Composite catalyst in Fe3O4 nanoparticle confinement carbon nanotube and application of composite catalyst in degradation of bisphenol pollutants in water

Abstract

The invention discloses a composite catalyst in a Fe3O4 nanoparticle confined carbon nanotube and application of the composite catalyst in degradation of bisphenol pollutants in water, and belongs to the technical field of environmental protection and water treatment. According to the catalyst, Fe3O4 nano-particles with the particle size of 1-5 nm are confined in inner channels of multi-walled carbon nanotubes (CNTs), stable Fe-C bonds are formed between Fe atoms and carbon atoms on the inner walls of the CNTs, a nano confinement structure is constructed, and the stability and electron transfer efficiency of the catalyst are improved. When the catalyst is used for activating peracetic acid (PAA), bisphenol pollutants in water can be quickly and efficiently removed. The catalyst can keep high-efficiency degradation performance in a wide range of pH value of 4-12, the degradation efficiency is still kept at 95% or above after the catalyst is recycled for 10 times, and the catalyst shows remarkable stability and practicability. The invention provides a novel catalyst which is excellent in performance, economical and environment-friendly and a process method for the field of actual water treatment.

Description

Technical Field

[0001] This invention belongs to the field of environmental protection and water treatment technology, specifically relating to a composite catalyst confined within carbon nanotubes by Fe3O4 nanoparticles and its application in the degradation of bisphenol pollutants in water. Background Technology

[0002] Bisphenol A (BPA) is a widely used organic compound found in products such as polycarbonate plastics, epoxy resins, and thermal paper. Due to its significant endocrine-disrupting activity, BPA can mimic or inhibit the function of hormones in the body, posing a potential threat to ecosystems and human health. With the increasing severity of BPA pollution, developing efficient technologies for removing BPA from water bodies has become a key issue in environmental remediation.

[0003] Advanced oxidation processes (AOPs) are widely used for the removal of recalcitrant organic pollutants due to their ability to generate various highly active oxidants, such as hydroxyl radicals (·OH), singlet oxygen (1O2), and high-valence metal oxides (e.g., Fe(IV)). However, traditional AOP catalytic systems generally suffer from low catalytic efficiency, short lifetime of active species, catalyst loss and deactivation, and are easily affected by coexisting ions and natural organic matter in complex water bodies. In recent years, the nanoconfinement strategy has been developed by encapsulating metal or metal oxide nanoparticles within the channels of multi-walled carbon nanotubes (CNTs). Utilizing the high conductivity and spatial confinement effect of CNTs, nanoparticle aggregation and metal leaching are effectively suppressed, while electron transfer and the generation of non-radical active species (such as 1O2 and high-valence metal oxides) are accelerated, thereby significantly improving catalytic activity and durability. Therefore, developing a novel catalyst system that combines the confinement effect of carbon nanotubes with high efficiency, stability and interference resistance is of great practical significance for achieving rapid removal of BPA and other persistent bisphenol pollutants in the real environment. Summary of the Invention

[0004] The present invention aims to provide a highly efficient, stable and environmentally friendly catalyst, its preparation method and application, in order to solve the problems of low catalytic efficiency and insufficient catalyst stability in the prior art.

[0005] The first objective of this invention is to provide a Fe3O4 nanoparticle-confined carbon nanotube composite catalyst. Through a nanoconfining strategy, Fe3O4 nanoparticles are encapsulated within multi-walled carbon nanotubes (CNTs), forming Fe-C bonds within the catalyst and significantly enhancing electron transfer efficiency. The second objective of this invention is to provide a method for preparing the Fe3O4 nanoparticle-confined carbon nanotube composite catalyst. The third objective of this invention is to provide the application of the Fe3O4 nanoparticle-confined carbon nanotube composite catalyst in the degradation of bisphenol A (BPA) pollutants in water. The provided confined Fe3O4-in-CNTs composite catalyst is used to activate peracetic acid (PAA) for efficient removal of BPA from water, significantly improving the activation efficiency of PAA.

