CN115032253B

CN115032253B - High-efficiency electropolymerization L-arginine modified electrode and method for improving performance of microbial electrochemical system

Info

Publication number: CN115032253B
Application number: CN202210517719.7A
Authority: CN
Inventors: 易越; 罗霖; 毛执鹏; 罗爱芹
Original assignee: Beijing Institute of Technology BIT
Current assignee: Beijing Institute of Technology BIT
Priority date: 2022-05-12
Filing date: 2022-05-12
Publication date: 2023-05-05
Anticipated expiration: 2042-05-12
Also published as: CN115032253A

Abstract

The invention relates to a high-efficiency electropolymerization L-arginine modified electrode and a method for improving the performance of a microbial electrochemical system, wherein the pH and CV scanning parameters of electrolyte of electropolymerization L-arginine are optimized, the L-arginine is subjected to high-efficiency electropolymerization on the surface of an electrode attached by electrochemically active microorganisms in the microbial electrochemical system, the poly L-arginine modified electrode is obtained, and the electrode modified by poly L-arginine is used for replacing an unmodified electrode to start and run the microbial electrochemical system, so that the adsorption of the electrochemically active microorganisms on the surface of the electrode can be promoted, the formation of a biological film is accelerated, the biological film biomass on the surface of the electrode is improved, the internal resistance of charge transfer is reduced, and the performance of the microbial electrochemical system is improved. Compared with the prior art, the method does not need complex operation and does not consume a reagent with biological toxicity, thereby providing a new green and effective material modification method for improving the operation performance of the microbial electrochemical system.

Description

High-efficiency electropolymerization L-arginine modified electrode and method for improving performance of microbial electrochemical system

Technical Field

The invention relates to the technical field of microbial electrochemistry, in particular to a high-efficiency electropolymerization L-arginine modified electrode and a method for improving the performance of a microbial electrochemistry system.

Background

The microbial electrochemical system (Microbial electrochemical system, MES) is a novel electrochemical device that utilizes electrochemically active microorganisms (Electrochemically active bacteria, EAB) to catalyze polarized reactions. The most common form of MES is a microbial fuel cell (Microbial fuel cell, MFC). MFC is capable of catalytically oxidizing organics in wastewater with EAB and converting chemical energy in the organics into electrical energy. The technology realizes synchronous sewage treatment and energy recovery, and is expected to break through the bottleneck of high energy consumption existing in the traditional sewage treatment. In addition to MFC, microbial cells (Microbial electrolysis cell, MEC) are another common form of MES. Unlike MFC, MEC utilizes EAB catalytic reduction, i.e., conversion of electrical energy into high-value chemical energy (e.g., hydrogen, acetic acid), and has shown good application prospects in the field of biochemistry. The MES utilizes EAB to realize energy conversion between electric energy and chemical energy, and has the advantages of mild reaction condition, green reaction process and the like. However, limited by the lower electrochemical performance, practical applications of MES also present a technical bottleneck.

An important factor affecting MES electrochemical performance is EAB biofilm on the electrode surface, and the primary and very important step in biofilm formation is microbial attachment to the electrode surface. Electrostatic forces are an important driving force for the adsorption of microorganisms on the electrode surfaces, and two classical material modification methods have been reported to enhance the electrostatic interaction between EAB and electrodes. Cheng et al increased positively charged functional groups such as amino groups on the electrode surface by heat treating the electrode in an ammonia gas environment. Since EAB is negatively charged under physiological pH conditions, the electrode shows stronger electrostatic attraction effect on EAB after treatment, so that the adhesion of EAB and the formation of a biological film are promoted, the starting time of MFC is shortened by 50%, and the power generation capacity is improved by 20%. Zhu et al also increased the amino content of the electrode surface by treating the electrode with nitric acid and ethylenediamine, promoted EAB adhesion, reduced MFC start-up time by 45%, and increased power generation capacity by 51%. Although these material treatment methods have been widely used by subsequent studies, there are problems in that the reaction conditions are severe, and toxic and harmful reagents are required to be consumed. Therefore, there is also a need to study green and gentle material modification methods that can promote EAB adhesion.

