Binary pseudocapacitance composite material for promoting anaerobic digestion of kitchen waste as well as preparation method and application of binary pseudocapacitance composite material

Abstract

The invention discloses a binary pseudocapacitance composite material for promoting anaerobic digestion of kitchen waste and a preparation method and application thereof, and belongs to the technical field of organic solid waste recycling and renewable energy sources. The wood chip biochar-polydopamine-Fe3O4 composite material with a core-shell structure is constructed by taking wood chips as raw materials, preparing biochar through low-temperature pyrolysis, forming an interface modification layer through polydopamine coating, loading Fe < 3 + > and carrying out secondary pyrolysis to generate Fe3O4 nanoparticles (40-110nm). The material can be recovered through a magnetic field (the recovery rate is greater than or equal to 90%), when the dosage is 0.8-1.2 g / L, the peak value of volatile fatty acid in an anaerobic digestion system is obviously reduced to be less than or equal to 400 mg / L, the methane accumulation yield is improved to be greater than or equal to 45%, the electron transfer efficiency of acid-producing bacteria and methanogens is synchronously optimized, and the system operation is stabilized.

Description

Technical Field

[0001] This invention belongs to the field of organic solid waste resource utilization and renewable energy technology, specifically relating to a binary pseudocapacitor composite material that promotes anaerobic digestion of kitchen waste, its preparation method, and its application. Background Technology

[0002] With the rapid development of urban and rural economies and the continuous improvement of residents' consumption levels, the generation of kitchen waste and agricultural straw has been steadily increasing, becoming a significant challenge to environmental pollution and ecological governance. Anaerobic co-digestion technology, as a highly efficient and green method for the resource utilization of organic solid waste, can adjust the substrate carbon-to-nitrogen ratio to an ideal range, increase methane production, and reduce waste volume by mixing kitchen waste with agricultural straw. However, traditional anaerobic co-digestion technologies still suffer from problems in practical applications, such as low electron transfer efficiency, susceptibility to acidification and collapse, limited material functionality, and difficulties in recycling.

[0003] In existing technologies, to improve electron transfer efficiency, researchers have attempted to add exogenous conductive materials, such as iron-based materials (e.g., zero-valent iron, iron oxides) and carbon-based materials (e.g., activated carbon, biochar). For example, Chinese patent CN117620199A discloses a method for preparing nano-zero-valent iron biochar without the addition of a reducing agent. This method involves mixing iron salts and pretreated sawdust, followed by alkali modification and a single pyrolysis process (pyrolysis temperature below 800℃) to prepare nano-zero-valent iron-biochar. Although this method simplifies the preparation process, it has the following drawbacks: Particle agglomeration problem: Due to the lack of an effective interface modification layer, iron ions are prone to uneven adsorption and agglomeration during loading, resulting in uneven distribution of Fe3O4 particles and reducing the material's conductivity and electron transfer efficiency. Particle agglomeration also reduces the specific surface area, affecting the performance of pseudocapacitive properties.

[0004] Functional limitations: The single pyrolysis process cannot effectively control the porous structure, and the pores of biochar are easily blocked, limiting the electron buffering capacity; at the same time, a single material cannot synergistically solve the dual problems of low electron transfer efficiency and acidification inhibition.

[0005] Difficult to recycle: The material lacks magnetic design, making it difficult to separate efficiently from digested sludge, resulting in low recovery rates (typically <60%) and increased long-term application costs.

[0006] Therefore, developing a new type of composite material that can prevent particle agglomeration, achieve functional synergy, and is easy to recycle has become the key to breaking through the technological bottleneck. Summary of the Invention

[0007] In order to overcome the shortcomings of the prior art, the present invention aims to provide a binary pseudocapacitive composite material for promoting anaerobic digestion of kitchen waste, its preparation method and application, so as to solve the technical problems of Fe3O4 particle agglomeration, low electron transfer efficiency and difficulty in material recycling caused by the lack of interface modification layer in the prior art.

[0008] To achieve the above objectives, the present invention employs the following technical solution: This invention provides a method for preparing a binary pseudocapacitor composite material that promotes anaerobic digestion of kitchen waste, comprising the following steps: pretreated sawdust undergoes a first low-temperature pyrolysis under inert gas protection, and after cooling, sawdust biochar is obtained; dopamine is dissolved and added to the sawdust biochar to obtain a mixed solution; the pH of the mixed solution is adjusted to 8.0-9.0, and after stirring, a polydopamine interface modification layer is formed; then, the mixture is centrifuged and washed to obtain polydopamine-modified biochar; the polydopamine-modified biochar is added to FeCl3 solution, stirred and adsorbed, dehydrated and dried; and a second low-temperature pyrolysis is performed under inert gas protection to convert iron species into Fe3O4 and form a Fe3O4 particle loading layer on the polydopamine interface modification layer, finally obtaining a binary pseudocapacitor composite material with a sawdust biochar-polydopamine-Fe3O4 core-shell structure. Preferably, the temperature of the first low-temperature pyrolysis and the second low-temperature pyrolysis are both 400-600℃, the heating rate is both 5-7℃ / min, and the holding time is both 1.5-2.5 hours.

