A nanometer carbon tube self-assembled catalyst and its application

Abstract

The application discloses a kind of nanometer carbon tube self-assembly catalyst and its application.The application uses dicyandiamide as precursor, after dissolving with water, mix uniformly with nanometer carbon tube, dry, grind the mixture obtained after, under the atmosphere of inert gas protection, high-temperature annealing polymerization, with different content dicyandiamide Construct different scale g-C3N4 support can be assembled to nanometer carbon tube in different degrees, the target catalyst is prepared, and the obtained catalyst is used to activate persulfate to remove organic pollutants in water.Compared with the widely reported metal-based catalyst, the repair process in the application, the catalyst preparation cost is low, the reaction is efficient, and there is no secondary pollution.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to a self-assembled carbon nanotube catalyst and its application in activating persulfate treatment drugs in water. Background Technology

[0002] Advanced oxidation technologies (AORs) utilize the combination of electricity, light radiation, catalysts, and oxidants to generate highly reactive free radicals in the reaction. These free radicals then oxidize and degrade large organic molecules in water into smaller molecules, or even directly mineralize them into carbon dioxide and water, through addition, substitution, electron transfer, and bond breaking. Persulfate activation is one such AOR technology, releasing strong oxidizing species and finding wide application in the chemical treatment of environmental water bodies. This process releases highly oxidizing free radicals, such as sulfate radicals (SO42-). ·- 2.5-3.1 V NHE ), hydroxyl radicals ( · OH, 1.8-2.7 V NHE Even superoxide anion radicals (O2) ·- -0.28 V NHE In the process of treating chemicals in water, these highly oxidizing free radicals exhibit excellent degradation and mineralization capabilities for organic pollutants, especially in laboratory-scale experiments. However, in practical water remediation applications, varying water quality conditions and complex compositions, such as the presence of different natural organic matter and inorganic anions, increase the difficulty of degradation. Therefore, it is essential to induce the release of highly efficient active species for the targeted and selective degradation of organic pollutants, avoiding interference from complex components in the water.

[0003] The above-mentioned active species with highly efficient and selective degradation of organic pollutants include non-radical singlet oxygen (…). 1 O2, 2.2 V NHE The process involves electron transfer and oxidation of high-valence metals, which can selectively degrade target organic matter. The key step in inducing persulfate activation to generate active species, according to the needs of water treatment drugs, lies in the rational design of the catalyst. In water remediation, metal-based catalysts are prone to deactivation and dissolution of metal catalytic sites when activating persulfate, leading to increased catalyst preparation costs and secondary pollution. Therefore, non-metallic catalysts show broad application prospects, overcoming the shortcomings of metal-based catalysts and possessing unique advantages such as low cost, tunable electronic structure, and effective catalysis in acidic or alkaline media. However, to date, there are few reports on using carbon nanotube self-assembly methods to prepare catalysts for activating persulfate to remove water-borne drugs. Summary of the Invention

[0004] The purpose of this invention is to provide a self-assembled carbon nanotube catalyst and its application in activating persulfate-treated water treatment drugs.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A self-assembled carbon nanotube catalyst is obtained by adding carbon nanotubes to an aqueous solution of dicyandiamide, mixing, drying, grinding, and then annealing and polymerizing the resulting mixture at high temperature under an inert gas atmosphere.

[0007] Add 0.5g of carbon nanotubes to 35 mL of an aqueous solution containing 0.1-2.0g of dicyandiamide;

[0008] The conditions for the high-temperature annealing polymerization are 550~900 ℃ for 1~3 hours.

[0009] Furthermore, the carbon nanotubes are pretreated before being added to an aqueous solution of dicyandiamide. The pretreatment process involves adding 0.5 g of commercially available carbon nanotubes to a mixed solution of 6 M concentrated nitric acid and concentrated sulfuric acid at 80°C and refluxing for 12 hours. The carbon nanotubes are then washed with deionized water until the washing solution is neutral, and the resulting carbon nanotubes are dried for later use.

[0010] Furthermore, the conditions for the high-temperature annealing polymerization are 550°C for 2 hours.

[0011] The above-mentioned carbon nanotube self-assembled catalyst is used in the removal of organic pollutants from water by activating persulfate.

[0012] In one embodiment of the present invention, the persulfate is potassium persulfate.

[0013] In one embodiment of the present invention, the organic pollutant is 2,4-dichlorophenol, sulfamethoxazole, or tetracycline hydrochloride.

