A CDI electrode active material and preparation and use thereof

Abstract

The application belongs to the technical field of desalination of salt-containing solution, and particularly relates to a CDI electrode active material, which is a carbon nanogrid-coated nanobismuth material, wherein the carbon nanogrid is an oxocarbon material with an atomic level thickness, and an O-Bi chemical bond exists between the carbon nanogrid and the nanobismuth; in the CDI electrode active material, the weight content of bismuth is 92-97%. The application further provides a preparation method of the material, wherein a C1-C3 bismuth carboxylate is heated to a temperature T1, and the CDI electrode active material is prepared through carbonization; the T1 is 350-850 DEG C. The application further provides application of the material in CDI. The material has excellent CDI capacity and selectivity.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical capacitor deionization, and specifically relates to the preparation of an electrode active material. Background Technology

[0002] Chloride ions are widely present in wastewater discharged from industries such as chemical, food, and metallurgy. High concentrations of chloride ions can corrode equipment and pipes, severely impact crops, and even affect drinking water sources through leaching. Among the many technologies for removing chloride ions, including traditional adsorption, chemical methods, electrodialysis, and membrane separation, capacitive deionization (CDI) is a commonly used technique. However, the excessive addition of reagents in chemical precipitation and the expensive membranes in electrolysis make these technologies unsuitable. CDI is an emerging, energy-efficient seawater desalination technology based on the principle of storing charged cations and anions using two electrodes under electrical drive. It provides an effective method for removing chloride ions from brine.

[0003] Typically, charge-displacement distillation (CDI) is an electroadsorption method that captures chloride ions by forming an electrical double layer on carbon materials. However, the poor capacitance of conventional carbon materials limits their electroadsorption capacity (approximately 5-10 mg / g) and removal efficiency during desalination. In most cases, employing high charge-transfer Faraday electrodes to enhance chloride ion adsorption performance has become a primary method for efficient chloride ion removal. Ag / AgCl has been explored as a charge storage material and is frequently used for chloride ion removal due to its strong affinity for chloride ions and high theoretical adsorption capacity. However, the high cost of Ag metals and the poor conductivity of converted AgCl are insufficient for practical application. Recently, Bi metals have been widely used as alternative electrode materials for chloride ion removal in desalination due to their specific binding with Cl-. However, the severe volume expansion (up to ~158%) during the conversion of Bi to BiOCl destroys the active components on the electrode, leading to a rapid decline in performance.

[0004] To overcome this limitation, bismuth-carbon composite materials prepared through interfacial coupling between Bi and the carbon matrix surface can effectively mitigate the loss of Bi particles during electroadsorption. However, due to the weak binding ability of Bi nanoparticles to the carbon matrix, the active components may be lost to varying degrees. Furthermore, existing carbon-coated bismuth materials mainly rely on the composite carbonization of exogenous carbon and bismuth sources. The resulting carbon layer and bismuth composite exhibit unsatisfactory compactness and uniformity, with a relatively thick carbon layer, inhomogeneous bismuth grains, and suboptimal material performance. Summary of the Invention

[0005] To address the shortcomings of existing CDI electrode active materials, the primary objective of this invention is to provide a novel CDI electrode active material with a new concept and structure, aiming to improve the material's electroadsorption performance, cycle performance, and high selectivity.

[0006] The second objective of this invention is to provide a method for preparing the CDI electrode active material, which aims to utilize the characteristics of the raw materials to prepare a new material with a special physicochemical structure and excellent CDI capacity and selectivity in one step through carbonization.

[0007] A third objective of this invention is to provide a CDI electrode containing the aforementioned CDI electrode active material.

[0008] The fifth objective of this invention is to provide a method for preparing the CDI electrode described above.

[0009] The sixth objective of this invention is to provide an application of the aforementioned CDI electrode.

[0010] The main objective of this invention is to solve the problem of CDI adsorption and selectivity of anions in salt solutions. To this end, this invention provides a CDI electrode active material, which is a carbon nanogrid coated with nano-bismuth material. The carbon nanogrid is an oxygen-hybridized carbon material with atomic-level thickness, and there is an O-Bi chemical bond between the carbon nanogrid and the nano-bismuth.

