Nitrogen vacancy-rich iron nitride coupled cobalt catalytic electrode and preparation method and application thereof

Abstract

The application discloses a nitrogen vacancy-rich ferrocyanide coupled cobalt catalytic electrode and a preparation method thereof, which comprises a base electrode, a carrier layer and an active layer which are sequentially coated on the base electrode; the carrier layer is an Fe2N layer, and the active layer is a cobalt elementary sub-nanometer cluster layer; the loading capacity of the cobalt elementary sub-nanometer cluster layer is 50-600 μg / cm 2 The ferrocyanide coupled cobalt catalytic electrode has high activity and high stability, can construct a bifunctional synergistic catalytic system of "nitrogen vacancy stable active hydrogen + cobalt cluster activated C-Cl bond", and improves the electrochemical reduction dehalogenation efficiency on halogen-containing organic pollutants.

Description

Technical Field

[0001] This invention relates to the field of electrocatalytic materials technology, and in particular to an iron nitride coupled cobalt catalytic electrode rich in nitrogen vacancies, its preparation method, and its application. Background Technology

[0002] Chlorophenols are an important class of industrial chemicals and intermediates, widely used in wood preservation, pesticide synthesis, and other fields. These substances, by simultaneously introducing chlorine and hydroxyl atoms onto the benzene ring, exhibit significant chemical stability, high toxicity, and bioaccumulation, posing a serious threat to ecosystems and human health. Studies have shown that the toxicity of chlorophenols increases with the number of chlorine substituents. They can damage aquatic organisms and soil microorganisms by interfering with cellular energy metabolism and inhibiting enzyme activity, and can enter the human body through the food chain. Long-term exposure may lead to risks such as carcinogenicity, teratogenicity, and endocrine disruption.

[0003] Currently, the treatment technologies for chlorophenol pollutants are mainly divided into three categories: physical methods, biological methods, and chemical methods. Physical methods, such as adsorption and membrane separation, are simple to operate, but they only achieve phase transfer of pollutants and fail to completely degrade them, and are prone to secondary pollution. Biological methods rely on microbial degradation, which has limitations such as long treatment cycles and great susceptibility to environmental factors. Among chemical methods, advanced oxidation technologies such as the Fenton process and photocatalysis can achieve pollutant mineralization, but they generally face problems such as high energy consumption, large reagent dosage, easy generation of toxic intermediate products, and poor catalyst stability.

[0004] Electrochemical reduction technology, as an emerging green treatment method, uses water as a proton source and generates active hydrogen species (H*) through electrocatalysis under mild conditions to achieve targeted attack and breakage of C-Cl bonds. It has advantages such as controllable energy consumption, clean process, and compatibility with renewable energy sources.

[0005] Chinese patent document CN115532317A discloses a Pd / ZIFs-8@Ti3C2Tx electrocatalyst, its preparation method, and its application in the electrocatalytic hydrogenation reduction dechlorination of chlorophenol compounds. The Pd / ZIFs-8@Ti3C2Tx electrocatalyst comprises Pd nanoparticles and a ZIFs-8@Ti3C2Tx composite support. The ZIFs-8@Ti3C2Tx composite support is formed by modifying two-dimensional layered Ti3C2Tx with ZIFs-8, and the Pd nanoparticles are supported on the ZIFs-8@Ti3C2Tx composite support.

[0006] Chinese patent document CN103301887A discloses a catalyst for treating chlorinated organic matter in water. The active components are four metals: bismuth, palladium, platinum, and ruthenium. The support is a titanium dioxide / activated carbon composite support, and the catalyst surface contains 0.15% polytetrafluoroethylene.

[0007] However, the practical application of existing electrochemical reduction technology is still limited by the following key bottlenecks: (1) Existing catalysts are mostly precious metals, which are expensive and it is difficult to balance catalytic activity and stability; (2) H* is prone to self-combining and hydrogen evolution on the electrode surface, resulting in low utilization rate, and its migration from the generation site to the reaction interface often has a high energy barrier; (3) Most studies are limited to ideal laboratory systems and lack performance verification in actual complex water quality environments such as industrial wastewater with high salt and high organic matter backgrounds. The practicality and stability of the catalytic system need to be improved.

[0008] Therefore, developing an electrocatalyst that combines high activity and high stability with suitability for practical aquatic environments is of great significance for promoting the engineering application of electrochemical reduction technology. Summary of the Invention

[0009] This invention provides an iron nitride-coupled cobalt catalytic electrode rich in nitrogen vacancies and its preparation method, which has both high activity and high stability.

[0010] The technical solution of the present invention is as follows: A nitrogen-vacancy-rich iron nitride-coupled cobalt catalytic electrode includes a substrate electrode and a support layer and an active layer sequentially coated on the substrate electrode; the support layer is an Fe2N layer, and the active layer is a cobalt elemental subnano cluster layer; the loading of the cobalt elemental subnano cluster layer is 50-600 μg / cm³. 2 .

[0011] The iron nitride-coupled cobalt catalytic electrode of this invention can construct a bifunctional synergistic catalytic system of "nitrogen vacancy stabilizing active hydrogen + cobalt cluster activating C-Cl bond". It utilizes nitrogen-rich vacancy iron nitride as a carrier for capturing and stabilizing active hydrogen species (H*) and constructs a synergistic interface with atomically dispersed cobalt clusters to improve the electrochemical reduction and dehalogenation efficiency of halogenated organic pollutants. It breaks through the bottleneck of easy recombination and loss of H* and insufficient C-halogen bond activation ability in traditional catalysts, and realizes the efficient utilization and targeted delivery of H*.

[0012] Preferably, the loading of the cobalt elemental sub-nano cluster layer is 150-400 μg / cm³. 2 .

