Micron flower type composite metal oxide adsorption electrode material, preparation method and application

Abstract

The invention belongs to the field of environmental protection and water resource purification, and particularly relates to a micron flower type composite metal oxide adsorption electrode material, a preparation method and application. The electrode material is mainly composed of Co3O4 / CeO2 (at) C and is of a micron petal structure, and the preparation method of the electrode material comprises the steps that PBA serves as a precursor, corresponding metal salts are added, preparation of the precursor is completed under normal-temperature stirring, and then the composite micron flower material can be obtained through a low-temperature air roasting process. The obtained material is a stacked petal-shaped micron sheet and presents multistage pores and an ultra-large specific surface area, an excellent conductive network and a stable skeleton structure are formed through staggered arrangement of petals and in-situ uniform doping of carbon, and an electrode is endowed with excellent cycle stability and long-term operation performance. The prepared material has excellent performance in the aspect of capacitive deionization applied to seawater desalination, and compared with traditional carbon-based material synthesis conditions, the universality is high, and application and popularization are more facilitated.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of environmental protection and water resource purification, and particularly relates to a micron-flower type composite metal oxide adsorption electrode material, a preparation method and application thereof. BACKGROUND

[0002] With the continuous evolution of human civilization, many technologies that once promoted social progress are gradually being eliminated, and their potential negative effects are becoming increasingly prominent. For example, problems such as acid rain, light pollution, the greenhouse effect, and water pollution have deeply affected people's basic life. Water is the source of life, and water resource protection is particularly important. However, the current water pollution situation is severe, and freshwater resources are also becoming increasingly scarce. How to effectively reduce pollution and promote wastewater treatment and recycling has become an inevitable trend. The widely used water purification technologies currently include reverse osmosis (RO), multi-stage flash distillation (MSF), and electrodialysis (ED). Although these technologies are relatively mature, there are still disadvantages such as high energy consumption, complex operation, and potential secondary pollution. Under this background, it is particularly crucial to develop more efficient, low-energy, and environmentally friendly innovative desalination and water purification technologies.

[0003] Capacitive deionization (CDI) is considered as a promising solution for future freshwater production due to its low energy consumption and no secondary pollution. In the CDI system, cations and anions in salt water migrate and are adsorbed on the cathode and anode under the action of an external electric field, thereby realizing water desalination. The electrode material plays a decisive role in the entire process. Current researches mainly focus on carbon-based electrode materials (such as biomass carbon, graphene, carbon nanotubes, etc.). Such materials have excellent electrical conductivity and high specific surface area, and can realize fast and efficient ion adsorption at low energy consumption. However, there are still two inherent problems in practical application: (1) the preparation process is complex and costly, usually involving high-temperature pyrolysis, chemical vapor deposition (CVD), and soft and hard template processes; (2) the cost and performance are not matched. Since the salt storage mechanism of carbon-based materials mainly depends on the double-layer capacitance, the salt adsorption capacity is relatively limited (usually less than 30 mg / g), which is difficult to form an effective value return with the cost of material preparation.

[0004] Therefore, how to develop adsorption electrode materials with high activity and easy synthesis has become a key problem for promoting CDI technology. SUMMARY

[0005] Based on the deficiencies of the prior art, the present application provides a micron flower type composite metal oxide adsorption electrode material, a preparation method and application, through the chemical precipitation method of mixing cobalt and cerium metal salts at room temperature, a Prussian blue precursor (Co-Ce-PBA) is synthesized, and Co3O4 / CeO2@C petal-shaped microparticles are obtained by low-temperature air calcination, which exhibit multi-level pores and super large specific surface area. These characteristics in morphology greatly improve the ion migration and adsorption kinetics process in the capacitive deionization technology. The staggered arrangement of the petals and the in-situ uniform doping of carbon form an excellent conductive network and stable skeleton structure, which endows the electrode with excellent conductivity and long-term running performance.

