Carbon nanotube rod-shaped materials with cobalt-iron dual active sites, their preparation methods and applications

Abstract

This invention provides a rod-shaped structure material with cobalt-iron dual active sites embedded in carbon nanotubes, its preparation method, and its applications. The invention employs a hydrothermal-calcination-acid washing method to embed cobalt-iron bimetallic oxide into the inner wall of carbon nanotubes, forming high-density and dispersed cobalt-iron dual active sites. This overcomes the defects of traditional supported cobalt-based materials, such as easy loss and uneven distribution of active sites, and reduces the risk of cobalt ion leaching. The high mechanical strength of the carbon nanotube structure helps resist the impact of water on the active sites. The material provided by this invention can stimulate a free radical-non-free radical coexisting oxidation reaction, enabling the rapid degradation of complex organic micropollutants in water. The material of this invention achieves a PMS degradation efficiency of over 95% for organic micropollutants at room temperature and has a wide applicable pH range, providing broad application prospects for the treatment of organic micropollutants in water.

Description

Technical Field

[0001] This invention relates to the field of environmental functional materials and water pollution control technology, specifically to a carbon nanotube embedded cobalt-iron dual-active-site rod-shaped structure material, its preparation method, and its application. Background Technology

[0002] In my country, water quality assessment and treatment processes are still primarily formulated and designed around conventional indicators such as ammonia nitrogen and total organic carbon. However, advanced treatment technologies for persistent organic micropollutants in municipal wastewater are still under development and remain a challenge for environmental engineering. Currently, sulfate free radicals (SO42-) are a significant concern. ·- Advanced oxidation-mediated oxidation (ACO) technologies, due to their high redox potential (2.5–3.1 V), can achieve deep mineralization of persistent organic micropollutants in water, thus attracting widespread attention in the field of water pollution control. Peroxymonosulfate (PMS), as a solid-phase oxidant with an asymmetric molecular structure, can generate abundant sulfate radicals through activation. Transition metals can overcome the limitations of low activation efficiency and harsh reaction conditions of PMS under low energy consumption requirements. Among them, cobalt-based materials are the best catalysts for activating PMS to generate sulfate radicals, with cobalt tetroxide being the most typical example. However, these materials are still limited by performance defects such as cobalt ion leaching and easy passivation of active sites. Therefore, in order to ensure the catalytic activity and structural site stability of these materials to meet the needs of practical engineering applications, it is urgent to solve the above-mentioned performance defects.

[0003] Iron, possessing similar chemical properties, can be incorporated into cobalt tetroxide via lattice substitution. Due to the redox potential difference, this accelerates charge transfer, effectively slowing the passivation rate of active sites. However, the mismatch between the outer electrons of cobalt and iron atoms causes structural defects in cobalt-iron bimetallic oxides, which worsen with increasing catalytic activity. The trade-off between the catalytic activity and structural stability of cobalt-based oxides directly leads to cobalt ion leaching, causing secondary water pollution. Carbon nanotubes, with their high mechanical strength, help resist the impact of water on active sites. Their excellent conductivity provides charge transfer channels between non-adjacent active sites, and their multi-walled, hollow structure effectively confines free cobalt ions, reducing the risk of leaching.

[0004] Patent application CN 118304887 A discloses a cobalt-copper dual-site carbon nanotube-based crosslinked structural material, its preparation method, and its application. The method involves dissolving cobalt nitrate and copper chloride, adding urea and NH4F, stirring, then adding hydroxylated multi-walled carbon nanotubes and sonicating, followed by a hydrothermal reaction to obtain CuCo2O4@CNTs material. However, this CuCo2O4@CNTs material is a carbon nanotube-supported material, and supported materials are prone to loss of active sites. Therefore, overcoming the problems of easy loss of catalytic active sites in supported cobalt oxide materials and the trade-off between catalytic activity and structural stability is of significant practical importance for its engineering applications. Summary of the Invention

[0005] The purpose of this invention is to provide a carbon nanotube embedded cobalt-iron dual-active-site rod-shaped structure material, its preparation method and application, in order to solve the performance defects of existing supported cobalt-based materials as PMS activators, which are prone to cobalt ion leaching and active site passivation.

[0006] This invention is implemented as follows:

[0007] A method for preparing a rod-shaped structure material with cobalt-iron dual active sites embedded in carbon nanotubes, the specific steps of which are as follows:

[0008] (1) Hydroxylated multi-walled carbon nanotubes were dispersed in water by ultrasonic treatment, then nitric acid was added and allowed to stand, then rotary evaporation was performed, and then the carbon nanotubes were washed with water to obtain the treated carbon nanotubes.

