Method for preparing a hybrid electrode for the reduction of heavy metal ions in catalytic wastewater

Abstract

The application discloses a preparation method of a hybrid electrode for catalyzing reduction of heavy metal ions in wastewater, and belongs to the technical field of catalytic electrode materials. Firstly, the three-dimensional porous carbon framework is immersed in a mixed solution of NiCl2 / FeCl3 and urea, and 3D-PC@NiFe-SACs are obtained through high-temperature carbon thermal reduction; then, the 3D-PC@NiFe-SACs are subjected to acid etching pretreatment with Ti3AlC2 powder in HF, and in-situ nitriding modification is carried out by introducing NH3 gas in a tube furnace to obtain 3D-PC@NiFe-SACs / MXene hybrid electrodes; finally, the hybrid electrodes are subjected to pH intelligent response treatment to endow the hybrid electrodes with excellent properties such as self-cleaning. The novel hybrid electrode breaks the mass transfer limitation under low-concentration wastewater through the effect of multiple synergistic mechanisms, greatly improves the electrocatalytic reduction efficiency of Ni 2+ and other heavy metal ions in wastewater, and endows the electrode with excellent in-situ self-cleaning ability, and has great application prospect in the field of heavy metal industrial wastewater deep treatment.

Description

Technical Field

[0001] This invention relates to the field of catalytic electrode materials technology, specifically to a method for preparing a hybrid electrode for catalytic reduction of heavy metal ions in wastewater. Background Technology

[0002] Electrochemical reduction is one of the core technologies for treating wastewater containing heavy metal ions. Its core lies in using an applied electric potential to drive electron transfer of heavy metal ions on the electrode surface, reducing them to a less toxic or elemental form for deposition and recovery. This process places stringent requirements on the conductivity, catalytic activity, and resistance to poisoning of the electrode materials. Currently, the mainstream electrode materials include the following: 1) Noble metal electrodes (Pt, Au, Pd): have a wide electrochemical window and high catalytic activity, but are expensive and easily poisoned by sulfides or organic matter; 2) Titanium-based DSA anodes (RuO2 / Ti, IrO2 / Ti): Used for oxidation assistance to indirectly improve reduction efficiency, but do not directly participate in the reduction of heavy metals; 3) Carbon-based materials (graphene, carbon nanotubes, activated carbon): provide high specific surface area and good conductivity, but have low intrinsic catalytic activity and require functionalization modification; 4) Metal oxides (Cu2O, NiO, Co3O4): During reduction, they can undergo in-situ reconstruction to form an active metallic state, such as Cu2O in NO3. - During reduction, it is dynamically stable as the Cu2O1-δ phase, providing catalytic-like sites for the reduction of heavy metals; With the continuous development of electrode materials, hybrid electrodes have emerged to overcome the limitations of single materials. Through the synergistic coupling of multiple components, hybrid electrodes can overcome the limitations of single materials in terms of conductivity, active site density, and stability, and have become a cutting-edge direction in the electrocatalytic reduction of heavy metals. However, currently, the application of Ni in wastewater... 2+ Hybrid electrodes for the efficient electrocatalytic reduction of heavy metal ions are still not ideal, and their surfaces are easily contaminated by organic matter or sulfides during long-term operation, resulting in a short cycle life. Therefore, a new type of hybrid electrode is needed to improve its application in the reduction of heavy metal ions in catalytic wastewater. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a method for preparing a hybrid electrode for catalytic reduction of heavy metal ions in wastewater.

[0004] The technical solution of this invention is: a method for preparing a hybrid electrode for catalytic reduction of heavy metal ions in wastewater, comprising the following steps: S1. The three-dimensional porous carbon framework was immersed in a NiCl2 / FeCl3 mixed solution, and urea was added as a nitrogen source. The impregnation was carried out for 3-4 h, and then vacuum dried for 12±2 h. The framework was then carbothermally reduced in a tube furnace at 800-850 ℃ under N2 atmosphere for 2-3 h. After that, it was naturally cooled to room temperature and washed several times with deionized water and ethanol. The framework was then vacuum dried for 2±0.5 h to achieve the anchoring of Ni and Fe atoms to N-doped carbon sites in the form of single atoms, thus obtaining 3D-PC@NiFe-SACs. The NiCl2 / FeCl3 mixed solution was obtained by dissolving NiCl2·6H2O and FeCl3·6H2O in an ethanol-water solution. 2+ with Fe 3+ A mixed solution with a total concentration of 3-6 mM, wherein the molar ratio of Ni to Fe is 2-4:1, and the amount of urea used is 4-6 times the total molar amount of Ni and Fe; the volume ratio of ethanol to water in the ethanol-water solution is 3-5:1. S2. Immerse 3D-PC@NiFe-SACs and Ti3AlC2 powders in 40% HF solution and stir magnetically for 18-24 h. After centrifugation, the powders are washed and dried multiple times with deionized water and anhydrous ethanol to obtain solid powder. Transfer the obtained solid powder to a tube furnace and introduce NH3 gas at 400±10℃ for 2-3 h. Then, allow it to cool naturally to room temperature to finally obtain the 3D-PC@NiFe-SACs / MXene hybrid electrode. The amount of 3D-PC@NiFe-SACs added was 0.5~2.0 g / L and the amount of Ti3AlC2 powder added was 0.8~1.2 g / L, based on the volume of HF solution.

