Carbon nanotube modified CuFeO2 catalyst and its preparation method and application

Abstract

The present invention discloses a carbon nanotube modified CuFeO2 catalyst, its preparation method and application. The catalyst is prepared by depositing CuFeO2 nanoparticles on the surface of carbon nanotubes through a simple one-step low-temperature hydrothermal method. Compared with pure CuFeO2, the introduction of carbon nanotubes effectively alleviates the aggregation of CuFeO2 nanoparticles and significantly increases its specific surface area. By applying it to the field of water environment remediation, it is found that it can efficiently activate PMS to generate highly active 1 O2 to selectively degrade organic pollutants represented by tetracycline. And the catalyst has good anti-interference ability. In the presence of Cl ‑ , NO3 ‑ , CO3 2‑ and H2PO4 ‑ , or in the actual water sample containing tetracycline, the degradation efficiency of the CuFeO2 / CNTs / PMS system for tetracycline still reaches more than 90%, having potential practical water treatment application value.

Description

Technical Field

[0001] The present invention relates to a carbon nanotube modified CuFeO2 catalyst, a preparation method thereof and an application thereof. The catalyst can be used to activate PMS to generate highly active 1 O2, and can selectively degrade electron-rich organic pollutants represented by tetracycline, so as to realize the selective degradation of tetracycline in water, belonging to the technical fields of composite materials and water treatment. Background Art

[0002] As an important antibiotic widely used in medical health, animal husbandry and aquaculture, the annual consumption of tetracycline is as high as tens of thousands of tons, and it is often detected in the aquatic environment, which may pose a potential threat to the aquatic ecosystem and human physical health. In addition, studies have found that tetracycline can affect the normal growth and development of bones and teeth, easily enter the fetus through the placenta, and can cause fetal malformations, poor tooth bud development and liver and kidney damage in pregnant women. Therefore, it is urgent to effectively remove tetracycline in the water environment.

[0003] At present, a variety of technologies have been developed to remove tetracycline in the water environment. Among them, the advanced oxidation technology based on peroxymonosulfate (PMS) has attracted extensive attention and interest of researchers due to its unique advantages such as low activation energy, diverse reactive oxygen species and strong oxidation-reduction ability. In the Fenton-like system based on peroxymonosulfate, . OH and SO4 .- are usually the dominant reactive oxygen species. Although the catalytic degradation activity of these dominant free radicals is relatively high, in the actual water treatment application, they are easily affected by the background medium (such as inorganic anions and natural organic matter), quenched, and generate free radicals with lower activity, resulting in poor actual application effects. It has been found that the catalytic oxidation system dominated by non-radical 1 O2 has excellent anti-interference ability, and compared with . OH and SO4 .- 1 O2 shows excellent selectivity for electron-rich refractory pollutants due to its own electrophilicity. Therefore, the Fenton-like technology based on 1 O2 has a broader practical application prospect. The key to this technology lies in how to select a catalyst with high catalytic activity. However, some catalysts commonly used to activate PMS currently have problems such as low PMS utilization efficiency and low activation performance. Therefore, how to provide a catalyst with high catalytic activity to improve the utilization efficiency of PMS, so as to realize the efficient activation of PMS to degrade and remove tetracycline in the water environment is a technical problem to be solved urgently. Summary of the Invention

[0004] ​Aiming at the problems existing in the prior art, the purpose of the present invention is to provide a carbon nanotube modified CuFeO2 catalyst, its preparation method and application. This catalyst can efficiently activate PMS to generate highly active 1 O2, so as to selectively degrade electron-rich organic pollutants represented by tetracycline.

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

[0006] Copper-based materials and carbon-based materials are more conducive to the generation of non-radical 1 O2 due to their unique physical and chemical properties. Among them, CuFeO2 has been studied for its high economic benefits, low toxicity and simple synthesis method. However, pure CuFeO2 has bottlenecks such as high surface energy, small specific surface area and easy agglomeration. To solve these problems, combining CuFeO2 with a suitable carrier through strong interaction to form a composite material is one of the most effective strategies. Carbon nanotubes (CNTs) are regarded as a good carbon carrier material due to their rich surface functional groups, large specific surface area and good electrical conductivity. Based on this, the present invention deposits CuFeO2 on the surface of CNTs to form a Fenton-like catalyst CuFeO2 / CNTs, and applies it to catalytically activate PMS to generate highly active 1 O2 to selectively degrade pollutants represented by tetracycline (TC).

