Carbon fiber composite electrode, preparation method and method for removing chloride ions from raw water

Abstract

This invention discloses a carbon fiber composite electrode, a method for preparing the carbon fiber composite electrode, and a method for removing chloride ions from raw water. The method for preparing the carbon fiber composite electrode includes the following steps: loading a cobalt tetroxide nanoarray onto carbon fibers using a hydrothermal synthesis method; calcining the carbon fibers to form a solid; and then placing the solid on a graphite plate to form a composite electrode.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of water pollution treatment, and particularly relates to a carbon fiber composite electrode, a preparation method of the carbon fiber composite electrode and a method for removing chlorine ions from raw water. BACKGROUND

[0002] At present, the electric adsorption method is to apply a direct current voltage to an electrode, form a double electric layer between the positive and negative electrodes, generate capacitance in water, repeatedly charge and discharge, and make ions be adsorbed on the electrode without chemical reaction.

[0003] In comparison, the electric adsorption method has low processing cost, and only needs a voltage as low as several volts to reach the processing standard, has small energy consumption and low processing cost, and is widely used for removing salt ions in recent years, and has good development prospect.

[0004] The key of the electric adsorption method is the selection of electrode materials. Due to the advantages of economy and chemical stability, porous carbon materials are the first choice of electrode materials, mainly including activated carbon, activated carbon fiber, carbon aerogel, carbon nanomaterials, graphene and the like. SUMMARY

[0005] The inventors found in the process of making the present application that although the activated carbon fiber has a certain electric adsorption effect, the electric resistance and mass transfer resistance are relatively large, the electrode adsorption performance needs to be improved and enhanced, and the effect of removing chlorine ions in reclaimed water is not ideal.

[0006] Therefore, the embodiments of the present application provide a carbon fiber composite electrode, a preparation method of the carbon fiber composite electrode and a method for removing chlorine ions from raw water, which can improve or enhance the effect of removing chlorine ions in reclaimed water.

[0007] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0008] According to one aspect of the present application, a preparation method of a carbon fiber composite electrode is provided, comprising the following steps:

[0009] loading cobalt trioxide nanowire arrays on the carbon fiber by a hydrothermal synthesis method;

[0010] calcining to form a solid;

[0011] setting the solid on a graphite plate to form the carbon fiber composite electrode.

[0012] In some embodiments, the solid is set on the graphite plate to form the carbon fiber composite electrode by conductive glue.

[0013] In some embodiments, the step of loading cobalt trioxide nanowire arrays on the carbon fiber by the hydrothermal synthesis method comprises:

[0014] The active carbon fiber is immersed in a mixed solution prepared from a cobalt salt, an ammonium salt, urea and deionized water and is subjected to hydrothermal treatment in a reaction kettle to load the active carbon fiber with cobaltic oxide and is then dried.

[0015] In some embodiments, the cobalt salt comprises Co(N03)2 6H20, the concentration of Co(N03)2 6H20 is 0.02-0.08 mol / L, the ammonium salt comprises NH4F, the concentration of NH4F is 0.2-0.28 mol / L, the molar ratio of Co(N03)2 6H20, NH4F and urea is 1:1:1, the crystallization temperature of the hydrothermal synthesis method is 80-120°C,

[0016] The calcination is performed at 300-400°C under a protective atmosphere for 2-4 hours.

[0017] According to another aspect of the present application, there is provided a carbon fiber composite electrode, comprising:

[0018] A graphite plate;

[0019] Carbon fibers disposed on the graphite plate, the carbon fibers being loaded with an array of cobaltic oxide nanowires by a hydrolytic synthesis method, wherein the fiber stem of the carbon fibers is wrapped by the nanowires of cobaltic oxide, the cobaltic oxide being in the shape of needle-like nanostructure, the length being 3-5 microns,

[0020] wherein the carbon fiber composite electrode is prepared according to the preparation method of any one of the preceding embodiments.

[0021] According to yet another aspect of the present application, there is provided a method for removing chloride ions from raw water, comprising the following steps:

[0022] (1) taking active carbon fibers as a negative electrode;

[0023] (2) taking a carbon fiber composite electrode prepared according to the preparation method of the carbon fiber composite electrode of any one of the preceding embodiments or a carbon fiber composite electrode according to the preceding embodiments as a positive electrode;

[0024] (3) placing the positive electrode and the negative electrode in an electric adsorption module;

[0025] (4) injecting raw water into the electric adsorption module, connecting the positive electrode and the negative electrode to a power supply and electrifying for a first predetermined time;

[0026] (5) under the action of an electric field, chloride ions in the raw water migrate to the positive electrode and are adsorbed on the positive electrode, and as the enrichment of chloride ions on the positive electrode, chloride ions in the raw water are gradually removed.

[0027] In some embodiments, the raw water is reclaimed water; the activated carbon fiber is an activated carbon fiber which has been pretreated to remove impurities, and the cobalt tetraoxide includes a nanowire array prepared by a hydrothermal synthesis method after a dissolution reaction of cobalt nitrate hexahydrate, ammonium fluoride, urea and deionized water.

[0028] In some embodiments, the method for pretreating the activated carbon fiber to remove impurities is as follows: removing impurities in the activated carbon fiber by acid pickling immersion with dilute nitric acid, and then washing with water and rinsing with ethanol to make the activated carbon fiber neutral, the mass concentration of the dilute nitric acid being 25%, and the acid pickling time being 8 hours.

[0029] In some embodiments, in the step (4), during the chlorion electrosorption, a large number of oxygen-containing functional groups are formed on the surface of the activated carbon fiber after the nitric acid pretreatment, so that the cobalt tetraoxide grows into a dense and compact nanowire array on the activated carbon fiber.

[0030] The power supply is a direct current power supply, the voltage of the power supply is 0-2.5V, the plate spacing of the positive electrode and the negative electrode is 2-15mm, the first predetermined time of power-on is 30-70min, and the number of pairs of the positive electrode and the negative electrode is 2 pairs.

[0031] In some embodiments, the method further comprises, after the step (5):

[0032] detecting whether the positive electrode is saturated in adsorption;

[0033] when it is detected that the positive electrode is saturated in adsorption, the positive electrode and the negative electrode are short-circuited for a second predetermined time to make the chlorion desorb;

[0034] when the short-circuiting reaches the second predetermined time, the power supply is disconnected, and the desorbed chlorion is removed, and the second predetermined time is 10-25min.

[0035] The embodiments of the present application provide a carbon fiber composite electrode, a preparation method thereof and a method for removing chlorion from raw water, which can improve or enhance the effect of removing chlorion from reclaimed water.

