suitable. Hydrogen peroxide

60% hydrogen peroxide available on the market is used. Its density is 1.2505 g / cm ³ .

Sulfuric acid

In free sale, 100% sulfuric acid (monohydrate) is absent because it freezes at + 10 ° C and its transportation in cold weather is impossible. Because you have to cook it on the spot. To this end, a calculated amount of oleum with a known SO ₃ content (usually 24% in technical oleum or 60% in oleum of grade XC) is added to ordinary concentrated sulfuric acid of the grade ChC, containing about 5% free water. The stoichiometry point can be accurately controlled by the presence or absence of acid smoke when in contact with air moisture [A. Gordon, R. Ford. Companion chemist. M., "World", 1976. - S. 442]. According to the cited work, this simple method allows you to adjust the composition of sulfuric acid with an accuracy of + _0.02% for water. If sulfuric acid is monohydrate or contains water, it does not smoke. If it contains even a very small amount of free SO ₃ , a faint smoke appears upon contact with moist air. Potassium permanganate

ChDA brands were used in the form of small crystals. If fragile lumps are present, they must be kneaded through plastic wrap. The presence of a large number of durable lumps indicates that potassium permanganate does not meet the standard or was stored under inappropriate conditions. Such permanganate should not be used.

Equipment

A factory stainless steel reactor with a working zone volume of about 30 l was used, equipped with a stirrer, a thermostatic jacket and metering devices for loading / unloading solid and liquid components.

Filtration of the product and washing with a solution of sulfuric acid was carried out on a filter of nonwoven polypropylene material.

The removal of sulfuric acid from a suspension of graphene oxide was carried out by treatment in a drum dialyzer.

The rest of the equipment and accessories were standard.

Example 1

6.00 L of 100% sulfuric acid is poured into a dry and clean reactor at room temperature and 200 g of GSM-2 graphite are charged. Close the reactor with a lid with an attached stirrer. Turn on the stirrer.

In the first stage, with a continuously working stirrer, 60 ml of 60% hydrogen peroxide (density 1.2505 g / cm ³ , 60 ml = 75.03 g) are poured into the reactor with a thin stream through a capillary tube and the reaction mixture is stirred for 1 hour.

In the second stage, 166 ml of water are added to the reaction mixture with a fine jet dispenser through a capillary tube and stirred for another 30 minutes.

In the third stage, 600 g of potassium permanganate are loaded into the reactor for 3 hours; the temperature during the introduction of all potassium permanganate is maintained at 20 ° C. After loading all potassium permanganate, stirring at 20 ° C. is continued for another 1 hour.

In a fourth step, 331 ml of distilled water is added to the reaction mixture with continuous stirring over 40 minutes. In this form, leave the reactor with the reaction mixture overnight, since the implementation of all of the above technological operations takes a full shift.

The next day, turn on the stirrer and slowly pour 24 l of water into the reactor at a rate that excludes the temperature of the reaction mixture exceeding 60 ° C.

After that, 1 liter of 60% hydrogen peroxide is added to the reactor with continuous stirring, while the color of the reaction mixture changes from brown to golden yellow, which is associated with the reduction of manganese dioxide with hydrogen peroxide.

The resulting reaction mixture was a suspension of approximately 32 L containing shiny golden flakes. This suspension was poured onto a polypropylene filter, filtered and washed with 1 mol / L sulfuric acid solution (= 9.2%). Washing is carried out until the manganese sulfate is completely removed from the suspension. To test the completeness of washing, aqueous ammonia or an alkali solution is added to the filtrate sample until an alkaline reaction. The formation of a black or brown precipitate, or turbidity indicates the presence of manganese sulfate. When washing is completed, the filtrate sample after alkalization remains completely transparent and colorless.

The amount of 1M sulfuric acid required for a complete flush depends on the filtration mode, but is approximately 30-35 liters. It should be noted that the product cannot be washed immediately with water after unloading, because graphene oxide in acid-free water easily exfoliates to form a gel that clogs the filter and the water is filtered extremely slowly.

The resulting product containing a certain amount of sulfuric acid is washed from the acid using a drum-type dialyzer, after which the concentration of graphene oxide is adjusted to a standard concentration by adding water. The most convenient concentration for various applications is 0.5% based on the initial graphite. That is, if the loading of graphite in the reactor was 200 g, the final product was adjusted with water to a total weight of 40 kg and mixed thoroughly. It should be noted that the concentration is more convenient for calculating the starting graphite, because graphene oxide does not have a constant composition, in addition, its dry mass depends on air humidity.

When dried, the aqueous dispersion of graphene oxide forms a flexible transparent film, reddish-brown in light. When rapidly heated to 200-250 ° C, this substance flares up and turns into highly dispersed carbon.

In the production of graphene oxide according to the claimed invention, wastewater is formed containing sulfuric acid, potassium sulfate and manganese sulfate. To utilize them, ammonia is added to a slightly alkaline reaction and then a small amount of hydrogen peroxide is used to oxidize the precipitated divalent manganese hydroxide to tetravalent manganese hydroxide. The tetravalent manganese hydroxide is separated by filtration, and it can be used as a chemical reagent for various purposes (for example, as a depolarizer in chemical current sources). The solution contains ammonium sulfate with a small amount of potassium sulfate. This solution can be used as fertilizer in agriculture.

Theoretically, sulfuric acid can be regenerated, without neutralizing it with ammonia, by evaporation. The appropriateness of a particular disposal method is determined by economic considerations.

