Preparation method and application of nitrogen-sulfur co-doped modified layered double-oxide material

Abstract

The invention discloses a preparation method of a nitrogen-sulfur co-doped modified layered double-oxide material, and belongs to the technical field of water treatment.The preparation method comprises the following steps that 1, a carbon felt substrate is pretreated and dried, the treated substrate is placed in a uniform solution containing Fe (NO3) 3.9 H2O and Ni (NO3) 2.6 H2O to be subjected to a hydrothermal reaction, and after the hydrothermal reaction is completed, the substrate is taken out and dried; carrying out ultrasonic treatment and washing with deionized water to obtain a NiFe-LDH precursor; and (2) drying the obtained precursor, dipping the dried precursor in an ethanol solution of ammonium persulfate, and then carrying out high-temperature carbonization treatment in an inert gas atmosphere to prepare the nitrogen-sulfur co-doped modified nickel-iron layered double-oxide material. The difference of nitrogen and sulfur in atomic radius, electronegativity and doping form enables the co-doped structure to effectively regulate and control the electronic structure of the material: nitrogen doping improves conductivity, and sulfur doping promotes exposure and stability of active sites. The co-doping synergistically optimizes the electronic structure and catalytic activity of the material, so that the material has excellent capacitive deionization removal performance and electrocatalytic activity at the same time.

Description

Technical Field

[0001] This invention relates to the field of water treatment materials technology, specifically to a method for preparing and applying a nitrogen-sulfur co-doped modified layered double oxide material. Background Technology

[0002] With rapid industrialization, the problem of combined heavy metal and organic pollutant pollution in water bodies is becoming increasingly serious, posing a severe threat to the ecological environment and human health. Hexavalent chromium (Cr(VI)) has become a key focus of heavy metal pollution control due to its high toxicity and carcinogenicity; while p-nitrophenol (PNP), a typical recalcitrant organic pollutant, is chemically stable and bioaccumulative. In industrial wastewater, these two types of pollutants often coexist, making the development of methods for the simultaneous and efficient removal of both crucial.

[0003] Currently, while treatment methods for single types of pollutants each have their advantages, they also have limitations. Coupling capacitive deionization (CDI) with electro-Fenton technology can achieve functional complementarity between ion adsorption and pollutant degradation, facilitating their simultaneous removal. The key to realizing this coupled system lies in developing high-performance electrode materials. Currently, noble metals and oxides (such as Pt, IrO2, RuO2) exhibit excellent catalytic performance but are expensive; carbon materials are less expensive but have limited catalytic activity; non-noble metal catalysts such as transition metal-based phosphides, sulfides, and layered hydrogen hydroxides (LDHs) have attracted attention due to their low cost and tunable structure. However, existing LDH materials generally suffer from poor conductivity, insufficient exposure of active sites, and low structural stability, limiting their application in water treatment. Summary of the Invention

[0004] To address the problems existing in related technologies, this invention provides a method for preparing and applying nitrogen-sulfur co-doped modified layered double oxide materials. This preparation method can improve the conductivity of the obtained composite material, promote the exposure and stability of active sites, and thus achieve efficient and simultaneous removal of Cr(VI) and PNP.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows: a method for preparing a nitrogen-sulfur co-doped modified layered double oxide material, the innovation of which lies in the following steps: (1) The carbon felt substrate was pretreated and dried. The treated substrate was placed in a homogeneous solution containing Fe(NO3)3·9H2O and Ni(NO3)2·6H2O for hydrothermal reaction. After the reaction was completed, it was taken out, ultrasonically treated, washed with deionized water and dried to obtain NiFe-LDH precursor. (2) The obtained precursor was dried and then immersed in an ethanol solution of ammonium persulfate. Then, it was subjected to high-temperature carbonization under an inert gas atmosphere to finally obtain a nitrogen-sulfur co-doped modified nickel-iron layered double oxide material.

[0006] Preferably, in step (1), the pretreatment process is as follows: the carbon felt substrate is sequentially immersed in sulfuric acid solution, anhydrous ethanol solution, and deionized water and ultrasonically treated for 15 minutes respectively; wherein the concentration of the sulfuric acid solution is 0.5-1.5 mol / L.

[0007] Preferably, in step (1), 1 mmol Fe(NO3)3·9H2O and 1-3 mmol Ni(NO3)2·6H2O are added to every 10 mL of deionized water to form a homogeneous solution.

