Honeycomb confined iron oxide for delaying passivation of iron oxide in anaerobic digestion reactor, preparation method and application thereof

Abstract

The invention provides a honeycomb-shaped confined iron oxide for delaying passivation of iron oxide in an anaerobic digestion reactor, and a preparation method and application thereof, and relates to the technical field of iron oxide enhanced anaerobic digestion. Nanoscale ferrihydrite is formed through the network chain confinement effect of polydopamine, micron-sized composite particles are prepared firstly, then the micron-sized composite particles formed by polydopamine and ferrihydrite are packaged in a honeycomb confinement structure formed by carbonized resin, and the honeycomb confinement iron oxide is obtained. The prepared honeycomb confinement iron oxide can effectively inhibit passivation of ferrihydrite in an anaerobic digestion reactor, formation of 36% of inert iron minerals can be reduced, and the reduction efficiency of ferric iron reaches 97%, so that the utilization efficiency of the iron oxide is improved. Meanwhile, when the honeycomb-shaped confined iron oxide is applied to anaerobic digestion, the degradation efficiency of organic matters and the yield of methane can be improved.

Description

Technical Field

[0001] This invention relates to the field of iron oxide enhanced anaerobic digestion technology, specifically to a honeycomb-shaped confined iron oxide that delays the passivation of iron oxides in an anaerobic digestion reactor, its preparation method, and its application. Background Technology

[0002] Anaerobic digestion, as a low-carbon and environmentally friendly technology, is widely used in the treatment of organic wastewater and waste. However, traditional anaerobic digestion technologies often face problems such as slow hydrolysis and acidification rates of organic matter, low methane conversion rates, and poor system stability.

[0003] Current research has found that adding iron oxides to anaerobic digestion systems can act as terminal electron acceptors to enrich iron-reducing bacteria, inducing dissimilar iron reduction (FIR) and enhancing the anaerobic digestion effect. This is because during FIR, iron-reducing bacteria obtain metabolic energy by reducing ferric iron (Fe3+) to ferrous iron (Fe2+), accelerating the metabolism of organic matter. Generally, amorphous iron oxides, such as ferrihydrite, are more conducive to inducing FIR due to their high redox potential, large specific surface area, and reactive properties, compared to crystalline iron oxides such as hematite and magnetite. However, in anaerobic reactors, conventional ferrihydrite is easily passivated, leading to incomplete reactions and reduced ferric iron utilization efficiency. The main reason is that the ferrous iron generated during FIR covers the surface of unreacted ferric iron, catalyzing the phase transfer process of ferrihydrite, inducing crystallization and surface passivation, and generating inert crystalline iron oxides. Passivation of ferrous oxide not only reduces the reduction efficiency of dissimilar iron, resulting in a waste of iron resources, but also causes passivated iron oxides to deposit in the reactor, leading to anaerobic sludge compaction and disrupting the stability of the anaerobic reaction. Therefore, preventing the adsorption of ferrous iron on the surface of ferric iron and isolating ferric iron from direct contact with each other are key measures to delay the phase transformation and passivation of iron oxides in the anaerobic system.

[0004] Currently, the following methods are commonly used to delay the passivation of iron oxides in anaerobic systems: (1) using organic compounds rich in hydroxyl or carboxyl functional groups, such as tannic acid and humic acid, to complex with ferrous iron and remove ferrous iron from the surface of the ferrous ore; (2) adding chelating agents such as ethylenediaminetetraacetic acid (EDTA) to solubilize the passivated iron oxides and promote their reduction by iron-reducing bacteria; (3) reducing the particle size of iron oxides to the nanoscale to increase the specific surface area of ​​iron oxides, thereby increasing the contact area and reactivity of the surrounding environment. The disadvantage of the above techniques is that the added organic chemical reagents usually form a core-shell structure with the ferrous ore, which can only protect the passivation of ferric iron on the surface and does not fundamentally solve the passivation problem of the ferrous ore. In addition, the added chemical reagents are easily degraded by microorganisms and flow out with the effluent, so they need to be added and replenished continuously, which is not economical.

[0005] In summary, there is an urgent need to study a new method to delay the passivation of iron oxides in order to solve the above problems. Summary of the Invention

[0006] To address the shortcomings of the prior art, the present invention aims to provide a honeycomb-shaped confined iron oxide, its preparation method, and its application, which delays the passivation of iron oxides in an anaerobic digestion reactor. The confining effect slows down the passivation of ferrous iron by divalent iron, allowing ferrous iron to be fully reduced to divalent iron, thereby improving the reduction efficiency of dissimilar iron in ferrous ore.

