Capacitive deionization electrode for selectively removing calcium and magnesium ions and its application

Abstract

The present invention proposes a capacitive deionization electrode for selectively removing calcium and magnesium ions and its application. The capacitive deionization electrode uses a barium titanate-aluminum oxide composite material as the active material of the electrode, significantly improving the electrode's selectivity and performance. The present invention also provides a selective capacitive deionization device based on the electrode, using the capacitive deionization electrode as a core component. The device achieves targeted selective adsorption of calcium and magnesium ions by optimizing the composite structure and surface properties of the electrode material. The device is particularly suitable for purifying brackish water in the arid northwest region, effectively reducing the salt concentration in the water. In addition, the composite electrode overcomes the limitations of traditional carbon-based materials, not only significantly improving the adsorption capacity, but also maintaining good stability during multiple adsorption-desorption cycles, thereby extending the service life of the electrode.

Description

Technical Field

[0001] The present invention relates to the technical field of capacitive deionization, and in particular to a capacitive deionization electrode for selectively removing calcium and magnesium ions and applications thereof. Background Art

[0002] Brackish water, a water resource with a high salt content and a bitter taste, is primarily found in the northwest region. Its salinity typically ranges from 1,000 to 10,000 mg / L. In agriculture, using brackish water for irrigation can lead to soil salinization, causing salt accumulation in the soil, disrupting soil structure, leading to compaction and particle dispersion, which in turn affects water and nutrient absorption, inhibiting crop growth, and reducing crop yield and quality. In severe cases, it can even lead to land degradation and loss of productivity. Furthermore, high salt concentrations in brackish water can increase osmotic stress on crop roots, leading to water shortages and ion toxicity, impacting crop health and productivity. Calcium and magnesium ions are essential nutrients for plant growth and development, but excessive amounts can negatively impact plants. Excessive calcium ions can inhibit root elongation, weakening root growth and impairing water and nutrient absorption. Excessive magnesium ions can increase rhizosphere osmotic pressure, making it difficult for plants to absorb water from the soil and causing drought stress symptoms such as leaf wilting. Therefore, it is necessary to remove excess calcium and magnesium ions from brackish water. Research on removing excess calcium and magnesium ions in water is of great significance for increasing plant yields

[0003] Dialysis, reverse osmosis, membrane treatment, and capacitive deionization (CDI) are the primary methods for desalinating brackish water. Electrodialysis utilizes an electric field to separate and remove ions from a solution. Reverse osmosis utilizes a semipermeable membrane to remove ions, molecules, and larger particles from a solution. However, this involves high initial investment, membrane fouling, and difficult wastewater treatment, resulting in high costs. Membrane treatment, which combines ion exchange membranes with capacitive deionization, increases cost and complexity, limits ion migration, and can also lead to membrane fouling and performance degradation.

[0004] Capacitive deionization (CDI) is a new, environmentally friendly brackish water desalination technology. Compared to traditional technologies, it offers the advantages of low energy consumption, zero secondary pollution, and regenerable electrodes. Currently, electrodes used in brackish water desalination using CDI are primarily carbon-based materials, leveraging the double-layer effect to electrosorb a broad spectrum of charged ions from the water. The core of capacitive deionization consists of a pair of highly efficient adsorption electrodes, often made of high-surface-area materials or functionalized composite materials. Through the action of an electric field, positive and negative ions are adsorbed onto the positive and negative surfaces of the electrodes, respectively, thereby removing ions from the water.

[0005] Activated carbon is a common capacitive deionization electrode material, widely used for its high specific surface area, excellent conductivity, and low cost. However, when selectively deionizing, this material has difficulty selectively removing specific ions from mixed solutions and has a low adsorption capacity. Therefore, there is an urgent need to develop new electrode materials for selectively removing ions from water to soften hard water. Summary of the Invention

[0006] Through research, the inventors discovered that traditional electrode materials can be modified using composite materials. Combining traditional electrode materials with conductive polymers can combine the advantages of both, improving the conductivity and selectivity of the electrodes. For example, combining conductive polymers such as polypyrrole and polyaniline with carbon-based electrode materials can achieve selective adsorption and detection of specific ions by adjusting the polymer structure and functional groups.

