A novel Fe / Co-npc self-supporting electrode and a preparation method and application thereof

Abstract

The application discloses a novel Fe / Co-NPC self-supporting electrode and a preparation method and application thereof. The preparation method comprises the following steps: S1, preparing Fe / Co-MOF; S2, grinding sucrose, carbon black and Fe / Co-MOF in a mass ratio of 100-10:200-20:1 and melamine-formaldehyde resin in an un-solidified state, the use amount of the melamine-formaldehyde resin is 1-1.5 mL / g (sucrose+carbon black); S3, compressing and molding the substance after grinding in the step S2 to obtain a molded piece; S4, carbonizing the molded piece at 600-1000 DEG C. The novel Fe / Co-NPC self-supporting electrode has a large specific surface area, rich mesopores and good oxygen reduction reaction (ORR) activity, the hardness is 35.8-37.7 HV 1, and the loss rate of Fe and Co is 0.17%-0.2% after continuous electrolysis for 24 h. The novel Fe / Co-NPC self-supporting electrode is not easy to fall off, reduces the loss of Fe / Co-MOF material, the Fe / Co-MOF material in the electrode has strong catalytic activity, the mechanical strength is high, the stability is strong, and the electrode is suitable for a heterogeneous electro-Fenton system and can efficiently, stably and sustainably degrade macromolecular organic pollutants for multiple times.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of water pollution control, and more particularly to a novel Fe / Co-NPC self-supporting electrode and a preparation method and application thereof. BACKGROUND

[0002] Macromolecular organic pollutants have complex molecular structures (such as cationic xanthene dye rhodamine B-RhB, polychlorinated biphenyls PCBs, dioxins, etc.), and they degrade slowly in the natural environment and can be stored in soil, sediment and water for a long time.

[0003] Traditional treatment methods such as physical methods (sedimentation, adsorption), biological methods (anaerobic digestion, activated sludge method, biological filter) have poor treatment effect on macromolecular organic pollutants, and chemical advanced oxidation processes can be used for deep degradation, such as heterogeneous electro-Fenton (HEF) system. The HEF system generates H2O2 through electrode catalysis to occur oxygen reduction reaction, and the Fenton reaction occurs between H2O2 and ferrous in the system, which effectively degrades the refractory organic pollutants. Studies have shown that the H2O2 production capacity and Fenton catalytic performance in the HEF system are limited by the type and structure of the catalyst. At present, common methods are to dope metal (or non-metal) elements to regulate the electronic structure of the HEF catalyst, thereby improving the performance of the HEF catalyst, but a large amount of catalyst components are easy to fall off from the electrode surface and are not easy to recover, which not only makes it difficult to guarantee the effect of degrading organic matter, but also causes secondary pollution.

[0004] Therefore, there is currently a lack of HEF system electrodes that are stable and efficient in degrading macromolecular organic pollutants. SUMMARY

[0005] In view of the above shortcomings of the prior art, the purpose of the present application is to provide an HEF system electrode that is stable and efficient in degrading macromolecular organic pollutants, and a preparation method and application thereof.

[0006] More specifically, in a first aspect, the present application provides a preparation method of a novel Fe / Co-NPC self-supporting electrode, comprising the following steps:

[0007] S1, preparing Fe / Co-MOF;

[0008] S2, grinding sucrose, carbon black and the Fe / Co-MOF in a mass ratio of 100-10:200-20:1, and melamine-formaldehyde resin in an un-solidified state, the use amount of the melamine-formaldehyde resin being 1-1.5 mL / g (sucrose+carbon black);

[0009] S3, pressing the ground material in step S2 to form a molded part;

[0010] S4, carbonizing the shaped piece at 600-1000℃.

[0011] Preferably, step S1 comprises: FeCl3·6H2O, Co(NO3)2·6H2O and terephthalic acid are reacted at a molar ratio of 1-3:1-5:1-3 at 100-120℃ to prepare Fe / Co-MOF.

[0012] Preferably, step S1 comprises: FeCl3·6H2O, Co(NO3)2·6H2O and terephthalic acid are reacted at a molar ratio of 3:1:2 at 110℃ for 24h to prepare Fe / Co-MOF.

[0013] Preferably, the amount of formaldehyde solution used in the preparation of melamine-formaldehyde resin is 3-12g melamine per 10mL formaldehyde.

[0014] Preferably, the amount of formaldehyde solution used in the preparation of melamine-formaldehyde resin is 3-12g melamine per 10mL formaldehyde.

[0015] Preferably, step S2 comprises: sucrose, carbon black and Fe / Co-MOF in a mass ratio of 100:200:1 and melamine-formaldehyde resin in an un-solidified state are ground, and the amount of melamine-formaldehyde resin used is 1-1.5mL / g (sucrose+carbon black).

[0016] In a second aspect, the application provides a novel Fe / Co-NPC self-supporting electrode, which is prepared by the above-mentioned method for preparing a novel Fe / Co-NPC self-supporting electrode.

[0017] Preferably, the novel Fe / Co-NPC self-supporting electrode is in a block shape, and / or the hardness of the novel Fe / Co-NPC self-supporting electrode is 35.8-37.7HV 1.

[0018] Preferably, the loss rate of Fe and Co of the novel Fe / Co-NPC self-supporting electrode is 0.17%-0.2% after 24h continuous electrolysis.

[0019] In a third aspect, the application provides a heterogeneous electro-Fenton reaction system, which uses the above-mentioned novel Fe / Co-NPC self-supporting electrode as a cathode.

[0020] In a fourth aspect, the application provides the use of the above-mentioned novel Fe / Co-NPC self-supporting electrode or the above-mentioned heterogeneous electro-Fenton reaction system in the degradation of macromolecular organic pollutants.

[0021] Preferably, the macromolecular organic pollutants are RhB.

[0022] The technical solution of the present application achieves the following technical effects:

[0023] 1. The novel Fe / Co-NPC self-supporting electrode of the present application is suitable for a heterogeneous electro-Fenton (HEF) system, which can not only efficiently and stably degrade macromolecular organic pollutants (such as RhB), but also realize sustainable multiple use through recycling and processing.