[0007] Specifically, in a first aspect, the present invention provides a honeycomb-shaped confined iron oxide that delays the passivation of iron oxides in an anaerobic digester, the honeycomb-shaped confined iron oxide being obtained by the following means: The carbonized resin is mixed with potassium hydroxide to form potassium oxide particles on and inside the carbonized resin. The potassium oxide particles are then peeled off from the carbonized resin to create pores on and inside the carbonized resin, resulting in a honeycomb confined structure. Polydopamine is polymerized in situ on the surface of ferrohydrate. The network of polydopamine is used to confine and encapsulate the nanoscale ferrohydrate to form micron-sized particles. During the formation process, polydopamine occupies the active sites on the surface of ferrohydrate, which can prevent the adsorption of free ferrous iron on the surface of ferrohydrate in the subsequent anaerobic digestion process. By encapsulating micron-sized composite particles formed by polydopamine and ferrohydrate within a honeycomb confinement structure, honeycomb confinement iron oxide is obtained. This isolates each micron-sized composite particle from the others, delaying the polymerization of ferrohydrate and preventing the formation of inert iron minerals.

[0008] When molecules are confined in a nanoscale space, they exhibit dynamic processes completely different from those in a free state due to the restriction of this space. In this invention, polydopamine is formed by the self-polymerization of dopamine monomers at room temperature. By adjusting the polymerization time of polydopamine, (sub)micron-scale spatial network structures of different sizes are formed in the microstructure, thereby generating a confinement effect. During this process, Fe ions are added, which can form Fe(III) particles of corresponding sizes within the spatial structure. This cage-like partition structure can encapsulate each Fe(III) particle in an independent space and generate a confinement effect on the Fe(III) inside, delaying the phase transfer of iron oxides. At the same time, polydopamine is rich in catechol and amino functional groups, and has adhesion properties similar to mussel adhesive proteins. It can form extremely stable monodentate or polydentate coordination with Fe(III), which can further isolate Fe(III) from each other in the cage-like structure. Therefore, even if Fe(III) is reduced to Fe(II) by microorganisms, it will not come into contact with other unreacted Fe(III), thus potentially solving the problem of Fe(II) catalyzing the passivation of Fe(III). Polydopamine is formed through the π-π conjugation of dopamine monomers. The resulting delocalized electrons endow PDA with good electrical conductivity, promoting electron transfer between microorganisms and internal iron oxides, improving iron reduction efficiency, and ensuring the smooth reduction of dissimilar iron within the PDA's confined structure.

[0009] Secondly, the present invention provides a method for preparing honeycomb-shaped confined iron oxides that delay the passivation of iron oxides in an anaerobic digestion reactor, comprising the following steps: Step S1: Prepare the honeycomb confinement structure, which specifically includes the following sub-steps: S11. Resin is prepared by mixing resorcinol as monomer, formaldehyde as crosslinking agent and initiator, and ammonia water as pH adjuster, and by controlling the heating temperature and time. S12. Powdered resin is obtained by centrifugation, deionized water washing and drying. Then, the powdered resin is pyrolyzed in an oxygen-deficient environment by controlling the reaction temperature to form carbonized resin. S13. The carbonized resin is mixed with potassium hydroxide and pyrolyzed under an oxygen-deficient environment by controlling the reaction temperature to form potassium oxide particles on and inside the carbonized resin, thus obtaining an alkalized resin. Then, the potassium oxide is corroded by an acidic solution to peel off the potassium oxide particles from the carbonized resin, thereby creating pores on and inside the carbonized resin. A honeycomb confined structure is obtained by washing with deionized water and drying, and is labeled as KC. Step S2: Preparation of ferrous ore: Prepare a ferric solution, then adjust the pH to 7 with an alkaline solution, stir at room temperature, and then let the precipitate stand and retain the precipitate; Step S3: Encapsulate the ferrohydrate within a honeycomb confinement structure, specifically including the following sub-steps: S31. Mix ethanol, deionized water and ammonia to obtain solution A; transfer all the precipitate containing ferrohydrate from step S2 to solution A and stir to form mixture B; S32. Dissolve dopamine hydrochloride in deionized water to obtain solution C; then add solution C to mixture B and stir to form a polydopamine-iron complex, labeled Fe@PDA, and the corresponding solution is labeled solution D; S33. The honeycomb confined structure obtained in step S1 is added to solution D and stirred. The encapsulated honeycomb confined iron oxide is obtained by centrifugation, deionized water washing and freeze drying, and labeled as Fe@PDA / KC.

