Carbon nanotube encapsulated alloy material catalyst, method of making and use thereof

Abstract

This invention belongs to the field of wastewater oxidation treatment, specifically relating to a carbon nanotube-encapsulated alloy catalyst, its preparation method, and its application. To address the technical problems of low catalytic efficiency and secondary water pollution caused by the leaching of metal ions due to the use of transition metal ions in existing heterogeneous catalysts for organic wastewater treatment, this invention provides a carbon nanotube-encapsulated alloy catalyst. The catalyst is prepared by dissolving nickel and zinc salts in water, leaching the solution into a cyanamide compound powder, stirring, drying, calcining at 450–600°C, and then cooling to obtain a powder. The powder is then calcined at 700–1000°C under an inert atmosphere, acid-washed, and then washed with water and dried. The carbon nanotube-encapsulated alloy catalyst obtained by this method exhibits high catalytic activity against persulfate and shows significant removal effects for different pollutants in different water bodies.

Description

Technical Field

[0001] This invention belongs to the field of wastewater oxidation treatment, specifically relating to a carbon nanotube-encapsulated alloy material catalyst, its preparation method, and its application. Background Technology

[0002] With the gradual development of industry, emerging pollutants such as pesticides, dyes, and antibiotics from industrial wastewater, domestic sewage, and medical wastewater are being discharged into the environment through various pathways, causing enormous harm to human health and the ecological environment. Currently, the main methods for treating organic wastewater include physical methods, microbial degradation methods, and chemical methods.

[0003] Advanced oxidation technologies (AOCs) in chemical processes have attracted widespread attention due to their advantages such as high efficiency, stability, good solubility, and wide pH applicability. The catalytic processes of AOCs are divided into homogeneous catalysis and heterogeneous catalysis. Homogeneous catalysis mainly utilizes soluble metal salts as catalysts, but the catalyst and reaction products are not easily separated, leading to difficulties in catalyst recovery and potential secondary pollution. Heterogeneous catalysts are widely used because the catalyst and reaction products are easily separated. However, heterogeneous catalysts have lower catalytic efficiency. Therefore, doping with heterogeneous elements (N, S, P, B, etc.) can alter the electronic structure of the active sites, changing the adsorption of the oxidant or accelerating electron transfer between the oxidant and active sites, thereby improving catalytic activity. Simultaneously, activation using transition metals eliminates the need for external heat sources and light sources, and the catalyst can be reused. However, the use of transition metal ions can easily cause metal ion leaching, leading to secondary pollution of water bodies. Summary of the Invention

[0004] The purpose of this invention is to provide carbon nanotube-encapsulated alloy material catalysts, preparation methods, and applications, aiming to solve the technical problems of low catalytic efficiency of existing heterogeneous catalysts in organic wastewater treatment, and the use of transition metal ions easily causing metal ion leaching and secondary pollution of water bodies.

[0005] To achieve the above-mentioned objectives, the technical solution adopted by the present invention is as follows:

[0006] In a first aspect, the present invention provides a method for preparing a carbon nanotube-encapsulated alloy material catalyst, comprising the following steps:

[0007] S1. Preparation of catalyst precursor: Dissolve nickel salt and zinc salt in water and pour into cyanamide compound powder. Stir to fully impregnate the powder until a paste is formed, then stop stirring. Dry the paste and calcine it at 450-600℃. After calcination, cool it to make powder.

[0008] S2. Preparation of catalyst: The powder prepared in step S1 is calcined at 700-1000℃ under an inert atmosphere. After calcination, it is acid-washed, then washed with water and dried to obtain the carbon nanotube encapsulated alloy material catalyst.

[0009] The cyanamide compound is selected from at least one of melamine, cyanamide, or dicyandiamide.

[0010] The nickel salt is selected from at least one of Ni(NO3)2·6H2O or NiCl2·6H2O.

[0011] The zinc salt is selected from at least one of Zn(NO3)2·6H2O or ZnCl2.

[0012] In step S1, the molar ratio of nickel salt, zinc salt, and melamine is 1:(0.5-2.0):(18-20).

[0013] In step S1, the amount of water used is 0.42L to 0.5L per kilogram of cyanamide compound.

[0014] In step S1, the calcination time is 2.0 to 4.0 hours.

[0015] In step S2, the inert atmosphere is N2.

