Composite material, electrode loaded with the composite material, and method of preparation

Abstract

The application discloses a composite material, an electrode loaded with the composite material and a preparation method. The application relates to the technical field of fluorine ion removal. The composite material comprises cerium oxide and carbon nanotubes coated on the cerium oxide. In the composite material, the cerium oxide has unique affinity to F ions, but the F removal capacity and kinetics of the cerium oxide are not satisfactory due to the limited conductivity. Therefore, the application develops a composite material, in which a structure of carbon nanotubes (CNT) tightly wrapping cerium oxide (CeO2) particles is formed, so that the conductivity of the material is greatly improved and the mass transfer resistance in the electric adsorption and desorption of fluorine ions is weakened.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of fluoride ion removal, and in particular to a composite material, an electrode loaded with the composite material and a preparation method. BACKGROUND

[0002] Fluoride (F) is one of the essential elements for human life, which is usually derived from the weathering and dissolution of fluoride-containing minerals near natural water bodies around the world. However, long-term exposure to high levels of fluoride-containing environments can cause fluoride poisoning in the human body, further leading to nerve damage, limb dysfunction, and deformation of the body's bones and joints. In particular, in groundwater, due to the natural dissolution of fluoride-containing minerals, the concentration of fluoride ions can be as high as 10 mg / L, posing a potential threat to human health. Therefore, it is crucial to develop an effective and low-cost method to remove excessive fluoride ions in groundwater.

[0003] Due to its low cost and ease of operation, adsorption is one of the most commonly used methods for removing fluoride ions from water bodies. Although nano-adsorbents in adsorption methods have a large surface area and high activity, they show strong adsorption performance, but the tiny particles are not suitable for fixed bed columns, and they also face many difficulties in collection and regeneration. In addition, nano-materials are easily released into the target water body, causing secondary pollution. Furthermore, the commonly used materials in adsorption methods include cerium oxide and carbon nanotubes, but the current reported cerium oxide and CNT (carbon nanotube) composites are only simple physical mixtures, with low effectiveness.

[0004] Therefore, there is an urgent need to develop an electrode for selectively removing fluoride ions and a preparation method thereof. SUMMARY

[0005] The first technical problem to be solved by the present application is:

[0006] To provide a composite material.

[0007] The second technical problem to be solved by the present application is:

[0008] To provide a preparation method of the composite material.

[0009] The present application also provides an electrode comprising a capacitive deionization technology selective electrode and the composite material coated on the capacitive deionization technology selective electrode.

[0010] To solve the first technical problem, the technical solution adopted by the present application is:

[0011] A composite material, comprising cerium oxide and carbon nanotubes coated on the cerium oxide.

[0012] According to an embodiment of the present application, one of the technical solutions has at least one of the following advantages or beneficial effects:

[0013] The cerium oxide has a unique affinity for F ions in the composite material, but due to the limited conductivity, the F removal capacity and kinetics of cerium oxide are not satisfactory, based on which, the present application develops a composite material, in which a structure of carbon nanotubes (CNT) tightly wrapping cerium oxide (CeO2) particles is formed, thereby greatly improving the electrical conductivity of the material and reducing the mass transfer resistance in the electro-adsorption and desorption of fluorine ions. Further, the coating structure has the following advantages: 1. The coating structure can promote the doping and mixing of cerium oxide, making the mixing more uniform and tight, thereby facilitating electron transfer and improving the overall electrical conductivity of the material; 2. The coating structure also avoids the agglomeration of cerium oxide to some extent, fully exposing the surface area of cerium oxide, thereby increasing the sites for interaction with fluorine ions.

[0014] According to an embodiment of the present application, the mass ratio of cerium oxide to carbon nanotube is 80-90:10-20.

[0015] According to an embodiment of the present application, by adjusting the mass of carbon nanotubes, composite materials with CNT mass percentages of 10%, 15%, and 20% can be obtained, and the resulting products are named as 10-CNT-CeO2, 15-CNT-CeO2, and 20-CNT-CeO2, respectively.

[0016] To solve the second technical problem, the technical solution adopted by the present application is:

[0017] A method for preparing the composite material, comprising the following steps:

[0018] Mixing cerium hydroxide and carbon nanotubes, and obtaining the composite material through annealing reaction.

[0019] According to an embodiment of the present application, one of the technical solutions has at least one of the following advantages or beneficial effects:

[0020] The present application uses cerium hydroxide and carbon nanotubes as precursors, and directly synthesizes the composite material in one step through annealing reaction, which is efficient and fast.

[0021] In the process of preparing the composite material, cerium hydroxide is first oxidized to form cerium oxide, and the amorphous phase on the carbon nanotube is converted to the crystalline phase, which is equivalent to anchoring cerium oxide on the carbon nanotube. This way, the two are combined more tightly and it is very easy to form a coating structure. The generation of the coating structure can greatly improve the electrical conductivity of the material and reduce the mass transfer resistance in the electro-adsorption and desorption of fluorine ions.