[0010] Preferably, in step S11, resorcinol is prepared and formaldehyde solution is added to make the formaldehyde mass fraction 0.5%~0.6%, then ammonia water is added to make the ammonia water concentration 3%~4%, and the mixture is stirred for 0.5~1h; then the mixture is transferred to a sealed container and heated at 160℃ for 3-5h.

[0011] Preferably, in step S12, the heated solution is centrifuged to remove the supernatant and resuspended in deionized water. The above process is repeated three times. The final precipitate is dried at 60°C for 10-16 hours to obtain powdered resin. Then, the powdered resin is pyrolyzed at 450°C-550°C. Nitrogen gas is introduced during the pyrolysis process to maintain an anaerobic environment to obtain carbonized resin.

[0012] Preferably, in step S13, carbonized resin and potassium hydroxide are mixed in a mass ratio of 1:6 and placed in a quartz boat, and then pyrolyzed at 450℃~550℃. During the pyrolysis process, nitrogen gas is introduced to maintain an anaerobic environment to obtain alkalized resin. Then, the alkalized resin is soaked in a 3~6mol / L hydrochloric acid solution and stirred for 1~2h. After that, it is washed several times with deionized water to remove excess hydrochloric acid solution. Then, it is centrifuged to obtain a precipitate. The precipitate is dried at 60~80℃ to obtain a honeycomb confined structure, labeled as KC.

[0013] Preferably, in step S33, KC is added to solution D to make the KC mass concentration 5~7.5 g / L, and the mixture is stirred at room temperature for 24~30 h. Then, the mixture is centrifuged, the supernatant is discarded, and the mixture is resuspended in deionized water. This process is repeated three times to obtain a precipitate. The precipitate is freeze-dried to obtain a honeycomb confined iron oxide, labeled as Fe@PDA / KC.

[0014] Preferably, the iron salt in the ferric solution in step S2 is one or more of FeCl3, Fe(NO3)3, and Fe2(SO4)3.

[0015] Preferably, the honeycomb-shaped confined iron oxide in step S3 has the following characteristics: The mass ratio of polydopamine to ferrous sulfate is 1:1 to 5:1; KC has a porosity of 60-80% and an average pore size of 20-30 μm. Each Fe@PDA micron-sized particle has a size of 400~500nm and encapsulates 5~20nm ferrometallurgical crystals.

[0016] Thirdly, the present invention provides an application of a method for preparing honeycomb-shaped confined iron oxides that delays the passivation of iron oxides in an anaerobic digestion reactor. Applying honeycomb-shaped iron oxides to an anaerobic digestion system can delay the passivation of iron oxides.

[0017] Preferably, the application of honeycomb iron oxide in an anaerobic digestion system specifically involves: setting the concentration of introduced sludge at 10% to 20% in the anaerobic digestion reaction for treating organic wastewater, and adding 5 to 10 g / L of the honeycomb iron oxide material powder into the reactor.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The method of the present invention differs from the traditional method of adding organic complexing agents such as tannic acid and humic acid. The honeycomb confinement structure of the present invention delays the passivation of iron oxides in the anaerobic digestion reactor. It can utilize the small size structure of polydopamine to form a steric hindrance effect, which acts as a nano "shelter" to block external ferrous iron in a similar way to a spatial barrier, thus ensuring the activity and stability of the encapsulated ferrous iron. Ultimately, it prevents ferrous iron from adsorbing on the surface of ferric iron, effectively delaying the passivation of ferrous iron, allowing ferrous iron to be fully reduced to ferrous iron, thereby increasing the reduction rate of dissimilar iron.

[0019] (2) Although other studies have reduced the particle size of iron oxide to the nanoscale to increase the specific surface area of ​​iron oxide, or loaded nanoscale iron oxide onto the surface of biochar or other carbon materials, their purpose is to increase the contact area and reactivity of the surrounding environment. They cannot prevent the direct contact between ferrous and ferric iron, so they can only promote the utilization of ferric iron, but cannot prevent the catalytic passivation effect of ferrous iron on the phase transformation of ferric iron. The polydopamine used in this invention forms a very stable monodentate or polydentate coordination with Fe(III) through catechol and amino functional groups, which can further isolate ferrous and ferric iron in the cage structure. This not only increases the size and dispersion of nano-iron oxide, but also fundamentally solves the catalytic passivation effect of ferrous iron on the phase transformation of ferric iron.

