A method for in-situ electropolymerization of L-arginine

Abstract

The present invention discloses a method for in-situ electro-polymerization of L-arginine, which constructs a three-electrode electrochemical system and uses cyclic voltammetry to in-situ electro-polymerize L-arginine on the surface of the working electrode; the electrolyte includes 10 mmol / L sodium chloride, 1.3 mmol / L sodium acetate, 8.7 mmol / L acetic acid and 10 mmol / L arginine, solving the problems of electrode oxidation and high energy consumption existing in the prior art.

Description

Technical Field

[0001] The invention relates to the field of in-situ electrochemical modification of electrode materials, and in particular to a method for in-situ electropolymerization of L-arginine to modify an electrode. Background Art

[0002] As the most common material in electrochemical research, electrode performance can directly affect the electrochemical reaction kinetics. Therefore, improving electrode performance is an important direction of electrochemical research. Electrode modification is an important way to improve electrode performance, mainly including electrode treatment and electrode coating. Electrode treatment refers to changing the functional groups, surface structure, and specific surface area of ​​the electrode surface through specific environmental conditions. Common electrode treatment methods include heat treatment and acid treatment. For example, treating a common electrode material, carbon fiber felt, at 450°C for 30 minutes can improve the performance of the microbial electrochemical system by 25%. Soaking the carbon fiber felt in concentrated sulfuric acid for 15 minutes can improve the performance of the microbial electrochemical system by 8%. Electrode treatment may also be a combination of multiple treatment methods. For example, soaking the carbon fiber felt in concentrated sulfuric acid for 15 minutes and then treating it at 450°C for 30 minutes can improve the performance of the microbial electrochemical system by 34%. A series of studies in this field have shown that electrode treatment is an effective means to improve electrode performance and has the advantage of simple operation. However, electrode treatment often requires harsh environmental conditions and toxic and harmful chemical reagents, which is not conducive to its promotion and use in practical applications. Electrode coating refers to using an unmodified electrode as a substrate and coating the surface of the substrate with a material having good electrochemical properties. These materials with good electrochemical properties often have good hydrophilicity, good electrical conductivity, and abundant electrochemically active sites, such as carbon nanotubes, graphene, etc. The coating methods are mainly dip coating, drop coating, and spin coating. Although there are some differences in the specific operations of these three coating methods, they all have the problem of easy falling off. In order to solve this problem, researchers in the field have reported the use of in-situ electrochemical methods to in-situ electrochemically synthesize and deposit materials with good performance on the surface of the substrate. The modification process of the in-situ electrochemical method is irreversible, which can effectively avoid the problem of coating shedding, and therefore has become a hot spot in the field of material coating in recent years.

[0003] The basic principle of the in situ electrochemical method is to electro-oxidize or electro-reduce soluble monomers to form insoluble polymers, which are then deposited on the electrode surface. Therefore, the selection of monomers in the in situ electrochemical method is crucial. The most studied monomers are aniline and pyrrole. Under certain potential conditions, aniline or pyrrole can be electro-oxidized to form cationic radicals and polymerized into polyaniline or polypyrrole. For example, in situ electrochemical modification of polyaniline on the surface of carbon fiber felt can improve the performance of the microbial electrochemical system by 58.1%. However, both aniline and pyrrole are toxic and harmful chemicals, which may cause environmental pollution in practical applications. In order to overcome this problem, researchers have found that certain natural amino acids can also act as monomers to form polymers deposited on the electrode surface. The most widely studied amino acid is L-arginine. For example, L-arginine was in situ electropolymerized on the surface of a glassy carbon electrode, and the sensitivity of detecting p-nitrophenol was increased by 80% after electrode modification. In addition, there are a series of studies using in situ L-arginine electropolymerization to modify electrodes, which have improved the detection performance of dopamine, vitamin C, uric acid, L-tryptophan, dimethoate, xanthine, and casein. These studies have shown that in situ L-arginine electropolymerization modified electrodes have good prospects in practical applications.

