Preparation method of cathode electrophoretic deposition graphene film under acidic condition

Abstract

The invention relates to a method for preparing a graphene film through cathodic electrophoretic deposition under an acidic condition, which comprises the following steps: (1) adding graphene oxide into deionized water to prepare a graphene dispersion liquid A; performing centrifugal separation on the graphene dispersion liquid A to obtain graphene slurry, and adding the graphene slurry into deionized water again to prepare a graphene dispersion liquid B; adding the graphene dispersion liquid B into an inorganic acid solution to obtain a graphene electrophoresis solution; (2) taking a conductive material as a target base material, ultrasonically cleaning, fixing in an electrolytic bath as a cathode, taking a platinum sheet as an anode, and adding a graphene electrophoresis solution into the electrolytic bath for electrophoretic deposition to obtain a graphene film prototype sample; (3) cleaning the graphene film prototype sample, and fixing the graphene film prototype sample in an electrolytic cell as a cathode; and taking graphite or a platinum sheet as a counter electrode, and adding an inorganic acid solution for electrochemical reduction to obtain the final graphene film. The method has the characteristics of low cost, high carbon-oxygen ratio, greenness, no pollution and large-scale production.

Description

Technical Field

[0001] The invention relates to the technical fields of graphene solution stability, graphene film preparation and electrophoretic deposition, and in particular to a method for preparing a graphene film by cathode electrophoretic deposition under acidic conditions. Background Art

[0002] Graphene is a two-dimensional nanomaterial with excellent mechanical, thermal, optical, electrical and anti-corrosion properties. Graphene film has a wide range of application value. Its preparation methods mainly include chemical vapor deposition, spraying, spin coating and self-assembly. Among these methods, chemical vapor deposition (CVD) has the advantages of large-area deposition and few defects, and is the most widely used; but this method is costly and requires a metal substrate (Cu, Ni, etc.) with a certain catalytic effect or an epitaxial substrate with specific crystal plane characteristics, and the film is seriously polluted during the subsequent transfer process. Relatively speaking, electrophoretic deposition is a simple, efficient and low-cost method for preparing graphene film. Generally, it is achieved by anodic deposition of negatively charged graphene oxide in aqueous solution, but the obtained graphene film has a high oxygen content (>30%, and the carbon-oxygen ratio is relatively low). At the same time, some metal substrates are prone to electrochemical corrosion as anodes (such as Cu). In addition, it can also be prepared by metal ions (such as Mg) in organic solvents or aqueous solutions. 2+ 、Al 3+ The addition of organic solvents (such as ) to realize the cation-assisted cathode electrophoretic deposition of graphene oxide can avoid electrochemical corrosion of the metal substrate on the one hand, and on the other hand, the oxygen content of the obtained graphene film is relatively low, and the oxygen content in the graphene film can be further reduced by cathode reduction; but in this case, there will be more metal ions remaining in the obtained film, which will affect the performance of the film, and the use of organic solvents will have certain harm to the human body. Therefore, for graphene electrophoretic deposition technology, cation-assisted cathode electrophoretic deposition has obvious advantages, but reducing oxygen content and avoiding metal ion pollution have formed a dilemma of having one's cake and eating it too, or a contradiction.

[0003] In summary, in the face of the difficulties existing in the current graphene film preparation technology: high cost of CVD, transfer pollution, high oxygen content or metal ion pollution of electrophoretic deposition, it is urgent to develop a low-cost, high carbon-oxygen ratio, green and pollution-free graphene film preparation method through technological innovation. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for preparing a graphene film by cathode electrophoresis deposition under acidic conditions with low cost, high carbon-oxygen ratio and green and pollution-free.

