Application of Co3O4-Ti composite electrode in electrolytic removal of nitrate nitrogen from water

Abstract

The application discloses application of a Co3O4-Ti composite electrode in electrolytic removal of nitrate nitrogen in water and belongs to the technical field of electrochemical treatment of sewage. In the application, an electrolysis reaction tank is used for electrolysis, the cathode of the electrolysis reaction tank is the Co3O4-Ti composite electrode, the current density of electrolysis is 45 mA / cm 2 2 55 mA / cm 2 , and the pH of the electrolyte in the electrolysis reaction tank is 5-6. The application of the Co3O4-Ti composite electrode in electrolytic removal of nitrate nitrogen in water provided by the application remarkably improves the cycle stability of the Co3O4-Ti composite electrode in removal of nitrate nitrogen on the basis of ensuring high removal rate of nitrate nitrogen by improving the preparation method of the Co3O4-Ti composite electrode and synergistically optimizing the application conditions.

Description

Technical Field

[0001] This invention belongs to the field of wastewater electrochemical treatment technology, and more specifically, relates to the application of Co3O4-Ti composite electrode in the electrolytic removal of nitrate nitrogen from water. Background Technology

[0002] With the rapid development of industry and agriculture, nitrates have become a common pollutant in surface water and groundwater. While nitrates themselves are harmless, they are easily reduced to toxic nitrites by microorganisms in the human digestive system. Therefore, removing nitrates from drinking water and wastewater is crucial. In recent years, electrochemical reduction technology has attracted much attention due to its ability to directly convert nitrate nitrogen using electrons as a clean reducing agent. Its core research focuses on developing highly active and selective non-precious metal cathode materials, such as cobalt, copper, and silver catalysts. By controlling the electronic structure and reaction pathway at the electrode interface, the aim is to directionally convert nitrate nitrogen into harmless nitrogen gas rather than the byproduct ammonium salt, overcoming problems such as incomplete treatment, low removal rates, or secondary pollution inherent in traditional technologies. This has become an important development direction in this field.

[0003] Cobalt is a functional material with a unique spinel structure and mixed valence states, attracting widespread attention due to its excellent redox properties, stable electrochemical activity, and relatively low cost. Co3O4-Ti coated electrodes prepared from cobalt exhibit good performance in the removal of both inorganic and organic nitrogen in electrochemical cathodic reduction.

[0004] Chinese patent document publication number CN110980888A discloses a method for preparing a Ti / Co3O4 coated electrode. This method is simple, structurally stable, and the resulting Ti / Co3O4 coated electrode exhibits high treatment efficiency for recalcitrant organic wastewater. However, this method employs a traditional hydrothermal process, resulting in a loose, sheet-like Co3O4-Ti coating on the titanium substrate. The active components have weak adhesion to the substrate, making the active material prone to dissolution and detachment during electrochemical cycling, leading to significantly insufficient electrode stability. Furthermore, the inhomogeneity of the hydrothermal reaction system causes uneven distribution of active sites, resulting in a removal rate of only 76.85% for recalcitrant organic pollutants, and severe accumulation of the byproduct nitrite. To address the aforementioned issues, our laboratory's published literature, "Optimized Preparation of Co3O4-Ti Electrode and Its Application in Treating Nitrophenol-Containing Wastewater" (Xian Yubozhou. [D]. Yulin University, 2024. DOI:10.44520 / d.cnki.gylxy.2024.000002.), provides a method for preparing a Co3O4-Ti electrode. The prepared Co3O4-Ti electrode achieves a total nitrogen (TN) removal rate of up to 87.56%. However, the stability of this Co3O4-Ti electrode still needs improvement. For example, after four cycles, the nitrate nitrogen removal rate decreases from 81.5% to 70%, and after five cycles, it decreases to 60%. This may be due to the dissolution and detachment of the Co3O4-Ti coating formed on the titanium substrate surface under acidic conditions. Increasing the pH of the electrolyte does not significantly improve the cycling performance and severely reduces the nitrate nitrogen removal rate; for example, at pH 5, the nitrate nitrogen removal rate is only 52%. Furthermore, our laboratory found in subsequent studies that the removal rate of nitrate nitrogen by the Co3O4-Ti electrode differed significantly between summer and winter.

[0005] Therefore, while ensuring a high removal rate of nitrate nitrogen, improving the stability of the Co3O4-Ti electrode in the electrolytic removal of nitrate nitrogen from water is a technical problem that urgently needs to be solved. Summary of the Invention

[0006] 1. The problem to be solved

[0007] Based on the above-mentioned technical problems, the first objective of this invention is to provide a method for preparing a Co3O4-Ti composite electrode. Through repeated coating-pre-drying-pre-calcination processes, a dense and firmly bonded Co3O4 coating is successfully constructed on the surface of a titanium substrate, and the active component Co is uniformly distributed on the surface of the titanium substrate.

