Preparation of a Co / Co3O4@NCNT nanomaterial and its application method

Abstract

The present invention discloses a preparation method of Co / Co3O4@NCNT nanomaterials. A mixed solution containing polyethylene glycol, cobalt nitrate hexahydrate, urea and deionized water is strongly stirred. After the reaction is completed, the mixed solution is dried in an oven. The dried precursor is ground in a mortar, and the ground precursor is calcined in a nitrogen atmosphere to obtain a black powder. The black powder is washed with water and ethanol respectively, centrifuged and finally dried in an oven to obtain Co / Co3O4@NCNT nanomaterials. This method has developed a cathode material with low cost, simple and efficient preparation method. The cathode material is used in the electrocatalytic production of ammonia from nitrate and shows high ammonia production performance, providing a new idea for removing nitrate in environmental water bodies and waste recycling.

Description

Technical Field

[0001] The present invention relates to a method for preparing a nanomaterial and its application, in particular to a method for preparing a Co / Co3O4@NCNT nanomaterial and its application. Background Art

[0002] Water is the most abundant resource on Earth, with 70.8% of the Earth's surface covered by water. However, the fresh water on which humans depend for survival accounts for only 2.8% of the total water volume. Due to its stable properties, high solubility, and easy migration, nitrate has become the main pollution factor in fresh water and has attracted extensive attention from scholars worldwide.

[0003] The pollution of water bodies by nitrate has become a key issue of social concern at present. Investigations in recent years have shown that the nitrate content in landfill leachate has reached 100 - 1000 mg / L. The U.S. Environmental Protection Agency classifies nitrate pollution into point-source pollution and non-point-source pollution. Among them, the pollution caused by sewage directly discharged into water bodies through the sewage pipe network at the discharge point is called point-source pollution, mainly the discharge of domestic sewage and industrial wastewater; non-point-source pollution refers to the pollution of water bodies caused by pollutants through indirect means such as soil infiltration, mainly due to the large use of agricultural nitrogen fertilizers and the leaching and infiltration of nitrogen-containing solid waste.

[0004] When the nitrate concentration in drinking water exceeds the World Health Organization's standard (10 mg / L), it will cause harm to human health and the natural environment. After nitrate enters the human body, it is catalyzed by enzymes in the body to form nitrite, which is the precursor of carcinogenic nitrosamines. This may lead to methemoglobinemia in a high-hemoglobin hypoxia environment, and may even cause canceration, malformation, and mutation of human cells over time, especially in infants and pregnant women.

[0005] From the above review, it can be seen that the pollution of nitrate not only endangers human health but also has an adverse impact on the ecological environment. Because the sources of nitrate are extensive, covering many fields such as life, industry, and agriculture. The excessive presence of NO3 in water resources - has brought negative impacts to people's lives. However, NH3, which also contains nitrogen, is an important raw material for the production of nitrogen fertilizers and plays an important role in increasing crop yields and improving grain quality. Therefore, it is very necessary to efficiently convert harmful nitrate in the environment into ammonia with high added value and reapply it to industrial and agricultural production, so as to relieve the production pressure faced by industrial nitrogen fixation for ammonia synthesis while also treating nitrate pollution in water bodies. Thus, it is particularly important to develop an efficient and economical method for degrading nitrate in water, and its strategic significance is evident.

[0006] Electrochemical synthesis of NH3 is carried out at normal temperature and pressure, using H2O as the proton source and renewable electricity as the driving force. It is a synthetic NH3 alternative process with great development prospects. Nitrate (NO3- ), as a substance abundant in nature, the dissociation energy of its N=O bond (204 kJ mol -1 ) is much lower than the dissociation energy of the N≡N bond in N2 molecules (941 kJ mol -1 ). Therefore, from an energy perspective, using eNITRR as an alternative process for low-temperature synthesis of NH3 has great development potential and significance. Therefore, in an environmental aqueous solution, converting NO3 - into NH3 can not only provide a green and sustainable NH3 synthesis technology but also alleviate global energy and pollution problems. SUMMARY OF THE INVENTION

[0007] The object of the present invention is to provide a preparation method and application method of Co / Co3O4@NCNT nanomaterials. This method develops a cathode material that is inexpensive, simple to prepare, and highly efficient. When used in electrocatalytic nitrate ammonia production, it exhibits high ammonia production performance, providing a new idea for removing nitrates in environmental water bodies and waste recycling.

[0008] The technical solution of the present invention: A preparation method of Co / Co3O4@NCNT nanomaterials includes the following steps:

[0009] A: First, strongly stir a mixed solution of polyethylene glycol, cobalt nitrate hexahydrate, urea, and deionized water. After the reaction is completed, dry the mixed solution in an oven.