[0013] The present invention also provides a method for preparing the aforementioned iron nitride-coupled cobalt catalytic electrode, comprising the following steps: (1) Pretreatment of the substrate electrode; (2) The pretreated substrate electrode was placed in the iron-based precursor solution for hydrothermal reaction. The electrode after reaction was taken out and annealed in an inert atmosphere at 300-500℃ to obtain Fe2O3 / substrate electrode. (3) The Fe2O3 / substrate electrode is heated to 400-600°C in a pure ammonia atmosphere for 3-6 h to obtain the Fe2N / substrate electrode; (4) Co precursor solution is coated onto the surface of Fe2N / substrate electrode, dried, and heat-treated at 200-400℃ for 2-5 h in a hydrogen atmosphere to obtain a nitrogen-vacancy-rich iron nitride coupled cobalt catalytic electrode.

[0014] This invention utilizes a continuous process of hydrothermal-nitriding-impregnation to directly grow a Fe2N nanoforest array with a three-dimensional porous structure and load Co active centers on the surface of the substrate electrode, forming a stable and highly conductive self-supporting electrode. This avoids the problems of activity loss and detachment caused by the need to coat binders in traditional powder catalysts, thus improving the overall stability and applicability.

[0015] Preferably, step (1) pretreatment of the substrate electrode includes: cleaning the substrate electrode and etching it in an oxalic acid solution, rinsing the oxalic acid solution on the surface of the substrate electrode after etching, and drying it.

[0016] The substrate electrode is a Ti electrode; the oxalic acid solution has a mass concentration of 10%.

[0017] The surface of the substrate electrode is etched using oxalic acid solution to increase its surface roughness.

[0018] Preferably, in step (2), the iron-based precursor solution is an aqueous solution of soluble iron salt and sodium sulfate, wherein the concentration of soluble iron salt is 10-20 mg / mL and the concentration of sodium sulfate is 5-10 mg / mL.

[0019] Sodium sulfate, as a morphology modifier and ion environment regulator, modulates the Fe... 3+ The hydrolysis nucleation behavior and the preferred crystal growth process promote the uniform in-situ deposition of Fe-based precursors on the surface of the substrate electrode and inhibit particle agglomeration, thereby facilitating the formation of a structurally stable and uniformly dispersed self-supporting electrode precursor.

[0020] Preferably, in step (2), the hydrothermal reaction temperature is 100-150℃ and the hydrothermal reaction time is 4-8 h.

[0021] Preferably, in step (2), the inert atmosphere during the annealing process is argon; the annealing time is 2-4 h.

[0022] The Fe2N / substrate electrode is obtained by high-temperature phase transformation of the Fe2O3 / substrate electrode in a reducing atmosphere.

[0023] Preferably, step (3) includes: placing the Fe2O3 / substrate electrode in a tube furnace, heating it to 400-600°C in a pure ammonia atmosphere at a heating rate of 3-6°C / min for 3-6 h; after the heating program is completed, changing the pure ammonia atmosphere to argon, and cooling it to room temperature to obtain the Fe2N / Ti electrode.

[0024] Preferably, in step (4), the heat treatment includes: heating to 200-400℃ for 2-5 h in a hydrogen atmosphere at a heating rate of 3-6℃ / min; after the heating process is completed, the hydrogen atmosphere is changed to argon, and after cooling to room temperature, a nitrogen-vacancy-rich iron nitride coupled cobalt catalytic electrode is obtained.

[0025] The hydrogen concentration in the hydrogen-containing atmosphere is 5%.

[0026] The preparation method of this invention enables the controllable construction of Co species from single atoms and clusters to nanoparticles. By combining equal-volume impregnation with low-temperature hydrogen reduction, a preparation method for regulating the existence form of Co by "precursor concentration-heat treatment" is established, providing a material basis for the precise control of the active center structure.

[0027] The present invention also discloses the application of the iron nitride coupled cobalt catalytic electrode in the electrochemical reduction dehalogenation of halogen-containing organic pollutants, including: using the iron nitride coupled cobalt catalytic electrode as the working electrode, using a platinum sheet as the counter electrode, and using an Ag / AgCl electrode as the reference electrode, to carry out an electrochemical reduction reaction in wastewater containing halogen-containing organic pollutants containing electrolytes.

[0028] Preferably, in the halogenated organic pollutant wastewater, the electrolyte is sodium sulfate with a concentration of 30-100 mmol / L; and the halogenated organic pollutant is chlorophenolic organic matter.

[0029] The electrochemical reduction reaction system of this invention is particularly suitable for industrial wastewater in complex water environments with high salinity and high organic matter concentration.

[0030] Preferably, the halogenated organic pollutant wastewater contains 100-5000 mg / L of inorganic ions, 100-1500 mg / L of TOC, and 0.01-5 mmol / L of halogenated organic pollutants.

[0031] Preferably, the voltage for the electrochemical reduction reaction is -1.2 to -1.35 V (vs. Ag / AgCl).

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows: The preparation method of this invention is simple. The iron nitride coupled cobalt catalytic electrode has both high activity and high stability. The constructed dual-function synergistic catalytic system of "nitrogen vacancy stabilized active hydrogen + cobalt cluster activated C-Cl bond" improves the electrochemical reduction and dehalogenation efficiency of halogen-containing organic pollutants. It breaks through the bottleneck of easy recombination and loss of H* and insufficient carbon-halogen bond activation ability in traditional catalysts, and realizes the efficient utilization and targeted delivery of H*.

