A method of pulping electrolignin

Abstract

The application discloses a method for pulse electrolysis of lignin, and the method comprises the following steps: performing pulse electrolysis reaction on a lignin dimer model compound in a three-electrode system acetonitrile medium system to obtain a small molecule aromatic monomer; the pulse electrolysis condition is that the pulse electrolysis is performed at a pulse potential of ±1.4V-±2.4V for 4-8h, the cycle is 5-20s, the duty cycle is 0.25-0.75, and the electrolyte is tetraethylammonium perchlorate. The pulse electrochemical method can electro-oxidize and depolymerize the C-O bond of the model compound at a lower potential, the problem of overoxidation at a high potential is relieved, and the product yield and product selectivity of the model compound are improved. The method has wide substrate applicability and can be effectively applied to the breaking of various C-O bonds.

Description

Technical Field

[0001] This invention belongs to the field of biomass electrochemical conversion technology, and relates to a method for high-value conversion of lignin based on pulse electrochemical method. Background Technology

[0002] Lignocellulose, as a highly promising clean energy source, is expected to replace petroleum and has therefore attracted widespread attention. Lignin is one of the important components of lignocellulose, abundant and inexpensive, accounting for 15-30 wt.% of lignocellulose biomass. As the most abundant aromatic biopolymer on Earth, lignin has unique application value and potential in the energy field. However, the highly complex structure of lignin makes it difficult to degrade and utilize. In the chemical structure of lignin, carbon-oxygen-carbon (COC) bonds account for about 75%, while carbon-carbon (CC) bonds account for about 25%. Therefore, the breaking of CO bonds is crucial for the depolymerization of lignin, and its selective breaking process is of great significance. In the study of lignin CO bond cleavage, traditional methods include chemical oxidation, hydrogenolysis and reduction, biological methods, and thermal pyrolysis. However, these methods have limitations, such as requiring high temperature and pressure, long reaction time, dependence on additives, poor product selectivity, and low yield. For example, using a single-atom Co catalyst to oxidize phenoxyethylbenzene, only 12% was converted at 150℃, with a yield of 7%.

[0003] Compared to traditional methods such as chemical oxidation, hydrogenolysis and reduction, biological methods, and thermal pyrolysis, electrochemical methods exhibit numerous significant advantages. Their reaction conditions are relatively mild, aligning with green and environmentally friendly principles (relying on renewable energy sources like wind and solar power), and they are cost-effective. Furthermore, they allow for precise control of reaction activity and product selectivity through simple adjustment of experimental parameters. Therefore, electrochemical methods are a highly competitive technology in this field. Studies have shown that, without the addition of other additives, electrochemical methods, when applied at potentials significantly higher than the oxidation peak potential of the model compounds, result in very little formation of the target product; for example, phenoxyethylbenzene yields approximately 1% at constant potential. However, high potentials also lead to over-oxidation of the model compounds, preventing the selective conversion of most model compounds to the target aromatic compounds, resulting in low product yields and limiting the application prospects of this technology in the efficient utilization of lignin. Therefore, mitigating the over-oxidation problem is a pressing issue that needs to be addressed in the electrochemical depolymerization of lignin. Summary of the Invention

[0004] To alleviate the peroxidation problem of lignin, this invention proposes a pulsed electrolysis method for lignin. Specifically, this method involves the controlled electrochemical depolymerization of lignin molecules in an acetonitrile medium, achieving efficient utilization of lignin resources. Specifically, by precisely controlling the potential (U), period (T), duty cycle (D), and electrolysis time (t), selective cleavage of the CO bonds in the model compound is achieved at room temperature. Compared with traditional constant-potential electrolysis, pulsed electrolysis technology achieves electrochemical depolymerization of lignin dimers at lower voltages, mitigating the peroxidation phenomenon that occurs at high potentials, thereby obtaining higher substrate conversion and product yield.

[0005] This invention is achieved through the following technical solution:

[0006] A method for pulse electrolysis of lignin involves a three-electrode pulse electrolysis reaction of a lignin dimer model compound in an acetonitrile medium to obtain a small molecule aromatic monomer. The pulse electrolysis conditions are: electrolysis at a pulse potential of ±1.4V-±2.4V for 4-8 hours, with a cycle of 5-20 seconds, a duty cycle of 0.25-0.75, and tetraethylammonium perchlorate as the electrolyte.

