Preparation method and device of graphene based on coupling of ultrasonic phased array and micro-fluidic chip

Abstract

The invention belongs to the technical field of graphene preparation, and particularly discloses a graphene preparation method and device based on coupling of an ultrasonic phased array and a micro-fluidic chip, and the preparation method comprises the following steps: graphite oxide dispersion liquid enters a micro-fluidic main channel through a sample inlet of the micro-fluidic chip; in a standing wave sound field and a laminar flow state of an ultrasonic phased array, stripping the graphite oxide dispersion liquid through a micro-jet shear force generated by a cavitation effect of the standing wave sound field to obtain a graphene oxide sheet layer; graphene oxide lamellas are synchronously separated to a specified separation flow channel through fluid shear force generated by a micro-channel contraction section and an inertia focusing effect caused by curvature of an arc-shaped separation section, and non-single-layer graphene oxide lamellas are separated to a flow channel. The proportion of the single-layer graphene obtained by the preparation method provided by the invention is as high as 95%, and the problem of microchannel blockage can be relieved.

Description

Technical Field

[0001] The present invention relates to the technical field of graphene preparation, and in particular to a method and device for preparing graphene based on coupling of an ultrasonic phased array and a microfluidic chip. Background Art

[0002] Graphene, due to its unique two-dimensional structure and remarkable physical and chemical properties, holds enormous potential for application in energy, electronics, composite materials, and other fields. Currently, redox methods (such as the Hummers method and its improved methods) remain the mainstream process for large-scale graphene production. These methods involve graphite oxidation, graphene oxide (GO) exfoliation, and reduction. However, existing technologies face significant bottlenecks in practical applications, including exfoliation efficiency, separation technology, and dispersion stability.

[0003] Traditional ultrasonic exfoliation breaks up GO aggregates through the cavitation effect, but the uneven distribution of acoustic field energy results (the monolayer rate is usually <80%), and high-power and long-term ultrasound can easily cause damage to the graphene sheet structure. Although mechanical shear exfoliation can increase production, it is difficult to achieve precise control of the monolayer structure. Post-processing methods such as centrifugation and electrophoresis sorting have problems such as cumbersome procedures, high energy consumption, and difficulty in continuous production. Although microfluidic technology can achieve particle sorting through fluid dynamics, existing solutions are not sensitive enough to the number of GO sheets, and unexfoliated aggregates easily clog the microchannels, resulting in reduced sorting efficiency. Due to the high specific surface area and van der Waals forces, the exfoliated GO sheets are prone to re-agglomeration in subsequent processing, significantly reducing the dispersion stability of the final product. Existing technologies mostly rely on surfactants or polymer dispersants, but the introduction of these additives may contaminate the product and affect the intrinsic properties of graphene.

[0004] To address these issues, researchers have recently attempted to combine ultrasonic processing with microfluidic systems. For example, the University of Science and Technology of China (CN115738950A) disclosed a method for separating and purifying GO using microfluidics. However, the shearing effect of the fluid alone is limited in its ability to dissociate GO aggregates, leading to problems such as microfluidic channel blockage and incomplete separation. Currently, ultrasonic phased arrays are primarily used in cleaning (CN119793986A) and detection (CN119846067A), with limited application in graphene oxide exfoliation.

[0005] Therefore, developing a continuous preparation method that can achieve efficient GO exfoliation, precise sorting and anti-secondary agglomeration integration has become the key to breaking through the bottleneck of graphene industrial preparation. Summary of the Invention

[0006] In view of the above-mentioned shortcomings, the present invention provides a method and device for preparing graphene based on the coupling of an ultrasonic phased array and a microfluidic chip. The coupling of the ultrasonic phased array and the microfluidic chip of the present invention can resist secondary agglomeration and greatly alleviate the problem of microchannel blockage; the proportion of single-layer graphene obtained by the present invention is as high as 95%.