[0005] Description: This invention proposes a novel hybrid electrode with multiple synergistic mechanisms, specifically for Ni in wastewater. 2+ The 3D-PC@NiFe-SACs / MXene hybrid electrode achieves the first integration of a three-dimensional conductive framework, a bimetallic single-atom active center, and controllable defect engineering, compared to simple MXene-supported single-atom, COF adsorption electrode, or nano-zero-valent iron composite system, with high activity, high selectivity, long lifespan and self-cleaning ability. NiFe single-atom anchoring: By atomically dispersing bimetallic NiFe single-atom pairs (NiFe-SACs) on the pore walls of a three-dimensional porous carbon framework (3D-PC), Fe modulates the d-band center of Ni, reducing the *H adsorption energy and enhancing Ni's performance. 2+ →Ni 0 electron transfer efficiency; In-situ growth of MXene layer: By directionally introducing N-doped vacancies into the MXene layer (Ti3C2T) X-Nv) enhances the coordination and capture ability of heavy metal ions, and at the same time serves as a single-atom anchoring site to improve stability.

[0006] Furthermore, the preparation method of the three-dimensional porous carbon framework is as follows: 1) Agricultural waste that has been washed, dried, crushed and sieved is placed in a tube furnace and carbonized at 500±50℃ for 2-3 hours under N2 atmosphere to obtain carbonized biochar; wherein, the agricultural waste is any one of walnut shells, jujube pits and peach pits; 2) Immerse the carbonized biochar in a 70% ZnCl2 solution, stir magnetically for 12-24 h, and vacuum dry to obtain a solid material. Place the obtained solid material in a tube furnace and activate it at 800℃ for 1-1.5 h to obtain a three-dimensional porous carbon framework with high porosity. The mass ratio of ZnCl2 to carbonized biochar is 1-2:1.

[0007] Note: By using a three-dimensional porous carbon framework (3D-PC) as a conductive substrate, a high specific surface area and continuous electron transport channels are provided, overcoming the masking of active sites caused by the stacking of two-dimensional materials. Furthermore, the aforementioned method for preparing the three-dimensional porous carbon framework enables the fabrication of materials with a specific surface area exceeding 1250 μm². 2 / g).

[0008] Furthermore, in S1, ultrasonic-assisted impregnation is performed using 150~200 W during the impregnation process; the vacuum drying temperature is 60~80°C.

[0009] Explanation: The cavitation effect generated by ultrasound significantly enhances the diffusion rate of NiCl2 / FeCl3 mixed solution within the three-dimensional porous carbon framework, enabling metal ions to be uniformly distributed in the micropore and mesopore network. This avoids surface enrichment and agglomeration caused by traditional impregnation methods. At the same time, the ultrasonic field accelerates the contact frequency between urea molecules and metal ions, enhancing the formation of N–C and M–N (M=Ni,Fe) coordination precursors, laying the structural foundation for the construction of high-density Fe–N4 / Ni–N4 active centers in subsequent pyrolysis.

[0010] Meanwhile, controlling the temperature of vacuum drying within the aforementioned temperature range allows the solvent (water / ethanol) to evaporate slowly and uniformly, reducing pore wall shrinkage caused by capillary forces and effectively maintaining the integrity and high specific surface area of ​​the three-dimensional porous structure.

[0011] Furthermore, the preparation method of the hybrid electrode for catalytic reduction of heavy metal ions in wastewater also includes: pH intelligent response treatment of the 3D-PC@NiFe-SACs / MXene hybrid electrode.

[0012] Explanation: By performing pH-smart response treatment on the 3D-PC@NiFe-SACs / MXene hybrid electrode, it is protonated in acidic wastewater (pH 3.0–5.0), promoting the enrichment of heavy metal ions on the electrode surface; and deprotonated during the neutral / alkaline regeneration stage, triggering self-cleaning to release deposited metals.

[0013] As a pH intelligent response processing method of the present invention, the pH intelligent response processing method is as follows: The 3D-PC@NiFe-SACs / MXene hybrid electrode was immersed in a 0.1 M acrylic acid aqueous solution and deposited under a constant potential of –0.8 V vs. Ag / AgCl for 5-8 min to form a thin film with a thickness of 50-60 nm, thus obtaining the 3D-PC@NiFe-SACs / MXene-pH hybrid electrode.

[0014] Description: By grafting pH-responsive polyacrylic acid (PAA) onto the surface of a 3D-PC@NiFe-SACs / MXene hybrid electrode, a smart pH response can be achieved. After each reduction cycle (pH 3.0-5.0), the electrode switches to a pH 7.5 electrolyte (containing 0.1M Na2SO4). Through PAA deprotonation, metal (Ni) is deposited and automatically detached due to electrostatic repulsion, thus restoring the electrode's activity.