[0008] The second objective of this invention is to provide the application of the Co3O4-Ti composite electrode in the electrolytic removal of nitrate nitrogen from water, thereby improving the cyclic stability of the Co3O4-Ti composite electrode in the electrolytic removal of nitrate nitrogen by controlling the temperature and pH during electrolysis.

[0009] 2. Technical Solution

[0010] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0011] [1. Application of Co3O4-Ti composite electrode in electrolytic removal of nitrate nitrogen from water]

[0012] The first aspect of this invention provides the application of a Co3O4-Ti composite electrode in the electrolytic removal of nitrate nitrogen from water. In this application, an electrolytic reactor is used, the cathode of which is a Co3O4-Ti composite electrode, and the electrolysis current density is 45 mA / cm². 2 ~55 mA / cm 2 The pH of the electrolyte in the electrolytic reactor is 5-6;

[0013] The preparation method of Co3O4-Ti composite electrode includes the following steps:

[0014] S1. Place the titanium sheet in the etching solution for etching, and dry it after etching is completed for later use;

[0015] S2. Dissolve cobalt nitrate in an alcohol solvent to obtain an electrode solution;

[0016] S3. Take the electrode liquid prepared in S2, coat it evenly on both sides of the titanium sheet to be used in S1, and then dry it.

[0017] S4. Repeat the operation of S3 2 to 4 times, and then calcine at 300℃ to 600℃ for 3 to 7 minutes.

[0018] S5. Repeat the operation of S4 until the electrode liquid prepared in S2 is completely coated.

[0019] S6. The coated titanium sheet is calcined at 300℃~600℃ for 2.5~3.5h and cooled to room temperature to obtain the Co3O4-Ti composite electrode.

[0020] It should be noted that repeating the operation in S3 in S4 means taking the electrode liquid prepared in S2, coating it evenly on both sides of the titanium sheet to be used in S1, and then drying it; then taking the electrode liquid prepared in S2 again, coating it evenly on both sides of the titanium sheet to be used in S1, and then drying it.

[0021] In the preparation method of the Co3O4-Ti composite electrode provided by this invention, the titanium sheet is first chemically etched and activated to effectively remove the surface oxide layer and construct a micro-nano-scale rough structure, such as... Figure 1As shown in b, the specific surface area is significantly increased to provide a highly adhesive active substrate for subsequent coatings. Then, the active component, namely the cobalt functional layer, is loaded. Through repeated coating-pre-drying-pre-calcination processes, the cobalt element is uniformly immobilized on the titanium sheet surface in a highly active and stable form, resulting in a Co3O4-Ti composite electrode with excellent electrocatalytic performance.

[0022] Meanwhile, the combination of 2 to 4 pre-drying and calcination ensures that the active component Co is evenly distributed on the surface of the titanium substrate, ensuring that the composite electrode maintains a stable three-dimensional porous structure during long-term operation, which is beneficial to improving the removal rate of nitrate nitrogen by the Co3O4-Ti composite electrode.

[0023] Furthermore, the calcination temperature in S4 is preferably 350℃~450℃, most preferably 380℃~420℃, for example 390℃, 400℃, 410℃, and the calcination time is 4~6 minutes.

[0024] Furthermore, the calcination temperature in S6 is preferably 350℃~450℃, most preferably 380℃~420℃, for example 390℃, 400℃, 410℃.

[0025] As a preferred embodiment of any technical solution in the first aspect of the present invention, the temperature difference between calcination in S4 and S6 is less than or equal to 50°C.

[0026] Furthermore, the difference in calcination temperature between S4 and S6 is less than or equal to 20°C.

[0027] Furthermore, the calcination temperatures in S4 and S6 are the same.

[0028] As a preferred embodiment of any technical solution in the first aspect of the present invention, the volume-to-area ratio of the electrode liquid to the titanium sheet in S2 is 1 ml : (0.8 cm²) / ( ... 2 ~2cm 2 The concentration of cobalt nitrate in the electrode solution is 0.1~0.3 mol / L, and the alcohol solvent is selected from one or more of methanol, ethanol, propanol and butanol, and the alcohol solvent does not contain water.

[0029] Furthermore, the volume-to-area ratio of the electrode solution to the titanium sheet is 1 ml : (1 cm²) 2 ~1.5cm 2 The alcohol solvent is ethanol.

[0030] As a preferred embodiment of any technical solution in the first aspect of the present invention, the drying temperature in S3 is 60°C to 80°C, and more preferably 65°C to 75°C.

[0031] As a preferred embodiment of any technical solution in the first aspect of the present invention, the etching solution in S1 is selected from one or more of oxalic acid solution, hydrochloric acid solution, sulfuric acid solution, sodium hydroxide solution and potassium hydroxide solution, the mass percentage of the etching solution is 10% to 30%, and the etching temperature is 70°C to 90°C, more preferably 75°C to 85°C.

