Preparation method and application of magnetic cellulose carbon aerogel composite electrode material

Abstract

The present invention relates to the field of carbon aerogel technology, specifically disclosing a method for preparing a magnetic cellulose-carbon aerogel composite electrode material and its application. Using natural pulp as a precursor, the cellulose hydrogel is prepared via a sol-gel process. This hydrogel is then impregnated with ferric chloride, freeze-dried, and finally pyrolyzed in a tubular furnace to produce a magnetic cellulose-carbon aerogel (CA@Fe3O4) composite material. The magnetic cellulose-carbon aerogel prepared in this invention exhibits high specific surface area, good electrical conductivity, and excellent biocompatibility. Used in microbial fuel cell anodes, it can degrade dimethyl sulfide while converting chemical energy into electrical energy, enabling the renewable utilization of organic matter.

Description

Technical Field

[0001] The present invention relates to the field of composite material preparation, and in particular to a preparation method and application of a magnetic cellulose carbon aerogel composite electrode material. Background Art

[0002] Malodorous gas emissions pose a serious environmental problem. Volatile organic sulfide compounds (VOSCs) are the primary source of malodorous pollutants. VOSCs have extremely low odor thresholds and are highly toxic. Dimethyl sulfide (DMS) is a typical VOSC, with an odor threshold as low as 0.6–40 ppb. Low concentrations of DMS can cause nausea and vomiting, while high concentrations can paralyze the central nervous system and cause health problems. Therefore, addressing DMS emissions is crucial. Currently, biological methods are commonly used to treat malodorous gases.

[0003] Bioelectrochemical systems (BES) enable efficient and environmental degradation of pollutants through the action of microorganisms. Electroactive bacteria can also reduce the redox overpotential, further facilitating the degradation of difficult-to-degrade pollutants. Microbial fuel cells (MFCs) not only degrade pollutants but also convert chemical energy into electrical energy. Due to their multiple capabilities, MFCs have attracted widespread attention. Developing novel electrode materials is an effective means of increasing the power density and degradation rate of organic matter in MFCs.

[0004] Carbon aerogels (CAs) are a new class of porous carbon-based materials characterized by large surface area, high porosity, and excellent electrical conductivity. Formed by carbonizing fibrous materials, CAs possess excellent adsorption, energy storage, and catalytic properties. However, the preparation of CAs remains challenging, including manufacturing costs, redundant preparation processes, and toxic precursors, all of which limit their application. The readily available cellulose, a phenolic substance, offers the potential to reduce the cost and environmental impact of carbon aerogels. This is primarily due to the high reactivity of cellulose, which is attributed to the presence of various reactive functional groups, such as carboxyl, carbonyl, and hydroxyl groups. Similar to traditional porous carbon materials, cellulose-based porous carbon materials can also be manipulated at both the microscopic and macroscopic levels. Studies have shown that Fe₃O₄ doping can promote microbial growth and electrochemical activity. Fe₃O₄ nanoparticles not only enhance capacitance and electrochemical activity but also generate magnetic fields that affect the ion permeability of cell membranes, thereby enhancing biocatalytic processes. Electrode modifications based on carbon aerogel and Fe3O4 are more effective in improving conductivity and bioaffinity, while avoiding the toxicity of certain metal anodes (such as nickel foam) to microorganisms. Summary of the Invention

[0005] The purpose of the present invention is to provide a preparation method and application of a magnetic cellulose carbon aerogel composite electrode material. Using pulp as raw material, a porous magnetic cellulose carbon aerogel composite material is constructed. The aerogel is applied to a microbial fuel cell as a bioanode, which can not only improve the effect of degrading dimethyl sulfide, but also improve the output power.

[0006] In order to achieve the above-mentioned purpose of the invention, the technical solution adopted by this technology is:

[0007] A magnetic cellulose carbon aerogel composite electrode material, wherein the carbon aerogel has a specific surface area of 410-480m 2 / g, pore volume of 0.2-0.4 cm 3 / g, pore size is 5-10 nm.

