Method for electrocatalytic dehalogenation through nitrogen coordination monatomic cobalt cathode

Abstract

The invention relates to an electrocatalytic dehalogenation method of a nitrogen-coordinated monatomic cobalt cathode, which realizes high-efficiency and low-consumption removal of halogenated antibiotics. The nitrogen-coordinated monatomic cobalt is synthesized by using MOFs (Metal-Organic Frameworks) as a precursor through a simple and convenient preparation method. By regulating and controlling the preparation method, the nitrogen-coordinated monatomic cobalt exists in a Co-N4 structure, the dispersity is good, and the number of active sites is large. When the catalyst serves as a cathode to be applied to electrocatalytic dehalogenation, efficient and rapid removal of halogen-containing antibiotics can be achieved, and the catalyst is wide in pH application range, small in influence of coexisting ions, good in recyclability and extremely low in cobalt dissolution rate.

Description

Technical Field

[0001] The invention relates to the fields of materials and environment, and in particular to a method for electrocatalytic dehalogenation of a nitrogen-coordinated single-atom cobalt cathode. Background Art

[0002] Halogenated antibiotics are widely used in people's daily lives, but their overuse can lead to the generation of drug-resistant bacteria and drug-resistant genes, threatening the ecological environment. However, halogenated antibiotics are difficult to biodegrade, and physical methods cannot destroy the carbon-halogen bonds with strong bond energy, which will lead to secondary pollution. Chemical methods have harsh conditions, high energy consumption, and are prone to produce highly toxic halogenated intermediates. Therefore, a practical halogenated antibiotic removal technology is urgently needed. Electrochemical reduction is a clean and efficient dehalogenation method that does not require additional reagents, is simple to operate, and has no secondary pollution. The development of efficient and stable electrocatalysts is the key to electrochemical dehalogenation.

[0003] In dehalogenation reactions, palladium-based noble metal catalysts have been widely used. However, in practical applications, palladium often exists in the reaction system in the form of nanoparticles, and the palladium atoms inside the metal cannot be fully utilized, resulting in a significant reduction in atomic utilization. In addition, the scarcity and high cost of noble metals make it impossible to meet the growing catalytic demand. Therefore, the development of non-noble metal catalysts with high catalytic activity has become a research focus. Single-atom catalysts have been widely used in CO2 reduction, nitrate reduction, water splitting and other fields due to their advantages such as nearly 100% atomic utilization, high catalytic activity and selectivity, and unsaturated coordination environment. Therefore, it is economically feasible to apply non-noble metal single-atom catalysts to electrocatalytic dehalogenation, and it is worth exploring how to regulate the preparation method of single atoms to achieve efficient dehalogenation. Summary of the invention

[0004] The purpose of the present invention is to apply the prepared nitrogen-coordinated single-atom cobalt catalyst with many active sites as a cathode in electrocatalytic dehalogenation. The system has good stability and a wide pH application range, can produce more atomic hydrogen, and achieve efficient and low-consumption removal of halogenated antibiotics.

[0005] The present invention relates to a method for electrocatalytic dehalogenation of a nitrogen-coordinated single-atom cobalt cathode, which is characterized by: using a nitrogen-coordinated single-atom cobalt catalyst (Co-N / C) in the form of Co-N4 coordination as a cathode, adjusting the pH of the solution to 3-9 in a double-chamber reactor, and controlling the current to 0.125-2.5 mA cm -2 Electrocatalytic dehalogenation reaction.

[0006] The above-mentioned method of using the Co-N / C cathode in electrocatalytic dehalogenation is characterized in that the cathode single-atom cobalt catalyst loading is 1-5 mg cm -2 . The method for preparing the Co-N / C cathode is characterized by the following steps: (1) Dissolve 2-methylimidazole in methanol to form solution I, dissolve zinc nitrate and cobalt nitrate in methanol to form solution II, pour solution I into solution II, stir evenly at room temperature, transfer to a reactor, keep in an oven at 120° C. for 4 hours, cool to room temperature, wash with methanol and dry overnight to obtain Co / ZIF-8; (2) calcine the Co / ZIF-8 obtained in step (1) at 750-1000° C. for 2-5 hours under an inert atmosphere to obtain Co-N / C; (3) uniformly mix Co-N / C with ethanol and Nafion, coat the ink on carbon cloth and dry naturally.