[0016] In step S2, the calcination method is heating calcination, and the heating conditions are: from room temperature at 8-12℃·min. -1 Heat to 450–600℃ at a heating rate, hold for 15–30 min; then heat at a rate of 3–6℃·min -1 The temperature is increased to 680–750℃ at a heating rate and held at that temperature for 3–4 hours.

[0017] More preferably, the heating conditions are: from room temperature at a rate of 10°C / min. -1 The temperature was increased to 550℃ at a heating rate and held for 20 minutes; then increased at a rate of 5℃·min. -1 The temperature was increased to 700℃ at a certain rate and held for 3 hours.

[0018] In step S2, the pickling solution is at least one of sulfuric acid, nitric acid, or hydrochloric acid with a concentration of 0.1–0.2 mol / L.

[0019] The pickling temperature is 20–40°C, and the pickling time is 6–12 hours.

[0020] In step S2, after pickling, the solution is rinsed with water until neutral.

[0021] The drying temperature is 60-80℃ and the drying time is 24-32h.

[0022] Secondly, the present invention also provides a carbon nanotube encapsulated alloy material catalyst prepared by the above preparation method.

[0023] Thirdly, the present invention provides the application of the above-mentioned carbon nanotube encapsulated alloy material catalyst in the treatment of organic wastewater.

[0024] In this application, the catalyst is combined with persulfate (PMS) activation technology to remove recalcitrant organic pollutants.

[0025] Preferably, the 4 mg of organic matter requires 80–150 mg of catalyst and 18–25 mg of PMS.

[0026] Beneficial effects: This invention uses at least one of cyanamide compounds, such as melamine, cyanamide, or dicyandiamide, as carbon and nitrogen sources, along with nickel and zinc salts. A precursor (Ni-Zn-g-C3N4) of elemental Ni and Zn supported on graphitic carbon nitride is prepared through a first calcination at a lower temperature. Subsequently, a second calcination at a higher temperature yields carbon nanotube-encapsulated Ni3ZnC. 0.7 Alloy material catalysts.

[0027] Experimental results show that the catalyst of this invention combined with PMS activation can remove organic pollutants, represented by bisphenol A and dichlorophenol, within 30 minutes, with a removal rate as high as 99%, and the leaching content of metal ions in the water after degradation is low; at the same time, the removal rate of pollutants in different water bodies reaches more than 95%.

[0028] It is evident that the catalyst of this invention exhibits excellent catalytic activity. While ensuring good physical adsorption and PMS activation performance, it also effectively inhibits metal leaching and generates defect sites to regulate the surface charge distribution of the catalyst. Furthermore, the catalyst maintains good performance over a wide pH range, demonstrating good service life and stability. Its superior organic pollutant treatment capability is of significant value for practical wastewater treatment. Attached Figure Description

[0029] Figure 1 The catalyst Ni3ZnC prepared in Example 1 of this invention 0.7 XRD pattern of @CNT;

[0030] Figure 2 The catalyst Ni3ZnC prepared in Example 1 of this invention 0.7 SEM image of @CNT;

[0031] Figure 3 The catalyst Ni3ZnC prepared in Example 1 of this invention 0.7 @CNT's TEM image;

[0032] Figure 4 The catalyst Ni3ZnC prepared in Example 1 of this invention 0.7 Specific surface area diagram of @CNT;

[0033] Figure 5 The graphs show the degradation performance of bisphenol A in Example 2 and dichlorophenol in Example 3 of this invention.

[0034] Figure 6 The graphs show the degradation performance of bisphenol A dissolved in river water, lake water, and tap water in Examples 4, 5, and 6 of this invention. Detailed Implementation

[0035] In the field of wastewater treatment, to improve the efficiency of heterogeneous catalyst synergistic advanced oxidation technology (persulfate (PMS) activation) in removing recalcitrant organic pollutants, this invention employs a nitrogen-doped graphite layer surrounding transition metal particles. This nitrogen-doped graphite coating on the exterior of the transition metal alloy particles forms a novel carbon nanotube-encapsulated alloy catalyst. The nitrogen-doped graphite coating effectively inhibits the contact between H+ ions from persulfate dissociation and the metal particles, thereby reducing metal leaching.

[0036] In one embodiment of the present invention, Ni3ZnC is used. 0.7 As an alloy material, carbon nanotubes are used for coating. The specific implementation method includes the following steps:

[0037] S1. Preparation of catalyst precursor: Nickel salt and zinc salt are dissolved in water and then impregnated into cyanamide compound powder by impregnation. Stirring is carried out to ensure that the powder is fully impregnated until a light green paste is formed. Stirring is then stopped. The paste is dried and calcined at 450-600℃. After calcination, it is cooled to obtain powder.