[0006] Therefore, the technical solution adopted in this invention is: a Fe3O4 nanoparticle-confined carbon nanotube composite catalyst, comprising Fe3O4 nanoparticles and multi-walled carbon nanotubes (CNTs); wherein, the Fe3O4 nanoparticles are confined within the channels of the multi-walled carbon nanotubes (CNTs), and the Fe atoms on the surface of the Fe3O4 nanoparticles are connected to the carbon atoms on the inner wall of the carbon nanotubes (CNTs) through Fe-C covalent bonds, thereby forming a confined Fe3O4-in-CNTs composite catalyst.

[0007] Furthermore, by mass ratio, Fe3O4 nanoparticles : multi-walled carbon nanotubes (CNTs) = (0.1-10) : 1.

[0008] Furthermore, the Fe3O4 nanoparticles have a particle size distribution of 1nm-5nm and are uniformly distributed within the carbon nanotubes without particle agglomeration.

[0009] Furthermore, the inner diameter of the multi-walled carbon nanotubes (CNTs) is in the range of 10nm-15nm, and the length is 0.5μm-10μm.

[0010] A method for preparing a Fe3O4 nanoparticle-confined carbon nanotube composite catalyst includes the following steps: acid treatment of multi-walled carbon nanotubes (CNTs); ultrasonic dispersion of Fe3O4 nanoparticles with a particle size of 1nm-5nm in an ethanol solution to obtain a Fe3O4 suspension; placing the acid-treated multi-walled carbon nanotubes (CNTs) in the Fe3O4 suspension, ultrasonically mixing for 1h-2h, and then magnetically stirring at room temperature for 48h-120h; washing and drying the obtained product, and then heat-treating it at 500℃-600℃ under an inert atmosphere for 4h-5h to obtain a confined Fe3O4-in-CNTs composite catalyst.

[0011] Furthermore, the acid treatment of multi-walled carbon nanotubes (CNTs) specifically involves mixing multi-walled carbon nanotubes (CNTs) with nitric acid at a mass percentage concentration of 30%-50%, reacting hydrothermally at 120℃-160℃ for 6-12 hours, cooling, filtering, and washing to obtain acid-treated multi-walled carbon nanotubes (CNTs).

[0012] This invention provides the application of a composite catalyst confined within Fe3O4 nanoparticles and carbon nanotubes in the catalytic activation of peracetic acid (PAA) for the degradation of bisphenol pollutants in water.

[0013] Furthermore, the bisphenol contaminants include one or more of bisphenol A (BPA), bisphenol S (BPS), bisphenol C (BPC), and tetrafluorobisphenol A (BPAF).

[0014] Furthermore, the method includes the following steps: adjusting the initial pH value of the water containing bisphenol pollutants, adding Fe3O4 nanoparticles confined within carbon nanotubes as a composite catalyst and peracetic acid (PAA) to the water, and carrying out a catalytic reaction for 10-30 minutes.

[0015] Furthermore, the initial concentration of bisphenol-containing pollutants in the water was adjusted to 5 mg / L-20 mg / L; the pH value was adjusted to 4-12; the amount of composite catalyst confined within carbon nanotubes by Fe3O4 nanoparticles was 0.05 g / L-0.5 g / L; and the concentration of peracetic acid (PAA) was 1 μM-5 μM.

[0016] The beneficial effects of this invention are:

[0017] 1. This invention involves mixing multi-walled carbon nanotubes with nitric acid for acid treatment, which fully opens the carbon nanotube ports and removes impurities. Then, Fe3O4 nanoparticles are confined within the channels of multi-walled carbon nanotubes (CNTs) through capillary action, forming Fe-C bonds inside the catalyst. This significantly enhances the electron transfer efficiency in the catalyst and significantly improves the activation efficiency of PAA, thereby enhancing the generation and stability of non-radical active species (such as high-valence iron species Fe(IV) and singlet oxygen 1O2), achieving more efficient degradation of BPA.

