Method for preparing intrinsic defect graphene based on low-temperature plasma

Abstract

The invention discloses a method for preparing intrinsic defect graphene based on low-temperature plasma, and belongs to the technical field of new materials. According to the method, a graphene sheet is obtained through mechanical stripping, then the graphene sheet is placed on an insulating barrier medium, a large number of active particles are generated in inert gas argon through a high-voltage pulse power supply and the insulating barrier medium, the particles bombard the surface of graphene to cause fracture of C = C chemical bonds, and different vacancy defects are formed; and adjusting the plasma treatment time to enable the vacancy defect degree on the surface of the graphene to be optimal, thereby obtaining the pure intrinsic defect graphene. According to the method, the low-temperature plasma is generated by utilizing an insulation barrier dielectric barrier discharge mode to modify the mechanically stripped graphene sheet, and no new impurity functional group is brought while the vacancy defect is introduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of new materials, and particularly relates to a method for preparing intrinsic defect graphene based on low-temperature plasma. BACKGROUND

[0002] Early graphene research aimed to obtain ideal lattices with no defects and large areas, but with the deepening of applications, it was found that intrinsic defects are the key to regulating the performance, which has become the core driving force for technological development. There are many methods for preparing intrinsic defect graphene at present, mainly including reduction-oxidation method, chemical vapor deposition method and particle bombardment method. The defect types and defect densities of graphene prepared by different methods are different. The oxidation-reduction method introduces more oxygen-containing functional groups into graphene using a strong oxidizing agent, and after adding a reducing agent (NaBH4 or hydrazine hydrate), the functional groups are removed and defect structures appear. This method has low cost and simple operation, but a certain amount of oxygen-containing functional groups will always remain during the oxidation-reduction process; the chemical vapor deposition method uses hydrocarbon gases such as methane and methanol as carbon sources at a high temperature of about 1000℃, and grows a layer of graphene with relatively complete structure and uniform thickness on a metal foil catalyst medium through rapid quenching. This method has high quality and large output, but the defect density is very low and is not suitable for preparing graphene with high defect density. The particle bombardment method uses high-energy particles to irradiate the surface of graphene, and under the action of particle energy, the C=C bonds of graphene are broken, and carbon atoms escape from the lattice to form defects. This method is suitable for forming vacancy-type defects on the surface of graphene, and can control the size of defects within a certain range.

[0003] Dielectric barrier discharge (DBD) generates low-temperature plasma through the blocking effect of the insulating medium between the electrodes. DBD has the characteristics of stable and uniform discharge at low pressure, and is often used for functional modification of material surfaces. When DBD discharges, the gas ionizes to produce various active particles, including electrons, ions, excited-state particles, metastable-state particles and uncharged neutral particles. When the particle energy is greater than the bond energy between the atoms on the surface of the material being processed, the particle bombardment on the material surface may cause the chemical bond to break. Studies have shown that the average energy of electrons in DBD plasma is 1-10 eV, and the formation energy of single vacancy defects and double vacancy defects of graphene conforms to the energy interval. SUMMARY

[0004] In order to overcome the problem of residual impurity functional groups caused by the reduction oxidation method, the low defect density of the chemical vapor deposition method, and the possible introduction of non-uniform defects by particle bombardment, the present application provides a method for preparing intrinsic defect graphene based on low temperature plasma, which realizes the controllable introduction of defects and avoids external impurities by modifying under the condition of insulating barrier medium through low temperature plasma.

[0005] The present application is realized by the following technical solutions.

[0006] A method for preparing intrinsic defect graphene based on low temperature plasma, comprising the following steps:

[0007] Step one: mechanical exfoliation to obtain pure graphene sheets;

[0008] Step two: placing the graphene sheets on the insulating barrier medium of the dielectric barrier discharge (DBD) experimental platform, and filling the inert gas argon into the reaction gas chamber;

[0009] Step three: low temperature plasma treatment of the graphene sheets in the argon environment, the treatment time is not less than 1 minute, low temperature plasma is generated by dielectric barrier discharge, active particles bombard the surface of the graphene sheets, causing the C=C chemical bond to break and form vacancy defects, thereby obtaining intrinsic defect graphene.

[0010] Further, the mechanical exfoliation is one of ball milling, liquid phase exfoliation and three-roll grinding, and a large number of single-layer or few-layer graphene sheets are obtained by mechanical exfoliation.

[0011] Further, the dielectric barrier discharge (DBD) experimental platform in step two mainly includes a high-voltage pulse power supply, a flat plate electrode, a barrier medium, an oscilloscope, a measurement probe and a reaction gas chamber.