[0036] Under the action of electric field, the chloride ions in the raw water migrate to the positive electrode and are adsorbed on the positive electrode, and with the enrichment of the chloride ions on the positive electrode, the chloride ions in the raw water are gradually removed. Due to the strong oxidizing property of nitric acid, the mesoporosity of the activated carbon fiber (ACF) can be enhanced to a certain extent, and the increased number of oxygen-containing functional groups also improves the hydrophilicity of the ACF, thereby improving the electric adsorption efficiency of the activated carbon fiber. Then, Co3O4 is loaded on the activated carbon fiber, and the morphology growth and electrochemical performance thereof are controlled through preparation conditions (such as the concentration of cobalt salt and ammonium salt), the modified ACF grows vertical dense nanowires tightly wrapping the fiber rod, and the needle-like nanostructure is up to 5 μm at the longest, and a larger closed area appears in the cyclic voltammetry curve, and the successfully prepared modified electrode obviously effectively improves the conductivity of the ACF, and due to the priority of the hard base to combine with the hard acid, the specific adsorption function in the electrode adsorption process is enhanced, thereby accelerating the electric adsorption rate of the chloride ions and increasing the electric adsorption capacity of the electrode. BRIEF DESCRIPTION OF DRAWINGS

[0037] These and / or other aspects and advantages of the present application will become apparent and be more readily understood through consideration of the following description, taken in conjunction with the accompanying drawings, in which:

[0038] Figure 1 is a flow chart of a preparation method of a carbon fiber composite electrode according to an embodiment of the present application;

[0039] Figure 2 is a cyclic voltammogram of Co, original ACF, Co3O4 / ACF before and after modification according to an embodiment of the present application;

[0040] Figure 3 is an energy Nyquist diagram of Co, original ACF, Co3O4 / ACF before and after modification according to an embodiment of the present application;

[0041] Figure 4 is an N2 adsorption test diagram of activated carbon fiber ACF before and after pretreatment;

[0042] Figure 5 is a scanning electron microscope diagram of Co3O4 / ACF modified electrode prepared under different ammonium fluoride concentrations;

[0043] Figure 6 is a scanning electron microscope diagram of Co3O4 / ACF modified electrode prepared under different cobalt nitrate hexahydrate concentrations;

[0044] Figure 7 is an N2 adsorption test diagram of ACF electrode material before and after nitric acid pretreatment;

[0045] Figure 8 is an infrared spectrum diagram of Co3O4 / ACF before and after modification and without pretreatment modification;

[0046] Figure 9 is the XRD spectrum of Co304 / ACF before and after modification and without pre-treatment modification;

[0047] Figure 10 (a) and (b) are the chloride ion removal rate and adsorption capacity (plate spacing 10 mm) of Co304 / ACF prepared by the present application before and after modification and without pre-treatment modification;

[0048] Figure 11 is the curve of the chloride ion removal rate of the Co304 / ACF electrode prepared by the present application under different electrode plate spacing;

[0049] Figure 12 is the curve of the chloride ion removal rate of the Co304 / ACF electrode prepared by the present application under different electrode plate spacing. DETAILED DESCRIPTION

[0050] The technical solutions of the present application will be further specifically described below by way of examples in conjunction with the accompanying drawings. In the description, the same or similar reference numerals indicate the same or similar components. The following description of the embodiments of the present application with reference to the accompanying drawings is intended to explain the general inventive concept of the present application, and should not be understood as a limitation of the present application.

[0051] Referring to Figure 1 , a method for preparing a carbon fiber composite electrode according to an embodiment of the present application is provided, comprising the following steps:

[0052] loading a cobalt trioxide nanowire array on the carbon fiber by a hydrothermal synthesis method;

[0053] calcining to form a solid;

[0054] arranging the solid on a graphite plate to form a composite electrode.

[0055] In one embodiment, the calcining is performed in a muffle furnace at a temperature in the range of 300-400°C, for example 350°C. The atmosphere for calcining can be air or a protective atmosphere such as nitrogen. The calcining time is 2-4 hours, for example 3 hours.

[0056] In one embodiment, the solid is arranged on a graphite plate to form a composite electrode by means of conductive glue.

[0057] In one embodiment, the step of loading a cobalt trioxide nanowire array on the carbon fiber by a hydrothermal synthesis method comprises:

[0058] immersing the activated carbon fiber in a solution prepared from a cobalt salt, an ammonium salt, urea and deionized water by a hydrothermal synthesis method and placing it in a reaction kettle for hydrothermal treatment, so as to load cobalt trioxide on the activated carbon fiber, and then drying.

[0059] In one embodiment, the cobalt salt includes any one of Co(N03)2-6H20, cobalt chloride, cobalt sulfate, cobalt acetate. When Co(N03)2-6H20 is used, the concentration of Co(N03)2-6H20 is 0.02-0.08 mol / L. The ammonium salt includes any one of NH4F, ammonium chloride, ammonium nitrate. When NH4F is used, the concentration of NH4F is 0.2-0.28 mol / L. The concentration of urea is 0.28 mol / L. The hydrothermal synthesis method has a crystallization temperature of 80-120 °C.

[0060] Preferably, the concentration of NH4F is 0.24 mol / L, the concentration of Co(N03)2-6H20 is 0.06 mol / L, and the hydrothermal crystallization temperature is 100 °C.

[0061] The preparation method of the present application uses ammonium fluoride as a morphology control agent, uses urea as a precipitant, and controls the optimal loading amount on the surface of the activated carbon fiber by adjusting the concentration of the cobalt salt precursor and the concentration of the ammonium fluoride, thereby forming a nano needle structure. Ammonium fluoride has a very strong irreversible corrosion effect. According to the principle of solid solution re-nucleation by precipitation, in the initial stage of hydrothermal, the cobalt nitrate precursor is precipitated in a block structure under the action of the precipitant and grows on the surface of the activated carbon fiber rod, then forms a complex with cobalt ions under the corrosion of a high enough concentration of fluoride, the cobalt ions are gradually released into the reaction system, and under the action of temperature, a nucleus is reformed on the surface of the activated carbon fiber. A vertical and dense nanowire tightly wraps the fiber rod, and finally grows into a cobalt tetroxide needle array.

[0062] That is, the embodiments of the present application need to control the concentration of ammonium fluoride and the concentration of cobalt nitrate. When the concentration of ammonium fluoride is low, the corrosion effect of fluoride is weak and is not enough to corrode all the block structures, so that only a cubic structure of cobalt tetroxide can be formed in the later stage. When the concentration of ammonium fluoride is too high, the initial precipitated block structure is further accelerated to dissolve, and the nucleation speed of the loaded cobalt tetroxide is too fast in a short time, causing the unevenness of the surface of the carbon fiber. At this time, the Co304 nanowire formed has the tendency to clump and accumulate in a large amount, showing uneven coating. When the concentration of cobalt nitrate is low, the amount of cobalt ions is not enough to form a large amount of tight wrapping. When the concentration of cobalt nitrate is high, it causes a violent reaction when contacting the ACF during the hydrothermal process, forming a large area of accumulated block structure and thus overcoating. Therefore, when Co(N03)2-6H20 and NH4F are used, the concentration of Co(N03)2-6H20 is 0.02-0.08 mol / L, and the concentration of NH4F is 0.2-0.28 mol / L.