[0018] 2. This invention effectively suppresses the aggregation of Fe3O4 nanoparticles and the dissolution of iron ions through the confined structure of carbon nanotubes, thereby significantly improving the dispersibility, stability and recyclability of the catalyst.

[0019] 3. The catalyst system of this invention can maintain a removal efficiency of over 95% after more than 10 consecutive cycles and can operate stably in a wide pH range of 4-12, exhibiting excellent cycle life and pH adaptability. It is suitable for long-term water treatment applications and has significant environmental and economic advantages. Attached Figure Description

[0020] Figure 1 XRD characterization of Fe3O4-in-CNTs composite catalyst.

[0021] Figure 2 TEM characterization of the Fe3O4-in-CNTs composite catalyst.

[0022] Figure 3 Kinetic curves of BPA degradation (pH=8) by Fe3O4-in-CNTs composite catalyst.

[0023] Figure 4 A comparison of BPA degradation by Fe3O4-in-CNTs prepared with different Fe3O4 to CNTs mass ratios. Detailed Implementation

[0024] Example 1: A Fe3O4 nanoparticle-confined carbon nanotube composite catalyst (Fe3O4-in-CNTs) (I) Preparation method

[0025] 1. Purchased multi-walled carbon nanotubes (CNTs) (inner diameter 10nm-15nm, length 2μm-8μm) were mixed with a 40wt% nitric acid solution at a ratio of 1:50 (g / mL). The mixture was placed in a stainless steel high-pressure reactor lined with polytetrafluoroethylene and treated at 150℃ for 8 hours to open the ends of the carbon nanotubes, remove impurities, and improve surface hydrophilicity. Subsequently, the mixture was rinsed repeatedly with deionized water until the pH of the washing solution was neutral. After centrifugation, the mixture was dried under vacuum at 60℃ for 48 hours for later use.

[0026] 2. According to the mass ratio of Fe3O4 nanoparticles to multi-walled carbon nanotubes (CNTs) = 10:1, an appropriate amount of Fe3O4 nanoparticles with a particle size of 1nm-5nm are dispersed in an appropriate amount of anhydrous ethanol, and a uniform Fe3O4 nanoparticle ethanol suspension is formed by ultrasonic vibration for 30 minutes.

[0027] 3. Add an appropriate amount of the acid-treated CNTs from step 1 to the Fe3O4 nanoparticle ethanol suspension from step 2. First, perform ultrasonic treatment for 60 minutes to ensure that the carbon nanotubes and Fe3O4 particles are in full contact. Then, continue the magnetic stirring reaction at room temperature for 96 hours to allow the Fe3O4 nanoparticles to effectively enter the inner pores of the CNTs through capillary action and form a nano-confined structure.

[0028] 4. After the mixing reaction is complete, the product is centrifuged and repeatedly washed with deionized water and anhydrous ethanol to thoroughly remove any Fe3O4 nanoparticles that did not enter the tube, ensuring that there are no obvious adhering substances on the outer surface. Subsequently, it is vacuum dried at 60℃ for 24 hours.

[0029] 5. Place the dried mixture in a tube furnace and heat it to 550°C at a rate of 10°C / min under nitrogen protection. After heat treatment for 4 hours, allow it to cool naturally to obtain the final Fe3O4-in-CNTs composite catalyst.

[0030] (II) Characterization

[0031] Figure 1 The X-ray diffraction pattern of the Fe3O4-in-CNTs composite catalyst of this invention is shown. The catalyst exhibits significant characteristic diffraction peaks, with the prominent peaks at 2θ of 36°, 43°, and 63° corresponding to the characteristic peaks of the (311), (400), and (440) crystal planes of Fe3O4 crystals (standard PDF card number: 26-1136), indicating the intact crystal structure of the Fe3O4 nanoparticles. Furthermore, at approximately 2θ of 26°, a typical (002) crystal plane diffraction peak of carbon nanotubes is observed, indicating that the structure of CNTs in the catalyst remains stable without significant damage. Overall, the diffraction peaks are sharp and clear, indicating high crystallinity of the catalyst and successful and stable loading of Fe3O4 nanoparticles within the carbon nanotubes.

