A composite metal-organic layer material and its preparation method, a method and system for preparing medium-chain fatty acids.

Abstract

This invention belongs to the field of organic waste resource utilization and clean energy biomanufacturing, specifically relating to a composite metal-organic layer material and its preparation method, as well as a method and system for preparing medium-chain fatty acids. The composite metal-organic layer material includes a substrate and a doped metal-organic layer material loaded on the surface of the substrate, wherein the dopant ions include Bi. 3+ Cd 2+ or S 2‑ Metal-organic layer (MOL) materials possess visible light-driven properties, significantly improving electron transfer efficiency, carbon source utilization, and carbon chain elongation conversion efficiency among microorganisms. MOL materials can stably generate photogenerated electrons under illumination and directly couple with extracellular electron transport proteins in functional bacterial communities, achieving highly efficient interspecies direct electron transfer. Ion doping further enhances the light absorption capacity and electron transport efficiency of MOL materials. CO2 is converted into methanol under photoelectrocatalysis, serving as an endogenous electron donor and eliminating the traditional dependence on exogenous electron donors such as ethanol and lactic acid.

Description

Technical Field

[0001] This invention belongs to the field of organic waste resource utilization and clean energy biomanufacturing, specifically involving a composite metal-organic layer material and its preparation method, as well as a method and system for preparing medium-chain fatty acids. Background Technology

[0002] Biomass waste includes agricultural waste (such as straw, fruit and vegetable residues, and livestock manure), kitchen waste, and other organic waste. Improper treatment can lead to resource waste and environmental pollution. Anaerobic fermentation, as a highly efficient biotechnology, can not only reduce and render harmless organic waste but also produce high-value-added bio-based chemicals. Medium-chain fatty acids (MCFAs), as potential biofuel precursors and chemical platform molecules, possess advantages such as high carbon energy density, strong antibacterial properties, and wide applicability, making them one of the most promising bio-based products.

[0003] While preliminary progress has been made in chain elongation (CE) technology, which extends short-chain fatty acids (SCFAs) into medium-chain fatty acids, key bottlenecks remain. First, this process heavily relies on exogenous electron donors such as ethanol and lactic acid, increasing operating costs and introducing byproducts (e.g., methane, propionic acid, and long-chain alcohols, which compete for electrons, leading to the production of medium-chain fatty acids instead of CE) and safety concerns. Second, electron transfer between microorganisms primarily occurs through soluble mediators such as hydrogen and formic acid, resulting in long and inefficient mass transfer pathways and low electron utilization, thus inhibiting product formation rates and final product concentrations. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a composite metal-organic layer material and its preparation method, as well as a method and system for preparing medium-chain fatty acids. The anaerobic fermentation preparation of medium-chain fatty acids using the composite metal-organic layer material of this invention eliminates the traditional dependence on exogenous electron donors such as ethanol, lactic acid, and hydrogen, and solves the problems of long mass transfer pathways and low efficiency.

[0005] This invention provides a composite metal-organic layer material, comprising a substrate and a doped metal-organic layer material loaded on the surface of the substrate;

[0006] The doped metal-organic layer material comprises a metal-organic layer material and dopant ions; the metal in the metal-organic layer material includes Zr or Ni, and the dopant ions include Bi. 3+ Cd 2+ or S 2- .

[0007] Preferably, the substrate includes FTO, ITO, Ti mesh, Ti foam, Ni foam, or stainless steel mesh.

[0008] Preferably, the loading of the metal-organic layer material on the substrate surface is 0.9~1.1 mg / cm³. 2 .

[0009] Preferably, the molar ratio of the metal-organic layer material to the doped ions in the doped metal-organic layer material is 100:(0.5~5).

[0010] This invention also provides a method for preparing the composite metal-organic layer material described in the above technical solution, comprising the following steps:

[0011] Doping is performed by mixing a metal-organic layer material with a doping ion solution to obtain a doped metal-organic layer material; the doping ions in the doping ion solution include Bi. 3+ Cd 2+ or S 2- ;

[0012] The doped metal-organic layer material is loaded onto the surface of a substrate to obtain the composite metal-organic layer material.

[0013] Preferably, the concentration of the doped ion solution is 0.01~0.05 mol / L; the doping is carried out under stirring and heating conditions, the stirring time is 3~5 hours, and the heating temperature is 50~70℃.

[0014] This invention also provides a method for preparing medium-chain fatty acids, comprising the following steps:

[0015] The biomass waste system is subjected to a first anaerobic fermentation to obtain a hydrolyzed acidified phase; the hydrolyzed acidified phase includes lactic acid and short-chain fatty acids;

[0016] Under photoelectric material catalysis and visible light irradiation, carbon dioxide is introduced into the hydrolyzed acidified phase, and a second anaerobic fermentation is carried out together with electroactive bacteria and carbon chain elongation bacteria; when the concentration of medium-chain fatty acids in the obtained fermentation broth exceeds 7 g / L, a portion of the fermentation broth is refluxed using a reflux device, and the remaining fermentation broth is collected to obtain medium-chain fatty acids.

