Preparation method of biochar-based cobalt-iron-nitrogen coordination catalyst and application of biochar-based cobalt-iron-nitrogen coordination catalyst in improvement of utilization rate of H2O2
By preparing biochar-based cobalt-iron-nitrogen coordination catalysts, the problem of low H2O2 utilization in the Fenton reaction was solved, and efficient H2O2 utilization and removal of difficult-to-degrade organic matter were achieved, with good social, economic and environmental benefits.
Patent Information
- Application Number
- CN202511141787.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-15
- Publication Date
- 2025-10-21
AI Technical Summary
The utilization rate of H2O2 in the existing Fenton reaction is low, resulting in large reagent consumption. In addition, the traditional heterogeneous catalyst has insufficient exposure of active sites due to the agglomeration of metal particles, and the H2O2 utilization rate is less than 50%.
The preparation method of biochar-based cobalt-iron-nitrogen coordination catalyst is adopted. Pig manure is made into porous biochar, and a complex is formed with cobalt salt, iron salt and disodium ethylenediaminetetraacetic acid. Combined with ZnCl2-KCl mixed molten salt and dicyandiamide ball milling, gradient calcination is performed to form CoFe-N6 active sites and achieve symmetrical distribution of cobalt and iron atoms.
Nearly 100% utilization of H2O2 was achieved, and the removal capacity of difficult-to-degrade organic matter was improved. The catalyst showed excellent purification effect in complex environments, and the operation was simple and low-cost.
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Figure CN120815567A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the field of sewage treatment, specifically to the preparation of a catalyst for sewage treatment, and more specifically to a method for preparing a biochar-based cobalt-iron-nitrogen coordination catalyst, and the application of the biochar-based cobalt-iron-nitrogen coordination catalyst prepared by the method in improving the utilization rate of H2O2. Background Art
[0002] Antibiotics, such as tetracycline, are used extensively to prevent and treat bacterial infections in humans and animals. Furthermore, antibiotics are highly stable in the natural environment and resist direct oxidation. Therefore, without effective management, antibiotics are likely to persist and accumulate in ecosystems, leading to serious environmental pollution.
[0003] The Fenton reaction, an advanced oxidation process, is widely used in real-world wastewater treatment, particularly for the pretreatment or advanced treatment of refractory organic matter (e.g., dye and pharmaceutical wastewater). However, its practical application is hampered by high operating costs. A key issue is the low H2O2 utilization rate (typically less than 30%), resulting in high reagent consumption. While heterogeneous catalysts (such as Fe3O4 and Co3O4) can improve H2O2 utilization, due to the agglomeration of metal particles, which results in insufficient exposure of active sites, H2O2 utilization rates are generally below 50%. Summary of the Invention
[0004] To address these technical challenges, the present invention proposes a method for preparing a biochar-based cobalt-iron-nitrogen coordination catalyst and its application in improving H₂O₂ utilization. The biochar-based cobalt-iron-nitrogen coordination catalyst prepared in the present invention can achieve high H₂O₂ utilization, effectively removing antibiotics from water.
[0005] The technical solution adopted by the present invention is: A method for preparing a biochar-based cobalt-iron-nitrogen coordination catalyst comprises the following steps: (1) Dry and crush the pig manure, and pre-carbonize it under an inert atmosphere to produce primary biochar; (2) The primary biochar is mixed with KOH solution and then activated by heating to obtain porous biochar with a microporous-mesoporous hierarchical structure; (3) Dissolve the cobalt salt and iron salt in deionized water, then add disodium ethylenediaminetetraacetic acid and stir to form a complex solution; (4) adding the porous biochar into the complex solution for impregnation, and then freeze-drying in vacuum to obtain the metal-loaded biochar; (5) ball-milling the metal-loaded biochar, ZnCl2-KCl mixed molten salt, and dicyandiamide to obtain a mixture; (6) The mixture is first heated to a molten state for reaction, and then calcined in an argon / ammonia mixed atmosphere at a gradient temperature to obtain a biochar-based cobalt-iron-nitrogen coordination catalyst.