[0015] As another pH intelligent response processing method of the present invention, the pH intelligent response processing method is as follows: 1) After treatment with NH3 gas and in a undried state, the 3D-PC@NiFe-SACs / MXene hybrid electrode was immediately subjected to a closed thermal amination treatment in a reactor at 180±10℃ under a N2 atmosphere for 2~3 h to obtain the amination-treated 3D-PC@NiFe-SACs / MXene hybrid electrode; using Ti3C2T x The unsaturated Ti sites in the -Nv region undergo nucleophilic substitution reactions with the reactive NH2· radicals generated from pyrolysis of NH3, partially replacing the –OH / -F groups with –NH2, achieving a grafting density of 12 at.%; 2) The amination-treated 3D-PC@NiFe-SACs / MXene hybrid electrode was immersed in a mixed solution of aniline / ammonium persulfate / sulfuric acid, and a constant potential of –0.8 V vs. Ag / AgCl was applied for deposition for 10~15 min to obtain the deposited 3D-PC@NiFe-SACs / MXene hybrid electrode; The aniline / ammonium persulfate / sulfuric acid mixed solution is obtained by adding aniline and ammonium persulfate to a 0.5 M H2SO4 aqueous solution; wherein, based on the volume of the H2SO4 aqueous solution, the amount of aniline added is 0.1~0.2 mol / L, and the amount of ammonium persulfate added is 0.05~0.1 mol / L. 3) The deposited 3D-PC@NiFe-SACs / MXene hybrid electrode was immersed in a crosslinking solution at 80±2℃ for 1~1.5h to form a thin film with a thickness of 50-100 nm, thus obtaining the 3D-PC@NiFe-SACs / MXene-pH hybrid electrode. The crosslinking solution is a mixture of N-vinylcarbazole (NVK) and bis(4-phenylisocyanate)methane (MDI) in ethanol, with a total concentration of 0.2-0.3%. The molar ratio of N-vinylcarbazole (NVK) to bis(4-phenylisocyanate)methane (MDI) is 0.8-1.2:1. A reversible covalent bond is formed through the Diels-Alder reaction between the -N=C=O of MDI and the C=C of NVK. When the electrode is mechanically damaged, this bond can be reversibly broken and reformed, achieving room temperature self-repair.

[0016] Explanation: By introducing –NH2 in situ onto the defective MXene surface, covalent bonding with conductive polymers is achieved. Conductive polyaniline (PANI) is used to replace PAA, improving electron transport efficiency and pH response sensitivity. Furthermore, a dynamic Diels-Alder bond network is introduced, endowing the electrode with self-healing ability for mechanical damage. This breaks through the stability bottleneck of traditional pH-responsive electrodes and extends the service life of hybrid electrodes.

[0017] Furthermore, in S2, the gas flow rate of NH3 gas is 20~30 mL / min.

[0018] Note: By controlling the flow rate of NH3 gas to 20~30 mL / min, excessive oxidation is avoided, ensuring the effectiveness of in-situ growth of the MXene layer.

[0019] Furthermore, in S1, the natural cooling to room temperature requires natural cooling under an N2 atmosphere; in S2, the natural cooling to room temperature requires natural cooling under an N2 atmosphere.

[0020] Note: After carbothermic reduction and NH3 nitriding, the mixture needs to be naturally cooled in an N2 atmosphere. Oxidation is prevented by using N2 protection throughout the process.

[0021] The beneficial effects of this invention are: (1) The novel hybrid electrode of the present invention works through multiple synergistic mechanisms and is specifically designed for Ni in wastewater. 2+The highly efficient electrocatalytic reduction and in-situ self-cleaning of heavy metal ions are superior to those of simple MXene-supported single atoms, COF adsorption electrodes, or nano-zero-valent iron composite systems for treating heavy metal wastewater.

[0022] (2) The novel hybrid electrode of the present invention achieves the integration of a three-dimensional conductive framework, a bimetallic single-atom active center, and controllable defect engineering for the first time, and has high activity, high selectivity and long life.

[0023] (3) The novel hybrid electrode of the present invention is subjected to pH intelligent response treatment of 3D-PC@NiFe-SACs / MXene hybrid electrode, which is protonated in acidic wastewater to promote the enrichment of heavy metal ions on the electrode surface, and deprotonated in the neutral / alkaline regeneration stage to trigger self-cleaning release of deposited metal, thus significantly improving the service life of the hybrid electrode. Detailed Implementation

[0024] The present invention will now be described in more detail with reference to specific embodiments, so as to better demonstrate the advantages of the present invention.