[0008] Preferably, in step (1), the hydrothermal reaction temperature is 120-180℃ and the time is 6-12h.

[0009] Preferably, in step (2), the concentration of the ammonium persulfate ethanol solution is 2.5-10 mmol / L, and the precursor is immersed in the ammonium persulfate ethanol solution for 6-12 hours.

[0010] Preferably, in step (2), the temperature of the high-temperature carbonization treatment is 500-700℃ and the holding time is 1-3h.

[0011] Preferably, in step (2), the inert gas is nitrogen or argon.

[0012] This invention utilizes the nitrogen-sulfur co-doped modified nickel-iron layered double oxide material prepared by the above-mentioned preparation method in water treatment. The nitrogen-sulfur co-doped modified nickel-iron layered double oxide material is used as the cathode and the graphite plate is used as the anode to remove heavy metals Cr(VI) and p-nitrophenol from the water.

[0013] This invention provides a method for preparing and applying nitrogen-sulfur co-doped modified layered double oxide materials, which have the following beneficial effects: (1) This invention provides a nitrogen-sulfur co-doped modified NiFe-LDO material. Ammonium persulfate ((NH4)2S2O8) is uniformly adsorbed on the surface and interlayer of the precursor in an ethanol solution. During the subsequent high-temperature carbonization process in a nitrogen atmosphere, ammonium persulfate decomposes to produce nitrogen- and sulfur-containing species, which are co-doped into the layered double oxide (LDO) lattice converted from NiFe-LDH. Nitrogen atoms mainly enter the carbon framework in the form of pyridine nitrogen and graphitic nitrogen, while sulfur atoms are doped in the form of sulfides or sulfates. The method is simple and the doping is uniform. Ammonium persulfate has both nitrogen and sulfur dual-source functions and high doping efficiency.

[0014] (2) Nitrogen doping enhances the conductivity of the material, while sulfur doping introduces lattice distortion and increases oxygen vacancy concentration, promoting the exposure and stability of active sites. This nitrogen-sulfur co-doped structure can effectively regulate the electronic structure of the material, not only improving the specific surface area and conductivity, but also significantly enhancing the removal capacity of Ni / Fe active centers for Cr(VI) by regulating the electronic states of Ni and Fe active centers. At the same time, it promotes the generation of active oxygen species on the electrode surface, thereby improving the efficiency of electro-Fenton degradation of PNP. In the capacitive deionization-electro-Fenton coupling system, the material can achieve efficient and simultaneous removal of Cr(VI) and PNP, maintain stable performance over a wide pH range, and has good reusability.

[0015] (3) The material of the present invention exhibits faster removal kinetics and higher removal efficiency in the treatment of complex polluted water, and has significant technical advantages and application potential. Attached Figure Description

[0016] Figure 1 The image shows the SEM image of the electrode material prepared in Example 2.

[0017] Figure 2 The image shows the SEM image of the electrode material prepared in Comparative Example 1.

[0018] Figure 3 The image shows the SEM image of the electrode material prepared in Comparative Example 2.

[0019] Figure 4 This is a comparison chart showing the effects of the electrode material prepared in Example 1 and the unmodified NiFe-LDH in water treatment.

[0020] Figure 5 This is a comparison chart showing the effects of the electrode material prepared in Example 2 and the unmodified NiFe-LDH in water treatment.

[0021] Figure 6 This is a comparison chart showing the effects of the electrode material prepared in Example 3 and the unmodified NiFe-LDH in water treatment.

[0022] Figure 7 This is a comparison chart showing the effects of the electrode material prepared in Example 4 and the unmodified NiFe-LDH in water treatment.

[0023] Figure 8 This is a comparison chart showing the effects of the electrode material prepared in Example 5 and the unmodified NiFe-LDH in water treatment.

[0024] Figure 9 This is a comparison chart showing the effects of the electrode material prepared in Example 6 and the unmodified NiFe-LDH in water treatment.

[0025] Figure 10 The graph shows a comparison of the effects of the electrode material prepared in Comparative Example 1 and the electrode material in Example 2 on water treatment.

[0026] Figure 11 The image shows a comparison of the effects of the electrode material prepared in Comparative Example 2 and the electrode material in Example 2 on water treatment. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to specific embodiments and accompanying drawings, but the scope of protection of the present invention is not limited to the content described.

[0028] All chemical reagents not described in the embodiments and comparative examples of this invention were commercially available analytical grade reagents used in the experiments.