[0007] The small molecule aromatic monomer products are benzaldehyde, benzyl alcohol, phenylethanol, hydroquinone, etc.

[0008] Preferably, the concentration of the electrolyte is 0.01-0.10 mol / L. -1 TEAP / CH3CN.

[0009] Preferably, the concentration of the lignin dimer model compound is 0.01-0.10 mol / L. -1 .

[0010] Preferably, the lignin dimer model compound comprises lignin containing one or more of β-O-4 bonds, α-O-4 bonds, and 4-O-5 bonds.

[0011] Preferably, the lignin dimer model compound comprises one or more of phenoxyethylbenzene (1, containing a β-O-4 bond), benzylphenyl ether (2, containing an α-O-4 bond), and 4,4'-dihydroxydiphenyl ether (3, containing a 4-O-5 bond), with the following structure:

[0012]

[0013] Preferably, the pulse electrolysis conditions are: electrolysis at a pulse potential of ±1.8V for 6±1h, with a period of 10-15s and a duty cycle of 0.5±0.1.

[0014] Preferably, both the working electrode and the counter electrode are Pt sheet electrodes, and the reference electrode is Ag / Ag. +Non-aqueous reference electrode.

[0015] Preferably, Ag + The concentration was 0.1 ± 0.05 mol L. -1 Ag + / CH3CN.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] (1) The pulsed electrochemical method described in this invention can electro-oxidize and depolymerize the CO bond of the model compound at a lower potential, which alleviates the over-oxidation problem that occurs at a high potential and improves the product yield and product selectivity of the model compound.

[0018] (2) Pulse electrolysis technology can flexibly control reaction conditions by adjusting parameters such as potential, electrolysis time, cycle, and duty cycle, thereby optimizing the reaction.

[0019] (3) The method described in this invention has a wide range of substrate applicability and can be effectively applied to the breaking of various CO bonds. Attached Figure Description

[0020] Figure 1 The images show the gas chromatography-mass spectrometry analysis results of the systems after the reaction in Examples 1-4 and Comparative Examples 1-2, with detection performed using a flame ionization detector.

[0021] Figure 2 The images show the gas chromatography-mass spectrometry analysis results of the systems after the reactions in Examples 5-10, with detection performed using a flame ionization detector.

[0022] Figure 3 The images show the gas chromatography-mass spectrometry (GC-MS) analysis results of the systems after the reactions of Examples 11-12 and Comparative Examples 3-4, with detection performed using a flame ionization detector.

[0023] Note: Due to decreased column efficiency, an Agilent HP-5MS (30m × 320μm × 0.25μm) column was used successively. Figure 1 and Figure 3 ) and Phenomenex HP-5MS (30m×320μm×0.25μm) column ( Figure 2 ). Detailed Implementation

[0024] To better understand the present invention, the following embodiments are provided for further explanation, but the implementation of the present invention is not limited thereto.

[0025] In this specification, all percentages refer to mass percentages. The reaction is carried out at room temperature, and the entire reaction process is continuously conducted under magnetic stirring. The parameters of the pulsed current are controlled using a multi-potential step method, while the potential is controlled using a chronoamperometry method during constant potential electrolysis.

[0026] Example 1: In a 50mL integrated electrolytic cell, a 20mm×20mm×0.1mm Pt sheet electrode was used as the working electrode and counter electrode, and Ag / Ag + (1×10 -1 mol L -1 A three-electrode system was established using an AgNO3 / CH3CN non-aqueous reference electrode. The prepared electrolyte was 20 mL, with a TEAP electrolyte concentration of 10%. -2 mol L -1 The concentration of the substrate phenoxyethylbenzene (1) was 2.5 × 10⁻⁶. -2 mol L -1 Electrolysis was performed at a pulse potential of ±1.4V for 6 hours with a cycle of 15s and a duty cycle of 0.5. After the reaction was completed, 100 μL of dimethyl phthalate (5% wt.) was added as an internal standard. The product was detected and quantified by gas chromatography-mass spectrometry. The conversion rate and product yield are shown in Table 1.

