CN114447346A

CN114447346A - Chitosan-based three-dimensional porous conductive sponge and preparation method and application thereof

Info

Publication number: CN114447346A
Application number: CN202111635773.3A
Authority: CN
Inventors: 凌宇祥; 唐嘉丽; 于广平
Original assignee: Guangzhou Institute Of Industrial Intelligence; Shenyang Institute of Automation of CAS
Current assignee: Guangzhou Institute Of Industrial Intelligence; Shenyang Institute of Automation of CAS
Priority date: 2021-12-24
Filing date: 2021-12-24
Publication date: 2022-05-06

Abstract

The invention discloses a chitosan-based three-dimensional porous conductive sponge and a preparation method and application thereof, and relates to the technical field of porous materials. The preparation method of the chitosan-based three-dimensional porous conductive sponge comprises the following steps: firstly, filling chitosan with a conductive filler, then adding a pore-forming agent to form a pore structure, further increasing the specific surface area of the sponge body, and finally adding carbon fiber yarns to improve the connectivity between pores and further improve the conductivity of the material. The chitosan-based three-dimensional porous conductive sponge prepared by the method has good biocompatibility and higher specific surface area, can provide more attachment sites for microorganisms, and in addition, the elasticity and strength of the material can be enhanced by adding the carbon fiber yarns, so that the stability of the material can be improved.

Description

Chitosan-based three-dimensional porous conductive sponge and preparation method and application thereof

Technical Field

The invention relates to the technical field of porous materials, in particular to a chitosan-based three-dimensional porous conductive sponge and a preparation method and application thereof.

Background

At present, the most widely used commercial electrode materials are carbon-based materials, such as carbon felt, carbon cloth, graphite felt, carbon paper, etc., which have good electrical conductivity, biocompatibility, corrosion resistance, etc., however, the surface active area of the carbon-based materials is relatively small, the surface of the materials is relatively smooth, the surface pore structure is easily blocked, which is not favorable for the adhesion and growth of a large amount of bacteria on the surface of the materials, and most of the carbon-based electrode materials belong to two-dimensional materials, which can have great influence on mass transfer of substances, etc., and are unfavorable for substance exchange, thereby influencing the growth of microorganisms. Therefore, it is an urgent technical problem to provide a three-dimensional electrode material having good conductivity, biocompatibility, corrosion resistance, and certain mechanical strength and toughness.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide the chitosan-based three-dimensional porous conductive sponge as well as the preparation method and the application thereof.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows: a preparation method of a chitosan-based three-dimensional porous conductive sponge is characterized by comprising the following steps:

(1) adding a conductive filler and a surfactant into water, uniformly dispersing, then adding glacial acetic acid, and uniformly mixing to obtain an acidic mixed solution;

(2) adding chitosan into the acidic mixed solution, and uniformly stirring to obtain a chitosan mixed colloidal solution;

(3) adding a pore-foaming agent into the chitosan mixed colloidal solution, and uniformly dispersing;

(4) adding carbon fiber filaments into the solution prepared in the step (3), and uniformly dispersing;

(5) drying the solution obtained in the step (4) to obtain bubble-free slurry;

(6) freeze-drying the slurry, and then soaking the dried sample in an alkaline solution to obtain a porous sponge body;

(7) and cleaning the porous sponge body to be neutral to obtain the chitosan-based three-dimensional porous conductive sponge.

The three-dimensional carbon-based porous material has an adjustable three-dimensional pore structure, excellent conductivity, good biocompatibility, good surface electrochemical activity and the like. The three-dimensional porous structure provides a large enough specific surface area, provides more attachment sites for the growth of microorganisms, and is beneficial to improving the attachment amount of the microorganisms and forming a stable biological film; the internal three-dimensional structure is favorable for the transmission of substances, and the mass transfer resistance can be obviously reduced among the communicated pore channels, so that the growth and the propagation of microorganisms are more favorable; due to the property of the sponge body, the electrode has good elasticity, tensile resistance and compression resistance, is not easy to damage and can be kept in a long-term stable state.

Chitosan (Chitosan) is obtained by deacetylation of Chitin (Chitin) which is widely available in nature. As a natural biological macromolecule, the chitosan has extremely wide source, low price, safety and no biological toxicity, and compared with a common synthetic macromolecule, the chitosan has good biocompatibility and biodegradability, so that the three-dimensional porous electrode material prepared by the chitosan base has good environmental friendliness and biological safety. The conductivity of the material can be improved by adding the conductive filler; the pore-forming agent can form more pore structures in the material, further improve the specific surface area of the material and increase the attachment sites of microorganisms; the addition of the carbon fiber yarns can improve the connectivity among pores, further increase the conductivity of the material, and can be used as a buffer substance to enhance the elasticity and tensile resistance of the material and improve the stability of the material.