[0032] Figure 2 This is a TEM image of the Fe3O4-in-CNTs composite catalyst of the present invention. Figure 2 As can be clearly observed in (a), a large number of uniformly sized Fe3O4 nanoparticles are evenly distributed inside the CNTs cavity, with no obvious particle aggregation, indicating that the confinement of Fe3O4 particles was successfully achieved by the preparation method of this invention. Further from... Figure 2 The high-resolution transmission electron microscopy (HRTEM) image in (b) clearly shows the lattice fringes of the Fe3O4 particles, with a lattice spacing of approximately 0.20 nm, corresponding to the (400) crystal plane of Fe3O4, further confirming the complete crystal structure of Fe3O4. Furthermore, the carbon nanotube walls are uniformly thick, and the Fe3O4 nanoparticles are firmly fixed within the tubes, exhibiting good stability. This unique confined structure ensures that the catalyst exhibits excellent catalytic performance and stability during use.

[0033] Example 2 Application of Fe3O4-in-CNTs (I) Degradation of BPA by Fe3O4-in-CNTs Catalyst

[0034] Take 250 mL each of BPA solutions with pH = 8 and 10 mg / L, and BPA solutions with pH = 10 and 10 mg / L, and stir magnetically for 30 min to reach adsorption-desorption equilibrium. Add 0.20 g / L of the catalyst Fe3O4-in-CNTs prepared in Example 1, with a PAA concentration of 1 μM. Stir at a constant temperature (25 °C) for 15 min, filter through a 0.45 μm filter membrane, and determine the residual BPA concentration. Measure the peak area of ​​BPA using high performance liquid chromatography (HPLC), according to ln(C0 / C...). t )=k obs The apparent first-order rate constant k is obtained by linear fitting of t. obs The BPA concentration was calculated using the corresponding standard curve, and the degradation rate was calculated using the following formula:

[0035] Degradation rate = (C0 - C) t ) / C0×100%

[0036] Where C0 is the initial concentration, C t The concentrations are the concentrations after different reaction times.

[0037] like Figure 3 As shown, the degradation kinetics of PAA coupled with the Fe3O4-in-CNTs catalyst of this invention conforms to a pseudo-first-order model, and the apparent rate constant k for BPA (pH=8) is... obs =0.67min -1 After 15 minutes of reaction, the degradation rate of BPA reached 100%.

[0038] (II) Performance of Fe3O4-in-CNTs catalyst in activating peracetic acid degradation of bisphenol A under different pH conditions

[0039] To verify the applicability of the Fe3O4-in-CNTs catalyst of this invention under different pH conditions, a comparative experiment was conducted as follows: 250 mL of a 10 mg / L BPA solution was taken, and the initial pH was adjusted to 4, 6, 8, 10, and 12 with 0.1 mol / L NaOH or HCl, respectively. 0.20 g / L of the Fe3O4-in-CNTs catalyst prepared in Example 1 was added to each solution, along with 1 μM of peracetic acid (PAA). The mixture was magnetically stirred at 25 °C for 15 min. The peak area of ​​BPA was determined by high-performance liquid chromatography (HPLC), and the BPA concentration was calculated using the corresponding standard curve to determine the degradation rate. The results are shown in Table 1.

[0040] Table 1

[0041] pH 4 6 8 10 12 Degradation rate / % 84.3％ 91.2％ 100％ 99.1％ 100％

[0042] The results showed that as the solution pH increased from 4 to 12, the reaction rate and 15-minute removal rate of the catalytic system of this invention increased simultaneously. Under alkaline conditions with a pH of 8-12, BPA could be almost completely removed within 15 minutes. Even in an acidic environment with a pH of 4, the removal rate remained at approximately 84% within 15 minutes, demonstrating the catalyst's good adaptability to different acid and alkaline conditions. Therefore, the catalyst of this invention can operate stably and efficiently within a pH range of 4-12, with a preferred operating pH of 8-11 to balance treatment efficiency and subsequent wastewater requirements.

