CN111430765A

CN111430765A - Anode photosynthetic solar fuel cell system for in-situ remediation of wetland soil and preparation method thereof

Info

Publication number: CN111430765A
Application number: CN202010248461.6A
Authority: CN
Inventors: 杨彦; 余应新; 陈浩佳; 李向南; 高源�
Original assignee: Shantou Guanggong University Collaborative Innovation Research Institute; Guangdong University of Technology
Current assignee: Shantou Guanggong University Collaborative Innovation Research Institute; Guangdong University of Technology
Priority date: 2020-04-01
Filing date: 2020-04-01
Publication date: 2020-07-17

Abstract

The invention discloses an anode photosynthetic solar fuel cell system for in-situ remediation of wetland soil and a preparation method thereof. The fuel cell system comprises the anode photosynthetic solar fuel cell and the resistor, and the fuel cell has lower maintenance and operation cost and higher pollutant removal effect and is widely applied and accepted. The preparation method of the battery can be used for restoring the wetland in situ, degrading pollutants in the wetland and achieving a good degradation rate.

Description

Anode photosynthetic solar fuel cell system for in-situ remediation of wetland soil and preparation method thereof

Technical Field

The invention belongs to the field of plant-microbial fuel cells, and particularly relates to an anode photosynthetic solar fuel cell system for in-situ remediation of wetland soil and a preparation method thereof.

Background

China has 6600 more than ten thousand hectares of wetland area, which accounts for about 10 percent of the world wetland area and is the first place in Asia. The wetland is the first choice of farming land due to the abundant biodiversity, fertile soil and high production value. Along with the development of social economy, a large amount of waste water, waste gas and other wastes are continuously discharged into the wetland, human activities greatly occupy natural resources, unreasonable development and utilization cause numerous resource damages, and the wetland faces the practical problems of ecological function decline and the like caused by aggravation of pollution.

Chromium (Cr) is present in the natural environment in a trivalent or hexavalent form, is very unstable, and is one of the most toxic heavy metals. In earlier researches, various scientific researchers at home and abroad find that Cr is a characteristic pollutant with high detection rate and high pollution concentration in the soil of the Chinese wetland. Many researches and researches that the total Cr concentration of a plurality of places and soil layers in the wetland exceeds a moderate pollution level, and the heavy metal pollution remediation of the wetland is not slow.

The excessive application of chemical nitrogen fertilizers is a main cause of nitrate pollution, and agricultural producers unreasonably use fertilizers in large quantities, especially nitrogen fertilizers, to obtain greater economic benefits. The nitrogen fertilizer applied to the soil is partially discharged to the atmosphere in the forms of ammonia volatilization, denitrification and the like, and is partially discharged to a water body through leaching loss, so that the nitrate of the water body is polluted, but most of the nitrogen fertilizer is retained in the soil, and the farmland soil is polluted by the nitrate. The wetland is the first choice of farming land, and nitrate pollution of the wetland should be removed and repaired.

At present, the Anode Photosynthetic Solar Fuel Cells (APSFCs) which are researched more in the prior art are mainly researched aiming at the environmental purification effect and the biological electricity generation characteristic of the cells which are constructed by using low-grade aquatic plants such as phytoplankton such as green algae and blue-green algae and large-scale aquatic energy plants such as paddy rice, water hyacinth, reed, sweet fescue and the like.

Disclosure of Invention

In order to overcome the defects and shortcomings in the prior art, the invention aims to provide the preparation method of the in-situ restoration wetland anode photosynthetic solar fuel cell system, which can perform in-situ restoration on the wetland, degrade pollutants in the wetland and achieve a good degradation rate.

The invention also aims to provide an in-situ remediation wetland anode photosynthetic solar fuel cell system, which has lower maintenance and operation cost and higher pollutant removal effect and is widely applied and accepted.

One of the purposes of the invention is realized by the following technical scheme:

a preparation method of an in-situ restoration wetland anode photosynthetic solar fuel cell system comprises the following steps:

(1) preparing a matrix: taking soil of the riverside wetland, air-drying, grinding and sieving to obtain a matrix for cultivating plants;

(2) plant material and propagation culture: selecting green aquatic plants, and culturing the green aquatic plants in a container filled with sandy soil;

(3) construction of a single-cell air cathode: selecting at least one of graphite felt, carbon cloth and platinum-containing catalyst as a cathode electrode by using a light-tight and non-conductive container as a reactor;

(4) anode material selection and modification: taking foamed nickel as a 3D support, and modifying porous carbon or graphene to prepare a porous carbon/foamed nickel electrode plate or a graphene/foamed nickel electrode plate as an anode;

(5) the construction mode of the cathode and the anode is as follows: planting green aquatic plants in a growth box, and placing a system cathode and an anode in a symmetrical structure according to the length of a root system, wherein the anode is buried in the vicinity of the root system of the cattail, and the cathode is placed at a water-soil interface so as to be easy to contact oxygen in the air;

(6) recording the voltage value: the cathode potential, the cathode area pH value and the dissolved oxygen concentration are measured through the data acquisition unit, the oxygen secretion rate of the root system is measured, the porosity of the root system is calculated, and the anode potential value is calculated.

Preferably, the soil in the step (1) is collected from the riverside wetland with the depth of less than 10-15 cm, ground and sieved by a sieve with 20-100 meshes.

Preferably, the green aquatic plant in the step (2) is any one of typha orientalis, iris tectorum, alternanthera philoxeroides and reed.

Preferably, the plant cultured in the step (2) is selected from bud stem segments or seedlings thereof, the plant is a cattail plant which can resist a water-wet environment and grow healthily, and the sandy soil contains less than 2% of organic matters.