[0011] In the CDI electrode active material, the bismuth content is 92-97% by weight.

[0012] This invention provides a novel material in which atomically scaled carbon nanogrids are coated onto the surface of bismuth nanoparticles. The atomically scaled coating is an ultrathin, oxygen-hybridized layer, and the atomically scaled carbon layer uniformly encapsulates the bismuth nanoparticles and forms O-Bi chemical bonds with them. Applying this novel material with its unique physicochemical structure to CDI effectively improves the CDI adsorption capacity of ions and also helps to improve selectivity.

[0013] In this invention, the carbon layer of the oxygen heteroatom-level nanogate structure and its chemical bonding characteristics with nano-bismuth are key to synergistically improving the capacity and selectivity of the material in terms of CDI.

[0014] In this invention, the carbon nanogrid is tightly coated on the surface of the nano-bismuth;

[0015] Preferably, the thickness of the carbon nanogrid is less than or equal to 10 nm, and more preferably 1 to 6 nm.

[0016] Preferably, the specific surface area of ​​the CDI electrode active material is 4-12 m². 2 / g.

[0017] The present invention also provides a method for using the aforementioned CDI electrode active material, wherein C 1～ The CDI electrode active material is obtained by heating bismuth carboxylate of C3 to temperature T1 (the final heating temperature) and carbonizing it.

[0018] The T1 is 350–850℃.

[0019] Unlike conventional methods of exogenous carbonization following bismuth-carbon source compositing, this invention provides a novel approach to preparing the new material through intrinsic carbon coating. To successfully achieve the intrinsic carbonization preparation of this new material, this invention addresses issues such as controlling the uniformity, tightness, and stability of the atomic-level carbon layer coating, controlling the bismuth grain size, and improving the material's CDI properties. To address these preparation challenges, this invention innovatively employs C... 1～ Bismuth carboxylate of C3 is used as the sole raw material for direct carbonization, thus achieving simultaneous carbonization-reduction and encapsulation. This allows for the construction of atomically-level oxygen-hybridized carbon nanogates, improving the grain size of bismuth particles and enhancing the tightness and chemical stability of the bond between the carbon and bismuth layers. In this invention, based on C... 1～ By combining the carbonization of C3 bismuth carboxylate with the control of T1 temperature, a material with the special physicochemical structure can be obtained, and the material can exhibit excellent CDI capacity, cycle stability and CDI selectivity.

[0020] In this invention, C 1～ The CDI electrode active material is prepared by directly heating the raw material, which is composed of bismuth carboxylate (C3), to T1 and then carbonizing it.

[0021] Preferably, the C 1～ C3 bismuth carboxylate is bismuth acetate. In this invention, bismuth acetate is intrinsically carbonized without the assistance of external components. By further controlling the carbonization temperature, uniform and chemically bonded encapsulation of atomic-level carbon nanogratings can be achieved. It is also possible to control the bismuth grain size and impart appropriate active sites between the particles. This can synergistically improve the CDI capacity and selectivity of the novel material.

[0022] In this invention, C is prepared in advance. 1～ Bismuth carboxylate C3 was dried, ground, and sieved into 200-mesh particles.

[0023] In this invention, C 1～ Bismuth carboxylate of C3 is heated to T1, and intrinsic carbonization of bismuth carboxylate is performed by utilizing the temperature gradient during the heating process. This controls the activity of the layer, the grain size of bismuth, and the chemical bonding ability between the layer and bismuth, thereby improving its CDI performance. The present invention also found that, under the intrinsic heat treatment of bismuth carboxylate, further control of T1 helps to further improve the CDI performance of the material.

[0024] Preferably, T1 is 400–600°C, and more preferably 400–450°C. In this invention, under the intrinsic carbonization concept of bismuth carboxylate, the preferred T1 helps to improve the capacity of the material, especially the CDI capacity and selectivity at lower current densities, such as less than 100 mA / g, preferably 10–50 mA / g, and more preferably 20–30 mA / g.

