Bimetal MOF (Metal Organic Framework) modified cellulose-derived carbon aerogel catalyst as well as preparation method and application thereof

Abstract

The invention relates to the field of water environment pollution treatment, in particular to a bimetal MOF modified cellulose derived carbon aerogel catalyst as well as a preparation method and application thereof. The method comprises the following steps: 1) dissolving a transition metal salt and an organic ligand in an organic solvent to prepare a bimetallic MOF precursor solution; 2) dissolving a cellulose derivative in water, and treating to prepare cellulose aerogel; (3) immersing cellulose aerogel into the precursor solution, and carrying out in-situ growth to prepare MOF modified cellulose gel; and 4) carrying out carbonization treatment on the modified cellulose gel to prepare the bimetallic MOF modified cellulose-derived carbon aerogel catalyst. The catalyst has extremely high physical and chemical stability, meanwhile, the catalytic performance of the catalyst is effectively improved by means of mechanisms such as bi-metal synergism, graded electron transfer and high-dispersion active sites, and the catalyst can be effectively used for effective and efficient catalytic degradation of organic pollutants in a water body and is beneficial to separation and recovery.

Description

Technical Field

[0001] This invention relates to the field of water pollution control, specifically to a bimetallic MOF-modified cellulose-derived carbon aerogel catalyst, its preparation method, and its application. Background Technology

[0002] In recent years, antibiotics have received widespread attention as a new type of pollutant. Most antibiotics are difficult to degrade under natural conditions, and long-term exposure to the environment promotes the growth of antibiotic resistance genes (ARGs), posing a serious threat to human health and ecosystems. Traditional water treatment technologies are ineffective in removing these organic pollutants, leading researchers to explore novel advanced oxidation technologies. Among these, PMS-based advanced oxidation processes have attracted considerable attention due to their advantages, including high redox potential, wide pH range, and high mineralization rate of organic pollutants.

[0003] However, existing PMS catalysts still face several challenges. First, they suffer from high metal leaching rates, leading to secondary pollution and low regeneration cycles. Second, they agglomerate due to nanosize effects, resulting in poor dispersibility, which affects their surface active sites and specific surface area, thereby reducing catalytic performance.

[0004] MOFs possess advantages such as ease of regulation and modification, and good catalytic activity. Calcination of metallic MOFs forms a core-shell structure with a carbon skeleton encapsulating a transition metal, which can reduce metal leaching. Furthermore, compared to monometallic MOFs, bimetallic MOFs exhibit better catalytic performance, and the synergistic effect between metals can accelerate PMS activation. Cellulose is environmentally friendly and renewable, and as a substrate material, it can improve the dispersibility and recyclability of catalysts. Moreover, carbonized cellulose exhibits high conductivity, improving electron transfer efficiency and accelerating free radical generation. However, most existing MOF-cellulose interfacial bonding technologies are physical, making it easy for MOFs to detach from cellulose. Therefore, in-situ growth is employed to improve the interfacial bonding strength. Summary of the Invention

[0005] This invention addresses the problems of high metal leaching, poor dispersibility, and unsatisfactory cycle performance of existing catalysts by providing a bimetallic MOF-modified cellulose-derived carbon aerogel catalyst, its preparation method, and its application.

[0006] The main objective of this invention is: I. To provide a catalyst with low metal leaching, high dispersibility and excellent cycle stability; II. Enhancing catalytic performance through bimetallic synergy and shell-core structure design; Third, an in-situ growth strategy is adopted to enhance the interfacial binding strength between the carrier and the active component.

[0007] To achieve the above objectives, the present invention adopts the following technical solution.

[0008] A method for preparing a bimetallic MOF-modified cellulose-derived carbon aerogel catalyst. The method includes: 1) Prepare a bimetallic MOF precursor solution by dissolving transition metal salt A and transition metal salt B with organic ligands in an organic solvent; 2) Cellulose aerogels were prepared by dissolving cellulose derivatives in water, dispersing, aging, and freeze-drying. 3) The cellulose aerogel was immersed in the precursor solution and in situ grown to obtain MOF-modified cellulose gel. 4) The modified cellulose gel was carbonized to obtain a bimetallic MOF-modified cellulose-derived carbon aerogel catalyst.

[0009] As a preferred option Step 1) The transition metal salt A is a soluble iron salt and / or a soluble zinc salt and / or a soluble copper salt; Step 1) The transition metal salt B is a soluble cobalt salt and / or a soluble manganese salt and / or a soluble nickel salt; Step 1) The organic ligand is terephthalic acid and / or 2,5-dihydroxyterephthalic acid and / or 2-methylimidazole; Step 1) The organic solvent includes N,N-dimethylformamide.

[0010] As a preferred option Step 1) The molar ratio of transition metal salt A, transition metal salt B and organic ligand is (1-1.5):(1.1-2.1):1; Step 1) The total concentration of transition metal salt A and transition metal salt B in the organic solvent is 0.2 to 0.5 g / mL.

[0011] As a preferred option Step 2) The mass ratio of the cellulose derivative to water is 1:10 to 20.

[0012] As a preferred option Step 2) The aging time is 0.5–1.5 h; The freeze-drying time in step 2) is 24–72 h.