[0024] 2. The novel Fe / Co-NPC self-supporting electrode of the present application, due to the addition of sucrose and carbon black, after high-temperature carbonization, the pore structure is affected by the pyrolysis process, volatile release and carbon skeleton reorganization, generating a large number of microporous and mesoporous structures, on the one hand, the Fe / Co-NPC self-supporting electrode has a large specific surface area, and the Fe / Co-MOF is more uniformly doped; on the other hand, it provides abundant active sites and gas transmission channels, improves the oxygen reduction reaction (ORR) activity; on the other hand, it enhances the conductivity of the self-supporting electrode, reduces the charge transfer resistance, and is more conducive to the transfer of electrons.

[0025] 3. The novel Fe / Co-NPC self-supporting electrode of the present application, due to the addition of melamine-formaldehyde resin, introduces N element, changes the internal electron density distribution, optimizes the O2 reduction path, and effectively improves the oxygen reduction reaction (ORR) activity; at the same time, the N-C bond structure enhances the chemical stability of the electrode compared with C-C.

[0026] 4. Compared with the existing powdered Fe / Co-MOF material which is carbonized and then smeared on the electrode (easy to fall off), the novel Fe / Co-NPC self-supporting electrode of the present application is a formed piece (such as a block), on the one hand, it is not easy to fall off, reducing the loss of Fe / Co-MOF material (the loss rate of Fe and Co is 0.17%~0.2% after 24h continuous electrolysis), on the other hand, the Fe / Co-MOF material inside the electrode also has strong catalytic activity and is not easy to be inactivated; on the other hand, it has a certain hardness (35.8-37.7HV 1), high mechanical strength and strong stability, which can greatly improve the number of cycles.

[0027] 5. The novel Fe / Co-NPC self-supporting electrode of the present application has less Fe and Co leaching, good stability, easy to recycle, and the electrode after recycling still has a high degradation rate on macromolecular organic pollutants.

[0028] The concept, specific structure and technical effects of the present application will be further described below with reference to the accompanying drawings, so as to fully understand the purpose, features and effects of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is the finished product figure of the novel Fe / Co-NPC self-supporting electrode of the present application.

[0030] Figure 2 is the scanning electron microscope figure of the novel Fe / Co-NPC self-supporting electrode of the present application.

[0031] Figure 3 is the elemental mapping figure of the novel Fe / Co-NPC self-supporting electrode of the present application.

[0032] Figure 4 is the XRD spectrum figure of the novel Fe / Co-NPC self-supporting electrode of the present application.

[0033] Figure 5 is the FTIR spectrum figure of the novel Fe / Co-NPC self-supporting electrode of the present application.

[0034] Figure 6 is the nitrogen adsorption-desorption curve figure of the novel Fe / Co-NPC self-supporting electrode of the present application.

[0035] Figure 7 is the pore size distribution figure of the novel Fe / Co-NPC self-supporting electrode of the present application.

[0036] Figure 8 is the XPS spectrum figure of the novel Fe / Co-NPC self-supporting electrode of the present application.

[0037] Figure 9 is the CV curve figure comparing the novel Fe / Co-NPC self-supporting electrode of the present application and the NPC electrode of undoped Fe / Co-MOF.

[0038] Figure 10 shows the Vickers hardness of Fe / Co-NPC before carbonization, about 40HV 1.

[0039] Figure 11 shows the Vickers hardness of Fe / Co-NPC after carbonization, between 35.8-37.7HV 1.

[0040] Figure 12 is the schematic diagram of the heterogeneous electro-Fenton reaction system of the present application.

[0041] Figure 13 is the degradation effect figure of the heterogeneous electro-Fenton reaction system of the present application on RhB wastewater when the initial applied current is 0, 25, 50, 100, 150 mA, respectively.

[0042] Figure 14 is the degradation effect figure of the heterogeneous electro-Fenton reaction system of the present application after multiple cycles.

[0043] Figure 15The figure shows the change of degradation rate K of the heterogeneous electro-Fenton reaction system of the present application after multiple cycles.

[0044] Figure 16 The figure shows the change of Fe and Co metal ion leaching amount of the heterogeneous electro-Fenton reaction system of the present application after multiple cycles.

[0045] Figure 17 The figure shows the degradation effect of the heterogeneous electro-Fenton reaction system of the present application on wastewater with different concentrations of RhB. DETAILED DESCRIPTION

[0046] The embodiments of the present application will be described in detail below with specific reference to specific examples. Those skilled in the art can easily understand other advantages and effects of the present application from the disclosure of the present specification. The present application can also be implemented or applied in other different specific embodiments, and various modifications or changes can be made to the details in the specification based on different views and applications without departing from the spirit of the present application. It should be noted that the following examples and features in the examples can be combined with each other without conflict.

[0047] Some example embodiments of the present application are described for illustrative purposes. It should be understood that the present application can be implemented in other ways not specifically shown in the drawings.

[0048] “NPC” stands for Nitrogen-Doped Porous Carbon, i.e. nitrogen-doped porous carbon material.

[0049] In a first aspect, the present application discloses a preparation method of a novel Fe / Co-NPC self-supporting electrode. The method is to hydrothermally synthesize a Fe / Co-doped precursor (Fe / Co-MOF), and then mix and press sucrose, carbon black and melamine-formaldehyde resin to form a Fe / Co-NPC self-supporting electrode after carbonization. The synthesis method involves a series of pyrolysis, carbonization, metal reduction and nitrogen-doping reactions of raw materials, and finally forms a composite material of high-conductivity N-doped porous carbon loaded with Fe / Co nanoparticles.

[0050] The above synthesis method generally includes the following steps: S1, preparing Fe / Co-MOF; S2, grinding a certain proportion of sucrose, carbon black and Fe / Co-MOF, and melamine-formaldehyde resin in a non-solidified state; S3, pressing the ground material in step S2 to form a molded part; S4, carbonizing the molded part obtained in step S3. Each step will be described in detail below.