[0006] To achieve the above object, the present application provides the following technical scheme: The present application provides a micron flower type composite metal oxide adsorption electrode material, the active material is petal-shaped microparticles, the petals are uniform, and the length is about 8 microns; the material exhibits multi-level pores and super large specific surface area and ultrathin sheet structure; the material exhibits multi-level pores and super large specific surface area and ultrathin sheet structure; and the element ratio of cobalt (Co) to cerium (Ce) in the active material Co3O4 / CeO2@C nanoflower is close to 1:1.5~2, and is uniformly and densely distributed in the whole structure. The carbon phase forms a stable composite structure with the metal oxide by in-situ doping, and the three synergistically optimize the electrochemical performance of the material.

[0007] The present application designs and prepares a Co3O4 / CeO2@C petal-shaped microparticle heterostructure, the staggered petals provide sufficient channels for ion migration, the multi-level pores and super large specific surface area significantly increase the adsorption active sites, and the ultrathin sheet morphology effectively shortens the ion diffusion distance, directly improving the adsorption kinetics efficiency from the structural level; at the same time, the element molar ratio of cobalt (Co) to cerium (Ce) is 1:1.5~2, which ensures the uniform and dense distribution of the double metal elements in the material, and lays a structural foundation for the synergistic effect.

[0008] In addition, by utilizing the high electrochemical activity of Co3O4 and the stable structure characteristics of CeO2, the double metal synergistic effect is realized by precise molar ratio control, the electron / ion transmission rate is accelerated; by means of in-situ carbon doping in the pyrolysis process of the Prussian blue precursor, a stable conductive network and skeleton structure are formed, which not only improves the conductivity of the material, but also guarantees the long-term running stability of the electrode, solving the problem that the conductivity and stability of traditional materials are difficult to be considered.

[0009] The present application provides a preparation method of a micron flower type composite metal oxide adsorption electrode material, and the specific steps are as follows: S1. Preparation of Co-Ce-PBA precursor: 1-3 mmol of cerium nitrate hexahydrate (Ce(NO3)3·6H2O) is dispersed in a mixed solvent of 100-150 mL of ethanol and 45-65 mL of deionized water to obtain a uniformly dispersed solution A; under stirring conditions, 5-7.5 mL of 0.2 mol / L potassium hexacyanocobaltate aqueous solution (K3Co(CN)6) is added dropwise to solution A, and after continuous stirring for 10-15 minutes, it is left to stand at room temperature for 12-15 hours to form a precipitate product; S2. Preparation of composite metal oxide by low-temperature calcination: the precipitate product obtained in step S1 is centrifuged and washed with ethanol several times, and then dried in an oven at 70-80℃ overnight; the dried product is heated to 350-400℃ at a heating rate of 3-5℃ / min, and calcined at this temperature for 6-8 hours, and then cooled to obtain a Co3O4 / CeO2@C material, which is a micron flower-shaped composite metal oxide adsorption electrode material; S3. Preparation of adsorption electrode: the Co3O4 / CeO2@C material in step S2 is ground into a fine powder, and the Co3O4 / CeO2@C material, Ketjen black and adhesive PVDF are mixed in a weight ratio of 20:1:1, N-methyl pyrrolidone (NMP) is used as the solvent, and the mixture is stirred uniformly to form an electrode slurry; the slurry is coated on the surface of the current collector titanium sheet, and after drying in an oven, a positive electrode for capacitive deionization is obtained.

[0010] The application also provides an application of the micron flower-shaped composite metal oxide adsorption electrode material, specifically, the negative electrode and the carbon material-based positive electrode are assembled to form an asymmetric capacitive deionization (CDI) device, which can be used for adsorption and removal of heavy metal ions in water, and realizes water resource purification.

[0011] Advantages of the application (1) Structural innovation enables efficient adsorption: the prepared Co3O4 / CeO2@C material has a petal-shaped micron sheet structure, with 8 μm uniform petals arranged in an alternating manner, and in combination with multi-level pores, a large specific surface area and an ultrathin sheet morphology, which not only provides sufficient ion migration channels, but also significantly increases the adsorption active sites, shortens the ion diffusion distance, and greatly improves the adsorption kinetic efficiency.

