Cobalt-iron-embedded double-active-site rod-like structure material in carbon nano tube as well as preparation method and application thereof

Abstract

The invention provides a cobalt-iron double-active-site rod-like structure material embedded in a carbon nano tube as well as a preparation method and application of the cobalt-iron double-active-site rod-like structure material. The cobalt-iron bimetallic oxide is embedded into the inner wall of the carbon nano tube by adopting a hydrothermal-calcining-pickling method, so that high-density and dispersed cobalt-iron double active sites can be formed, the defects that the active sites of the traditional supported cobalt-based material are easy to lose and are not uniformly distributed are overcome, and the leaching risk of cobalt ions is reduced. The carbon nanotube has a high mechanical strength structure, and is helpful for resisting the impact of a water body on active sites. The material provided by the invention can excite free radical-non-free radical coexisting oxidation reaction, and can realize rapid degradation of complex organic micropollutants in a water body. The effect of activating PMS to degrade organic micropollutants at normal temperature reaches 95% or above, the applicable pH value range is wide, and a wide application prospect is provided for treating the organic micropollutants in water.

Description

Technical Field

[0001] The present invention relates to the technical field of water pollution treatment by environmental functional materials, and specifically to a carbon nanotube-embedded cobalt-iron dual active site rod-shaped structure material, a preparation method thereof, and an application thereof. Background Art

[0002] The water quality evaluation and water treatment processes commonly used in China still mainly focus on the formulation and design of conventional indicators such as ammonia nitrogen and total organic carbon. However, the deep treatment technology for persistent organic micro-pollutants in municipal sewage is still in the development stage and has always been a difficult problem and challenge in the environmental engineering discipline. At present, the sulfate radical (SO4 ·- )-mediated advanced oxidation technology has received extensive attention in the field of water pollution treatment because it has a relatively high redox potential (2.5 - 3.1 V) and can achieve the deep mineralization of persistent organic micro-pollutants in water bodies. Peroxymonosulfate (PMS), as a solid-phase oxidant with an asymmetric molecular structure, can generate abundant sulfate radicals through an activation process. Transition metals can also break through the limitations of low PMS activation efficiency and harsh reaction conditions under low energy consumption requirements. Among them, cobalt-based materials are the best catalysts for activating PMS to generate sulfate radicals, and cobalt tetroxide is regarded as the most typical representative. However, such materials are still limited by the performance defects of cobalt ion leaching and easy passivation of active sites. Therefore, in order to ensure the catalytic activity and structural site stability of such materials to meet the actual engineering application requirements, it is urgent to solve the above performance defects.

[0003] Iron element has similar chemical properties and can be incorporated into cobalt tetroxide by lattice substitution. Due to the existence of a redox potential difference, it will accelerate the rapid transfer of charges and effectively slow down the rate of active site passivation. However, the mismatch of the outer electrons of cobalt atoms and iron atoms will cause structural defects in cobalt-iron bimetallic oxides, and the severity will increase with the enhancement of catalytic activity. Due to the mutually restrictive relationship between the catalytic activity and structural stability of cobalt-based oxides, it will directly lead to the secondary pollution of water bodies caused by cobalt ion leaching. Carbon nanotubes have a high mechanical strength structure, which helps to resist the impact of water bodies on active sites. Their good electrical conductivity provides a charge transfer channel between non-adjacent active sites, and the multi-walled hollow structure can effectively bind free cobalt ions to reduce the leaching risk.

[0004] The patent application document CN 118304887 A discloses a cobalt-copper dual-site carbon nanotube-based cross-linked structure material, its preparation method and application. In this method, cobalt nitrate and copper chloride are dissolved, then urea and NH4F are added and stirred together. After that, hydroxylated multi-walled carbon nanotubes are added and ultrasonicated, and then a hydrothermal reaction is carried out to obtain the CuCo2O4@CNTs material. However, this CuCo2O4@CNTs material is a material with a loading type on the outer wall of carbon nanotubes, and for loading type materials, their active sites are prone to loss. Therefore, how to overcome the problems of easy loss of catalytic active sites in the supported cobalt-based oxide materials and the mutual restraint relationship between catalytic activity and structural stability has important practical significance for its actual engineering applications. Summary of the Invention

[0005] The object of the present invention is to provide a carbon nanotube-embedded cobalt-iron dual-active-site rod-shaped structure material, its preparation method and application, so as to solve the performance defects of existing supported cobalt-based materials as PMS activators, such as easy leaching of cobalt ions and passivation of active sites.