[0051] 1. Preparation of Fe / Co-MOF

[0052] The raw materials FeCl3·6H2O, Co(NO3)2·6H2O and terephthalic acid and the solvent N,N-dimethylformamide (DMF) are added to a reactor, and after stirring at room temperature to make them completely dissolved, the reaction is transferred to a high-pressure reaction kettle for hydrothermal reaction. The molar ratio of FeCl3·6H2O, Co(NO3)2·6H2O and terephthalic acid is 1-3:1-5:1-3, for example, it can be 3:1:2, 1:1:1, 1:5:3, it should be understood that the listed several ratios do not constitute a limitation of the present application, and those skilled in the art can select within the range of 1-3:1-5:1-3 or adjust according to the actual situation. The hydrothermal reaction conditions are 100-120℃ for 22-26h. For example, it can be reacted at 110℃ for 24h, at 120℃ for 22h, etc.

[0053] After the hydrothermal reaction is completed, the reaction kettle is naturally cooled, and a brown solid is obtained by centrifugation, and then washed with DMF and ethanol respectively by centrifugation for several times, and then placed in a vacuum drying oven for vacuum drying, to obtain a brownish yellow powder, i.e. Fe / Co-doped metal organic framework compound (Fe / Co-MOF). The purpose of placing in a vacuum drying oven for drying is to remove the solvent (such as water, alcohol, etc.) and residual impurities in it, while maintaining the structural integrity of the material, to ensure the performance stability of the Fe / Co-MOF. For example, it can be vacuum dried in a vacuum drying oven at 60℃ for 12h, and those skilled in the art can make corresponding adjustments to the drying temperature and time as long as the above purpose is achieved.

[0054] 2. Preparation of melamine-formaldehyde resin

[0055] The melamine-formaldehyde resin in the present application can be prepared by itself or directly purchased from the market, and the nitrogen content of the melamine-formaldehyde resin is preferably 30wt%-48wt%. The self-preparation method of the melamine-formaldehyde resin is introduced below.

[0056] Take 10mL formaldehyde solution (concentration 35%-40%, for example 38%) in a 50mL beaker, add 0.024g urotropin and stir, then heat on a graphite plate at 100℃, then add 3g-12g melamine and continuously stir until the solution is clear, continue to heat for 10min to obtain the melamine-formaldehyde resin.

[0057] It should be understood that those skilled in the art can adjust the reaction time, reaction temperature and dosage of the materials according to the above method, and when a larger amount of melamine-formaldehyde resin is needed, the above raw materials can be increased in the same proportion.

[0058] 3. Novel Fe / Co-NPC self-supporting electrode

[0059] Put sucrose, carbon black and the prepared Fe / Co-MOF into a grinding pot, add melamine-formaldehyde resin in un-solidified state (which can be commercially available or self-prepared by the above method). Put the grinding pot into a grinder, take out the mud-like solid after sufficient grinding, and put it into a press to shape and press into a shaped piece after the hardness is slightly suitable, then put it into a vacuum drying oven for drying, and then carbonize the dried shaped piece at high temperature, and finally perform subsequent cleaning and drying steps to obtain the target product, a novel Fe / Co-NPC self-supporting electrode.

[0060] In the formula, the mass ratio of sucrose, carbon black and Fe / Co-MOF is 100-10:200-20:1, for example, it can be 100:200:1, 20:40:1, 10:20:1, and it should be understood that the listed several ratios do not constitute a limitation of the present application, and those skilled in the art can select within the range of 100-10:200-20:1 or adjust according to actual conditions.

[0061] The amount of melamine-formaldehyde resin used is 1-1.5 mL / g (sucrose + carbon black), and the amount of melamine-formaldehyde resin used is related to the total mass of sucrose and carbon black, for example, if the total mass of sucrose and carbon black is 2 g, then the amount of melamine-formaldehyde resin used is 2-3 mL. The reason for choosing un-solidified melamine-formaldehyde resin is to mix more uniformly and fully with sucrose, carbon black and Fe / Co-MOF during grinding.

[0062] The "after the hardness is slightly suitable" in "after the hardness is slightly suitable, put it into a press to shape and press" can be understood as slightly cold, and the purpose is to facilitate subsequent pressing and molding. It should be understood that the degree of slight hardness or the degree of slight coldness can be selected according to actual conditions or the experience of those skilled in the art, as long as subsequent pressing and molding can be achieved.

[0063] The thickness of the shaped piece is selected to be greater than 2 mm, preferably 2-5 mm, and if it is too thin, it is easy to break during subsequent high-temperature carbonization. The shape of the shaped piece is not required in the present application, which can be regular shapes such as circular, square, polygonal, etc., or irregular shapes.

[0064] The purpose of putting the shaped piece into a vacuum drying oven for drying is to remove solvents and water (such as water in the resin or humidity generated during grinding, and the residual solvents and water will affect the subsequent structural stability), and during subsequent high-temperature heat treatment (such as carbonization), the structure will not collapse due to solvent evaporation or instability. The drying condition is preferably 210-230°C for 1.5-2.5h to promote the preliminary solidification of melamine-formaldehyde resin and improve the mechanical strength of the material.

[0065] The high-temperature carbonization can be carried out in a tube furnace. After drying, the shaped piece is placed in a tube furnace, and is subjected to high-temperature carbonization at 600-1000°C for 100-140 min at a temperature rising rate of 5-8°C / min under N2 atmosphere, and is taken out after natural cooling. The reaction process of high-temperature carbonization mainly includes three stages: a low-temperature stage, a medium-temperature stage and a high-temperature stage. In the low-temperature stage (<300°C), the melamine-formaldehyde resin in the shaped piece is crosslinked and cured, the sucrose is partially dehydrated, and an early thermal decomposition process occurs to form a preliminary carbonized precursor. In the medium-temperature stage (300-600°C), the melamine-formaldehyde resin decomposes to release NH3, H2O, CO2 and CO to form a N-doped carbon skeleton, the structure of Fe / Co-MOF collapses, the organic ligand (terephthalic acid) decomposes at 350-500°C to obtain Fe and Co ions, and the sucrose pyrolyzes to form amorphous carbon and nitrogen-doped carbon (N-C), and at this time, the Fe and Co ions interact with the resin and sucrose carbonization products. In the high-temperature stage (600-800°C), the carbonization and metal reduction processes mainly occur, the melamine-formaldehyde resin and sucrose are completely carbonized to form a high-conductivity N-C structure, the Fe / Co ions combine with carbon black and sucrose carbon skeleton to form Fe / Co metal nanoparticles, and part of the Fe / Co still exists in the form of oxide, and at the same time, the Fe / Co atoms combine with the nitrogen-doped carbon matrix to form a Fe-N4 / Co-N4 structure.