[0012] (2) Element synergy optimizes electrochemical performance: the molar ratio of Co to Ce is precisely controlled to be 1:1.5-2, so that the two metal elements are uniformly and densely distributed, and in combination with the high electrochemical activity of Co3O4 and the structural stability of CeO2, the synergistic effect is achieved to accelerate the electron / ion transmission rate; in-situ carbon doping forms a stable conductive network and skeleton structure, which takes into account the high conductivity and long-term running stability of the material, and the specific capacitance retention rate reaches 91.12% after 1000 electrochemical cycles.

[0013] (3) Excellent and stable desalination performance: The asymmetric CDI device constructed has outstanding desalination performance. After 300 cycles of adsorption-desorption at 500 mg / L NaCl solution and 1.2 V voltage, the performance retention rate is 96.8%, and the adsorption-desorption reversibility is good. The salt solution concentration adaptation range is wide, and the unit desalination amount increases steadily with the increase of concentration.

[0014] (4) Green and economical preparation process: The precursor is synthesized by room temperature chemical precipitation, and the target material can be obtained by air calcination at low temperature (350-400℃). No complex process such as high-temperature pyrolysis and CVD is needed, the process is simple and the energy consumption is low. The raw materials are easy to obtain and the cost is controllable. The problem of complex preparation, cost and performance mismatch of traditional carbon-based electrode materials is solved, and the material is easy to scale up.

[0015] (5) Wide application prospect: The material and device are suitable for adsorption and removal of metal ions in water and water resource purification, which meets the needs of environmental protection and water resource recycling, and provides an efficient and low-cost electrode material solution for the industrialization of capacitive deionization technology. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 SEM image of the Co3O4 / CeO2@C material obtained in Example 1; Figure 2 EDS image of the Co3O4 / CeO2@C material obtained in Example 1; Figure 3 XRD image of the Co3O4 / CeO2@C material obtained in Example 1; Figure 4 Electrochemical cycle test image of the Co3O4 / CeO2@C material obtained in Example 1; Figure 5 Reversible adsorption-desorption image of the Co3O4 / CeO2@C material obtained in Example 1 at different voltages; Figure 6 Desalination capacity image of the Co3O4 / CeO2@C material obtained in Example 1 at different concentrations; Figure 7 Cycle desalination capacity image of the Co3O4 / CeO2@C material obtained in Example 1; Figure 8 Retention rate of the material after cycle application in Example 1, Examples 4-6 and Comparative Examples 1-2. DETAILED DESCRIPTION

[0017] In order to make the above objectives, characteristics and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application will be described in detail below in combination with examples. The following content is only an example and description of the concept of the present application. Those skilled in the art can make various modifications or supplements to the described specific implementation cases or use similar ways instead, as long as they do not deviate from the concept of the present application, which shall belong to the protection scope of the present application.

[0018] The above preparation method of the present application will be described below through specific examples and comparative examples.

[0019] Example 1 A preparation method of a micron-flower type composite metal oxide adsorption electrode material, the specific steps are as follows: S1. Preparation of Co-Ce-PBA precursor: 2 mmol of cerium nitrate hexahydrate (Ce(NO3)3·6H2O) is dispersed in a mixed solvent of 100 mL of ethanol and 45 mL of deionized water to obtain a uniformly dispersed solution A; under stirring conditions, 5 mL of 0.2 mol / L potassium hexacyanocobaltate aqueous solution (K3Co(CN)6) is added dropwise into solution A, and after continuous stirring for 10 minutes, it is left to stand at room temperature for 12 hours to form a precipitate product; S2. Preparation of composite metal oxide by low-temperature calcination: the precipitate product obtained in step S1 is centrifuged and washed with ethanol for several times, and then dried in an oven at 70°C overnight; the dried product is heated to 350°C at a heating rate of 3°C / min, and calcined at this temperature for 6 hours, and then cooled to obtain Co3O4 / CeO2@C material, which is a micron-flower type composite metal oxide adsorption electrode material; S3. Preparation of adsorption electrode: the above Co3O4 / CeO2@C material is ground into fine powder, and Co3O4 / CeO2@C, Ketjen black and adhesive PVDF are mixed in a weight ratio of 20:1:1, N-methyl pyrrolidone (NMP) is used as solvent, and the mixture is stirred uniformly to form electrode slurry; the slurry is coated on the surface of the current collector titanium sheet, and after drying in an oven, a positive electrode for capacitive deionization is obtained.