Preferably, in the step (6), the freeze-drying process is as follows: pre-freezing at-40-60 deg.c and freeze drying in a freeze drier. The soaking process is carried out at 85-95 ℃, and the soaking time is 1-3 h; the alkaline solution is at least one of a sodium hydroxide solution or a potassium hydroxide solution, and the mass fraction of the sodium hydroxide or the potassium hydroxide in the alkaline solution is 5-10%.

Preferably, the conductive filler is at least one of conductive graphite and conductive carbon black; the surfactant is Cetyl Trimethyl Ammonium Bromide (CTAB); the pore-foaming agent is silica gel. The SiO in the silica gel has the function of making holes₂The material can also be used as a supporting framework of the material, so that the phenomenon of structural collapse of the material is prevented, and the structural integrity and the three-dimensional property of the material are kept.

Preferably, the mesh number of the silica gel is 100-400 meshes. When the size of the silica gel meets the above limit, the prepared chitosan-based three-dimensional porous conductive sponge has a large specific surface area and good stability.

Preferably, the conductive filler is a compound of conductive carbon black and conductive graphite, and the mass ratio of the conductive carbon black to the conductive graphite is (1-4): 1. The conductive carbon black has small specific gravity, and compared with graphite, carbon black with the same mass occupies larger volume fraction in a polymer, so that a conductive network is favorably formed, and the conductive carbon black has better conductive effect than graphite, but the conductive carbon black has small specific gravity and large volume density, and is difficult to disperse uniformly in a mixed system. If more surfactant is added to achieve the purpose of uniform dispersion, more non-conductive impurities are introduced into the electrode, which greatly affects the performance of the electrode and increases the preparation cost.

Preferably, the mass ratio of the conductive filler to the chitosan is 1 (0.5-5); the mass ratio of the conductive filler to the surfactant is (3-8) to 1. The purpose of the above limitation of the amount of each component is to improve the electrical conductivity of the material while ensuring the biocompatibility of the material.

Preferably, the mass ratio of the pore-foaming agent to the chitosan is 1 (3-20); the mass ratio of the carbon fiber yarns to the chitosan is 1 (2-10); further preferably, the mass ratio of the pore-foaming agent to the chitosan is 1: (3-10), wherein the mass ratio of the carbon fiber yarns to the chitosan is 1: (3-10). The inventor of the application proves through a large number of experiments that when the proportion of the pore-foaming agent, the chitosan and the carbon fiber wire accords with the limit, the chitosan-based three-dimensional porous conductive sponge is taken as an electrode to be measured, and the integral area and the conductivity of a Cyclic Voltammetry (CV) curve measured by taking a platinum electrode as a counter electrode and an Ag/AgCl electrode as a reference electrode are higher.

Meanwhile, the invention also discloses the chitosan-based three-dimensional porous conductive sponge prepared by the method and application of the sponge in the field of microbial fuel cells.

Compared with the prior art, the invention has the beneficial effects that:

(1) the chitosan with good biocompatibility is used as the main body base material of the sponge body, so that a good growth carrier can be provided for microorganisms, and meanwhile, the carbon-series conductive substance is used as a conductive filler, so that the specific surface area of the material is increased while the conductivity is realized, more attachment sites can be provided for the microorganisms, and the chitosan sponge is very suitable for being applied to microbial fuel cells.

(2) The silica gel powder is used as a pore-forming agent, holes with different sizes can be prepared according to the size of the selected silica gel powder, the pore structure in the sponge body is adjusted, the specific surface area of the sponge body is further increased, and meanwhile, SiO in the silica gel₂The material can also be used as a supporting framework of the material, so that the phenomenon of structural collapse of the material is prevented, and the integrity and the three-dimensional property of the material are kept.

(3) And a certain amount of carbon fiber yarns are added and irregularly interpenetrated in the material, so that the connectivity between holes can be improved, and the internal resistance of the material can be further reduced due to the conductivity of the carbon fiber yarns, so that the high conductivity of the material is realized.

(4) The carbon fiber yarns can be used as a buffer substance to enhance the elasticity and tensile resistance of the material, and can also be used as a supporting framework to improve the strength and stability of the material.

