A fenton-like composite catalyst, a preparation method and application thereof

Abstract

This invention belongs to the field of water treatment technology, specifically disclosing a Fenton-like composite catalyst, its preparation method, and its application. The Fenton-like composite catalyst is prepared from the following components in parts by mass: 10-25 parts high-entropy spinel, 60-80 parts carbon support, 8-15 parts binder, and 1-2 parts pore-forming agent. The high-entropy spinel is a composite material composed of transition metal doped cobalt. The high-entropy spinel in this catalyst regulates the Co content through high-entropy configuration. 3+ The transition from low-spin to high-spin enhances the hybridization of Co 3d-O 2p orbitals, enabling ring-opening and chain breaking of pollutants such as benzene rings and heterocyclic rings. This invention's Fenton-like composite catalyst, used as a catalytic packing material in a fixed-bed reactor to remove pollutants from wastewater, constructs a gradient oxidation process. This allows different types of active species to synergistically cooperate within each gradient region, thereby achieving highly efficient degradation of various types of pollutants and significantly improving the utilization efficiency of reactive oxygen species.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, specifically to a Fenton-like composite catalyst, its preparation method, and its application. Background Technology

[0002] Pharmaceutical wastewater is generally characterized by high COD concentration, extremely poor biodegradability (B / C < 0.1), strong biotoxicity, high salt content, and complex composition. It often contains recalcitrant organic pollutants such as benzene compounds, phenols, pyridine, quinoline, antibiotics, and halogenated hydrocarbons. Conventional processes such as coagulation, sedimentation, biochemical treatment, and adsorption are insufficient to achieve stable compliance with standards, and the treatment process is both difficult and costly.

[0003] Heterogeneous Fenton-like technologies have become the mainstream technology for the pretreatment of recalcitrant wastewater due to their advantages such as strong oxidation capacity, mild reaction conditions, and low iron sludge production. Fenton-like catalysts include monometallic / iron-based catalysts and Co3O4 catalysts. However, monometallic / iron-based catalysts have a powder structure, resulting in a single active site, low electron transfer efficiency, and insufficient H2O2 utilization; metal ion leaching easily causes secondary pollution, and their lifespan is short; powder catalysts are difficult to engineer, and molded packings struggle to balance activity and mechanical strength. In contrast, Co3O4 catalysts contain Co... 3+ Existing in a low-spin state, the high energy barrier for breaking the OO bond severely limits the catalytic activation efficiency.

[0004] High-entropy metal oxides are formed by the disordered solid solution of five or more metal cations to form a single lattice. They have unique advantages such as high configurational entropy, lattice distortion, multiple active sites, oxygen vacancy enrichment, and tunable electronic structure. They can precisely control the metal spin state and orbital hybridization, significantly improving catalytic activity and structural stability. Summary of the Invention

[0005] This invention aims to provide a Fenton-like composite catalyst, its preparation method, and its application. It features high activity and high strength, and establishes a matching gradient oxidation treatment process to achieve stepwise ring-opening and chain breaking of pollutants in high-concentration, recalcitrant organic wastewater from chemical and pharmaceutical industries, significantly improving biodegradability and efficiently removing COD, thus meeting the requirements for efficient laboratory catalysis and continuous and stable operation of industrial fixed-bed catalysts.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: The first objective of this invention is to provide a Fenton-like composite catalyst, which is prepared from the following components in parts by mass: 10-25 parts of high-entropy spinel 60-80 parts of carbon support 8-15 parts adhesive 1-2 parts of pore-forming agent, The high-entropy spinel is a composite material composed of cobalt doped with transition metals, wherein the transition metals are selected from any four of Fe, Ni, Mn, Cu, Zn, and Al. The carbon support is a modified carbon support, which is prepared by adding a carbon matrix to nitric acid and then oxidizing it by introducing ozone.

[0007] In a further embodiment, the preparation steps of the high-entropy spinel are as follows: (1) A soluble metal salt is added to a solvent and stirred to obtain a mixed precursor solution; the soluble metal salt is a cobalt salt and four transition metal salts; the metals in the transition metal salts are selected from any four of Fe, Ni, Mn, Cu, Zn and Al; (2) Add a complexing agent, stir, and complex to form a stable sol; (3) The above sol is first concentrated to form a viscous wet gel; then the viscous wet gel is dried to obtain a dry gel; then the dry gel is pretreated at low temperature to obtain the precursor powder. (4) The precursor powder was crystallized at high temperature by segmented calcination process, cooled and ground to obtain disordered pentagonal high-entropy spinel powder.

[0008] This high-entropy spinel powder (HEP-Co) possesses a high-spin Co structure with spinel characteristics. 3+ Active center. A segmented calcination process is employed to avoid cracking, deformation, and pulverization caused by excessive temperature differences. Furthermore, it effectively separates crystal nucleation and growth, resulting in fine, uniform grains with controllable size, preventing agglomeration and abnormal growth.

[0009] In a further embodiment, in step (1), the molar ratio of metal ions in the four transition metal salts is (0.1~1):(0.1~1):(0.1~1):(0.1~1); and / or, The molar ratio of metal to Co in the four transition salts is 1:2.