[0022] According to one embodiment of the present application, the temperature of the annealing reaction is greater than or equal to 450°C. Different temperatures affect the crystallinity and oxygen vacancy level of cerium oxide, which are related to the removal effect and electrode stability.

[0023] According to one embodiment of the present application, the temperature of the annealing reaction is 400-500°C.

[0024] According to one embodiment of the present application, if the temperature of the annealing reaction exceeds 500°C, it will have an adverse effect on the structure of carbon nanotubes and will destroy the structure to some extent.

[0025] According to one embodiment of the present application, if the temperature of the annealing reaction is less than 400°C, the carbon nanotubes will not be sufficiently extended, thereby affecting the combination of carbon nanotubes and cerium oxide, resulting in the structure of carbon nanotubes tightly wrapping cerium oxide as claimed in the present application.

[0026] According to one embodiment of the present application, the preparation method of cerium hydroxide comprises the following steps:

[0027] Mixing a cerium source, an organic acid, and a metal hydroxide in a solvent, and then heating to obtain cerium hydroxide.

[0028] According to one embodiment of the present application, the molar ratio of the cerium source, the organic acid, and the metal hydroxide is 1.6-2.9:1:1.6-2.9.

[0029] According to one embodiment of the present application, the amount of the cerium source is the same as that of the metal hydroxide.

[0030] According to one embodiment of the present application, the solvent comprises an organic solvent and an inorganic solvent. The inorganic solvent comprises water, and the organic solvent comprises ethanol, glycerol, etc. The selection of the solvent can be screened as needed, and generally, the selection of the solvent does not affect the reaction.

[0031] According to one embodiment of the present application, the cerium source comprises at least one of cerium halide and cerium nitrate.

[0032] According to one embodiment of the present application, the halogen in cerium halide is halogen or halogen group, which refers to F, Cl, Br, or I. The presence of halogen provides a reactive site, and therefore, it should be considered that any cerium halide can achieve the technical effects or synthesis of the target product as claimed in the present application, and it should not be considered that only a certain cerium halide can achieve the technical effects or synthesis of the target product as claimed in the present application.

[0033] According to one embodiment of the present application, when the cerium source is cerium nitrate, the target product can still be synthesized by the scheme of the present application. Whether the cerium source is cerium nitrate or cerium halide, it will not have a significant effect on the structure or performance of the target product.

[0034] According to an embodiment of the present application, the metal hydroxide comprises at least one of sodium hydroxide and potassium hydroxide. The purpose of the metal hydroxide is to provide hydroxyl, therefore, any metal hydroxide with hydroxyl is deemed to achieve the technical effects or synthesis target products claimed by the present application.

[0035] According to an embodiment of the present application, the temperature of the heating reaction is 180-200℃.

[0036] According to an embodiment of the present application, the temperature of the heating reaction is selected from any one of the following temperatures or a temperature range formed by any two of the following temperatures: 180℃, 181℃, 182℃, 183℃, 184℃, 185℃, 186℃, 187℃, 188℃, 189℃, 190℃, 191℃, 192℃, 193℃, 194℃, 195℃, 196℃, 197℃, 198℃, 199℃, 200℃.

[0037] According to an embodiment of the present application, the method for preparing the composite material comprises the following steps:

[0038] The cerium source, the organic acid, and the metal hydroxide are mixed in a solvent, stirred to form a homogeneous solution, the solution is transferred to a hydrothermal reactor, heated to react to obtain a mixed solution, the mixed solution is filtered and washed, and dried to obtain cerium hydroxide. Subsequently, the cerium hydroxide is mixed with carbon nanotubes, and annealed to obtain a composite material.

[0039] According to an embodiment of the present application, the hydrolysis reaction (equation 1) involved in the above cerium hydroxide reaction is:

[0040] (Equation 1).

[0041] According to an embodiment of the present application, the reaction involved in the annealing reaction process comprises:

[0042] (Equation 2).

[0043] According to an embodiment of the present application, the filtration uses a 0.45μm PTFE membrane.

[0044] According to an embodiment of the present application, the washing uses ultrapure water and ethanol.

[0045] According to an embodiment of the present application, the drying uses a vacuum oven.

[0046] According to an embodiment of the present application, the drying temperature is 60-70℃.

[0047] According to an embodiment of the present application, the drying time is 12-24 hours.

[0048] In still another aspect of the present application, an electrode is provided, comprising the composite material and a capacitive deionization technology selective electrode.