[0007] The present invention aims to at least partially address one of the technical problems in the related art. To this end, embodiments of the present invention provide a capacitive deionization electrode for selectively removing calcium and magnesium ions and its application, which can achieve selective adsorption of calcium and magnesium ions in brackish water.

[0008] In one aspect, an embodiment of the present invention provides a method for preparing a capacitive deionization electrode for selectively removing calcium and magnesium ions, comprising the following steps: mixing and stirring a barium titanate-alumina composite material, a conductive agent, an adhesive, and NMP to form a slurry, wherein the mass ratio of the barium titanate-alumina composite material, the conductive agent, and the adhesive is 80-95:5-10:5-10, and the volume of NMP and the mass ratio of the barium titanate-alumina composite material is 5-7.5 ml:1 g. The slurry is evenly coated on a current collector, allowed to stand at room temperature, and assembled after drying to obtain a capacitive deionization electrode for selectively removing calcium and magnesium ions.

[0009] In some embodiments, the preparation method of the barium titanate-aluminum oxide composite material is a one-step solid phase method, wherein the one-step solid phase method comprises the following steps:

[0010] Barium titanate powder and alumina powder are mixed in a mass ratio of 1:2, deionized water is added, and the volume of the deionized water is 20-30% of the total mass of the barium titanate powder and the alumina powder. The mixture is stirred evenly for 30-40 minutes, and then calcined at a calcination temperature of 900-1000°C and a calcination time of 2-3 hours to obtain a barium titanate-alumina composite material.

[0011] In some embodiments, the barium titanate-aluminum oxide composite material is in the form of nanoparticles, and the particle size of the nanoparticles is 100-400 nm.

[0012] In some embodiments, the particle size of the barium titanate-aluminum oxide composite nanoparticles is 250 nm.

[0013] In some embodiments, the conductive agent is acetylene black or carbon black, the adhesive is PVDF, PTFE or Nafion, and the current collector is titanium sheet, graphite paper or carbon paper.

[0014] The second embodiment of the present invention provides a capacitor deionization electrode prepared by the above-mentioned preparation method.

[0015] A third embodiment of the present invention provides a capacitive deionization device, comprising a positive electrode and a negative electrode, wherein the negative electrode is the capacitive deionization electrode described above, and the positive electrode is an electrode using carbon material as an active material.

[0016] A fourth embodiment of the present invention proposes the use of a capacitive deionization device in brackish water desalination, wherein the capacitive deionization device is used to selectively adsorb calcium and magnesium ions in the brackish water.

[0017] In some embodiments, the voltage between the positive and negative electrodes of the capacitive deionization device is 0.8-1.8V. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings.

[0019] in:

[0020] Figure 1 Schematic diagram of the structure of a capacitive deionization device in an embodiment of the present invention;

[0021] Description of reference numerals:

[0022] 1. Glass plate; 2. Silicone sheet; 3. Current collector; 4. Plastic gasket. DETAILED DESCRIPTION

[0023] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0024] The following describes a capacitive deionization electrode for selectively removing calcium and magnesium ions, a capacitive deionization device, and applications thereof according to embodiments of the present invention with reference to the accompanying drawings.

[0025] In one aspect, an embodiment of the present invention provides a method for preparing a capacitive deionization electrode for selectively removing calcium and magnesium ions, comprising the following steps: mixing and stirring a barium titanate-alumina composite material, a conductive agent, an adhesive, and NMP to form a slurry, wherein the mass ratio of the barium titanate-alumina composite material, the conductive agent, and the adhesive is 80-95:5-10:5-10, and the volume of NMP and the mass ratio of the barium titanate-alumina composite material is 5-7.5 ml:1 g. The slurry is evenly coated on a current collector 3, allowed to stand at room temperature, and assembled after drying to obtain a capacitive deionization electrode for selectively removing calcium and magnesium ions.