[0032] Furthermore, the etching solution in S1 is an oxalic acid solution with a mass percentage of 20% ± 2%.

[0033] As a preferred embodiment of any technical solution in the first aspect of the present invention, a pretreatment step is further included before S1. The pretreatment step includes: grinding the titanium sheet, immersing it in an oxalic acid solution with a mass percentage of 10% to 30%, boiling it for 20 to 40 minutes, and then cleaning it.

[0034] As a preferred embodiment of any technical solution in the first aspect of the present invention, the mass concentration of nitrate nitrogen is 15 mg / L to 20 mg / L.

[0035] As a preferred embodiment of any technical solution in the first aspect of the present invention, nitrate nitrogen includes one or more of trinitrophenol, potassium nitrate, p-nitrophenol, and o-nitrophenol.

[0036] As a preferred embodiment of any technical solution in the first aspect of the present invention, the removal rate of nitrate nitrogen is greater than or equal to 85%, and the degradation rate of total organic carbon is greater than or equal to 75%.

[0037] As a preferred embodiment of any technical solution in the first aspect of the present invention, the anode of the electrolytic reactor is a ruthenium-iridium-titanium electrode, the electrode spacing between the cathode and the anode is 10~30 mm, and the electrolysis temperature is 25℃~35℃.

[0038] Furthermore, the output voltage range of the electrolytic reactor is 0~30 V, the output current range is 0~25 A, the electrolyte in the electrolytic reactor is sodium sulfate, and the concentration of the electrolyte is 0.01 mol / L~0.2 mol / L.

[0039] [2. A method for preparing a Co3O4-Ti composite electrode]

[0040] A second aspect of the present invention provides a method for preparing a Co3O4-Ti composite electrode, the method comprising the following steps:

[0041] S1. Place the titanium sheet in the etching solution for etching, and dry it after etching is completed for later use;

[0042] S2. Dissolve cobalt nitrate in an alcohol solvent to obtain an electrode solution;

[0043] S3. Take the electrode liquid prepared in S2, coat it evenly on both sides of the titanium sheet to be used in S1, and then dry it.

[0044] S4. Repeat the operation of S3 2 to 4 times, and then calcine at 350℃ to 450℃ for 3 to 7 minutes.

[0045] S5. Repeat the operation of S4 until the electrode liquid prepared in S2 is completely coated.

[0046] S6. The coated titanium sheet is calcined at 350℃~450℃ for 2.5~3.5h and cooled to room temperature to obtain a Co3O4-Ti composite electrode.

[0047] Furthermore, the calcination temperature in S4 is preferably 350℃~450℃, most preferably 380℃~420℃, for example 390℃, 400℃, 410℃, and the calcination time is 4~6 minutes.

[0048] Furthermore, the calcination temperature in S6 is preferably 350℃~450℃, most preferably 380℃~420℃, for example 390℃, 400℃, 410℃.

[0049] As a preferred embodiment of any technical solution in the first aspect of the present invention, the temperature difference between calcination in S4 and S6 is less than or equal to 50°C.

[0050] Furthermore, the difference in calcination temperature between S4 and S6 is less than or equal to 20°C.

[0051] Furthermore, the calcination temperatures in S4 and S6 are the same.

[0052] As a preferred embodiment of any technical solution in the first aspect of the present invention, the volume-to-area ratio of the electrode liquid to the titanium sheet in S2 is 1 ml : (0.8 cm²) / ( ... 2 ~2cm 2 The concentration of cobalt nitrate in the electrode solution is 0.1~0.3 mol / L, and the alcohol solvent is selected from one or more of methanol, ethanol, propanol and butanol, and the alcohol solvent does not contain water.

[0053] Furthermore, the volume-to-area ratio of the electrode solution to the titanium sheet is 1 ml : (1 cm²) 2 ~1.5cm 2 The alcohol solvent is ethanol.

[0054] As a preferred embodiment of any technical solution in the first aspect of the present invention, the drying temperature in S3 is 60°C to 80°C, and more preferably 65°C to 75°C.

[0055] As a preferred embodiment of any technical solution in the first aspect of the present invention, the etching solution in S1 is selected from one or more of oxalic acid solution, hydrochloric acid solution, sulfuric acid solution, sodium hydroxide solution and potassium hydroxide solution, the mass percentage of the etching solution is 10% to 30%, and the etching temperature is 70°C to 90°C, more preferably 75°C to 85°C.

[0056] Furthermore, the etching solution in S1 is an oxalic acid solution with a mass percentage of 20% ± 2%.