[0006] Preferably, in step (1): the dried pig manure is crushed to 80-100 mesh, and then heated to 300-350°C at 5-10°C / min under a N2 atmosphere and maintained for 2-3 h.
[0007] Preferably, in step (2): the concentration of the KOH solution is 2-3 mol / L, the mass ratio of primary biochar to KOH solution is 1:2-3; the activation temperature is controlled to be 600-650°C, and the activation time is 1-2h.
[0008] Preferably, in step (3), the cobalt salt is Co(NO3)2•6H2O or CoCl2•6H2O; the iron salt is FeCl3•6H2O; the molar ratio of the cobalt salt, the iron salt and the disodium ethylenediaminetetraacetic acid is 1:1:1.5-2; the stirring temperature is controlled to be 50-60°C and the stirring time is 1.5-2h; the complex in the complex solution is a tetrahedral [CoFe-EDTA] 4- complex.
[0009] Preferably, in step (4): the impregnation adopts an equal volume impregnation method; and the vacuum freeze-drying conditions are controlled to be -50°C and 10 Pa.
[0010] Preferably, in step (5): the mass ratio of the metal-loaded biochar to the ZnCl2-KCl mixed molten salt is 1:5-6; the ZnCl2-KCl mixed molten salt is composed of ZnCl2 and KCl in a 1:1 molar ratio; and the amount of dicyandiamide used is 50%-100% of the mass of the metal-loaded biochar.
[0011] Preferably, in step (6): the mixture is controlled to be heated to 250-350°C at a rate of 10°C / min in an argon / hydrogen mixture, and reacted at this temperature for 1-3 hours.
[0012] Preferably, in step (6), the gradient temperature calcination process is as follows: first raise the temperature to 400-450°C in an argon / ammonia mixture, keep warm for 1-1.5 hours, then raise the temperature to 800-900°C at a rate of 20-50°C / min, and calcine for 2-3 hours.
[0013] In the biochar-based cobalt-iron-nitrogen coordination catalyst obtained by the above preparation method, cobalt and iron atoms are symmetrically distributed on the biochar surface in a CoFe-N6 configuration, and the Co-Fe atomic distance is 2.4-2.6 Å.
[0014] The biochar-based cobalt-iron-nitrogen coordination catalyst prepared by the above method can achieve a H2O2 utilization rate of 99.7% while removing antibiotics.
[0015] The beneficial technical effects of the present invention are as follows: 1. The method of the present invention combines chelate coordination with molten salt dynamic synthesis, resulting in atomically symmetrical dispersion of cobalt and iron within the catalyst framework, where metal atoms and biochar form the CoFeN6 active sites. This catalyst demonstrates excellent catalytic performance in the Fenton-like reaction for the removal of antibiotics by activating hydrogen peroxide. The CoFeN6 active coordination in the intermediate spin state forms a unique electronic structure at the activation interface, thereby optimizing the adsorption and dissociation of H2O2 and achieving nearly 100% H2O2 utilization, demonstrating significant commercial potential.
[0016] 2. The present invention is based on an advanced oxidation process. The addition of CoFeN6 active sites greatly improves the ability to effectively oxidize and remove difficult-to-degrade organic matter that cannot be removed by traditional wastewater treatment technologies. Its essence is that H2O2 generates highly reactive hydroxyl radicals •OH under the catalytic action of CoFeN6. •OH can react with most organic matter to degrade it.
[0017] 3. The atomically symmetrical CoFeN6 active sites in this invention are in a medium-spin state. The spin reconstruction effect of the FeCo diatoms creates a unique electronic structure at the active site interface, thereby optimizing the H2O2 adsorption and dissociation processes. This ultimately promotes the continuous decomposition of H2O2 to produce •OH, effectively overcoming the short half-life of •OH. This allows for ultra-high H2O2 utilization during pollutant degradation, significantly extending the lifetime of •OH.
[0018] 4. The catalyst prepared by the present invention is little affected by the pH range and the presence of other ions during application, and can have a good purification effect within a complex range, with good social, economic and environmental benefits.