[0008] Preferably, the specific surface area of the carbon aerogel is 440-445 m 2 / g, pore volume of 0.26-0.30 cm 3 / g, pore size is 6-7 nm.

[0009] The present invention also provides a method for preparing a magnetic cellulose carbon aerogel composite electrode material, the method comprising the following steps:

[0010] S1: Sodium hydroxide, urea and deionized water are mixed in a certain proportion, pre-cooled to -8°C to -16°C (preferably -12°C), the pulp is slowly added thereto and stirred evenly, and then epichlorohydrin is added for cross-linking;

[0011] S2: The obtained material is placed into a mold and aged at 60-80°C, and then replaced with deionized water until the pH is neutral to obtain a cellulose hydrogel;

[0012] S3: immersing the cellulose hydrogel in a ferric chloride solution at room temperature for 30-120 min to obtain an iron-loaded cellulose hydrogel;

[0013] S4: The hydrogel is freeze-dried to obtain cellulose aerogel, which is then carbonized to obtain a magnetic cellulose-carbon aerogel composite material.

[0014] The macroporous magnetic cellulose carbon aerogel prepared by the present invention is applied to microbial fuel cells. The large specific surface area is helpful to promote the formation of biofilm and the adsorption of dimethyl sulfide. The introduced Fe 3+ / Fe 2+ The redox couple can promote electron transfer. These properties enable the magnetic cellulose carbon aerogel anode to efficiently remove dimethyl sulfide and convert chemical energy into electrical energy.

[0015] Preferably, in step S1, the mass ratio of sodium hydroxide, urea, deionized water and pulp is 6-8:10-14:76-86:3-5 (more preferably 7:12:81:4).

[0016] Preferably, in step S1, the mass ratio of epichlorohydrin to cellulose is 1:2-6;

[0017] Preferably, the mold in step S2 is 3 cm*3 cm*1 cm polytetrafluoroethylene; the aging time is 6-8 h;

[0018] Preferably, the concentration of the ferric chloride solution in step S3 is 20-100 mM;

[0019] Preferably, the freeze-drying step in step S4 is performed by freezing at -20 to -193°C for 2 to 6 hours, and then freeze-drying for 36 to 54 hours to remove moisture;

[0020] Preferably, in step S4, the heating rate is 5-10°C / min, and the carbonization temperature is 700-900°C;

[0021] More preferably, the carbonization is performed in an inert atmosphere such as nitrogen or argon.

[0022] Preferably, the mass ratio of iron element to carbon element in magnetic cellulose carbon aerogel is m Fe :m C 1:20-100.

[0023] The present invention also provides an application of the magnetic cellulose carbon aerogel in a microbial fuel cell, wherein the magnetic cellulose carbon aerogel is used as a binder-free electrode in the microbial fuel cell to degrade dimethyl sulfide.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] The present invention uses pulp as raw material to construct a porous magnetic cellulose carbon aerogel composite material, and applies the aerogel to a microbial fuel cell as a bioanode, which can not only improve the effect of degrading dimethyl sulfide, but also improve the output power.

[0026] This invention uses natural pulp as a precursor to prepare a cellulose hydrogel via a sol-gel method. This hydrogel is then impregnated with ferric chloride, freeze-dried, and finally pyrolyzed in a tubular furnace to produce a magnetic cellulose carbon aerogel (CA@Fe3O4) composite material. This magnetic cellulose carbon aerogel exhibits high surface area, good electrical conductivity, and excellent biocompatibility. Used as the anode in microbial fuel cells, it can degrade dimethyl sulfide while converting chemical energy into electrical energy, enabling the renewable utilization of organic matter. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 XRD patterns of CA@Fe3O4 prepared at different temperatures in Example 1;

[0028] Figure 2 This is a graph showing the test results of the hysteresis loop test of the magnetic carbon aerogel in Example 1;

[0029] Figure 3 Schematic diagram of the MFC reactor in Example 2;

[0030] Figure 4 ab are scanning electron micrographs of the magnetic cellulose carbon aerogel bioanode before and after biofilm formation in Example 2;