[0013] As a preferred option Step 3) The in-situ growth is carried out in an environment with a temperature of 60-100 ℃ for 12-36 h.

[0014] As a preferred option Step 4) The carbonization process is carried out under the following conditions: nitrogen atmosphere, gas flow rate of 100-300 cc / min, heating rate of 5 ℃ / min, carbonization temperature of 600-900 ℃, and holding time of 1-3 h.

[0015] A bimetallic MOF-modified cellulose-derived carbon aerogel catalyst.

[0016] Application of a bimetallic MOF-modified cellulose-derived carbon aerogel catalyst in the degradation of organic pollutants in water.

[0017] The organic pollutants include at least one of antibiotics, dyes, and phenolic compounds. The core of this invention lies in constructing a bimetallic MOF-modified cellulose-derived carbon aerogel composite catalyst, which significantly improves catalytic performance, structural stability, and recyclability, providing an innovative solution for the development of highly efficient and environmentally friendly catalysts.

[0018] This invention employs a transition bimetallic system, leveraging the synergistic electronic effect between 3d transition metals to enhance catalytic performance. When both metals coexist in the MOF structure, they form intermetallic compounds or alloy phases, resulting in a redistribution of electron density. This electronic regulation effect optimizes the d-orbital energy level distribution of the metal active centers, lowering the activation energy barrier. Synergistic catalysis is also reflected in the complementarity of redox properties. Different transition metal redox pairs have different standard electrode potentials, enabling hierarchical electron transfer in the catalytic reaction. This hierarchical electron transfer mechanism improves the selectivity and efficiency of the catalytic reaction while expanding the applicable reaction range of the catalyst. Furthermore, the spatial distribution of bimetallic sites is crucial for the synergistic effect. By controlling the ratio and coordination environment of the two transition metal salts, specific bimetallic active centers can be formed in the MOF framework. These centers possess catalytic properties that cannot be achieved by a single metal, such as enhanced oxygen reduction activity and optimized hydrogen evolution performance.

[0019] In this invention, bimetallic MOF-derived carbon, with its carbon skeleton-encased core-shell structure, enhances the catalyst's corrosion resistance through a dual mechanism of physical isolation and chemical stabilization. The outer carbon shell acts as a protective barrier, effectively blocking direct contact between the corrosive medium and the core metal, preventing the dissolution of metal ions and structural damage. The hydrophobic properties of the carbon shell further reduce the penetration rate of water molecules and corrosive ions. The chemical bonding at the core-shell interface enhances the overall structural stability. The structural design of this invention also considers stress release and defect control. The flexible characteristics of the carbon shell can accommodate the volume expansion of the metal core during temperature changes, preventing structural cracking caused by thermal stress. Simultaneously, the uniform shell thickness avoids localized stress concentration, improving the material's mechanical stability.

[0020] In this invention, cellulose-derived carbon aerogel serves as a support for bimetallic MOF-derived carbon. Its high specific surface area provides ample loading sites for the uniform dispersion of MOF crystals, preventing the aggregation of active components. The hierarchical pore structure ensures efficient mass transfer between reactants and products. Cellulose-derived carbon aerogel possesses excellent chemical stability and mechanical properties, ensuring the integrity of the catalyst during recycling to a certain extent. Recyclability stems from the biocompatibility of the cellulose-derived carbon aerogel and alters the powder characteristics of the catalyst, facilitating catalyst separation and regeneration.

[0021] Furthermore, this invention employs an in-situ growth strategy to achieve strong interfacial bonding between bimetallic MOF-derived carbon and cellulose-derived carbon aerogels through chemical bonding. During MOF crystal formation, the active functional groups on the cellulose molecular chains coordinate with metal ions, forming chemical bonds. This in-situ bonding avoids the weak interfacial bonding problems commonly encountered in physical mixing. The enhanced interfacial bonding strength is based on the synergistic effect of coordination bonds and covalent bonds. Metal ions form stable coordination bonds with the oxygen atoms of cellulose molecules, while dehydration reactions may occur during high-temperature processing to form covalent bonds. This multiple bonding mechanism ensures the stability of the interface under harsh reaction conditions. In-situ growth also enables precise control of MOF crystal size and distribution. By adjusting the reaction conditions, uniformly dispersed nanoscale MOF crystals can be obtained, avoiding mass transfer limitations and the burial of active sites caused by large-size crystals.