[0020] (3) The polydopamine of the present invention is formed by the π-π conjugation of dopamine hydrochloride monomers. The generated delocalized electrons endow polydopamine with good electrical conductivity, which can mediate the electron transfer process between microorganisms and Fe(III), and ensure the smooth reduction of dissimilar iron within the confined structure.

[0021] (4) The honeycomb confinement material prepared by the present invention can further ensure that each ferrous ore nanoparticle is isolated from each other, prevent them from agglomerating, delay the formation of inert iron oxides, effectively inhibit the passivation phenomenon of ferrous ore in the anaerobic digestion reactor, and at the same time, when honeycomb confinement iron oxides are applied to anaerobic digestion, the degradation efficiency of organic matter and methane production can be improved, the formation of inert iron minerals can be reduced by 36%, the reduction efficiency of ferric iron can reach 97%, and the utilization efficiency of iron oxides can be significantly improved.

[0022] (5) The Fe@PDA / KC prepared by this invention is beneficial for enriching iron-reducing bacteria. Compared with other bacteria, iron-reducing bacteria can enhance the degradation of organic matter and improve the anaerobic digestion effect. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the honeycomb-shaped confined iron oxide preparation process of the present invention; Figure 2 This is a schematic diagram of the honeycomb confined iron oxide structure of the present invention; Figure 3 This is a morphology diagram of the honeycomb confinement material KC prepared in Example 1 of the present invention; Figure 4 This is a morphology diagram of the polydopamine-iron complex, Fe@PDA, prepared in Example 1 of this invention. Figure 5 This is a graph showing the dissolution rate of divalent iron in conventional ferrous ore and Fe@PDA / KC in Example 2 of this invention; Figure 6 This is a graph showing the iron reduction rate of conventional ferroalloy and Fe@PDA / KC in Example 2 of the present invention. Figure 7 This is a schematic diagram showing the form and proportion of iron oxide in the reactor after the reaction in Example 2 of the present invention; Figure 8 This is a comparison chart of the organic matter removal rate of wastewater in the reactor in Example 2 of the present invention; Figure 9 This is a comparison chart of methane production in the reactor in Example 3 of the present invention; Figure 10 This is a comparison diagram of sludge reduction in the reactor in Embodiment 3 of the present invention. Detailed Implementation

[0024] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0025] Specifically, in a first aspect, the present invention provides a honeycomb-shaped confined iron oxide that delays the passivation of iron oxides in an anaerobic digester, the honeycomb-shaped confined iron oxide being obtained by the following means: A carbonized resin is mixed with potassium hydroxide to form potassium oxide particles on and inside the carbonized resin. The potassium oxide particles are then peeled off from the carbonized resin to create pores on and inside the resin, resulting in a honeycomb confined structure.

[0026] Polydopamine is polymerized in situ on the surface of ferrohydrate, and the network of polydopamine is used to confine and encapsulate nanoscale ferrohydrate to form micron-sized particles. In this process, polydopamine can prevent the adsorption of free ferrous iron on the surface of ferrohydrate by occupying the active sites on the surface of ferrohydrate in the subsequent anaerobic digestion process.

[0027] By encapsulating micron-sized composite particles formed by polydopamine and ferrohydrate within a honeycomb confinement structure, honeycomb confinement iron oxide is obtained. This isolates each micron-sized composite particle from the others, delaying the polymerization of ferrohydrate and preventing the formation of inert iron minerals.

[0028] Secondly, the present invention provides a method for preparing honeycomb-shaped confined iron oxides that delay the passivation of iron oxides in an anaerobic digestion reactor, such as... Figure 1 and Figure 2 As shown, it includes the following steps: Step S1: Prepare the honeycomb confinement structure, which specifically includes the following sub-steps: S11. Resorcinol is used as a monomer, formaldehyde as a crosslinking agent and initiator, and ammonia as a pH adjuster. The resin is prepared by controlling the heating temperature and time. In one embodiment, the process is as follows: prepare 2.75 g / L of resorcinol, then add formaldehyde solution to make the formaldehyde mass fraction 0.5%~0.6%, then add 30% ammonia water to make the ammonia concentration 3%~4%, and then stir the mixture for 0.5~1 h; transfer the mixture from step S1 into a polytetrafluoroethylene container and seal it, then heat it at 160°C for 3-5 h, preferably 4 h.