[0029] Example 1 This embodiment provides a method for preparing a nitrogen-sulfur co-doped modified layered double oxide material, including the following steps: (1) Pretreatment of carbon felt substrate: The carbon felt substrate was immersed in sulfuric acid solution, anhydrous ethanol solution and deionized water in sequence and ultrasonically treated in the three solutions for 15 minutes respectively; wherein the concentration of sulfuric acid solution was 1 mol / L.

[0030] 4 mmol Fe(NO3)3·9H2O and 8 mmol Ni(NO3)2·6H2O were dissolved in 40 mL of deionized water to form a homogeneous solution. The pretreated carbon felt substrate was immersed in the homogeneous solution and placed in a reaction vessel. The hydrothermal reaction was carried out at 150 °C for 9 hours. After the reaction was completed, the sample was removed, sonicated for 5 minutes, washed with deionized water, and dried to obtain the NiFe-LDH precursor. (2) The obtained precursor was immersed in an ethanol solution of ammonium persulfate with a concentration of 5 mmol / L for 8 hours. After drying, it was subjected to high-temperature carbonization treatment at 600°C for 2 hours under a nitrogen atmosphere to finally obtain a nitrogen-sulfur co-doped modified nickel-iron layered double oxide material, which was used as an electrode material for water treatment.

[0031] The electrode material prepared in Example 1 was used as the cathode, and a graphite plate (4cm × 4cm) was used as the anode. The removal of p-nitrophenol and heavy metal ions Cr(VI) was studied in a two-electrode degradation device. Specifically, the prepared electrode material (3×3cm) was used as the cathode, and a graphite plate (4cm × 4cm) was used as the anode. The device was placed in a 150mL solution containing 50mg / L p-nitrophenol and 20mg / L Cr(VI) as the degradation solution, with a 0.1mol / L Na₂SO₄ solution as the supporting electrolyte, and a current density of 20mA·cm⁻¹. -2The electrocatalytic degradation was conducted in a two-electrode degradation apparatus at 25°C and pH 7. 1 mL was taken every 3 minutes, diluted to 10 mL, and its absorbance was measured to calculate the removal rate.

[0032] Depend on Figure 4 It can be seen that the electrode material prepared in Example 1, when used in electrocatalytic degradation studies, showed a 15-minute removal rate of nitrophenol (e.g., Figure 4 Removal rates of Cr(VI) and Cr(VI) over 30 min (e.g., left) Figure 4 The right side is higher than the unmodified NiFe-LDH electrode. In this invention, the unmodified NiFe-LDH electrode refers to the NiFe-LDH precursor obtained by step (1) of each corresponding embodiment or comparative example without being treated by step (2). The electrode material of the corresponding embodiment or comparative example is replaced by the unmodified NiFe-LDH electrode. The above steps are used for water treatment to remove p-nitrophenol and Cr(VI)).

[0033] Example 2 This embodiment provides a method for preparing a nitrogen-sulfur co-doped modified layered double oxide material, including the following steps: (1) Pretreatment of carbon felt substrate: The carbon felt substrate was immersed in sulfuric acid solution, anhydrous ethanol solution and deionized water in sequence, and ultrasonically treated for 15 minutes respectively; the concentration of sulfuric acid solution was 1 mol / L.

[0034] 4 mmol Fe(NO3)3·9H2O and 12 mmol Ni(NO3)2·6H2O were dissolved in 40 mL of deionized water to form a homogeneous solution. The pretreated carbon felt substrate was immersed in the homogeneous solution and placed in a reaction vessel. The hydrothermal reaction was carried out at 150 °C for 9 hours. After the reaction was completed, the sample was removed, sonicated for 5 minutes, washed with deionized water, and dried to obtain the NiFe-LDH precursor. (2) The obtained precursor was immersed in an ammonium persulfate ethanol solution with a concentration of 7.5 mmol / L for 8 hours. After drying, it was subjected to high-temperature carbonization treatment at 600℃ for 2 hours under a nitrogen atmosphere to finally obtain a nitrogen-sulfur co-doped modified nickel-iron layered double oxide material, which was used as an electrode material for water treatment.

