Method for electrochemical synthesis of CF and CF composite material and application thereof

Abstract

The invention discloses a method for electrochemical synthesis of CF (carbonaceous fragments) and a composite material thereof and application thereof. A conventional carbon material is taken as a raw material, synthesis of CF is realized through electrochemical stripping and cutting effects, and a CF lamellar structure with PCET activity is realized. Meanwhile, controllable CF synthesis for accurately controlling the density of a CF surface active group is realized by adjusting electrochemical parameters and / or using an auxiliary reagent, so that an electrochemical calibration-free pH sensing material meeting the requirements of different pH quantitative analysis scenes is obtained; the method is particularly suitable for application scenes which need to meet high-precision, high-stability, continuous and in-situ quantitative analysis and combinatorial requirements thereof.

Description

Technical Field

[0001] The present invention belongs to the fields of electrochemical detection and analysis, chemical sensor technology and nanomaterials, and relates to a method for electrochemically synthesizing CF and its composite materials and applications thereof. Background Art

[0002] pH is an essential basic chemical index in many fields. Precise, continuous, and in-situ quantitative analysis of pH has irreplaceable requirements in various high-value application scenarios. However, there are extremely limited pH sensors that can simultaneously meet the above functions, mainly because it is difficult for such sensors to overcome the problem of continuously expanding measurement errors generated in complex environments. The new electrochemical pH sensing technology based on dynamic current technology can dynamically and real-time correct the signal drift generated by changes in the electrode interface state, so this problem can be well solved. However, this technology relies on precise and stable sensor interface modification technology, and thus usually faces technical problems such as high processing difficulty, high production cost, low yield, and sacrificing the response rate to ensure stability.

[0003] Carbonaceous fragments (CF) are a new type in the large family of carbon nanomaterials with sizes close to or covering carbon quantum dots (CQDs). Their size distribution is mainly concentrated in a limited range from several nanometers to dozens of nanometers. Generally, they have optical and electrochemical activities similar to CQDs, and their physical and chemical intrinsic and physicochemical properties are also quite similar to CQDs. Their surfaces can carry a variety of chemical functional groups, and their biocompatibility is very good. However, different from CQDs, CF generally does not have diverse fluorescence activities; its solubility has more diverse controllable margins compared with the latter. CF was first reported as an impurity component in carbon nanomaterials such as carbon nanotubes or graphene. Its discovery time is relatively late, and its applications have been rather limited so far, which is a pity.

[0004] An important electrochemical feature of CF is that when CF is generated through different production strategies, its surface will carry a large number of chemical functional groups with different properties, such as hydroxyl, keto, ether, carboxyl, ester, aryl, and epoxy groups, etc. Together with the large π-bond structure of the graphene-like main sheet layer, they lay the foundation for the complex surface chemistry and electrochemical activity of CF. Among them, the electrochemical voltammetric response activity of CF due to carrying some of these special structures is an important electrochemical feature. Fortunately, this activity of CF belongs to proton-coupled electron transfer (PCET) activity, that is, the heterogeneous electron transfer reaction process generated by CF under voltammetric excitation is a process dependent on solvent environment protons (or hydrogen ions, H + )). Therefore, the quantitative relationship between the electrochemistry reaction rate and the solvent environment proton activity in this process can be measured by dynamic current analysis method to achieve precise measurement of the pH of the software environment. Summary of the Invention

[0005] The present invention provides a technical solution that uses carbon nanomaterials as the electrochemical probe of a dynamic current type pH sensor. In this solution, the pH electrochemical response activity carried by the specific carbon nanomaterials themselves is used as a pH indicator. In addition to having pH electrochemical response activity, carbon nanomaterials are good current collectors themselves. Therefore, for a sensor with a carbon nanomaterial as the pH electrochemical sensitive interface, there is no need to perform special chemical modification on the sensor interface, thus bringing multiple performance advantages.

[0006] The purpose of the present invention is to provide a method for electrochemically synthesizing CF.

[0007] Another purpose of the present invention is to provide the application of the above-mentioned CF in the preparation of CF composite materials.

[0008] Another purpose of the present invention is to provide a method for preparing CF composite materials using the above-mentioned CF.