[0006] The present invention is realized as follows:

[0007] A preparation method of a carbon nanotube-embedded cobalt-iron dual-active-site rod-shaped structure material, the specific steps are as follows:

[0008] (1) Dispersing hydroxylated multi-walled carbon nanotubes in water by ultrasonic treatment, then adding nitric acid and standing, and then performing rotary evaporation treatment, and then washing with water to obtain the treated carbon nanotubes;

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

[0010] (3) Adding the treated carbon nanotubes in step (1) to the solution obtained in step (2), then placing it in a high-pressure hydrothermal reaction kettle for heating treatment, and then cooling to room temperature. The product is centrifuged, washed, dried, and finally subjected to high-temperature calcination treatment to obtain the carbon nanotube-embedded cobalt-iron dual-active-site rod-shaped structure material.

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

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

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

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

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

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

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

[0018] Further, in step (2), the dosage of urea is 8.0 mg.

[0019] Further, in step (3), the washing is carried out by washing 3 times with 15 wt% HCl and distilled water respectively, and the washing time for each time does not exceed 30 min.

[0020] Further, in step (3), the high-temperature calcination temperature is 300 °C, the duration is 4 h, the high-temperature calcination is carried out in a muffle furnace, and the heating rate of the muffle furnace is 5 °C / 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 on the inner wall of hydroxylated multi-walled carbon nanotubes. The appearance of this material shows an obvious rod-shaped structure, its average length is less than 1 μm, and the content of the active component element 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 peroxymonosulfate (PMS) for the oxidative degradation of refractory organic micro-pollutants in water. The specific steps are as follows: Add CNTs*Co2FeO4 and PMS to the water containing organic micro-pollutants and react under normal temperature and pressure conditions.

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

[0024] Further, the initial concentration of the organic micro-pollutant is 5 mg / L.

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

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

[0027] Furthermore, the organic micro-pollutants 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.

[0028] In the present invention, CNTs*Co2FeO4 is used as a catalyst, and a removal rate of more than 95% can be achieved within 10 min of oxidative degradation.

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

[0030] (1) The present invention firstly proposes CNTs*Co2FeO4 and its preparation method. The preparation method has low requirements for synthesis equipment, high purity of synthetic materials, and is convenient for mass production.

[0031] (2) The CNTs*Co2FeO4 synthesized in the present invention overcomes the defects of traditional cobalt-based materials supported on the outer wall of carbon nanotubes, such as easy loss and uneven distribution of active sites. Moreover, it can protect against the impact of water on active sites by means of the carbon nanotube structure, and can effectively bind free cobalt ions to reduce their leaching risk.

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

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

[0034] (5) No additional energy input (such as light, electricity, and heat) is required during the activation of PMS by the CNTs*Co2FeO4 synthesized in the present invention, which reduces the operation cost. Moreover, the process flow is simple, the operability is strong, the material usage is small, and the performance is stable, having broad practical application prospects.

[0035] (6) The CNTs*Co2FeO4 synthesized in the present invention not only reduces the leaching risk of cobalt ions and the preparation cost of materials, but also can be applied to the oxidative degradation of various typical organic micro-pollutions in water by activating PMS under mild reaction conditions, and has better performance compared with traditional processes. Description of the Drawings

[0036] Figure 1XRD pattern of carbon nanotubes embedded with cobalt-iron bimetallic oxide CNTs*Co2FeO4 prepared in Example 1.

[0037] Figure 2 TEM and STEM images of carbon nanotubes embedded with cobalt-iron bimetallic oxide CNTs*Co2FeO4 prepared in Example 1; where a is the TEM image, b is the STEM image, and c, d, e, f are the EDX spectra of carbon, oxygen, iron, and cobalt elements of the CNTs*Co2FeO4 material, respectively.

[0038] Figure 3 XPS spectra of carbon nanotubes embedded with cobalt-iron bimetallic oxide CNTs*Co2FeO4 prepared in Example 1; where a and b are the XPS spectra of cobalt and iron elements of the CNTs*Co2FeO4 material, respectively.

