Preparation method of Co3O4 modified foamed nickel electrode and application of Co3O4 modified foamed nickel electrode in waste salt purification

Abstract

The invention provides a preparation method of a Co3O4 modified foam nickel electrode and application of the Co3O4 modified foam nickel electrode in waste salt purification, and relates to the technical field of waste salt purification, Co3O4 with high catalytic reduction activity on NO3 <-> is synthesized through a calcination method, the surface of the electrode is coated with the Co3O4, the performance of the electrode is effectively improved, the electrode is easy to prepare and has excellent selectivity, and the Co3O4 modified foam nickel electrode is suitable for industrial production. The coupling process is high in safety, low in actual consumption and free of secondary pollution and has industrial application potential, sodium chloride in the salt-containing organic wastewater is purified through the Fenton-electro-catalysis coupling process, and efficient utilization of salt-containing organic wastewater resources is achieved.

Description

Technical Field

[0001] The present invention relates to the technology of waste salt purification, and specifically to a preparation method of a Co3O4 modified nickel foam electrode and its application in waste salt purification. Background Art

[0002] Waste salt purification refers to the purification operation of saline organic wastewater, which mainly comes from industries such as coal chemical industry, printing and dyeing, and pharmaceuticals. The wastewater is characterized by high COD, high chroma, and high salt (NaCl) content, with great water quality hazards. Moreover, due to the presence of nitrate in the wastewater, it is difficult to recover the salt with high purity. Therefore, the efficient removal of nitrate during the waste salt purification process is extremely crucial.

[0003] Electrocatalytic reduction can effectively remove nitrate without the need to add additional reducing agents. It relies on the transfer of electrons or hydrogen atoms electrochemically deposited, adsorbing the ions to be reduced onto the electrode surface and then triggering the reduction reaction. However, the selection of the electrocatalytic electrode is particularly important, and factors such as excellent electrode performance, simple preparation, and low cost are important reference indicators.

[0004] Among them, CN109896685 B discloses a method for harmless treatment of high-concentration printing and dyeing wastewater. This invention combines ozone oxidation and Fenton oxidation to remove organic substances in the wastewater, and recovers inorganic salts through electrodialysis and evaporation crystallization. This process has a high water recovery rate and no harmful substance emissions, but the process equipment is difficult to be industrially applied, and the cost of the membrane in electrodialysis is relatively high.

[0005] In view of this, this paper proposes a preparation method of a Co3O4 modified nickel foam electrode and its application in waste salt purification, using the Fenton-electrocatalytic process to remove organic substances and nitrate in the wastewater, with a simple process, low cost, and high purity of the recovered salt. Summary of the Invention

[0006] (I) Technical Problems to be Solved

[0007] Aiming at the deficiencies of the prior art, the present invention provides a preparation method of a Co3O4 modified nickel foam electrode and its application in waste salt purification, solving the problems of complex process, high cost, and low purity of the recovered salt when removing organic substances and nitrate in the wastewater.

[0008] (II) Technical Solutions

[0009] To achieve the above objectives, the present invention is realized through the following technical solutions:

[0010] In the present invention, on the first aspect, a preparation method of a Co3O4 modified nickel foam electrode includes:

[0011] Weigh NaCl and CoCl2·6H2O, dissolve them in an ethanol solution, and stir evenly;

[0012] Continue to add hexamethylenetetramine for reaction. After the reaction is completed, centrifuge. The solid product after centrifugation is dried and calcined to obtain the final product Co3O4;

[0013] Place the nickel foam in an acetone solution and ultrasonicate. After that, continue to ultrasonicate it in absolute ethanol, and then dry it for later use;

[0014] Take Co3O4, acetylene black, and PTFE and grind them thoroughly in a mortar. Apply them evenly on both sides of the electrode and dry them in an oven. Finally, obtain the Co3O4 modified nickel foam electrode (Co3O4 / NFE).

[0015] Furthermore, the concentration of the ethanol solution is 10%.

[0016] Furthermore, the temperature during the calcination process is controlled at 400 - 500 °C.

[0017] Furthermore, the calcination time is 1 - 5 h.