[0033] The electrochemical reduction system of this invention is applicable to actual aquatic environments and is of great significance for promoting the engineering application of electrochemical reduction technology. Attached Figure Description

[0034] Figure 1 Scanning electron microscope images of the catalytic electrode surfaces with different loadings, (a)-(f) correspond to Examples 1-6 respectively; Figure 2 Transmission electron microscopy images of catalytic electrodes with different loading capacities; Figure 3 HAADF-STEM aberration-corrected electron micrographs of catalytic electrodes with different loadings, (a)-(c) correspond to Example 1, Example 2 and Example 4, respectively; Figure 4 The EDS spectrum of Co / Fe2N-200 prepared in Example 2; Figure 5 The concentration-peak area standard curves for 4-CP and phenol are shown. Figure 6 The catalytic performance test results of Co / Fe2N-200 and the control group are shown in (a) the curve of 4-CP concentration changing with time, (b) the first-order reaction kinetic fitting curve, and (c) the reaction rate constant. Figure 7 The catalytic performance test results of electrodes with different Co loadings are shown in (a) the curve of 4-CP concentration versus time, (b) the first-order reaction kinetic fitting curve, and (c) the reaction rate constant. Figure 8 The results of catalytic performance tests at different operating voltages are as follows: (a) is the curve of 4-CP concentration versus time, (b) is the first-order reaction kinetic fitting curve, and (c) is the reaction rate constant. Figure 9 The results of catalytic performance tests for different initial pollutant concentrations are shown in (a) as the curve of 4-CP concentration versus time, (b) as the fitted curve of first-order reaction kinetics, and (c) as the reaction rate constant. Figure 10 The following are the catalytic performance test results for different catalytic electrodes: (a) is the curve of 4-CP concentration changing with time, (b) is the first-order reaction kinetic fitting curve, and (c) is the reaction rate constant. Figure 11The results are from the stability test of Co / Fe2N-200; Figure 12 The graph shows the FT-ICR-MS analysis results of pollutants in actual pharmaceutical wastewater before and after electrochemical treatment. Figure 13 The changes in halogenated pollutants in actual pharmaceutical wastewater before and after electrochemical treatment are shown in (a) and (b). (a) shows the change in the quantity of halogenated pollutants, and (b) shows the change in the concentration of halogenated pollutants. Detailed Implementation

[0035] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be noted that the embodiments described below are intended to facilitate the understanding of the present invention and do not limit it in any way.

[0036] Example 1 Preparation method of nitrogen-vacancy-rich iron nitride coupled cobalt catalyst Co / Fe2N-Ti (1) Ti wafer pretreatment. First, the Ti wafer is pretreated to increase its surface roughness. The Ti wafer is ultrasonically cleaned in ethanol and acetone solution for 30 minutes, and then boiled in a 10% oxalic acid solution for 2 hours to complete the surface etching. After the solution cools to room temperature, the Ti wafer is taken out and rinsed to remove residual oxalic acid. After drying, it is stored in ethanol for later use.

[0037] (2) Preparation of Fe2O3 / Ti and Fe2N / Ti electrodes. 0.8 g FeCl3·6H2O and 0.4 g Na2SO4 were dissolved in 60 mL of water. The mixed solution was then transferred to a high-pressure autoclave with a polytetrafluoroethylene liner containing a pretreated Ti sheet (3 cm × 3 cm). The autoclave was heated in a drying oven at 120°C for 6 hours. After the reaction was completed, the hydrothermal autoclave was cooled to room temperature. The electrode sheet was removed and washed several times with ultrapure water. Finally, the electrode was annealed in argon at 450°C for 3 hours to obtain a self-supporting Fe2O3 / Ti electrode.

[0038] The Fe2N / Ti electrode was obtained by high-temperature phase change of the Fe2O3 / Ti electrode prepared above in a reducing atmosphere. First, Fe2O3 / Ti was evenly spread into a quartz boat and placed in a tube furnace. Then, in a pure ammonia atmosphere, the temperature was increased to 500°C at a rate of 5°C per minute and maintained for 5 hours. After the heating program was completed, the gas was changed to argon, and the electrode was cooled to room temperature to obtain the Fe2N / Ti electrode.

[0039] (3) Preparation of Co / Fe2N-n catalyst. First, 50 mg Co(NO3)2·6H2O was mixed with 5 mL of ethanol to form a Co mixed precursor solution. Under infrared lamp irradiation, 100 μL of the Co precursor solution was added dropwise to Fe2N / Ti four times (100 μL each time). Then, Co / Fe2N-200 was spread evenly in a quartz boat and placed in a tube furnace. It was heat-treated at 300°C for 180 minutes in a hydrogen (5%) atmosphere at a heating rate of 5°C / min. After the heating program was completed, the gas was changed to argon. After cooling to room temperature, Co-Fe2N-100 (Co loading on the electrode surface was 90 μg / cm) was finally obtained. 2 ).

[0040] Example 2 Based on Example 1, in step (3) of Examples 2-6, under infrared lamp irradiation, 200 μL, 400 μL, 600 μL, 800 μL, and 1000 μL of Co precursor solutions were added dropwise to Fe2N / Ti four times. Other operations were the same as in Example 1, resulting in Co-Fe2N-200, Co-Fe2N-400, Co-Fe2N-600, Co-Fe2N-800, and Co-Fe2N-1000 (with Co loading on the electrode surface of 180, 360, 540, 720, and 900 μg / cm³, respectively). 2 ).

[0041] The surface morphology of the electrodes prepared in Examples 1-6 was observed by SEM, and the results are as follows: Figure 1 As shown, a uniform and well-oriented Fe2N nanoforest array was successfully constructed on a Ti substrate by growing an α-Fe2O3 precursor array on a Ti substrate via hydrothermal growth and further high-temperature nitriding in an ammonia atmosphere. This array, composed of interconnected nanorods, forms a high specific surface area structure. This structure not only facilitates electrolyte permeation and mass transfer but also provides abundant surface active sites for catalytic reactions, promoting contact and transport between reactants and active hydrogen species. Furthermore, after loading Co species onto the Fe2N support using an impregnation-reduction method, its SEM morphology did not change significantly, the three-dimensional nanoforest structure was fully preserved, and no structural collapse or blockage caused by cobalt species aggregation was observed. This indicates that cobalt species mainly exist in a highly dispersed form on the surface or in the pores of the Fe2N support, without compromising the macroscopic structural integrity and hierarchical pore characteristics of the support itself.