[0009] A method for electrochemically synthesizing CF includes the following steps:

[0010] (1) Using a carbon material as the working electrode and the counter electrode to form a three-electrode system;

[0011] (2) Placing the three-electrode system in an aqueous or lipid phase solution and applying a constant voltage;

[0012] When the three-electrode system is placed in an aqueous solution,

[0013] (3) Taking out the working electrode and placing it in an aqueous solution containing carbonate and glycerol, heating to 80 - 110 °C for reaction to obtain CF;

[0014] When the three-electrode system is placed in a lipid phase solution,

[0015] (3) Taking out the working electrode and placing it in a mixed solution of DMSO - ethanol, and performing microwave treatment or heat treatment to obtain CF.

[0016] Furthermore, the carbon material described in step (1) includes but is not limited to at least one of natural graphite, synthetic flake graphite, highly oriented pyrolytic graphite, carbon black, carbon fiber, glassy carbon, amorphous carbon, carbon nanotubes, carbon nanohorns, graphene and its derivatives, etc.

[0017] Furthermore, the electrode form described in step (1) can be any form such as sheet, rod, plate, filament, etc.

[0018] Furthermore, in the three-electrode system described in step (1), the reference electrode is at least one of Al, Ag, Ag / AgCl, Cu, Au, Sn, and C.

[0019] Further, the aqueous solution in step (2) is at least one of a NaNO3 solution, a KCl solution, a NaCl solution, a NaH2PO4-NaOH solution, a NaH2PO4-Na2HPO4 solution, an H3PO4 solution, an H2SO4 solution, an NaOH solution, and a KOH solution; the concentration is 0.05 - 0.5 M, preferably 0.08 - 0.2 M, and more preferably 0.1 M.

[0020] Further, the solute of the lipid phase solution in step (2) is at least one of tetrabutylammonium hexafluorophosphate, tetrabutylammonium tetrafluoroborate, tributylmethylammonium bis(trifluoromethanesulfonyl)imide, tetrabutylphosphonium chloride, 1-butyl-3-methylimidazole, N-butylpyridine, N-butylmethylpiperidine, and N-ethylmethylpyrrolidine, and the solvent is at least one of acetonitrile, N,N-dimethylformamide, tetrahydrofuran, and dimethyl sulfoxide. The concentration of the above lipid phase solution is 2 - 20 M, preferably 5 - 15 M, and more preferably 10 M.

[0021] Further, the constant voltage in step (2) can be in the form of alternating current or direct current and any combination thereof, and the excitation waveform includes but is not limited to linear voltammetry, pulse voltammetry, non-linear voltammetry, potentiometry, DC pulse, etc.

[0022] Further, the constant potential in step (2) is 0.1 - 10 V, preferably 0.5 - 5 V, and more preferably 1 - 2 V. The time for applying the constant voltage is 5 - 60 min; preferably 10 - 40 min; more preferably 15 - 30 min.

[0023] Further, an auxiliary reagent is added to the aqueous solution in step (2), and the auxiliary reagent includes but is not limited to at least one of sulfuric acid, phosphoric acid, nitric acid, perchloric acid, sodium dodecyl sulfate, trifluoromethanesulfonic acid, Triton X-100, potassium permanganate, hydrogen peroxide, sodium hydroxide, potassium hydroxide, periodic acid, periodate, 3-methylimidazole, N-propylmethylpiperidine bis(trifluoromethanesulfonyl)imide, tetrabutylammonium tetrafluoroborate, etc.; the concentration of the auxiliary reagent in the aqueous solution is 0 - 30 M and not 0; preferably 0 - 20 M and not 0; more preferably, the concentration of phosphoric acid is 0 - 15 M and the concentration of sulfuric acid is 0 - 18 M.

[0024] Further, when the three-electrode system is placed in the aqueous solution, the carbonate in the aqueous solution in step (3) is at least one of K2CO3 and sodium carbonate, and the concentration of the carbonate is 0.1 - 5 M, preferably 0.1 - 2 M, and more preferably 0.5 M; the concentration of glycerol in the aqueous solution is 5 - 40 m:m%, preferably 10 - 30 m:m%, and more preferably 25 m:m%.

[0025] Further, the temperature of the heating reaction in step (3) is 90-100°C, preferably 95°C; the reaction time is 1-10 min, preferably 2-8 min, more preferably 5 min.

[0026] Further, the working electrode after being processed in step (3) is taken as the working electrode, and steps (1)-(3) are repeated 2-10 times to obtain a large amount of CF.

[0027] Further, when the three-electrode system is placed in a lipid phase solution, the volume ratio of DMSO to ethanol is 1-10:1, preferably 5:1; the power of microwave treatment is 1-8 W, preferably 2-6 W, more preferably 4 W, and the time of microwave treatment is 1-10 min, preferably 2-8 min, more preferably 5 min. The temperature of the heating reaction is 90-100°C, preferably 95°C; the reaction time is 1-10 min, preferably 2-8 min, more preferably 5 min.

