A carbon-permeated iron @C / N-C composite CDI electrode active material and its preparation and application

Abstract

The present invention belongs to the field of water treatment, and particularly relates to an iron carbide@C / N-C composite CDI electrode active material, which comprises an N-C framework and nano iron carbide@C active particles loaded on the surface of the framework. Among them, the N-C framework is a nitrogen-doped carbon framework with a honeycomb structure; the nano iron carbide@C active particles include an iron carbide core and a nitrogen-doped carbon layer coated on its surface. Among them, the iron carbide core has exposed crystal planes of 201 and 031, and there is an N-Fe chemical bond between it and the nitrogen-doped carbon layer. The present invention also includes the preparation and application of the above-mentioned material. The material of the present invention has excellent CDI performance.

Description

Technical Field

[0001] The present invention belongs to the field of water treatment, and particularly relates to the field of CDI adsorption of water. Background Art

[0002] Metal composite carbon-based materials have attracted more and more attention from scientific researchers due to interface effects, size effects, and structural controllability. In the field of CDI, due to the differences in metals in metal composite carbon materials, the compatibility between the two is poor, and shedding is likely to occur during the cycling process. However, at present, there are few metal elements that can form with carbon (such as iron, tungsten, molybdenum, and zirconium). Due to the low cost, controllable valence state of iron-based materials, and they are widely used as electrode materials in CDI. Therefore, iron is selected as the metal material. Existing iron-based composite materials are often loaded on the surface of carbon-based materials with high specific surface area. This kind of weak interaction force (such as van der Waals force and electrostatic adsorption) causes the iron-based materials to agglomerate on the surface, reducing the exposed area of active metals. Another method is to reduce iron-based ions by a reducing agent to deposit them on the surface of the material. However, due to the difficult control of the rate of redox reaction, large-scale agglomeration of metal materials on the surface often occurs. Further, there are also the following two types of problems in the actual CDI process of such metal-C composite materials; (1) Iron is easily oxidized into an ionic state during the electroadsorption process and agglomerates when reduced again. (2) The binding force between iron and carbon in iron-based materials is poor, resulting in large electron transport resistance. Summary of the Invention

[0003] Aiming at the deficiencies of existing CDI electrode active materials, the first object of the present invention is to provide a carbon-infiltrated iron@C / N-C composite CDI electrode active material with a new concept and a new structural form (the present invention is also called the CDI electrode active material), aiming to improve the CDI adsorption capacity, cycling performance, and selectivity of the material.

[0004] The second object of the present invention is to provide a preparation method of the carbon-infiltrated iron@C / N-C composite CDI electrode active material, aiming to prepare the CDI active material with a special phase, structure and excellent CDI performance.

[0005] The third object of the present invention is to provide a CDI electrode containing the carbon-infiltrated iron@C / N-C composite CDI electrode active material.

[0006] The fourth object of the present invention is to provide a preparation method of the CDI electrode.

[0007] The fifth object of the present invention is to provide an application of the CDI electrode.

[0008] Metallic iron and carbon have poor compatibility, are prone to agglomeration during the preparation process, and are likely to fall off during the use of CDI, which affects the performance of CDI. To address this problem, the present invention provides the following solutions:

[0009] A carbon-doped iron@C / N-C composite CDI electrode active material, comprising an N-C skeleton and nano-carbon-doped iron@C active particles loaded on the surface of the skeleton. Among them, the N-C skeleton is a nitrogen hybridized carbon skeleton with a honeycomb structure;

[0010] The nano-carbon-doped iron@C active particles include a carbon-doped iron core and a nitrogen-doped carbon layer coated on its surface. Among them, the carbon-doped iron core has exposed crystal planes of 201 and 031, and there is an N-Fe chemical bond between it and the nitrogen-doped carbon layer.

[0011] The present invention provides a brand-new material, which uses nitrogen-doped honeycomb carbon as the skeleton, composites nano-carbon-doped iron@C active particles on the surface of the skeleton, and the active particles use the carbon-doped iron phase material with exposed crystal planes of 201 and 031 as the core and nitrogen-doped carbon as the coating layer, and there is a special N-Fe chemical bond between the core and the carbon coating layer. The present invention finds through research that innovatively using the composite of the brand-new phase and structure as CDI adsorption helps to solve the problems of difficult preparation caused by poor Fe-C compatibility, and the unsatisfactory CDI capacity, stability and selectivity.