[0010] In a further embodiment, in step (1), the soluble metal salt and cobalt salt are both nitrates, acetates, sulfates, or chlorides; and / or, The solvent is a mixture of deionized water and anhydrous ethanol in a volume ratio of 1:1.

[0011] In a further embodiment, in step (2), the complexing agent is one or more of citric acid monohydrate, polyvinylpyrrolidone, and urea; and / or, The amount of the complexing agent added is 30-50 mmol / L of the volume of the mixed precursor solution.

[0012] In a further embodiment, in step (3), the preliminary concentration involves slowly evaporating the sol in a water bath at 80-90°C to form a viscous wet gel; and / or, The drying process involves placing the viscous wet gel in a constant temperature drying oven at 100-110℃ for 12-18 hours.

[0013] In a further embodiment, in step (3), the low-temperature pretreatment involves placing the dry gel in a muffle furnace and pretreating it at 200°C for 2-4 hours to remove residual organic matter and adsorbed water from the dry gel, thereby obtaining a loose and porous precursor powder.

[0014] In a further embodiment, in step (4), the segmented calcination process refers to heating the temperature in air at a rate of 3℃ / min to 300~400℃ and holding it for 1~2h; then heating it at a rate of 2℃ / min to 650~750℃ and holding it for 3~5h.

[0015] In a further embodiment, the nitric acid concentration is 10-15 wt%, the ozone flow rate is 0.15-0.25 L / min, and the oxidation time is 4-6 h.

[0016] In this application, the carbon matrix may be activated carbon, carbon black, mesoporous carbon, carbon nanotubes, carbon fibers, carbon black, or biochar.

[0017] In this application, the modified carbon support is treated with ozone combined with nitric acid etching, which can both generate more active groups on the surface and ensure the stability of the carbon skeleton.

[0018] In this application, the modified carbon support employs a synergistic treatment of the carbon matrix using nitric acid and ozone. Nitric acid moderately oxidizes and opens pores, unblocking closed micropores and increasing pore connectivity. However, prolonged use or high concentrations of nitric acid alone can easily lead to excessive corrosion of the carbon skeleton, collapse of the microporous structure, and a decrease in specific surface area. Therefore, ozone is introduced to inhibit excessive etching by nitric acid, thereby protecting the microporous structure of the carbon skeleton. Furthermore, ozone decomposition produces active oxygen species such as ·OH, which can gently oxidize the carbon surface and introduce oxygen-containing functional groups (such as carboxyl, hydroxyl, and carbonyl groups), increasing the density of surface active sites without corroding internal pores.

[0019] In a further embodiment, the binder is one of kaolin, bentonite, or red clay; and / or, The pore-forming agent is one or a mixture of two or more of oxalic acid, sodium carbonate, and calcium carbonate. The pore-forming agent decomposes or reacts at high temperatures to generate gas, thereby forming pores in the catalyst. The pore-forming agent should be uniformly dispersed in the packing material, and the maximum dosage should not exceed 2% of the total weight to prevent packing collapse due to excessive gas release during calcination.

[0020] This invention transforms the active center of cobalt element into a highly active high-spin configuration through high-entropy metal doping, resulting in a crushing strength of >1100N for the prepared Fenton-like composite catalyst.

[0021] The second objective of this invention is to provide a method for preparing the aforementioned Fenton-like composite catalyst, characterized by comprising the following steps: High-entropy spinel powder, carbon carrier, binder and pore-forming agent are mixed evenly, then pressed into shape, and dried, sintered and cooled to obtain the final product.

[0022] In a further embodiment, the compression molding is performed using a press at 3-6 bar; the compressed granules are cylinders with a diameter of 1-2 cm. The drying process refers to vacuum drying at 50-60℃ for 20-26 hours.

[0023] In a further embodiment, the sintering is carried out at 1200-1300℃ for 2-3 hours under nitrogen pressure protection of 0.05~0.1MPa. The cooling refers to quenching and cooling using a 1-3 wt% sodium chloride solution.

[0024] A third objective of this invention is to provide an application of the aforementioned Fenton-like composite catalyst, which is used as a catalytic packing material in a fixed-bed reactor for the removal of pollutants from wastewater.

[0025] A further proposed method involves adjusting the pH of the wastewater to 3.0-4.0, then adding an oxidant at a dosage of 1.5-3.0‰ of the mass of the wastewater to be treated, with a hydraulic retention time of 40-90 minutes. This results in a COD removal rate of over 48% and increases the B / C ratio of the wastewater from 0.05-0.1 to no less than 0.26.

[0026] Using the Fenton-like composite catalyst of this invention, raw water with extremely low biodegradability (B / C < 0.1) can be treated to have a B / C ratio of not less than 0.26, thus meeting the basic requirements for biodegradable treatment. This demonstrates that the Fenton-like composite catalyst of this invention converts large, recalcitrant organic molecules into small, easily degradable substances through catalytic oxidation, phase transfer, and adsorption-desorption, significantly increasing the proportion of biodegradable organic matter in wastewater.