[0066] After the addition of sucrose and carbon black, the pore structure of the shaped piece after high-temperature carbonization is affected by the pyrolysis process, the release of volatile matter and the recombination of carbon skeleton, and a large number of microporous and mesoporous structures are generated. On the one hand, the shaped piece has a large specific surface area, and the Fe / Co-MOF is more uniformly doped; on the other hand, a large number of active sites and gas transmission channels are provided to improve the oxygen reduction reaction (ORR) activity; and on the other hand, the conductivity of the self-supporting electrode is enhanced, and the charge transfer resistance is reduced, which is more conducive to the transfer of electrons.

[0067] The addition of melamine-formaldehyde resin introduces N element, changes the internal electron density distribution, optimizes the O2 reduction path, and effectively improves the oxygen reduction reaction (ORR) activity; at the same time, the N-C bond structure enhances the chemical stability of the electrode compared with C-C.

[0068] The shaped piece taken out after carbonization is naturally cooled, soaked in dilute hydrochloric acid, washed with deionized water for several times, and then placed in a vacuum drying oven (50-70°C) for constant temperature drying for 10-14 h to obtain a Fe / Co-NPC self-supporting electrode.

[0069] In a second aspect, the application provides a Fe / Co-NPC self-supporting electrode prepared by the above method. Preferably, the novel Fe / Co-NPC self-supporting electrode is in a block shape, has a hardness of 35.8-37.7 HV 1, and a Fe and Co loss rate of 0.17%-0.2% after 24 h of continuous electrolysis. Compared with the existing Fe / Co-MOF material which is in a powder form and is coated on the electrode after carbonization (easily falling off), the novel Fe / Co-NPC self-supporting electrode of the application is in a formed piece (for example, a block shape), which is not easy to fall off on one hand, thereby reducing the loss of Fe / Co-MOF material; on the other hand, the Fe / Co-MOF material inside the electrode also has strong catalytic activity and is not easy to be deactivated; and on the other hand, the electrode has a certain hardness (35.8-37.7 HV 1), high mechanical strength and strong stability, and can greatly improve the number of cycles. The electrode is suitable for a heterogeneous electro-Fenton system (as a cathode), which can not only efficiently and stably degrade macromolecular organic pollutants, but also can be recycled and processed to achieve sustainable multiple use.

[0070] In a third aspect, the application provides a heterogeneous electro-Fenton reaction system, which uses the novel Fe / Co-NPC self-supporting electrode prepared by the above method as a cathode, and a platinum sheet electrode can be selected as an anode. The system can deeply degrade macromolecular organic pollutants. The specific reaction mechanism is as follows:

[0071] O2 is reduced to active oxygen H2O2 and ·O2 on the surface of the electrode - , H2O2 is further converted to ·OH under the action of Fe 2+ . The large porosity of Fe / Co-NPC makes H2O2 easy to undergo a Fenton-like reaction with metal sites. Under the action of H2O2, Fe 2+ is oxidized to Fe 3+ , and strong oxidizing ·OH is generated at the same time. Then, Fe 3+ is reduced to Fe 2+ by Co 0 , Fe 2+ and other particles to re-enter the oxygen reduction process, thereby achieving a dynamic cycle process of Fe and Co. The main reaction process is shown in formulas (1-6). Macromolecular organic pollutants are oxidized by ·OH / ·O2 - , degraded through multiple steps (such as N-deethylation process, chromophore rupture, ring opening, mineralization, etc., it should be understood that the degradation process is different for different organic substances), and finally oxidized to simple inorganic substances such as carbon dioxide, as shown in formula (7).

[0072] O2+e - →·O2 - (1)

[0073] O2+2H+ + 2e - → H2O2 (2)

[0074] Fe 2+ + H2O2 → Fe 3+ + ·OH + OH - (3)

[0075] Fe 3+ + CO 2+ → Fe 2+ + Co 3+ (4)

[0076] 2Fe 3+ + Fe 0 → 3Fe 2+ (5)

[0077] Fe 3+ / Co 3+ + H2O2 → Fe 2+ / Co 2+ + ·O2 - + 2H + (6)

[0078] Macromolecular organic pollutants + ·OH / ·O2 - → …… → H2O + CO2 (7)

[0079] The above heterogeneous electro-Fenton reaction system has the ability to efficiently and stably degrade macromolecular pollutants, wherein the novel Fe / Co-NPC self-supporting electrode has higher electrical conductivity and ORR catalytic activity, achieves the purpose of deep degradation of macromolecular organic pollutants, and is easy to recover and reuse.

[0080] In a fourth aspect, the application provides an application of the above novel Fe / Co-NPC self-supporting electrode or the above heterogeneous electro-Fenton reaction system in degrading macromolecular organic pollutants. The application presents the degradation effect of the above novel Fe / Co-NPC self-supporting electrode or the above heterogeneous electro-Fenton reaction system by taking the example of the refractory macromolecular organic pollutant RhB. It should be understood that RhB does not constitute a limitation on the types of macromolecular organic pollutants that can be degraded by the application, and in addition to RhB, the novel Fe / Co-NPC self-supporting electrode or the above heterogeneous electro-Fenton reaction system of the application can still degrade almost all other macromolecular organic pollutants.

[0081] Example 1 Preparation of novel Fe / Co-NPC self-supporting electrode

[0082] 1. Preparation of Fe / Co-MOF

[0083] 4.5 mmol of FeCl3·6H2O, 1.5 mmol of Co(NO3)2·6H2O, 3.0 mmol of p-phenylenediamine, were added into a solution containing 35 mL of DMF, and after complete dissolution by magnetic stirring at room temperature, the solution was transferred into a high-pressure reaction kettle, and was reacted at 110°C for 24 h. After natural cooling, a brown solid was obtained by centrifugation, and was washed with DMF and ethanol by centrifugation for several times, and was placed in a vacuum drying box at 60°C for vacuum drying for 12 h, to obtain a brownish yellow powder Fe / Co-MOF.

