Method for preparing graphene nanoparticles in neutral medium

Abstract

The invention belongs to the field of graphene nanoparticle preparation, and particularly discloses a neutral medium graphene nanoparticle preparation device and method, and the device comprises an electrolytic bath, a cathode and anode space separated by a high-density membrane, and an anode with a clamp box. According to the innovation, an anode porous filtering partition plate intercepts coarse particles, a cathode porous filtering partition plate slows down mixing, and a lithium hydroxide electrolyte is injected into a cathode space through a floating ball valve. The graphite foil is moved at the speed of 0.5-3.0 cm / h under the electric field intensity of 4-30 V / cm and the current density of 2-60 mA / cm < 2 >, and a neutral medium extraction area (pH 6.8-7.2) is formed between the partition plate and the membrane after electrolysis is carried out for 60-90 minutes. And a regulating valve is opened through a pH meter and photodiode linkage control device to collect the suspension. The problem of alkaline residual loss in the prior art (CN114132921A) is solved in a breakthrough mode, and the method has the advantages that 1) washing-free production is achieved, and graphene loss is reduced by 30-60%; 2) the number of particle size intervals is increased to 8 (30-800 nm); and 3) the consumption of lithium hydroxide is reduced by 40%.

Description

Technical Field

[0001] This invention belongs to the field of graphene nanoparticle preparation, and specifically discloses a method for preparing graphene nanoparticles in a neutral medium. Background Technology

[0002] Graphene nanoparticles, due to their unique electrical, mechanical, and thermal properties, have shown great application potential in energy storage (such as supercapacitors and lithium-ion batteries), composite materials, and sensors. Electrochemical exfoliation has become one of the mainstream technologies for preparing graphene nanoparticles due to its advantages such as simple process, low cost, and continuous production capability.

[0003] In the prior art, patent CN114132921A discloses a method for continuous electrochemical preparation of graphene nanoparticles. This method uses potassium hydroxide as the electrolyte, and a glass fiber reinforced foil (anode) made of thermally expanded graphite is driven by a mechanical device through an electrolytic cell at a speed of 0.5-3.0 cm / h. The electrolytic cell is divided into anode and cathode spaces by a membrane. A porous filter is installed in the anode area to achieve product separation, and a float valve is used to control the electrolyte flow rate. The production process is adjusted through optical density feedback. Although this method achieves continuous production, it still has the following significant drawbacks:

[0004] 1. Alkaline residue leads to material loss:

[0005] The reaction is always carried out in a strongly alkaline medium (pH 9-11), and the resulting graphene suspension must be repeatedly washed until it is neutral (pH 5-7) before it can be used in electronic devices.

[0006] During the washing process, 30-60% of graphene nanoparticles are lost with the waste liquid. Producing 1 kg of graphene requires 1.2-2 tons of deionized water, increasing the investment in post-treatment equipment such as centrifugation and filtration.

[0007] 2. Insufficient particle size control precision:

[0008] Controlling particle size solely by adjusting the electric field strength (2-30V / cm) and strip speed (0.5-3.0cm / h) results in:

[0009] The particle size distribution range is wide (±50nm), and there are multiple peaks under the same parameter combination (such as the 30-70nm span of Example 1 in Table 1, which reaches 40nm), making it impossible to stably obtain a specific narrow range of particle size (such as the yield rate <65% when 60±5nm particles are required).

[0010] 3. Rapid mixing of electrolytes can lead to reaction imbalance:

[0011] Conventional polypropylene film (thickness 0.5mm, density <300g / cm³) is used. 2The separate electrolytic cell has an excessively high ion permeability (>90%), leading to:

[0012] Yin and Yang polar regions H + The rapid mixing of OH- ions disrupts the local pH gradient.

[0013] The anode region is difficult to maintain an acidic environment (pH < 3), which reduces the graphite stripping efficiency by more than 20%.

[0014] The OH- concentration fluctuation in the cathode region is greater than 15%, which hinders the uniformity of particle size.

[0015] 4. Low potassium ion migration efficiency:

[0016] Using K + When (ionic radius 138 pm) acts as a charge carrier:

[0017] The migration speed through the diaphragm is only 1.2 × 10⁻⁶. -8 m 2 / (V·s).

[0018] The current density needs to be increased (>40mA / cm). 2 This compensation exacerbates electrolyte decomposition.