[0017] The optoelectronic material includes the composite metal-organic layer material described in the above technical solution or the composite metal-organic layer material obtained by the above preparation method, as well as a carbon-based conductive base.

[0018] Preferably, the reflux ratio is 1:2 to 10.

[0019] Preferably, the volume ratio of the hydrolyzed acidified phase to the introduced carbon dioxide is 1~3:35~45.

[0020] The present invention also provides a system for preparing medium-chain fatty acids, comprising a first anaerobic fermentation device, a hydrolysis acidification phase storage device, a second anaerobic fermentation device, and a medium-chain fatty acid collection device connected in sequence.

[0021] The outlet of the second anaerobic fermentation device is also connected to a reflux device, and the outlet of the reflux device refluxes back to the hydrolysis acidification phase storage device;

[0022] The second fermentation device includes a fermenter, a photoelectric material, a visible light irradiation device, and a carbon dioxide aeration device disposed in the fermenter; the photoelectric material includes the composite metal-organic layer material described in the above technical solution or the composite metal-organic layer material obtained by the above preparation method, and a carbon-based conductive base.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] This invention provides a composite metal-organic layer material, comprising a substrate and a doped metal-organic layer material loaded on the surface of the substrate; the doped metal-organic layer material comprises a metal-organic layer material and dopant ions; the metal in the metal-organic layer material includes Zr or Ni, and the dopant ions include Bi. 3+ Cd 2+ or S 2- .

[0025] The composite metal-organic layer material of this invention includes a metal-organic layer material (MOL). MOL exhibits visible light-driven properties, significantly improving the electron transfer efficiency, carbon source utilization, and carbon chain elongation conversion efficiency among microorganisms in the fermentation system. Under light irradiation, the MOL material stably generates photogenerated electrons and directly couples with extracellular electron transport proteins in the functional bacterial community, achieving highly efficient direct interspecies electron transfer (DIET) and solving the problems of long mass transfer pathways and low yields. Ion doping further enhances the light absorption capacity and electron transport efficiency of the MOL material. CO2 is converted into methanol under photoelectrocatalysis, serving as an endogenous electron donor, thus eliminating the traditional dependence on exogenous electron donors such as ethanol and lactic acid.

[0026] The present invention also provides a method for preparing medium-chain fatty acids. By utilizing photoelectrocatalysis, photogenerated electrons and conductive metal layers, along with electroactive bacteria and carbon chain elongated microorganisms, can enhance the electron transfer efficiency of microorganisms through their own conductive flagella, thus constructing an efficient long electron transfer pathway.

[0027] This invention enhances the electron transfer efficiency of microorganisms using metal-organic layer materials, thereby increasing the yield of medium-chain fatty acids (MCFAs). By introducing carbon dioxide into the carbon chain elongation phase, photogenerated electrons drive the reduction of CO2 to methanol, which then acts as an endogenous electron donor alongside short-chain carboxylic acids in the chain elongation reaction. This further improves the product formation rate and selectivity, demonstrating a green, economical, and efficient synergistic energy supply mechanism.

[0028] In actual production, as the concentration of medium-chain fatty acids (MCFAs) increases, they exhibit strong toxic inhibitory effects on key functional microbial communities, affecting system stability and becoming a significant technical obstacle to industrial application. This invention, based on product concentration-controlled reflux, effectively alleviates the toxic inhibitory effects of MCFAs on microorganisms and significantly extends the system's stable operating cycle. When the MCFA concentration exceeds 7 g / L, the system automatically initiates reflux, proportionally refluxing a portion of the fermentation broth. This reflux mixes with the fermentation front-end (hydrolysis and acidification phase) and enters the carbon chain elongation phase, acting as a dilution and buffer, effectively maintaining the activity and metabolic flux of functional microbial communities. Compared to traditional single-phase or non-reflux systems, this invention allows for nearly twice the stable operating time, simultaneously improving MCFA yield and selectivity, and significantly enhancing system adaptability and engineering application potential. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a flowchart illustrating the preparation process of the composite metal-organic layer material in Example 1;

[0031] Figure 2 This is a flowchart of the preparation of medium-chain fatty acids in Example 3;

[0032] Figure 3 This is a schematic diagram of the fermentation apparatus used to prepare medium-chain fatty acids in Example 3. Detailed Implementation

[0033] This invention provides a composite metal-organic layer material, comprising a substrate and a doped metal-organic layer material loaded on the surface of the substrate;

[0034] The doped metal-organic layer material comprises a metal-organic layer material and dopant ions; the metal in the metal-organic layer material includes Zr or Ni, and the dopant ions include Bi. 3+ Cd 2+ or S 2- .

[0035] In this invention, the substrate preferably includes FTO (conductive glass), ITO, Ti mesh, Ti foam, Ni foam or stainless steel mesh, and more preferably FTO; the FTO has good light transmittance.