[0009] Preferably, the inert gas is nitrogen, and the gas flow rate is 70-90 mL / min.

[0010] Preferably, the dopamine is dissolved in a Tris-HCl buffer solution with a concentration of 8-12 mM, the mass ratio of dopamine to wood biochar is 1:1, and the volume ratio of biochar to Tris-HCl buffer solution is 5 g: (400-600) mL.

[0011] Preferably, after adjusting the pH value, the stirring speed is 120-180 rpm and the stirring time is 10-14 hours; the centrifugation speed is 7000-9000 rpm and the centrifugation time is 8-12 minutes.

[0012] Preferably, the ratio of polydopamine-modified biochar to FeCl3 solution is 1g:(80-120)mL, and the concentration of FeCl3 solution is 15-25 mM; after adding polydopamine-modified biochar to FeCl3 solution, the adsorption time is 1.5-2.5 hours; the dehydration and drying conditions include drying at 55-65℃ and a vacuum degree of -0.10 to -0.08 MPa for 5-7 hours.

[0013] Preferably, the pretreated wood chips are obtained by washing, drying, crushing, and then passing them through an 80-120 mesh sieve.

[0014] The present invention also provides a binary pseudocapacitor composite material obtained by the above preparation method. The composite material has a wood-biochar-polydopamine-Fe3O4 core-shell structure. The core layer is wood-biochar, and the shell layer is a functional shell composed of a polydopamine interface modification layer and an Fe3O4 particle loading layer. The Fe3O4 particles have a particle size of 40 nm to 110 nm.

[0015] Preferably, the composite material can be recycled by an external magnetic field with a magnetic field strength of 0.2-0.4 T and a recycling rate of ≥90%.

[0016] This invention also provides the application of the above-mentioned binary pseudocapacitive composite material in the anaerobic digestion system of food waste. The dosage is calculated based on the total effective volume of the anaerobic digestion reactor as 0.8 g / L - 1.2 g / L. It can be directly added through existing peristaltic pumps or automatic dosing devices without the need to add dispersants. After addition, the peak concentration of volatile fatty acids in the anaerobic digestion system is ≤400 mg / L, and the cumulative methane yield is ≥45% higher than that of the control group. The material can be recycled, and the functional retention rate is ≥88% after 5 cycles.

[0017] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a method for preparing a binary pseudocapacitive composite material that promotes the anaerobic digestion of food waste. It employs an innovative process route of "in-situ PDA interface modification - low-temperature secondary pyrolysis," avoiding the dependence on high-temperature equipment and high energy consumption problems of traditional high-temperature solid-state methods (secondary pyrolysis temperature 500℃). The introduction of the PDA modification layer enables Fe... 3+ The uniform adsorption of ions ensures a high-density and uniform loading of Fe3O4 particles on the WBC surface, and effectively prevents the migration and aggregation of micron-sized particles. The entire preparation process uses only environmentally friendly raw materials such as sawdust, dopamine, and ferric chloride, without involving the use or emission of toxic or harmful reagents, which is in line with the concepts of green chemistry and clean production. At the same time, the core raw material, sawdust, comes from agricultural waste and is inexpensive (about 0.5 yuan / kg), which greatly reduces the overall preparation cost of the material and makes it economically feasible for large-scale production.

[0018] Specifically, the PDA interface modification layer interacts with Fe through the amino (-NH2) and phenolic hydroxyl (-OH) functional groups on its surface. 3+ Ions coordinate with each other, achieving directional adsorption. This avoids Fe... 3+Ions randomly aggregate during loading, ensuring that Fe3O4 particles are uniformly dispersed at the nanoscale (40-110 nm) on the surface of the wood biochar. From a microscopic perspective, the PDA layer acts as a "molecular anchor," carbonizing and shrinking during secondary pyrolysis. This both fixes the Fe3O4 particles and re-exposes the porous structure of the wood biochar, preventing particle migration and aggregation. Compared to existing technologies (such as the single-stage pyrolysis method in CN117620199A), this method improves material stability through chemical modification rather than physical mixing.