[0027] Example 2: In a 50mL integrated electrolytic cell, 20mm×20mm×0.1mm Pt sheet electrodes were used as the working and counter electrodes, and Ag / Ag... + (1×10 -1 mol L -1 A three-electrode system was established using an AgNO3 / CH3CN non-aqueous reference electrode. The prepared electrolyte was 20 mL, with a TEAP electrolyte concentration of 10%. -2 mol L -1 The concentration of the substrate phenoxyethylbenzene (1) was 2.5 × 10⁻⁶. -2 mol L -1 Electrolysis was performed at a pulse potential of ±1.8V for 6 hours with a cycle of 15s and a duty cycle of 0.5. After the reaction was completed, 100 μL of dimethyl phthalate (5% wt.) was added as an internal standard. The product was detected and quantified by gas chromatography-mass spectrometry. The conversion rate and product yield are shown in Table 1.

[0028] Example 3: In a 50mL integrated electrolytic cell, 20mm×20mm×0.1mm Pt sheet electrodes were used as the working and counter electrodes, and Ag / Ag... + (1×10 -1 mol L -1A three-electrode system was established using an AgNO3 / CH3CN non-aqueous reference electrode. The prepared electrolyte was 20 mL, with a TEAP electrolyte concentration of 10%. -2 mol L -1 The concentration of the substrate phenoxyethylbenzene (1) was 2.5 × 10⁻⁶. -2 mol L -1 Electrolysis was performed at a pulse potential of ±2.0 V for 6 h with a cycle of 15 s and a duty cycle of 0.5. After the reaction was completed, 100 μL of dimethyl phthalate (5% wt.) was added as an internal standard. The product was detected and quantified by gas chromatography-mass spectrometry. The conversion rate and product yield are shown in Table 1.

[0029] Example 4: In a 50mL integrated electrolytic cell, 20mm×20mm×0.1mm Pt sheet electrodes were used as the working and counter electrodes, and Ag / Ag... + (1×10 -1 mol L -1 A three-electrode system was established using an AgNO3 / CH3CN non-aqueous reference electrode. The prepared electrolyte was 20 mL, with a TEAP electrolyte concentration of 10%. -2 mol L -1 The concentration of the substrate phenoxyethylbenzene (1) was 2.5 × 10⁻⁶. -2 mol L -1 Electrolysis was performed at a pulse potential of ±2.4V for 6 hours with a cycle of 15s and a duty cycle of 0.5. After the reaction was completed, 100 μL of dimethyl phthalate (5% wt.) was added as an internal standard. The product was detected and quantified by gas chromatography-mass spectrometry. The conversion rate and product yield are shown in Table 1.

[0030] Comparative Example 1: In a 50mL integrated electrolytic cell, a 20mm×20mm×0.1mm Pt sheet electrode was used as the working electrode and counter electrode, and Ag / Ag + A three-electrode system was established using a non-aqueous reference electrode (1×10⁻¹ mol L⁻¹ AgNO₃ / CH₃CN). The prepared electrolyte was 20 mL, with a TEAP electrolyte concentration of 10%. -2 mol L -1 The concentration of the substrate phenoxyethylbenzene (1) was 2.5 × 10⁻⁶. -2 mol L -1 Electrolysis was performed at a constant potential of 1.8V for 6 hours. After the reaction was completed, 100 μL of dimethyl phthalate (5% wt.) was added as an internal standard. The product was detected and quantified by gas chromatography-mass spectrometry. The conversion rate and product yield are shown in Table 1.

[0031] Comparative Example 2: In a 50mL integrated electrolytic cell, a 20mm×20mm×0.1mm Pt sheet electrode was used as the working electrode and counter electrode, and Ag / Ag + (1×10 -1 mol L -1 A three-electrode system was established using an AgNO3 / CH3CN non-aqueous reference electrode. The prepared electrolyte was 20 mL, with a TEAP electrolyte concentration of 10%. -2 mol L -1 The concentration of the substrate phenoxyethylbenzene (1) was 2.5 × 10⁻⁶. -2 mol L -1 Electrolysis was performed at a constant potential of 2.5V for 6 hours. After the reaction was completed, 100 μL of dimethyl phthalate (5% wt.) was added as an internal standard. The product was detected and quantified by gas chromatography-mass spectrometry. The conversion rate and product yield are shown in Table 1.