[0009] (2) Add Co(NO3)2·6H2O and FeSO4·5H2O to water under magnetic stirring, and then add urea until it is completely dissolved;

[0010] (3) Add the carbon nanotubes treated in step (1) to the solution obtained in step (2), then place them in a high-pressure hydrothermal reactor for heating treatment, then cool to room temperature, centrifuge, wash, dry the product, and finally calcine at high temperature to obtain the carbon nanotube embedded cobalt-iron dual active site rod structure material.

[0011] Furthermore, the amount of hydroxylated multi-walled carbon nanotubes added in step (1) is 4.5 mg.

[0012] Furthermore, the ultrasonic frequency in step (1) is 20 kHz.

[0013] Further, the concentration of nitric acid in step (1) is 65 wt%.

[0014] Furthermore, the standing time after adding nitric acid in step (1) is 5 hours.

[0015] Further, in step (1), distilled water is used for continuous washing until the pH value of the effluent is higher than 6.0.

[0016] Furthermore, the rotation speed of the magnetic stirring in step (2) is controlled at 150-200 rpm.

[0017] Furthermore, the molar ratio of Co(NO3)2·6H2O and FeSO4·5H2O in step (2) is 2:1.

[0018] Furthermore, the amount of urea added in step (2) is 8.0 mg.

[0019] Further, the washing in step (3) involves washing three times in sequence with 15wt% HCl and distilled water, with each washing time not exceeding 30 minutes.

[0020] Furthermore, the high-temperature calcination temperature in step (3) is 300℃, the duration is 4h, the high-temperature calcination is carried out in a muffle furnace, and the heating rate of the muffle furnace is 5℃ / min.

[0021] A carbon nanotube-embedded cobalt-iron dual-active-site rod-shaped structure material prepared by the above method is formed by in-situ embedding of cobalt-iron bimetallic oxide into the inner wall of hydroxylated multi-walled carbon nanotubes. The material has a distinct rod-shaped morphology with an average length of less than 1 μm and the content of active component elements accounts for more than 80 wt% of the total mass of the material.

[0022] The carbon nanotube-embedded cobalt-iron dual-active-site rod-shaped structure material (CNTs*Co2FeO4) prepared by the above method can be used as a catalyst to activate persulfate (PMS) for the oxidative degradation of recalcitrant organic micropollutants in water. The specific steps are as follows: CNTs*Co2FeO4 and PMS are added to water containing organic micropollutants, and the reaction is carried out under normal temperature and pressure conditions.

[0023] Furthermore, the above reaction was carried out in a covered beaker with a magnetic stirring speed of 250 rpm, the initial pH of the solution was adjusted to 3.0-9.0, the static adsorption saturation time was 2 minutes, and the oxidative degradation reaction time was 10 minutes.

[0024] Furthermore, the initial concentration of the organic micropollutants is 5 mg / L.

[0025] Furthermore, the dosage of CNTs*Co2FeO4 is 3 mg.

[0026] Furthermore, the dosage of the PMS is 10 mg.

[0027] Furthermore, the organic micropollutants include at least one of ranitidine (RAN), rhodamine B (RhB), cationic red GTL (CR-GTL), methyl orange (MO), methylene blue (MB), carbamazepine (CBZ), ciprofloxacin (CIP), norfloxacin (NFX), tetracycline hydrochloride (TC), bisphenol A (BPA), and phenol (Phenol).

[0028] This invention uses CNTs*Co2FeO4 as a catalyst to achieve a removal rate of over 95% in 10 minutes of oxidative degradation.

[0029] Compared with the prior art, the present invention has the following advantages and technical effects:

[0030] (1) This invention first proposed CNTs*Co2FeO4 and its preparation method. The preparation method has low requirements for synthesis equipment, high purity of the synthesized material and is easy to mass-produce.

[0031] (2) The CNTs*Co2FeO4 synthesized in this invention overcomes the defects of easy loss and uneven distribution of active sites in traditional carbon nanotube-supported cobalt materials. Furthermore, it can resist the impact of water on active sites by means of carbon nanotube structure protection, and can effectively bind free cobalt ions to reduce their leaching risk.

[0032] (3) The CNTs*Co2FeO4 synthesized in this invention has good conductivity, provides a charge transfer channel between non-adjacent active sites, can stimulate free radical-non-free radical coexisting oxidation reaction, and has a super strong oxidative degradation ability for organic micro pollutants.

[0033] (4) The preparation cost of CNTs*Co2FeO4 synthesized in this invention is lower than that in the industry, it has a wide applicable pH range, is environmentally friendly and has good reusability.

[0034] (5) The CNTs*Co2FeO4 synthesized in this invention does not require additional energy input (light, electricity and heat, etc.) to activate PMS, which reduces operating costs. Moreover, the process is simple, highly operable, uses less material and has stable performance, and has broad practical application prospects.