Recently, several new material modification methods have been reported to improve the electropositivity of the electrode surface. Xie et al reported that covering the electrode surface with melamine increases the Zeta potential of the electrode. Jurg et al treat electrode materials with N plasma technology to increase the N element content and nitrogen containing functional groups on the electrode surface. However, these two methods have limited effects on improving positive charges such as amino groups on the electrode surface (N element content. Ltoreq.3%), which results in that the improvement effect of the modified material on MFC start-up and operation in these studies is not obvious. The electrode material surface is modified by utilizing a cationic flocculant by Zhong et al, and a good thought is provided for promoting the adhesion of EAB on the electrode surface. After polydiallyl dimethyl ammonium chloride (PDDA) is modified on the surface of the electrode, the hysteresis period in the starting process of the MFC is eliminated, the starting time of the MFC is greatly shortened by 92.5%, and the power generation capacity is improved by 3.3 times. However, PDDA still has a certain biotoxicity, and may cause secondary pollution to the environment, and meanwhile, modification of the electrode by the soaking-drying method also has the problems of complicated operation, low stability, poor repeatability and the like.

The L-arginine is hopefully formed into a green and environment-friendly material modification method capable of promoting the adhesion of EAB by covering the electrode surface by an in-situ electro-polymerization method. This is because L-arginine has 2 amino groups, is a nontoxic natural amino acid having the highest isoelectric point (isoelectric point of ph=10.7), and is capable of ionizing to have a positive charge under neutral or near neutral pH conditions. Meanwhile, L-Arginine can be electropolymerized in situ on the electrode surface to form Poly L-Arginine (PLA), and PLA modified electrodes have been demonstrated to increase the conductivity, hydrophilicity of the electrodes. The Xiao et al modify PLA on the surface of the eG/SPE electrode by in-situ electropolymerization, so that the electrochemical active site on the surface of the electrode is increased, the electrochemical performance of the electrode is improved by about 80%, and the sensitivity and the detection range of detecting the p-nitrophenol are improved. Similarly, the use of PLA modified electrodes by in situ electropolymerization also improves the detection performance of dopamine, vitamin c, uric acid, epinephrine, 8-OHdG. Therefore, the inventors believe that in situ electropolymerization of L-arginine on the electrode surface to which EAB of MES is attached can not only increase the conductivity of the electrode, but also increase the electropositivity of the electrode surface, promote EAB adsorption and increase biomass, and finally increase the electrochemical performance of MES. However, studies using PLA for MES have not been reported, nor has the effect of PLA on EAB biofilm formation and MES electrochemical performance clear. Meanwhile, how to polymerize more PLA on the electrode surface is still to be studied due to the vague electropolymerization mechanism of L-arginine.

Disclosure of Invention

The invention relates to a high-efficiency electropolymerization L-arginine modified electrode and a method for improving the performance of a Microbial Electrochemical System (MES), which comprises the following specific principles: l-arginine has 2 amino groups and is nontoxic natural amino acid with highest isoelectric point, the L-arginine can be ionized to have positive charges under neutral or near neutral pH conditions, meanwhile, by utilizing the preferable electrolyte containing the L-arginine and the preferable operation parameters of a cyclic voltammetry (Cyclic voltammetry, CV), the L-arginine can be efficiently and electrically polymerized to form poly L-arginine (PLA) on the surface of an electrode, and the PLA has good conductivity and hydrophilicity, so that the electrochemical active microorganisms (EAB) in MES are negatively charged, and the electrode attached to the EAB in MES is modified by the electropolymerized L-arginine, so that the conductivity of the electrode can be increased, the amino content and positive charges on the surface of the electrode can be increased, the electrostatic attraction effect of the EAB and the surface of the electrode can be increased, the adsorption of the EAB on the surface of the electrode can be improved, the formation of a biological film can be accelerated, the biological quantity of the biological film can be increased, and the operation performance of the MES can be improved.

