High-proportion single-layer graphene oxide and preparation method thereof

Abstract

The invention discloses high-proportion single-layer graphene oxide and a preparation method thereof, and belongs to the technical field of preparation of novel two-dimensional nanometers.The preparation method comprises the steps that firstly, natural flake graphite is subjected to intercalation and oxidation reaction in an electrochemical reactor to obtain a graphene oxide precursor, and then the graphene oxide precursor is subjected to water washing and ultrasonic treatment to obtain graphene oxide; and finally, carrying out ball milling on the formed slurry to obtain the graphene oxide with relatively high single-layer rate. According to the method, centrifugal separation in a traditional method is changed into ball milling, the single-layer rate of graphene oxide is increased, waste is avoided, and therefore the yield is increased.

Description

Technical Field

[0001] The present invention relates to the technical field of novel two-dimensional nanomaterial preparation, and in particular to a high-proportion single-layer graphene oxide and a preparation method thereof. Background Art

[0002] At present, the use of graphite powder to prepare graphene with a high monolayer rate usually uses a chemical method. The chemical method process is seriously polluting and has wastewater discharge; and the graphene oxide obtained by the chemical method, after the structure is destroyed and then reduced to obtain the reduced graphene oxide, the conductivity is not high enough. In the invention patent with the publication number: CN113603084A and the name "A method for preparing graphene oxide by electrochemistry", it is proposed to obtain a graphene precursor by intercalation and oxidation of graphite, and then obtain a dispersion of a few layers of graphene oxide by ultrasound, and obtain graphene oxide by centrifugal drying. Although this method avoids the shortcomings of preparing graphene oxide precursors by chemical methods, a centrifugal separation method is used to prepare graphene oxide in subsequent operations. Centrifugal separation removes graphene with a large number of layers, and the monolayer rate of the remaining product is significantly improved, but this approach increases the operation links and produces a certain amount of waste, and the output of graphene oxide will be reduced.

[0003] Based on this problem, a high-ratio single-layer graphene oxide and a preparation method thereof are proposed. Summary of the invention

[0004] The purpose of the present invention is to provide a high-ratio single-layer graphene oxide and a preparation method thereof to solve the problems in the background technology.

[0005] To achieve the above object, the present invention provides a method for preparing a high-ratio single-layer graphene oxide, the steps of which are as follows: Firstly, natural flake graphite is intercalated and oxidized in an electrochemical reactor to obtain a graphene oxide precursor. Secondly, the graphene oxide precursor is washed with water and ultrasonically treated. Finally, ball milling is performed to obtain graphene oxide with a higher monolayer rate.

[0006] Preferably, the intercalation and oxidation reaction process is as follows: pouring natural flake graphite into a reactor and flattening it to obtain a reaction bed, and compacting the reaction bed with three layers of glass fiber membranes; then pouring an electrolyte into the reactor, using a pressure column to repeatedly press and expel the bubbles in the reaction bed, and then connecting the reactor to an electrochemical workstation through an electrode line to start an electrochemical reaction; wherein the electrolyte is sulfuric acid with a concentration of 50-85 wt.%, and a current density of 10-20 mA / cm 2 , graphite loading 30~300 mg / cm 2 .

[0007] Preferably, the specific process of water washing and ultrasonic treatment is as follows: first, the graphene oxide precursor is dispersed in deionized water, and the filtrate is fully washed with deionized water until the filtrate becomes neutral, and then the washed graphene oxide precursor is placed in deionized water for ultrasonic treatment, and vacuum filtration is performed after the ultrasonic treatment is completed, and finally freeze-dried to obtain graphene oxide; after the electrochemical reaction is completed, the product mostly exists in the form of graphite intercalation compounds, and after contacting water, the graphite intercalation compounds further react with water, and the graphite intercalation compounds are separated into a few layers of graphene oxide by ultrasonic treatment in water. The product is washed to be close to neutral and then ultrasonicated, which is more conducive to the peeling of graphene oxide sheets.

[0008] Preferably, the ultrasonic treatment lasts for 5 to 20 minutes. Ultrasound is a mechanical wave that is not absorbed by molecules and causes vibration of the graphene oxide sheets during propagation. This vibration can promote the exfoliation of the graphene oxide sheets.

[0009] Preferably, the ball milling process is: placing the product after the ultrasound and deionized water in a ball milling jar for ball milling, the ball milling time is 6 to 18 hours, the ball milling speed is 240 to 360 r / min, ball milling helps thinning and peeling of graphene oxide sheets, and during the ball milling process, strong impact and shear forces will be generated on the material, wherein the shear force helps to separate the graphene oxide sheets, and the impact force will reduce the size of the graphene oxide sheets. The purpose of the ball milling study is to prepare graphene oxide with a high monolayer rate by combining electrochemical and physical ball milling.