[0007] This catalyst deposits CuFeO2 nanoparticles on the surface of carbon nanotubes by a simple one-step low-temperature hydrothermal method to form a composite material CuFeO2 / CNTs. Compared with pure CuFeO2, the introduction of carbon nanotubes (CNTs) effectively alleviates the agglomeration of CuFeO2 nanoparticles and significantly increases its specific surface area. By applying it to the field of water environment restoration, it is found that it can efficiently activate PMS to generate highly active 1 O2 to selectively degrade organic pollutants represented by tetracycline. And this catalyst has good anti-interference ability. In the presence of Cl - 、NO3 - 、CO3 2- and H2PO4 - , or in actual water samples containing tetracycline, the degradation efficiency of the CuFeO2 / CNTs / PMS system for tetracycline still reaches more than 90%, having potential practical water treatment application value.

[0008] A preparation method of a carbon nanotube modified CuFeO2 catalyst includes the following steps:

[0009] (1)Disperse copper salts and iron salts in water, add carbon nanotubes and strong base, and mix evenly to obtain a mixed solution; preferably, the copper salt is copper chloride, copper nitrate or copper sulfate; the iron salt is ferric chloride, ferric nitrate or ferric sulfate; the molar ratio of the copper salt to the iron salt is 1:1.

[0010] (2)Transfer the mixed solution to a hydrothermal reactor. After hydrothermal reaction, cool it to room temperature. The reaction product is washed and dried to obtain a carbon nanotube modified CuFeO2 catalyst. Preferably, the temperature of the hydrothermal reaction is 160 - 200 °C, specifically, it can be 160 °C, 180 °C or 200 °C, etc.; the time of the hydrothermal reaction is 12 - 36 h, specifically, it can be 12 h, 24 h or 36 h, etc. The washing method is to wash alternately with anhydrous ethanol and deionized water several times until the pH of the supernatant is neutral; the drying is freeze-drying, the drying temperature is -40 to -77 °C, and the time is 6 - 12 h.

[0011] In a further embodiment, the carbon nanotube is a carboxylated multi-walled carbon nanotube; the mass fraction of the carbon nanotube in the carbon nanotube modified CuFeO2 catalyst is 20 - 40 wt%, further, it can be 20 wt%, 25 wt%, 30 wt% or 40 wt%, etc. The surface of the carboxylated multi-walled carbon nanotube has abundant oxygen-containing functional groups. This structural feature not only helps to establish a strong interaction with CuFeO2 to achieve the successful construction of the composite material, but also is beneficial to enhancing the adsorption of the prepared composite material CuFeO2 / CNTs on target pollutants. At the same time, it is found that carbon nanotubes can activate persulfate through reduction. Based on this, the present invention utilizes the reducibility of carbon nanotubes themselves to successfully prepare the CuFeO2 composite material without adding additional reducing agents, thereby reducing the preparation cost of the material. Since the cost of commercial carbon nanotubes is very high, in order to control the cost, the dosage of carbon nanotubes in this embodiment is controlled within a relatively low range, and no additional reducing agent is added by using its reduction characteristics, and the target product with good crystallinity and stable size is prepared within a relatively short reaction time.

[0012] The present invention also discloses the use of the above-mentioned carbon nanotube modified CuFeO2 catalyst for activating PMS to degrade tetracycline in water. Further preferably, the pH of the water is 3 - 9, the dosage of the carbon nanotube modified CuFeO2 catalyst is 0.05 - 0.3 g / L, preferably 0.2 g / L; the dosage of PMS is 0.1 - 0.4 g / L, preferably 0.2 g / L; the degradation efficiency of tetracycline is as high as 99%.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0014] (1) In this invention, carboxylated multi-walled carbon nanotubes are selected as the carbon substrate material. The surface of the carbon nanotubes has abundant functional groups (such as -COOH, -OH, etc.). This structural feature not only helps to establish a strong interaction with metal oxides to successfully construct the composite material, but also is conducive to enhancing the adsorption of tetracycline in water by the prepared composite material CuFeO2 / CNTs, thereby significantly improving the degradation efficiency of the target pollutant.

[0015] (2) Compared with pure CuFeO2, the introduction of carbon nanotubes, on the one hand, effectively alleviates the aggregation of CuFeO2 nanoparticles, significantly increases its specific surface area, improves its conductivity, and thus regulates the electron transfer between CuFeO2 nanoparticles to achieve synergistic catalysis; on the other hand, in the field of water treatment, the effective degradation of pollutants is mainly achieved by the synergistic transformation between transition metal ions and the generation of more reactive species. The degradation activity of the material prepared in this invention mainly comes from the redox properties of the metal active sites in the material, and the reducibility of the carbon nanotubes in the material is also conducive to accelerating the reduction of high-valent metals, thus breaking through the bottleneck of the slow oxidation-reduction cycle rate of effective metals in the system.