[0032] Comparative Example 3: In a 50mL integrated electrolytic cell, a 20mm×20mm×0.1mm Pt sheet electrode was used as the working electrode and counter electrode, and Ag / Ag + (1×10 -1 mol L -1 A three-electrode system was established using an AgNO3 / CH3CN non-aqueous reference electrode. The prepared electrolyte was 20 mL, with a LiClO4 electrolyte concentration of 10%. -2 mol L -1 The concentration of the substrate phenoxyethylbenzene (1) was 2.5 × 10⁻⁶. -2 mol L -1 Electrolysis was performed at a pulse potential of ±1.8V for 6 hours. After the reaction was completed, 100 μL of dimethyl phthalate (5% wt.) was added as an internal standard. The product was detected and quantified by gas chromatography-mass spectrometry. The conversion rate and product yield are shown in Table 1.

[0033] Example 5: In a 50mL integrated electrolytic cell, 20mm×20mm×0.1mm Pt sheet electrodes were used as the working and counter electrodes, and Ag / Ag... + (1×10 -1 mol L -1 A three-electrode system was established using an AgNO3 / CH3CN non-aqueous reference electrode. The prepared electrolyte was 20 mL, with a TEAP electrolyte concentration of 10%. -2 mol L -1 The concentration of the substrate phenoxyethylbenzene (1) was 2.5 × 10⁻⁶. -2 mol L -1Electrolysis was performed at a pulse potential of ±1.8V for 4 hours, with a cycle of 15s and a duty cycle of 0.5. After the reaction was completed, 100 μL of dimethyl phthalate (5% wt.) was added as an internal standard. The product was detected and quantified by gas chromatography-mass spectrometry. The conversion rate and product yield are shown in Table 2.

[0034] Example 6: In a 50mL integrated electrolytic cell, 20mm×20mm×0.1mm Pt sheet electrodes were used as the working electrode and counter electrode, and Ag / Ag... + (1×10 -1 mol L -1 A three-electrode system was established using an AgNO3 / CH3CN non-aqueous reference electrode. The prepared electrolyte was 20 mL, with a TEAP electrolyte concentration of 10%. -2 mol L -1 The concentration of the substrate phenoxyethylbenzene (1) was 2.5 × 10⁻⁶. -2 mol L -1 Electrolysis was performed at a pulse potential of ±1.8V for 8 hours with a period of 15s and a duty cycle of 0.5. After the reaction was completed, 100 μL of dimethyl phthalate (5% wt.) was added as an internal standard. The product was detected and quantified by gas chromatography-mass spectrometry. The conversion rate and product yield are shown in Table 2.

[0035] Example 7: In a 50mL integrated electrolytic cell, 20mm×20mm×0.1mm Pt sheet electrodes were used as the working and counter electrodes, and Ag / Ag... + (1×10 -1 mol L -1 A three-electrode system was established using an AgNO3 / CH3CN non-aqueous reference electrode. The prepared electrolyte was 20 mL, with a TEAP electrolyte concentration of 10%. -2 mol L -1 The concentration of the substrate phenoxyethylbenzene (1) was 2.5 × 10⁻⁶. -2 mol L -1 Electrolysis was performed at a pulse potential of ±1.8V for 6 hours with a cycle of 5 seconds and a duty cycle of 0.5. After the reaction was completed, 100 μL of dimethyl phthalate (5% wt.) was added as an internal standard. The product was detected and quantified by gas chromatography-mass spectrometry. The conversion rate and product yield are shown in Table 2.

[0036] Example 8: In a 50mL integrated electrolytic cell, a 20mm×20mm×0.1mm Pt sheet electrode was used as the working electrode and counter electrode, and Ag / Ag + (1×10 -1 mol L -1A three-electrode system was established using an AgNO3 / CH3CN non-aqueous reference electrode. The prepared electrolyte was 20 mL, with a TEAP electrolyte concentration of 10%. -2 mol L -1 The concentration of the substrate phenoxyethylbenzene (1) was 2.5 × 10⁻⁶. -2 mol L -1 Electrolysis was performed at a pulse potential of ±1.8V for 6 hours with a cycle of 30 seconds and a duty cycle of 0.5. After the reaction was completed, 100 μL of dimethyl phthalate (5% wt.) was added as an internal standard. The product was detected and quantified by gas chromatography-mass spectrometry. The conversion rate and product yield are shown in Table 2.