[0042] The series of Co-Fe2N / Ti materials with different loadings prepared in Examples 1-6 were systematically characterized using HRTEM, and the results are as follows: Figure 2As shown in the images, the presence of Co species on the Fe2N support exhibits a significant structural evolution with increasing loading. When the Co loading is low (100, 200 μL), no obvious cobalt nanoparticles or independent crystalline phases are observed in the images. At this point, the Co species exist in a highly dispersed state, likely uniformly anchored on the Fe2N support surface or embedded in its lattice as atomic-level dispersions or sub-nano clusters. This highly dispersed structure facilitates electronic synergy between the support and the active component. However, when the Co loading increases to 400 μL and above (600, 800, 1000 μL), clearly visible cobalt-based nanoparticles are observed, indicating the existence of a critical Co loading threshold (approximately 180-360 μg / cm³). 2 Below this threshold, Co species can achieve atomic-level integration with Fe2N. Above this threshold, Co species tend to migrate and aggregate on the surface, forming independent nanoparticles.

[0043] To further clarify the precise existence form and distribution evolution of Co species on the Fe2N support at the atomic scale, the Co-Fe2N / Ti samples prepared in Examples 1, 2, and 4 were characterized at atomic resolution using Cs-HAADF-STEM. The results are as follows: Figure 3 As shown in the figure, the characterization results intuitively reveal the morphological evolution of Co species with increasing loading: at low loading (100 µL), they appear as isolated bright spots in the image, corresponding to atomically dispersed Co single atoms; when the loading increases to 200 µL, the bright spots locally aggregate, forming sub-nano clusters composed of several to dozens of Co atoms; and when the loading is further increased (≥400 µL), Co nanoparticles with well-defined sizes appear, confirming that Co species have multiple dispersion states on the Fe2N support. This provides a material basis for subsequent precise control of the active center structure at the atomic / near-atomic scale and systematic study of the structure-activity relationship of different Co morphologies in electrochemical dechlorination reactions.

[0044] Figure 4 The EDS spectrum of Co / Fe2N-200 prepared in Example 2 clearly shows the characteristic X-ray signals of four elements: Co, Fe, N, and O, indicating that the target elements have been successfully introduced into the composite material system. Fe and N show high signal intensities and good distribution matching, corresponding to the main matrix components of the Fe2N support. The Co signal is clearly discernible in the overall spectrum, and its surface scan elemental distribution map shows a highly uniform and continuous spatial distribution of the Co signal on the sample surface, without obvious local enrichment or aggregation. This is consistent with the results of HRTEM and Cs-HAADF-STEM observations, which did not detect obvious Co nanoparticles, further supporting the existence of Co in a highly dispersed state under low loading conditions.

[0045] Testing of the ultra-high catalytic performance of the nitrogen-vacancy-rich iron nitride coupled cobalt catalyst Co / Fe2N-n To establish an accurate basis for quantitative analysis, the target pollutant 4-CP and its electrochemical reduction product phenol were first determined using high-performance liquid chromatography (HPLC) to obtain a standard curve. The results are as follows: Figure 5 As shown, a series of standard solutions with different concentrations were prepared, and the peak area was used to perform linear fitting on the concentration. Each pollutant showed a good linear relationship within its corresponding concentration range, with a correlation coefficient R0. 2 All values ​​were greater than 0.9, verifying the reliability of the analytical method and providing a basis for the accurate quantification of pollutant concentration and the calculation of degradation efficiency in the subsequent reaction process.

[0046] Test Example 1 Through systematic physical adsorption control experiments, the potential contribution of physical adsorption, a non-electrochemical process, to the removal of target substances was determined.

[0047] Co / Fe₂N-200 was placed in an electrolyte system containing 4-CP and reacted for 8 hours. The concentration of 4-CP in the electrolyte system was analyzed by high-performance liquid chromatography (HPLC). The electrochemical reduction reaction was carried out at room temperature in an H-type electrolytic cell separated by a Nafion-117 proton exchange membrane. All electrochemical experiments were performed using a CHI 760E electrochemical workstation; the immersion area of ​​the working electrode (using Co / Fe₂N-n as the working electrode) was 9 cm². 2 (3 cm × 3 cm). An Ag / AgCl electrode was used as the reference electrode, and a 1.0 cm × 1.0 cm platinum sheet was used as the counter electrode. The electrolyte was a sodium sulfate buffer solution with a concentration maintained at 50 mM, and the concentration of the target pollutant 4-CP (4-chlorophenol) was 0.3 mM. During the experiment, samples were collected at regular intervals using a syringe and a filter with a pore size of 0.22 μm. The peak areas of the reactant 4-CP and the product phenol were obtained by high performance liquid chromatography (HPLC). The specific content of 4-CP was determined based on the standard curves of 4-CP and phenol, thereby analyzing the conversion rate, reaction kinetics, and material balance of 4-CP.

[0048] Two control groups were set up under open-circuit potential conditions: an electrolyte system containing only 4-CP and a mixed system containing 4-CP and Fe2N catalyst.

[0049] The results are as follows Figure 6As shown, within the 8-hour reaction time, the concentration of 4-CP in both control systems did not decrease detectably, and no new degradation products were found to be generated by high performance liquid chromatography. This indicates that 4-CP is chemically stable under experimental conditions and does not exhibit significant spontaneous decomposition or hydrolysis. Furthermore, the physical adsorption effect of Fe2N catalyst on 4-CP under static conditions is negligible.