[0038] S2, Ni3ZnC 0.7 Preparation of @CNT: The powder prepared in step S1 is calcined at 700-1000℃ under an inert atmosphere. After calcination, it is acid-washed, then washed with water and dried to obtain Ni3ZnC. 0.7 @CNT catalyst.

[0039] The above embodiments use cyanamide compounds, preferably melamine, as the carbon and nitrogen source, along with nickel and zinc salts. A first low-temperature calcination pyrolysis is used to prepare a precursor (Ni-Zn-g-C3N4) of elemental Ni and elemental Zn supported on graphitic carbon nitride. Subsequently, a second calcination pyrolysis at a higher temperature is used to prepare carbon nanotube-encapsulated Ni3ZnC. 0.7 Alloy material catalysts. Similar carbon and nitrogen sources can also be cyanamide and dicyandiamide.

[0040] The first step of this invention, low-temperature pyrolysis, allows the metal elemental particles to come into relatively uniform contact with g-C3N4 (carbon source and nitrogen source). Subsequently, the surface of the metal elemental crystal generated by the second high temperature continuously dissolves and precipitates carbon atoms, forming a regular carbon nanotube encapsulation structure. At the same time, the unprecipitated carbon atoms are converted into alloys with metals Ni and Zn.

[0041] After the second high-temperature calcination of this invention, the initially obtained carbon nanotubes are encapsulated with Ni3ZnC. 0.7 The alloy material undergoes acid etching because, as the calcination temperature increases, some larger metal particles rapidly expand, breaking through the graphite layer and becoming exposed. However, these large metal particles exposed outside the graphite layer can be removed by acid etching, leaving smaller metal particles tightly encapsulated within the graphite layer. This process produces Ni3ZnC tightly coated with carbon nanotubes. 0.7 @CNT catalyst.

[0042] In the above embodiments, the transition metal elements catalyze the formation of graphitized carbon nanotubes from the carbon structure at the high temperature of the second calcination, effectively improving the graphitization degree of the carbon material and further enhancing its catalytic performance. Simultaneously, during the high-temperature calcination process, the volatilization of the metal element increases the pore volume and pore specific surface area of ​​the carbon material, thereby improving its catalytic performance. Furthermore, acid washing removes large-sized and some loosely bonded metal particles exposed outside the graphite layer, further increasing the pore volume and pore specific surface area of ​​the catalyst, which also further enhances the catalyst performance.

[0043] Therefore, the catalyst prepared in the above embodiments not only ensures good physical adsorption performance and PMS activation performance, but also effectively inhibits metal leaching and generates defect sites to regulate the surface charge distribution of the catalyst. Furthermore, the catalyst can maintain good performance over a wide pH range and has good service life and stability.

[0044] The following specific embodiments will be provided to explain the solution of the present invention. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0045] Example 1

[0046] In this embodiment, the carbon nanotube-encapsulated alloy catalyst is prepared using the following steps:

[0047] Preparation of the catalyst precursor: 5.9 g of NiCl2·6H2O and 3.4 g of ZnCl2 were dissolved in 25 mL of deionized water. The prepared solution was slowly poured into 60 g of melamine powder by impregnation, with continuous stirring with a glass rod to ensure thorough wetting until a light green paste was formed. The paste was then placed in a 200 mL ceramic crucible and dried overnight in an oven at 80 °C. The dried paste clumped in the crucible, which was then wrapped with aluminum foil and covered. It was then calcined in a muffle furnace at 550 °C for 3 h at a heating rate of 15 °C / min. -1 After roasting and cooling to room temperature, the solid was removed and ground into powder.

