Non-noble metal catalytic electrode material, preparation method and application thereof

Abstract

The invention provides a non-noble metal catalytic electrode material as well as a preparation method and application thereof, and the method comprises the following steps: rapidly adding a methanol mixed solution containing Co salt and Zn salt into a methanol solution of 2-methylimidazole, stirring for reaction, centrifuging, washing and drying; adding DMF (Dimethyl Formamide) into the dried material and ultrasonically dispersing; after dispersing, adding PAN, and heating in a water bath to obtain an electrostatic spinning precursor; then carrying out an electrostatic spinning process; and calcining in an inert atmosphere to obtain the Co-N / CNF electrode material. The preparation method is easy to operate, and the prepared Co-N / CNF electrode material has a stable catalytic effect and has a remarkable degradation effect on pollutants in wastewater.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemical water treatment, and in particular relates to a non-precious metal Co-N / CNF electrode and a preparation method and application thereof. Background Art

[0002] Electrochemical reduction is a clean and efficient dehalogenation method that does not require additional reagents, is simple to operate, and has no secondary pollution. During the electroreduction process, the intermediate substance atomic hydrogen produced by indirect reduction has strong catalytic reduction activity and is usually adsorbed on the surface of precious metal catalysts, with extremely high electroreduction activity.

[0003] The indirect reduction mediated by atomic hydrogen (H*) plays a key role in the electrocatalytic dehalogenation process. By adsorbing free hydrogen in the solution to receive electrons from the catalytic electrode, adsorbed hydrogen (H*) can be generated on the electrode surface. ads *) and hydrogen absorbed in the electrode material lattice (H abs *), has good performance for the hydrodehalogenation of halogenated pollutants. However, the electrocatalytic dehalogenation reaction process is often accompanied by hydrogen evolution side reactions, resulting in the consumption of H* and low dehalogenation efficiency. In practical applications, precious metals such as palladium and platinum are usually used. However, as precious metals, their scarcity and high cost make it impossible to meet the growing catalytic demand. Non-precious metal catalysts with high catalytic activity have aroused people's interest in the field of catalysis due to their low cost, large specific surface area, effective mass / electron transfer and unique physicochemical properties.

[0004] Carbon-based catalysts have good stability, high surface area, and excellent conductivity. In particular, appropriate doping of heteroatoms (such as N, S, P) and transition metals (such as Co, Fe) to obtain optimal electronic and geometric structures can improve carbon catalytic activity. In addition, MNC catalysts co-doped with transition metals and heteroatoms N have good electrocatalytic activity, good stability, and low cost.

[0005] Among them, zeolite imidazolate framework-8 (ZIF-8) is a crystalline material composed of Zn nodes and N-rich organic ligands. 2+ and Co 2+ Similar coordination properties, in ZIF-8, Co 2+ Can partially replace Zn 2+ , and are spatially separated by organic ligands and Zn, increasing the distance between adjacent Co atoms. Co-N single-atom sites are obtained by evaporating Zn at high temperatures and anchored on the porous carbon matrix derived from ZIF-8 to inhibit the aggregation and migration of Co, which is expected to improve the dispersion of the catalyst and thus improve the hydrodehalogenation performance. Summary of the invention

[0006] The present invention proposes a method for preparing a non-precious metal Co-N / CNF catalytic hydrogenation electrode and its application in the field of water treatment technology for electrochemical hydrogenation and dehalogenation. Through the conditions such as the ratio of precursors and the regulation of pyrolysis temperature, a Co-N / CNF composite electrode with non-precious metal Co as the active center is obtained, and it is used to carry a penetrating electrode reactor for the removal of halogenated pollutants in wastewater, and has excellent catalytic performance.

[0007] In a first aspect, the present invention provides a method for preparing a non-precious metal Co-N / CNF electrode material, comprising the following steps:

[0008] 1) Pour the methanol mixture containing Co salt and Zn salt into the methanol solution of 2-methylimidazole (MeIm) quickly and stir to react;

[0009] 2) After the obtained reaction solution is centrifuged, washed and dried, the obtained material (Co-ZIF-8) is added to N,N-dimethylformamide (DMF) and ultrasonically dispersed;

[0010] 3) adding polyacrylonitrile (PAN) to the dispersion obtained in step 2), and heating in a water bath to obtain an electrospinning precursor solution;

[0011] 4) Co-ZIF-8 / PAN composite material was obtained by electrospinning;

[0012] 5) The obtained Co-ZIF-8 / PAN composite material is calcined under an inert atmosphere to obtain a Co-N / CNF electrode material.

[0013] Furthermore, the Co salt is Co(NO3)2·6H2O, the Zn salt is Zn(NO3)2·6H2O, and the mass ratio of Co to Zn is 1:4.

[0014] Furthermore, the mass ratio of 2-methylimidazole to Co salt and Zn salt is 22:1:0.02.