[0018] In the second aspect, an application of the preparation method of the Co3O4 modified nickel foam electrode in waste salt purification, using the prepared Co3O4 modified nickel foam electrode to electrocatalytically remove nitrate in the saline organic wastewater, includes the following steps:

[0019] S1. Take 200 mL of saline organic wastewater, add acid solution to adjust the pH of the wastewater. After the pH is stabilized, add an oxidant and a catalyst to carry out the Fenton reaction. After the reaction is completed, carry out neutralization, flocculation, and filtration to obtain clear Fenton effluent;

[0020] S2. Use the coated titanium electrode (DSA) as the anode and Co3O4 / NFE as the cathode, and place the electrodes in the Fenton effluent obtained in step S1 for electrolytic catalysis;

[0021] S3. Carry out vacuum distillation on the final effluent. The concentrated liquid in the salt evaporation process is returned to the Fenton - electrocatalytic process for re - treatment, the distillate is discharged, and the precipitated sodium chloride is dried to achieve high - purity recovery.

[0022] Furthermore, in step S1, the acid solution is 1:1 HNO3, and the pH of the wastewater is 1.0 - 5.0.

[0023] Furthermore, in step S1, the oxidant is 30% H2O2, and the volume ratio of the addition amount of 30% H2O2 is 0.40 - 1.40%.

[0024] Furthermore, in step S1, the catalyst is FeSO4·7H2O, the addition amount is 0.8 - 2.4 g / L, and the reaction time is 1 - 5 h.

[0025] Further, in the electrolytic catalysis process in step S2, the current density is 0.06 - 0.14 A / cm 2 , the pH is 1.0 - 6.0, and the electrode area is 2.0 - 5.0 cm 2 .

[0026] Further, the temperature of the vacuum distillation in step S3 is 70 °C.

[0027] (III) Beneficial Effects

[0028] The present invention provides a preparation method of a Co3O4 modified nickel foam electrode and its application in waste salt purification. Compared with the prior art, it has the following beneficial effects:

[0029] The present invention uses a Fenton-electrocatalysis coupling process to purify sodium chloride in saline organic wastewater, and discloses a Co3O4 modified nickel foam electrode. Co3O4 with strong catalytic reduction activity for NO 3 - is synthesized by a calcination method and coated on the electrode surface, effectively improving the electrode performance. The electrode preparation is simple, with excellent selectivity. The coupling process has high safety, low actual consumption, and no secondary pollution, and has the potential for industrial application. Description of the Drawings

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0031] Figure 1 It shows the influence of different Fenton pH values on the COD removal of wastewater in Example 1;

[0032] Figure 2 It shows the influence of different dosages of H2O2 (30%) on the COD removal of wastewater in Example 2;

[0033] Figure 3 It shows the influence of different dosages of the catalyst (FeSO4·7H2O) on the COD removal of wastewater in Example 3;

[0034] Figure 4 It shows the influence of different Fenton reaction times on the COD removal of wastewater in Example 4;

[0035] Figure 5 It shows the influence of different synthesis calcination temperatures of Co3O4 on nitrate removal (a) and sodium chloride purity (b) in Example 5;

[0036] Figure 6 Effect of different synthesis and calcination times of Co3O4 on nitrate removal (a) and sodium chloride purity (b) in Example 6;

[0037] Figure 7 Effect of different electrocatalytic current densities on nitrate removal (a) and sodium chloride purity (b) in Example 7;

[0038] Figure 8 Effect of different electrocatalytic pH values on nitrate removal (a) and sodium chloride purity (b) in Example 8;

[0039] Figure 9 Effect of different electrocatalytic electrode areas on nitrate removal (a) and sodium chloride purity (b) in Example 9. Detailed implementation manners

[0040] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0041] By providing a preparation method of a Co3O4 modified nickel foam electrode and its application in waste salt purification, the embodiments of the present application solve the problems of complex processes, high costs and low purity of the recovered salt during the removal of organic matter and nitrate in wastewater, and realize the efficient utilization of saline organic wastewater resources.

[0042] To better understand the above technical solutions, the above technical solutions will be described in detail below in conjunction with the accompanying drawings of the specification and specific implementation manners.