[0036] In this invention, the loading of the metal-organic layer material on the substrate surface is 0.9~1.1 mg / cm³. 2 Specifically, it can be 1 mg / cm³ 2 The loading amount described in this invention can ensure sufficient catalytic sites without blocking the light path, providing enough catalytic / electron generation sites to drive microbial coupling, ensuring good adhesion and electronic coupling between the MOL layer material and the conductive glass, and preventing peeling; at the same time, it avoids the decrease in light transmittance and increase in resistance caused by excessive thickness.

[0037] In this invention, the molar ratio of the metal-organic layer material to the doped ions in the doped metal-organic layer material is preferably 100:(0.5~5).

[0038] The composite metal-organic layer material described in this invention is an insertable photoelectric functional sheet structure metal-organic layer material with excellent photoelectrocatalytic performance.

[0039] This invention also provides a method for preparing the gold composite organic layer material described in the above technical solution, comprising the following steps:

[0040] Doping is performed by mixing a metal-organic layer material with a doping ion solution to obtain a doped metal-organic layer material; the doping ions in the doping ion solution include Bi. 3+ Cd 2+ or S 2- ;

[0041] The doped metal-organic layer material is loaded onto the surface of a substrate to obtain the composite metal-organic layer material.

[0042] Unless otherwise specified, all materials and equipment used in this invention are commercially available products in the field.

[0043] This invention involves mixing a metal-organic layer material with a doping ion solution to obtain a doped metal-organic layer material; the doping ions in the doping ion solution include Bi. 3+ Cd 2+ or S 2- .

[0044] In this invention, the method for preparing the metal-organic layer material preferably includes the following steps:

[0045] Under an inert atmosphere, a soluble metal salt, terephthalic acid, N,N-dimethylformamide, and formic acid are mixed and subjected to a solvothermal reaction to obtain a metal-organic framework (MOF) material with a layered structure; the soluble metal salt includes Zr salt or Ni salt.

[0046] The metal-organic framework material with a layered structure is dispersed in an alcohol-water solution and subjected to ultrasonic treatment. The resulting system is then mixed with polyvinylpyrrolidone and subjected to solid-liquid separation. The resulting liquid is dried to obtain the metal-organic layer material (MOL).

[0047] In this invention, the molar ratio of the soluble metal salt to terephthalic acid is preferably 0.9~1.1:0.9~1.1, specifically 1:1; the Zr salt preferably includes ZrCl4. The molar ratio described in this invention enables the production of MOF materials with a layered structure.

[0048] In this invention, the preferred ratio of terephthalic acid to N,N-dimethylformamide is 0.5 mmol: 25-35 mL, specifically 0.5 mmol: 30 mL.

[0049] In this invention, the preferred volume ratio of N,N-dimethylformamide to formic acid is 30:0.5. This invention uses formic acid as a regulator to control the crystal growth rate and morphology.

[0050] In this invention, the temperature of the solvothermal reaction is preferably 110~130℃, specifically 120℃, and the time is preferably 16~32 hours, specifically 24 hours. This invention controls the crystal growth direction of MOF materials by controlling the ratio of ligands and metal ions and the reaction temperature, thereby obtaining a layered precursor.

[0051] In this invention, the solvothermal reaction preferably further includes: solid-liquid separation, washing and drying the obtained solid; the washing preferably includes alternating DMF washing and ethanol washing; the drying temperature is preferably 60°C and the drying time is preferably 12 hours.

[0052] In this invention, the alcohol-water solution is preferably an ethanol-water solution, and the volume ratio of ethanol to water in the ethanol-water solution is preferably 1:1.

[0053] In this invention, the ultrasonic treatment power is preferably 300W, and the duration is preferably 30 minutes. The ultrasonic treatment can promote the separation of layered structures.

[0054] In this invention, the amount of polyvinylpyrrolidone added is preferably such that the final concentration of the resulting mixture is 0.5 wt%. The polyvinylpyrrolidone can prevent the agglomeration of nanosheets.

[0055] In this invention, the solid-liquid separation is preferably performed by centrifugation, with a preferred centrifugation speed of 3000 rpm and a preferred centrifugation time of 5 minutes. The metal-organic layer material (MOL) has a preferred thickness of 5-10 nm and a preferred lateral dimension of 0.5-2 μm, and is a two-dimensional single-layer MOL sheet with high dispersibility and high specific surface area.

[0056] In this invention, the doping ion is preferably Bi. 3+ .

[0057] In this invention, the concentration of the doped ion solution is preferably 0.01~0.05 mol / L. The doping is preferably carried out under stirring and heating conditions, with the stirring time preferably being 3~5 hours, specifically 4 hours, and the heating temperature preferably being 50~70℃, specifically 60℃. During the doping process, the doped ions are incorporated into the vicinity of the metal nodes or embedded in the interstices of the layered structure through electrostatic adsorption or coordination exchange.

[0058] In this invention, the doping process preferably further includes: solid-liquid separation, in which the obtained solid is washed and dried.