Specifically, the method for efficiently electropolymerizing L-arginine modified electrode and improving MES performance uses an EAB (electrode-electrode) attached electrode of MES as a working electrode, constructs a three-electrode electrochemical system, configures a preferable electrolyte containing L-arginine, efficiently electropolymerizes L-arginine on the surface of the working electrode by CV (constant velocity) scanning by utilizing a preferable CV (constant velocity) operation parameter to obtain a PLA modified electrode, and utilizes the PLA modified electrode to replace an unmodified electrode to start and run the MES so as to improve the running performance of the MES.

The method comprises the following specific steps:

(1) An electrochemical cell (Electrochemical cell, EC) containing a working electrode, a counter electrode and a reference electrode is constructed by taking an EAB (electrode attached) of MES as a working electrode, wherein the EC working volume is 10mL, the working electrode is fixed by an electrode clamp, and the counter electrode and the reference electrode respectively adopt a 1cm multiplied by 1cm platinum sheet electrode and an Ag/AgCl reference electrode;

(2) Adding electrolyte containing L-arginine into EC, wherein each liter of electrolyte contains 50mmol of disodium hydrogen phosphate, 10mmol of NaCl and 10mmol of L-arginine;

(3) Connecting EC with a multichannel potentiostat, performing electropolymerization of L-arginine on the surface of a working electrode by CV scanning at 25+ -0.5 ℃, wherein the CV scanning range is 0.5V-2V, the scanning speed is 10mV/s, the number of turns is 10, the scanning initial direction is forward scanning, and the rest time is 0s;

(4) After CV scanning is completed, a PLA modified electrode is obtained, and the PLA modified electrode is used for replacing an unmodified electrode to be used as an EAB attached electrode of MES, so that the running performance of the MES can be improved.

The invention has the following advantages:

compared with the reported method for electropolymerizing L-arginine, the method of the invention can electropolymerize L-arginine with high efficiency; the electrolyte of the electropolymerized L-arginine which is reported to be basically neutral or nearly neutral (namely, the pH value is about 7), the inventor finds that the L-arginine is more easily electropolymerized under alkaline conditions to form PLA, the pH value of the electrolyte is increased from 7 to 9, and the content of PLA obtained by electropolymerized L-arginine can be increased by 37 percent calculated by nitrogen element; the CV scanning range of the electropolymerized L-arginine which is reported at present is generally-2V-2V or-1V-2V, the inventor finds that the electro-oxidation of the L-arginine is the first step of the electro-polymerization to form PLA, the electro-oxidation initial potential of the L-arginine is 0.5V and the initial potential of the oxidized L-arginine which is reduced is-0.7V under the condition that the pH value of electrolyte is 9, so that the L-arginine which is prevented from being reduced can improve the electro-polymerization efficiency of the L-arginine, and the PLA content obtained by the electro-polymerization of the L-arginine can be improved by 54 percent by calculating N elements after the CV scanning range of the electro-polymerization of the L-arginine is adjusted from-2V-2V to 0.5V-2V.

Meanwhile, the invention provides a green material modification method for promoting the attachment of the EAB on the electrode surface, improving the biological membrane biomass of the EAB and enhancing the MES performance; the reported material modification method for promoting the EAB to be attached to the electrode surface is basically divided into material treatment and material coverage, the material treatment needs to consume toxic reagents such as ammonia gas and the like, and also depends on severe reaction conditions such as high temperature and the like, while the material coverage needs to be coated with reagents such as melamine, PDDA and the like which are biologically toxic, the modified materials are mainly covered on the electrode surface by a soaking-drying method, are easy to fall off and are not high in stability, by using the method, the Zeta potential on the electrode surface can be positively moved by 22mV through the PLA modified electrode, the effect of the electrode is basically similar to that of the electrode modified by using the melamine and the PDDA, and the complex operation is not needed, and the reagent which is biologically toxic is not consumed.