Preferably, the reactor in step (3) is a black plastic bucket.

Preferably, the specific preparation step of the anode material porous carbon/foamed nickel electrode sheet in the step (4) is as follows:

a. preparation of biomass porous carbon: drying and grinding the waste bean dregs, and sieving the ground waste bean dregs with a sieve of 100-300 meshes to obtain waste bean dregs powder; mixing the waste bean dregs powder with an active agent in N₂Heating and carbonizing under the atmosphere; sequentially soaking the carbonized waste bean dreg powder in HCl and HF solutions, washing to be neutral, and drying to obtain the biomass porous carbon;

b. preparing a porous carbon/foamed nickel electrode slice: according to the biomass porous carbon in the step a: the preparation method comprises the following steps of preparing a conductive agent and a binder in a mass ratio of 5-10: 1-2, fully mixing porous carbon and the conductive agent, dripping a binder dispersion liquid, slowly grinding the mixture to be pasty, uniformly coating the paste on a foamed nickel electrode sheet, drying, and pressing and flattening the electrode sheet in a double-roller machine; sequentially arranging the pressed electrode plates in an H mode₂SO₄And (3) carrying out ultrasonic treatment on the solution and NaOH solution, washing to be neutral, and drying to obtain the porous carbon/foamed nickel electrode plate.

Preferably, the carbonization condition in the step a is to heat the waste bean dregs powder and the activating agent to 400 ℃ at a heating rate of 8-12 ℃/min and keep the temperature for 0.4-0.6 h; the mass percentage of the HCl solution is 4-6%, the soaking time is 5-7 h, the mass percentage of the HF solution is 2-5%, and the soaking time is 5-7 h.

Preferably, the carbonization condition in the step a is to heat the waste bean dregs powder and the active agent to 400 ℃ at a heating rate of 10 ℃/min for 0.5 h; the mass percentage of the HCl solution is 5%, the soaking time is 6h, the mass percentage of the HF solution is 3%, and the soaking time is 6 h.

Preferably, the ratio of the waste bean dregs powder to the active agent is 2-5: 1, and the active agent is KOH, NaOH or H₃PO₄And ZnCl₂Or (2) to (d).

Preferably, the ratio of the waste bean dregs powder to the active agent is 3:1, and the active agent is KOH.

Preferably, the conductive agent in the step b is one of acetylene black, Ketjen black, Ks-6, Ks-15 and S-O; the adhesive is one of polytetrafluoroethylene, polyvinyl acetate and perchloroethylene; said H₂SO₄The solution molar concentration is 0.3-0.6 mol/L, the ultrasonic time is 10-20 min, the NaOH solution molar concentration is 0.3-0.6 mol/L, the ultrasonic time is 10-20 min, and the ultrasonic frequency is 50-100 Hz.

Preferably, the conductive agent in the step b is acetylene black; the adhesive is polytetrafluoroethylene; the biomass porous carbon: the H is prepared from acetylene black and polytetrafluoroethylene with the mass ratio of 8:1:1₂SO₄The solution molar concentration is 0.5 mol/L, the ultrasonic time is 15min, the NaOH solution molar concentration is 0.5 mol/L, the ultrasonic time is 15min, and the ultrasonic frequency is 50 Hz.

Preferably, the specific surface area of the biomass porous carbon is 2500-3500 m²The specific capacitance is 250-300F/g.

Preferably, the specific preparation step of the anode material graphene/nickel foam electrode sheet in the step (4) is as follows:

c. preparing graphene oxide: graphite powder: h₂SO₄：HNO₃：KMnO₄：H₂O₂The weight ratio of 0-1 g to 10-40 ml to 5-15 ml to 2-4 g: preparing 2-5 ml: mixing graphite powder and H₂SO₄Solution and HNO₃Mixing the solutions in a cold water bath to form a suspension, and slowly adding KMnO into the suspension₄Stirring for the first time until the reaction temperature is lower than 20 ℃, raising the reaction temperature to 35 ℃, stirring for the second time, diluting with deionized water, standing for 12 hours, adding deionized water into the solution again for further dilution, and slowly adding the deionized water with the volume fraction of 30 percentH₂O₂Precipitating, centrifuging, filtering and separating, washing the graphite oxide precipitate with deionized water, and ultrasonically dispersing in the deionized water to obtain graphene oxide;

d. preparing a graphene/foamed nickel electrode plate: placing the prepared foamed nickel electrode plate in a high-pressure reaction kettle, adding a graphene oxide aqueous solution, carrying out hydrothermal treatment for 3 times, and placing the obtained graphene/foamed nickel substrate in a tubular furnace H₂And annealing in the atmosphere to obtain the porous carbon/graphene/foamed nickel electrode plate.

Preferably, the first stirring time in the step c is 10-20 min, the second stirring time is 2-4H, and H is₂O₂The volume fraction of (A) is 20-40%, the centrifugation rate is 1000-2000 r/min, the centrifugation time is 20-40 min, the ultrasonic time is 2-4 h, and the ultrasonic frequency is as follows: 50-100 Hz.

Preferably, the ratio of graphite powder in step c: h₂SO₄：HNO₃：KMnO₄：H₂O₂The ratio of 0.5g to 23ml to 10ml to 3.0 g: 3.0ml, the first stirring time is 15min, the second stirring time is 3H, and the volume ratio of H is₂O₂The volume fraction of (2) is 30%, the centrifugation rate is 1500rpm, the centrifugation time is 30min, the ultrasonic time is 2-4 h, and the ultrasonic frequency is: 50 Hz.