[0022] The beneficial effects of this invention are: The catalyst of this invention has extremely high physicochemical stability. At the same time, it effectively improves its catalytic performance through mechanisms such as bimetallic synergy, hierarchical electron transfer and highly dispersed active sites. It can be effectively and efficiently catalyzed to degrade organic pollutants in water, and it has spectral effectiveness, which is also conducive to separation and recovery. Detailed Implementation

[0023] The present invention will be further described clearly and in detail below with reference to specific embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0024] Unless otherwise specified, all raw materials used in the embodiments of the present invention are commercially available or obtainable by those skilled in the art; unless otherwise specified, all methods used in the embodiments of the present invention are methods mastered by those skilled in the art. Example 1

[0025] A method for preparing a bimetallic MOF-modified cellulose aerogel-derived carbon catalyst. The method includes: 1) A bimetallic MOF precursor solution with a concentration of 0.2 g / mL was prepared by dissolving ferric chloride hexahydrate, cobalt acetate tetrahydrate, and 2,5-dihydroxyterephthalic acid in N,N-dimethylformamide at a molar ratio of 1.2:1.1:1. 2) Carboxymethyl cellulose was dissolved in water at a mass ratio of 1:10, dispersed, aged for 0.5 h, and freeze-dried for 24 h to prepare cellulose aerogel; 3) Immerse the cellulose aerogel in the precursor solution and let it stand for 36 h at an ambient temperature of 60 °C to obtain MOF-modified cellulose gel through in-situ growth. 4) The modified cellulose gel was carbonized under nitrogen atmosphere, gas flow rate of 100 cc / min, heating rate of 5 ℃ / min, carbonization temperature of 600 ℃, and holding time of 3 h to obtain bimetallic MOF modified cellulose-derived carbon catalyst.

[0026] The materials prepared in the examples were subjected to performance testing, and the specific characterization results are as follows.

[0027] Catalyst performance testing: A 250 mL stoppered conical flask was used as the reactor to avoid loss of volatile substances. 100 mL of levofloxacin solution with an initial concentration of 20 mg / L and 0.08 g of catalyst were added to each reactor. The flasks were placed in a constant-temperature shaking incubator at 25 °C and shaken at 150 rpm for 30 min to reach adsorption-desorption equilibrium. After equilibrium, 20 mg of PMS was quickly added to initiate the reaction. At set time intervals (0, 5, 10, 20, 30, 40, 50, 60 min), 5 mL of the suspension sample was taken and immediately filtered through a nylon needle filter to remove catalyst particles. The filtrate was collected in a sample vial for later use. Concentration analysis was performed using high-performance liquid chromatography (HPLC) to determine the residual concentration of levofloxacin. The degradation rate was calculated as (C0-Ce) / C0×100%, where C0 is the initial concentration and Ce is the final concentration after the reaction. This quantitatively characterized the degradation performance of the catalyst.

[0028] Metal leaching rate detection: After the catalyst performance testing, a 20 mL sample of the reaction solution was taken and filtered to remove catalyst particles as described above. The concentrations of iron and cobalt in the filtrate were directly determined using inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0029] Cyclic stability testing: After each degradation experiment, the catalyst was recovered from the reaction solution by filtration, washed multiple times with deionized water and anhydrous ethanol to remove surface-adsorbed contaminants and salts, and then dried overnight in a vacuum drying oven at 60 °C for later use. The recovered and regenerated catalyst was reused, and degradation experiments were repeated under identical conditions (catalyst mass, PMS mass, LEV concentration, and volume). The LEV degradation rate after each cycle was recorded according to the aforementioned method. At least 20 cycles were performed to observe catalyst performance degradation and quantitatively assess the catalyst's cyclic stability and lifespan.

[0030]

[0031] Analysis of the above characterization results shows that the bimetallic MOF-modified cellulose-derived carbon aerogel catalyst prepared in this invention exhibits excellent comprehensive performance. Highly efficient degradation performance: the degradation rate of levofloxacin (LEV) reached 98.3% within 60 min, confirming the high efficiency of the catalyst in activating persulfate (PMS) to generate strongly oxidizing species. This is mainly due to the synergistic effect of the Fe-Co bimetallic catalyst. 3+ / Fe 2+ and Co 3+ / Co 2+ The synergistic catalysis of the redox pair significantly accelerates the activation process of PMS. The electronic regulation effect formed between the two metals optimizes the d-orbital energy level distribution of the active center, lowers the reaction energy barrier, and improves reaction efficiency and selectivity through a hierarchical electron transfer mechanism. The highly conductive carbon skeleton, with its high conductivity derived from cellulose, promotes rapid electron transfer within the catalyst, accelerating the generation of free radicals and the oxidative decomposition of pollutant molecules. Good dispersibility and abundant active sites: the three-dimensional network structure and in-situ growth strategy of cellulose aerogel ensure uniform dispersion and high-density loading of FeCo-MOF nanocrystals on the support, providing sufficient active sites. Effective mass transfer: the hierarchical pore structure derived from aerogel facilitates the diffusion and transport of reactant and product molecules.

[0032] Extremely low metal leaching; the concentrations of iron and cobalt ions detected in the solution after the reaction were both below 0.1 mg / L. This excellent performance is mainly attributed to the following factors: 1. Effective carbon shell protection: The carbon shell layer formed by in-situ carbonization tightly encapsulates the MOF-derived metal / carbon core, effectively blocking the erosion of the active metal component by water molecules and reaction intermediates, and significantly inhibiting the dissolution of metal ions; 2. Strong interfacial bonding: The chemical bonding formed by the in-situ growth strategy ensures a strong interfacial bond between the MOF-derived structure and the carbon support, preventing the active component from detaching during the reaction process; 3. MOF structural stability: The structural stability of the bimetallic MOF itself in the reaction environment is also an important factor in low leaching.