[0084] 2. Preparation of melamine-formaldehyde resin

[0085] 10 mL of 38% formaldehyde solution was added into a 50 mL beaker, and after stirring after adding 0.024 g of urotropine, the solution was heated on a graphite plate at 100°C, while 6.3 g of melamine was added and stirred until the solution was clear, and the heating was continued for 10 min, to obtain melamine-formaldehyde resin.

[0086] 3. Novel Fe / Co-NPC self-supporting electrode

[0087] 1 g of sucrose, 2 g of carbon black and 100 mg of Fe / Co-MOF were taken in a grinding tank, and 4 mL of the hot melamine-formaldehyde resin prepared above without cooling and solidification was added. After grinding by a grinder, a muddy solid was obtained, which was placed in a press to be molded into a round block with a diameter of 20 mm and a thickness of 2 mm, and was placed in a vacuum drying box for drying at 220°C for 2 h. The round block was placed in a tube furnace, and was carbonized at 800°C for 120 min under the atmosphere of 0.5 L / min of N2 at a heating rate of 7°C / min. After natural cooling, the round block was taken out, and was soaked in 0.1 mol / L HCl for 20 min, and was washed with deionized water for several times, and was placed in a vacuum drying box for constant temperature drying at 60°C for 12 h, to obtain a novel Fe / Co-NPC self-supporting electrode (as shown in Figure 1 ).

[0088] The morphology of the novel Fe / Co-NPC self-supporting electrode prepared in this embodiment was observed by a scanning electron microscope, and the result is shown in Figure 2 . It can be seen that the surface of the Fe / Co-NPC self-supporting electrode is rough, and has developed pores.

[0089] Figure 3 The energy spectrum shown in indicates that the Fe / Co-NPC self-supporting electrode is mainly composed of C, N, O, Fe and Co, and is uniformly distributed, and has a good doping effect.

[0090] Figure 4The crystal phase structure of the Fe / Co-NPC self-supporting electrode was analyzed by X-ray diffractometer (XRD), and obvious diffraction peaks appeared at 2θ = 25.5° and 43.5°, indicating that the self-supporting electrode had been partially graphitized and belonged to amorphous carbon.

[0091] Figure 5 The functional group changes of the Fe / Co-NPC self-supporting electrode before and after carbonization were analyzed by Fourier infrared spectrometer FTIR, and obvious absorption peaks appeared at 1650 and 3440 cm -1 of the Fe / Co-NPC self-supporting electrode before and after carbonization at 800°C, which were respectively caused by the stretching vibration of C=O and -OH. By comparing the absorption peak intensity before and after carbonization, it was found that the peak intensity at 1650 cm -1 was slightly enhanced after carbonization, indicating that the number of C=O increased slightly after carbonization. Absorption peaks appeared at 1420 and 1530 cm -1 before carbonization, which were related to the stretching vibration of C-N and the bending vibration of NH. After carbonization, the two absorption peaks disappeared.

[0092] Figure 6 and Figure 7 The specific surface area and pore characteristics of the Fe / Co-NPC self-supporting electrode were tested by a full-automatic specific surface and porosity analyzer BET, and the nitrogen adsorption / desorption curve of the Fe / Co-NPC self-supporting electrode was type IV isotherm, and H4 type hysteresis loop appeared in the middle region. The specific surface area of the Fe / Co-NPC self-supporting electrode was 455.7181 m 2 / g, the average pore size was 3.3086 nm, and the average mesopore size was 3.7629 nm. Combined with the pore size distribution graph ( Figure 7 ), it can be concluded that the pore type of Fe / Co-NPC is mainly mesopore and micropore.

[0093] Figure 8 The functional groups and element valence states of the Fe / Co-NPC self-supporting electrode were analyzed by XPS, and it was concluded from the spectrum ( Figure 8 a) that the Fe / Co-NPC self-supporting electrode contained five elements of C, N, O, Fe and Co, which was consistent with the SEM characterization analysis result. The C1s spectrum ( Figure 8 b) could be divided into five parts of 248.8 eV (C-C / C=C bond), 285.22 eV (C-N bond), 286.43 eV (C-O bond), 288.48 eV (O-C=O bond) and 291.25 eV (π-π* satellite peak). From the O1s spectrum ( Figure 8 c), it can be seen that there are three forms of oxygen, which are C=O (531.95 eV), C-O (533.32 eV) and Fe-O (529.85 eV). The N 1s spectrum (Figure 8 In d), the three peaks at 398.80, 400.50, and 401.40 eV correspond to three nitrogen species: pyridine N, pyrrole N, and graphitic N, respectively. Among them, pyrrole N exhibits excellent catalytic selectivity for two-electron ORR. Fe 2p spectrum ( Figure 8 In e), the peak at 706.95 eV is attributed to Fe. 0 The peaks at 710.45 and 723.25 eV are attributed to Fe. 2+ Fe 3+ The binding energies of the corresponding peaks are 712.68 eV and 725.42 eV. The peaks at 715.57 and 728.25 eV correspond to Fe... 2+ The satellite peaks at 719.56 and 732.38 eV correspond to Fe. 3+ The satellite peak. In the Co2p spectrum ( Figure 8 In f), the peaks at 779.87 eV and 782.91 eV are attributed to Co 2p3 / 2, respectively. 2+ With Co 3+ The peaks at 793.52 eV and 798.34 eV correspond to the Co ions of Co 2p1 / 2, respectively. 2+ With Co 3+ Correspondingly, the binding energies of the two satellite peaks of Co are 787.13 and 802.36 eV, respectively.

[0094] To investigate the catalytic activity of the Fe / Co-NPC self-supported electrode, the CV curves of the Fe / Co-NPC self-supported electrode and the NPC electrode without Fe / Co-MOF were compared. The results are as follows: Figure 9 As shown, the CV curve of the NPC electrode basically presents a rectangular background, indicating that almost no oxygen reduction reaction occurred. However, the Fe / Co-NPC self-supporting electrode shows a curve that is inconsistent with that of the NPC electrode. The reduction peak of the Fe / Co-NPC self-supporting electrode appears between -0.15 and -0.05 V, indicating that an oxygen reduction reaction occurred on the Fe / Co-NPC self-supporting electrode, and it has higher catalytic activity and is more conducive to electron transfer.