[0019] Residual potassium impurities (>500ppm) in the product affect the cycle life of the supercapacitor. Summary of the Invention

[0020] To address the aforementioned problems, this invention improves upon the existing technology and discloses a method for preparing graphene nanoparticles in a neutral medium. This invention achieves a breakthrough through three core improvements:

[0021] ① Restructuring of the electrolyzer: The electrolyte supply path is changed from the anode space to the cathode space, and a high-barrier filter plate is added to the cathode area to establish a stable pH gradient field;

[0022] ② Optimization of ion transport system: Li+ (ionic radius 76 pm) was used instead of K. + The migration speed has been increased to 3.5×10 - 8 m 2 / (V·s), combined with a high-density membrane (440g / m²) 2 Controlling ion flux;

[0023] ③ Dynamic closed-loop control: Integrating a pH meter and optical density sensor, it accurately captures the 60-90 minute reaction window period to achieve in-situ extraction in neutral media.

[0024] To achieve the above objectives, the present invention includes the following technical solutions:

[0025] A neutral medium graphene nanoparticle preparation device, comprising:

[0026] The electrolytic cell is internally divided into an anode space and a cathode space by a high-density membrane.

[0027] The cathode and anode assemblies are installed in the electrolytic cell, and the anode assembly includes a fixture box and a glass fiber reinforced graphite foil strip that runs through the electrolytic cell;

[0028] A porous filtration baffle is set in the anode space to form a filtration channel that allows the graphene nanoparticle suspension to pass through but retains coarse particles.

[0029] A porous cathode filter baffle is installed in the cathode space to reduce the electrolyte mixing rate in order to maintain the ion gradient;

[0030] The lithium hydroxide electrolyte container, which is connected to the cathode space via a float valve, constitutes the electrolyte supply system.

[0031] The neutral medium extraction zone is located between the porous anode filter and the high-density membrane.

[0032] The optical density monitoring unit, positioned facing the neutral medium extraction region, includes a photodiode and a light-emitting diode.

[0033] A control device connected to the optical density monitoring unit, which controls the regulating valve in conjunction with the regulating valve driver;

[0034] A container for a suspension of graphene nanoparticles connected to a neutral medium extraction zone via a regulating valve.

[0035] A coarse particle discharge valve located at the bottom of the anode space, and a coarse dispersed graphite collection container connected to its pipeline, constitute a coarse particle recovery system.

[0036] A pH meter inserted into the neutral medium extraction zone forms a closed-loop feedback with the control device.

[0037] Furthermore, in the aforementioned apparatus, the high-density membrane has a density of 440 g / m³. 2 KS-34 grade polypropylene film with a thickness of 0.5mm.

[0038] Furthermore, in the above-mentioned device, the pore density of the cathode porous filter is 120-150 PPI, and the pore density of the anode porous filter is 80-100 PPI; the PPI of the cathode porous filter is set to be 20-30% higher than that of the anode porous filter.

[0039] Furthermore, in the aforementioned device, the control device is configured to automatically activate the regulating valve when the pH meter detects a pH of 6.8-7.2 and the photodiode detects a light density value deviating from the preset range of ±0.03.

[0040] This invention also discloses a method for preparing graphene nanoparticles using the above-described apparatus, comprising the following steps:

[0041] a) Inject lithium hydroxide electrolyte into the cathode space through a float valve;

[0042] b) Apply an electric field strength of 4-30V / cm and a current density of 2-60mA / cm. 2 Direct current;

[0043] c) Move the graphite foil strip at a speed of 0.5-3.0 cm / h;

[0044] d) After electrolysis for 60-90 minutes, when the pH meter detects that the pH value of the neutral medium extraction zone is 6.8-7.2, start the regulating valve to collect the suspension.

[0045] Furthermore, in the above method, in step d), when the current density is 40-60 mA / cm² 2 At that time, the neutral dielectric formation time was 60 ± 2 minutes; the current density was 2-9 mA / cm². 2 The formation time is 90±3 minutes.

[0046] Furthermore, the above method also includes step e) periodically discharging the coarsely dispersed graphite deposited at the bottom of the anode space into a container through a coarse particle discharge valve, with a discharge frequency of 50-100 ml of coarse particle slurry for every 1 liter of suspension collected.

[0047] This invention also discloses a method for controlling the particle size of graphene nanoparticles. Using the above method, a specific particle size range is achieved by combining the following parameters A)-C):

[0048] A) The bulk density of thermally expanded graphite is 0.8-6.0 g / dm³ 3 ;

[0049] B) Graphite foil moving speed: 0.5-3.0 cm / h;

[0050] C) Current density 2-60 mA / cm² 2 ;

[0051] When 30-60nm particles are required, a bulk density of 0.8-1.5g / dm³ is used. 3 +Moving speed 0.5cm / h +Current density 2mA / cm² 2 The combination of .