[0049] With the development of supercapacitor materials, capacitive deionization technology (CDI) has attracted more and more attention due to its low energy consumption, high efficiency, low operating cost and environmental friendliness. The electrode materials used in this technology are mostly carbon materials. For example, a pair of porous carbon electrodes can be used in capacitive deionization technology. After a direct current voltage is applied, the ions in the solution will be adsorbed onto the electrode plate with opposite voltage and stored in the pores inside the porous carbon material. When the adsorption saturation is reached, the ions will be released from the electrode by removing or reversing the voltage, and the electrode will restore its original ion adsorption capacity.

[0050] In order to improve the selectivity and applicability of capacitive deionization technology (CDI) in complex environments, the present application introduces a functional material with unique affinity for target F ions into the electrode. Cerium dioxide is considered as a potential fluoride ion adsorbent. The strong affinity between F and CeO2 makes it a promising material for CDI selective electrode. However, when used as the only material in CDI process, the F removal capacity and kinetics may not be satisfactory due to the limited electrical conductivity. Therefore, the present application combines the unique affinity between CeO2 and fluoride with the accelerated kinetics achieved by the enhanced electrical conductivity of the electrode in CDI, and utilizes the structure of carbon nanotubes (CNT) tightly wrapped around cerium oxide (CeO2) particles formed in the material, to develop an effective and low-cost point of use (POU) device for selectively removing fluoride ions from groundwater with high efficiency.

[0051] Further, the electrode for selectively removing fluoride ions of the present application also has the following advantages or beneficial effects: (1) CDI as a fixed technology, this process not only avoids the problem of subsequent separation caused by the material entering the water body, but also is easy to operate, which makes the electrode for selectively removing fluoride ions of the present application have strong practicability and meet the requirements of industrial production; (2) In CDI, the effluent after cyclic purification reaches the standard faster with the electric field force as the power, which can reduce the processing time cost. (3) The electrode for selectively removing fluoride ions of the present application is easy to regenerate under reverse voltage in CDI, so that the long-term and multiple cycle stability is excellent. (4) The composite material used in the electrode of the present application includes cerium oxide and carbon nanotubes coated with cerium oxide, which has good desorption and regeneration performance, and completely solves the problem of existing powder cerium oxide adsorbing fluoride ions that cannot be regenerated (or high cost).

[0052] Other features and advantages of the present application will be set forth in the description that follows, and in part will be apparent from the description, or can be learned by practice of the application. BRIEF DESCRIPTION OF DRAWINGS

[0053] The above and / or additional aspects and advantages of the present application will become apparent and be readily understood from the following description, taken in conjunction with the accompanying drawings, in which:

[0054] Figure 1 The figure is a characterization graph of the composite material obtained in Example 1.

[0055] Figure 2 The figure is a high-angle annular dark-field scanning transmission electron microscopy test graph of the CeO2 material and the composite material obtained in Example 1.

[0056] Figure 3 The figure is a physical graph of the electrode obtained in Example 1.

[0057] Figure 4 The figure is a self-circulation system established for testing the electrosorption performance of the composite material obtained in Example 1.

[0058] Figure 5 The figure is a test graph of the chloride ion and fluoride ion adsorption performance of the electrode obtained in the comparative example.

[0059] Figure 6 The figure is a test graph of the fluoride ion adsorption performance of the electrode of Example 1-3 and the comparative example.

[0060] Figure 7 The figure is a test graph of the desorption regeneration performance of the electrode of the comparative example.

[0061] Figure 8 The figure is a test graph of the desorption regeneration performance of the electrode of Example 1.

[0062] Figure 9 The figure is a test graph of the cycle stability of the electrode of Example 1. DETAILED DESCRIPTION

[0063] In the description of the present application, if the first, second, etc. are described, it is only for the purpose of distinguishing technical features, and cannot be understood as indicating or implying the relative importance of the indicated technical features or implying the number of the indicated technical features or the sequence of the indicated technical features.

[0064] In the description of the present application, it is to be understood that the orientation description, such as the upper, lower, etc. indicated orientation or position relationship is based on the orientation or position relationship shown in the examples, only for the purpose of facilitating the description of the present application and simplifying the description, and is not to indicate or imply that the indicated device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present application.

[0065] The words "preferably," "more preferably," and the like, in the present invention, mean embodiments of the invention that can provide certain benefits under some circumstances. However, other embodiments can also exhibit the benefits, and thus the words are not intended as an express limitation of the scope of the invention. By way of example, the word "preferably" is used to express an embodiment where certain benefits can be provided in some circumstances. However, other embodiments can also exhibit the benefits, and thus the word "preferably" is not intended to exclude other embodiments from the scope of the invention.

