Cobalt-iron-manganese-doped catalyst based on carbon nanotubes

Abstract

The invention relates to a cobalt-iron-manganese-doped catalyst based on a carbon nano tube, which is prepared by taking the carbon nano tube as a substrate material, modifying the surface of the carbon nano tube with three transition metal compounds of cobalt, iron and manganese, and specifically, performing hydrothermal reaction on a mixed solution of cobalt salt, iron salt and manganese salt and sodium hydroxide, modifying with sodium bicarbonate and the carbon nano tube, and performing hydrothermal reaction for the second time, thereby obtaining the cobalt-iron-manganese-doped catalyst based on the carbon nano tube. And drying, grinding and calcining to obtain the cobalt-iron-manganese doped catalyst based on the carbon nanotube. The catalyst provided by the invention has high catalytic activity, good stability and reusability, can significantly improve the degradation efficiency of tetracycline and reduce secondary pollution, is suitable for the field of water treatment, and has the advantages of simple preparation method, low cost and wide application prospect.

Description

Technical Field

[0001] The invention relates to a catalyst based on carbon nanotubes doped with cobalt, iron and manganese, and particularly belongs to the technical field of water treatment. Background Art

[0002] Tetracycline is a widely used antibiotic, but its residue in aquatic environments poses a serious threat to ecosystems and human health. Traditional wastewater treatment methods have limited effectiveness in degrading tetracycline, making complete removal difficult. In recent years, advanced persulfate (PMS) oxidation technology has become a research hotspot in water treatment due to its high efficiency and environmental friendliness.

[0003] The activation of PMS usually requires a transition metal catalyst, so there are countless methods for preparing catalysts. Among them, transition metal catalysts represented by iron-manganese bimetallic compounds have attracted much attention from researchers because of their outstanding performance in degrading pollutants that surpasses single metal catalysts. The preparation methods include impregnation, co-precipitation, sol-gel and hydrothermal methods. The above methods have their application advantages in different scenarios, but there are also many limitations. For example, the impregnation method will lead to uneven distribution of active components, easy sintering during calcination, and small specific surface area; the co-precipitation method has strict requirements on the precipitation pH and is easy to introduce impurities; the sol-gel method has a large number of micropores in the preparation, and shrinkage and cracking due to gas escape during the drying process; the hydrothermal method has poor batch reproducibility.

[0004] Recent research progress in the use of modified iron-manganese bimetallic catalysts for the activation of oxygen and persulfate to degrade emerging pollutants has revealed several challenges with the iron-manganese catalyst / advanced oxidation system: ① low catalyst crystallinity and yield; ② insufficient utilization of the PMS; ③ poor catalyst structural stability, prone to metal agglomeration and dissolution, resulting in poor recyclability; and ④ the non-magnetic material hinders separation from water, making it difficult to recycle and reuse. (Lü Kewei. Study on the Behavior and Mechanism of Modified Iron-Manganese Bimetallic Catalysts for Efficient Degradation of Emerging Pollutants [D]. East China University of Science and Technology, 2024.) Therefore, the exploration of new catalysts is crucial.

[0005] Carbon materials are promising non-metallic catalysts with advantages such as large specific surface area and good electron transfer properties, but their catalytic activity is relatively low. For example, doping heteroatoms into carbon materials can generate holes or excess electrons, creating new active sites, which can improve the catalytic activity of carbon materials. However, currently, heteroatom-doped carbon materials mostly use single metals or bimetallic materials as doping raw materials and biochar as a carrier. The preparation process often uses complex precursors, resulting in high calcination energy consumption, and the catalytic activity of the prepared materials still needs to be improved. To this end, the present invention proposes a carbon nanotube-doped cobalt iron manganese catalyst and a preparation method thereof. Based on carbon nanotubes, three transition metals, Co, Fe, and Mn, are selected as dopants. Due to the easy binding of transition elements with carbon atoms and the synergistic effect of multiple transition metals, the prepared carbon nanotube-doped cobalt iron manganese catalyst has high activity and can promote the effective degradation of tetracycline and other substances in wastewater. Moreover, cobalt is a ferromagnetic material, which facilitates the recovery and reuse of the catalyst from wastewater, making it convenient for practical application. Summary of the Invention

[0006] In view of the above situation, the present invention proposes a catalyst based on carbon nanotubes doped with cobalt, iron and manganese.