[0027] In a further embodiment, the oxidant in this invention is persulfate or hydrogen peroxide; The catalytic packing material located inside the fixed-bed reactor forms three annular oxidation gradient regions in a radial direction from its center outwards, namely the third oxidation gradient region, the second oxidation gradient region, and the first oxidation gradient region. The active substances in the first oxidation gradient region are sulfate radicals or superoxide radicals, the active substances in the second oxidation gradient region are high-valence metals, and the active substances in the third oxidation gradient region are hydroxyl radicals, which work together to degrade pollutants in wastewater.

[0028] That is, if the added oxidant is hydrogen peroxide, the active substance in the first oxidation gradient region is superoxide radical, and H2O2 is the precursor. If the added oxidant is persulfate, then the active substance in the first oxidation gradient region is persulfate free radical (SO4· ... - ) and a small amount of superoxide radicals (O2· - ).

[0029] The advantages of this invention compared to the prior art are as follows: (1) In this invention, high-entropy metal doping transforms the active center of cobalt into a highly active high-spin Co element. 3+ The crystal field splitting energy is high and the orbital hybridization is weak, resulting in a high activation energy barrier for the oxidant. In contrast, the octahedral Co in traditional Co3O4... 3+ In the low-spin state, this invention induces strong lattice distortion by allowing high-entropy metals to randomly occupy tetrahedral and octahedral sites, disrupting octahedral symmetry, significantly reducing the crystal field splitting energy Δ0, and driving Co... 3+ The transition from a low-spin to a high-spin state increases the number of unpaired electrons in the eg orbital, significantly enhancing the hybridization of the Co 3d-O 2p orbitals and lowering the OO bond breaking energy barrier.

[0030] (2) In the Fenton-like composite catalyst of this invention, high-entropy spinel will form Fe 2+ / Fe 3+ Co 2+ / Co 3+ Cu + / Cu 2+ Ni 2+ / Ni 3+ Zn 2+ / Zn 3+ Multiple redox cycles are constructed to create a continuous electron transport channel, significantly reducing electron transfer resistance. Multi-metal synergy enables rapid electron regeneration, avoids active site deactivation, and improves H2O2 utilization.

[0031] (3) High-temperature crystallization of catalyst: The precursor powder is crystallized at high temperature using a segmented calcination process. The calcination atmosphere is air. The heating program is as follows: heat up to 300~400℃ at a rate of 3℃ / min, then hold for 1~2h, then heat up to 650~750℃ at a rate of 2℃ / min, hold for 3~5h, and then cool naturally to room temperature. After grinding, disordered pentagonal high-entropy spinel (HEP-Co) is obtained, which is a Fenton-like composite catalyst.

[0032] This invention controls single-phase purity through segmented high-temperature crystallization, avoids preferential growth at a single high temperature step, suppresses impurity phase precipitation, and significantly improves single-phase yield. Simultaneously, the resulting catalyst crystals are uniform in size. Furthermore, the exposure of highly active crystal faces is controlled by setting temperature gradients at each stage.

[0033] (4) Preparation of modified carbon support: Ozone combined with nitric acid treatment of carbon matrix is ​​the core of simultaneously enhancing the electron transfer capacity, number of active sites, surface hydrophilicity and structural stability of carbon matrix, thereby systematically solving the problems of low utilization rate and poor stability of traditional Fenton-like composite catalysts, and significantly improving catalytic efficiency and practical application value.

[0034] High-density active sites are constructed in the catalyst through surface chemical modification, specifically by introducing a large number of active groups such as carboxyl, phenolic hydroxyl, and carbonyl groups through nitric acid treatment. This results in increased oxygen content on the carbon matrix surface and diversification of active sites. Since oxygen-containing functional groups enhance the adsorption and activation of oxidants, the activation energy of the reaction is reduced. In addition, moderate oxidation removes amorphous carbon while retaining the highly graphitized carbon framework, suppressing carbon loss and structural collapse during long-term operation and improving cycle stability.

[0035] (5) Gradient oxidation functional zoning: The Fenton-like composite catalyst in this invention is used as a catalytic packing material in a fixed-bed reactor to remove pollutants from wastewater. Within the local space of the Fenton catalyst material, multiple functional regions with continuously varying oxidation intensities and active sites are formed along the radial direction of the material, thus constructing a gradient oxidation. This allows different types of active species to work synergistically within this gradient region, thereby achieving efficient degradation of various types of pollutants, significantly improving the utilization efficiency of reactive oxygen species, and ultimately achieving deep removal of pollutants and a high removal rate of total organic carbon (TOC).

[0036] Gradient oxidation is an advanced oxidation strategy that achieves graded oxidation intensity and zoned action of reactive oxygen species by regulating the material structure and catalytic performance. It can match the stepwise degradation requirements of pollutants and improve mineralization efficiency and oxidant utilization.

[0037] Specifically, the first oxidation gradient region is characterized by low-intensity, long-lived reactive oxygen species, such as superoxide radicals or sulfate radicals, which preferentially activate large-molecule, highly aromatic, highly toxic, and recalcitrant parent pollutants. Long-lived reactive oxygen species have a wide diffusion range, preventing instantaneous high concentrations. The rapid self-quenching of OH molecules breaks down macromolecules into smaller carboxylic acids, aldehydes, ketones, and aromatic intermediates.