[0066] When a range of values is disclosed, the disclosure is to be construed to include all values within the range, including the upper and lower values, and not just discrete values arbitrarily close to the upper or lower value of the range. Further, these disclosed ranges are to be understood to encompass by inclusion of every value falling within the range. Additionally, it is intended that every combination of values described by the disclosed ranges is contemplated, even if not explicitly listed. In other words, if a range of values is disclosed, it is intended to include every possible combination of the values within the range. Moreover, it is intended that every possible combination of claimed elements can be explicitly enumerated, even if not explicitly listed.

[0067] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of the present application.

[0068] The reagents, methods and devices employed in the present application are conventional in the art, unless otherwise specified.

[0069] Capacitive deionization (CDI), also known as electro-sorption, is an emerging electrochemical technology that uses porous electrodes to remove charged species from solution. Compared to traditional adsorption methods, CDI can significantly enhance the removal kinetics in the porous electrodes and can be easily regenerated by shorting or applying a reverse voltage. In recent years, CDI technology has been used to remove or recover a series of charged species. In terms of natural water, the concentration of fluoride ions is much lower than that of other coexisting compounds, such as chloride ions. Fluoride ions have a larger hydration radius (0.352 nm) and slower mobility (1.48 × 10 9 m 2 s 1 ) Fluoride ions have a larger hydration radius (0.352 nm) and slower mobility (1.48 × 10 9 m 2 s 1). Thus, the CDI process has very low fluorine removal efficiency in the presence of competing ions when using a porous carbon electrode that lacks selectivity to remove specific species.

[0070] Example 1

[0071] A composite material, the composite material comprising cerium oxide and carbon nanotubes coated with cerium oxide.

[0072] Preparation of the composite material, comprising the following steps:

[0073] Dissolve 1.6 mmol CeCl3·7H2O, 0.55 mmol citric acid and 1.6 mmol NaOH in 40 mL deionized water and stir for at least 30 min to form a homogeneous solution. Then transfer the solution to a 50 mL polytetrafluoroethylene (PTFE) hydrothermal reactor and heat in an oven at 180°C for 24 hours. Subsequently, filter the Ce(OH)3 through a 0.45 μm PTFE membrane and wash several times with ultrapure water and ethanol, then dry in a vacuum oven at 60°C for 12 hours;

[0074] Put the Ce(OH)3 powder and CNT into an alumina crucible to obtain a mixed powder, wherein the mass percentage of CNT is 10%, and anneal the mixed powder in air at 450°C for 4 h to obtain a composite material, which is named as 10-CNT-CeO2.

[0075] Test the composite material obtained in Example 1, as shown in Figure 1 , wherein Figure 1 (a) in FIG. 1 is an X-ray diffraction (XRD) pattern, from which it can be seen that the composite material comprises CeO2, Figure 1 (b) in FIG. 1 is a Raman spectrum, from which it can be seen that the composite material contains both cerium oxide and carbon nanotube components, indicating that the material is successfully synthesized. Figure 1 , wherein 2theta is the diffraction angle, Raman shift is the Raman shift, and Intensity is the intensity.

[0076] Perform high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) test on the CeO2 material and the composite material obtained in Example 1, and the test results are shown in Figure 2 , wherein Figure 2 (a) in FIG. 2 is an electron microscopy test performed on the CeO2 material alone, Figure 2 (b) in FIG. 2 is an electron microscopy test of the composite material of Example 1, from which it can be seen that, Figure 2 (b) in FIG. 2, at the edge of the material, there is a layer of material coating the CeO2 material, and the result Figure 1As a result, it can be known that the CNTs coat the CeO2 in the composite material obtained in Example 1.

[0077] An electrode for selectively removing fluoride ions, comprising a capacitive deionization technology selective electrode and a composite material coated on the capacitive deionization technology selective electrode.

[0078] A method of manufacturing the electrode for selectively removing fluoride ions, comprising the steps of:

[0079] A uniform slurry for functionalized anode electrode manufacturing was prepared by mixing 120 mg of the above composite material, 15 mg of polyvinylidene fluoride (PVDF) dispersion as a binder, and 15 mg of carbon black in an N-methyl pyrrolidone (NMP) solvent. Then, the uniform slurry was carefully coated on a titanium plate with a surface area of 5 x 5 cm 2 , dried in a vacuum oven at 60°C overnight to obtain an electrode for selectively removing fluoride ions, which can be used in CDI technology, and a physical diagram of the electrode is shown in Figure 3 .

[0080] Example 2

[0081] Example 2 is different from Example 1 in that the amount of CNTs is different, wherein the mass percentage of CNTs in Example 2 is 15%.

[0082] A composite material, the composite material comprising cerium oxide and carbon nanotubes coated with the cerium oxide.