In FIG. 1 shows an X-ray diffraction pattern of an air-dry film of graphene oxide obtained according to Example 1. As can be seen, the strip corresponding to graphite (interlayer distance 0.3354 nm, which corresponds to 2teta = 39.94 ° at an X-ray wavelength of 2.29091 A) is absent , which indicates the completeness of the oxidation of graphite. The observed intense band with a maximum at 2teta = 9.28 ° corresponds to an interlayer distance of 1.416 nm. In various literature sources, the interlayer distance for graphene oxide varies widely, 0.6-1.2 nm, depending on the degree of oxidation of graphite and the moisture content of the sample. Judging by the observed interlayer distance, the obtained graphene oxide has a rather high oxidation state.

Thus, it is obvious that in the claimed invention, the completeness of the oxidation of graphite with potassium permanganate in sulfuric acid without the addition of nitrate is achieved by preliminary exfoliation of graphite during its interaction with peroxomonosulfuric acid, which, in turn, is formed in the reaction of hydrogen peroxide with sulfuric acid with a minimum content free water in the system. This, the claimed invention differs from the prototype method, in which, when the graphite is treated with a peroxide compound in sulfuric acid, only oxidative intercalation of graphite occurs, and partial exfoliation occurs already during hydrolysis and washing with water. Moreover, the degree of exfoliation is small.

In order to find out the limits of the mass ratio of hydrogen peroxide to graphite at which graphite exfoliates effectively, a series of experiments was carried out in which a suspension of graphite in 100% sulfuric acid was treated with various amounts of 60% hydrogen peroxide, which under these conditions turned into peroxomonosulfuric acid. In these experiments, the ratio of sulfuric acid to graphite was constant, namely, 75 ml of 100% sulfuric acid per 2.5 g of graphite, which corresponds to the ratio in example 1. The reaction mixture was kept for 1 h at 60 ° C until the expansion of intercalated graphite was completed. . The degree of expansion (exfoliation) was estimated by the apparent volume of the floating layer of the expanded graphite compound (without stirring, it floated due to the presence of pores containing oxygen gas). It was found that the apparent volume of the expanded graphite compound layer increases with an increase in the amount of hydrogen peroxide (respectively, peroxomonosulfuric acid), the data are shown in the table.

Table.

The dependence of the apparent volume of the layer of the expanded graphite compound in the graphite system —H ₂ SO ₅ —H ₂ SO ₄ on the mass ratio of the peroxide compound to graphite, moreover, the peroxide compound is converted to the mass of 100% H ₂ O ₂ .

The mass ratio of H ₂ O ₂ to graphite in experiment No. 2 corresponds to the synthesis of exhaust gas according to example 1.

The table shows that the apparent volume of the layer of expanded graphite compounds formed in the reaction of graphite with peroxomonosulfuric acid increases approximately in proportion to the mass ratio of H ₂ O ₂ to graphite. The larger this volume, the more efficient the exfoliation of graphite occurs, which means that the subsequent oxidation of the expanded graphite substance with potassium permanganate will be more complete. However, technological limitations should be considered. The reaction mass should be easily mixed. When the ratio of H ₂ About ₂ to graphite, equal to 0.225 (experiment No. 2, = example 1), the suspension is liquid and easily mixed, so this ratio can be considered optimal. With a mass ratio of H ₂ O ₂ to graphite equal to 0.300 (experiment 3), the system can still be mixed. However, even with a mass ratio of H ₂ O ₂ to graphite equal to 0.375 (experiment 4), the system is such a thick paste that it is almost impossible to work with it, introduce into it and evenly mix any reagents. Of course, you can increase the amount of sulfuric acid in the system to dilute this paste and make it fluid. However, an increase in the amount of sulfuric acid leads to an unjustified increase in the costs of both the synthesis itself and the subsequent disposal of waste. Therefore, we consider the mass ratio of H ₂ O ₂ to graphite equal to 0.300 as the upper practically acceptable limit.

As for the lower limit of the mass ratio of H ₂ O ₂ to graphite, we can take it equal to 0.150 (experiment 1), at which significant expansion (exfoliation) of graphite is still observed. Further reducing this ratio is not advisable, because we will lose the quality of the product, and there is no point in saving on cheap hydrogen peroxide.

The process for producing graphene oxide according to the claimed invention is easily scalable, the resulting product can be widely used in engineering and technology.

Claims (6)

1. A method of producing graphene oxide, comprising treating the carbon material with a first oxidizing agent (potassium permanganate) in concentrated sulfuric acid, diluting the reaction mixture with water, then treating with a second oxidizing agent (hydrogen peroxide) and washing the resulting carbon-containing oxidation product with an acid solution, then with water, characterized in that graphite is used as a carbon material, and before treatment with potassium permanganate, graphite is additionally treated with a solution of hydrogen peroxide in sulfuric acid those wherein the amount of hydrogen peroxide charge of from 0.15 to 0.30 phr for 1 mass.h. graphite in terms of 100% hydrogen peroxide. 2. The method according to p. 1, characterized in that the process of oxidation of graphite is carried out in four stages with a controlled water content in the reaction mixture in stages in accordance with the following scheme: - at the first stage of processing graphite with hydrogen peroxide, the amounts of reagents are calculated so that the total concentration of free water in the reaction mixture does not exceed 0.5%, taking into account the water formed in the reaction H ₂ O ₂ + H ₂ SO ₄ = H ₂ SO ₅ + H ₂ O; - in the second stage, water is added to the reaction mixture in such an amount that the concentration of free water becomes close to 2%; - at the third stage, potassium permanganate is added to the system while maintaining the concentration of free water of the second stage; - in the fourth stage, water is added to the reaction mixture in an amount providing a concentration of free water close to 5%.

Images