[0010] B: Grind the dried precursor in a mortar, and calcine the ground precursor in a nitrogen atmosphere. After calcination, a black powder is obtained.

[0011] C: Wash the black powder with water and ethanol respectively, centrifuge and separate, and finally dry it in an oven to obtain Co / Co3O4@NCNT nanomaterials.

[0012] In the aforementioned preparation method of Co / Co3O4@NCNT nanomaterials, the specific preparation method includes the following steps:

[0013] A: First, strongly stir a mixed solution containing 0.087 g of cobalt nitrate hexahydrate, 5 g of urea, 0.5 g of polyethylene glycol, and 50 mL of deionized water for 30 min. Then, place it in an 80°C oven and dry it for 36 h.

[0014] B: Grind the dried precursor in a mortar for 5 minutes, and calcine it at 900°C in a nitrogen atmosphere with a heating rate of 5°C / min for 4 h to obtain a black powder.

[0015] C: Wash the black powder twice with water and ethanol respectively, centrifuge and separate, and finally dry it in an oven at 60 °C to obtain the Co / Co3O4@NCNT nanomaterial.

[0016] An application method of Co / Co3O4@NCNT nanomaterial, using the Co / Co3O4@NCNT nanomaterial as the cathode and applying it to the study of electrocatalytic nitrate ammonia production.

[0017] In the aforementioned application method of Co / Co3O4@NCNT nanomaterial, the method for electrocatalytic nitrate ammonia production is as follows: Mix the Co / Co3O4@NCNT material, ethanol and Nafion evenly by ultrasonic dispersion. The dosage ratio of the Co / Co3O4@NCNT material, ethanol and Nafion is 1 mg: 950 μL: 50 μL; then drop-coat it on the carbon cloth as the working electrode, and the loading amount of the drop-coating is 0.125 mg / cm -2 , load the solution containing nitrate in a single-chamber reactor, and use a platinum sheet as the counter electrode and mercuric oxide as the reference electrode for electrocatalytic nitrate ammonia production.

[0018] In the aforementioned application method of Co / Co3O4@NCNT nanomaterial, during the electrocatalytic nitrate ammonia production process, NO3 - The concentration is 0.1 M; the applied voltage is -1.2 to -1.7 V.

[0019] Beneficial effects of the present invention: Compared with the prior art, the Co / Co3O4@NCNT nanomaterial of the present invention has an increased surface area due to the nanotube structure of the material, providing a large specific surface area for the distribution of active sites. The combination of Co and Co3O4 promotes the conversion of nitrate to ammonia and improves the ammonia production rate. When the material prepared by this method is used for electrocatalytic nitrate reduction to ammonia, a high ammonia production rate can be achieved, greatly alleviating the global nitrate pollution and energy problems. Description of the Drawings

[0020] Figure 1 It is a synthesis schematic diagram of the Co / Co3O4@NCNT nanomaterial of the present invention;

[0021] Figure 2 It is a schematic diagram of the morphological characterization result of Co / Co3O4@NCNT prepared by the method of the present invention;

[0022] (In the figure, (a) is the SEM of Co / Co3O4@NCNT; (b-d) are the TEM of Co / Co3O4@NCNT; (e) is the SAED of Co / Co3O4@NCNT; (f) is the elemental mapping of C, N, O, Co of Co / Co3O4@NCNT);

[0023] Figure 3 Schematic diagram of the structural characterization results of Co / Co3O4@NCNT prepared by the method of the present invention;

[0024] (In the figure, (a) is the XRD spectrum of Co / Co3O4@NCNT, (b) is the XPS full spectrum, (c) is the C 1s fine spectrum, (d) is the O 1s fine spectrum, (e) is the N 1s fine spectrum, and (f) is the Co 2p fine spectrum)

[0025] Figure 4 Schematic diagram of the electrocatalytic nitrate-to-ammonia production performance when Co / Co3O4@NCNT prepared by the present invention is used as the cathode material;

[0026] (In the figure, (a) is the linear sweep voltammogram (LSV) of Co / Co3O4@NCNT, (b) is the ammonia production rate under the condition of applying a voltage of -1.2 to -1.7 V; (c) in the figure is the ammonia production rate with and without nitrate; (d) is the ammonia production experiment with 10 cycles of the electrode (applying a voltage of -1.5 V). Embodiment

[0027] The present invention will be further described below with reference to the accompanying drawings and embodiments, but it shall not be used as a basis for limiting the present invention.