[0043] In a first aspect, a preparation method of a Co3O4 modified nickel foam electrode, the method comprising:

[0044] Weigh NaCl and CoCl2·6H2O and dissolve them in an ethanol solution, and stir evenly;

[0045] Continue to add hexamethylenetetramine for reaction. After the reaction ends, centrifuge, and the solid product after centrifugation is dried and calcined to obtain the final product Co3O4;

[0046] Place the nickel foam in an acetone solution for ultrasonic treatment, then continue to place it in absolute ethanol for ultrasonic treatment, and then dry for standby;

[0047] Take Co3O4, acetylene black, and PTFE and grind them thoroughly in a mortar. Apply the mixture evenly on both sides of the electrode and dry it in an oven to finally obtain a Co3O4-modified nickel foam electrode (Co3O4 / NFE).

[0048] During the process of preparing the Co3O4-modified nickel foam electrode, specifically, accurately weigh 0.3418 g of NaCl and 0.5844 g of CoCl2·6H2O, dissolve them in 200 mL of ethanol solution, and stir well;

[0049] Continue to add 1.68 g of hexamethylenetetramine, react at 90 °C for 1 h. After the reaction, perform centrifugation and wash several times with deionized water. The centrifuged solid product is dried and calcined to obtain the final product Co3O4;

[0050] Place the nickel foam in an acetone solution and ultrasonicate for 20 min. Then continue to ultrasonicate it in absolute ethanol for 20 min, and then dry it in an oven at 60 °C for 12 h for standby;

[0051] Take 0.02 g of Co3O4, 0.01 g of acetylene black, and an appropriate amount of 6% PTFE, grind them thoroughly in a mortar, apply the mixture evenly on both sides of the electrode, and dry it in an oven at 60 °C to finally obtain a Co3O4-modified nickel foam electrode (Co3O4 / NFE).

[0052] Specifically, the concentration of the ethanol solution is 10%;

[0053] During the calcination process, the temperature is controlled at 400 - 500 °C, the calcination time is 1 - 5 h, and the calcination atmosphere is air.

[0054] In the second aspect, an application of a Co3O4-modified nickel foam electrode in waste salt purification, using this electrode for electrocatalytic reduction to remove nitrate in saline organic wastewater, includes the following steps:

[0055] S1. Take 200 mL of saline organic wastewater, add acid solution to adjust the pH of the wastewater. After the pH is stabilized, add an oxidant and a catalyst for Fenton reaction. After the reaction, perform neutralization, flocculation, and filtration to obtain clear Fenton effluent;

[0056] S2. Use a coated titanium electrode (DSA) as the anode and Co3O4 / NFE as the cathode, and place the electrodes in the Fenton effluent obtained in step S1 for electrolytic catalysis;

[0057] S3. Perform vacuum distillation on the final effluent. The concentrated liquid in the salt evaporation process is returned to the Fenton-electrocatalytic process for reprocessing, the distillate is discharged, and the precipitated sodium chloride is dried to achieve high-purity recovery.

[0058] Specifically, the sodium chloride content of the saline organic wastewater described in step S1 is 8-9%, the COD content is 1500-1800 mg / L, the nitrate content is 90-100 mg / L, and pH = 8.5;

[0059] In step S1, to avoid introducing impurities, the acid solution is 1:1 HNO3, and the pH of the wastewater is 1.0-5.0;

[0060] In step S1, the oxidant is 30% H2O2, and the volume ratio of the 30% H2O2 added is 0.40-1.40%;

[0061] In step S1, the catalyst is FeSO4·7H2O, the dosage is 0.8-2.4 g / L, and the reaction time is 1-5 h;

[0062] In the electrolytic catalysis process described in step S2, the current density is 0.06-0.14 A / cm 2 , the pH is 1.0-6.0, and the electrode area is 2.0-5.0 cm 2 ;

[0063] In step S3, the temperature of the vacuum distillation is 70 °C.

[0064] The present invention uses a Fenton-electrocatalysis coupling process to purify sodium chloride in saline organic wastewater, and discloses a Co3O4 modified nickel foam electrode. Co3O4 with strong catalytic reduction activity is synthesized by a calcination method and coated on the electrode surface, effectively improving the electrode performance. Moreover, the electrode preparation is simple, with excellent selectivity. The coupling process has high safety, low actual consumption, and no secondary pollution, showing potential for industrial application. 3 -

[0065] Specifically, the following examples are included:

[0066] It should be noted that the saline organic wastewater used in the following experimental examples is the wastewater of a large factory, with a sodium chloride content of 8-9%, a COD content of 1500-1800 mg / L, a nitrate content of 90-100 mg / L, and pH = 8.5.