Preferably, the hydrothermal treatment in the step d specifically comprises the steps of putting the high-pressure reaction kettle into an oven with the temperature of 100-150 ℃ for reaction for 4-6 hours, cooling at room temperature, washing and drying; the annealing treatment conditions are that the temperature in the tubular furnace is 380-420 ℃, and the annealing time is 0.4-0.6 h.

The foamed nickel electrode modified by the biomass porous carbon and the graphene in the step (4) has the advantages of low density, high porosity up to 98%, 3D network structure, large specific surface area, uniform quality and strong corrosion resistance, is an ideal electrode substrate material for batteries, and is widely applied to the fields of filtration, heat exchange, heat insulation, shock absorption, catalyst carriers and the like. The porous carbon and graphene modification can effectively reduce the internal charge transfer resistance of the foamed nickel anode, improve the electrode conductivity and biocompatibility, facilitate the attachment growth of microorganisms, and obtain the biomembrane electrode with excellent performance, and the porous carbon modified electrode is superior to the foamed nickel electrode in various performances.

Preferably, the specific step in said step (5) is not planting the plants in a volume of 12dm³In a growth box (20 × 20 × 30cm), the cathode and the anode of the system are placed in a symmetrical structure according to the length of a root system, wherein the anode is 15 × 15cm in size and is deeply buried in the vicinity of the root system of the cattail by about 10cm, and the cathode is 10 × 10cm in size and is placed at a water-soil interface to enable the anode to be easily contacted with oxygen in the air.

The second purpose of the invention is realized by the following technical scheme:

the utility model provides an in situ remediation wetland anode photosynthetic solar fuel cell system, includes anode photosynthetic solar fuel cell and resistance, anode photosynthetic solar fuel cell is the unicellular structure, including soil, water, green aquatic plant and two electrodes, inside the water was placed in to the root of green aquatic plant passed the water, and one of them electrode tiling is as the anode in soil is inside, and another electrode tiling is as the negative pole at the interface of soil and water, the both ends of resistance link to each other with anode, negative pole respectively.

Preferably, the cathode electrode is at least one of graphite felt, carbon cloth, platinum-containing catalyst.

Preferably, the cathode is a graphite felt.

Preferably, the cathode is 10-15 × 10-15 cm in size and is placed at a water-soil interface to enable the cathode to easily contact oxygen in air.

Preferably, the size of the anode is 10-20 × 10-20 cm, the anode is buried deep near the root system of the green aquatic plant of about 8-12 cm so that the root system can be fully contacted with the anode electrode, and the distance between the cathode and the anode is 8-15 cm.

Preferably, the in-situ remediation wetland anode photosynthetic solar fuel cell is externally connected with a data collector to collect data of the detection system, and two ends of the data collector are respectively connected with the cathode and the anode.

Preferably, the model of the data acquisition device is align 34970A, US. During the experiment, a digital multimeter (UNI-T UT58A, china) is commonly used to calibrate the voltage data collected by the data collector to ensure the reliability of the data.

The invention discloses a working principle of in-situ restoration of a wetland anode photosynthetic solar fuel cell, which comprises the following steps:

the in-situ remediation wetland anode photosynthetic solar fuel cell improves the electricity generation performance by combining the photosynthesis of the green aquatic plants with the microbial fuel cell, thereby further improving the electric energy conversion rate. The microbial fuel cell uses microbes as a catalyst, so that chemical energy in organic matters or inorganic matters is directly converted into a novel device of electric energy, and the specific principle is as follows: the microorganisms in the anode region generate electrons through substrate metabolic activity, which pass from the anode through a wire and an external resistor. The basic principle of the anode photosynthetic solar fuel cell for in-situ remediation of the wetland is that the biomass is accumulated by collecting solar energy through green plants, and the biomass can be used as a substrate of the anode electrogenesis microorganisms of the fuel cell to be further oxidized and converted into electric energy. 20-40% of organic matters synthesized by photosynthesis of green plants in the in-situ remediation wetland anode photosynthetic solar fuel cell are synthesized at the root, so that nutrients are provided for the growth of a microbial community in soil, and the electrochemically active microbes use the secretion of a plant root system in situ and directly or indirectly transfer electrons to the anode by using the organic matters in a rhizosphere environment, so that continuous electron flow can be generated.

The in-situ remediation wetland anode photosynthetic solar fuel cell is developed on the basis of a deposited microbial fuel cell (SMFC). In the soil or sediment saturated with water, because the soil or sediment contains rich organic matters, the top of the soil or sediment contains dissolved oxygen in an oxidation state, and the like, an anode and a cathode are arranged inside and on the surface of the system and are connected by a lead, so that the system meets the construction conditions of a Microbial Fuel Cell (MFC), namely, can generate stable current, and is called as a deposited microbial fuel cell (SMFC). International researchers found that deposited microbial fuel cells (SMFC) output power in the presence of plants is much greater than without plant treatment; and the electricity generation is a process driven by light energy, and the electricity generation capacity is obviously higher than that in the absence of illumination when illumination is available.

The green plants can collect and utilize solar energy to accumulate biomass, and the biomass can be used as a substrate of anode electricity-generating microorganisms to be further oxidized and converted into electric energy in the in-situ remediation wetland anode photosynthetic solar fuel cell. In addition to accumulating biomass, plant roots also synthesize and secrete large amounts of organic matter into the soil, including sugars, organic acids, and polymeric carbohydrates. 20-40% of organic matters synthesized by the solar photosynthesis are synthesized at roots, and nutrients are provided for the growth of microbial communities in soil. Electrochemically active microorganisms utilize secretions from the plant root system in situ, and are capable of generating a sustained flow of electrons.