[0010] The present invention also provides a high-ratio single-layer graphene oxide, which is prepared by the above-mentioned preparation method.

[0011] Preferably, the single-layer graphene oxide is used in the preparation of cement material, and the graphene oxide and the polycarboxylate water reducer are mixed in a mass ratio of 1:3 to prepare the cement material.

[0012] Therefore, the present invention discloses a high-ratio single-layer graphene oxide and a preparation method thereof, which has the following beneficial effects: (1) In the preparation process of the present invention, the graphene oxide precursor is washed, ultrasonicated and ball-milled, the ball-milling time is controlled to be 6 to 18 h, and the ball-milling speed is controlled to be 240 to 360 r / min. Under these conditions, a large amount of single-layer graphene oxide is obtained, thereby avoiding the generation of waste and improving the yield.

[0013] (2) Compared with the traditional chemical method, the electrochemical method used in the present invention to prepare the graphene oxide precursor has the advantages of being environmentally friendly, high yield, and good product conductivity. In addition, the electrochemical method usually requires centrifugal separation to obtain graphene oxide with a high monolayer rate, and produces a certain amount of waste. The present method does not require centrifugal separation, but directly ball mills the entire product, thereby increasing the monolayer rate of graphene oxide, and the yield is greater than 100%.

[0014] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is an AFM image of the product of Example 1 of the present invention; Figure 2 This is an AFM image of the product of Comparative Example 2 of the present invention; Figure 3 It is the BET diagram of the products of Example 1 and Comparative Example 2 of the present invention; Figure 4 The XRD diagrams of the products of Examples 1 to 5 of the present invention are as follows; Figure 5 It is the BET diagram of the products of Examples 1 and 5 of the present invention; Figure 6 It is the BET diagram of the products of Examples 6 to 8 of the present invention; DETAILED DESCRIPTION

[0016] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0017] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0018] Example 1 1) Intercalation and oxidation of natural flake graphite in an electrochemical reactor; Pour natural flake graphite into the reactor and lay it flat to obtain a reaction bed, which is then compressed with three layers of glass fiber membranes; then pour electrolyte into the reactor, use a pressure column to repeatedly press and expel the bubbles in the reaction bed, and then connect the reactor to the electrochemical workstation through the electrode line to start the electrochemical reaction. In this process, the current density is controlled to be 15 mA / cm 2 , graphite loading 50 mg / cm 2 ; 2) After the reaction is completed, pour the electrolyte from the upper end of the reactor for recovery. Take out the glass fiber membrane, transfer the product to 100 mL of deionized water, and wash it thoroughly with deionized water until the filtrate becomes neutral; 3) The washed graphene oxide precursor was dispersed in water and ultrasonicated for 12 min; 4) The ultrasonically treated graphene oxide was further ball-milled, and the ball-milling time was controlled to be 13 h and the ball-milling speed was 300 r / min. After the ball-milling was completed, a slurry containing a high proportion of single-layer graphene oxide was obtained, and further freeze-drying was performed to obtain a solid sample.

[0019] The graphene oxide product obtained in Example 1 was characterized using atomic force microscopy (AFM). Figure 1 It can be seen that the flakes are not completely flat, and the flake height is about 1 nm, which is the same as the height of a single-layer graphene oxide flake. A statistical analysis of the graphene oxide flakes was performed, and 50 flakes were randomly selected, and it was found that most of them were single-layer structures; this shows that the ball-milled graphene oxide can be effectively peeled off to obtain graphene oxide with a higher single-layer rate.

[0020] Comparative Example 1 The specific preparation steps are the same as those in Example 1, except that step 4) is changed to centrifugal separation of the slurry formed after the ultrasonic treatment to obtain the graphene oxide product.

[0021] The products in Example 1 were compared with those in Comparative Example 1. The content of the product obtained in Comparative Example 1 was less than that of the product obtained in Example 1, and the proportion of single-layer graphene obtained after ultrasonic treatment in Comparative Example 1 was lower. Centrifugal separation was used to remove graphene oxide with a larger number of layers, resulting in a certain amount of waste.

[0022] By comparison, a high proportion of single-layer graphene oxide can be obtained by the method protected in this embodiment 1. The graphene oxide prepared by this method is used in the preparation of cement materials, which is beneficial to the dispersion in cement materials and the improvement of application performance.

[0023] Comparative Example 2 100 mg of natural flake graphite was ball milled, the ball milling time was controlled to be 13 h, the ball milling speed was controlled to be 300 r / min, and the product was obtained after the ball milling was completed.

