An in-situ metal-doped flower-shaped carbon microsphere material, its preparation method and application

Abstract

This invention provides an in-situ metal-doped flower-shaped carbon microsphere material, its preparation method, and its application, relating to the field of seawater desalination. The preparation method includes the following steps: acrylonitrile is added dropwise to an ethanol-ethyl acetate solution, followed by the addition of a metal salt and azobisisobutyronitrile (AIBN), wherein the metal salt is nickel acetylacetonate or cobalt acetylacetonate, and the mixture is reacted; the mixture is filtered and dried to obtain metal-doped polymer seed microspheres; the metal-doped polymer seed microspheres are mixed with divinylbenzene and added to anhydrous ethanol, followed by the addition of AIBN; the mixture is reacted; the mixture is filtered and dried to obtain a metal-doped carbon microsphere precursor; the precursor is placed in a tube furnace for carbonization treatment to obtain metal-doped flower-shaped carbon microspheres. The material of this invention has a controllable structure and excellent performance, achieving good salt adsorption effects and enabling efficient, stable, and deep desalination of seawater, which is of great significance for alleviating freshwater resource shortages.

Description

Technical Field

[0001] This invention relates to the field of seawater desalination, and in particular to an in-situ metal-doped flower-shaped carbon microsphere material, its preparation method, and its application. Background Technology

[0002] With the global freshwater shortage becoming increasingly severe, traditional seawater desalination technologies such as reverse osmosis and distillation have limitations such as high energy consumption, large equipment investment, and susceptibility to membrane fouling and secondary pollution, making it difficult to meet the application requirements of low-cost, green, efficient, and large-scale water treatment. Capacitive deionization (CDI) technology, with its advantages of low energy consumption, environmental friendliness, ease of operation, and no secondary pollution, has shown broad application prospects in seawater desalination and other fields, and has become a research hotspot in the field of water resource management.

[0003] Electrode materials are the core factor determining the desalination performance, cycle stability, and lifespan of capacitive deionization devices. Currently, commercially available carbon-based electrode materials such as carbon nanotubes, while possessing certain conductivity and specific surface area, still suffer from problems such as limited ion transport channels, non-uniform pore structure, limited specific capacitance, poor hydrophilicity, and insufficient structural stability. These issues result in low actual desalination capacity, failing to meet the engineering requirements for efficient and deep desalination of high-salinity seawater.

[0004] Therefore, developing a metal-doped carbon microsphere material with controllable structure and excellent performance is of great significance for seawater desalination. Existing methods for preparing metal-doped carbon microspheres mostly employ post-doping or multi-step processes, which typically suffer from complex steps, uneven metal dispersion, and difficulty in precisely controlling morphology. Furthermore, the regulatory mechanisms of different metal elements in the nucleation and growth processes of carbon microspheres have not been effectively utilized, making it difficult to achieve controllable construction of carbon microsphere particle size and morphology through simple methods, which is detrimental to the large-scale preparation and stable application of the material. In addition, different metal elements exhibit significantly different regulatory effects on the morphology, particle size, and structural evolution of carbon microspheres during formation, but the underlying mechanisms remain unclear. Summary of the Invention

[0005] In view of this, the present invention proposes an in-situ metal-doped flower-shaped carbon microsphere material, its preparation method and application.

[0006] The technical solution of this invention is implemented as follows: A method for preparing in-situ metal-doped flower-shaped carbon microspheres includes the following steps: (1) Preparation of metal-doped polymer seed microspheres: Using AN (acrylonitrile) as the main comonomer, nickel acetylacetonate or cobalt acetylacetonate was selected as the dopant component. The above raw materials were added to a mixed solvent of anhydrous ethanol and ethyl acetate, and then AIBN (azobisisobutyronitrile) was added as a free radical initiator. Specific operation: Acrylonitrile was added dropwise to the ethanol-ethyl acetate solution, and a metal salt and azobisisobutyronitrile were added. The metal salt was nickel acetylacetonate or cobalt acetylacetonate. After mixing, the mixture was reacted at 60-80℃ for 3-5 h. After the reaction was completed, the product was filtered, and the solid was dried to obtain metal-doped polymer seed microspheres. (2) Preparation of metal-doped carbon microsphere precursor: The metal-doped polymer seed microspheres were mixed with divinylbenzene and then added to anhydrous ethanol. Azobisisobutyronitrile was then added as a free radical initiator. After the system was thoroughly mixed, it was reacted at 60-80℃ for 3-5 h. After the reaction was completed, the product was filtered and the obtained solid was dried to obtain the metal-doped carbon microsphere precursor. (3) Preparation of metal-doped carbon microspheres: The metal-doped carbon microsphere precursor is placed in a tube furnace for carbonization treatment; the carbonization treatment is carried out in an inert atmosphere, the carbonization temperature is 900-1100℃, the holding time is 1.5-3 hours, and metal-doped flower-shaped carbon microspheres are obtained after carbonization.