[0033] Furthermore, it exhibits excellent cycle stability; after 20 cycles of repeated use, the catalyst still maintains a high level of LEV degradation rate. This fully demonstrates the catalyst's outstanding structural stability and lifespan, with key factors including: 1. Low metal leaching; 2. Robust core-shell structure, where the physical protection of the carbon shell and the chemical bonding at the core-shell interface effectively resist chemical corrosion and physical wear (such as vibration and friction during recycling) during the reaction process; 3. Stable support structure, where the carbon skeleton derived from cellulose aerogel has good mechanical strength and can maintain its three-dimensional network structure even after multiple cycles, preventing the collapse of the overall catalyst structure.

[0034] The bimetallic MOF-modified cellulose-derived carbon aerogel catalyst successfully prepared by this method fully achieves the expected goals of this invention: through the FeCo bimetallic synergistic effect, the shell-core structure design protected by carbon shell, and the in-situ growth strong interface bonding strategy, the degradation activity of the catalyst is significantly improved, the metal leaching rate is reduced, and it is endowed with excellent cycle stability, providing a new solution for efficient, stable, and environmentally friendly water treatment catalysts. Example 2

[0035] A method for preparing a bimetallic MOF-modified cellulose-derived carbon aerogel catalyst. The method includes: 1) Ferric chloride hexahydrate, cobalt acetate tetrahydrate, and 2,5-dihydroxyterephthalic acid were dissolved in N,N-dimethylformamide in a molar ratio of 1.4:1.3:1 to prepare a bimetallic MOF precursor solution with a concentration of 0.4 g / mL; 2) Dissolve carboxymethyl cellulose in water at a mass ratio of 1:15, disperse, age for 1 h, and freeze dry for 48 h to prepare cellulose aerogel; 3) Immerse the cellulose aerogel in the precursor solution and let it stand for 24 h at an ambient temperature of 80 °C to obtain MOF-modified cellulose gel through in-situ growth. 4) The modified cellulose gel was carbonized under nitrogen atmosphere, gas flow rate of 200 cc / min, heating rate of 5 ℃ / min, carbonization temperature of 750 ℃, and holding time of 2 h to obtain bimetallic MOF modified cellulose-derived carbon catalyst.

[0036] The materials prepared in the examples were subjected to performance testing, and the specific characterization results are as follows.

[0037] Catalyst performance testing: A 250 mL stoppered conical flask was used as the reactor to avoid loss of volatile substances. 100 mL of levofloxacin solution with an initial concentration of 20 mg / L and 0.08 g of catalyst were added to each reactor. The flasks were placed in a constant-temperature shaking incubator at 25 °C and shaken at 150 rpm for 30 min to reach adsorption-desorption equilibrium. After equilibrium, 20 mg of PMS was quickly added to initiate the reaction. At set time intervals (0, 5, 10, 20, 30, 40, 50, 60 min), 5 mL of the suspension sample was taken and immediately filtered through a nylon needle filter to remove catalyst particles. The filtrate was collected in a sample vial for later use. Concentration analysis was performed using high-performance liquid chromatography (HPLC) to determine the residual concentration of levofloxacin. The degradation rate was calculated as (C0-Ce) / C0×100%, where C0 is the initial concentration and Ce is the final concentration after the reaction. This quantitatively characterized the degradation performance of the catalyst.

[0038] Metal leaching rate detection: After the catalyst performance testing, a 20 mL sample of the reaction solution was taken and filtered to remove catalyst particles as described above. The concentrations of iron and cobalt in the filtrate were directly determined using inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0039] Cyclic stability testing: After each degradation experiment, the catalyst was recovered from the reaction solution by filtration, washed multiple times with deionized water and anhydrous ethanol to remove surface-adsorbed contaminants and salts, and then dried overnight in a vacuum drying oven at 60 °C for later use. The recovered and regenerated catalyst was reused, and degradation experiments were repeated under identical conditions (catalyst mass, PMS mass, LEV concentration, and volume). The LEV degradation rate after each cycle was recorded according to the aforementioned method. At least 20 cycles were performed to observe catalyst performance degradation and quantitatively assess the catalyst's cyclic stability and lifespan.

[0040]

[0041] Analysis of the characterization results indicates that the bimetallic MOF-modified cellulose-derived carbon aerogel catalyst prepared under the specific parameters of this embodiment exhibits superior overall performance. The degradation rate of levofloxacin reached 99.9% within 60 min, a further improvement compared to Example 1. This is mainly attributed to the following optimizations: 1) Higher MOF precursor concentration and metal salt ratio significantly increased the loading density of FeCo-MOF crystals grown in situ on the cellulose aerogel, exposing more abundant Fe-Co bimetallic active sites; 2) Higher carbonization temperature promoted the increased graphitization degree of the cellulose-derived carbon framework, further enhancing the conductivity of the material and accelerating the transfer efficiency of electrons within the catalyst and between the catalyst and PMS / pollutants; 3) The in-situ growth temperature of 80 °C may have helped form smaller, more uniformly distributed MOF nanocrystals, optimizing the accessibility of active sites. The synergistic catalytic effect between the Fe-Co bimetals, the rapid electron conduction of the highly conductive carbon framework, and the optimized hierarchical pore structure collectively contributed to near-complete pollutant degradation.