[0012] In the present invention, the combination of the core crystal plane, phase, N-Fe chemical bond composite mode between the core and the shell of the nano-active particles and the honeycomb structure of the N-C skeleton is the key to synergistically improving the CDI capacity, cycle stability and selectivity of the composite material.

[0013] The nano-carbon-doped iron@C active particles are uniformly and diffusely distributed on the surface of the N-C skeleton;

[0014] Preferably, in the nano-carbon-doped iron@C active particles, the thickness of the nitrogen-doped carbon layer is less than or equal to 10 nm, preferably 1-6 nm;

[0015] Preferably, the particle size of the nano-carbon-doped iron@C active particles is less than or equal to 2-50 nm;

[0016] Preferably, the N-C skeleton and the nitrogen-doped carbon layer of the nano-carbon-doped iron@C active particles contain graphene;

[0017] Preferably, in the carbon-doped iron@C / N-C composite CDI electrode active material, the content of carbon-doped iron is 20-40 Wt.%; the N content is 0.5-10 atm%;

[0018] Preferably, the specific surface area of the carbon-doped iron@C / N-C composite CDI electrode active material is 100-400 m2 / g.

[0019] The present invention also provides a method for preparing the iron carbide@C / N-C composite CDI electrode active material described above. A mixed solution of chitosan, graphene oxide, and an iron salt is subjected to gelation and freeze-drying treatments to obtain a precursor.

[0020] The precursor is subjected to carbonization treatment to prepare the iron carbide@C / N-C composite CDI electrode active material described above.

[0021] Innovatively, in the present invention, chitosan and an iron salt are gelated with the assistance of graphene oxide, and then carbonization treatment is carried out. In this way, it is unexpectedly beneficial to form an iron carbide phase, induce the formation of active nuclei of the said dominant crystal planes, and is also beneficial to form nitrogen-doped ultrathin carbon in-situ encapsulated in the form of N-Fe chemical bonds on its surface. In addition, it can control the grain size and dispersion distribution state of active particles. Moreover, it can simultaneously form a honeycomb-structured N-C skeleton. In the present invention, based on the control of the said preparation method, synergy can be achieved, a new material with a brand-new phase, structure, and crystal plane orientation can be obtained, and the said new material has excellent adsorption capacity, stability, and CDI selectivity in CDI adsorption.

[0022] In the present invention, the iron salt is a water-soluble iron salt; for example, it can be at least one of ferric sulfate, ferric nitrate, ferric chloride, ferric acetate, and ferric citrate.

[0023] Preferably, the weight ratio of chitosan, graphene oxide, and the iron salt is 1:0.01 - 0.6:0.05 - 1, and more preferably 1:0.3 - 0.5:0.1 - 0.2;

[0024] Preferably, the solvent in the mixed solution is water or a mixed solvent of water - organic solvent;

[0025] Preferably, in the initial mixed solution, the concentration of chitosan is 1 - 100 g / L, and more preferably 5 - 20 g / L.

[0026] In the present invention, chitosan and an iron salt are innovatively gelated with the assistance of graphene oxide. In this way, it is unexpectedly beneficial to improve the physical and chemical state of the gel, is beneficial to form an iron carbide phase, induce the said crystal planes, and form active particles with a coating structure modified in the form of N-Fe chemical bonds, improve the dispersion distribution state and composite stability of active particles, and more importantly, is beneficial to improve the CDI adsorption ability of the prepared material.

[0027] In the present invention, the atmosphere in the carbonization stage is a protective gas, and more preferably at least one of nitrogen and inert gas;

[0028] Preferably, the carbonization temperature is 500 to 1000 °C, more preferably 600 to 800 °C, and even more preferably 650 to 750 °C; in the present invention, under the above synthetic preparation idea, further combined with the preferred T1, it is helpful to improve the capacity of the material, especially the CDI capacity at a lower current density, such as a current density less than 100 mA / g, preferably 10 to 50 mA / g, and more preferably 20 to 30 mA / g.

[0029] Preferably, the heating rate of the carbonization temperature during heating is 1 to 15 °C / min; preferably 5 - 10 °C / min.

[0030] Preferably, the carbonization time is 0.3 to 2 h, preferably 0.5 to 1 h.

[0031] The present invention also provides an application of the carbonized iron@C / N-C composite CDI electrode active material described above for capacitive deionization treatment of anions in a salt-containing solution. The application method can adopt the existing methods.