[0007] Further, in step (1), the mass ratio of acrylonitrile, metal salt, and azobisisobutyronitrile is (7-9):(0.15-0.25):(0.25-0.35); the mass-to-volume ratio of acrylonitrile to ethanol-ethyl acetate solution (g / ml) is (7-9):40-60; and the volume ratio of ethanol to ethyl acetate in the ethanol-ethyl acetate solution is 0.9-1.1:0.9-1.1.

[0008] Furthermore, in steps (1) and (2), the drying temperature is 50-55℃ and the drying time is 10-16h.

[0009] Further, in step (2), the mass ratio of the metal-doped polymer seed microspheres, divinylbenzene, and azobisisobutyronitrile is 2:(1.2-1.8):(0.4-0.6); the mass-volume ratio of the metal-doped polymer seed microspheres to anhydrous ethanol is 2:90-110.

[0010] Furthermore, in step (3), the carbonization process is heated at a rate of 1-6℃ / h.

[0011] The present invention relates to the application of in-situ metal-doped flower-shaped carbon microspheres in seawater desalination.

[0012] Furthermore, the in-situ metal-doped flower-shaped carbon microsphere material is used in a capacitive deionization seawater desalination device, where it serves as the positive electrode active material.

[0013] Compared with the prior art, the beneficial effects of the present invention are: (1) The present invention prepares flower-shaped in-situ metal-doped polymer seed microspheres from acrylonitrile and metal salts, which are then coated with nickel-doped or cobalt-doped flower-shaped carbon microspheres obtained by carbonization. The present invention develops a preparation method that can achieve in-situ metal doping during the synthesis process and controllably regulate the morphology of the microspheres. The material achieves good salt adsorption effect and can be well used for seawater desalination, thus having important research significance and application value.

[0014] (2) The metal-doped carbon microsphere material of the present invention is used in capacitive deionization technology to achieve efficient, stable and deep desalination of seawater, which has important theoretical value and engineering significance for alleviating the shortage of freshwater resources. Attached Figure Description

[0015] Figure 1 Scanning electron microscope (SEM) images of the nickel-doped polymer seed microspheres NiPAN, the nickel-doped carbon microsphere precursor NiPAN@DVB, and the nickel-doped carbon microspheres NiCF obtained after carbonization prepared in this invention. Figure 1 In the image, 'a' represents the SEM image of the prepared nickel-doped polymer seed microspheres NiPAN. Figure 1 In the image, b is a SEM image of the nickel-doped carbon microsphere precursor NiPAN@DVB; Figure 1 In the image, c represents the SEM image of the nickel-doped carbon microspheres NiCF obtained after carbonization.

[0016] Figure 2 Scanning electron microscopy (SEM) images of the cobalt-doped polymer seed microspheres CoPAN, the cobalt-doped carbon microsphere precursor CoPAN@DVB, and the cobalt-doped carbon microspheres CoCF obtained after carbonization, prepared according to this invention. Figure 2 In the image, 'a' represents the SEM image of the cobalt-doped polymer seed microspheres CoPAN. Figure 2 In the image, b represents the SEM image of the cobalt-doped carbon microsphere precursor CoPAN@DVB. Figure 2 In the image, c represents the SEM image of cobalt-doped carbon microspheres (CoCF) obtained after carbonization.

[0017] Figure 3 This is a TEM image of the NiCF prepared according to the present invention.

[0018] Figure 4 Here is a TEM image of the CoCF prepared according to the present invention, wherein, Figure 4 In the image, 'a' represents the TEM image of CoCF. Figure 4b in the image is a TEM image of the CoCF region.

[0019] Figure 5 The N2 adsorption-desorption isotherms and pore size distributions of NiCF and CoCF prepared in this invention are shown below. Figure 5 In the figure, 'a' represents the N2 adsorption-desorption isotherm of NiCF and CoCF; Figure 5 In the figure, b represents the specific surface area and pore size distribution of NiCF and CoCF.

[0020] Figure 6 The SAC curve of NiCF prepared according to this invention.