[0028] Example 1 of the present invention: A preparation method of Co / Co3O4@NCNT nanomaterial, as Figure 1 shown, the specific preparation method includes the following steps:

[0029] A: First, a mixed solution containing 0.087 g of cobalt nitrate hexahydrate, 5 g of urea, 0.5 g of polyethylene glycol, and 50 mL of deionized water is strongly stirred for 30 min, and then placed in an 80°C oven and dried for 36 h;

[0030] B: Grind the dried precursor in a mortar for 5 minutes, and calcine it at 900°C in a N2 atmosphere at a heating rate of 5°C / min for 4 h to obtain a black powder;

[0031] C: Wash the black powder twice with water and ethanol respectively, centrifuge and separate, and finally place it in a 60°C oven and dry to obtain Co / Co3O4@NCNT nanomaterial.

[0032] An application method of Co / Co3O4@NCNT nanomaterial, using Co / Co3O4@NCNT nanomaterial as the cathode material and applying it to electrocatalytic nitrate-to-ammonia production.

[0033] The method for electrocatalytic nitrate production of ammonia is as follows: Mix the Co / Co3O4@NCNT material, ethanol, and Nafion and disperse them evenly by ultrasonic treatment. The dosage ratio of the Co / Co3O4@NCNT material, ethanol, and Nafion is 1 mg: 950 μL: 50 μL. Then, it is drop-coated on the carbon cloth as the working electrode, and the loading amount of the drop coating is 0.125 mg / cm -2 , and a solution containing nitrate is loaded into a single-chamber reactor, and an electrocatalytic nitrate production of ammonia experiment is carried out using a platinum sheet as the counter electrode and mercury oxide as the reference electrode.

[0034] During the electrocatalytic nitrate production of ammonia, the NO3 - concentration is 0.1 M; the applied voltage is -1.2 to -1.7 V (Hg / HgO).

[0035] Figure 2 are the scanning electron microscope image (SEM) and transmission electron microscope image (TEM) of Co / Co3O4@NCNT. It can be observed from the figure that Co / Co3O4@NCNT as a whole presents a nanotube morphology, with some small particles loaded on it, and has a large number of active sites. It can be seen from the elemental mapping diagram that the four elements C, N, O, and Co of the prepared catalyst are very evenly distributed.

[0036] The crystal structure of the catalyst was characterized by XRD diffraction ( Figure 3 (a)), and obvious diffraction peaks of Co and Co3O4 were observed. Figure 3 (b) is the XPS full spectrum of Co / Co3O4@NCNT. In addition, the XPS fine spectrum of C 1s of Co / Co3O4@NCNT shows three main peaks at 284.6, 285.8, and 289.7 eV ( Figure 3 (c)), corresponding to C-C, C-O, and C=O functional groups respectively. By comparing Figure 3 the XPS fine spectrum of O 1s in 2- (d), it is found that Co / Co3O4@NCNT shows three main peaks at 529.7 eV, 531 eV, and 532.3 eV, corresponding to lattice oxygen (O1, O 2- ), adsorbed oxygen (O2, O2 - / O - ), and hydroxyl species (O3, OH Figure 3 (e) shows two different types of nitrogen, pyridine N (398.7 eV) and graphitic N (400.9 eV), in the XPS fine spectrum of N 1s of Co / Co3O4@NCNT. The XPS fine spectrum of Co 2p ( Figure 3(f)) includes two vibrational satellite peaks at 789.5 and 804.2 eV, and two peaks at 780.3 and 795.5 eV correspond to Co 3+ 2p 3 / 2 and Co 3+ 2p 1 / 2 , and two peaks at 781.1 and 797.0 eV correspond to Co 2+ 2p 3 / 2 and Co 2+ 2p 1 / 2 . Two peaks at 779.7 and 794.6 eV correspond to Co 0 2p 3 / 2 and Co 0 2p 1 / 2 which confirms the successful preparation of Co / Co3O4@NCNT.

[0037] In order to verify the performance of the Co / Co3O4@NCNT nanomaterials prepared by the method of the present invention, the following tests were specifically carried out:

[0038] Under natural conditions, the performance of Co / Co3O4@NCNT as a cathode material for electrocatalytic nitrate reduction to ammonia was studied.