[0012] Further, the low temperature plasma treatment time in step three cannot be too short to prevent the defect density from being too low, the low temperature plasma treatment time increases from 0 to 5 min, the ratio of D peak value to G peak value of graphene increases from 0.14 to 0.92, and the ratio of D peak value to G peak value gradually decreases when the time is more than 5 min, preferably 1-7 min; most preferably 5 min.

[0013] Further, the dielectric barrier discharge in step three adopts a single-layer dielectric barrier mode, and the flat plate electrode spacing is 5-10 mm.

[0014] Further, the output voltage of the high-voltage pulse power supply is set to 1kV, the frequency is 1kHz, the pulse rising edge is 50ns, and the pulse width is 0.5ms.

[0015] Furthermore, the dielectric barrier discharge mode described in step three is a uniform discharge mode, with no filamentary discharge channels in the discharge area and an average power density of 180~500mW / cm². The purpose is to make the defect positions on the graphene surface uniformly dispersed and to prevent large-area carbon atom loss.

[0016] Furthermore, the defect density can be adjusted by regulating the low-temperature plasma treatment time.

[0017] Furthermore, the insulating barrier medium is quartz glass.

[0018] This invention utilizes dielectric barrier discharge to generate low-temperature plasma to modify mechanically exfoliated graphene, introducing vacancy defects without introducing new impurity functional groups. The defect density can be precisely controlled by adjusting the plasma treatment time. The intrinsically defective graphene prepared using this method exhibits high purity and tunable defect levels, representing a highly stable and reproducible method for preparing intrinsically defective graphene. Attached Figure Description

[0019] Figure 1 This is a flowchart of the method of the present invention.

[0020] Figure 2 The voltage and current waveforms at the moment when a stable and uniform discharge is formed in a low-pressure argon environment; Figure 2 In the diagram, 'a' represents the voltage and current waveforms at the discharge moment; Figure 2 b is Figure 2 a. Enlarged view of a specific area.

[0021] Figure 3 Raman spectra of graphene after different low-temperature plasma treatment times.

[0022] Figure 4 The graph shows the response sensitivity curve of intrinsically defective graphene to SOF2 gas.

[0023] Figure 5 The graph shows the response sensitivity curve of intrinsically defective graphene to SO2F2 gas. Specific implementation methods

[0024] The invention will now be explained in further detail with reference to the accompanying drawings.

[0025] like Figure 1 As shown, a method for preparing intrinsically defective graphene based on low-temperature plasma includes the following steps: Step 1: Mechanical exfoliation to obtain pure graphene flakes; the mechanical exfoliation is one of ball milling, liquid phase exfoliation and three-roll milling, and a large number of single-layer or few-layer graphene flakes are obtained through mechanical exfoliation; Step two: place the graphene sheet on the insulating barrier medium of the dielectric barrier discharge (DBD) experimental platform, and fill the inert gas argon into the reaction chamber, the gas pressure in the reaction chamber is 1kPa; the dielectric barrier discharge (DBD) experimental platform includes a high-voltage pulse power supply, a flat plate electrode, a barrier medium, an oscilloscope, a measurement probe and a reaction chamber; the barrier mode is single-layer dielectric barrier, the flat plate electrode spacing is 5-10mm; the output voltage of the high-voltage pulse power supply is set to 1kV, the frequency is 1kHz, the pulse rising edge is 50ns, and the pulse width is 0.5ms; Step three: low temperature plasma treatment is carried out on the graphene sheet in the argon environment, the treatment time is 1-7 minutes, the low temperature plasma is generated by dielectric barrier discharge, the active particles bombard the surface of the graphene sheet, the C=C chemical bond is broken to form vacancy defects, and the intrinsic defect graphene is obtained. Among them, the dielectric barrier discharge mode should be uniform discharge mode, there is no obvious filament discharge channel in the discharge area, the purpose is to make the defect position of the graphene surface uniform and dispersed, and there is no large area of carbon atom loss; the average power density of DBD discharge is 180~500mW / cm 2 .

[0026] The application will be further illustrated in detail in combination with examples.

[0027] Example 1: preparation of intrinsic defect graphene with a treatment time of 1 minute 1. Obtain graphene sheet by mechanical exfoliation: adopt ball milling method for mechanical exfoliation. Add graphite raw material and grinding medium into the ball mill according to appropriate proportion, set appropriate rotating speed and grinding time, separate the graphite layers by mechanical force, and finally obtain pure single-layer or few-layer graphene sheet.

