Co-Cu / rGO-Ti electrode and preparation method and application thereof

Abstract

The invention discloses a Co-Cu / rGO-Ti electrode and a preparation method and application thereof, and belongs to the technical field of sewage electrochemical treatment.The preparation method comprises the following steps that a Ti net is pretreated, and the pretreated Ti net is obtained; gO is dispersed in deionized water, and a GO dispersion liquid is obtained; co salt and Cu salt are mixed in deionized water, and a Co-Cu mixed salt solution is obtained; immersing the pretreated Ti net into the GO dispersion liquid, taking out the Ti net, and drying the Ti net to obtain dried GO-Ti; dipping in a Co-Cu mixed salt solution at a constant temperature, taking out and drying to obtain a dipped and dried electrode; and putting the GO into a muffle furnace for calcination, reducing the GO into rGO by adopting a high-temperature calcination method, and decomposing the Co-Cu salt into metal oxide nanoparticles, thereby finally obtaining the Co-Cu / rGO-Ti electrode. According to the invention, agglomeration of Co-Cu particles can be avoided, uniform distribution and long-term stability of active sites are ensured, cyclic utilization of the electrode is ensured, dissolution of Co-Cu metal can be reduced, and secondary pollution is avoided.

Description

Technical Field

[0001] The present invention relates to a Co-Cu / rGO-Ti electrode and a preparation method and application thereof, belonging to the technical field of sewage electrochemical treatment. Background Art

[0002] As an environmentally friendly pollution control technology, the electrochemical reduction method has been applied to the field of nitrate nitrogen pollution control. N2 is an ideal reduction product, but the efficiency of reducing to N2 is currently low due to the competitive effect of the hydrogen evolution reaction (HER), and the electrodes are generally precious metals, which limits their widespread application. Although many bimetallic alloy electrodes have been developed in recent years, their nitrate nitrogen reduction efficiency is far lower than that of precious metals and the metal leaching concentration is high. This is because the electrical conductivity of the alloy is low, which affects its charge transfer efficiency in the electrochemical reaction, and its stability is poor, and it is easy to be leached and inactivated during long-term electrolysis. In addition, the preparation of alloy electrodes requires precise control of composition and process conditions, which further limits its promotion in some large-scale applications. Among the many bimetallic alloy electrodes, the combination of Co (cobalt) and Cu (copper) shows unique advantages. On the one hand, Co can promote NO3 - initial adsorption and activation of NO2, while Cu tends to promote - The further reduction of Co-Cu can synergistically optimize the reaction pathway and improve N2 selectivity. Furthermore, the introduction of Cu can inhibit HER and reduce competition for side reactions. However, Co-Cu particles are prone to agglomeration, resulting in a reduction in active sites and poor electrode recyclability. Furthermore, the high dissolution of Co-Cu metal can easily cause secondary contamination. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to overcome the defects of the existing technology and provide a Co-Cu / rGO-Ti composite electrode that can avoid the agglomeration of Co-Cu particles, ensure the uniform distribution and long-term stability of active sites, ensure the recycling of the electrode, and reduce the dissolution of Co-Cu metal to avoid secondary pollution.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0005] In a first aspect, the present invention provides a method for preparing a Co-Cu / rGO-Ti electrode, comprising the following steps:

[0006] Step a, pre-treating the Ti mesh to obtain a pre-treated Ti mesh;

[0007] Step b, dispersing GO in deionized water to obtain a GO dispersion;

[0008] Step c, mixing Co salt and Cu salt in deionized water to obtain a Co-Cu mixed salt solution;

[0009] Step d, immersing the pretreated Ti mesh in a GO dispersion, taking it out and drying it to obtain dried GO-Ti;

[0010] Step e, immersing the dried GO-Ti in a Co-Cu mixed salt solution at a constant temperature, taking it out and drying it, and repeating this step several times to obtain an immersed and dried electrode;

[0011] Step f, placing the impregnated and dried electrode in a muffle furnace for calcination, using a high-temperature calcination method to reduce GO to rGO and decompose the Co-Cu salt into metal oxide nanoparticles, ultimately obtaining a Co-Cu / rGO-Ti electrode.