[0052] Furthermore, in the above method, the number of particle size ranges is increased by adjusting the current density value (C), with each increase of 5 mA / cm 2 The current density can add a new particle size sub-range, and the particle size control accuracy reaches ±15nm.

[0053] This invention also discloses the application of a neutral graphene nanoparticle suspension. The suspension prepared above can be directly used in the manufacture of supercapacitor electrodes without the need for a washing process. The conductivity of the prepared electrodes is 18-22% higher than that of products prepared with alkaline media.

[0054] Technical Principles

[0055] The core mechanism of this invention for in-situ preparation of graphene nanoparticles in a neutral medium is based on the directional regulation of electrochemical reactions and the control of ion migration equilibrium. The specific process is as follows:

[0056] 1) Electrochemical reaction mechanism

[0057] In lithium hydroxide electrolyte, the following reaction occurs at the electrode:

[0058] Anode (positive electrode) reaction:

[0059] 4OH - +4e=O2+2H2O– For bases.

[0060] 2H₂O – 4e = O₂ + 4H + –Regarding water.

[0061] This leads to the formation of an acidic dielectric (H) near the electrode layer of the anode. + (Excessive), some H + Insertion between graphite layers promotes exfoliation.

[0062] Cathode (negative electrode) reaction:

[0063] 2H₂O - 2e = H₂ + 2OH⁻ –

[0064] An alkaline medium (excess OH-) is formed, while Li+ migrates to the cathode, and at high concentrations, precipitation may occur.

[0065] 2) Neutral medium formation mechanism

[0066] Stripped from the anode (H) + Graphene nanoparticles migrate towards the cathode under the influence of an electric field, where they neutralize the charge of OH- ions in the cathode region.

[0067] Graphene-H + +OH - → Neutral graphene + H2O

[0068] The reaction is completed in the extraction zone (10) between the anolyte porous filter (5) and the high-density membrane (7), which is designed to achieve a neutral environment of pH 6.8-7.2:

[0069] High-density membrane (7) selectively permeates ions (blockage rate > 40%), preventing H+ ions from passing through. + / OH - Direct mixing;

[0070] The porous cathode filter (6) slows down the electrolyte flow rate and maintains the ion gradient balance.

[0071] 3) Core parameters for particle size control

[0072] Current intensity is the decisive factor in particle size control:

[0073] The current density (2-60mA / cm²) is precisely controlled through a constant current mode power supply. 2 );

[0074] Every 5mA / cm increase 2 The current density can add a new particle size sub-range (eight ranges are achieved as in Example 9);

[0075] Current density is negatively correlated with the formation time of the neutral medium.

[0076] 40-60mA / cm 2 →60±2 minutes (high current density accelerates the reaction)

[0077] 2-9mA / cm 2 →90±3 minutes (low current density delays the reaction)

[0078] Synergistic effect of optical density feedback and pH monitoring:

[0079] Optical density values ​​(0.08-0.55) are associated with particle size (e.g., 0.08±0.01 corresponds to 30-60 nm);

[0080] The pH meter (19) captures the neutral window (pH 6.8-7.2) in real time, triggering product collection.

[0081] Compared with the prior art, the present invention has the following outstanding advantages:

[0082] This invention addresses three major shortcomings of prior art document 1 (CN114132921A): high losses due to alkaline residue, coarse particle size control, and unstable reaction environment. It achieves a breakthrough through three core improvements:

[0083] 1. Restructuring:

[0084] The traditional route described in Comparative Document 1, where the electrolyte is directly supplied to the anode space (see its instruction manual attached), is different.Figure 1 The container 7 (anode) was innovatively changed to cathode space injection (components 8→9→cathode area), which, together with the buffering effect of the cathode porous filter plate (6), established a stable pH gradient field in the electrolytic cell for the first time. Combined with the high-density membrane (7) (ion permeability 40-60%, which is >40% lower than the conventional membrane in the comparative document 1), it effectively blocked H + / OH - The rapid neutralization causes the neutral medium extraction zone (10) (between the anode diaphragm 5 and the membrane 7) to spontaneously form a reaction window with a pH of 6.8-7.2, thus completely solving the problem of alkaline residue.

[0085] 2. Innovation in ion transport systems:

[0086] Instead of using the potassium hydroxide electrolyte in Comparative Document 1, lithium hydroxide (component 8) is innovatively adopted. Utilizing Li... + The ionic radius (76 pm) is only K + (138pm) 55%, migration speed increased to 3.5×10 -8 m 2 / (V·s)(K + 1.2×10 -8 ),accomplish:

[0087] In-situ generation of graphene nanoparticles in a neutral medium eliminates the need for a washing process and avoids the 30-60% graphene loss observed in comparison document 1.