Drawings

FIG. 1 is a schematic diagram showing the efficient electropolymerization L-arginine modified electrode and the improvement of MES performance in the present invention

FIG. 2 is a graph showing the effect of pH on the photopolymerization of L-arginine in example 1 of the present invention

FIG. 3 is a graph showing the effect of CV scan range on L-arginine photopolymerization in example 1 of the present invention

FIG. 4 is a graph showing the effect of CV scan speed and number of turns on the electropolymerization of L-arginine in example 1 of the present invention

FIG. 5 is a graph showing the effect of PLA modified electrode on EAB adsorption in example 2 of the invention

FIG. 6 shows the effect of PLA modified electrode on the Zeta potential and functional groups on the electrode surface in example 2 of the invention

FIG. 7 is a short term effect of PLA modified electrode on MES performance in example 3 of the invention

FIG. 8 shows the long-term effect of PLA-modified electrode on MES performance in example 3 of the invention

FIG. 9 is a graph showing the effect of PLA-modified electrodes on the colonization of EAB in MES in example 3 of the invention

Detailed Description

Example 1

An Electrochemical Cell (EC) containing a working electrode, a counter electrode and a reference electrode was constructed, the EC working volume was 10mL, the working electrode was fixed by an electrode clamp (JJ 110, shanghai European science and technology center) using 1cm×2cm carbon cloth (WOS 1009, taiwan carbon energy Co.); the counter electrode and the reference electrode are respectively adopted

Platinum sheet electrode (PT 009, shanghai European science and technology center) and Ag/AgCl reference electrode (R0303, shanghai European science and technology center; 0.205V vs. standard hydrogen electrode). In situ electropolymerization of L-arginine on the surface of the working electrode using CV scanning. Firstly, adding electrolyte containing L-arginine into EC, wherein each liter of electrolyte contains 50mmol of phosphate buffer solution, 10mmol of NaCl and 10mmol of L-arginine; then, EC was connected to a multichannel potentiostat (CHI 1040C, shanghai Chenhua) and L-arginine was electropolymerized in situ on the working electrode surface by CV scanning at 25.+ -. 0.5 ℃.The initial electropolymerization parameters were: PBS pH=7, CV scan range-2V-2V, 10mV/s sweep speed, 10 turns. And comparing the element composition and electrochemical properties of the PLA modified carbon cloth under different pH conditions, and optimizing the pH. Three pH levels, including 5, 7, 9 were selected and obtained by varying the ratio of sodium dihydrogen phosphate to disodium hydrogen phosphate in the phosphate buffer. And comparing the element composition and electrochemical performance of the PLA modified carbon cloth under different CV scanning range conditions, and optimizing the CV scanning range. According to the experimentally obtained oxidation potential of L-arginine and the reduced potential of L-arginine in the oxidized state, CV scan ranges are selected comprising: -2V-2V, -2V-1V, -2V-0.5V, -2V-1V, 0.5V-2V. Based on the pH value and CV scanning range obtained by the optimization, CV scanning speed and turns of the electropolymerization of the L-arginine are further optimized, and finally parameters of the electropolymerization of the L-arginine are obtained.

As shown in fig. 2a, the current exhibited a classical S-shape when the potential was varied from-2V to 2V under each pH and control condition. The first derivative of the voltammogram for forward scanning (FIG. 2 b) showed a distinct oxidation peak (peak potential of about 1V-1.3V) at each pH compared to the control group without L-arginine in the electrolyte, indicating that L-arginine was oxidized by the electrode. Meanwhile, the oxidation peak positions are obviously different under three different pH conditions, and the initial potential and the peak potential of the oxidation of L-arginine under alkaline conditions (pH=9) are corrected to be 0.5V and 1V respectively, which indicates that the alkaline conditions are more favorable for the oxidation of L-arginine. Furthermore, by first order derivation of the voltammogram of the reverse scan (FIG. 2 c), only a small reduction peak appears near-0.7V at each pH, indicating that oxidized L-arginine is mostly consumed for forming the polymer. The XPS results further demonstrate this inference (fig. 2 d). The surface of the carbon cloth used as a control is basically C element (the element content reaches 94%), the N element content is only 1.2%, the N element on the surface of the electrode is obviously increased under each pH condition, and the L-arginine contains one amino group and one guanidine group, so that the L-arginine can be electrically polymerized on the surface of the electrode under three pH conditions. Comparing the respective pH values, it was found that the N element content on the electrode surface was highest and reached 8.1% when the pH of the electrolyte was 9, which suggests that the alkaline condition was more favorable for the electropolymerization of L-arginine.