[0025] Preferably, T1 is 750–800°C. In this invention, under the intrinsic carbonization concept of bismuth carboxylate, further combining it with the preferred T1 helps to unexpectedly improve the CDI capacity of the prepared material at high currents, such as greater than or equal to 100 mA / g, preferably 100–120 mA / g.

[0026] Preferably, the heating rate is 1–15 °C / min, and more preferably 8–12 °C / min.

[0027] Preferably, the atmosphere during the carbonization process is at least one of nitrogen and an inert gas;

[0028] Preferably, the total heating time during the carbonization stage is 0.3 to 2 hours, and more preferably 0.5 to 1 hour.

[0029] This invention also provides an application of the aforementioned CDI electrode active material for capacitive deionization of anions in salt solutions. The application method can employ existing techniques.

[0030] The present invention also provides a CDI electrode, comprising a current collector and an electrode material layer composited on the surface of the current collector; the active material comprises a conductive agent, a binder, and the CDI electrode active material.

[0031] Preferably, the current collector is carbon paper, graphite paper, carbon cloth, or titanium plate, with titanium plate being the preferred current collector.

[0032] Preferably, the conductive agent is at least one of acetylene black and conductive carbon black.

[0033] Preferably, the adhesive is at least one of PVDF and PTFE.

[0034] Preferably, the electrode material layer contains 1-10 wt.% of a conductive agent and 1-10 wt.% of a binder, with the remainder being the CDI electrode active material.

[0035] The present invention also provides a method for preparing the CDI electrode, wherein the conductive agent, binder and CDI electrode active material are slurried with a solvent to obtain a slurry, which is then coated on the surface of the current collector and dried to obtain the final product.

[0036] The total mass of the electrodes coated on the current collector is approximately 45-59 mg per electrode.

[0037] For example: 80 wt% of the active material, 10 wt% of acetylene black, and 10 wt% of PVDF as a binder were dissolved in 2 mL of NMP, then sonicated and stirred for 30 minutes to form a homogeneous slurry. 1 mL of the mixed slurry was coated onto the current collector and dried overnight at 120°C to completely remove the NMP. The total mass of the electrodes coated on the current collector was approximately 45 mg per electrode.

[0038] This invention also provides an application of the aforementioned CDI electrode for capacitive deionization of anions in salt solutions. A preferred application is for removing Cl-containing... - NO3 - SO4 2- Selective electroadsorption of Cl in mixed solutions - .

[0039] During capacitive deionization (electroadsorption), the current density is 20-100 mA / g, and the cutoff voltage is 1.2-1.6V.

[0040] Compared with the prior art, the superior effects of the present invention are:

[0041] 1. This invention provides a novel CDI electrode active material, which benefits from the combination of a special atomic-level oxygen-hybridized carbon nanogrid layer and the chemical bonding between the carbon nanogrid layer and bismuth particles, thereby enhancing the binding force of Bi metal to reduce its volume expansion, improving the compatibility of chloride ions, improving chloride ion transport and storage performance, and synergistically improving the adsorption capacity, stability and selectivity of CDI.

[0042] For example, when the active material is used as a CDI electrode, in the original solution of 500 mg / L -1 Cl - In ionic solutions, at a current density of 20 mA / g, the effect on Cl was observed. - The ions are 110 mg g -1 The electroadsorption capacity was significantly improved. Furthermore, after 50 cycles at a current density of 100 mA, the performance only decreased by 15.61%, far exceeding the 65.07% decrease of commercial bismuth powder. Simultaneously, in a mixed solution of 10 mM NaNO3, 10 mM NaCl, and 10 mM NaSO4, or a solution of 30 mM NaNO3, 30 mM NaCl, and 30 mM NaSO4 at a current density of 100 mA / g, the electroadsorption capacity of Cl- was significantly improved. - It has high selectivity.