[0016] (3) During the catalytic degradation of tetracycline in water by the CuFeO2 / CNTs / PMS system, not only strong oxidizing free radicals ( . OH and SO4 .- ) will be generated, but also highly active non-free radicals 1 O2 will be generated. Among them, 1 O2 plays a leading role to achieve the selective degradation of tetracycline in water. The specific reaction process is shown in the following formulas (1)-(8):

[0017] Cu(I) + HSO5 - → Cu(II) + HO – + SO4 ·- (1)

[0018] Cu(II) + HSO5 - → Cu(I) + H + + SO5 ·- (2)

[0019] Fe(III) + Cu(I) → Fe(II) + Cu(II) (3)

[0020] Fe(II) + HSO5 - → Fe(III) + HO – + SO4 ·- (4)

[0021] SO4·- + HO – / H2O → SO4 2- + HO· (5)

[0022] 2SO5 ·- + H2O → 1.5 1 O2 +2HSO4 - (6)

[0023] HSO5 - + *O → HSO4 - + 1 O2 (7)

[0024] SO4 ·- / HO· / 1 O2+ TC→ intermediates → CO2 + H2O (8)

[0025] (4) CuFeO2 / CNTs has good anti-interference ability. In the presence of Cl - , NO3 - , CO3 2- and H2PO4 - or in the actual water sample containing tetracycline, the degradation efficiency of tetracycline by the CuFeO2 / CNTs / PMS system still reaches more than 90%, showing potential practical application value in water treatment. Description of the Drawings

[0026] Figure 1 SEM image of the CuFeO2 / CNTs catalyst prepared in the example;

[0027] Figure 2 XRD comparison chart of the CuFeO2 / CNTs catalyst and CuFeO2 prepared in the example;

[0028] Figure 3 N2 adsorption-desorption curve comparison chart of the CuFeO2 / CNTs catalyst and CuFeO2 prepared in the example;

[0029] Figure 4 FT-IR comparison chart of the CuFeO2 / CNTs catalyst and CNTs prepared in the example;

[0030] Figure 5 Degradation effect diagram of tetracycline in water by different catalytic materials;

[0031] Figure 6 Degradation effect diagram of the CuFeO2 / CNTs catalyst prepared in the example under different pH conditions;

[0032] Figure 7 Degradation effect diagrams of the CuFeO2 / CNTs catalyst prepared in the example in the presence of Cl - , NO3 - , CO3 2- and H2PO4 - ;

[0033] Figure 8 Degradation effect diagrams of the CuFeO2 / CNTs catalyst prepared in the example in the actual water sample containing tetracycline;

[0034] Figure 9 Quenching experiment diagram of tetracycline degradation in this application example;

[0035] Figure 10 EPR diagrams (using DMPO as the capturer) of different catalytic materials activating PMS to degrade TC in the application example;

[0036] Figure 11 EPR diagrams (using TEMP as the capturer) of different catalytic materials activating PMS to degrade TC in the application example; Specific implementation manners

[0037] The following further illustrates the present invention in conjunction with the examples, so that those skilled in the art can better understand the present invention and be able to implement it, but the examples cited do not limit the present invention.

[0038] In addition, in the preparation processes in the following examples, if not otherwise specified, they are all conventional means in the prior art in this field, so they will not be described in detail; the raw materials and reagents used in the following examples are all commercially available products and can be obtained commercially.

[0039] Examples

[0040] Preparation of carbon nanotube modified CuFeO2 catalyst:

[0041] Dissolve 7.5 mmol of Cu(NO3)2 . 3H2O and 7.5 mmol of Fe(NO3)3 . 9H2O in 60 mL of ultrapure water, then successively add 0.5 g of carbon nanotubes and 2.5 g of NaOH, and stir vigorously for 3 h to make them fully mixed. Transfer the mixed solution to a hydrothermal reactor for hydrothermal reaction. The hydrothermal temperature is 180 °C, the reaction time is 24 h, cool to room temperature, centrifuge and wash, and finally dry at -77 °C for 6 h to obtain the carbon nanotube modified CuFeO2 catalyst, denoted as CuFeO2 / CNTs.