[0038] The second oxidation gradient region is primarily composed of medium-strength, medium-potential reactive oxygen species. For example, high-valence metal oxygen species in the catalyst possess both oxidizing and selective properties, efficiently decomposing nitrogen- and sulfur-containing heterocyclic pollutants, removing most COD, color, and toxicity, and constructing a multi-metal ion cycling system.

[0039] The third oxidation gradient region contains high-intensity, high-potential, short-lived ROS, such as hydroxyl radicals, which are mainly generated at local interfaces and can react with pollutants nearby, thereby reducing long-distance diffusion losses. Attached Figure Description

[0040] Figure 1 XRD patterns of HEP-Co and Co3O4 prepared in Example 1; Figure 2 The SEM image of HEP-Co prepared in Example 1; Figure 3 EDS elemental map of HEP-Co prepared in Example 1; Figure 4 Raman spectra of HEP-Co and Co3O4 prepared in Example 1; Figure 5 Electrochemical spectra of HEP-Co and Co3O4 prepared in Example 1, where a is an impedance diagram and b is a cyclic voltammetry diagram; Figure 6 XPS full spectra of HEP-Co and Co3O4 prepared in Example 1; Figure 7 Magnetic curves of HEP-Co and Co3O4 prepared in Example 1 at room temperature; Figure 8 A photograph of the Fenton-like composite catalyst prepared in Example 1. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0042] Example 1 I. Preparation of high-entropy spinel: S1. Dissolve 0.253g of ferric nitrate nonahydrate, 0.182g of nickel nitrate hexahydrate, 0.186g of zinc nitrate hexahydrate, 0.151g of copper nitrate trihydrate, and 1.46g of cobalt nitrate hexahydrate in a mixed solution consisting of 50mL of pure water and 50mL of anhydrous ethanol; stir magnetically until completely dissolved to obtain a homogeneous and transparent pentagonal metal mixed precursor solution. S2. Dissolve 1.05g of citric acid monohydrate in 100mL of pure water, then add it to the pentagonal metal mixed precursor solution and mix thoroughly for 30min to obtain a sol.

[0043] S3. The above sol is first concentrated in an 80°C water bath and slowly evaporated to form a viscous wet gel. The viscous wet gel is then placed in a 105°C constant temperature drying oven for 12 hours to obtain a dry gel. Subsequently, the dry gel is placed in a muffle furnace and pretreated at 200°C for 2 hours to remove organic residues and adsorbed water, thereby obtaining a loose and porous precursor powder. S4. Place the above precursor powder in a muffle furnace, heat it to 400°C at a rate of 3°C / min, hold it for 1 hour, then continue to heat it to 650°C at a rate of 2°C / min, and hold it for 3 hours; then cool it naturally to room temperature, and grind it to obtain disordered pentagonal high-entropy spinel powder (HEP-Co).

[0044] Using commercially available catalyst Co3O4 as a control, the following comparison is made with HEP-Co prepared in Example 1: Figure 1 The XRD patterns of HEP-Co and Co3O4 prepared in Example 1 were compared with the standard XRD pattern card of Co3O4 (PDF#42-1467). It was found that the XRD pattern of HEP-Co prepared in this example showed crystal planes 220, 311, 222, 400, 511, and 440. This indicates that HEP-Co has a cubic spinel structure, and the characteristic peaks shifted to lower angles after doping, indicating that the crystal plane configuration was changed by high-entropy metal doping.

[0045] Figure 2 The SEM image of HEP-Co prepared in this embodiment shows that its morphology is cubic.

[0046] Figure 3 The image shows the EDS elemental composition of the HEP-Co prepared in this embodiment. The composition of metals Co, Fe, Zn, Ni, and Cu is 29.7%, 8.1%, 7.4%, 3.4%, and 2.8%, respectively. This indicates that Co is the main metal in spinel, with other elements uniformly doped within it.

[0047] Figure 4 The Raman spectra of HEP-Co and Co3O4 prepared in this embodiment show that some peaks of HEP-Co are significantly weakened and disappear. This is due to lattice distortion caused by multi-metal doping, which changes the electronic environment of the Co active center and promotes the electronic spin state transition.

[0048] Figure 5 The electrochemical curves of HEP-Co and Co3O4 prepared in this embodiment are shown in the impedance diagram and cyclic voltammetry diagram. Figure 5 Figure a shows that HEP-Co has a smaller arc radius and is more conductive; Figure b shows that HEP-Co has a higher redox potential peak, indicating that the electrochemical performance of HEP-Co is significantly better than that of Co3O4.

[0049] Figure 6 The above are the XPS full spectra of HEP-Co and Co3O4 prepared in this embodiment. Co is present in Co. 2+ and Co 3+ Furthermore, HEP-Co possesses a spinel-structured high-spin Co. 3+ Active center. Compared to Co3O4, after doping, Co... 3+ The increase in the proportion indicates that there is a redox relationship in the valence state changes among the multiple metals.