[0088] Current density requirement reduced by 35% (minimum 2mA / cm) 2 (Still operational), reducing electrolyte decomposition.

[0089] The product has a residual metal impurity of <50 ppm (compared to >500 ppm potassium impurity in document 1).

[0090] 3. Upgraded dynamic closed-loop control:

[0091] Based on the single optical density feedback in Reference Document 1, a pH meter (19) is added to monitor the neutral medium extraction zone (10) in real time, forming a dual-signal linkage with the photodiode (11). When the pH is 6.8-7.2 and the optical density reaches the preset value, the control device (13) activates the regulating valve (15) to collect the product. This mechanism accurately captures the 60-90 minute reaction window, reducing the particle size distribution range by 40% (e.g., 30-60nm → ±15nm), breaking through the ±50nm fluctuation limitation under the same parameters in Reference Document 1.

[0092] Overall benefits:

[0093] Material utilization rate: Graphene loss reduced by 30-60%, deionized water consumption reduced by 1.2 tons / kg.

[0094] Particle size controllability: through bulk density (0.8-6.0 g / dm³) 3 The particle size sub-ranges were increased from 5 in Comparative Document 1 to 8 (full coverage of 30-800nm) through coordinated regulation of moving speed and current density.

[0095] Energy efficiency: Lithium hydroxide consumption is reduced by 40%, eliminating the need for investment in centrifuge / filtration equipment.

[0096] Product performance: Supercapacitor electrode specific capacitance increased by 18-22% (220-250 F / g), electronic conductivity increased by 15-20%. Attached Figure Description

[0097] Figure 1 An apparatus for preparing neutral medium graphene nanoparticles according to the present invention;

[0098] The components are: 1-electrolytic cell, 2-cathode, 3-clamp box, 4-graphite foil strip, 5-anode porous filter plate (for passing nanoparticles and retaining coarse particles), 6-cathode porous filter plate (for reducing electrolyte mixing speed), 7-high-density membrane, 8-container containing lithium hydroxide electrolyte, 9-float valve, 10-neutral medium extraction zone, 11-photodiode, 12-light-emitting diode, 13-control device, 14-regulating valve actuator, 15-regulating valve, 16-graphene nanoparticle suspension container, 17-coarse particle discharge valve, 18-coarse dispersed graphite collection container, 19-pH meter. Detailed Implementation

[0099] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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.

[0100] In practice, the method of the present invention is implemented according to the following steps:

[0101] Assembly of device a:

[0102] The cathode (2), the fixture box (3), the glass fiber reinforced graphite foil strip as the anode (4), the high-density membrane (7), the anode porous filter plate (5), and the cathode porous filter plate (6) are inserted into the electrolytic cell (1);

[0103] The solution is injected into the container (8) containing lithium hydroxide electrolyte (concentration 1.0M). The electrolyte flows into the electrolytic cell (1) through the float valve (9) and fills the preset liquid level.

[0104] b. Electrolytic start-up:

[0105] A constant voltage is applied to electrodes (2) and (4), with the electric field strength set to 4-30V / cm and the current density to 2-60mA / cm. 2 ;

[0106] Start the clamp box (3) drive mechanism to move the graphite foil strip (4) at a speed of 0.5-3.0 cm / h;

[0107] Electrochemical stripping occurs when an electric current is applied to the surface of the anode (4), and the graphene nanoparticles pass through the porous filter plate (5) of the anode and enter the neutral medium extraction zone (10).

[0108] c. Reaction control:

[0109] The porous cathode filter (6) reduces the electrolyte mixing rate and maintains the ion gradient (as described in the technical principle H). + (OH- equilibrium);

[0110] After electrolysis for 60-90 minutes, graphene nanoparticles accumulate in the extraction zone (10):

[0111] The photodiode (11) monitors the increase in optical density through the light source of the light-emitting diode (12);

[0112] pH meter (19) detects the pH value of extraction zone (10) in real time.

[0113] d. Product collection:

[0114] When both conditions are met:

[0115] a) The pH meter (19) showed a pH of 6.8-7.2;

[0116] b) The optical density value reaches the preset range (e.g., 0.08±0.01);

[0117] The control device (13) opens the regulating valve (15) through the regulating valve driver (14), so that the suspension enters the container (16) at a constant optical density flow rate;

[0118] Coarse particle treatment: Unstripped coarse dispersed graphite settles to the bottom of the anode space and is periodically discharged into the collection container (18) through the coarse particle discharge valve (17).

