Process for the preparation of graphite oxide and graphene oxide

Abstract

The application discloses a preparation method of graphite oxide and graphene oxide, which comprises the following steps: (1) adding a nitric acid compound, concentrated sulfuric acid and graphite into a reaction system first, then adding a defect manufacturing agent, and reacting for 10-20 minutes at a temperature of 40-80 DEG C; according to the mass, the adding proportion of the concentrated sulfuric acid, the defect manufacturing agent and the graphite is 80-100:0.3-0.1:1, and the adding amount of the nitric acid compound is 10-40% of the solute H2SO4 of the concentrated sulfuric acid; the defect manufacturing agent is a high-valence salt or high-valence oxide of a vanadium group, a chromium group or a manganese group metal; (2) continuously adding 2-5 parts of an oxidant according to the mass of the graphite, and reacting for no less than 6 hours at the same reaction temperature to obtain graphite oxide. The Hummers method is improved, the use amount of a strong oxidant is greatly reduced, the oxidation performance requirement of the oxidant is lowered, the reaction process is more gentle, and the obtained graphite oxide can be ultrasonically stripped to obtain graphene oxide, and the post-processing is simple.

Description

Technical Field

[0001] This invention relates to a method for preparing graphite oxide and a method for preparing graphene oxide, belonging to the field of functional materials technology. Background Technology

[0002] The main methods for preparing graphene include liquid phase exfoliation, mechanical exfoliation, redox method, vapor deposition, and epitaxial growth. Among these, the products formed by the redox method have the advantages of low preparation cost and short production cycle. The redox method is currently the most promising and industrialized production method, alongside the vapor deposition method. Its basic mechanism is to intercalate graphite with a strong acid, oxidize graphite with an oxidant to obtain graphite oxide, clean the graphite oxide and ultrasonically exfoliate it to obtain graphene oxide, and finally obtain graphene through chemical reduction or thermal reduction.

[0003] The carbon atoms in graphite are separated by sp. 2 Hybrid orbitals bond and form large conjugated structures. Therefore, graphite is stable and inert; successful graphite oxidation requires strong oxidants or harsh environments. Current technologies, based on the type of oxidant used in graphite oxidation, can be divided into two main categories: the Hummers method (potassium permanganate method) and the Brodie method (chlorate method). The Brodie method has an extremely high explosion risk and is practically unsuitable for industrial application. The Hummer method is relatively safer than the Brodie method, but it requires potassium permanganate with a mass 3-8 times greater than the graphite equivalent as the main oxidant. During the reaction, high concentrations and large amounts of potassium permanganate can form explosive Mn₂O₇ compounds. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide a method for synthesizing graphene oxide with mild reaction conditions and simple operation; another purpose of this invention is to provide a method for preparing graphene.

[0005] Technical solution: The method for synthesizing graphite oxide according to the present invention is characterized by comprising the following steps:

[0006] (1) Nitric acid compound, concentrated sulfuric acid, and graphite are added to the reaction system first, followed by the defect-creating agent. The reaction is carried out at 40-80°C for 10-20 minutes. The ratio of concentrated sulfuric acid, defect-creating agent, and graphite by mass is 80-100:0.3-0.1:1. The amount of nitrate compound added is 10-40% of the concentrated sulfuric acid solute H2SO4. The defect-creating agent is a salt or high-valence oxide corresponding to a high-valence oxide of a vanadium group, chromium group, or manganese group metal.

[0007] (2) Add 2 to 5 parts of oxidant based on the mass of graphite, and react for no less than 2 days at the same reaction temperature to obtain graphite oxide.