[0039] The specific test method is as follows: The Co / Co3O4@NCNT material, ethanol and Nafion were mixed and ultrasonically dispersed evenly, and the dosage ratio of the Co / Co3O4@NCNT material, ethanol and Nafion was 1 mg: 950 μL: 50 μL; then it was drop-coated on the carbon cloth as the working electrode, and the drop-coated loading amount was 0.125 mg / cm -2 , and a nitrate solution containing 0.1 M was loaded into a single-chamber reactor, and the ammonia production rate was tested at different voltages with a platinum sheet as the counter electrode and mercury oxide as the reference electrode. The Nessler colorimetric method was used. When testing, 0.1 mL of the sample was taken, mixed and shaken evenly with 4.9 mL of the test water sample, 0.1 mL of the potassium sodium tartrate solution and 0.1 mL of the Nessler reagent were added thereto, and after standing for 10 min, the absorbance was measured at 425 nm with a UV spectrophotometer, and the ammonia concentration was calculated according to the standard curve.

[0040] As Figure 4 (a) shows, the LSV of Co / Co3O4@NCNT in the presence and absence of nitrate was studied, and the results show that the current density with nitrate is larger than that without nitrate, indicating that the electrocatalytic nitrate reduction reaction has occurred. As Figure 4(As shown in (b), when the applied voltages are -1.2V, -1.3V, -1.4V, -1.5V, -1.6V, and -1.7V, as the applied voltage increases from -1.2V to -1.7V, the ammonia production rate also increases. The ammonia production rate is the highest when the voltage is -1.7V. When the voltage is higher than -1.7V, the Faraday efficiency is low. Therefore, the applied voltage should not be higher than -1.7V. However, when the applied voltage is lower than -1.2V, the ammonia production is too low and it is not recommended to choose. To detect the source of ammonia, as Figure 4 (As shown in (c), the ammonia concentration was detected in the presence and absence of nitrate. When there is no nitrate, the ammonia concentration is 0, while when there is nitrate, the ammonia concentration increases significantly, indicating that the production of ammonia comes from nitrate. To evaluate the stability of the material, an electrode was reused 10 times. From Figure 4 (d), it can be seen that after the electrode loaded with Co / Co3O4@NCNT was reused 10 times, the ammonia production rate did not decrease significantly, indicating that the material has good cycling stability.

Claims

1. A preparation method of Co / Co3O4@NCNT nanomaterials, characterized in that: It includes the following steps: A: First, strongly stir the mixed solution of polyethylene glycol, cobalt nitrate hexahydrate, urea and deionized water. After the reaction is completed, dry the mixed solution in an oven; B: Grind the dried precursor in a mortar. Calcinate the well-ground precursor at 900 °C in a nitrogen atmosphere to obtain a black powder; C: Wash the black powder with water and ethanol respectively, centrifuge and separate, and finally dry it in an oven to obtain the Co / Co3O4@NCNT nanomaterial.

2. The preparation method of Co / Co3O4@NCNT nanomaterials according to claim 1, characterized in that: The specific preparation method includes the following steps: A: First, strongly stir the mixed solution containing 0.087 g of cobalt nitrate hexahydrate, 5 g of urea, 0.5 g of polyethylene glycol and 50 mL of deionized water for 30 min. Then, dry it in an 80 °C oven for 36 h; B: Grind the dried precursor in a mortar for 5 minutes, and calcinate it at 900 °C in a nitrogen atmosphere at a heating rate of 5 °C / min for 4 h to obtain a black powder; C: Wash the black powder with water and ethanol twice respectively, centrifuge and separate, and finally dry it in a 60 °C oven to obtain the Co / Co3O4@NCNT nanomaterial.

3. An application of a product prepared by the preparation method of Co / Co3O4@NCNT nanomaterials according to any one of claims 1-2, characterized in that: Apply the Co / Co3O4@NCNT nanomaterial as the cathode in the electrocatalytic production of ammonia from nitrate.

4. The application of Co / Co3O4@NCNT nanomaterials according to claim 3, characterized in that: The method for electrocatalytic nitrate ammonia production is as follows: The Co / Co3O4@NCNT material, ethanol and Nafion are mixed and ultrasonically dispersed evenly. The dosage ratio of the Co / Co3O4@NCNT material, ethanol and Nafion is 1 mg: 950 μL: 50 μL. Then it is drop-coated on the carbon cloth as the working electrode, and the loading amount of the drop coating is 0.125 mg / cm -2 , A solution containing nitrate is loaded into a single-chamber reactor, and a platinum sheet is used as the counter electrode and mercuric oxide is used as the reference electrode for electrocatalytic nitrate ammonia production.

5. The application of Co / Co3O4@NCNT nanomaterials according to claim 4, characterized in that: During the electrocatalytic production of ammonia from nitrate, NO3 - The concentration is 0.1 M; the applied voltage is -1.2 to -1.7 V.

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