Drawings

FIG. 1 is an SEM image of a chitosan-based three-dimensional porous conductive sponge according to examples 5-6; (a) example 5 internal cross-sectional view, 250 times; (b) example 5 internal cross-sectional view, 1500 times; (c) example 5 longitudinal section view, 250 times; (d) example 5 longitudinal section view, 1500 times; (e) example 6 internal cross-sectional view, 250 times; (f) example 6 internal cross-sectional view, 1500 times; (g) example 6 longitudinal section view, 250 times; (h) example 6 longitudinal section view, 1500 times;

FIG. 2 is a CV curve diagram of the chitosan-based three-dimensional porous conductive sponge according to examples 2-7;

FIG. 3 is a graph showing the effect of the chitosan-based three-dimensional porous conductive sponge according to example 3 applied to a microbial fuel cell;

FIG. 4 is a polarization curve and a power density curve of the chitosan-based three-dimensional porous conductive sponge applied to a microbial fuel cell in example 3 when the operation is stable.

Detailed Description

To better illustrate the objects, aspects and advantages of the present invention, the present invention will be further described with reference to the accompanying drawings and specific embodiments.

Example 1

According to the embodiment of the chitosan-based three-dimensional porous conductive sponge, the influence of the components of the conductive filler on the material performance is researched. The preparation method of the chitosan-based three-dimensional porous conductive sponge comprises the following steps:

(1) respectively weighing the following conductive carbon black and conductive graphite in different proportions, and uniformly mixing in a beaker: the method comprises the following steps of weighing conductive carbon black 4.0g, conductive carbon black 3.2g, conductive carbon black 2.8g, conductive carbon black 2.0g, conductive carbon black 1.2g, conductive carbon black 0.8g, conductive carbon black 0g, conductive carbon black 0.8g, conductive carbon black 1.2g, conductive carbon black 2.8g, conductive carbon black 3.2g, conductive carbon black 4.0g, conductive carbon black 7# and conductive carbon black 7# 1, conductive carbon black 8, conductive carbon black 3, conductive carbon black 7, conductive carbon black 5, conductive carbon black 6 and conductive carbon black 7;

(2) adding 80mL of pure water into the mixed carbon powder in the step (1), adding 0.5g of surfactant CTAB into the water, and ultrasonically mixing uniformly to obtain a uniformly dispersed mixed solution; dropwise adding 2.0mL of glacial acetic acid into the mixed solution, and uniformly mixing to obtain an acidic mixed solution;

(3) adding 4.0g of chitosan powder into the acidic mixed solution, and uniformly stirring to obtain a chitosan mixed colloidal solution;

(4) adding 0.4g of silica gel (200 meshes) into the chitosan mixed colloidal solution, uniformly stirring, and performing ultrasonic dispersion to obtain a chitosan matrix solution;

(5) adding 1.2g of carbon fiber filaments into the chitosan matrix solution, and uniformly stirring;

(6) putting the solution obtained in the step (5) in a vacuum drying oven, vacuumizing, standing, and removing bubbles in the solution to obtain bubble-free slurry;

(7) injecting the slurry obtained in the step (6) into a mold, pre-freezing at-50 ℃, and then placing in a freeze dryer for freeze drying for 24 h;

(8) placing the dried sample in a sodium hydroxide solution with the mass fraction of 5% of sodium hydroxide, and heating in a constant-temperature water bath kettle at 90 ℃ for 2h to obtain a porous sponge body;

(9) and (3) cleaning the porous sponge body with distilled water until the pH is neutral to obtain the chitosan-based three-dimensional porous conductive sponge.

Firstly, measuring the sheet resistance value of the surface of a sample 1# to 7# by adopting a four-probe method, selecting 5 different points on the surface of the sample, respectively measuring the sheet resistance value of the position, and finally calculating the average value, wherein the result is shown in a table 1; the actual resistance of each sample was then measured using a resistance measuring instrument and the results are shown in Table 2 (where 1# and 7# samples exceeded the range of the apparatus due to too large resistance and no square resistance was detected).

TABLE 1

TABLE 2

As can be seen from tables 1-2, the resistances of samples No. 2-4 are obviously smaller than those of other samples, and the chitosan-based three-dimensional porous conductive sponge prepared when the mass ratio of the conductive carbon black to the conductive graphite is (1-4): 1 has better conductivity.

