A method of preparing graphene oxide

Abstract

The application relates to a method for preparing graphene oxide, which comprises the following steps: taking seawater and standing, filtering with a large-pore filter membrane, and then filtering again with a micropore filter membrane to collect the seawater after the secondary filtration for standby; taking the seawater after the twice filtration as an electrolyte, taking a graphite sheet as a working electrode, i.e. an anode, and taking a platinum wire as a counter electrode, i.e. a cathode, placing the working electrode and the counter electrode into the electrolyte formed by the seawater, and placing the two electrodes in parallel to each other; applying a constant voltage to the graphite sheet to perform a mild intercalation reaction; increasing the constant voltage of an electrolysis device to perform oxidation and peeling of the graphite sheet after the mild intercalation, GO is gradually peeled off and dispersed in the electrolyte along with the reaction, and the graphene oxide is completely peeled off along with the extension of the reaction time; filtering and cleaning the obtained graphene oxide to remove the residual impurities, and then obtaining pure graphene oxide; the scheme is not used with strong acid as an electrolyte, and is more green, environmental protection, economic, efficient and simple and easy to operate.

Description

Technical Field

[0001] This application relates to the technical field of graphene oxide, and more specifically to a method for preparing graphene oxide. Background Technology

[0002] Graphene oxide (GO) is a common derivative of graphene, a two-dimensional nanomaterial formed by a single layer of carbon atoms in an sp2 hybridization configuration. In addition to sp2 hybridization regions, GO also contains a large number of sp3 hybridization regions. Unlike graphene, GO contains numerous oxygen-containing groups and defects. Hydroxyl and epoxy groups are mainly distributed within the layers of GO sheets, while carbonyl and carboxyl groups are mainly distributed at the edges. These characteristics give GO its hydrophilicity and ease of modification. Furthermore, its excellent thermal conductivity, chemical stability, and mechanical strength demonstrate that GO is a promising nanomaterial. In the field of electronics, GO can be used as an electrode material, capacitor material, and conductive material, and can be used to manufacture flexible electronic devices. In the field of energy storage, GO can be used to prepare energy storage devices such as lithium-ion batteries and supercapacitors. In the biomedical field, GO can be used to prepare biosensors and drug delivery systems. In the field of environmental protection, GO can be used to prepare adsorbents and photocatalysts for water pollution control and waste gas purification. To date, GO has been applied in multiple fields and has broad application prospects.

[0003] Currently, the most common method for preparing GO is still the traditional chemical oxidation method, such as the Brodie process, the Staudenmaier process, and the Hummers process. All of these methods involve the use of strong oxidants and strong acids, such as concentrated sulfuric acid, nitric acid, and potassium permanganate. In large-scale GO production, the excessive use of these strong oxidants and acids is almost inevitable, they are expensive, pose an explosion risk, and may cause serious potential threats to the surrounding environment. Therefore, in recent years, researchers have attempted to prepare GO using electrochemical stripping methods. Electrochemical methods effectively avoid the explosion risks associated with traditional chemical oxidation methods, offer milder reaction conditions, are relatively simpler in process, and are more controllable.

[0004] Although electrochemical methods for GO production effectively avoid some problems, most related studies still use strong oxidizing electrolytes, including sulfuric acid, nitric acid, hydrochloric acid, and perchloric acid, which still pose a potential environmental pollution risk. Furthermore, industrial-scale GO production requires significant expenditure on purchasing sufficient reagents to prepare the electrolytes to meet production needs, and wastewater treatment remains costly, contradicting economic efficiency and the principles of clean production. Therefore, developing an appropriate, economical, and environmentally friendly method for GO production remains a pressing issue. Summary of the Invention

[0005] This application addresses the aforementioned shortcomings of the prior art by providing a method for preparing graphene oxide that does not use strong acids as electrolytes and is more environmentally friendly, economical, efficient, simple, and easy to operate.

[0006] To solve the above-mentioned technical problems, the technical solution adopted in this application is: a method for preparing graphene oxide, the steps of which include:

[0007] (1) Seawater pretreatment: Take seawater and let it stand, then filter it with a large-pore filter membrane. After filtration, filter the seawater a second time with a microporous filter membrane and collect the seawater after the second filtration for later use.

[0008] (2) Mild intercalation of graphite sheets: Take the seawater filtered twice in step (1) as the electrolyte, use graphite sheets as the working electrode (anode) and platinum wire as the counter electrode (cathode), and then put the working electrode and the counter electrode into the electrolyte, placing them in parallel; apply a constant voltage with a regulated DC power supply to perform mild intercalation of the graphite sheets.

