A method for folding graphene oxide

Abstract

This invention discloses a method for folding graphene oxide. This method involves uniformly mixing a graphene oxide (GO) solution with an electrospinnable polymer solution, then subjecting the mixed solution to electrospinning to produce polymer fibers containing folded GO. This is then heat-treated to produce folded reduced GO. By reducing the GO content in the mixed solution, the GO flakes can be separated by electrospinning. Taking advantage of the high von Karman number and high deformability of GO flakes, an electric field is used to stretch the GO and polymer mixed solution, creating spatial compression that causes the GO flakes to fold.

Description

Technical Field

[0001] The present invention relates to folded graphene oxide, in particular to a method for folding graphene oxide. Background Art

[0002] Due to its unique electronic structure, graphene and its derivatives are increasingly emerging in optoelectronics, sensing, and superconductivity, with a strong potential for application. However, for optoelectronic applications, graphene and its derivatives lack nonlinear optical properties due to their high lattice symmetry. Folding a two-dimensional sheet to create a lattice rotation between adjacent layers, thereby breaking new symmetries, is an important method for endowing graphene and its derivatives with new physical properties. Currently, folding two-dimensional materials directly is typically performed using sophisticated micro- and nano-instruments such as atomic force microscopes (AFMs) or scanning tunneling microscopes (STMs) (e.g., patent CN111439746B). While this method can produce micro- and nano-folded structures with precise folding, it can only process one sheet at a time, resulting in very low production efficiency. Furthermore, due to the small tips of AFMs and STMs, the area of the sheet that can be manipulated at any one time is limited, making it difficult to achieve complex folded structures. The large-scale production of folded graphene oxide with precisely controllable structures remains a challenge. Summary of the Invention

[0003] To solve the above problems, the present application provides a method for folding graphene oxide. A dispersion of GO is mixed with a polymer solution, combined with special electrospinning parameters, and then subjected to heat treatment to obtain folded reduced graphene oxide. This method is simple to operate and suitable for scale-up. By reducing the content of GO in the mixed solution, it can be separated into pieces by electrospinning. Taking advantage of the high von Karman number and easy deformation of GO sheets, the electric field is used to stretch the mixed solution of GO and polymer to produce spatial compression, causing the GO sheets to fold. The prepared folded reduced graphene oxide has a multilayer structure, and its structure is precisely adjustable.

[0004] The present invention provides the following technical solution: a method for folding graphene oxide, comprising uniformly mixing a graphene oxide solution with an electrospinnable polymer solution, electrospinning the mixed solution to prepare polymer fibers containing folded graphene oxide, and then heat-treating the fibers to obtain folded reduced graphene oxide with a controllable folding number n:

[0005] The number of folding times is controlled by adjusting the electrospinning voltage U and the distance L between the electrospinning nozzle and the receiver. Specifically, by adjusting U, the diameter D of the polymer fiber containing folded graphene oxide is controlled to obtain the polymer fiber containing folded graphene oxide with the desired number of folding times.

[0006] D=(91.18713×(1 / U)×kV+3.84237)×μm,

[0007] n=(4 / π)×(a / D)-1,

[0008] At this time, L is controlled at 15cm~23cm;

[0009] Alternatively, by adjusting L, D can be controlled to obtain a polymer fiber of folded graphene oxide with a desired number of folds.

[0010] D=(511.79063×(1 / L)×cm-13.03775)×μm,

[0011] n=(4 / π)×(a / D)-1,

[0012] At this time, U is controlled at 18kV~22kV;

[0013] Here, a is the average sheet diameter of graphene oxide.

[0014] Where n is the number of folds, such as Figure 1 , take the cross section of the polymer fiber containing folded graphene oxide, draw a straight line through the center of the circle in the cross section, and the maximum number of intersections formed by the straight line with the folded graphene oxide minus one is the number of folds;

[0015] like Figure 1 , D is the diameter of the polymer fiber containing folded graphene oxide, in μm; a is the average sheet diameter of graphene oxide, in μm; Figure 2 , L is the distance from the electrospinning nozzle to the receiver.