[0050] Figure 7 The magnetic curves of HEP-Co and Co3O4 prepared in this embodiment at room temperature are shown. HEP-Co exhibits significantly higher magnetization across the entire magnetic field range than Co3O4, and its magnetization increases more rapidly under low magnetic fields, demonstrating superior magnetic susceptibility. This indicates that the high-entropy modification of HEP-Co significantly enhances the ferromagnetism of the materials.

[0051] The above SEM and EDS images are used to characterize the morphology of the material using scanning electron microscopy; The XPS full spectrum is obtained using an X-ray energy dispersive spectrometer. The XRD pattern was obtained using an X-ray diffractometer. The Raman spectrum was obtained using a laser Raman spectrometer. Electrochemical spectra were detected using an electrochemical workstation; The magnetic curve was detected using a magnetic measurement system (SQUID-VSM).

[0052] II. Preparation of modified carbon support: 100g of carbon matrix (activated carbon) was weighed into a 10% nitric acid solution, and ozone was simultaneously introduced into the solution at a flow rate of 0.2L / min for 4 hours. This process not only generates more active sites on the surface of the carbon material but also ensures the stability of the carbon framework.

[0053] III. Preparation of Fenton-like composite catalysts: Weigh 10g of the high-entropy spinel powder (HEP-Co), 73g of the modified carbon support, 15g of bentonite, and 2g of sodium carbonate prepared above, and mix them evenly in a mixer.

[0054] It was pressed into shape under a press at 6 bar, and then placed in a vacuum dryer at 60°C for 24 hours.

[0055] Then, under nitrogen pressure protection of 0.05 MPa, it was sintered at 1200℃ for 2 hours.

[0056] Then, it was quenched and cooled with a 1wt% sodium chloride solution to obtain a Fenton-like composite catalyst, which has high hardness and does not exhibit cracking. Specifically, as shown below... Figure 8As shown, it has a cylindrical structure with a diameter of 1-2 cm.

[0057] IV. Removal of pollutants from wastewater: The Fenton-like composite catalyst prepared above was used as a catalytic packing material in a fixed-bed reactor to remove pollutants from wastewater.

[0058] A Fenton-like composite catalyst was packed into a fixed-bed reactor. The thickness of the packing layer was designed to be 0.8–2.0 m based on an HRT of 1–2 h and an empty bed flow rate of 5–15 m / h. The height of the packing layer accounted for a certain percentage of the total height of the fixed-bed reactor. ~½. An online pH meter is installed at the top of the fixed-bed reactor to precisely control the pH of the liquid within the reactor to 3-4. At the bottom of the fixed-bed reactor, a material pump separately pumps in acid and oxidant to regulate the pH of the reaction solution and the dosage of the oxidant.

[0059] When the aforementioned Fenton-like composite catalyst is applied to a Fenton-like oxidation system, three annular oxidation gradient regions are formed radially from the center of the catalytic packing material inside the fixed-bed reactor. The active substances within each oxidation gradient region perform their specific functions, targeting and degrading both large and small molecular fragments.

[0060] The added oxidant is hydrogen peroxide, so the active substance in the first oxidation gradient region is superoxide radical, and H2O2 is the precursor. If persulfate is added, the active substance in the first oxidation gradient region is persulfate free radical (SO4· ... - ) and a small amount of superoxide radicals (O2· - ).

[0061] The active substances in the second oxidation gradient region are high-valence metals, while the active substances in the third oxidation gradient region are hydroxyl radicals.

[0062] The three oxidation gradient regions are determined by the spatial structure of the Fenton-like composite catalyst itself. During the diffusion of oxygen from the surface to the inside, there is a mass transfer resistance, which forms a spatial concentration gradient of active species along the radial direction of the catalytic packing. This further induces the active components to form a differentiated species distribution and concentration arrangement from the outside to the inside. Combined with the spatial differences in the mass transfer resistance of the reaction products, a continuous and progressive catalytic oxidation functional gradient is finally constructed in the surface, middle and inner layers of the catalytic packing, realizing a multi-region synergistic catalytic effect.

[0063] V. Application in pharmaceutical wastewater: Antibiotic wastewater from a pharmaceutical factory was treated using catalytic packing material. The antibiotic wastewater had strong antibacterial properties and very low biochemical properties (0.09); its COD was 12000 mg / L and its BOD was 1100 mg / L.

[0064] After adjusting the pH of the wastewater to 3.0, it was introduced into a reactor filled with the Fenton-like catalytic packing material prepared above. Simultaneously, hydrogen peroxide was added at 1.5‰ of the wastewater mass. The hydraulic retention time was 60 minutes. Under the catalysis of the packing material, large, recalcitrant organic molecules were rapidly decomposed into smaller molecules or directly mineralized, significantly reducing pollutants in the wastewater.

[0065] The COD of the effluent was then measured to be 5600 mg / L and the BOD to be 1500 mg / L, indicating a COD removal rate of 53.3%. Furthermore, the B / C ratio of the pharmaceutical wastewater can be increased from 0.09 to over 0.27.