[0035] The SEM image of the electrode material prepared in this embodiment is shown below. Figure 2 As shown, the overall structure presents a nanosheet flower-like microsphere structure. This flower-like structure provides a huge specific surface area and channels, which is conducive to the full exposure of active sites. At the same time, the three-dimensional conductive network formed by the interconnection between nanosheets helps to improve the conductivity of the material, thereby enhancing its efficient and simultaneous removal of Cr(VI) and PNP from water.

[0036] The electrode material prepared in Example 2 was used for electrocatalytic degradation research. The research process was the same as in Example 1, except that the electrode material prepared in Example 1 was replaced with the electrode material prepared in Example 2. Figure 5 It can be seen that the removal rate of p-nitrophenol in 15 minutes (e.g.) Figure 5 Removal rates of Cr(VI) and Cr(VI) at 30 minutes (e.g., left) Figure 5 The removal rates of Cr(VI) and p-nitrophenol by the right electrode were higher than those of the unmodified NiFe-LDH electrode.

[0037] Example 3 This embodiment provides a method for preparing a nitrogen-sulfur co-doped modified layered double oxide material, including the following steps: (1) Pretreatment of carbon felt substrate: The carbon felt substrate was immersed in sulfuric acid solution, anhydrous ethanol solution and deionized water in sequence, and ultrasonicated for 15 minutes respectively; the concentration of sulfuric acid solution was 1 mol / L.

[0038] 4 mmol Fe(NO3)3·9H2O and 12 mmol Ni(NO3)2·6H2O were dissolved in 40 mL of deionized water to form a homogeneous solution. The pretreated carbon felt substrate was immersed in the homogeneous solution and placed in a reaction vessel. The hydrothermal reaction was carried out at 180 °C for 9 hours. After the reaction was completed, the sample was removed, sonicated for 5 minutes, washed with deionized water, and dried to obtain the NiFe-LDH precursor. (2) The obtained precursor was immersed in a 10 mmol / L ammonium persulfate ethanol solution for 8 hours. After drying, it was subjected to high-temperature carbonization treatment at 700°C for 2 hours under a nitrogen atmosphere to finally obtain a nitrogen-sulfur co-doped modified nickel-iron layered double oxide material, which was used as an electrode material for water treatment.

[0039] The electrode material prepared in Example 3 was used for electrocatalytic degradation research. The research process was the same as in Example 1, except that the electrode material prepared in Example 1 was replaced with the electrode material prepared in Example 3. Figure 6 It can be seen that the removal rate of p-nitrophenol in 15 minutes (e.g.) Figure 6 Removal rates of Cr(VI) and Cr(VI) over 30 min (e.g., left) Figure 6 The removal rates of p-nitrophenol and Cr(VI) by the right electrode were higher than those of the unmodified NiFe-LDH electrode.

[0040] Example 4 This embodiment provides a method for preparing a nitrogen-sulfur co-doped modified layered double oxide material, including the following steps: (1) Pretreatment of carbon felt substrate: The carbon felt substrate was immersed in sulfuric acid solution, anhydrous ethanol solution and deionized water in sequence, and ultrasonically treated for 15 minutes respectively; the concentration of sulfuric acid solution was 1 mol / L.

[0041] 4 mmol Fe(NO3)3·9H2O and 4 mmol Ni(NO3)2·6H2O were dissolved in 40 mL of deionized water to form a homogeneous solution. The pretreated carbon felt substrate was immersed in the homogeneous solution and placed in a reaction vessel. The hydrothermal reaction was carried out at 120 °C for 9 hours. After the reaction was completed, the sample was removed, sonicated for 5 minutes, washed with deionized water, and dried to obtain the NiFe-LDH precursor.

[0042] (2) The obtained precursor was immersed in an ammonium persulfate ethanol solution with a concentration of 2.5 mmol / L for 8 hours. After drying, it was subjected to high-temperature carbonization treatment at 500°C for 2 hours under a nitrogen atmosphere to finally obtain a nitrogen-sulfur co-doped modified nickel-iron layered double oxide material, which was used as an electrode material for water treatment.

[0043] The electrode material prepared in Example 4 was used for electrocatalytic degradation studies. The research process was the same as in Example 1, except that the electrode material prepared in Example 1 was replaced with the electrode material prepared in Example 4. Figure 7 It can be seen that the removal rate of p-nitrophenol in 15 minutes (e.g.) Figure 7 Removal rates of Cr(VI) and Cr(VI) over 30 min (e.g., left) Figure 7 The removal rates of Cr(VI) and p-nitrophenol by the right electrode were higher than those of the unmodified NiFe-LDH electrode.