[0016] In this application, U, L, D, and a are all conventional parameters in the art.

[0017] Furthermore, the concentration of the graphene oxide solution is 10 mg / g.

[0018] Furthermore, the electrospinnable polymer is one of polyvinyl alcohol (PVA), sodium polyacrylate (PAAS), and polyethylene oxide (PEO).

[0019] Furthermore, the solvents of the graphene oxide solution and the electrospinnable polymer solution are independently selected from one of water, N,N-dimethylformamide (DMF), and N-methylpyrrolidone (NMP).

[0020] Furthermore, the concentration of the electrospinnable polymer solution is 10-20 mg / g.

[0021] Furthermore, the mass ratio of the electrospinnable polymer to the graphene oxide is 100:1 to 10:1.

[0022] Furthermore, the heat treatment temperature is 300° C. to 500° C., and the time is one hour.

[0023] The beneficial effects of the present invention are as follows:

[0024] (1) The GO dispersion is mixed with the polymer solution to make the graphene oxide spinnable. Combined with special electrospinning parameters, folded reduced graphene oxide can be obtained after heat treatment. This method is simple to operate and suitable for scale-up.

[0025] (2) By reducing the content of GO in the mixed solution, it can be separated into pieces by electrospinning.

[0026] (3) Taking advantage of the high von Karman number and easy deformation of GO sheets, the electric field is used to stretch the mixed solution of GO and polymer to produce spatial compression, causing the GO sheets to fold.

[0027] (4) The prepared folded reduced graphene oxide has a multilayer structure, and its structure is precisely adjustable. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the method for folding graphene oxide of the present invention to obtain folded reduced graphene oxide;

[0029] Figure 2 is a schematic diagram of an electrospinning device used in the present invention;

[0030] Figure 3 are optical microscope (OM) photographs of polymer fibers containing folded graphene oxide prepared in Examples 1 to 3 of the present invention, wherein a is the OM image of the polymer fiber prepared in Example 1, b is the OM image of the polymer fiber prepared in Example 2, and c is the OM image of the polymer fiber prepared in Example 3;

[0031] Figure 4 are SEM images of the folded reduced graphene oxide prepared in Examples 1 to 4 of the present invention, wherein a is an SEM image of the folded reduced graphene oxide prepared in Example 1, b is an SEM image of the folded reduced graphene oxide prepared in Example 2, c is an SEM image of the folded reduced graphene oxide prepared in Example 3, and d is an SEM image of the folded reduced graphene oxide prepared in Example 4;

[0032] Figure 5are electron diffraction patterns of folded graphene oxide in the polymer fibers prepared in Examples 1 to 4 of the present invention, wherein a is the electron diffraction pattern of folded graphene oxide in the polymer fibers prepared in Example 1, b is the electron diffraction pattern of folded graphene oxide in the polymer fibers prepared in Example 2, c is the electron diffraction pattern of folded graphene oxide in the polymer fibers prepared in Example 3, and d is the electron diffraction pattern of folded graphene oxide in the polymer fibers prepared in Example 4;

[0033] Figure 6 a is the OM diagram of the polymer fiber of Comparative Example 2, Figure 6 b is the SEM image after heat treatment;

[0034] Figure 7 is the OM image of the polymer fiber of Comparative Example 4;

[0035] Figure 8 are SEM images of Example 2 of the present invention, wherein a is a SEM image of the polymer fiber containing folded graphene oxide before heat treatment, and b is a SEM image of the folded reduced graphene oxide after heat treatment;

[0036] Among them, the diameter D of the polymer fiber containing folded graphene oxide, the nozzle 1, the receiver 2, and the distance L from the electrospinning nozzle to the receiver. DETAILED DESCRIPTION

[0037] In order to further illustrate the technical means and effects adopted by the present invention to achieve the predetermined purpose of the invention, the specific implementation methods, structures, features and effects of the present invention are described in detail below in conjunction with the accompanying drawings and preferred embodiments.