[0032] The present invention also provides a CDI electrode, including a current collector, and an electrode material layer compounded on the surface of the current collector; the active material includes a conductive agent, a binder, and the carbonized iron@C / N-C composite CDI electrode active material.

[0033] Preferably, the current collector is carbon paper, graphite paper, carbon cloth or a titanium plate, and preferably a titanium plate is used as the current collector.

[0034] Preferably, the conductive agent is at least one of acetylene black and conductive carbon black.

[0035] Preferably, the binder is at least one of PVDF and PTFE.

[0036] Preferably, in the electrode material layer, the content of the conductive agent is 1 to 10 wt.%; the content of the binder is 1 to 10 wt.%, and the balance is the carbonized iron@C / N-C composite CDI electrode active material.

[0037] The present invention also provides a preparation method of the CDI electrode described above, by slurrying the conductive agent, the binder, and the carbonized iron@C / N-C composite CDI electrode active material with a solvent to obtain a slurry, and then coating it on the surface of the current collector and drying it to obtain the electrode.

[0038] The total mass of the electrode coated on the current collector is about 45 - 59 mg for each electrode.

[0039] 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, and then sonicated and stirred for 30 minutes to form a homogeneous slurry. 1 mL of the mixed slurry was coated on the current collector and dried overnight at 120 °C to completely remove NMP. The total mass of the electrode coated on the current collector was approximately 45 mg per electrode.

[0040] During the capacitive deionization process (electrosorption), the current density was 20 - 100 mA / g, and the cut-off voltage was 1.2 - 1.6 V.

[0041] Compared with the prior art, the excellent effects of the present invention are as follows:

[0042] 1. The present invention provides a brand-new carbon-infiltrated iron@C / N-C composite CDI electrode active material. Thanks to the combined control of specially oriented carbon-infiltrated iron, N-Fe chemical coating method, and honeycomb-structured N-C skeleton, synergy can be achieved, which can enhance the binding force between iron metal and carbon to reduce the agglomeration phenomenon during high-temperature synthesis, improve the transport and storage performance of anions such as chloride ions, and can synergistically improve the CDI adsorption capacity and stability.

[0043] For example, when the active material is used as a CDI electrode, in an original solution of 500 mg L -1 of Cl - ion solution, at a current density of 10 mA / g, it shows an electroadsorption capacity of 82.08 mg / g for Cl - ions. At the same time, when cycled 50 times at a current density of 100 mA, the performance only decays by 25.8%, which is much higher than 99% of iron oxide.

[0044] 2. Aiming at the preparation problems of the new material of the present invention, such as being difficult to form the carbon-infiltrated iron phase, difficult to obtain the exposure of dominant crystal planes, difficult to achieve the N-Fe chemical coating structure, easy to agglomerate, and the CDI performance of the prepared material being not ideal, the present invention innovatively adopts the coordination gelation of chitosan-iron assisted by graphene oxide, and then combines with carbonization treatment. In this way, the carbon-infiltrated iron active particles with special crystal plane exposure coated by the N-Fe chemical method can be formed in one step, which helps to control the grain size, phase purity, and dispersion distribution stability. Moreover, a honeycomb-structured carbon skeleton can be formed synchronously. The method of the present invention can obtain a brand-new material, and the brand-new material has excellent CDI performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1Materials-related measurements and electrochemical performance diagrams for Example 1, where (a, b, and c) are SEM images of Fe3C@GNC; (d, e, and f) are TEM images of Fe3C@GNC; (g) is the XRD pattern of Fe3C@GNC; (h) is the Raman spectrum of Fe3C@GNC; (i, j, k, and l) are the TEM, EDS (Fe), EDS (N), and EDS (C) of Fe3C@GNC respectively, (m) is the BET diagram of Fe3C@GNC; (n) is the pore size test diagram, (o) is the thermogravimetric diagram of Fe3C@GNC, and (p, q, and r) are the survey spectrum, Fe 2p, and N1s spectra of the XPS of Fe3C@GNC;

[0046] Figure 2 Measurements related to Fe3C@GNC-600 prepared in Example 2, where (a) is the XRD pattern of Fe3C@GNC-600; (b and c) are SEM images of Fe3C@GNC-600; (d) is the Raman spectrum of Fe3C@GNC-600; (e and f) are the BET diagrams of Fe3C@GNC-600; (g) is the thermogravimetric diagram of Fe3C@GNC-600;