[0026] The capacitive deionization electrode material prepared by the above-described method in the embodiments of the present invention can selectively adsorb calcium and magnesium ions in water at high capacities. Compared to traditional nitrogen-doped carbon electrode materials, the capacitive deionization electrode material prepared in the embodiments of the present invention is green, efficient, low-carbon, and sustainable, playing an important role in addressing major challenges such as resource shortages, energy crises, and environmental degradation.

[0027] The embodiment of the present invention uses a barium titanate-aluminum oxide composite material as the active material of the electrode, which significantly improves the selectivity and performance of the electrode.

[0028] It should be noted that the coating thickness of the slurry on the current collector 3 can be adjusted according to actual needs.

[0029] In some embodiments, the preparation method of the barium titanate-aluminum oxide composite material is a one-step solid phase method, wherein the one-step solid phase method comprises the following steps:

[0030] Barium titanate powder and alumina powder are mixed in a mass ratio of 1:2, deionized water is added, and the volume of the deionized water is 20-30% of the total mass of the barium titanate powder and the alumina powder. The mixture is stirred evenly for 30-40 minutes, and then calcined at a calcination temperature of 900-1000°C and a calcination time of 2-3 hours to obtain a barium titanate-alumina composite material.

[0031] In some embodiments, the barium titanate-aluminum oxide composite material is in the form of nanoparticles, and the particle size of the nanoparticles is 100-400 nm.

[0032] In some embodiments, the particle size of the barium titanate-aluminum oxide composite nanoparticles is 250 nm, which can enable the prepared capacitive deionization electrode to have better selective adsorption and greater adsorption capacity for calcium and magnesium ions.

[0033] In some embodiments, the conductive agent is acetylene black or carbon black, the adhesive is PVDF, PTFE or Nafion, and the current collector 3 is a titanium sheet, graphite paper or carbon paper.

[0034] It should be noted that the full name of Nafion is perfluorosulfonic acid polymer, and its Chinese name is naphthol. It is a polymer with ionic properties and can be used as an adhesive.

[0035] A second embodiment of the present invention provides a capacitive deionization electrode prepared by the above-described preparation method. Due to the addition of barium titanate-alumina, the electrode of this embodiment overcomes the limitations of traditional carbon-based materials, not only improving the electrode's adsorption capacity for calcium and magnesium ions, but also imparting excellent cyclic electrosorption stability, enabling more than two cycles of electrosorption, thereby extending the electrode's service life.

[0036] A third embodiment of the present invention provides a capacitive deionization device, comprising a positive electrode and a negative electrode, wherein the negative electrode is the capacitive deionization electrode described above, and the positive electrode is an electrode using carbon material as an active material.

[0037] The capacitive deionization device of the present invention optimizes the composite structure and surface properties of the electrode material to achieve targeted selective adsorption of calcium and magnesium ions. This device has broad application potential and can optimize the treatment of water sources with different salinity compositions. It is particularly significant in the fields of brackish water desalination and resource recovery, providing an efficient and economical water purification solution for the arid and semi-arid regions of Northwest China. This capacitive deionization device utilizes the synergistic effect of the high dielectric properties of barium titanate and the excellent chemical stability of aluminum oxide, enabling the electrodes to demonstrate excellent selective adsorption capacity and significant desalination efficiency in the removal of calcium and magnesium ions from brackish water, effectively reducing the salt concentration in the water.

[0038] like Figure 1 As shown, the capacitive deionization device includes a glass plate 1, a silicone sheet 2, a current collector 3, and a plastic spacer 4, wherein the positive electrode and the negative electrode are respectively located on the current collector 3 on both sides.

[0039] In practical applications, regeneration can be achieved by short-circuiting the positive and negative electrodes after electrical adsorption.