[0083] A method of manufacturing the composite material, comprising the steps of:

[0084] Dissolve 1.6 mmol of CeCl3·7H2O, 0.55 mmol of citric acid, and 1.6 mmol of NaOH in 40 mL of deionized water, and stir for at least 30 min to form a homogeneous solution. Then, transfer the solution to a 50 mL polytetrafluoroethylene (PTFE) hydrothermal reactor, and heat in an oven at 180°C for 24 hours. Subsequently, filter the Ce(OH)3 through a 0.45 μm PTFE membrane, and wash with ultrapure water and ethanol several times, and then dry in a vacuum oven at 60°C for 12 hours;

[0085] Put the Ce(OH)3 powder and CNTs into an alumina crucible to obtain a mixed powder, wherein the mass percentage of CNTs is 15%, and anneal the mixed powder at 450°C in air for 4 h to obtain a composite material, which is named as 15-CNT-CeO2.

[0086] An electrode for selectively removing fluoride ions, comprising a capacitive deionization technology selective electrode and a composite material coated on the capacitive deionization technology selective electrode.

[0087] The electrode for selective removal of fluoride ions is prepared by the following steps:

[0088] A homogeneous slurry for functionalized anode electrode fabrication is prepared by mixing 120 mg of the above composite material, 15 mg of polyvinylidene fluoride (PVDF) dispersion as a binder and 15 mg of carbon black in N-methyl pyrrolidone (NMP) solvent. The homogeneous slurry is then carefully coated on a titanium plate with a surface area of 5 x 5 cm 2 and dried in a vacuum oven at 60°C overnight to obtain the electrode for selective removal of fluoride ions.

[0089] Example 3

[0090] Example 3 differs from Example 1 in that the amount of CNT used is different, wherein the mass percentage of CNT in Example 3 is 20%.

[0091] A composite material, the composite material comprising cerium oxide and carbon nanotubes coated with cerium oxide.

[0092] The composite material is prepared by the following steps:

[0093] Dissolve 1.6 mmol of CeCl3-7H2O, 0.55 mmol of citric acid and 1.6 mmol of NaOH in 40 mL of deionized water and stir for at least 30 min to form a homogeneous solution. Then transfer the solution to a 50 mL polytetrafluoroethylene (PTFE) hydrothermal reactor and heat in an oven at 180°C for 24 hours. Subsequently, filter the Ce(OH)3 through a 0.45 μm PTFE membrane and wash several times with ultrapure water and ethanol, then dry in a vacuum oven at 60°C for 12 hours;

[0094] Put the Ce(OH)3 powder and CNT into an alumina crucible to obtain a mixed powder, wherein the mass percentage of CNT is 20%, and anneal the mixed powder in air at 450°C for 4 h to obtain the composite material, which is named 20-CNT-CeO2.

[0095] An electrode for selective removal of fluoride ions, comprising a capacitive deionization technology selective electrode and a composite material coated on the capacitive deionization technology selective electrode.

[0096] The electrode for selective removal of fluoride ions is prepared by the following steps:

[0097] A homogeneous slurry for functionalized anode electrode fabrication was prepared by mixing 120 mg of the above composite material, 15 mg of polyvinylidene fluoride (PVDF) dispersion as a binder, and 15 mg of carbon black in N-methyl pyrrolidone (NMP) solvent. The homogeneous slurry was then carefully coated on a titanium plate with a surface area of 5 x 5 cm 2 and dried in a vacuum oven at 60 °C overnight to obtain a fluoride ion-selective electrode.

[0098] Example 4

[0099] Example 4 differs from Example 1 in that the temperature of the annealing in Example 4 is 550 °C.

[0100] A composite material, the composite material comprising cerium oxide and carbon nanotubes coated with cerium oxide.

[0101] The composite material is prepared, comprising the steps of:

[0102] CeCl3-7H2O, 0.55 mmol of citric acid, and 1.6 mmol of NaOH were dissolved in 40 mL of deionized water and stirred for at least 30 min to form a homogeneous solution. The solution was then transferred to a 50 mL polytetrafluoroethylene (PTFE) hydrothermal reactor and heated in an oven at 180 °C for 24 hours. Subsequently, the Ce(OH)3was filtered through a 0.45 pm PTFE membrane and washed several times with ultrapure water and ethanol, and then dried in a vacuum oven at 60 °C for 12 hours;

[0103] The Ce(OH)3powder and CNT were placed in an alumina crucible to obtain a mixed powder, wherein the mass percentage of CNT is 10%, and the mixed powder was annealed at 550 °C in air for 4 h to obtain the composite material.

[0104] A fluoride ion-selective electrode, comprising a capacitive deionization technology selective electrode and a composite material coated on the capacitive deionization technology selective electrode.

[0105] The fluoride ion-selective electrode is prepared, comprising the steps of:

[0106] A homogeneous slurry for functionalized anode electrode fabrication was prepared by mixing 120 mg of the above composite material, 15 mg of polyvinylidene fluoride (PVDF) dispersion as a binder, and 15 mg of carbon black in N-methyl pyrrolidone (NMP) solvent. The homogeneous slurry was then carefully coated on a titanium plate with a surface area of 5 x 5 cm 2 and dried in a vacuum oven at 60 °C overnight to obtain a fluoride ion-selective electrode.