[0047] Figure 3 Measurements related to Fe3C@GNC-800 prepared in Example 3, where (a) is the XRD pattern of Fe3C@GNC-800; (b and c) are SEM images of Fe3C@GNC-800; (d) is the Raman spectrum of Fe3C@GNC-800; (e and f) are the BET diagrams of Fe3C@GNC-800; (g) is the thermogravimetric diagram of Fe3C@GNC-800;

[0048] Figure 4 Materials-related measurements and electrochemical performance diagrams for Comparative Example 1; where (a, b, and c) are SEM images of Fe x NFe@NC; (d, e, and f) are TEM images of Fe x NFe@NC; (g) is the XRD pattern of Fe x NFe@NC; (h) is the Raman spectrum of Fe x NFe@NC; (i and j) are the BET diagrams of Fe x NFe@NC; (k, l, m, and n) are the survey spectrum, Fe 2p, C 1s, and N1s spectra of the XPS of Fe x NFe@NC;

[0049] Figure 5Relevant measurement diagrams of the material prepared in Comparative Example 2, where (a, b, and c) are SEM diagrams of GNC; (d, e, and f) are TEM diagrams of GNC; (g) is the XRD diagram of GNC; (h) is the Raman diagram of GNC; (i and j) are BET diagrams of GNC; (k, l, m) are survey spectra of XPS of GNC, C1s and N1s diagrams;

[0050] Figure 6 Identification diagrams of the material prepared in Comparative Example 3, where diagrams (a, b, and c) are SEM diagrams of NC; (d) is the XRD diagram of NC; (e) is the Raman diagram of NC; (f) is the BET diagram of NC;

[0051] Figure 7 Electrochemical performance diagrams of Examples 1 to 3, (a) cyclic voltammogram of Fe3C@GNC; (b) galvanostatic charge-discharge diagram of Fe3C@GNC; (c and d) electrochemical impedance spectroscopy diagrams of Fe3C@GNC; (e) cyclic voltammogram of Fe3C@GNC-600; (f) galvanostatic charge-discharge diagram of Fe3C@GNC-600; (g and h) electrochemical impedance spectroscopy of Fe3C@GNC-600; (i) cyclic voltammogram of Fe3C@GNC-800; (j) galvanostatic charge-discharge diagram of Fe3C@GNC-800; (k and l) electrochemical impedance spectroscopy of Fe3C@GNC-800;

[0052] Figure 8 Electrochemical performance diagrams of the comparative examples, (a) cyclic voltammogram of GNC; (b) galvanostatic charge-discharge diagram of GNC; (c and d) electrochemical impedance spectroscopy diagrams of GNC; (e) cyclic voltammogram of FexNFe@NC; (f) galvanostatic charge-discharge diagram of FexNFe@NC; (g and h) electrochemical impedance spectroscopy of FexNFe@NC; (i) cyclic voltammogram of NC; (j) specific capacitance values of NC under different current density conditions; (k) electrochemical impedance spectroscopy of NC;

[0053] Figure 9 Cycling performance diagrams of Fe3C@GNC prepared in Example 1 and commercial Fe2O3 Detailed implementation manners

[0054] The present invention will be further described in detail below in combination with the detailed implementation manners, so that the purpose, technical solutions and advantages of the present invention become clearer. It should be understood that the description presented here is only a preferred example for illustrative purposes to explain the present invention and does not constitute a limitation to the present invention. In actual 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.

[0055] In the following examples, the experimental methods described are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0056] Example 1

[0057] First, 0.5000 g of chitosan was dissolved in 50 mL of 2% acetic acid aqueous solution, 1 mL of 1 M Fe(NO3)3 solution was added, and then 50 mg of graphene oxide was added. After stirring for 2 h to form a uniform gel, it was then placed in a refrigerator at -85 °C for freeze-drying; the freeze-dried sample was placed in an alumina crucible, and argon was continuously introduced for 30 min. The heating rate in the heating program was 5 °C / min to heat to 700 °C (the heating end temperature, marked as T1). After holding for 1 h, it was cooled to room temperature. After rinsing three times with pure water and alcohol respectively, it was placed in a vacuum drying oven at 60 °C and dried for 6 h. The prepared sample was named Fe3C@GNC. The material characterization and electrochemical performance characterization of the prepared materials are shown in Figure 1 and Figure 7 (a-d).