[0042] The concentrations of iron and cobalt ions in the solution after the reaction were both strictly below 0.1 mg / L. This verifies that even with higher metal loading and more stringent carbonization temperatures, the core design strategy of this invention remains effective: 1) The strong chemical bonds formed by in-situ growth ensure a robust interface between the MOF-derived structure and the carbon support; 2) The dense carbon shell formed by high-temperature carbonization does not negatively affect the protection of the internal FeCo-MOF-derived core, and can still effectively block the contact between the active metal components and the aqueous phase, inhibiting the dissolution of metal ions; 3) The intrinsic stability of the bimetallic MOF structure is maintained under optimized growth conditions.

[0043] After 20 cycles of reuse, the catalyst still exhibited a LEV degradation rate of 94.8%, demonstrating superior stability compared to Example 1. This fully demonstrates that: 1) extremely low metal leaching rate is the cornerstone of maintaining long-term catalytic activity; 2) the carbon shell structure formed by carbonization at 750 °C possesses higher mechanical strength and chemical inertness, effectively resisting physical wear (and chemical oxidation corrosion) during repeated cycles, thus protecting the internal active components; 3) strong interfacial bonding prevents the shedding of active components during cycling; and 4) the cellulose-derived carbon skeleton maintains good structural integrity at high carbonization temperatures, providing stable support for the catalyst as a whole.

[0044] This embodiment further optimizes the degradation activity and cycle stability of the catalyst based on Example 1 by adjusting the preparation parameters, fully demonstrating the adjustability and universality of the preparation method described in this invention, and successfully obtaining a bimetallic MOF-modified cellulose-derived carbon aerogel catalyst with superior performance. Example 3

[0045] A method for preparing a bimetallic MOF-modified cellulose-derived carbon aerogel catalyst. The method includes: 1) Ferric chloride hexahydrate, cobalt acetate tetrahydrate, and 2,5-dihydroxyterephthalic acid were dissolved in N,N-dimethylformamide in a molar ratio of 1.5:1.4:1 to prepare a bimetallic MOF precursor solution with a concentration of 0.5 g / mL. 2) Carboxymethyl cellulose was dissolved in water at a mass ratio of 1:20, dispersed, aged for 1.5 h, and freeze-dried for 72 h to prepare cellulose aerogel; 3) Immerse the cellulose aerogel in the precursor solution and let it stand for 12 hours at 100 °C to obtain MOF-modified cellulose gel through in-situ growth. 4) The modified cellulose gel was carbonized under nitrogen atmosphere, gas flow rate of 300 cc / min, heating rate of 5 ℃ / min, carbonization temperature of 900 ℃, and holding time of 1 h to obtain a bimetallic MOF modified cellulose-derived carbon catalyst.

[0046] The materials prepared in the examples were subjected to performance testing, and the specific characterization results are as follows.

[0047] Catalyst performance testing: A 250 mL stoppered conical flask was used as the reactor to avoid loss of volatile substances. 100 mL of levofloxacin solution with an initial concentration of 20 mg / L and 0.08 g of catalyst were added to each reactor. The flasks were placed in a constant-temperature shaking incubator at 25 °C and shaken at 150 rpm for 30 min to reach adsorption-desorption equilibrium. After equilibrium, 20 mg of PMS was quickly added to initiate the reaction. At set time intervals (0, 5, 10, 20, 30, 40, 50, 60 min), 5 mL of the suspension sample was taken and immediately filtered through a nylon needle filter to remove catalyst particles. The filtrate was collected in a sample vial for later use. Concentration analysis was performed using high-performance liquid chromatography (HPLC) to determine the residual concentration of levofloxacin. The degradation rate was calculated as (C0-Ce) / C0×100%, where C0 is the initial concentration and Ce is the final concentration after the reaction. This quantitatively characterized the degradation performance of the catalyst.

[0048] Metal leaching rate detection: After the catalyst performance testing, a 20 mL sample of the reaction solution was taken and filtered to remove catalyst particles as described above. The concentrations of iron and cobalt in the filtrate were directly determined using inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0049] Cyclic stability testing: After each degradation experiment, the catalyst was recovered from the reaction solution by filtration, washed multiple times with deionized water and anhydrous ethanol to remove surface-adsorbed contaminants and salts, and then dried overnight in a vacuum drying oven at 60 °C for later use. The recovered and regenerated catalyst was reused, and degradation experiments were repeated under identical conditions (catalyst mass, PMS mass, LEV concentration, and volume). The LEV degradation rate after each cycle was recorded according to the aforementioned method. At least 20 cycles were performed to observe catalyst performance degradation and quantitatively assess the catalyst's cyclic stability and lifespan.