[0066] The COD of the above-mentioned wastewater was detected using a COD digester, and the BOD was detected using a dissolved oxygen analyzer. The B / C ratio was calculated by dividing the BOD5 value measured for the same sample by the COD value, thereby assessing the biodegradability of the wastewater.

[0067] Example 2 I. Preparation of high-entropy spinel: S1, 0.202g ferric nitrate nonahydrate, 0.145g nickel nitrate hexahydrate, 0.297g zinc nitrate hexahydrate, 0.121g copper nitrate trihydrate, and 1.46g cobalt nitrate hexahydrate were dissolved together in a mixed solution consisting of 50mL pure water and 50mL anhydrous ethanol; the solution was stirred magnetically until completely dissolved to obtain a homogeneous and transparent pentagonal metal mixed precursor solution; S2. Dissolve 0.56g of polyvinylpyrrolidone in 100mL of pure water; mix the above pentagonal metal mixed precursor solution and stir thoroughly for 30min to obtain a sol.

[0068] S3. The above sol is first concentrated in a 90°C water bath and slowly evaporated to form a viscous wet gel. The viscous wet gel is then placed in a 110°C constant temperature drying oven for 12 hours to obtain a dry gel. Subsequently, the dry gel is placed in a muffle furnace and pretreated at 200°C for 4 hours to remove organic residues and adsorbed water, thereby obtaining a loose and porous precursor powder. S4. Place the above precursor powder in a muffle furnace and heat it to 300°C at a rate of 3°C / min. Then hold it at that temperature for 2 hours. Then continue to heat it to 700°C at a rate of 2°C / min and hold it for 3 hours. Then cool it naturally to room temperature and grind it to obtain disordered pentagonal high-entropy spinel powder (HEP-Co).

[0069] II. Preparation of modified carbon support: 100g of carbon matrix (carbon black) was weighed into a 15% nitric acid solution, and ozone was simultaneously introduced into the solution at a flow rate of 0.25L / min for 5 hours. This process achieves both increased activity on the carbon material surface and ensures the stability of the carbon framework.

[0070] III. Preparation of Fenton-like composite catalysts: Weigh 15g of the prepared HEP-Co powder, 80g of modified carbon support, 10g of red kaolin, and 1g of calcium carbonate, and mix them evenly in a mixer. Press the mixture into shape under 5 bar, and then vacuum dry it at 60℃ for 20h. Then sinter it at 1300℃ for 2h under nitrogen pressure protection of 0.08MPa. Finally, quench and cool it with 2wt% sodium chloride solution to obtain a Fenton-like composite catalyst with high hardness and integrity, and a crushing strength of 1150N.

[0071] IV. Removal of pollutants from pharmaceutical wastewater: The Fenton-like composite catalyst prepared above was used as the catalytic packing material in a fixed-bed reactor to remove pollutants from wastewater. Same as Example 1.

[0072] The wastewater reaction pH was 4.0, the PMS dosage was 1.5‰ of the mass of the wastewater to be treated, and the hydraulic retention time was 40 min.

[0073] The raw water had a COD of 12000 mg / L and a BOD of 1100 mg / L; the effluent had a COD of 6200 mg / L and a BOD of 1600 mg / L. The COD removal rate was 48.3%, which can increase the wastewater B / C ratio from 0.09 to 0.26.

[0074] Example 3 I. Preparation of high-entropy spinel: S1, 0.404g ferric nitrate nonahydrate, 0.145g nickel nitrate hexahydrate, 0.149g zinc nitrate hexahydrate, 0.121g copper nitrate trihydrate, and 1.46g cobalt nitrate hexahydrate were dissolved together in a mixed solution of 50mL pure water and 50mL ethanol. The solution was magnetically stirred until completely dissolved to obtain a homogeneous and transparent pentagonal metal mixed precursor solution. S2. Dissolve 0.3g of urea in 100mL of pure water, then add it to the pentagonal metal mixed precursor solution and mix thoroughly for 30min to obtain a sol.

[0075] S3. The above sol is first concentrated in an 85°C water bath and slowly evaporated to form a viscous wet gel. The viscous wet gel is then placed in a 100°C constant temperature drying oven for 18 hours to obtain a dry gel. Subsequently, the dry gel is placed in a muffle furnace and pretreated at 200°C for 3 hours to remove organic residues and adsorbed water, thereby obtaining a loose and porous precursor powder. S4. The precursor powder above is heated to 350°C at a rate of 3°C / min and held for 1.5 h. Then, the temperature is increased to 700°C at a rate of 2°C / min and held for 4 h. Then, it is naturally cooled to room temperature and ground to obtain disordered pentagonal high-entropy spinel powder (HEP-Co).

[0076] II. Preparation of modified carbon support: 100g of carbon matrix (mesoporous carbon) was weighed into a 10% nitric acid solution, and ozone was simultaneously introduced into the solution at a flow rate of 0.15L / min for 6 hours. This process achieves both increased activity on the carbon material surface and ensures the stability of the carbon framework.