[0058] The specific surface area of nitrogen adsorption and desorption is 268.20 m 2 / g, and the iron content is 26.03%. From the attachment Figure 1 , it can be seen that the Fe3C@GNC material is mainly a composite structure of carbon-encapsulated iron carbide infiltrated with carbon ([ Figure 1 as shown in a, b, c, d, e and f). Figure 1 When the pore size was measured as shown in n, it was found that the pore size was mainly concentrated in 4.16 and 3.93 nm, which was beneficial to the migration and diffusion of chloride ions inside the carbon layer. At the same time, it was found that adding graphene oxide could effectively change the crystal plane curve of iron carbide; the exposed crystal planes of Fe3C with added graphene oxide were mainly (201) and (031) crystal planes. This preferred crystal plane orientation might improve its CDI performance; and there were Fe-N and Fe-C covalent bonds that could fix the material and prevent the material from agglomerating, thereby improving the cycling performance of this type of material.

[0059] Figure 1 In, Fe3C@GNC refers to the product after the treatment of Example 1. It can be clearly found that the material is a composite structure of carbon-encapsulated iron carbide infiltrated with carbon. Overall, the material is composed of ellipsoidal particles, and the surface layer of the iron carbide infiltrated with carbon material is coated with a 5-nm carbon layer. Through the elemental scanning of TEM, it was found that the signals of iron elements and carbon elements overlapped. Further indicating that a carbon-coated iron carbide infiltrated with carbon material was formed after carbonization. Combining Figure 1 (a-l) shown, highly dispersed honeycomb carbon-encapsulated iron carbide infiltrated with carbon nanoparticles have been successfully synthesized; combining Figure 1 shown (p, q and r), there is an Fe-N bond in the nitrogen splitting peak, and there is Fe 3+ and Fe 2+The key is that there is a heterojunction structure of Fe-N bonds between the carbonized iron nanoparticles and the carbon layer. According to cyclic voltammetry and galvanostatic charge-discharge, its adsorption mechanism is a redox reaction, as Figure 7 (a-d) shows.

[0060] Example 2

[0061] Compared with Example 1, the only difference is that T1 is changed to 600 °C. Other operations and parameters are the same as in Example 1. The material characterization and electrochemical performance characterization of the prepared materials are shown in Figure 2 and Figure 7 (e-h).

[0062] The prepared sample is named Fe3C@GNC-600. Its specific surface area by nitrogen adsorption and desorption is 200.65 m 2 / g, and the iron content is 26.03%; from the attachment Figure 2 , it can be seen that the Fe3C@GNC-600 material is mainly a composite structure of carbonized iron supported by honeycomb carbon ( Figure 2 shown). Figure 2 (When measuring the pore size in (e and f), it is found that the pore size is mainly concentrated at 4.16 and 3.93 nm, which is conducive to the migration and diffusion of chloride ions inside the carbon layer; compared with Example 1, in terms of morphology, both are composite structures of carbonized iron supported by honeycomb carbon, but as the temperature decreases, it can be more obvious that the particle size of the carbonized iron particles coated with the carbon layer decreases, but the graphitization degree of carbon is lower and the oxygen content is higher, Figure 2 as shown in d. According to cyclic voltammetry and galvanostatic charge-discharge, its adsorption mechanism is a redox reaction, as Figure 7 (e-h) shows.

[0063] Example 3

[0064] Compared with Example 1, the only difference is that the temperature of T1 is 800 °C. Other operations and parameters are the same as in Example 1. The prepared sample is named Fe3C@GNC-800. The material characterization and electrochemical performance characterization of the prepared materials are shown in Figure 3 and Figure 7 (i-l).

[0065] Its specific surface area by nitrogen adsorption and desorption is 286.42 m 2 / g, and the iron content is 34.27%; from the attachment Figure 3 it can be seen that the Fe3C@GNC-800 material is mainly a composite structure of carbonized iron supported by honeycomb carbon ( Figure 3 shown). Figure 3When measuring the pore size, it was found that the pore size was mainly concentrated at 4.16 and 3.93 nm, which was beneficial to the migration and diffusion of chloride ions inside the carbon layer. Compared with Example 1, in terms of morphology, both were composites of honeycomb carbon supported carbon infiltrated with iron. However, as the temperature increased, it could be clearly seen that the particle size of the iron particles increased. According to cyclic voltammetry and galvanostatic charge-discharge, the adsorption mechanism was a redox reaction, as shown in Figure 7 (i-l).