And comparing the electrochemical performance of each electrode sample by adopting a cyclic voltammetry method, wherein the testing equipment is an electrochemical workstation (model: CHI 600E, Shanghai Chenghua). A three-electrode system is adopted, wherein a working electrode is connected with an electrode to be detected, a counter electrode is connected with a platinum electrode, an Ag/AgCl electrode is used as a reference electrode, and a 100mM Phosphate Buffer Solution (PBS) is used as an electrolyte solution. The potential range of the CV scan was set as: -0.5V, and the scanning speed is as follows: 5mV/s, number of scanning cycles: 20 turns. The performance of the samples was judged by comparing the integrated areas of the CV scan curves of the samples, and the results are shown in Table 3.

TABLE 3

As can be seen from Table 3, the specific capacity of the chitosan-based three-dimensional porous conductive sponge of samples 2# to 4# is also obviously higher than that of other samples.

The I/U curve is obtained by applying a linearly varying voltage under a two-electrode system of an electrochemical workstation. The sample to be tested is led out by two copper wires, a working electrode of the electrochemical workstation is connected with one copper wire, and a reference electrode and a counter electrode are connected with the other copper wire. The scanning potential range is-1.0 to 1.0V, and the scanning speed is 0.01V/s. On the basis of the I/U curve, when U is 0V, the conductivity value (S/m) of the electrode to be measured is calculated by the following equation:

in the formula: w is the width of the electrode, m;

t is the thickness of the electrode, m;

l represents the distance between the copper wires connecting the electrodes, m.

The test results for each sample are shown in table 4.

TABLE 4

As can be seen from table 4, the conductivity of samples # 2, # 3 and # 4 is higher than that of other samples, and thus the samples are more suitable for being applied to microbial fuel cells.

Examples 2 to 7

In the embodiment of the chitosan-based three-dimensional porous conductive sponge, the preparation method of the embodiment 2-7 is as follows, and the mass ratio of silica gel to chitosan and the mass ratio of carbon fiber filaments to chitosan used in the preparation process are shown in table 5:

(1) weighing 2.8g of conductive carbon black and 1.2g of conductive graphite, uniformly mixing, adding 80mL of pure water, adding 0.5g of surfactant CTAB into the water, and uniformly mixing by ultrasonic to obtain a mixed solution; dropwise adding 1.0-3.0 mL of glacial acetic acid into the mixed solution, and uniformly mixing to obtain an acidic mixed solution;

(2) adding 4.0g of chitosan powder into the acidic mixed solution, and uniformly stirring to obtain a chitosan mixed colloidal solution;

(3) adding silica gel (200 meshes) into the chitosan mixed colloidal solution, uniformly stirring, and performing ultrasonic dispersion to prepare a uniformly mixed chitosan matrix solution;

(4) adding carbon fiber filaments into the chitosan matrix solution, and uniformly stirring;

(5) putting the solution obtained in the step (4) in a vacuum drying oven, vacuumizing, standing, and removing bubbles in the solution to obtain bubble-free slurry;

(6) injecting the slurry into a mold, pre-freezing at-50 ℃, and freeze-drying in a freeze-drying machine for 24 h;

(7) soaking the freeze-dried sample in a sodium hydroxide solution with the mass fraction of 5% of sodium hydroxide, and heating for 2 hours in a constant-temperature water bath kettle at the temperature of 90 ℃ to obtain a porous sponge body;

(8) and cleaning the porous sponge body with distilled water to be neutral to obtain the chitosan-based three-dimensional porous conductive sponge.

TABLE 5

Item

Example 2

Example 3

Example 4

Example 5

Example 6

Example 7

Silica gel: chitosan

1:20

1:10

1:3.3

1:2

Carbon fiber yarn: chitosan

1:3.3

1:2

1:10

1:3.3

FIG. 1 is an SEM photograph of examples 5-6; wherein (a) is an internal cross-sectional view of example 5, 250 times; (b) is an internal cross-sectional view of example 5, 1500 times; (c) is a longitudinal sectional view of example 5, 250 times; (d) is a longitudinal section view of example 5, 1500 times; (e) is an internal cross-sectional view of example 6, 250 times; (f) is the internal cross-sectional view of example 6, 1500 times; (g) is a longitudinal sectional view of example 6, 250 times; (h) is a longitudinal sectional view of example 6, 1500 times. As can be seen from fig. 1, the embodiments 5 to 6 are all three-dimensional network structures, and the amount of the porogen silica gel used in the process of preparing the embodiment 6 is more, which results in larger pores in the embodiment 6, and as can be seen from the enlarged image of 1500 times, the carbon fiber filaments in the chitosan-based three-dimensional porous conductive sponge described in the embodiments 5 to 6 are inserted between the pores, so that the pores can be communicated with each other.