[0012] In step a, the pretreatment is specifically as follows: polishing the Ti mesh with coarse sandpaper and fine sandpaper to remove oxides on its surface, placing the polished Ti mesh in 20% sulfuric acid solution and boiling it for 2 hours to form a uniform rough surface, and then placing it in anhydrous ethanol and deionized water for ultrasonic treatment for 15 minutes each to remove stains and grease on the surface of the Ti mesh.

[0013] In step b, the concentration of GO in the GO dispersion is 0.5-3.0 mg / L, and the dispersion is carried out by ultrasonic method for 1 h.

[0014] In step c, the Co salt is cobalt sulfate hexahydrate, the Cu salt is anhydrous copper sulfate, and the molar concentrations of Co and Cu in the Co-Cu mixed salt solution are both 0.75 mol / L.

[0015] In step d, the immersion time is 30 minutes, the temperature is room temperature, and the drying temperature is 110° C., and the time is 15 minutes.

[0016] In step e, the immersion temperature is 60°C and the time is 30 min, so that the metal ions are evenly adsorbed on the GO surface; the drying temperature is 110°C and the time is 15 min.

[0017] In step e, repeat this step 3 to 5 times.

[0018] In step f, the calcination temperature is 500° C., the calcination time is 1 h, the muffle furnace heating rate is 5° C. / min, and the product is naturally cooled to room temperature after the calcination.

[0019] In a second aspect, the present invention provides a Co-Cu / rGO-Ti electrode prepared by the Co-Cu / rGO-Ti electrode preparation method.

[0020] In a third aspect, the present invention provides an application of a Co-Cu / rGO-Ti electrode, using Co-Cu / rGO-Ti as a cathode and DSA (titanium anode metal oxide coating electrode) as an anode to carry out an electrolytic reaction for removing nitrate pollutants.

[0021] Compared with the prior art, the technical solution of this application has the following beneficial technical effects:

[0022] The present invention anchors Co-Cu bimetallic nanoparticles on a Ti (titanium) substrate modified with rGO (reduced graphene oxide). The oxygen-containing functional groups (such as -COOH and -OH) on the rGO surface can effectively anchor the Co-Cu nanoparticles, preventing them from agglomerating during high-temperature calcination or electrochemical processes, ensuring the uniform distribution and long-term stability of active sites, and avoiding the deterioration of electrode recyclability. In addition, due to the high fixation effect of rGO on the particles, the dissolution of Co-Cu metal can be reduced, avoiding secondary pollution.

[0023] The high conductivity and large specific surface area of rGO effectively promote the rapid transfer of electrons from the Ti substrate to the active sites. The hydrophobicity and electronic regulation of rGO can optimize the local microenvironment of the Co-Cu active sites, inhibit the competition of HER, and promote the formation of nitrate intermediates (such as NO2 - ) further reduction, significantly improving the selectivity of N2 and ultimately improving the ability to reduce nitrate;

[0024] The present invention prepares the Co-Cu / rGO-Ti electrode material by a constant temperature impregnation-calcination method. The preparation method is simple and one-step synthesis, does not require repeated calcination, reduces the number of impregnation times, is energy-saving and low-consumption, and has good engineering application prospects. In addition, the material source is widely available, the cost is low, it has good electrical conductivity and shows excellent catalytic activity in the electrocatalytic reduction of nitrates. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the changes in the concentrations of nitrate nitrogen, nitrite nitrogen, and ammonia nitrogen during the reduction of nitrate nitrogen by the Co-Cu / -Ti cathode of the comparative example of the present invention;

[0026] Figure 2 Schematic diagram of the changes in the concentrations of nitrate nitrogen, nitrite nitrogen, and ammonia nitrogen during the reduction of nitrate nitrogen by the cathode Co-Cu / rGO-Ti (GO=0.5 mg / L) in Example 1 of the present invention;