[0043] (III) Degradation of Bisphenol (BP) Series Organic Pollutants by Fe3O4-in-CNT Catalyst

[0044] To verify the versatility of the Fe3O4-in-CNTs catalyst of this invention for bisphenol (BP) series organic pollutants, water samples containing bisphenol S (BPS), bisphenol C (BPC), and tetrafluorobisphenol A (BPAF) were treated according to the operating conditions in (I) (initial pollutant concentration 10 mg / L, pH = 8, Fe3O4-in-CNTs catalyst dosage prepared in Example 1 0.20 g / L, peracetic acid 1 μM, stirring at 25℃ for 15 min). The results are shown in Table 2.

[0045] Table 2

[0046] BP BPA BPS BPC BPAF Degradation rate / % 100％ 98％ 96％ 92％

[0047] The results show that the Fe3O4-in-CNTs catalytic system of this invention exhibits rapid and efficient degradation capabilities not only for BPA, but also for BP series pollutants with similar structures.

[0048] Therefore, by utilizing the confined structure and interfacial electronic effect of the present invention, the Fe3O4-in-CNTs catalyst can be applied to the removal of multiple BP pollutants under a single process condition, further expanding the application range of the catalyst in actual industrial and municipal wastewater treatment.

[0049] (iv) Performance of Fe3O4-in-CNTs catalysts prepared with different Fe3O4 to CNTs ratios in activating peracetic acid degradation of bisphenol A

[0050] Preparation of Fe3O4-in-CNTs: The method is the same as in Example 1. The only difference is that in step 2, Fe3O4 nanoparticles and multi-walled carbon nanotubes (CNTs) are taken in different mass ratios of 0.1:1, 0.5:1, 1:1, 5:1 and 10:1 to prepare Fe3O4-in-CNTs catalysts with different Fe3O4 to CNTs ratios.

[0051] Under constant temperature of 25℃ and initial pH of 8, a 10 mg / L BPA solution was used as the target system, with 1 μM peracetic acid (PAA) added. The total dosage of Fe3O4-in-CNTs catalyst with different Fe3O4 to CNTs ratios was kept constant at 0.20 g / L. The reaction was carried out with magnetic stirring (500 rpm), and samples were taken from 0 min to 15 min. After filtration through a 0.45 μm filter membrane, the residual BPA concentration was determined, and the peak area of ​​BPA was determined by high performance liquid chromatography (HPLC). The concentration was calculated as ln(C0 / C10). t )=k obs The apparent first-order rate constant k is obtained by linear fitting of t. obs The removal rate was calculated over 15 minutes. Representative results are listed below. Figure 4 .

[0052] Depend on Figure 4 It can be seen that as the Fe3O4 content increases, the K content of the system increases. obs The removal rate exhibited a non-linear change with a "first decrease, then increase" trend over 15 minutes, with the highest rate and removal rate observed when the Fe3O4 to CNTs ratio was 10:1. Therefore, this invention preferably uses a Fe3O4 to CNTs mass ratio of 10:1.

[0053] (v) Catalyst reusability

[0054] Under constant temperature conditions of 25℃, using a 10 mg / L BPA solution as the target system and pH=8, 0.20 g / L of the Fe3O4-in-CNTs catalyst of this invention was added, followed by the addition of 1 μM peracetic acid (PAA) for a 15 min reaction. After the reaction, the catalyst was separated through a 0.45 μm filter membrane, washed sequentially with 10 mM NaOH and deionized water, and then vacuum dried at 60℃ for 2 h. This cycle was repeated 10 times. The results showed that the BPA removal rates in the 1st, 5th, and 10th cycles were 99.2%, 97.6%, and 95.4%, respectively, with an efficiency decay of less than 4%. After the cycle, the catalyst was analyzed by ICP-OES, and the cumulative Fe leaching amount was <0.05 mg / L, far below the Class III surface water quality standard of 0.3 mg / L.