[0007] The above-mentioned method for preparing the nitrogen-coordinated single-atom cobalt catalyst is characterized in that the molar ratio of zinc nitrate to cobalt nitrate is 70:1 to 5:1.

[0008] The present invention has the following outstanding features: (1) The catalyst preparation method is simple, and the synthesized single-atom cobalt has good dispersion and many active sites.

[0009] (2) The system has low energy consumption in electrocatalytic dehalogenation, a wide pH application range, can remove a variety of halogenated antibiotics, is less affected by coexisting ions in water, can maintain stable dehalogenation performance after ten cycles, and has low cobalt dissolution. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is a spherical aberration electron microscope image of the Co-N / C catalyst prepared in the present invention; Figure 2 This is a synchrotron radiation image of the Co-N / C catalyst prepared in the present invention; Figure 3 A diagram showing the dehalogenation effect of the Co-N / C cathode prepared by the present invention with a molar ratio of zinc nitrate to cobalt nitrate of 7:1 for electrocatalytic dehalogenation of florfenicol; Figure 4 The Co-N / C cathode with different molar ratios of zinc nitrate and cobalt nitrate prepared by the present invention is used for electrocatalytic dehalogenation of florfenicol; Figure 5 The Co-N / C cathode prepared in the present invention is used for electrocatalytic dehalogenation and the dehalogenation effect of florfenicol at different pH values; Figure 6 The Co-N / C cathode prepared by the present invention is used for electrocatalytic dehalogenation of different halogenated antibiotics; Figure 7 The Co-N / C cathode prepared in the present invention is used for electrocatalytic dehalogenation and the dehalogenation effect of florfenicol under the influence of coexisting ions; Figure 8The Co-N / C cathode prepared in the present invention is used for electrocatalytic dehalogenation, and the dehalogenation effect diagram of florfenicol and the cobalt dissolution diagram after ten cycles; Fig. 9 Atomic hydrogen diagram produced for the Co-N / C cathode prepared in the present invention; Implementation

[0011] Implementation Case 1 2-Methylimidazole was dissolved in methanol to form solution I, zinc nitrate and cobalt nitrate were dissolved in methanol at a molar ratio of 7:1 to form solution II, solution I was poured into solution II, stirred at room temperature for 30 minutes, and then transferred to a reactor, kept in an oven at 120°C for 4 hours, cooled to room temperature, washed with methanol, and dried at 70°C overnight to obtain Co / ZIF-8; the obtained Co / ZIF-8 was calcined at 950°C under an inert atmosphere for 3 hours to obtain nitrogen-coordinated single-atom cobalt (Co-N / C). Figure 1 This is the spherical aberration electron microscope image of Co-N / C. It can be seen that the atomically dispersed cobalt is evenly distributed on the porous carbon, indicating that cobalt exists in the form of single atoms. Figure 2 This is the synchrotron radiation image of Co-N / C. The results show that Co-N / C presents Co-N4 coordination, does not contain obvious metal-metal coordination, and Co-N / C is a single-atom structure.

[0012] In a dual-chamber reactor, the carbon cloth supported by Co-N / C catalyst was used as cathode, the shape-stable electrode DSA was used as anode, and 50 mM sodium sulfate was added as supporting electrolyte. -2 Degraded 10 mg L -1 Florfenicol, unadjusted pH, as Figure 3 As shown in Figure 2, the removal efficiency of florfenicol by Co-N / C cathode can reach 98.7%, and the energy consumption is relatively low, which is 22.7 kWhkg -1 , achieving efficient and low-consumption removal of halogenated antibiotics.

[0013] Implementation Case 2 The steps of Example 2 are basically the same as those of Example 1, except that the molar ratios of zinc nitrate and cobalt nitrate are 70:1, 14:1, 7:1 and 5:1, respectively denoted as Co-N / C-1, Co-N / C-2, Co-N / C-3 and Co-N / C-4. Figure 4 As shown, Co-N / C-1, Co-N / C-2, Co-N / C-3 and Co-N / C-4 cathodes removed 73.7%, 88.7%, 98.7% and 91.0% respectively at 120 minutes. The dehalogenation effect was enhanced by adjusting the molar ratio of zinc nitrate to cobalt nitrate during the preparation process.

