A method for preparing porous graphene nanoplatelets

Abstract

The application relates to the technical field of graphene, in particular to a preparation method of porous graphene nanosheets, which is based on the lightning rod effect of nanowires, utilizes the electrochemical reaction confined area with high charge density formed by the tip of the nanowires, and combines direct electrochemical oxidation and indirect oxidation to prepare the porous graphene nanosheets. The preparation method is simple in operation, few in steps, green and environment-friendly, does not introduce impurities, is uniform in composition, adjustable in pore size, and contains various functional groups, so that the functional modification in the later period is facilitated.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of graphene, in particular to a preparation method of porous graphene nanosheets. BACKGROUND

[0002] Graphene is a two-dimensional carbon material, which is usually used as a building material for high-performance materials due to its ultra-thin thickness, ultra-high specific surface area, and excellent electrical and thermal conductivity and mechanical stability, and is used in the fields of battery and supercapacitor manufacturing, functional composite material preparation, and membrane separation.

[0003] Porous graphene is graphene with nanoscale holes in its two-dimensional plane, which has a larger specific surface area and is more conducive to energy and material migration, material catalysis, and increased reaction area.

[0004] For example, a high-efficiency membrane assembled from porous graphene nanosheets has a nanopore structure and optimized interlayer channels that facilitate enhanced molecular permeation to improve mass transfer of substances.

[0005] Therefore, porous graphene is more suitable as a building material for energy storage, high-performance sensors, and catalytic adsorption of substances, and also has great application potential in the fields of gas / liquid separation, seawater desalination, and DNA sequencing.

[0006] Using porous graphene as a building material for high-performance materials requires forming high-density, high-consistency, and uniformly distributed holes in the two-dimensional plane of graphene, rather than generating a small number of holes of varying sizes. Currently, porous graphene is often prepared by oxidation etching methods, such as constant potential / voltage electrochemical oxidation (patent CN111320166B, article High Yield Controlled Synthesis of Nano-Graphene Oxide by Water Electrolytic Oxidation of Glassy Carbon for Metal-Free Catalysis), strong acid / strong oxidant etching (patent CN108821269B, patent CN105923627B, patent CN103663438B), which mainly generates holes by expanding the surface defects of graphene through an oxidation process. Since grain boundaries are more reactive than basal planes, using oxidation etching methods often results in holes of varying sizes in the two-dimensional plane of graphene.

[0007] The present application is based on the lightning rod effect of nanowires, forming an electrochemical reaction confined area with high charge density, whose field strength can reach 10 7V / m, higher than the carbon knock-off potential (about 80kV), while generating oxidative free radicals in the limited area, and by direct oxidation and indirect oxidation, high-density, high-consistency, uniformly distributed holes are generated on the graphene two-dimensional plane. SUMMARY

[0008] To overcome the deficiencies and shortcomings of the prior art, the purpose of the present application is to provide a method for preparing porous graphene nanosheets, which can punch holes with uniform size distribution, high density and high consistency in the graphene two-dimensional plane, and has the advantages of low cost, simple operation and no impurities introduction.

[0009] To achieve the above purpose, the present application provides the following technical scheme: based on the lightning rod effect of nanowires, under the condition of applying low external voltage (<10V), the nanowires of the anode can promote the concentration of electric charge at the tip of the nanowire, forming an electrochemical reaction limited area with high charge density, which has very high electrochemical catalytic activity.

[0010] The device adopts an overflow type, that is, the graphene nanosheet solution is first reduced by the cathode and then oxidized by the anode nanowire, and the porous cathode promotes the generation of OH- by H2O electrolysis, and makes the graphene nanosheet have a negative charge, which is more easily migrated to the electrochemical reaction limited area at the tip of the nanowire, and forms a perforation through direct oxidation.

[0011] At the same time, OH- produced by the cathode and Cl-, SO4 2- Plasma also generates ·OH, Cl·, SO4· free radicals in the electrochemical reaction limited area at the tip of the nanowire, and makes the graphene nanosheet perforated through indirect oxidation.

[0012] Through direct oxidation and indirect oxidation, adjustable nanoscale holes are made in the two-dimensional plane of the graphene nanosheet;

[0013] Specifically includes the following steps:

[0014] (A) The graphene nanosheet is uniformly dispersed in the electrolyte solution by ultrasonic, and a uniform dispersion of graphene nanosheet aqueous solution is obtained;

[0015] (B) The porous conductive material is used as the cathode, and the porous nanowire electrode is used as the anode, which are connected to the negative and positive electrodes of the power supply respectively, the graphene nanosheet aqueous solution is pumped into the perforation device, and the water inlet, cathode, anode and water outlet are sequentially passed from bottom to top, the flow rate of the pump is adjusted and the power supply is started;

[0016] (C) The water outlet of the collection device is collected, centrifuged, washed and freeze-dried, and the porous graphene nanosheet is obtained.