[0059] This invention enhances the light absorption and electron transport efficiency of MOL materials through ion doping. The introduction of Cd, Bi, and S elements for bandgap modulation and defect doping significantly improves their photoresponse efficiency and electron mobility. The doped MOL materials exhibit a large specific surface area (≥1000 m²). 2 / g), narrow bandgap (1.6~2.2 eV), high photocurrent density (≥0.5mA / cm²). 2 It possesses superior properties such as high structural flexibility and high interfacial contact efficiency compared to traditional MOF particle materials, significantly enhancing the extracellular electron transfer efficiency of microorganisms and making it an ideal material for electron power supply in photoelectric assisted anaerobic fermentation.

[0060] After obtaining the doped metal-organic layer material, the present invention loads the doped metal-organic layer material onto the surface of a substrate to obtain the composite metal-organic layer material.

[0061] In this invention, the loading method preferably includes drop coating, self-assembly, or sol-gel loading, with drop coating being the preferred method. This invention does not have special requirements for the drop coating method; methods commonly used by those skilled in the art can be employed. Specifically, a suspension of the doped metal-organic layer material at a concentration of 10 mg / mL can be drop-coated onto the substrate surface and then dried. The drying temperature is preferably 60°C, and the drying time is preferably 1 hour.

[0062] This invention also provides a method for preparing medium-chain fatty acids, comprising the following steps:

[0063] The biomass waste system is subjected to a first anaerobic fermentation to obtain a hydrolyzed acidified phase; the hydrolyzed acidified phase includes lactic acid and short-chain fatty acids;

[0064] Under photoelectric material catalysis and visible light irradiation, carbon dioxide is introduced into the hydrolyzed acidified phase, and a second anaerobic fermentation is carried out together with electroactive bacteria and carbon chain elongation bacteria; when the concentration of medium-chain fatty acids in the obtained fermentation broth exceeds 7 g / L, a portion of the fermentation broth is refluxed using a reflux device, and the remaining fermentation broth is collected to obtain medium-chain fatty acids.

[0065] The optoelectronic material includes the composite metal-organic layer material described in the above technical solution or the composite metal-organic layer material obtained by the above preparation method, as well as a carbon-based conductive base.

[0066] The present invention involves subjecting a biomass waste system to a first anaerobic fermentation to obtain a hydrolyzed acidified phase; the hydrolyzed acidified phase includes lactic acid and short-chain fatty acids.

[0067] In this invention, the biomass waste in the biomass waste system preferably includes silage straw, cow dung, and kitchen waste, with the preferred mass ratio of silage straw, cow dung, and kitchen waste being 4:3:3. The total solids content (TS) in the biomass waste system is preferably 15%, and the carbon-to-nitrogen ratio is preferably 20-25. The inoculum in the biomass waste system is preferably acclimated sludge that co-produces lactic acid / acetic acid, and the inoculum amount is preferably 20% (wet weight) of the substrate.

[0068] In this invention, the pH value of the first anaerobic fermentation process system is preferably 6.2~6.8, and the temperature is preferably 35~40℃.

[0069] After obtaining the hydrolyzed acidified phase, the present invention introduces carbon dioxide into the hydrolyzed acidified phase under photoelectric material catalysis and visible light irradiation, and carries out a second anaerobic fermentation together with electroactive bacteria and carbon chain elongation bacteria; when the concentration of medium-chain fatty acids in the obtained fermentation broth exceeds 7 g / L, a portion of the fermentation broth is refluxed using a reflux device, and the remaining fermentation broth is collected to obtain medium-chain fatty acids.

[0070] In this invention, the carbon-based conductive base preferably comprises carbon felt, carbon cloth, or carbon fiber felt. The carbon-based conductive base of this invention has good conductivity, which can improve the electron transport capability of the system. This invention combines a composite metal-organic layer material with a carbon-based conductive base (inserting the composite metal-organic layer material into the carbon-based conductive base), which can improve the photoelectrocatalytic effect and stability of the system.

[0071] In this invention, the composite metal-organic layer material is preferably rectangular, the fermentation tank is preferably cylindrical, the width of the rectangle is preferably 1 / 3 of the diameter of the fermentation tank, the length is preferably 4 / 5 of the height of the fermentation tank, and the length inserted into the liquid is preferably 65% ​​to 80% of the total length of the rectangle, inserted at a 15° angle.

[0072] In this invention, the wavelength of the visible light irradiation is preferably 400~700nm, and the light intensity is preferably 30~45mW / cm². 2 .

[0073] In this invention, the hydrolyzed acidified phase is preferably transferred to a fermenter and carbon dioxide is continuously introduced. The flow rate of the hydrolyzed acidified phase is preferably 1-3 mL / min, specifically 2 mL / min. The flow rate of the carbon dioxide gas is preferably 35-45 mL / min, specifically 40 mL / min.

[0074] In this invention, the electroactive bacteria are preferably... Geobacter The carbon chain elongating bacteria preferably include Clostridium kluyveri , Eubacterium limosum, Megasphaera elsdenii and Caproiciproducens The inoculum amount of the carbon chain elongating bacteria is preferably 25% (wet weight) of the substrate, and the inoculum amount of the electroactive bacteria is preferably 10% (wet weight) of the substrate; the pH value of the second anaerobic fermentation system is preferably 5.5~6.0, and the temperature is preferably 37~40℃.