[0077] III. Preparation of Fenton-like composite catalysts: S4. Weigh 25g of the prepared HEP-Co powder, 60g of the modified carbon support, 8g of kaolin, and 1g of calcium carbonate, and mix them evenly in a mixer. Press the mixture into shape under 3 bar, and then dry it under vacuum at 50℃ for 26h. Then sinter it at 1300℃ for 2h under nitrogen pressure protection of 0.1MPa. Finally, quench and cool it with 3wt% sodium chloride solution to obtain a Fenton-like composite catalyst with high hardness and no cracks, and a crushing strength of 1200N.

[0078] IV. Removal of pollutants from pharmaceutical wastewater: The Fenton-like composite catalyst prepared above was used as the catalytic packing material in a fixed-bed reactor to remove pollutants from wastewater. Same as Example 1.

[0079] The wastewater reaction pH was 3.0, the hydrogen peroxide dosage was 3‰ of the mass of the wastewater to be treated, and the hydraulic retention time was 90 min.

[0080] The test results showed that the COD in the raw water was 12000 mg / L and the BOD was 1100 mg / L; the COD in the effluent was 5400 mg / L and the BOD was 1550 mg / L. Therefore, the COD removal rate was 55%, and the B / C ratio of the pharmaceutical wastewater could be increased from 0.09 to 0.29.

[0081] Comparative Example 1 Traditional Fenton-like composite catalyst 1: SR series Fenton-like composite catalyst from Shandong Shanruo Environmental Technology Co., Ltd. The catalyst packing material is spherical with a diameter of 2~3mm.

[0082] Traditional Fenton-like composite catalyst 2: Shandong Senyang Environmental Fenton-like composite catalyst, with a spherical shape of 2~3cm in diameter, mainly composed of traditional iron-based iron oxide.

[0083] Similar to Example 1, 10g of the two conventional Fenton-like composite catalysts, 73g of modified carbon support, 15g of bentonite, and 2g of sodium carbonate were uniformly mixed in a mixer. The mixture was pressed into shape under 6 bar pressure and then vacuum dried at 60℃ for 24h. It was then sintered at 1200℃ for 2h under nitrogen pressure protection of 0.05MPa. Finally, it was quenched and cooled with a 1wt% sodium chloride solution to obtain catalyst fillers 1 and 2.

[0084] The two types of catalytic packing materials 1 and 2 were used as catalytic packing materials in a fixed-bed reactor to treat antibiotic production wastewater with an initial COD concentration of 12000 mg / L. The amount of hydrogen peroxide added was 3‰ of the mass of the wastewater to be treated, and the reaction time was 60 min.

[0085] The COD removal rate was 32%, which is lower than that of Example 1, indicating that the catalyst prepared in this application can form a gradient oxidation region, which is more conducive to improving catalytic efficiency.

[0086] Comparative Example 2 Same as Example 1, except that in the preparation of high-entropy spinel, step S4 involves placing the above-mentioned precursor powder in a muffle furnace and directly heating it to 700°C at 2°C / min, and then holding it at that temperature for 4 hours to obtain high-entropy spinel powder 1.

[0087] Similar to Example 1, high-entropy spinel powder 1, modified carbon support, bentonite, and sodium carbonate were mixed, pressed, dried, sintered, and cooled to obtain Fenton-like catalyst filler 1.

[0088] The Fenton-like catalytic packing 1 prepared above was used to treat antibiotic production wastewater with an initial COD concentration of 12000 mg / L. The amount of hydrogen peroxide added was 3‰ of the mass of the wastewater to be treated, and other treatment parameters were the same as in Example 1.

[0089] Tests showed an average COD removal rate of 32.4%, and a B / C ratio of 0.15 in the post-reaction wastewater, significantly lower than in Example 1. This demonstrates that gradient high-temperature crystallization is the condition for forming highly active HEP-Co in this invention.

[0090] Comparative Example 3 Same as Example 1, except that the modified carbon support was obtained by soaking carbon-based activated carbon in nitric acid for 1 hour. The Fenton-like catalyst packing 2 was finally prepared.

[0091] The Fenton-like catalytic packing material 2 prepared above was used as the catalytic packing material in a fixed-bed reactor to treat antibiotic production wastewater with an initial COD concentration of 12000 mg / L. The amount of hydrogen peroxide added was 3‰ of the mass of the wastewater to be treated, and other treatment parameters were the same as in Example 1.

[0092] The average COD removal rate was 33.5% as tested. This indicates that the modified carbon support in this invention is treated with ozone combined with nitric acid, which has a significant impact on catalytic performance and the formation of the oxidation gradient.

[0093] Those skilled in the art should understand that the above descriptions are merely several specific embodiments of the present invention, and not all embodiments. It should be noted that many modifications and improvements can be made by those skilled in the art, and all modifications or improvements not exceeding the scope of the claims should be considered within the protection scope of the present invention.

Claims

1. A Fenton-like composite catalyst, characterized in that, It is prepared from the following components in parts by mass: 10-25 parts of high-entropy spinel 60-80 parts of carbon carrier 8-15 parts of adhesive 1-2 parts of pore-forming agent, The high-entropy spinel is a composite material composed of cobalt doped with transition metals, wherein the transition metals are selected from any four of Fe, Ni, Mn, Cu, Zn, and Al. The carbon support is a modified carbon support, which is prepared by adding a carbon matrix to nitric acid and then oxidizing it by introducing ozone.