Compared with the prior art, the invention has the following advantages and beneficial effects:

(1) the invention utilizes the in-situ remediation wetland anode photosynthetic solar fuel cell, the wetland remediation is an engineering technology for purifying pollutants by utilizing natural processes including wetland plants, soil or matrix and microbial metabolic activity, and the current research shows that the oxidation-reduction potentials at different positions in the wetland system are different, so that the construction of the anode photosynthetic solar fuel cell system by utilizing the wetland environment becomes possible due to the wide application and recognition of the wetland system with lower maintenance and operation cost and higher pollutant removal effect.

(2) The technology for in-situ remediation of the wetland anode photosynthetic solar fuel cell takes microorganisms as a catalyst, combines the photosynthesis of plants, and utilizes an electrode as an electron donor or an electron acceptor to generate electricity, thereby removing environmental pollutants and almost having no secondary pollution.

(3) After the in-situ remediation wetland anode photosynthetic solar fuel cell system provided by the invention is compared with the initial operation of each experimental group, the activities of soil urease, sucrase, catalase and alkaline phosphatase are improved to different degrees, which shows that the application of the system can effectively improve the soil health degree.

Drawings

FIG. 1 is a schematic view of an apparatus system for carrying out the method of the present invention;

wherein, 1-anode, 2-cathode, 3-green aquatic plant, 4-resistance, 5-data collector, 6-water and 7-soil;

FIG. 2 shows the variation of contaminant degradation concentration for each experimental group (a: group C; b: group N; C: group R);

FIG. 3 shows the soil enzyme activities of the experimental groups (a: urease; b sucrase; c: catalase; d: alkaline phosphatase);

FIG. 4 is a CV graph of cyclic voltammetry tests performed on different materials modified foam nickel electrodes;

FIG. 5 is an SEM image of porous carbon D-800-3-1(a, b), D-800-6-1(c, D);

FIG. 6 shows porous carbon N prepared by different activation temperatures of D-700-4-1, D-800-4-1 and D-900-4-1₂Adsorption and desorption isotherms (a);

FIG. 7 is a pore size distribution curve (b) of porous carbon N2 prepared at different activation temperatures of D-700-4-1, D-800-4-1 and D-900-4-1;

FIG. 8 is a porous carbon CV curve (a) prepared at different activation temperatures for D-700-4-1, D-800-4-1, and D-900-4-1;

FIG. 9 is a porous carbon constant current charge and discharge curve (b) prepared at different activation temperatures of D-700-4-1, D-800-4-1, and D-900-4-1;

FIG. 10 is a graph showing porous carbon impedance spectra (c) prepared at different activation temperatures for D-700-4-1, D-800-4-1, and D-900-4-1;

FIG. 11 is a porous carbon XRD spectrum diagram prepared by different activation temperatures of D-700-4-1, D-800-4-1 and D-900-4-1;

FIG. 12 shows porous carbon N prepared by different activation times of D-800-4-1, D-800-4-1.5 and D-800-4-2₂Adsorption and desorption isotherms (a);

FIG. 13 shows porous carbon N prepared by different activation times of D-800-4-1, D-800-4-1.5 and D-800-4-2₂Pore size distribution curve (b);

FIG. 14 is a graph (a) of porous carbon CV prepared by different activation times for D-800-4-1, D-800-4-1.5, and D-800-4-2;

FIG. 15 is a porous carbon constant current charge and discharge curve (b) prepared by different activation times of D-800-4-1, D-800-4-1.5 and D-800-4-2;

FIG. 16 is a graph showing porous carbon impedance spectra (c) prepared by different activation times for D-800-4-1, D-800-4-1.5, and D-800-4-2;

FIG. 17 is a porous carbon XRD spectrum of prepared porous carbon of D-800-4-1, D-800-4-1.5 and D-800-4-2 with different activation times;

FIG. 18 shows porous carbon N prepared by different activation ratios of D-800-2-1, D-800-3-1, D-800-4-1, D-800-5-1 and D-800-6-1₂Adsorption and desorption isotherms (a);

FIG. 19 shows porous carbon N prepared by different activation ratios of D-800-2-1, D-800-3-1, D-800-4-1, D-800-5-1 and D-800-6-1₂Pore size distribution curve (b);

FIG. 20 is a porous carbon CV curve (a) prepared from D-800-2-1, D-800-3-1, D-800-4-1, D-800-5-1 and D-800-6-1 at different activation ratios;

FIG. 21 is a porous carbon constant current charge and discharge curve (b) prepared by different activation ratios of D-800-2-1, D-800-3-1, D-800-4-1, D-800-5-1 and D-800-6-1;

FIG. 22 is a porous carbon impedance spectrum (c) prepared by different activation ratios of D-800-2-1, D-800-3-1, D-800-4-1, D-800-5-1 and D-800-6-1;

FIG. 23 is a porous carbon XRD spectrum diagram prepared from D-800-2-1, D-800-3-1, D-800-4-1, D-800-5-1 and D-800-6-1 with different activation ratios.

Detailed Description

The present invention will be described in further detail with reference to examples and drawings, but the embodiments of the present invention are not limited thereto.

And (3) inquiring and integrating the exposure concentration of the wetland characteristic pollutants in China according to literature, and setting a contamination gradient: preparing Cr solutions with mass concentrations of 200, 400, 600 and 800mg/kg respectively, and preparing HuNO with mass concentrations of 50, 100, 200 and 400mg/kg respectively₃-N solution, preparing composite pollutants (Cr + NO) with mass concentration of 200+50, 400+100, 600+200 and 800+400mg/kg₃-N). The control group was not contaminated, and there were 2 groups of 3 replicates each with no plants planted.