[0042] Comparative examples

[0043] Preparation of pure CuFeO2:

[0044] Dissolve 7.5 mmol of Cu(NO3)2 . ·3H2O and 7.5 mmol of Fe(NO3)3 . ·9H2O in 60 mL of ultrapure water, then successively add 2.5 g of NaOH and 2.5 mL of ethylene glycol, and stir vigorously for 3 h to mix them thoroughly. Transfer the mixed solution to a hydrothermal reactor for hydrothermal reaction. The hydrothermal temperature is 180 °C, the reaction time is 24 h, cool to room temperature, centrifuge and wash, and finally dry at -77 °C for 6 h to obtain pure CuFeO2.

[0045] Performance characterization

[0046] Figures 1 to 4 They are the SEM, XRD, N2 adsorption-desorption isotherm curves, and FT-IR images of the CuFeO2 / CNTs catalyst prepared in the examples, respectively. The SEM image shows that CuFeO2 is mainly deposited on the surface of carbon nanotubes and there is no obvious agglomeration, indicating that compared with pure CuFeO2, the introduction of carbon nanotubes can effectively alleviate the agglomeration of CuFeO2 and expose more active sites. As can be seen from Figure 2 , the XRD pattern of pure CuFeO2 is consistent with the literature report, and the XRD pattern of CuFeO2 / CNTs corresponds to the main peaks of pure CuFeO2 one by one, indicating that the CuFeO2 / CNTs catalyst was successfully prepared without adding any reducing agent. At the same time, the six impurity peaks of CuFeO2 / CNTs at 2θ = 24.14°, 33.15°, 49.48°, 54.09°, 62.45°, and 63.99° correspond to the (012), (104), (024), (116), (214), and (300) crystal planes of Fe2O3, respectively; in addition, the four impurity peaks of CuFeO2 / CNTs at 2θ = 38.96°, 48.72°, 66.25°, and 68.09° correspond to the (200), (-202), (-311), and (-220) crystal planes of CuO, respectively, indicating that there are a small amount of Fe2O3 and CuO by-products in the catalyst prepared in the examples. From the BET specific surface area test and analysis results, the specific surface area of pure CuFeO2 is 11.60 m 2 / g, while the specific surface area of CuFeO2 / CNTs is 46.03 m 2 / g, indicating that the introduction of carbon nanotubes can significantly increase its surface area, thereby effectively improving the catalytic degradation performance of the material. FT-IR was used to further analyze the surface functional groups of CuFeO2 / CNTs and CNTs. As can be seen from Figure 5 , the main absorption bands at 3450 cm -1 and 1610 cm -1Stretching vibration peaks attributed to -OH and C=O, respectively. In addition, compared with CNTs, two new stretching vibration peaks appear at 560 cm -1 and 650 cm -1 for CuFeO2 / CNTs, corresponding to the stretching vibrations of Fe-O and Cu-O bonds, respectively.

[0047] Application Example

[0048] Using the CuFeO2 / CNTs prepared in the examples as the catalyst and PMS as the oxidant, the degradation behavior of CuFeO2 / CNTs catalyst-activated PMS on organic pollutants represented by tetracycline was studied.

[0049] The experimental method was as follows: 20 mg of the CuFeO2 / CNTs catalyst prepared in the examples was added to 100 mL of a tetracycline solution with a concentration of 20 ppm, and ultrasonic treatment was carried out for 5 min. Subsequently, the conical flask containing the suspension was placed in a constant-temperature shaker, the temperature of the shaker was set at 25 °C, then 20 mg of PMS was added to initiate the reaction and timing was started. Samples were taken at 0 min, 2 min, 5 min, 10 min, 20 min, and 30 min during the reaction. After each sampling, filtration was immediately carried out using a 0.22 μm needle filter, and the concentration of tetracycline in the sample was analyzed using a UV-visible spectrophotometer.

[0050] In addition, taking only adding 20 mg of the CuFeO2 / CNTs prepared in the examples, 20 mg of the pure CuFeO2 prepared in the comparative example, 20 mg of CNTs, 20 mg of PMS, 20 mg of CNTs + 20 mg of PMS, and 20 mg of CuFeO2 + 20 mg of PMS as a comparison, the results are as Figure 5 shown.

[0051] Result Analysis

[0052] It can be seen from Figure 5 that the CuFeO2 / CNTs material has certain adsorption properties, and the removal rate of TC is about 58.8% in 30 min; in addition, compared with the pure CuFeO2 and CNTs materials, the prepared CuFeO2 / CNTs catalyst has stronger ability to catalytically activate PMS; when CuFeO2 / CNTs and PMS are added simultaneously, the degradation efficiency of tetracycline reaches 99.7% within 30 min.

[0053] Figure 6 This is the degradation effect diagram of tetracycline by the CuFeO2 / CNTs prepared in the examples of the present invention under different pH conditions. It can be found that in the CuFeO2 / CNTs / PMS system, the solution pH has little effect on the degradation of tetracycline, and the degradation effect is the best when the solution pH is slightly neutral.