[0019] Furthermore, the pyrolysis parameter range (temperature 400-600℃, heating rate 5-7℃ / min, holding time 1.5-2.5 hours) ensures the controllability and energy efficiency of the pyrolysis process. The lower limit of the temperature (400℃) avoids excessive energy consumption, while the upper limit (600℃) prevents excessive carbonization that could lead to pore blockage. The heating rate and holding time optimize the pyrolysis efficiency. As shown in the embodiments of this invention, within this range, the porous structure of the wood biochar is intact, and the Fe3O4 loading is uniform (as in Example 1, there is no particle agglomeration at 500℃), which directly supports the improvement of electron transfer efficiency and avoids the sintering problems of traditional high-temperature methods (1000-1500℃).

[0020] Furthermore, the inert gas parameters (nitrogen, flow rate 70-90 mL / min) prevent oxidation, and the gas flow rate range ensures a stable pyrolysis environment. Too low a flow rate may result in residual oxygen, while too high a flow rate wastes resources; the flow rate of 70-90 mL / min verified the material consistency in the embodiments of this invention, providing ideal conditions for the reduction and conversion of Fe3O4.

[0021] Furthermore, the dopamine concentration and mass ratio (8-12 mM concentration, 1:1 mass ratio) optimized the formation thickness and uniformity of the PDA layer. Too low a concentration (e.g., <8 mM) may result in incomplete coverage, while too high a concentration (e.g., >12 mM) would waste raw materials; the 1:1 mass ratio ensured sufficient bonding between the PDA and biochar.

[0022] Furthermore, stirring speed of 120-180 rpm and time of 10-14 hours ensure uniform dopamine self-polymerization, while centrifugation speed of 7000-9000 rpm and time of 8-12 minutes ensure thorough cleaning of the PDA layer. These range values ​​cover process tolerances and avoid Fe... 3+ Uneven adsorption. Example 1 of this invention (150 rpm, 12 hours) shows that the PDA coverage was complete under these conditions, supporting particle dispersion.

[0023] Furthermore, the FeCl3 concentration and adsorption time range ensured that Fe 3+ Sufficient but not excessive adsorption of ions; drying conditions to prevent material deformation, i.e., drying at 55℃ to avoid moisture residue, and drying at 65℃ to avoid over-drying.

[0024] Furthermore, the sawdust pretreatment sieving range ensures that the sawdust particles are uniform in size, and particles from 80 mesh (coarser) to 120 mesh (fineer) can form an ideal porous structure.

[0025] This invention also provides a binary pseudocapacitive composite material prepared by the above-mentioned method, which integrates three core functions: WBC has a rich porous structure and surface redox active functional groups; through PDA bonding and the synergistic effect of WBC and Fe3O4, the material is endowed with excellent pseudocapacitive properties, which can act as an "electron buffer" or "electron warehouse" to balance the electron generation and consumption rates between acid-producing bacteria and methanogens, and avoid system imbalance caused by electron accumulation; on the other hand, the highly dispersed Fe3O4 micron particles provide efficient electron transfer channels, significantly promote interspecies direct electron transfer (DIET), shorten start-up time, and improve methane yield and system operation stability. Practical application data shows that after adding this material, the cumulative methane production of the food waste and straw co-digestion system increased by 47.90% (reaching 601.32 mL / gVS), the maximum methane production rate increased by 26.30% (reaching 194.52 mL / (gVS·d)), the peak concentration of VFAs decreased by 41.26%, and the removal rates of total solids (TS) and volatile solids (VS) increased to 69.11% and 73.52%, respectively, effectively solving the problems of efficiency, stability and product conversion rate of traditional anaerobic co-digestion processes.

[0026] The material obtained by this invention has a particle size of 40 nm to 110 nm, possessing sufficient specific surface area to perform its function and being able to disperse naturally under the conventional hydraulic stirring action of anaerobic digestion systems, without the need for additional expensive dispersants or complex dispersion equipment. Furthermore, the material is in dry powder form, and its flowability, density, and other physical properties are fully compatible with commonly used automatic dosing systems in existing anaerobic digestion devices (such as powder feeders and peristaltic pump feeding systems). It can be directly added through existing dosing ports without any modification to the reaction tank structure, agitator type, or control system, significantly reducing the application threshold and equipment investment costs for users. In addition, the functional design of this material is universally applicable, not only suitable for the anaerobic co-digestion of kitchen waste and straw, but also applicable to anaerobic digestion treatment systems for various organic solid wastes such as municipal sludge, livestock and poultry manure, and fruit and vegetable waste, with a very wide range of market applications.