[0067] Example 1:

[0068] S01. Take 200 mL of saline organic wastewater, add 1:1 HCl to adjust the pH of the wastewater to 1.0-5.0. After the pH is stabilized, add 0.4 g of FeSO4·7H2O as an oxidant and dissolve it in the wastewater. Then add 1.0% H2O2 as a catalyst and react for 4 h;

[0069] S02. After the reaction ended, 4.0 mol / L NaOH was added to adjust the pH of the wastewater to 8.0 for neutralization precipitation. After the precipitation separated out, 0.5% polyacrylamide with a concentration of 1.5 g / L was added for flocculation sedimentation and filtration.

[0070] The COD removal rates under different pH conditions were 49.79%, 60.95%, 82.09%, 55.66%, and 29.38% respectively. The results are as Figure 1 shown. It can be seen that when the pH of the wastewater is adjusted to 3.0 under the same other conditions, the COD removal rate is better.

[0071] Example 2:

[0072] S01. Take 200 mL of saline organic wastewater, add 1:1 HCl to adjust the pH of the wastewater to 3.0. After the pH stabilizes, add 0.4 g of FeSO4·7H2O as an oxidant and dissolve it in the wastewater. Then add 0.4 - 1.4% H2O2 as a catalyst and react for 4 h.

[0073] S02. After the reaction ended, 4.0 mol / L NaOH was added to adjust the pH of the wastewater to 8.0 for neutralization precipitation. After the precipitation separated out, 0.5% polyacrylamide with a concentration of 1.5 g / L was added for flocculation sedimentation and filtration.

[0074] The COD removal rates under different dosages of the catalyst H2O2 were 54.24%, 71.58%, 81.25%, 94.34%, 92.51%, and 93.69% respectively. The results are as Figure 2 shown. It can be seen that when 1.0% H2O2 is added as a catalyst under the same other conditions, the COD removal rate is better.

[0075] Example 3:

[0076] S01. Take 200 mL of saline organic wastewater, add 1:1 HCl to adjust the pH of the wastewater to 3.0. After the pH stabilizes, add 0.16 - 0.48 g of FeSO4·7H2O and dissolve it in the wastewater, and add 1.0% H2O2 and react for 4 h.

[0077] S02. After the reaction ended, 4.0 mol / L NaOH was added to adjust the pH of the wastewater to 8.0 for neutralization precipitation. After the precipitation separated out, 0.5% polyacrylamide with a concentration of 1.5 g / L was added for flocculation sedimentation and filtration.

[0078] The COD removal rates under different dosages of the oxidant FeSO4·7H2O were 52.20%, 59.26%, 68.61%, 86.72%, 79.53%, and 93.69% respectively. The results are as Figure 3As shown, it can be seen that under the same other conditions, when 0.40gFeSO4·7H2O is added as an oxidant and dissolved in the wastewater, the COD removal rate is better.

[0079] Embodiment 4:

[0080] S01, take 200mL of salt-containing organic wastewater, add 1:1 HCl to adjust the pH of the wastewater to 3.0, after the pH stabilizes, add 0.40g FeSO4·7H2O to dissolve in the wastewater, add 1.0% H2O2 to react for 1 to 5h;

[0081] S02. After the reaction is completed, 4.0 mol / L NaOH is added to adjust the pH of the wastewater to 8.0 for neutralization and precipitation. After the precipitate is precipitated, 0.5% 1.5 g / L polyacrylamide is added for flocculation and sedimentation and filtered.

[0082] The COD removal rates under different Fenton reaction time conditions were 61.83%, 84.44%, 92.07%, 94.34% and 93.25%, respectively. Figure 4 As shown, it can be seen that under the same other conditions, the COD removal rate is better when the Fenton reaction time is 4h.

[0083] In summary, Examples 1 to 4 are multiple experiments conducted on the Fenton reaction in the Fenton-electrocatalytic process. It can be seen that when the steps of Example 4 are adopted and the Fenton reaction time is controlled to 4 hours, the COD removal rate is better.

