Application of three-dimensional self-supporting iron-nitrogen co-doped carbon nanotube / carbon felt composite cathode in degradation of organic pollutants by electro-catalysis of peroxymonosulfate

Abstract

The invention provides application of a three-dimensional self-supporting iron-nitrogen co-doped carbon nanotube / carbon felt composite cathode in degradation of organic pollutants by electro-catalysis of peroxymonosulfate, and belongs to the technical field of electrochemical advanced oxidation water treatment. The three-dimensional self-supporting iron-nitrogen co-doped carbon nanotube / carbon felt composite cathode takes a carbon felt as a conductive substrate, a carbon nanotube three-dimensional interlocking network structure is constructed on the surface of the conductive substrate, and iron and nitrogen active sites are loaded on the surfaces of a carbon nanotube and the carbon felt. The cathode is kept stable in a wide pH range (3-11) and under various water matrix conditions, the degradation rate is still kept to be 98% or above after 20 times of circulation, and the cathode has a universal removal effect on various new pollutants (antibiotics, phenols, azo dyes and aromatic acids) in a water body. The invention provides a new material and a new technical support for high-efficiency low-carbon treatment of antibiotic wastewater, and shows good potential in practical application.

Description

Technical Field

[0001] The present invention relates to the technical field of electrochemical advanced oxidation water treatment, and in particular to the application of a three-dimensional self-supporting iron and nitrogen co-doped carbon nanotube / carbon felt composite cathode in electrocatalytic degradation of organic pollutants by peroxymonosulfate. Background Art

[0002] New pollutants in water bodies have attracted wide attention due to their destructiveness to the ecological environment and multiple risks to human health. However, the commonly used biological treatment methods are difficult to effectively remove them. The advanced oxidation technology based on peroxymonosulfate (PMS-AOPs) has been widely studied in the field of water treatment as an advantageous chemical treatment method due to its excellent removal effect, rapid reaction efficiency, and wide range of applicable reaction conditions. However, the inactivation of catalysts and the recovery problem in repeated use are inherent defects of heterogeneous Fenton reactions, which are also considered to be the direct reasons restricting the application of advanced oxidation processes based on persulfate in actual water treatment.

[0003] Activating the reaction of PMS by fixing the catalyst on the electrode using the action of an electric field may provide a promising strategy to overcome the challenges of PMS-AOPs. Some pioneering works have reported the development of catalysts as anodes, cathodes, and particle electrodes in the electrochemical advanced oxidation process based on peroxymonosulfate (PMS-EAOPs) for water purification, and have shown effective removal effects and application potentials. Among them, carbon materials have good electrical conductivity and superior chemical, mechanical, and thermal stabilities. At the same time, special structures such as porous, laminated, and defective structures endow their surfaces with rich active sites. Therefore, they are excellent choices whether as heterogeneous catalysts for PMS activation or electrode materials in electrocatalysis. Carbon nanotubes (CNT) are composed of sp 2 Conjugated carbon in a curved, extended, and complete hexagonal network, with relatively low contents of defects and functional groups. By doping with metals and heteroatoms, the redox potential and electrical conductivity of carbon nanotubes can be effectively improved, thereby providing more active catalytic sites. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides the application of a three-dimensional self-supporting iron and nitrogen co-doped carbon nanotube / carbon felt composite cathode in electrocatalytic degradation of organic pollutants by peroxymonosulfate. The cathode material obtained by the present invention has the advantages of high PMS conversion rate, strong persistence, and good stability. By combining iron, nitrogen, carbon nanotubes with a carbon felt having good electrical conductivity and spatial structure, the composite material has a three-dimensional structure, which can effectively inhibit the shedding of iron nanoparticles, and at the same time can also produce a synergistic effect, improve the catalytic activity of the material, and ultimately achieve the efficient activation of PMS and the continuous removal of pollutants.