[0025] Example 1: A method for preparing a hybrid electrode for catalytic reduction of heavy metal ions in wastewater, comprising the following steps: S1. The three-dimensional porous carbon framework was immersed in a NiCl2 / FeCl3 mixed solution, and urea was added as a nitrogen source. The impregnation was carried out for 3.5 h, and ultrasonic impregnation was assisted by 180 W. The framework was then vacuum dried for 12 h at a temperature of 65 °C. The framework was then carbothermally reduced in a tube furnace at 820 °C under a N2 atmosphere for 2.5 h. After that, it was naturally cooled to room temperature under a N2 atmosphere. The framework was washed several times with deionized water and ethanol, and then vacuum dried for 2 h at a temperature of 75 °C to obtain 3D-PC@NiFe-SACs. The NiCl2 / FeCl3 mixed solution was obtained by dissolving NiCl2·6H2O and FeCl3·6H2O in an ethanol-water solution. 2+ with Fe 3+ A mixed solution with a total concentration of 5 mM, wherein the molar ratio of Ni to Fe is 3:1, and the amount of urea used is 5 times the total molar amount of Ni and Fe; the volume ratio of ethanol to water in the ethanol-water solution is 3:1. The method for preparing the three-dimensional porous carbon framework is as follows: 1) Agricultural waste that has been washed, dried, crushed and sieved is placed in a tube furnace and carbonized at 500°C for 2.5 h under a N2 atmosphere to obtain carbonized biochar; wherein, the agricultural waste is walnut shells; 2) The carbonized biochar was immersed in a 70% ZnCl2 solution and magnetically stirred for 22 h. After vacuum drying, a solid material was obtained. The obtained solid material was placed in a tube furnace and activated at 800℃ for 1.2 h to obtain a three-dimensional porous carbon framework with high porosity (pore size distribution: 2–50 nm). The mass ratio of ZnCl2 to carbonized biochar was 1.1:1.

[0026] S2. 3D-PC@NiFe-SACs and Ti3AlC2 powders were immersed in a 40% HF solution and magnetically stirred at 300 rpm for 22 h. After centrifugation, the powders were washed and dried repeatedly with deionized water and anhydrous ethanol to obtain solid powders. The solid powders were transferred to a tube furnace and NH3 gas was introduced at 400℃ for 2.5 h at a flow rate of 28 mL / min. Subsequently, the powders were naturally cooled to room temperature under an N2 atmosphere to introduce N vacancies (Nv) onto the MXene surface, forming Ti3C2T. x -Nv; 3D-PC@NiFe-SACs / MXene hybrid electrode is obtained; The amount of 3D-PC@NiFe-SACs added was 1.0 g / L based on the volume of HF solution, and the amount of Ti3AlC2 powder added was 1.0 g / L.

[0027] Example 2: The difference between this example and Example 1 is that the three-dimensional porous carbon framework is immersed in a NiCl2 / FeCl3 mixed solution, and urea is added as a nitrogen source. The immersion is carried out for 3 hours, and 150W ultrasonic assisted immersion is used during the immersion.

[0028] Example 3: The difference between this example and Example 1 is that the three-dimensional porous carbon framework is immersed in a NiCl2 / FeCl3 mixed solution, and urea is added as a nitrogen source. The immersion time is 4 h, and 200 W ultrasonic assisted immersion is used during the immersion.

[0029] Example 4: This example differs from Example 1 in that the impregnation is followed by vacuum drying for 10 hours at a temperature of 60°C; and the washing is followed by vacuum drying for 1.5 hours at a temperature of 60°C.

[0030] Example 5: This example differs from Example 1 in that the impregnation is followed by vacuum drying for 14 hours at a temperature of 80°C; and the washing is followed by vacuum drying for 2.5 hours at a temperature of 80°C.

[0031] Example 6: This example differs from Example 1 in that the NiCl2 / FeCl3 mixed solution is obtained by dissolving NiCl2·6H2O and FeCl3·6H2O in an ethanol-water solution. 2+ with Fe 3+A mixed solution with a total concentration of 3 mM, wherein the molar ratio of Ni to Fe is 2:1, and the amount of urea used is 4 times the total molar amount of Ni and Fe; the volume ratio of ethanol to water in the ethanol-water solution is 4:1.

[0032] Example 7: This example differs from Example 1 in that the NiCl2 / FeCl3 mixed solution is obtained by dissolving NiCl2·6H2O and FeCl3·6H2O in an ethanol-water solution. 2+ with Fe 3+ A mixed solution with a total concentration of 6 mM, wherein the molar ratio of Ni to Fe is 4:1, and the amount of urea used is 6 times the total molar amount of Ni and Fe; the volume ratio of ethanol to water in the ethanol-water solution is 5:1.

[0033] Example 8: This example differs from Example 1 in that the method for preparing the three-dimensional porous carbon framework is as follows: 1) Agricultural waste that has been washed, dried, crushed and sieved is placed in a tube furnace and carbonized at 450°C for 2 h under a N2 atmosphere to obtain carbonized biochar; wherein, the agricultural waste is jujube pits; 2) The carbonized biochar was immersed in a 70% ZnCl2 solution and magnetically stirred for 12 h. After vacuum drying, a solid material was obtained. The obtained solid material was placed in a tube furnace and activated at 800℃ for 1 h to obtain a three-dimensional porous carbon framework with high porosity (pore size distribution: 2–50 nm). The mass ratio of ZnCl2 to carbonized biochar was 1:1.