[0057] As a preferred embodiment of any technical solution in the first aspect of the present invention, a pretreatment step is further included before S1. The pretreatment step includes: grinding the titanium sheet, immersing it in an oxalic acid solution with a mass percentage of 10% to 30%, boiling it for 20 to 40 minutes, and then cleaning it.

[0058] [3. A Co3O4-Ti composite electrode]

[0059] A third aspect of the present invention provides a Co3O4-Ti composite electrode used in the first aspect of the present invention, wherein the coverage of Co on the titanium substrate is greater than or equal to 90%, and the mass-to-area ratio of Co3O4 to the titanium substrate is 1 g : (80 cm²) 2 ~85cm 2 ).

[0060] The Co3O4-Ti composite electrode provided by the second aspect of the present invention can effectively enhance the interfacial reaction efficiency and long-term operational stability, and is suitable for various electrochemical water treatment scenarios.

[0061] 3. Beneficial effects

[0062] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0063] (1) The application of the Co3O4-Ti composite electrode provided by the present invention in the electrolytic removal of nitrate nitrogen in water, by improving the preparation method of the Co3O4-Ti composite electrode and synergistically optimizing the application conditions, significantly improves the cyclic stability of the Co3O4-Ti composite electrode for nitrate nitrogen removal while ensuring a high removal rate of nitrate nitrogen.

[0064] Specifically, this invention involves coating a titanium substrate with an electrode solution containing cobalt nitrate, followed by pre-drying and pre-calcination. By repeating this process multiple times, a dense and firmly bonded Co3O4 coating is successfully constructed on the surface of the titanium substrate after final calcination. This effectively solves the technical problem of active components easily dissolving and detaching during electrolysis, thus improving the stability of the electrode. Simultaneously, the 2-4 pre-drying and calcination cycles ensure a uniform distribution of the active component Co on the surface of the titanium substrate, guaranteeing that the composite electrode maintains a stable three-dimensional porous structure during long-term operation. This is beneficial for improving the removal rate of nitrate nitrogen by the Co3O4-Ti composite electrode and avoids the accumulation of the byproduct nitrite.

[0065] Meanwhile, the pH during the electrolysis of the Co3O4-Ti composite electrode is controlled at 5~6 to reduce the corrosiveness of the electrolysis environment on the Co3O4-Ti composite electrode; the temperature during electrolysis is controlled at 25℃~35℃ to further improve the cycle stability of nitrate nitrogen removal.

[0066] In summary, the Co3O4-Ti composite electrode prepared by the method provided in this invention achieves a nitrate nitrogen removal rate of up to 85% under the application conditions of this invention, which is a significant improvement compared to the Ti / Co3O4 coated electrode prepared by the traditional hydrothermal method. More importantly, after nine consecutive cycles of use, the electrode performance retention rate is not less than 95%, with no significant degradation, demonstrating excellent electrochemical stability, thereby achieving efficient and long-lasting electrolytic denitrification.

[0067] (2) The Co3O4-Ti composite electrode provided by the present invention can remove nitrate nitrogen from water by electrolysis and also achieve a degradation rate of up to 75% of total organic carbon.

[0068] (3) The preparation method of the Co3O4-Ti composite electrode provided by the present invention reduces the amount of cobalt nitrate from 1.16g to 0.55g compared with the preparation method of Ti / Co3O4 coated electrode in the background technology, and reduces the raw material cost by 52%. It does not require the use of a large amount of urea and ammonium fluoride as precipitants, which reduces production costs and alleviates environmental pressure. Moreover, the preparation process does not require special equipment such as high pressure reactors, the steps are simple and the design is reasonable, which significantly enhances the economic efficiency and large-scale production feasibility of the process. Attached Figure Description

[0069] Figure 1 :

[0070] a is a SEM image of the Ti wafer surface before etching in Embodiment 1 of the present invention;

[0071] b is a SEM image of the Ti wafer surface after etching in Embodiment 1 of the present invention;

[0072] Figure 2 This is a SEM image of the surface of the Co3O4-Ti composite electrode prepared in Example 1 of this invention;

[0073] Figure 3 The image shows the EDS spectrum of the Co3O4-Ti composite electrode surface prepared in Example 1 of this invention.

[0074] Figure 4 :

[0075] a is a SEM image of the surface of the Co3O4-Ti composite electrode prepared in Example 2 of this invention;

[0076] b is a SEM image of the surface of the Co3O4-Ti composite electrode prepared in Example 3 of this invention;

[0077] c is a SEM image of the surface of the Co3O4-Ti composite electrode prepared in Example 4 of this invention;

[0078] d is a SEM image of the surface of the Co3O4-Ti composite electrode prepared in Comparative Example 1 of this invention;

[0079] Figure 5 The image shows the EDS spectrum of the Co3O4-Ti composite electrode surface prepared in Comparative Example 1 of this invention.