[0063] According to another embodiment of the present application, a carbon fiber composite electrode is provided, the carbon fiber composite electrode including:

[0064] Graphite plate

[0065] Carbon fibers disposed on the graphite plate, the carbon fibers being loaded with an array of nanowires of tricobalt tetroxide by a hydrolytic synthesis method, wherein a fiber stem of the carbon fibers is wrapped by the nanowires of tricobalt tetroxide, the tricobalt tetroxide being in a shape of needle-like nanostructure and having a length of 3-5 microns.

[0066] The carbon fiber composite electrode of the embodiment of the present application can be prepared according to the preparation method of the above embodiment.

[0067] According to another embodiment of the present application, a method for removing chloride ions from raw water is provided, comprising the following steps:

[0068] (1) taking activated carbon fibers as a negative electrode;

[0069] (2) taking a carbon fiber composite electrode prepared according to the preparation method of the carbon fiber composite electrode as a positive electrode;

[0070] (3) placing the positive electrode and the negative electrode in an electric adsorption module;

[0071] (4) injecting raw water into the electric adsorption module, connecting the positive electrode and the negative electrode to a power supply and electrifying for a first predetermined time;

[0072] (5) under the action of an electric field, chloride ions in the raw water migrate to the positive electrode and are adsorbed on the positive electrode, and as the enrichment of chloride ions on the positive electrode, chloride ions in the raw water are gradually removed.

[0073] The raw water is reclaimed water; the activated carbon fibers are activated carbon fibers with impurities removed by pretreatment, and the tricobalt tetroxide includes an array of nanowires prepared by a hydrothermal synthesis method after a dissolution reaction of cobalt nitrate hexahydrate, ammonium fluoride, urea and deionized water.

[0074] The method for removing impurities from the activated carbon fibers by pretreatment is: removing impurities in the activated carbon fibers by acid pickling immersion with dilute nitric acid, and then washing with water and ethanol to make the activated carbon fibers neutral, the mass concentration of the dilute nitric acid being 25%, and the acid pickling time being 8 hours (h).

[0075] In the step (4), during the chloride ion electric adsorption process, a large number of oxygen-containing functional groups are formed on the surface of the activated carbon fibers after pretreatment with dilute nitric acid, so that the tricobalt tetroxide grows into a dense and compact array of nanowires on the activated carbon fibers;

[0076] The power supply is a direct current power supply, the voltage of the power supply is 0-2.5V, the distance between the positive electrode and the negative electrode is 2-15mm, the first predetermined time of electrification is 30-70min, and the number of pairs of the positive electrode and the negative electrode is 2 pairs.

[0077] The method after step (5) further comprises:

[0078] detecting at least whether the positive electrode is saturated with adsorption;

[0079] when the positive electrode is detected to be saturated with adsorption, then short-circuiting the positive electrode and the negative electrode for a second predetermined time to desorb the chloride ions;

[0080] when the short-circuiting reaches the second predetermined time, disconnecting the power supply and removing the desorbed chloride ions, and the second predetermined time is 10-25 min.

[0081] Embodiments of the present application provide a preparation method of a carbon fiber composite electrode, which is formed by loading cobalt tetroxide (Co3O4) on activated carbon fiber (ACF) and is denoted as Co3O4 / ACF electrode, wherein the ACF without nitric acid pretreatment is denoted as Co3O4 / ACF-0 after modification, and the ACF with nitric acid pretreatment is denoted as Co3O4 / ACF-1, and both of them are in solid state. Figure 2 is cyclic voltammetry curves of the electrodes before and after modification and pure cobalt under the test conditions of potential window-0.6-1.2V and scanning rate of 10mV·s -1 .

[0082] In this embodiment, the impedance characteristics of the modified ACF are characterized and analyzed by using the alternating current impedance method (EIS), Figure 3 which represents the alternating current impedance spectrum of the Co3O4 / ACF electrode before and after modification and pure cobalt.

[0083] The Co3O4 / ACF provided in this embodiment is that the cobalt tetroxide is loaded on the activated carbon fiber, and the morphology growth and electrochemical performance thereof are controlled by preparation conditions, the modified ACF grows vertical and dense nanowires tightly wrapping the fiber rod, and the longest needle-like nanostructure can reach 5μm, and the cyclic voltammetry curve also has a large closed area, and the maximum specific capacitance is 31.29F / g, and the prepared modified electrode obviously and effectively improves the conductivity of the ACF, and since the hard base preferentially combines with the hard acid, the specific adsorption function in the electrode adsorption process is enhanced, thereby accelerating the ion electric adsorption rate, and the removal rate of chloride ions at adsorption equilibrium is 82.45%.

[0084] In the carbon fiber composite electrode, the fiber rod of the carbon fiber is wrapped by the nanowires of cobalt tetroxide. The cobalt tetroxide has a needle-like nanostructure and a length of 3-5 microns.

[0085] Through test verification, the electric adsorption capacity of the Co3O4 / ACF electrode to chloride ions can reach 27.34mg / g, and the electric adsorption performance has good stability and can maintain a certain adsorption capacity in multiple experiments.

[0086] First, cobalt trioxide nanometer arrays are loaded on carbon fibers by a hydrothermal synthesis method.

[0087] The raw materials for preparing cobalt trioxide nanometer arrays mainly include Co(NO3)2·6H2O, NH4F, urea, and deionized water.

[0088] A certain weight or molar number of Co(NO3)2·6H2O, NH4F, and a certain amount of urea are dissolved in 180 mL of deionized water, and placed on a magnetic stirrer for fully stirring for 30 min to obtain a mixed solution (NH4F can corrode glass, so a plastic container (such as a cup) is used for the reaction). Subsequently, a piece of pretreated activated carbon fiber (about 2.5 g) is immersed in the above mixed solution and transferred to a 250 ml hydrothermal reaction kettle, and after constant temperature at 100℃ in an oven for 12 h, it is naturally cooled to room temperature. The hydrothermal product is sequentially washed with anhydrous ethanol and deionized water and dried, and the obtained product is dried in a blast oven at 100℃ for 8 h to obtain a precursor of Co and ACF.

[0089] Secondly, the activated carbon fiber is immersed in a 25% mass fraction nitric acid solution and placed in a water bath, heated at 30℃ for 8 h, and stirred every 30 min, and after modification, washed with deionized water several times, and then washed with anhydrous ethanol until the modified material shows neutral pH and is dried.

[0090] The activated carbon fiber is a pretreated activated carbon fiber with impurities removed, see Figure 4 , a purified activated carbon fiber, and the N2 adsorption test graph; the method for removing impurities from the activated carbon fiber is to remove impurities in the activated carbon fiber by nitric acid pickling and deionized water ultrasonic washing.