[0119] The following materials were used to implement the method:

[0120] - Glass fiber reinforced foil made of thermally expanded graphite with different bulk densities (0.8-6.0 g / dm3), conforming to TUU 26.8-30969031-002-2002 standard;

[0121] - Lithium hydroxide, analytical grade or pure grade conforming to GOST 8595-83 standard;

[0122] - The membrane is made of material with a thickness of 0.5 mm and a density of 440 g / m³. 2 Made of KS-34 grade high-density polypropylene fabric, manufacturer: TechnoTkan, Kharkiv, Ukraine;

[0123] - A porous filter plate made of E3-100 glass fiber; E3-100 glass fiber conforms to GOST 19907-2015 standard and is manufactured by "StandardK" company in Zaporizhzhia, Ukraine;

[0124] - Transmitter (photodiode C503B-RAS / RAN, manufacturer "CREE" Ukraine), receiver (light-emitting diode) BPW34 (34S), manufacturer "OSRAM" Ukraine.

[0125] - A jig box for glass fiber reinforced graphite foil strip (the jig box is an open structure with two spools that drive the graphite foil strip to continuously pass through the electrolytic cell);

[0126] -Control device;

[0127] - A regulating valve with an actuator;

[0128] -Masteram MR 5020E constant current power supply unit;

[0129] -Zetasizer-3 spectrometer (Malvin Instruments, UK);

[0130] -pH meter AZ-86505.

[0131] Basic Implementation

[0132] like Figure 1 As shown, a neutral medium graphene nanoparticle preparation device includes:

[0133] Electrolytic cell 1, the interior of which is divided into an anode space and a cathode space by a high-density membrane 7;

[0134] The cathode 2 and anode assembly are installed in the electrolytic cell 1. The anode assembly includes a clamp box 3 and a glass fiber reinforced graphite foil strip 4 that runs through the electrolytic cell.

[0135] The porous anode filter 5, which is set in the anode space, is used to form a filter channel that allows the graphene nanoparticle suspension to pass through but retains coarse particles.

[0136] A porous cathode filter 6 is installed in the cathode space to reduce the electrolyte mixing rate in order to maintain the ion gradient.

[0137] The lithium hydroxide electrolyte container 8, which is connected to the cathode space via the float valve 9, constitutes an electrolyte supply system.

[0138] Neutral medium extraction zone 10 is located between the anode porous filter plate 5 and the high-density membrane 7;

[0139] The optical density monitoring unit facing the neutral medium extraction region 10 includes a photodiode 11 and a light-emitting diode 12.

[0140] A control device 13 is connected to the optical density monitoring unit via a signal, and the device controls the regulating valve 15 in conjunction with the regulating valve driver 14.

[0141] The graphene nanoparticle suspension container 16 is connected to the neutral medium extraction zone 10 via the regulating valve 15.

[0142] The coarse particle discharge valve 17 located at the bottom of the anode space and the coarse dispersed graphite collection container 18 connected to it by a pipeline constitute a coarse particle recovery system.

[0143] A pH meter 19 is inserted into the neutral medium extraction zone 10, forming a closed-loop feedback with the control device 13.

[0144] Preferably, the high-density membrane 7 has a density of 440 g / m³. 2 KS-34 grade polypropylene film with a thickness of 0.5mm.

[0145] Preferably, the pore density of the cathode porous filter 6 is 120-150 PPI, and the pore density of the anode porous filter 5 is 80-100 PPI; the PPI of the cathode porous filter 6 is set to be 20-30% higher than that of the anode porous filter 5.

[0146] Preferably, the control device 13 is configured to automatically activate the regulating valve 15 when the pH meter 19 detects a pH of 6.8-7.2 and the photodiode 11 detects a light density value that deviates from the preset range of ±0.03.

[0147] Preferably, the method for preparing graphene nanoparticles using the above-mentioned apparatus includes the following steps:

[0148] a) Inject lithium hydroxide electrolyte (concentration between 0.1 and 0.5 M) into the cathode space through float valve 9;

[0149] b) Apply an electric field strength of 4-30V / cm and a current density of 2-60mA / cm. 2 Direct current;

[0150] c) Move the graphite foil strip 4 at a speed of 0.5-3.0 cm / h;

[0151] d) After electrolysis for 60-90 minutes, when pH meter 19 detects that the pH value of the neutral medium extraction zone 10 is 6.8-7.2, start regulating valve 15 to collect the suspension.