[0080] Figure 6 This is a bar chart showing the removal of trinitrophenol from water by the Co3O4-Ti composite electrode prepared in Example 1 of this invention;

[0081] Figure 7 This is a line graph showing the total organic carbon degradation during the removal of trinitrophenol from the Co3O4-Ti composite electrode prepared in Example 1 of this invention.

[0082] Figure 8 A bar chart showing the continuous degradation of trinitrophenol by nine cycles using the Co3O4-Ti composite electrode prepared in Example 1 of this invention.

[0083] Figure 9 Line graph showing the removal of trinitrophenol from water by the Co3O4-Ti composite electrode prepared in Comparative Example 7 of this invention. Detailed Implementation

[0084] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0085] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0086] Concentration, amount, and other numerical data may be presented in range format herein. It should be understood that such range format is used solely for convenience and brevity and should be flexibly interpreted to include not only the values ​​explicitly stated as the limits of the range, but also all individual values ​​or subranges encompassed within the range, as if each value and subrange were explicitly stated. For example, a numerical range of 1 to 4.5 should be interpreted to include not only the explicitly stated limits of 1 to 4.5, but also individual numbers (such as 2, 3, 4) and subranges (such as 1 to 3, 2 to 4, etc.). The same principle applies to ranges that describe only a single value, such as "less than 4.5," which should be interpreted to include all the aforementioned values ​​and ranges. Furthermore, this interpretation should apply regardless of the breadth of the range or characteristic described.

[0087] The present invention will be further described below with reference to specific embodiments.

[0088] Materials used in preparation:

[0089] Titanium sheets were purchased from Shandong Hongteng Fengda Metal Materials Co., Ltd.; oxalic acid solution (20wt%) was purchased from Shenyang Chemical Reagent Factory; anhydrous ethanol was purchased from Tianjin Hongyan Chemical Reagent Factory; and cobalt nitrate hexahydrate (Co(NO3)2·6H2O) was purchased from Guangdong Guanghua Technology Co., Ltd.

[0090] Example 1

[0091] This embodiment provides a method for preparing a Co3O4-Ti composite electrode, specifically including the following steps:

[0092] 1. Prepare a 5cm×2.5cm titanium (Ti) sheet with a thickness of 1mm, and polish both sides of the Ti sheet with 60-grit and 320-grit sandpaper to remove surface oxides.

[0093] 2. Place the polished Ti sheet into a 20% oxalic acid solution and boil it for 30 minutes using a universal electric furnace. Then remove the Ti sheet and sonicate it for 15 minutes each with anhydrous ethanol and ultrapure water.

[0094] 3. Immerse the Ti wafer again in a fresh oxalic acid solution (20% by mass) and etch it using a CNC ultrasonic cleaner at 80°C for 3 hours. After etching, place the Ti wafer in a drying oven and dry it at 45°C until ready for use. The scanning electron microscope (SEM) image of the etched Ti wafer is shown below. Figure 1 As shown.

[0095] 4. Weigh 0.55g of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) and dissolve it in 10ml of anhydrous ethanol to obtain the electrode solution.

[0096] 5. Soak a cotton ball in electrode solution and coat it evenly on both sides of the dried Ti wafer. Then dry it in a forced-air drying oven at 70°C.

[0097] 6. After repeating step 5 three times, place it in a tube furnace and calcine at 400℃ for 5 minutes.

[0098] 7. Repeat step 6 until the electrode solution prepared in step 4 is completely coated.

[0099] 8. The coated Ti sheet was placed in a tube furnace and calcined at 400℃ for 3 hours. After calcination, it was naturally cooled to room temperature, then washed once with anhydrous ethanol and twice with ultrapure water. After drying, the Co3O4-Ti composite electrode was obtained. The scanning electron microscope (SEM) image of the Co3O4-Ti composite electrode is shown below. Figure 2 As shown.

[0100] from Figure 1 As can be seen, the etched Ti substrate surface forms a uniform rough morphology, and its specific surface area increases significantly. The roughened surface of the Ti substrate provides more anchoring points for the subsequent loading of the Co3O4 active layer, which is beneficial to enhance the bonding force and dispersion between the metal oxide Co3O4 and the Ti substrate, thereby improving the structural stability and electrochemical active area of ​​the electrode.

[0101] from Figure 2 As can be seen, a uniform and dense metal oxide coating was formed on the surface of the Co3O4-Ti composite electrode obtained after calcination.

[0102] The results of energy-dispersive X-ray (EDS) surface scanning of the Co3O4-Ti composite electrode are shown in Table 1 and... Figure 3 As shown, the weight percentage of active component Co on the Ti sheet surface is 92.12%, which can be considered as the coverage of active component Co being no less than 90%, and the distribution of Co on the Ti sheet surface is good. That is, the Co3O4 active layer can effectively cover the Ti sheet substrate surface, which helps to provide sufficient electrocatalytic active sites and enhance the electronic conductivity and structural stability of the Co3O4-Ti composite electrode in the electrochemical reduction process, thus providing a material basis for efficient and long-lasting denitrification performance.