[0019] 5. The biochar prepared from pig manure in the present invention has a rich pore structure and natural nitrogen-containing functional groups. Combined with chelation coordination and molten salt dynamic synthesis methods, it can better anchor cobalt and iron elements.
[0020] 6. The preparation method of the present invention is simple to operate, easy to implement on a large scale, and low in cost. At the same time, it achieves a high efficiency in the utilization of H2O2, which is beneficial to solving the defect of low utilization of H2O2 in traditional Fenton technology. BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Figure 1Figure 1 is a spectral image of the catalyst prepared in Example 1 of the present invention. Figures a and b are XANES spectra of the Co K-edge, b are XANES spectra of the Fe K-edge, c are FT-EXAFS spectra of the catalyst at the Co K-edge, d are FT-EXAFS spectra of the Fe K-edge, e are EXAFS spectrum fitting curves of the catalyst at the Co K-edge, and f are EXAFS spectrum fitting curves of the catalyst at the Fe K-edge. Figure 1 is a wavelet transform (WT) image of the catalyst and a standard sample.
[0022] Figure 2 It is a biochar-based cobalt-iron-nitrogen coordination catalyst structure with a CoFeN6 symmetrical coordination configuration.
[0023] Figure 3 Schematic diagram comparing the degradation effect of different types of catalysts and H2O2 utilization rate; a shows the degradation effect of different types of catalysts, b shows the K obs value and H2O2 utilization.
[0024] Figure 4 Schematic diagram comparing the degradation effects of the catalyst prepared in Example 1 of the present invention under different conditions; wherein, a is a comparison of the degradation effects under different pH conditions, b is a comparison of the degradation effects under conditions of different ions, and c is a comparison of the degradation effects under conditions of different water qualities. DETAILED DESCRIPTION
[0025] The present invention will be further described below with reference to specific embodiments.
[0026] Example 1 Pig manure was dried and then pulverized to 80-100 mesh. Primary biochar was then pre-carbonized at 300°C for 2 hours under a nitrogen atmosphere at a rate of 5°C / min. The primary biochar was then mixed with a 2 mol / L KOH solution at a mass ratio of 1:2. The mixture was then activated at 600°C for 1 hour to produce a porous biochar with a hierarchical micro-mesoporous structure. Pre-carbonization of the pig manure generated a porous biochar rich in a cellulose-derived carbon network, which was then activated with KOH to increase the specific surface area, resulting in porous biochar (BC).
[0027] Dissolve CoCl2•6H2O and FeCl3•6H2O in deionized water, then add disodium EDTA. The molar ratio of CoCl2•6H2O, FeCl3•6H2O, and disodium EDTA is 1:1:2. Stir and chelate in deionized water at 50℃ for 2 hours to obtain a complex solution. The complex solution contains tetrahedral [CoFe-EDTA] 4- complex.
[0028] The porous biochar with a hierarchical microporous-mesoporous structure prepared in the above steps is then added to the complex solution and impregnated until the complex solution just covers the porous biochar. After impregnation, vacuum freeze-drying is performed at -50°C and 10 Pa to produce the metal-loaded biochar. This step involves filling the biochar grooves with the complex through an equal volume impregnation method. Vacuum freeze-drying is then used to inhibit metal ion migration, fix the metal sites, and achieve atomic-level dispersion.
[0029] Metal-loaded biochar was ball-milled with a ZnCl₂-KCl mixed molten salt and dicyandiamide (80 wt%) to produce a mixture. The mass ratio of the metal-loaded biochar to the ZnCl₂-KCl mixed molten salt was 1:5; the ZnCl₂-KCl mixed molten salt was composed of ZnCl₂ and KCl in a 1:1 molar ratio. The dicyandiamide was added at 80% of the mass of the metal-loaded biochar. In an Ar / H₂ (95 / 5 by volume) atmosphere, the mixture was heated at 10°C / min to 300°C in a tube furnace until it reached a molten state and reacted at this temperature for 2 h. The molten ZnCl₂-KCl provided a highly ionic conductive medium, promoting the dynamic coordination of NH₂• radicals generated by the thermal decomposition of dicyandiamide with the metal ions, preferentially occupying four planar sites to form Co-N₄ and Fe-N₄ precursors. Primary coordination of CoFe-N₄ occurred in the molten salt liquid phase. Then, gradient calcination was carried out in an Ar / NH3 (volume ratio 90 / 10) atmosphere, first heating to 400℃ at 10℃ / min, pre-oxidation at this temperature for 1h, then heating to 800℃ at 50℃ / min, and calcining at this temperature for 2h, and then naturally cooling and annealing. The gradient calcination can strengthen the carbon-nitrogen skeleton, and finally a biochar-based cobalt-iron-nitrogen coordination catalyst with a CoFeN6 symmetrical coordination configuration is obtained.