[0017] The electrolyte solution in the step (A) is an electrolyte solution capable of generating oxidizing substances, including but not limited to a solution prepared from chlorides, sulfates, persulfates, basic salts, hypochlorite, chlorine dioxide, chloramine and the like.

[0018] The concentration of the electrolyte solution in the step (A) is 1-10000 mmol / L.

[0019] The concentration of the graphene nanosheet water solution in the step (A) is 20-200 μg / mL.

[0020] The cathode material in the step (B) is a carbon-based or metal-based porous conductive material, including but not limited to metal and alloy materials, carbon-based conductive materials, semiconductor materials.

[0021] The metal and alloy materials include but are not limited to platinum, copper, gold, silver, cobalt, titanium, nickel.

[0022] The carbon-based conductive material includes but is not limited to carbon nanotube sponge, carbon fiber felt, carbon paper, graphite foil.

[0023] The semiconductor material includes but is not limited to silicon, germanium, gallium nitride, manganese oxide, copper oxide.

[0024] The porous carrier material of the anode material in the step (B) is the same as the cathode, and the nanowire loaded on the porous carrier material includes but is not limited to cobalt trioxide nanowire, (reduced) titanium dioxide nanowire, copper oxide nanowire, zinc oxide nanowire, copper phosphide nanowire, etc.

[0025] The pore size of the porous cathode and the porous nanowire anode in the step (B) is 2-5 times larger than that of the graphene nanosheet, which can avoid physical entrapment of the graphene nanosheet in the flow-through electrode.

[0026] The perforating device further comprises a power supply.

[0027] The applied voltage in the step (B) is 1-10 V, and the flow rate of the pump is 1-50 mL / min.

[0028] Compared with the prior art, the present application has the following advantages:

[0029] 1. The present application is based on the nanowire lightning rod effect, which generates an electrochemically active reaction confined region with high charge density at the tip of the nanowire, and provides a preparation method for porous graphene nanosheets by combining direct electrochemical oxidation and indirect oxidation, which has the advantages of simple operation, few steps, low cost, green environmental protection and the like.

[0030] 2. The method for preparing porous graphene of the present invention can control the pore size of the prepared porous graphene nanosheets by changing the applied voltage, flow rate, type and concentration of electrolyte solution, and the preparation method does not introduce impurities, resulting in uniform composition and high purity.

[0031] 3. The porous graphene nanosheets prepared by this invention have abundant functional group configurations, containing a large number of functional groups such as C-OH, -COOH, COC, and -C=O, which facilitates subsequent functionalization modification and can be used in fields such as electrocatalysis, supercapacitors, lithium-ion batteries, and organic catalysis. Attached Figure Description

[0032] Figure 1 The present invention relates to a perforation device and preparation process for the preparation of porous graphene.

[0033] Figure 2 This is a mechanism diagram of the present invention (taking Example I as an example);

[0034] Figure 3 AFM image of the porous graphene prepared in Example I of the present invention;

[0035] Figure 4 This is a TEM image of the porous graphene prepared in Example I of the present invention;

[0036] Figure 5 XPS spectra and functional group content of porous graphene prepared in Example I of the present invention.

[0037] In the diagram: 1. Inlet; 2. Cathode; 3. Anode; 4. Outlet; 5. External power supply; 6. Peristaltic pump; 7. Graphene nanosheets in the aqueous solution. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] The atomic force microscope (AFM) used in this invention is a multimode nasoscope.

[0040] The transmission electron microscope (TEM) used in the characterization of this invention is a JEM-2100.

[0041] The X-ray photoelectron spectroscopy (XPS) used in this invention is PHI-5000C ESCA.

[0042] Example I

[0043] Referring to Figures 1-5 A method for preparing porous graphene nanosheets, specifically comprising the following steps: (A) adding graphene oxide nanosheets (40 mg) into deionized water (40 mL) to prepare a graphene oxide nanosheet stock solution with a concentration of 1.0 mg / mL. The stock solution is subjected to ultrasonic treatment to be fully dispersed, and is centrifuged at a speed of 4000 rpm to remove possible undispersed powder;

[0044] The graphene oxide nanosheet stock solution is diluted into an electrolyte solution, and is uniformly dispersed by ultrasonic treatment to obtain a graphene oxide nanosheet feed solution with a concentration of 20 μg / mL;

[0045] (B) taking a titanium mesh as a cathode, and a cobaltosic oxide nanowire electrode as an anode, and connecting the cathode and the anode to a negative pole and a positive pole of a power supply, respectively. The graphene oxide nanosheet feed solution is pumped into a perforated device, and sequentially passes through a water inlet, the cathode, the anode, and a water outlet from bottom to top, and the flow rate of the pump is adjusted and the power supply is started;

[0046] (C) collecting the water outlet of the device, centrifuging at a speed of 4000 rpm, and washing by resuspending multiple times, and then freeze-drying to obtain the prepared porous graphene oxide nanosheets.