[0007] The present invention discloses a carbon nanotube-doped cobalt, iron and manganese catalyst, which uses carbon nanotubes as a base material and is surface-modified with three transition metal compounds: cobalt, iron and manganese. The specific preparation process is as follows: Step 1: Dissolve cobalt salt, iron salt and manganese salt in deionized water, then slowly add sodium hydroxide solution while stirring, ultrasonically disperse them evenly, and hydrothermally react at 120°C for 12 hours; Step 2: After the reaction product is cooled, filtered, washed, and dried, carbon nanotubes, sodium bicarbonate, and deionized water are added, stirred for 0.5 h, and hydrothermally reacted again at 120° C. for 12 h to obtain a cobalt-iron-manganese-modified carbon nanotube composite material solution; Step 3: After the cobalt-iron-manganese modified carbon nanotube composite material solution is cooled, it is filtered, washed, dried, and then ground. It is then placed in a muffle furnace and heated to 400°C at a rate of 5°C / min. After calcination for 2 hours, a catalyst based on carbon nanotubes doped with cobalt-iron-manganese is obtained.

[0008] In the step 1, the cobalt salt, the iron salt and the manganese salt are cobalt nitrate hexahydrate, iron nitrate nonahydrate and manganese sulfate monohydrate, respectively, and the molar ratio is 5:5:1.

[0009] The amount of the carbon nanotubes used is an equimolar amount of the cobalt salt.

[0010] The concentration of the sodium hydroxide solution is 10 mol / L.

[0011] Beneficial effects of the present invention: The present invention is based on carbon nanotubes and selects three transition metals, Co, Fe and Mn, as dopants to prepare carbon nanotube-doped cobalt-iron-manganese catalysts with high activity. The carbon nanotubes used in the present invention have high specific surface area and strong dispersibility, which avoids catalyst agglomeration and deactivation. Moreover, with the help of the one-dimensional tubular structure of the carbon nanotubes, it is conducive to forming a continuous electron transmission channel, which is particularly advantageous in the persulfate activation system. By combining transition elements with carbon atoms and synergistic action of multiple transition metals, the prepared catalyst has a shell-core structure, which not only improves the activity and stability of the catalyst, but also because the valence state of 3d transition metals is variable and has rich redox behavior, the introduction of Co can further optimize the original electronic structure and form new active centers. This synergistic action between multiple metals can be used to regulate the interface during the degradation process, and has better selectivity, strengthens the adsorption-degradation path of organic matter, and can promote the effective degradation of tetracycline and the like in wastewater. Moreover, cobalt is a ferromagnetic material, which facilitates the recovery and reuse of the catalyst from wastewater, is convenient for practical application, and can effectively inhibit metal leaching in existing metal catalysts, reduce secondary pollution, and is more in line with the principles of green chemistry. The catalyst preparation method of the present invention is simple, low-cost and has broad application prospects. DETAILED DESCRIPTION

[0012] Example 1 5 mmol (1.45 g) of cobalt nitrate hexahydrate, 5 mmol (2.02 g) of ferric nitrate nonahydrate, and 1 mmol (0.17 g) of manganese sulfate monohydrate were dissolved in 20 ml of deionized water. The mixed solution was then slowly added to 20 mL of 10 mol / L NaOH solution with stirring. After ultrasonic dispersion for 10 min, the mixture was stirred for 0.5 h and then transferred to a 50 mL hydrothermal reactor for hydrothermal reaction at 120 °C for 12 h.

[0013] After the reaction product is cooled, it is filtered with a suction flask and washed with deionized water. The filter residue and filter paper are placed in a culture dish with tweezers, wrapped with plastic wrap on the culture dish, pierced with holes and placed in an electric furnace for drying. The 5 mmol of filtered product is taken out and poured into a beaker. 5 mmol of carbon nanotubes, 1 mmol of NaHCO3 and deionized water are added to make a 50 ml solution. The solution is stirred for 0.5 h and transferred to a 50 mL hydrothermal reactor. A second hydrothermal reaction is carried out at 120 ° C for 12 h to obtain a cobalt-iron-manganese modified carbon nanotube composite material solution. After the cobalt-iron-manganese modified carbon nanotube composite material solution is cooled, it is filtered with a suction flask and washed with deionized water. It is dried in an electric furnace and then ground. It is then placed in a muffle furnace and heated to 400°C at a rate of 5°C / min. After calcination for 2 hours, a catalyst based on carbon nanotubes doped with cobalt-iron-manganese is obtained.

[0014] Example 2 5 mmol (1.45 g) of cobalt nitrate hexahydrate, 5 mmol (2.02 g) of ferric nitrate nonahydrate, and 1 mmol (0.17 g) of manganese sulfate monohydrate were dissolved in 20 ml of deionized water. The mixed solution was then slowly added to 20 mL of 10 mol / L NaOH solution with stirring. After ultrasonic dispersion for 10 min, the mixture was stirred for 0.5 h and then transferred to a 50 mL hydrothermal reactor for hydrothermal reaction at 120 °C for 12 h.