[0039] Figure 4 Kinetic comparison of the removal of RAN by the present invention and other different advanced oxidation technologies in Example 2.

[0040] Figure 5 Comparison of the leaching concentrations of cobalt and iron ions of CNTs*Co2FeO4 prepared by the present invention, Co2FeO4@CNTs material with Co2FeO4 loaded on the outer wall of carbon nanotubes, and commercial Co2FeO4 material in Example 3.

[0041] Figure 6 AC impedance diagrams (inset: equivalent circuit) of CNTs*Co2FeO4 prepared by the present invention, Co2FeO4@CNTs material with Co2FeO4 loaded on the outer wall of carbon nanotubes, and commercial Co2FeO4 material in Example 4.

[0042] Figure 7 EPR spectra of detecting reactive oxygen species in the reaction system using TEMP and DMPO as scavengers in Example 5. Detailed implementation manners

[0043] To more clearly illustrate the purpose, technology, and advantages of the present invention, the following provides a detailed description in combination with specific examples and drawings. The examples are only for illustrating the present invention and do not limit the present invention.

[0044] The raw materials used in the present invention are all conventional commercially available products.

[0045] In this invention, ranitidine (RAN) is used as a typical organic micro-pollutant. To prove the high-efficiency oxidative degradation ability of this invention for organic micro-pollutants in water, at least one of 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 is selected as the target pollutant.

[0046] Example 1

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

[0048] (1) Preparation of CNTs*Co2FeO4: At room temperature (25 °C), under ultrasonic treatment (20 kHz), 4.5 mg of hydroxylated multi-walled carbon nanotubes are uniformly dispersed in a beaker containing 50 mL of distilled water for 10 min. Then, 10 mL of 65 wt% HNO3 is added to the above aqueous solution and left standing for 5 h. After rotary evaporation treatment (100 rpm), continuous washing is carried out with distilled water until the pH value of the washing water is higher than 6.0, and the treated carbon nanotubes are obtained. Under magnetic stirring at a speed of 150 - 200 rpm, Co(NO3)2·6H2O (2 mmol) and FeSO4·5H2O (1 mmol) are added to a beaker containing 50 mL of distilled water, and then urea (8.0 mg) is slowly added until completely dissolved to obtain a mixed solution. The treated carbon nanotubes are added to the above mixed solution and placed in a 50 mL high-pressure hydrothermal reaction kettle with a polytetrafluoroethylene inner liner, and heated at 120 °C for 6 h. After cooling to room temperature (25 °C), the reaction mixture is transferred to a centrifuge tube, and solid-liquid separation is achieved by centrifugation at 10000 rpm for 15 min. Then, the separated material is washed 3 times with 15 wt% HCl and distilled water respectively, with each washing time not exceeding 30 min, followed by centrifugation. After repeating 3 times, it is placed in a blast drying oven and dried at 60 °C for 6 h. The dried material is calcined at a high temperature of 300 °C (the heating rate of the muffle furnace is 5 °C / min) for 4 h, and then cooled to room temperature and ground to obtain a black powder, which is a carbon nanotube-embedded cobalt-iron double active site rod-like structure material, labeled as CNTs*Co2FeO4.

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

[0050] The TEM and STEM-EDX images of the obtained CNTs*Co2FeO4 are as Figure 2 shown. By Figure 2 observing, it can be found that cobalt-iron bimetallic oxides are embedded in the inner wall of carbon nanotubes, forming high-density and dispersed cobalt-iron double active sites.

[0051] Figure 3 The XPS spectra of cobalt and iron elements in the CNTs*Co2FeO4 material are shown.

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

[0053] (3) Use a 200 mL conical flask as the reactor, add 200 mL of RAN solution and 3 mg of CNTs*Co2FeO4 to it, adjust the initial pH value of the solution (pH = 6.0), let it stand for 2 minutes until adsorption saturation is reached, then add 10 mg of PMS to it, and carry out magnetic stirring (rotation speed 250 rpm) under the control of temperature (25 °C) in a water bath pot, and take samples at fixed points for analysis.