[0066] Comparative Example 1

[0067] Compared with Example 1, the only difference was that graphene oxide was not added, and other operations and parameters were the same as those in Example 1. The prepared sample was named FexNFe@NC (also named Fe x NFe@NC-700). The characterization of the prepared materials and the electrochemical performance characterization are shown in Figure 4 and Figure 8 (e-h).

[0068] It was found experimentally that the gel morphology used was inferior to that of Example 1, and a high-purity carbon infiltrated with iron phase and an active coating structure of the N-Fe chemical form were not obtained. The various tests are shown in Figure 4 . In the case of not adding graphene oxide, its metal was composed of a composite of Fe and Fe3C, and the exposed crystal planes were mainly 122 and 200, as shown in Figure 4 f; according to cyclic voltammetry and galvanostatic charge-discharge, the adsorption mechanism was a redox reaction, as shown in Figure 8 (e-h).

[0069] Comparative Example 2

[0070] Compared with Example 1, the difference was that ferric nitrate was not added, and other operations and parameters were the same as those in Example 1. The prepared sample was named GNC. The characterization of the prepared materials and the electrochemical performance characterization are shown in Figure 5 and Figure 8 (a-d).

[0071] The specific surface area of nitrogen adsorption and desorption was 27.74 m 2 / g; from Figure 5 (k-m), it could be seen that the surface of the GNC material was composed of C, N, and O elements, and it was a composite structure of honeycomb carbon supported carbon infiltrated with iron, but it did not have the active particles as described in Example 1 ( Figure 5 shown). According to cyclic voltammetry and galvanostatic charge-discharge, the adsorption mechanism was a double-layer reaction, as shown in Figure 8 (a-d).

[0072] Comparative Example 3

[0073] Compared with Example 1, the difference is only that chitosan is used as the raw material, and Go and iron nitrate are omitted. Other operations and parameters are the same as those in Example 1. The prepared sample is named NC. For the material characterization and electrochemical performance characterization of the prepared materials, see Figure 6 and Figure 8 (i-k).

[0074] The specific surface area of nitrogen adsorption and desorption is 27.74 m 2 / g; From the attachment Figure Six , it can be seen that the surface of the NC material is composed of C, N, and O elements, and the nitrogen-doped carbon is a bulk powder ( Figure 6 as shown); According to cyclic voltammetry and galvanostatic charge-discharge, its adsorption mechanism is a double-layer reaction, as Figure 8 (i-k) shown.

[0075] Application Example 1

[0076] Electrochemical tests were carried out on the biochar materials prepared in Example 1 above. The specific operation process is as follows: 8 mg of Example 1 (Fe3C@GNC), Example 2 (Fe3C@GNC-600), Example 3 (Fe3C@GNC-800), Comparative Example 1 (Fe x NFe@NC), Comparative Example 2 (GNC) or Comparative Example 3 (NC) were respectively mixed with 1 mg of conductive carbon black and 1 mg of PVDF as a binder and dissolved in 1 mL of NMP, and then ultrasonically treated and stirred for 30 minutes to form a uniform slurry. Then, 100 μL of the mixed slurry was coated on a 1×1 cm 2 graphite paper and dried overnight at 120 °C. The prepared electrode was placed in a 0.5 mol / L NaCl electrolyte solution, with a graphite rod as the counter electrode and silver / silver chloride as the reference electrode, and electrochemical tests were carried out using a three-electrode test method.

[0077] The cyclic voltammograms of the three porous carbon materials were obtained at a scanning rate of 10 mV / s. The CV curve of the electrode at a scanning rate of 10 mV / s showed redox peaks, indicating that Example 1 (Fe3C@GNC), Example 2 (Fe3C@GNC-600), and Example 3 (Fe3C@GNC-800) belong to the redox process during the adsorption and desorption process, as Figure 7 shown; Comparative Example 1 (FexNFe@NC) belongs to the redox process during the adsorption and desorption process, as Figure 8 (e-h); The adsorption process of Comparative Example 2 (GNC) or Comparative Example 3 (NC) is double-layer adsorption, as Figure 8 (a-d) and Figure 8 (i-k)