On the other hand, PLA modified electrodes can increase the conductivity of the electrode. As shown in fig. 2e, the peak current of potassium ferricyanide/potassium ferrocyanide oxidation by cyclic voltammetry was only 4580 μa when PLA was not modified on the carbon cloth surface, whereas when PLA was modified on the electrode surface, the peak currents reached 5980 μa (ph=5), 7440 μa (ph=7), 8260 μa (ph=9), respectively. The electrochemical active area of the electrode surface was calculated according to Randles-Sevcik equation, and the result showed that the electrochemical active area of the unmodified electrode as a control group was 13.8cm ² After modification by poly L-arginine, the electrochemical active area of the electrode surface reaches 18.1cm ² (pH＝5)、22.5cm ² (pH＝7)、25.0cm ² (ph=9). This phenomenon suggests that poly-L-arginine modification can effectively increase the electrochemical active sites and enhance the electrochemical performance of the electrode. Meanwhile, more poly-L-arginine can be obtained under alkaline conditions, and the poly-L-arginine modified electrode shows better electrochemical performance under the condition of pH 9.

The electropolymerization of L-arginine was compared under different CV scan ranges. As shown in FIG. 3a, the elemental composition of the electrode surface and the electrochemical properties of the electrode were only slightly altered when CV scan ranges were-2V-1V and-2V-0.5V (FIGS. 3 a-b), indicating that no significant polymerization of L-arginine occurred on the electrode surface. While when the CV scan range was-2V-1V, an increase in the N element on the electrode surface from 1.4% to 4.0% was clearly observed, and the oxidation peak current of the CV scan was also increased by 30.1% (FIGS. 3 a-b). Considering that the oxidation initiation potential of L-arginine is 0.5V, this illustrates that the electro-oxidation of L-arginine is the first step in the formation of PLA. On the other hand, when the cyclic voltammetric scan potential is-2V-2V, a very small reduction peak (FIG. 2 c) associated with reduction of oxidized L-arginine can be observed, which may be detrimental to the electropolymerization of L-arginine. In order to eliminate the electro-reduction of oxidized L-arginine, the potential range of CV scanning is set to be 0.5V-2V, and compared with CV scanning of-2V-2V, N element and O element on the surface of an electrode after the electro-polymerization of L-arginine are greatly increased by 54.2% and 38.1% respectively (figure 3 c). Meanwhile, as more PLA was formed on the electrode surface, the modified electrode exhibited higher electrochemical activity, and the peak current of CV scan increased to 9290 μa (fig. 3 d).

The speed and number of turns of the CV scan are further optimized according to the N content of the element surface (FIGS. 4 a-b). Based on the above results, the optimized parameters for the L-arginine electropolymerization are: ph=9, cv scan range 0.5V-2V, scan speed 10mV/s, and number of scan turns 10. Under the optimized process condition, the content of N element reaches 12.6% after the in-situ electropolymerization of L-arginine on the surface of the electrode, which is 3 times of the electropolymerization level of the L-arginine reported by recent researches, and provides an efficient method for the electropolymerization of the L-arginine.

Example 2

Based on an optimized L-arginine electropolymerization process, PLA-modified carbon cloth (PLA-CC) is prepared. Utilization mode EAB Strain Shewanella loihica PV-4%

ATCC, usa), the effect of PLA-modified electrodes on EAB adsorption and the mechanism were analyzed by comparing the attachment of bacteria to PLA-CC and Carbon Cloth (CC) surfaces. First, shewanella loihica PV-4 was grown by expansion with LB medium, centrifuged and resuspended to od600=2 with DM medium when grown to exponential growth phase (od600≡2.0). Each liter of LB medium contains 10g peptone, 10g NaCl, 5g yeast extract. 1.12g sodium lactate, 0.5g yeast extract, 2.50g NaHCO per liter DM medium ₃ 、0.08g CaCl ₂ ·2H ₂ O、1.00g NH ₄ Cl、0.20g MgCl ₂ ·6H ₂ O, 10.00g NaCl, 7.20g HEPES. Then, PLA-CC and Carbon Cloth (CC) were immersed in Shewanella loihica PV-4 bacterial suspension for 12 hours, and EAB attached to the electrode surface was visually observed by scanning electron microscopy (Scanning electron microscope, SEM). Sampling, glutaraldehyde fixation, ethanol dehydration with different concentration gradients and metal spraying treatment are carried out before SEM observation.