[0091] Furthermore, the activated carbon fiber is immersed in a solution formed by dissolving 6 mmol of cobalt nitrate and 40 mmol of urea in 150 mL of deionized water, and adding different amounts of ammonium fluoride to form 0.12 mol / L, 0.16 mol / L, 0.2 mol / L, 0.24 mmol, and 0.28 mol / L ammonium fluoride solutions, respectively. The activated carbon fiber is dried after hydrothermal synthesis of cobalt trioxide.

[0092] The activated carbon fiber is a cobalt trioxide-loaded activated carbon fiber, see Figure 5 , a morphology graph of the Co3O4 / ACF electrode prepared by modification under different concentrations of ammonium fluoride under scanning electron microscopy;

[0093] Alternatively, the active carbon fibers are respectively immersed in 36 mmol of ammonium fluoride (0.24 mol / L), 40 mmol (0.28 mol / L) of urea dissolved in 150 mL of deionized water, and different amounts of cobalt nitrate hexahydrate are added to prepare 0.02 mol / L, 0.04 mol / L, 0.06 mol / L, and 0.08 mol / L cobalt nitrate solutions, respectively, and the active carbon fibers are hydrothermally synthesized with the tricobalt tetraoxide and then dried.

[0094] The active carbon fibers are active carbon fibers loaded with tricobalt tetraoxide, as shown in Figure 6 The Co3O4 / ACF electrode prepared by modification at different concentrations of cobalt nitrate is shown in the morphology diagram under a scanning electron microscope.

[0095] The application also provides a method for removing chlorine ions in raw water based on the electrode, wherein the raw water is reclaimed water, and the method comprises the following steps:

[0096] In S110, the active carbon fibers are used as a negative electrode; the active carbon fibers are also active carbon fibers with impurities removed by pretreatment, as shown in Figure 7 The purified active carbon fibers are shown in the N2 adsorption test diagram.

[0097] In S120, the Co3O4 / ACF electrode prepared in the foregoing step is used as a positive electrode.

[0098] In S130, the positive electrode and the negative electrode are placed in an electro-adsorption module.

[0099] In S140, a certain amount of raw water is injected into the electro-adsorption module, and the positive electrode and the negative electrode are connected to a power supply and powered for a first predetermined time.

[0100] The power supply is a direct current power supply, the voltage of the power supply is 0-2.5 V, the distance between the positive electrode and the negative electrode is 2-15 mm, and the number of positive electrode-negative electrode pairs is 1-10 pairs; preferably, the voltage is 2 V, the distance between the positive electrode and the negative electrode is 5 mm, and the number of electrode pairs is 2 pairs.

[0101] The length of the power-on time is related to the adsorption capacity of the electrode and the content of chlorine ions in the raw water; in some embodiments, the single treatment volume of the raw water is 800 mL, the concentration of chlorine ions in the raw water is 254 mg / L, and the first predetermined time is 30-70 min, preferably 70 min.

[0102] In S150, under the action of an electric field, the chlorine ions in the raw water migrate to the positive electrode and are adsorbed on the positive electrode, and the chlorine ions in the raw water are gradually removed as the chlorine ions are enriched on the positive electrode.

[0103] The embodiment of the present application loads Co3O4 on activated carbon fiber, controls its morphology growth and electrochemical performance through preparation conditions, and the modified ACF grows vertical and dense nanowires tightly wrapping the fiber rod, and the needle-like nanostructure can reach 5 μm, and the cyclic voltammetry curve also has a large closed area, and the successfully prepared modified electrode significantly improves the conductivity of the ACF. Specifically, the long line structure of the nanowires accelerates the ion adsorption efficiency of the material surface, and the formed crystals also block certain microporous structures, resulting in a hierarchical porous structure, and the mesopores can also promote the rapid penetration of ions, so that the chloride ions fully contact the surface of the ACF; the nanowires grown after modification can reduce the resistance of the material and accelerate the electron transmission rate; the three-dimensional nanostructure grown on the ACF provides good stability, and compared with the original ACF, it is more conducive to maintaining the stability of the results in the process of electric adsorption, and therefore exhibits good regeneration performance. Moreover, since the hard base preferentially combines with the hard acid, the specific adsorption function in the electrode adsorption process is enhanced, so that the chloride ions migrate to the surface of the activated carbon fiber more quickly, thereby accelerating the electric adsorption rate of the chloride ions and increasing the electric adsorption capacity of the electrode.

[0104] In an example, since the strong oxidizing property of nitric acid in the pretreatment can enhance the mesoporosity of the ACF to a certain extent, and the increased number of oxygen-containing functional groups also improves the hydrophilicity of the ACF, it is beneficial for a large amount of cobalt tetroxide load to grow on the activated carbon fiber rod in the form of dense and compact nanoneedles, thereby enhancing the conductivity of the electrode material and improving the electric adsorption efficiency of the activated carbon fiber.

[0105] It can be understood that when the electrode is saturated, it is meaningless to apply electricity again. Therefore, as an optional embodiment, during the process that the chloride ions in the raw water are gradually removed as the chloride ions are enriched on the positive electrode, the method further comprises: detecting whether the positive electrode is saturated at least;

[0106] If the saturation is reached, the positive and negative electrodes are short-circuited for a second predetermined time to make the chloride ions desorb; the second predetermined time is 10-30 min, and preferably, the second predetermined time is 20 min.

[0107] When the short-circuiting reaches the second predetermined time, the power is turned off, and the desorbed chloride ions are removed.

[0108] In the embodiment, after the power is turned off, the desorbed chloride ions are washed away by the raw water, and the flow rate of the raw water is 10-120 mL / min. Preferably, the flow rate of the raw water is 30 mL / min, and the time is 25 min.

[0109] The conductivity meter is used to detect the conductivity of the treated water flowing into the water container from the electric adsorption module, and the removal effect of the chloride ions is judged according to the conductivity.

[0110] The foregoing steps S110 to S150 are repeated to continue removing the chloride ions in the raw water.

[0111] The electrode used in the embodiment of the present application has an increased hydrophilicity and enhanced adsorption effect on polar substances due to the increased acidic functional groups on the surface of the ACF modified by HNO3, which may eventually affect the effect of the electrode on adsorbing and removing chloride. The Co3O4 nanowires grow uniformly and perpendicularly on the surface of the ACF in the form of pine needles, and the unique design of the needle-shaped series has high electrochemical performance and good mesoporous structure.

[0112] It can be proved from the SEM characterization analysis above that the long wire structure of the nanowires accelerates the ion adsorption efficiency on the surface of the material, and the formed crystals also block certain microporous structures, resulting in a hierarchical porous structure. Meanwhile, the mesopores can promote the rapid penetration of ions, so that the chloride ions can fully contact the surface of the ACF, which is also consistent with the N2 adsorption test results. Second, the directly grown nanowire array can ensure good mechanical adhesion and reduce the cost of using a polymer binder and a conductive material, which can also be seen from the electrochemical characterization. The grown nanowires after modification can reduce the resistance of the material, accelerate the electron transmission rate, and improve the electrochemical performance. Third, the three-dimensional nanometer structure grown on the ACF provides good stability, which is more conducive to maintaining the stability of the results in the process of electro-adsorption compared with the original ACF, and therefore exhibits good regeneration performance.