[0005] The object of the present invention is to provide an application of a three-dimensional self-supporting iron and nitrogen co-doped carbon nanotube / carbon felt composite cathode in electrocatalytic degradation of organic pollutants by peroxymonosulfate. The three-dimensional self-supporting iron and nitrogen co-doped carbon nanotube / carbon felt composite cathode uses a carbon felt as a conductive substrate, constructs a three-dimensional interlocking network structure of carbon nanotubes on the surface of the conductive substrate, and iron and nitrogen active sites are loaded on the surface of the carbon nanotubes and the carbon felt (wherein, iron exists in the forms of FeC and Fe2O3, and nitrogen exists in various forms including pyridine nitrogen, pyrrole nitrogen, graphitic nitrogen and oxidized nitrogen). That is, the cathode uses a carbon felt as a conductive substrate, in-situ constructs a three-dimensional interlocking network of carbon nanotubes on the surface of its fibers by a hydrothermal-thermal decomposition method, and synchronously anchors iron and nitrogen active sites to form an integrated self-growing composite structure.

[0006] In some embodiments of the present invention, the three-dimensional self-supporting iron and nitrogen co-doped carbon nanotube / carbon felt composite cathode is prepared by the following method: Heat the carbon nanotubes in air, then treat them with acid, and heat them in an inert atmosphere to obtain pretreated carbon nanotubes; to remove residual oxygen-containing functional groups and adsorbed gases or solvents.

[0007] Disperse the carbon felt, pretreated carbon nanotubes (CNTs), iron source, nitrogen source and reducing agent in water, carry out a hydrothermal reaction, pyrolyze in an inert atmosphere after drying, wash and dry to obtain the three-dimensional self-supporting iron and nitrogen co-doped carbon nanotube / carbon felt composite cathode (FeNCNT@CF).

[0008] In some embodiments of the present invention, the temperature of heating in air is 350-500 °C, and the time is 8-10 hours; The acid includes hydrochloric acid and / or nitric acid; The temperature of acid treatment is 70-90 °C, and the time is 10-12 hours; The inert gas in the inert atmosphere includes argon and / or nitrogen; The temperature of heating in the inert atmosphere is 800-950 °C, and the time is 1-3 hours; the flow rate of the inert gas is 35-50 mL / min.

[0009] In some embodiments of the present invention, the nitrogen source includes one or more of urea, ethylenediamine and melamine; the reducing agent includes ascorbic acid and / or hydrazine hydrate.

[0010] In some embodiments of the present invention, the iron source includes one or more of iron nitrate, ferrous sulfate, ferrous chloride, ferric chloride.

[0011] In some embodiments of the present invention, the dosage ratio of pretreated carbon nanotubes (CNTs), iron source, nitrogen source and reducing agent is 1:(2-5):(1-3):(0.5-1.5).

[0012] In some embodiments of the present invention, the temperature of the hydrothermal reaction is 150 - 180 °C, and the hydrothermal time is 10 - 12 hours.

[0013] In some embodiments of the present invention, the conditions of the pyrolysis reaction are: pyrolysis at 700 - 900 °C for 1 - 3 hours, and the heating rate is 2 - 10 °C / min.

[0014] In some embodiments of the present invention, the organic pollutants include one or more of antibiotic pollutants, phenolic pollutants, azo dyes, and aromatic acid pollutants; Further, the organic pollutants include one or more of sulfamethoxazole, carbamazepine, 4 - chlorophenol, bisphenol A, rhodamine B, and benzoic acid.

[0015] The concentration of the organic pollutants is 5 - 20 mg / L.

[0016] In some embodiments of the present invention, the electrolytic cell for electrocatalysis uses a two - chamber electrolytic cell, and the electrolyte in the electrolyte is a 50 - 100 mmol / L sodium sulfate solution; the distance between the anode and cathode electrodes is 4 - 8 cm, and the size of the platinum sheet counter - electrode is 1×1 cm 2 ; Electrocatalysis is carried out using a three - electrode system, where the cathode potential is - 0.25 to - 1.0 V vs. SCE, and the degradation temperature is 20 - 25 °C.

