An in-situ grown Co / CNT catalyst and its application

Abstract

The present invention discloses an in-situ grown Co / CNT catalyst and its application. The in-situ grown Co / CNT catalyst uses cobalt nitrate hexahydrate and dicyandiamide as the metal Co, carbon and nitrogen source precursors, and is prepared by means of grinding and high-temperature annealing polymerization. The Co nanoparticles in this catalyst grow in-situ inside the CNTs, increasing the active sites, achieving confined catalysis, improving the efficiency of pollutant degradation, reducing Co leaching, increasing the stability of the catalyst, and providing a broader idea for water environment remediation.

Description

Technical Field

[0001] The present invention belongs to the technical fields of materials engineering and environmental engineering, and particularly relates to an in-situ grown Co / CNT catalyst and its application for activating potassium peroxymonosulfate, sodium peroxymonosulfate, potassium persulfate, sodium persulfate, and peracetic acid to generate strongly oxidizing substances for removing organic pollutants in sewage water. Background Art

[0002] With the development of the global social economy, environmental pollution has become increasingly serious. In particular, the water environmental pollution caused by the production and waste discharge of chemical plants and pharmaceutical factories threatens the entire ecosystem and the lives and health of all mankind. In recent years, the abuse of antibiotics has led to the continuous detection of antibiotic organic pollutants in water bodies. The Fenton reaction is an advanced oxidation technology. Its non-selectivity for pollutants and strong oxidation ability can efficiently repair the water environment and remove antibiotic pollutants. Metal-based Fenton reaction catalysts have good stability, high selectivity, and a wide range of applications.

[0003] The present invention is designed to obtain an in-situ grown Co / CNT catalyst using cobalt nitrate hexahydrate and dicyandiamide as metal Co, carbon, and nitrogen source precursors. Co nanoparticles grow in-situ inside CNTs, increasing the active sites, achieving confined catalysis, improving the efficiency of degrading pollutants, reducing Co leaching, and increasing the catalyst stability, providing a broader idea for water environment restoration. Summary of the Invention

[0004] The purpose of the present invention is to provide an in-situ grown Co / CNT catalyst and its application, which uses precursors of materials containing metal Co and carbon and nitrogen elements to synthesize an in-situ grown Co / CNT catalyst through high-temperature annealing polymerization and activate persulfates (such as potassium peroxymonosulfate and potassium persulfate) to remove tetracycline organic pollutants in water bodies.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions:

[0006] An in-situ grown Co / CNT catalyst is synthesized by using cobalt nitrate hexahydrate and dicyandiamide as metal Co, carbon, and nitrogen source precursors through grinding and high-temperature annealing polymerization.

[0007] This catalyst has carbon nanotubes and Co nanoparticles as adsorption sites and catalytic oxidation sites respectively. First, the adsorption effect of carbon nanotubes is used to adsorb organic pollutants remotely to the vicinity of the singlet oxygen active species generated by Co nanoparticles catalyzing persulfate, achieving efficient removal of the model pollutant tetracycline. The use of a relatively small amount of oxidant avoids excessive oxidation of the material during use, facilitates the reuse of the material, and reduces the reaction cost.

[0008] The preparation method of this catalyst includes the following steps:

[0009] (1) Mix cobalt nitrate hexahydrate and absolute ethanol, and conduct the first grinding to obtain a preliminary mixture.

[0010] (2) Add dicyandiamide to the preliminary mixture, and conduct the second grinding to obtain the target mixture.

[0011] (3) Subject the target mixture to high-temperature annealing polymerization under the protection of an inert gas atmosphere. After the obtained solid is cooled, an in-situ grown Co / CNT catalyst is obtained.

[0012] Furthermore, the dosage ratio of cobalt nitrate hexahydrate, absolute ethanol, and dicyandiamide is 0.5 g - 2.0 g : 2 mL : 1 g - 3 g : 2 g - 4 g. Preferably, the dosage ratio of cobalt nitrate hexahydrate, absolute ethanol, and dicyandiamide is 1.01 g : 2 ml : 2.94 g.

[0013] Furthermore, the conditions for the high-temperature annealing polymerization are: high-temperature annealing polymerization at 700 - 900 °C for 1 - 4 hours. Preferably, high-temperature annealing polymerization at 700 - 800 °C for 1 - 4 hours. More preferably, high-temperature annealing polymerization at 700 - 800 °C for 3.5 hours. In an embodiment of the present invention, the in-situ grown Co / CNT catalyst prepared under the preferred conditions has very high catalytic activity when removing tetracycline.

[0014] The above-mentioned application of the in-situ grown Co / CNT catalyst in removing organic pollutants in sewage.

[0015] Furthermore, the application is that the in-situ grown Co / CNT catalyst can catalyze potassium peroxymonosulfate, sodium peroxymonosulfate, potassium persulfate, sodium persulfate, or peracetic acid to remove organic pollutants in sewage.

[0016] The present invention has the following beneficial effects:

[0017] 1. The in-situ grown Co / CNT catalyst prepared by the present invention can rapidly remove the water body polluted by tetracycline antibiotics by activating potassium peroxymonosulfate and potassium persulfate. When activating potassium peroxymonosulfate, the fastest reaction rate can achieve 99.8% removal of a 20 mg / L tetracycline solution within 1 min, and its pseudo-first-order reaction kinetic constant is 6.15 min -1 , and this value has quite an advantage in the current relevant research reports; during the process of activating potassium persulfate, 97.0% removal of a 20 mg / L tetracycline solution is achieved within 120 min, and its pseudo-first-order reaction kinetic constant is 0.05 min -1 .