[0020] Example 2 A preparation method of a micron-flower type composite metal oxide adsorption electrode material, the specific steps are as follows: S1. Preparation of Co-Ce-PBA precursor: 2.5 mmol of cerium nitrate hexahydrate (Ce(NO3)3·6H2O) was dispersed in a mixed solvent of 120 mL of ethanol and 50 mL of deionized water to obtain a uniformly dispersed solution A; under stirring conditions, 6 mL of 0.2 mol / L potassium hexacyanocobaltate aqueous solution (K3Co(CN)6) was added dropwise into solution A, and after continuous stirring for 12 minutes, it was left to stand at room temperature for 13 hours to form a precipitate product; S2. Preparation of composite metal oxide by low-temperature calcination: the precipitate product obtained in step S1 was centrifuged and washed with ethanol for multiple times, and then dried in an oven at 75℃ overnight; the dried product was heated to 370℃ at a heating rate of 4℃ / min, and then calcined at this temperature for 7 hours, and after cooling, a Co3O4 / CeO2@C material was obtained, which was a micron flower type composite metal oxide adsorption electrode material; S3. Preparation of adsorption electrode: the above Co3O4 / CeO2@C material was ground into fine powder, and Co3O4 / CeO2@C, Ketjen black and adhesive PVDF were mixed in a weight ratio of 20:1:1, N-methyl pyrrolidone (NMP) was used as the solvent, and the mixture was stirred uniformly to form an electrode slurry; the slurry was coated on the surface of the current collector titanium sheet, and after drying in an oven, a positive electrode for capacitive deionization was obtained.

[0021] Example 3 The application provides a preparation method of a micron flower type composite metal oxide adsorption electrode material, and the specific steps are as follows: S1. Preparation of Co-Ce-PBA precursor: 2.5 mmol of cerium nitrate hexahydrate (Ce(NO3)3·6H2O) was dispersed in a mixed solvent of 120 mL of ethanol and 50 mL of deionized water to obtain a uniformly dispersed solution A; under stirring conditions, 6 mL of 0.2 mol / L potassium hexacyanocobaltate aqueous solution (K3Co(CN)6) was added dropwise into solution A, and after continuous stirring for 12 minutes, it was left to stand at room temperature for 13 hours to form a precipitate product; S2. Preparation of composite metal oxide by low-temperature calcination: the precipitate product obtained in step S1 was centrifuged and washed with ethanol for multiple times, and then dried in an oven at 75℃ overnight; the dried product was heated to 370℃ at a heating rate of 4℃ / min, and then calcined at this temperature for 7 hours, and after cooling, a Co3O4 / CeO2@C material was obtained, which was a micron flower type composite metal oxide adsorption electrode material; S3. Preparation of adsorption electrode: The above Co3O4 / CeO2@C material is ground into fine powder, and Co3O4 / CeO2@C, Ketjen black and adhesive PVDF are mixed in a weight ratio of 20:1:1. N-methyl pyrrolidone (NMP) is used as the solvent, and the mixture is stirred uniformly to form an electrode slurry. The slurry is coated on the surface of the current collector titanium sheet, and after drying in an oven, a positive electrode for capacitive deionization is obtained.

[0022] Example 4 The amount of added cerium nitrate hexahydrate (Ce(NO3)3·6H2O) is changed to 1.0 mmol, and the steps and other parameters are the same as in Example 1.

[0023] Example 5 The amount of added cerium nitrate hexahydrate (Ce(NO3)3·6H2O) is changed to 1.5 mmol, and the steps and other parameters are the same as in Example 1.