Claims

1. A Fe3O4 nanoparticle confined carbon nanotube inner composite catalyst, characterized in that, The composite catalyst comprises Fe3O4 nanoparticles and multi-walled carbon nanotubes CNTs; wherein the Fe3O4 nanoparticles are confined in the internal channel of the multi-walled carbon nanotubes CNTs, and the Fe atoms on the surface of the Fe3O4 nanoparticles and the carbon atoms on the inner wall of the carbon nanotubes CNTs are connected to each other through Fe-C covalent bonds, thereby forming the Fe3O4-in-CNTs composite catalyst with a confined structure.

2. The Fe304 nanoparticle confined carbon nanotube inner composite catalyst according to claim 1, characterized in that, The mass ratio of the Fe3O4 nanoparticles to the multi-walled carbon nanotubes CNTs is (0.1-10):

1.

3. The Fe304 nanoparticle confined carbon nanotube inner composite catalyst according to claim 1 or 2, characterized in that, The Fe3O4 nanoparticles have a particle size distribution of 1-5 nm and are uniformly distributed in the internal space of the carbon nanotubes without particle agglomeration.

4. The Fe304 nanoparticle confined carbon nanotube inner composite catalyst according to claim 1 or 2, characterized in that, The multi-walled carbon nanotubes CNTs have an inner diameter of 10-15 nm and a length of 0.5-10 μm.

5. A method for preparing a Fe3O4 nanoparticle confined carbon nanotube inner composite catalyst according to any one of claims 1-4, characterized in that, The method comprises the following steps: acid treatment of the multi-walled carbon nanotubes CNTs; ultrasonic dispersion of Fe3O4 nanoparticles with a particle size of 1-5 nm in an ethanol solution to obtain a Fe3O4 suspension; placing the acid-treated multi-walled carbon nanotubes CNTs in the Fe3O4 suspension, ultrasonic mixing for 1-2 h, and then magnetic stirring at room temperature for 48-120 h; washing and drying the obtained product, and then heat treatment under an inert atmosphere at 500-600 ℃ for 4-5 h to obtain the Fe3O4-in-CNTs composite catalyst with a confined structure.

6. The preparation method of the Fe3O4 nanoparticles confined carbon nanotube inner composite catalyst according to claim 5, characterized in that, The acid treatment of the multi-walled carbon nanotubes CNTs is specifically as follows: mixing the multi-walled carbon nanotubes CNTs with nitric acid with a mass percentage concentration of 30-50%, hydrothermal reaction at 120-160 ℃ for 6-12 h, filtration after cooling, and washing to obtain the acid-treated multi-walled carbon nanotubes CNTs.

7. Use of the Fe3O4 nanoparticle confined carbon nanotube-in composite catalyst according to any one of claims 1-4 in catalytic activation of peracetic acid PAA for degradation of bisphenol pollutants in water.

8. Use according to claim 7, characterized in that, The bisphenol pollutants include one or more of bisphenol A, bisphenol S, bisphenol C, and tetrafluorobisphenol A.

9. Use according to claim 8, characterized in that, The method comprises the following steps: adjusting the initial pH value of water containing bisphenol pollutants, adding the Fe3O4 nanoparticle confined carbon nanotube-in composite catalyst and peracetic acid PAA to the water, and performing a catalytic reaction for 10-30 min.

10. Use according to claim 9, characterized in that, The initial concentration of the water containing bisphenol pollutants is adjusted to 5-20 mg / L; the pH value is adjusted to 4-12; the addition amount of the Fe3O4 nanoparticle confined carbon nanotube-in composite catalyst is 0.05-0.5 g / L; and the addition concentration of the peracetic acid PAA is 1-5 μM.

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