2. The Fenton-like composite catalyst according to claim 1, characterized in that, The preparation steps of the high-entropy spinel are as follows: (1) A soluble metal salt is added to a solvent and stirred to obtain a mixed precursor solution; the soluble metal salt is a cobalt salt and four transition metal salts; the metals in the transition metal salts are selected from any four of Fe, Ni, Mn, Cu, Zn and Al; (2) Add a complexing agent, stir, and complex to form a stable sol; (3) The above sol is first concentrated to form a viscous wet gel; The viscous wet gel is then dried to obtain a dry gel; the dry gel is then subjected to low-temperature pretreatment to obtain the precursor powder. (4) The precursor powder was crystallized at high temperature by segmented calcination process, cooled and ground to obtain disordered pentagonal high-entropy spinel powder.

3. The Fenton-like composite catalyst according to claim 2, characterized in that, In step (1), the molar ratio of metal ions in the four transition metal salts is (0.1~1):(0.1~1):(0.1~1):(0.1~1); and / or, The molar ratio of metal to Co in the four transition salts is 1:

2.

4. The Fenton-like composite catalyst according to claim 2, characterized in that, In step (1), the soluble metal salt and cobalt salt are both nitrates, acetates, sulfates, or chlorides; and / or, The solvent is a mixture of deionized water and anhydrous ethanol in a volume ratio of 1:

1.

5. The Fenton-like composite catalyst according to claim 2, characterized in that, In step (2), the complexing agent is one or more of citric acid monohydrate, polyvinylpyrrolidone, and urea; and / or, The amount of the complexing agent added is 30-50 mmol / L of the volume of the mixed precursor solution.

6. The Fenton-like composite catalyst according to claim 2, characterized in that, In step (3), the preliminary concentration involves slowly evaporating the sol in a water bath at 80-90°C to form a viscous wet gel; and / or, The drying process involves placing the viscous wet gel in a constant temperature drying oven at 100-110℃ for 12-18 hours.

7. The Fenton-like composite catalyst according to claim 2, characterized in that, In step (3), the low-temperature pretreatment involves placing the dry gel in a muffle furnace and pretreating it at 200°C for 2-4 hours to remove residual organic matter and adsorbed water from the dry gel, thereby obtaining a loose and porous precursor powder.

8. The Fenton-like composite catalyst according to claim 2, characterized in that, In step (4), the segmented calcination process refers to heating the temperature to 300~400℃ in air at a rate of 3℃ / min and holding it for 1~2h; then heating the temperature to 650~750℃ at a rate of 2℃ / min and holding it for 3~5h.

9. The Fenton-like composite catalyst according to claim 1, characterized in that, The concentration of nitric acid is 10-15 wt%, the ozone flow rate is 0.15-0.25 L / min, and the oxidation time is 4-6 h.

10. A Fenton-like composite catalyst according to claim 1, characterized in that, The binder is one of kaolin, red clay, or bentonite; and / or... The pore-forming agent is one or a mixture of two or more of oxalic acid, sodium carbonate, and calcium carbonate.

11. The Fenton-like composite catalyst according to claim 1, characterized in that, The crushing strength of the Fenton-like composite catalyst is >1100N.

12. A method for preparing a Fenton-like composite catalyst according to any one of claims 1-11, characterized in that, Includes the following steps: High-entropy spinel powder, carbon carrier, binder and pore-forming agent are mixed evenly, then pressed into shape, and dried, sintered and cooled to obtain the final product.

13. The preparation method according to claim 12, characterized in that, The compression molding is performed using a press at 3-6 bar. The drying process refers to vacuum drying at 50-60℃ for 20-26 hours.

14. The preparation method according to claim 12, characterized in that, The sintering is carried out at 1200-1300℃ for 2-3 hours under nitrogen pressure protection of 0.05~0.1MPa. The cooling refers to quenching and cooling using a 1-3 wt% sodium chloride solution.

15. The application of a Fenton-like composite catalyst as described in any one of claims 1-11, characterized in that, Catalytic packing material is used in fixed-bed reactors to remove pollutants from wastewater.

16. The application according to claim 15, characterized in that, Adjust the pH of the wastewater to 3.0-4.0, then add an oxidant. The dosage of the oxidant is 1.5-3.0‰ of the mass of the wastewater to be treated. The hydraulic retention time is 40-90 minutes. The COD removal rate in the wastewater reaches more than 48%, and the B / C ratio of the wastewater can be increased from 0.05-0.1 to not less than 0.

26.

17. The application according to claim 16, characterized in that, The oxidant is persulfate or hydrogen peroxide; The catalytic packing material located inside the fixed-bed reactor forms three annular oxidation gradient regions in a radial direction from its center outwards, namely the third oxidation gradient region, the second oxidation gradient region, and the first oxidation gradient region. The active substances in the first oxidation gradient region are sulfate radicals or superoxide radicals, the active substances in the second oxidation gradient region are high-valence metals, and the active substances in the third oxidation gradient region are hydroxyl radicals, which work together to degrade pollutants in wastewater.

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