[0043] 2. This invention provides a C 1～The novel material is prepared by intrinsic carbonization of C3 carboxylic acids. Furthermore, by jointly controlling the intrinsic carbonization and the carbonization endpoint temperature, a new material with a unique physicochemical structure can be prepared, exhibiting excellent CDI adsorption capacity, cycling stability, and selectivity. Attached Figure Description

[0044] Figure 1 The graph shows the material-related measurements and electrochemical performance of Example 1; Figure 1 (a) XRD pattern of BiAC@C-400; (b and c) SEM images of BiAC@C-400; (d, e and f) HRTEM images of BiAC@C-400; (g, h and i) O1s, Bi 4f and C1s peaks of BiAC@C-400, respectively; (o) BET image of BiAC@C-400; (p) CV image of BiAC@C-400 and (q) CC image of BiAC@C-400;

[0045] Figure 2 The following measurements were performed on BiAC@C-600 prepared in Example 2: (a) XRD pattern of BiAC@C-600; (b and c) SEM images of BiAC@C-600; (d, e and f) HRTEM images of BiAC@C-600; (d) BET image of BiAC@C-600; (e) CV image of BiAC@C-600; and (f) CC image of BiAC@C-600.

[0046] Figure 3 The relevant tests for BiAC@C-800 prepared in Example 3 are shown below: (a) XRD pattern of BiAC@C-800; (b and c) SEM images of BiAC@C-800; (d, e and f) HRTEM images of BiAC@C-800; (d) BET image of BiAC@C-800; (e) CV image of BiAC@C-800; and (f) CC image of BiAC@C-800.

[0047] Figure 4 The XRD patterns of BiNO3@glucose, BiNO3@PmPD and BiNO3@GO prepared for Comparative Example 1 show that all three are metallic bismuth materials.

[0048] Figure 5 SEM images and performance diagrams of BiAC@G-400, BiAC@G-600, and BiAC@G-800 prepared for Comparative Example 2 are shown. In the images, a) are SEM images of BiAC@G-400, c) are performance diagrams of BiAC@G-400, BiAC@G-600, and BiAC@G-800, and d) are thermogravimetric analyses of BiAC@G-400 and BiAC@G-600.

[0049] Figure 6 BiAC@C-400 prepared in Example 1, BiAC@C-600 prepared in Example 2, and BiAC@C-800 prepared in Example 3 were prepared. The Bi particles were commercially available bismuth particles. As the temperature increased, the electrochemical performance generally showed a decreasing trend, but the performance of Example 1 was higher than that of Example 2 and Example 3. The carbon nanogate can play an electron transport role, and the smaller particle size can effectively improve the reaction effect of bismuth.

[0050] Figure 7 The cycling performance graph of BiAC@C-400, prepared in Example 1, compared to commercial Bi particles, clearly shows that its cycling performance is much higher than that of bismuth metal particles. This is attributed to its unique carbon nanogrid coating structure, which effectively alleviates the performance degradation problem caused by the volume expansion of bismuth. Detailed Implementation

[0051] The present invention will be further described in detail below with reference to specific embodiments, so that the objectives, technical solutions and advantages of the present invention will be clearer. It should be understood that the description presented herein is merely a preferred example for illustrative purposes and does not constitute a limitation of the present invention. In practical applications, improvements and adjustments made by those skilled in the art based on the present invention still fall within the protection scope of the present invention.

[0052] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; the reagents and materials described are commercially available unless otherwise specified.

[0053] Example 1

[0054] Bismuth acetate was weighed, ground in a grinder, and sieved through a 200-mesh sieve. The resulting sample was then placed in an alumina crucible, which was placed in a tube furnace. Argon gas was continuously introduced for 30 minutes. The heating program was run at a rate of 10℃ / min, heating to 400℃ (the final heating temperature, denoted as T1), and then cooled to room temperature. The sample was rinsed three times each with pure water and alcohol, and then dried in a vacuum drying oven at 60℃ for 6 hours. The resulting sample was named BiAC@C-400.