[0015] Furthermore, in step 1), the reaction is stirred for 6 hours.

[0016] Furthermore, in step 3), the mass ratio of the obtained material to PAN is 3:4.

[0017] Furthermore, the electrospinning parameters were: spinning voltage was 10-20 kV, receiving distance was 10-20 cm, and injection speed was fixed at 0.08 mm min -1 .

[0018] Further, the calcination was carried out by heating the temperature to 950° C. at a heating rate of 5° C. / min and keeping the temperature for 3 hours.

[0019] In a second aspect, the present invention proposes a Co-N / CNF electrode material prepared by the method described in the first aspect.

[0020] In a third aspect, the present invention further proposes an application of the Co-N / CNF electrode material prepared by the method described in the first aspect in removing pollutants from wastewater.

[0021] Further, the contaminant includes florfenicol (FLO).

[0022] Furthermore, the pH of the wastewater to be treated is 3-9.

[0023] Furthermore, the Co-N / CNF electrode material is filled as a cathode material in a penetrating electrode reactor, and the wastewater to be treated is continuously pumped into the reactor to degrade pollutants.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] The present invention aims to enhance the production of H* by electrolysis of water to dehalogenate pollutants, and proposes a method for preparing Co-N / CNF electrode materials. The obtained electrode material can improve the efficiency of hydrogenation dehalogenation. The prepared electrode is used in a penetrating electrode reactor with the aid of a microflow field to enhance the generation and utilization of free radicals, thereby improving the reaction interface between the pollutant and the electrode. Through the generation of H*, the CX bond is attacked, thereby achieving the purpose of dehalogenation, reducing the toxicity of the pollutants, and making them easier to remove by subsequent oxidation.

[0026] The preparation method and application method of the electrode material proposed in the present invention are simple and reasonable, with stable effects. The immobilized electrode can be reused. In the process of electrocatalytic hydrogenation and dehalogenation degradation of pollutants FLO, the effect is remarkable, and the application prospect in the field of water treatment is good. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0028] Figure 1 Transmission electron microscopy image (100 nm) of the Co-N / CNF electrode material prepared in the embodiment of the present invention;

[0029] Figure 2 This is a scanning electron microscope image of the Co-N / CNF electrode material prepared in an embodiment of the present invention;

[0030] Figure 3 XRD diagram of the Co-N / CNF electrode material prepared in the embodiment of the present invention;

[0031] Figure 4This is a diagram showing the degradation effect of removing various pollutants in an application example of the present invention;

[0032] Figure 5 This is a diagram showing the degradation effect of pollutants in wastewater with different pH values ​​in the application example of the present invention;

[0033] Figure 6 A cyclic voltammetry diagram of the pollutant removal process in an application example of the present invention;

[0034] Figure 7 This is an EPR spectrum during the process of removing pollutants in an application example of the present invention.

[0035] Figure 8 This is a diagram showing the degradation effects of Co-N / CNF electrode materials and conventional commercial materials in removing FLO pollutants. DETAILED DESCRIPTION

[0036] The present application is further described below in conjunction with specific embodiments.

[0037] It should be noted that the terms such as "upper", "lower", "left", "right", "middle", etc. cited in this specification are only for the convenience of description and are not used to limit the scope of implementation. Changes or adjustments to their relative relationships should be regarded as the scope of implementation of this application without substantially changing the technical content.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the term "and / or" used herein includes any and all combinations of one or more of the associated listed items.

[0039] If the specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or conditions recommended by the manufacturer. If the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0040] As used herein, the term "about" is used to provide flexibility and imprecision associated with a given term, measurement or value. The degree of flexibility for a particular variable can be easily determined by one skilled in the art.

[0041] As used herein, the term "at least one of" is intended to be synonymous with "one or more of." For example, "at least one of A, B, and C" expressly includes only A, only B, only C, and combinations of each thereof.

[0042] Concentration, amount and other numerical data can be presented in range format herein.It should be understood that such range format is only used for convenience and simplicity, and should be flexibly interpreted as not only including the numerical value clearly described as range limit, but also including all single numerical values ​​or sub-ranges contained in the range, just as each numerical value and sub-range are clearly described.For example, the numerical range of about 1 to about 4.5 should be interpreted as not only including the limit value of 1 to about 4.5 clearly described, but also including single numerals (such as 2,3,4) and sub-ranges (such as 1 to 3,2 to 4, etc.).The same principle is applicable to the scope of only narrating a numerical value, such as "less than about 4.5", which should be interpreted as including all the above-mentioned values ​​and ranges.In addition, no matter how the breadth of the described range or feature is, this explanation should be applicable.