[0018] 2. Less dosage of oxidant. In the present invention, the dosages of oxidants are 0.3 mM potassium peroxymonosulfate (PMS) and 0.7 mM potassium persulfate (PDS) respectively. The addition of a small amount of oxidant not only saves the reaction cost but also reduces the loss of the catalyst, which is beneficial to the multiple reuse of the catalyst. Description of the Drawings

[0019] Figure 1 High-resolution transmission electron microscopy images and X-ray diffraction patterns of the in-situ grown Co / CNT catalyst polymerized at different annealing temperatures in Examples 1-3.

[0020] Figure 2 Removal of the pollutant tetracycline by the in-situ grown Co / CNT catalyst activating potassium peroxymonosulfate in Examples 1-3.

[0021] Figure 3 Removal of the pollutant tetracycline by the in-situ grown Co / CNT catalyst activating potassium persulfate in Examples 1-3. Detailed Embodiments

[0022] The preferred embodiments of the present invention will be described in detail below in conjunction with the examples. It should be understood that the following examples are given only for the purpose of illustration and are not used to limit the scope of the present invention. Those skilled in the art can make various modifications and substitutions to the present invention without departing from the purpose and spirit of the present invention.

[0023] The experimental methods used in the following examples are all conventional methods unless otherwise specified.

[0024] The materials, reagents, etc. used in the following examples can be obtained from commercial sources unless otherwise specified.

[0025] Examples 1-3

[0026] The preparation method of the in-situ grown Co / CNT catalyst includes the following steps:

[0027] ① Add 1.01 g of cobalt nitrate hexahydrate and 2 ml of absolute ethanol to a mortar and conduct the first grinding to obtain a preliminary mixture;

[0028] ② Add 2.94 g of dicyandiamide to the preliminary mixture and conduct the second grinding to obtain the target mixture;

[0029] ③The target mixture was annealed and polymerized at different temperatures (550, 700, and 800 °C) for 3.5 h under an inert gas atmosphere. After the obtained solid was naturally cooled, it was ground for standby to obtain the in-situ grown Co / CNT catalyst. The in-situ grown Co / CNT catalyst obtained by annealing and polymerizing at 550 °C for 3.5 h was denoted as Co / CNT-550, the in-situ grown Co / CNT catalyst obtained by annealing and polymerizing at 700 °C for 3.5 h was denoted as Co / CNT-700, and the in-situ grown Co / CNT catalyst obtained by annealing and polymerizing at 800 °C for 3.5 h was denoted as Co / CNT-800.

[0030] As Figure 1 shown in A, Co / CNT-700 has a carbon nanotube structure, and Co nanoparticles are successfully loaded inside the carbon nanotubes. After dicyandiamide is annealed at high temperature in the presence of metallic Co, Co nanoparticles grow in-situ inside the CNTs. Figure 1 B in shows the X-ray diffraction pattern of the catalysts polymerized at different annealing temperatures. It can be seen from the figure that the material exhibits the (111), (200), and (220) planes of Co nanoparticles at about 2θ = 44°, 51°, and 76°, confirming that this series of materials contains metallic Co nanoparticle components.

[0031] 0.1 g / L of the prepared catalyst Co / CNT-700 was added to 50 mL of tetracycline antibiotic sewage with a concentration of 20 mg / L; 0.3 mM of potassium peroxymonosulfate (PMS) and 0.7 mM of potassium persulfate (PDS) were added respectively, and the reaction started to be timed; at the preset time points, 1.0 mL of the sample was taken and added to 1.0 mL of sodium thiosulfate pentahydrate solution (concentration: 0.006 mol / L) to terminate the reaction; the samples were subjected to high performance liquid chromatography to detect the residual tetracycline concentration to determine the removal efficiency.

[0032] As Figure 2 shown, Co / CNT-700 exhibits very strong catalytic activity, achieving 99.8% removal of a 20 mg / L tetracycline solution within 1 min, and the pseudo-first-order kinetic constant for the removal of tetracycline antibiotics is 6.15 min -1 . This reaction rate constant shows quite an advantage in the system of activating persulfate by metal-based materials for the removal of organic pollutants reported in the existing literature.

[0033] As Figure 3 shown, in the system of activating potassium persulfate, after 2 h of reaction, the removal rates of tetracycline using PDS or Co / CNT alone are 0% and 55% respectively, while the removal rate of tetracycline in the Co / CNT-PDS system is as high as 97%.

Claims

1. An in-situ grown Co / CNT catalyst, characterized in that, It is prepared by using cobalt nitrate hexahydrate and dicyandiamide as metal Co, carbon and nitrogen source precursors through grinding and high-temperature annealing polymerization. The preparation process includes the following steps: (1) Mix cobalt nitrate hexahydrate and absolute ethanol, and conduct the first grinding to obtain a preliminary mixture; (2) Add dicyandiamide to the preliminary mixture and conduct the second grinding to obtain the target mixture; (3) Subject the target mixture to high-temperature annealing polymerization under the protection of an inert gas atmosphere, and the obtained solid is cooled to obtain an in-situ grown Co / CNT catalyst; The dosage ratio of the cobalt nitrate hexahydrate, absolute ethanol and dicyandiamide is 1.01 g: 2 mL: 2.94 g; The conditions for the high-temperature annealing polymerization are: high-temperature annealing polymerization at 700 °C to 900 °C for 1 to 4 hours.

2. Application of the in-situ grown Co / CNT catalyst described in claim 1 in removing organic pollutants in sewage.

3. The application according to claim 2, wherein The in-situ grown Co / CNT catalyst can catalyze potassium peroxymonosulfate, sodium peroxymonosulfate, potassium persulfate, sodium persulfate or peracetic acid to remove organic pollutants in sewage.

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