[0014] This invention uses dicyandiamide as a precursor, which is dissolved in water at 80 °C and then uniformly mixed with carbon nanotubes. After drying and grinding, the resulting mixture is annealed and polymerized at 550 °C for 2 hours under an inert gas atmosphere. Different amounts of dicyandiamide are used to construct g-C3N4 scaffolds of varying sizes, allowing for different degrees of assembly of carbon nanotubes, thus obtaining the target catalyst. The resulting catalyst is used to activate persulfate to remove organic pollutants from water. The relatively small amount of oxidant used avoids excessive oxidation of the material during use, facilitating material reuse and reducing reaction costs.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] (1) A one-step pyrolysis method is used to prepare a self-assembled catalyst for carbon nanotubes. The preparation process is green, environmentally friendly, simple and fast. All precursors are converted into valuable catalysts without generating metal residues or other wastes.

[0017] (2) This paper reports for the first time a method for the nanoscale assembly of carbon nanotubes and its application in the remediation of organic pollutants in water bodies using activated persulfate. Compared with widely reported metal-based catalysts, the remediation process in this invention has low catalyst preparation cost, high reaction efficiency, and no secondary pollution. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the self-assembly process of carbon nanotubes in Example 1 and its corresponding transmission electron microscope morphology image.

[0019] Figure 2 The X-ray diffraction patterns of carbon nanotubes with different assembly degrees in Example 1 are shown, along with their X-ray photoelectron spectra and the corresponding mass percentages of carbon, nitrogen, and oxygen at different assembly degrees.

[0020] Figure 3 The graph shows the effect of the carbon nanotube self-assembled catalyst prepared in Example 1 activating different concentrations of PMS to remove 2,4-dichlorophenol and other pollutants from water.

[0021] Figure 4 The graph shows the effect of carbon nanotube catalysts with different assembly degrees prepared in Example 1 on the activation of PMS to remove 2,4-dichlorophenol from water, and their corresponding pseudo-first-order rate constants. Implementation

[0022] This invention prepares a non-metallic catalyst for self-assembly of carbon nanotubes, and adjusts the amount of g-C3N4 scaffold used in the catalyst assembly to achieve different degrees of assembly. It activates persulfate to remove organic pollutants in water, and has been effectively applied.

[0023] The preferred embodiments of the present invention will now be described in detail with reference to specific examples. It should be understood that the following examples are given for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications and substitutions to the present invention without departing from its spirit and essence.

[0024] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0025] Unless otherwise specified, all materials and reagents used in the following examples are commercially available. Example 1

[0026] A method for preparing a self-assembled catalyst using carbon nanotubes includes the following steps:

[0027] ① 0.5 g of commercial carbon nanotubes (approximately 25 nm in diameter) were placed in a mixed solution of 200 mL of 6 M concentrated nitric acid and concentrated sulfuric acid (volume ratio 1:1) at 80 °C and refluxed for 12 hours.

[0028] ② Wash the carbon nanotubes after the above reaction is completed with deionized water until the washing solution is neutral. Dry the obtained carbon nanotubes in an oven at 60 ℃ for later use and mark them as pretreated carbon nanotubes.

[0029] ③ Add 0 g, 0.1 g, 0.5 g, 1.0 g, and 2.0 g of dicyandiamide and 35 ml of distilled water to a beaker respectively, and stir to dissolve at 80°C to obtain a preliminary preparation solution;

[0030] ④ Add 0.5 g of carbon nanotubes to the initial preparation solution, stir at 100 °C, and after the water has completely evaporated, take out the solid and grind it in a mortar to obtain the target mixture;

[0031] ⑤ The target mixture was subjected to high-temperature annealing and polymerization at 550 °C for 2 hours under an inert gas atmosphere. The resulting solid was naturally cooled and then ground for later use to obtain a self-assembled catalyst of carbon nanotubes.

[0032] High-temperature annealing polymerization at different concentrations of dicyandiamide (0, 0.1, 0.5, 1.0, and 2.0 g) for 2 hours yielded carbon nanotube self-assembly catalysts with varying degrees of self-assembly. The self-assembly catalyst obtained by high-temperature annealing polymerization at 0 g for 2 hours was labeled CT, the self-assembly catalyst obtained by high-temperature annealing polymerization at 0.1 g for 2 hours was labeled CT-1, the self-assembly catalyst obtained by high-temperature annealing polymerization at 0.5 g for 2 hours was labeled CT-2, the self-assembly catalyst obtained by high-temperature annealing polymerization at 1.0 g for 2 hours was labeled CT-3, and the self-assembly catalyst obtained by high-temperature annealing polymerization at 2.0 g for 2 hours was labeled CT-4.