[0027] Figure 3 Schematic diagram of the changes in the concentrations of nitrate nitrogen, nitrite nitrogen, and ammonia nitrogen during the reduction of nitrate nitrogen by the cathode Co-Cu / rGO-Ti (GO=1.0 mg / L) in Example 2 of the present invention;

[0028] Figure 4 Schematic diagram of the changes in the concentrations of nitrate nitrogen, nitrite nitrogen, and ammonia nitrogen during the reduction of nitrate nitrogen by the cathode Co-Cu / rGO-Ti (GO=2.0 mg / L) in Example 3 of the present invention;

[0029] Figure 5 Schematic diagram of the changes in the concentrations of nitrate nitrogen, nitrite nitrogen, and ammonia nitrogen during the reduction of nitrate nitrogen by the cathode Co-Cu / rGO-Ti (GO=3.0 mg / L) in Example 4 of the present invention;

[0030] Figure 6 This is a comparison chart of the effects of Co-Cu / rGO-Ti with different GO concentrations in Examples 1 to 4 of the present invention on reducing nitrate nitrogen. DETAILED DESCRIPTION

[0031] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention.

[0032] Example 1

[0033] The present invention discloses a method for preparing a Co-Cu / rGO-Ti composite electrode, and the preparation method includes the following steps:

[0034] The experimental water in this embodiment is ultrapure water.

[0035] Step 1, Ti-based pretreatment: The cut 10cm×6cm titanium mesh was polished with coarse and fine sandpaper to remove the surface oxide, and then the polished Ti mesh was boiled in 20% concentrated sulfuric acid for 2 hours, followed by ultrasonic treatment with anhydrous ethanol and ultrapure water for 15 minutes respectively. After the ultrasonic treatment, the Ti mesh was placed in a drying oven for drying and then used to obtain the pretreated Ti mesh.

[0036] Step 2: Preparation of GO dispersion: 10 ml of commercially available GO dispersion (10 mg / L) was transferred to a 200 mL volumetric flask and diluted to the mark to obtain a 0.5 mg / L GO dispersion. Ultrasonication was performed for 1 h to uniformly disperse the GO to obtain a GO dispersion.

[0037] Step 3, preparation of Co-Cu salt mixture: Weigh 42.166g of CoSO4·6H2O and 24g of CuSO4, dissolve them in a beaker filled with 100mL of ultrapure water. After complete dissolution, transfer them to a 200mL volumetric flask and dilute to the mark to prepare an impregnation solution with a Co:Cu molar ratio of 1:1 and a molar concentration of 0.75mol / L.

[0038] Step 4: Soak the pretreated Ti mesh in GO dispersion for 30 min (room temperature), take it out and place it in a drying oven at 110°C for 15 min.

[0039] Step 5: Place the soaked electrode in a Co-Cu mixed salt solution heated to 60°C for 30 minutes (maintain constant temperature) to allow the metal ions to be evenly adsorbed on the GO surface. After taking it out, gently wash it with deionized water to remove the unadsorbed ions, dry it at 110°C for 15 minutes, and repeat this step 4 times.

[0040] Step 6: Place the dried electrode in a muffle furnace and calcine it at 500°C for 1 hour at a heating rate of 5°C / min. Keep annealing in the muffle furnace. After calcination, cool it naturally to room temperature. Wash it several times with anhydrous ethanol and ultrapure water, wash it and dry it for later use.

[0041] The Co-Cu / rGO-Ti composite electrode prepared by the present invention was subjected to an electrolytic reaction: a hole was opened on each side of the electrolytic cell, a hose was connected, a peristaltic pump was installed, and water flowed from the cathode to the anode. A commercial DSA was used as the anode and the homemade Co-Cu / rGO-Ti was used as the cathode. A circulating flow electrolysis reaction was performed. The peristaltic pump flow rate was 20.4 mL / min, the temperature was 25°C, and the distance between the anode and cathode was 2.5 cm. The electrolyte contained the following components: 200 mg / L NO3 - -N, 500mg / LKCl, 1000mg / LNa2SO4; the initial pH of the electrolyte is 6.4. The electrolysis process is: current density 17mA / cm 2 The electrolysis time is 90 min. The power supply used in the electrolysis process is a DC regulated power supply with an output voltage of 0-30 V and an output current of 0-25 A.