[0050] 4-CP concentration change curve over time ( Figure 6 (a) clearly reveals the dynamic behavior of pollutants in different systems. The concentration curves of the blank control group containing only 4-CP and the adsorption control group containing Fe2N+4-CP are close to horizontal within 8 h. Measurements show that the final retention rate of 4-CP in both systems is approximately 100%, indicating that 4-CP molecules have high chemical stability in this experimental system and do not undergo spontaneous hydrolysis or photochemical degradation. Simultaneously, under no applied voltage, the physical adsorption of 4-CP molecules on the Fe2N electrode surface is extremely weak and negligible. To further quantify this difference, pseudo-first-order reaction kinetics were fitted to the reaction data (…). Figure 6 In (b), the -ln(C / C0) values ​​of the blank group and the adsorption group hardly changed with time, and the reaction rate constant k values ​​of the two groups ( Figure 6 The values ​​in (c) are only 0.0028 h. -1 and 0.0065h -1 The results showed significant differences compared to the electrocatalytic experimental group containing Co / Fe2N-200. Based on these results, it can be determined that in this study, simple physical adsorption contributed almost nothing to the removal of 4-CP. The highly efficient 4-CP removal observed in the Co / Fe2N electrode system was attributed to the electrocatalytic hydrodechlorination process driven by an applied electric field.

[0051] Test Example 2 Under a fixed potential of -1.25 V (vs. Ag / AgCl) and neutral electrolyte conditions, the electrochemical hydrodechlorination performance of the target pollutant 4-CP by different Co precursor loadings, namely Co / Fe₂N-100, 200, 400, 600, 800, and 1000 electrodes, was systematically studied. Through a systematic evaluation of the electrochemical reduction performance of Co / Fe₂N-n catalysts with different cobalt loadings, it was found that the Co loading and its form have a decisive influence on the catalytic effect, as shown in the following results. Figure 7 As shown in the figure, the Co / Fe2N-200 catalyst exhibited the best degradation performance, and reaction kinetic analysis showed that the calculated rate constant of the Co / Fe2N-200 catalyst increased to a maximum value of 0.2 h⁻¹. -1The optimal catalytic activity was observed. Combined with previous Cs-HAADF-STEM characterization results, the Co species at this loading level were highly dispersed on the Fe2N support surface primarily in the form of sub-nano clusters. Based on these findings, the optimal synthesis parameters for the Co / Fe2N nanocatalyst with a loading of 200 µL can be determined, at which point the catalyst exhibits the most efficient catalytic hydrodefluorination capability.

[0052] according to Figure 7 In (a), all Co / Fe2N samples exhibited 4-CP removal capacity, but the removal rate showed a pattern of first increasing and then decreasing with different loading amounts. When the Co precursor addition was only 100 µL, although the Co species existed in a highly dispersed single-atom form, the removal rate of 4-CP was only about 32% after 8 h of reaction due to insufficient number of active sites. When the loading amount increased to 200 µL, the removal rate of 4-CP reached as high as 80%, indicating that the sub-nano cluster structure formed at this loading amount successfully balanced the site density and intrinsic activity. As the loading amount further increased, the catalytic activity began to decline significantly. The final removal rate of the 400 µL sample decreased to 62%, while that of the 600 µL sample further decreased to 45%. This obvious performance inflection point is consistent with the morphological phase transition threshold from sub-nano clusters to nanoparticles observed by electron microscopy. When the loading amount reached 800 µL and 1000 µL, the excess Co species underwent severe aggregation on the electrode surface, and the final removal rates were only 30% and 28%, respectively, slightly lower than 100 µL. Low loading of µL of sample indicates that excessive loading not only failed to provide more effective active sites, but also led to a decline in catalytic performance due to severe pore blockage and specific surface area loss. To quantify the reaction rate, pseudo-first-order reaction kinetics were fitted to the concentration data (e.g., Figure 7 As shown in (b), the fitting curves of all samples exhibit a good linear relationship R. 2 The value >0.99 indicates that the electrochemical hydrodechlorination process conforms to pseudo-first-order reaction kinetics, and the fitted linear rate constant of Co / Fe2N-200 is 0.205 h⁻¹. -1 It exhibits optimal reaction kinetics performance, with the Co / Fe2N-400 rate constant decreasing to 0.128 h⁻¹. -1 Doubling the loading only resulted in an activity loss of approximately 40%, with the Co / Fe2N-600 ratio further decreasing to 0.076 h⁻¹. -1 The three catalyst groups, Co / Fe2N-100, 800, and 1000, exhibited the lowest activity, all below 0.050 h⁻¹. -1 .

[0053] Test Example 3 To determine the optimal operating voltage and initial concentration, the effects of voltage in the range of -1.1 V to -1.35 V (vs. Ag / AgCl) on the degradation performance of 4-CP by the Co / Fe2N-200 electrode were investigated, while keeping other conditions constant. The effects of the initial 4-CP concentration on the degradation performance of the Co / Fe2N-200 electrode at a potential of -1.25 V (vs. Ag / AgCl) were also examined. The results of the systematic investigation of the effects of voltage and initial contaminant concentration on the electrochemical reduction degradation of 4-CP are as follows: Figure 8 and Figure 9 As shown, the optimal operating conditions for this reaction system were determined to be: voltage -1.25 V and initial contaminant concentration of 0.3 mM. Under these conditions, the catalyst exhibited the highest contaminant removal rate. The voltage of -1.25 V was thermodynamically sufficient to drive the formation of H* and the breaking of C-Cl bonds, while effectively suppressing competing reactions such as excessive hydrogen evolution. At an initial concentration of 0.3 mM, the mass transfer and reaction of contaminants on the electrode surface reached kinetic equilibrium, which fully utilized the active sites while avoiding the accumulation of intermediate products or catalyst poisoning that might be caused by high concentrations.