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

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

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

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

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

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

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

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

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

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

[0064] After a 10-minute rapid catalytic oxidation reaction, the removal effects of different organic micropollutants 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] As can be seen from Table 1, during the 10-minute oxidation degradation process, the removal rates of the eleven organic micropollutants oxidized and degraded by CNTs*Co2FeO4 activating PMS are all above 95%. It shows 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 the multi-walled carbon nanotube structure, and it exhibits non-selective oxidation degradation ability. Therefore, good treatment effects on organic micropollutants in water can be achieved.

[0068] Example 2

[0069] In this example, ranitidine (RAN) with the best pollution treatment effect screened in Example 1 is used as the target pollutant, and the efficacy of CNTs*Co2FeO4 prepared in Example 1 and different advanced oxidation technologies activating PMS to oxidize and degrade RAN is compared.

[0070] (1) Prepare a 5 mg / L ranitidine (RAN) solution for standby.

[0071] (2) Use a 200 mL conical flask as the reactor, add 200 mL of RAN solution and 3 mg of CNTs*Co2FeO4 to it, adjust the initial pH value of the solution (pH = 6.0), and let it stand for 2 minutes to reach adsorption saturation. Then add 10 mg of PMS to it, and carry out magnetic stirring (rotation speed 250 rpm) under the condition of controlling the temperature (25 °C) in a water bath pot, and take samples at fixed points for analysis.

[0072] (3) Use the currently most scientific reaction kinetic formula (1) to calculate and compare the reaction rates (k) of different advanced oxidation technologies to evaluate the oxidation degradation efficacy of RAN.

[0073] k = 1 / m × dCRAN / dt(1)

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

[0075] The evaluation and comparison of the removal efficiency of RAN when different advanced oxidation technologies are used are shown in Table 2 and Figure 4 as follows.

[0076] Table 2 Comparison table of the evaluation of the removal efficiency of RAN when different advanced oxidation technologies are used

[0077]

[0078] Other catalytic materials and the corresponding data in Table 2 except for the present 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 degradation efficiency of different oxidation technologies for RAN. By comparing the commonly used advanced oxidation technologies, the oxidation degradation efficiency of CNTs*Co2FeO4 prepared in the present invention by activating PMS has significant advantages. Under the same application conditions, the dosage of the catalyst is the least, and no additional energy input is required, and the operating cost is the most advantageous. The reaction rate constant of the oxidation degradation of RAN by CNTs*Co2FeO4 prepared in the present invention by activating PMS is 2.63 - 3204.40 times that of the above-mentioned advanced oxidation technologies, indicating that the present invention has the ability of rapid oxidation degradation and great practical potential.

[0080] Example 3

[0081] Examples 1 and 2 jointly verified that CNTs*Co2FeO4 prepared in the present invention has significant practical potential, but the problem of metal ion leaching is the key problem restricting heterogeneous advanced oxidation technologies. In this example, ICP-OES / MS was used to detect and compare the leaching concentrations of cobalt and iron ions of CNTs*Co2FeO4 prepared in the present invention, Co2FeO4@CNTs loaded on the outer wall of carbon nanotubes, and commercial Co2FeO4 materials.

[0082] (1) The preparation of CNTs*Co2FeO4 was 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 continuously magnetically stirred (250 rpm) for 30 minutes until completely dissolved. Then, an aqueous solution of 3.5 mg of hydroxylated multi-walled carbon nanotubes was ultrasonically treated (20 kHz) for 15 minutes and uniformly dispersed. The above mixture was placed in a 50 mL high-pressure hydrothermal reaction kettle equipped with a polytetrafluoroethylene inner liner, heated at 120 °C for 6 hours. After cooling to room temperature (25 °C), the reaction mixture was transferred to a centrifuge tube; solid-liquid separation was achieved by centrifugation at 10000 rpm for 15 minutes; the separated solid was then poured into a beaker, washed with deionized water and ethanol for 30 minutes each, centrifuged, and repeated 3 times. Then, it was dried in a forced-air drying oven at 60 °C for 6 hours. The dried solid was calcined at 280 °C (the heating rate of the muffle furnace was 5 °C / min) for 3 hours, and then cooled to room temperature and ground to obtain a black powder, which was cobalt-iron bimetallic oxide supported 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 standby.