[0034] Example 9: This example differs from Example 1 in that the method for preparing the three-dimensional porous carbon framework is as follows: 1) Agricultural waste that has been washed, dried, crushed and sieved is placed in a tube furnace and carbonized at 550°C for 3 h under a N2 atmosphere to obtain carbonized biochar; wherein, the agricultural waste is peach pits; 2) The carbonized biochar was immersed in a 70% ZnCl2 solution and magnetically stirred for 24 h. After vacuum drying, a solid material was obtained. The obtained solid material was placed in a tube furnace and activated at 800℃ for 1.5 h to obtain a three-dimensional porous carbon framework with high porosity (pore size distribution: 2–50 nm). The mass ratio of ZnCl2 to carbonized biochar was 2:1.

[0035] Example 10: The difference between this example and Example 1 is that 3D-PC@NiFe-SACs and Ti3AlC2 powders were immersed in 40% HF solution and magnetically stirred at 300 rpm for 18 h.

[0036] Example 11: The difference between this example and Example 1 is that 3D-PC@NiFe-SACs and Ti3AlC2 powders were immersed in 40% HF solution and magnetically stirred at 300 rpm for 24 h.

[0037] Example 12: The difference between this example and Example 1 is that after washing and drying, NH3 gas at 400±10℃ was directly introduced into a tube furnace for 2 hours, and the gas flow rate of NH3 gas was 20 mL / min.

[0038] Example 13: The difference between this example and Example 1 is that after washing and drying, NH3 gas at 400±10℃ was directly introduced into a tube furnace for 3 hours, and the gas flow rate of NH3 gas was 30 mL / min.

[0039] Example 14: The difference between this example and Example 1 is that, based on the volume of HF solution, the amount of 3D-PC@NiFe-SACs added is 0.5 g / L, and the amount of Ti3AlC2 powder added is 0.8 g / L.

[0040] Example 15: The difference between this example and Example 1 is that, based on the volume of HF solution, the amount of 3D-PC@NiFe-SACs added is 2.0 g / L, and the amount of Ti3AlC2 powder added is 1.2 g / L.

[0041] Example 16: This example differs from Example 1 in that it further includes pH-intelligent response treatment of the 3D-PC@NiFe-SACs / MXene hybrid electrode. The method for pH-intelligent response treatment is as follows: The 3D-PC@NiFe-SACs / MXene hybrid electrode was immersed in 0.1 M acrylic acid aqueous solution (pH≈3.5) and a constant potential of –0.8 V vs. Ag / AgCl was applied for deposition for 6 min; a film with a thickness of 55 nm was formed to obtain the 3D-PC@NiFe-SACs / MXene-pH hybrid electrode. Specifically, the working electrode is a 3D-PC@NiFe-SACs / MXene hybrid electrode; the counter electrode is a platinum wire; and the reference electrode is Ag / AgCl (saturated KCl).

[0042] Example 17: This example differs from Example 16 in that the 3D-PC@NiFe-SACs / MXene hybrid electrode is immersed in a 0.1 M acrylic acid aqueous solution (pH≈3.5), and a constant potential deposition of –0.8 V vs. Ag / AgCl is applied for 5 min; a film with a thickness of 50 nm is formed to obtain the 3D-PC@NiFe-SACs / MXene-pH hybrid electrode.

[0043] Example 18: This example differs from Example 16 in that the 3D-PC@NiFe-SACs / MXene hybrid electrode was immersed in a 0.1 M acrylic acid aqueous solution (pH≈3.5), and a constant potential deposition of –0.8 V vs. Ag / AgCl was applied for 8 min; a film with a thickness of 60 nm was formed to obtain the 3D-PC@NiFe-SACs / MXene-pH hybrid electrode.

[0044] Example 19: This example differs from Example 1 in that it further includes pH-intelligent response treatment of the 3D-PC@NiFe-SACs / MXene hybrid electrode. The method for pH-intelligent response treatment is as follows: 1) After treatment with NH3 gas and in a non-drying state (this must be carried out under oxygen-free, continuous humid conditions to prevent MXene from being oxidized to TiO2), the 3D-PC@NiFe-SACs / MXene hybrid electrode is immediately subjected to a closed-loop thermal amination treatment in a reactor at 180℃ under an N2 atmosphere for 2.5 h to obtain the amination-treated 3D-PC@NiFe-SACs / MXene hybrid electrode; using Ti3C2T x The unsaturated Ti sites in the -Nv region undergo nucleophilic substitution reactions with the reactive NH2· radicals generated from pyrolysis of NH3, partially replacing the –OH / -F groups with –NH2, achieving a grafting density of 12 at.%; 2) Immerse the amination-treated 3D-PC@NiFe-SACs / MXene hybrid electrode in a mixed solution of aniline / ammonium persulfate / sulfuric acid, and deposit it at a constant potential of –0.8 V vs. Ag / AgCl for 12 min to obtain the deposited 3D-PC@NiFe-SACs / MXene hybrid electrode; after deposition, no washing is required, proceed directly to step 3) to avoid PAIN desorption; The aniline / ammonium persulfate / sulfuric acid mixed solution is obtained by adding aniline and ammonium persulfate to a 0.5 M H2SO4 aqueous solution; wherein, based on the volume of the H2SO4 aqueous solution, the amount of aniline added is 0.15 mol / L and the amount of ammonium persulfate added is 0.08 mol / L; the solution should be prepared and used immediately to avoid oxidation and discoloration of aniline; 3) The deposited 3D-PC@NiFe-SACs / MXene hybrid electrode was immersed in a crosslinking solution at 80℃ for 1.2 h to form a thin film with a thickness of 80 nm, thus obtaining the 3D-PC@NiFe-SACs / MXene-pH hybrid electrode. Specifically, the working electrode is a post-deposited 3D-PC@NiFe-SACs / MXene hybrid electrode; the counter electrode is a platinum wire; and the reference electrode is Ag / AgCl (saturated KCl). The crosslinking solution is a mixture of N-vinylcarbazole (NVK) and bis(4-phenylisocyanate)methane (MDI) in ethanol, with a total concentration of 0.28%. The molar ratio of N-vinylcarbazole (NVK) to bis(4-phenylisocyanate)methane (MDI) is 1:1. A reversible covalent bond is formed by the Diels-Alder reaction between the -N=C=O of MDI and the C=C of NVK. When the electrode is mechanically damaged, this bond can be reversibly broken and reformed, achieving room temperature self-repair.