[0054] Figure 8 During the reaction, as the applied potential increased from -1.1 V to -1.35 V, the concentration decay of 4-CP exhibited a pattern of first promoting and then inhibiting. In the low potential region of -1.1 to -1.15 V, due to insufficient reaction driving force, the degradation rate of 4-CP was relatively slow. After 8 hours of reaction, the pollutant removal rate under the -1.1 V condition was less than 20%, at which point sufficient H+ was not generated on the electrode surface. * To effectively attack the C-Cl bond. At -1.25 V, Co / Fe2N-200 exhibited the best dechlorination performance, with a 4-CP removal rate exceeding 80% within 8 hours. However, as the potential shifted further negatively, the catalytic activity declined, with the final removal rate at -1.35 V even lower than at -1.2 V. Furthermore, kinetic fitting results further confirmed that the reaction followed pseudo-first-order kinetics at all test potentials. The summarized apparent reaction rate constant quantified this "volcano-like" structure-activity relationship, with the k value reaching its maximum of 0.20 h at -1.25 V. -1 These are 10 times that of -1.1 V and 2.5 times that of -1.35 V, respectively.

[0055] like Figure 9As shown, the degradation curve of 4-CP exhibits a segmented pattern with increasing initial concentration. In the range of 0.1–0.6 mM, where the initial concentration is relatively low, the degradation curves of the three sample groups are quite similar. After 8 hours of reaction, the removal rate of 4-CP exceeds 80%, demonstrating a rapid removal rate. This indicates that within this concentration range, the active sites on the electrode surface are relatively sufficient, enabling rapid treatment of pollutant molecules diffused to the interface. When the initial concentration is further increased to 1 mM and 2 mM, the degradation rate decreases significantly. At the high concentration of 2 mM, the removal rate after 8 hours is only about 45%, indicating that the catalytic system has reached saturation. The reaction rate constant k value provides a more intuitive view. In the low concentration range of 0.1–0.6 mM, the rate constant remains at a relatively high level, approximately 0.2 h. -1 When the concentration exceeds 1 mM, the rate constant drops sharply, with the k value at 1 mM decreasing to approximately 0.1 h. -1 At 2 mM, it was only 0.08 h. -1 The concentration was less than half that of the low-concentration group. Based on the experimental results, and considering both processing efficiency and practical application, an initial concentration of 0.3 mM can ensure that the reaction is in a highly efficient kinetic range while providing sufficient reaction substrate to fully utilize electrical energy.

[0056] Comparative Example 1 Preparation of Co / TiO2 catalyst. A 3.0 cm × 3.0 cm Ti sheet was heated to 300°C at a rate of 5°C / min under a 5% hydrogen atmosphere and held at this temperature for 3 h to obtain TiO2 / Ti. 50 mg of Co(NO3)2·6H2O was mixed with 5 mL of ethanol and ultrasonically treated for 10–15 min in an ultrasonic cleaner to form a homogeneous Co precursor solution. Then, under infrared lamp irradiation, 200 μL of the Co precursor solution was slowly and uniformly added dropwise to the electrode surface, a total of 4 drops. Finally, under a 5% hydrogen atmosphere, the electrode was heat-treated at 300°C for 180 min at a rate of 5°C / min to obtain Co / TiO2-200 (Co loading on the electrode surface is 180 μg / cm²). 2 ).

[0057] Comparative Example 2 Preparation of Co / TiN catalyst. The obtained TiO2 / Ti was heated to 500°C at a rate of 5°C / min in an ammonia atmosphere for 5 h to obtain TiN / Ti. Then, 50 mg of Co(NO3)2·6H2O was mixed with 5 mL of ethanol and sonicated for 10–15 min to form a Co mixed precursor solution. Under infrared irradiation, 200 μL of the Co mixed precursor solution was slowly and uniformly added dropwise to the TiN surface, four times in total. Then, under a 5% hydrogen atmosphere, it was heat-treated at 300°C for 180 min at a heating rate of 5°C / min to obtain Co / TiN-200 (with a Co loading of 180 μg / cm² on the electrode surface). 2 ).

[0058] Comparative Example 3 Preparation of Co / Fe2O3 catalyst. 50 mg Co(NO3)2·6H2O was mixed with 5 mL ethanol and ultrasonically treated for 10–15 min in an ultrasonic cleaner to form a Co mixed precursor solution. Under infrared lamp irradiation, 200 μL of the Co mixed precursor solution was slowly and uniformly added dropwise to the prepared Fe2O3 / Ti electrode surface, a total of 4 drops. Then, under a 5% hydrogen atmosphere, the electrode was heat-treated at 300 °C for 180 min at a heating rate of 5 °C / min to obtain Co / Fe2O3-200 (Co loading on the electrode surface is 180 μg / cm³). 2 ).

[0059] Test Example 4 The electrochemical hydrodechlorination performance of Co / TiO2-200, Co / Fe2O3-200, Co / TiN-200, and Co / Fe2N-200 working electrodes for the target pollutant 4-CP was systematically studied under the conditions of 0.3 mM 4-CP concentration, fixed potential of -1.25 V (vs. Ag / AgCl) and neutral electrolyte. The results are as follows: Figure 10As shown, by exploring the influence of different support materials on the electrochemical hydrogen reduction performance, it was found that Fe2N, as a support, exhibits significantly better catalytic effects than other comparative materials. Compared with common supports such as TiO2, TiN, and Fe2O3, Fe2N shows significant advantages in degradation efficiency and reaction kinetics for 4-CP under the same loading of active components. This result can be attributed to the promoting effect of nitrogen vacancies unique to the Fe2N support. Nitrogen vacancies in Fe2N can serve as efficient H* capture and storage sites, effectively stabilizing active hydrogen and suppressing hydrogen evolution side reactions. At the same time, Fe2N has metal-like conductivity, which is conducive to rapid charge transport on the electrode surface and improves reaction kinetics. Furthermore, there is a strong electronic interaction between the Fe2N surface and Co species, which can further optimize the generation and transfer pathways of H*. The structural advantages of Fe2N as an efficient H* reservoir and electron conduction support are clearly defined.