[0055] The specific surface area of ​​nitrogen adsorption / desorption is 12.503 m². 2 / g, bismuth content is 93.22%. From the attached... Figure 1 It can be seen that the BiAC@C-400 material is mainly a composite structure of nano-gate carbon coated with nano-bismuth particles. Figure 1 (as shown in b, c, d, e, and f). Figure 1When the pore size was determined as shown in o, it was found that the pore size was mainly concentrated at 1.47, 3.31 and 4.54 nm, which is conducive to the migration and diffusion of chloride ions inside the carbon layer.

[0056] Figure 1 In this text, BiAC@C-400 refers to the product after treatment in Example 1. It is clearly observed that the material is a carbon-coated composite material, with bismuth particles coated by a carbon layer. The material as a whole consists of ellipsoidal particles, with a 5nm carbon layer covering the surface. Elemental scanning using TEM revealed that the signals of bismuth and carbon overlapped. This further indicates that the carbonization of bismuth acetate resulted in carbon-coated bismuth. Combined with... Figure 1 As shown in (g, h, and j), CO bonds are present in the carbon peak and Bi-O bonds are present in the Bi peak, indicating that there is a heterojunction structure of Bi-O bonds between the bismuth nanoparticles and the carbon layer.

[0057] Example 2

[0058] Compared to Example 1, the only difference is that T1 is changed to 600°C. All other operations and parameters are the same as in Example 1. Relevant measurements of the prepared material are shown in [link to relevant data]. Figure 2 .

[0059] The prepared sample was named BiAC@C-600, and its specific surface area under nitrogen adsorption-desorption was 8.456 m². 2 / g, bismuth content is 94.71%; from the attached Figure 2 It can be seen that the BiAC@C-600 material is mainly a composite structure of nano-gate carbon coated with nano-bismuth particles. Figure 2 (As shown). Figure 2 When the pore size was measured, it was found that the pore size was mainly concentrated at 1.47, 3.31 and 4.54 nm, which can facilitate the migration and diffusion of chloride ions inside the carbon layer. Compared with Example 1, in terms of morphology, both are composite materials of carbon nanogrids coated with nano-bismuth particles. However, as the temperature increases, the increase of bismuth particles can be seen more obviously.

[0060] Example 3

[0061] Compared with Example 1, the only difference is that the temperature of T1 is 800℃, and all other operations and parameters are the same as in Example 1. The obtained sample was named BiAC@C-800, and its specific surface area under nitrogen adsorption-desorption was 11.744 m². 2 / g, bismuth content is 96.28%; from the attached Figure 3 It can be seen that the BiAC@C-800 material is mainly a composite structure of nano-gate carbon coated with nano-bismuth particles. Figure 3 (As shown). Figure 3When the pore size was measured, it was found that the pore size was mainly concentrated at 1.47, 3.31 and 4.54 nm, which can facilitate the migration and diffusion of chloride ions inside the carbon layer. Compared with Example 1, in terms of morphology, both are composite materials of carbon nanogrids coated with nano-bismuth particles. However, as the temperature increases, the increase of bismuth particles can be seen more obviously.

[0062] Comparative Example 1

[0063] Compared to Example 1, the only difference is the intrinsic carbonization approach of bismuth acetate; the experimental groups are as follows:

[0064] Group A: Bismuth nitrate and glucose (in a mass ratio of 5:1), the resulting material is labeled BiNO3@glucose;

[0065] Group B: Bismuth nitrate and poly(m-phenylene diamine) (in a mass ratio of 5:1) were used to prepare a material labeled BiNO3@PmPD;

[0066] Group C: Bismuth nitrate and graphene (in a mass ratio of 5:1), the resulting material is labeled BiNO3@GO;

[0067] Specifically, the following steps were taken: Bismuth nitrate and glucose raw materials from group A, or bismuth nitrate and poly(m-phenylenediamine) raw materials from group B, or bismuth nitrate and glucose raw materials from group C, with a mass ratio of 5:1, were ground in a grinder and sieved through a 200-mesh sieve. The mixture was then placed in an alumina crucible, and the crucible containing the sample was placed in a tube furnace. Argon gas was continuously introduced for 30 minutes. The heating rate in the heating program was 10℃ / min, with a termination temperature of 400℃, followed by cooling to room temperature. After rinsing three times each with pure water and alcohol, the samples were placed in a vacuum drying oven at 60℃ and dried for 6 hours. The resulting samples were named BiNO3@glucose, BiNO3@PmPD, and BiNO3@GO. Figure 4 (As shown).