[0050]

[0051] Analysis of the characterization results shows that the bimetallic MOF-modified cellulose-derived carbon aerogel catalyst prepared under the more stringent preparation parameters of this embodiment exhibits unique performance characteristics. It achieves complete degradation of levofloxacin within 60 min. This exceptional performance can be attributed to the superposition of multiple optimization effects: 1) The increased metal salt ratio and precursor concentration significantly increase the loading density of FeCo-MOF nanocrystals grown in situ on the cellulose aerogel, exposing extremely abundant Fe-Co bimetallic synergistic active sites; 2) The high carbonization temperature of 900 °C greatly promotes the graphitization of the cellulose-derived carbon framework, forming a highly ordered graphite microcrystalline structure, resulting in peak conductivity of the carbon framework, thereby significantly accelerating the electron transfer rate within the catalyst and to PMS / pollutant molecules; 3) The in-situ growth temperature of 100 °C may be beneficial for forming smaller, more uniformly distributed MOF nanocrystals, which, combined with the more developed hierarchical pore structure formed by the aerogel support under extended freeze-drying time, jointly optimize the diffusion and transport of reactants to active sites and the desorption and removal pathways of product molecules. The strong synergistic catalytic effect between Fe-Co bimetals, the peak conductivity of the carbon skeleton, and the optimized pore structure all contribute to the complete and rapid mineralization of LEV.

[0052] The concentrations of iron and cobalt ions in the solution after the reaction remained strictly below the detection limit. This fully demonstrates that even under the most stringent preparation conditions and the highest metal loading, the core protection mechanism of this invention remains stable: 1) Ultra-high temperature carbonization forms an extremely dense and highly graphitized carbon shell, which has the strongest physical barrier effect, almost completely blocking the erosion of the internal FeCo-MOF-derived active core by the aqueous environment and reaction intermediates; 2) The chemical bonds formed by the in-situ growth strategy remain stable at high carbonization temperatures, ensuring a strong connection between the active component and the carbon support, effectively preventing detachment; 3) Optimized growth conditions and high-temperature derivatization processes may enhance the intrinsic stability of the bimetallic MOF-derived structure.

[0053] After 20 cycles of reuse, the catalyst maintained a high LEV degradation rate of 90.3%. Although slightly lower than in Example 2, this cycling stability is still excellent and in line with expectations, considering the extreme increase in initial activity and the stringent preparation conditions. Its stability stems from: 1) continuous low metal leaching, which is the fundamental guarantee for maintaining long-term activity; 2) a robust core-shell structure; the carbon shell formed at 900 °C possesses extremely high mechanical strength and chemical inertness, providing excellent protection for the internal active core despite repeated cycles of physical friction and chemical oxidation; 3) enhanced interfacial bonding at high carbonization temperatures, effectively resisting stress during cycling; and 4) the vitamin-derived carbon framework maintaining good macroscopic structural integrity after treatment at 900 °C, providing a solid support framework for the overall catalyst. The slight decrease in initial activity may be related to the collapse of some microporous structures or subtle changes in the surface properties of active sites at extremely high carbonization temperatures, but the overall structural stability remains excellent.

[0054] This embodiment successfully obtained a bimetallic MOF-modified cellulose-derived carbon aerogel catalyst with the highest initial degradation activity by pushing the preparation parameters to their limits, while maintaining strict control over metal leaching and high cycle stability. This further verifies the scalability of the preparation method of this invention; by adjusting the parameters, an optimized balance can be achieved with different emphases on activity and stability, providing a high-performance catalyst selection for specific application scenarios. Comparative Example 1

[0055] Based on Example 2, this example verifies the Fe-Co bimetallic synergistic catalytic effect. The process of Example 2 is modified as follows:

[0056] The performance testing method for the comparative product was completely consistent with that of Example 1. Partial performance characterization was performed, and the characterization results are shown in the table below:

[0057] Analysis of the characterization results shows that the catalytic performance and stability of the single-metal catalyst are significantly lower than those of the bimetallic system, demonstrating the necessity of bimetallic synergy. Deviations in the metal ratio from the optimal value also lead to performance degradation. Specifically, the degradation rates of D1-1 and D1-2 are much lower than those of the bimetallic system, while the metal leaching rates are significantly higher, and the cycle stability is also significantly reduced. This clearly indicates that a single Fe or Co active site cannot effectively trigger or maintain efficient and stable PMS activation and pollutant degradation cycles, while the electronic interactions between the Fe and Co bimetals are crucial for promoting radical or non-radical pathways. Furthermore, although the D1-3 group uses a bimetal, the Fe:Co ratio deviates from the optimal ratio of the examples. While its degradation rate and cycle stability are better than those of the single-metal catalyst, they are still lower than those of Example 2, and the metal leaching is also slightly higher. This suggests that an imbalance in the metal ratio may affect the formation efficiency, distribution uniformity, or intrinsic catalytic activity of the bimetallic active sites, disrupting the optimal synergistic effect and leading to a decrease in catalytic performance and stability. Comparative Example 2

[0058] Based on Example 2, this example verifies the strong interface bonding constructed by in-situ growth. The process of Example 2 is modified as follows:

[0059] The performance testing method for the comparative product was completely consistent with that of Example 1. Partial performance characterization was performed, and the characterization results are shown in the table below:

[0060] Analysis of the characterization results shows that physical mixing leads to weak interfacial bonding and easy metal leaching; calcination at too low a temperature results in incomplete carbonization and failure to form a core-shell structure; while excessively high temperatures, although strengthening the bonding, reduce the specific surface area, affecting mass transfer. Comparative Example 2 indicates that the strong interfacial bonding constructed by the in-situ growth strategy is the core element for maintaining high catalyst activity and low metal leaching.