[0054] Figure 7 Degradation effect diagram of the CuFeO2 / CNTs catalyst prepared in the embodiment of the present invention in the presence of Cl - 、NO3 - 、CO3 2- and H2PO4 - . It can be seen from the figure that Cl - and NO3 - have little effect on the degradation of tetracycline, while CO3 2- and H2PO4 - have a slight inhibitory effect on the removal of tetracycline, but the removal rate of tetracycline can still reach more than 95% within 30 min, indicating that the CuFeO2 / CNTs / PMS system has good anti-ion interference ability.

[0055] Figure 8 Degradation effect diagram of the CuFeO2 / CNTs catalyst prepared in the embodiment of the present invention in the actual water sample containing tetracycline. The results show that in ultrapure water (Control), tap water (Tap water) and natural water (Lake water), the degradation rates of the CuFeO2 / CNTs / PMS system for tetracycline are 99.7%, 96.7% and 91.8% respectively within 30 min. Therefore, the CuFeO2 / CNTs / PMS system has good application prospects in the actual water environment.

[0056] Figure 9 Quenching experiment diagram of tetracycline degradation in Application Example 1 of the present invention. It can be seen from the figure that when 1 M TBA and 1 M EtOH are added, the degradation of tetracycline is slightly inhibited, and the efficiency drops to 91.4% and 84.8% respectively. When 1 M FFA is added, the degradation efficiency of tetracycline drops to 28.4% under the same conditions, indicating that in the catalytic degradation process of tetracycline, . OH, SO4 .- and 1 O2 all participate in the reaction, but 1 O2 plays a leading role.

[0057] Figure 10 and Figure 11 are the EPR diagrams of different catalytic materials activating PMS to degrade TC in Application Example 1. It can be seen that in the CuFeO2 / CNTs / PMS system, the characteristic EPR signals of DMPO-HO . , DMPO-SO4 .- and TEMP- 1 O2 are clearly observed, which further proves that in the catalytic degradation process of tetracycline, . OH, SO 4.- and 1 O2. In addition, compared with the CuFeO2 / PMS and CNTs / PMS systems, in the CuFeO2 / CNTs / PMS system, DMPO-HO . , DMPO-SO 4. - and TEMP- 1 O2 have stronger signals, indicating that the CuFeO2 / CNTs catalyst has a stronger ability to catalytically activate PMS.

[0058] Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

Claims

1. A preparation method of a carbon nanotube modified CuFeO2 catalyst, characterized in that: It includes the following steps: (1) Disperse copper salt and iron salt in water, add carboxylated multi-walled carbon nanotubes and strong base, and mix evenly to obtain a mixed solution; the carbon nanotubes are carboxylated multi-walled carbon nanotubes; the mass fraction of carbon nanotubes in the carbon nanotube-modified CuFeO2 catalyst is 20-40 wt%; (2) Transfer the mixed solution to a hydrothermal reactor. After hydrothermal reaction, cool it to room temperature. Wash and dry the reaction product to obtain a carbon nanotube-modified CuFeO2 catalyst; the drying is freeze-drying, the drying temperature is -40 ~ -77 °C, and the time is 6-12 h.

2. The preparation method of the carbon nanotube modified CuFeO2 catalyst according to claim 1, characterized in that: The copper salt is copper chloride, copper nitrate or copper sulfate; the iron salt is ferric chloride, ferric nitrate or ferric sulfate; the molar ratio of the copper salt to the iron salt is 1:

1.

3. The preparation method of the carbon nanotube modified CuFeO2 catalyst according to claim 1, wherein: The temperature of the hydrothermal reaction is 160-200 °C, and the time is 12-36 h.

4. The preparation method of the carbon nanotube modified CuFeO2 catalyst according to claim 1, characterized in that: The washing method is to wash alternately with absolute ethanol and deionized water several times until the pH of the supernatant is neutral.

5. A carbon nanotube modified CuFeO2 catalyst, characterized in that: It is prepared by the preparation method described in any one of claims 1 to 4.

6. The carbon nanotube-modified CuFeO2 catalyst according to claim 5 is used to activate PMS to degrade tetracycline in water.

7. The carbon nanotube-modified CuFeO2 catalyst according to claim 6 is used for activating PMS to degrade tetracycline in water, characterized in that: The dosage of the carbon nanotube-modified CuFeO2 catalyst is 0.05~0.3 g / L, and the dosage of PMS is 0.1~0.4 g / L.

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