[0037] Example 9: In a 50mL integrated electrolytic cell, a 20mm×20mm×0.1mm Pt sheet electrode was used as the working electrode and counter electrode, and Ag / Ag + (1×10 -1 mol L -1 A three-electrode system was established using an AgNO3 / CH3CN non-aqueous reference electrode. The prepared electrolyte was 20 mL, with a TEAP electrolyte concentration of 10%. -2 mol L -1 The concentration of the substrate phenoxyethylbenzene (1) was 2.5 × 10⁻⁶. -2 mol L -1 Electrolysis was performed at a pulse potential of ±1.8V for 6 hours with a cycle of 15 seconds and a duty cycle of 0.25. After the reaction was completed, 100 μL of dimethyl phthalate (5% wt.) was added as an internal standard. The product was detected and quantified by gas chromatography-mass spectrometry. The conversion rate and product yield are shown in Table 2.

[0038] Example 10: In a 50mL integrated electrolytic cell, 20mm×20mm×0.1mm Pt sheet electrodes were used as the working and counter electrodes, and Ag / Ag... + (1×10 -1 mol L -1 A three-electrode system was established using an AgNO3 / CH3CN non-aqueous reference electrode. The prepared electrolyte was 20 mL, with a TEAP electrolyte concentration of 10%. -2 mol L -1 The concentration of the substrate phenoxyethylbenzene (1) was 2.5 × 10⁻⁶. -2 mol L -1 Electrolysis was performed at a pulse potential of ±1.8V for 6 hours with a cycle of 15 seconds and a duty cycle of 0.75. After the reaction was completed, 100 μL of dimethyl phthalate (5% wt.) was added as an internal standard. The product was detected and quantified by gas chromatography-mass spectrometry. The conversion rate and product yield are shown in Table 2.

[0039] Example 11: In a 50mL integrated electrolytic cell, 20mm×20mm×0.1mm Pt sheet electrodes were used as the working and counter electrodes, and Ag / Ag... + (1×10 -1 mol L -1 A three-electrode system was established using an AgNO3 / CH3CN non-aqueous reference electrode. The prepared electrolyte was 20 mL, with a TEAP electrolyte concentration of 10%. -2 mol L -1 The concentration of the substrate benzylphenyl ether (2) was 2.5 × 10⁻⁶. -2 mol L -1 Electrolysis was performed at a pulse potential of ±1.8V for 6 hours with a cycle of 15 seconds and a duty cycle of 0.75. After the reaction was completed, 100 μL of dimethyl phthalate (5% wt.) was added as an internal standard. The product was detected and quantified by gas chromatography-mass spectrometry. The conversion rate and product yield are shown in Table 3.

[0040] Comparative Example 3: In a 50mL integrated electrolytic cell, a 20mm×20mm×0.1mm Pt sheet electrode was used as the working electrode and counter electrode, and Ag / Ag + (1×10 -1 mol L -1 A three-electrode system was established using an AgNO3 / CH3CN non-aqueous reference electrode. The prepared electrolyte was 20 mL, with a TEAP electrolyte concentration of 10%. -2 mol L -1 The concentration of the substrate benzylphenyl ether (2) was 2.5 × 10⁻⁶. -2 mol L -1 Electrolysis was performed at a constant potential of 1.8V for 6 hours. After the reaction was completed, 100 μL of dimethyl phthalate (5% wt.) was added as an internal standard. The product was detected and quantified by gas chromatography-mass spectrometry. The conversion rate and product yield are shown in Table 3.

[0041] Example 12: In a 50mL integrated electrolytic cell, 20mm×20mm×0.1mm Pt sheet electrodes were used as the working and counter electrodes, and Ag / Ag... + (1×10 -1 mol L -1 A three-electrode system was established using an AgNO3 / CH3CN non-aqueous reference electrode. The prepared electrolyte was 20 mL, with a TEAP electrolyte concentration of 10%. -2 mol L -1 The concentration of substrate 4,4'-dihydroxydiphenyl ether (3) was 2.5 × 10⁻⁶. -2 mol L -1Electrolysis was performed at a pulse potential of ±1.4V for 6 hours with a cycle of 15s and a duty cycle of 0.75. After the reaction was completed, 100 μL of dimethyl phthalate (5% wt.) was added as an internal standard. The product was detected and quantified by gas chromatography-mass spectrometry. The conversion rate and product yield are shown in Table 3.