[0103] Table 1. EDS results analysis of the Co3O4-Ti composite electrode prepared in Example 1

[0104]

[0105] Example 2

[0106] This embodiment provides a method for preparing a Co3O4-Ti composite electrode, which is basically the same as that in Embodiment 1, except that the calcination temperature in step 6 is 300℃ and the calcination temperature in step 8 is 300℃.

[0107] The scanning electron microscope (SEM) image of the prepared Co3O4-Ti composite electrode is shown below. Figure 4 As shown in a.

[0108] Example 3

[0109] This embodiment provides a method for preparing a Co3O4-Ti composite electrode, which is basically the same as that in Embodiment 1, except that the calcination temperature in step 6 is 500℃ and the calcination temperature in step 8 is 500℃.

[0110] The scanning electron microscope (SEM) image of the prepared Co3O4-Ti composite electrode is shown below. Figure 4 As shown in b.

[0111] Example 4

[0112] This embodiment provides a method for preparing a Co3O4-Ti composite electrode, which is basically the same as that in Example 1, except that the calcination temperature in step 8 is 600℃.

[0113] The scanning electron microscope (SEM) image of the prepared Co3O4-Ti composite electrode is shown below. Figure 4 As shown in c.

[0114] Comparative Example 1

[0115] This comparative example provides a method for preparing a Co3O4-Ti composite electrode, which is basically the same as that in Example 1, except that the calcination temperature in step 6 is 700℃ and the calcination temperature in step 8 is 700℃.

[0116] The scanning electron microscope (SEM) image of the prepared Co3O4-Ti composite electrode is shown below. Figure 4 As shown in d.

[0117] The results of energy-dispersive X-ray (EDS) surface scanning of the Co3O4-Ti composite electrode are shown in Table 2 and... Figure 5 As shown, the weight percentage of the active ingredient Co on the Ti sheet surface is 60.25%, which can be considered as the coverage of the active ingredient Co being about 60%. Furthermore, the continuity of the distribution of Co on the Ti sheet surface is poor, meaning that the Co3O4 active layer cannot effectively cover the Ti sheet substrate surface, and therefore cannot provide sufficient electrocatalytic active sites.

[0118] Table 2. EDS results analysis of the Co3O4-Ti composite electrode prepared in Comparative Example 1

[0119]

[0120] Comparative Example 2

[0121] This comparative example provides a method for preparing a Co3O4-Ti composite electrode, which is basically the same as that in Example 1, except that the calcination time in step 8 is 2 hours.

[0122] Comparative Example 3

[0123] This comparative example provides a method for preparing a Co3O4-Ti composite electrode, which is basically the same as that of comparative example 2, except that the calcination temperature in step 8 is 300℃.

[0124] Comparative Example 4

[0125] This comparative example provides a method for preparing a Co3O4-Ti composite electrode, which is basically the same as that of comparative example 2, except that the calcination temperature in step 8 is 500℃.

[0126] Comparative Example 5

[0127] This comparative example provides a method for preparing a Co3O4-Ti composite electrode, which is basically the same as that of comparative example 2, except that the calcination temperature in step 8 is 600℃.

[0128] Comparative Example 6

[0129] This comparative example provides a method for preparing a Co3O4-Ti composite electrode, which is basically the same as that of comparative example 2, except that the calcination temperature in step 8 is 700℃.

[0130] Comparative Example 7

[0131] This comparative example provides a method for preparing a Co3O4-Ti composite electrode, which is basically the same as that in Example 1. The only difference is that in step 5, the entire electrode liquid is soaked in degreased cotton and evenly coated on both sides of the dried Ti sheet, and then dried in a forced-air drying oven at 70°C. Steps 6 and 7 are omitted.

[0132] Test Example 1

[0133] This test example demonstrates the effect of the Co3O4-Ti composite electrode prepared in Example 1 on NO3. - Electrolytic removal effect test of -N.

[0134] The Co3O4-Ti composite electrode prepared in Example 1 was used as the cathode of the electrolysis reactor, and the ruthenium-iridium-titanium electrode was used as the anode to electrolyze an electrolyte containing trinitrophenol. The concentration of trinitrophenol was 100 mg / L, and the electrolyte also contained 0.1 mol / L anhydrous sodium sulfate. The initial pH of the electrolyte was 5.82.

[0135] The electrolysis process parameters are set as follows: the electrode spacing between the cathode and anode is 20 mm, and the current density is 50 mA / cm². 2 The electrolysis time is 210 min. Electrolysis is powered by a DC regulated power supply with an output voltage range of 0~30 V and an output current range of 0~25 A.