[0043] Most of the catalytic materials used are powder materials. Using adhesives (PTFE, naphthol, etc.) to make fixed electrodes will also sacrifice a lot of active sites, and there are problems such as catalyst powder aggregation. The self-supporting electrode can not only fully disperse the active sites, but also avoid the introduction of adhesives and the like to occupy the active sites, and has greater potential in improving mass transfer efficiency and practical applications. The integrated electrode material prepared by the electrospinning coupling pyrolysis technology of the present invention can be equipped with a penetrating electrode reactor, which can effectively improve the utilization of atomic hydrogen and the mass transfer efficiency of pollutants compared to the fixed electrodes prepared by adhesives in the prior art. In addition, most of the prior art uses immersed electrodes, and the electrocatalytic reaction usually only occurs on the electrode surface, resulting in low utilization of active sites and pollutant degradation efficiency. In the penetrating reaction mode, water flows vertically through two parallel porous electrodes in turn. Under the action of forced mass transfer, the resistance is greatly reduced, and the extremely narrow space between the electrodes allows the target pollutants to contact more active sites, thereby improving the efficiency of electrohydrogenation and dehalogenation. The self-supporting electrode prepared by the method can match the penetrating reaction system. The product produced by the previous electrode can enter the next electrode as a reactant along with the water flow, thereby improving the removal effect of pollutants and reducing energy consumption.

[0044] The self-supporting electrode prepared by the present invention has many advantages, the most important of which are: (1) it avoids the inactivation of active sites caused by the use of adhesives. (2) The nanofiber electrode prepared by electrospinning has abundant pores and can be equipped with a penetrating electrode reactor. Compared with ordinary flat electrodes (or immersed electrodes), the water flow is forced to pass through the penetrating electrode reactor, so the mass transfer efficiency is high. Atomic hydrogen adsorbed on the Co-based surface can be used immediately. If the atomic hydrogen is not used immediately to participate in the reaction, the two atomic hydrogens will easily turn into hydrogen and leave the water phase, and cannot play a catalytic role.

[0045] In addition, the inventors found that Co is the main electrode material during the experiment, which is a cheap alternative to the precious metal Pd-based materials. The present invention uses ZIF-67 as the Co source. Considering that ZIF-67, as a type of MOF material, has a unique cage structure, it can effectively disperse Co particles and avoid their aggregation and inactivation. The Zn in ZIF-8 has a similar coordination with Co. 2+ Can replace part of Co 2+ With the pyrolysis process, Zn evaporates at high temperature, leaving more vacancies and pores, which not only optimizes the pore structure of the electrode material, but also further avoids the aggregation of Co. As a result, Co is more dispersedly anchored on the binder-free self-supporting Co-N / CNF nanofiber electrode.

[0046] In the present invention, the mass ratio of Co to Zn is 1:4, because only at this ratio can the self-supporting electrode of the present invention have relatively good mechanical properties. If there is too much ZIF-8, the flexibility of the nanofibers is reduced and they are very brittle. The calcination temperature is 950°C because this temperature is higher than the evaporation temperature of Zn, which can make Zn evaporate and fully dissipate to leave vacancies.

[0047] Example

[0048] A method for preparing a Co-N / CNF electrode material comprises the following steps:

[0049] 1) Dissolve 6 mM Co(NO3)2·6H2O and 2.22 mM Zn(NO3)2·6H2O in 6 mL methanol to obtain solution A, dissolve 134 mM 2-methylimidazole in 40 mL methanol to obtain solution B, quickly pour solution A into solution B, seal with plastic wrap and stir;

[0050] 2) The obtained solution was centrifuged at a speed of 9000 r / min for 3 min, washed three times with methanol, and dried in a 60°C oven; 0.6 g of the dried material was added with 6 mL of DMF and ultrasonicated for more than 1 h to disperse; after dispersion, 0.8 g of PAN was added and heated in a water bath for 4 h to obtain an electrospinning precursor, and an electrospinning process was performed to obtain a composite material, which was named Co-ZIF-8 / PAN;

[0051] 3) calcining Co-ZIF-8 / PAN under an inert atmosphere at a heating rate of 5°C / min to 950°C and keeping the temperature for 3 hours to obtain a Co-N / CNF composite.

[0052] The structure of the electrospun composite electrode material obtained in the embodiment was characterized by transmission electron microscopy. Figure 1 shown.

[0053] The structure of the electrospun composite electrode material obtained in the embodiment was characterized by scanning electron microscopy. Figure 2shown.

[0054] The XRD characterization results were used to determine the crystal structure of the material. Figure 3 shown.

[0055] Application Examples

[0056] Experiment on removing pollutants from water using Co-N / CNF electrode materials

[0057] The Co-N / CNF electrode material obtained in the example was filled into a penetrating electrode reactor, which mainly consisted of two plates and a filter membrane in the middle. During the experiment, water was pumped in from a hole on one side of the plate and flowed out from a hole on the other side of the plate back to the beaker, thus achieving the removal of pollutants.