[0029] S12. Powdered resin is obtained through centrifugation, washing with deionized water, and drying. The powdered resin is then pyrolyzed under an anaerobic environment with controlled reaction temperature to form carbonized resin. In one specific embodiment, this step involves: centrifuging the solution heated in step S2 at 8000 rpm for 5 minutes, discarding the supernatant, and resuspending it in deionized water. This process is repeated three times. The final precipitate is dried at 60°C for 10-16 hours, preferably 12 hours, to obtain powdered resin. The powdered resin from step S3 is then pyrolyzed in a tube furnace at 450°C-550°C for 4 hours, with nitrogen gas introduced during the pyrolysis process to maintain an anaerobic environment, to obtain carbonized resin.

[0030] S13. The carbonized resin is mixed with potassium hydroxide and pyrolyzed under an anaerobic environment by controlling the reaction temperature. Potassium oxide particles are formed on and inside the carbonized resin, resulting in an alkalized resin. Then, the potassium oxide is etched off with an acidic solution to create pores on the surface and inside the carbonized resin. A honeycomb-like confined structure, labeled KC, is obtained after washing with deionized water and drying. In one specific embodiment, this step involves: mixing carbonized resin and potassium hydroxide at a mass ratio of 1:6 in a quartz boat, and then pyrolyzing at 450℃~550℃ for 8 hours. Nitrogen gas is introduced during pyrolysis to maintain an anaerobic environment, resulting in an alkalized resin. The alkalized resin is then immersed in a 3-6 mol / L hydrochloric acid solution and stirred for 1-2 hours. It is then washed three times with deionized water to remove excess hydrochloric acid solution, followed by centrifugation at 8000 rpm for 5 minutes to obtain a precipitate. The precipitate is dried at 60-80℃ for 12 hours, finally obtaining a honeycomb-like confined structure, labeled KC.

[0031] Step S2: Preparation of ferrous ore: Prepare a ferric solution, then adjust the pH to 7 with an alkaline solution, stir at room temperature, and then allow the precipitate to stand, retaining the precipitate. In one specific embodiment, this step is as follows: Prepare a 50 mM ferric solution, then adjust the pH to 7 with a 0.4 M NaOH solution, stir at room temperature for 12-20 h, then allow the precipitate to stand for 0.5-1.0 h, discard the supernatant, and retain the precipitate.

[0032] In a specific embodiment, the iron salt in the ferric solution in step S2 is one or more of FeCl3, Fe(NO3)3, and Fe2(SO4)3.

[0033] Step S3: Encapsulate the ferrohydrate within a honeycomb confinement structure, specifically including the following sub-steps: S31. Mix ethanol, deionized water, and ammonia to obtain solution A; transfer all the precipitate containing ferrohydrate from step S2 to solution A and stir to form mixture B. In a specific embodiment, this step is as follows: mix ethanol, deionized water, and 30% ammonia at a mass ratio of 53:120:1 and stir for 0.5 h to obtain solution A. Then, mix the precipitate from step S2 with solution A at a volume ratio of 1:13 and stir for 10-30 min to form mixture B.

[0034] S32. Dissolve dopamine hydrochloride in deionized water to obtain solution C; then add solution C to mixture B and stir to form a polydopamine-iron complex, labeled Fe@PDA, and the corresponding solution is labeled solution D. In a specific embodiment, this step is as follows: prepare a 50 g / L dopamine hydrochloride solution with deionized water, labeled solution C. Add solution C dropwise to mixture B using a dropper, with a volume ratio of solution C to solution B of 1:14. Stir at room temperature for 24-30 h to form a polydopamine-iron complex labeled Fe@PDA, and the solution containing Fe@PDA is labeled solution D.

[0035] S33. The honeycomb confined structure obtained in step S1 is added to solution D and stirred. The encapsulated honeycomb confined iron oxide is obtained through centrifugation, deionized water washing, and freeze-drying, labeled Fe@PDA / KC. In one specific embodiment, this step involves adding KC to solution D to achieve a KC mass concentration of 5-7.5 g / L, stirring at room temperature for 24-30 h, followed by centrifugation at 8000 rpm for 5 min, discarding the supernatant, and resuspending in deionized water. This process is repeated three times to obtain the precipitate. Finally, the precipitate from step S12 is freeze-dried for 24 h to obtain the honeycomb confined iron oxide, labeled Fe@PDA / KC.

[0036] Preferably, the honeycomb-shaped confined iron oxide in step S3 has the following characteristics: The mass ratio of polydopamine to ferrous ore is 1:1 to 5:1.

[0037] KC has a porosity of 60-80% and an average pore size of 20-30 μm.

[0038] Each Fe@PDA micron-sized particle has a size of 400~500nm and encapsulates 5~20nm ferrometallurgical crystals.