[0024] Example 6 The amount of added cerium nitrate hexahydrate (Ce(NO3)3·6H2O) is changed to 2.5 mmol, and the steps and other parameters are the same as in Example 1.

[0025] Comparative Example 1 Single Co-based oxide electrode material (Co3O4@C) S1, prepare a 5 mL potassium hexacyanocobaltate aqueous solution (K3Co(CN)6) with a concentration of 0.2 mol / L, and obtain a precursor powder sample after drying.

[0026] The steps and other parameters are the same as in Example 1.

[0027] Comparative Example 2: Single Ce-based oxide electrode material (CeO2@C) S1, disperse 2 mmol of cerium nitrate hexahydrate (Ce(NO3)3·6H2O) in a mixed solvent of 100 mL of ethanol and 45 mL of deionized water, and obtain a precursor powder sample after drying.

[0028] The steps and other parameters are the same as in Example 1.

[0029] Application and testing 1. Electrochemical performance test of Co3O4 / CeO2@C electrode A CHI 660E electrochemical workstation is used to test the charge and discharge cycles of the electrode material (reference electrode silver / silver chloride, counter electrode platinum mesh, and working electrode active material composite electrode) in a three-electrode system, with a current density of 1 A / g, a voltage window of -0.6 V to 0.6 V, and an electrolyte of 1.0 mol / L sodium chloride solution.

[0030] 2. Electrochemical desalination test of Co3O4 / CeO2@C electrode The charging and discharging cycle test of the electrode material (the reference electrode is silver / silver chloride, the counter electrode is a platinum mesh, and the working electrode is the active material composite electrode) was carried out by using a CHI 660E electrochemical workstation under a three-electrode system, the current density was 1 A / g, the voltage window was -0.6 V to 0.6 V, and the electrolyte was a 1.0 mol / L sodium chloride solution.

[0031] Figure 1 The SEM image of the Co3O4 / CeO2@C material obtained in Example 1; the active material is petal-shaped microparticle, the petals are uniform, and the length is about 8 μm; the material has a multi-level pore and has a super large specific surface area and a super thin sheet structure; the material has a multi-level pore and has a super large specific surface area and a super thin sheet structure.

[0032] Figure 2 The EDS image of the Co3O4 / CeO2@C material obtained in Example 1; from the energy spectrum, it can be analyzed that the elements of cobalt (Co) and cerium (Ce) are uniformly and densely distributed in the whole structure.

[0033] Figure 3 The XRD image of the Co3O4 / CeO2@C material obtained in Example 1; as shown in the figure, the characteristic diffraction peaks appearing in the spectrum can be one-to-one corresponding to the standard cards of Co3O4 and CeO2, and all the characteristic peaks are sharp and clear, indicating that the material has good crystallinity. In addition, there are no diffraction peaks of cobalt, cerium and other impurity phases in the spectrum, which proves that the pure phase composite structure of Co3O4 and CeO2 is successfully synthesized by the preparation method of the application; at the same time, no obvious carbon phase diffraction peak is observed, it is speculated that the in-situ doped carbon is uniformly dispersed in the metal oxide matrix in amorphous form, and forms a stable composite structure with the metal oxide, which is consistent with the description of the application content that "the carbon phase forms a stable composite structure with the metal oxide through in-situ doping".

[0034] Figure 4 The cyclic charge-discharge curve (GCD) and the cyclic voltammetry test curve in the above table 1 show that after 1000 cycles of GCD test, the triangular curve characteristics do not change obviously, and the specific capacitance retention rate reaches 91.12%, which powerfully proves the excellent stability of the electrode in the electrochemical experiment.

[0035] 2. Electrochemical desalination test of Co3O4 / CeO2@C electrode In order to detect the adsorption effect of the application on ions in the salt solution, the Co3O4 / CeO2@C electrode of Example 1 and activated carbon were used to construct an asymmetric capacitive deionization adsorption device, desalination experiments were carried out under different conditions, and corresponding performance detection was carried out. Figure 5 Data of Co3O4 / CeO2@C electrode prepared in Example 1 for treating 500 mg / L NaCl salt solution at different voltages. The results show that adsorption and desorption can occur reversibly, demonstrating the regeneration ability of the material, and the conductivity decrease amplitude and desalination capacity gradually increase with the increase of voltage.