[0107] Example 5

[0108] Example 5 differs from Example 1 in that the cerium source in Example 5 is cerium bromide.

[0109] A composite material comprising cerium oxide and carbon nanotubes coated with cerium oxide.

[0110] Preparation of the composite material comprising the steps of:

[0111] Dissolve 1.6 mmol CeBr3, 0.55 mmol citric acid and 1.6 mmol NaOH in 40 mL of deionized water and stir for at least 30 min to form a homogeneous solution. Then transfer the solution to a 50 mL polytetrafluoroethylene (PTFE) hydrothermal reactor and heat in an oven at 180 °C for 24 hours. Subsequently, filter the Ce(OH)3 through a 0.45 μm PTFE membrane and wash several times with ultrapure water and ethanol, then dry in a vacuum oven at 60 °C for 12 hours;

[0112] Put the Ce(OH)3 powder and CNT into an alumina crucible to obtain a mixed powder, wherein the mass percentage of CNT is 10%, and anneal the mixed powder at 450 °C in air for 4 h to obtain the composite material.

[0113] An electrode for selective removal of fluoride ions, comprising a capacitive deionization technology selective electrode and a composite material coated on the capacitive deionization technology selective electrode.

[0114] Preparation of the electrode for selective removal of fluoride ions comprising the steps of:

[0115] A uniform slurry for functionalized anode electrode manufacturing is prepared by mixing 120 mg of the composite material, 15 mg of polyvinylidene fluoride (PVDF) dispersion as a binder and 15 mg of carbon black in N-methyl pyrrolidone (NMP) solvent. Then the uniform slurry is carefully coated on a titanium plate with a surface area of 5 x 5 cm 2 , dried in a vacuum oven at 60 °C overnight to obtain the electrode for selective removal of fluoride ions.

[0116] Example 6

[0117] Example 6 differs from Example 1 in that the cerium source in Example 6 is cerium iodide.

[0118] A composite material comprising cerium oxide and carbon nanotubes coated with cerium oxide.

[0119] Preparation of the composite material comprising the steps of:

[0120] Ce(OH)3powder and CNT were put into an alumina crucible to obtain a mixed powder, wherein the mass percentage of CNT was 10%, and the mixed powder was annealed at 450°C in air for 4 h to obtain a composite material.

[0121] Ce(OH)3powder and CNT were put into an alumina crucible to obtain a mixed powder, wherein the mass percentage of CNT was 10%, and the mixed powder was annealed at 450°C in air for 4 h to obtain a composite material.

[0122] An electrode for selectively removing fluoride ions, comprising a capacitive deionization technology selective electrode and a composite material covering the capacitive deionization technology selective electrode.

[0123] The electrode for selectively removing fluoride ions is prepared by the following steps:

[0124] A uniform slurry for functionalized anode electrode manufacturing was prepared by mixing 120 mg of the above-mentioned composite material, 15 mg of polyvinylidene fluoride (PVDF) dispersion as a binder, and 15 mg of carbon black in an N-methyl pyrrolidone (NMP) solvent. Then, the uniform slurry was carefully coated on a titanium plate with a surface area of 5 x 5 cm 2 , dried in a vacuum oven at 60°C overnight to obtain the electrode for selectively removing fluoride ions.

[0125] Example 7

[0126] Example 7 differs from Example 1 in that the metal hydroxide in Example 7 is potassium hydroxide.

[0127] A composite material, the composite material comprising cerium oxide and carbon nanotubes coated with cerium oxide.

[0128] The composite material is prepared by the following steps:

[0129] Ce(OH)3powder and CNT were put into an alumina crucible to obtain a mixed powder, wherein the mass percentage of CNT was 10%, and the mixed powder was annealed at 450°C in air for 4 h to obtain a composite material.

[0130] Ce(OH)3 powder and CNTs were placed in an alumina crucible to obtain a mixed powder, wherein the mass percentage of CNTs was 10%, and the mixed powder was annealed in air at 450°C for 4 h to obtain a composite material.

[0131] An electrode for selectively removing fluoride ions, comprising a capacitive deionization technology selective electrode and a composite material coated on the capacitive deionization technology selective electrode.

[0132] Preparation of the above-mentioned electrode for selectively removing fluoride ions, comprising the following steps:

[0133] A uniform slurry for functional anode electrode manufacturing was prepared by mixing 120 mg of the above-mentioned composite material, 15 mg of polyvinylidene fluoride (PVDF) dispersion as a binder, and 15 mg of carbon black in an N-methyl pyrrolidone (NMP) solvent. Then the uniform slurry was carefully coated on a titanium plate with a surface area of 5x5 cm 2 in a vacuum oven at 60°C overnight to obtain an electrode for selectively removing fluoride ions.