[0152] In step d), when the current density is 40-60 mA / cm² 2 At that time, the neutral dielectric formation time was 60 ± 2 minutes; the current density was 2-9 mA / cm². 2 The formation time is 90±3 minutes.

[0153] Preferably, the method further includes step e) periodically discharging coarsely dispersed graphite deposited at the bottom of the anode space into container 18 through coarse particle discharge valve 17, with a discharge frequency of 50-100 ml of coarse particle slurry for every 1 liter of suspension collected.

[0154] Preferably, the particle size control method for graphene nanoparticles in the above method achieves a specific particle size range by combining the following parameters A)-C):

[0155] A) The bulk density of thermally expanded graphite is 0.8-6.0 g / dm³ 3

[0156] B) Graphite foil moving speed: 0.5-3.0 cm / h

[0157] C) Current density 2-60 mA / cm² 2

[0158] When 30-60nm particles are required, a bulk density of 0.8-1.5g / dm³ is used. 3 +Moving speed 0.5cm / h +Current density 2mA / cm² 2 The combination of .

[0159] Preferably, the number of particle size ranges is increased by adjusting the current density value (C), with each increase of 5 mA / cm 2 The current density can add a new particle size sub-range, and the particle size control accuracy reaches ±15nm.

[0160] Example 1

[0161] The apparatus and method used in the basic embodiments (as in Examples 2-9) are applied for preparation, with specific parameters and operations as follows:

[0162] 1. Parameters:

[0163] Graphite bulk density: 1.2 g / dm³ 3 (Range 0.8-1.5)

[0164] Movement speed: 0.5cm / h

[0165] Electric field strength: 4V / cm

[0166] Current density: 2 mA / cm 2

[0167] Target optical density: 0.08±0.01

[0168] Target particle size: 30-60nm

[0169] 2. Operation:

[0170] After 90 minutes of electrolysis, pH meter 19 showed that the pH of the extraction zone (10) was 7.0.

[0171] The optical density measured by photodiode 11 is 0.08.

[0172] Control device 13 activates regulating valve 15 to collect the suspension into container 16.

[0173] 3. Results:

[0174] Particle size distribution: 38-58 nm (Zetasizer-3 detection)

[0175] The suspension has a pH of 6.9 and can be used directly for electrode coating.

[0176] Coarse particle recovery rate > 92% (discharged via valve 17)

[0177] Example 2

[0178] 1. Parameters:

[0179] Bulk density: 1.8 g / dm³ 3 (1.0-2.0)

[0180] Movement speed: 2.0 cm / h

[0181] Electric field strength: 15.0 V / cm

[0182] Current density: 9 mA / cm 2

[0183] Optical density: 0.10±0.02

[0184] Target particle size: 60-120nm

[0185] 2. Operation:

[0186] After electrolysis for 85 minutes, the pH was 7.1 and the optical density was 0.11.

[0187] The regulating valve 15 collects at a flow rate of 2.0 L / min.

[0188] 3. Results:

[0189] Particle size: 75-115nm (in the range of 60-120nm)

[0190] Potassium impurity residue: Not detected (comparison file 1CN114132921A > 500 ppm)

[0191] Innovation: Cathode inlet + lithium-ion system avoids potassium contamination.

[0192] Example 3

[0193] 1. Parameters:

[0194] Bulk density: 2.5 g / dm³ 3 (2.0-3.0)

[0195] Movement speed: 0.5cm / h

[0196] Electric field strength: 4.0 V / cm

[0197] Current density: 7 mA / cm 2

[0198] Optical density: 0.25±0.02

[0199] Target particle size: 120-170nm

[0200] 2. Results:

[0201] Measured particle size: 128-168nm

[0202] Particle size standard deviation: ±8nm (comparison file 1 ±50nm)

[0203] Example 4

[0204] 1. Parameters:

[0205] Bulk density: 2.2 g / dm³ 3 (2.0-3.0)

[0206] Movement speed: 1.0 cm / h

[0207] Electric field strength: 7.0 V / cm

[0208] Current density: 14 mA / cm 2

[0209] Optical density: 0.30±0.02

[0210] Target particle size: 130-180nm

[0211] 2. Results:

[0212] Particle size: 135-175nm

[0213] Deionized water consumption: 0 tons (Comparison document 1 requires 1.5 tons / kg)

[0214] Example 5

[0215] 1. Parameters:

[0216] Bulk density: 4.3 g / dm³ 3 (4.0-5.0)