[0017] In the present invention, the carbon nanotube network is beneficial for providing a high specific surface area and through - pores, which can effectively promote the mass transfer of PMS and interfacial electron transfer. The electron coupling effect between iron, nitrogen sites and sp 2 hybridized carbon reduces the activation energy barrier of PMS, and degrades organic pollutants such as antibiotics in water through the synergistic path of free radicals (·OH / SO4·⁻ / O2·⁻) and non - free radicals ( 1 O2 / Fe(IV)=O) (the removal rate of sulfamethoxazole > 99.9% in 60 min). At the same time, the three - dimensional confinement effect can effectively inhibit the loss of active components (the Fe dissolution concentration < 0.01 mg / L).

[0018] The above - mentioned technical solutions of the present invention have the following advantages compared with the prior art: (1) The present invention provides a preparation method and an application method of an electrocatalytic peroxymonosulfate cathode catalyst, i.e., a three-dimensional self-supporting iron and nitrogen co-doped carbon nanotube / carbon felt composite cathode, for removing refractory emerging pollutants in water bodies. The synthesis method is simple, the effect is obvious, and the raw materials are inexpensive and environmentally friendly. A composite system of a carbon felt substrate / carbon nanotube intertwined framework / iron and nitrogen nanoparticles is prepared by a hydrothermal-pyrolysis method, and a three-dimensional self-supporting cathode with synergistic enhancement of hierarchical pores and a conductive network is constructed. The in-situ growth of carbon nanotubes on the surface of carbon felt fibers not only provides a large number of anchoring sites for iron and nitrogen doping, but also inhibits the shedding of active components (iron dissolution rate < 0.01 mg / L) through a spatial confinement effect, solving the engineering bottleneck of easy deactivation and difficult recovery of traditional powder catalysts.

[0019] (2) This cathode realizes the dual-path activation of PMS through the synergistic effect of interfacial iron active sites (confirmed by XPS that the Fe 2+ / Fe 3+ redox pair dominates) and the carbon-based conductive network: ① a non-radical oxidation path dominated by surface high-valent iron oxide species; ② a free radical chain reaction path of ·OH / SO4 ⁻ / O2 ⁻ . The synergy of the two significantly improves the degradation efficiency of organic pollutants, and has strong resistance to complex water quality interference, and can effectively degrade sulfamethoxazole within a wide pH range.

[0020] (3) The integrated self-growth structure endows the cathode with excellent mechanical stability (activity retention rate > 98% after 20 cyclic reactions). Its three-dimensional intertwined structure can alleviate the diffusion and mass transfer limitations of pollutants, accelerate the reaction rate, and combined with the high conductivity of the carbon felt substrate, it can operate stably when degrading various organic pollutants, and has the potential to treat actual organic wastewater. Description of the Drawings

[0021] In order to make the content of the present invention easier to be clearly understood, the following further details the present invention according to specific embodiments of the present invention and in combination with the drawings, wherein, Figure 1 are SEM images of the three-dimensional self-supporting iron and nitrogen co-doped carbon nanotube / carbon felt composite cathode (FeNCNT@CF) in Example 1 of the present invention and the iron and nitrogen co-doped carbon felt cathode (FeN@CF) in Comparative Example 1. Among them, Fig. a is the SEM image of the pretreated carbon felt (CF), Figs. b and c are FeNCNT@CF after hydrothermal treatment and after pyrolysis and cleaning respectively, and Fig. d is FeN@CF.

[0022] Figure 2 are elemental dimensional distribution spectrum images (SEM-mapping) of the three-dimensional self-supporting iron and nitrogen co-doped carbon nanotube / carbon felt composite cathode (FeNCNT@CF) in Example 1 of the present invention and the iron and nitrogen co-doped carbon felt cathode (FeN@CF) in Comparative Example 1.

[0023] Figure 3 XPS full spectra and high-resolution spectra of the Fe 2p orbital for the carbon felt (CF), three-dimensional self-supporting iron and nitrogen co-doped carbon nanotube / carbon felt composite cathode (FeNCNT@CF) in Example 1 of the present invention, and the iron and nitrogen co-doped carbon felt cathode (FeN@CF) in Comparative Example 1.

[0024] Figure 4 Degradation schematic diagram of electro-activated PMS for the degradation of sulfamethoxazole by the three-dimensional self-supporting iron and nitrogen co-doped carbon nanotube / carbon felt composite cathode (FeNCNT@CF) in Example 1 of the present invention and the iron and nitrogen co-doped carbon felt cathode (FeN@CF) in Comparative Example 1.