[0008] In this invention, the Hummers method is improved to greatly reduce the amount of strong oxidant used. Specifically, in step (1), in a strongly acidic medium, a very small amount of strong oxidizing, high-valence transition metal oxide is used as a defect-creating agent to destroy the conjugated structure and inertness of graphite, causing defects to form in the layered structure of graphite. These defects then become the starting point, initiation point, and attachment point of the oxidation reaction in step (2). At the same time, nitric acid from nitric acid compounds is protonated and dehydrated to form a small amount of electrophilic positive ions NO2 dissolved in the medium. + NO2 + Approaching the defective graphite, electrons are taken from the graphite, providing oxygen to the graphite, which is then reduced to NO. The graphite is successfully oxidized, and the reduced NO cannot participate in the reaction. In step (2), a mild transition metal oxide is introduced as an oxidant to re-oxidize the reduced NO, forming NO2, which has the ability to oxidize graphite. + This leads back to the reaction of graphite oxide.

[0009] The stronger the oxidizing environment formed in step (1), the lower the C / O ratio of the final product and the higher the oxygen content. When the nitrate ions introduced by the nitrate compound are higher than 40% of the concentrated sulfuric acid solute H2SO4, the reaction cannot proceed normally; when they are lower than 10%, the reaction is difficult to occur. The quenching step at the end of the reaction in step (2) is no different from the quenching method of the general Hummers process.

[0010] Preferably, the defect-creating agent is one or a mixture of potassium permanganate, potassium dichromate, potassium chromate, and chromium trioxide. Taking potassium permanganate as an example, potassium permanganate forms the intermediate MnO3. + This disrupts the structural stability of graphite (Li C, Chen X, Shen L, et al. Revisiting the Oxidation of Graphite: Reaction Mechanism, Chemical Stability, and Structure Self-Regulation[J]. ACS Omega, 2020, 5, 3397−3404. DOI:10.1021 / acsomega.9b03633.). When the defect-creating agent is vanadate or chromate, the catalytic intermediate formed in the reaction system is CrO2. 2+ or VO 2+ The C / O ratio and XRD pattern of the final product will vary slightly depending on the defect-creating agent. In this reaction, even a trace amount of defect-creating agent can disrupt the graphite structure.

[0011] Preferably, the amount of the nitric acid compound added is 10-20% of the concentrated sulfuric acid solute H2SO4. Adding more than 20% would be wasteful, while 10-20% would have no significant impact on the overall reaction.

[0012] Preferably, the nitrate compound is one or a mixture of two selected nitric acid and alkali metal nitrates. When the electrophilic catalyst is an aqueous solution of nitric acid, the mass fraction of nitric acid is greater than 68%. A fraction lower than this increases the reaction risk, and transition metal nitrates are poorly soluble in this system and are not suitable for this application. More preferably, the nitrate compound is one or a mixture of two selected potassium nitrate and sodium nitrate.

[0013] Preferably, the concentrated sulfuric acid is concentrated sulfuric acid with a mass fraction greater than 90%.

[0014] Preferably, in step (2), the reaction time is 2-6 days. The reaction time is related to the concentration of the defect-creating agent.

[0015] Preferably, the reaction temperature is 50~60℃. This reaction is exothermic, and the heat generated by the reaction itself can sustain the reaction.

[0016] Preferably, the oxidant is one or a mixture of manganese dioxide, chromium trioxide, potassium persulfate, oxygen, and ozone, and the amount of the oxidant added is 3 to 4 parts. More preferably, the oxidant is manganese dioxide.

[0017] The method for preparing graphene oxide according to the present invention is characterized in that the graphene oxide in the aforementioned portion is subjected to impurity removal and ultrasonic exfoliation treatment to obtain graphene oxide.

[0018] Preferably, the impurity removal step includes: adding the obtained graphene oxide to a reducing agent, stirring, centrifuging, and washing to obtain graphene, wherein the reducing agent is a 3-5% (w / w) aqueous solution of hydrogen peroxide; the ultrasonic exfoliation step includes: placing the impurity-removed graphene oxide in deionized water, wherein the mass fraction of graphene oxide is not higher than 10%, and ultrasonically exfoliating for 25-35 minutes. Hydrogen peroxide is used to reduce the high-valence oxidant, making it a low-valence soluble ion, which facilitates separation, while preventing the oxidant from further damaging the graphene oxide after the addition of water.