[0005] In order to solve the above problems, the present invention provides a method for preparing a graphene film by cathode electrophoresis deposition under acidic conditions, comprising the following steps: ⑴ Add graphene oxide to deionized water and stir mechanically to a concentration of 0.01~3 mg·ml -1 The graphene dispersion A is centrifuged to obtain a graphene slurry, which is added to deionized water again and mechanically stirred to a concentration of 0.01~3 mg·ml -1 The graphene dispersion B is added with an inorganic acid solution to adjust the pH value thereof within the range of 1 to 6 while maintaining its dispersion stability, so as to obtain a concentration of 0.01 to 3 mg ml -1 , graphene electrophoresis solution with pH=1~6; (2) Using a conductive material as the target substrate, after ultrasonic cleaning, fix it in an electrolytic cell as a cathode; using a platinum sheet as an anode, applying a -1V protective electric field to the cathode before deposition; then adding the graphene electrophoresis solution into the electrolytic cell for electrophoretic deposition, thereby obtaining a graphene film sample; ⑶ The graphene film sample is washed with deionized water and fixed in an electrolytic cell as a cathode; a graphite or platinum sheet is used as a counter electrode, an inorganic acid solution is added, and its pH value is adjusted within the range of 1 to 6 for electrochemical reduction to obtain a final graphene film.

[0006] The centrifugal separation conditions in step (1) are a speed of 1000-10000 rpm and a time of 60 min.

[0007] The inorganic acid solution in step (1) and step (3) refers to any one of H2SO4, HCl, H3PO4 or HNO3.

[0008] The conductive material in step (2) refers to one of silicon wafer, Cu, Au, Ag, and stainless steel.

[0009] The electrophoretic deposition condition in step (2) is that the current density is 0.1~2mA·cm -2 , time is 180 minutes.

[0010] The electrochemical reduction condition in step (3) refers to a current density of 0.001 to 1 mA·cm -2 , time is 30 minutes.

[0011] Compared with the prior art, the present invention has the following advantages: 1. The present invention is based on traditional graphene electrophoretic deposition technology (anodic electrophoretic deposition and cation-assisted cathodic electrophoretic deposition). Through cathode deposition and cathode reduction under acidic conditions, it breaks through the technical bottleneck of reducing oxygen content and avoiding metal ion pollution.

[0012] 2. The graphene electrophoresis solution used in the present invention is a graphene dispersion with a certain pH value, acidity, controllable sheet size, and stable dispersion. It is achieved by dispersing the graphene-centrifugal separation-redispersion and regulating the pH value of the solution, without adding metal cations or organic reagents.

[0013] 3. The combination of cathode electrophoretic deposition and cathode electrochemical reduction in the present invention can significantly improve the carbon-oxygen ratio of the film (the carbon-oxygen ratios of the graphene film obtained by conventional anodic electrophoretic deposition, acidic cathode electrophoretic deposition, and acidic cathode electrophoretic deposition + cathode electrochemical reduction are 0.4-2.3, 1.0-2.5, and 1.3-2.6, respectively).

[0014] 4. In the present invention, the thin film is directly deposited on the target substrate without damaging the substrate, and there is no subsequent transfer pollution. It has the characteristics of low cost, high carbon-oxygen ratio, green and pollution-free, and can be produced on a large scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The specific implementation modes of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0016] Figure 1 is the Zeta potential of graphene in the graphene electrophoresis solution of the present invention (before adding acid, -61 mV).

[0017] Figure 2 is the Zeta potential of graphene in the graphene electrophoresis solution of the present invention (after adding acid, -20 mV).

[0018] Figure 3 This is a surface morphology of the graphene film of the present invention (before acid addition).

[0019] Figure 4 This is a surface morphology of the graphene film of the present invention (after adding acid). DETAILED DESCRIPTION

[0020] A method for preparing a graphene film by cathode electrophoresis deposition under acidic conditions comprises the following steps: ⑴ Add graphene oxide to deionized water and stir mechanically to a concentration of 0.01~3 mg·ml -1 The graphene dispersion A is centrifuged at a rate of 1000-10000 rpm for 60 min to obtain a graphene slurry, which is again added into deionized water and mechanically stirred to a concentration of 0.01-3 mg·ml -1 Graphene dispersion B; add inorganic acid solution to graphene dispersion B and adjust its pH value to the range of 1 to 6 while maintaining its dispersion stability, so as to obtain a concentration of 0.01 to 3 mg ml -1 , graphene electrophoresis solution with pH=1~6.