[0042] In this embodiment, the sampling port is set at the water outlet near the anode, and the water sample after a certain reaction time is filtered through a 0.45 μm polyethersulfone filter membrane, and the NO3 content in the solution is determined by ultraviolet spectrophotometry. - -N, according to the NO3 in the solution before and after the reaction - -N concentration change, calculate NO3 - -N removal rate; NO2 was determined by N-(1-naphthyl)-ethylenediamine spectrophotometry and Nessler's reagent spectrophotometry - -N and NH4 + -N, calculate the NO2 generated during the electrolysis reaction - -N and NH4 + -N concentration; the concentrations of metal Co and Cu in the solution were determined using inductively coupled plasma mass spectrometry.

[0043] Example 2

[0044] This example is used to prepare a Co-Cu / rGO-Ti (GO = 1.0 mg / L) electrode for nitrate reduction. The specific steps are the same as those in Example 1, with the only difference being that in step 2, a 1.0 mg / L GO dispersion is used to prepare the Co-Cu / rGO-Ti electrode.

[0045] Example 3

[0046] This example is used to prepare a Co-Cu / rGO-Ti (GO = 2.0 mg / L) electrode for nitrate reduction. The specific steps are the same as those in Example 1, with the only difference being that in step 2, a 2.0 mg / L GO dispersion is used to prepare the Co-Cu / rGO-Ti electrode.

[0047] Example 4

[0048] This example is used to prepare a Co-Cu / rGO-Ti (GO = 3.0 mg / L) electrode for nitrate reduction. The specific steps are the same as those in Example 1, with the only difference being that in step 2, a 3.0 mg / L GO dispersion is used to prepare the Co-Cu / rGO-Ti electrode.

[0049] Comparative Example

[0050] This example is used to prepare a Co-Cu / Ti (GO=0 mg / L) electrode for reducing nitrate, specifically comprising the following steps:

[0051] The experimental water in this embodiment is ultrapure water.

[0052] Step 1, Ti-based pretreatment: The cut 10cm×6cm titanium mesh was polished with coarse and fine sandpaper to remove surface oxides, and then the polished Ti mesh was boiled in 20% concentrated sulfuric acid for 2 hours, followed by ultrasonic treatment with anhydrous ethanol and ultrapure water for 15 minutes respectively. After the ultrasonic treatment, the Ti mesh was placed in a drying oven for drying.

[0053] Step 2, preparation of Co-Cu salt mixture: Weigh 42.166g of CoSO4·6H2O and 24g of CuSO4, dissolve them in a beaker filled with 100mL of ultrapure water. After complete dissolution, transfer them to a 200mL volumetric flask and dilute to the mark to prepare an impregnation solution with a Co:Cu molar ratio of 1:1 and a molar concentration of 0.75mol / L.

[0054] Step 3: Soak the pretreated Ti mesh in a Co-Cu mixed salt solution heated to 60°C for 30 minutes (maintain constant temperature) to allow the metal ions to be evenly adsorbed on the surface of the Ti mesh. After taking it out, gently wash it with deionized water to remove the unadsorbed ions, dry it at 110°C for 15 minutes, and repeat this step 4 times.

[0055] Step 4: Place the dried electrode in a muffle furnace and calcine it at 500°C for 1 hour at a heating rate of 5°C / min. Keep annealing in the muffle furnace. After calcination, cool it naturally to room temperature. Wash it several times with anhydrous ethanol and ultrapure water, wash it and dry it for later use.