[0004] At present, the in situ L-arginine electropolymerization modified electrodes all use cyclic voltammetry. MaWei et al. first reported in situ L-arginine electropolymerization modified electrodes (2007). In his study, a cyclic voltammetry scan range of -1.1V to 2.3V was used (compared to the silver / silver chloride reference electrode). After that, Fengyuan Zhang et al. used a cyclic voltammetry scan range of -2.3V to 2.5V; MRAli et al. used a cyclic voltammetry scan range of -2V to 2.2V. At present, the in situ L-arginine electropolymerization modified electrodes reported have basically used a wider range of cyclic voltammetry scan ranges. At the same time, the electrolyte used is basically a neutral (or partially neutral) phosphate buffer. Although it can cause the electropolymerization reaction of L-arginine and deposit poly-L-arginine on the electrode surface. However, a wider range of cyclic voltammetry scan ranges will also lead to electro-oxidation of the electrode, increase the oxygen-containing functional groups on the electrode surface, and change the surface characteristics of the electrode unpredictably. For example: Yue Yi et al. used a phosphate buffer with a pH of 9.0 and a cyclic voltammetry scan range of -2V to 2.0V to electropolymerize L-arginine. The N element on the electrode surface increased by 6.42%, while the O element increased by 14.39%. This shows that the latter cyclic voltammetry scan range obviously caused electrode oxidation and increased the oxygen-containing functional groups on the electrode surface. Lowering the high potential value of the cyclic voltammetry scan range is expected to avoid the electrode oxidation process, but it may also cause L-arginine to be unable to form cationic radicals and polymerize into polymers. For example: Yue Yi et al. found that when the cyclic voltammetry scan range of the in situ electropolymerization of L-arginine was -2V to 0.5V, the elements on the electrode surface did not change significantly, indicating that poly-L-arginine was not formed. Therefore, how to achieve in situ L-arginine electropolymerization modification of the electrode while avoiding electrode oxidation remains to be solved. Summary of the invention

[0005] The invention provides a method for in-situ electropolymerization of L-arginine, which solves the problems of electrode oxidation and high energy consumption in the prior art.

[0006] In order to solve this technical problem, the present invention provides the following technical solution:

[0007] A method for in-situ electropolymerization of L-arginine, comprising constructing a three-electrode electrochemical system, and utilizing cyclic voltammetry to in-situ electropolymerize L-arginine on the surface of a working electrode; the electrolyte used for the in-situ electropolymerization comprises 10 mmol L -1 Sodium chloride, 1.3 mmol L -1 Sodium acetate, 8.7 mmol L -1 Acetic acid and 10 mmol L -1 Arginine.

[0008] When the three-electrode electrochemical system of the present invention is working, the cyclic voltammetry method utilizes the preferred cyclic voltammetry potential range and electrolyte formula, and utilizes the preferred cyclic voltammetry scanning number to achieve efficient electropolymerization of L-arginine and avoid electrode oxidation;

[0009] The working electrode is carbon fiber felt, carbon felt or carbon fiber paper.

[0010] The counter electrode of the three-electrode electrochemical system is a platinum electrode.

[0011] The reference electrode of the three-electrode electrochemical system is a silver / silver chloride electrode in saturated potassium chloride solution.

[0012] The cyclic voltammetry potential ranged from 0.5V to 1.5V.

[0013] The preferred cyclic voltammetry potential range can cause the electro-oxidation and polymerization reaction of L-arginine without causing oxygen evolution reaction on the electrode surface, thus avoiding electrode oxidation;

[0014] Preferably, the number of cyclic voltammetry scans is 10-20.

[0015] Preferably, the number of cyclic voltammetry scans is 10.

[0016] The preferred cyclic voltammetry scanning number can saturate the deposition of poly-L-arginine on the electrode surface, avoiding the problem of low poly-L-arginine content on the electrode surface due to insufficient cyclic voltammetry scanning number, or waste of time and energy costs due to excessive cyclic voltammetry scanning number.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] When the three-electrode electrochemical system of the present invention is working, the cyclic voltammetry method utilizes the preferred cyclic voltammetry potential range and electrolyte formula, and utilizes the preferred cyclic voltammetry scanning number to achieve efficient electropolymerization of L-arginine and avoid electrode oxidation;

[0019] The preferred cyclic voltammetric potential range and electrolyte formula can cause the electro-oxidation and polymerization reaction of L-arginine without causing oxygen evolution reaction on the electrode surface, thus avoiding electrode oxidation;