[0036] Figure 6 Data of Co3O4 / CeO2@C electrode prepared in Example 1 for treating different concentrations of salt solution at a voltage of 1.2 V, and the results show that the unit desalination amount also increases with the increase of the concentration of the salt solution.

[0037] Figure 7 Data of Co3O4 / CeO2@C electrode prepared in Example 1 for cyclic adsorption-desorption experiment at a voltage of 1.2 V and 500 mg / L NaCl salt solution, and it can be seen from the figure that after 300 cycles of test data, the adsorption and desorption performance of the electrode is 96.8% of the first cycle, which is sufficient to show that the material has stable performance and can be used in long-term desalination equipment.

[0038] Figure 8 Cyclic retention rates of electrode materials after application in Example 1, Examples 4-6 and Comparative Examples 1-2, and it can be seen from the figure that Ce and Co have a synergistic effect, and the performance when they coexist is significantly higher than that when a single element exists, and in addition, the performance is best when the molar ratio of Co to Ce is 1:1.5-2.

[0039] From the above electrochemical test and electric adsorption performance test results, it can be seen that the electrode active material involved in the present application not only has high electric adsorption capacity for metal ions in the salt solution, but also performs well in long-term cyclic tests, and the desalination equipment is simple to make, the material synthesis is green and friendly, the process cost is low, and has broad development prospects.

Claims

1. A method for preparing a micron-sized flower-shaped composite metal oxide adsorption electrode material, characterized in that, The method comprises the following steps: S1. Preparing Co-Ce-PBA precursor: dispersing 1-3 mmol Ce(NO3)3·6H2O in a mixed solvent of 100-150 mL of ethanol and 45-65 mL of deionized water to obtain solution A; under stirring, 5-7.5 mL of K3Co(CN)6 with a concentration of 0.2 mol / L is added dropwise into solution A, stirring, and standing at room temperature to form a precipitate product; S2. Preparing composite metal oxide by low-temperature calcination: the precipitate product obtained in step S1 is centrifuged and washed with ethanol for multiple times, and then dried in an oven at 70-80℃ overnight; the dried product is heated to 350-400℃, and calcined at constant temperature for 6-8 hours, and then cooled to obtain Co3O4 / CeO2@C material, which is a micron-flower type composite metal oxide adsorption electrode material; S3. Preparing adsorption electrode: the Co3O4 / CeO2@C material in step S2 is ground into fine powder, and the Co3O4 / CeO2@C material, Ketjen black and adhesive PVDF are mixed to form electrode slurry by stirring uniformly with NMP as solvent; the slurry is coated on the surface of the current collector titanium sheet, and then dried to obtain a negative electrode for capacitive deionization.

2. The production method according to claim 1, characterized by, The stirring time in step S1 is 10-15 minutes, and the standing time at room temperature is 12-15 hours.

3. The production method according to claim 1, characterized by, The heating rate in step S2 is 3-5℃ / min.

4. The method of claim 1, wherein, The mass ratio of the Co3O4 / CeO2@C material, Ketjen black and adhesive PVDF in step S3 is 20:1:

1.

5. A microflower type composite metal oxide adsorbing electrode material, characterized in that, The material is prepared by the method in any one of claims 1-4.

6. The use of the microflower composite metal oxide adsorbent electrode material of claim 5, characterized in that, The positive electrode prepared from the material and the carbon material-based negative electrode are assembled to form an asymmetric capacitive deionization device, which is used for adsorption and removal of metal ions in water and water resource purification.

7. Use according to claim 6, characterized in that, The asymmetric capacitive deionization device has a performance retention rate of ≥96.8% after 300 cycles of adsorption-desorption under the condition of 500 mg / L NaCl solution and 1.2 V voltage.

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