A method for preparing a graphene film by zeta potential control electrophoretic deposition

Abstract

The application relates to a method for preparing a graphene film through Zeta potential control electrophoretic deposition, which comprises two steps of graphene dispersion liquid preparation (dispersion-centrifugal separation-redispersion) and graphene electrophoretic deposition, wherein the structure size (micron-level sheet layer or nanometer-level particle structure) and property (carbon oxygen ratio) of the graphene film after the electrophoretic deposition are mainly controlled through the control of the Zeta potential of the graphene dispersion liquid, and the control of the Zeta potential of the graphene is realized through the control of the centrifugal separation speed and the pH value of the dispersion liquid.

Description

TECHNICAL FIELD

[0001] The application relates to a graphene film preparation method, in particular to a method for preparing a graphene film through Zeta potential control electrophoretic deposition, and belongs to the technical field of centrifugal separation and electrophoretic deposition. BACKGROUND

[0002] As is known, graphene is a two-dimensional nanomaterial with excellent electrical, mechanical, thermal and optical properties, and graphene films (single-layer or multi-layer films) have very wide application or potential application values, such as in flexible displays, touch screens, organic light-emitting diodes (OLEDs), supercapacitors, semiconductors, catalysis, biosensors, water pollution treatment and solid lubrication. At present, the methods for preparing graphene films mainly include chemical vapor deposition, spraying, spin coating and self-assembly. These methods have many advantages, but also have some disadvantages. For example, the chemical vapor deposition method (CVD) which is widely used has the advantages of large-area deposition and few defects, but the equipment used in this method is expensive, the cost is high, and a specific substrate or catalyst (Cu, Ni, etc.) is needed, and the subsequent film transfer process is seriously polluted.

[0003] The electrophoretic deposition method is a method for depositing a film by controlling the movement of charged particles in a solution through an applied electric field, and the method has relatively simple equipment and process. At present, relatively mature graphene oxide and reduced graphene oxide products on the market can be used as deposition raw materials. The selection of the substrate only needs to have certain conductivity, such as metal and semiconductor materials. Therefore, this method is an efficient, low-cost and promising graphene film preparation method. As the name implies, the graphene film should be a single-layer or multi-layer film composed of two-dimensional graphene sheets. However, the film obtained through electrophoretic deposition at present is a film composed of zero-dimensional graphene nanoparticles or a film composed of zero-dimensional graphene nanoparticles and two-dimensional graphene sheets, which is not a strict graphene film (this is determined by the characteristics of the electrophoretic deposition technology, that is, particles with larger Zeta potential are deposited first); at the same time, the graphene film sheets obtained without centrifugal separation have large ohmic contact resistance between the particles, which has become a bottleneck for the application of the method in graphene conductive films. The addition of metal cations in the solution, such as Mg 2+ , Al 3+Also, graphene films can be obtained, but these ions can only change the polarity of the charged particles of graphene and the electrophoretic deposition direction (from anode deposition to cathode deposition), and cannot change the essential composition of the graphene film or the tendency of nanoparticulation, and inevitably brings in metal impurities. In this case, the electrical, mechanical and corrosion resistance performance of the obtained film are greatly reduced, and cannot be compared with graphene prepared by chemical vapor deposition. Therefore, it is of great significance to develop the electrophoretic deposition technology with low cost and great development potential into a real graphene film preparation technology.

[0004] For the preparation of graphene films, none of the methods can effectively control the size of graphene sheets. According to Stokes law and Henry equation, the movement velocity (or mobility) of charged particles in the electrophoretic deposition process is mainly controlled by its own Zeta potential, solution viscosity and dielectric constant, etc. in addition to the electric field, and the Zeta potential is mainly determined by the charge amount, radius of the charged particles, and pH value, dielectric constant of the solution. For graphene, the Zeta potential is mainly determined by the number of surface ionizable functional groups or adsorbed ions, the size of the sheet, and the pH value and dielectric constant of the solution. Therefore, under certain conditions, the method of combining Zeta potential regulation and electrophoretic deposition is used to control the quality of graphene film, so as to obtain a graphene film composed of graphene sheets, which is a scientific, novel and feasible graphene film preparation technology or method. SUMMARY

[0005] The purpose of the present application is to provide a method for preparing graphene films by Zeta potential control electrophoretic deposition, so as to obtain a graphene film composed of two-dimensional graphene sheets with controllable sheet size.