[0030] In the biochar-based cobalt-iron-nitrogen coordination catalyst obtained in this embodiment, cobalt and iron atoms are symmetrically distributed on the biochar surface in a CoFe-N6 configuration, and the Co-Fe atomic distance is 2.4-2.6 Å.
[0031] like Figure 1 The catalyst structure was characterized. Figure 1 Spectral images of the catalyst prepared in Example 1 of the present invention. Figures a and b are XANES spectra of the Co K-edge, b are XANES spectra of the Fe K-edge, c are FT-EXAFS spectra of the catalyst at the Co K-edge, d are FT-EXAFS spectra of the Fe K-edge, e are EXAFS spectrum fitting curves of the catalyst at the Co K-edge, and f are EXAFS spectrum fitting curves of the catalyst at the Fe K-edge. Figures g1 and g1 are wavelet transform (WT) images of the catalyst and standard samples (Co foil, Fe foil, Co3O4, and Fe2O3).
[0032] Figure 1 As shown in Figures ab, XANES reveals that the valence state of Co is between +2 and +8 / 3, and the valence state of Fe is between +2 and +3. Figure 1 As shown in cd, it is proved that the catalyst has Fe-N, Co-N, and Co-Fe coordination bonds, and there are no Co-Co and Fe-Fe coordination peaks at 2.2nm, indicating that the Fe-Co atomic pairs are distributed on the catalyst surface in atomic form. Figure 1 As shown in Figure ef, the FT-EXAFS spectra of Co and Fe K edges in the catalyst are well fitted; and combined with the wavelet transform (WT) map ( Figure 1 In the graph (gl), obvious Fe-N and Co-N signals are observed in the catalyst, and there are also obvious Co-Fe bond characteristic signals. The calculation results obtained by least squares fitting show that, as shown in Table 1, the coordination configuration of the active site of the catalyst can be determined to be CoFeN6 (see Figure 2 ).
[0033] Table 1 shows the EXAFS data fitting results of the catalyst (CoFe-N6).
[0034] Table 1
[0035] Figure 2 The structure of a biochar-based cobalt-iron-nitrogen coordination catalyst with a symmetrical CoFeN6 coordination configuration is shown. Pink represents Co atoms, green represents Fe atoms, blue represents N atoms, and black represents the carbon network structure.
[0036] Example 2 Pig manure was dried and then crushed to 80-100 mesh. The mixture was then heated to 350°C at a rate of 10°C / min in a nitrogen atmosphere and held for 3 hours for pre-carbonization to produce primary biochar. The primary biochar was then mixed with a 2 mol / L KOH solution at a mass ratio of 1:3 and activated at 650°C for 2 hours to produce a porous biochar with a microporous-mesoporous hierarchical structure.
[0037] Co(NO3)2•6H2O and FeCl3•6H2O were dissolved in deionized water, and then disodium EDTA was added. The molar ratio of Co(NO3)2•6H2O, FeCl3•6H2O, and disodium EDTA was 1:1:1.5. The mixture was stirred and chelated in deionized water at 50℃ for 2 hours to obtain a complex solution. The complex solution contained tetrahedral [CoFe-EDTA] 4- complex.
[0038] The porous biochar with a microporous-mesoporous hierarchical structure prepared in the above steps is added to the complex solution for impregnation. After the impregnation is completed, it is vacuum freeze-dried at -50°C and 10Pa to obtain metal-loaded biochar.
