A nitrogen-doped carbon nanotube modified magnetic pyrite composite catalyst, a preparation method and application thereof

Abstract

The application discloses a nitrogen-doped carbon nanotube modified magnetic pyrite composite catalyst and a preparation method and application thereof, and belongs to the technical field of water treatment. The raw materials of the nitrogen-doped carbon nanotube modified magnetic pyrite composite catalyst include multi-walled carbon nanotubes, concentrated nitric acid solution, melamine, magnetic pyrite powder and sodium carbonate peroxide. In the application, the magnetic pyrite and the nitrogen-doped carbon nanotube are mixed at a ratio of 15:1, the mixture is subjected to nitrogen heat treatment at 600 DEG C for 3 hours to form a composite carrier, and then the catalyst is obtained through sodium carbonate peroxide activation treatment. The catalyst has enhanced electron transfer capacity and adsorption performance through the nitrogen-doped carbon nanotube, and can realize the dual effects of efficient activation of sodium carbonate peroxide to generate free radicals to degrade pollutants and rapid recovery through magnetism in cooperation with Fe 2+ / Fe 3+ cycle of the magnetic pyrite. The catalyst prepared by the application is suitable for deep treatment of organic matters and heavy metals in industrial wastewater, and has the advantages of wide pH adaptation range, no secondary pollution and recyclability.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to a nitrogen-doped carbon nanotube modified magnetic pyrite composite catalyst, its preparation method, and its application. Background Technology

[0002] With the acceleration of global industrialization, treating the high concentrations, high toxicity, and recalcitrant organic pollutants generated from industrial wastewater poses a severe challenge to the water treatment industry. Treatment technologies such as membrane filtration, ozonation, coagulation, and adsorption are limited by issues such as high treatment costs, high sludge production, membrane fouling, and poor adaptability to pollutants.

[0003] Advanced oxidation processes (AOPs) are currently considered a highly efficient method for decomposing organic pollutants. Pyrite, primarily composed of iron disulfide, is widely used in AOPs to degrade organic pollutants due to its unique chemical composition and serves as a potential catalyst for pollutant degradation. However, pyrite suffers from poor dispersibility, insufficient surface reactivity, poor stability, and difficulties in separation and recovery, limiting its application in water treatment. Therefore, improving and controlling the dispersibility, surface reactivity, and stability of pyrite, and solving its recovery difficulties, are key to its practical application.

[0004] Nitrogen-doped carbon nanomaterials modified pyrite can effectively solve the problem of poor dispersibility of pyrite when applied to advanced oxidation processes. This is because the functional groups introduced by nitrogen doping form strong interfacial bonds with pyrite particles through chemical bonds or electrostatic interactions. At the same time, its high specific surface area and porous structure provide more attachment sites for pyrite, preventing particle agglomeration. In addition, nitrogen doping optimizes the conductivity of carbon materials, promotes electron transfer of pyrite in advanced oxidation technologies, and further stabilizes the dispersion system.

[0005] Catalysts prepared by modifying pyrite with carbon nanomaterials can effectively enhance the efficiency of photocatalytic pollutant removal. Currently, there are patents on using graphene oxide-modified metal sulfide composite photocatalysts to remove organic pollutants from water, and related research on enhancing the reactivity of pyrite in removing organic pollutants through carbon nanotube modification. However, current carbon nanomaterial-modified pyrite still suffers from drawbacks such as high hydrogen peroxide consumption and a small required optimal pH range.

[0006] Persulfate oxidation is a commonly used advanced oxidation method for degrading recalcitrant organic pollutants. As a promising advanced oxidation method, the pyrite-activated persulfate system has several advantages in aquatic remediation, including good stability, ease of transport, good solubility, long free radical lifetime, and a wide applicable pH range. However, persulfates have relatively poor stability and a short reaction time; furthermore, the addition of persulfates in wastewater treatment may lead to excessive sulfate levels in the treated water, causing secondary pollution.