[0045] Example 20: This example differs from Example 19 in that, after treatment with NH3 gas and in a undried state, the 3D-PC@NiFe-SACs / MXene hybrid electrode is immediately subjected to a closed thermal amination treatment in a reactor at 170°C under an N2 atmosphere for 2 hours.

[0046] Example 21: The difference between this example and Example 19 is that, after treatment with NH3 gas and in a undried state, the 3D-PC@NiFe-SACs / MXene hybrid electrode was immediately subjected to a closed thermal amination treatment in a reactor at 190°C under an N2 atmosphere for 3 hours.

[0047] Example 22: This example differs from Example 19 in that the amination-treated 3D-PC@NiFe-SACs / MXene hybrid electrode is immersed in a mixed solution of aniline / ammonium persulfate / sulfuric acid, and a constant potential deposition of –0.8 V vs. Ag / AgCl is applied for 10 min.

[0048] Example 23: This example differs from Example 19 in that the amination-treated 3D-PC@NiFe-SACs / MXene hybrid electrode is immersed in a mixed solution of aniline / ammonium persulfate / sulfuric acid, and a constant potential deposition of –0.8 V vs. Ag / AgCl is applied for 15 min.

[0049] Example 24: This example differs from Example 19 in that the aniline / ammonium persulfate / sulfuric acid mixed solution is a mixed solution obtained by adding aniline and ammonium persulfate to a 0.5 M H2SO4 aqueous solution; wherein, based on the volume of the H2SO4 aqueous solution, the amount of aniline added is 0.1 mol / L and the amount of ammonium persulfate added is 0.05 mol / L.

[0050] Example 25: This example differs from Example 19 in that the aniline / ammonium persulfate / sulfuric acid mixed solution is a mixed solution obtained by adding aniline and ammonium persulfate to a 0.5 M H2SO4 aqueous solution; wherein, based on the volume of the H2SO4 aqueous solution, the amount of aniline added is 0.2 mol / L and the amount of ammonium persulfate added is 0.1 mol / L.

[0051] Example 26: This example differs from Example 19 in that the deposited 3D-PC@NiFe-SACs / MXene hybrid electrode is immersed in a crosslinking solution at 80±2℃ for 1 h to form a thin film with a thickness of 50 nm.

[0052] Example 27: This example differs from Example 19 in that the deposited 3D-PC@NiFe-SACs / MXene hybrid electrode is immersed in a crosslinking solution at 80±2℃ for 1.5 h to form a thin film with a thickness of 100 nm.

[0053] Example 28: This example differs from Example 19 in that the crosslinking solution is a mixture of N-vinylcarbazole (NVK) and bis(4-phenylisocyanate)methane (MDI) with a total concentration of 0.2% obtained by adding ethanol, wherein the molar ratio of N-vinylcarbazole (NVK) to bis(4-phenylisocyanate)methane (MDI) is 0.8:1.

[0054] Example 29: This example differs from Example 19 in that the crosslinking solution is a mixture of N-vinylcarbazole (NVK) and bis(4-phenylisocyanate)methane (MDI) with a total concentration of 0.3% obtained by adding N-vinylcarbazole (NVK) and bis(4-phenylisocyanate)methane (MDI) to ethanol, wherein the molar ratio of N-vinylcarbazole (NVK) to bis(4-phenylisocyanate)methane (MDI) is 1.2:1.