[0028] 2. Build experimental platform and prepare reaction environment: place the obtained graphene sheet on the quartz glass (insulating barrier medium) of the dielectric barrier discharge (DBD) experimental platform. The experimental platform includes a high-voltage pulse power supply with an output voltage of 1kV, a frequency of 1kHz, a pulse rising edge of 50ns and a pulse width of 0.5ms, a flat plate electrode (spacing 5mm), an oscilloscope, a measurement probe and a reaction chamber. Then fill the inert gas argon into the reaction chamber, and adjust the gas pressure in the chamber to 1kPa.

[0029] 3. Low temperature plasma treatment: start the high-voltage pulse power supply, adopt single-layer dielectric barrier discharge mode, ensure that the discharge mode is uniform discharge mode (no filament discharge channel), and control the average power density at 199mW / cm². Perform 1 minute of low temperature plasma treatment on the graphene sheet in the argon environment, during which the active particles bombard the surface of the graphene sheet, causing the C=C chemical bond to break and form vacancy defects, and the intrinsic defect graphene is obtained after the treatment.

[0030] 4. Product detection and results: The prepared intrinsic defect graphene was detected by Raman spectroscopy, and the ratio of D peak value to G peak value was about 0.35, the defect density was low, and it was suitable for basic research scenes with low defect density requirements.

[0031] Example 2: Preparation of intrinsic defect graphene with a treatment time of 3 minutes 1. Obtain graphene flakes by mechanical exfoliation: Select liquid exfoliation method. Disperse graphite powder in a specific organic solvent, provide mechanical force by ultrasonic oscillation and other methods, make the graphite interlayer exfoliate, and obtain pure single-layer or few-layer graphene flakes through centrifugal separation and other steps.

[0032] 2. Build experimental platform and prepare reaction environment: consistent with the operation of step 2 of example 1, place the graphene flakes on the quartz glass, build the DBD experimental platform containing the same parameter high-voltage pulse power supply, flat plate electrode, etc., fill argon into the reaction gas chamber and adjust the gas pressure to 1 kPa.

[0033] 3. Low-temperature plasma treatment: the experimental platform parameters are the same as step 3 of example 1, only the low-temperature plasma treatment time is extended to 3 minutes, so that the active particles can fully bombard the graphene surface and promote more C=C chemical bonds to break and form vacancy defects.

[0034] 4. Product detection and results: Raman spectroscopy detection shows that the ratio of D peak value to G peak value of the intrinsic defect graphene prepared under this condition is about 0.68, the defect density is moderate, and it can be used in application fields such as semiconductor device manufacturing which have certain requirements for defect density.

[0035] Example 3: Preparation of intrinsic defect graphene with a treatment time of 5 minutes 1. Obtain graphene flakes by mechanical exfoliation: adopt three-roll grinding method. Put the graphite raw material into the three-roll grinding machine, realize the interlayer exfoliation of graphite through the extrusion and shearing action between the three rollers, and finally obtain pure single-layer or few-layer graphene flakes.

[0036] 2. Build experimental platform and prepare reaction environment: repeat the operation of step 2 of example 1 to complete the placement of graphene flakes, the construction of experimental platform, and the argon filling and pressure adjustment of reaction gas chamber.

[0037] 3. Low-temperature plasma treatment: the experimental platform parameters are still consistent with step 3 of example 1, and the low-temperature plasma treatment time is set to 5 minutes to form more vacancy defects on the graphene surface.

[0038] 4. Product detection and results: Raman spectroscopy detection shows that the ratio of D peak value to G peak value reaches 0.92, the defect density is the highest, and it is suitable for application scenarios such as energy storage materials which need high defect density to improve performance.

[0039] Example 4: Preparation of intrinsic defect graphene with a treatment time of 7 minutes 1. Obtain graphene flakes by mechanical exfoliation: use a three-roll grinding method. Put the graphite raw material into a three-roll grinding machine, and realize the interlayer exfoliation of graphite through the extrusion and shearing action between the three rollers, finally obtain pure single-layer or few-layer graphene flakes.

[0040] 2. Build the experimental platform and prepare the reaction environment: repeat the operation of step 2 of example 1, complete the placement of graphene flakes, the construction of experimental platform, and the argon filling and pressure adjustment of reaction gas chamber.

[0041] 3. Low temperature plasma treatment: the parameters of the experimental platform remain consistent with step 3 of example 1, and the low temperature plasma treatment time is set to 7 minutes, so that more vacancy defects are formed on the surface of graphene.

[0042] Product detection and results: Raman spectrum detection shows that the ratio of D peak value to G peak value reaches 0.92, the defect density is the highest, and it is suitable for energy storage materials and other application scenarios that require high defect density to improve performance.