[0019] The graphene oxide obtained by this method is surface-modified, water-soluble graphene, which can be used as a barrier material, self-assembled graphene hydrogels, etc. It can also be reduced in a stronger atmosphere, such as by surface deoxygenation under the action of hydroxylamine, hydrazine hydrate, sodium borohydride, etc., to convert it into reduced graphene oxide (rGO).

[0020] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: 1. The reaction is a catalytic oxidation reaction, the reaction process is mild, the oxidant required for the reaction can be added at once, and the operation process is simple; 2. The requirements for oxidant are reduced; 3. The obtained graphene oxide can be obtained by removing impurities and ultrasonic treatment, and the operation is simple. Attached Figure Description

[0021] Figure 1 This is the Raman spectroscopy test spectrum of the first embodiment of the present invention.

[0022] Figure 2 This is the Raman spectroscopy test spectrum of the second embodiment of the present invention.

[0023] Figure 3 This is the Raman spectroscopy test spectrum of the third embodiment of the present invention.

[0024] Figure 4 This is an X-ray diffraction (XRD) test spectrum of the first embodiment of the present invention.

[0025] Figure 5 This is an X-ray diffraction (XRD) test spectrum of the second embodiment of the present invention.

[0026] Figure 6 This is an X-ray diffraction (XRD) test spectrum of the third embodiment of the present invention. Detailed Implementation

[0027] The technical solution of the present invention will be further described below with reference to the accompanying drawings. In the following embodiments, unless otherwise specified, the reagents used do not require additional purification and can be used directly.

[0028] Example 1: Step 1: By mass, add 1 part graphite, 80 parts sulfuric acid (concentration greater than 90%) as the reaction medium, and 20 parts nitric acid as the catalyst to a reaction vessel. Stir, add 0.3 parts potassium permanganate as a defect-creating agent, and react at 40°C for 15 minutes. The resulting reaction product is subjected to Raman spectroscopy. The test results are shown below. Figure 1 The formation of defect peaks (d peak, around 1350) and the decrease of graphitization peaks (g peak, around 1580) were observed in the Raman spectrum.

[0029] In step two, according to the amount of graphite added, 3 parts of manganese dioxide were added as an oxidant. The reaction temperature was 40℃, and the reaction was carried out for 6 days. Microscopic observation showed that the black graphite flakes had completely transformed into a light yellow color. X-ray diffraction (XRD) observation showed that the characteristic peak of the graphite intercalation compound (GIC) at a 2θ diffraction angle of 22.5° disappeared, confirming the completion of the reaction. XRD analysis of the obtained reaction product was performed, and the results are shown below. Figure 4 .

[0030] Step 3: Slowly pour the reaction mixture obtained in Step 2 into an ice-water mixture containing 3% hydrogen peroxide and stir. Centrifuge to collect the solid, wash away the free acid, and obtain the product.

[0031] The obtained product was tested by X-ray photoelectron spectroscopy (XPS). The C / O ratio was 1.6, and the oxygen / carbon ratios on the surfaces of natural graphite and expandable graphite were 0.05 and 0.14, respectively (Han Zhidong, Wang Jianqi. XRD / XPS study on graphite oxidation process [J]. Journal of Inorganic Chemistry, 2003, (12): 1366-1370.). It can be seen that the raw material graphite in this embodiment was effectively oxidized.

[0032] Example 2: Step 1: By mass, add 1 part graphite, 90 parts sulfuric acid (concentration greater than 90%) as the reaction medium, 10 parts nitric acid as the catalyst, and 0.5 parts potassium permanganate as the defect-creating agent to the reaction vessel. The reaction temperature is 40°C, and the mixture is stirred for 15 minutes. Raman spectroscopy is performed on the obtained reaction product. The test results are shown below. Figure 2 .