[0048] Ni3ZnC 0.7 Preparation of CNTs: The above precursor was spread evenly in a quartz boat and placed in a tube furnace for calcination in a N2 atmosphere. The heating program was as follows: from room temperature at 10℃·min. -1 The temperature was increased to 550℃ at a heating rate and held at 550℃ for 20 min. Then the temperature was increased again at a rate of 5℃·min. -1 The temperature was increased to 700℃ at a heating rate and held for 3 hours. After calcination, it was cooled to room temperature and removed. The obtained black solid was immersed in 0.2 mol / L H2SO4 and acid-washed for 8 hours. After acid washing, the black solid was washed with deionized water until neutral, and then dried overnight at 60℃. After drying, the carbon nanotube encapsulated alloy catalyst was obtained and named Ni3ZnC. 0.7 @CNT. From Figure 1 The XRD pattern of the catalyst showed diffraction peaks at 26.4°, 42.8°, 49.8°, 73.1°, and 88.6°. The diffraction peak at 26.4° belongs to the (002) crystal plane of C (JCPDS No. 75-1621), while the diffraction peaks at 42.8°, 49.8°, and 73.1° belong to Ni3ZnC. 0.7 The (111), (200), and (220) crystal planes (JCPDS No. 28-0713). From Figure 1 It can be seen that the vast majority of peak energies match the standard diffraction peaks, indicating that the prepared catalyst has high purity. According to... Figure 2 The SEM images show that the prepared catalyst has a very obvious nanotube structure; and according to Figure 3 TEM images show that a carbon nanotube-encapsulated alloy catalyst has been successfully prepared; from Figure 4 It can be seen that the prepared carbon nanotube-encapsulated alloy catalyst has a large specific surface area. When the catalyst precursor is calcined at 700–1000℃ under an inert atmosphere, its surface area is 100–300 m². 2 / g, when calcined at 700℃, its specific surface area is the largest, at 233.40m².2 / g.

[0049] The following examples illustrate the use of the Ni3ZnC catalyst prepared as described above. 0.7 @CNT was used in experiments to test the removal efficiency of different organic pollutants.

[0050] Example 2

[0051] The catalyst Ni3ZnC prepared in Example 1 0.7 Weigh 100mg of CNT and add it to 200mL of solution containing 20mg·L⁻¹. -1 In a bisphenol A (BPA) solution, 20 mg of PMS was added, and the degradation experiment was carried out at a reaction temperature of 30 °C. During the experiment, 1 mL of water was sampled every 5 min. The sample was filtered through a 0.22 μm polyethersulfone membrane, and the filtered solution was mixed with 10 μL of 0.2 M Na₂S₂O₃ terminator solution to quench free radicals and prevent further degradation of the pollutant. The degradation was then analyzed using high-performance liquid chromatography (HPLC) (detection conditions: pollutant: BPA; mobile phase: 40% ultrapure water, 60% methanol; flow rate: 0.80 mL / min). -1 (Detection wavelength: 276nm; column temperature: 30±1℃) The change in BPA concentration over time was measured, and analysis revealed that the removal rate of BPA could reach as high as 98% within 30 minutes. Figure 5 As shown. After degradation, Ni was detected in the water. 2+ With Zn 2+ The ion dissolution rates were 0.32 mg / L and 1.1 mg / L, respectively.

[0052] Example 3

[0053] The catalyst Ni3ZnC prepared in Example 1 0.7 Weigh 100mg of CNT and add it to 200mL of solution containing 20mg·L⁻¹. -1 In a 2,4-dichlorophenol (DCP) solution, 20 mg of PMS was added, and the degradation experiment was carried out at a reaction temperature of 30 °C. During the experiment, 1 mL of water was sampled every 5 minutes. The sample was filtered through a 0.22 μm polyethersulfone membrane, and the filtered solution was mixed with 10 μL of 0.2 M Na₂S₂O₃ terminator solution to quench free radicals and prevent further degradation of the pollutant. The change in 2,4-DCP concentration over time was then determined using high-performance liquid chromatography (HPLC). Analysis showed that the removal rate of 2,4-DCP could reach as high as 99% within 60 minutes. Figure 5 As shown.

[0054] Example 4

[0055] The prepared catalyst Ni3ZnC 0.7Weigh 100mg of CNT and add it to 200mL of solution containing 20mg·L. -1 A BPA solution dissolved in water from the Fuxi River in Zigong was added with 20 mg of PMS, and a degradation experiment was conducted at a reaction temperature of 30℃. During the experiment, 1 mL of water was sampled every 5 minutes. The sample was filtered through a 0.22 μm polyethersulfone membrane, and the filtered solution was mixed with 10 μL of a 0.2 M Na₂S₂O₃ terminator solution to quench free radicals and prevent further degradation of the pollutant. The change in BPA concentration over time was then measured using high-performance liquid chromatography (HPLC). Analysis showed that the BPA removal rate could reach as high as 99% within 30 minutes. Figure 6 As shown.