[0009] (3) Preparation of graphene oxide: Increase the constant voltage of the electrolysis device in step (2) to oxidize and peel off the graphite sheet after gentle intercalation. As the reaction proceeds, GO gradually falls off and disperses in the electrolyte. As the reaction time increases, all of GO is peeled off. After filtering the obtained GO and washing off the residual impurities, pure GO is obtained.

[0010] Furthermore, the seawater mentioned in step (1) is 200-400 mL, and the seawater is left to stand for 2-4 hours.

[0011] Furthermore, the pore size of the macroporous filter membrane mentioned in step (1) is 5-25 μm, and the pore size of the microporous filter membrane is 0.1-0.22 μm.

[0012] Furthermore, in step (2), the ratio of seawater after two filtrations to graphite sheets is 100-200 mL: 0.2-0.3 g; (the ratio can be increased or decreased proportionally depending on the specific reaction apparatus).

[0013] Furthermore, the constant voltage applied in step (2) is 2-3V.

[0014] Furthermore, the reaction time for the mild intercalation described in step (2) is 30-60 min.

[0015] Furthermore, the constant voltage mentioned in step (3) is 15-25V.

[0016] Furthermore, in step (3), the reaction time after increasing the constant voltage of the electrolysis device in step (2) is 2-4 hours.

[0017] The advantages and beneficial effects of this application are as follows:

[0018] 1. This application is the first to directly use seawater as the electrode solution to prepare GO via an electrochemical method. The seawater only needs to be filtered twice before it can be used directly. The first filtration uses a large-pore membrane to filter out small particles of silt, suspended solids, and other impurities. The second filtration uses a microporous membrane to filter out impurities and microorganisms that the large-pore membrane did not remove. This effectively removes impurities from the seawater, preventing them from affecting the subsequent electrolysis effect, minimizing the risk of contamination of graphene oxide, and avoiding damage to the equipment. More importantly, this method of directly using seawater as the electrolyte eliminates the need for traditional strong acids such as sulfuric acid, nitric acid, hydrochloric acid, and perchloric acid, thus reducing the possibility of environmental pollution. It also eliminates the need to purchase chemicals to prepare the electrolyte and saves on waste liquid treatment, making it more economical, environmentally friendly, and green.

[0019] 2. In the specific preparation process of graphene oxide (GO), this application not only directly uses seawater as the electrolyte but also reasonably controls the range of the constant voltage. During the gentle intercalation process of the graphite sheets, the constant voltage is controlled at 2-3V, and the reaction time is 30-60 minutes. Under these conditions, anions in the seawater, such as Cl-, SO42-, and CO32-, can be inserted between the graphite layers, increasing the interlayer spacing and causing graphite expansion. Furthermore, it effectively avoids premature exfoliation due to excessively high voltage, which could affect the intercalation process. Then, in the GO preparation step, the constant voltage of the electrolysis device in step 2 is increased to a reasonable range of 15-25V, and the reaction time is increased to 2-4 hours. This is because increasing the applied voltage during the reaction process... While accelerating the peeling speed, it reduces the oxidation degree and increases the number of GO layers. This is because water is split into hydroxyl radicals and oxygen radicals, which attack sp2 carbon atoms to produce hydroxyl groups. The hydroxyl groups on the basal surface and edges are converted into epoxy groups and carbonyl groups, respectively. The carbonyl groups are further oxidized to carboxyl groups. If the voltage and reaction time are not properly controlled, the rate at which water is split into hydroxyl radicals and oxygen radicals will be accelerated, but at the same time, a large amount of oxygen will be generated. Excessive oxygen will cause GO to peel off prematurely, leading to an increase in the number of GO layers and a decrease in the oxidation degree. However, this application effectively avoids the above-mentioned shortcomings by controlling the above process conditions. The prepared graphene oxide product has more wrinkles, thinner sheets, and better flexibility, with more ideal size, oxygen content, and ID / IG value, which is significantly better than the product prepared in the comparative example. Attached Figure Description

[0020] Figure 1 This is a photograph of an aqueous dispersion of GO.

[0021] Figure 2 This is a scanning electron microscope image of GO.

[0022] Figure 3 This is the Raman spectrum of GO.

[0023] Figure 4 This is the X-ray photoelectron spectrum of GO. Detailed Implementation

[0024] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are merely preferred embodiments, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this invention.

[0025] Example 1:

[0026] Step 1: Seawater pretreatment: After letting 300 mL of seawater stand for 3 hours, filter it with a filter membrane with a pore size of 10 μm. After filtration, filter the seawater a second time with a microporous filter membrane with a pore size of 0.1 μm and collect the seawater after the second filtration for later use.