[0058] 100mL of 10mg / L aqueous solutions of halogen-containing pollutants florfenicol (FLO), atrazine (ATZ), trichlorophenol (TCP), and chloramphenicol (CAP) were prepared as simulated wastewater. Before the electrocatalytic process, nitrogen was bubbled into the beaker for 30 minutes. During the electrocatalytic process, after the peristaltic pump was turned on, the solution in the beaker was continuously pumped into the cathode chamber of the penetrating electrode reactor. After the solution entered the anode chamber, it circulated back to the beaker. The timing started when the first drop of liquid flowed out of the peristaltic tube returning to the beaker. Samples were taken at intervals to detect the concentration of pollutants. The results are as follows: Figure 4 shown.

[0059] Depend on Figure 4 It can be seen that the degradation effect of Co-N / CNF electrode materials on various pollutants can reach nearly 100%, among which the degradation of FLO is the fastest.

[0060] Taking 10mg / L aqueous solution containing pollutant FLO as an example, a simulated wastewater pH test was conducted. Figure 5 It can be seen that during the experiment, the pH was adjusted and it was found that FLO had a good degradation effect in the pH range of 3-9, indicating that it has a relatively wide range of applicability in the actual application of water treatment processes.

[0061] During the experiment, the reaction was carried out by cyclic voltammetry (CV) under a standard three-electrode system, in which the prepared electrode material was the working electrode, the platinum wire electrode was the counter electrode, the Ag / AgCl electrode was the reference electrode, the electrolyte was 1 M sodium sulfate solution, the CV voltage window was -1.5-0.5 V, and the scan rate of the CV test was 50 mV s -1 There is an obvious H* response in the reaction, such as Figure 6 shown.

[0062] During the experiment, an electron paramagnetic resonance spectrometer (EPR) was used to measure the active species produced during the reaction, and DMPO was used to capture atomic hydrogen. The EPR experiment showed that Co-N / CNF could observe the same peak as Pd / C, which was a nine-fold peak of atomic hydrogen. The test conditions were: [FLO] = 10.0 mg L -1 ,

[0063] [Na2SO4] = 50 mM, pH = 6, [catalyst] = 0.2 g L -1 , current density, 2.5 mA cm -1 , as attached Figure 7 shown.

[0064] Figure 8 The performance comparison of Co-N / CNF and traditional precious metal materials on FLO removal is shown, that is, the performance effect diagram of various electrode materials on FLO removal, wherein the various electrode materials include Co-N / CNF prepared in the embodiment of the present invention, as well as Co-N / C, Pd / C and Pt / C. In the flat plate mode: [FLO] = 10.0 mg L -1 , [Na2SO4] = 50 mM, pH = 6, [catalyst] = 0.2 g L -1 , current density, 2.5 mA cm -2 Tested under conditions.

[0065] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a non-precious metal Co-N / CNF electrode material, characterized in that: The steps include: 1) Rapidly add the methanol mixture containing Co salt and Zn salt into the methanol solution of 2-methylimidazole and stir to react; 2) After the obtained reaction solution is centrifuged, washed and dried, the obtained Co-ZIF-8 material is added to N,N-dimethylformamide and ultrasonically dispersed; 3) adding polyacrylonitrile to the dispersion obtained in step 2), and heating in a water bath to obtain an electrospinning precursor solution; 4) Co-ZIF-8 / PAN composite material was obtained by electrospinning; 5) The obtained Co-ZIF-8 / PAN composite material is calcined under an inert atmosphere to obtain a Co-N / CNF electrode material.

2. The method according to claim 1, characterized in that The Co salt is Co(NO3)2·6H2O, the Zn salt is Zn(NO3)2·6H2O, and the mass ratio of Co to Zn is 1:

4.

3. The method according to claim 1, characterized in that The mass ratio of 2-methylimidazole to Co salt and Zn salt is 22:1:0.

02.

4. The method according to claim 1, characterized in that In step 1), the reaction was stirred for 6 h.

5. The method according to claim 1, characterized in that The mass ratio of Co-ZIF-8 material and PAN is 3:

4.

6. The method according to claim 1, characterized in that The electrospinning parameters are: spinning voltage is 10-20 kV, receiving distance is 10-20 cm, and injection speed is fixed at 0.08 mm min -1 .

7. The method according to claim 1, characterized in that The calcination was carried out at a heating rate of 5°C / min to 950°C and kept at this temperature for 3 hours.

8. A Co-N / CNF electrode material prepared by the method according to any one of claims 1 to 7.

9. Use of the Co-N / CNF electrode material prepared by the method according to any one of claims 1 to 7 in removing pollutants from wastewater.

10. The use according to claim 9, characterized in that The pollutants include florfenicol; and the pH of the wastewater to be treated is 3-9.

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