[0021] Wherein: the inorganic acid solution refers to any one of H2SO4, HCl, H3PO4 or HNO3.

[0022] ⑵ The conductive material is used as the target substrate. The conductive material refers to one of silicon wafer, Cu, Au, Ag, and stainless steel. After ultrasonic cleaning, it is fixed in the electrolytic cell as the cathode; the platinum sheet is used as the anode, and a -1V protective electric field is applied to the cathode before deposition; then the graphene electrophoresis solution is added to the electrolytic cell, and the current density is 0.1~2mA·cm -2 Electrophoretic deposition was carried out under the conditions of 0.0547 W / m2 and 1.500 W / m2 for 180 min to obtain a graphene film sample.

[0023] ⑶ The graphene film sample was washed with deionized water and fixed in the electrolytic cell as the cathode; a graphite or platinum sheet was used as the counter electrode, an inorganic acid solution was added, and its pH value was adjusted to be in the range of 1 to 6 for electrochemical reduction. The inorganic acid solution was the same as step ⑴, and the current density was 0.001 to 1 mA cm -2 , time is 30min, and the final graphene film is obtained.

[0024] The present invention is different from the conventional anodic electrophoretic deposition of graphene as anion and the cathodic electrophoretic deposition of graphene anions assisted by cations. It is essentially a cathodic electrophoretic deposition of charged graphene "particles" in a metastable state with a positive Zeta potential shift under acidic conditions.

[0025] Example 1 (no acid added, anodic deposition): (1) Disperse 0.5 mg of graphene into 1 ml of deionized water by mechanical stirring to obtain a graphene dispersion solution (0.5 mg ml -1 ); The graphene dispersion solution A was centrifuged at a rate of 1000-10000 rpm for 60 min to obtain a graphene slurry; the graphene slurry was added into deionized water again and mechanically stirred to a concentration of 0.5 mg ml -1 Stable graphene dispersion.

[0026] ⑵ The target substrate (such as single crystal silicon, Cu, stainless steel, etc.) was ultrasonically cleaned in acetone, fixed to the electrolytic cell as the anode, and the platinum sheet was used as the cathode. Then, the graphene stabilizing dispersion was added and the current density was 1 mA cm -2 Anodic electrophoretic deposition was carried out under the conditions of 0.0547 W for 2 hours and 30 minutes to obtain a graphene film.

[0027] The Zeta potential of the graphene film was tested. Figure 1 As shown in the figure, it can be seen that the Zeta potential is -61mV, the graphene nanoparticles are very stable, and mainly anodic electrophoretic deposition occurs.

[0028] The morphology of the obtained graphene film is as follows Figure 3 As shown in the figure, it can be found that there are more graphene sheets, the deposition speed is faster, and the color is darker (the carbon-oxygen ratio is about 0.4~2.3, XPS results).

[0029] Example 2 (acid addition, cathode deposition): (1) 0.5 mg of graphene was dispersed into 1 ml of deionized water by mechanical stirring to obtain graphene dispersion solution A (0.5 mg ml -1 ); The graphene dispersion solution A was centrifuged at a rate of 1000-10000 rpm for 60 min to obtain a graphene slurry; the graphene slurry was added into deionized water again and mechanically stirred to a concentration of 0.5 mg ml -1 Graphene dispersion B. Graphene dispersion B is added with an inorganic acid solution (such as H2SO4, HCl, etc.) to adjust its pH value within the range of 1 to 6 while maintaining its dispersion stability, so that the concentration is 0.5 mg ml -1 , graphene electrophoresis solution with pH=1~6.