[0055] Experimental example: The catalytic reduction effects of 3D-PC@NiFe-SACs / MXene hybrid electrode, 3D-PC@NiFe-SACs / MXene-pH(I) hybrid electrode, and 3D-PC@NiFe-SACs / MXene-pH(II) hybrid electrode on heavy metal ion reduction in wastewater were verified. Based on the emission limits of the "Electroplating Pollutant Emission Standard" (GB 21900—2008), the simulation conditions for heavy metal wastewater parameters in low-to-medium concentration industrial wastewater are shown in Table 1 below: Table 1 Simulation conditions and parameters for heavy metal wastewater

[0056] A control group was also set up: NiO / C electrode; a three-electrode system was used, as shown in Table 2 below: Table 2. Three-electrode system setup parameters

[0057] The hybrid electrode was attached to a conductive substrate (such as FTO or carbon cloth). In this example, an FTO glass substrate with a thickness of approximately 50–100 nm was used. The scan rate was 10 mV / s (CV), the constant potential was -1.2 V, and the reaction time was 90 min. ICP-MS was used for detection, and the detection limit was: Ni 2+ =0.02 μg / L; each experiment was repeated 5 times, and the data were taken as mean ± standard deviation. The results are shown in Table 3 below: Table 3 Treatment effect of heavy metal wastewater

[0058] As shown in Table 3 above, the 3D-PC@NiFe-SACs / MXene hybrid electrode (Example 1), the 3D-PC@NiFe-SACs / MXene-pH(I) hybrid electrode (Example 16), and the 3D-PC@NiFe-SACs / MXene-pH(II) hybrid electrode (Example 19) show significant improvements compared to the NiO / C electrode (control). Taking the 3D-PC@NiFe-SACs / MXene-pH(II) hybrid electrode as an example, compared to the NiO / C electrode, Ni... 2+ The reduction rate increased by 30.8%.

[0059] Meanwhile, a comparison of pH intelligent response processing technologies revealed that the 3D-PC@NiFe-SACs / MXene-pH(II) hybrid electrode exhibited better stability in use compared to the 3D-PC@NiFe-SACs / MXene-pH(I) hybrid electrode. After five cycles, the performance retention rate was significantly better than that of the 3D-PC@NiFe-SACs / MXene-pH(I) hybrid electrode. This demonstrates that by introducing –NH2 in situ onto the defective MXene surface to achieve covalent bonding with the conductive polymer and replacing PAA with intrinsically conductive polyaniline (PANI), electron transport efficiency and pH response sensitivity can be effectively improved. Furthermore, by introducing a dynamic Diels-Alder bond network, the electrode can be endowed with self-healing ability for mechanical damage, thereby overcoming the stability bottleneck of traditional pH response electrodes and extending the service life of the hybrid electrode.

[0060] To further investigate the influence of pH intelligent response processing parameters on the performance of the hybrid electrode of this invention, the following investigation is conducted: Investigation 1 (3D-PC@NiFe-SACs / MXene-pH(I) hybrid electrode): The 3D-PC@NiFe-SACs / MXene-pH(I) hybrid electrodes prepared in Examples 17 and 18 were used for experiments (film thickness). The scan rate was 10 mV / s (CV), the constant potential was -1.2 V, and the reaction time was 90 min. ICP-MS was used for detection. The detection limit was: Ni 2+ =0.02 μg / L; each experiment was repeated 5 times, and the data were taken as mean ± standard deviation. The results are shown in Table 4 below: Table 4 Treatment effect of heavy metal wastewater

[0061] As can be seen from the results in Table 4 above, the thickness of the PAA film has a certain influence on the 3D-PC@NiFe-SACs / MXene-pH(I) hybrid electrode. Among them, the 3D-PC@NiFe-SACs / MXene-pH(I) hybrid electrode prepared in Example 18 has the best effect on the treatment of heavy metal wastewater.

[0062] Investigation 2 (3D-PC@NiFe-SACs / MXene-pH(II) hybrid electrode): The 3D-PC@NiFe-SACs / MXene-pH(I) hybrid electrodes prepared in Examples 26 and 27 were used for experiments (film thickness). The scan rate was 10 mV / s (CV), the constant potential was -1.2 V, and the reaction time was 90 min. ICP-MS was used for detection. The detection limit was: Ni 2+ =0.02 μg / L; each experiment was repeated 5 times, and the data were taken as mean ± standard deviation. The results are shown in Table 5 below: Table 5 Treatment effect of heavy metal wastewater

[0063] As can be seen from the results in Table 5 above, the thickness of the PANI film has a certain influence on the 3D-PC@NiFe-SACs / MXene-pH(II) hybrid electrode. Among them, the 3D-PC@NiFe-SACs / MXene-pH(II) hybrid electrode prepared in Example 19 has the best effect on the treatment of heavy metal wastewater.

Claims

1. A method for preparing a hybrid electrode for catalytic reduction of heavy metal ions in wastewater, characterized in that, Includes the following steps: S1. The three-dimensional porous carbon framework was immersed in a NiCl2 / FeCl3 mixed solution, and urea was added as a nitrogen source. The impregnation was carried out for 3-4 h, vacuum dried for 12±2 h, and then carbothermally reduced in a tube furnace at 800-850 ℃ under N2 atmosphere for 2-3 h. After that, it was naturally cooled to room temperature, washed with deionized water and ethanol several times in sequence, and vacuum dried for 2±0.5 h to obtain 3D-PC@NiFe-SACs. The NiCl2 / FeCl3 mixed solution was obtained by dissolving NiCl2·6H2O and FeCl3·6H2O in an ethanol-water solution. 2+ with Fe 3+ A mixed solution with a total concentration of 3-6 mM, wherein the molar ratio of Ni to Fe is 2-4:1, and the amount of urea used is 4-6 times the total molar amount of Ni and Fe; the volume ratio of ethanol to water in the ethanol-water solution is 3-5:

1. S2. Immerse 3D-PC@NiFe-SACs and Ti3AlC2 powders in 40% HF solution and stir magnetically for 18-24 h. After centrifugation, the powders are washed and dried multiple times with deionized water and anhydrous ethanol to obtain solid powder. Transfer the obtained solid powder to a tube furnace and introduce NH3 gas at 400±10℃ for 2-3 h. Then, allow it to cool naturally to room temperature to finally obtain the 3D-PC@NiFe-SACs / MXene hybrid electrode. The amount of 3D-PC@NiFe-SACs added was 0.5~2.0 g / L and the amount of Ti3AlC2 powder added was 0.8~1.2 g / L, based on the volume of HF solution.

2. The method for preparing a hybrid electrode for catalytic reduction of heavy metal ions in wastewater according to claim 1, characterized in that, The method for preparing the three-dimensional porous carbon framework is as follows: 1) Agricultural waste that has been washed, dried, crushed and sieved is placed in a tube furnace and carbonized at 500±50℃ for 2-3 hours under N2 atmosphere to obtain carbonized biochar; wherein, the agricultural waste is any one of walnut shells, jujube pits and peach pits; 2) Immerse the carbonized biochar in a 70% ZnCl2 solution, stir magnetically for 12-24 h, and vacuum dry to obtain a solid material. Place the obtained solid material in a tube furnace and activate it at 800℃ for 1-1.5 h to obtain a three-dimensional porous carbon framework. The mass ratio of ZnCl2 to carbonized biochar is 1-2:

1.

3. The method for preparing a hybrid electrode for catalytic reduction of heavy metal ions in wastewater according to claim 1, characterized in that, In S1, ultrasonic impregnation with 150~200 W is used during impregnation; the temperature of the vacuum drying is 60~80℃.

4. The method for preparing a hybrid electrode for catalytic reduction of heavy metal ions in wastewater according to claim 1, characterized in that, Also includes: pH-smart response treatment was applied to the 3D-PC@NiFe-SACs / MXene hybrid electrode.

5. The method for preparing a hybrid electrode for catalytic reduction of heavy metal ions in wastewater according to claim 4, characterized in that, One method of the pH intelligent response processing is as follows: The 3D-PC@NiFe-SACs / MXene hybrid electrode was immersed in a 0.1 M acrylic acid aqueous solution and deposited under a constant potential of –0.8 V vs. Ag / AgCl for 5-8 min to form a thin film with a thickness of 50-60 nm, thus obtaining the 3D-PC@NiFe-SACs / MXene-pH hybrid electrode.

6. The method for preparing a hybrid electrode for catalytic reduction of heavy metal ions in wastewater according to claim 4, characterized in that, Another method for the pH intelligent response processing is: 1) After treatment with NH3 gas and in a undried state, the 3D-PC@NiFe-SACs / MXene hybrid electrode was immediately subjected to a closed thermal amination treatment in a reactor at 180±10℃ under a N2 atmosphere for 2~3 h to obtain the amination electrode; 2) The amination-treated 3D-PC@NiFe-SACs / MXene hybrid electrode was immersed in a mixed solution of aniline / ammonium persulfate / sulfuric acid, and a constant potential of –0.8 V vs. Ag / AgCl was applied for deposition for 10~15 min to obtain the deposited 3D-PC@NiFe-SACs / MXene hybrid electrode; The aniline / ammonium persulfate / sulfuric acid mixed solution is obtained by adding aniline and ammonium persulfate to a 0.5 M H2SO4 aqueous solution; wherein, based on the volume of the H2SO4 aqueous solution, the amount of aniline added is 0.1~0.2 mol / L, and the amount of ammonium persulfate added is 0.05~0.1 mol / L. 3) The deposited 3D-PC@NiFe-SACs / MXene hybrid electrode was immersed in a crosslinking solution at 80±2℃ for 1~1.5 h to form a thin film with a thickness of 50-100 nm, thus obtaining the 3D-PC@NiFe-SACs / MXene-pH hybrid electrode. The crosslinking solution is a mixture of N-vinylcarbazole and bis(4-phenylisocyanate)methane in ethanol, with a total concentration of 0.2-0.3%, wherein the molar ratio of N-vinylcarbazole to bis(4-phenylisocyanate)methane is 0.8-1.2:

1.

7. The method for preparing a hybrid electrode for catalytic reduction of heavy metal ions in wastewater according to claim 1, characterized in that, In S2, NH3 gas is introduced at 400±10℃ for 2~3 h, and the gas flow rate of NH3 gas is 20~30 mL / min.

8. The method for preparing a hybrid electrode for catalytic reduction of heavy metal ions in wastewater according to claim 1, characterized in that, In S1, the natural cooling to room temperature requires natural cooling under an N2 atmosphere; in S2, the natural cooling to room temperature requires natural cooling under an N2 atmosphere.

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