[0025] Figure 5 Detection diagram of reactive species generated by the electro-activated PMS system (E-FeNCNT@CF-PMS) of the three-dimensional self-supporting iron and nitrogen co-doped carbon nanotube / carbon felt composite cathode constructed in the present invention.

[0026] Figure 6 Degradation schematic diagram of the adsorption, electro-adsorption, catalyst activation and electro-activated PMS for the degradation of sulfamethoxazole by the three-dimensional self-supporting iron and nitrogen co-doped carbon nanotube / carbon felt composite cathode in Example 1 of the present invention.

[0027] Figure 7 Degradation schematic diagram of the electro-activated PMS system (E-FeNCNT@CF-PMS) of the three-dimensional self-supporting iron and nitrogen co-doped carbon nanotube / carbon felt composite cathode constructed in the present invention for sulfamethoxazole under different pH conditions.

[0028] Figure 8 Degradation schematic diagram of the electro-activated PMS system (E-FeNCNT@CF-PMS) of the three-dimensional self-supporting iron and nitrogen co-doped carbon nanotube / carbon felt composite cathode constructed in the present invention for sulfamethoxazole in the presence of common environmental anions and humic acid.

[0029] Figure 9 Degradation schematic diagram of the electro-activated PMS system (E-FeNCNT@CF-PMS) of the three-dimensional self-supporting iron and nitrogen co-doped carbon nanotube / carbon felt composite cathode constructed in the present invention for different types of emerging pollutants.

[0030] Figure 10 Multiple cycle schematic diagram of the electro-activated PMS system (E-FeNCNT@CF-PMS) of the three-dimensional self-supporting iron and nitrogen co-doped carbon nanotube / carbon felt composite cathode constructed in the present invention for the degradation of sulfamethoxazole. Detailed implementation manners

[0031] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the embodiments cited are not intended to limit the present invention.

[0032] Example 1 This example provides a three-dimensional self-supporting iron and nitrogen co-doped carbon nanotube / carbon felt composite cathode material and a preparation method, which include the following steps: (1) Heat the carbon nanotubes in air at a heating rate of 5 °C / min to 400 °C, keep for 10 hours and then cool with the furnace. Add 6 mol / L hydrochloric acid and heat to 80 °C, reflux for 12 hours and then cool to room temperature. Wash with deionized water until neutral, put into a vacuum drying oven and dry at 60 °C for 12 hours. Then heat in an argon atmosphere at a heating rate of 5 °C / min to 900 °C and keep for 1 hour, with an argon flow rate of 50 mL / min. After cooling with the furnace, set aside for use; (2) Immerse the carbon felt in a 30 wt% nitric acid solution, heat in a water bath to 80 °C and keep for 3 hours. After cooling to room temperature, wash thoroughly with deionized water until neutral, put into a vacuum drying oven and dry at 60 °C for 12 h, set aside for use; (3) Weigh 0.03 g of the pretreated carbon nanotubes in step (1), 0.08 g of ferric nitrate, 0.03 g of urea and 0.025 g of ascorbic acid into a Teflon inner liner, add 10 mL of deionized water and mix well to obtain a mixed solution; (4) Cut the pretreated carbon felt in step (2) into a size of 1.5×1 cm 2 and immerse it in the mixed solution obtained in step (3) to make full contact. Then put it into a reaction kettle for hydrothermal reaction, set the temperature to 160 °C and the reaction time to 10 hours; (5) Take out the carbon felt material after the hydrothermal reaction in step (4), put it into a vacuum drying oven and dry at 60 °C for 12 h. After complete drying, place it in a tubular furnace and heat in argon with a flow rate of 50 mL / min at a heating rate of 5 °C / min to 800 °C and keep for 1 hour for pyrolysis, and then cool with the furnace; (6) Take out the carbon felt material after the pyrolysis reaction in step (5), remove the loose surface precipitate or unreacted metal salt through ultrasonic cleaning and rinsing with deionized water, and then place it in a vacuum drying oven and dry at 60 °C for 12 h to finally obtain the three-dimensional self-supporting iron and nitrogen co-doped carbon nanotube / carbon felt composite cathode material (FeNCNT@CF).