[0024] The product of Comparative Example 2 was characterized by AFM. Figure 2As shown, it can be seen from the figure that the size of the graphite is small, which means that during the ball milling process, the size of the graphite becomes smaller but no graphene with a few layers is obtained. Characterization of multiple layers shows that the height of the layers is tens of nanometers, indicating that ball milling does not directly process natural flake graphite into single-layer graphene or graphene oxide, but in Example 1, the graphene oxide obtained by electrochemical oxidation is ball milled to obtain a single-layer graphene oxide, indicating that electrochemical oxidation must be combined with ball milling to obtain graphene oxide with a high single-layer rate.

[0025] In addition, the products obtained in Example 1 and Comparative Example 2 were characterized by BET. Figure 3 As shown, 1 # The N2 adsorption-desorption isotherm of the product in Example 1 has a specific surface area of ​​301.4 m² / g; # The N2 adsorption-desorption isotherm of the product in comparative example 2; its specific surface area is 68.3 m² / g; the isothermal adsorption-desorption lines of the two are quite different in shape, and the specific surface areas are also very different, indicating that the structures of the two are very different, because the force of ball milling on natural flake graphite is mostly impact force, which reduces the size of graphite. The force on graphene oxide is mostly shear stress, which causes the graphene oxide flakes to peel off, indicating that only by combining electrochemical oxidation and physical ball milling can graphene oxide with a larger specific surface area be obtained.

[0026] Example 2 The operation of Example 1 was repeated, except that the ultrasonic time in step 3) of Example 1 was changed to 3 min.

[0027] Example 3 The operation of Example 1 was repeated, except that the ultrasonic time in step 3) of Example 1 was changed to 5 min.

[0028] Example 4 The operation of Example 1 was repeated, except that the ultrasonic time in step 3) of Example 1 was changed to 20 min.

[0029] Example 5 The operation of Example 1 was repeated, except that the ultrasonic operation in step 3) of Example 1 was removed.

[0030] The products of Examples 1-5 were subjected to XRD characterization analysis. Figure 4As shown, 1# is the XRD curve of the product without ultrasonic treatment, followed by the XRD curves of the products obtained under ultrasonic treatment for 3 min, 5 min, 12 min, and 20 min. The characteristic peak near 11° in the corresponding product XRD graph comes from graphene oxide, the characteristic peak near 22° comes from graphite intercalation compounds, and the characteristic peak near 26° comes from graphite. The peak area ratios near 11°, 22°, and 26° are shown in Table 1.

[0031] Table 1 Peak area ratio

[0032] It can be seen from the above table that ultrasound is beneficial to the exfoliation of graphite intercalation compounds, among which the graphene oxide ratio obtained by 12 min ultrasound is higher, indicating that the effect is better when the ultrasound time is controlled at about 12 min.

[0033] In addition, the products in Example 1 and Example 5 were characterized by BET. Figure 5 As shown, 1 # and 2 # These are the N2 adsorption-desorption isotherms of the products of Example 1 and Example 5. As can be seen from the figure, the adsorption-desorption curves of the two are similar, indicating that they have similar structures, but the specific surface areas of the two are quite different, where the specific surface area of ​​the product in Example 1 is 301.4 m² / g, while the specific surface area of ​​the product in Example 5 is 147.5 m² / g. This indicates that ultrasound combined with ball milling promotes the exfoliation of graphene oxide sheets.

[0034] Example 6 The operation of Example 1 was repeated, except that the ball milling conditions in step 4) of the example were changed to: the ball milling time was controlled to be 6 h, and the ball milling speed was controlled to be 300 r / min.

[0035] Example 7 The operation of Example 1 was repeated, except that the ball milling conditions in step 4) of the example were changed to: the ball milling time was controlled to be 12 h, and the ball milling speed was controlled to be 300 r / min.

[0036] Example 8 The operation of Example 1 was repeated, except that the ball milling conditions in step 4) of the example were changed to: the ball milling time was controlled to be 18 h, and the ball milling speed was controlled to be 300 r / min.

[0037] The products of Examples 6 to 8 were characterized by BET. Figure 6 As shown, 1 # , 2 # , 3 #The N2 adsorption-desorption isotherms of the products obtained after ball milling for 6 h, 12 h, and 18 h, respectively. At a rotation speed of 300 r / min, the specific surface areas of the products after ball milling for 6 h, 12 h, 18 h, and 6 h were 172.2 m² / g, 301.4 m² / g, and 205.8 m² / g, respectively. The specific surface area of ​​the product with a ball milling time of 12 h is the largest, and the specific surface area of ​​the product with a ball milling time of 6 h is the smallest. The results show that the longer the ball milling time is, the larger the specific surface area of ​​the product. From the above experimental data, it can be obtained that the optimal ball milling time is 12 h.