[0007] In order to achieve the above object, the present invention provides a method for preparing graphene based on coupling of an ultrasonic phased array and a microfluidic chip, comprising the following steps:

[0008] S1, the graphite oxide dispersion enters the main channel of the microfluidic chip through the injection port;

[0009] S2. In the standing wave acoustic field and laminar flow state of the ultrasonic phased array, the graphene oxide dispersion is exfoliated by the microjet shear force generated by the cavitation effect of the standing wave acoustic field to obtain graphene oxide sheets; the graphene oxide sheets are synchronously separated into designated sorting channels by the fluid shear force generated by the microchannel contraction section and the inertial focusing effect caused by the curvature of the arc-shaped separation section, and non-monolayer graphene oxide sheets are separated into the flow channel;

[0010] The sound field frequency of the standing wave sound field is 0.01-100 MHz, the sound pressure amplitude is 0.01-100 MPa, and the power density is 0.5-150 W / cm 3 The linear velocity of the fluid in the microfluidic chip is 0.3-50 cm / s; the power density of the standing wave acoustic field and the flow rate of the microfluidic chip meet the following conditions: P / v = 0.01-500 W·s / cm 2 ; P is the power density of the standing wave acoustic field, v is the linear velocity of the fluid in the microfluidic system;

[0011] The microfluidic chip is a three-stage sorting unit, including a first sorting unit, a second sorting unit and a third sorting unit, and the heights of the main channels of adjacent sorting units decrease by 10-30%; the main channel of each sorting unit includes a microchannel contraction section, an arc-shaped separation section and a sorting flow channel; the designated sorting flow channel of the sorting flow channel of the previous sorting unit is connected to the microchannel contraction section of the next sorting unit; one end of the microchannel contraction section of the first sorting unit is connected to the injection port, and the other end is connected to the arc-shaped separation section; the width of the microchannel contraction section near the injection port is greater than the width of the arc-shaped separation section near the microchannel contraction section; the arc-shaped separation section includes an arc section; one end of the arc-shaped separation section is connected to the microchannel contraction section, and the other end is connected to the sorting flow channel; the sorting flow channel includes a designated sorting flow channel and a channel, the designated sorting flow channel and a section of the channel are both connected to the same point of the arc-shaped separation section, the other end of the channel is connected to the next sorting unit, and the other end of the designated sorting flow channel is connected to the post-processing process.

[0012] According to one aspect of the present invention, the graphite oxide dispersion is prepared by a modified Hummers method; the method for preparing the graphite oxide dispersion comprises the following steps:

[0013] A1. The flake graphite is subjected to ball milling, vibrating screen classification, and soaked in a mixture of hydrochloric acid and hydrofluoric acid to obtain pretreated graphite powder;

[0014] A2. Place graphite powder, concentrated sulfuric acid, and sodium nitrate in a mass ratio of 1:20-50:0.5 in a corrosion-resistant reactor. Slowly add potassium permanganate (the mass ratio of potassium permanganate to the total mass of graphite powder, concentrated sulfuric acid, and sodium nitrate is 1:3-6) at a temperature controlled at 0-5°C. Mechanically stir for 4-6 hours. Then, raise the temperature to 35-40°C and continue the reaction for 12-18 hours until the system turns brown. Finally, add water in a gradient (≤5 mL / min) and raise the temperature to 90-95°C. Maintain for 2-3 hours to obtain a graphite oxide dispersion.

[0015] According to one aspect of the present invention, the post-treatment process includes reduction and post-treatment of the graphene oxide sheet; the reduction and post-treatment of the graphene oxide sheet includes the following steps:

[0016] The graphene oxide sheet slurry discharged from the designated sorting flow channel is mixed with a reducing agent and stirred to perform a reduction reaction. After filtering, dehydration, spray drying, and secondary reduction treatment, the graphene sheet is obtained.

[0017] It should be noted that the reducing agent includes any one of hydrazine hydrate, ascorbic acid, sodium borohydride, and HI.

[0018] According to one aspect of the present invention, the frequency of the standing wave sound field is 0.1-3 MHz, the sound pressure amplitude is 0.5-10 MPa, and the power density is 1-50 W / cm 3 ; The linear velocity of the fluid in the microfluidic chip is 0.3-50cm / s; The power density of the standing wave acoustic field and the flow rate of the microfluidic chip meet: P / v = 1-50W·s / cm 2 .

[0019] According to one aspect of the present invention, the reduction reaction temperature is 80-90°C and the time is 8-12 hours; the spray drying is carried out using a spray drying tower, and the inlet air temperature of the spray drying tower is 180-200°C; the secondary reduction treatment is a heat treatment at 400-700°C for 0.5-3 hours under argon protection.