[0068] Comparative Example 2

[0069] Compared to Example 1, the only difference is the addition of graphene as a carbon additive, as follows: Bismuth acetate and graphene were weighed in a mass ratio of 5:1, ground in a grinder, and sieved through a 200-mesh sieve. The mixture was then placed in an alumina crucible, which was placed in a tube furnace. Argon gas was continuously introduced for 30 minutes. The heating rate in the heating program was 10°C / min, with a termination temperature of 400°C, 600°C, or 800°C, followed by cooling to room temperature. After rinsing three times each with pure water and alcohol, the sample was placed in a vacuum drying oven at 60°C and dried for 6 hours. The resulting sample was named BiAC@G-400, BiAC@G-600, or BiAC@G-800; the bismuth content of BiAC@G-400 was 70.54%; the bismuth content of BiAC@G-600 was 65.47%; from the attached... Figure 5 It can be seen that the BiAC@G-400 material mainly consists of bismuth nanoparticles uniformly grown on graphene sheets. Figure 5 (As shown).

[0070] Comparative Example 3

[0071] Compared to Example 1, the only difference was the addition of graphene as a carbon additive, as follows: Bismuth acetate and graphene were weighed in a mass ratio of 10:1 or 20:1; they were ground in a grinder and sieved through a 200-mesh sieve, then placed in an alumina crucible. The alumina crucible containing the sample was placed in a tube furnace. Argon gas was continuously introduced for 30 minutes. The heating rate in the heating program was 10℃ / min, with a final temperature of 400℃, followed by cooling to room temperature. After rinsing three times each with pure water and alcohol, the samples were placed in a vacuum drying oven at 60℃ and dried for 6 hours. The obtained samples were named BiAC@G-10 and BiAC@G-20.

[0072] Application Example 1

[0073] Electrochemical tests were performed on the biocarbon material prepared in Example 1 above. The specific procedure was as follows: 8 mg of each of Example 1 (BiAC@C-400), Example 2 (BiAC@C-600), or Example 3 (BiAC@C-800) was mixed with 1 mg of conductive carbon black and 1 mg of PVDF as a binder, dissolved in 1 mL of NMP, then sonicated and stirred for 30 minutes to form a homogeneous slurry. 100 μL of the mixed slurry was then coated onto a 1×1 cm... 2 Graphite paper was dried overnight at 120°C. The prepared electrode was placed in a 0.5 mol / L NaCl electrolyte, with a graphite rod as the counter electrode and silver / silver chloride as the reference electrode, and electrochemical tests were performed using a three-electrode method.

[0074] The porous carbon materials obtained from these three materials were subjected to cyclic voltammetry (CV) curves at a scan rate of 10 mV / s. The CV curves of this electrode at a scan rate of 10 mV / s showed redox peaks, indicating that the adsorption-desorption process of these three materials is a redox process. Figure 1 (p), Figure 2 (e) and Figure 3 (e).

[0075] Application Example 2

[0076] Compared with Application Example 1, the only difference is that the active material is changed, while other operations and parameters are the same as in Example 1.