[0033] The surface morphology and structure of the obtained FeNCNT@CF were characterized, and the results are shown in Figures 1-2 , from Figure 1 a, it can be seen that the surface of the pure carbon felt is smooth, and the surface of the carbon felt after hydrothermal treatment is wrapped with a carbon shell layer (Figure 1 b), After pyrolysis and cleaning, a large number of carbon nanotubes and uniformly distributed nanoparticles were coated on the fiber surface of the carbon felt in FeNCNT@CF, indicating that iron nitride nanoparticles and carbon nanotubes were successfully loaded on the carbon felt; from Figure 2 it can be seen that the C element is widely distributed on the surface of FeNCNT@CF, constituting the basic framework of the material and serving as the carrier of the iron nanoactive component. The three elements Fe, N, and O are significantly and uniformly distributed in the region, confirming the successful loading of the active component.

[0034] Comparative Example 1 (This comparative example is similar to Example 1, the difference is the lack of addition of carbon nanotubes) This comparative example provides an iron-nitrogen co-doped carbon felt cathode material and a preparation method. The method of this comparative example includes the following steps: (1) Immerse the carbon felt in a 30 wt% nitric acid solution, heat it in a water bath to 80 °C and keep it for 3 hours. After cooling to room temperature, wash it thoroughly with deionized water until neutral, and put it into a vacuum drying oven to dry at 60 °C for 12 h for later use; (2) Weigh 0.08 g of iron nitrate, 0.03 g of urea, and 0.025 g of ascorbic acid in a Teflon liner, and add 10 mL of deionized water to mix well; (3) Cut the pretreated carbon felt in step (1) into a size of 1.5×1 cm 2 , immerse it in the mixed solution obtained in step (2) for sufficient contact, and then put it into a reaction kettle for hydrothermal reaction. Set the temperature to 160 °C and the reaction time to 10 hours; (4) Take out the carbon felt material after hydrothermal reaction in step (3), put it into a vacuum drying oven to dry at 60 °C for 12 h. After complete drying, place it in a tube furnace, heat it to 800 °C at a heating rate of 5 °C / min in argon with a flow rate of 50 mL / min and keep it for 1 hour for pyrolysis, and then cool it with the furnace; (5) Take out the carbon felt material after pyrolysis reaction in step (4), remove the loose surface precipitate or unreacted metal salt through ultrasonic cleaning and rinsing with deionized water, and then place it in a vacuum drying oven to dry at 60 °C for 12 h to finally obtain an iron-nitrogen co-doped carbon felt cathode (FeN@CF).

[0035] Perform surface morphology and structure characterization on the obtained FeN@CF, and the results are shown in Figures 1-2 , from Figure 1 d it can be seen that some irregular blocky particles are loaded on the surface of FeN@CF, and the particle size is relatively large, which is not conducive to the exposure of active sites and the catalytic activity is relatively low. From Figure 2 it can be seen that the particles are mainly iron oxides, and the loading of nitrogen element is significantly less.

[0036] Test Example 1 XPS scans were performed on the carbon felt after the pretreatment in step (2) of Example 1, FeNCNT@CF in Example 1, and FeN@CF in Comparative Example 1. The results are as Figure 3 shown.

[0037] As Figure 3 shown in a, the XPS spectra of both FeNCNT@CF and FeN@CF show characteristic peaks of C, N, O, and Fe, confirming the successful loading of Fe and N into the cathode material. Figure 3 In b, the high-resolution Fe 2p XPS spectra of FeNCNT@CF and FeN@CF can be deconvoluted and split into Fe 2p 3 / 2 orbital at around 711.2 eV, Fe 2p 1 / 2 orbital at around 724.7 eV, and the shake-up satellite peak of Fe 2p 3 / 2 near 718 eV, indicating that Fe in the FeNCNT@CF catalyst obtained in Example 1 and the FeN@CF catalyst obtained in Comparative Example 1 mainly exists in the form of Fe 2+ and Fe 3+ .