[0039] Thirdly, this invention provides an application of a method for preparing honeycomb-shaped confined iron oxides to delay the passivation of iron oxides in an anaerobic digestion reactor. Applying honeycomb-shaped iron oxides to an anaerobic digestion system can delay the passivation of iron oxides. Specifically, applying honeycomb-shaped iron oxides to an anaerobic digestion system involves setting the concentration of introductory sludge at 10%–20% within the anaerobic digestion reaction treating organic wastewater, and adding 5–10 g / L of honeycomb-shaped iron oxide powder to the reactor.

[0040] The method and application of the present invention will be further described below with reference to embodiments: Example 1 Preparation process as follows Figure 1As shown, 2.2 g of resorcinol was weighed and dissolved in 800 mL of deionized water, then 4.65 mL of formaldehyde solution and 2.5 mL of 30% ammonia solution were added. The mixture was then stirred for 0.5 h. The mixture was transferred to a polytetrafluoroethylene container and sealed, and heated at 160 °C for 4 h. The heated solution was centrifuged at 8000 rpm for 5 min, the supernatant was discarded, and the solution was resuspended in deionized water. This process was repeated three times. The final precipitate was dried at 60 °C for 12 h to obtain powdered resin. The powdered resin was pyrolyzed in a tube furnace at 450 °C for 4 h, with nitrogen gas introduced during the pyrolysis process to maintain an anaerobic environment, to obtain carbonized resin. The carbonized resin and potassium hydroxide were mixed at a mass ratio of 1:6 and placed in a quartz boat, and then pyrolyzed at 450 °C for 8 h, with nitrogen gas introduced during the pyrolysis process to maintain an anaerobic environment, to obtain alkalized resin. The alkalizing resin was immersed in a 6 mol / L hydrochloric acid solution and stirred for 1 hour. It was then washed three times with deionized water to remove excess hydrochloric acid. The solution was then centrifuged at 8000 rpm for 5 minutes to obtain a precipitate. The precipitate was dried at 60°C for 12 hours to obtain a honeycomb confinement material, labeled KC. Figure 4 As shown, the porosity of the formed honeycomb confined material KC is 60-80% in carbonized resin KC, with an average pore size of 20-30 μm.

[0041] Prepare 200 mL of a 50 mM ferric iron solution, then adjust the pH to 7 with 0.4 M NaOH solution. Stir at room temperature for 12 h, then allow to stand for 0.5 h to precipitate. Discard the supernatant and retain the precipitate. Mix 200 mL of ethanol, 450 mL of deionized water, and 3.75 mL of ammonia solution, and stir for 0.5 h to obtain solution A. Transfer all the precipitate to solution A and stir for 30 min to form mixture B. Dissolve 2.5 g of dopamine hydrochloride in 50 mL of water to obtain solution C. Add solution C dropwise to mixture B using a dropper, and stir at room temperature for 24 h to form a polydopamine-iron complex solution, i.e., Fe@PDA solution. Figure 3 As shown, the formed ferrohydrate has a size of 5-20 nm and is distributed inside the polydopamine. The overall particle size of Fe@PDA is about 500 nm. 5 g of KC was added to the Fe@PDA solution and stirred at room temperature for 24 h. Then, it was centrifuged at 8000 rpm for 5 min, the supernatant was discarded, and the solution was resuspended in deionized water. This process was repeated three times to obtain the precipitate. The precipitate was freeze-dried for 24 h to obtain honeycomb confined iron oxide, labeled as Fe@PDA / KC.

[0042] Example 2 Nine 100 mL anaerobic bottles were divided into three groups, with three parallel experiments per group. All sample bottles were inoculated with 20 mL of anaerobic initiation sludge and 80 mL of organic wastewater. The main components of the organic wastewater were: 1.8 g / L glucose, 0.46 g / L ammonium chloride, 0.10 g / L potassium dihydrogen phosphate, and 15 mM sodium dibromoacetate sulfonate. The first group served as a control group, with no added materials. The remaining two sample bottles were inoculated with 30 mmol of ferrohydrate and Fe@PDA / KC, respectively. The sample bottles were placed in a constant temperature incubator at 35 ℃, and the free Fe2+ in the wastewater was measured every two days. + Content, including free Fe2+ in the ferrohydrate reactor + The highest concentration was 40.3 mg / L, and the highest concentration of Fe@PDA / KC in the reactor was 150.5 mg / L. For example... Figures 5 to 7 As shown, after the experiment, the total Fe2+ in the water-iron ore reactor was measured. + The concentration was 475.4 mg / L, corresponding to a ferric iron reduction rate of 27%; the total Fe2+ concentration in the Fe@PDA / KC reactor was 1287.4 mg / L, corresponding to a ferric iron reduction rate of 97%, which is 70% higher than that of the ferrous iron ore reactor. After the reaction, the contents of crystalline and highly crystalline iron oxides in the ferrous iron ore reactor were 9% and 39%, respectively, while the contents of crystalline and highly crystalline iron oxides in the Fe@PDA / KC reactor were 4% and 8%, respectively, meaning that Fe@PDA / KC can reduce the formation of inert iron oxides by 36%. Meanwhile, if... Figure 8 As shown, the COD removal rates of the blank water-iron reactor, the mineral reactor, and the Fe@PDA / KC reactor were 39%, 45%, and 53%, respectively, indicating that a higher iron reduction rate can improve the removal efficiency of organic matter.

