Method for electrocatalytic dehalogenation by nitrogen-coordinated single-atom cobalt cathode

Abstract

The present application relates to a kind of nitrogen coordination monatomic cobalt cathode electrocatalytic dehalogenation method, realize efficient low consumption removal halogenated antibiotic.The present application is synthesized nitrogen coordination monatomic cobalt by simple and convenient preparation method with MOFs as precursor.By adjusting preparation method, nitrogen coordination monatomic cobalt exists with Co-N4 structure, and has good dispersibility and many active sites.The catalyst can realize efficient and rapid removal of halogenated antibiotic when being applied to electrocatalytic dehalogenation as cathode, and has wide pH application, is little affected by coexisting ions, has good cyclic use, and has very low cobalt elution.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of materials and environment, in particular, the present application relates to a method for electrocatalytic dehalogenation of nitrogen-coordinated single-atom cobalt cathode. BACKGROUND

[0002] Halogenated antibiotics are widely used in people's daily life, 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 break the strong carbon-halogen bond, which can cause secondary pollution. Chemical methods have harsh conditions, high energy consumption, and are prone to produce halogen-containing intermediates with high toxicity. Therefore, there is an urgent need for a practical halogenated antibiotic removal technology. Electrochemical reduction is a clean and efficient dehalogenation method that does not require additional reagents, is simple to operate, and has no secondary pollution. Developing efficient and stable electrocatalysts is the key to electrochemical dehalogenation.

[0003] In the dehalogenation reaction, palladium-based noble metal catalysts have been widely used. However, in practical applications, palladium often exists in the form of nanoparticles in the reaction system, 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 difficult to meet the growing demand for catalysis. Therefore, developing 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 near 100% atomic utilization, high catalytic activity and selectivity, and unsaturated coordination environment. Therefore, applying non-noble metal single-atom catalysts to electrocatalytic dehalogenation is economically feasible, and how to regulate the preparation method of single atoms to achieve efficient dehalogenation is worth exploring. SUMMARY

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

[0005] A method for electrocatalytic dehalogenation of nitrogen-coordinated single-atom cobalt cathode, characterized in that: a nitrogen-coordinated single-atom cobalt catalyst Co-N / C with Co-N4 coordination form of cobalt is used as a cathode, the pH of the solution is adjusted to 3-9 in a double-chamber reactor, the current is controlled to be 0.125-2.5 mA·cm -2 for electrocatalytic dehalogenation reaction.

[0006] In the above method, the feature is that the loading of the single-atom cobalt catalyst on the cathode is 1-5 mg·cm -2 .

[0007] The method, characterized in that the Co-N / C cathode is prepared by the following steps:

[0008] (1) 2-methylimidazole is dissolved in methanol to form solution I, zinc nitrate and cobalt nitrate are dissolved in methanol to form solution II, solution I is poured into solution II, and after stirring uniformly at room temperature, it is transferred into a reaction kettle, kept in an oven at 120 DEG C for 4 hours, cooled to room temperature, washed with methanol and dried overnight to obtain Co / ZIF-8; (2) the Co / ZIF-8 obtained in step (1) is calcined at 750-1000 DEG C for 2-5 hours under an inert atmosphere to obtain Co-N / C; (3) Co-N / C is uniformly mixed with ethanol and Nafion, and then coated on carbon cloth and naturally dried.

[0009] The Co-N / C cathode preparation method, characterized in that the molar ratio of zinc nitrate and cobalt nitrate is 70:1 to 5:1.

[0010] The present application has the following outstanding features:

[0011] (1) The catalyst preparation method is simple, the synthesized single-atom cobalt has good dispersity, and has many active sites;

[0012] (2) The system has low energy consumption in electrocatalytic dehalogenation, has a wide pH application range, can remove various halogenated antibiotics, is less interfered by coexisting ions in water bodies, can still maintain stable dehalogenation performance after ten cycles, and has low cobalt elution. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 The spherical difference electron microscope image of the Co-N / C catalyst prepared in the present application;

[0014] Figure 2 The synchrotron radiation image of the Co-N / C catalyst prepared in the present application;

[0015] Figure 3 The dehalogenation effect diagram of the Co-N / C cathode prepared in the present application with a molar ratio of zinc nitrate and cobalt nitrate of 7:1 for electrocatalytic dehalogenation of florfenicol;

[0016] Figure 4 The dehalogenation effect diagram of the Co-N / C cathode prepared in the present application with different molar ratios of zinc nitrate and cobalt nitrate for electrocatalytic dehalogenation of florfenicol;

[0017] Figure 5 The dehalogenation effect diagram of the Co-N / C cathode prepared in the present application for electrocatalytic dehalogenation of florfenicol at different pH values;

[0018] Figure 6 The dehalogenation effect diagram of the Co-N / C cathode prepared in the present application for electrocatalytic dehalogenation of different halogenated antibiotics;

[0019] Figure 7 The dehalogenation effect of the Co-N / C cathode prepared in this invention on florfenicol under the influence of coexisting ions is shown in the figure.

[0020] Figure 8 The diagram shows the dehalogenation effect of the Co-N / C cathode prepared for this invention on florfenicol after ten cycles and the cobalt dissolution diagram.