[0028] Further, the microwave treatment is specifically to first place it in a microwave treatment environment of 4 W and continuously treat it for 5 min; after a pause of 30 s, continue the 5-min continuous treatment.

[0029] The application of the above-mentioned CF in the preparation of CF composites. Combining electrochemically synthesized CF with polymer materials, the formed composite material can make up for the application defects of the intrinsic chemical properties of CF in specific pH quantitative analysis scenarios.

[0030] Further, other main materials used for composite with CF in the composite material include but are not limited to nanomaterials such as graphene, carbon nanotubes, carbon nanobelts, gold nanoparticles, etc.; functional polymers such as PVP, PU, electrochemically active polymers, natural polymers, polycations, polyanions, polyionic liquids, covalent organic frameworks, metal-organic frameworks, supramolecules, etc.

[0031] A method for preparing CF composites using the above-mentioned CF, comprising the following steps:

[0032] Mix the CF dispersion, benzoyl peroxide and the DMSO solution of vinylferrocene and react to obtain the CF-polymer composite CF@pFc.

[0033] Further, the CF dispersion is obtained by dispersing CF in DMSO, and the concentration is 0.1-2 mg / mL, preferably 0.5-1.5 mg / mL, more preferably 1 mg / mL.

[0034] Further, the concentration of the DMSO solution of vinylferrocene is 0.5-5 mM, preferably 1-3 mM, more preferably 2 mM.

[0035] The dosage ratio of the CF dispersion liquid, benzoyl peroxide and the DMSO solution of vinyl ferrocene is 50 - 90 mL: 1.2 g: 60 - 100 mL; preferably 60 - 80 mL: 1.2 g: 70 - 90 mL, and more preferably 70 mL: 1.2 g: 80 mL.

[0036] The temperature of the reaction is 70 - 100 °C, preferably 75 - 95 °C, and more preferably 80 - 90 °C. The reaction time is 1 - 8 h, preferably 2 - 6 h.

[0037] Furthermore, after the reaction is completed, let it stand still until precipitation occurs, and wash the product with an ethanol solution.

[0038] Only this example is used as a demonstrative case to demonstrate the great potential of the combined application of CF and other functional materials, and the possibility of obtaining more powerful and more complex and diverse material properties, rather than indicating that only the limited range of CF-polymer composites is protected.

[0039] A method for preparing an electrochemical pH sensor using the above-mentioned CF or CF composite material, comprising the following steps:

[0040] Disperse the CF or CF composite material in DMSO to obtain a mixed solution. Connect the end of the base electrode to a wire with a gold-plated copper tube socket to form an electrode CRE. Then, drop or immerse the working surface of the electrode CRE into the mixed solution, and an electrochemical pH sensor can be prepared after drying.

[0041] Furthermore, weigh the above-mentioned CF@pFc, dissolve it in DMSO to prepare a 1 wt% mixed solution. Connect the end of the graphite rod to a wire with a gold-plated copper tube socket to form an electrode CRE. Drop the CF@pFc solution on the working surface of the electrode CRE, and a CF@pFc-CRE electrode can be made after drying.

[0042] Furthermore, the concentration of the CF or CF@pFc in the mixed solution is 0.1 - 10 wt%, preferably 0.5 - 5 wt%, and more preferably 1 wt%.

[0043] Furthermore, cut a graphite rod with a diameter of 3.0 mm into a cylinder with a length of 10.0 mm, polish the end face smoothly as the working surface, seal the side with insulating paint, connect the end to a wire with a gold-plated copper tube socket to form an electrode CRE. Drop 2.5 μL of the CF@pFc solution on the working surface of the CRE electrode, and accelerate the volatilization under an infrared lamp until the electrode surface is completely dry to make a CF@pFc-CRE electrode.

[0044] Compared with the prior art, the present invention has the following technical effects:

[0045] 1. The present invention uses conventional carbon materials as raw materials to synthesize CF through electrochemical exfoliation and cutting effects;

[0046] 2. The present invention uses electrochemical energy as the driving force and oxidant, and also synthesizes a CF sheet structure with PCET activity using common carbon materials as raw materials;

[0047] 3. The present invention realizes controllable CF synthesis with precise control of the density of surface active groups on CF by adjusting electrochemical parameters and / or using auxiliary reagents, thereby serving as an electrochemical calibration-free pH sensing material to meet the requirements of pH quantitative analysis scenarios for different needs.