[0007] To address the challenges of separating and recovering pyrite, environmentally friendly catalysts such as magnetically recyclable pyrite catalysts have emerged, allowing for recycling and reuse. However, the preparation of these catalysts is relatively complex. Pyrrhotite, a natural mineral, also exists in nature and can be used as an activator to treat organic pollutants. It has a higher Fe content than pyrite, and its specific ferromagnetic properties allow for phase separation after pollutant treatment to extract pyrite for reuse. Although the raw material cost of pyrrhotite may be higher than that of pyrite, its high catalytic activity and reusability can reduce the overall cost over long-term use.

[0008] Currently, many materials used to modify the catalytic performance of pyrite have certain limitations. There is still much room for research on how to use these materials to overcome these limitations and make composite material-modified pyrite catalysts more effective in removing pollutants from water. Summary of the Invention

[0009] The purpose of this invention is to provide a nitrogen-doped carbon nanotube-modified magnetic pyrite composite catalyst, its preparation method, and its application. The composite catalyst prepared by modifying magnetic pyrite with nitrogen-doped carbon nanotubes can be used to construct a highly efficient activated percarbonate system, which can effectively solve the problems of poor dispersibility, insufficient surface reactivity, poor stability, and difficulty in separation and recovery when pyrite is used as a catalyst in the field of water treatment.

[0010] To achieve the above objectives, this invention provides a method for preparing a nitrogen-doped carbon nanotube-modified magnetic pyrite composite catalyst, comprising the following steps:

[0011] S1. Preparation of nitrogen-doped carbon nanotubes

[0012] S2, Preparation of Modified Composite Catalyst

[0013] The ball-milled magnetic pyrite powder and the nitrogen-doped carbon nanotubes obtained in step S1 were mixed at a mass ratio of 15:1, placed in a tube furnace and heat-treated under nitrogen protection, and then cooled to obtain the modified composite catalyst.

[0014] S3, activated with sodium percarbonate

[0015] The modified composite catalyst obtained in step S2 was dispersed in deionized water, sodium percarbonate was added and stirred, ultrasonicated and allowed to stand, separated and washed with water / ethanol and dried to obtain the target catalyst.

[0016] Preferably, in step S2, the specific operation of the heat treatment is as follows: the temperature is increased to 600°C at a heating rate of 10°C / min, and held at that temperature for 3 hours.

[0017] Preferably, in step S3, the ultrasonic treatment lasts for 30 minutes and the settling time is 12 hours.

[0018] Preferably, in step S3, the mass ratio of the modified composite catalyst to sodium percarbonate is 1:3 to 1:5.

[0019] Preferably, the specific operation of step S1 is as follows: multi-walled carbon nanotubes are pretreated with concentrated nitric acid solution, mixed and stirred with melamine, dried, and then placed in a tube furnace for heat treatment under nitrogen protection. After cooling, they are washed and dried to obtain nitrogen-doped nanotubes.

[0020] Preferably, the mass ratio of multi-walled carbon nanotubes to melamine is 1:1 to 1:4.

[0021] Preferably, the concentrated nitric acid solution has a mass fraction of 45-55%.

[0022] Preferably, the specific operation of the heat treatment is as follows: heat to 900°C at a heating rate of 10°C / min and hold at that temperature for 1 hour.

[0023] The present invention also provides a nitrogen-doped carbon nanotube modified magnetic pyrite composite catalyst prepared by the above preparation method.

[0024] This invention also provides the application of the above-mentioned nitrogen-doped carbon nanotube modified magnetic pyrite composite catalyst in the removal of heavy metals and organic matter in industrial wastewater treatment.

[0025] This catalyst catalyzes the decomposition of sodium percarbonate to generate highly oxidizing reactive oxygen species (such as hydroxyl radicals and superoxide radicals), which can efficiently remove heavy metals and organic matter from industrial wastewater, thereby reducing chemical oxygen demand and toxicity, improving the biodegradability of wastewater, and enabling it to meet discharge or reuse standards. It can also be used to remove ammonia nitrogen and phosphorus from domestic sewage, improving treatment efficiency, reducing sludge production, and lowering treatment costs. Furthermore, the catalyst's magnetic separation properties facilitate recovery and recycling, further reducing treatment costs and demonstrating good environmental friendliness and sustainability.