[0021] Figure 7 The SAC curve of CoCF prepared according to the present invention. Detailed Implementation

[0022] Unless otherwise specified, the experimental methods used in the embodiments of this invention are conventional methods; Unless otherwise specified, all materials and reagents used in the embodiments of this invention are commercially available.

[0023] The Chinese meanings of some abbreviations or English terms in this invention are as follows: AN: Acrylonitrile; AIBN: Azobisisobutyronitrile; DVB: Divinylbenzene; PVDF: Polyvinylidene fluoride; NMP: N-methylpyrrolidone.

[0024] Example 1 (1) Preparation of metal-doped polymer seed microspheres Raw materials: Acrylonitrile (AN), nickel acetylacetonate (Ni(acac)2), anhydrous ethanol, ethyl acetate, azobisisobutyronitrile (AIBN).

[0025] Preparation: 8 g of AN was added dropwise to 50 ml of ethanol-ethyl acetate solution (volume ratio 1:1), followed by the addition of 0.2 g of Ni(acac)2 and 0.3 g of AIBN. After thorough mixing, the mixture was reacted at 70-80 °C for 3 h. After the reaction was completed, the product was filtered, and the resulting solid was dried in an oven at 50 °C for 12 h to obtain nickel-doped polymer seed microspheres, denoted as NiPAN.

[0026] (2) Preparation of metal-doped carbon microsphere precursors Raw materials: NiPAN, DVB (divinylbenzene), anhydrous ethanol, AIBN.

[0027] Preparation: 2 g of the prepared nickel-doped polymer seed microspheres (NiPAN) were thoroughly mixed with 1.5 g of DVB and then added to 100 g of anhydrous ethanol. Subsequently, 0.5 g of AIBN was added as a free radical initiator. After thorough mixing, the mixture was reacted at 70-80 °C for 4 h. After the reaction, the product was filtered, and the resulting solid was dried in a 50 °C oven for 12 h to obtain the nickel-doped carbon microsphere precursor, denoted as NiPAN@DVB.

[0028] (3) Preparation of metal-doped carbon microspheres Raw material: Nickel-doped carbon microsphere precursor (NiPAN@DVB).

[0029] Preparation: The metal-doped carbon microsphere precursors prepared above were placed in a tube furnace for carbonization. The carbonization was carried out in an argon atmosphere at a carbonization temperature of 1000℃, a heating rate of 5℃ / h, and a holding time of 2 hours. Nickel-doped flower-like carbon microspheres were obtained after carbonization, denoted as NiCF.

[0030] (4) Assembly of the capacitive deionization (CDI) test device ① Preparation of electrode sheets Raw materials: polyvinylidene fluoride (PVDF), N-methylpyrrolidone (NMP), carbon black (acetylene black), nickel-doped flower-shaped carbon microspheres (NiCF), activated carbon.

[0031] Weigh out 0.04 g of active material (NiCF) or activated carbon, 0.005 g of carbon black, and 0.005 g of PVDF in a mass ratio of 8:1:1, and grind the three powders evenly in a mortar. Then, slowly add NMP dropwise, stir to form a paste, and then coat it evenly onto a current collector titanium plate using a coating applicator. Dry the titanium plate at 60°C for 12 h. The active material forms the positive electrode, and the activated carbon forms the negative electrode.

[0032] ② Assembly of CDI testing equipment Raw materials: Titanium plates with active materials and activated carbon, CDI current collector, anion and cation exchange membranes, storage bottle, circulating peristaltic pump, DC power supply, conductivity meter, magnetic stirrer Titanium plates containing active material and activated carbon were used as positive and negative electrodes, respectively, and assembled with anion and cation exchange membranes and a CDI current collector to form a CDI seawater desalination device. A circulating peristaltic pump, the CDI seawater desalination device, and a storage bottle were connected together via plastic water pipes. 50 ml of 500 ppm NaCl was used as the seawater desalination stock solution. The conductivity of the solution was tested using a conductivity meter. A DC current of 1.2~1.8V was applied to the CDI seawater desalination device using a DC power supply. The solution was stirred with a magnetic stirrer throughout the test to ensure uniform mixing of the inlet and outlet solutions.

[0033] Example 2 (1) Preparation of metal-doped polymer seed microspheres Raw materials: Acrylonitrile (AN), cobalt acetylacetonate (Co(acac)2), anhydrous ethanol, ethyl acetate, azobisisobutyronitrile (AIBN).