[0042] Comparative Example 4: In a 50mL integrated electrolytic cell, 20mm×20mm×0.1mm Pt sheet electrodes were used as the working and counter electrodes, and Ag / Ag... + (1×10 -1 mol L -1 A three-electrode system was established using an AgNO3 / CH3CN non-aqueous reference electrode. The prepared electrolyte was 20 mL, with a TEAP electrolyte concentration of 10%. -2 mol L -1 The concentration of substrate 4,4'-dihydroxydiphenyl ether (3) was 2.5 × 10⁻⁶. -2 mol L -1 Electrolysis was performed at a constant potential of 1.4V for 6 hours. After the reaction was completed, 100 μL of dimethyl phthalate (5% wt.) was added as an internal standard. The product was detected and quantified by gas chromatography-mass spectrometry. The conversion rate and product yield are shown in Table 3.

[0043] Table 1 Evaluation results of electrolysis of p-phenoxyethylbenzene (1) at different potentials

[0044]

[0045]

[0046] a: The electrolyte used in Comparative Example 3 was LiClO4.

[0047] Table 2. Evaluation results of electrolysis of phenoxyethylbenzene (1) under different pulse electrolysis conditions.

[0048]

[0049] Table 3. Evaluation results of electrolysis of benzylphenyl ether and 4,4'-dihydroxydiphenyl ether under different electrolysis conditions.

[0050]

[0051] Note: The values ​​in the table represent the molar conversion of the product relative to the substrate, where “-” indicates that the corresponding product was not detected by GC-MS.

[0052] Examples 1-4 demonstrate that the cleavage of the β-O-4 bond yields significantly better results than the control group, regardless of whether the potential is high or low. Conversion rate and yield are greatly improved, and product selectivity is also effectively enhanced. Under the same potential conditions, the pulse method exhibits far stronger oxidizing power than the constant potential electrolysis method. This characteristic allows the pulse method to efficiently drive the electro-oxidation reaction at relatively low potentials, effectively avoiding the over-oxidation problem commonly encountered under high potential conditions.

[0053] As can be seen from the test results in Table 2, electrolysis time, cycle and duty cycle are all important parameters that affect the reaction results. By adjusting these parameters, better electrolysis results can be obtained.

[0054] As can be seen from the test results in Table 3, this invention can be applied to other model compounds. Compared with the traditional constant potential electrolysis mode, pulse electrolysis can effectively improve the yield and conversion rate of products from the breaking of different types of CO bonds (α-O-4 bond represented by model compound 2 and 4-O-5 bond represented by model compound 3).

[0055] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method of pulping electrolignin, characterized in that, A small molecule aromatic monomer is obtained by pulse electrolysis of a lignin dimer model compound in an acetonitrile medium system in a three-electrode system; The pulse electrolysis conditions are: electrolysis for 4-8 h at a pulse potential of ±1.4 V to ±2.4 V, a cycle of 5-20 s, a duty cycle of 0.25-0.75, and a tetraethylammonium perchlorate electrolyte; The lignin dimer model compound comprises lignin containing one or more of β-O-4 bonds, α-O-4 bonds and 4-O-5 bonds.

2. The method of claim 1, wherein, The concentration of the electrolyte is 0.01-0.10 mol L -1 .

3. The method of claim 2, wherein, The concentration of the lignin dimer model compound is 0.01-0.10 mol L -1 .

4. The method of claim 3, wherein, The lignin dimer model compound comprises one or two or more of phenoxyethylbenzene, benzyl phenyl ether and 4,4'-dihydroxy diphenyl ether.

5. The method according to any one of claims 1 to 4, characterized in that, The pulse electrolysis conditions are: electrolysis for 6±1 h at a pulse potential of ±1.8 V, a cycle of 10-15 s, and a duty cycle of 0.5±0.

1.

6. The method of claim 5, wherein, The working electrode and the counter electrode are both Pt sheet electrodes, and the reference electrode is Ag / Ag + Non-aqueous reference electrode.

7. The method of claim 6, wherein, Ag + The concentration of AgNO3 was 0.1 ± 0.05 mol L -1 .

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