[0060] Figure 10 As can be seen, the change in the support directly led to the change in catalytic performance. Co / Fe2N achieved a 4-CP removal rate of approximately 80% after 8 hours of reaction, while the degradation curves of TiO2, Fe2O3, and the common nitride TiN were relatively flat, with final removal rates generally in the low range of 20% to 40% after 8 hours. In the kinetic rate constant graph, the reaction rate constant for Co / Fe2N was 0.201 h⁻¹. -1 The Co / TiO2 ratio is 0.069 h. -1 The Co / TiN ratio is 0.060 h. -1 The Co / Fe2O3 ratio is 0.051 h. -1 This performance difference proves that relying solely on the role of Co is far from sufficient to achieve efficient dechlorination, and the special physicochemical properties of the Fe2N support itself also play an important role.

[0061] Test Example 5 Under optimal reaction conditions (voltage: -1.25 V vs. Ag / AgCl; electrolyte: 50 mM Na2SO4 buffer solution; initial 4-CP concentration: 0.3 mM), a 7-cycle 4-CP degradation experiment was conducted on the same catalyst-modified electrode (Co / Fe2N-200) to determine the stability of the catalyst's electrocatalytic activity during long-term continuous operation. The results are as follows: Figure 11 As shown.

[0062] After seven consecutive cycles, the degradation rate decreased by less than 10% compared to the first cycle, and the catalyst maintained a high degradation efficiency for 4-CP, demonstrating good electrochemical stability and proving that the catalytic system has strong anti-interference ability.

[0063] Application Example 1 To scientifically evaluate the purification efficiency and application potential of the developed catalyst in real-world complex environments, typical pharmaceutical wastewater was selected as the treatment target, with a focus on investigating the catalyst's deep dehalogenation performance on halogenated organic pollutants in the wastewater. By comparing the changes in the types and concentrations of halides in the wastewater before and after treatment, the catalyst's effectiveness was systematically explored from both qualitative and quantitative perspectives.

[0064] Actual wastewater collected from the wastewater discharge outlet of a pharmaceutical factory in Shanghai was selected as the research object. After sampling, the raw wastewater was first pretreated using a 0.22 μm microporous membrane to remove suspended particles, large impurities, and some microorganisms, reducing the interference of particulate matter on subsequent electrochemical reactions and detection analyses. The filtered real water sample was then directly added to the cathode chamber of the electrochemical reactor as the cathode electrolyte. The electrocatalytic reaction was initiated under a three-electrode system with a constant operating potential of -1.25 V (vs. Ag / AgCl) and continued until the set time. After the reaction, the solution in the cathode chamber was collected as the post-reaction water sample for subsequent testing and analysis of target pollutant removal efficiency and product formation. Through electrocatalytic experiments under real wastewater conditions, the actual reaction performance of the catalyst in complex water quality environments and its engineering application potential were further evaluated.

[0065] Pharmaceutical wastewater contains a complex variety of organic pollutants, mainly including phenols, anilines, antibiotics, nitrogen-containing heterocyclic compounds, and esters. The total organic carbon (TOC) is 757 mg / L, while the chloride (Cl) content is also high. - and SO4 2- The concentrations were approximately 350 mg / L and 980 mg / L, respectively, and were accompanied by a complex coexisting ion environment.

[0066] By enriching water samples before and after treatment using solid-phase extraction (SPE), ultra-high precision mass spectra were obtained. The specific types of halogenated organic compounds (HOCs) containing chlorine, bromine, and iodine were identified and statistically analyzed based on the characteristic peaks of halogen isotopes. Comparison of the spectra before and after treatment visually demonstrates the disappearance of characteristic peaks for various HOCs, thus confirming the broad-spectrum dehalogenation capability of the catalyst at the molecular level. The solid-phase extraction operation is as follows: (1) Filtering raw water: Filter 200 mL of water sample using a 0.7 µm filter membrane.

[0067] (2) Adjust the pH of the filtered water sample: Adjust the pH of the water sample to 6.5-7.2 with hydrochloric acid or sodium hydroxide.

[0068] (3) Activation of the column: A 6 mL Copure HLB extraction column was selected, and the mixed column was activated by 2 volumes (2×6 mL) of methanol and 2 volumes (2×6 mL) of ultrapure water in sequence.

[0069] (4) Passing water sample: Pass the previously prepared 500 mL water sample through the mixing column at a flow rate of 5~10 mL / min.

[0070] (5) Rinsing and desalting: Use 2×6 mL of ultrapure water to rinse and desalt the column body through the mixing column.

[0071] (6) Nitrogen blowing column: Use gentle nitrogen gas to blow the mixed column dry to a fine sand-like state.

[0072] (7) Elution: Pass through 6 mL of ethyl acetate / methanol (1:1, v / v) containing 2% ammonia, followed by 3 mL of ethyl acetate / methanol (1:1, v / v) containing 1.7% formic acid.

[0073] (8) Nitrogen blowing: Place the eluted water sample into a nitrogen blowing apparatus to dry it.

[0074] (9) Volume adjustment: Finally, redissolve in methanol to 1 mL, filter through a 0.22 µm filter membrane, transfer to a chromatographic bottle, and store in a refrigerator at -20℃ for instrumental analysis.

[0075] The results are as follows Figure 12 and Figure 13 By comparing the pollutants in actual pharmaceutical wastewater before and after electrochemical treatment using FT-ICR-MS, it was found that the characteristic peak intensities of various halogenated organic compounds in the wastewater decreased significantly or even disappeared completely after the reaction. GC-MS quantitative detection showed that the total amount of detectable adsorbable organic halogens in the wastewater was significantly reduced, and the free Cl-... - ,Br - I - The corresponding increase in ion concentration proves that halogen atoms have broken from the organic framework and mineralized into inorganic halide ions, indicating that the catalytic system has a broad-spectrum dehalogenation capability and can simultaneously and efficiently destroy multiple strong bonds such as C-Cl, C-Br, and Cl, achieving synergistic deep degradation of polyhalogenated organics in complex wastewater and has practical application value. Even in highly complex and highly disturbed industrial wastewater, the catalyst can still maintain high selective reduction activity for multiple halogenated pollutants without obvious poisoning or deactivation.