[0039] Metal-loaded biochar was ball-milled with a ZnCl2-KCl mixed molten salt and dicyandiamide (80 wt%) to produce a mixture. The mass ratio of the metal-loaded biochar to the ZnCl2-KCl mixed molten salt was 1:6. The ZnCl2-KCl mixed molten salt was composed of ZnCl2 and KCl in a 1:1 molar ratio. The dicyandiamide was added in an amount of 60% of the metal-loaded biochar mass. In an Ar / H2 (95 / 5 by volume) atmosphere, the mixture was heated at a rate of 10°C / min to 350°C until it reached a molten state and remained at this temperature for 2 h. The mixture was then calcined in an Ar / NH3 (90 / 10 by volume) atmosphere, first at a rate of 10°C / min to 400°C, where it was pre-oxidized for 1 h. The mixture was then heated at a rate of 50°C / min to 900°C, where it was calcined for 2 h. The mixture was then cooled naturally to obtain a biochar-based cobalt-iron-nitrogen coordination catalyst with a symmetrical CoFeN6 coordination structure.
[0040] Example 3 The application of the biochar-based cobalt-iron-nitrogen coordination catalyst with CoFeN6 symmetrical coordination configuration prepared in Example 1 in the treatment of antibiotic wastewater.
[0041] Specifically, the method for treating antibiotic wastewater using the catalyst prepared in Example 1 comprises the following steps: adding the catalyst into wastewater containing antibiotics, then adding hydrogen peroxide as an oxidant, and obtaining treated wastewater after reaction.
[0042] The concentration of the catalyst in the wastewater is controlled to be 300 mg / L, the concentration of hydrogen peroxide is 3 mM, the reaction temperature is 20-30° C., the reaction time is 20 min, stirring is performed during the reaction process, the stirring speed is 200-300 r / min, and the type of antibiotic is amoxicillin.
[0043] Example 4 Comparison of the degradation effects of antibiotics and H2O2 utilization rates of different types of catalysts.
[0044] The preparation process is the same as that of Example 1, except that the addition of certain materials is omitted, thereby obtaining catalysts containing different active coordination structures: N-BC (CoCl2·6H2O and FeCl3·6H2O are not added during the preparation process), CoFe-BC (dicyandiamide is not added during the preparation process), Co-N-BC (FeCl3·6H2O is not added during the preparation process), and Fe-N-BC (CoCl2·6H2O is not added during the preparation process). The biochar-based cobalt-iron-nitrogen coordination catalyst finally obtained in Example 1 is CoFe-N-BC. 30 mg of catalyst and 3 mM H2O2 were respectively placed in 100 ml of water sample with an antibiotic concentration of 10 mg / L, and the initial pH was controlled to be 5.5. Sampling and filtration were performed within the specified time, and the concentrations of antibiotics and H2O2 were measured using an ultraviolet spectrophotometer to obtain the antibiotic removal rate and H2O2 utilization rate in different time periods. As Figure 3 It can be seen that the CoFeN6 active site (catalyst prepared in Example 1) has the best effect, with a degradation rate of 100% and Kobs = 0.238 min -1 , H2O2 utilization rate is 99.7%.
[0045] Example 5 Verification of the degradation effect of catalysts on antibiotics in complex environments.
[0046] Prepare dilute hydrochloric acid and sodium hydroxide solutions with pH values of 3.0, 5.0, 6.0, 7.0, 9.0 and 5 mM Cl in advance. - 、NO3 - 、SO4 2- 、H2PO4 - 100 ml of different antibiotic solution water samples were prepared using different water qualities. 10 mg / L antibiotic solutions were then added to each water sample. 30 mg of the catalyst prepared in Example 1 and 3 mM H2O2 were then added. Samples were taken and filtered within a specified time period, and the absorbance was measured using an ultraviolet spectrophotometer to obtain the antibiotic removal rate at different time periods. The results are shown in Figure 2. Figure 4 As shown in the results, the CoFeN6 active site can maintain a high degradation rate (>95%) for antibiotics under different pH, different ion and different water quality conditions, thus proving the degradation effect of this catalyst on antibiotics in a complex environment.
[0047] The above content is only for explaining the technical idea of the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.