[0040] A fourth embodiment of the present invention proposes the use of a capacitive deionization device in brackish water desalination, wherein the capacitive deionization device is used to selectively adsorb calcium and magnesium ions in the brackish water.

[0041] It should be noted that brackish water refers to water containing high concentrations of soluble salts (such as chlorides and sulfates) and hardness ions (calcium and magnesium). The salts in brackish water not only affect the water's hardness but also impart a distinctly bitter and salty taste. Its total dissolved solids (TDS) content is typically above 1000 ppm, significantly higher than that of ordinary drinking water. Cations in brackish water include calcium, magnesium, sodium, and potassium, while anions include chloride, nitrate, and sulfate. Calcium and magnesium are the primary ions that need to be removed.

[0042] The capacitive deionization device of the embodiment of the present invention has a high adsorption capacity for calcium and magnesium ions in brackish water, effectively solving the problem of capacity limitation when using carbon materials as electrodes. It has strong universality, simple operation, and does not require the addition of ion exchange membranes.

[0043] In some embodiments, the positive and negative voltages of the capacitive deionization device are between 0.8 and 1.8 V, allowing for the maximum and stable adsorption of calcium and magnesium ions. If the voltage is lower than 0.8 V or higher than 1.8 V, the adsorption of calcium and magnesium ions decreases.

[0044] Unless otherwise specified, the experimental materials and reagents used in the above examples can be obtained from commercial sources. If no specific techniques or conditions are specified in the examples, they can be carried out according to the techniques or conditions described in the literature in the field or according to the product instructions.

[0045] In the present invention, the term "some embodiments" and the like means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment. Moreover, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in any one or more embodiments. In addition, those skilled in the art may combine and combine the different embodiments and features of different embodiments described in this specification unless they are mutually inconsistent.

[0046] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a capacitive deionization electrode for selectively removing calcium and magnesium ions, characterized in that: The steps include: The barium titanate-alumina composite material, a conductive agent, an adhesive, and NMP are mixed and stirred uniformly to form a slurry, wherein the mass ratio of the barium titanate-alumina composite material, the conductive agent, and the adhesive is 80-95:5-10:5-10, and the mass ratio of the volume of NMP to the barium titanate-alumina composite material is 5-7.5 ml:1 g. The slurry is evenly coated on a current collector, allowed to stand at room temperature, and assembled after drying to obtain a capacitive deionization electrode that selectively removes calcium and magnesium ions. The preparation method of the barium titanate-alumina composite material is a one-step solid-phase method. The barium titanate-alumina composite material is in the form of nanoparticles, and the particle size of the nanoparticles is 100-400 nm. The one-step solid phase method includes the following steps: Barium titanate powder and alumina powder are mixed in a mass ratio of 1:2, deionized water is added, and the volume of the deionized water is 20-30% of the total mass of the barium titanate powder and the alumina powder. The mixture is stirred evenly for 30-40 minutes, and then calcined at a calcination temperature of 900-1000°C and a calcination time of 2-3 hours to obtain a barium titanate-alumina composite material.

2. The preparation method according to claim 1, wherein The particle size of the barium titanate-aluminum oxide composite nanoparticles is 250 nm.

3. The preparation method according to claim 1, characterized in that The conductive agent is acetylene black or carbon black, the adhesive is PVDF, PTFE or Nafion, and the current collector is titanium sheet, graphite paper or carbon paper.

4. A capacitor deionization electrode prepared by the preparation method according to any one of claims 1 to 3.

5. A capacitive deionization device comprising a positive electrode and a negative electrode, characterized in that: The negative electrode is the capacitor deionization electrode according to claim 4, and the positive electrode is an electrode using carbon material as an active material.

6. Application of a capacitive deionization device in brackish water desalination, characterized in that: The capacitive deionization device according to claim 5 is used to selectively adsorb calcium and magnesium ions in brackish water.

7. The use according to claim 6, characterized in that The positive and negative pole voltages of the capacitive deionization device are 0.8-1.8V.

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