[0113] In order to prove the improvement of the electro-adsorption performance of the Co3O4 / ACF electrode prepared in the embodiment of the present application, the following examples are provided:

[0114] The first group: active carbon fibers with a model number of carbon fiber STF-1300 produced by Jiangsu Sutong Company, and a specific surface area greater than 1048m 2 / g. First, the active carbon fibers are immersed in a 25% nitric acid solution in a water bath, and the cut ACF material is placed in the prepared acid solution. The water bath is heated at 30°C for 8h, and stirred every 30min. After modification, the material is washed with deionized water several times, and then washed with anhydrous ethanol until the modified material shows neutral pH.

[0115] The ACF electrode is attached to the graphite plate with conductive glue, and after the conductive glue is cured for a period of time, the wires are connected to the direct current source for use. In this group of examples, the components of the electrode are active carbon fibers.

[0116] The second group:

[0117] (1) The active carbon fibers with a model number of carbon fiber STF-1300 produced by Jiangsu Sutong Company, and a specific surface area greater than 1048m 2 / g.

[0118] (2) 9 mmol of Co(N03)2-6H20 (0.06 mol / L), 36 mmol of NH4F (0.24 mol / L) and 40 mmol of urea (0.27 mol / L) were weighed and dissolved in 150 mL of deionized water, and placed on a magnetic stirrer for sufficient stirring for 30 min to obtain a mixed solution. Then the pretreated piece of activated carbon fiber (about 2.5 g) was immersed in the above mixed solution and transferred to a 250 ml hydrothermal reactor, and after constant temperature at 100°C for 12 h in an oven, it was naturally cooled to room temperature. The hydrothermal product was washed with anhydrous ethanol and deionized water in turn and dried, and the obtained product was dried in a blast oven at 100°C for 8 h to obtain a precursor of Co and ACF. Finally, the hydrothermally synthesized product was placed in a muffle furnace, heated to 350°C at a heating rate of 5°C / min and kept constant for 3 h to complete the annealing process, and finally the composite material was synthesized and named Co304 / ACF-0.

[0119] (3) The Co304 / ACF electrode was pasted on the graphite plate with conductive glue, and after the conductive glue was cured for a period of time, the wires were connected to the direct current source for standby. In this group of examples, the components of the electrode are activated carbon fiber loaded with cobalt tetroxide.

[0120] Third group:

[0121] (1) The activated carbon fiber with model Jiangsu Sutong Carbon Fiber STF-1300 was selected, and the specific surface area was greater than 1048 m 2 / g. First, the activated carbon fiber was immersed in a 25% mass fraction nitric acid solution in a water bath, and the cut ACF material was placed in the prepared acid solution, heated at 30°C for 8 h in a water bath, and stirred every 30 min. After modification, the modified material was washed with deionized water several times, and then washed with anhydrous ethanol until the pH of the modified material showed neutral.

[0122] (2) 9 mmol of Co(N03)2-6H20 (0.06 mol / L), 36 mmol of NH4F (0.24 mol / L) and 40 mmol of urea (0.27 mol / L) were weighed and dissolved in 150 mL of deionized water, and placed on a magnetic stirrer for sufficient stirring for 30 min to obtain a mixed solution.

[0123] Subsequently, one piece of pretreated activated carbon fiber (about 2.5 g) was immersed in the above mixed solution and transferred into a 250 ml hydrothermal reactor. After being kept in an oven at 100°C for 12 h, the hydrothermal product was naturally cooled to room temperature, washed with absolute ethanol and deionized water in turn and dried. The obtained product was dried in a blast oven at 100°C for 8 h to obtain a precursor of Co and ACF. Finally, the hydrothermally synthesized product was placed in a muffle furnace, heated to 350°C at a heating rate of 5°C / min and kept at 350°C for 3 h to complete the annealing process, and finally the composite material was synthesized and named Co3O4 / ACF-1.

[0124] (3) The Co3O4 / ACF electrode was attached to the graphite plate with conductive glue, and after the conductive glue was cured for a period of time, a wire was connected to a direct current power supply for use. In this group of examples, the components of the electrode were activated carbon fiber loaded with cobalt tetroxide.

[0125] The N2 adsorption performance of the ACF, Co3O4 / ACF-0 and Co3O4 / ACF-1 electrodes prepared in the above groups of experiments was tested, and the specific surface area and pore size distribution were compared, as shown in Table 1. Figure 4

[0126] It can be observed that the materials in the figure all show typical type I isotherms, and the Co3O4 / ACF-1 electrode material has a small hysteresis loop, indicating the presence of mesoporous structures. At a low relative pressure, the isotherm curve of the Co3O4 / ACF-1 electrode material is lower, indicating that the micropore filling phenomenon is reduced, and the micropores of the modified material are reduced. The Co3O4 / ACF-1 electrode material has a H3-type hysteresis loop at the end of adsorption, which is due to the occurrence of microporous and mesoporous capillary condensation, which can be explained by the capillary condensation theory.

[0127] Table 1 Specific surface area and pore size distribution parameters of ACF before and after modification

[0128]

[0129] Table 1 shows the parameters of the pore structure characterization. It can be seen that after the composite material is formed by hydrothermal loading and growth of Co3O4 metal oxide, the BET surface area of the composite material is significantly reduced. The material without nitric acid pretreatment is reduced to 948.34 m 2 / g, and the corresponding pore volume is 0.038 cm 3 / g, and the average pore size is 3.8 nm. The material after nitric acid pretreatment is reduced to 697.02 m 2 / g, and the corresponding pore volume is 0.084 cm 3 / g, and the average pore size is 3.81 nm. It can be seen that the Co3O4 / ACF-1 electrode composite material is mainly mesoporous, and most of the reduction in surface area is also due to the presence of mesopores.​

[0130] From the pore size distribution Figure 4 (b) can also be seen in the peak at 3-4 nm, the original ACF pore area is the largest, but with the increase of pore diameter, the pore area of the modified material is followed by rising, which also shows that the micropore of the modified material is mostly converted into mesoporous. It should be emphasized that the micropore increases the EDL overlap effect, so it may not contribute much to the electric adsorption process. In contrast, mesoporous with improved mass transfer and good pore accessibility can provide greater accessible surface area in the electric adsorption process. Therefore, Co3O4 / ACF composite materials with high mesoporous are expected to be preferred, and have potential use for electric adsorption process.