[0038] The structure of the electrospinning device used in this application is shown in the following figure: Figure 2 As shown, it includes a nozzle 1, which is connected to a container. The container contains a mixed solution of graphene oxide (GO) solution and electrospinnable polymer solution, which is received by a receiver 2 under the action of voltage.

[0039] The embodiments of the present invention are further described below with reference to a number of embodiments.

[0040] Example 1

[0041] A method for folding graphene oxide comprises uniformly mixing 1 g of a 10 mg / g graphene oxide (GO) aqueous solution with 100 g of a 10 mg / g polyvinyl alcohol (PVA) N,N-dimethylformamide (DMF) solution, wherein the mass ratio of the polyvinyl alcohol (PVA) to the graphene oxide in the mixed solution is 100:1. The mixed solution is then electrospun, and the electrospinning parameters are adjusted according to the following formula:

[0042] In this embodiment, a is 70 μm, U is 5 kV, L is 15 cm, D = (91.18713 × (1 / U) × kV + 3.84237) × μm = 22.0798, n = (4 / π) × (a / D) - 1 = 3.03, where n is 3.

[0043] Prepared into polymer fibers containing folded graphene oxide, such as Figure 3 A. Then heat treatment is performed to obtain folded reduced graphene oxide, the heat treatment temperature is 300 ° C, and the time is one hour.

[0044] The heat-treated samples can be tested by scanning electron microscopy (SEM). Figure 4 From the a of , we can see that the obtained GO is in a folded state. Using TEM, electron diffraction is performed on the sample. By observing the number of diffraction spots, the number of folded layers can be determined, such as Figure 5 Among them, the number of diffraction spots is 18, and the corresponding electron diffraction pattern shows 18 bright spots in one circle, indicating that there are three layers of hexagonal grids, that is, three layers of GO, which can prove that three-layer folded reduced graphene oxide has been successfully obtained, that is, n=3.

[0045] Example 2

[0046] A method for folding graphene oxide comprises uniformly mixing 1.5 g of a 10 mg / g graphene oxide (GO) solution in N-methylpyrrolidone (NMP) with 50 g of a 15 mg / g sodium polyacrylate (PAAS) aqueous solution, wherein the mass ratio of the sodium polyacrylate (PAAS) to the graphene oxide in the mixed solution is 50:1. The mixed solution is then electrospun, and the electrospinning parameters are adjusted according to the following formula:

[0047] In this embodiment, a is 38 μm, U is 30 kV, L is 23 cm, D = (91.18713 × (1 / U) × kV + 3.84237) × μm = 6.8819, n = (4 / π) × (a / D) - 1 = 6.03, where n is 6.

[0048] Prepared into polymer fibers containing folded graphene oxide, such as Figure 3 b. Folded reduced graphene oxide was then heat treated at 400°C for one hour. After the heat treatment, the sodium carbonate produced by the decomposition of PAAS was removed using hydrochloric acid.

[0049] The treated samples can be tested by scanning electron microscope (SEM). Figure 4 From the results of b, we can see that the GO is in a folded state. Using TEM, we can perform electron diffraction on the sample and determine the number of folded layers by observing the number of diffraction spots. Figure 5b. Among them, the number of diffraction spots is 36, so the folded reduced graphene oxide obtained is six-layer folded, that is, n=6.

[0050] Example 3

[0051] A method for folding graphene oxide comprises uniformly mixing 1 g of a 10 mg / g graphene oxide (GO) solution in N,N-dimethylformamide (DMF) and 5 g of a 20 mg / g polyethylene oxide (PEO) solution in N-methylpyrrolidone (NMP), wherein the mass ratio of polyethylene oxide (PEO) to graphene oxide in the mixed solution is 10:1. Electrospinning parameters are adjusted according to the following formula:

[0052] In this embodiment, a is 120 μm, U is 22 kV, L is 8 cm, D = (511.79063 × (1 / L) × cm - 13.03775) × μm = 50.9360, n = (4 / π) × (a / D) - 1 = 1.9996, and n is 2.