[0026] Sodium percarbonate, composed of 32.5% hydrogen peroxide and 67.5% sodium carbonate, is a solid-phase, environmentally friendly oxidant that can replace liquid H₂O₂ and exhibits good thermal stability and water solubility. It has a wide pH range, low cost, and is easy to store and transport. The alkaline sodium percarbonate and its carbonate derivative can act as buffers to prevent water acidification, and the final product of percarbonate oxidation is CO₃²⁻. 2- HCO3 - CO2 and H2O are beneficial to the subsequent bioremediation process.

[0027] The technical principle of this invention is as follows:

[0028] 1) Catalytic activation: Nitrogen-doped carbon nanotubes provide high conductivity and abundant active sites (such as oxygen-containing functional groups and nitrogen-doped groups), adsorbing sodium percarbonate molecules and lowering their decomposition activation energy. Subsequently, iron ions (Fe2+) on the surface of magnetic pyrite... 2+ / Fe 3+ The nitrogen-doped carbon nanotubes react with hydrogen peroxide produced from the decomposition of sodium percarbonate in a Fenton-like reaction, generating highly oxidizing hydroxyl radicals (·OH), which further accelerates the decomposition of sodium percarbonate. The synergistic effect between nitrogen-doped carbon nanotubes and pyrrhotite enhances the catalytic activity of the catalyst, significantly improving the efficiency of sodium percarbonate decomposition to generate reactive oxygen species (hydroxyl radicals and sulfate radicals, etc.), while the magnetic components (such as Fe3O4) ensure the stability of the catalytic active sites.

[0029] 2) Redox reaction: The reactive oxygen species (hydroxyl radicals and sulfate radicals, etc.) generated by the catalyst activation of this invention are strong oxidants. Through redox reactions, they attack the functional groups (carboxyl groups, hydroxyl groups, benzene rings, etc.) of pollutants in water, causing them to break or oxidize, generating small molecule intermediates, which are ultimately mineralized into carbon dioxide and water. Magnetic pyrite can undergo redox reactions during the process: Fe... 3+ It can directly oxidize reducing pollutants such as inorganic sulfides, nitrites, and organic phenols, reducing their toxicity; in addition, when magnetic pyrite catalyzes the decomposition of sodium percarbonate to generate reactive oxygen species, Fe... 2+ Oxidized to Fe 3+ Meanwhile, S 2- Oxidized to SO4 2- Then Fe 3+ It can be reduced and regenerated to Fe by sodium percarbonate. 2+ This forms a dynamic redox cycle, maintaining the long-term activity of the catalytic system. Nitrogen-doped carbon nanotubes possess excellent electrical conductivity, accelerating electron transfer and promoting Fe... 3+ Reduced to Fe 2+ This increases Fe 2+ The regeneration efficiency is improved. The synergistic effect of reactive oxygen species and iron ions on the surface of magnetic pyrite further enhances the efficiency of the redox reaction and promotes the removal of pollutants from water.

[0030] 3) Adsorption and precipitation: Nitrogen-doped carbon nanotubes possess a large specific surface area and abundant pore structure, enabling them to adsorb organic pollutants in water. After nitrogen doping, the chemical activity of the carbon nanotube surface is enhanced, allowing it to capture heavy metal ions in water through electrostatic interactions or chemisorption, enriching these ions on the catalyst surface and providing conditions for subsequent redox reactions. After the redox reaction, some pollutants may react with the active substances on the catalyst surface, transforming into insoluble precipitates (such as hydroxides or sulfides), which are then separated from the water through precipitation. Some intermediate products are adsorbed onto the catalyst surface due to increased hydrophobicity or charge neutralization, preventing secondary release.

[0031] 4) Recycling and reuse: Magnetic pyrite is magnetic, and the catalyst can be separated from the aqueous solution by an external magnetic field, achieving efficient recovery while avoiding secondary pollution caused by catalyst loss (>90% recovery rate); the coating effect of nitrogen-doped carbon nanotubes inhibits the oxidative corrosion of FeS2, reduces the dissolution of metal ions (e.g., Fe leaching amount <0.1mg / L), and extends the service life (80% activity is maintained after ≥3 cycles); the recovered catalyst can be reused after simple cleaning (e.g., ethanol, deionized water) or heat treatment, which greatly reduces operating costs.