[0078] Application Example 2

[0079] 80 wt% of Example 1 (Fe3C@GNC), Example 2 (Fe3C@GNC-600), Example 3 (Fe3C@GNC-800), Comparative Example 1 (Fe x NFe@NC), Comparative Example 2 (GNC), or Comparative Example 3 (NC), 10 wt% acetylene black, and 10 wt% PVDF were dissolved in 2 mL of NMP, and then sonicated and stirred for 30 minutes to form a homogeneous slurry. 1 mL of the mixed slurry was coated on the current collector and dried overnight at 120 °C. The resulting CDI electrode was assembled into a CDI unit, and a certain external voltage was applied between the positive and negative electrodes. The salt solution to be treated was pumped into the CDI unit through a peristaltic pump for capacitive deionization testing. The voltage in the CDI device was controlled at 1.0, 1.2, and 1.4 V, and the flow rate of the NaCl salt solution was 10 mL / min. The initial concentration of Cl - was 500 mg / L. As shown in Table 1. The material properties of Fe3C@GNC synthesized at a temperature within the preferred range are better.

[0080] Table 1

[0081]

[0082] In summary, it can be seen that the preparation method described in the present invention can utilize the honeycomb carbon-supported nano-carbon iron-permeated composite material to construct a material with a special physical and chemical structure, and the material can unexpectedly obtain excellent chloride ion adsorption performance.

[0083] Application Example 3

[0084] Compared with Application Example 2, the difference is only that the Cl - ion concentration and voltage magnitude are changed, and other operations and parameters are the same as in Example 1.

[0085] 80 wt% of Example 1 (Fe3C@GNC), 10 wt% acetylene black, and 10 wt% PVDF were dissolved in 2 mL of NMP, and then sonicated and stirred for 30 minutes to form a homogeneous slurry. 1 mL of the mixed slurry was coated on the current collector and dried overnight at 120 °C. The resulting CDI electrode was assembled into a CDI unit, and a certain external voltage was applied between the positive and negative electrodes. The salt solution to be treated was pumped into the CDI unit through 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 of Cl - was 100, 300, and 500 mg / L. As shown in Table 2. The material properties of Fe3C@GNC synthesized at a temperature within the preferred range are better.

[0086] Table 2

[0087]

[0088] In summary, in the preparation method of the present invention, the concentration and voltage affect the adsorption performance of the material. As the concentration and voltage increase, the adsorption capacity of the material increases.

[0089] Application Example 4

[0090] Compared with Application Example 2, the only difference is that the voltage type is changed, and other operations and parameters are the same as those in Example 1.

[0091] 80 wt% of Example 1 (Fe3C@GNC) or Comparative Example 3 (NC), 10 wt% of acetylene black and 10 wt% of PVDF were dissolved in 2 mL of NMP, and then sonicated and stirred for 30 minutes to form a homogeneous slurry. 1 mL of the mixed slurry was coated on the current collector and dried overnight at 120 °C. The obtained CDI electrode was assembled into a CDI unit, and a certain external voltage was applied between the positive and negative electrodes. The salt solution to be treated was transported into the CDI unit by a peristaltic pump for capacitive deionization testing. The current density in the CDI device was controlled to be 10, 20, 30, 50, 100 mA / g, and the flow rate of the NaCl salt solution was 10 mL / min, and the initial concentration of Cl - was 100, 300, and 500 mg / L. As shown in Table 3. The material properties of Fe3C@GNC synthesized at a temperature within the preferred range are better.

[0092] Table 3

[0093]

[0094]

[0095] In summary, the material prepared by the present invention can also have a large adsorption capacity under different current density conditions.

[0096] Application Example 5

[0097] Dissolve 80 wt% of Fe3C@GNC (prepared in Example 1) or commercial iron oxide, 10 wt% of acetylene black, and 10 wt% of PVDF in 2 mL of NMP, and then ultrasonically treat and stir for 30 minutes to form a homogeneous slurry. Coat 1 mL of the mixed slurry on the current collector and dry it overnight at 120 °C. Assemble the obtained CDI electrode into a CDI unit, apply a certain external voltage between the positive and negative electrodes, and pump the salt solution to be treated into the CDI unit through a peristaltic pump for capacitive deionization testing. Control the current density in the CDI device at 100 mA / g, the cut-off 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. As Figure 9 . The cycling performance of the synthesized carbon-based material is improved to a great extent.