[0027] This invention also provides the application of the aforementioned binary pseudocapacitive composite material in an anaerobic digestion system for food waste. Due to the loading of magnetic Fe3O4 particles, the material prepared by this invention possesses excellent magnetic properties. After the anaerobic digestion process, only a common permanent magnet or electromagnet with a strength of 0.3 T needs to be installed at the reactor outlet or sludge pipeline to achieve efficient and rapid separation of the material from the digested sludge, with a recovery rate of over 92%, far exceeding that of traditional centrifugal or filtration separation methods (which typically have a recovery rate of <60%). The recovered material can be reused after simple deionized water washing and low-temperature drying. This characteristic reduces the unit cost of the material from 0.5 yuan / ton of solid waste for single use to less than 0.2 yuan / ton of solid waste after recycling, greatly improving the economics and long-term commercial application potential of this technology. Attached Figure Description

[0028] Figure 1 This is a SEM analysis image of the Fe3O4@WBC composite material of the present invention; wherein, Figure 1 (a) Wood chip biochar (WBC) with a porous structure Figure 1 (b) is polydopamine biochar (PDA@WBC). Figure 1 (c) is a Fe3O4@WBC composite material; Figure 2 The infrared spectra of WBC and Fe3O4@WBC in the Fe3O4@WBC composite material of the present invention are shown. Figure 3 The image shows the XPS characterization of the Fe3O4@WBC composite material of this invention; wherein, Figure 3 (a) is the C 1s spectrum. Figure 3 (b) is the O 1s spectrum. Figure 3 (c) is the Fe 2p spectrum. Figure 3 (d) is the full spectrum; Figure 4 The diagram shows the electrochemical performance of the Fe3O4@WBC composite material of this invention; wherein, Figure 4 (a) is the cyclic voltammetry curve. Figure 4 (b) For electron-donating and electron-acquiring capabilities, Figure 4 (c) represents electrical conductivity; Figure 5 This is a schematic diagram of the synthesis process of the Fe3O4@WBC composite material of the present invention; Figure 6 A schematic diagram of the anaerobic digestion system using the Fe3O4@WBC composite material of this invention; Figure 7(a) Daily methane production and (b) Cumulative methane production in the control group, WBC group, Fe3O4@WBC group and Fe3O4 group of the Fe3O4@WBC composite material of the present invention; Figure 8 The graph shows the combined performance of the blank control group, the group treated with single WBC, the group treated with single Fe3O4, and the group treated with the Fe3O4@WBC composite material prepared in Example 1 of this invention; wherein, Figure 8 (a) Changes in VFAs, pH, and NH4+-N in the blank control group. Figure 8 (b) Changes in VFAs, pH, and NH4+-N in a single WBC group. Figure 8 (c) Changes in VFAs, pH, and NH4+-N in the Fe3O4@WBC group prepared in Example 1. Figure 8 (d) Changes in VFAs, pH and NH4+-N in the group with a single Fe3O4 addition. Detailed Implementation

[0029] To enable those skilled in the art to understand the features and effects of the present invention, the following descriptions and definitions are only general descriptions of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in the event of any conflict, the definitions in this specification shall prevail.

[0030] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0031] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0032] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0033] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0034] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0035] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" represents weight percentage, "parts" represents parts by weight, and "ratio" represents weight proportion.

[0036] Example 1 This embodiment 1 provides a method for preparing Fe3O4@WBC binary pseudocapacitor composite material, including the following steps: 1) Raw material pretreatment: Take sawdust, wash, dry and crush it, then pass it through a 100-mesh sieve. Take the portion that passes through the sieve for later use to ensure the uniformity and dryness of the raw materials. 2) Preparation of WBC: Pretreated sawdust was placed in a tube furnace and heated to 500°C at a heating rate of 6°C / min under nitrogen protection, and held at that temperature for 2 hours to ensure complete pyrolysis and carbonization of the raw material. After pyrolysis, the system was cooled to room temperature, and the product was removed to obtain WBC. 3) Polydopamine (PDA) interface modification and Fe 3+ Adsorption: 5 g of dopamine was dissolved in 500 mL of 10 mM Tris-HCl buffer solution, and 5 g of WBC was added. The pH of the mixture was adjusted to 8.5. The mixture was stirred at 150 rpm for 12 h at room temperature to allow dopamine to self-polymerize and form a uniform PDA coating on the WBC surface. After the reaction was complete, PDA-modified biochar (PDA@WBC) was obtained by centrifugation at 8000 rpm for 10 min and washed three times with ultrapure water. The washed PDA@WBC was added to 20 mM FeCl3 solution and stirred at room temperature for 2 h to allow for complete adsorption of iron ions. 4) Low-temperature secondary pyrolysis to form Fe3O4@WBC: The product after adsorbing iron ions was dehydrated and dried, then placed in a tube furnace and heated to 500℃ at a heating rate of 6℃ / min under nitrogen protection and held for 2 hours. This secondary pyrolysis process realizes the carbonization and shrinkage of PDA and the conversion of Fe to Fe3O4, finally obtaining the binary pseudocapacitor composite material Fe3O4@WBC.