Example 1

(1) Preparing a matrix: taking soil with the depth of less than 10-15 cm of the riverside wetland, air-drying, grinding, and sieving with a 20-100-mesh sieve to obtain a matrix for cultivating plants;

(2) plant material and propagation culture: selecting cattail plants, and culturing the cattail plants in a container filled with sandy soil;

(3) construction of a single-cell air cathode: a lightproof and non-conductive plastic barrel is used as a reactor, and a graphite felt material is selected as a cathode electrode;

(4) anode material selection and modification: taking foamed nickel as a 3D support, performing surface modification on the foamed nickel by using porous carbon, and preparing a porous carbon/foamed nickel electrode plate as an anode;

(5) planting Typha plants in a growth box, and arranging the cathodes and the anodes of the system in a symmetrical structure according to the length of root systems, wherein the size of the anode is 15 × 15cm, the anode is buried deep near the root system of the Typha with the depth of 10cm, the size of the cathode is 10 × 10cm, the cathode is arranged on a water-soil interface, so that the anode can be easily contacted with oxygen in the air, and the distance between the cathode and the anode is 10 cm;

(6) recording the voltage value: measured directly by a data acquisition device (align 34970A, US). During the experiment, a digital multimeter (UNI-T UT58A, china) is commonly used to calibrate the voltage data collected by the data collector to ensure the reliability of the data.

Example 2 selection of plant Material

In the experiment, an Anode Photosynthetic Solar Fuel Cell (APSFCs) system is constructed by adopting wetland swamp plants such as cattail, iris, alternanthera philoxeroides and reed to carry out the experiment, the plant root system can provide an additional electron donor for the anode, different plant environments have different adaptive capacities, and different water-soluble conductivities exist in the growth process, so that the electricity generation effect has difference. The experimental plants were purchased from the persistent botanical garden of Jiangsu. The data collector is used for collecting the 10d output voltage and measuring the COD degradation rate, and the highest output voltage, the power density and the COD degradation rate are shown in the following table 1.

TABLE 1

Plant and method for producing the same	Cattail fruit	Iris root	Water peanuts	Reed
					Maximum output voltage/(mV)	278	116	257	239
Maximum power density/(mW/m)²)	37.57	10.53	18.59	24.35
					COD degradation rate/(%)	76.24	51.58	56.48	65.24

Through comparison of pollution tolerance of 4 kinds of marsh plants and electricity generation performance in an Anode Photosynthetic Solar Fuel Cell (APSFCs) system, the constructed typha-APFSCs system is found to have optimal performance, the highest output voltage is 278mV, and the highest power density is 37.57mW/m²The highest COD degradation rate is 76.24%. Besides, the cattail can grow in a laboratory environment and is suitable for the soil with higher heavy metal pollution concentration. Therefore, cattail which has strong pollution tolerance, wide adaptability and wide distribution and certain ornamental value is finally selected as the plant to be tested.

Example 3 preparation of anode Material

The foam nickel is a novel functional material with low density, porosity up to 98 percent and 3D net-shaped structure, has large specific surface area, uniform quality and strong corrosion resistance, is an ideal electrode substrate material of a battery, and is widely applied to the fields of filtration, heat exchange, heat insulation, shock absorption, catalyst carriers and the like.

The preparation method of the waste bean dreg precursor biomass porous carbon comprises the steps of preparing the porous carbon to be prepared from agricultural waste bean dregs, wherein the waste bean dregs are provided by grain feed companies in Hongkong, Jiangsu province, and Hongkong province, drying the waste bean dregs in an air-blast drying oven at 80 ℃ for 5 hours to enable the water content of the waste bean dregs to be lower than 5%, grinding the waste bean dregs, sieving the waste bean dregs with a 200-mesh sieve to obtain powder, drying the powder at 120 ℃ to constant mass to obtain the raw material of the waste bean dreg powder prepared from the porous carbon, and measuring C, H, N, S mass fractions of the raw material to be 42.07%, 6.41%, 8.40% and 0.48% respectively by an elemental analyzer (Vario E L III, Elementar company.

In high purity N₂Heating to 400 ℃ at a heating rate of 10 ℃/min in an atmosphere tube furnace for 0.5h, mixing the waste bean dregs powder and an activating agent KOH according to a ratio of 3:1, and carbonizing to form a sample. And then sequentially placing the carbonized sample into 5 wt% HCl and 3 wt% HF for soaking for 6h, washing to be neutral, and drying at 80 ℃ until the water content is lower than 5%.

Testing the specific surface area and specific capacitance value of different activators, selecting KOH, NaOH and H respectively₃PO₄、ZnCl₂The 4 activators were pre-tested by mixing the waste okara powder with the activator at a ratio of 3:1, in N₂Keeping the heating rate at 10 ℃/min under the atmosphere, heating to 800 ℃, and keeping the time for 1 h. Respectively carrying out N on porous carbon prepared by 4 activators₂Adsorption and desorption, CV test, and specific surface area and specific capacitance value are calculated, and the results are shown in Table 2.

TABLE 2

Activating agent	KOH	NaOH	H₃PO₄	ZnCl₂
					Specific surface area/(m)²/g)	3096	1538	1987	1052
Specific capacitance/(F/g)	268.49	220.45	105.64	255.37

As can be seen from the above Table 2, the porous carbon prepared by using KOH as an activator has obviously better performance than the porous carbon prepared by using other 3 activators, and the specific surface areas of the porous carbon are respectively 2.01 times of NaOH, and H is₃PO₄1.56 times of that of ZnCl₂2.84 times of; specific capacitance is NaOH and H respectively₃PO₄、ZnCl₂1.22, 2.54, 1.05 times of.