[0038] Application Example 1 FeNCNT@CF in Example 1 and FeN@CF in Comparative Example 1 were respectively applied to an electrocatalytic reaction system (applied current E-FeNCNT@CF-PMS system and applied current E-FeN@CF-PMS system) to evaluate the ability to in-situ activate PMS for sulfamethoxazole degradation on the surface of this series of cathode materials.

[0039] The electrochemical degradation test was carried out using a three-electrode system in an H-type electrolytic cell separated by a Nafion-117 proton exchange membrane. FeNCNT@CF and FeN@CF were used as working electrodes, with an immersion area of 1×1 cm 2 , a saturated calomel electrode (SCE), and a platinum sheet electrode (1×1 cm 2)(They) were used as the reference electrode and the counter electrode respectively. The electrolyte and reactant solution in the cathode chamber were 20 mL of 50 mM Na2SO4 and 10 mg / L sulfamethoxazole or other pollutant solution (magnetic stirring at 300 rpm), and the electrolyte solution in the anode chamber was 20 mL of 50 mM Na2SO4. The voltage of the working electrode was -0.5 V vs. SCE. PMS was added to the cathode chamber to make the concentration in the cathode chamber 2.5 mM, marking the start of the electrocatalytic degradation reaction. The reaction solution was taken out from the cathode chamber at set time intervals, filtered through a 0.22 μm cellulose acetate membrane into a solution containing 0.5 M Na2S2O3 for quenching, and the removal rate of sulfamethoxazole or other pollutants in the filtrate was analyzed by high performance liquid chromatography. The results are as Figure 4 shown.

[0040] As Figure 4 can be seen, the E-FeNCNT@CF-PMS system almost completely degraded sulfamethoxazole in water within 60 min, and the degradation rate was 97.82%. In contrast, the degradation rate of the E-FeN@CF-PMS system at 60 min was 89.55%, and the degradation rate was slower. This indicates that the addition of carbon nanotubes significantly improved the catalytic efficiency of the cathode catalyst and promoted the degradation of sulfamethoxazole by the electro-activated PMS system. The improvement of the catalytic performance by the introduction of carbon nanotubes (CNTs) can be attributed to their unique physical and chemical properties. On the one hand, carbon nanotubes have a high specific surface area, which can provide more anchoring sites for active sites, thus increasing the number of active sites. On the other hand, the sp 2 hybrid carbon structure of carbon nanotubes endows them with excellent electrical conductivity, providing a fast channel for the transfer of electrons from the carbon felt substrate to the iron-nitrogen active sites. The acceleration of this electron transfer helps to improve the efficiency of the electrocatalytic reaction, thereby promoting the activation of PMS and the degradation of sulfamethoxazole. In addition, the addition of carbon nanotubes may also further improve its performance during the electrochemical reaction by enhancing the structural stability of the catalyst. This structural stability helps to maintain the high efficiency of the active sites of the catalyst during the long-term reaction, thus achieving the efficient degradation of sulfamethoxazole.

[0041] Test Example 1 The E-FeNCNT@CF-PMS and E-FeN@CF-PMS systems in Application Example 1 were respectively used with 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and 2,2,6,6-tetramethylpiperidine (TEMP) as spin trapping agents for electrochemical EPR tests, and the signal of high-valent iron-oxo species in the system was judged through the methyl phenyl sulfoxide (PMSO) probe experiment. The results are as Figure 5 shown.

[0042] AsFigure 5 It can be seen that no obvious signal peak was observed when only PMS was present; while in the E-CF-PMS (electrified carbon felt electrode system), E-FeNCNT@CF-PMS, and E-FeN@CF-PMS systems, the DMPO-·OH signal with a characteristic peak intensity ratio of 1:2:2:1, the weak DMPO-SO4 ·- signal, and the DMPO-O2 ·- sextet signal with a characteristic peak ratio of 1:1:1:1:1:1 were observed, indicating that the electric field can activate PMS to generate ·OH, SO4 ·- and O2 ·- radical species through electron transfer. Similarly, the observed 1:1:1 TEMP- 1 O2 signal also proved the generation of O2 in the three electro-activated PMS systems 1 . Compared with the E-FeN@CF-PMS system, the EPR signal in the E-FeNCNT@CF-PMS system was significantly enhanced, indicating that the improvement of the cathode catalyst can effectively promote the electron transfer process, thereby generating more active species. In addition, after adding PMSO to the E-FeNCNT@CF-PMS system, PMSO was rapidly consumed in the system, and PMSO2 was generated simultaneously. As the reaction continued, the consumption rate of PMSO was always almost the same as the generation rate of PMSO2, indicating that high-valent iron-oxygen species were continuously and abundantly generated in the E-FeNCNT@CF-PMS system.