[0084] Embodiment 5:

[0085] S01. Accurately weigh 0.3418 g NaCl and 0.5844 g CoCl2·6H2O and dissolve them in 200 mL ethanol solution. Add 1.68 g hexamethylenetetramine and react at 90°C for 1 h. After the reaction, centrifuge and wash. After drying, calcine the product at 400-500°C for 4 h to obtain the product Co3O4.

[0086] S02. Place the nickel foam in an acetone solution for ultrasonic treatment for 20 minutes, then continue to place it in anhydrous ethanol for ultrasonic treatment for 20 minutes, and then place it in a 60°C oven to dry for 12 hours. Take 0.02g Co3O4, 0.01g acetylene black and an appropriate amount of 6% PTFE, put them in a mortar and grind them thoroughly, evenly apply them on both sides of the electrode, and place it in a 60°C oven to dry to obtain Co3O4 / NFE.

[0087] S03, using the coated titanium electrode (DSA) as the anode and Co3O4 / NFE as the cathode, the electrodes were placed in Fenton effluent and the current density was controlled to 0.10A / cm 2 , solution pH is 3.0, electrode area is 5 cm 2 The electrocatalysis was carried out for 2 h.

[0088] At different calcination temperatures, the nitrate removal rates were 82.19%, 84.49%, 96.01%, 98.40%, and 98.09%, respectively, and the sodium chloride purities were 96.15%, 97.02%, 97.15%, 98.66%, and 98.50%, respectively. Figure 5 As shown, it can be seen that under the same other conditions, when the calcination temperature is 470°C, the nitrate removal rate is better and the purity of the obtained sodium chloride is higher.

[0089] Embodiment 6:

[0090] S01. Accurately weigh 0.3418 g NaCl and 0.5844 g CoCl2·6H2O, dissolve them in 200 mL ethanol solution, add 1.68 g hexamethylenetetramine, react at 90°C for 1 h, centrifuge and wash after the reaction, dry the product, and calcine at 470°C for 1 to 5 h to obtain the product Co3O4;

[0091] S02, place the nickel foam in an acetone solution for 20 minutes of ultrasonic treatment, then continue to place it in anhydrous ethanol for 20 minutes of ultrasonic treatment, and then place it in a 60°C oven for drying for 12 hours, take 0.02g Co3O4, 0.01g acetylene black and an appropriate amount of 6% PTFE, put them in a mortar and grind them thoroughly, apply them evenly on both sides of the electrode, and place it in a 60°C oven for drying to obtain Co3O4 / NFE;

[0092] S03, using the coated titanium electrode (DSA) as the anode and Co3O4 / NFE as the cathode, the electrodes were placed in Fenton effluent and the current density was controlled to 0.10A / cm 2 , solution pH is 3.0, electrode area is 5 cm 2 The electrocatalysis was carried out for 2 h.

[0093] At different calcination times, the nitrate removal rates were 39.52%, 87.76%, 93.02%, 95.15%, and 75.10%, respectively, and the sodium chloride purities were 91.76%, 96.98%, 97.68%, 98.12%, and 94.22%, respectively. Figure 6 As shown, it can be seen that under the same other conditions, when the calcination time is 4h, the nitrate removal rate is better and the purity of the obtained sodium chloride is higher.

[0094] Embodiment 7:

[0095] S01, accurately weigh 0.3418g NaCl and 0.5844g CoCl2·6H2O, dissolve them in 200mL ethanol solution, add 1.68g hexamethylenetetramine, react at 90℃ for 1h, centrifuge and wash after the reaction, dry the product and calcine at 470℃ for 4h to obtain the product Co3O4;

[0096] S02, place the nickel foam in an acetone solution for 20 minutes of ultrasonic treatment, then continue to place it in anhydrous ethanol for 20 minutes of ultrasonic treatment, and then place it in a 60°C oven for drying for 12 hours, take 0.02g Co3O4, 0.01g acetylene black and an appropriate amount of 6% PTFE, put them in a mortar and grind them thoroughly, apply them evenly on both sides of the electrode, and place it in a 60°C oven for drying to obtain Co3O4 / NFE;

[0097] S03, using the coated titanium electrode (DSA) as the anode and Co3O4 / NFE as the cathode, the electrodes were placed in Fenton effluent and the current density was controlled at 0.06-0.14 A / cm 2 , solution pH is 3.0, electrode area is 5 cm 2 The electrocatalysis was carried out for 2 h.