[0006] The present application adopts the method of combining Zeta potential regulation and electrophoretic deposition to obtain a graphene film composed of two-dimensional graphene sheets with controllable sheet size, which solves the problem of zero-dimensional nanoparticles and two-dimensional sheet structure in the electrophoretic deposition of graphene film under normal circumstances, so the method is a simple and effective graphene film preparation method, and also an effective method for improving the quality of graphene film.

[0007] The method for preparing graphene films by Zeta potential control electrophoretic deposition of the present application comprises the following steps:

[0008] (1) Preparation of graphene electrophoretic solution: first, disperse graphene in water, and prepare a graphene electrophoretic solution with a concentration of 0.01-3 mg·ml -1a graphene dispersion liquid; then, graphene slurries in different speed intervals are obtained by centrifugal separation at different speeds; finally, the graphene slurries in different speed intervals are dispersed in water again to prepare graphene dispersion liquids with a concentration of 0.01-3 mg·ml -1 a graphene dispersion liquid; then, graphene slurries in different speed intervals are obtained by centrifugal separation at different speeds; finally, the graphene slurries in different speed intervals are dispersed in water again to prepare graphene dispersion liquids with a concentration of 0.01-3 mg·ml

[0009] (2) Preparation of a graphene film: first, a conductive material is used as an electrophoretic deposition target substrate, which is ultrasonically cleaned and fixed in an electrolytic cell as an anode, a graphite or platinum sheet is used as a cathode, and a graphene electrophoretic solution with different Zeta potentials is added; then, the graphene film with different sheet sizes is obtained by electrophoretic deposition under the condition of a current density of 0.1-2 mA·cm -2

[0010] The graphene is one or more of graphene oxide, reduced graphene oxide and electrochemically exfoliated graphene.

[0011] The conductive material is a semiconductor single crystal silicon wafer or a metal (stainless steel, Cu or Au).

[0012] The power source for the electrophoretic deposition is a direct current or pulse direct current power source.

[0013] When the centrifugal separation speed is low, such as 5000 rpm (product less than 5000 rpm), the Zeta potential of the graphene slurry is -51.5 mV (see Figure 1 a), and the structure of the graphene film prepared by electrophoretic deposition is a micron-level sheet structure. The microscope photo is shown in Figure 2 a, the size of the graphene film sheet is 1-19 μm, and the carbon-oxygen ratio is 2.36.

[0014] When the centrifugal separation speed is high, such as 20000 rpm (product of 15000-20000 rpm), the Zeta potential of the graphene slurry is -56.0 mV (see Figure 1 b), and the structure of the graphene film prepared by electrophoretic deposition is a nano-level particle structure. The microscope photo is shown in Figure 2 b, the particle size of the graphene film particle is ≤1 μm (occasionally 1-8 μm large pieces appear), and the carbon-oxygen ratio is 2.30.

[0015] In summary, the graphene electrophoretic deposition solution is prepared through the dispersion, centrifugal separation and re-dispersion of graphene, and the Zeta potential of the graphene electrophoretic deposition solution is controlled by the centrifugal separation speed and the pH value, so that the structure size (graphene sheet size, carbon-oxygen ratio and other factors) of the graphene film is controlled, and the controllability of the properties of the graphene film is realized.

[0016] ​The two steps of preparation of graphene solution (including graphene dispersion-centrifugation-redispersion and pH control) and electrophoretic deposition have influence on the preparation of graphene film, and the centrifugation and pH control have decisive influence on the regulation of Zeta potential of graphene electrophoretic solution and size of graphene sheet, and the close cooperation of Zeta potential regulation and electrophoretic deposition is the fundamental guarantee to obtain high-quality graphene film. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 Digital photos of different Zeta potential graphene solutions (a. -51.5 mV; b. -56.0 mV) obtained by the application.

[0018] Figure 2 Microscope photos of different graphene films (a. 1-19 μm; b. ≤1 μm, occasionally 1-8 μm large pieces appear; scale: 20 μm) obtained by the application. DETAILED DESCRIPTION

[0019] In order to better understand the application, the following examples are used for illustration.

[0020] Example 1

[0021] A certain amount of graphene oxide is mechanically stirred and dispersed into deionized water to obtain a graphene dispersion solution (1 mg·ml -1 ). The dispersion solution is centrifuged (5000 rpm) to obtain a graphene slurry (0-5000 rpm). The slurry is again dispersed into deionized water under mechanical stirring to obtain a graphene dispersion solution (0.1 mg·ml -1 ), and the pH value thereof is adjusted by using a NaOH solution (pH=5) to obtain a graphene electrophoretic solution (see Figure 1 a, the Zeta potential is -51.5 mV).