[0043] Application Example 2 The steps of Application Example 2 were basically the same as those of Application Example 1, and the contribution of the electro-activated PMS in Example 1 to the degradation of sulfamethoxazole was evaluated. The degradation of sulfamethoxazole by adding only FeNCNT@CF (FeNCNT@CF in the figure), applying current to FeNCNT@CF (E-FeNCNT@CF), activating PMS with FeNCNT@CF (FeNCNT@CF-PMS), and the E-FeNCNT@CF-PMS system was tested respectively, and the results are as Figure 6 shown.

[0044] It can be Figure 6 seen that the physical adsorption (FeNCNT@CF) and electro-adsorption process (E-FeNCNT@CF) of FeNCNT@CF hardly played a role in the removal of sulfamethoxazole, indicating that the improvement of the performance of the electro-activated PMS system for degrading pollutants mainly depends on the activation performance of PMS. The degradation rate of sulfamethoxazole by FeNCNT@CF-activated PMS was 72.88% within 60 min, indicating that the cathode catalytic material itself played a certain role in the activation of PMS and the degradation of pollutants.

[0045] Application Example 3 Application Example 3 is basically the same as Application Example 1, except that the pH of the cathode chamber solution was adjusted to 3, 5, 7, 9, and 11 respectively, and the dissolution of iron ions under different pH conditions was tested by inductively coupled plasma optical emission spectrometer (ICP-OES). The results are as Figure 7 shown in Table 1.

[0046] Table 1 Dissolution of iron ions during the degradation of sulfamethoxazole in the E-FeNCNT@CF-PMS system

[0047] As Figure 7 can be seen, almost all sulfamethoxazole can be completely degraded within a relatively wide initial pH range of 3 - 11, indicating that the E-FeNCNT@CF-PMS system is almost not limited by the solution pH. However, relatively speaking, the degradation efficiency of the system is faster under weakly acidic conditions, while the degradation rate decreases under alkaline conditions. In addition, no iron ion dissolution (lower than the detection limit of 0.01 mg·L -1 ) was detected in the E-FeNCNT@CF-PMS system under different pH conditions, indicating that the carbon nanotubes loaded on the cathode played a good protective role for the iron active sites, effectively inhibiting the shedding and dissolution of iron in the cathode material.

[0048] Application Example 4 Application Example 4 is basically the same as Application Example 1. Common anions in water bodies (HCO3 - , PO4 3- , NO3 - , and Cl - ) and humic acid (HA) were added to the cathode chamber solution to observe the adaptability of the E-FeNCNT@CF-PMS system in complex water bodies. The results are as Figure 8 shown.

[0049] As Figure 8 can be seen, the addition of HCO3 - and PO4 3- had almost no effect on the degradation of SMX in the system, while the presence of NO3 - , Cl - , and HA would cause a certain inhibitory effect on the removal of SMX, probably due to the reaction with ·OH and SO4· - . However, due to the strong resistance of non-radical and surface electron transfer to inorganic anions and natural organic matter, the removal rate of SMX could still be maintained at about 85%, indicating the potential anti-interference performance of the E-FeNCNT@CF-PMS system.

[0050] Application Example 5 Application Example 5 is basically the same as Application Example 1, except that 10 mg / L of sulfamethoxazole is replaced with 10 mg / L of other pollutants, including antibiotic pollutants (sulfamethoxazole, carbamazepine), phenolic pollutants (4-chlorophenol, bisphenol A), azo dyes (rhodamine B), and aromatic acid pollutants (benzoic acid), to observe the degradation ability of the E-FeNCNT@CF-PMS system for other pollutants. The results are as Figure 9 shown.