[0031] Figure 5 1 is a cyclic voltammetry curve of different bioanodes in Example 2;

[0032] Figure 6 Output voltage diagram of the magnetic cellulose carbon aerogel bioanode at different stages in Example 2;

[0033] Figure 7 1 is a graph showing the power density curves and polarization curves of different bioanodes in Example 2;

[0034] Figure 8 is a performance diagram of the treatment effect of dimethyl sulfide by different microbial fuel cells in Example 3;

[0035] Figure 9 This is a diagram of the intermediate products during the DMS degradation process in Example 3. DETAILED DESCRIPTION

[0036] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0037] Example 1:

[0038] A method for preparing a magnetic cellulose carbon aerogel (CA@Fe3O4) composite material, comprising the following steps:

[0039] (1) 12 g, 7 g, and 81 g of NaOH, urea, and deionized water were thoroughly mixed in a beaker. The beaker containing the mixed solution was then pre-cooled at -12°C for 20 min. 4 g of crushed pulp (bleached kraft softwood pulp, Dalian Yangrun Trading Co., Ltd.) was slowly added to the mixed solution for dissolution. The mixture was then magnetically stirred for 2 h. 1 mL of epichlorohydrin was added and stirred for 1 h for cross-linking.

[0040] (2) The above materials were transferred into a 2.5 cm × 2.5 cm × 1 cm polytetrafluoroethylene mold, and then aged at 80 °C for 8 h. The materials were taken out and regenerated several times with deionized water until the pH was neutral to obtain a cellulose hydrogel.

[0041] (3) Add 1.5 g of FeCl3·6H2O to 100 mL of deionized water to obtain a 56 mM FeCl3 solution. Immerse the above hydrogel in the FeCl3 solution for 1 h.

[0042] (4) The impregnated hydrogel was frozen at -80°C for 4 h and then freeze-dried at -60°C for 48 h to obtain cellulose aerogel.

[0043] (5) The cellulose aerogel obtained in step (4) was placed in a tubular furnace and pyrolyzed under an argon atmosphere for 2 h. After the tubular furnace was evacuated, argon was introduced at a rate of 100 mL / s, and the temperature was raised to 800°C at a rate of 5°C / min and maintained at that temperature for 2 h. The temperature was then naturally cooled to room temperature (25°C), thereby obtaining a black magnetic cellulose carbon aerogel sample. In other embodiments of the present invention, the pyrolysis temperature may also be 600, 700, or 900°C. Figure 1 The XRD patterns of CA@Fe3O4 prepared at different temperatures show that Fe3O4 is successfully loaded on the carbon aerogel. To explore the magnetic properties of magnetic cellulose carbon aerogel, the carbon aerogel (CA) and magnetic cellulose carbon aerogel (CA@Fe3O4) prepared in Example 1 were subjected to hysteresis loop tests. The test results are shown in Figure 2. Figure 2 As shown by Figure 2 It can be seen that the magnetization intensity of CA@Fe3O4 is significantly enhanced compared with CA, and the magnetic saturation value reaches 53 emu / g.

[0044] The CA@Fe3O4 anode for microbial fuel cells prepared in this invention offers advantages such as low production cost, easy availability, good mechanical strength, and excellent biocompatibility. The large pores of the three-dimensional cellulose aerogel provide numerous active sites for microbial growth, making it suitable for biological growth. The carbonized aerogel also exhibits excellent electrical conductivity. The presence of Fe(II) / Fe(III) not only improves the anode's electron transfer capacity but also facilitates the formation of biofilms.

[0045] The microbial fuel cell based on the microbial fuel cell anode has excellent ability to degrade methyl sulfide and excellent electricity generation performance.