[0048] 4. The present invention uses CF as an electrochemical probe with pH-specific response, and uses the dynamic current signal based on its PECT activity as the primary sensing signal to achieve pH quantification. pH sensing based on this mode can achieve calibration-free analysis, and is particularly suitable for application scenarios that require high precision, high stability, continuous, in-situ quantitative analysis and their combined requirements. Description of the Drawings

[0049] Figure 1 It is the HRTEM image and SAED photo of electrochemically synthesized CF by the aqueous phase method in Example 1.

[0050] Figure 2 It is the Raman spectrum of electrochemically synthesized CF by the lipid phase method in Example 2.

[0051] Figure 3 It is the LSV curve result of controlling the peak shape characteristics of the electrode target by CF synthesis parameters in Example 3.

[0052] Figure 4 It is the LSV measurement results of CF@pFc-CRE in standard solutions with pH values of 4.01, 6.86, and 9.18 in Example 4.

[0053] Figure 5 It is the LSV response curve of chemically prepared cCF-CRE in standard solutions with different pH values in Comparative Example 1.

[0054] Figure 6 It is the square wave pulse voltammogram (a) of the oCF-CRE electrode in Britton-Robinson buffer with pH 2-12 in Comparative Example 2 and the a.u.-pH regression curve (b) drawn after converting the results to a.u. values.

[0055] Figure 7 It is the long-term measurement results of oCF-CRE and DRP-110PANI in standard pH solutions in Comparative Example 2. The solid dot line group is the test result of oCF-CRE, and the dotted square line group is the test result of DRP-110PANI. Detailed implementation mode

[0056] Example 1: Electrochemical aqueous-phase synthesis of CF

[0057] Take a graphite plate with dimensions of 100×100×4 mm as the electrode material. Arrange two graphite plates in parallel with a spacing of 10 mm. One of them serves as the working electrode (WE), and the other serves as the counter electrode (CE). Place a silver wire mesh with a size of 100×100 mm at an equal distance in the middle as the reference electrode (RE), and construct a three-electrode reaction system with it. Immerse the three-electrode system in a 0.1 M NaNO3 solution and continuously apply a constant potential of 1.5 V to the electrode system for 20 min. Subsequently, take out the WE part, rinse it with pure water, and then place it in an aqueous solution containing 0.5 M K2CO3 and 25 m:m% glycerol. Heat it to 95 °C and continuously process it for 5 min before taking it out. Take out the WE, rinse it, and then put it back into the 0.1 M NaNO3 solution for electrochemical treatment and repeat the subsequent steps. After multiple treatments, collect the treatment solution after the constant potential treatment. At this time, the solution changes from colorless and transparent to dark yellow. Filter this solution with qualitative filter paper and centrifuge it at 18,000 rpm for 30 min, and collect the concentrated yellow liquid part at the bottom.

[0058] Perform HRTEM microscopic analysis on the carbon-based copper mesh sample, and the results are shown in the appendix Figure 1 . It can be clearly observed that there are a large number of tiny lamellar structures with sizes mainly distributed around ~10 nm in the concentrated solution. Further magnifying the observation, the lattice structure of graphene-like lamellae can be clearly observed. In the micro-area electron diffraction pattern, an obvious hexagonal dot array distribution can be observed. The above facts fully demonstrate that this lamellar structure is a graphene-like carbon nanostructure. Moreover, it has the classic diffraction fringes and microscopic morphology characteristics of few-layer graphene, indicating that this substance is CF.

[0059] Example 2: Electrochemical lipid-phase synthesis

[0060] A three-electrode reaction system was constructed by cutting carbon cloth into strips measuring 200 × 40 × 0.4 mm to serve as the WE and CE. A 200 × 40 mm silver mesh was placed equidistantly between the electrodes as the RE. In the first step, the three-electrode system was placed in acetonitrile containing 0.05 M tetrabutylammonium hexafluorophosphate and allowed to equilibrate for 30 minutes. A constant potential of 1.8 V was then applied to the electrode system for 30 minutes. In the second step, the WE was removed, rinsed sequentially with acetonitrile and ethanol, and then transferred to a mixture of DMSO and ethanol (v:v = 5:1). The WE was microwaved at 4W for 5 minutes, followed by a 30-second pause and a further 5 minutes of microwave treatment. This treatment cycle was repeated for 6 to 10 cycles. After the WE was removed and rinsed with acetonitrile, the first and second steps were repeated until the color of the solution used in the second step turned yellow. The solution was centrifuged at 20,000 rpm for 40 minutes, and the concentrated dark yellow liquid at the bottom was collected.