[0051] As Figure 9 can be seen, at 60 min of reaction, the degradation rates of the E-FeNCNT@CF-PMS system for carbamazepine, 4-chlorophenol, rhodamine B, and benzoic acid are all 100%, and the degradation rate for bisphenol A is 99.17%. This demonstrates the strong degradation ability of the E-FeNCNT@CF-PMS system for the above-mentioned various types of pollutants.

[0052] Application Example 6 Application Example 6 is basically the same as Application Example 1. After the reaction, the FeNCNT@CF is rinsed and then used in the next degradation experiment to test the performance of the E-FeNCNT@CF-PMS system in multiple repeated experiments. The results are as Figure 10 shown.

[0053] As Figure 10 can be seen, the system can almost reach a degradation rate of 100% in 20 cyclic tests, which is a great improvement compared with traditional solid catalysts, fully demonstrating the repeatability of the FeNCNT@CF cathode material and the high stability of the E-FeNCNT@CF-PMS system.

[0054] Obviously, the above embodiments are merely examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of this invention.

Claims

1. Application of a three-dimensional self-supporting iron and nitrogen co-doped carbon nanotube / carbon felt composite cathode in electrocatalytic degradation of organic pollutants by peroxymonosulfate, characterized in that, The three-dimensional self-supporting iron and nitrogen co-doped carbon nanotube / carbon felt composite cathode uses a carbon felt as a conductive substrate, constructs a three-dimensional interlocking network structure of carbon nanotubes on the surface of the conductive substrate, and iron and nitrogen active sites are loaded on the surface of the carbon nanotubes and the carbon felt; the three-dimensional self-supporting iron and nitrogen co-doped carbon nanotube / carbon felt composite cathode is prepared by the following method: Heat the carbon nanotubes in air, then treat them with acid, and heat them in an inert atmosphere to obtain pretreated carbon nanotubes; Disperse the carbon felt, pretreated carbon nanotubes, iron source, nitrogen source and reducing agent in water, carry out a hydrothermal reaction, dry and then pyrolyze in an inert atmosphere, wash and dry to obtain the three-dimensional self-supporting iron and nitrogen co-doped carbon nanotube / carbon felt composite cathode.

2. The application according to claim 1, wherein The temperature of heating in air is 350-500 °C and the time is 8-10 hours; The acid includes hydrochloric acid and / or nitric acid; The temperature of acid treatment is 70-90 °C and the time is 10-12 hours; The inert gas in the inert atmosphere includes argon and / or nitrogen; The temperature of heating in the inert atmosphere is 800-950 °C and the time is 1-3 hours.

3. The application according to claim 1, wherein The nitrogen source includes one or more of urea, ethylenediamine and melamine; 4. The application according to claim 1, characterized in that The reducing agent includes ascorbic acid and / or hydrazine hydrate; 5. The application according to claim 1, characterized in that, The iron source includes one or more of iron nitrate, ferrous sulfate, ferrous chloride and ferric chloride; 6. The application according to claim 1, characterized in that The dosage ratio of the pretreated carbon nanotubes, iron source, nitrogen source and reducing agent is 1:(2-5):(1-3):(0.5-1.5).

7. The application according to claim 1, characterized in that, The temperature of the hydrothermal reaction is 150-180 °C and the time is 10-12 hours.

8. The application according to claim 1, characterized in that, The reaction conditions of pyrolysis: pyrolyze at 700-900 °C for 1-3 hours, and the heating rate is 2-10 °C / min.

9. The application according to claim 1, wherein The organic pollutants include one or more of antibiotic pollutants, phenolic pollutants, azo dyes and aromatic acid pollutants; The concentration of the organic pollutants is 5-20 mg / L.

10. The application according to claim 1, characterized in that The electrolytic cell for electrocatalysis uses a two-chamber electrolytic cell, and the electrolyte in the electrolyte is a 50-100 mmol / L sodium sulfate solution; Electrocatalysis is carried out using a three-electrode system, where the cathode potential is -0.25 to -1.0 V vs. SCE, and the degradation temperature is 20-25 °C.

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