[0021] Figure 9 A hydrogen atom diagram of the Co-N / C cathode prepared in this invention; Detailed Implementation

[0022] Implementation Case 1

[0023] 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 and stirred at room temperature for 30 minutes. The mixture was then transferred to a reaction vessel and kept in an oven at 120°C for 4 hours. After cooling to room temperature, the mixture was washed with methanol and dried overnight at 70°C to obtain Co / ZIF-8. The obtained Co / ZIF-8 was calcined at 950°C for 3 hours under an inert atmosphere to obtain nitrogen-coordinated single-atom cobalt Co-N / C. Figure 1 The image shows a spherical aberration electron microscope image of Co-N / C, which reveals that atomically dispersed cobalt is uniformly distributed on porous carbon, indicating that cobalt exists in the form of single atoms. Figure 2 The synchrotron radiation diagram of Co-N / C shows that Co-N / C exhibits Co-N4 coordination and does not contain obvious metal-metal coordination, indicating that Co-N / C has a single-atom structure.

[0024] In a two-chamber reactor, carbon cloth supported on a Co-N / C catalyst was used as the cathode, and a shape-stabilized electrode DSA was used as the anode. 50 mM sodium sulfate was added as the supporting electrolyte, and the reactor was operated at a current density of 2.5 mA·cm⁻¹. -2 Degradation 10 mg L -1 Florfenicol, without pH adjustment, such as Figure 3 As shown, the Co-N / C cathode can achieve a removal rate of 98.7% for florfenicol, with low energy consumption of 22.7 kWh / kg. -1 This achieves efficient and low-consumption removal of halogenated antibiotics.

[0025] Implementation Case 2

[0026] The steps in Implementation Case 2 are basically the same as those in Implementation Case 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 4As 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. By adjusting the molar ratio of zinc nitrate to cobalt nitrate in the preparation process, the dehalogenation effect was enhanced.

[0027] Example 3

[0028] The steps of Example 3 were basically the same as those of Example 1, except that the pH of the wastewater to be treated was adjusted to 3-9, such as Figure 5 As shown, the removal rates of Co-N / C were all above 80% at pH 3-9, indicating that Co-N / C has a wide pH application range.

[0029] Example 4

[0030] The steps of Example 4 were basically the same as those of Example 1, except that the pollutants were 10 mg L -1 of florfenicol, chloramphenicol and thiamphenicol, such as Figure 6 As shown, for different halogenated antibiotics, the Co-N / C cathode can achieve a removal rate of more than 84%. This shows that the Co-N / C cathode is suitable for the removal of a variety of different halogenated antibiotics.

[0031] Example 5

[0032] The steps of Example 5 were basically the same as those of Example 1, except that nitrate (NO3 - ), carbonate (CO3 2- ), chloride (Cl - ) and humic acid were added to the solution to be treated, respectively, such as Figure 7 As shown, the Co-N / C cathode is less affected by coexisting ions and humic acid. After adding coexisting ions and humic acid, the removal rate of florfenicol is more than 87%. This shows that the Co-N / C cathode has a wide application prospect.

[0033] Example 6

[0034] The steps of Example 6 were basically the same as those of Example 1, except that the Co-N / C cathode was reused ten times. As shown, Figure 8 After the Co-N / C cathode was reused ten times, the removal rate of florfenicol was still above 90%. The dechlorination rate and the defluorination rate remained stable, maintaining at more than 60% and 90% respectively. In particular, the cobalt elution was extremely low, at 0.3-5.7 μg L -1 This shows that the Co-N / C cathode has good stability and low cobalt elution, which is conducive to practical application.

[0035] Example 7

[0036] The procedure of Example 7 was essentially the same as Example 1, except that no contaminant florfenicol was added for electron spin resonance testing (EPR). As shown in Figure 9 The active species produced by the Co-N / C cathode is atomic hydrogen.

[0037] The above description is only one embodiment of the present application, and does not limit the present application in any form; any person skilled in the art can successfully implement the present application according to the drawings and the above description; however, any person skilled in the art can make some changes, modifications and equivalent changes within the scope of the technical solutions of the present application, and the equivalent embodiments of the present application are equivalent to the above description; meanwhile, any equivalent changes, modifications and evolution of the above embodiments according to the essential technology of the present application are within the protection scope of the technical solutions of the present application.

Claims

1. A method of electrocatalytic removal of halogenated antibiotics by nitrogen-coordinated single-atom cobalt cathode, characterized in that: (1) 2-methylimidazole is dissolved in methanol to form solution I, zinc nitrate, cobalt nitrate is dissolved in methanol to form solution II, solution I is poured into solution II, stirred uniformly at room temperature, then transferred to a reaction kettle, kept in an oven at 120 DEG C for 4 hours, cooled to room temperature, washed with methanol and dried overnight to obtain Co / ZIF-8; (2) Co / ZIF-8 obtained in step (1) is calcined at 750-1000 DEG C for 2-5 hours under inert atmosphere to obtain a nitrogen-coordinated single-atom cobalt catalyst Co-N / C; (3) Co-N / C is uniformly mixed with ethanol and Nafion, then coated on carbon cloth and naturally dried to obtain a cathode; (4) the cathode is placed in a double-chamber reactor, the pH of the solution is adjusted to 3-9, and the current is controlled to be 0.125-2.5 mA·cm -2 to carry out electrocatalytic dehalogenation reaction.

2. The method of claim 1, wherein: The monatomic cobalt catalyst loading of the cathode is 1-5 mg-cm -2 .

3. The method of claim 1, wherein The molar ratio of zinc nitrate and cobalt nitrate is from 70:1 to 5:

1. The molar ratio of zinc nitrate and cobalt nitrate is from 70:1 to 5:1.

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