Preparing a porous carbon/foamed nickel electrode slice: according to the experimental result, KOH is finally selected as an activating agent to prepare the waste bean dreg precursor biomass porous carbon, and the porous carbon with the optimal performance (the specific surface area is 3096 m) is selected²/g, specific capacitance 268.49F/g), the optimal preparation temperature, proportion, time and the like of the porous carbon are shown in table 3.

TABLE 3

Weighing the materials according to the mass ratio of waste bean dreg precursor biomass porous carbon to acetylene black to polytetrafluoroethylene of 8:1:1, fully mixing active substances (the porous carbon and the acetylene black) in a mortar, dripping polytetrafluoroethylene dispersion liquid, slowly grinding the mixture into paste, uniformly coating the paste on the surface of foamed nickel (1 × 2cm), wherein the coating area is 1 × 1cm, transferring the paste into a drying box at 80 ℃ for drying for 12h, taking out the paste, and pressing and flattening an electrode plate in a double-roller machine to enable the foamed nickel to be fully contacted with the active substances.

In order to remove the surface oxide layer of the foamed nickel, the foamed nickel is sequentially put into H with the concentration of 0.5 mol/L₂SO₄And carrying out ultrasonic treatment in 0.5 mol/L NaOH solution for 15min respectively, wherein the ultrasonic frequency is 50Hz, washing to be neutral, drying at 50 ℃, weighing the mass of the foamed nickel before and after coating, and obtaining the mass of the active substance according to the proportion for calculating the electrochemical performance of the material.

Preparation of Graphene Oxide (GO), namely synthesizing the Graphene Oxide (GO) by using a Hummers method, weighing 0.5g of graphite powder, and adding 23m L concentrated H₂SO₄And 10m L concentrated HNO₃The mixture was cooled in an ice bath and 3.0g KMnO was slowly added₄. Adding KMnO₄Thereafter, the reaction temperature was kept below 20 ℃ and stirred for 15min, after which the reaction temperature was raised to 35 ℃ and stirred for 3H, then diluted with 40m L deionized water, after 12H, 200m L deionized water was added to further dilute the solution, then 3.0m L H was slowly added₂O₂(30% v/v), gradually converting the black graphite suspension solution into a bright yellow graphite oxide solution, centrifuging at 1500rpm for 30min, washing with deionized water, dispersing in 500m L deionized water, wherein the concentration of graphite oxide is about 1mg/m L, carrying out ultrasonic treatment on the graphite oxide aqueous solution for 2-4 h, and the ultrasonic frequency is 50Hz, so as to obtain the laminated graphite oxide sheets, and stripping the laminated graphite oxide sheets into single-layer or multi-layer Graphene Oxide (GO).

Preparing a graphene/foamed nickel electrode plate: putting the cut foam nickel into the diePressing a reaction kettle (with a polytetrafluoroethylene lining), adding Graphene Oxide (GO) aqueous solution with the volume of 25m L and the mass concentration of 1mg/ml, putting the reaction kettle into an oven, reacting for 5 hours at 120 ℃, cooling at room temperature, changing light yellow foam nickel into black (covering GO sheets), washing a product (GO-Ni) with deionized water, drying at room temperature, repeating the hydrothermal treatment for 3 times to increase the loading capacity of the Graphene Oxide (GO), and putting the obtained GO-Ni substrate in a tubular furnace H₂Annealing at 400 ℃ for 0.5h under the atmosphere.

Different porous carbon material modified foam nickel electrodes are subjected to cyclic voltammetry tests, a three-electrode system is adopted, the porous carbon/graphene modified electrode is used as a working electrode, a platinum electrode is used as a counter electrode, a saturated calomel electrode is used as a reference electrode, the scanning speed is 10mV/s, the working potential range is-0.8V-0.6V, and the result is shown in figure 4.

As can be seen from fig. 4, the CV curve of the blank nickel foam electrode is approximately rectangular, has no oxidation reduction peak, and shows typical conductor capacitance characteristics, and the area surrounded by the curve is the smallest, which indicates that the specific capacitance of the blank nickel foam electrode is the lowest. The graphene modified nickel foam electrode has 1 pair of obvious redox peaks (the oxidation peak is-0.67V, and the reduction peak is 0.59V), the curve surrounding area is obviously increased, and the limiting current is increased, which indicates that the electrochemical active surface area of the nickel foam electrode can be improved by graphene modification. The surrounding area of the CV curve of the porous carbon modified electrode is increased sharply, the limiting current is increased, and no obvious oxidation reduction peak exists. The specific surface area of the electrode modified by graphene and porous carbon is increased, the conductivity is enhanced, the electron transfer capability of the surface of the electrode is promoted, the electrocatalytic performance of the electrode is improved, and the promotion effect of the porous carbon is better.

After the biofilm is formed, the surrounding area of the CV curve of the electrode is increased, and after the graphene modified electrode loads the electroactive biofilm, 2 oxidation peaks appear on the CV curve and are respectively positioned at-0.54V and-0.27V. The porous carbon modified electrode is in a quasi-rectangular shape, and the surrounding area is the largest, which means that the electrode has the highest specific capacitance and electrochemical active surface area. The success of the biomembrane loading is shown, so that the electron transfer rate of the electrode is greatly enhanced, and the charge transfer impedance is reduced.