[0033] Figure 1 This is the self-assembly process of carbon nanotubes and its corresponding transmission electron microscope image. Figure 1 In section 'a', we see the self-assembly process of carbon nanotubes. The carbon nanotubes and their assembly scaffold, g-C3N4, are assembled by annealing and polymerization at 550 °C. Increasing the amount of g-C3N4 in the assembly scaffold can enhance the assembly of carbon nanotubes and allow for different degrees of assembly. Figure 1 Image b is a transmission electron microscope image of carbon nanotubes without any assembly, clearly showing the tubular structure of the carbon nanotubes. Figure 1In the middle, c is the transmission electron microscope spectrum of carbon nanotubes after the first assembly, and the area circled by the curve is C3N4. Figure 1 In the middle, d and e are transmission electron microscope (TEM) spectra after gradually increasing the amount of g-C3N4 scaffold assembled. As the amount of C3N4 increases, the density increases and the carbon nanotube assembly process gradually intensifies.

[0034] Figure 2 Figure 'a' shows the X-ray diffraction pattern of the catalyst with four self-assemblies of carbon nanotubes. The (100) and (002) planes are characteristic peaks of the assembled scaffold g-C3N4, while the (101) plane is the characteristic peak of the carbon nanotubes. As the self-assembly process proceeds, the C3N4 content gradually increases, thus increasing the peak intensity of the (100) and (002) planes of the assembled scaffold g-C3N4. At the same time, the carbon nanotube content gradually decreases, and the peak intensity of the (101) plane of the carbon nanotubes weakens. Figure 2 Figure b shows the X-ray photoelectron spectrum of a catalyst that has undergone four self-assemblies of carbon nanotubes. As the number of assembly times increases, the carbon spectrum peak intensity gradually decreases, the nitrogen spectrum peak intensity gradually increases, and the oxygen spectrum peak intensity first gradually increases and then reaches a stable state. Figure 2 The image d is the carbon X-ray photoelectron spectroscopy (XPS) spectrum of a catalyst that has undergone four self-assemblies of carbon nanotubes. As the number of assembly cycles increases, the content of the assembly scaffold gradually increases, thereby limiting the steric hindrance around certain carbon atoms, causing the carbon spectrum peak to shift to the left from 288.7 eV. Figure 2 In the figure, 'c' represents the mass ratio of carbon, nitrogen, and oxygen as catalyst elements in the four self-assemblies of carbon nanotubes. As the number of assembly times increases, the carbon content gradually decreases, while the nitrogen content gradually increases, and the oxygen content first increases and then remains stable.

[0035] Due to the advantages of persulfate as an oxidant, such as low price, convenient storage and transportation, and the fact that 2,4-dichlorophenol contains a large amount of chlorine, making it difficult to convert and degrade in advanced oxidation processes, this embodiment selects persulfate (PMS) as the persulfate oxidant and 2,4-dichlorophenol as a typical organic pollutant. To verify the general applicability of this system, various aquatic agents were selected for degradation. A certain amount of the catalyst prepared above was added to a solution of 2,4-dichlorophenol or other aquatic pollutants of a certain concentration. The mixture was stirred for 30 min using a magnetic stirrer to allow the catalyst and pollutants to reach adsorption-desorption equilibrium, in order to better evaluate the subsequent Fenton-like oxidation performance. Subsequently, a certain amount of PMS was added to induce a Fenton-like reaction to degrade 2,4-dichlorophenol or other pollutants in the water. Within a set time period, 1.0 mL of the reaction solution was added to 0.8 mL of sodium thiosulfate pentahydrate solution (concentration of 0.006 mol / L) to terminate the reaction. After passing through a membrane, the solution was analyzed by high performance liquid chromatography to determine the concentration of the target organic compound 2,4-dichlorophenol or other contaminants, in order to evaluate the catalytic performance of the catalyst.

[0036] The application process of the above catalyst is as follows:

[0037] ① Take 5 mg of the catalyst prepared in the above example and add it to 50 mL of wastewater containing 10 mg / L of organic pollutants, including 2,4-dichlorophenol, sulfamethoxazole, tetracycline hydrochloride and atenolol.

[0038] ② Stir with a magnetic stirrer for 30 minutes to achieve an adsorption-desorption equilibrium between the catalyst and the organic matter.

[0039] ③ Subsequently, 1.5 mg of potassium persulfate (PMS) oxidant was added to induce a Fenton-like reaction to degrade and remove organic pollutants from the water.