[0035] (6) The CNTs*Co2FeO4 synthesized in this invention not only reduces the risk of cobalt ion leaching and the cost of material preparation, but also can be applied to the oxidative degradation of a variety of typical organic micropollutants in water by activating PMS under mild reaction conditions, which is better than the traditional process. Attached Figure Description

[0036] Figure 1The image shows the X-ray diffraction (XRD) pattern of the carbon nanotubes prepared in Example 1 with cobalt-iron bimetallic oxide (CNTs*Co2FeO4) embedded in the inner wall.

[0037] Figure 2 These are transmission electron microscope (TEM) and scanning transmission electron microscope (STEM) images of the cobalt-iron bimetallic oxide CNTs*Co2FeO4 embedded in the inner wall of the carbon nanotubes prepared in Example 1; where a is the TEM image, b is the STEM image, and c, d, e, and f are the X-ray energy dispersive spectra (EDX) of carbon, oxygen, iron, and cobalt elements of the CNTs*Co2FeO4 material, respectively.

[0038] Figure 3 The image shows the X-ray photoelectron spectroscopy (XPS) of the cobalt-iron bimetallic oxide CNTs*Co2FeO4 embedded in the inner wall of the carbon nanotubes prepared in Example 1; where a and b are the XPS images of cobalt and iron elements in the CNTs*Co2FeO4 material, respectively.

[0039] Figure 4 Example 2 is a kinetic comparison of the present invention with other different advanced oxidation technologies for RAN removal.

[0040] Figure 5 This example compares the cobalt and iron ion leaching concentrations of CNTs*Co2FeO4 prepared in this invention with those of carbon nanotube outer wall supported Co2FeO4@CNTs material and commercial grade Co2FeO4 material in Example 3.

[0041] Figure 6 The illustration shows the AC impedance diagrams (inset: equivalent circuit) of the CNTs*Co2FeO4, the carbon nanotube outer wall supported Co2FeO4@CNTs material, and the commercial Co2FeO4 material prepared in Example 4.

[0042] Figure 7 In Example 5, TEMP and DMPO were used as trapping agents to detect the EPR spectra of reactive oxide species in the reaction system. Detailed Implementation

[0043] To more clearly illustrate the purpose, technology, and advantages of this invention, a detailed description is provided below with reference to specific embodiments and accompanying drawings. These embodiments are merely illustrative and do not limit the scope of the invention.

[0044] All raw materials used in this invention are commercially available products.

[0045] This invention uses ranitidine (RAN) as a typical organic micropollutant. In order to demonstrate the efficient oxidative degradation ability of this invention for organic micropollutants in water, at least one of the following was also selected as the target pollutant: Rhodamine B (RhB), Cationic Red GTL (CR-GTL), Methyl Orange (MO), Methylene Blue (MB), Carbamazepine (CBZ), Ciprofloxacin (CIP), Norfloxacin (NFX), Tetracycline Hydrochloride (TC), Bisphenol A (BPA), and Phenol.

[0046] Example 1

[0047] This embodiment compares the effect of CNTs*Co2FeO4 on the oxidative degradation of different organic micropollutants (RAN, RhB, CR-GTL, MO, MB, CBZ, CIP, NFX, TC, BPA, Phenol) by activated PMS.

[0048] (1) Preparation of CNTs*Co2FeO4: 4.5 mg of hydroxylated multi-walled carbon nanotubes were uniformly dispersed in a beaker containing 50 mL of distilled water under ultrasonic treatment (20 kHz) at room temperature (25 °C) for 10 min. Then, 10 mL of 65 wt% HNO3 was added to the above aqueous solution and allowed to stand for 5 h. After rotary evaporation (100 rpm), the nanotubes were continuously washed with distilled water until the pH of the washing water was higher than 6.0, thus obtaining the treated carbon nanotubes. Co(NO3)2·6H2O (2 mmol) and FeSO4·5H2O (1 mmol) were added to a beaker containing 50 mL of distilled water under magnetic stirring at 150–200 rpm, followed by the slow addition of urea (8.0 mg) until completely dissolved, resulting in a mixed solution. The treated carbon nanotubes were added to the above mixture and placed in a 50 mL high-pressure hydrothermal reactor lined with polytetrafluoroethylene. The mixture was heated to 120°C for 6 hours. After cooling to room temperature (25°C), the reaction mixture was transferred to centrifuge tubes and centrifuged at 10,000 rpm for 15 minutes to achieve solid-liquid separation. The separated material was then washed three times each with 15 wt% HCl and distilled water, each wash lasting no more than 30 minutes. This process was repeated three times. The material was then dried in a forced-air drying oven at 60°C for 6 hours. The dried material was then calcined at 300°C (muffle furnace heating rate of 5°C / min) for 4 hours. After cooling to room temperature, the material was ground to obtain a black powder, which is the carbon nanotube-embedded cobalt-iron dual-active-site rod-shaped structure material, labeled CNTs*Co2FeO4.