[0015] After the reaction product is cooled, it is filtered with a suction flask and washed with deionized water. The filter residue and filter paper are placed in a culture dish with tweezers, wrapped with plastic wrap on the culture dish, pierced with holes and placed in an electric furnace for drying. The 5 mmol of filtered product is taken out and poured into a beaker. 5 mmol of carbon nanotubes, 4 mmol of NaHCO3 and deionized water are then added to make a 50 ml solution. The solution is stirred for 0.5 h and transferred to a 50 mL hydrothermal reactor. A second hydrothermal reaction is carried out at 120 ° C for 12 h to obtain a cobalt-iron-manganese modified carbon nanotube composite material solution. After the cobalt-iron-manganese modified carbon nanotube composite material solution is cooled, it is filtered with a suction flask and washed with deionized water. It is dried in an electric furnace and then ground. It is then placed in a muffle furnace and heated to 400°C at a rate of 5°C / min. After calcination for 2 hours, a catalyst based on carbon nanotubes doped with cobalt-iron-manganese is obtained.

[0016] Example 3 The carbon nanotube-doped cobalt-iron-manganese catalyst prepared in Example 1 was used to catalytically degrade wastewater containing 10 mg / L of tetracycline. 1 mM / L PMS was used to degrade tetracycline for 1 hour.

[0017] The mixture was stirred magnetically in a water bath at 30°C. Before adding PMS to the wastewater, the first point was taken after reacting for 0.5 h. After adding PMS, 1.5 mL of sample was taken every 2 min, and the solution was immediately quenched with 1.5 mL of methanol solution. The solution was filtered through a 0.22 μm syringe filter. After the 6 min point, samples were taken at time periods of 10 min, 15 min, 20 min, and 30 min. Finally, the tetracycline concentration was determined by ultraviolet spectrophotometer at 355 nm.

[0018] The concentration of tetracycline remaining after the reaction was calculated based on the absorbance of the solution measured after the reaction (A=abc). It was found that after the catalyst prepared in Example 1 degraded the wastewater containing tetracycline, the final content of tetracycline pollutants in the wastewater was 24.39%, and the degradation rate reached 75.61%.

[0019] Example 4 The carbon nanotube-doped cobalt-iron-manganese catalyst prepared in Example 2 was used to catalytically degrade wastewater containing 10 mg / L of tetracycline. 1 mM / L PMS was used to degrade tetracycline for 1 hour.

[0020] The mixture was stirred magnetically in a water bath at 30°C. Before adding PMS to the wastewater, the first point was taken after reacting for 0.5 h. After adding PMS, 1.5 mL of sample was taken every 2 min, and the solution was immediately quenched with 1.5 mL of methanol solution. The solution was filtered through a 0.22 μm syringe filter. After the 6 min point, samples were taken at time periods of 10 min, 15 min, 20 min, and 30 min. Finally, the tetracycline concentration was determined by ultraviolet spectrophotometer at 355 nm.

[0021] The concentration of tetracycline remaining after the reaction was calculated based on the absorbance of the solution measured after the reaction (A=abc). It can be concluded that after the catalyst prepared in Example 2 degraded the wastewater containing tetracycline, the final content of tetracycline pollutants in the wastewater was 19.35%, and the degradation rate reached 80.65%.

Claims

1. A catalyst based on carbon nanotubes doped with cobalt, iron and manganese, characterized by: The catalyst is made of carbon nanotubes as a base material, and the surface is modified with three transition metal compounds: cobalt, iron and manganese. The specific preparation process is as follows: Step 1: Dissolve cobalt salt, iron salt and manganese salt in deionized water, then slowly add sodium hydroxide solution while stirring, ultrasonically disperse them evenly, and hydrothermally react at 120°C for 12 hours; Step 2: After cooling, the reaction product is filtered, washed, and dried, and then carbon nanotubes, sodium bicarbonate, and deionized water are added and hydrothermally reacted again at 120° C. for 12 hours to obtain a cobalt-iron-manganese-modified carbon nanotube composite material solution; Step 3: After the cobalt-iron-manganese modified carbon nanotube composite material solution is cooled, it is filtered, washed, dried, and then ground. It is then placed in a muffle furnace and heated to 400°C at a rate of 5°C / min. After calcination for 2 hours, a catalyst based on carbon nanotubes doped with cobalt-iron-manganese is obtained.

2. The carbon nanotube-doped cobalt-iron-manganese catalyst according to claim 1, characterized in that: In the step 1, the cobalt salt, the iron salt and the manganese salt are cobalt nitrate hexahydrate, iron nitrate nonahydrate and manganese sulfate monohydrate, respectively, and the molar ratio is 5:5:

1.

3. The carbon nanotube-doped cobalt-iron-manganese catalyst according to claim 1, characterized in that: The amount of the carbon nanotubes used is an equimolar amount of the cobalt salt.

4. The carbon nanotube-doped cobalt-iron-manganese catalyst according to claim 1, characterized in that: The concentration of the sodium hydroxide solution is 10 mol / L.