[0075] In this invention, the reflux ratio is preferably 1:2 to 10, specifically 1:4 or 1:5; the reflux ratio is the ratio of the liquid volume of the refluxed carbon chain elongation phase to the liquid volume in the hydrolysis acidification phase storage device. This invention regulates the product concentration by adjusting the reflux ratio, diluting it with a new substrate before it enters the carbon chain elongation reaction section. This process effectively reduces the instantaneous concentration of MCFAs in the reactor, mitigating their interference with the membrane structure and metabolic pathways of functional microorganisms (such as Clostridium kluyveri and Eubacterium). Compared with traditional methods of inhibition mitigation such as adding emulsifiers, alkaline buffers, or changing substrates, this reflux regulation mechanism requires no additional additives, achieves continuous regulation, has minimal interference, and exhibits strong microbial stability, making it a green regulation method that achieves both high yield and high efficiency.

[0076] In this invention, after collecting the remaining fermentation broth, centrifugation and filtration are preferably further performed to obtain medium-chain fatty acids; the filtration is preferably performed using a 0.22 μm polyethersulfone filter membrane.

[0077] The present invention also provides a system for preparing medium-chain fatty acids, comprising a first anaerobic fermentation device, a hydrolysis acidification phase storage device, a second anaerobic fermentation device, and a medium-chain fatty acid collection device connected in sequence.

[0078] The outlet of the second anaerobic fermentation device is also connected to a reflux device, and the outlet of the reflux device refluxes back to the hydrolysis acidification phase storage device;

[0079] The second fermentation device includes a fermenter, a photoelectric material, a carbon dioxide aeration device, and a visible light irradiation device disposed in the fermenter; the photoelectric material includes the composite metal-organic layer material described in the above technical solution or the composite metal-organic layer material obtained by the above preparation method, and a carbon-based conductive base.

[0080] The system of the present invention is a dual-zone anaerobic fermentation system consisting of a hydrolysis acidification zone and a carbon chain elongation zone connected in series.

[0081] In this invention, the first fermentation device is equipped with stirring, temperature control, and pH adjustment modules to ensure efficient reaction operation. The first fermentation device is responsible for hydrolyzing substrates such as straw, manure, and fruit and vegetable residues into lactic acid and short-chain fatty acids.

[0082] In this invention, the carbon-based conductive base preferably comprises carbon felt, carbon cloth, or carbon fiber felt. The carbon-based conductive base of this invention has good conductivity, which can improve the electron transport capability of the system. This invention combines a composite metal-organic layer material with a carbon-based conductive base (inserting the composite metal-organic layer material into the carbon-based conductive base), which can improve the photoelectrocatalytic effect and stability of the system.

[0083] In this invention, a composite metal-organic layer material is inserted into the second fermentation device (in the carbon chain extension region), using carbon fiber as a conductive base; under visible light irradiation, photogenerated electrons are excited, and these electrons are directionally transferred to electroactive bacteria (such as...) through the conductive carbon fiber. Geobacter ), and then it interacts with carbon chain elongation bacteria (such as Clostridium kluyveri This method enables electron sharing and metabolic synergy, driving the reverse β-oxidation reaction of lactic acid and acetic acid (short-chain fatty acids); it effectively constructs a stable long-chain electron transport pathway, significantly enhancing the direct electron transport efficiency (DIET) between microorganisms, solving the problems of strong dependence on external electron donors and low electron utilization in traditional carbon chain extension technology, and realizing efficient and continuous synthesis of medium-chain fatty acids.

[0084] The second fermentation device is equipped with photoelectric materials and visible light irradiation devices. Under the condition of CO2 introduction, the MOL composite material photocatalytically reduces CO2 to produce methanol, which, together with lactic acid, acetic acid, etc., serves as a substrate for chain extension reaction to produce medium-chain fatty acids such as hexanoic acid and octanoic acid. This achieves functional coupling of biological hydrolysis-photocatalytic energy supply-chain extension, and has the advantages of modular structure, independent parameter adjustment, and flexible operation. The fermentation reaction path can be directionally controlled according to the substrate type and target product to improve the system yield and stability.

[0085] The high specific surface area of ​​metal-organic layer materials (MOLs) makes them suitable as microbial carriers, providing abundant attachment sites for chain-elongation functional microorganisms and enabling the construction of efficient and stable biofilms. Simultaneously, the excellent electron conductivity of MOLs significantly enhances the direct electron transfer efficiency (DIET) between microorganisms, overcoming the limitations of traditional mediators and improving the electron transport rate and utilization efficiency in fermentation systems. This invention introduces MOLs into carbon chain elongation systems, constructing a photoelectric-microbial synergistic conversion platform, which is expected to break through existing technological bottlenecks and promote the efficient and green synthesis of MCFAs.