[0098] At different current densities, the nitrate removal rates were 46.53%, 81.93%, 95.58%, 95.05%, and 91.74%, respectively, and the sodium chloride purities were 92.55%, 95.68%, 97.52%, 97.21%, and 96.21%, respectively. The results are shown in Figure 7 As shown, it can be seen that under the same other conditions, the current density is 0.10A / cm 2 When the nitrate removal rate is better, the purity of the obtained sodium chloride is higher.

[0099] Embodiment 8:

[0100] S01, accurately weigh 0.3418g NaCl and 0.5844g CoCl2·6H2O, dissolve them in 200mL ethanol solution, add 1.68g hexamethylenetetramine, react at 90℃ for 1h, centrifuge and wash after the reaction, dry the product and calcine at 470℃ for 4h to obtain the product Co3O4;

[0101] S02, place the nickel foam in an acetone solution for 20 minutes of ultrasonic treatment, then continue to place it in anhydrous ethanol for 20 minutes of ultrasonic treatment, and then place it in a 60°C oven for drying for 12 hours, take 0.02g Co3O4, 0.01g acetylene black and an appropriate amount of 6% PTFE, put them in a mortar and grind them thoroughly, apply them evenly on both sides of the electrode, and place it in a 60°C oven for drying to obtain Co3O4 / NFE;

[0102] S03, using the coated titanium electrode (DSA) as the anode and Co3O4 / NFE as the cathode, the electrodes were placed in Fenton effluent and the current density was controlled to 0.10A / cm 2 , solution pH 1.0-6.0, electrode area 5cm 2 The electrocatalysis was carried out for 2 h.

[0103] Under different electrolytic solution pH conditions, the nitrate removal rates were 40.56%, 93.02%, 95.69%, 67.43%, 57.19%, and 44.39%, respectively, and the sodium chloride purities were 91.97%, 97.10%, 97.95%, 94.25%, 92.68%, and 92.32%, respectively. The results are shown in Figure 8 As shown, it can be seen that under the same other conditions, when the pH of the electrolytic solution is 3.0, the nitrate removal rate is better and the purity of the obtained sodium chloride is higher.

[0104] Embodiment 9:

[0105] S01. Accurately weigh 0.3418 g NaCl and 0.5844 g CoCl2·6H2O and dissolve them in 200 mL ethanol solution. Add 1.68 g hexamethylenetetramine and react at 90°C for 1 h. After the reaction, centrifuge and wash. After drying, calcine the product at 470°C for 4 h to obtain the product Co3O4.

[0106] S02. Place the nickel foam in an acetone solution for ultrasonic treatment for 20 minutes, then continue to place it in anhydrous ethanol for ultrasonic treatment for 20 minutes, and then place it in a 60°C oven to dry for 12 hours. Take 0.02g Co3O4, 0.01g acetylene black and an appropriate amount of 6% PTFE, put them in a mortar and grind them thoroughly, evenly apply them on both sides of the electrode, and place it in a 60°C oven to dry to obtain Co3O4 / NFE.

[0107] S03, using the coated titanium electrode (DSA) as the anode and Co3O4 / NFE as the cathode, the electrodes were placed in Fenton effluent and the current density was controlled to 0.10A / cm 2 , solution pH is 3.0, electrode area is 2-5 cm 2 The electrocatalysis was carried out for 2 h.

[0108] Under different electrode area conditions, the nitrate removal rates were 24.77%, 42.53%, 97.58%, and 98.61%, respectively, and the sodium chloride purities were 88.22%, 92.15%, 97.69%, and 98.44%, respectively. Figure 9 As shown, it can be seen that under the same other conditions, the electrode area is 5cm 2 When the nitrate removal rate is better, the purity of the obtained sodium chloride is higher.

[0109] In summary, Examples 5 to 9 are multiple experiments on the preparation of Co3O4 / NFE in the Fenton-electrocatalysis process and the electrolytic catalysis after the Fenton reaction. It can be seen that by adopting the steps of Example 9 and controlling the electrode area to 5 cm 2 , the nitrate removal rate is better and the purity of the obtained sodium chloride is higher.