[0020] It should be noted that the secondary reduction is to address the problem of incomplete primary reduction, and its purpose is to improve the stability and quality of the product.

[0021] According to one aspect of the present invention, the ultrasonic phased array includes a linear array consisting of 8-64 array elements, the spacing between adjacent array elements is 1-2 mm, and each array element uses a phase difference of 0°-180° for dynamic focusing scanning; the width of the narrowest part of the microchannel contraction section is 50-200 μm, and the width of the widest part is 100-600 μm; the curvature radius of the arc segment is 1-500 μm; the height of the main channel of the first sorting unit is 20-80 μm.

[0022] It should be noted that the narrowest part of the microchannel contraction section is always smaller than the width of the widest part of the microchannel contraction section.

[0023] According to one aspect of the present invention, the temperature in the main channel of the microfluidic chip decreases at a cooling rate of 5-20°C / m along the fluid flow direction, and the temperature control accuracy is ±0.5°C.

[0024] According to one aspect of the present invention, the inner surface of the main channel of the microfluidic chip is treated by plasma grafting to obtain a graft layer; the graft layer is a zwitterionic polymer containing carboxyl groups, and the graft density is 0.1-1.5 chains / nm 2 .

[0025] It should be noted that the function of the zwitterionic polymer containing a carboxyl group is to inhibit the adsorption of graphene oxide sheets on the inner surface, maintain the dispersion stability of the graphene oxide sheets and the anti-pollution effect.

[0026] According to one aspect of the present invention, the carboxyl group-containing zwitterionic polymer comprises polycarboxybetaine.

[0027] Based on the same inventive concept, the present invention also provides a device based on the above preparation method, including a microfluidic chip module and an ultrasonic phased array module;

[0028] The microfluidic chip module comprises a microfluidic chip, wherein the inner surface of the main channel of the microfluidic chip is provided with a graft layer, and the graft layer is a zwitterionic polymer containing a carboxyl group;

[0029] The ultrasonic phased array module includes an ultrasonic phased array, a programmable phased array transducer group and an impedance matching network.

[0030] According to one aspect of the present invention, the microfluidic chip is a three-stage sorting unit, comprising a first sorting unit, a second sorting unit and a third sorting unit, the heights of the main channels of adjacent sorting units decrease by 10-30%; the main channel of each sorting unit comprises a microchannel contraction section, an arc-shaped separation section and a sorting flow channel; the designated sorting flow channel of the sorting flow channel of the upper-stage sorting unit is connected to the microchannel contraction section of the lower-stage sorting unit; one end of the microchannel contraction section of the first sorting unit is connected to the injection port, and the other end is connected to the arc-shaped separation section; the width of the microchannel contraction section near the injection port is greater than the width of the arc-shaped separation section near the microchannel contraction section; the arc-shaped separation section comprises an arc segment; one end of the arc-shaped separation section is connected to the microchannel contraction section, and the other end is connected to the sorting flow channel; the sorting flow channel comprises a designated sorting flow channel and a channel, a section of the sorting flow channel and the channel are both connected to the same point of the arc-shaped separation section, the other end of the channel is connected to the lower-stage sorting unit, and the other end of the designated sorting flow channel is connected to the post-processing process;

[0031] The ultrasonic phased array comprises a linear array consisting of 8-64 array elements, with a spacing of 1-2 mm between adjacent array elements, and each array element performs dynamic focus scanning using a phase difference of 0°-180°;

[0032] The narrowest width of the microchannel contraction section is 50-200 μm, and the widest width is no more than twice the narrowest width; the curvature radius of the arc section is 1-500 μm; and the height of the main channel of the first sorting unit is 20-80 μm.