After immersing both PLA-CC and CC electrodes in Shewanella loihica PV-4 bacterial suspension for 12h, it was clearly observed that EAB cells were attached to both electrode surfaces (FIGS. 5a and 5 e), which is also the first step in the formation of biological films by EAB. Meanwhile, in SEM pictures at high magnification (fig. 5d and 5 h), it was found that EAB cells secreted extracellular polymers, which could enhance the attachment of cells to the electrode surface. Notably, the EAB biomass attached to the surface of the two electrodes was significantly different. The PLA-CC surface almost forms a monolayer of EAB biofilm (FIG. 5 a) while the CC surface has only a small amount of EAB attached (FIG. 5 e), which intuitively demonstrates that PLA-modified electrodes can promote EAB attachment. This phenomenon is mainly derived from the better electropositivity of PLA-CC. The Zeta potential of CC was-29.3 mV and that of PLA-CC was-6.6 mV (FIG. 6 a). Considering that Shewanella loihica PV-4 has a Zeta potential of-28.7 mV (FIG. 6 a), PLA-CC has a more positive Zeta potential, which can enhance the electrostatic force between EAB and electrode, promoting EAB adhesion.

PLA-modified electrodes are able to increase the electropositivity of the electrode, mainly because PLA-CC has more abundant functional groups than CC (fig. 6 b). Specifically, the C element in CC showed a distinct peak at 284.8eV only, which represents a C-C bond, and the content reached 93.7% (FIG. 6 d). After PLA modification, the C-C bond content in PLA-CC was reduced to 31.1% and two peaks at 286.1eV and 288.8eV, representing C-O-C and O-c=o, respectively, were present (fig. 6 d). The O-c=o bond represents a carboxyl group in the amino acid, and modification of the carboxyl group at the electrode surface can enhance the hydrophilicity of the electrode, which is advantageous for EAB attachment. On the other hand, the CC surface has no obvious N-containing functional groups (FIG. 6 d), while the N element in PLA-CC has a distinct peak at 400eV (FIG. 6 c), which represents an amino group. The amino groups on the surface of the electrode can enhance the positive charges on the surface of the electrode and the electropositivity of the electrode, increase the electrostatic force between the EAB and the electrode and promote the attachment of the EAB.

Example 3

8 MES (MES 1-8) were constructed, each using exactly the same electrochemical cell as the electropolymerized L-arginine. The 8 MES's are divided into two groups, including PLA-CC-MES (MES 1-4) and CC-MES (MES 5-8). Wherein, the working electrode of PLA-CC-MES adopts PLA-modified carbon cloth (PLA-CC), and PLA is obtained by utilizing optimized L-arginine electropolymerization parameters. The working electrode of CC-MES used unmodified Carbon Cloth (CC) as a control.

All MES were sterilized prior to inoculation. Mode EAB strain Shewanella loihica PV-4 was used to inoculate MES. Shewanella loihica PV-4 was grown by expansion with LB medium, and when grown to exponential growth phase (OD 600. Apprxeq.2.0), 5mL of the bacterial suspension was mixed with 5mL of DM medium and inoculated with MES in a sterile environment. After inoculation, the working electrode of each MES was set at 0.5V (vs. Ag/AgCl reference electrode) and run at 25.+ -. 0.5 ℃. The output current of the MES is collected by using a chronoamperometry method, and when the MES current is reduced to less than 50 microamps, the electrolyte of the MES is completely replaced by the sterile DM culture solution.