[0095] To investigate the hardness and strength of the prepared Fe / Co-NPC self-supporting electrode before and after carbonization, the Vickers hardness of the Fe / Co-NPC self-supporting electrode was tested before and after high-temperature carbonization. Three points on the material were evaluated at each stage. Before carbonization, the Vickers hardness of Fe / Co-NPC was approximately 40 HV 1 ( Figure 10 After carbonization, its Vickers hardness is between 35.8 and 37.7 HV 1. Figure 11). This is because the carbonization process leads to the decomposition of the electrode material and the escape of the pores, resulting in an increase in the specific surface area and a slight decrease in hardness, but still has a certain compressive strength, ensuring its stability and integrity under hydraulic impact conditions, which is beneficial for recycling.

[0096] Example 2 Preparation of a novel Fe / Co-NPC self-supporting electrode

[0097] 1. Preparation of Fe / Co-MOF

[0098] 1.5 mmol of FeCl3·6H2O, 1.5 mmol of Co(NO3)2·6H2O and 4.5 mmol of terephthalic acid were added to a solution containing 35 mL of DMF, and after complete dissolution under magnetic stirring at room temperature, it was transferred to a high-pressure reaction kettle and reacted at 100°C for 26 h. After natural cooling, a brown solid was obtained by centrifugation, and then washed with DMF and ethanol by centrifugation several times, and then placed in a 60°C vacuum drying oven for 12 h to obtain a brownish yellow powder Fe / Co-MOF.

[0099] 2. Preparation of melamine-formaldehyde resin

[0100] 10 mL of 35% formaldehyde solution was added to a 50 mL beaker, 0.024 g of urotropine was added and stirred, and then heated to 100°C on a graphite plate, while 3.0 g of melamine was added and continuously stirred until the solution was clear. After 10 min of continuous heating, melamine-formaldehyde resin was obtained.

[0101] 3. Novel Fe / Co-NPC self-supporting electrode

[0102] 10 g of sucrose, 20 g of carbon black and 100 mg of Fe / Co-MOF were taken in a grinding tank, and 30 mL of the aforementioned hot melamine-formaldehyde resin which had not been cooled and solidified was added. After grinding with a grinder, a muddy solid was obtained, which was placed in a press after the hardness was slightly suitable, and was pressed into a circular block with a diameter of 20 mm and a thickness of 5 mm, and was placed in a vacuum drying oven at 210°C for 2.5 h. The circular block was placed in a tube furnace and carbonized at 600°C for 140 min under a N2 atmosphere of 0.5 L / min at a heating rate of 6°C / min. After natural cooling, it was taken out and soaked in 0.1 mol / L HCl for 20 min, then washed with deionized water several times and placed in a vacuum drying oven at 50°C for 14 h. Finally, a novel Fe / Co-NPC self-supporting electrode was obtained (the performance parameters of this electrode are similar to those of the electrode prepared in Example 1, and are not described here).

[0103] Example 3 Preparation of a novel Fe / Co-NPC self-supporting electrode

[0104] 1. Preparation of Fe / Co-MOF

[0105] 4.5 mmol of FeCl3·6H2O, 7.5 mmol of Co(NO3)2·6H2O and 4.5 mmol of p-phenylenediamine were added to a solution containing 35 mL of DMF, and after complete dissolution by magnetic stirring at room temperature, the solution was transferred to a high-pressure reaction kettle and reacted at 120°C for 22 h. After natural cooling, a brown solid was obtained by centrifugation, and then washed with DMF and ethanol by centrifugation several times, and then placed in a vacuum drying oven at 60°C for 12 h to obtain a brownish yellow powder of Fe / Co-MOF.

[0106] 2. Preparation of melamine-formaldehyde resin

[0107] 10 mL of 40% formaldehyde solution was added to a 50 mL beaker, 0.024 g of urotropine was added and stirred, and after complete dissolution, it was heated on a graphite plate at 100°C, while 12.0 g of melamine was added and continuously stirred until the solution was clear. After 10 min of continuous heating, melamine-formaldehyde resin was obtained.

[0108] 3. Preparation of novel Fe / Co-NPC self-supporting electrode

[0109] 1 g of sucrose, 2 g of carbon black and 100 mg of Fe / Co-MOF were taken in a grinding tank, and 4.5 mL of the aforementioned hot melamine-formaldehyde resin which had not been cooled and solidified was added. After grinding by a grinder, a muddy solid was obtained, which was placed in a press after the hardness was slightly suitable, and was pressed into a round block with a diameter of 20 mm and a thickness of 3 mm, and was placed in a vacuum drying oven at 230°C for 1.5 h. The round block was placed in a tube furnace, and was carbonized at 1000°C for 100 min under the atmosphere of 0.5 L / min N2 at a heating rate of 8°C / min. After natural cooling, it was taken out and soaked in 0.1 mol / L HCl for 20 min, and then washed with deionized water several times and placed in a vacuum drying oven at 70°C for 10 h to obtain a novel Fe / Co-NPC self-supporting electrode (the performance parameters of the electrode are similar to those of the electrode prepared in Example 1, and are not described here).

[0110] Example 4 Preparation of novel Fe / Co-NPC self-supporting electrode

[0111] 1. Preparation of Fe / Co-MOF

[0112] FeCl3·6H2O, 1.5 mmol of Co(NO3)2·6H2O and 1.5 mmol of p-phenylenediamine were added into a solution containing 35 mL of DMF, and after complete dissolution by magnetic stirring at room temperature, the solution was transferred into a high-pressure reaction kettle and reacted at 110°C for 24 h. After natural cooling, a brown solid was obtained by centrifugation, and then washed with DMF and ethanol by centrifugation for several times, and then placed in a vacuum drying oven at 60°C for 12 h to obtain a brownish yellow powder Fe / Co-MOF.

[0113] 2, Preparation of melamine-formaldehyde resin

[0114] A 38% formaldehyde solution of 10 mL was added into a 50 mL beaker, and after stirring after adding 0.024 g of urotropin, the solution was heated on a graphite plate at 100°C, while 6.3 g of melamine was added and stirred until the solution was clear, and then heated for another 10 min to obtain a melamine-formaldehyde resin.