In order to better analyze the microstructure of the modified foam nickel electrode loaded with the biological membrane, SEM is utilized to carry out observation and analysis, and the experimental result is seen in SEM scanning electron microscope images.

In the microbial fuel cell, because the performance of the electrode is mainly influenced by electrode reaction kinetics and mass diffusion factors, in order to clarify the size and distribution of electrode mass transfer impedance and charge impedance, electrochemical impedance tests are carried out on different porous carbon material modified foam nickel electrodes in the research.

Cyclic voltammograms (CV curves) control the electrode potential to be scanned at different equal rates, one or more times in a triangular waveform over time, with the potential range being such that different reduction and oxidation reactions can occur alternately at the electrode, and the current-potential curves are recorded. The reversible degree of the electrode reaction, the possibility of adsorption of intermediates and phase boundaries or formation of new phases, the property of the coupling chemical reaction and the like can be judged according to the curve shape, and the reversible degree, the possibility of adsorption of intermediates and phase boundaries or formation of new phases and the like are used for measuring the electrode reaction parameters.

As can be seen from fig. 5 to 23, the better the representation in the images, the higher the electrochemical performance, and the higher the application value of the porous carbon/nickel foam material.

Example 4

Preparing a matrix: collecting a soil sample at a plant root layer (10-15 cm) of a wetland park in Changzhou city of Jiangsu, removing impurities from the sample, naturally drying, mashing, grinding, sieving with a 100-mesh sieve, and storing in a ventilated and cool place for later use. Soil characteristic indexes are as follows: the water content is 31.27%, the salt content is 0.62%, the organic matter content is 17.52g/kg, the total nitrogen content is 2.98g/kg, the quick-acting potassium content is 98.06mg/kg, and the quick-acting phosphorus content is 40.26mg/kg, and specific experimental groups are shown in Table 4.

TABLE 4

Weighing 4kg of air-dried soil respectively, and placing in a volume of 12dm³(20 × 20 × 30cm) growth chamber, control group (CK group), Cr test group (C group), NO₃N test group (N group), Cr and NO₃-N composite experimental group (R group).

By K₂Cr₂O₇And NaNO₃Separately prepare Cr⁶⁺And NO₃-N aqueous solution, slowly added to the soil with continuous stirring. The experimental group was first exposed to Cr, aged in a fume hood for 2 weeks, and then NO was added at 13d₃And (4) carrying out N contamination treatment, placing the mixture in a fume hood for aging for 2d, and periodically supplementing deionized water during aging to ensure that the saturated water holding capacity reaches 800 g/kg.

After the soil is aged, placing an electrode, adopting biomass porous carbon/foamed nickel as an electrode material, and sequentially placing the electrode material at 0.5 mol/L H₂SO₄The method comprises the steps of carrying out ultrasonic treatment on distilled water and 0.5 mol/L NaOH for 15min respectively, washing the distilled water to be neutral, then putting the neutral solution into a 50-DEG C oven for drying, constructing two poles of a battery with a symmetrical structure by adopting porous carbon modified foamed nickel, burying an anode (15 × 15cm) deeply in the position (about 10cm) of a plant root system, burying a cathode (10 × 10cm) in a water-soil interface, connecting the anode with a wire, adding a load resistor (1000 omega), and obtaining an experimental device shown in figure 1.

Selecting healthy cattail plants which grow well, have mature roots, 5-7 leaves and 50-60 cm of plant height and do not have plant diseases and insect pests, domesticating the cattail plants with deionized water for 10 days, planting the cattail plants in soil, and planting 2-3 cattail plants in each barrel.

The experimental period is 100d, after the operation system is started, the soil is sampled every 25d, and after 100d, the plants are sampled, and pollutants Cr and NO are analyzed and detected₃-the concentration of N to monitor the degradation effect of the system on the contaminants.

And (3) taking a soil sample at the 100 th day after the system is started, detecting the activities of urease, sucrase, catalase and alkaline phosphatase, and judging the health degree of the soil by taking the activity of the soil enzyme as a biological index, wherein the experimental result is shown in figure 2.

The repair effect detection is as shown in fig. 2: the degradation rates of the pollutants in the C group 100d are respectively C1(70.28 +/-1.22%), C2(57.81 +/-1.01%), C3(58.13 +/-2.26%) and C4(50.60 +/-1.27%). The degradation rates of the N groups of pollutants in 100 days of system operation are respectively N1(59.27 +/-4.11%), N2(65.13 +/-2.17%), N3(57.81 +/-2.28%) and N4(53.43 +/-3.43%). It can be seen that the APFSCs system is in Cr and NO₃-N single contamination eventsUnder the condition, when the pollution concentration is 150-250 mg/kg and 50-150 mg/kg respectively, the degradation effect is optimal.

R group Cr and NO₃The degradation rates of-N are respectively R1(61.35 + -3.08%, 87.96 + -2.77%), R2(57.23 + -1.01%, 88.58 + -1.83%), R3(52.21 + -2.18%, 88.86 + -1.49%), and R4(49.66 + -1.28%, 59.57 + -1.67%). Under the exposure of the composite pollution, the degradation rate is in a gradually decreasing trend along with the increase of the concentration of the pollutant.

Cr and NO under the operation state of the APFSCs system₃Higher repairing effect can be obtained when the-N pollution concentration is 150-250 and 50-200 mg/kg respectively.

Testing the soil health degree: urease, sucrase, catalase and alkaline phosphatase activities were measured in different experimental groups and the results are shown in FIG. 3. The results show that the pollution stress has obvious influence on the activity of the soil enzyme, and causes the difference of the soil enzyme in each experimental group. In general, the soil enzyme activity control group is larger than the experimental group, and of various enzymes, urease has the largest variation amplitude in the experimental group and the control group, and the activity of sucrase is the highest.