[0085] (4) Use a 200 mL conical flask as the reactor, add 200 mL of RAN solution and 3 mg of CNTs*Co2FeO4 to it, adjust the initial pH value of the solution (pH = 6.0), and let it stand for 2 minutes until adsorption saturation is reached. Then, add 10 mg of PMS to it, and perform magnetic stirring (rotation speed 250 rpm) under the control of temperature (25 °C) in a water bath. Samples were taken at fixed points for analysis, and the ion concentration leached in the solution was analyzed and detected using an Agilent 5110 model ICP-OES / MS in the United States.

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

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

[0088] After 10 minutes of catalytic oxidation reaction, the leaching concentrations of cobalt and iron ions in the CNTs*Co2FeO4 prepared by the present invention, the Co2FeO4@CNTs supported on the outer wall of carbon nanotubes, and the commercial Co2FeO4 material were detected. The results are shown in Table 3 and Figure 5 as follows.

[0089] Table 3 Comparison table of leaching concentrations of cobalt and iron ions

[0090] Material name Leaching concentration of cobalt ions (mg / L) Leaching concentration of iron ions (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] As can be seen from Table 3 and Figure 5 it can be seen that during the catalytic oxidation degradation process with a reaction time of 10 minutes, the ICP-OES / MS was used to detect the leaching concentrations of cobalt and iron ions in the effluent of the CNTs*Co2FeO4 prepared by the present invention, the Co2FeO4@CNTs supported on the outer wall of carbon nanotubes, and the commercial Co2FeO4 material. In comparison, the leaching concentrations of cobalt and iron ions in the effluent after the activation of PMS by the CNTs*Co2FeO4 prepared by the present invention to oxidize and degrade RAN were reduced to 0.333 times and 0.427 times of the Co2FeO4@CNTs supported on the outer wall of carbon nanotubes, and were reduced to 0.206 times and 0.228 times of the commercial Co2FeO4, respectively. This shows that the hollow structure of the multi-walled carbon nanotubes in the CNTs*Co2FeO4 prepared by the present invention can also effectively bind free cobalt and iron ions to reduce the leaching risk and can solve the problem of secondary water pollution. Combining Figure 2 with this, the carbon nanotubes in the CNTs*Co2FeO4 prepared by the present invention have a high mechanical strength structure, overcoming the defects of easy loss and uneven distribution of active sites in the traditional cobalt-based materials supported on the outer wall of carbon nanotubes, and can protect against the impact of water on the active sites by means of the carbon nanotube structure, effectively binding free cobalt and iron ions to reduce the leaching risk.

[0092] Example 4

[0093] In this example, a VersaSTAT4 electrochemical workstation was used to test the electrochemical impedance spectroscopy (EIS) to compare the charge transfer resistances of the CNTs*Co2FeO4 prepared by the present invention, the Co2FeO4@CNTs supported on the outer wall of carbon nanotubes, and the commercial Co2FeO4 material.

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

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

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

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

[0098] The charge transfer resistances of the CNTs*Co2FeO4, Co2FeO4@CNTs with Co2FeO4 loaded on the outer wall of carbon nanotubes, and commercial-grade Co2FeO4 materials prepared in the present invention are shown in Table 4 and Figure 6 as follows.

[0099] Table 4 Charge transfer resistances 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] As Figure 6 seen, the Nyquist plot consists of a semicircle in the high / medium frequency range and a straight line in the low frequency range, which is related to the charge transfer resistance (R ct ) associated with lithium ion diffusion in the electrode and the Warburg impedance. Combining with Table 4, the R ct (124.7 Ω) of the CNTs*Co2FeO4 prepared in the present invention is significantly smaller than that of Co2FeO4@CNTs (159.2 Ω) with Co2FeO4 loaded on the outer wall of carbon nanotubes and commercial-grade Co2FeO4 materials (181.6 Ω), indicating that the CNTs*Co2FeO4 prepared in the present invention has a greater charge transfer ability. The good conductivity of its carbon nanotube structure provides a charge transfer channel between non-adjacent active sites, and thus can exhibit a better RAN oxidation degradation effect.

[0102] Example 5

[0103] Example 1 and Example 3 jointly confirmed that the CNTs*Co2FeO4 prepared by the present invention has excellent catalytic activity and exhibits remarkable practical potential. In this example, RAN was used as the target pollutant, and common actual water bodies were selected to compare the removal effects of CNTs*Co2FeO4 on the activation of PMS to oxidize and degrade RAN in different water bodies.