[0061] The D2-1 catalyst, prepared by physical mixing, lacks chemical bonding, resulting in only weak physical adsorption between the active component and the support. This loose interfacial bonding easily leads to the detachment of MOF particles during the reaction, reducing the number of effective active sites and significantly exacerbating the dissolution of metal ions, causing a simultaneous deterioration in catalytic performance and stability.

[0062] Group D2-2 underwent low-temperature carbonization at 400 ℃. Although it retained some MOF structure and exhibited certain catalytic activity, the insufficient carbonization temperature prevented the cellulose from being fully converted into a dense carbon layer. The results were: 1) a significant reduction in the conductivity of the carbon skeleton, hindering electron transfer; 2) the crucial protective core-shell structure failed to form effectively, exposing internal metal active sites directly to the aqueous environment, leading to an increased metal leaching rate.

[0063] Although the D2-3 group used ultra-high temperature carbonization at 1000 ℃ to improve interfacial bonding strength and carbon layer protection by enhancing graphitization, the excessively high temperature caused partial collapse of microporous structures and shrinkage of mesopores, significantly reducing the specific surface area of ​​the catalyst. The increased mass transfer resistance weakened the diffusion efficiency of pollutant molecules to active sites, offsetting some of the advantages brought by high conductivity, ultimately resulting in a degradation rate lower than that of Example 2 at the optimal carbonization temperature. Comparative Example 3

[0064] Based on Example 2, this example verifies the unique three-dimensional network structure of the cellulose aerogel carrier. The process of Example 2 is modified as follows:

[0065] The performance testing method for the comparative product was completely consistent with that of Example 1. Partial performance characterization was performed, and the characterization results are shown in the table below:

[0066] Analysis of the above characterization results shows that the aerogel structure is crucial for dispersibility and recyclability; too low a moisture content or insufficient freeze-drying time will affect the formation of the pore structure, leading to a decline in performance.

[0067] Specifically, group D3-1 used ordinary cellulose paper as a carrier, which lacks the three-dimensional interconnected network structure unique to aerogels. This resulted in uneven distribution of FeCo-MOF nanocrystals on the carrier surface, making them prone to physical aggregation. During the reaction oscillation, the aggregates settled more rapidly due to gravity, making complete recovery difficult through conventional filtration. SEM observation showed that MOF crystals accumulated on the surface of cellulose fibers, forming blocky structures of varying sizes. This significantly reduced the exposed area of ​​effective active sites, hindered the diffusion pathway of reactant molecules to the active sites, and ultimately caused a sharp decrease in degradation rate.

[0068] For group D3-2, the CMC to water mass ratio was reduced to 1:5. This excessively low water ratio resulted in excessively high viscosity of the precursor solution, limiting the full hydration and extension of the cellulose molecular chains. During freeze-drying, ice crystal template growth was restricted, leading to a narrower pore size distribution and a significantly reduced proportion of macropores in the resulting aerogel, resulting in a smaller specific surface area compared to Example 2. This underdeveloped pore structure limited in-situ MOF growth, decreased crystal loading density, and localized agglomeration in some areas due to insufficient support. The degradation rate decreased, with the recovery rate dropping to 90.3%, indicating that pore structure defects weakened the catalyst's mass transfer efficiency and mechanical stability.

[0069] In group D3-3, the freeze-drying time was shortened to 12 h, resulting in incomplete sublimation of ice crystals. Residual moisture generated capillary stress during subsequent heating, causing localized collapse of the aerogel framework. The resulting support exhibited pore size inhomogeneity, with some micropores closing and mesopores expanding, weakening the overall strength of the three-dimensional network. During the MOF growth stage, the support's shrinkage and deformation led to uneven distribution of active sites, and SEM showed slight signs of aggregation. Although the degradation rate remained at 88.5%, the recovery rate decreased to 92.7%, and the aggregation trend intensified significantly after recycling, confirming the necessity of thorough freeze-drying to maintain the structural integrity of the support.

[0070] The above results collectively demonstrate that the three-dimensional network of cellulose aerogel, through its high porosity and hierarchical pore structure, provides uniform anchoring points for MOF, effectively inhibiting the migration and aggregation of nanocrystals. Simultaneously, the optimized water ratio ensures sufficient penetration and diffusion of the precursor solution within the support, while freeze-drying guarantees the complete removal of the ice crystal template and the stable formation of the pore structure, ultimately achieving high catalyst dispersibility and near-complete recovery. Comparative Example 4

[0071] Based on Example 2, this example verifies the core-shell structure formed by carbonization and its stability. The process of Example 2 is modified as follows:

[0072] The performance testing method for the comparative product was completely consistent with that of Example 1. Partial performance characterization was performed, and the characterization results are shown in the table below:

[0073] Analysis of the above characterization results shows that insufficient in-situ growth conditions lead to low MOF loading and weak binding; in-situ growth results in poor interfacial binding, making MOFs prone to detachment and affecting cycling performance.