[0053] Prepared into polymer fibers containing folded graphene oxide, such as Figure 3 The folded reduced graphene oxide was obtained by heat treatment at a temperature of 500°C for one hour.

[0054] The heat-treated samples can be tested by scanning electron microscopy (SEM). Figure 4 From the c of the GO, we can see that the GO is already in a folded state. Using TEM, we can perform electron diffraction on the sample and determine the number of folded layers by observing the number of diffraction spots, such as Figure 5 Among them, the number of diffraction spots is 12, so the folded reduced graphene oxide obtained is two-layer folded, that is, n=2.

[0055] Example 4

[0056] A method for folding graphene oxide comprises uniformly mixing 1 g of a 10 mg / g graphene oxide (GO) solution in N,N-dimethylformamide (DMF) and 5 g of a 20 mg / g polyethylene oxide (PEO) solution in N-methylpyrrolidone (NMP), wherein the mass ratio of polyethylene oxide (PEO) to graphene oxide in the mixed solution is 10:1. Electrospinning parameters are adjusted according to the following formula:

[0057] In this embodiment, a is 16 μm, U is 18 kV, L is 30 cm, D = (511.79063 × (1 / L) × cm - 13.03775) × μm = 4.0219, n = (4 / π) × (a / D) - 1 = 4.0652, n is 4;

[0058] The polymer fiber containing folded graphene oxide is prepared and then heat-treated to obtain folded reduced graphene oxide at a temperature of 500° C. for one hour.

[0059] The heat-treated samples can be tested by scanning electron microscopy (SEM). Figure 4 From the c of the GO, we can see that the GO is already in a folded state. Using TEM, we can perform electron diffraction on the sample and determine the number of folded layers by observing the number of diffraction spots, such as Figure 5 Among them, the number of diffraction spots is 24, so the obtained folded reduced graphene oxide is four-layer folded, that is, n=4.

[0060] Comparative Example 1

[0061] A method for folding graphene oxide comprises uniformly mixing 1 g of a 10 mg / g graphene oxide (GO) aqueous solution with 100 g of a 10 mg / g polyvinyl alcohol (PVA) N,N-dimethylformamide (DMF) solution, wherein the mass ratio of the polyvinyl alcohol (PVA) to the graphene oxide in the mixed solution is 100:1, and then performing electrostatic spinning using the mixed solution.

[0062] In this embodiment, a is 70 μm, U is 3 kV, and L is 15 cm. Since the voltage of electrospinning is too low, the stretching effect of the electric field is insufficient and no fibers can be obtained.

[0063] Comparative Example 2

[0064] A method for folding graphene oxide comprises uniformly mixing 1 g of a 10 mg / g graphene oxide (GO) aqueous solution with 100 g of a 10 mg / g polyvinyl alcohol (PVA) N,N-dimethylformamide (DMF) solution, wherein the mass ratio of the polyvinyl alcohol (PVA) to the graphene oxide in the mixed solution is 100:1, and then performing electrostatic spinning using the mixed solution.

[0065] In this embodiment, a is 70 μm, U is 35 kV, L is 23 cm;

[0066] The voltage of electrospinning is too high, e.g. Figure 6 a, due to the excessive stretching effect of the electric field, the spinning solution is overstretched and the collected fibers are too thin. The heat treatment temperature is 300℃ and the time is one hour. After the heat treatment, it can be seen that Figure 6 b, the GO sheet is severely deformed.

[0067] Comparative Example 3

[0068] A method for folding graphene oxide, comprising uniformly mixing 1g of a 10mg / g aqueous solution of graphene oxide (GO) and 100g of a 10mg / g N,N-dimethylformamide (DMF) solution of polyvinyl alcohol (PVA), wherein the mass ratio of polyvinyl alcohol (PVA) to graphene oxide in the mixed solution is 100:1, and then performing electrospinning using the mixed solution.