4 MES's, including 2 PLA-CC-MES (MES 1-2) and 2 CC-MES (MES 5-6), for measuring electrochemical performance of MES and biomembrane metabolic structure of electrode surface when running for 4 hours after inoculation, analyzing short-term effect of PLA modified electrode on MES performance; another 4 MES, including 2 PLA-CC-MES (MES 3-4) and 2 CC-MES (MES 7-8), were used to measure electrochemical performance of MES, biofilm metabolic structure on electrode surface after 1 complete cycle after inoculation, and microbial community structure of MES after 3 complete cycles after inoculation, demonstrating the long term impact of PLA modified electrodes on MES performance.

As shown in fig. 7a, both MES (PLA-CC-MES and CC-MES) can generate output current immediately after inoculation, since Shewanella loihica PV-4 can be rapidly attached to the electrode surface, forming early biofilm while generating bioelectric signals. As the MES run, the capacitive current vanishes and both MES currents tend to stabilize. Notably, when the MES current stabilized, the average current value of PLA-CC-MES reached 39.5 μA, which is 1.76 times that of CC-MES (FIG. 6 a). A similar phenomenon was also observed by epicyclic CV scanning, with a limiting current of 105.5. Mu.A for PLA-CC-MES, and only 75.4. Mu.A for CC-MES (FIG. 7 b). These phenomena indicate that PLA-CC can significantly improve MES performance in a short time. Since PLA-CC is able to promote EAB attachment, better power generation may result from more biomass at the electrode surface. As shown in fig. 7d and 7g, laser confocal microscopy (Confocal laser scanning microscopy, CLSM) visually demonstrates the metabolic structure of the electrode surface biofilm, green fluorescence representing active bacteria, fluorescence intensity being able to characterize the biomass of the biofilm. P was found by comparing the early biofilm on the surface of PLA-CC (FIG. 7 d) and CC (FIG. 7 g)The LA-CC electrode surface had more green fluorescence, indicating that more EAB was attached to the PLA-CC surface. By quantifying the fluorescence intensity of CLSM, the integrated optical density of PLA-CC surface was about 405.1, whereas the integrated optical density of CC-MES was only 253.5, indicating that the biomass of PLA-CC surface was 1.60 times that of CC (fig. 7 c). Higher biomass can reduce the internal resistance of the polarization reaction, as shown in FIGS. 7e-f, the charge transfer internal resistance of PLA-CC-MES (R _ct ) About 4390Ω, also almost half of the CC-MES. Therefore, the short-term influence of PLA modified electrode on MES can be summarized, and because PLA can increase the electropositivity of the electrode surface, the adhesion of EAB on the electrode surface is promoted, the charge transfer internal resistance of MES is reduced, and the electricity generating performance of MES is enhanced.

As shown in fig. 8a, the first cycle of two MES starts and runs, after inoculation of both MES, the current rises rapidly to peak and then falls slowly over a short hysteresis period. Since PLA-CC can promote EAB attachment and mass transfer of polarization reaction in a short time, PLA-CC-MES can be observed to have a shorter hysteresis period. Specifically, PLA-CC-MES started to rise rapidly after about 320min of inoculation, while CC-MES took about 2 times (FIG. 8 a). Moreover, when the MES current reached a peak, the current was 169.0 μA, while the CC-MES current peaked only at 135.5 μA. The limiting current obtained by epicyclic CV scanning also indicated that PLA-CC-MES had higher power generation capacity (FIG. 8 b). Furthermore, PLA-CC-MES was able to run steadily for 1200min at peak duration, while the CC-MES current was dropped almost immediately after reaching peak (FIG. 8 a). By calculating the power generation of two MES in one cycle, the power generation of PLA-CC-MES can be found to be 1.20C and the power generation of CC-MES is only 0.68C, which indicates that the PLA modified electrode can improve the power generation capacity of MES by 76%. This result is comparable to the effect of heat treating electrodes, strong acid electrodes in an ammonia environment, without the need for harsh experimental conditions and toxic reagents. The promotion of MES performance by PLA results from higher biofilm biomass and lower internal resistance to charge transfer. As shown in fig. 8c-d and 8g, PLA-CC surface area spectroscopic density was 1581.8 and the integrated optical density of the CC surface was only 986.8, indicating that PLA modified electrodes accelerated biofilm formation due to the promotion of EAB attachment at the beginning of biofilm formation by PLA. At the same time, higher biomass reduced the internal charge transfer resistance of MES by 62% with PLA modified electrodes (fig. 8 e-f). Therefore, the result is summarized, and the PLA proves that the PLA can promote the adsorption of the EAB on the electrode surface, accelerate the formation of a biological film, improve the biological film biomass on the electrode surface, reduce the internal resistance of charge transfer and realize the improvement of the performance of MES.