[0056] Example 5

[0057] The prepared catalyst Ni3ZnC 0.7 Weigh 100mg of CNT and add it to 200mL of solution containing 20mg·L. -1 BPA solution dissolved in water from Qinglong Lake in Zigong was added with 20 mg of PMS, and degradation experiments were conducted at a reaction temperature of 30℃. During the experiment, 1 mL of water was sampled every 5 minutes. The sample was filtered through a 0.22 μm polyethersulfone membrane, and the filtered solution was mixed with 10 μL of 0.2 M Na₂S₂O₃ terminator solution to quench free radicals and prevent further degradation of pollutants. The change in BPA concentration over time was then measured using high-performance liquid chromatography (HPLC). Analysis showed that the BPA removal rate could reach as high as 97% within 30 minutes. Figure 6 As shown.

[0058] Example 6

[0059] The prepared catalyst Ni3ZnC 0.7 Weigh 100mg of CNT and add it to 200mL of solution containing 20mg·L. -1 A BPA solution dissolved in tap water was further modified by adding 20 mg of PMS, and a degradation experiment was conducted at a reaction temperature of 30°C. During the experiment, 1 mL of water was sampled every 5 minutes. The sample was filtered through a 0.22 μm polyethersulfone membrane, and the filtered solution was mixed with 10 μL of a 0.2 M Na₂S₂O₃ terminator solution to quench free radicals and prevent further degradation of the pollutant. The change in BPA concentration over time was then measured using high-performance liquid chromatography (HPLC). Analysis showed that the BPA removal rate could reach as high as 95% within 30 minutes. Figure 6 As shown.

[0060] The results above demonstrate that the carbon nanotube-encapsulated alloy material catalyst-assisted advanced oxidation technology prepared in this invention exhibits significant effects in removing recalcitrant organic pollutants such as BPA and 2,4-DCP, and also demonstrates excellent treatment performance in various actual water bodies. Therefore, this invention has promising prospects for practical application.

Claims

1. A method for preparing a carbon nanotube-encapsulated alloy catalyst, characterized in that: Includes the following steps: S1. Preparation of catalyst precursor: Nickel salt and zinc salt are dissolved in water and then poured into cyanamide compound powder. The mixture is stirred until it is fully wetted and a paste is formed, at which point stirring is stopped. The paste is dried and calcined at 450–600°C. After calcination, it is cooled to obtain a powder. The precursor Ni-Zn-g-C3N4 is obtained. The cyanamide compound is selected from at least one of melamine, cyanamide, or dicyandiamide. The molar ratio of nickel salt, zinc salt, and melamine is 1:(0.5–2.0):(18–20). S2. Catalyst Preparation: The powder prepared in step S1 is calcined at 700–1000℃ under an inert atmosphere. After calcination, it is acid-washed, then washed with water and dried to obtain the carbon nanotube encapsulated alloy material catalyst Ni3ZnC. 0.7 @CNT.

2. The preparation method according to claim 1, characterized in that: Meet at least one of the following: The nickel salt is selected from at least one of Ni(NO3)2•6H2O or NiCl2•6H2O; The zinc salt is selected from at least one of Zn(NO3)2•6H2O or ZnCl2.

3. The preparation method according to claim 1, characterized in that: The amount of water used in step S1 is 0.42 L to 0.5 L of water per kilogram of cyanamide compound.

4. The preparation method according to claim 1, characterized in that: In step S1, the calcination time is 2.0 to 4.0 hours.

5. The preparation method according to claim 1, characterized in that: In step S2, the calcination method is heating and roasting, and the heating conditions are: from room temperature at 8-12 °C / min. -1 The temperature is increased to 450–600 °C at a heating rate, held for 15–30 min, and then increased at a rate of 3–6 °C / min. -1 The temperature was increased to 680–750 °C at a heating rate and held for 3–4 hours.

6. The preparation method according to claim 1, characterized in that: In step S2, the pickling solution is at least one of sulfuric acid, nitric acid or hydrochloric acid with a concentration of 0.1 to 0.2 mol / L.

7. The preparation method according to claim 6, characterized in that: In step S2, the pickling temperature is 20–40°C and the pickling time is 6–12 h.

8. The preparation method according to claim 1, characterized in that: In step S2, the drying temperature is 60-80℃ and the drying time is 24-32 h.

9. The carbon nanotube encapsulated alloy material catalyst prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the carbon nanotube encapsulated alloy material catalyst according to claim 9 in the treatment of organic wastewater.

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