[0032] Therefore, the catalyst prepared in this invention improves surface activity and reactivity by adding active sites to the nitrogen-doped carbon nanotube modified catalyst. The increased specific surface area and pore structure facilitate the adsorption and removal of pollutants. The construction of the pyrrhotite-activated sodium percarbonate system helps improve the stability and durability of the catalyst, resulting in less environmental harm after the reaction compared to other catalysts. Magnetic pyrrhotite is magnetic, allowing the catalyst to be separated from aqueous solution using an external magnetic field, achieving efficient recovery and solving the problem of difficult recycling. The synergistic effect of these factors significantly enhances photocatalytic efficiency and further improves the degradation efficiency of pollutants in water.

[0033] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0034] Figure 1 A schematic diagram of the process for preparing a nitrogen-doped carbon nanotube-modified magnetic pyrite-activated sodium percarbonate catalyst according to an embodiment of the present invention;

[0035] Figure 2 The nitrogen-doped carbon nanotube-modified magnetic pyrite composite catalyst prepared in this embodiment of the invention exhibits different reaction times for Cd in industrial wastewater. 2+ Removal rates of ciprofloxacin and acetonitrile;

[0036] Figure 3The removal rates of ciprofloxacin by the nitrogen-doped carbon nanotube-modified magnetic pyrite composite catalyst prepared in the embodiments of the present invention under different pH conditions (3, 5, 7, 9 and 10). Detailed Implementation

[0037] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention should be considered equivalent substitutions and are included within the protection scope of the present invention. Furthermore, it should be understood that after reading the contents of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims and are all within the protection scope of the present invention.

[0038] In this document, the term "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The term "embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment, nor does it specifically limit its independence or connection with other embodiments. In principle, in this application, as long as there are no technical contradictions or conflicts, the technical features mentioned in each embodiment can be combined in any way to form corresponding implementable technical solutions.

[0039] Unless otherwise defined, the technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the use of related terms herein is merely for the purpose of describing particular embodiments and is not intended to limit this application.

[0040] Unless otherwise specified, the reagents, instruments, equipment, and performance testing methods used in this invention are all commonly used by those skilled in the art.

[0041] Example

[0042] like Figure 1 As shown, this embodiment provides a method for preparing a nitrogen-doped carbon nanotube-modified magnetic pyrite composite catalyst, including the following steps:

[0043] (1) Pretreatment of multi-walled nanotubes: 1.5g of multi-walled carbon nanotubes were placed in 50% concentrated nitric acid solution and stirred under reflux for 4 hours to remove impurities. The treated multi-walled carbon nanotubes were washed with deionized water several times until neutral, and then dried in a vacuum drying oven at 80℃ for later use.

[0044] (2) Preparation of nitrogen-doped carbon nanotubes: Dried multi-walled carbon nanotubes were mixed with 3g of melamine and magnetically stirred at room temperature for 5h to ensure complete reaction. The mixture was then dried at 120℃ to evaporate excess solvent. The mixture was then placed in a tube furnace and heated to 900℃ at a rate of 10℃ / min under nitrogen protection, held at that temperature for 1h, and then naturally cooled to room temperature to obtain nitrogen-doped carbon nanotubes. Finally, the sample was washed by centrifugation with distilled water to remove excess melamine, and then dried at 80℃ to obtain nitrogen-doped carbon nanotubes.

[0045] (3) Preparation of nitrogen-doped carbon nanotube-modified magnetic pyrite composite catalyst: 15g of magnetic pyrite powder sample obtained by ball milling was mixed with 1g of nitrogen-doped carbon nanotubes. The mixture was placed in a tube furnace and heated to 600℃ at a heating rate of 10℃ / min under nitrogen protection, held at that temperature for 3h, and then naturally cooled to room temperature to obtain nitrogen-doped carbon nanotube-modified magnetic pyrite composite catalyst.