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

[0105] (2) Different water bodies were used as solvents to prepare a ranitidine (RAN) solution with a concentration of 5 mg / L for standby.

[0106] (3) A 200 mL conical flask was used as the reactor. 200 mL of RAN solution dissolved in different water bodies and 3 mg of CNTs*Co2FeO4 were added thereto. The initial pH value of the solution (pH = 6.0) was adjusted, and after standing for 2 minutes to reach adsorption saturation, 10 mg of PMS was added thereto. Magnetic stirring (rotation speed 250 rpm) was carried out under the control of the temperature (25 °C) in a water bath, and samples were taken at fixed points for analysis.

[0107] (4) 50 μL of an aqueous solution of the scavenger (DMPO, TEMP) was added, and after mixing evenly, it was sucked with a capillary tube, then put into the sample chamber of an EPR (Bruker EMXplus-6 / 1, Germany) after being sleeved with a quartz tube for the determination of active oxygen species, and the results are as Figure 7 shown.

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

[0109] Table 5 Removal rates of RAN in different water bodies

[0110] Different water bodies Ultra-pure water Tap water Urban river water Lake water Secondary effluent Removal rate % 100％ 99.8％ 98.6％ 99.2％ 96.8％

[0111] As can be seen from Table 5, when the CNTs*Co2FeO4 prepared by the present invention was used as the medium in ultrapure water, tap water, urban river water, lake water, and secondary effluent from a sewage treatment plant, after a reaction process of 10 min, the oxidation and degradation removal rates of RAN in the above various water bodies all exceeded 95%, indicating that the CNTs*Co2FeO4 material prepared by the present invention has strong application performance and can be applied to different water environment media. In addition, as Figure 7 can be seen, during the oxidation and degradation of RAN, DMPO-SO4 ·- , DMPO-·OH and TEMP- 1The signals of O2 can all be captured, indicating that the composite catalytic material developed in this invention can stimulate the free radical-non-free radical co-existing oxidation reaction, and can efficiently degrade the refractory organic pollutants in water. Its advantages of being green, environmentally friendly and highly efficient show great application potential in the field of water pollution control.

[0112] Example 6

[0113] This example examines the recycling situation of the degradation of RAN by the CNTs*Co2FeO4 prepared in Example 1 for catalytic activation of PMS.

[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 standby.

[0116] (3) Use a 200 mL conical flask as the reactor, add 200 mL of RAN solution and 3 mg of CNTs*Co2FeO4 to it, adjust the initial pH value of the solution (pH = 6.0), and let it stand for 2 minutes to reach adsorption saturation. Then add 10 mg of PMS to it, and carry out magnetic stirring (rotation speed 250 rpm) under the control of temperature (25 °C) in a water bath pot, and take samples at fixed points for analysis.

[0117] (4) Use deionized water / 0.1 mM sodium borohydride aqueous solution to filter the CNTs*Co2FeO4 in the reaction solution of (3) through a water-based membrane with a pore size of 0.22 μm, and then put it into the reactor for the second time, with other conditions the same as (3).

[0118] (5) Use deionized water / 0.1 mM sodium borohydride aqueous solution to filter the CNTs*Co2FeO4 in the reaction solution of (3) through a water-based membrane with a pore size of 0.22 μm, and then put it into the reactor for the third time, with other conditions the same as (3).

[0119] (6) Use deionized water / 0.1 mM sodium borohydride aqueous solution to filter the CNTs*Co2FeO4 in the reaction solution of (3) through a water-based membrane with a pore size of 0.22 μm, and then put it into the reactor for the fourth time, with other conditions the same as (3).

[0120] (7) Use deionized water / 0.1 mM sodium borohydride aqueous solution to filter the CNTs*Co2FeO4 in the reaction solution of (3) through a water-based membrane with a pore size of 0.22 μm, and then put it into the reactor for the fifth time, with other conditions the same as (3).

[0121] (8) Using deionized water / 0.1 mM sodium borohydride aqueous solution through a water-based membrane with a pore size of 0.22 μm, filter CNTs*Co2FeO4 in the reaction solution of (3) successively, and put it into the reactor for the sixth time, with other conditions the same as (3).

[0122] (9) Using deionized water / 0.1 mM sodium borohydride aqueous solution through a water-based membrane with a pore size of 0.22 μm, filter CNTs*Co2FeO4 in the reaction solution of (3) successively, and put it into the reactor for the seventh time, with other conditions the same as (3).