[0046] Example 2: Power Generation Performance of MFC Anodes Using Fe3O4 / Cellulose-Derived Carbon Aerogels

[0047] The present invention is applied to a dual-chamber MFC reactor using dimethyl sulfide as a substrate, and has achieved good results. Specific examples are described below:

[0048] In this embodiment, Nafion 117 proton exchange membrane is used to separate the microbial fuel cell. The schematic diagram of the MFC reactor is as follows: Figure 3 As shown, the reactor used CA@Fe3O4 electrode as the bioanode, Ag / AgCl as the reference electrode, and carbon cloth (CC) as the cathode. The anode electrode of the control group was carbon cloth and cellulose carbon aerogel electrode (CA) without iron loading.

[0049] The anode liquid in the anode chamber is an inorganic salt solution. The exogenously added carbon source is divided into three stages as the reaction proceeds. The carbon source in the first stage is 250 mg / L sodium acetate; the carbon source in the second stage is 50 mg / L dimethyl sulfide and 250 mg / L sodium acetate; the carbon source in the third stage is 50 mg / L dimethyl sulfide. Each stage runs for three cycles.

[0050] The cathode liquid in the cathode chamber is a potassium ferrocyanide buffer solution, and the positive and negative electrodes are connected to an external circuit through a platinum electrode clamp to form a closed loop.

[0051] In this example, anaerobic sludge from a sludge plant is first inoculated at a volume ratio of 20%. 250 mg / L sodium acetate is also added as a carbon source to allow the bacteria to form biofilms on the anode of the microbial fuel cell. The microbial fuel cell anode operates at a temperature of 30°C. When the anode voltage of the microbial fuel cell drops below 50 mV, it is considered the end of a cycle and the feedstock needs to be replaced to maintain biofilm growth and the normal operation of the reactor. The specific replacement method is to drain 1 / 3 to 1 / 2 of the original solution in the reactor and replenish it with an inorganic salt solution containing sodium acetate. The microbial fuel cell anode biofilm formation requires 2 to 3 cycles, during which the reactor output voltage needs to be regularly observed.

[0052] When the maximum output voltage of the reactor is ≥0.6 V for three consecutive cycles, it means that the anode membrane has been successfully formed, and then all the anode liquids are replaced. The external circuit voltage with different carbon sources as substrates is measured by a paperless recorder to evaluate the power generation performance of the reactor.

[0053] After the operation, the bioanode CA@Fe3O4 biofilm was collected and the microbial morphology was observed using a scanning electron microscope.

[0054] Figure 4 a is the surface of CA@Fe3O4 electrode before acclimation, where a uniform pore size distribution can be observed. Figure 4b shows the electrode surface after microbial domestication. A large number of microorganisms, primarily rod-shaped, have accumulated on the anode surface. The abundance of microorganisms on the anode surface indicates successful microbial domestication in the MFC system.

[0055] In this embodiment, microorganisms act as anode catalysts to oxidize dimethyl sulfide through an oxidation reaction, and the redox characteristics of the bioanode surface are analyzed by cyclic voltammetry curves. Figure 5 The cyclic voltammograms for the three bioanodes are shown below. The figure shows a redox front at -0.3 V, indicating that the redox performance of CA@Fe3O4 is significantly superior to that of CC and CA. Furthermore, the area enclosed by the CV curve represents the capacitance of the bioanod. The area of the CV curve for the bioanod after acclimation of CA@Fe3O4 is significantly larger than that for CC and CA, indicating that CA@Fe3O4 has good bioactivity and is a good charge carrier.

[0056] In this case, the power generation performance of a microbial fuel cell is evaluated by monitoring its output voltage and power density.

[0057] Figure 6 This is the output voltage performance diagram of different substrates when CA@Fe3O4 is used as the bioanode. It can be seen from the figure that in the first stage, when sodium acetate is used as the substrate, the maximum output voltage is 0.68 V, and it can continue to operate for 3 days in the plateau period; in the second stage, when dimethyl sulfide and sodium acetate are used as substrates, the maximum output voltage drops from 0.68 V to 0.62 V. Due to the certain biological toxicity of dimethyl sulfide, the output voltage drops. At the same time, this stage is also the stage of acclimating active bacteria that degrade dimethyl sulfide; in the third stage, when dimethyl sulfide is used as the substrate, the maximum output voltage is 40 mV, and the output voltage is relatively stable within three cycles, indicating that the degradation performance of the biofilm for dimethyl sulfide has reached a stable state.