[0076] Statistical results show that the total number of halogenated organic compounds detected in the wastewater decreased from 265 before the reaction to 57 after the reaction, with an overall removal rate of 78.5%. Specifically, the changes in various halogenated compounds are as follows: iodinated organic compounds (Org-I) decreased from 181 in the original wastewater to 20, with a removal rate of approximately 89%; chlorinated organic compounds (Org-Cl) decreased from 59 to 24, with a removal rate of approximately 59%; the trace amounts of brominated (Org-Br), chloriodine coexistence (Org-ClI), and chlorobromine coexistence (Org-ClBr) also showed a significant decreasing trend, further verifying the universality of Co / Fe2N. Furthermore, due to the weak bond energy of the Cl bond, Co / Fe2N exhibits extremely high activation and cleavage capabilities for Org-I.

[0077] Before electrocatalytic treatment, the pharmaceutical wastewater contained high concentrations of organohalides, with organochlorine (Org-Cl) reaching a maximum concentration of 4050 ppb, organoiodine (Org-I) around 3250 ppb, and organobromine (Org-Br) around 1050 ppb. After electrocatalytic treatment, the concentrations of all organohalides decreased. Specifically, the Org-I concentration decreased from 3250 ppb to below 200 ppb, with a removal rate exceeding 93%; the Org-Br concentration decreased from 1050 ppb to around 100 ppb, with a removal rate of approximately 90%; and the Org-Cl concentration decreased from 4050 ppb to 450 ppb, with a removal rate of 89%. This significant concentration reduction indicates that the vast majority of halogenated organic pollutants in the wastewater have been successfully degraded.

[0078] The embodiments described above provide a detailed explanation of the technical solutions and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A nitrogen-vacancy-rich iron nitride-coupled cobalt catalytic electrode, characterized in that, The product includes a substrate electrode and a carrier layer and an active layer sequentially coated on the substrate electrode; the carrier layer is an Fe2N layer, and the active layer is a cobalt elemental sub-nano cluster layer; the loading of the cobalt elemental sub-nano cluster layer is 50-600 μg / cm³. 2 .

2. A method for preparing the iron nitride-coupled cobalt catalytic electrode according to claim 1, characterized in that, Includes the following steps: (1) Pretreatment of the substrate electrode; (2) The pretreated substrate electrode was placed in the iron-based precursor solution for hydrothermal reaction. The electrode after reaction was taken out and annealed in an inert atmosphere at 300-500℃ to obtain Fe2O3 / substrate electrode. (3) The Fe2O3 / substrate electrode is heated to 400-600°C in a pure ammonia atmosphere for 3-6 h to obtain the Fe2N / substrate electrode; (4) Co precursor solution is coated onto the surface of Fe2N / substrate electrode, dried, and heat-treated at 200-400℃ for 2-5 h in a hydrogen atmosphere to obtain a nitrogen-vacancy-rich iron nitride coupled cobalt catalytic electrode.

3. The method for preparing the iron nitride-coupled cobalt catalytic electrode according to claim 2, characterized in that, Step (1) Pretreatment of the substrate electrode includes: cleaning the substrate electrode and etching it in an oxalic acid solution; rinsing the oxalic acid solution off the surface of the substrate electrode after etching and drying it.

4. The method for preparing the iron nitride-coupled cobalt catalytic electrode according to claim 2, characterized in that, In step (2), the iron salt solution is an aqueous solution of soluble iron salt and sodium sulfate, with the concentration of soluble iron salt being 10-20 mg / mL and the concentration of sodium sulfate being 5-10 mg / mL.

5. The method for preparing the iron nitride-coupled cobalt catalytic electrode according to claim 2, characterized in that, In step (2), the hydrothermal reaction temperature is 100-150℃ and the hydrothermal reaction time is 4-8 h.

6. The method for preparing the iron nitride-coupled cobalt catalytic electrode according to claim 2, characterized in that, Step (3) includes: placing the Fe2O3 / substrate electrode in a tube furnace, heating it to 400-600℃ in a pure ammonia atmosphere at a heating rate of 3-6℃ / min for 3-6 h; after the heating program is completed, changing the pure ammonia atmosphere to argon, and cooling it to room temperature to obtain the Fe2N / Ti electrode.

7. The method for preparing the iron nitride-coupled cobalt catalytic electrode according to claim 2, characterized in that, In step (4), the heat treatment includes: heating to 200-400℃ for 2-5 h in a hydrogen atmosphere at a heating rate of 3-6℃ / min; after the heating program is completed, the hydrogen atmosphere is changed to argon, and after cooling to room temperature, a nitrogen-vacancy-rich iron nitride coupled cobalt catalytic electrode is obtained.

8. The application of the iron nitride-coupled cobalt catalytic electrode as described in claim 1 in the electrochemical reduction dehalogenation of halogen-containing organic pollutants, characterized in that, include: Using the aforementioned iron nitride-coupled cobalt catalytic electrode as the working electrode, a platinum sheet as the counter electrode, and an Ag / AgCl electrode as the reference electrode, an electrochemical reduction reaction was carried out in halogenated organic pollutant wastewater containing electrolytes.

9. The application according to claim 8, characterized in that, The halogenated organic pollutant wastewater contains 100-5000 mg / L of inorganic ions, 100-1500 mg / L of TOC, and 0.01-5 mmol / L of halogenated organic pollutants.

10. The application according to claim 8, characterized in that, The voltage for the electrochemical reduction reaction is -1.2 to -1.35 V (vs. Ag / AgCl).

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