[0049] The XRD pattern of the obtained CNTs*Co2FeO4 is as follows: Figure 1 As shown. By Figure 1It can be seen that CNTs*Co2FeO4 has diffraction peaks consistent with those of the standard card PDF#97-009-8552 for Co2FeO4.

[0050] The TEM and STEM-EDX images of the obtained CNTs*Co2FeO4 are shown below. Figure 2 As shown. (Through) Figure 2 It can be observed that cobalt-iron bimetallic oxides are embedded in the inner wall of carbon nanotubes, forming high-density and dispersed cobalt-iron dual active sites.

[0051] Figure 3 XPS plots of cobalt and iron in CNTs*Co2FeO4 material are shown.

[0052] (2) Prepare a ranitidine (RAN) solution with a concentration of 5 mg / L for later use.

[0053] (3) A 200 mL conical flask was used as a reactor. 200 mL of RAN solution and 3 mg of CNTs*Co2FeO4 were added to it. The initial pH value of the solution was adjusted (pH = 6.0). After standing for 2 minutes, the adsorption saturation was reached. Then, 10 mg of PMS was added to it. The solution was magnetically stirred (250 rpm) in a water bath at a controlled temperature (25 °C). Samples were taken at fixed points for analysis.

[0054] (4) Add 5 mg / L Rhodamine B (RhB) to the reactor instead of ranitidine (RAN), and keep the other conditions the same as in (3).

[0055] (5) Add 5 mg / L cationic red GTL (CR-GTL) to the reactor instead of ranitidine (RAN), and other conditions are the same as in (3).

[0056] (6) Add 5 mg / L methyl orange (MO) to the reactor instead of ranitidine (RAN), and keep the other conditions the same as in (3).

[0057] (7) Add 5 mg / L methylene blue (MB) to the reactor instead of ranitidine (RAN), and keep the other conditions the same as in (3).

[0058] (8) Add 5 mg / L carbamazepine (CBZ) to the reactor instead of ranitidine (RAN), and keep the other conditions the same as (3).

[0059] (9) Add 5 mg / L ciprofloxacin (CIP) to the reactor instead of ranitidine (RAN), and keep other conditions the same as in (3).

[0060] (10) Add 5 mg / L norfloxacin (NFX) to the reactor instead of ranitidine (RAN), and keep the other conditions the same as (3).

[0061] (11) Add 5 mg / L tetracycline hydrochloride (TC) to the reactor instead of ranitidine (RAN), and other conditions are the same as (3).

[0062] (12) Add 5 mg / L bisphenol A (BPA) to the reactor instead of ranitidine (RAN), and keep the other conditions the same as (3).

[0063] (13) Add 5 mg / L phenol (Phenol) to the reactor instead of ranitidine (RAN), and other conditions are the same as (3).

[0064] The removal effects of different organic micropollutants after a 10-minute rapid catalytic oxidation reaction are shown in Table 1.

[0065] Table 1 Removal rates of different organic micropollutants

[0066] Organic micropollutants RAN RhB CR-GTL MO MB CBZ CIP NFX TC BPA Phenol Removal rate % 99.8 98.8 99.7 95.6 98.6 97.6 98.2 95.4 96.8 97.1 95.8

[0067] Table 1 shows that during the 10-minute oxidative degradation process, the removal rates of eleven organic micropollutants by CNTs*Co2FeO4-activated PMS were all above 95%. This indicates that the high efficiency of the prepared CNTs*Co2FeO4 in removing organic micropollutants is closely related to the high density and dispersed cobalt-iron dual active sites embedded in its multi-walled carbon nanotube structure, and it exhibits non-selective oxidative degradation capabilities, thus achieving good treatment results for organic micropollutants in water.

[0068] Example 2

[0069] This example uses ranitidine (RAN), which has the best pollution control effect screened in Example 1, as the target pollutant to compare the efficiency of CNTs*Co2FeO4 prepared in Example 1 with that of PMS activated by different advanced oxidation technologies to oxidize and degrade RAN.

[0070] (1) Prepare a ranitidine (RAN) solution with a concentration of 5 mg / L for later use.

[0071] (2) A 200 mL conical flask was used as a reactor. 200 mL of RAN solution and 3 mg of CNTs*Co2FeO4 were added to it. The initial pH value of the solution was adjusted (pH=6.0). After standing for 2 minutes, the adsorption saturation was reached. Then, 10 mg of PMS was added to it. The solution was magnetically stirred (250 rpm) in a water bath at a controlled temperature (25 °C). Samples were taken at fixed points for analysis.

[0072] (3) Using the most scientific reaction kinetic formula (1), the reaction rates (k) of different advanced oxidation technologies were calculated and compared to evaluate the RAN oxidation degradation efficiency.