[0027] Step 2: Gentle intercalation of graphite sheets: Take 150 mL of the seawater filtered twice in Step 1 as the electrolyte, use 0.25 g of graphite sheet as the working electrode (anode) and platinum wire as the counter electrode (cathode), and then place the working electrode and counter electrode in the electrolyte, placing them parallel to each other. Apply a constant voltage of 2.5 V using a regulated DC power supply to gently intercalate the graphite sheet for 45 min;

[0028] Step 3: Preparation of GO: Then increase the constant voltage of the electrolysis device in step 2 to 20V to oxidize and peel off the gently intercalated graphite sheet. As the reaction proceeds, GO gradually falls off and disperses in the electrolyte. After 3 hours of reaction, all GO is peeled off. After filtering and washing away the residual impurities, pure GO is obtained.

[0029] Taking the GO prepared in Example 1 as an example, characterization and performance determination were performed:

[0030] Figure 1 The image shows an actual sample of an aqueous dispersion of GO. It can be observed that GO is uniformly dispersed in the aqueous solution without precipitation, indicating that GO has good oxidizing power and good dispersibility in aqueous solution.

[0031] Figure 2 This is a scanning electron microscope (SEM) image of GO. The image shows the typical morphological characteristics of GO nanosheets, with numerous wrinkles on the surface, demonstrating the two-dimensional and flexible nature of GO. The largest GO nanosheet in the image is approximately 30 μm, illustrating the possibility and advantages of this method for preparing large-sized GO.

[0032] Figure 3 This is the Raman spectrum of GO. Raman spectroscopy can reflect the internal structure of GO, such as... Figure 3 As shown, four peaks at different positions can be clearly observed: the D peak (1351 cm⁻¹), the G peak (1599 cm⁻¹), the 2D peak (2693 cm⁻¹), and the D+G peak (2931 cm⁻¹). The calculated ID / IG value of GO is 0.94, which is within the typical range, indicating that this method successfully prepared GO with a reasonable degree of oxidation.

[0033] Figure 4 The image shows the X-ray photoelectron spectrum of GO. Characterization results show that the oxygen content of GO prepared by this method is 18.2 at.%, indicating that GO was successfully prepared by this method and that the obtained GO has good oxidation degree.

[0034] Example 2:

[0035] Step 1: Seawater pretreatment: After letting 200 mL of seawater stand for 2 hours, filter it with a filter membrane with a pore size of 10 μm. After filtration, filter the seawater a second time with a microporous filter membrane with a pore size of 0.1 μm. Collect the seawater after the second filtration for later use.

[0036] Step 2: Gentle intercalation of graphite sheets: Take 100 mL of the seawater filtered twice in Step 1 as the electrolyte, use 0.2 g of graphite sheet as the working electrode (anode) and platinum wire as the counter electrode (cathode), and then place the working electrode and counter electrode in the electrolyte, placing them parallel to each other. Apply a constant voltage of 2 V using a regulated DC power supply to gently intercalate the graphite sheet for 30 min;

[0037] Step 3: Preparation of GO: Increase the constant voltage of the electrolysis device in Step 2 to 15V to oxidize and peel off the gently intercalated graphite sheets. As the reaction proceeds, GO gradually detaches and disperses in the electrolyte. After 2 hours of reaction, all GO is peeled off. Filter the obtained GO and wash away any remaining impurities to obtain pure GO.

[0038] Example 3:

[0039] Step 1: Seawater pretreatment: After letting 400 mL of seawater stand for 4 hours, filter it with a filter membrane with a pore size of 10 μm. After filtration, filter the seawater a second time with a microporous filter membrane with a pore size of 0.1 μm. Collect the seawater after the second filtration for later use.

[0040] Step 2: Gentle intercalation of graphite sheets: Take 200 mL of the seawater filtered twice in Step 1 as the electrolyte, use 0.3 g of graphite sheet as the working electrode (anode) and platinum wire as the counter electrode (cathode), and then place the working electrode and counter electrode in the electrolyte, placing them parallel to each other. Apply a constant voltage of 3V using a regulated DC power supply to gently intercalate the graphite sheet for 60 min.

[0041] Step 3: Preparation of GO: Increase the constant voltage of the electrolysis device in step 2 to 25V to oxidize and peel off the gently intercalated graphite sheet. As the reaction proceeds, GO gradually falls off and disperses in the electrolyte. After 4 hours of reaction, all GO is peeled off. After filtering and washing away the residual impurities, pure GO is obtained.