[0136] Ultraviolet spectrophotometry was used to determine the electrolysis process (such as...). Figure 6 NO3 in the electrolyte at the time points shown - -N concentration, based on NO3- in the electrolyte during electrolysis. - Calculate the NO3 concentration change. - The removal rate of -N was determined and calculated using N-(1-naphthyl)-ethylenediamine spectrophotometry and Nessler's reagent spectrophotometry, respectively. - -N and NH4 + The concentration of -N, the results are as follows Figure 6 As shown. From Figure 6 As can be seen from the above, when the Co3O4-Ti composite electrode prepared in Example 1 is subjected to electrolysis, NO3... - The removal rate of nitrate nitrogen (N-N) increased significantly with reaction time, reaching 39.31% at 30 minutes and increasing to 91.11% at 210 minutes. This increasing trend indicates that the electrode of this invention exhibits superior catalytic activity and stability during continuous electrolysis. In the initial stage of the reaction, the active sites on the electrode surface rapidly adsorb and initiate the initial reduction of nitrate ions. As electrolysis progresses, the continuous reduction potential, combined with the activation effect on the catalyst surface, effectively promotes the multi-step conversion of nitrate to ammonia nitrogen and the final gaseous products, while simultaneously enhancing the mass transfer process of nitrate ions from the liquid phase to the electrode interface. These results demonstrate that the Co3O4-Ti electrode provided by this invention possesses efficient and sustained nitrate nitrogen removal capabilities, making it suitable for advanced wastewater treatment.

[0137] The total organic carbon (TOC) during electrolysis was determined using a total organic carbon (TOC) analyzer. Figure 7 The concentration of total organic carbon in the electrolyte at the time points shown is calculated, and the degradation rate (D) of total organic carbon during electrolysis is calculated according to formula (1). The results are as follows: Figure 7 As shown, the degradation rate of total organic carbon in p-trinitrophenol wastewater was 80.87%.

[0138] D=(A0-A t ) / A0*100%(1)

[0139] In the formula, D is the degradation rate (%); A0 is the initial concentration of total organic carbon; A t This represents the concentration of total organic carbon at the time of measurement.

[0140] The Co3O4-Ti composite electrodes prepared in Examples 2, 3, and 4 react with NO3. - The electrolytic removal effect of -N is similar to that of Test Example 1.

[0141] Test Example 2

[0142] This test example demonstrates the effect of the Co3O4-Ti composite electrode prepared in Example 1 on NO3. - Stability test of electrolytic removal of -N.

[0143] The Co3O4-Ti composite electrode prepared in Example 1 was continuously tested for 9 cycles according to the test conditions and procedures of Test Example 1, and NO3 was calculated. - The removal rate of -N, the test results are as follows: Figure 8 As shown.

[0144] from Figure 8 As can be seen from the above, the Co3O4-Ti composite electrode prepared in Example 1 is effective against NO3. - The removal rate of -N remained at no less than 95% after nine consecutive uses. This indicates that the catalytic active layer structure of the Co3O4-Ti composite electrode of the present invention is robust and has strong adhesion to the substrate. No significant dissolution or peeling of active components occurred during repeated use, demonstrating excellent durability and industrial application potential.

[0145] The Co3O4-Ti composite electrodes prepared in Examples 2, 3, and 4 react with NO3. - The stability of electrolytic removal of -N is similar to that of Test Example 2.

[0146] Test Example 3

[0147] This test example demonstrates the effect of the Co3O4-Ti composite electrode prepared in Comparative Example 7 on NO3. - The electrolytic removal effect of -N was tested using the same procedure as in Test Example 1, and the results are as follows: Figure 9 As shown, without steps 6 and 7 in Example 1, the NO3-N removal rate was significantly reduced to 73%, which is significantly lower than the 91% in Example 1. This indicates that steps 6 and 7 are the key to achieving efficient removal in Example 1.

[0148] Test Example 4

[0149] This test example demonstrates the effect of the Co3O4-Ti composite electrodes prepared in Comparative Examples 2, 3, 4, 5, and 6 on NO3. - The electrolytic removal effect of -N was tested using essentially the same procedure as in Test Example 1, except that the current density was 0.5 mA / cm². 2 The results are shown in Table 3.

[0150] Table 3 shows the effects of the Co3O4-Ti composite electrodes prepared in Comparative Examples 2, 3, 4, 5, and 6 on NO3. - -N removal rate

[0151]

[0152] As can be seen from Table 3, the calcination temperatures in steps 6 and 8 of the Co3O4-Ti composite electrode preparation process should not differ too much, otherwise it will seriously affect the removal rate of NO3-N by the Co3O4-Ti composite electrode.