[0123] (10) Using deionized water / 0.1 mM sodium borohydride aqueous solution through a water-based membrane with a pore size of 0.22 μm, filter CNTs*Co2FeO4 in the reaction solution of (3) successively, and put it into the reactor for the eighth time, with other conditions the same as (3).

[0124] (11) Using deionized water / 0.1 mM sodium borohydride aqueous solution through a water-based membrane with a pore size of 0.22 μm, filter CNTs*Co2FeO4 in the reaction solution of (3) successively, and put it into the reactor for the ninth time, with other conditions the same as (3).

[0125] (12) Using deionized water / 0.1 mM sodium borohydride aqueous solution through a water-based membrane with a pore size of 0.22 μm, filter CNTs*Co2FeO4 in the reaction solution of (3) successively, and put it into the reactor for the tenth time, with other conditions the same as (3).

[0126] The recycling situation of CNTs*Co2FeO4-activated PMS for the oxidative degradation of RAN is shown in Table 6.

[0127] Table 6 Recycling situation of CuCo2O4@CNTs-activated PMS for the oxidative degradation of RAN

[0128] Number of cycles Removal rate of RAN after deionized water treatment % Removal rate of RAN 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 can be seen from Table 6, in the continuous ten-cycle experiment of CNTs*Co2FeO4-activated PMS for the oxidative degradation of the organic micro-pollutant RAN in water, as the number of cycles increases, the removal rate of RAN will decrease to a certain extent. In comparison, the treatment method with sodium borohydride aqueous solution proposed in the present invention can ensure that the overall RAN removal rate is still above 65%. Verifying together with Example 3, the reasons for the decrease in the RAN removal rate are mainly due to the passivation of the surface active sites of CNTs*Co2FeO4 and the loss of some materials during the washing and filtration process, and it also shows that this material can be reactivated by the reduction treatment method with sodium borohydride aqueous solution, and the operation cost of the process can be reduced by extending the service life.

Claims

1. A preparation method of a carbon nanotube-embedded cobalt-iron dual-active-site rod-shaped structure material, characterized in that It includes the following steps: (1) Hydroxylated multi-walled carbon nanotubes are dispersed in water by ultrasonic treatment, then nitric acid is added and left standing, followed by rotary evaporation treatment, and then washed with water to obtain treated carbon nanotubes; (2) Co(NO3)2·6H2O and FeSO4·5H2O are added to water under magnetic stirring, and then urea is added until completely dissolved; (3) The treated carbon nanotubes in step (1) are added to the solution obtained in step (2), then placed in a high-pressure hydrothermal reaction kettle for heat treatment, and then cooled to room temperature. The product is centrifuged, washed, dried, and finally subjected to high-temperature calcination treatment to obtain a carbon nanotube-embedded cobalt-iron dual active site rod-like structure material.

2. The preparation method of 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 standing time is 5 h, and the washing is stopped until the pH value of the washing water effluent is higher than 6.

0.

3. The preparation method of the carbon nanotube-embedded cobalt-iron dual-active-site rod-shaped structure material according to claim 1, characterized in that In step (2), the molar ratio of Co(NO3)2·6H2O to FeSO4·5H2O is 2:1, and the rotation speed of magnetic stirring is controlled at 150-200 rpm.

4. The preparation method of the carbon nanotube-embedded cobalt-iron dual-active-site rod-shaped structure material according to claim 1, characterized in that, In step (3), the washing process is: washing three times with 15 wt% hydrochloric acid and distilled water respectively.

5. The preparation method of 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 means maintaining the temperature at 300 °C for 4 h.

6. A carbon nanotube-embedded cobalt-iron dual active site rod-like structure material prepared by the method according to any one of claims 1 to 5.

7. Use of the carbon nanotube-embedded cobalt-iron dual active site rod-like structure material according to claim 6 as a catalyst to activate peroxymonosulfate for the oxidative degradation of organic micro-pollutants in water.

8. The application according to claim 7, characterized in that, The organic micro-pollutants include ranitidine, rhodamine B, cationic red GTL, methyl orange, methylene blue, carbamazepine, ciprofloxacin, norfloxacin, tetracycline hydrochloride, bisphenol A and phenol.

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