[0131] Reference Figure 2 is carried out under the test conditions of potential window-0.6-1.2V, scan rate 10mV·s -1 The CV curve of the original ACF has a much smaller closed area than the modified composite material (10.82F / g), indicating that the contribution of ACF to the composite material is small. The specific capacitance of the Co3O4 / ACF composite material is significantly higher than that of pure Co3O4, which is mainly because ACF as the matrix of Co3O4 effectively alleviates the volume expansion of Co3O4 nanowires during charging when acting alone, to a certain extent, alleviates the agglomeration of nanoparticles, and improves the conductivity of the material. When ACF without nitric acid pretreatment is used as the carrier, the specific capacitance of the modified composite electrode also decreases to 17.26F / g, which is due to the poor hydrophilicity of ACF itself, and the growth of Co3O4 nanowires on the surface of ACF is not good, resulting in the final loading amount not meeting the ideal standard.

[0132] It is known that only in mesoporous and macroporous with small mass transfer resistance, double electric layers can be formed within a certain scanning time period, while microporous with large resistance requires a longer time to form double electric layers. Therefore, when the number of mesopores in the material is small and the number of micropores is large, it is difficult to form double electric layers in the pore channel, and the capacitance of the micropore is small or even non-existent, resulting in a small specific capacitance of the electrode. It can be seen that the modified Co3O4 / ACF composite electrode has high pore volume and electrochemical properties.

[0133] Reference Figure 3The figures show the AC impedance spectra of the Co3O4 / ACF electrode before and after modification, as well as that of pure cobalt. The figures show that the Co3O4-modified ACF electrode without pretreatment has the largest impedance semicircle, while the composite electrode modified with nitric acid pretreatment has a smaller impedance semicircle. Based on the spectra, the charge transfer resistance (Rs) of the modified Co3O4ACF electrode is calculated to be 4.07 Ω. The impedance spectrum of pure cobalt is very similar to that of the modified electrode, indicating that cobalt ions significantly influence the electrochemical performance of the material during ACF modification, thereby improving its adsorption efficiency. Furthermore, the transverse intercepts of both are smaller than those of the original ACF, indicating that the original resistances of the membrane, electrolyte, and current collector in this adsorption system are lower.

[0134] See Figure 5 SEM images of Co3O4 / ACF modified electrodes prepared by hydrothermal treatment at 100℃ for 12 hours with ammonium fluoride concentrations of 18 mmol (0.12 mol / L), 24 mmol (0.16 mol / L), 30 mmol (0.2 mol / L), 36 mmol (0.24 mol / L), and 40 mmol (0.28 mol / L) are shown. Figure 5 (a) and (b) are SEM images of Co3O4 / ACF prepared under trace ammonium fluoride conditions. As can be seen from the images, only a small amount of material is loaded onto the surface of ACF fibers, and needle-like structures have not yet been formed. Figure 5 Images (c) and (d) are SEM images of Co3O4ACF obtained at a concentration of 0.16 mol / L. As shown in the images, the supported material has grown very densely on the surface of the ACF and is uniformly coated. However, the formed Co3O4 exhibits an elliptical block structure, indicating that the ammonium fluoride concentration at this level is insufficient to allow the Co3O4 to form complete needle-like structures. The ammonium fluoride concentration at 0.2 mol / L is... Figure 5 In (e) and (f), the elliptical blocky structure completely disappears, replaced by the growth of uniform and dense nanowires. The nanowires gradually taper from the bottom upwards, resembling pine needles, and are approximately 3 μm in length. However, at this stage, the nanowires are distributed very randomly on the fiber rods, exhibiting tilting and haphazard insertion. When the ammonium fluoride concentration increases to 0.24 mol / L, as... Figure 5 As shown in (g) and (h), it can be clearly seen from the figures that the Co3O4 nanowires grow uniformly and vertically on the ACF surface, and the growth positions are distributed very regularly. At this point, the nanowire length is approximately 4 μm. When the ammonium fluoride concentration increases to 0.28 mol / L, the results are as follows... Figure 5 As shown in (i) and (j), the Co3O4 nanowires formed at this time tend to agglomerate, accumulating in large quantities and exhibiting an uneven coating.

[0135] SeeFigure 6 are SEM images of Co304 / ACF modified electrodes prepared by adding 3 mmol (0.02 mol / L concentration), 6 mmol (0.04 mol / L concentration), 9 mmol (0.06 mol / L concentration), and 12 mmol (0.08 mol / L concentration) of cobalt nitrate hexahydrate, respectively, and hydrothermal treatment at 100°C for 12 hours. Among them Figure 6 (a) and (b) are SEM images of Co304 / ACF prepared when the concentration of cobalt nitrate is only 0.02 mol / L, from which it can be seen that only a small amount of needle-like results are grown on the surface of the ACF, and apparently the amount of cobalt ions is not enough to form a large amount of tight wrapping. Figure 6 (c) and (d) are nanowires grown at the optimal concentration of ammonium fluoride of 0.24 mol / L, which are the most tightly and uniformly wrapped, and the length of the nanoneedles is the longest. When the concentration of cobalt nitrate is changed to 0.06 mol / L, the results are Figure 6 (e) and (f), the nanowires still present a vertical and dense growth state, and the needle-like nanostructures are lengthened to 5 μm, which is longer than Figure 6 (c) and (d) are about 1 μm long, and the needles are obviously increased. When the concentration of cobalt nitrate is increased to 0.08 mol / L, the load has become a blocky wrapping structure of 2-3 μm, which is because the cobalt nitrate is excessive, causing a violent reaction in the hydrothermal process when contacting the ACF, forming a large area of accumulated blocky structure and thus excessive coating. From the Figure 6 (g) and (h) it can be seen that the blocky structure shows a very obvious bright surface, reflecting that such a sample has poor electrical conductivity, because a substance with a large resistivity will cause charge accumulation, and when the electron beam is scanned across the surface of the sample, the electrons will accumulate on the surface, thus appearing a very bright case of reflection. Therefore, by adjusting the concentration of cobalt nitrate, it is found that the nanowires grown at a concentration of 0.06 mol / L grow the most luxuriantly and the nanoneedles are the longest.

[0136] Figure 7 N2adsorption test figures of ACF electrode materials before and after nitric acid pretreatment, the pore structure of ACF treated by nitric acid becomes rich under short-term oxidation, and the structure parameters are improved to some extent. This is because the nitric acid pretreatment can remove the impurities blocked in the pore channel of the active carbon fiber, increase the pore size of the carbon material itself, and at the same time, the nitric acid has an etching effect on the pore structure of the active carbon fiber during the modification process, so the specific surface area will decrease, as shown in Table 2, the specific surface area of the ACF after HNO3 treatment decreased by 175 m 2 / g, at the same time, the formation of oxygen-containing groups after HNO3 pretreatment will cause the blockage of the entrance of the micropore, resulting in the decrease of the pore volume.