Claims
1. A method for preparing a biochar-based cobalt-iron-nitrogen coordination catalyst, characterized in that The following steps are involved: (1) Dry and crush the pig manure, and pre-carbonize it under an inert atmosphere to produce primary biochar; (2) The primary biochar is mixed with KOH solution and then activated by heating to obtain porous biochar with a microporous-mesoporous hierarchical structure; (3) Dissolve the cobalt salt and iron salt in deionized water, then add disodium ethylenediaminetetraacetic acid and stir to form a complex solution; (4) adding the porous biochar into the complex solution for impregnation, and then freeze-drying in vacuum to obtain the metal-loaded biochar; (5) ball-milling the metal-loaded biochar, ZnCl2-KCl mixed molten salt, and dicyandiamide to obtain a mixture; (6) The mixture is first heated to a molten state for reaction, and then calcined in an argon / ammonia mixed atmosphere at a gradient temperature to obtain a biochar-based cobalt-iron-nitrogen coordination catalyst.
2. The method for preparing a biochar-based cobalt-iron-nitrogen coordination catalyst according to claim 1, characterized in that: In step (1): the dried pig manure is crushed to 80-100 mesh, and then heated to 300-350°C at 5-10°C / min under N2 atmosphere and maintained for 2-3 h.
3. The method for preparing a biochar-based cobalt-iron-nitrogen coordination catalyst according to claim 1, characterized in that: In step (2), the concentration of the KOH solution is 2-3 mol / L, the mass ratio of primary biochar to KOH solution is 1:2-3; the activation temperature is controlled to be 600-650°C, and the activation time is 1-2h.
4. The method for preparing a biochar-based cobalt-iron-nitrogen coordination catalyst according to claim 1, wherein: In step (3), the cobalt salt is Co(NO3)2•6H2O or CoCl2•6H2O; the iron salt is FeCl3•6H2O; the molar ratio of the cobalt salt, the iron salt and the disodium ethylenediaminetetraacetic acid is 1:1:1.5-2; the stirring temperature is controlled to be 50-60°C and the stirring time is 1.5-2h; the complex in the complex solution is a tetrahedral complex [CoFe-EDTA] 4- complex.
5. The method for preparing a biochar-based cobalt-iron-nitrogen coordination catalyst according to claim 1, characterized in that: In step (4): the impregnation adopts the equal volume impregnation method; the vacuum freeze-drying conditions are controlled to be -50°C and 10 Pa.
6. The method for preparing a biochar-based cobalt-iron-nitrogen coordination catalyst according to claim 1, characterized in that: In step (5), the mass ratio of the metal-loaded biochar to the ZnCl2-KCl mixed molten salt is 1:5-6; the ZnCl2-KCl mixed molten salt is composed of ZnCl2 and KCl in a 1:1 molar ratio; and the amount of dicyandiamide used is 50%-100% of the mass of the metal-loaded biochar.
7. The method for preparing a biochar-based cobalt-iron-nitrogen coordination catalyst according to claim 1, characterized in that: In step (6): the mixture is heated to 250-350°C at a rate of 10°C / min in an argon / hydrogen mixture and reacted at this temperature for 1-3 hours.
8. The method for preparing a biochar-based cobalt-iron-nitrogen coordination catalyst according to claim 1, characterized in that: In step (6), the gradient temperature rise calcination process is as follows: first raise the temperature to 400-450°C in an argon / ammonia mixture, keep warm for 1-1.5 hours, then raise the temperature to 800-900°C at a rate of 20-50°C / min, and calcine for 2-3 hours.
9. The method for preparing a biochar-based cobalt-iron-nitrogen coordination catalyst according to claim 1, characterized in that: In the biochar-based cobalt-iron-nitrogen coordination catalyst obtained by this method, cobalt and iron atoms are symmetrically distributed on the biochar surface in a CoFe-N6 configuration, and the Co-Fe atomic distance is 2.4-2.6 Å.
10. The biochar-based cobalt-iron-nitrogen coordination catalyst prepared by the method according to any one of claims 1 to 9 can achieve a H2O2 utilization rate of 99.7% while removing antibiotics.