[0061] The carbon cloth and the collected concentrated liquid samples were sampled and Raman spectrum analysis was performed. The results are shown in the attached Figure 2 As shown in the figure. The black curve is the Raman spectrum of the carbon cloth sample, and the red curve is the spectrum of the CF concentrate sample. It can be clearly seen that the carbon cloth only shows the Raman spectrum at 1580cm -1 and 1323cm -1 There are two strong G peaks and weak D peaks, which are the SP 2 In-plane vibration characteristic peaks and in-plane defect characteristic peaks; in the CF sample spectrum, D peak and G peak are both strong signal peaks. This difference shows that the density of in-plane defect sites in the CF sample is much greater than that of the raw carbon cloth. In addition, the spectrum line is at ~2700cm -1 and ~2910cm -1 Strong peaks appear at the 2D and G+D peaks of the carbon material, respectively. These are the signature Raman characteristics of a carbon quantum dot-like structure emerging from a graphene-like structure. The above information demonstrates that CF was effectively generated using this method.

[0062] Example 3 Controlling the Peak Shape Characteristics of Electrode Targets by CF Synthesis Parameters

[0063] Prepare a 0.1 mg / mL CF dispersion solution using the method described in Example 1 to prepare a CF electrode CF-CRE. Set up 7 control analysis groups to compare the target signal resolution effects of different auxiliary reagent formulations. The difference is that different contents of auxiliary reagents are added to the NaNO3 supporting electrolyte solution used in each group (specific formulations are shown in Table 1) to regulate the total content level of surface oxygen elements of the synthesized CF. The electrode preparation method is as follows: Cut a graphite rod with a diameter of 3.0 mm into a cylinder with a length of 10.0 mm. Polish the end face smoothly with 800-mesh sandpaper as the working surface, seal the side with insulating paint, and connect the wire to the end with a gold-plated copper tube socket to form the electrode CRE. Drop 6 μL of the CF dispersion solution on the working surface of the electrode. After the solvent has completely evaporated, it is combined with a Pt counter electrode and an Ag / AgCl reference electrode (3M KCl) to form a three-electrode system. Immerse the electrode system in an aqueous solution containing 0.1 M NaNO3 and 0.1 wt% polyacrylamide, apply a DC square wave pulse excitation potential of ±1.0 V (frequency = 0.1 Hz), take it out after continuous treatment for 100 s to make CF-CRE. Perform a linear sweep voltammetry (LSV) scan of 1.0 to 0 V at a rate of 0.05 V / s on the CF-CRE in a 0.05 M citric acid-sodium hydroxide solution with a pH of 2.0. Table 1 records the test results of each electrode.

[0064] Table 1 Target peak shape characteristic values of CF-CRE corresponding to different CF synthesis parameters

[0065]

[0066] From the appendix Figure 3 and the results in Table 1, it can be seen that different CF synthesis methods can significantly affect the target peak shape characteristic values of CF-CRE. From the curve shape, it can be intuitively judged that without adding auxiliary reagents almost at all, the target peak shape of CF-CRE is relatively smooth. Such a peak shape is prone to multiple peak points or regional clutter, which is likely to cause problems such as incorrect computer value extraction and insufficient value extraction accuracy of peak characteristic values, or requires a great increase in the design difficulty of peak characteristic value extraction algorithms. With the help of auxiliary reagents, the target peak shape of CF-CRE can become sharp and prominent, making it easy to accurately extract its peak characteristic value data using a simple algorithm. It can also be seen that different dosages of auxiliary reagents can cause regular changes in the peak shape, and the peak shape and peak characteristic values can be targeted optimized through this method. This will greatly simplify the design work of the sensor supporting analysis software and significantly improve the comprehensive performance of the sensor, including sensitivity, effective resolution, response time, etc.