[0042] Example 4:

[0043] Step 1: Seawater pretreatment: After letting 400 mL of seawater stand for 4 hours, filter it with a filter membrane with a pore size of 20 μm. After filtration, filter the seawater a second time with a microporous filter membrane with a pore size of 0.22 μm. Collect the seawater after the second filtration for later use.

[0044] Step 2: Gentle intercalation of graphite sheets: Take 200 mL of the seawater filtered twice in Step 1 as the electrolyte, use 0.3 g of graphite sheet as the working electrode (anode) and platinum wire as the counter electrode (cathode), and then place the working electrode and counter electrode in the electrolyte, placing them parallel to each other. Apply a constant voltage of 3V using a regulated DC power supply to gently intercalate the graphite sheet for 60 min;

[0045] Step 3: Preparation of GO: Increase the constant voltage of the electrolysis device in Step 2 to 25V to oxidize and peel off the gently intercalated graphite sheets. As the reaction proceeds, GO gradually detaches and disperses in the electrolyte. After 4 hours of reaction, all GO is peeled off. Filter the obtained GO and wash away any remaining impurities to obtain pure GO.

[0046] Comparative Example 1

[0047] Step 1: Seawater pretreatment: After letting 400 mL of seawater stand for 4 hours, filter it with a filter membrane with a pore size of 10 μm. After filtration, filter the seawater a second time with a microporous filter membrane with a pore size of 0.1 μm. Collect the seawater after the second filtration for later use.

[0048] Step 2: Gentle intercalation of graphite sheets: Take 200 mL of the seawater filtered twice in Step 1 as the electrolyte, use 0.3 g of graphite sheet as the working electrode (anode) and platinum wire as the counter electrode (cathode), and then place the working electrode and counter electrode in the electrolyte, placing them parallel to each other. Apply a constant voltage of 3V using a regulated DC power supply to gently intercalate the graphite sheet for 60 min;

[0049] Step 3: Preparation of GO: Increase the constant voltage of the electrolysis device in step 2 to 30V (the difference between the graphene oxide prepared in this comparative example and the scheme of this application lies in the adjustment of the constant voltage here) to oxidize and peel off the gently intercalated graphite sheet. As the reaction proceeds, GO gradually falls off and disperses in the electrolyte. After 4 hours of reaction, all GO is peeled off. After filtering the obtained GO and washing off the residual impurities, pure GO is obtained.

[0050] Comparative Example 2

[0051] Step 1: Seawater pretreatment: After letting 400 mL of seawater stand for 4 hours, filter it with a filter membrane with a pore size of 10 μm. After filtration, filter the seawater a second time with a microporous filter membrane with a pore size of 0.1 μm. Collect the seawater after the second filtration for later use.

[0052] Step 2: Gentle intercalation of graphite sheets: Take 200 mL of the seawater filtered twice in Step 1 as the electrolyte, use 0.3 g of graphite sheet as the working electrode (anode) and platinum wire as the counter electrode (cathode), and then place the working electrode and counter electrode in the electrolyte, placing them parallel to each other. Apply a constant voltage of 3V using a regulated DC power supply to gently intercalate the graphite sheet for 60 min;

[0053] Step 3: Preparation of GO: Increase the constant voltage of the electrolysis device in step 2 to 10V (the difference between the graphene oxide prepared in this comparative example and the scheme of this application lies in the adjustment of the constant voltage here) to oxidize and peel off the gently intercalated graphite sheet. As the reaction proceeds, GO gradually falls off and disperses in the electrolyte. After 4 hours of reaction, all GO is peeled off. After filtering the obtained GO and washing off the residual impurities, pure GO is obtained.

[0054] The reaction conditions corresponding to the embodiments and comparative examples of this application are shown in Table 1 below:

[0055] Table 1. Reaction conditions for the examples and comparative examples.

[0056] Serial Number electrolyte graphene Filter membrane microporous filter membrane Step 3 Voltage Example 1 150ml 0.25g 10μm 0.1μm 20V Example 2 200ml 0.3g 10μm 0.1μm 25V Example 3 100ml 0.2g 10μm 0.1μm 15V Example 4 200ml 0.3g 20μm 0.22μm 25V Comparative Example 1 200ml 0.3g 10μm 0.1μm 30V Comparative Example 2 200ml 0.3g 10μm 0.1μm 10V

[0057] Table 2 below shows the performance test results of the graphene oxide prepared in the embodiments and comparative examples of this application:

[0058] Table 2 shows the performance testing results of the graphene oxide prepared in the embodiments and comparative examples of this application.