[0020] The preferred cyclic voltammetry scanning number can saturate the deposition of poly-L-arginine on the electrode surface, avoiding the problem of low poly-L-arginine content on the electrode surface due to insufficient cyclic voltammetry scanning number, or waste of time and energy costs due to excessive cyclic voltammetry scanning number. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0022] Figure 1 A physical diagram of a three-electrode electrochemical cell of the present invention;

[0023] Figure 2 The surface element composition of the unmodified electrode and the modified electrode under different conditions of the present invention;

[0024] Figure 3 This is the optimization result of the cyclic voltammetry scanning number in Example 2 of the present invention. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments. The illustrative embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0026] Example 1

[0027] like Figure 1 As shown, a three-electrode electrochemical cell (EC1-2) containing a working electrode, a counter electrode and a reference electrode was constructed. The working volume of EC1-2 was 50 mL. The working electrode was made of 1 cm × 2 cm carbon cloth, fixed by an electrode clamp. The counter electrode was a 2 cm × 2 cm platinum sheet electrode. The reference electrode was an Ag / AgCl reference electrode saturated with potassium chloride. 40 mL of electrolyte containing L-arginine monomer was added to EC1. The electrolyte included 50 mmol L -1 Phosphate buffer (pH = 9), 10 mmol L -1 NaCl and 10mmolL -1 Arginine; then, EC1 was placed in a constant temperature biochemical incubator, the temperature was set to 25±0.5℃, and the electrochemical cell was connected to a multi-channel constant potential instrument; finally, L-arginine was in situ electropolymerized on the surface of the working electrode by cyclic voltammetry scanning, the number of cyclic voltammetry scanning cycles was 20, and the cyclic voltammetry scanning range of EC1 was 0.5V-2.4V.

[0028] Example 2

[0029] like Figure 1 As shown, a three-electrode electrochemical cell (EC2) containing a working electrode, a counter electrode and a reference electrode was constructed. The working volume of EC2 was 50 mL. The working electrode was made of 1 cm × 2 cm carbon cloth and fixed by an electrode clamp. The counter electrode was a 2 cm × 2 cm platinum sheet electrode. The reference electrode was an Ag / AgCl reference electrode saturated with potassium chloride. EC2 used cyclic voltammetry to scan the potential range to in situ electropolymerize L-arginine on the surface of the working electrode. 40 mL of electrolyte containing L-arginine monomer was added to EC1-2. The electrolyte was 10 mmol L -1Sodium chloride, 1.3 mmol L -1 Sodium acetate, 8.7 mmol L -1 Acetic acid and 10 mmol L -1 Arginine; then, EC2 was placed in a constant temperature biochemical incubator, the temperature was set to 25±0.5℃, and the electrochemical cell was connected to a multi-channel constant potential instrument; finally, L-arginine was in situ electropolymerized on the surface of the working electrode by cyclic voltammetry scanning, the number of cyclic voltammetry scanning cycles was 20, and the cyclic voltammetry scanning range of EC2 was 0.5V-1.5V.

[0030] Adjust the number of scanning circles to conduct parallel tests.

[0031] Comparative Example 1

[0032] A three-electrode electrochemical cell EC3 containing a working electrode, a counter electrode and a reference electrode was constructed. EC3 adopted a process similar to that of Example 1, with a cyclic voltammetry scan range of 0.5V-2.4V, but the electrolyte used did not contain L-arginine, i.e., no in situ electropolymerization of L-arginine occurred, as a positive control.

[0033] Comparative Example 2

[0034] A three-electrode electrochemical cell EC4 containing a working electrode, a counter electrode and a reference electrode was constructed. The difference between EC4 and Example 2 is that no cyclic voltammetry scan was performed, and it served as a negative control.

[0035] The element content on the surface of each EC working electrode of Example 1-2 and Comparative Example 1-2 was analyzed by X-ray photoelectron spectroscopy (XPS). The specific results are as follows: Figure 2 shown.

[0036] Figure 2 a is the element content on the working electrode surface of EC4. It can be seen that when no cyclic voltammetry scanning is performed, the electrode surface is basically composed of C elements, with a content of 94.02%, N element content of only 1.59%, and O element content of only 4.16%.