[0038] The concrete compressive strength modification test is carried out in combination with specific application examples.

[0039] Application Example 1 1) Preparation of concrete test blocks: First add coarse aggregate and then fine aggregate into the concrete mixer, turn on the mixer, and stir for 30 seconds to allow the coarse aggregate and fine aggregate to be fully mixed. Then add cement, fly ash and mineral powder, turn on the mixer, and stir again for 30 seconds.

[0040] 2) Pour the graphene oxide dispersion and polycarboxylate water reducer prepared in Example 1 into water and mix them evenly. The addition ratio of the graphene oxide dispersion is 0.05 wt.% of the gel material. Turn on the mixer and add the mixed solvent while stirring for 2 minutes. After stirring evenly. Unload, manually stir and put into the mold. Vibrate the concrete in the mold on a vibration table for 30 seconds to discharge the bubbles in the concrete. After each stirring, the mixer needs to be cleaned with water and then wiped dry with a wet rag to reduce the error of the test.

[0041] 3) Wait for one day, remove the film after the test block solidifies, and put the test block into the curing room for curing. The curing room temperature is 20±2℃, and the relative humidity is above 95%.

[0042] Application Comparative Example 1 The operation of Example 1 was repeated, except that the graphene oxide dispersion added in step 2) of Example 1 was replaced by the graphene oxide dispersion prepared in Comparative Example 1.

[0043] Application Comparative Example 2 The operation of Example 1 was repeated, except that the dispersion of graphene oxide added in step 2) of Example 1 was replaced by the dispersion obtained by ball milling in Comparative Example 2.

[0044] The reference set of test blocks was prepared according to the method in Application Example 1, but without adding the graphene oxide dispersion.

[0045] The test blocks prepared above were subjected to 7-day and 28-day compressive strength tests, respectively. The test results are shown in Tables 2 and 3. Table 2 7-day compressive strength test results of test blocks with different reagent groups

[0046] Table 3 28-day compressive strength test results of test blocks in different reagent groups

[0047] From Table 2 and Table 3, in the application of comparative example 2, the compressive performance of concrete is not greatly improved, and the compressive strength at 7 days and 28 days is increased by 2.1% and 2.0% respectively. In the application of comparative example 1, the compressive strength at 7 days and 28 days is increased by 10.1% and 11.2% respectively. The compressive strength of the test block of application example 1 is increased by 16.1% and 18.1% at 7 days and 28 days respectively, which shows that the addition of graphene oxide obtained by the method protected by the present invention has the greatest improvement on the performance of concrete, with the largest specific surface area and the best dispersion state. In the cement hydration process, the cement pores are reduced. In summary, the dispersibility and number of flake layers of graphene oxide are important factors affecting the application of graphene oxide.

[0048] Therefore, the present invention relates to a high-proportion single-layer graphene oxide and a preparation method thereof. A graphene oxide precursor is prepared by an electrochemical method, which has the advantages of being environmentally friendly, high in yield, and good in product conductivity. The graphene oxide precursor is then ball-milled to increase the single-layer rate of the graphene oxide, avoid the generation of waste, and thus increase the yield.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for preparing a high-proportion single-layer graphene oxide, characterized in that: Here are the steps: Firstly, natural flake graphite is intercalated and oxidized in an electrochemical reactor to obtain a graphene oxide precursor. Secondly, the graphene oxide precursor is washed with water and ultrasonically treated. Finally, ball milling is performed to obtain graphene oxide with a higher monolayer rate.

2. The method for preparing a high-proportion single-layer graphene oxide according to claim 1, characterized in that: The specific process of water washing and ultrasonic treatment is as follows: first, the graphene oxide precursor is dispersed in deionized water, and is fully washed with deionized water until the filtrate becomes neutral. Then, the washed graphene oxide precursor is placed in deionized water for ultrasonic treatment, and a graphene oxide slurry is formed after the ultrasonic treatment.

3. The method for preparing a high-proportion single-layer graphene oxide according to claim 2, characterized in that: The ultrasonic treatment time is 5 to 20 min.

4. The method for preparing a high-proportion single-layer graphene oxide according to claim 1, characterized in that: The ball milling process is as follows: placing the graphene oxide slurry after the ultrasonic treatment in a ball milling jar for ball milling, wherein the ball milling time is 6 to 18 hours and the ball milling speed is 240 to 360 r / min.

5. A high proportion of single-layer graphene oxide, characterized in that: The single-layer graphene oxide is prepared by the preparation method described in any one of claims 1 to 4.

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