[0074] Specifically, group D4-1 lowered the in-situ growth environment temperature to 40 °C, significantly lower than the 100 °C in Example 2. The lower temperature significantly reduced the reaction kinetics and solubility of the metal ions and organic ligands, leading to a slower MOF nucleation rate and limited crystal growth. As a result, the coverage density and loading of MOF nanocrystals on the cellulose aerogel surface were greatly reduced, and the crystal size was larger and more unevenly distributed. Simultaneously, the chemical bonds formed at low temperatures were insufficient in strength, making them prone to breakage during subsequent carbonization and recycling, resulting in weakened interfacial bonding. After cycling, the MOF shedding rate was as high as 20.2%. Insufficient number of active sites and weak bonding combined to cause a degradation rate of only 80.5%.

[0075] Group D4-2 shortened the in-situ growth settling time to 6 h. This excessively short settling time resulted in insufficient diffusion of metal ions and ligands into the aerogel, preventing the reaction from reaching equilibrium. Consequently, MOFs primarily deposited on the surface of the aerogel support. This led to a low MOF loading with a significant distribution gradient and sparse active sites within the support. Furthermore, insufficient crystal growth time resulted in smaller MOF crystals with poor crystallinity and insufficient structural integrity. During subsequent carbonization and catalytic cycling, these structural defects were more prone to breakage and detachment, leading to a faster decline in the number of effective active sites and ultimately a degradation rate of 85.2%.

[0076] Group D4-3 employed a non-in-situ spraying method instead of an in-situ growth strategy. Although spraying can control the loading of MOFs on the aerogel surface to some extent, the MOF particles and the support rely solely on physical adsorption and van der Waals forces, lacking chemical bonding. This weak interfacial bonding is highly susceptible to failure during subsequent high-temperature carbonization and the harsh catalytic reaction environment due to thermal stress, fluid shear forces, and the erosion of reaction intermediates, leading to a large number of MOF particles detaching from the support surface. The detached active components not only directly lose their catalytic function but also exacerbate the dissolution of metal ions. Furthermore, the spraying method struggles to achieve a uniform distribution of MOFs within the pores of the support, resulting in low utilization of effective active sites and ultimately a degradation performance of only 75.8%.

Claims

1.A method for preparing a bimetallic MOF modified cellulose-derived carbon aerogel catalyst, characterized in that, the method comprises: 1) dissolving transition metal salt A and transition metal salt B and an organic ligand in an organic solvent to prepare a bimetallic MOF precursor solution; 2) dissolving a cellulose derivative in water, dispersing, aging, and freeze-drying to prepare a cellulose aerogel; 3) immersing the cellulose aerogel in the precursor solution to perform in-situ growth to obtain a MOF modified cellulose gel; and 4) performing carbonization treatment on the modified cellulose gel to obtain a bimetallic MOF modified cellulose-derived carbon aerogel catalyst. 2.The method for preparing a bimetallic MOF modified cellulose-derived carbon aerogel catalyst according to claim 1, characterized in that, in step 1), the transition metal salt A is a soluble iron salt and / or a soluble zinc salt and / or a soluble copper salt; in step 1), the transition metal salt B is a soluble cobalt salt and / or a soluble manganese salt and / or a soluble nickel salt; in step 1), the organic ligand is terephthalic acid and / or 2,5-dihydroxyterephthalic acid and / or 2-methylimidazole; and in step 1), the organic solvent comprises N, N-dimethylformamide. 3.The method for preparing a bimetallic MOF modified cellulose-derived carbon aerogel catalyst according to claim 1 or 2, characterized in that, in step 1), the molar ratio of transition metal salt A, transition metal salt B and organic ligand is (1-1.5) : (1.1-2.1) : 1; and in step 1), the total concentration of the transition metal salt A and the transition metal salt B in the organic solvent is 0.2-0.5 g / mL. 4.The method for preparing a bimetallic MOF modified cellulose-derived carbon aerogel catalyst according to claim 1, characterized in that, in step 2), the mass ratio of the cellulose derivative to water is 1: 10-20. 5.The method for preparing a bimetallic MOF modified cellulose-derived carbon aerogel catalyst according to claim 1 or 4, characterized in that, in step 2), the aging time is 0.5-1.5 h; and in step 2), the freeze-drying time is 24-72 h. 6.The method for preparing a bimetallic MOF modified cellulose-derived carbon aerogel catalyst according to claim 1, characterized in that, in step 3), the in-situ growth is performed under the environmental conditions of a temperature of 60-100 ℃ for 12-36 h. 7.The method for preparing a bimetallic MOF modified cellulose-derived carbon aerogel catalyst according to claim 1, characterized in that, in step 4), the carbonization treatment is performed under the conditions of a nitrogen atmosphere, a gas flow rate of 100-300 cc / min, a temperature rising rate of 5 ℃ / min, a carbonization temperature of 600-900 ℃, and a holding time of 1-3 h. 8.A bimetallic MOF modified cellulose-derived carbon aerogel catalyst prepared by any one of the methods according to claims 1 to 7. 9.Use of the bimetallic MOF modified cellulose-derived carbon aerogel catalyst according to claim 8 in degrading organic pollutants in water. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

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