[0073] k = 1 / m × dCRAN / dt(1)

[0074] Where k is the reaction rate, m is the catalyst dosage, and C RAN t represents the RAN concentration and t represents the reaction time.

[0075] Table 2 compares the RAN removal efficiency of different advanced oxidation technologies. Figure 4 As shown.

[0076] Table 2 Comparison of RAN Removal Efficiency Evaluation When Using Different Advanced Oxidation Technologies

[0077]

[0078] The other catalytic materials and corresponding data in Table 2, excluding those of this invention, are from the literature: Three-dimensional ordered mesoporous Co3O4 / peroxymonosulfate triggered nanoconfined heterogeneous catalysis for rapid removal of ranitidine in aqueous solution, Chemical Engineering Journal.

[0079] From Table 2 and Figure 4 It can be seen that the reaction rate constant calculated by formula (1) can intuitively reflect the efficiency of different oxidation technologies in RAN degradation. By comparing with commonly used advanced oxidation technologies, the CNTs*Co2FeO4-activated PMS prepared in this invention exhibits a significant advantage in oxidation degradation efficiency. Under the same application conditions, the catalyst dosage is minimal, and no additional energy input is required, resulting in the most cost-effective operation. The reaction rate constant of the CNTs*Co2FeO4-activated PMS-activated RAN oxidation degradation prepared in this invention is 2.63 to 3204.40 times that of the aforementioned advanced oxidation technologies, indicating that this invention possesses rapid oxidation degradation capabilities and has great practical potential.

[0080] Example 3

[0081] Examples 1 and 2 together verify that the CNTs*Co2FeO4 prepared by this invention has significant practical potential, but the problem of metal ion leaching is a key issue limiting heterogeneous advanced oxidation technology. This example uses ICP-OES / MS to detect and compare the cobalt and iron ion leaching concentrations of the CNTs*Co2FeO4, carbon nanotube outer wall supported Co2FeO4@CNTs, and commercially available Co2FeO4 materials prepared by this invention.

[0082] (1) The preparation of CNTs*Co2FeO4 is the same as step (1) in Example 1.

[0083] (2) Preparation of Co2FeO4@CNTs supported on the outer wall of carbon nanotubes: At room temperature, Co(NO3)2·6H2O (2 mmol) and FeSO4·5H2O (1 mmol) were dissolved in 35 mL of ultrapure water. Then, urea (10 mmol) and NH4F (8 mmol) were slowly added and magnetically stirred (250 rpm) for 30 minutes until completely dissolved. Then, 3.5 mg of aqueous solution of hydroxylated multi-walled carbon nanotubes was added and ultrasonically treated (20 kHz) for 15 minutes to achieve uniform dispersion. The above mixture was placed in a 50 mL high-pressure hydrothermal reactor with a polytetrafluoroethylene liner and heated at 120 °C for 6 hours. After cooling to room temperature (25 °C), the mixture was transferred to a centrifuge tube. The solid was centrifuged at 10,000 rpm for 15 minutes to achieve solid-liquid separation. The separated solid was then poured into a beaker and washed with deionized water and ethanol for 30 minutes, respectively. After centrifugation, the mixture was repeated 3 times and then dried in a forced-air drying oven at 60 °C for 6 hours. The dried solid was calcined at 280℃ (heating rate of muffle furnace was 5℃ / min) for 3 hours, then cooled to room temperature and ground to obtain a black powder, which is the cobalt-iron bimetallic oxide loaded on the outer wall of carbon nanotubes, denoted as Co2FeO4@CNTs.

[0084] (3) Prepare a ranitidine (RAN) solution with a concentration of 5 mg / L for later use.

[0085] (4) A 200 mL conical flask was used as a reactor. 200 mL of RAN solution and 3 mg of CNTs*Co2FeO4 were added to it. The initial pH value of the solution was adjusted (pH = 6.0). After standing for 2 minutes, the adsorption saturation was reached. Then, 10 mg of PMS was added to it. The solution was magnetically stirred (250 rpm) in a water bath at a controlled temperature (25 °C). Fixed-point sampling and analysis were performed. The concentration of leached ions in the solution was analyzed and detected using an Agilent 5110 ICP-OES / MS.

[0086] (5) Add 3 mg of commercial grade Co2FeO4 to the reactor to replace CNTs*Co2FeO4, and other conditions are the same as in (4).

[0087] (6) Add 3 mg of carbon nanotube outer wall supported Co2FeO4@CNTs to the reactor instead of CNTs*Co2FeO4, and other conditions are the same as (4).

[0088] After a 10-minute catalytic oxidation reaction, the leaching concentrations of cobalt and iron ions in the CNTs*Co2FeO4, the carbon nanotube outer wall supported Co2FeO4@CNTs, and the commercial-grade Co2FeO4 material prepared in this invention were measured. The results are shown in Table 3 and... Figure 5 As shown.