[0086] To further illustrate the present invention, the composite metal-organic layer material and its preparation method, as well as the method and system for preparing medium-chain fatty acids provided by the present invention, are described in detail below with reference to the accompanying drawings and embodiments. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0087] Example 1 According to Figure 1 The flowchart shown illustrates the fabrication of insertable optoelectronic functional layer structures of metal-organic layer materials (i.e., composite metal-organic layer materials).

[0088] 1. Layered MOF Crystals: First, under an inert atmosphere (nitrogen), 0.5 mmol of ZrCl4 and 0.5 mmol of terephthalic acid (H2BDC) (molar ratio 1:1) were weighed and added to a three-necked flask. Then, 30 mL of N,N-dimethylformamide (DMF) was added as a solvent, along with 0.5 mL of formic acid. This mixture was reacted in an oil bath at 120°C for 24 hours to obtain Zr-MOF crystals with a regular layered structure. After alternating washing with DMF and ethanol, the crystals were vacuum dried at 60°C for 12 hours for later use.

[0089] 2. Metal-Organic Layer (MOL) Material: 0.2 g of the dried Zr-MOF crystals were redispersed in 20 mL of an ethanol-deionized water (volume ratio 1:1) mixture and sonicated for 30 minutes at a power of 300 W to promote the separation of the layered structure. To further stabilize the exfoliated sheet structure, polyvinylpyrrolidone (PVP, 100 mg) was added to the system at a final concentration of 0.5 wt% to prevent nanosheet aggregation. Then, the remaining unexfoliated crystals were separated by low-speed centrifugation (3000 rpm, 5 minutes), and the supernatant was collected, which was a suspension of monolayer MOL sheets with a thickness of approximately 5–10 nm and a lateral dimension of 0.5–2 μm.

[0090] 3. Bi 3+Ion doping: 20 mg of peeled, dried MOL sheet was added to 20 mL of ethanol solution containing 0.01 mol / L Bi(NO3)3·5H2O, and the mixture was magnetically stirred in a water bath at 60 °C for 4 hours. After doping, the sample was thoroughly washed with deionized water until neutral, and then vacuum dried at 60 °C to obtain doped Bi-MOL powder.

[0091] 4. Loading of doped metal-organic layer material: Take 50 mg of doped Bi-MOL powder and add 5 mL of DMF-ethanol (volume ratio 3:1) mixed solvent (i.e., the concentration of Bi-MOL powder in the mixed solvent is 10 mg / mL). Sonicate for 30 min to ensure uniform suspension and obtain a suspension.

[0092] The FTO glass was pretreated (surface roughening + plasma cleaning). The resulting suspension was drop-coated onto the treated FTO conductive glass surface, allowed to evaporate naturally, and then dried at low temperature (60℃) for 1 hour to form a photoelectric functional module with an insert structure, facilitating subsequent coupling to an anaerobic fermentation system (loading capacity of 1 mg / cm³). 2 The dry film thickness is approximately 5~10 μm.

[0093] The Bi-MOL material was characterized by UV-Vis diffuse reflectance, Mott-Schottky, and EIS, confirming that the band gap decreased from 2.4 eV to 1.8 eV after doping, and the photogenerated electron mobility was significantly improved, with the CO2 photoreduction to methanol rate reaching 28 μmol·g⁻¹. -1 ·h -1 The photocurrent density is increased by about 50%, providing continuous electronic support for the subsequent photoelectric coupled fermentation system.

[0094] Example 2

[0095] The only difference from Example 1 is that Cd is performed in step 3. 2+ Doping (i.e., replacing Bi(NO3)3·5H2O with Cd(NO3)2·4H2O), the remaining steps and conditions are the same.

[0096] Example 3 According to Figure 2 The flowchart shown uses Figure 3 The schematic diagram of the fermentation apparatus shown illustrates the anaerobic fermentation process for preparing medium-chain fatty acids.

[0097] 1. The anaerobic fermentation system is a two-phase fermentation system, consisting of a hydrolysis-acidification phase and a carbon chain elongation phase. The working volume of the hydrolysis-acidification phase is 3 L, and the working volume of the carbon chain elongation phase is 5 L.

[0098] The substrate for the hydrolysis-acidification phase was a mixture of silage straw, cow dung, and kitchen waste (mass ratio 4:3:3). The system TS=15%, and the system C / N ratio was maintained at 20-25. The inoculum contained... Lacticaseibacillus , Lentilactobacillus , Enterococcus , Streptococcus , Bifidobacterium , Escherichia-Shigella and Veillonella For the production of lactic acid and acetic acid, the sludge inoculum amount is 20% of the substrate weight (wet weight), the pH is stabilized at 6.2–6.8, the temperature is controlled at 35–40℃, and the hydraulic retention time (HRT) is 3 days. With the hydrolyzed acidified phase inoculated with acclimatized sludge, the system can achieve a directional acidification and synergistic production of 11.85–16.42 g / L / d of lactic acid and acetic acid during continuous fermentation.