[0034] Preparation: 8 g of AN was added dropwise to 50 ml of ethanol-ethyl acetate solution (volume ratio 1:1), followed by the addition of 0.2 g of Co(acac)₂ and 0.3 g of AIBN. After thorough mixing, the mixture was reacted at 70-80 °C for 3 h. After the reaction was completed, the product was filtered, and the resulting solid was dried in an oven at 50 °C for 12 h to obtain cobalt-doped polymer seed microspheres, denoted as CoPAN.

[0035] (2) Preparation of metal-doped carbon microsphere precursors Raw materials: CoPAN, DVB, anhydrous ethanol, AIBN.

[0036] Preparation: 2 g of the cobalt-doped polymer seed microspheres (CoPAN) prepared above were thoroughly mixed with 1.5 g of DVB and then added to 100 g of anhydrous ethanol. Subsequently, 0.5 g of AIBN was added as a free radical initiator. After thorough mixing, the mixture was reacted at 70-80 °C for 4 h. After the reaction was complete, the product was filtered, and the resulting solid was dried in a 50 °C oven for 12 h to obtain the cobalt-doped carbon microsphere precursor, denoted as CoPAN@DVB.

[0037] (3) Preparation of metal-doped carbon microspheres Raw material: Cobalt-doped carbon microsphere precursor.

[0038] Preparation: The metal-doped carbon microsphere precursors prepared above were placed in a tube furnace for carbonization. The carbonization was carried out in an argon atmosphere at a carbonization temperature of 1000℃, a heating rate of 5℃ / h, and a holding time of 2 hours. Cobalt-doped flower-shaped carbon microspheres, denoted as CoCF, were obtained after carbonization.

[0039] (4) Assembly of the capacitive deionization (CDI) test device ① Preparation of electrode sheets Raw materials: polyvinylidene fluoride (PVDF), N-methylpyrrolidone (NMP), carbon black (acetylene black), cobalt-doped flower-shaped carbon microspheres (CoCF), activated carbon.

[0040] Weigh out 0.04 g of active material (CoCF) or activated carbon, 0.005 g of carbon black, and 0.005 g of PVDF in a mass ratio of 8:1:1, and grind the three powders evenly in a mortar. Then, slowly add NMP dropwise, stir to form a paste, and then coat it evenly onto a current collector titanium plate using a coating tool. Dry the titanium plate at 60°C for 12 h. The active material is used as the positive electrode, and the activated carbon is used as the negative electrode.

[0041] ② Assembly of CDI testing equipment Raw materials: Titanium plate with active materials and activated carbon, CDI current collector, anion and cation membrane, storage bottle, circulating peristaltic pump, DC power supply, conductivity meter, magnetic stirrer.

[0042] Titanium plates containing active materials and activated carbon were used as positive and negative electrodes, respectively, and assembled with anion and cation exchange membranes and a CDI current collector to form a CDI seawater desalination device. The circulating peristaltic pump, the CDI seawater desalination device, and the storage bottle were connected together through plastic water pipes. 50 ml of 500 ppm NaCl was used as the seawater desalination stock solution. The conductivity of the solution was tested using a conductivity meter. A DC current of 1.2~1.8V was applied to the CDI seawater desalination device using a DC power supply. The solution was stirred with a magnetic stirrer throughout the test to ensure that the solution at the inlet and outlet was mixed evenly.

[0043] The microstructures of the nickel-doped polymer seed microspheres NiPAN, the nickel-doped carbon microsphere precursor NiPAN@DVB, and the nickel-doped carbon microspheres NiCF obtained after carbonization prepared in Example 1 are shown in the scanning electron microscope. Figure 1 As shown, the seed microspheres have a distinctly thick petal structure. After being coated with DVB, the petals become even thicker, and the petal structure is well preserved after carbonization.

[0044] The microstructures of the cobalt-doped polymer seed microspheres CoPAN, the cobalt-doped carbon microsphere precursor CoPAN@DVB, and the cobalt-doped carbon microspheres CoCF obtained after carbonization, as shown in Example 2, are as follows: Figure 2 As shown, the seed microspheres have a petal structure. After being coated with DVB, the petals become significantly thicker, and the petal structure is well preserved after carbonization.

[0045] TEM image of NiCF prepared in Example 1 is shown below. Figure 3 As shown, several scattered dark dot-like areas can be seen on the surface and local edges of the petals. This can usually be attributed to the distribution of nickel in the carbon matrix, indicating that nickel doping is well retained in the material structure during the carbonization process.

[0046] TEM image of CoCF prepared in Example 2 is shown below. Figure 4 As shown, uniformly distributed high-contrast dots can be observed on the surface of the petal structure, which is attributed to the uniform presence of cobalt in the carbon matrix.