[0037] When the alkaline electrolyte containing L-arginine was used for cyclic voltammetry scanning in the high potential range (0.5V-2.4V), it was found that the C element content decreased to 60.41%, the N element content increased to 15.21%, and the O element content increased to 24.38% ( Figure 2 b). It is worth noting that the ratio of N to O in L-arginine is 2:1, and after cyclic voltammetry scanning in the high potential range (0.5V-2.4V), the N element increased by 13.62%, while the O element increased by 20.32%. Therefore, we speculate that the cyclic voltammetry scanning under this condition led to electrode oxidation and increased the oxygen-containing functional groups on the electrode surface.

[0038] To verify this hypothesis, we can see that when the same cyclic voltammetry scan range is used but the electrolyte does not contain L-arginine, the C element on the electrode surface is 67.35%, the O element is as high as 30.19%, and the N element is only 2.46% ( Figure 2 c). This indicates that cyclic voltammetry scans in the high potential range (0.5 V-2.4 V) can lead to electrode oxidation.

[0039] When we reduce the cyclic voltammetry scan range and change to an acidic electrolyte formulation, the N element content is 15.85% and the O element content is 16.49% when the cyclic voltammetry scan is performed using a lower potential range (0.5V-1.5V) and a preferred acidic electrolyte formulation. Figure 2 Compared with the results of Figure 2, the N content is basically the same as that of Figure 2, while the O content is greatly reduced. This shows that the electrode oxidation process during the electropolymerization of L-arginine can be effectively reduced by using a cyclic voltammetric scan in a lower potential range (0.5V-1.5V) and a preferred electrolyte.

[0040] On this basis, we analyzed the element content on the surface of the electropolymerized L-arginine electrode at different cyclic voltammetry scans in a lower potential range (0.5V-1.5V). It can be seen that when the scan number increased to 10, the content of N and O elements on the electrode surface increased significantly, indicating that poly-L-arginine was continuously deposited on the electrode surface. When the scan number exceeded 10, the element content on the electrode surface did not change significantly. This shows that when the scan number was 10, the electrode surface was saturated with poly-L-arginine. On the other hand, we can see that during the in-situ electropolymerization of L-arginine, the ratio of N and O elements was close to 1:1 under all scan numbers. In other words, regardless of low or high scan numbers, the trend of element content changes on the electrode surface is always consistent. Therefore, it is reasonable to speculate that only one reaction occurred during the cyclic voltammetry scan, namely the in-situ electropolymerization of L-arginine. That is to say, if electrode oxidation still occurs during the cyclic voltammetry scan, it is reasonable to predict that as the number of cyclic voltammetry scans increases, poly-L-arginine deposition tends to saturation (i.e., the N element no longer increases), while electrode oxidation can continue to occur (i.e., the O element increases with the number of cycles). Obviously, our experimental results are obviously inconsistent with the above speculation. Therefore, we can conclude that the low potential (0.5V-1.5V) cyclic voltammetry scan range and optimized acidic electrolyte can avoid electrode oxidation.

[0041] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for in-situ electropolymerization of L-arginine, characterized in that: A three-electrode electrochemical system was constructed, and L-arginine was in situ electropolymerized on the working electrode surface using cyclic voltammetry. The electrolyte used for in situ electropolymerization included 10 mmol L -1 Sodium chloride, 1.3 mmol L -1 Sodium acetate, 8.7 mmol L -1 Acetic acid and 10 mmol L -1 Arginine, cyclic voltammetry potential range is 0.5V-1.5V.

2. The method for in-situ electropolymerization of L-arginine according to claim 1, characterized in that: The working electrode is carbon fiber felt, carbon felt or carbon fiber paper.

3. The method for in-situ electropolymerization of L-arginine according to claim 1, characterized in that: The counter electrode of the three-electrode electrochemical system is a platinum sheet electrode.

4. The method for in-situ electropolymerization of L-arginine according to claim 1, characterized in that: The reference electrode of the three-electrode electrochemical system is a silver / silver chloride electrode in a saturated potassium chloride solution.

5. The method for in-situ electropolymerization of L-arginine according to claim 1, characterized in that: The number of cyclic voltammetry scans was 10-20 cycles.

6. The method for in-situ electropolymerization of L-arginine according to claim 4, characterized in that: The number of cyclic voltammetry scans was 10.

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