[0137] Table 2 Specific surface area and pore size distribution parameters of ACF before and after nitric acid pre-treatment

[0138]

[0139] Figure 8 Figure 1 is the FTIR spectra of Co304 / ACF before and after modification and without pre-treatment modification. Reference Figure 8 It can be seen that the broad absorption peak at 3420 cm -1 is attributed to -OH functional groups. Weak deformation vibration waveforms at 2980, 2860 cm"1may be C=C and C=0 bonds; the peak observed at 1650 cm -1 corresponds to the skeleton vibration of the aromatic ring C=C graphite carbon domain; the bands observed at 1000-1400 cm -1 are attributed to the bending vibration of -OH deformation and interlayer water molecules. The peaks at 580 cm -1 and 665 cm -1 are attributed to the stretching vibration of Co304metal. After Co304loading, the absorption peak at 3420 cm -1 indicates that some compounds with hydroxyl functional groups still exist in the modified ACF sample. In particular, when Co304is loaded on the ACF matrix without nitric acid pre-treatment, the peak value specific to Co304metal changes very weakly, which can be concluded that without nitric acid pre-treatment, the hydrophilicity of ACF is not good and the amount of loaded Co304is not much, while the functional group peaks at 580 cm -1 and 665 cm -1 are very obvious after nitric acid modification, at which time the Co304nanowires grow well on the ACF surface. The FTIR results prove the perfect coupling of the original ACF and Co304composites.

[0140] Figure 9 Figure 2 is the XRD spectra of Co304 / ACF before and after modification and without pre-treatment modification. Reference Figure 9, the original ACF in 2 theta about 22 ° and 43 ° appear relatively wide diffraction peak, this is because the ACF is mainly amorphous carbon base. Pure Co3O4 appear diffraction peak complete correspondence Co3O4 standard card JCPDS card No. 42-1467. After loading modification Co3O4 / ACF electrode front tip slightly up, this is because the influence of activated carbon base material. In which not by nitric acid pretreatment of Co3O4 / ACF-0 electrode 19.53 ° diffraction peak corresponding to Co3O4 standard card (111) crystal surface, at 34.27 ° appeared other oxide diffraction peak, show that Co3O4 precursor is not a large number of loading to the surface of ACF. After nitric acid pretreatment of Co3O4 / ACF-1 electrode in 19.53 °, 30.68 °, 35.07 °, 44.54 °, 58.76 ° and 64.89 ° diffraction peak angle under the appearance of diffraction peak are more obvious, with Co3O4 standard card and pure Co3O4 diffraction peak, respectively, corresponding to Co3O4 cubic spinel structure of (111), (220), (311), (400), (511) and (440) and other crystal surface diffraction peak, this shows that Co3O4 and ACF combination is very good.

[0141] Example 1: applied to the research of the electrode material, improve the existing electrode material, can improve the electrode adsorption performance.

[0142] Preparation of 20 cm * 10 cm electrode sheet each 2 pairs, keep the electrode spacing 10 mm embedded in the electric adsorption module, the electrode sheet connected to the positive and negative of the DC power supply. Preparation of 254 mg / L of chloride solution 800 ml, used as a simulation of water, research different electrode adsorption of chloride ions, injected into the electric adsorption module, connected to the water pump to make the regeneration water circulation. On each pair of electrode plate 2 V voltage for electric adsorption process.

[0143] ACF, Co3O4 / ACF-0, Co3O4 / ACF-1 electrode adsorption of chloride ion removal rate change comparison as shown in Figure 10 (a) shown, ACF, Co3O4 / ACF-0, Co3O4 / ACF-1 electrode adsorption of chloride ions as shown in Figure 10 (b).

[0144] Figure 10The electroadsorption performance of the Co3O4 / ACF electrode before and after modification and the original ACF electrode was compared. As can be seen from the figure, the original ACF electrode reached the electroadsorption saturation early, and the removal rate of chloride ions was only 26.18%, and the adsorption capacity was 10.64 mg / g. After the Co3O4 modification on the activated carbon fiber-based Co3O4 / ACF electrode without nitric acid pretreatment, the removal rate of chloride ions was improved to some extent, but it was still slightly worse than that of the Co3O4 / ACF electrode after the nitric acid pretreatment. The best removal rate of the Co3O4 / ACF modified electrode after the nitric acid pretreatment was 82.45%, and the adsorption capacity was 27.34 mg / g, which was consistent with the above characterization results. In the subsequent experiment, the influence of the operation and regeneration conditions on the removal effect of chloride ions in the electroadsorption process will be further investigated to further improve the removal rate of chloride ions.

[0145] Application Example 2: Application to the influence of different electrode spacing on the removal effect of electrode materials on chloride ions.

[0146] The electrode plate spacing is an important parameter affecting the electroadsorption performance. The influence of the electrode plate spacing on the capacitive deionization performance was studied by adjusting the spacing between the electrode plates. Under room temperature conditions, 2 pairs of electrodes were used, the experimental voltage was 2 V, the water volume was 800 mL, the initial concentration of chloride ions was 254 mg / L, and the influence of different plate spacings 2 mm, 5 mm, 10 mm and 15 mm on the adsorption capacity of the Co3O4 / ACF composite modified electrode was investigated.

[0147] According to the electrode preparation method provided in the foregoing embodiments, 2 pairs of Co3O4 / ACF electrode sheets with a size of 20 cm*10 cm were prepared, as shown in Figure 11 The electroadsorption rate decreases with the increase of the electrode plate spacing. When 50 min is reached, the removal rate of the solution gradually slows down, and after 70 min, the electrode reaches the adsorption equilibrium, at which time the removal rates of chloride ions are 88.37%, 82.45% and 61.19%, respectively. The reason for the decrease in the electroadsorption rate is that the adsorption capacity of the electrode is inversely proportional to the electrode spacing, and the smaller the electrode spacing, the greater the removal rate of chloride ions. As the electrode spacing increases, the double electric layer formed between the electrodes disappears slowly, and the resistance of ion migration between the electrode plates also increases, so the electrode spacing becomes larger. When the electrode plate spacing is 2 mm, the ion concentration in the solution starts to rise rapidly after 40 min, which may be because the small electrode spacing causes electrolysis of the treated water and electrolysis of the current collector, resulting in an increase in the ion concentration in the water and a rapid increase in the conductivity. The results show that when the electrode plate spacing is 5 mm, the removal effect of the composite modified electrode is best, and the removal rate of chloride ions is 88.37%. Therefore, the electrode plate spacing is strictly controlled to be 5 mm in the subsequent electroadsorption experiment.

[0148] Example 3: Verify the effect of dechlorine ion after regeneration of the electrode prepared in this example

[0149] Two pairs of 20cm*10cm Co3O4 / ACF electrode sheets were prepared according to the electrode preparation method provided in this example, embedded in the electric adsorption module with an electrode spacing of 5mm, and connected to the positive and negative electrodes of the direct current power supply according to the aforementioned connection method. The electrodes have a certain service life during use. During the process of removing chlorine ions by electric adsorption, the flow of water will cause a certain degree of wear on the electrode, and a small part of the adsorbed chlorine ions will also be chemically adsorbed in the double electric layer and difficult to desorb. In this section, two pairs of electrodes with an electrode spacing of 5mm, 800mL of water, a voltage of 2V, a regeneration condition of 15min of short-circuiting time, and a flushing flow rate of 30mL / min were used.