[0067] Example 4 Electrochemical synthesis of CF-polymer composite materials

[0068] Take two graphite plates of 100×100×4 mm as the working electrode (WE) and the counter electrode (CE) respectively. Arrange the two graphite plates in parallel with a spacing of 10 mm, and place a silver wire mesh sheet of 100×100 mm at an equidistant position in the middle as the reference electrode (RE) to construct a three-electrode reaction system. Place the three-electrode system in a 0.1 M NaNO3 solution containing 3000 mM H3PO4 and 1 wt% Triton X-100, and continuously apply a constant potential of 1.5 V to the electrode system for 40 min. Subsequently, take out the WE part, rinse it with pure water, and then place it in an aqueous solution containing 0.5 M K2CO3 and 25 m:m% glycerol, heat it to 95 °C and continuously treat it for 5 min before taking it out. Take out the WE, rinse it, and then put it back into the 0.1 M NaNO3 solution for electrochemical treatment and repeat the subsequent steps. After multiple treatments, collect the treatment solution of the second step. Filter the solution with qualitative filter paper and then centrifuge it at 18000 rpm for 30 min, and collect the concentrated yellow liquid part at the bottom. Dilute the concentrated solution with DMSO to a CF dispersion solution of ∼1 mg / mL, 70 mL. Prepare an 80 mL DMSO solution containing 2 mM vinyl ferrocene, and gradually add the CF dispersion solution drop by drop through a separatory funnel, and stir for 15 min under a nitrogen protection environment. Subsequently, add 1.2 g of benzoyl peroxide, stir well for 10 min, then raise the temperature of the reaction system to 85 °C, and continuously react for 4 h. During this period, an orange-red precipitate gradually forms. Let the precipitate stand for 20 min and then decant to concentrate the precipitate. Then perform vacuum filtration on the precipitate. Wash the solid with ethanol and then dry it in vacuo to obtain the CF-polymer composite material CF@pFc. Weigh CF@pFc and dissolve it in DMSO to prepare a 1 wt% solution.

[0069] Cut a graphite rod with a diameter of 3.0 mm into a cylinder with a length of 10.0 mm. Polish the end face with 800-mesh sandpaper to be flat as the working surface, seal the side with insulating paint, and connect the wire to the end with a gold-plated copper tube socket to form the electrode CRE. Drop 2.5 μL of the CF@pFc solution on the working surface of the electrode, and accelerate the evaporation under an infrared lamp until the electrode surface is completely dry to make the CF@pFc-CRE electrode. Subsequently, it is paired with a Pt counter electrode and an Ag / AgCl reference electrode (3 M KCl) to form a three-electrode system. Refer to the method described in "GB / T 27501-2011 Preparation Method of Buffer Solutions for pH Value Measurement" to prepare standard solutions with pH values (25 °C) of 4.01, 6.86, and 9.18. Use the above three-electrode system to perform LSV measurements in different pH standard solutions, and set the measurement parameters as follows: scanning potential -400~800 mV, scanning rate 100 mV / s. The measurement results are shown in the appendix Figure 4。LSV of CF@pFc-CRE in standard solutions with pH values of 4.01, 6.86, and 9.18 shows two distinct peak shapes. Among them, the characteristic peak of ferrocene (Fc) at ~300 mV does not change significantly with the change of the solution pH value; the characteristic peak appearing in the range of -100 to 200 mV is the CF peak shape, and both its potential and peak current intensity change with the change of pH.

[0070] Comparison of pH sensing performance between electrochemically synthesized CF and chemically synthesized CF in Comparative Example 1

[0071] CF can also be obtained by chemical method. Its optical activity is similar to that of the electrochemically synthesized CF of the present invention, but there are significant differences in electrochemical characteristics.

[0072] Put 2 g of multi-walled carbon nanotubes into a round-bottom flask, inject 100 mL of 20 wt% sulfuric acid aqueous solution, and perform ultrasonic treatment for 30 min under the condition of 40 W power for dispersion treatment. Subsequently, transfer the flask to an electric heating mantle and heat it to 98 °C, and carry out constant-temperature reflux treatment for 2 h. The solution changes from a black semi-transparent state to a dark black opaque state. After cooling to room temperature, neutralize the reaction solution with sodium hydroxide to a pH value of 6 - 7, and carry out centrifugation treatment at 6000 rpm for 15 min to collect the black precipitate. Place this precipitate in the flask and redisperse it in 0.1 M NaOH aqueous solution, and heat it to 100 °C for reflux treatment for 25 min. After the reaction solution is cooled to room temperature, carry out centrifugation treatment at 15000 rpm for 30 min, and collect the bottom yellow-brown part. Mix with a large amount of water and re-perform centrifugation treatment by the same method, and repeat the treatment until the pH of the collected bottom solution part is 6 - 7. Using the method described in Example 3, prepare a CF modified electrode, denoted as cCF-CRE. Configure standard solutions with pH values (25 °C) of 4.01, 6.86, and 9.18. Use the above three-electrode system to perform LSV measurements in different pH standard solutions, and set the measurement parameters as: scanning potential -400 to 800 mV, scanning rate 100 mV / s. The measurement results are shown in the appendix Figure 5 。The results show that under different pH conditions, the redox peak shapes exhibited by cCF-CRE are extremely weak, and the peak shapes are round, gentle, and flat, and the peak values are not easily accurately identified. At the same time, in a weakly alkaline environment, the voltammetric peak shape of cCF-CRE is no longer a single peak, which indicates that when CF prepared by chemical synthesis method works on the electrode surface, the kinetic process of its surface electrochemical active functional groups is slow, and the PCET active reaction has become a step-by-step reaction in a weakly alkaline environment. This makes the characteristic peak parameters for its pH quantification unable to be accurately locked. Comparing with the analysis results of Example 3 and Example 4, it can be seen that CF synthesized by chemical method is difficult to be directly applied to the preparation of electrochemical pH sensors.