[0037] Example 2 This embodiment 2 provides a method for preparing Fe3O4@WBC binary pseudocapacitor composite material, including the following steps: 1) Raw material pretreatment: Same as in Example 1, the sawdust is washed, dried, crushed and then passed through a 100-mesh sieve; 2) Preparation of WBC: Pretreated wood chips were placed in a tube furnace and heated to 400°C at a heating rate of 5°C / min under nitrogen protection. The temperature was kept constant for 1.5 hours. After pyrolysis, WBC was obtained by cooling. 3) PDA interface modification and Fe 3+ Adsorption: 5 g of dopamine was dissolved in 500 mL of 8 mM Tris-HCl buffer solution, and 5 g of WBC was added to adjust the pH of the mixture to 8.0. The mixture was stirred at 120 rpm for 10 hours at room temperature to allow dopamine to self-polymerize and form a PDA coating. The mixture was centrifuged at 7000 rpm for 12 minutes and washed to obtain PDA@WBC. The PDA@WBC was then added to 15 mM FeCl3 solution and stirred for 1.5 hours for adsorption. 4) Low-temperature secondary pyrolysis: After adsorption, the product is dehydrated and dried, and then heated to 400℃ at a heating rate of 5℃ / min under nitrogen protection and held for 1.5 hours to obtain Fe3O4@WBC composite material.

[0038] Example 3 1) Raw material pretreatment: Same as in Example 1, the sawdust is washed, dried, crushed and then passed through a 100-mesh sieve; 2) Preparation of WBC: Pretreated sawdust was placed in a tube furnace and heated to 600°C at a heating rate of 7°C / min under nitrogen protection, and held at this temperature for 2.5 hours. WBC was obtained by cooling after pyrolysis. 3) PDA interface modification and Fe 3+ Adsorption: Dissolve 5 g of dopamine in 500 mL of 12 mM Tris-HCl buffer solution, add 5 g of WBC, and adjust the pH of the mixture to 9.0. Stir at 180 rpm for 14 hours at room temperature to allow dopamine to self-polymerize and form a PDA coating. Centrifuge at 9000 rpm for 8 minutes and wash to obtain PDA@WBC. Add PDA@WBC to 25 mM FeCl3 solution (maximum concentration) and stir for 2.5 hours (maximum time). 4) Low-temperature secondary pyrolysis: After adsorption, the product is dehydrated and dried, and then heated to 600℃ at a heating rate of 7℃ / min under nitrogen protection and held for 2.5 hours to obtain Fe3O4@WBC composite material.

[0039] Example 4 This embodiment 4 provides a method for preparing a binary pseudocapacitive composite material that promotes the anaerobic digestion of kitchen waste, including the following steps: 1) Wood chip pretreatment: Same as in Example 1, but after crushing, it is passed through an 80-mesh sieve; 2) Preparation of WBC: Under nitrogen protection, the temperature was increased to 500℃ at 6℃ / min and pyrolyzed for 2 hours; 3) PDA interface modification: Dopamine was dissolved in 10 mM Tris-HCl buffer, the pH was adjusted to 8.5, WBC was added and stirred at 120 rpm for 10 hours; centrifugation was carried out at 7000 rpm for 12 minutes. 4) Fe3O4 loading: FeCl3 concentration 15 mM, adsorption for 1.5 hours; dehydration and drying conditions: drying at 55℃ and vacuum degree -0.10MPa for 7 hours; secondary pyrolysis as in Example 1.

[0040] Example 5 This embodiment 5 provides a method for preparing a binary pseudocapacitive composite material that promotes the anaerobic digestion of kitchen waste, comprising the following steps: 1) Wood chip pretreatment: Same as in Example 1, but after crushing, pass through a 120-mesh sieve; 2) WBC preparation: Same as in Example 1; 3) PDA interface modification: After dopamine was dissolved, the pH was adjusted to 8.5, WBC was added, and the mixture was stirred at 180 rpm for 14 hours; centrifugation was carried out at 9000 rpm for 8 minutes. 4) Fe3O4 loading: FeCl3 concentration 25 mM, adsorption for 2.5 hours; dehydration and drying conditions: drying at 65℃ and vacuum degree -0.08MPa for 5 hours; secondary pyrolysis as in Example 1.

[0041] like Figure 1 As shown in the image, this figure reveals the microstructure of the material using scanning electron microscopy. It shows polydopamine (PDA) acting as a conductive medium covering the surface of porous wood biochar (WBC). After FeCl3 adsorption and secondary pyrolysis, the PDA layer carbonizes and shrinks, re-exposing the porous structure of the WBC. Simultaneously, iron ions are oxidized to form Fe3O4 micro-particles. The image clearly shows the uniform loading of Fe3O4 particles on the WBC surface, confirming that PDA modification effectively inhibits particle aggregation. For example, ... Figure 1 (a) shows wood chip biochar (WBC) with a porous structure; as shown Figure 1 As shown in (b), after being impregnated with dopamine solution, a polydopamine layer is formed on the surface of wood chip biochar (WBC), forming polydopamine biochar (PDA@WBC). Figure 1 As shown in (c), through the adsorption and secondary pyrolysis of FeCl3, the PDA layer undergoes carbonization and shrinkage, accompanied by redox reactions of iron species, which exposes the previously hidden pore structure and forms particulate Fe3O4. This achieves uniform loading of Fe3O4 nanoparticles on WBC, ultimately forming the Fe3O4@WBC composite material.