[0134] Example 8

[0135] Example 8 differs from Example 1 in that the temperature of the oven for heating the reaction in Example 8 is 200°C.

[0136] A composite material, the composite material comprising cerium oxide and carbon nanotubes coated with cerium oxide.

[0137] Preparation of the above-mentioned composite material, comprising the following steps:

[0138] Dissolve 1.6 mmol of CeCl3·7H2O, 0.55 mmol of citric acid, and 1.6 mmol of NaOH in 40 mL of deionized water, and stir for at least 30 min to form a homogeneous solution. Then transfer the solution to a 50 mL polytetrafluoroethylene (PTFE) hydrothermal reactor, and heat in an oven at 200°C for 24 hours. Subsequently, filter the Ce(OH)3 through a 0.45 μm PTFE membrane, and wash with ultrapure water and ethanol several times, and then dry in a vacuum oven at 60°C for 12 hours;

[0139] Ce(OH)3 powder and CNTs were placed in an alumina crucible to obtain a mixed powder, wherein the mass percentage of CNTs was 10%, and the mixed powder was annealed in air at 450°C for 4 h to obtain a composite material.

[0140] An electrode for selectively removing fluoride ions, comprising a capacitive deionization technology selective electrode and a composite material coated on the capacitive deionization technology selective electrode.

[0141] The electrode for selective removal of fluoride ions is prepared by the following steps:

[0142] A homogeneous slurry for functionalized anode electrode fabrication is prepared by mixing 120 mg of the composite material, 15 mg of polyvinylidene fluoride (PVDF) dispersion as a binder, and 15 mg of carbon black in N-methyl pyrrolidone (NMP) solvent. The homogeneous slurry is then carefully coated on a titanium plate with a surface area of 5 x 5 cm 2 and dried in a vacuum oven at 60 °C overnight to obtain the electrode for selective removal of fluoride ions.

[0143] Example 9

[0144] Example 9 differs from Example 1 in that the cerium source in Example 9 is cerium nitrate.

[0145] A composite material, the composite material comprising cerium oxide and carbon nanotubes coated with cerium oxide.

[0146] The composite material is prepared by the following steps:

[0147] Dissolve 1.6 mmol of Ce(N03)3-6H20, 0.55 mmol of citric acid, and 1.6 mmol of NaOH in 40 mL of deionized water and stir for at least 30 min to form a homogeneous solution. Then transfer the solution to a 50 mL polytetrafluoroethylene (PTFE) hydrothermal reactor and heat in an oven at 180 °C for 24 hours. Subsequently, filter the Ce(OH)3through a 0.45 pm PTFE membrane and wash with ultrapure water and ethanol several times, then dry in a vacuum oven at 60 °C for 12 hours;

[0148] Put the Ce(OH)3powder and CNT into an alumina crucible to obtain a mixed powder, wherein the mass percentage of CNT is 10%, and anneal the mixed powder at 450 °C in air for 4 h to obtain the composite material.

[0149] An electrode for selective removal of fluoride ions, comprising a capacitive deionization technology selective electrode and a composite material covering the capacitive deionization technology selective electrode.

[0150] The electrode for selective removal of fluoride ions is prepared by the following steps:

[0151] A homogeneous slurry for functionalized anode electrode fabrication is prepared by mixing 120 mg of the composite material, 15 mg of polyvinylidene fluoride (PVDF) dispersion as a binder, and 15 mg of carbon black in N-methyl pyrrolidone (NMP) solvent. The homogeneous slurry is then carefully coated on a titanium plate with a surface area of 5 x 5 cm2 The titanium plate was dried overnight in a vacuum oven at 60 °C to obtain the electrode with selective removal of fluoride ions.

[0152] Comparative Example

[0153] The difference between the comparative example and Example 1 is that the composite material of the comparative example does not include carbon nanotubes.

[0154] A material is cerium oxide.

[0155] A cerium oxide electrode, the manufacturing process, including the following steps:

[0156] A uniform slurry for functional anode electrode manufacturing was prepared by mixing 120 mg of cerium oxide, 15 mg of polyvinylidene fluoride (PVDF) dispersion as a binder, and 15 mg of carbon black in N-methyl pyrrolidone (NMP) solvent. Then the uniform slurry was carefully coated on a titanium plate with a surface area of 5 x 5 cm 2 The titanium plate was dried overnight in a vacuum oven at 60 °C to obtain the electrode with selective removal of fluoride ions.