[0077] 80 wt% of BiAC@C-400 (prepared in Example 1), BiAC@C-600 (prepared in Example 2), BiNO3@glucose (prepared in Comparative Example 1), BiNO3@PmPD (prepared in Comparative Example 1), BiNO3@GO (prepared in Comparative Example 1), BiAC@C-800 (prepared in Example 3), 10 wt% acetylene black, and 10 wt% PVDF were dissolved in 2 mL of NMP, then sonicated and stirred for 30 minutes to form a homogeneous slurry. 1 mL of the mixed slurry was coated onto a current collector and dried overnight at 120°C. The resulting CDI electrodes were assembled into a CDI unit. A certain applied voltage was applied between the positive and negative electrodes, and the salt solution to be treated was delivered to the CDI unit via a peristaltic pump for capacitive deionization testing. The current density in the CDI device was controlled at 20, 30, 50, and 100 mA / g, and the flow rate of the NaCl salt solution was 10 mL / min. - The initial concentration was 500 mg / L. For example... Figure 6 See Table 1. BiAC@C materials synthesized at the preferred temperature range exhibit better material properties.

[0078] Table 1

[0079]

[0080]

[0081] Bismuth: 100nm.

[0082] In summary, the preparation method described in this invention can utilize the intrinsic properties of bismuth acetate in conjunction with the carbonization temperature treatment to construct materials with special physicochemical structures, and these materials can unexpectedly acquire excellent chloride ion adsorption properties.

[0083] Application Example 3

[0084] 80 wt% of BiAC@G-400 (prepared in Comparative Example 2), or BiAC@G-600 (prepared in Comparative Example 2), or BiAC@G-800 (prepared in Comparative Example 2), or BiAC@G-10 (prepared in Comparative Example 3), or BiAC@G-20 (prepared in Comparative Example 3), 10 wt% of acetylene black, and 10 wt% of PVDF were dissolved in 2 mL of NMP, then sonicated and stirred for 30 minutes to form a homogeneous slurry. 1 mL of the mixed slurry was coated onto a current collector and dried overnight at 120 °C. The resulting CDI electrodes were assembled into a CDI unit. A certain applied voltage was applied between the positive and negative electrodes, and the salt solution to be treated was delivered to the CDI unit via a peristaltic pump for capacitive deionization testing. The voltage in the CDI device was controlled at 1.4 V, the flow rate of the NaCl salt solution was 10 mL / min, and the Cl... -The initial concentration was 500 mg / L. As shown in Table 2, this indicates that the performance actually decreased after adding exogenous carbon materials.

[0085] Table 2

[0086]

[0087] In summary, the preparation method described in this invention can utilize bismuth acetate for direct carbonization, which results in a greater adsorption capacity than further adding a carbon source.

[0088] Application Example 4 - Selectivity Determination

[0089] 80 wt% BiAC@C-400, 10 wt% acetylene black, and 10 wt% PVDF were dissolved in 2 mL of NMP, then sonicated and stirred for 30 minutes to form a homogeneous slurry. 1 mL of the mixed slurry was coated onto a current collector and dried overnight at 120°C. The resulting CDI electrodes were assembled into a CDI unit. A specific external voltage was applied between the positive and negative electrodes, and the salt solution to be treated was delivered to the CDI unit via a peristaltic pump for capacitive deionization testing. The voltage in the CDI device was controlled at 1.2 V, and the solution was tested at 10 mM Cl. - 10mMNO3 - 5mM SO4 2 - Adsorption properties in solution. See Table 3.

[0090] Using similar test conditions as in Application Example 2, the electroadsorption capacity of each embodiment and comparative example was measured. The test conditions and results are shown in Table 1.

[0091] Table 3 Selective adsorption parameters of BiAC@C-400 electrode.

[0092]

[0093]

[0094] In summary, the preparation method described in this invention utilizes bismuth acetate for direct carbonization, exhibiting a strong adsorption capacity for chloride ions while also possessing a relatively weak adsorption capacity for sulfate ions.