[0033] Beneficial effects of the present invention:

[0034] The present invention is based on the integration of efficient exfoliation, precise sorting and resistance to secondary agglomeration of graphene oxide by coupling an ultrasonic phased array with a microfluidic chip, and efficiently prepares single-layer graphene. Based on the improved Hummers method, the present invention innovatively couples ultrasonic phased array technology with a microfluidic chip system during the graphene oxide exfoliation stage. A programmable high-intensity acoustic field region is constructed in the microchannel through the ultrasonic phased array, and the microjets generated by the collapse of cavitation bubbles are used to directionally shear GO agglomerates; at the same time, based on the laminar flow characteristics of the microchannel, the spatial sorting of GO layers with different numbers of layers is achieved through the fluid shear force and inertial focusing effect. Through the coordinated matching of ultrasonic energy density, microfluidic flow rate and channel structure, the GO layers are efficiently exfoliated within the residence time of the acoustic field, and instant sorting is achieved through spatial coupling design, effectively suppressing secondary agglomeration. The present invention can obtain a graphene product with a single-layer rate of >95%, and has the characteristics of continuous process, low energy consumption and good dispersion stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1Schematic diagram of a device for the method for preparing graphene based on coupling of an ultrasonic phased array and a microfluidic chip as described in Example 1 of the present invention;

[0036] Figure 2 This is a schematic structural diagram of the main channel of the sorting unit according to Example 1 of the present invention;

[0037] Figure 3 Schematic diagram of an array element of the ultrasonic phased array described in Example 1 of the present invention.

[0038] Explanation of the accompanying symbols: 1. Ultrasonic phased array module; 2. Third sorting unit; 3. Second sorting unit; 4. First sorting unit; 5. Inlet; 6. Microchannel contraction section; 7. Arc-shaped separation section; 8. Arc-shaped section; 9. Designated sorting flow channel; 10. Channel; 11. Array element. DETAILED DESCRIPTION

[0039] To make the present invention easier to understand, the present invention is further described below with reference to specific examples. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Unless otherwise defined, the professional terms used below are consistent with the meanings understood by professional and technical personnel in this field; unless otherwise specified, the raw materials and reagents involved in this article can be purchased from the market or prepared by known methods.

[0040] Example 1

[0041] A device for preparing graphene based on coupling of ultrasonic phased array and microfluidic chip, such as Figure 1As shown, it includes an ultrasonic phased array module 1 at the bottom and a microfluidic chip module located above the ultrasonic phased array module 1; the ultrasonic phased array module 1 includes an ultrasonic phased array; the microfluidic chip module includes a microfluidic chip; the microfluidic chip is a three-stage sorting unit, including a first sorting unit 4, a second sorting unit 3 and a third sorting unit 2, and the height of the main channel of adjacent sorting units decreases by 25%; the main channel of each sorting unit includes a microchannel contraction section 6, an arc-shaped separation section 7 and a sorting flow channel; the designated sorting flow channel 9 of the sorting flow channel of the upper-level sorting unit is connected to the microchannel contraction section 6 of the lower-level sorting unit; the microchannel contraction section 6 of the first ... One end of segment 6 is connected to the injection port 5, and the other end is connected to the arc-shaped separation segment 7; the width of the end 5 of the microchannel contraction segment 6 near the injection port is greater than the width of the arc-shaped separation segment 7 near the microchannel contraction segment 6; the arc-shaped separation segment 7 includes an arc segment 8, and the curvature radius of the arc segment is 200 μm; one end of the arc-shaped separation segment 7 is connected to the microchannel contraction segment 6, and the other end is connected to the sorting channel; the sorting channel includes a designated sorting channel 9 and a channel 10, and a section of the designated sorting channel 9 and the channel 10 are both connected to the same point of the arc-shaped separation segment 7, the other end of the channel 10 is connected to the next-level sorting unit, and the other end of the designated sorting channel 9 is connected to the post-processing process. The ultrasonic phased array includes a linear array composed of 27 array elements 11, the spacing between adjacent array elements is 1 mm, and each array element uses a 0° phase difference for dynamic focusing scanning. The sound field frequency of the standing wave sound field is 2 MHz, the sound pressure amplitude is 6 MPa, and the power density is 20 W / cm 3 ; The linear velocity of the fluid in the microfluidic chip is 10 cm / s; the power density of the standing wave acoustic field and the flow rate of the microfluidic chip meet: P / v = 2W·s / cm 2 The narrowest width of the microchannel contraction section is 100 μm, and the widest width is 200 μm; the height of the main channel of the first sorting unit is 50 μm. The inner surface of the main channel of the microfluidic chip is treated by plasma grafting to obtain a grafted layer; the grafted layer is a zwitterionic polymer containing carboxyl groups, and the grafting density is 0.7 chains / nm 2 The carboxyl group-containing zwitterionic polymer includes polycarboxybetaine;

[0042] A method for preparing graphene based on coupling an ultrasonic phased array with a microfluidic chip comprises the following steps:

[0043] Raw material pretreatment: Graphite flakes are ground to a particle size of 30 μm using a ball mill and then graded using a vibrating screen. Metal impurities are then removed by soaking in a mixture of hydrochloric acid and hydrofluoric acid (3:1 by volume) and dried to obtain graphite powder.