Claims

1. Application of a carbon-permeated iron @C / N-C composite CDI electrode active material, characterized in that Anion capacitive deionization treatment for saline solutions; The carbon-infiltrated iron@C / N-C composite CDI electrode active material described above includes an N-C framework and nano-carbon-infiltrated iron@C active particles loaded on the surface of the framework. Among them, the N-C framework is a nitrogen-doped carbon framework with a honeycomb structure; The nano-carbon-infiltrated iron@C active particles include a carbon-infiltrated iron core and a nitrogen-doped carbon layer coated on its surface. Among them, the carbon-infiltrated iron core has exposed crystal planes of 201 and 031, and there is an N-Fe chemical bond between it and the nitrogen-doped carbon layer.

2. The application according to claim 1, wherein The nano-carbon-infiltrated iron@C active particles are uniformly dispersed on the surface of the N-C framework; In the nano-carbon-infiltrated iron@C active particles, the thickness of the nitrogen-doped carbon layer is less than or equal to 10 nm; The particle size of the nano-carbon-infiltrated iron@C active particles is less than or equal to 2 - 50 nm; The N-C framework and the nitrogen-doped carbon layer of the nano-carbon-infiltrated iron@C active particles contain graphene. In the carbon-infiltrated iron@C / N-C composite CDI electrode active material, the content of carbon-infiltrated iron is 20 - 40 Wt.%; the N content is 0.5 - 10 atm%; The specific surface area of the carbon-impregnated iron @C / N-C composite CDI electrode active material is 100 - 400 m 2 / g.

3. The application according to claim 1, characterized in that, The preparation method of the carbon-infiltrated iron@C / N-C composite CDI electrode active material described above is: subjecting a mixed solution of chitosan, graphene oxide, and iron salt to gelation and freeze-drying treatments to obtain a precursor; Subjecting the precursor to carbonization treatment to obtain the carbon-infiltrated iron@C / N-C composite CDI electrode active material.

4. The application according to claim 3, wherein The iron salt is a water-soluble iron salt.

5. The application according to claim 3, characterized in that The weight ratio of chitosan, graphene oxide, and iron salt is 1:0.01 - 0.6:0.05 - 1.

6. The application according to claim 3, characterized in that The solvent in the mixed solution is water or a mixed solvent of water - organic solvent; In the initial mixed solution, the concentration of chitosan is 1 - 100 g / L.

7. The application according to claim 3, wherein The atmosphere in the carbonization stage is a protective gas.

8. The application according to claim 3, characterized in that, The carbonization temperature is 500 - 1000 °C.

9. The application according to claim 3, characterized in that, The carbonization temperature is 600 - 800 °C.

10. The application according to claim 3, wherein The heating rate of the carbonization temperature is 1 - 15 °C / min.

11. The application according to claim 3, wherein The carbonization time is 0.3 - 2 h.

12. A CDI electrode, characterized in that, It includes a current collector and an electrode material layer compounded on the surface of the current collector; the active material includes a conductive agent, a binder, and the carbon-infiltrated iron@C / N-C composite CDI electrode active material described in any one of claims 1 - 11.

13. The CDI electrode according to claim 12, wherein, The current collector is carbon paper, graphite paper, carbon cloth, or titanium plate; The conductive agent is at least one of acetylene black and conductive carbon black; The binder is at least one of PVDF and PTFE.

14. The CDI electrode according to claim 13, wherein, In the electrode material layer, the content of the conductive agent is 1 - 10 wt.%; the content of the binder is 1 - 10 wt.%, and the balance is the carbon-infiltrated iron@C / N-C composite CDI electrode active material.

15. A method for preparing the CDI electrode according to any one of claims 12 to 14, characterized in that, Pulp the conductive agent, binder, and carbon-infiltrated iron@C / N-C composite CDI electrode active material with a solvent to obtain a slurry, and then coat it on the surface of the current collector and dry it to obtain.

16. Use of the CDI electrode according to any one of claims 12 to 14, characterized in that, For the capacitive deionization treatment of anions in salt solutions.

17. The application of the CDI electrode according to claim 16, characterized in that, During the capacitive deionization treatment, the current density is 20 - 100 mA / g, and the cut-off voltage is 1.2 - 1.6 V.

18. The application of the CDI electrode according to claim 16 or 17, characterized in that, The anion in the salt solution is Cl - , NO3 - , SO4 2- and at least one of them.

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