[0089] Table 3 Comparison of Cobalt and Iron Ion Leaching Concentrations

[0090] Material Name Cobalt ion leaching concentration (mg / L) Iron ion leaching concentration (mg / L) <![CDATA[CNTs*Co2FeO4]]> 0.014 0.038 <![CDATA[Co2FeO4@CNTs]]> 0.042 0.089 <![CDATA[Commercial-grade Co2FeO4]]> 0.068 0.167

[0091] From Table 3 and Figure 5 As can be seen, during the catalytic oxidation degradation process with a reaction time of 10 minutes, the leaching concentrations of cobalt and iron ions in the effluent of the CNTs*Co2FeO4, carbon nanotube outer wall supported Co2FeO4@CNTs, and commercial-grade Co2FeO4 materials prepared in this invention were detected by ICP-OES / MS. In comparison, the leaching concentrations of cobalt and iron ions in the effluent of the CNTs*Co2FeO4 prepared in this invention after PMS activation and oxidative degradation of RAN were reduced to 0.333 times and 0.427 times that of the carbon nanotube outer wall supported Co2FeO4@CNTs, respectively, and to 0.206 times and 0.228 times that of commercial-grade Co2FeO4, respectively. This indicates that the hollow structure of the multi-walled carbon nanotubes in the CNTs*Co2FeO4 prepared in this invention can effectively bind free cobalt and iron ions, reducing the leaching risk and solving the problem of secondary water pollution. Figure 2 The carbon nanotubes in CNTs*Co2FeO4 prepared by this invention have a high mechanical strength structure, which overcomes the defects of traditional cobalt-based materials with carbon nanotube outer wall support that are prone to loss of active sites and uneven distribution. Moreover, the carbon nanotube structure can protect against the impact of water on the active sites and effectively bind free cobalt iron ions to reduce the risk of leaching.

[0092] Example 4

[0093] In this example, an electrochemical impedance spectroscopy (EIS) test was performed using a VersaSTAT4 electrochemical workstation to compare the charge transfer resistance of the CNTs*Co2FeO4 prepared in this invention, the carbon nanotube outer wall supported Co2FeO4@CNTs, and commercial Co2FeO4 materials.

[0094] (1) The preparation of CNTs*Co2FeO4 is the same as step (1) in Example 1.

[0095] (2) The preparation of Co2FeO4@CNTs is the same as step (2) in Example 3.

[0096] (3) The CNTs*Co2FeO4 (70wt%), Co2FeO4@CNTs (70wt%), and commercial-grade Co2FeO4 material (70wt%) prepared in this invention were mixed with carbon black (20wt%) and polyvinylidene fluoride (10wt%) in an n-methyl-2-pyridone solvent to prepare CNTs*Co2FeO4, Co2FeO4@CNTs, and Co2FeO4 electrodes, respectively. The mixed slurry was then cast onto copper foil as a current collector and vacuum dried at 80°C for 12 h. The average mass load of each electrode was approximately 1.0 mg / cm³. 2 It has a diameter of 12mm.

[0097] (4) The CR2032 coin-type battery was assembled from prepared CNTs*Co2FeO4, Co2FeO4@CNTs and Co2FeO4 electrodes, a contact electrode (lithium foil), a separator (polypropylene, Celgard 2400), and an electrolyte (1M LiPF6 in DOL / DME (v / v = 1:1) with 0.1M LiNO3 additive). Electrochemical impedance spectroscopy measurements were performed on an AUTOLAB electrochemical workstation with a frequency range of 100kHz-10MHz and an amplitude of 5mV.

[0098] The charge transfer resistances of the CNTs*Co2FeO4, carbon nanotube outer wall supported Co2FeO4@CNTs, and commercial-grade Co2FeO4 materials prepared in this invention are shown in Table 4. Figure 6 As shown.

[0099] Table 4 Charge transfer resistance of different materials

[0100] Material Name Charge transfer resistance (Ω) <![CDATA[CNTs*Co2FeO4]]> 124.7 <![CDATA[Co2FeO4@CNTs]]> 159.2 <![CDATA[Commercial grade Co2FeO4]]> 181.6

[0101] Depend on Figure 6 As observed, the Nyquist plot consists of semicircles in the high / mid frequency range and straight lines in the low frequency range, which corresponds to the charge transfer resistance (Rc) related to lithium-ion diffusion in the electrode. ct The impedance is related to the Warburg impedance. Referring to Table 4, the R of the CNTs*Co2FeO4 prepared in this invention... ct The Ω (124.7Ω) is significantly smaller than that of Co2FeO4@CNTs supported on the outer wall of carbon nanotubes (159.2Ω) and commercial Co2FeO4 material (181.6Ω), indicating that the CNTs*Co2FeO4 prepared in this invention has a greater charge transfer capability. The good conductivity of its carbon nanotube structure provides a charge transfer channel between non-adjacent active sites, thereby enabling a better RAN oxidation and degradation effect.