[0044] Preparation of graphite oxide: Graphite powder, concentrated sulfuric acid (98%), and sodium nitrate were placed in a corrosion-resistant reactor in a mass ratio of 1:35:0.5. Potassium permanganate was slowly added at 0°C (the mass ratio of potassium permanganate to the total mass of graphite powder, concentrated sulfuric acid, and sodium nitrate was 1:4). Mechanical stirring was performed for 4 hours. The temperature was then raised to 35°C and the reaction was continued for 15 hours until the system turned brown. Finally, water was added gradually (3 mL / min) and the temperature was raised to 90°C and maintained for 3 hours to obtain a graphite oxide dispersion.

[0045] Graphene oxide exfoliation: A graphite oxide dispersion is introduced into the main channel of the microfluidic chip through the sampling port of the above-mentioned device. In the standing wave sound field and laminar flow state of the ultrasonic phased array (the ultrasonic phased array sound field frequency is 2 MHz and the sound pressure amplitude is 6 MPa), the graphite oxide dispersion is exfoliated by the microjet shear force generated by the cavitation effect of the standing wave sound field to obtain a graphene oxide sheet slurry; the graphene oxide sheets are simultaneously separated into the designated sorting channel by the fluid shear force generated by the microchannel contraction section and the inertial focusing effect caused by the curvature of the arc-shaped separation section, and non-single-layer graphene oxide sheets are separated into the flow channel.

[0046] Graphene oxide reduction: The graphene oxide sheet slurry (solid content 1%) discharged from the designated sorting channel was mixed with hydrazine hydrate (reducing agent) in a volume ratio of 1:0.5, and reduced with stirring at a constant temperature of 80°C for 9 hours. Subsequently, it was continuously dehydrated through a belt vacuum filter, and the black filter cake was collected.

[0047] Post-treatment: The black filter cake was spray dried in a spray drying tower (inlet air temperature 180°C) to prepare a powder, and then heat treated at 600°C for 1 hour in a tubular furnace under argon protection for secondary reduction to obtain graphene sheets.

[0048] Example 2

[0049] The difference between this embodiment and embodiment 1 is that the sound field frequency of the ultrasonic phased array is 1 MHz, and the sound pressure amplitude is 6 MPa.

[0050] Example 3

[0051] The difference between this embodiment and embodiment 1 is that the sound field frequency of the ultrasonic phased array is 3 MHz, and the sound pressure amplitude is 6 MPa.

[0052] Example 4

[0053] The difference between this embodiment and embodiment 1 is that the sound field frequency of the ultrasonic phased array is 2 MHz, and the sound pressure amplitude is 1 MPa.

[0054] Example 5

[0055] The difference between this embodiment and embodiment 1 is that the sound field frequency of the ultrasonic phased array is 2 MHz, and the sound pressure amplitude is 9 MPa.

[0056] Comparative Example 1

[0057] This comparative example differs from Example 1 in that the graphite oxide dispersion was placed in a high-pressure homogenizer and circulated six times at 160 MPa, followed by ultrasonication at a frequency of 1 MHz for 5 hours to exfoliate the graphene oxide. The raw material pretreatment, graphene oxide preparation, graphene oxide reduction, and post-treatment procedures were the same as in Example 1.

[0058] Comparative Example 2

[0059] This comparative example differs from Comparative Example 1 in that a microfluidic chip is added at the end of the graphene oxide exfoliation stage to achieve precise isolation of a single layer of graphene oxide. Raw material pretreatment, graphene oxide preparation, graphene oxide reduction, and post-processing are the same as in Example 1. However, the microfluidic chip in this comparative example suffers from severe microchannel clogging.