[0046] (4) Sodium percarbonate activated nitrogen-doped carbon nanotube-modified magnetic pyrite composite catalyst: 1g of nitrogen-doped carbon nanotube-modified magnetic pyrite composite catalyst was dispersed in 500mL of deionized water, and 5g of sodium percarbonate was added and stirred evenly. The mixture was placed in an ultrasonic disperser and ultrasonically treated for 30 minutes to promote full contact and activation between the catalyst and the percarbonate. The ultrasonically treated mixture was allowed to stand at room temperature for 12h to allow the catalyst and percarbonate to fully react.

[0047] (5) Separation and drying of nitrogen-doped carbon nanotube-modified magnetic pyrite composite catalyst activated by sodium percarbonate: The catalyst was separated from the solution, washed with deionized water and ethanol, and dried to obtain the catalyst of nitrogen-doped carbon nanotube-modified magnetic pyrite activated percarbonate system.

[0048] Application examples

[0049] This application example provides an experimental method for applying the nitrogen-doped carbon nanotube-modified magnetic pyrite composite catalyst prepared in the above embodiments to simulate industrial wastewater treatment, specifically including the following steps:

[0050] (1) Solution preparation and composition: Based on the common pollutant composition and concentration range in industrial wastewater, deoxygenated deionized water was used to prepare a solution containing 20 mg / L Cd. 2+ A simulated industrial wastewater solution containing 10 mg / L ciprofloxacin and 30 mg / L acetonitrile.

[0051] (2) Reaction conditions: 100 mL of simulated industrial wastewater was placed in a 250 mL Erlenmeyer flask. The flask was placed on a constant-temperature shaker at a speed of 200 rpm. The temperature was controlled at 25 ± 1 °C using a water bath. The pH was adjusted to 7. Then, 1 g of nitrogen-doped carbon nanotube-modified magnetic pyrite composite catalyst was added to the flask. Water samples were collected after different reaction times (15, 30, 45, and 60 min). In addition, different pH conditions (3, 5, 7, 9, and 10) were set during the experiment. Ciprofloxacin was used as a representative pollutant. The concentration change of ciprofloxacin under different pH conditions and after different reaction times was detected to determine the applicable pH range for the removal of pollutants by the nitrogen-doped carbon nanotube-modified magnetic pyrite composite catalyst. After completing one catalytic reaction, the catalyst is removed from the reactor by an external magnetic field, rinsed with deionized water until the effluent is clear, and then added back into the reactor. Simulated industrial wastewater is added again to conduct the next round of experiments. The above operation is repeated for 3 cycles.

[0052] (3) Water sample testing: The collected water samples were tested for Cd using atomic absorption spectrometry (AAS). 2+ The remaining concentration, calculate Cd 2+ The removal rates of ciprofloxacin and acetonitrile in the water sample were determined by qualitative and quantitative analysis using gas chromatography-mass spectrometry (GC-MS) and the removal rates of both were calculated.

[0053] (4) Cyclic experiment: In each catalytic experiment, the concentration of pollutants in the samples taken after different reaction times was measured and the removal rate was calculated. The changes in the removal rate of pollutants in the three cyclic catalytic experiments were compared.

[0054] (5) Removal results: Figure 2 This indicates the effect of the nitrogen-doped carbon nanotube-modified magnetic pyrite composite catalyst prepared in the embodiments of the present invention on Cd at different reaction times in three cycles of experiments. 2+ The removal rates of ciprofloxacin and acetonitrile are shown in Table 1 below. Figure 3 The values ​​represent the removal rates of ciprofloxacin by nitrogen-doped carbon nanotube-modified magnetic pyrite composite catalysts under different pH conditions (3, 5, 7, 9, and 10).

[0055] Table 1. Removal rates of different pollutants by nitrogen-doped carbon nanotube-modified magnetic pyrite composite catalysts at different reaction times in three cycles of experiments.