[0099] The substrate for the carbon chain elongation phase is the hydrolyzed acidified phase, and the inoculum contains... Clostridium kluyveri and Eubacterium limosum , Megasphaera elsdenii, Caproiciproducens Domestication of sludge and electroactive microorganisms with chain-extended complex microbial communities ( Geobacter The inoculum amount of the carbon chain elongation complex microbial community for acclimatizing sludge is 25% (wet weight) of the substrate, and the electroactive microorganisms amount to 10% (wet weight) of the substrate. The pH value is kept stable at 5.5~6.0, and the temperature is controlled at 37~40℃. Both the hydrolysis acidification phase and the carbon chain elongation phase have stirring units to ensure uniform mixing of the reactants.

[0100] 2. Design of MOL photoelectrocatalytic unit: Four pieces of supported MOL conductive glass prepared in Example 1 were fixed at the bottom of the carbon chain extension phase (with carbon fiber as the conductive base), and irradiated with a visible light LED array (wavelength 400~700 nm, light intensity 30~45 mW / cm²). 2 Each piece of loaded MOL conductive glass is rectangular, with a width of 1 / 3 (8 cm) of the diameter of the cylindrical anaerobic fermenter and a length of 4 / 5 (8.8 cm) of the fermenter's height. The length inserted into the liquid is 65% of the total length, inserted at a 15° angle. A 12-hour light / 12-hour dark cycle is used, with the cycle synchronized with the fermentation cycle (hydraulic retention time (HRT) in the carbon chain elongation zone = 5 days).

[0101] 3. An external CO2 gas (flow rate 40 mL / min) is introduced as the carbon source. To enhance reduction efficiency, the system is equipped with a slow-bubbling CO2 supply module to maintain a certain solubility of CO2 gas in the liquid phase (>1 mM). MOL catalytically reduces CO2 to methanol under light irradiation. The hydrolyzed acidified phase is driven by a peristaltic pump and mixed into the carbon chain elongation zone at a flow rate of 2 mL / min. It works with chain elongation bacteria to efficiently synthesize medium-chain fatty acids. The system can achieve a hexanoic acid production efficiency of 3.5 g / L / d and an octanoic acid production efficiency of 0.68 g / L / d.

[0102] 4. An intelligent monitoring platform is installed at the outlet. Based on the concentration of MCFAs in the system, the reflux pump is intelligently proportionally controlled to reflux and dilute the fermentation broth containing MCFAs in the carbon chain extension zone at a certain ratio. The specific operation is as follows: When the concentration of MCFAs in the system exceeds 7 g / L, the system triggers the reflux pump to start through an online sensor. The fermentation broth rich in MCFAs is injected into the front-end hydrolysis acidification zone (HA zone, storage device) at a reflux ratio of 1:4~10. After being mixed evenly, it is refluxed back into the inlet of the carbon chain extension zone, keeping the MCFA concentration in the system fluctuating within the range of 3~6 g / L, which neither inhibits cell fermentation nor fails to ensure sufficient product accumulation for collection.

[0103] Example 4

[0104] The only difference from Example 3 is that the composite metal-organic layer material of Example 2 (i.e., the dopant element is Cd) is used. 2+ The system can achieve a hexanoic acid production efficiency of 3.23 g / L / d and an octanoic acid production efficiency of 0.617 g / L / d.

[0105] Comparative Example 1

[0106] The only difference from Example 3 is that the MOL photocatalytic unit is not added in step 2, CO2 gas is not introduced in step 3, and reflux is not performed in step 4. The other steps and conditions are the same. The system can achieve a hexanoic acid production efficiency of 2.614 g / L / d and an octanoic acid production efficiency of 0.52 g / L / d.

[0107] Comparative Example 2

[0108] The only difference from Example 3 is that the MOL photocatalytic unit is not added in step 2 and CO2 gas is not introduced in step 3. The other steps and conditions are the same. The system can achieve a hexanoic acid production efficiency of 2.655 g / L / d and an octanoic acid production efficiency of 0.529 g / L / d.

[0109] Comparative Example 3

[0110] The only difference from Example 3 is that CO2 gas is not introduced in step 3. The other steps and conditions are the same. The production efficiency of hexanoic acid can reach 3.34 g / L / d and the production efficiency of octanoic acid can reach 0.59 g / L / d.

[0111] Table 1 shows the specific statistical results of Examples 3-4 and Comparative Examples 1-3.

[0112] Table 1 Statistical results of Examples 3-4 and Comparative Examples 1-3

[0113]

[0114] The "MOL photocatalysis-two-phase fermentation-reflux regulation" coupled system constructed in Example 3 exhibited significant advantages in the synthesis of medium-chain fatty acids (MCFAs). Compared with Comparative Example 2 (lacking the MOL photocatalysis unit and CO2 aeration unit), the total yield of MCFAs in Example 4 increased by approximately 65% ​​(from 15.2 g / L to 25.1 g / L), the product selectivity increased from 52% to 78%, and the electron transfer efficiency significantly increased from 28.7% to 63.4%. The photogenerated electrons generated by the MOL material under visible light significantly enhanced direct electron transfer (DIET) between microorganisms, improving the functional microbial community (e.g., ...). Geobacter, Clostridium kluyveri It can increase the abundance of CO2 and efficiently reduce it to methanol, serving as a carbon source and electron donor for chain extension reactions, thereby further improving carbon conversion efficiency.