[0060] Comparative Example 3

[0061] This comparative example differs from Comparative Example 1 in that during the graphene oxide exfoliation stage, the high-pressure homogenizer and ultrasonic equipment were replaced with an ultrasonic phased array. The ultrasonic phased array had a sound field frequency of 2 MHz and a sound pressure amplitude of 6 MPa. Raw material pretreatment, graphene oxide preparation, graphene oxide reduction, and post-processing were the same as in Example 1.

[0062] Performance testing and result analysis:

[0063] The key differences and parameters of Examples 1-5 and Comparative Examples 1-3 were compared, and the results are shown in Table 1. Raman analysis was used to infer the mass ratio of the monolayer graphene to the graphene sheet obtained from Examples 1-5 and Comparative Examples 1-3, and the results are shown in Table 2.

[0064] Table 1 Key differences and parameter comparisons between Examples 1-5 and Comparative Examples 1-3

[0065]

[0066] Table 2 Comparison of single-layer graphene ratio test of Examples 1-5 and Comparative Examples 1-3

[0067]

[0068]

[0069] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for preparing graphene based on coupling of an ultrasonic phased array and a microfluidic chip, characterized in that: The following steps are involved: S1, the graphite oxide dispersion enters the main channel of the microfluidic chip through the injection port; S2. In the standing wave acoustic field and laminar flow state of the ultrasonic phased array, the graphene oxide dispersion is exfoliated by the microjet shear force generated by the cavitation effect of the standing wave acoustic field to obtain graphene oxide sheets; the graphene oxide sheets are synchronously separated into designated sorting channels by the fluid shear force generated by the microchannel contraction section and the inertial focusing effect caused by the curvature of the arc-shaped separation section, and non-monolayer graphene oxide sheets are separated into the flow channel; The sound field frequency of the standing wave sound field is 0.01-100 MHz, the sound pressure amplitude is 0.01-100 MPa, and the power density is 0.5-150 W / cm 3 ; The linear velocity of the fluid in the microfluidic chip is 0.3-50 cm / s; The power density of the standing wave acoustic field and the flow rate of the microfluidic chip meet: P / v = 0.01-500W·s / cm 2 ; P is the power density of the standing wave acoustic field, v is the linear velocity of the fluid in the microfluidic system; The microfluidic chip is a three-stage sorting unit, including a first sorting unit, a second sorting unit, and a third sorting unit. The heights of the main channels of adjacent sorting units decrease by 10-30%. The main channel of each sorting unit includes a microchannel contraction section, an arc-shaped separation section, and a sorting channel. The designated sorting channel of the sorting channel of the previous sorting unit is connected to the microchannel contraction section of the next sorting unit. One end of the microchannel contraction section of the first sorting unit is connected to the injection port, and the other end is connected to the arc-shaped separation section. The width of the microchannel contraction section near the injection port is greater than the width of the microchannel contraction section near the arc-shaped separation section. The arc-shaped separation section includes an arc-shaped section; one end of the arc-shaped separation section is connected to the microchannel contraction section, and the other end is connected to the sorting flow channel; the sorting flow channel includes a designated sorting flow channel and a channel, and a section of the designated sorting flow channel and the channel are both connected to the same point of the arc-shaped separation section, the other end of the channel is connected to the next-level sorting unit, and the other end of the designated sorting flow channel is connected to the post-processing process.

2. The method for preparing graphene based on coupling of ultrasonic phased array and microfluidic chip according to claim 1, characterized in that: The graphite oxide dispersion is prepared by the Hummers modified method; the preparation method of the graphite oxide dispersion comprises the following steps: A1. The flake graphite is subjected to ball milling, vibrating screen classification, and soaked in a mixture of hydrochloric acid and hydrofluoric acid to obtain pretreated graphite powder; A2. Place graphite powder, concentrated sulfuric acid, and sodium nitrate into a corrosion-resistant reactor, slowly add potassium permanganate at a temperature of 0-5°C, and mechanically stir for 4-6 hours; then raise the temperature to 35-40°C and continue the reaction for 12-18 hours until the system turns brown; finally, add water gradually and raise the temperature to 90-95°C, maintaining for 2-3 hours to obtain a graphite oxide dispersion.