[0022] The single crystal silicon substrate is ultrasonically cleaned in acetone and fixed on an electrolytic cell as an anode, and a graphite sheet or a metal platinum sheet is used as a cathode. The above graphene electrophoretic solution is added and electrophoretically deposited under the condition of a current density of 0.1 mA·cm -2 for 6 h to obtain a graphene film.

[0023] The above graphene film is examined by using a microscope and XPS to examine the surface morphology and chemical composition thereof, respectively. The microscope photo thereof is as shown in Figure 2 a, the size of the graphene film sheet layer is 1-19 μm, and the carbon oxygen ratio thereof is 2.36.

[0024] Example 2

[0025] A certain amount of graphene oxide is mechanically stirred and dispersed into deionized water to obtain a graphene dispersion solution (1 mg·ml-1 The dispersion was centrifuged (20000 rpm) to obtain a graphene slurry (15000-20000 rpm). The slurry was again dispersed in deionized water under mechanical stirring to obtain a graphene dispersion (0.1 mg·ml -1 ), and the pH value thereof was adjusted with a NaOH solution (pH=5) to obtain a graphene electrophoresis solution (see Figure 1 b, and the zeta potential was -56.0 mV);

[0026] The monocrystalline silicon substrate was ultrasonically cleaned in acetone and fixed on an electrolytic cell as an anode, and a graphite sheet or a metal platinum sheet was used as a cathode. The graphene electrophoresis solution was added, and graphene thin films were obtained by electrophoretic deposition at a current density of 0.1 mA·cm -2 for 6 h.

[0027] The graphene thin films were observed by microscopy and XPS to investigate the surface morphology and chemical composition, respectively. The microscopy photograph is shown in Figure 2 b, the size of the graphene thin film sheet layer was ≤1 μm, and 1-8 μm large pieces occasionally appeared, and the carbon oxygen ratio was 2.30.

Claims

1. A method for preparing graphene thin films by zeta potential-controlled electrophoretic deposition, comprising the following steps: A certain amount of graphene oxide was taken and dispersed in deionized water by mechanical stirring to obtain a concentration of 1 mg / ml. -1 A graphene dispersion was prepared; the dispersion was centrifuged at 5000 rpm to obtain a graphene slurry; the slurry was then redispersed in deionized water under mechanical stirring to obtain a concentration of 0.1 mg / ml. -1 A graphene dispersion was prepared, and its pH was adjusted to 5 with NaOH solution to obtain a graphene electrophoresis solution with a Zeta potential of -51.5 mV. The monocrystalline silicon substrate was ultrasonically cleaned in acetone and fixed on an electrolytic cell as the anode. A graphite sheet or platinum sheet was used as the cathode. The aforementioned graphene electrophoresis solution was added, and the electrophoresis was performed at 0.1 mA·cm⁻¹. -2 Graphene films were obtained by electrophoretic deposition for 6 hours under current density conditions; the size of the graphene film sheets was 1-19 μm and the carbon-oxygen ratio was 2.

36.

2. A method for preparing graphene thin films by zeta potential-controlled electrophoretic deposition, comprising the following steps: A certain amount of graphene oxide was taken and dispersed in deionized water by mechanical stirring to obtain a concentration of 1 mg / ml. -1 A graphene dispersion was prepared; the dispersion was centrifuged at 20,000 rpm to obtain a graphene slurry; the slurry was then redispersed in deionized water under mechanical stirring to obtain a concentration of 0.1 mg / ml. -1 A graphene dispersion was prepared, and its pH was adjusted to 5 with NaOH solution to obtain a graphene electrophoresis solution with a Zeta potential of -56.0 mV. The monocrystalline silicon substrate was ultrasonically cleaned in acetone and fixed on an electrolytic cell as the anode. A graphite sheet or platinum sheet was used as the cathode. The aforementioned graphene electrophoresis solution was added, and the electrophoresis was performed at 0.1 mA·cm⁻¹. -2 Graphene films were obtained by electrophoretic deposition for 6 hours under current density conditions. The size of the graphene film sheets was ≤1μm, with occasional large sheets of 1-8μm. The carbon-oxygen ratio was 2.30.

Images