[0153] The above description provides an illustrative overview of the present invention and its embodiments. This description is not restrictive, and the embodiments shown are merely one example of the invention's implementation. Actual implementations are not limited to these examples. Therefore, if those skilled in the art are inspired by this description and design similar implementations and examples without departing from the spirit of the invention, such designs should fall within the scope of protection of the present invention.

Claims

1. The application of a Co3O4-Ti composite electrode in the electrolytic removal of nitrate nitrogen from water, wherein the electrolysis is performed using an electrolytic reactor, characterized in that... The cathode of the electrolytic reactor is a Co3O4-Ti composite electrode, and the electrolysis current density is 45 mA / cm². 2 ~55 mA / cm 2 The pH of the electrolyte in the electrolytic reactor is 5-6, and the electrolysis temperature is 25℃-35℃. The preparation method of the Co3O4-Ti composite electrode includes the following steps: S1. Place the titanium sheet in the etching solution for etching, and dry it after etching is completed for later use; S2. Dissolve cobalt nitrate in an alcohol solvent to obtain an electrode solution; S3. Take the electrode liquid prepared in S2, coat it evenly on both sides of the titanium sheet to be used in S1, and then dry it. S4. Repeat the operation of S3 2 to 4 times, and then calcine at 300℃ to 600℃ for 3 to 7 minutes. S5. Repeat the operation of S4 until the electrode liquid prepared in S2 is completely coated. S6. The coated titanium sheet is calcined at 300℃~600℃ for 2.5~3.5h and cooled to room temperature to obtain the Co3O4-Ti composite electrode.

2. The application of the Co3O4-Ti composite electrode according to claim 1 in the electrolytic removal of nitrate nitrogen from water, characterized in that, The temperature difference between calcination in S4 and S6 is less than or equal to 50°C.

3. The application of the Co3O4-Ti composite electrode according to claim 1 in the electrolytic removal of nitrate nitrogen from water, characterized in that, The volume-to-area ratio of the electrode solution in S2 to the titanium sheet is 1 mL : (0.8 cm²) 2 ~2cm 2 The concentration of cobalt nitrate in the electrode solution is 0.1~0.3 mol / L, and the alcohol solvent is selected from one or more of methanol, ethanol, propanol and butanol.

4. The application of the Co3O4-Ti composite electrode according to claim 1 in the electrolytic removal of nitrate nitrogen from water, characterized in that, The drying temperature in S3 is 60℃~80℃.

5. The application of the Co3O4-Ti composite electrode according to claim 1 in the electrolytic removal of nitrate nitrogen from water, characterized in that, The etching solution in S1 is selected from one or more of oxalic acid solution, hydrochloric acid solution, sulfuric acid solution, sodium hydroxide solution and potassium hydroxide solution, the mass percentage of the etching solution is 10%~30%, and the etching temperature is 70℃~90℃.

6. The application of the Co3O4-Ti composite electrode according to claim 1 in the electrolytic removal of nitrate nitrogen from water, characterized in that, Before step S1, a pretreatment step is included, which includes: grinding the titanium sheet, immersing it in an oxalic acid solution with a mass percentage of 10% to 30%, boiling it for 20 to 40 minutes, and then rinsing it.

7. The application of the Co3O4-Ti composite electrode according to claim 1 in the electrolytic removal of nitrate nitrogen from water, characterized in that, The mass concentration of the nitrate nitrogen is 15 mg / L to 20 mg / L.

8. The application of the Co3O4-Ti composite electrode according to claim 1 in the electrolytic removal of nitrate nitrogen from water, characterized in that, The nitrate nitrogen includes one or more of trinitrophenol, potassium nitrate, p-nitrophenol, and o-nitrophenol.

9. The application of the Co3O4-Ti composite electrode according to claim 1 in the electrolytic removal of nitrate nitrogen from water, characterized in that, The anode of the electrolytic reactor is a ruthenium-iridium-titanium electrode, and the electrode spacing between the cathode and the anode is 10~30 mm.

10. A method for preparing a Co3O4-Ti composite electrode, characterized in that, The preparation method includes the following steps: S1. Place the titanium sheet in the etching solution for etching, and dry it after etching is completed for later use; S2. Dissolve cobalt nitrate in an alcohol solvent to obtain an electrode solution; S3. Take the electrode liquid prepared in S2, coat it evenly on both sides of the titanium sheet to be used in S1, and then dry it. S4. Repeat the operation of S3 2 to 4 times, and then calcine at 300℃ to 600℃ for 3 to 7 minutes. S5. Repeat the operation of S4 until the electrode liquid prepared in S2 is completely coated. S6. The coated titanium sheet is calcined at 300℃~600℃ for 2.5~3.5h and cooled to room temperature to obtain the Co3O4-Ti composite electrode.

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