[0150] From Figure 12 It can be seen that the removal rate of chlorine ions is the highest at 89% when the electrode is used for the first time. In the second use, the electric adsorption rate decreases to a small extent, which may be due to the chemical reaction between the cobalt tetroxide loaded on the electrode surface and the chlorine ions. At the same time, due to the high specific surface area of the activated carbon fiber itself, the chlorine ions occupy some pores inside through physical adsorption, and the physical adsorption is not easy to be desorbed by the electrode regeneration method, so the adsorption performance of the regenerated electrode decreases slightly. In the subsequent regenerated electrode, the removal rate of chlorine ions decreases, but the decrease is very small. Therefore, it can be concluded that the composite electrode prepared in this paper has good regeneration performance.

[0151] The method for removing chlorine ions from regenerated water by electric adsorption provided by the present application does not introduce anion impurities other than chlorine ions in the system from the reaction medium, which is convenient for the development of comparative experiments.

[0152] The unique nanoneedle series of the Co3O4 / ACF electrode prepared in the present design has high electrochemical performance and good mesoporous structure. The above SEM characterization analysis can prove that the long wire structure of the nanowire accelerates the ion adsorption efficiency of the material surface, and the formed crystals also block a certain amount of microporous structure, resulting in a hierarchical porous structure. At the same time, the mesopores can also promote the rapid penetration of ions, so that the chlorine ions can fully contact the ACF surface, which is consistent with the N2 adsorption test results. Second, the directly grown nanometer array can ensure good mechanical adhesion, reducing the cost of using polymer adhesives and conductive materials. This can also be seen from the electrochemical characterization that the modified nanowire growth can reduce the resistance of the material, accelerate the electron transmission rate, and improve the electrochemical performance. Third, the three-dimensional nanometer structure grown on the ACF provides good stability, which is more conducive to maintaining the stability of the results during the electric adsorption process compared to the original ACF, and therefore has good regeneration performance.

[0153] Further, in the process of removing chloride ions, normal temperature operation is adopted, compared with the traditional electrosorption process, reaction temperature does not need to be controlled, thereby saving energy consumption. Further, the prepared electrode adopts activated carbon fiber as a matrix, has low preparation cost, is convenient for mass production, can bring good economic and social benefits, and has good application prospect.

[0154] While some embodiments of the general inventive concept have been shown and described, it is to be understood that changes can be made in these embodiments without departing from the principles and spirit of the general inventive concept, the scope of which is defined in the claims and their equivalents.

Claims

1. A method for preparing a carbon fiber composite electrode, comprising the following steps: loading a nitric acid pretreated activated carbon fiber with a tri-cobalt tetroxide nanowire array by a hydrothermal synthesis method, wherein the tri-cobalt tetroxide nanowire is needle-shaped structure and has a length of 3-5 microns; carrying out calcination to form a solid; arranging the solid on a graphite plate to form a carbon fiber composite electrode; in the hydrothermal synthesis method, the concentration of Co(NO3)2·6H2O is 0.02-0.08 mol / L, the concentration of NH4F is 0.2-0.28 mol / L, the concentration of urea is 0.28 mol / L, and the crystallization temperature is 80-120℃; the calcination is carried out at 300-400℃ under a protective atmosphere, and the calcination time is 2-4 hours; the method for pretreating the activated carbon fiber with nitric acid is to remove impurities in the activated carbon fiber by soaking in dilute nitric acid pickling, and then washing with water and rinsing with ethanol to make the activated carbon fiber neutral, and the mass concentration of the dilute nitric acid is 25%, and the pickling time is 8 hours.

2. The production method according to claim 1, characterized by, arranging the solid on a graphite plate by conductive glue to form a carbon fiber composite electrode.

3. The preparation method according to claim 1, characterized in that, the step of loading a nitric acid pretreated activated carbon fiber with a tri-cobalt tetroxide nanowire array by a hydrothermal synthesis method comprises: immersing the activated carbon fiber in a mixed solution prepared from a cobalt salt, an ammonium salt, urea and deionized water and placing it in a reaction kettle for hydrothermal treatment, and drying after loading the activated carbon fiber with tri-cobalt tetroxide. 4.The method according to any one of claims 1-3, characterized in that, the concentration of Co(NO3)2·6H2O is 0.06 mol / L, the concentration of NH4F is 0.24 mol / L, the crystallization temperature of the hydrothermal synthesis method is 100℃, the calcination is carried out at 350℃ under a protective atmosphere, and the calcination time is 3 hours. 5.A carbon fiber composite electrode, comprising: a graphite plate; carbon fibers arranged on the graphite plate, the carbon fibers being loaded with a tri-cobalt tetroxide nanowire array by a hydrothermal synthesis method, wherein the fiber stem of the carbon fiber is wrapped by the nanowire of tri-cobalt tetroxide, and the tri-cobalt tetroxide nanowire is needle-shaped structure and has a length of 3-5 microns; wherein the carbon fiber composite electrode is prepared according to the method for preparing a carbon fiber composite electrode according to any one of claims 1-4. 6.A method for removing chloride ions from raw water, comprising the following steps: (1) taking activated carbon fiber as a negative electrode; (2) taking a carbon fiber composite electrode prepared according to the method for preparing a carbon fiber composite electrode according to any one of claims 1-4 or a carbon fiber composite electrode according to claim 5 as a positive electrode; (3) placing the positive electrode and the negative electrode in an electric adsorption module; (4) injecting raw water, which is reclaimed water, into the electric adsorption module, connecting the positive electrode and the negative electrode to a direct current power supply and electrifying for a first predetermined time, the voltage being 0-2.5V, the electrode plate spacing of the positive electrode and the negative electrode being 2-15mm, the first predetermined time being 30-70min, and the number of positive electrode and negative electrode pairs being 2 pairs. (5) Under the action of electric field, the chloride ions in the raw water migrate to the positive electrode and are adsorbed on the positive electrode, and with the enrichment of the chloride ions on the positive electrode, the chloride ions in the raw water are gradually removed.

7. The method of claim 6, wherein, In the process of electro-adsorption of chloride ions, the carbon fiber composite electrode utilizes a large number of oxygen-containing functional groups formed on the surface of the activated carbon fiber after the pre-treatment by nitric acid, so that the cobaltosic oxide grows into a dense and compact nanowire array on the activated carbon fiber.

8. The method of claim 6, wherein, The method further comprises, after step (5): detecting whether the positive electrode is saturated with adsorption; when it is detected that the positive electrode is saturated with adsorption, the positive electrode and the negative electrode are short-circuited for a second predetermined time to make the chloride ions desorb; when the short-circuiting reaches the second predetermined time, the power supply is disconnected, and the desorbed chloride ions are removed, and the second predetermined time is 10-25 min.

Images