After three consecutive cycles of operation of both MESs, the PLA-CC-MES was able to generate approximately 90. Mu.A of repetitive current, while the second and third cycles of the CC-MES had little current (FIG. 9 a). By high throughput sequencing, it was found that after 3 cycles of operation, more than 70% Shewanella bacteria were still present on the PLA-CC-MES electrode surface, whereas only 40% Shewanella were present in CC-MES (FIG. 9 b). Furthermore, escherichia/Shigella capable of secreting biotoxins is also present in large amounts in CC-MES (FIG. 9 b), which suggests that the loss of power to produce CC-MES may originate from microbial contamination, which suggests that PLA-modified electrodes can also enhance the colonization of the electrode surface by EAB, reducing microbial contamination at early stages of biofilm.

Claims

1. A method for improving the performance of a microbial electrochemical system, comprising: constructing a three-electrode electrochemical system, wherein a working electrode comprises carbon cloth, carbon felt, carbon brush, graphite felt, graphite sheet or graphite rod, preparing an electrolyte containing L-arginine, wherein each liter of electrolyte comprises 10mM arginine, 10mM NaCl and 50mM phosphate buffer solution, the pH value of the phosphate buffer solution is 9, the pH value is 9, the cyclic voltammetry operation parameters are utilized, the scanning range is 0.5V-2V, the scanning speed is 10mV/s, the scanning number is 10 circles, the L-arginine is efficiently and electrically polymerized on the surface of the working electrode through the cyclic voltammetry to obtain a poly L-arginine modified electrode, and the poly L-arginine modified electrode is utilized to replace an unmodified electrode to serve as an electrode for attaching electrochemical active microorganisms in the microbial electrochemical system, wherein the microbial electrochemical system comprises a microbial fuel cell or a microbial electrolytic cell, and the microbial electrochemical system is started and operated to realize the improvement of the operation performance of the microbial electrochemical system; the principle of the method is as follows: l-arginine is provided with 2 amino groups, is nontoxic natural amino acid with highest isoelectric point, can ionize and carry positive charges under neutral or near neutral pH conditions, and simultaneously, by utilizing the electrolyte containing L-arginine and the operation parameters of the cyclic voltammetry, L-arginine can be efficiently and electrically polymerized to form poly-L-arginine on the surface of the electrode, and poly-L-arginine has good conductivity and hydrophilicity.

2. The method for improving the performance of a microbial electrochemical system according to claim 1, wherein the poly-L-arginine modified electrode is prepared by the following steps:

(1) An electrochemical cell containing a working electrode, a counter electrode and a reference electrode is constructed, the working volume of the electrochemical cell is 10mL, the working electrode is fixed through an electrode clamp, and the counter electrode and the reference electrode respectively adopt a 1cm multiplied by 1cm platinum sheet electrode and an Ag/AgCl reference electrode;

(2) Adding an electrolyte containing L-arginine into an electrochemical cell, wherein each liter of electrolyte contains 50mmol of disodium hydrogen phosphate, 10mmol of NaCl and 10mmol of arginine;

(3) Connecting an electrochemical cell with a multichannel potentiostat, scanning by cyclic voltammetry at 25+/-0.5 ℃, electropolymerizing L-arginine on the surface of a working electrode, wherein the scanning range of the cyclic voltammetry is-0.5V-2V, the scanning speed is 10mV/s, the number of turns is 10, the scanning initial direction is forward scanning, and the rest time is 0s;

(4) After the cyclic voltammetry scanning is completed, the poly L-arginine modified electrode is obtained, and the poly L-arginine modified electrode is used as an electrode for adhesion of electrochemically active microorganisms in a microbial electrochemical system instead of an unmodified electrode, so that the running performance of the microbial electrochemical system can be improved.