[0058] Figure 7 The output power density diagram of the experimental group and the control group in the third stage and the third cycle, the highest output density of the different anode CC, CA, CA@Fe3O4 electrodes are 43.07 mW / m 2 、37.30 mW / m 2 、19.16 mW / m 2 , and the corresponding area current density is 231.74 mW / m 2 、215.79 mW / m 2 、109.17 mW / m 2 , CA@Fe3O4 electrode is significantly better than the other two groups.

[0059] In addition, in this embodiment, the composition of the inorganic salt buffer solution is: 32.2 mM Na2HPO4, 17.8 mM NaH2PO4·2H2O, 1.7 mM KCl, 5.8 mM NH4Cl, and the solvent is deionized water.

[0060] Example 3: MFC degradation effect of dimethyl sulfide

[0061] In this embodiment, the reactor was operated based on the reactor acclimated in Example 2. An anolyte containing 50 mg / L dimethyl sulfide as the carbon source was added to the anode chamber of the reactor, and a potassium ferrocyanide buffer solution was used as the cathode liquid. The cathode and cathode were connected to an external circuit via a platinum electrode clamp to form a closed loop.

[0062] As in Example 2, the control group was set up with the anode electrode being carbon cloth and cellulose carbon aerogel, and the experimental group was set up with the anode electrode being magnetic cellulose carbon aerogel (CA@Fe3O4).

[0063] During operation, the methyl sulfide in the reactor was monitored every 5 hours by gas chromatography. The monitoring results were as follows: Figure 8 shown. Figure 8 The figure shows the degradation rate of dimethyl sulfide treated with different reactors. The CA@Fe3O4 electrode can completely degrade dimethyl sulfide in the 16th hour, which is 2 times higher than CC and 1.5 times higher than CA. Figure 9 This is the intermediate product diagram of the degradation process of dimethyl sulfide. The intermediate products of the reaction process metabolism are mainly SO4 2- 、S 0 、S 2- As the reaction proceeds, DMS gradually decreases and SO4 2- It is the main intermediate product and has a large growth rate.

[0064] The contents described in this specification are merely an enumeration of implementation forms of the inventive concept, and the protection scope of the present invention should not be considered as being limited to the specific forms described in the embodiments.

Claims

1. A method for preparing a magnetic cellulose carbon aerogel composite electrode material, characterized in that: The steps include: S1: Sodium hydroxide, urea and deionized water are mixed evenly, pre-cooled to -8°C to -16°C, pulp is added and stirred evenly, and then epichlorohydrin is added for cross-linking to obtain a material; The mass ratio of the sodium hydroxide, urea, deionized water and pulp is (6-8): (10-14): (76-86): (3-5); The mass ratio of epichlorohydrin to pulp is 1: (2-6); S2: The obtained material is put into the mold and aged at 60-80℃ for 6-8h, then Deionized water is replaced to neutrality to obtain cellulose hydrogel; S3: immersing the cellulose hydrogel in a ferric chloride solution for 30-120 min to obtain a cellulose hydrogel loaded with ferric chloride; The concentration of the ferric chloride solution is 20-100 mM; S4: freeze-drying the ferric chloride-loaded cellulose hydrogel to obtain a cellulose aerogel, and then carbonizing it to obtain a magnetic cellulose-carbon aerogel composite electrode material; Freeze drying is as follows: first freeze at -20 to -193℃ for 2-6 hours, then freeze dry for 36-54 hours to remove moisture; The heating rate before carbonization is 5-10°C / min, the carbonization temperature is 700-900°C, and the carbonization time is 2h.

2. A use of the magnetic cellulose carbon aerogel composite electrode material prepared by the preparation method according to claim 1 in the preparation of a microbial fuel cell, characterized in that: The magnetic cellulose carbon aerogel composite electrode material is used as a binder-free electrode in a microbial fuel cell.

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