[0047] The N2 adsorption-desorption isotherms and pore size distributions of NiCF and CoCF prepared in Examples 1 and 2 were measured using a BELSORP-Max surface area and pore size analyzer manufactured by Macch-Baier. The results are as follows: Figure 5 As shown; where, Figure 5 In the figure, 'a' represents the N2 adsorption-desorption isotherms of NiHCF and CoHCF. The specific surface area and pore size distribution of NiHCF and CoHCF were determined. NiHCF exhibited typical Type I adsorption-desorption isotherm characteristics, indicating the presence of micropores in the material, while CoHCF exhibited a Type IV adsorption-desorption isotherm, indicating that the material contains both micropores and mesopores. The specific surface area of ​​CoHCF calculated by BET (170.5 m²) is... 2 The g / g ratio is significantly higher than that of NiCF material (9.6 m). 2 / g).

[0048] Example 1: After assembling the capacitive deionization (CDI) seawater desalination test device, the test results are as follows: Figure 6 Table 1 shows the SAC curves of the NiCF prepared in Example 1. The SAC of the NiCF material increases with increasing voltage, and the salt adsorption capacity reaches 12.0 mg / g when the applied voltage reaches 1.8 V.

[0049] Example 2: After assembling the capacitive deionization (CDI) seawater desalination test device, the test results are as follows: Figure 7 Table 1 shows the SAC curves of the CoCF prepared in Example 2. The SAC of the CoCF material increases with increasing voltage. When the applied voltage reaches 1.8 V, the salt adsorption capacity reaches 17.5 mg / g. This is attributed to the fact that the higher specific surface area of ​​CoCF provides more available adsorption active sites, while the hierarchical pore structure reduces ion diffusion resistance and improves the utilization rate of the electrode material.

[0050] Table 1 Salt adsorption capacity of materials in Examples 1-2

[0051] The results showed that the NiCF and CoCF prepared in Examples 1 and 2 of the present invention had good salt adsorption capacity, and the CoCF prepared in Example 2 had better salt adsorption capacity and could be better used for seawater desalination.

[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the scope of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing in-situ metal-doped flower-like carbon microspheres, characterized in that, Includes the following steps: (1) Acrylonitrile was added dropwise to an ethanol-ethyl acetate solution, and a metal salt and azobisisobutyronitrile were added. The metal salt was nickel acetylacetonate or cobalt acetylacetonate. After mixing, the mixture was reacted at 60-80℃ for 3-5 h. After the reaction was completed, the product was filtered and the obtained solid was dried to obtain metal-doped polymer seed microspheres. (2) The metal-doped polymer seed microspheres were mixed with divinylbenzene and then added to anhydrous ethanol. Azobisisobutyronitrile was then added and the mixture was reacted at 60-80℃ for 3-5 h. After the reaction was completed, the product was filtered and the resulting solid was dried to obtain the metal-doped carbon microsphere precursor. (3) The metal-doped carbon microsphere precursor is placed in a tube furnace for carbonization treatment; the carbonization treatment is carried out in an inert atmosphere, the carbonization temperature is 900-1100℃, the holding time is 1.5-3 hours, and metal-doped flower-shaped carbon microspheres are obtained after carbonization. In step (1), the mass ratio of acrylonitrile, metal salt, and azobisisobutyronitrile is (7-9):(0.15-0.25):(0.25-0.35); the mass-to-volume ratio of acrylonitrile to ethanol-ethyl acetate solution (g / ml) is 7-9:40-60; and the volume ratio of ethanol to ethyl acetate in the ethanol-ethyl acetate solution is 0.9-1.1:0.9-1.

1. In steps (1) and (2), the drying temperature is 50-55℃ and the drying time is 10-16h. In step (2), the mass ratio of the metal-doped polymer seed microspheres, divinylbenzene, and azobisisobutyronitrile is 2:(1.2-1.8):(0.4-0.6); the mass-to-volume ratio of the metal-doped polymer seed microspheres to anhydrous ethanol is 2:90-110. Step (3), the carbonization process is heated at a rate of 1-6℃ / h.

2. An in-situ metal-doped flower-shaped carbon microsphere material, characterized in that, It is obtained by the preparation method described in claim 1.

3. Application of the in-situ metal-doped flower-shaped carbon microsphere material according to claim 2 in seawater desalination.

4. Use according to claim 3, characterized in that, The in-situ metal-doped flower-shaped carbon microsphere material is used in a capacitive deionization seawater desalination device, and the in-situ metal-doped flower-shaped carbon microsphere material is a positive electrode active material.

Images