[0069] In this embodiment, a is 70 μm, U is 22 kV, and L is 5 cm.

[0070] Since the distance between the positive and negative electrodes is too close (positive electrode: contact port; negative electrode: receiving plate), it is easy to break through the air and cause a short circuit, making successful preparation impossible.

[0071] Comparative Example 4

[0072] A method for folding graphene oxide comprises uniformly mixing 1 g of a 10 mg / g aqueous solution of graphene oxide (GO) with 100 g of a 10 mg / g N,N-dimethylformamide (DMF) solution of polyvinyl alcohol (PVA), wherein the mass ratio of the polyvinyl alcohol (PVA) to the graphene oxide in the mixed solution is 100:1, and then performing electrospinning using the mixed solution:

[0073] In this embodiment, a is 70 μm, U is 18 kV, and L is 40 cm.

[0074] Since the receiving distance L is too large, the instability of the polymer fiber increases during long-distance flight, such as Figure 7 The collected fibers were severely spirally twisted, of varying thicknesses, and had poor folding controllability.

[0075] The present invention obtains folded reduced graphene oxide by mixing a GO dispersion with a polymer solution, combining special electrospinning parameters, and then subjecting the mixture to heat treatment.

[0076] As is well known in the art, there is no significant change in the folded state of the folded graphene oxide in the polymer fiber before heat treatment and the folded reduced graphene oxide after heat treatment. Taking Example 2 as an example, Figure 8 a in the figure is the SEM image of the polymer fiber containing folded graphene oxide before heat treatment. Figure 8 Figure b is the SEM image of the folded reduced graphene oxide after heat treatment, and it can be seen that there is no obvious change in the folding state.

[0077] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as above in terms of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can, without departing from the scope of the technical solution of the present invention, make some changes or modifications to equivalent embodiments using the technical contents disclosed above. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for folding graphene oxide, characterized in that, The graphene oxide solution and the electrospinnable polymer solution are uniformly mixed, and the mixed solution is then used for electrospinning to prepare polymer fibers containing folded graphene oxide. The graphene oxide sheets are separated and then heat-treated to obtain folded reduced graphene oxide with a controllable number of folds n, wherein the mass ratio of the electrospinnable polymer to the graphene oxide is 100:1 to 10:1; the heat treatment temperature is 300° C. to 500° C., and the time is one hour; The number of folding times is controlled by adjusting the electrospinning voltage U and the distance L between the electrospinning nozzle and the receiver. Specifically, by adjusting U, the diameter D of the polymer fiber containing folded graphene oxide is controlled to obtain the polymer fiber containing folded graphene oxide with the desired number of folding times. D=(91.18713×(1 / U)×kV+3.84237)×μm, n=(4 / π)×(a / D)-1, At this time, L is controlled at 15cm~23cm; Alternatively, by adjusting L, D can be controlled to obtain a polymer fiber of folded graphene oxide with a desired number of folds. D=(511.79063×(1 / L)×cm-13.03775)×μm, n=(4 / π)×(a / D)-1, At this time, U is controlled at 18kV~22kV; Here, a is the average sheet diameter of graphene oxide.

2. The method according to claim 1, characterized in that The concentration of the graphene oxide solution is 10 mg / g.

3. The method according to claim 1, characterized in that The electrospinnable polymer is one of polyvinyl alcohol (PVA), sodium polyacrylate (PAAS), and polyethylene oxide (PEO).

4. The method according to claim 1, wherein The solvents of the graphene oxide solution and the electrospinnable polymer solution are independently selected from one of water, N,N-dimethylformamide (DMF) and N-methylpyrrolidone (NMP).

5. The method according to claim 1, wherein The concentration of the electrospinnable polymer solution is 10-20 mg / g.

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