[0014] Implementation Case 3 The steps of implementation case 3 are basically the same as those of implementation case 1, except that the pH of the wastewater to be treated is adjusted to 3-9. Figure 5 As shown in the figure, at pH 3-9, the removal rate of Co-N / C is above 80%, indicating that Co-N / C has a wide pH application range.

[0015] Implementation Case 4 The steps of implementation case 4 are basically the same as those of implementation case 1, except that the pollutant is 10 mg L -1 of florfenicol, chloramphenicol, and thiamphenicol, such as Figure 6 As shown in the figure, for different halogenated antibiotics, the Co-N / C cathode can achieve a removal rate of more than 84%, which shows that the Co-N / C cathode is suitable for the removal of a variety of different halogenated antibiotics.

[0016] Implementation Case 5 The steps of implementation case 5 are basically the same as those of implementation case 1, except that nitrate (NO3 - ), carbonate (CO3 2- ), chloride ion (Cl - ) and humic acid, such as Figure 7 As shown in the figure, the Co-N / C cathode is less affected by the coexisting ions and humic acid. After adding the coexisting ions and humic acid, the removal rate of florfenicol is above 87%. This shows that the Co-N / C cathode has a wide range of application prospects.

[0017] Implementation Case 6 The steps of Example 6 are basically the same as those of Example 1, except that the Co-N / C cathode is reused ten times. Figure 8 As shown in the figure, after the Co-N / C cathode was reused ten times, the florfenicol removal rate was still above 90%. The dechlorination rate and defluorination rate remained stable, maintaining above 60% and 90%, respectively. In particular, the dissolution amount of cobalt was extremely low, ranging from 0.3 to 5.7 μg L -1 This indicates that the Co-N / C cathode has good stability and low cobalt dissolution, which is beneficial for practical applications.

[0018] Implementation Case 7 The steps of implementation case 7 are basically the same as those of implementation case 1, except that the contaminant florfenicol is not added for electron spin resonance (EPR) testing. Fig. 9 As shown, the active species produced by the Co-N / C cathode is atomic hydrogen.

[0019] The above is only an implementation example of the present invention and does not limit the present invention in any form. Any ordinary technician in the industry can successfully implement the present invention as shown in the drawings and above. However, any technician familiar with the profession can make some changes, modifications and evolutions of the contents shown above without departing from the scope of the technical solution of the present invention, which are all equivalent implementation examples of the present invention. At the same time, any equivalent changes, modifications and evolutions made to the above implementation examples based on the essential technology of the present invention are within the protection scope of the technical solution of the present invention.

Claims

1. The present invention relates to a method for electrocatalytic dehalogenation of a nitrogen-coordinated single-atom cobalt cathode, characterized in that: The nitrogen-coordinated single-atom cobalt catalyst (Co-N / C) in the form of Co-N4 coordination was used as the cathode. In a dual-chamber reactor, the pH of the solution was adjusted to 3-9 and the current was controlled to be 0.125-2.5 mA cm -2 Electrocatalytic dehalogenation reaction.

2. The method of using a Co-N / C cathode in electrocatalytic dehalogenation according to claim 1, characterized in that: The single-atom cobalt catalyst loading at the cathode is 1–5 mg cm -2 .

3. The method for preparing the Co-N / C cathode according to claim 1, characterized by the following steps: (1) Dissolve 2-methylimidazole in methanol to form solution I, dissolve zinc nitrate and cobalt nitrate in methanol to form solution II, pour solution I into solution II, stir evenly at room temperature, transfer to a reactor, keep in an oven at 120° C. for 4 hours, cool to room temperature, wash with methanol and dry overnight to obtain Co / ZIF-8; (2) calcine the Co / ZIF-8 obtained in step (1) at 750-1000° C. for 2-5 hours under an inert atmosphere to obtain Co-N / C; (3) uniformly mix Co-N / C with ethanol and Nafion, coat the ink on carbon cloth and let it dry naturally.

4. The method for preparing the Co-N / C cathode according to claim 3, characterized in that The molar ratio of zinc nitrate to cobalt nitrate is 70:1 to 5:1.

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