[0095] Application Example 5

[0096] 80 wt% BiAC@C-400 (prepared in Example 1) or commercial bismuth, 10 wt% acetylene black, and 10 wt% PVDF were dissolved in 2 mL of NMP, then sonicated and stirred for 30 minutes to form a homogeneous slurry. 1 mL of the mixed slurry was coated onto a current collector and dried overnight at 120°C. The resulting CDI electrodes were assembled into a CDI unit. A certain applied voltage was applied between the positive and negative electrodes, and the salt solution to be treated was delivered to the CDI unit via a peristaltic pump for capacitive deionization testing. The current density in the CDI device was controlled at 100 mA / g, the cutoff voltage at 1.4 V and -1.4 V, the flow rate of the NaCl salt solution at 10 mL / min, and the initial concentration of Cl- at 500 mg / L. Figure 7 The cycling performance of the synthesized carbon-based materials has been greatly improved.

Claims

1. A CDI electrode active material, characterized in that, The material is a carbon nanogrid coated with bismuth nanoparticles. The carbon nanogrid is an oxygen-hybridized carbon material with atomic-level thickness, and there is an O-Bi chemical bond between it and the bismuth nanoparticles. In the CDI electrode active material, the bismuth content is 92-97% by weight; The method for preparing the CDI electrode active material is characterized in that C 1~ The CDI electrode active material is obtained by heating bismuth carboxylate of C3 to temperature T1 and carbonizing it. The T1 is 350~850℃.

2. The CDI electrode active material as described in claim 1, characterized in that, The carbon nanogrid is tightly coated on the surface of the nano-bismuth; The thickness of the carbon nanogrid is less than or equal to 10 nm; The specific surface area of ​​the CDI electrode active material is 4-12 m². 2 / g.

3. A method for preparing the CDI electrode active material according to claim 1, characterized in that, C 1~ The CDI electrode active material is obtained by heating bismuth carboxylate of C3 to temperature T1 and carbonizing it. The T1 is 350~850℃.

4. The preparation method according to claim 3, characterized in that, The bismuth carboxylate mentioned is bismuth acetate.

5. The preparation method according to claim 3, characterized in that, The atmosphere during the carbonization process is at least one of nitrogen or an inert gas.

6. The preparation method according to claim 3, characterized in that, T1 is 400~600℃; or, T1 is 750~800℃.

7. The preparation method according to claim 3, characterized in that, The heating rate is 1~15℃ / min.

8. The application of the CDI electrode active material according to any one of claims 1-2 or the CDI electrode active material prepared by any one of claims 3-7, characterized in that, Used for deionization treatment of anion capacitors in salt solutions.

9. The application as described in claim 8, characterized in that, Used from Cl - NO3 - SO4 2- Selective electroadsorption of Cl in mixed solutions - .

10. A CDI electrode, characterized in that, It includes a current collector and an electrode material layer composited on the surface of the current collector; the electrode material layer comprises a conductive agent, a binder, and a CDI electrode active material, wherein the CDI electrode active material is the CDI electrode active material according to any one of claims 1 to 2 or the CDI electrode active material prepared by the preparation method according to any one of claims 3 to 7.

11. The CDI electrode as claimed in claim 10, characterized in that, The current collector is made of carbon paper, graphite paper, carbon cloth, or titanium plate; The conductive agent is at least one of acetylene black and conductive carbon black; The adhesive is at least one of PVDF and PTFE; In the electrode material layer, the content of conductive agent is 1~10 wt.%; the content of binder is 1~10 wt.%; and the balance is the CDI electrode active material.

12. A method for preparing a CDI electrode according to claim 10 or 11, characterized in that, The conductive agent, binder, and CDI electrode active material are slurried with a solvent to obtain a slurry, which is then coated on the surface of the current collector and dried to obtain the final product.

13. An application of the CDI electrode according to claim 10 or 11, characterized in that, Capacitive deionization treatment for anions in salt solutions.

14. The application of the CDI electrode as described in claim 13, characterized in that, During the capacitive deionization process, the current density is 20-100 mA / g, and the cutoff voltage is 1.2-1.6 V.

15. The application of the CDI electrode as described in claim 13, characterized in that, The anion in the salt solution is Cl. - NO3 - SO4 2- At least one of them.

16. The application of the CDI electrode as described in claim 15, characterized in that, Used for selective capacitive deionization of Cl from the salt solution - .

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