The activity ranges of the urease, the sucrase, the catalase and the alkaline phosphatase in the experimental group are 0.43-3.97, 20.32-53.42, 4.01-8.97 and 0.19-0.46 mg/g respectively. The urease activity in the N group is the highest, and the catalase activity in the soil of different experimental groups is in the following order: CK group > N group > C group > R group, catalase activity in CK group soil is 8.21mg/g, which is 1.01, 1.22 and 1.82 times of average enzyme activity of N, C and R group soil respectively. The average enzyme activity of alkaline phosphatase in each experimental group was less different.

Comparing the initial enzyme activities of the experimental groups, after the APSFCs system is operated, the activities of soil urease, sucrase, catalase and alkaline phosphatase are all improved to different degrees, which shows that the system can effectively improve the soil health degree.

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.

Claims

1. A preparation method of an in-situ restoration wetland anode photosynthetic solar fuel cell system is characterized by comprising the following steps:

2. The method for preparing an in-situ remediation wetland anode photosynthetic solar fuel cell system as claimed in claim 1, wherein the green aquatic plant in step (2) is any one of typha orientalis, iris tectorum, alternanthera philoxeroides and reed.

3. The preparation method of the in-situ remediation wetland anode photosynthetic solar fuel cell system according to claim 1, wherein the specific preparation step of the anode material being a porous carbon/foamed nickel electrode sheet in the step (4) is as follows:

4. The preparation method of the in-situ remediation wetland anode photosynthetic solar fuel cell system according to claim 3, wherein the ratio of the waste bean dregs powder to the active agent in the step a is 2-5: 1, and the active agent is KOH, NaOH or H₃PO₄And ZnCl₂One of (a) and (b); the carbonization condition is that the waste bean dregs powder and the active agent are heated to 400 ℃ at a heating rate of 8-12 ℃/min and are kept for 0.4-0.6 h; the mass percentage of the HCl solution is 4-6%, the soaking time is 5-7 h, the mass percentage of the HF solution is 2-5%, and the soaking time is 5-7 h.

5. The method for preparing the in-situ remediation wetland anode photosynthetic solar fuel cell system as claimed in claim 3, wherein the conductive agent in the step b is one of acetylene black, ketjen black, Ks-6, Ks-15, and S-O; the adhesive is one of polytetrafluoroethylene, polyvinyl acetate and perchloroethylene; said H₂SO₄The solution molar concentration is 0.3-0.6 mol/L, the ultrasonic time is 10-20 min, the NaOH solution molar concentration is 0.3-0.6 mol/L, the ultrasonic time is 10-20 min, and the ultrasonic frequency is 50-100 Hz.

6. The preparation method of the in-situ remediation wetland anode photosynthetic solar fuel cell system as claimed in claims 3 to 5, wherein the specific surface area of the biomass porous carbon is 2500-3500 m²The specific capacitance is 250-300F/g.

7. The preparation method of the in-situ remediation wetland anode photosynthetic solar fuel cell system according to claim 1, wherein the specific preparation step of the anode material graphene/nickel foam electrode sheet in the step (4) is as follows:

c. preparing graphene oxide: graphite powder: h₂SO₄：HNO₃：KMnO₄：H₂O₂The weight ratio of 0-1 g to 10-40 ml to 5-15 ml to 2-4 g: preparing 2-5 ml: mixing graphite powder and H₂SO₄Solution and HNO₃Mixing the solutions in a cold water bath to form a suspension, and slowly adding KMnO into the suspension₄Stirring for the first time until the reaction temperature is lower than 20 ℃, raising the reaction temperature to 35 ℃, stirring for the second time, diluting with deionized water, standing for 12 hours, adding deionized water into the solution again for further dilution, and slowly adding H with the volume fraction of 30%₂O₂Precipitating, centrifuging, filtering and separating, washing the graphite oxide precipitate with deionized water, and ultrasonically dispersing in the deionized water to obtain graphene oxide;

8. The preparation method of the in-situ remediation wetland anode photosynthetic solar fuel cell system according to claim 7, wherein the first stirring time in the step c is 10-20 min, the second stirring time is 2-4H, and the H is₂O₂Volume fraction ofThe number is 20-40%, the centrifugation rate is 1000-2000 rpm, the centrifugation time is 20-40 min, the ultrasonic time is 2-4 h, and the ultrasonic frequency is as follows: 50-100 Hz.

9. The preparation method of the in-situ remediation wetland anode photosynthetic solar fuel cell system according to claim 7, wherein the hydrothermal treatment in the step d specifically comprises the steps of putting a high-pressure reaction kettle into an oven with the temperature of 100-150 ℃ for reaction for 4-6 hours, cooling at room temperature, washing and drying; the annealing treatment conditions are that the temperature in the tubular furnace is 380-420 ℃, and the annealing time is 0.4-0.6 h.

10. An in-situ remediation wetland anode photosynthetic solar fuel cell system prepared by the preparation method of any one of claims 1 to 9, which comprises an anode photosynthetic solar fuel cell and a resistor, wherein the anode photosynthetic solar fuel cell is of a single-chamber structure and comprises soil, a water body, green aquatic plants and two electrodes, the roots of the green aquatic plants penetrate through the water body and are placed in the soil, one of the electrodes is flatly laid in the soil to serve as an anode, the other electrode is flatly laid at the interface of the soil and the water body to serve as a cathode, and two ends of the resistor are respectively connected with the anode and the cathode.