[0043] Example 3 Two experimental groups were set up using 125 mL serum bottles: one group served as a control reactor without any added materials, and the other group received 30 mmol of Fe@PDA / KC. 10 mL of microbial inoculum and 90 mL of municipal waste sludge were added to the reactor bottle, and anaerobic digestion was carried out at 37°C. After 30 days of anaerobic digestion, the cumulative methane production in the control group was 702 mL. Figure 9 As shown, the cumulative methane yield in the Fe@PDA / KC reactor was 1050 mL, a 50% increase compared to the control group. Figure 10 As shown, the total solids and volatile solids removal rates of the control group sludge were 34% and 37%, respectively, while those of the Fe@PDA / KC reactor sludge were 46% and 53%, respectively.

[0044] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A honeycomb confined iron oxide for retarding passivation of iron oxides in an anaerobic digestion reactor, characterized by: The honeycomb-like confined iron oxide is obtained by the following method: The carbonized resin is mixed with potassium hydroxide to form potassium oxide particles on the surface and inside of the carbonized resin, and the potassium oxide particles are stripped from the carbonized resin to realize pore formation on the surface and inside of the carbonized resin, thereby obtaining a honeycomb-like confined structure; The polydopamine is in-situ polymerized on the surface of the ferrihydrite, and the polydopamine is used to confine and encapsulate the nanoscale ferrihydrite to form micrometer-sized particles, and in the forming process, the polydopamine occupies the active sites on the surface of the ferrihydrite to prevent free divalent iron from being adsorbed on the surface of the ferrihydrite in the subsequent anaerobic digestion process; The micrometer-sized composite particles formed by the polydopamine and the ferrihydrite are encapsulated in the honeycomb-like confined structure to obtain the honeycomb-like confined iron oxide, so that each micrometer-sized composite particle is isolated from each other, and the polymerization of the ferrihydrite is delayed to prevent the formation of inert iron minerals.

2. A method for the preparation of a honeycomb confined iron oxide for retarding passivation of iron oxides in an anaerobic digestion reactor according to claim 1, characterized in that: It comprises the following steps: Step S1, preparing a honeycomb-like confined structure, specifically comprising the following sub-steps: S11, mixing resorcinol as a monomer, formaldehyde as a crosslinking agent and an initiator, and ammonia as a pH regulator, and preparing a resin by controlling the heating temperature and time; S12, obtaining a powder resin through the steps of centrifugation, deionized water washing and drying, and then pyrolyzing the powder resin in an anoxic environment by controlling the reaction temperature to form a carbonized resin; S13, mixing the carbonized resin with potassium hydroxide, and pyrolyzing in an anoxic environment by controlling the reaction temperature to form potassium oxide particles on the surface and inside of the carbonized resin, obtaining an alkali resin, and then etching the potassium oxide with an acidic solution to strip the potassium oxide particles from the carbonized resin to realize pore formation on the surface and inside of the carbonized resin, and obtaining a honeycomb-like confined structure through the steps of deionized water washing and drying, marked as KC; Step S2: preparing ferrihydrite: configuring a trivalent iron solution, then adjusting the pH to 7 with an alkaline solution, stirring at room temperature, then standing the precipitate, and retaining the precipitate; Step S3: encapsulating the ferrihydrite in the honeycomb-like confined structure, specifically comprising the following sub-steps: S31, mixing ethanol, deionized water and ammonia to obtain solution A; transferring the precipitate containing ferrihydrite in step S2 to solution A, and stirring to form a mixed solution B; S32, dissolving dopamine hydrochloride in deionized water to obtain solution C; then adding solution C to mixed solution B to stir to form a polydopamine-iron complex, marked as Fe@PDA, and the corresponding solution is marked as solution D; S33, adding the honeycomb-like confined structure obtained in step S1 to solution D and stirring, and obtaining the encapsulated honeycomb-like confined iron oxide through the steps of centrifugation, deionized water washing and freeze-drying, marked as Fe@PDA / KC.