[0044] Example 5 This embodiment provides a method for preparing a nitrogen-sulfur co-doped modified layered double oxide material, including the following steps: (1) Pretreatment of carbon felt substrate: The carbon felt substrate was immersed in sulfuric acid solution, anhydrous ethanol solution and deionized water in sequence, and ultrasonicated for 15 minutes respectively; the concentration of sulfuric acid solution was 1.5 mol / L.

[0045] 4 mmol Fe(NO3)3·9H2O and 12 mmol Ni(NO3)2·6H2O were dissolved in 40 mL of deionized water to form a homogeneous solution. The pretreated carbon felt substrate was immersed in the homogeneous solution and placed in a reaction vessel. The hydrothermal reaction was carried out at 120 °C for 12 hours. After the reaction was completed, the sample was removed, sonicated for 5 minutes, washed with deionized water, and dried to obtain the NiFe-LDH precursor. (2) The obtained precursor was immersed in an ethanol solution of ammonium persulfate with a concentration of 2.5 mmol / L for 6 hours. After drying, it was subjected to high-temperature carbonization treatment at 500°C for 3 hours under an argon atmosphere to finally obtain a nitrogen-sulfur co-doped modified nickel-iron layered double oxide material, which was used as an electrode material for water treatment.

[0046] The electrode material prepared in Example 5 was used for electrocatalytic degradation research. The research process was the same as in Example 1, except that the electrode material prepared in Example 1 was replaced with the electrode material prepared in Example 5. Figure 8 It can be seen that the removal rate of p-nitrophenol in 15 minutes (e.g.) Figure 8 Removal rates of Cr(VI) and Cr(VI) over 30 min (e.g., left) Figure 8 (Right), which is higher than the removal rate of Cr(VI) and p-nitrophenol by the unmodified NiFe-LDH electrode.

[0047] Example 6 This embodiment provides a method for preparing a nitrogen-sulfur co-doped modified layered double oxide material, including the following steps: (1) Pretreatment of carbon felt substrate: The carbon felt substrate was immersed in sulfuric acid solution, anhydrous ethanol solution and deionized water in sequence, and ultrasonicated for 15 minutes respectively; the concentration of sulfuric acid solution was 0.5 mol / L.

[0048] 4 mmol Fe(NO3)3·9H2O and 4 mmol Ni(NO3)2·6H2O were dissolved in 40 mL of deionized water to form a homogeneous solution. The pretreated carbon felt substrate was immersed in the homogeneous solution and placed in a reaction vessel. The hydrothermal reaction was carried out at 180 °C for 6 hours. After the reaction was completed, the sample was removed, sonicated for 5 minutes, washed with deionized water, and dried to obtain the NiFe-LDH precursor. (2) The obtained precursor was immersed in a 10 mmol / L ammonium persulfate ethanol solution for 12 hours. After drying, it was subjected to high-temperature carbonization treatment at 700°C for 1 hour under an argon atmosphere to finally obtain a nitrogen-sulfur co-doped modified nickel-iron layered double oxide material, which was used as an electrode material for water treatment.

[0049] The electrode material prepared in Example 6 was used for electrocatalytic degradation research. The research process was the same as in Example 1, except that the electrode material prepared in Example 1 was replaced with the electrode material prepared in Example 6. Figure 9 It can be seen that the removal rate of p-nitrophenol in 15 minutes (e.g.) Figure 9 Removal rates of Cr(VI) and Cr(VI) over 30 min (e.g., left) Figure 9 The removal rates of Cr(VI) and p-nitrophenol by the right electrode were slightly higher than those of the unmodified NiFe-LDH electrode.

[0050] Comparative Example 1 This example provides a method for preparing a nitrogen-sulfur co-doped modified layered double oxide material, including the following steps: (1) Pretreatment of carbon felt substrate: The carbon felt substrate was immersed in sulfuric acid solution, anhydrous ethanol solution and deionized water in sequence, and ultrasonicated for 15 minutes respectively; the concentration of sulfuric acid solution was 1 mol / L.