[0043] Comparison of intrinsic defect graphene gas sensing performance 1. Sensor preparation: use interdigital electrodes as the base element of resistance type gas sensor. Spray the untreated graphene and intrinsic defect graphene gas sensitive material treated by plasma for 5 minutes on the surface of interdigital electrodes to form a gas sensitive film, and obtain a resistance type gas sensor.

[0044] 2. Build a gas sensing test experimental platform: build a gas sensing test experimental platform, the test system mainly includes gas flow meter, gas mixer, gas inlet pipe, gas pressure gauge, reaction gas chamber, gas outlet pipe and vacuum pump, and use LCR digital bridge (WayneKerr 4100) to test the resistance value of resistance type graphene sensor in real time.

[0045] 3. Sensing performance detection: place the sensor in a sealed gas chamber, connect the two ends of the interdigital electrode and the LCR digital bridge through the lead wire; during the test, when the measured gas is introduced into the gas chamber, the gas molecules will adsorb or chemically react on the surface of the gas sensitive film, causing the change of the carrier concentration of the gas sensitive film, so that the change of the sensor resistance is detected, and according to the size of the resistance change, the type and concentration of gas molecules can be determined.

[0046] 4. Product detection and results: The test gas is SOF2 and SO2F2, two common decomposition components in SF6 electrical equipment. The response sensitivity of untreated graphene to the two gases is less than 0.8%, and no obvious selectivity is shown. The intrinsic defect graphene after plasma treatment has a response sensitivity of -2.2% and -0.6% to SOF2 and SO2F2 gases with a concentration of 100ppm, and the selectivity of the intrinsic defect graphene to SOF2 gas is obviously improved.

[0047] The above merely describes the preferred embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art should be within the protection scope of the present application according to the technical solutions and inventive concepts of the present application, equivalent replacement or change, and should be within the protection scope of the present application.

Claims

1. A method for preparing intrinsically defective graphene based on low-temperature plasma, characterized in that, Includes the following steps: Step 1: Mechanically peel off to obtain pure graphene sheets; Step 2: Place the graphene sheet on the insulating barrier dielectric of the dielectric barrier discharge experimental platform, and fill the reaction chamber with inert argon gas. Step 3: Perform low-temperature plasma treatment on the graphene sheet in an argon atmosphere for no less than 1 minute. Low-temperature plasma is generated by dielectric barrier discharge, which causes active particles to bombard the surface of the graphene sheet, resulting in the breakage of C=C chemical bonds and the formation of vacancy defects, thereby obtaining intrinsic defect graphene.

2. The method for preparing intrinsically defective graphene based on low-temperature plasma according to claim 1, characterized in that, The mechanical stripping method is one of ball milling, liquid phase stripping, and three-roll milling.

3. The method for preparing intrinsically defective graphene based on low-temperature plasma according to claim 1, characterized in that, The dielectric barrier discharge experimental platform includes a high-voltage pulse power supply, a flat plate electrode, a barrier dielectric, an oscilloscope, a measurement probe, and a reaction gas chamber.

4. The method for preparing intrinsically defective graphene based on low-temperature plasma according to claim 1, characterized in that, The low-temperature plasma treatment time is 1-7 minutes.

5. The method for preparing intrinsically defective graphene based on low-temperature plasma according to claim 1, characterized in that, The gas pressure in the reaction chamber is 1 kPa.

6. The method for preparing intrinsically defective graphene based on low-temperature plasma according to claim 1, characterized in that, The dielectric barrier discharge described in step three uses a single-layer dielectric barrier method, with a spacing of 5-10 mm between the flat electrode plates.

7. The method for preparing intrinsically defective graphene based on low-temperature plasma according to claim 3, characterized in that, The output voltage of the high-voltage pulse power supply is set to 1kV, the frequency is 1kHz, the pulse rise time is 50 nanoseconds, and the pulse width is 0.5 milliseconds.

8. The method for preparing intrinsically defective graphene based on low-temperature plasma according to claim 1, characterized in that, The dielectric barrier discharge mode described in step three is a uniform discharge mode, with no filamentary discharge channels in the discharge area and an average power density of 180~500mW / cm², to ensure uniform defect distribution.

9. The method for preparing intrinsically defective graphene based on low-temperature plasma according to claim 1, characterized in that, Defect density can be adjusted by regulating the low-temperature plasma treatment time.

10. The method for preparing intrinsically defective graphene based on low-temperature plasma according to claim 1, characterized in that, The insulating barrier medium is quartz glass.

Images