[0030] ⑵ The target substrate (such as single crystal silicon, Cu, stainless steel, etc.) was ultrasonically cleaned in acetone and fixed to the electrolytic cell as the cathode; a metal platinum sheet was used as the anode, and a -1V protective electric field was applied to the cathode before deposition; then the graphene electrophoresis solution was added to the electrolytic cell and the current density was 1mA·cm -2 Electrophoretic deposition was carried out under the conditions of 0.0547 W / m2 and 1.500 W / m2 for 180 min to obtain a graphene film sample.

[0031] ⑶ The graphene film sample was washed with deionized water and fixed in another electrolytic cell as the cathode; a platinum sheet was used as the anode, and an inorganic acid solution (such as H2SO4, HCl, etc.) was added to adjust its pH value to 2. At a current density of 0.001 mA cm -2 , and time for 30 min to obtain the final graphene film.

[0032] The Zeta potential of the graphene film was tested. Figure 2 As shown in the figure, it can be seen that the Zeta potential is -20mV, the graphene nanoparticles are in a metastable state, protonated under acidic conditions, and the van der Waals force with the substrate enables cathode deposition.

[0033] The morphology of the obtained graphene film is as follows Figure 4 As shown in the figure, it can be found that there are fewer graphene sheets, the deposition speed is slower, and the color is transparent (the carbon-oxygen ratio is about 1.3~2.6, XPS results).

Claims

1. A method for preparing a graphene film by cathode electrophoretic deposition under acidic conditions, comprising the following steps: ⑴ Add graphene oxide to deionized water and stir mechanically to a concentration of 0.01~3 mg·ml -1 The graphene dispersion A is centrifuged to obtain a graphene slurry, which is added to deionized water again and mechanically stirred to a concentration of 0.01~3 mg·ml -1 The graphene dispersion B is added with an inorganic acid solution to adjust the pH value thereof within the range of 1 to 6 while maintaining its dispersion stability, so as to obtain a concentration of 0.01 to 3 mg ml -1 , graphene electrophoresis solution with pH=1~6; (2) Using conductive material as the target substrate, it is fixed in the electrolytic cell as the cathode after ultrasonic cleaning; A platinum sheet is used as the anode, and a -1V protective electric field is applied to the cathode before deposition; then the graphene electrophoresis solution is added to the electrolytic cell for electrophoretic deposition to obtain a graphene film sample; (3) washing the graphene film sample with deionized water and fixing it in an electrolytic cell as a cathode; Using graphite or platinum sheet as the counter electrode, adding inorganic acid solution, adjusting the pH value in the range of 1 to 6 for electrochemical reduction, the final graphene film is obtained.

2. The method for preparing a graphene film by cathode electrophoretic deposition under acidic conditions according to claim 1, characterized in that: The centrifugal separation conditions in step (1) refer to a speed of 1000-10000 rpm and a time of 60 min.

3. The method for preparing a graphene film by cathode electrophoretic deposition under acidic conditions according to claim 1, characterized in that: The inorganic acid solution in step (1) and step (3) refers to any one of H2SO4, HCl, H3PO4 or HNO3.

4. The method for preparing a graphene film by cathode electrophoretic deposition under acidic conditions according to claim 1, characterized in that: The conductive material in step (2) refers to one of silicon wafer, Cu, Au, Ag, and stainless steel.

5. The method for preparing a graphene film by cathode electrophoretic deposition under acidic conditions according to claim 1, characterized in that: The electrophoretic deposition condition in step (2) is that the current density is 0.1~2mA·cm -2 , time is 180 minutes.

6. The method for preparing a graphene film by cathode electrophoretic deposition under acidic conditions according to claim 1, characterized in that: The electrochemical reduction condition in step (3) refers to a current density of 0.001 to 1 mA·cm -2 , time is 30 minutes.

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