[0042] like Figure 2 As shown, the major functional groups of WBC and Fe3O4@WBC were analyzed by FTIR spectra. The major functional groups of WBC and Fe3O4@WBC were at 960 and 1056 cm⁻¹, respectively. 1 Characteristic absorption peaks of aliphatic groups and carbon skeleton CO bonds are present at 1393 cm⁻¹. 1 The position is a CH bond, at 3600 cm. 1 The position is an OH bond

[95] . 1605 cm 1 The C=O bond is a quinone compound. Studies have shown that the presence of such C=O bonds can also enhance the porous properties of biochar, thereby improving its adsorption capacity

[96] . In addition, only Fe3O4@WBC showed a 580 cm⁻¹ bond. 1 The Fe-O bond peaks indicate the presence of iron oxide on the surface of the biochar.

[0043] like Figure 3 As shown in the figure, the surface chemical composition of the material was characterized by XPS analysis. The C1s spectra of WBC and Fe3O4@WBC show characteristic peaks for CC / C=C, CO, and C=O at 284.4, 286.1, and 287.6 eV. The O1s spectra show that 530.2, 531.9, and 533.6 eV correspond to Fe-O, OH, and COC structures, respectively. The crucial Fe2p spectra show characteristic peaks at 710.2 eV and 723.4 eV, consistent with the standard Fe3O4 spectrum, confirming the successful loading of Fe3O4 onto biochar. Figure 3 As shown in (a), both WBC and Fe3O4@WBC exhibit similar carbon-oxygen functional groups, with characteristic peaks at binding energies of 284.4 eV, 286.1 eV, and 287.6 eV, respectively, corresponding to C / C=C bonds, CO bonds, and quinone-type C=O structures, which are consistent with the aliphatic CH, CO, and C=O vibrational signals detected by FTIR. Figure 3As shown in (b), the three characteristic peaks at binding energies of 530.2 eV, 531.9 eV and 533.6 eV can be attributed to the FO bond, the surface OH bond and the ether bond COC structure. Figure 3 (c) shows that splitting peaks appear at 710.2 eV (Fe 2p3 / 2) and 723.4 eV (Fe 2p1 / 2), and their binding energy positions and satellite peak characteristics are highly consistent with the standard spectrum of Fe3O4; Figure 3 (d) Display the full spectrum.

[0044] like Figure 4 As shown, the performance of the material was evaluated using electrochemical tests such as CV curves and chronoamperometry. Based on the original data, CV curve analysis showed that the pseudocapacitance of Fe3O4@WBC was 0.85 F / g, higher than the 0.69 F / g of the original WBC. Choroamperometry evaluation indicated that the electron-donating capacity (EDC) and electron-accepting capacity (EAC) of Fe3O4@WBC were 25.39 μmol e⁻¹. - / g and 273.40μmol e - The composite material exhibits a high degree of conductivity (14.35 μS / cm), significantly higher than the WBC's 3.42 μS / cm. These data directly demonstrate that the composite material possesses both excellent pseudocapacitive properties and electronic conductivity. Figure 4 As shown in (a), the pseudocapacitive properties of the three materials were evaluated using CV curves. The CV curves revealed differences in the redox properties of the functional groups in the different materials. The results showed that the pseudocapacitive properties of the three materials differed significantly, with the pseudocapacitive values ​​(quantified by the area under the curve) in the following order: Fe3O4@WBC (0.85 F / g) > WBC (0.69 F / g) > Fe3O4 (0.34 F / g). This indicates that the loading of Fe3O4 on WBC increases the number of redox functional groups to a certain extent, thereby increasing the pseudocapacitance. Simultaneously, the electron-donating capacity (EDC) and electron-accepting capacity (EAC) of the materials were evaluated using the chronoamperometry method. Figure 4 As shown in (b), the EDC / EAC ratios of WBC, Fe3O4@WBC, and Fe3O4 are 21.59 / 170.90, 25.39 / 273.40, and 11.49 / 45.00 μmol e, respectively. / g; Figure 4 As shown in (c), Fe3O4 (52.50 μS / cm) > Fe3O4@WBC (14.35 μS / cm) > WBC (3.42 μS / cm). Although the conductivity of Fe3O4@WBC is lower than that of Fe3O4, it is higher than that of WBC, indicating that the composite material significantly improves the conductivity of WBC by introducing Fe3O4. Figure 4(d) shows that Fe3O4@WBC increases both pseudocapacitance and conductivity, making it a highly efficient electron transport medium.