[0047] In the embodiment, the electrolyte solution in step (A) is a sodium chloride solution with a concentration of 50 mmol / L.

[0048] In the embodiment, the porous carrier of the cobaltosic oxide nanowire electrode in step (B) is a carbon-based conductive material, specifically a graphite felt, and the pore size is 50-200 μm.

[0049] In the embodiment, the pore size of the titanium mesh in step (B) is 2 mm.

[0050] In the embodiment, the applied voltage in step (B) is 3 V, 6 V, or 9 V.

[0051] In the embodiment, the flow rate of the pump in step (B) is 15 mL / min.

[0052] The porous graphene oxide nanosheets are obtained after steps (A), (B), and (C).

[0053] Example II

[0054] The technical features of the embodiment are the same as those of Example I except for the following technical features:

[0055] In the embodiment, the electrolyte solution in step (A) is a sodium hypochlorite solution with a concentration of 10 mmol / L.

[0056] In the embodiment, the applied voltage in step (B) is 1V, 5V or 10V.

[0057] In the embodiment, the flow rate of the pump in step (B) is 5mL / min.

[0058] The porous graphene oxide nanosheet is obtained through steps (A), (B) and (C).

[0059] Embodiment III

[0060] In the embodiment, the technical features are the same as those in Embodiment I except that:

[0061] In the embodiment, the electrolyte solution in step (A) is a sodium hydroxide solution with a concentration of 50mmol / L.

[0062] In the embodiment, the cathode electrode material in step (B) is a platinum mesh.

[0063] In the embodiment, the nanowire electrode in step (B) is a reduced titanium dioxide nanowire electrode.

[0064] The porous graphene oxide nanosheet is obtained through steps (A), (B) and (C).

[0065] Embodiment IV

[0066] In the embodiment, the technical features are the same as those in Embodiment I except that:

[0067] In the embodiment, the concentration of the graphene oxide nanosheet in step (A) is 50μg / mL.

[0068] In the embodiment, the electrolyte solution in step (A) is a sodium sulfate solution with a concentration of 50mmol / L.

[0069] The porous graphene oxide nanosheet is obtained through steps (A), (B) and (C).

[0070] It is to be noted that the relative terms such as first and second, and the like, are used herein only to distinguish one entity or operation from another entity or operation, without necessarily requiring or implying any such actual relationship or order between such entities or operations. Moreover, the terms "comprising", "including", or any other variant thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can also include other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0071] While embodiments of the application have been shown and described, it is to be understood that the embodiments described are merely exemplary of the principles and application of the present application. Numerous modifications and adaptions can be effected without departing from the spirit and scope of the present application, which is not limited to the exact construction and arrangement described. It is intended, therefore, to cover all modifications and adaptions that fall within the scope of the claims and their equivalents.

Claims

1. A method of preparing porous graphene nanoplatelets, characterized by: Based on the lightning rod effect of nanowires, the porous graphene nanosheets are prepared by direct electrochemical oxidation and indirect oxidation combined method through the electrochemical reaction confined area with high charge density formed by the tip of nanowires; Specifically comprising the following steps: (A) uniformly dispersing the graphene nanosheets in an electrolyte solution by ultrasonic to obtain a graphene nanosheet water solution; (B) connecting a porous conductive material as a cathode and a porous nanowire electrode as an anode to the negative and positive poles of a power supply respectively, pumping the graphene nanosheet water solution into a perforating device, sequentially passing through a water inlet, a cathode, an anode and a water outlet from bottom to top, adjusting the flow rate of the pump and starting the power supply, and applying a voltage of 6-10V; (C) collecting the water outlet of the device, and after centrifugation, washing and freeze-drying, obtaining the porous graphene nanosheets.

2. The method of claim 1, wherein: The graphene nanosheet water solution is an electrolyte solution.

3. The method of claim 1, wherein: The electrolyte solution is prepared from chlorides, sulfates, persulfates, alkaline salts and hypochlorite, and chlorine dioxide.

4. The method of claim 1, wherein: The cathode material is a carbon-based or metal-based porous conductive material.

5. The method of claim 1, wherein: The anode material is a porous conductive material loaded with nanowire arrays.

6. The method of claim 1, wherein: The perforating device is a flow-through perforating device, which sequentially includes a water inlet, a porous cathode, a porous nanowire anode and a water outlet from bottom to top, and the porous cathode and the porous nanowire anode are connected to the negative and positive poles of the power supply respectively.

7. The method of claim 6, wherein: The flow-through perforating device further comprises a power supply.

8. The method of claim 1, wherein: The flow rate of the pump in step (B) is 1-50mL / min.

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