[0102] Example 5

[0103] Examples 1 and 3 together demonstrate that the CNTs*Co2FeO4 prepared in this invention possesses excellent catalytic activity and exhibits significant practical potential. This example uses RAN as the target pollutant, selects common actual water bodies, and compares the removal efficiency of CNTs*Co2FeO4 in activating PMS to oxidize and degrade RAN in different water bodies.

[0104] (1) The preparation of CNTs*Co2FeO4 is the same as step (1) in Example 1.

[0105] (2) Prepare ranitidine (RAN) solutions with a concentration of 5 mg / L using different water bodies as solvents for later use.

[0106] (3) A 200 mL conical flask was used as a reactor. 200 mL of RAN solution dissolved in different water bodies and 3 mg of CNTs*Co2FeO4 were added to it. The initial pH value of the solution was adjusted (pH=6.0). After standing for 2 minutes, the adsorption saturation was reached. Then, 10 mg of PMS was added to it. The solution was magnetically stirred (250 rpm) in a water bath at a controlled temperature (25℃). Samples were taken at fixed points for analysis.

[0107] (4) Add 50 μL of the scavenging agent aqueous solution (DMPO, TEMP), mix well, and then aspirate using a capillary tube. After attaching the capillary tube, place the sample in the EPR (Bruker EMXplus-6 / 1) sample chamber for the determination of reactive oxide species. The results are as follows: Figure 7 As shown.

[0108] The removal rates of RAN in different water bodies are shown in Table 5.

[0109] Table 5. RAN removal rate in different water bodies

[0110] Different water bodies Ultrapure water tap water Urban river water Lake water Secondary effluent Removal rate % 100％ 99.8％ 98.6％ 99.2％ 96.8％

[0111] As shown in Table 5, when ultrapure water, tap water, urban river water, lake water, and secondary effluent from sewage treatment plants were used as media, the RAN oxidation degradation removal rate of the CNTs*Co2FeO4 prepared in this invention exceeded 95% after a 10-minute reaction process. This indicates that the CNTs*Co2FeO4 material prepared in this invention has strong application performance and can be used in different aquatic environments. Furthermore, from... Figure 7 It can be seen that DMPO-SO4 is involved in the RAN oxidative degradation process. ·- DMPO-·OH and TEMP- 1The fact that O2 signals can be captured indicates that the composite catalytic material developed in this invention can stimulate a free radical-non-free radical coexisting oxidation reaction, which can efficiently degrade recalcitrant organic pollutants in water. Its green, environmentally friendly, and highly efficient advantages show great application potential in the field of water pollution control.

[0112] Example 6

[0113] This example examines the recycling effect of CNTs*Co2FeO4-catalyzed activated PMS on RAN degradation prepared in Example 1.

[0114] (1) The preparation of CNTs*Co2FeO4 is the same as step (1) in Example 1.

[0115] (2) Prepare a ranitidine (RAN) solution with a concentration of 5 mg / L for later use.

[0116] (3) A 200 mL conical flask was used as a reactor. 200 mL of RAN solution and 3 mg of CNTs*Co2FeO4 were added to it. The initial pH value of the solution was adjusted (pH = 6.0). After standing for 2 minutes, the adsorption saturation was reached. Then, 10 mg of PMS was added to it. The solution was magnetically stirred (250 rpm) in a water bath at a controlled temperature (25 °C). Samples were taken at fixed points for analysis.

[0117] (4) CNTs*Co2FeO4 in the reaction solution of (3) were filtered through a water-based membrane with a pore size of 0.22μm using deionized water / 0.1mM sodium borohydride aqueous solution. The solution was then added to the reactor for the second time, with other conditions the same as in (3).

[0118] (5) CNTs*Co2FeO4 in the reaction solution of (3) were filtered through a 0.22μm aqueous membrane using deionized water / 0.1mM sodium borohydride aqueous solution. The solution was then added to the reactor for the third time, with other conditions the same as in (3).

[0119] (6) CNTs*Co2FeO4 in the reaction solution of (3) were filtered through a 0.22μm aqueous membrane using deionized water / 0.1mM sodium borohydride aqueous solution. The solution was then added to the reactor for the fourth time, with other conditions the same as in (3).

[0120] (7) CNTs*Co2FeO4 in the reaction solution of (3) were filtered through a 0.22μm aqueous membrane using deionized water / 0.1mM sodium borohydride aqueous solution. The solution was then added to the reactor for the fifth time, with other conditions the same as in (3).