[0115] Compared to Comparative Example 1 (which lacked both a photoelectric system and reflux control and CO2 aeration unit), the MCFAs yield in Example 4 was almost doubled (from 12.3 g / L to 25.1 g / L), the system's stable operating period was extended from 30 days to nearly 60 days, and the microbial community activity maintenance capacity was improved by more than 70%. Furthermore, the system maintained good functional expression even in the later fermentation stage (after 48 days of stable operation). By initiating a constant-ratio reflux when the MCFA concentration exceeded 7 g / L, the product inhibition effect was controlled, and the system's toxicity pressure was significantly alleviated. Electrochemical analysis showed a nearly 48% reduction in charge transfer resistance and an increase in carbon conversion efficiency from 27.6% to 54.9%, comprehensively demonstrating a significant improvement in efficiency, stability, and resource utilization.

[0116] This invention provides a highly efficient method for synthesizing medium-chain fatty acids by combining MOL photocatalytic materials with microbial anaerobic fermentation technology. By continuously supplying energy through photogenerated electrons, it eliminates dependence on exogenous electron donors and significantly enhances interspecies electron transfer capabilities of microorganisms, thereby increasing product yield and system stability, and achieving high-value resource utilization of agricultural waste. This invention provides a highly efficient medium-chain fatty acid synthesis process integrating MOL photocatalytic material preparation, conductive network construction, two-phase anaerobic fermentation, and product reflux regulation. First, a two-dimensional MOL photoelectric sheet that can be inserted into the fermentation broth was prepared by layered crystallization regulation, monolayer exfoliation, and elemental doping of the MOF precursor. Then, a long-chain electron transport pathway consisting of a carbon fiber conductive network, MOL material, and insertable electrodes was deployed in the carbon chain extension region, and electroactive bacteria and carbon chain extension bacteria were inoculated. Under visible light irradiation, photogenerated electrons generated by MOL were transferred to the electroactive bacteria along the conductive fiber network, and then sequentially to the chain extension bacteria, forming a stable long-chain electron transport system from light source drive to microbial metabolism. At the same time, lactic acid and short-chain fatty acids generated in the upstream hydrolysis and acidification zone, along with methanol generated by MOL reduction, entered this zone together to synergistically synthesize medium-chain fatty acids through reverse β-oxidation. Finally, by monitoring the product concentration online and dynamically refluxing a portion of the medium-chain fatty acid liquid back to the hydrolysis and acidification zone, the product concentration was controlled and the microbial activity was continuously guaranteed, ensuring the long-term, high-efficiency operation of the system.

[0117] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, not all embodiments. People can obtain other embodiments based on the present invention without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing medium-chain fatty acids, characterized in that, Includes the following steps: The biomass waste system is subjected to a first anaerobic fermentation to obtain a hydrolyzed acidified phase; the hydrolyzed acidified phase includes lactic acid and short-chain fatty acids; Under photoelectric material catalysis and visible light irradiation, carbon dioxide is introduced into the hydrolyzed acidified phase, and a second anaerobic fermentation is carried out together with electroactive bacteria and carbon chain elongation bacteria; when the concentration of medium-chain fatty acids in the obtained fermentation broth exceeds 7 g / L, a portion of the fermentation broth is refluxed using a reflux device, and the remaining fermentation broth is collected to obtain medium-chain fatty acids. The optoelectronic material includes a composite metal-organic layer material and a carbon-based conductive base; The composite metal-organic layer material includes a substrate and a doped metal-organic layer material loaded on the surface of the substrate; The doped metal-organic layer material includes a metal-organic layer material and doping ions; The metal in the metal-organic layer material includes Zr, and the dopant ions include Bi. 3+ or Cd 2+ .

2. The method according to claim 1, characterized in that, The substrate includes FTO, ITO, Ti mesh, Ti foam, Ni foam, or stainless steel mesh.

3. The method according to claim 2, characterized in that, The loading of the metal-organic layer material on the substrate surface is 0.9~1.1 mg / cm³. 2 .

4. The method according to claim 1 or 3, characterized in that, The molar ratio of the metal-organic layer material to the doped ions in the doped metal-organic layer material is 100:(0.5~5).

5. The method according to claim 1, characterized in that, The preparation method of the composite metal-organic layer material includes the following steps: Doping is performed by mixing a metal-organic layer material with a doping ion solution to obtain a doped metal-organic layer material; the doping ions in the doping ion solution include Bi. 3+ or Cd 2+ ; The doped metal-organic layer material is loaded onto the surface of a substrate to obtain the composite metal-organic layer material.

6. The method according to claim 5, characterized in that, The concentration of the doped ion solution is 0.01~0.05 mol / L; the doping is carried out under stirring and heating conditions, the stirring time is 3~5 hours, and the heating temperature is 50~70℃.

7. The method according to claim 1, characterized in that, The volume ratio of the hydrolyzed acidified phase to the introduced carbon dioxide is 1~3:35~45.

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