[0110] In summary, compared with the prior art, the following beneficial effects are achieved:

[0111] 1. In the present invention, Co3O4 with strong catalytic reduction activity for NO 3 - is synthesized by the calcination method and coated on the electrode surface, effectively improving the electrode performance. The Co3O4 / NFE electrode is simple to prepare, has excellent selectivity, and the coupling process has high safety, low actual consumption, and no secondary pollution, showing potential for industrial application.

[0112] 2. Moreover, the present invention uses the Fenton-electrocatalysis coupling process to purify sodium chloride in saline organic wastewater, effectively improving the nitrate removal rate in saline organic wastewater and achieving an increase in the purity of sodium chloride purification.

[0113] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "including a..." does not exclude the existence of additional identical elements in the process, method, article or device including the said element.

[0114] The above examples are only used to illustrate the technical solutions of the present invention and are not intended to limit it; although the present invention has been described in detail with reference to the foregoing examples, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing examples, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various examples of the present invention.

Claims

1. A preparation method of a Co3O4 modified nickel foam electrode, characterized in that, The method includes: Weigh NaCl and CoCl2·6H2O and dissolve them in ethanol solution, and stir evenly; Continue to add hexamethylenetetramine to react, centrifuge after the reaction is completed, and dry and calcine the solid product after centrifugation to obtain the final product Co3O4; The nickel foam is placed in an acetone solution for ultrasonication, and then placed in anhydrous ethanol for ultrasonication, and then dried for later use; Co3O4, acetylene black and PTFE were put into a mortar and ground thoroughly, and then evenly applied on both sides of the electrode and dried in an oven to finally obtain a Co3O4 modified nickel foam electrode (Co3O4 / NFE).

2. The preparation method of a Co3O4 modified nickel foam electrode according to claim 1, characterized in that, The concentration of the ethanol solution is 10%.

3. The preparation method of a Co3O4 modified nickel foam electrode according to claim 1, characterized in that, The calcination process is controlled at a temperature of 400-500°C.

4. The preparation method of a Co3O4-modified nickel foam electrode according to claim 1, characterized in that, The calcination time is 1 to 5 hours.

5. Application of a preparation method of a Co3O4 modified nickel foam electrode in waste salt purification, wherein the Co3O4 modified nickel foam electrode prepared by the preparation method described in any one of claims 1-4 is used for electrocatalytic removal of nitrate in saline organic wastewater, characterized in that The following steps are involved: S1. Take 200 mL of salt-containing organic wastewater, add acid to adjust the pH of the wastewater, add oxidant and catalyst to carry out Fenton reaction after the pH is stable, neutralize, flocculate and filter after the reaction to obtain clarified Fenton effluent; S2, using the coated titanium electrode (DSA) as the anode and Co3O4 / NFE as the cathode, placing the electrode in the Fenton effluent of step S1 for electrolytic catalysis; S3. The final effluent is subjected to vacuum distillation, the concentrated liquid in the salt evaporation process is returned to the Fenton-electrocatalytic process for reprocessing, the distillate is discharged, and the precipitated sodium chloride is dried to achieve high-purity recovery.

6. Use of the method for preparing a Co3O4-modified nickel foam electrode according to claim 5 in waste salt purification, characterized in that The acid solution in step S1 is 1:1 HNO3, and the pH value of the wastewater is 1.0-5.

0.

7. Use of the method for preparing a Co3O4-modified nickel foam electrode according to claim 5 in waste salt purification, characterized in that, The oxidant in step S1 is 30% H2O2, and the volume ratio of the H2O2 added is 0.40-1.40% at a concentration of 30%.

8. Use of the preparation method of a Co3O4-modified nickel foam electrode according to claim 5 in waste salt purification, characterized in that, The catalyst in step S1 is FeSO4·7H2O, the dosage is 0.8-2.4 g / L, and the reaction time is 1-5 h.

9. Use of the method for preparing a Co3O4-modified nickel foam electrode according to claim 5 in waste salt purification, characterized in that, In the electrolytic catalysis process described in step S2, the current density is 0.06 - 0.14 A / cm 2 , the pH is 1.0 - 6.0, and the electrode area is 2.0 - 5.0 cm 2 .

10. Use of the method for preparing a Co3O4-modified nickel foam electrode according to claim 5 in waste salt purification, characterized in that, The temperature of the reduced pressure distillation in step S3 is 70°C.

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