The electrochemical performances of the examples 2 to 7 were compared by cyclic voltammetry, and the test equipment was an electrochemical workstation (model: CHI 600E, Shanghai Chenghua). A three-electrode system is adopted, wherein a working electrode is connected with an electrode to be detected, a counter electrode is connected with a platinum electrode, an Ag/AgCl electrode is used as a reference electrode, and a buffer solution is used as an electrolyte solution. The potential range of the CV scan was set as: -0.5V, and the scanning speed is: 5mV/s, number of scanning cycles: 20 turns. CV curves as shown in fig. 2, it can be seen from fig. 2 that the integrated area of the CV curve of the chitosan-based three-dimensional porous conductive sponge prepared according to the present invention is significantly higher compared to the carbon felt.

The I/U curve is obtained by applying a linearly varying voltage under a two-electrode system of an electrochemical workstation. The sample to be tested is led out by two copper wires, a working electrode of the electrochemical workstation is connected with one copper wire, and the reference electrode and the counter electrode are connected with the other copper wire together. The scanning potential range is-1.0V, and the scanning speed is 0.01V/s. On the basis of the I/U curve, when U is 0V, the conductivity value (S/m) of the electrode to be measured is calculated by the following equation:

in the formula: w is the width of the electrode, m;

t is the thickness of the electrode, m;

Table 6 reports the integrated area of CV curves for examples 2-7, and Table 7 reports the conductivity values for examples 2-7.

TABLE 6

Examples	2	3	4	5	6	7
							Integral area (× 10)^-4)	12.438	47.093	33.664	16.523	44.398	30.146

The integrated area of CV curve measured by carbon felt (carbon in North sea, 3mm) is 3.4826X 10^-4。

TABLE 7

Examples	2	3	4	5	6	7
							Conductivity delta (S/m)	0.61200	2.51948	0.80310	1.4735	4.29092	3.29596

From the test results, the chitosan-based three-dimensional porous conductive sponges described in examples 2-7 all have high conductivity and electrochemical active area.

The porosities of the chitosan-based three-dimensional porous conductive sponges described in examples 3, 5 and 6 were measured by mercury porosimetry, and the test results are shown in table 8.

TABLE 8

Item	Example 3	Example 5	Example 6
				Porosity (%)	89.9829	82.6691	87.7055

As can be seen from Table 8, the porosity of the chitosan-based three-dimensional porous conductive sponge prepared by the method of the present invention can reach more than 80%.

Example 8

The invention discloses an application example of a chitosan-based three-dimensional porous conductive sponge in a microbial fuel cell. The application method comprises the following steps:

(1) assembling a microbial fuel cell reactor: a microbial fuel cell reactor with double chambers and air cathodes is adopted, the sections of an anode chamber and a cathode chamber are both circular, the diameters of the chambers are both 3cm, the widths of the chambers are both 2cm, and the effective volumes of the chambers are 14cm respectively³The cathode chamber and the anode chamber are separated by a Nafion117 proton exchange membrane (DuPont company in the United states), and the end plate on one side of the cathode chamber is provided with a circular hole which has the same size as the area of the cathode electrode, so that one side of the cathode can be directly contacted with air, and aeration is not needed in the operation process. The chitosan-based three-dimensional porous conductive sponge prepared in example 3 was used as the anode electrode, the hydrophobic carbon cloth (taiwan carbon energy brand) was pretreated as the cathode electrode, and the cathode pretreatment method was: the PTFE diffusion layer is prepared by a film scraping method, the catalyst layer is prepared by a brush coating method, a 20% Pt/C catalyst is selected, 0.5mg Pt is finally ensured to be coated on carbon cloth per square centimeter, and then the carbon cloth is naturally dried. The diameter of each electrode is 3cm, the distance between the electrodes is 4cm, and the external resistance is 1000 omega.