[0217] Movement speed: 0.5cm / h

[0218] Electric field strength: 5.0 V / cm

[0219] Current density: 6 mA / cm 2

[0220] Optical density: 0.35±0.02

[0221] Target particle size: 150-250nm

[0222] 2. Results:

[0223] Particle size: 155-240nm

[0224] Current efficiency improvement: 35% (due to Li) + (Faster migration speed)

[0225] Example 6

[0226] 1. Parameters:

[0227] Bulk density: 4.8 g / dm³ 3 (4.0-5.0)

[0228] Movement speed: 2.0 cm / h

[0229] Electric field strength: 10.0 V / cm

[0230] Current density: 25 mA / cm 2

[0231] Optical density: 0.55±0.03

[0232] Target particle size: 250-450nm

[0233] 2. Results:

[0234] Particle size: 265-430nm

[0235] Electrolysis time: 65 minutes (high current density shortens the reaction window)

[0236] Example 7

[0237] 1. Parameters:

[0238] Bulk density: 5.5 g / dm3 (5.0-6.0)

[0239] Movement speed: 2.0 cm / h

[0240] Electric field strength: 20.0 V / cm

[0241] Current density: 40 mA / cm 2

[0242] Optical density: 0.40±0.03

[0243] Target particle size: 450-600nm

[0244] 2. Results:

[0245] Particle size: 470-580nm

[0246] Lithium hydroxide consumption: reduced by 40% (comparative document 1, same particle size).

[0247] Example 8

[0248] 1. Parameters:

[0249] Bulk density: 5.7 g / dm³ 3 (5.0-6.0)

[0250] Movement speed: 3.0 cm / h

[0251] Electric field strength: 25.0 V / cm

[0252] Current density: 50 mA / cm 2

[0253] Optical density: 0.50±0.03

[0254] Target particle size: 550-700nm

[0255] 2. Results:

[0256] Particle size: 565-685nm

[0257] Electrode specific capacitance: 245F / g (comparative document 1, similar product, 195F / g).

[0258] Example 9

[0259] 1. Parameters:

[0260] Bulk density: 5.9 g / dm 3 (5.0-6.0)

[0261] Movement speed: 3.0 cm / h

[0262] Electric field strength: 30.0 V / cm

[0263] Current density: 60 mA / cm 2

[0264] Optical density: 0.55±0.03

[0265] Target particle size: 650-800nm

[0266] 2. Operation:

[0267] After electrolysis for 58 minutes, the pH was 7.0 and the optical density was 0.54.

[0268] Control device 13 triggers regulating valve 15

[0269] 3. Results:

[0270] Particle size: 670-790nm

[0271] Number of particle size intervals: 8 independent sub-intervals.

[0272] Test case

[0273] The test results of Examples 1-9 are shown in Table 1.

[0274] Table 1 Summary of Test Results

[0275]

[0276] Through system testing of the nine sets of embodiments in Table 1, the following core conclusions can be drawn:

[0277] 1) Precision of particle size control:

[0278] The actual particle size of all embodiments strictly falls within the target range (deviation < 5%). For example, the target size of Embodiment 3 is 120-170nm, and the actual measured size is 128-168nm.

[0279] The highest accuracy reaches ±8nm (Example 3), which is more than 6 times higher than that of Comparative Document 1 (±50nm);

[0280] Current density is the most sensitive parameter for particle size control: for every 5 mA / cm increase... 2 A new sub-interval can be added (e.g., in Example 9, 8 sub-intervals are implemented within the 650-800nm ​​range).

[0281] 2) Stability of neutral medium formation mechanism:

[0282] Electrolysis time is strictly negatively correlated with current density:

[0283] High current density (40-60 mA / cm) 2 → Formation time 60±2 minutes (Examples 7-9);

[0284] Low current density (2-9 mA / cm) 2 → Formation time 90±3 minutes (Examples 1-3);

[0285] The pH value remained stable at 6.9-7.1 (not listed in Table 1 but verified in all examples), proving that the cathode inlet + high-barrier membrane (7) successfully maintained the pH value. + / OH- balance.

[0286] 3) Strong correlation between optical density and particle size.

[0287] The comprehensive benefits of this invention are verified as shown in Table 2.

[0288] Table 2 Comparison of Comprehensive Benefits

[0289]

[0290]

[0291] Conclusion: Through the synergistic effect of the cathode liquid inlet path (component 8→9→cathode area), high barrier film (7) and Li+ migration system, in-situ preparation in neutral medium is achieved, completely solving the loss problem caused by alkaline residue and breaking through the bottleneck of particle size control.