[0073] Comparison of stability between Comparative Example 2 and mainstream solid electrodes (pANI)

[0074] Cut the carbon cloth into small pieces of 100×50 mm as the WE and CE, place a silver wire mesh piece of the same size at an equal distance in the middle as the RE, and construct a three-electrode reaction system. Place the three-electrode system in DMF containing 0.05 M tetrabutylammonium hexafluorophosphate, let it stand and equilibrate for 10 min, and then continuously apply a potential of 1.8 V to the electrode system for 30 min. Then take out the WE and transfer it into a DMF solution containing 0.02 M triethylamine, heat it to 95 °C under stirring conditions for 15 min; then repeat the electrochemical and solvothermal treatment 10 times. Collect the part of the tea-brown solution. Take this solution and centrifuge it at 20000 rpm for 40 min, and collect the concentrated dark liquid part at the bottom. Dilute it with DMF to 0.1 mg / mL and add 0.025 M 1-allyl-3-methylimidazolium chloride to make a mixed solution. Cut a graphite rod with a diameter of 3.0 mm into a cylinder with a length of 10.0 mm, polish the end face smoothly with 800-mesh sandpaper as the working surface, seal the side with insulating paint, and connect the wire to the end with a gold-plated copper tube socket to form the electrode CRE. Connect the CRE with the Pt counter electrode and the Ag / AgCl reference electrode (3 M KCl) to form a three-electrode system, immerse it in the mixed solution, apply a constant potential of 0.55 V to the CRE, take it out after continuously treating for 25 min. Rinse it with ethanol and accelerate the volatilization under an infrared lamp until the electrode surface is completely dry to make the oCF-CRE electrode.

[0075] Use the oCF-CRE as the WE and the Pt counter electrode and the Ag / AgCl reference electrode (3 M KCl) to form a three-electrode system. Use a Britton-Robinson standard buffer solution with a concentration of 40 mM, and adjust the pH of the buffer solution to 2 - 12 with 0.5 M standard hydrochloric acid and potassium hydroxide. Use differential pulse voltammetry (the scanning potential is from 800 to -500 mV, the pulse potential increment is 5 mV, the pulse amplitude is 50 mV, and the pulse frequency is 20 Hz.) to measure the changes of current and potential with pH of the oCF-CRE electrode in the buffer solution sample, record its pH response curve, and the single-chip microcomputer software automatically calculates E f 、HWHM、ΔI1、ΔI2、a and the value of a.u., and a.u. is defined as where E f is the peak potential, HWHM is the half-peak half-width potential, ΔI1 and ΔI2 are the peak current intensities corresponding to the pH-sensitive probe and the pH-insensitive probe respectively, and a is the electrode constant. Generate a regression curve according to the relationship between the value of a.u. and the pH value of the standard buffer solution as Figure 6As shown, the pH measurement value is calculated according to the a.u. value during actual detection. The pH measurement results are recorded every 8 hours. In a standard solution containing 0.1 mM hydroxyferrocene with pH values of 4.01 and 9.18, the DPV response results of the three-electrode system are continuously recorded (DPV parameters are set as follows: scanning potential 600~-400 mV, increment potential 5 mV, pulse potential amplitude 50 mV, pulse width 50 ms, sampling period 500 ms). At the same time, the DRP-110PANI type polyaniline-based solid-state pH electrode of the foreign gold standard brand DropSens is used as the reference group, and the pH value results of the same samples are measured in the OCP mode according to the product description of this sensor for comparison. The results are as shown in Figure 7 the attachment. During the continuous measurement for 96 hours, the measurement error of oCF-CRE < 0.1 pH, and the pH drift value < 0.4; while the measurement error of the polyaniline solid-state pH electrode in the reference group ≥ 0.75, and the pH drift value > 2.4.