3. The method for preparing honeycomb-shaped confined iron oxides that delay the passivation of iron oxides in an anaerobic digester according to claim 2, characterized in that: In step S11, resorcinol is configured and formaldehyde solution is added, so that the mass fraction of formaldehyde is 0.5%~0.6%, then ammonia water is added so that the concentration of ammonia water is 3%~4%, and the mixed solution is stirred for 0.5~1h; then the mixed solution is transferred to a sealed container and heated at 160℃ for 3~5h.

4. The method for preparing honeycomb-shaped confined iron oxide that delays the passivation of iron oxides in an anaerobic digester according to claim 2, characterized in that: In step S12, the heated solution is centrifuged to remove the supernatant, and resuspended with deionized water, and the above process is repeated three times. The final obtained precipitate is dried at 60°C for 10-16h to obtain a powder resin. Then the powder resin is pyrolyzed at 450-550°C, and nitrogen is introduced during the pyrolysis process to maintain an anaerobic environment, to obtain a carbonized resin.

5. The method for preparing honeycomb-shaped confined iron oxides that delay the passivation of iron oxides in an anaerobic digester according to claim 4, characterized in that: In step S13, the carbonized resin is mixed with potassium hydroxide at a mass ratio of 1:6 and placed in a quartz boat, and then pyrolyzed at 450-550°C, and nitrogen is introduced during the pyrolysis process to maintain an anaerobic environment, to obtain an alkalized resin. Then the alkalized resin is soaked in a 3-6mol / L hydrochloric acid solution, stirred for 1-2h, then washed with deionized water several times to remove excess hydrochloric acid solution, and then centrifuged to obtain a precipitate. The precipitate is dried at 60-80°C to obtain a honeycomb confined structure, marked as KC.

6. The method of claim 2, wherein the honeycomb confined iron oxides are prepared by the steps of: a) providing a honeycomb structure; b) coating the honeycomb structure with a layer of iron oxide; c) coating the layer of iron oxide with a layer of a passivating agent; d) heating the coated honeycomb structure to a temperature of about 300 °C to about 500 °C; and e) cooling the coated honeycomb structure to room temperature. In step S33, KC is added to solution D to make the mass concentration of KC 5-7.5g / L, and stirring is continued at room temperature for 24-30h, then centrifuged, the supernatant is discarded, and resuspended with deionized water, and the above process is repeated three times, and finally the precipitate is obtained. The precipitate is freeze-dried to obtain a honeycomb confined iron oxide, marked as Fe@PDA / KC.

7. The method of claim 2, wherein the honeycomb confined iron oxides are prepared by the steps of: a) providing a honeycomb structure; b) coating the honeycomb structure with a layer of iron oxide; c) coating the layer of iron oxide with a layer of a passivating agent; d) heating the coated honeycomb structure to a temperature of about 300 °C to about 600 °C; and e) cooling the coated honeycomb structure to room temperature. In step S2, the iron salt in the ferric iron solution is one or more of FeCl3, Fe(NO3)3, and Fe2(SO4)3.

8. The method of claim 2, wherein the honeycomb confined iron oxides are prepared by the process of: The honeycomb confined iron oxide in step S3 has the following characteristics: ​ The mass ratio of polydopamine to ferrihydrite is 1:1-5:1; The KC porosity is 60-80%, and the average pore size is 20-30μm; Each Fe@PDA microparticle has a size of 400-500nm, and encapsulates 5-20nm ferrihydrite crystals.

9. Use of a method for the preparation of a honeycomb confined iron oxide based on the method for retarding passivation of iron oxides in an anaerobic digestion reactor according to claim 2, characterized in that: The application of the honeycomb iron oxide to the anaerobic digestion system can delay the passivation of the iron oxide.

10. Use of the process for the preparation of honeycomb confined iron oxides for retarding passivation of iron oxides in an anaerobic digestion reactor according to claim 9, characterized in that: The application of the honeycomb iron oxide to the anaerobic digestion system is as follows: in the anaerobic digestion reaction for treating organic wastewater, the inoculum sludge concentration is set to 10%-20%, and 5-10g / L of the honeycomb iron oxide material powder is added to the reactor.

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