[0056] The Co-Cu / Ti electrode prepared by the present invention was subjected to an electrolytic reaction: a hole was opened on each side of the electrolytic cell, a hose was connected, and a peristaltic pump was installed. Water flowed from the cathode to the anode, and a commercial DSA was used as the anode and the homemade Co-Cu / rGO-Ti was used as the cathode. A circulating flow electrolysis reaction was performed. The peristaltic pump flow rate was 20.4 mL / min, the temperature was 25°C, and the distance between the anode and cathode was 2.5 cm. The electrolyte contained the following components: 200 mg / L NO3 - -N, 500mg / L KCl, 1000mg / L Na2SO4; the initial pH of the electrolyte is 6.4. The electrolysis process is: current density 17mA / cm 2 The electrolysis time is 90 min. The power supply used in the electrolysis process is a DC regulated power supply with an output voltage of 0-30 V and an output current of 0-25 A.

[0057] In this embodiment, the sampling port is set at the water outlet near the anode, and the water sample after a certain reaction time is filtered through a 0.45 μm polyethersulfone filter membrane, and the NO3 content in the solution is determined by ultraviolet spectrophotometry. - -N, according to the NO3 in the solution before and after the reaction - -N concentration change, calculate NO3 - -N removal rate; NO2 was determined by N-(1-naphthyl)-ethylenediamine spectrophotometry and Nessler's reagent spectrophotometry - -N and NH4 + -N, calculate the NO2 generated during the electrolysis reaction - -N and NH4 + -N concentration; the concentrations of metal Co and Cu in the solution were determined using inductively coupled plasma mass spectrometry.

[0058] from Figures 1 to 5 It can be seen that the reaction trends of the Co-Cu / rGO-Ti composite electrode prepared in the present invention and the Co-Cu / Ti electrode prepared in the comparative example for reducing nitrate are basically the same. - The reduction of NO3 mainly occurs in the first 30 minutes, after which - The concentration slowly decreases until it reaches a stable state. At the same time, within the first 10 minutes of the reaction, NH4 + -N concentration continued to rise, and then continued to decrease after reaching the highest point, and finally stabilized. This shows that in NO3 - During the reduction process, in addition to the generation of N2, NH4 + However, as the peristaltic pump drives the water to flow, NH4 + It will be oxidized to N2 near the anode. NO2 is detected during the reaction. - The concentration is very low, indicating that most of the NO3 -The product of reduction is N 2， A small part is NH4 + , NH4 + When it reaches the vicinity of the anode, it has been rapidly oxidized into N2.

[0059] The reaction principle of the present invention is: nitrate undergoes a multi-step reduction reaction on the cathode surface, Co and Cu bimetallic catalysis, rGO acts as a conductive carrier to promote electron transfer, NO3 - The specific reaction process of reduction:

[0060] (1) Initial adsorption and activation of nitrate.

[0061] NO3 - First adsorbed on the Co active site:

[0062] NO3 - +Co→Co-NO3 -

[0063] (2) Nitrate is reduced to nitrite (rate-controlling step).

[0064] Two-electron reduction occurs at the Co site:

[0065] Co-NO3 - +H2O+2e - →Co-NO2 - +2OH -

[0066] (3) Further transformation of nitrite.

[0067] Nitrite transfers to the Cu site for subsequent reduction:

[0068] Cu+NO2 - →Cu-NO2 -

[0069] Path A: Cu-NO2 - +H2O+e - →Cu-NO+2OH -

[0070] 2Cu-NO+2H2O+2e - →N2+2Cu+4OH -

[0071] Path B: Cu-NO2 - +6H2O+6e - →NH4 + +Cu+8OH -

[0072] (4) The mechanism of action of rGO.

[0073] Enhanced electron conduction: rGO+e - →rGO(e - )

[0074] Intermediate stability: rGO+NO→rGO-NO (preventing NO desorption and promoting NN coupling).