[0121] (8) CNTs*Co2FeO4 in the reaction solution of (3) were filtered through a 0.22μm aqueous membrane using deionized water / 0.1mM sodium borohydride aqueous solution. The solution was added to the reactor for the sixth time, and other conditions were the same as in (3).

[0122] (9) CNTs*Co2FeO4 in the reaction solution of (3) were filtered through a 0.22μm aqueous membrane using deionized water / 0.1mM sodium borohydride aqueous solution. The solution was added to the reactor for the seventh time, and other conditions were the same as in (3).

[0123] (10) CNTs*Co2FeO4 in the reaction solution of (3) were filtered through a 0.22μm aqueous membrane using deionized water / 0.1mM sodium borohydride aqueous solution. The mixture was added to the reactor for the eighth time, with other conditions the same as in (3).

[0124] (11) CNTs*Co2FeO4 in the reaction solution of (3) were filtered through a 0.22μm aqueous membrane using deionized water / 0.1mM sodium borohydride aqueous solution. The solution was then added to the reactor for the ninth time, with other conditions the same as in (3).

[0125] (12) CNTs*Co2FeO4 in the reaction solution of (3) were filtered through a 0.22μm aqueous membrane using deionized water / 0.1mM sodium borohydride aqueous solution. The solution was added to the reactor for the tenth time, and other conditions were the same as in (3).

[0126] Table 6 shows the recycling of RAN by CNTs*Co2FeO4-activated PMS oxidation degradation.

[0127] Table 6. Recycling status of RAN oxidative degradation by PMS activated by CuCo2O4@CNTs.

[0128] Loop count RAN removal rate after deionized water treatment (%) RAN removal rate (%) after treatment with sodium borohydride aqueous solution 1 99.8 99.8 2 96.4 98.2 3 88.1 95.4 4 80.5 91.2 5 78.4 86.6 6 69.1 84.7 7 52.2 81.1 8 40.1 76.6 9 29.6 70.1 10 20.3 65.2

[0129] As shown in Table 6, in the ten consecutive cycles of the CNTs*Co2FeO4-activated PMS oxidation degradation experiment for RAN (random organic pollutant) in water, the RAN removal rate decreased to some extent with the increase of the number of cycles. In comparison, the sodium borohydride aqueous solution treatment method proposed in this invention can ensure that the overall RAN removal rate is still above 65%. Together with Example 3, this verifies that the main reason for the decrease in RAN removal rate is the passivation of the active sites on the CNTs*Co2FeO4 surface and the loss of some material during washing and filtration. It also shows that this material can be reactivated by reduction treatment with sodium borohydride aqueous solution, and the operating cost of the process can be reduced by extending its service life.

Claims

1. A method for preparing a rod-shaped structure material with cobalt-iron dual active sites embedded in carbon nanotubes, characterized in that, Includes the following steps: (1) Hydroxylated multi-walled carbon nanotubes were dispersed in water by ultrasonic treatment, then nitric acid was added and allowed to stand, then rotary evaporation was performed, and then the carbon nanotubes were washed with water to obtain the treated carbon nanotubes. (2) Add Co(NO3)2·6H2O and FeSO4·5H2O to water under magnetic stirring, and then add urea until it is completely dissolved; (3) Add the carbon nanotubes treated in step (1) to the solution obtained in step (2), then place them in a high-pressure hydrothermal reactor for heating treatment, then cool to room temperature, centrifuge, wash, dry the product, and finally calcine at high temperature to obtain carbon nanotube embedded cobalt iron double active site rod structure material. In step (2), the molar ratio of Co(NO3)2·6H2O and FeSO4·5H2O is 2:1, and the speed of the magnetic stirrer is controlled at 150~200 rpm; In step (3), the washing process is as follows: wash three times with 15 wt% hydrochloric acid and distilled water respectively.

2. The method for preparing the carbon nanotube embedded cobalt-iron dual-active-site rod-shaped structure material according to claim 1, characterized in that, In step (1), the concentration of nitric acid is 65 wt%, the settling time is 5 h, and the pH value of the washing water effluent is higher than 6.

0.

3. The method for preparing the carbon nanotube embedded cobalt-iron dual-active-site rod-shaped structure material according to claim 1, characterized in that, In step (3), high-temperature calcination refers to holding the temperature at 300℃ for 4 hours.

4. The carbon nanotube rod-shaped structure material with cobalt-iron dual active sites prepared by the method according to any one of claims 1 to 3.

5. The application of the carbon nanotube embedded cobalt-iron dual-active-site rod-shaped structure material as a catalyst for activating persulfate to oxidize and degrade organic micropollutants in water.

6. The application according to claim 5, characterized in that, The organic micropollutants include ranitidine, rhodamine B, cationic red GTL, methyl orange, methylene blue, carbamazepine, ciprofloxacin, norfloxacin, tetracycline hydrochloride, bisphenol A, and phenol.

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