3. The method for preparing graphene based on coupling of ultrasonic phased array and microfluidic chip according to claim 1, characterized in that: The post-treatment process includes reduction and post-treatment of the graphene oxide sheet; the reduction and post-treatment of the graphene oxide sheet includes the following steps: The graphene oxide sheet slurry discharged from the designated sorting flow channel is mixed with a reducing agent and stirred to perform a reduction reaction. After filtering, dehydration, spray drying, and secondary reduction treatment, the graphene sheet is obtained.

4. The method for preparing graphene based on coupling of ultrasonic phased array and microfluidic chip according to claim 3, characterized in that: The reduction reaction temperature is 80-90°C and the time is 8-12h; the spray drying is carried out using a spray drying tower with an air inlet temperature of 180-200°C; the secondary reduction treatment is a heat treatment at 400-700°C for 0.5-3h under argon protection.

5. The method for preparing graphene based on coupling of ultrasonic phased array and microfluidic chip according to claim 1, characterized in that: The ultrasonic phased array includes a linear array consisting of 8-64 array elements, with a spacing of 1-2 mm between adjacent array elements, and each array element uses a phase difference of 0°-180° for dynamic focus scanning; the width of the narrowest part of the microchannel contraction section is 50-200 μm, and the width of the widest part is 100-600 μm; the curvature radius of the arc segment is 1-500 μm; the height of the main channel of the first sorting unit is 20-80 μm.

6. The method for preparing graphene based on coupling of ultrasonic phased array and microfluidic chip according to claim 1, characterized in that: The temperature in the main channel of the microfluidic chip decreases at a cooling rate of 5-20°C / m along the fluid flow direction, and the temperature control accuracy is ±0.5°C.

7. The method for preparing graphene based on coupling of ultrasonic phased array and microfluidic chip according to claim 1, characterized in that: The inner surface of the main channel of the microfluidic chip is treated by plasma grafting to obtain a graft layer; the graft layer is a zwitterionic polymer containing carboxyl groups, and the graft density is 0.1-1.5 chains / nm 2 .

8. The method for preparing graphene based on coupling of ultrasonic phased array and microfluidic chip according to claim 7, characterized in that: The carboxyl group-containing zwitterionic polymer includes polycarboxybetaine.

9. A device based on the preparation method according to any one of claims 1 to 8, characterized in that: Including microfluidic chip module and ultrasonic phased array module; The microfluidic chip module comprises a microfluidic chip, wherein the inner surface of the main channel of the microfluidic chip is provided with a graft layer, and the graft layer is a zwitterionic polymer containing a carboxyl group; The ultrasonic phased array module includes an ultrasonic phased array, a programmable phased array transducer group and an impedance matching network.

10. The device according to claim 9, characterized in that The microfluidic chip is a three-stage sorting unit, including a first sorting unit, a second sorting unit and a third sorting unit, wherein the heights of the main channels of adjacent sorting units decrease by 10-30%; the main channel of each sorting unit includes a microchannel contraction section, an arc-shaped separation section and a sorting channel; the designated sorting channel of the sorting channel of the upper-stage sorting unit is connected to the microchannel contraction section of the lower-stage sorting unit; one end of the microchannel contraction section of the first sorting unit is connected to the injection port, and the other end is connected to the arc-shaped separation section; the width of the microchannel contraction section near the injection port is greater than the width of the microchannel contraction section near the arc-shaped separation section; The arc-shaped separation section includes an arc-shaped section; one end of the arc-shaped separation section is connected to the microchannel contraction section, and the other end is connected to the sorting flow channel; the sorting flow channel includes a designated sorting flow channel and a channel, a section of the sorting flow channel and the channel are both connected to the same point of the arc-shaped separation section, the other end of the channel is connected to the next-level sorting unit, and the other end of the designated sorting flow channel is connected to the post-processing process; The ultrasonic phased array comprises a linear array consisting of 8-64 array elements, with a spacing of 1-2 mm between adjacent array elements, and each array element performs dynamic focus scanning using a phase difference of 0°-180°; The narrowest width of the microchannel contraction section is 50-200 μm, and the widest width is no more than twice the narrowest width; the curvature radius of the arc section is 1-500 μm; and the height of the main channel of the first sorting unit is 20-80 μm.

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