[0045] like Figure 5 As shown, the step-by-step synthesis route of the material is clearly demonstrated, including: preparation of the WBC substrate, interface modification of the WBC surface with PDA, and Fe... 3+ The adsorption and anchoring of ions in the PDA layer, and the eventual carbonization and shrinkage of the PDA and uniform loading of Fe3O4 particles through low-temperature secondary pyrolysis, form the final "wood biochar-PDA-Fe3O4" core-shell structure.

[0046] like Figure 6 The diagram shown is a schematic flow chart of an anaerobic digestion system using the materials of this invention; this schematic chart should clearly show the step-by-step synthesis route of the materials. It includes: preparation of the WBC substrate, interface modification of the WBC surface with PDA, and Fe... 3+ The adsorption and anchoring of ions in the PDA layer, and the eventual carbonization and shrinkage of the PDA and uniform loading of Fe3O4 particles through low-temperature secondary pyrolysis, form the final "wood biochar-PDA-Fe3O4" core-shell structure.

[0047] exist Figure 7 middle, Figure 7 As shown in (a), the daily methane production of all reactors exhibits a consistent trend, peaking on the second day after startup and then gradually declining due to the rapid consumption of readily degradable organic matter. This phenomenon indicates that the intervention of electroactive materials does not alter the basic degradation pathway of the substrate, but rather enhances the upper limit of energy conversion by improving electron transfer efficiency. Specifically, Figure 7As shown in (b), the cumulative methane yields of the blank control group, the group with single WBC, the group with Fe3O4@WBC composite material prepared in Example 1, and the group with single Fe3O4 were 406.58, 508.67, 601.32, and 448.73 mL / g VS, respectively. Compared with the blank control group, the cumulative methane yields of the group with single WBC, the group with Fe3O4@WBC composite material prepared in Example 1, and the group with single Fe3O4 increased by 25.11%, 47.90%, and 10.37%, respectively. It is worth noting that the group with Fe3O4@WBC composite material prepared in Example 1 not only significantly led in cumulative yield with 601.32 mL / g VS, but its maximum daily methane production rate (26.30% higher than the blank control group) further highlights the electronic mediation advantage of the composite material. This aligns with the findings of Deng et al.'s study on the enhancement of methane production using iron-coated biochar (500BC@Fe), validating the universality of the strategy of combining conductive materials with metal oxides. Deng et al.'s research showed that the addition of iron-coated biochar (500BC@Fe) prepared at 500℃ resulted in a 53.11% higher methane yield compared to the original biochar (500BC) group prepared at 500℃. The performance advantage of Fe3O4@WBC can be attributed to its combination of the pseudocapacitive properties of biochar and the high conductivity of Fe3O4. The synergistic effect of these two properties provides a highly efficient electron transport network for methanogens, ultimately leading to a significant increase in methane production.

[0048] The daily methane production of both the blank control group and the group with single WBC addition peaked on day 2, indicating a consistent substrate degradation pathway. However, the group with single WBC addition enhanced electron transfer, resulting in a cumulative methane production of 508.67 mL / g VS, which was 25.11% higher than the blank control group (406.58 mL / g VS), demonstrating the electronic regulation effect of biochar.

[0049] The daily methane yield trend of the Fe3O4@WBC composite material group prepared in Example 1 was the same as that of the blank control group. However, the composite material has both the pseudocapacitive properties of biochar and the conductivity of Fe3O4. Its cumulative methane yield reached 601.32 mL / gVS, which is 47.90% higher than that of the control group. The maximum daily methane production rate also increased by 26.30%, showing a significant synergistic effect.

[0050] The daily methane production of the Fe3O4-added group was consistent with that of the blank control group. The cumulative methane production was 448.73 mL / g VS, which was 10.37% higher than that of the blank control group, but weaker than that of the WBC group and the Fe3O4@WBC group.