[0033] In step two, according to the amount of graphite added, 3 parts of manganese dioxide were added as an oxidant. The reaction temperature was 80℃, and the reaction was carried out for 2 days. After the reaction was completed, the resulting reaction product was subjected to XRD analysis. The test results are shown in [Figure 2]. Figure 5 .

[0034] Step 3: Slowly pour the reaction mixture obtained in Step 2 into a mixture of 3% hydrogen peroxide and ice water, stir, centrifuge to collect the solid, wash away the free acid, and obtain the product. XPS analysis of the obtained product showed a C / O ratio of 1.5.

[0035] Example 3: Step 1: By mass, add 1 part graphite, 90 parts sulfuric acid (concentration greater than 90%) as the reaction medium, 10 parts nitric acid as the catalyst, and 0.5 parts chromium trioxide as the defect-creating agent to the reaction vessel. The reaction temperature is 60℃, and the reaction is stirred for 10 minutes. Raman spectroscopy is performed on the obtained reaction product. The test results are shown in […]. Figure 3 .

[0036] In step two, according to the amount of graphite added, 3 parts of manganese dioxide were added as an oxidant. The reaction temperature was 60℃, and the reaction was carried out for 4 days until completion. The resulting reaction product was subjected to XRD analysis, and the results are shown below. Figure 6 .

[0037] Step 3: Slowly pour the reaction mixture obtained in Step 2 into a mixture of 3% hydrogen peroxide and ice water, stir, centrifuge to collect the solid, wash away the free acid, and obtain the product. XPS analysis of the obtained product showed a C / O ratio of 1.8.

Claims

1. A method for preparing graphite oxide, characterized in that, Includes the following steps: (1) Nitric acid compound, concentrated sulfuric acid, and graphite are added to the reaction system first, followed by the defect-creating agent. The reaction is carried out at 40-80°C for 10-20 minutes. The ratio of concentrated sulfuric acid, defect-creating agent, and graphite by mass is 80-100:0.3-0.1:

1. The amount of nitric acid compound added is 10-40% of the concentrated sulfuric acid solute. The defect-creating agent is a high-valence oxide salt or high-valence oxide of vanadium, chromium, or manganese group metals. (2) Based on the mass of graphite, add 2 to 5 parts of oxidant and react for no less than 2 days at the same reaction temperature to obtain graphite oxide. The oxidant is one or more of manganese dioxide, potassium persulfate, oxygen, and ozone.

2. The method for preparing graphite oxide according to claim 1, characterized in that, In step (1), the defect-creating agent is one or more of potassium permanganate, potassium dichromate, potassium chromate, and chromium trioxide.

3. The method for preparing graphite oxide according to claim 1, characterized in that, In step (1), the amount of the nitric acid compound added is 10-20% of the concentrated sulfuric acid solute.

4. The method for preparing graphite oxide according to claim 1, characterized in that, In step (1), the concentrated sulfuric acid is concentrated sulfuric acid with a mass fraction greater than 90%.

5. The method for preparing graphite oxide according to claim 3, characterized in that, In step (1), the nitric acid compound is an alkali metal nitrate, and the nitric acid is a mixture of two of them. The nitric acid is an aqueous solution of nitric acid with a mass fraction of not less than 68%.

6. The method for preparing graphite oxide according to claim 1, characterized in that, In step (2), the amount of oxidant added is 3 to 4 parts.

7. The method for preparing graphite oxide according to claim 1, characterized in that, In step (2), the reaction time is 2-6 days.

8. The method for preparing graphite oxide according to claim 1, characterized in that, In step (1), the reaction temperature is 40~60℃.

9. A method for preparing graphene oxide, characterized in that: The graphene oxide described in claim 1 is subjected to impurity removal and ultrasonic exfoliation to obtain graphene oxide.

10. The method for preparing graphene oxide according to claim 9, characterized in that, The impurity removal step includes: adding the obtained graphene oxide to a reducing agent, stirring, centrifuging, washing, and obtaining graphene, wherein the reducing agent is a 3-5% (w / w) aqueous solution of hydrogen peroxide.

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