[0051] 4 mmol Fe(NO3)3·9H2O and 12 mmol Ni(NO3)2·6H2O were dissolved in 40 mL of deionized water to form a homogeneous solution. The pretreated carbon felt substrate was immersed in the homogeneous solution and placed in a reaction vessel. The hydrothermal reaction was carried out at 150 °C for 9 hours. After the reaction was completed, the sample was removed, sonicated for 5 minutes, washed with deionized water, and dried to obtain the NiFe-LDH precursor. (2) The obtained precursor was immersed in an ammonium persulfate ethanol solution with a concentration of 7.5 mmol / L for 8 hours. After drying, a nitrogen-sulfur co-doped modified nickel-iron layered double oxide material was finally obtained, which was used as an electrode material for water treatment. The SEM image of the electrode material in this comparative example is shown below. Figure 2 As shown, Comparative Example 1, based on unmodified LDH, only underwent immersion in an ethanol solution of ammonium persulfate without carbonization. The resulting material exhibited a microsphere structure similar to unmodified LDH, with a size of approximately 10 µm. Compared to Example 2, which underwent immersion in ammonium persulfate followed by carbonization (with a size of approximately 5 µm), the microsphere size of the electrode material obtained under these conditions was approximately twice that of Example 2. This is mainly due to the inherent characteristics of the layered double hydroxide precursor before calcination: the water molecules and anions present between the layers, as well as the hydroxyl groups on the surface of the layers, create significant steric hindrance, inhibiting the close packing of the layers and thus forming larger microspheres.

[0052] The electrode material prepared in Comparative Example 1 was used for electrocatalytic degradation studies. The research process was the same as in Example 1, except that the electrode material prepared in Example 1 was replaced with the electrode material prepared in Comparative Example 1. Figure 10 It can be seen that Comparative Example 1, using only ammonium persulfate soaking, showed slightly better treatment results compared to the unmodified version, but the difference was not significant. The removal rate of nitrophenol by this electrode within 15 minutes (…) Figure 10 Removal rates of Cr(VI) and Cr(VI) over 30 min (left) Figure 10 (Right), lower than the removal rate of p-nitrophenol and Cr(VI) for organic pollutants by the electrode in Example 2. The large-sized, loosely packed LDH microspheres formed in Comparative Example 1 have low removal efficiency, mainly due to the limited catalytic performance and poor conductivity of the material itself. The large size and loose packing of the microspheres lead to low mass transfer efficiency. However, in an inert atmosphere, the NiFe-LDH crystal structure is reorganized by heating, transforming from LDH into LDO with a more stable structure and better conductivity. At the same time, ammonium persulfate decomposes to produce nitrogen- and sulfur-containing compounds. This co-doped structure can effectively regulate the electronic structure of the material, which not only improves the specific surface area and conductivity of the material, but also significantly enhances the catalytic activity of the electrode by regulating the electronic states of the Ni and Fe active centers.

[0053] Comparative Example 2 This example provides a method for preparing a nitrogen-sulfur co-doped modified layered double oxide material, including the following steps: (1) Pretreatment of carbon felt substrate: The carbon felt substrate was immersed in sulfuric acid solution, anhydrous ethanol solution and deionized water in sequence, and ultrasonicated for 15 minutes respectively; the concentration of sulfuric acid solution was 1 mol / L.

[0054] 4 mmol Fe(NO3)3·9H2O and 12 mmol Ni(NO3)2·6H2O were dissolved in 40 mL of deionized water to form a homogeneous solution. The pretreated carbon felt substrate was immersed in the homogeneous solution and placed in a reaction vessel. The hydrothermal reaction was carried out at 150 °C for 9 hours. After the reaction was completed, the sample was removed, sonicated for 5 minutes, washed with deionized water, and dried to obtain the NiFe-LDH precursor. (2) The obtained precursor was subjected to high-temperature carbonization treatment at 600°C for 2 hours under nitrogen atmosphere to finally obtain a nitrogen-sulfur co-doped modified nickel-iron layered double oxide material, which was used as an electrode material for water treatment.

[0055] The electrode in this comparative example only underwent carbonization treatment based on the precursor LDH, and its SEM image is shown below. Figure 3 As shown, the microspheres exhibit a structure similar to the precursor LDH, with a size of approximately 5 µm. Compared to Example 2, the electrode material obtained by direct carbonization in Comparative Example 2 has a similar microsphere size, but the microspheres are more sparsely distributed, and some lamellar structures are thicker, with denser stacking between layers and less developed pores. This is because during the high-temperature carbonization process, water molecules and intercalated anions between LDH layers are removed, resulting in a smaller interlayer spacing and a smaller size compared to unmodified LDH. Similar to Example 2, which also underwent carbonization, the absence of ammonium persulfate treatment and the lack of nitrogen, sulfur, or other heteroatoms, coupled with the lack of heteroatom doping lattice regulation, prevented the formation of an open structure during dehydration and shrinkage, resulting in thicker layers and denser stacking.