[0040] ④ At a preset time point, take a 1.0 mL sample and add 0.8 mL of sodium thiosulfate pentahydrate solution (concentration of 0.006 mol / L) to terminate the reaction. After passing through a membrane, analyze the concentration of the target organic compound by high performance liquid chromatography to evaluate the degradation performance of the system.

[0041] Figure 3 Figure a shows the time distribution and technical comparison of 2,4-dichlorophenol removal using CT-1 activated persulfate. The results indicate that organic matter cannot be degraded in the absence of either the catalyst or the oxidant. However, when both the catalyst CN-1 and the oxidant persulfate are present, the pollutant can be degraded by 99.9%, demonstrating the highly efficient catalytic activity of this system. Figure 3 Figure b shows the presence of 2,4-dichlorophenol before and after the reaction, determined by high performance liquid chromatography. The horizontal axis of the figure indicates that the elution time of 2,4-dichlorophenol is approximately 4.7 minutes, and the vertical axis represents the detection wavelength of 2,4-dichlorophenol at 287 nm. Figure 3 Figure c shows the degradation effect of persulfate on 2,4-dichlorophenol at different concentration gradients activated by CT-1. As can be seen from the figure, the degradation of 2,4-dichlorophenol significantly improves with increasing persulfate concentration to 48.80 μM, and then the degradation effect remains unchanged with further gradual increases in persulfate concentration. This indicates that as the oxidant concentration increases, the active sites on the CN-1 surface are fully occupied, thus the degradation effect on pollutants reaches a peak with increasing persulfate concentration and then remains constant. Figure 3 As shown in d, in Figure 3Based on the experimental results in section a, to verify the general applicability of the system, several drugs commonly found in environmental water bodies but difficult to degrade were selected, including sulfamethoxazole, tetracycline hydrochloride, and atenolol. Sulfamethoxazole and tetracycline hydrochloride were degraded to varying degrees, but atenolol showed almost no degradation. This result indicates that the catalyst activated by the self-assembled carbon nanotubes in the PMS system exhibits selective degradation of pollutants, rather than non-selective strong oxidative degradation. This characteristic makes the catalyst proposed in this invention a promising candidate for effectively treating real-world water bodies. Because real-world water bodies have complex compositions, active species with selective degradation capabilities can meet this challenge.

[0042] Figure 4 This graph shows the effect of carbon nanotube catalysts with different assembly numbers on the removal of 2,4-dichlorophenol from water by PMS and their corresponding pseudo-first-order rate constants. Figure 4 As shown in section a, CT-activated persulfate alone can degrade approximately 60% of 2,4-dichlorophenol, while CN-1-activated persulfate after the first assembly of carbon nanotubes can degrade approximately 99.9% of 2,4-dichlorophenol, indicating a significant improvement in the catalytic effect of the assembled carbon nanotubes. With the second and third assemblies, the catalytic activity significantly weakens. This may be because the surface density of the carbon nanotubes increases sharply with the increase in the content of g-C3N4 in the assembly scaffold, leading to a decrease in the active area, thereby reducing or blocking the active sites on the surface of the carbon nanotubes, ultimately resulting in the inhibition of 2,4-dichlorophenol degradation. Figure 4 Presentation of results in b Figure 4 Consistent with the experimental results in section a, the pseudo-first-order rate constant first increases and then decreases with the increase of the number of carbon nanotube assembly steps, with the maximum pseudo-first-order rate constant being 0.26 min. -1 .

Claims

1. The application of carbon nanotube self-assembled catalysts in the removal of organic pollutants from water by activated persulfate, characterized in that, The persulfate is potassium persulfate, and the organic pollutant is 2,4-dichlorophenol; The preparation process of the carbon nanotube self-assembled catalyst is as follows: carbon nanotubes are added to an aqueous solution of dicyandiamide, mixed, dried, ground, and the resulting mixture is annealed and polymerized at high temperature under an inert gas atmosphere to obtain the catalyst; Add 0.5g of carbon nanotubes to 35 mL of an aqueous solution containing 0.1g of dicyandiamide; The conditions for the high-temperature annealing polymerization are 550°C for 2 hours; The carbon nanotubes are first pretreated before being added to an aqueous solution of dicyandiamide. The pretreatment process involves placing 0.5 g of commercially available carbon nanotubes in a 200 mL mixed solution of 6 M concentrated nitric acid and concentrated sulfuric acid at 80 °C (volume ratio of concentrated nitric acid to concentrated sulfuric acid is 1:1) and refluxing for 12 hours. Afterward, the carbon nanotubes are washed with deionized water until the washing solution is neutral, and the resulting carbon nanotubes are dried for later use.

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