[0051] like Figure 8As shown, bar charts or curves were used to compare the performance differences of the blank control group, the group with single WBC addition, the group with single Fe3O4 addition, and the group with Fe3O4@WBC composite material prepared in Example 1 of this invention in terms of cumulative methane production, methane production rate, VFAs concentration trend, and system pH stability, visually demonstrating the comprehensive advantages of the material of this invention. Among them, Figure 8 As shown in (a), during the anaerobic digestion process of the blank control group, the concentration of VFAs rose to 663.36 mg / L on day 4, with a high proportion of propionic acid and butyric acid. As VFAs accumulated, the pH dropped to 5.97, and the ammonia nitrogen concentration continued to rise to 283.25 mg / L, indicating a significant risk of acidification in the overall system. Figure 8 As shown in (b), the concentration of VFAs in the single WBC group decreased to 548.05 mg / L on day 4, and the pH recovery rate was better than that in the control group, which alleviated acidification. At the end of the reaction, the proportions of propionic acid and butyric acid (44.93% and 46.89%) were relatively high, and the final concentration of ammonia nitrogen was 258.62 mg / L, which was lower than that in the blank control group throughout the process. Figure 8 (c) shows that the addition of Fe3O4@WBC composite material prepared in Example 1 has the most significant effect on VFAs control, with only 389.68 mg / L on the 4th day, low proportions of propionic acid and butyric acid; pH is stable at 6.8~7.2 throughout the process, and the final concentration of ammonia nitrogen is 229.89 mg / L, indicating strong system stability. Figure 8 As shown in (d), the concentration of VFAs in the group with single Fe3O4 addition decreased to 653.91 mg / L on day 4, with a low proportion of propionic acid and butyric acid; the ammonia nitrogen control effect was the best, with a final concentration of only 202.52 mg / L, and the duration of acidification was shortened.

[0052] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for preparing a binary pseudo-capacitive composite material for promoting anaerobic digestion of food waste, characterized in that, The method comprises the following steps: The pretreated sawdust is subjected to first low-temperature pyrolysis under inert gas protection, and after cooling, sawdust biochar is obtained; after dopamine is dissolved, the sawdust biochar is added to obtain a mixed solution; the pH value of the mixed solution is adjusted to 8.0-9.0; after stirring, a polydopamine interface modification layer is formed; then centrifugal separation and washing are performed to obtain polydopamine-modified biochar; the polydopamine-modified biochar is added to an FeCl3 solution, stirring and adsorption are performed, and then dehydration and drying are performed; second low-temperature pyrolysis is performed under inert gas protection, so that the iron species is converted into Fe3O4 and a Fe3O4 particle loading layer is formed on the polydopamine interface modification layer; and finally, a binary pseudo-capacitive composite material with a sawdust biochar-polydopamine-Fe3O4 core-shell structure is obtained.

2. The production method according to claim 1, characterized by, The temperature of the first low-temperature pyrolysis and the second low-temperature pyrolysis is 400-600℃, the heating rate is 5-7℃ / min, and the holding time is 1.5-2.5 hours.

3. The production method according to claim 1, characterized by, The inert gas is nitrogen, and the gas flow rate is 70-90 mL / min.

4. The preparation method according to claim 1, characterized in that, The dopamine is dissolved in a Tris-HCl buffer solution with a concentration of 8-12 mM, the mass ratio of dopamine to sawdust biochar is 1:1, and the dosage ratio of biochar to Tris-HCl buffer solution is 5g:(400-600)mL.

5. The preparation method according to claim 1, characterized in that, After adjusting the pH value, the stirring speed is 120-180 rpm, and the stirring time is 10-14 hours; the centrifugal separation speed is 7000-9000 rpm, and the centrifugal separation time is 8-12 minutes.

6. The method of claim 1, wherein, The dosage ratio of the polydopamine-modified biochar to the FeCl3 solution is 1g:(80-120)mL, and the concentration of the FeCl3 solution is 15-25 mM; after adding the polydopamine-modified biochar to the FeCl3 solution, the adsorption time is 1.5-2.5 hours; and the dehydration and drying conditions include drying at 55-65℃ under a vacuum degree of-0.10 to-0.08 MPa for 5-7 hours.

7. The preparation method according to claim 1, characterized in that, The pretreated sawdust is washed, dried, crushed, and then sieved through an 80-120 mesh sieve.

8. The binary pseudocapacitive composite material prepared by the method of any one of claims 1-7, characterized in that, The composite material has a sawdust biochar-polydopamine-Fe3O4 core-shell structure, the core layer is sawdust biochar, the shell layer is composed of a polydopamine interface modification layer and a Fe3O4 particle loading layer to form a functional shell, and the particle size of the Fe3O4 particles is 40nm-110nm.

9. The binary pseudocapacitive composite material of claim 8, wherein, The composite material can be recycled by an external magnetic field, the magnetic field strength is 0.2-0.4 T, and the recovery rate is ≥90%.

10. The use of the binary pseudo-capacitive composite material according to claim 8 or 9 in an anaerobic digestion system of kitchen waste, characterized in that, The dosage is 0.8-1.2 g / L based on the total effective volume of the anaerobic digestion reactor, and is directly added by using an existing peristaltic pump or an automatic dosing device without adding a dispersant; after adding, the peak concentration of volatile fatty acids in the anaerobic digestion system is ≤400 mg / L, and the cumulative methane yield is increased by ≥45% compared with the blank group; the material can be recycled, and the functional retention rate is ≥88% after 5 cycles.

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