[0075] Figure 6 The reduction performance of the Co-Cu / rGO-Ti electrode prepared at different GO concentrations is more intuitively compared. Comparing the embodiment of the present invention with the comparative example, it can be seen that after adding GO, NO 3- -N removal rate is significantly improved compared to before. In addition, it can be seen that when GO is 0-2 mg / L, as the concentration of loaded GO increases, NO 3- -N removal rate is also greater. When GO continues to increase to 3 mg / L, NO 3- The -N removal rate is slightly reduced. This is because when there is no GO, the Co-Cu active sites are easy to agglomerate, the electron transfer efficiency is low, and the reaction rate is slow; when there is an excess of GO, it will cause interlayer stacking, partially block the active sites, and hinder mass transfer; at the optimal concentration (GO = 2 mg / L), rGO completely covers the Ti substrate, forming a three-dimensional conductive network, the Co-Cu nanoparticles are highly dispersed, the active sites are exposed the most, and NO 3- -N has the best reduction efficiency.

[0076] In summary, the Co-Cu / rGO-Ti electrode of the present invention achieves a synergistic improvement in catalytic activity, stability and selectivity through the doping of rGO, providing an efficient and stable electrocatalytic solution for nitrate pollution control.

[0077] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a Co-Cu / rGO-Ti electrode, characterized in that: The method comprises the following steps: step a, pre-treating the Ti mesh to obtain a pre-treated Ti mesh; Step b, dispersing GO in deionized water to obtain a GO dispersion; Step c, mixing Co salt and Cu salt in deionized water to obtain a Co-Cu mixed salt solution; Step d, immersing the pretreated Ti mesh in a GO dispersion, taking it out and drying it to obtain dried GO-Ti; Step e, immersing the dried GO-Ti in a Co-Cu mixed salt solution at a constant temperature, taking it out and drying it, and repeating this step several times to obtain an immersed and dried electrode; Step f, placing the impregnated and dried electrode in a muffle furnace for calcination, using a high-temperature calcination method to reduce GO to rGO and decompose the Co-Cu salt into metal oxide nanoparticles, ultimately obtaining a Co-Cu / rGO-Ti electrode.

2. The method for preparing a Co-Cu / rGO-Ti electrode according to claim 1, wherein: In step a, the pretreatment is specifically as follows: polishing the Ti mesh with coarse sandpaper and fine sandpaper to remove oxides on its surface, placing the polished Ti mesh in 20% sulfuric acid solution and boiling it for 2 hours to form a uniform rough surface, and then placing it in anhydrous ethanol and deionized water for ultrasonic treatment for 15 minutes each to remove stains and grease on the surface of the Ti mesh.

3. The method for preparing a Co-Cu / rGO-Ti electrode according to claim 1, wherein: In step b, the concentration of GO in the GO dispersion is 0.5-3.0 mg / L, and the dispersion is carried out by ultrasonic method for 1 h.

4. The method for preparing a Co-Cu / rGO-Ti electrode according to claim 1, wherein: In step c, the Co salt is cobalt sulfate hexahydrate, the Cu salt is anhydrous copper sulfate, and the molar concentrations of Co and Cu in the Co-Cu mixed salt solution are both 0.75 mol / L.

5. The method for preparing a Co-Cu / rGO-Ti electrode according to claim 1, wherein: In step d, the immersion time is 30 minutes, the temperature is room temperature, and the drying temperature is 110° C., and the time is 15 minutes.

6. The method for preparing a Co-Cu / rGO-Ti electrode according to claim 1, wherein: In step e, the immersion temperature is 60° C. and the time is 30 min; the drying temperature is 110° C. and the time is 15 min.

7. The method for preparing a Co-Cu / rGO-Ti electrode according to claim 1, wherein: In step e, repeat this step 3 to 5 times.

8. The method for preparing a Co-Cu / rGO-Ti electrode according to claim 1, wherein: In step f, the calcination temperature is 500° C., the calcination time is 1 h, the muffle furnace heating rate is 5° C. / min, and the product is naturally cooled to room temperature after the calcination.

9. A Co-Cu / rGO-Ti electrode, characterized in that: The Co-Cu / rGO-Ti electrode is prepared by the preparation method of any one of claims 1 to 8.

10. Use of the Co-Cu / rGO-Ti electrode according to claim 9, characterized in that: Using Co-Cu / rGO-Ti as cathode and DSA as anode, an electrolytic reaction for removing nitrate pollutants was carried out.

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