[0056] The electrode material prepared in Comparative Example 2 was used for electrocatalytic degradation studies. The research process was the same as in Example 1, except that the electrode material prepared in Example 1 was replaced with the electrode material prepared in Comparative Example 2. Figure 11 It can be seen that the removal rate of nitrophenol by this electrode within 15 minutes ( Figure 11 Removal rates of Cr(VI) and Cr(VI) over 30 min (left) Figure 11The removal efficiency of the electrode for organic pollutants p-nitrophenol and Cr(VI) in Comparative Example 2 was lower than that in Example 2. The material obtained by direct carbonization without doping in Comparative Example 2 exhibited a morphology of thick, tightly stacked layers and underdeveloped pores, resulting in low removal efficiency. This was due to factors such as limited catalyst performance, insufficient exposure of active sites, low electrochemical active area, and large diffusion resistance caused by blocked mass transfer channels. However, soaking in an ethanol solution of ammonium persulfate facilitated uniform adsorption and penetration of ammonium persulfate, achieving heteroatom doping while maintaining the LDO layer structure during carbonization. The catalytic performance of the material was further improved by co-doping with N and S elements.

[0057] In Comparative Example 2, the precursor was directly carbonized. During the high-temperature carbonization process, the structure collapsed to some extent, but the electrochemical active area increased to a certain extent. The removal effect was better than that of Comparative Example 1 and better than that of the unmodified material, but lower than that of the electrode material prepared by soaking and high-temperature carbonization (Example 2).

[0058] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a nitrogen-sulfur co-doped modified layered double oxide material, characterized in that: Includes the following steps: (1) The carbon felt substrate was pretreated and dried. The treated substrate was placed in a homogeneous solution containing Fe(NO3)3·9H2O and Ni(NO3)2·6H2O for hydrothermal reaction. After the reaction was completed, it was taken out, ultrasonically treated, washed with deionized water and dried to obtain NiFe-LDH precursor. (2) The obtained precursor was dried and then immersed in an ethanol solution of ammonium persulfate. Then, it was subjected to high-temperature carbonization under an inert gas atmosphere to finally obtain a nitrogen-sulfur co-doped modified nickel-iron layered double oxide material.

2. The method for preparing a nitrogen-sulfur co-doped modified layered double oxide material according to claim 1, characterized in that: In step (1), the pretreatment process is as follows: the carbon felt substrate is immersed in sulfuric acid solution, anhydrous ethanol solution and deionized water in sequence and ultrasonically treated for 15 minutes respectively; wherein the concentration of the sulfuric acid solution is 0.5-1.5 mol / L.

3. The method for preparing a nitrogen-sulfur co-doped modified layered double oxide material according to claim 1, characterized in that: In step (1), 1 mmol Fe(NO3)3·9H2O and 1-3 mmol Ni(NO3)2·6H2O are added to every 10 mL of deionized water to form a homogeneous solution.

4. The method for preparing a nitrogen-sulfur co-doped modified layered double oxide material according to claim 3, characterized in that: In step (1), the hydrothermal reaction temperature is 120-180℃ and the time is 6-12h.

5. The method for preparing a nitrogen-sulfur co-doped modified layered double oxide material according to claim 1, characterized in that: In step (2), the concentration of the ammonium persulfate ethanol solution is 2.5-10 mmol / L, and the precursor is immersed in the ammonium persulfate ethanol solution for 6-12 hours.

6. The method for preparing a nitrogen-sulfur co-doped modified layered double oxide material according to claim 1, characterized in that: In step (2), the high-temperature carbonization treatment is carried out at a temperature of 500-700℃ and for a duration of 1-3 hours.

7. The method for preparing a nitrogen-sulfur co-doped modified layered double oxide material according to claim 1, characterized in that: In step (2), the inert gas is nitrogen or argon.

8. The application of the nitrogen-sulfur co-doped modified nickel-iron layered double oxide material prepared by the preparation method according to any one of claims 1-7 in water treatment, characterized in that: A nitrogen-sulfur co-doped nickel-iron layered double oxide material was used as the cathode and a graphite plate as the anode to remove heavy metals Cr(VI) and p-nitrophenol from water.

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