[0056]

[0057] Depend on Figure 2As shown in Table 1, the nitrogen-doped carbon nanotube-modified magnetic pyrite composite catalyst prepared in this invention exhibits excellent pollutant degradation performance and cycle stability. Under pH 7 conditions, this catalyst, through synergistic activation of sodium percarbonate, effectively reduced the heavy metal Cd in simulated industrial wastewater within 60 minutes. 2+ The removal rates of the antibiotic ciprofloxacin and the recalcitrant organic compound acetonitrile reached 88%, 84%, and 70%, respectively, confirming its highly efficient ability to treat multiple pollutants simultaneously. The reaction kinetics showed a time-dependent increase (e.g., Cd). 2+ A 72% removal rate was achieved within 15 minutes. This is due to the rapid adsorption and electron transfer capabilities of nitrogen-doped carbon nanotubes and the Fe2+ driven by magnetic pyrite. 2+ / Fe 3+ The cycle continuously generates reactive oxygen species (·OH). Even after three cycles, the catalyst remains highly active: Cd 2+ The removal rates of ciprofloxacin and acetonitrile at 60 minutes were 83%, 78%, and 63%, respectively, with an activity retention rate of over 90%, demonstrating good cycle performance. Figure 3 Data shows that the removal rate of ciprofloxacin by the nitrogen-doped carbon nanotube-modified magnetic pyrite composite catalyst does not change significantly under different pH conditions (3-10), demonstrating that the catalyst possesses wide pH adaptability. Therefore, the catalyst prepared in this invention is a composite catalyst that combines nitrogen-doped carbon nanotubes (adsorption / electron transfer) with magnetic pyrite (Fe2+). 2+ / Fe 3+ The synergistic effect of circulation allows for the efficient activation of sodium percarbonate to degrade complex pollutants under a wide pH range. It combines high efficiency, stability, and environmental friendliness, making it suitable for advanced treatment of industrial wastewater.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a nitrogen-doped carbon nanotube-modified magnetic pyrite composite catalyst, characterized in that, Includes the following steps: S1. Preparation of nitrogen-doped carbon nanotubes Multi-walled carbon nanotubes were pretreated with concentrated nitric acid solution and then mixed with melamine. After drying, they were placed in a tube furnace for heat treatment under nitrogen protection. After cooling, they were washed and dried to obtain nitrogen-doped nanotubes. The mass ratio of multi-walled carbon nanotubes to melamine was 1:1 to 1:

4. S2, Preparation of Modified Composite Catalyst The ball-milled magnetic pyrite powder and the nitrogen-doped carbon nanotubes obtained in step S1 were mixed at a mass ratio of 15:1, placed in a tube furnace and heat-treated under nitrogen protection, and then cooled to obtain the modified composite catalyst. The specific operation of the heat treatment is as follows: heat up to 600℃ at a heating rate of 10℃ / min and hold for 3 hours; S3, activated with sodium percarbonate The modified composite catalyst obtained in step S2 is dispersed in deionized water, sodium percarbonate is added and stirred, ultrasonicated and allowed to stand, separated and washed with water / ethanol and dried to obtain the target catalyst; wherein the mass ratio of the modified composite catalyst to sodium percarbonate is 1:3 to 1:

5.

2. The preparation method of the nitrogen-doped carbon nanotube modified magnetic pyrite composite catalyst according to claim 1, characterized in that: In step S3, the ultrasonic treatment lasts for 30 minutes, and the settling time is 12 hours.

3. The method for preparing a nitrogen-doped carbon nanotube-modified magnetic pyrite composite catalyst according to claim 1, characterized in that: In step S1, the mass fraction of the concentrated nitric acid solution is 45-55%.

4. The method for preparing a nitrogen-doped carbon nanotube-modified magnetic pyrite composite catalyst according to claim 1, characterized in that: In step S1, the specific operation of the heat treatment is as follows: heat up to 900℃ at a heating rate of 10℃ / min and hold for 1 hour.

5. A nitrogen-doped carbon nanotube-modified magnetic pyrite composite catalyst, characterized in that: The composite modified magnetic pyrite catalyst is prepared by the preparation method described in any one of claims 1-4.

6. The application of the nitrogen-doped carbon nanotube-modified magnetic pyrite composite catalyst as described in claim 5, characterized in that: The composite modified magnetic pyrite catalyst is used for the removal of heavy metals and organic matter from industrial wastewater.

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