[0115] 3, Preparation of a novel Fe / Co-NPC self-supporting electrode

[0116] 2 g of sucrose, 4 g of carbon black and 100 mg of Fe / Co-MOF were taken in a grinding tank, and 6 mL of the aforementioned hot melamine-formaldehyde resin which was not cooled and solidified was added. After grinding by a grinder, a muddy solid was obtained, which was placed in a press after being slightly hard, and then pressed into a round block with a diameter of 20 mm and a thickness of 4 mm, and then placed in a vacuum drying oven at 220°C for 2 h. The round block was placed in a tube furnace, and carbonized at 800°C for 120 min under the atmosphere of 0.5 L / min N2 at a heating rate of 7°C / min. After natural cooling, it was taken out and soaked in 0.1 mol / L HCl for 20 min, and then washed with deionized water for several times and placed in a vacuum drying oven at 60°C for 12 h to obtain a novel Fe / Co-NPC self-supporting electrode (the performance parameters of the electrode are similar to those of the electrode prepared in Example 1, and thus will not be described here).

[0117] Example 5, Preparation of a novel Fe / Co-NPC self-supporting electrode

[0118] 1, Preparation of Fe / Co-MOF

[0119] FeCl3·6H2O 1.5 mmol, Co(NO3)2·6H2O 7.5 mmol and p-phenylenediamine 4.5 mmol were added into a 50 mL beaker containing 35 mL DMF solution, and after complete dissolution by magnetic stirring at room temperature, the solution was transferred into a high-pressure reaction kettle and reacted at 110°C for 24 h. After natural cooling, the brown solid was obtained by centrifugation, and then washed with DMF and ethanol by centrifugation for several times, and then placed in a vacuum drying oven at 60°C for 12 h to obtain a brownish yellow powder Fe / Co-MOF.

[0120] 2. Preparation of melamine-formaldehyde resin

[0121] A 38% formaldehyde solution of 10 mL was added into a 50 mL beaker, and after stirring after adding 0.024 g of urotropin, the solution was heated on a graphite plate at 100°C, and 6.3 g of melamine was added while stirring until the solution was clear. After 10 min of continuous heating, a melamine-formaldehyde resin was obtained.

[0122] 3. Novel Fe / Co-NPC self-supporting electrode

[0123] 1 g sucrose, 2 g carbon black and 100 mg Fe / Co-MOF were taken in a grinding tank, and 4 mL of the aforementioned hot melamine-formaldehyde resin which was not cooled and solidified was added. After grinding by a grinder, a muddy solid was obtained, which was placed in a press after being slightly hard, and then pressed into a round block with a diameter of 20 mm and a thickness of 2 mm, and then placed in a vacuum drying oven at 220°C for 2 h. The round block was placed in a tube furnace, and carbonized at 800°C for 120 min under the atmosphere of 0.5 L / min N2 at a heating rate of 7°C / min. After natural cooling, it was taken out and soaked in 0.1 mol / L HCl for 20 min, and then washed with deionized water for several times and placed in a vacuum drying oven at 60°C for 12 h to obtain a novel Fe / Co-NPC self-supporting electrode (the performance parameters of the electrode are similar to those of the electrode prepared in Example 1, and thus are not described herein).

[0124] Example 6. Construction of heterogeneous electro-Fenton reaction system

[0125] The present embodiment shows the use of the new Fe / Co-NPC self-supporting electrode prepared in Example 1 as an example to build a heterogeneous electro-Fenton reaction system. Specifically, the heterogeneous electro-Fenton reaction system includes a direct current power supply, anode waterproof wire and cathode waterproof wire, gas conduit, gas flow pump, corundum aeration disc (R = 50 mm, thickness = 10 mm, aeration amount is 0.2 L / min), borosilicate glass electrolytic cell (300 mL), cathode new Fe / Co-NPC self-supporting electrode prepared in Example 1 and anode platinum sheet electrode (10 mm x 10 mm x 0.1 mm), the positive pole of the power supply is connected with the anode waterproof wire, the anode water outlet wire is connected with the platinum sheet electrode, the negative pole of the power supply is connected with the cathode waterproof wire, the cathode water outlet wire is connected with the Fe / Co-NPC self-supporting electrode, the horizontal distance between the cathode electrode and the cathode electrode is 2 cm, and air enters the corundum aeration disc through the gas flow pump and is dispersed into the reaction solution.

[0126] Example 7 Treatment of macromolecular organic pollutants by heterogeneous electro-Fenton reaction system

[0127] In order to verify the treatment effect of the new Fe / Co-NPC self-supporting electrode prepared in the present application on macromolecular organic pollutants, the present embodiment takes the example of the difficult-to-degrade cationic xanthene dye rhodamine B (RhB) to illustrate. RhB has a polycyclic structure and has high color at low concentration, showing a peach red color, and can produce certain toxic effects on aquatic organisms through light penetration in natural water bodies.

[0128] Reference Figure 10 100 mL of RhB wastewater solution (initial RhB concentration is 10 mg / L, pH is 5.0, and aeration amount is 0.2 L / min) is added to the electrolytic cell of the heterogeneous electro-Fenton reaction system built in Example 6, and 0.01 mol of Na2SO4 solution is added. The direct current power supply is turned on, and the current intensity is adjusted to 0, 25, 50, 100, and 150 mA, respectively. After 35 min of reaction, the RhB degradation rate is measured, and the results are shown in Figure 11 At 0 mA, the C / C0 is 80% after 35 min of reaction, at which time the adsorption performance of the Fe / Co-NPC self-supporting electrode plays a dominant role. When the initial current is increased from 25 mA to 100 mA, the degradation rate gradually increases and the increase is more obvious, because the greater the current, the greater the electron transmission amount at the same time, the greater the H2O2 generation amount, and the higher the RhB degradation efficiency. However, when the initial current is increased from 100 mA to 150 mA, the degradation rate does not increase significantly, and the main reason for limiting the degradation rate at this time is not the H2O2 generation process, but the Fenton reaction process; at the same time, too high a current will enhance the anode hydrogen evolution side reaction, which will inhibit the generation of H2O2 to some extent. In summary, 100 mA is the preferred initial current condition for the system.