[0059] Serial Number Dispersion Morphological characteristics Size (μm) ID / IG value Oxygen content Example 1 Evenly dispersed, no sedimentation observed. Many folds 30 0.94 18.2 at.% Example 2 Evenly dispersed, no sedimentation observed. Many folds 25 0.81 16.8 at.% Example 3 Evenly dispersed, no sedimentation observed. Many folds 27 0.88 17.6 at.% Example 4 Evenly dispersed, no sedimentation observed. Many folds 24 0.79 16.4 at.% Comparative Example 1 Uniform and not dispersed, with a small amount of sediment. Fewer wrinkles 19 0.54 11.7 at.% Comparative Example 2 Uniform and not dispersed, with a small amount of sediment. Fewer wrinkles 16 0.42 9.4 at.%

[0060] As can be seen from the above embodiments and comparative examples, in the process of preparing graphene oxide, increasing the voltage will accelerate the peeling speed but reduce the degree of oxidation, and the number of GO layers will also increase. This is because water is split into hydroxyl radicals and oxygen radicals, which attack sp2 carbon atoms to produce hydroxyl groups. The hydroxyl groups on the basal surface and the edge are converted into epoxy groups and carbonyl groups, respectively, and the carbonyl groups are further oxidized to carboxyl groups. In this sense, increasing the voltage will accelerate the rate at which water is split into hydroxyl radicals and oxygen radicals, but at the same time, a large amount of oxygen will be generated. Too much oxygen will cause GO to peel off prematurely, resulting in an increase in the number of GO layers and a decrease in the degree of oxidation (the oxygen content of the graphene oxide prepared in the comparative examples is lower than the oxygen content of the graphene oxide prepared in the embodiments of this application). In addition, in the process of preparing graphene oxide, increasing the voltage will affect the entire peeling process, thus affecting the overall effect. Fewer wrinkles indicate that the prepared graphene oxide sheets are thicker and less flexible. Furthermore, if the voltage is too high and the peeling speed is too fast, it will lead to a decrease in the degree of oxidation, thereby leading to a decrease in the ID / IG value and oxygen content. The solution of this application, however, is reasonable. The preparation of graphene oxide within the specified voltage range not only maintains its exfoliation time within a reasonable range, but also yields a final product with more ideal size, oxygen content, and ID / IG value, significantly superior to the product prepared in the comparative example. This application directly uses seawater as the electrolyte to prepare graphene oxide, unlike existing seawater batteries. The technical solution of this application is an electrolytic cell, while seawater batteries are galvanic cells. The purpose of seawater batteries is to store and release electrical energy, while the purpose of this application is to prepare graphene oxide. The seawater used in this application is conventional seawater taken from the ocean that has been allowed to settle and then filtered twice. Seawater is rich in many elements, requiring no testing or range limitation, thus eliminating the need for other processing steps and methods. It is convenient to use, low in cost, and more green and environmentally friendly.

Claims

1. A method for preparing graphene oxide, characterized in that: The preparation steps of this method include: (1) Seawater pretreatment: Take seawater and let it stand, then filter it with a large-pore filter membrane. After filtration, filter the seawater a second time with a microporous filter membrane and collect the seawater after the second filtration for later use. (2) Mild intercalation of graphite sheets: Take the seawater filtered twice in step (1) as the electrolyte, use the graphite sheet as the working electrode (anode) and the platinum wire as the counter electrode (cathode), and then put the working electrode and the counter electrode into the electrolyte composed of seawater, with the two electrodes placed parallel to each other; apply a constant voltage with a regulated DC power supply to carry out a mild intercalation reaction on the graphite sheet. (3) Preparation of graphene oxide: Increase the constant voltage of the electrolysis device in step (2) to oxidize and peel off the graphite sheet after gentle intercalation. As the reaction proceeds, GO gradually falls off and disperses in the electrolyte, and as the reaction time extends, all the graphene oxide is peeled off. After filtering the obtained graphene oxide and cleaning the residual impurities, pure graphene oxide is obtained. The constant voltage applied in step (2) is 2-3V; the constant voltage applied in step (3) is 15-25V, and the reaction time is 2-4h.

2. The method for preparing graphene oxide according to claim 1, characterized in that: The seawater mentioned in step (1) is 200-400 mL, and the seawater is left to stand for 2-4 hours.

3. The method for preparing graphene oxide according to claim 1, characterized in that: The pore size of the large-pore filter membrane mentioned in step (1) is 5-25 μm, and the pore size of the microporous filter membrane is 0.1-0.22 μm.

4. The method for preparing graphene oxide according to claim 1, characterized in that: In step (2), the ratio of seawater and graphite sheets after two filtrations is 100-200 mL: 0.2-0.3 g.

5. The method for preparing graphene oxide according to claim 1, characterized in that: The reaction time for the mild intercalation described in step (2) is 30-60 min.

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