[0292] The above are merely a few preferred embodiments of the present invention, described in a relatively specific and detailed manner, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A device for preparing neutral medium graphene nanoparticles, characterized in that, include: The electrolytic cell (1) is divided into an anode space and a cathode space by a high-density membrane (7); The cathode (2) and anode assembly are installed in the electrolytic cell (1), the anode assembly including a fixture box (3) and a glass fiber reinforced graphite foil strip (4) penetrating the electrolytic cell; A porous filtration baffle (5) is set in the anode space to form a filtration channel that allows the graphene nanoparticle suspension to pass through but retains coarse particles. A porous cathode filter (6) is installed in the cathode space to reduce the electrolyte mixing rate in order to maintain the ion gradient; The lithium hydroxide electrolyte container (8), which is connected to the cathode space via the float valve (9), constitutes an electrolyte supply system; The neutral medium extraction zone (10) is located between the anode porous filter plate (5) and the high-density membrane (7); The optical density monitoring unit facing the neutral medium extraction area (10) includes a photodiode (11) and a light-emitting diode (12); A control device (13) connected to the optical density monitoring unit signal, which controls the regulating valve (15) in conjunction with the regulating valve driver (14); A graphene nanoparticle suspension container (16) is connected to the neutral medium extraction zone (10) via a regulating valve (15); The coarse particle discharge valve (17) located at the bottom of the anode space and the coarse dispersed graphite collection container (18) connected to it by pipe constitute a coarse particle recovery system. A pH meter (19) inserted into the neutral medium extraction zone (10) forms a closed-loop feedback with the control device (13).

2. The apparatus according to claim 1, characterized in that: The high-density membrane (7) has a density of 440 g / m³. 2 KS-34 grade polypropylene film with a thickness of 0.5mm.

3. The apparatus according to claim 1, characterized in that: The pore density of the cathode porous filter plate (6) is 120-150 PPI, and the pore density of the anode porous filter plate (5) is 80-100 PPI; the PPI of the cathode porous filter plate (6) is set to be 20-30% higher than that of the anode porous filter plate (5).

4. The apparatus according to claim 1, characterized in that: The control device (13) is configured to automatically start the regulating valve (15) when the pH meter (19) detects a pH of 6.8-7.2 and the photodiode (11) detects a light density value that deviates from the preset range of ±0.

03.

5. A method for preparing graphene nanoparticles using any one of the apparatuses of claims 1-4, characterized in that... Including the following steps: a) Inject lithium hydroxide electrolyte into the cathode space through float valve (9); b) Apply an electric field strength of 4-30V / cm and a current density of 2-60mA / cm. 2 Direct current; c) Move the graphite foil strip at a speed of 0.5-3.0 cm / h (4); d) After electrolysis for 60-90 minutes, when the pH meter (19) detects that the pH value of the neutral medium extraction zone (10) is 6.8-7.2, start the regulating valve (15) to collect the suspension.

6. The method according to claim 5, characterized in that: In step d), when the current density is 40-60 mA / cm² 2 At that time, the neutral dielectric formation time was 60 ± 2 minutes; the current density was 2-9 mA / cm². 2 The formation time is 90±3 minutes.

7. The method according to claim 5, characterized in that: It also includes step e) periodically discharging the coarse dispersed graphite deposited at the bottom of the anode space into the container (18) through the coarse particle discharge valve (17), with a discharge frequency of 50-100 ml of coarse particle slurry for every 1 liter of suspension collected.

8. A method for controlling the particle size of graphene nanoparticles, characterized in that, Using the method described in claim 5, a specific particle size range can be achieved by combining the following parameters A)-C): A) The bulk density of thermally expanded graphite is 0.8-6.0 g / dm³ 3 B) Graphite foil moving speed: 0.5-3.0 cm / h C) Current density 2-60 mA / cm² 2 When 30-60nm particles are required, a bulk density of 0.8-1.5g / dm³ is used. 3 +Moving speed 0.5cm / h +Current density 2mA / cm² 2 combination.

9. The method according to claim 8, characterized in that: The number of particle size ranges can be increased by adjusting the current density value (C). For every 5 mA / cm increase... 2 The current density can add a new particle size sub-range, and the particle size control accuracy reaches ±15nm.

10. An application of a neutral graphene nanoparticle suspension, characterized in that: The suspension prepared according to claim 5 can be directly used in the manufacture of supercapacitor electrodes without the need for a washing process. The conductivity of the prepared electrodes is 18-22% higher than that of products prepared with alkaline media.

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