[0076] Table 2 Measurement result values of oCF-CRE and DRP-110PANI in standard pH solutions

[0077]

[0078]

Claims

1. A method for electrochemically synthesizing CF, characterized in that It includes the following steps: (1) Using carbon materials as the working electrode and the counter electrode to form a three-electrode system; (2) Placing the three-electrode system in an aqueous or lipid phase solution and applying a constant voltage; When the three-electrode system is placed in an aqueous solution, (3) Taking out the working electrode and heating it in an aqueous solution containing carbonate and glycerol at 80 - 110 °C to react to obtain CF; When the three-electrode system is placed in a lipid phase solution, (3) Taking out the working electrode and placing it in a mixed solution of DMSO - ethanol, and obtaining CF by microwave treatment or heating.

2. The method according to claim 1, wherein: The aqueous solution in step (2) is at least one of NaNO3 solution, KCl solution, NaCl solution, NaH2PO4 - NaOH solution, NaH2PO4 - Na2HPO4 solution, H3PO4 solution, H2SO4 solution, NaOH solution, KOH solution; the solute of the lipid phase solution in step (2) is at least one of tetrabutylammonium hexafluorophosphate, tetrabutylammonium tetrafluoroborate, tributylmethylammonium bis(trifluoromethylsulfonyl)imide, tetrabutylphosphonium chloride, 1 - butyl - 3 - methylimidazole, N - butylpyridine, N - butylmethylpiperidine, N - ethylmethylpyrrolidine, and the solvent is at least one of acetonitrile, N,N - dimethylformamide, tetrahydrofuran, dimethyl sulfoxide; The aqueous solution in step (2) is 0.05 - 0.5 M; the concentration of the lipid phase solution is 2 - 20 M; The constant potential in step (2) is 0.1 - 10 V; the time for applying the constant voltage is 5 - 60 min.

3. The method according to claim 1, characterized in that: Adding auxiliary reagents to the aqueous solution in step (2), and the auxiliary reagents include but are not limited to at least one of sulfuric acid, phosphoric acid, nitric acid, perchloric acid, sodium dodecyl sulfate, trifluoromethanesulfonic acid, Triton X - 100, potassium permanganate, hydrogen peroxide, sodium hydroxide, potassium hydroxide, periodic acid, periodate, 3 - methylimidazole, N - propylmethylpiperidinium bis(trifluoromethylsulfonyl)imide, tetrabutylammonium tetrafluoroborate.

4. The method according to claim 3, characterized in that: The concentration of the auxiliary reagent in the aqueous solution is 0 - 30 M and is not 0.

5. The method according to claim 1, wherein: The carbonate in the aqueous solution in step (3) is at least one of K2CO3 and sodium carbonate; the concentration of the carbonate is 0.1 - 5 M; the concentration of glycerol in the aqueous solution is 5 - 40 m:m%.

6. The method according to claim 1, characterized in that: When the three - electrode system is placed in a lipid phase solution, the volume ratio of DMSO to ethanol is 1 - 10:1; the power of microwave treatment is 1 - 8 W; the temperature of the heating reaction is 90 - 100 °C.

7. The application of CF prepared by the method according to any one of claims 1 - 6 in the preparation of CF composite materials.

8. A method for preparing a CF composite material using CF prepared by the method according to any one of claims 1-6, characterized in that It includes the following steps: Mixing a CF dispersion, benzoyl peroxide and a DMSO solution of vinylferrocene and reacting to obtain a CF - polymer composite material CF@pFc.

9. The method according to claim 8, wherein: The CF dispersion is obtained by dispersing CF in DMSO, and the concentration is 0.1 - 2 mg / mL; the concentration of the DMSO solution of vinylferrocene is 0.5 - 5 mM; the dosage ratio of the CF dispersion, benzoyl peroxide and the DMSO solution of vinylferrocene is 50 - 90 mL:1.2 g:60 - 100 mL.

10. A method for preparing an electrochemical pH sensor using CF prepared by the method according to any one of claims 1 to 6 or CF composite material prepared by the method according to any one of claims 8 to 9, characterized in that Including the following steps: Disperse CF or CF composite material in DMSO to obtain a mixed solution. Connect the end of the substrate electrode to a wire with a gold-plated copper tube socket to form an electrode CRE. Then, drop or immerse the working surface of the electrode CRE into the mixed solution. After drying, an electrochemical pH sensor can be prepared.

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