[0157] Performance test:

[0158] In order to study the electrosorption performance of the CeO2 material of the comparative example and the CNT-CeO2 electrodes of Examples 1-8 in batch tests, a self-circulation system was established, as shown in Figure 4 , including a CDI unit, an external power supply, and a peristaltic pump. A mixed solution of 50 mL of NaF and NaCl (10 mg / L of fluoride ions and 100 mg / L of chloride ions) was used as the simulated fluorine-containing water. During the test, the flow rate and the applied voltage were maintained at 15 mL / min and 1.2 V, respectively, and 0.5 mL of solution was extracted at different time intervals to determine the residual concentrations of F - and Cl - by ion chromatography. Fluorine desorption was carried out at a potential of 1.2 V and a flow rate of 15 mL / min, with 200 mL of ultrapure water used as the receiving solution.

[0159] Among them, the water body to be treated is placed in the storage tank and pumped out by the peristaltic pump, flowing through the CDI adsorption pool under the action of the electric field force, and the anions migrate to the anode. Fluoride ions contacting the electrode will be combined with cerium oxide, and fluorine ions will continuously migrate from the body to the electrode. Chloride ions will only be adsorbed on the electrode surface as part of the double electric layer, and the removal amount is limited, so the task of selective adsorption of fluoride ions is completed.

[0160] First, the material and electrode obtained in the comparative example were tested by the above-mentioned self-circulation system, and the test results are shown in Figure 5 . Figure 5In this study, common activated carbon electrodes and comparative electrodes were used to test the adsorption properties of chloride and fluoride ions, respectively. Figure 5 As can be seen, compared to the common activated carbon electrode, which can only adsorb chloride ions present in large quantities in water to a limited extent, the cerium oxide electrode in the comparative example can effectively and continuously remove fluoride ions from the water at a low concentration, reducing the concentration from 10 mg / L to 1.5 mg / L within 300 minutes. This is an impossible task for activated carbon, proving that the cerium oxide electrode itself has a certain selective adsorption capacity for fluoride ions. Where Time represents time, fluoride concentration represents fluoride concentration, and chloride concentration represents chloride concentration.

[0161] Furthermore, the composite material and electrode in Example 1 were tested. The tests compared the individual carbon nanotube electrode, the electrode of the comparative example, and the electrodes of Examples 1-3. The test results are as follows: Figure 6 As shown. Among them, the electrode with 15% carbon nanotubes (the electrode of Example 2) has the fastest removal rate, reducing the fluoride ion concentration in the water from 10 ppm to below 1.5 ppm in 150 min, and the treatment time is reduced by half compared to the cerium oxide electrode in the comparative example.

[0162] The desorption and regeneration performance of the electrodes in the comparative example were tested, and the test results are as follows: Figure 7 As shown in the figure, the cerium oxide electrode can desorb 86% of fluoride ions at -1.4V for 240 minutes. The desorption-regeneration performance of the electrode in Example 1 was tested, and the results are as follows. Figure 8 As shown in the figure, the electrode can desorb 91% of fluoride ions in 240 minutes at -1.2V. In summary, both the cerium oxide electrode and the carbon nanotube-reinforced CNT-CeO2 electrode can efficiently desorb fluoride ions adsorbed on the electrode plate during the process, but the electrode incorporating CNTs exhibits better desorption performance. Here, "desorption" refers to the process of desorption.

[0163] Cyclic stability tests were performed on the electrode of Example 1, and the test results are as follows: Figure 9 As shown, after 20 complete adsorption-desorption cycles, the electrode of Example 1 can still efficiently remove fluoride ions from the water, and the desorption percentage remains above 85% throughout the cycle.

[0164] The above are merely embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent modifications made based on the content of the present invention specification, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method of making a composite material, characterized by: The method comprises the following steps: mixing cerium source, citric acid and metal hydroxide in water in a molar ratio of 2.9:1:2.9, stirring to form a homogeneous solution, transferring the solution to a hydrothermal reactor, heating the reaction at 180-200℃ for 24h to obtain a mixed solution, filtering, washing and drying to obtain cerium hydroxide Ce(OH)3, mixing the cerium hydroxide with carbon nanotubes, and annealing to obtain a composite material, wherein the composite material comprises cerium oxide and carbon nanotubes coated with the cerium oxide; the mass ratio of the cerium oxide to the carbon nanotubes is 80-90:10-20; the annealing temperature is 450-500℃; the cerium source is at least one of cerium halide and cerium nitrate; the metal hydroxide is at least one of sodium hydroxide and potassium hydroxide.

2. A composite material, characterized by: The composite material is prepared by the method of claim 1, wherein the composite material comprises cerium oxide and carbon nanotubes coated with the cerium oxide; the mass ratio of the cerium oxide to the carbon nanotubes is 80-90:10-20.

3. An electrode characterized by: The composite material prepared by the method of claim 1 is coated on a selective electrode of a capacitive deionization technology.

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