(2) Preparing an anolyte and a catholyte: the inoculated sludge used in the MFC start-up stage is anaerobically culturedExcess sludge of a secondary sedimentation tank of a sewage treatment plant in a certain city of Guangzhou city. The anolyte consists of: NH (NH)₄Cl 0.31g·L^-1， KCl 0.13g·L^-1，NaH₂PO₄·2H₂O 3.32g·L^-1，Na₂HPO₄·12H₂O 10.32g·L^-112.5 mL. L of trace elements^-1The substrate is C₆H₁₂O₆ 1.0g·L^-1(ii) a Wherein the specific components of the trace elements are as follows: n (CH)₂COOH)₃ 2.0mg·L^-1，MgSO₄ 3.0mg·L^-1，MnSO₄ 0.5mg·L^-1，NaCl 1.0mg·L^-1，GuSO₄·5H₂O 0.01mg·L^-1，KAl(SO₄)₂·12H₂O 0.01mg·L^-1，CoCl₂·6H₂O 0.1mg·L^-1GaCl₂·2H₂O 0.1mg·L^-1，ZnCl₂ 0.13mg·L^-1，H₃BO₃0.01mg·L^-1，Na₂MoO₄ 0.025 mg·L^-1，NiCl₂·6H₂O 0.024mg·L^-1，Na₂WO₄·2H₂O 0.025mg·L^-1. The catholyte consists of: NH (NH)₄Cl 0.31g·L^-1，KCl 0.13g·L^-1，NaH₂PO₄·2H₂O 3.32g·L^-1，Na₂HPO₄·12H₂O 10.32g·L^-1。

(3) Starting the microbial fuel cell reactor: the method adopts sequencing batch start, and 20mL & L of anode liquor is added in batches in the start stage^-1Inoculating the mud to promote the enrichment and domestication of the anode electrogenesis microorganisms. When the output voltage is below 50mV, it can be assumed that 1 cycle of operation of the cell is over and fresh anolyte and catholyte are replaced. Before replacing the anode liquid, nitrogen is required to be aerated for 30min to remove oxygen, and the anode liquid is quickly injected into an anode chamber by an injector during replacement, so that air is prevented from being brought into the anode chamber as much as possible. When the output voltage peak value of the battery in 1 period changes by less than +/-5% for 3 consecutive days, the battery can be considered to be successfully started. And after the system is started successfully, the anode does not feed inoculated sludge any more. Substrate replacement in anolyteChanged to 1.282 g.L^-1Sodium acetate. The voltage signal of the microbial fuel cell is acquired online by an Agilent digital multimeter (Agilent 34970A), and the time interval between data acquisition and recording is 10 min.

The voltage versus time curve for the start-up operation of the microbial fuel cell is shown in fig. 3. The reactor starts to generate electricity from about 60 hours, starts successfully about 240 hours, finally reaches the stable voltage of 450 +/-20 mV, has good periodic repeatability, the polarization curve and the power density curve after stable operation are shown in figure 4, and the maximum power density after stable operation is 190 W.m^-2. The results show that the chitosan-based three-dimensional porous conductive sponge electrode prepared by the invention has good structural and performance stability.

Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and not for limiting the protection scope of the present invention, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions can be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A preparation method of a chitosan-based three-dimensional porous conductive sponge is characterized by comprising the following steps:

(5) drying the solution obtained in the step (4) to obtain bubble-free slurry;

2. The method according to claim 1, wherein in the step (6), the freeze-drying process comprises: pre-freezing at-40 to-60 ℃, and then placing in a freeze drier for freeze drying; the alkaline solution is sodium hydroxide solution or potassium hydroxide solution.

3. The preparation method according to claim 1, wherein in the step (6), the soaking process is performed at 85-95 ℃ for 1-3 h, and the mass fraction of sodium hydroxide or potassium hydroxide in the alkaline solution is 5-10%.

4. The method according to claim 1, wherein the conductive filler is at least one of conductive graphite and conductive carbon black; the surfactant is cetyl trimethyl ammonium bromide; the pore-foaming agent is silica gel.

5. The method according to claim 4, wherein the silica gel has a mesh size of 100 to 400 mesh.

6. The preparation method according to claim 4, wherein the conductive filler is a compound of conductive carbon black and conductive graphite, and the mass ratio of the conductive carbon black to the conductive graphite is (1-4): 1.

7. The preparation method of claim 1, wherein the mass ratio of the conductive filler to the chitosan is 1 (0.5-5); the mass ratio of the conductive filler to the surfactant is (3-8) to 1.

8. The preparation method of claim 1, wherein the mass ratio of the pore-foaming agent to the chitosan is 1 (3-20); the mass ratio of the carbon fiber yarns to the chitosan is 1 (2-10).

9. A chitosan-based three-dimensional porous conductive sponge prepared according to the method of any one of claims 1 to 8.

10. The application of the chitosan-based three-dimensional porous conductive sponge as recited in claim 9 in the field of microbial fuel cells.