[0129] To investigate the cycling effect of the electrode, six cycles of degradation were carried out under the conditions of an initial current of 100 mA, an initial RhB concentration of 10 mg / L, and an aeration rate of 0.2 L / min, and the results are shown in Figure 12 and 13 It can be seen from Figure 12 that at 5 min, the RhB degradation rate slightly decreases, and the time required for complete degradation also slightly extends with the increase in the number of cycles, which indicates that there is a certain performance loss of the material during the cycling process, but the removal rate can approach 100% within 30 min, so the repeated use effect of the new Fe / Co-NPC self-supporting electrode is not significantly reduced, and it still has a high degradation rate. It can be seen from Figure 13 that with the increase in the number of cycles, the degradation rate K gradually decreases, because the number of active sites inside the catalyst decreases during the cycling process, resulting in a decrease in the degradation efficiency, however, after 6 cycles, the K value gradually stabilizes at about 0.2, which indicates that the material exhibits excellent catalytic performance and stability.

[0130] In order to investigate the stability of the new Fe / Co-NPC self-supporting electrode, the changes in the leaching of Fe and Co ions in the reaction system within 24 h were recorded, and the results are shown in Figure 14 At 5 min (initial pH of 5.0, initial RhB concentration of 10 mg / L, and aeration rate of 0.2 L / min), the leaching amounts of iron and cobalt ions are 0.55 and 0.17 mg / L, respectively. The reaction is rapid 5 min before the degradation experiment, and the Fe and Co ions are rapidly consumed and partially dissolved in the solution. Within 24 h thereafter, the leaching amount of iron ions remains at 0.54-0.64 mg / L, and the leaching amount of cobalt ions remains at 0.17-0.22 mg / L, and the leaching amounts of Fe and Co remain at a basically level state, the loss rate of Fe and Co of the Fe / Co-NPC self-supporting electrode is 0.17%-0.2%, which indicates that the material has good stability, the Fe / Co MOF is not easy to be dissolved, and exhibits excellent catalytic performance and stability.

[0131] In addition, this embodiment also verifies the treatment effect of the new Fe / Co-NPC self-supporting electrode prepared in this application on different concentrations of macromolecular organic pollutants (taking RhB as an example), a plurality of heterogeneous electro-Fenton reaction systems are built according to Example 6, 100 mL of RhB wastewater solutions with different concentrations are added into the corresponding electrolytic cells, 0.01 mol of Na2SO4 solution is added, a direct current power supply is turned on, the current intensity is adjusted to 100 mA, the RhB degradation rate is measured as the reaction proceeds, and the results are shown in Figure 15It can be seen that the degradation rate of RhB slows down with the increase of concentration. When the initial concentration of RhB C0 is 10-30 mg / L (initial current 100 mA, pH 5.0, aeration rate 0.2 L / min), the reaction time for complete degradation of RhB is 10-15 min; when C0 is 50-80 mg / L, the complete degradation time increases to 25 and 35 min, respectively, indicating that the production rate of ·OH, ·O2 - is relatively constant when the initial concentration of RhB is the same, but the intermediate product of RhB increases in the reaction process with the increase of the initial concentration of RhB, and there is competition between the intermediate product and RhB for free radicals, so the complete degradation time is prolonged. The degradation rate of RhB reaches 100% when the reaction time is 35 min, and it can be seen that the Fe / Co-NPC self-supporting electrode can maintain high and stable electro-Fenton catalytic performance even in high-concentration RhB solution.

[0132] The above examples are only illustrative of the principles and effects of the present application, and are not intended to limit the present application. Any person skilled in the art can modify or change the above examples without departing from the spirit and scope of the present application. Therefore, all equivalent modifications or changes completed by those skilled in the art without departing from the spirit and technical thought disclosed in the present application should be covered by the claims of the present application.

Claims

1. A method for preparing a novel Fe / Co-NPC self-supporting electrode, characterized in that, The method comprises the following steps: S1, preparing Fe / Co-MOF; S2, grinding sucrose, carbon black and the Fe / Co-MOF in a mass ratio of 100-10:200-20:1 and melamine-formaldehyde resin in an un-solidified state, the amount of the melamine-formaldehyde resin used being 1-1.5 mL / g (sucrose+carbon black); S3, pressing the substance ground in step S2 to form a molded piece; S4, carbonizing the molded piece at 600-1000℃.

2. The method for preparing novel Fe / Co-NPC self-supporting electrode according to claim 1, characterized in that, Step S1 comprises: hydrothermal reaction of FeCl3·6H2O, Co(NO3)2·6H2O and terephthalic acid in a molar ratio of 1-3:1-5:1-3 at 100-120℃ to prepare Fe / Co-MOF.

3. The method of claim 1, wherein the novel Fe / Co-NPC self-supporting electrode is prepared by the steps of: The amount of melamine used in the preparation of melamine-formaldehyde resin is 3-12g per 10 mL of formaldehyde solution.

4. The preparation method of novel Fe / Co-NPC self-supporting electrode according to claim 3, characterized in that, Step S2 comprises: grinding sucrose, carbon black and Fe / Co-MOF in a mass ratio of 100:200:1 and melamine-formaldehyde resin in an un-solidified state, the amount of the melamine-formaldehyde resin used being 1-1.5 mL / g (sucrose+carbon black).

5. A novel Fe / Co-NPC self-supporting electrode characterized in that, The novel Fe / Co-NPC self-supporting electrode is prepared by the method for preparing the novel Fe / Co-NPC self-supporting electrode according to any one of claims 1-4.

6. The novel Fe / Co-NPC self-supporting electrode according to claim 5, wherein The novel Fe / Co-NPC self-supporting electrode is in a block shape, and / or the hardness of the novel Fe / Co-NPC self-supporting electrode is 35.8-37.7 HV 1.

7. The novel Fe / Co-NPC self-supporting electrode according to claim 5, wherein The loss rate of Fe and Co of the novel Fe / Co-NPC self-supporting electrode after continuous electrolysis for 24h is 0.17%-0.2%.

8. A heterogeneous electro-Fenton reaction system characterized in that, The heterogeneous electro-Fenton reaction system uses the novel Fe / Co-NPC self-supporting electrode according to claim 7 as a cathode.

9. Use of the novel Fe / Co-NPC self-supporting electrode according to claim 7 or the heterogeneous electro-Fenton reaction system according to claim 8 in degrading macromolecular organic pollutants.

10. The use according to claim 9, wherein the macromolecular organic pollutants are RhB.

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