A ZnFe-PANI composite carbon material electrode based on pseudocapacitance and its application

Abstract

The present invention belongs to the technical field of composite materials and wastewater treatment, and relates to a ZnFe-PANI composite carbon material electrode and a preparation method thereof, and its application in the electrosorption of phosphate in capacitive deionization technology. The ZnFe-PANI composite carbon material electrode of the present invention comprises ZnFe-PANI nanoparticles and a carbon nanotube conductive network, and the ZnFe-PANI nanoparticles are uniformly dispersed in the carbon nanotube network by a precipitation method. Its preparation method comprises: preparation of polyaniline, preparation of ZnFe-PANI nanoparticles and preparation of an electrode. The ZnFe-PANI composite carbon nanotube electrode of the present invention can quickly remove phosphate from water bodies and meet phosphate discharge standards. The electrode of the present invention has the advantages of simple preparation process, low cost, rapid ion transport, good electrochemical stability and high adsorption capacity.

Description

Technical Field

[0001] The invention belongs to the technical field of composite materials and wastewater treatment, and relates to a ZnFe-PANI composite carbon material electrode, a preparation method thereof, and application thereof in capacitive deionization technology for electro-adsorption of phosphate. Background Art

[0002] With the advancement of human society, wastewater discharge from anthropogenic activities has become a major environmental concern worldwide. This can lead to severe eutrophication of water bodies, algal blooms, and reduced dissolved oxygen levels, threatening biodiversity and water purification capacity. Phosphorus, a major nutrient in wastewater, is also a significant limiting factor in accelerating eutrophication in lakes and natural water bodies. Furthermore, due to the non-renewable nature of phosphate rock, phosphorus resources are facing a critical shortage. Therefore, the development of cost-effective and efficient technologies for phosphorus removal and recovery is crucial.

[0003] Numerous technologies, including electrochemical, adsorption, and biological methods, have been developed to remove and recover phosphates. Among these, capacitive deionization (CDI) has proven to be a promising wastewater treatment technology due to its environmentally friendly, cost-effective, and efficient nature. It utilizes a low applied voltage to concentrate anions and cations at both electrodes and store them in the electrical double layer (EDL), resulting in relatively pure water. However, currently used, mature carbon-based composite materials (such as activated carbon (AC), carbon nanotubes (CNT), and redox graphene) suffer from high charge transfer resistance and limited phosphate ion storage capacity. Summary of the Invention

[0004] This invention addresses the low phosphate removal rate and high ion migration resistance inherent in CDI technology by providing a ZnFe-PANI composite carbon nanotube electrode for rapid phosphate removal from water, achieving compliance with phosphate discharge standards. The electrode offers advantages such as a simple preparation process, low cost, rapid ion transport, good electrochemical stability, and high adsorption capacity.

[0005] Composite materials containing Zn and Fe can tightly bind to phosphate through inner sphere complexation and coordination exchange, making them widely used phosphate adsorption materials. The conductive polymer polyaniline (PANI) has Faraday pseudocapacitance properties. It can achieve rapid electron transfer and high charge storage through reversible redox properties. However, due to its low electrochemical utilization rate and poor stability, it will have higher electrochemical performance when combined with carbon nanotubes with high specific surface area and good conductivity. Therefore, the present invention combines carbon nanotubes with pseudocapacitive ZnFe-PANI materials to prepare CDI electrodes for removing phosphate from water, directly meeting the first-level phosphate emission standard (0.5mg / L). The present invention is completed based on the above research.

[0006] The technical solution of the present invention is: preparing a ZnFe-PANI composite carbon nanotube electrode by a precipitation method, assembling a capacitor deionization device, and adsorbing and removing phosphate in water.

[0007] The present invention provides a method for preparing ZnFe-PANI composite carbon nanotubes, which specifically comprises the following steps:

[0008] S1. Preparation of polyaniline:

[0009] Equal amounts of aniline solution and ammonium persulfate (APS) solution were prepared respectively using hydrochloric acid solution as solvent, and the two solutions were mixed and stirred in an ice bath to slowly polymerize polyaniline to obtain a polyaniline solution.

[0010] S2. Preparation of ZnFe-PANI composite carbon nanotubes:

[0011] S201. Add terephthalic acid to an appropriate amount of deionized water, adjust the pH of the resulting solution by adding NaOH solution, and continuously stir to completely dissolve the solution, thereby obtaining solution A.

[0012] S202. Dissolve zinc chloride (ZnCl2·6H2O) and ferric chloride (FeCl3) in an appropriate amount of deionized water, then add the polyaniline solution prepared in step S1 and continue stirring to obtain solution B.

[0013] S203. Disperse a certain amount of carbon nanotubes (CNTs) in an appropriate amount of deionized water, dissolve them by ultrasonication, then add them to solution B, and mix them uniformly by ultrasonication to obtain solution C.

[0014] S204. Slowly add solution C to the continuously stirred solution A, maintain the pH of the mixed solution at a fixed value, and continue stirring until the reaction is completed.

[0015] S205, aging the obtained mixed solution in an oven, washing it by centrifugation, and drying it to obtain the desired ZnFe-PANI / CNT composite material.

[0016] S3. Preparation of electrode materials: Mix the electrode material ZnFe-PANI / CNT composite material, conductive agent and binder into a slurry, apply it on a plane, and form an electrode after vacuum drying.

[0017] In a preferred embodiment of the present invention, step S3 includes:

[0018] S301 , mixing the electrode material (ZnFe-PANI / CNT), the conductive agent and the binder in a certain proportion into a slurry, and coating the slurry on the carbon paper.

[0019] S302, drying the coated electrode at 60°C for 2 hours, and then drying in a vacuum drying oven.

[0020] Furthermore, in step S1, the hydrochloric acid solution is 0.5-1.0 mol / L, the aniline solution and the ammonium persulfate solution are 0.04-0.08 mol / L, and the ice bath reaction time is 5 hours. Equal amounts refer to a 1:1 molar ratio, or equivalent amounts of the substances. The ice bath can also be replaced with a liquid at 0-4°C. The reaction temperature is controlled at 0-4°C.

[0021] Furthermore, in step S201, the concentration of terephthalic acid is 0.01-0.03 mol / L, the concentration of NaOH solution is 2 mol / L, and the pH value is adjusted to 8-10.

[0022] Furthermore, in step S202, the molar ratio of zinc chloride to ferric chloride is (2-4):1, the volume of polyaniline is 3-6 mL, and stirring is continued for 15 minutes.

[0023] The molar ratio of terephthalic acid to ferric chloride is (2–4):1.

[0024] Furthermore, in step S203, the mass of the carbon nanotubes is 0.2-0.5 g, and the ultrasonication time is 0.5-1 h.

[0025] Furthermore, in step S204, the pH of the mixed solution is maintained at 8-10, and the stirring time is 1-2 hours.

[0026] Furthermore, in step S205, the aging temperature is 60-70°C, the aging time is 6-8 hours, the temperature of the blast drying oven is 70-80°C, and the drying time is 24 hours.

[0027] Furthermore, in step S3, the ratio of the electrode material, conductive agent, and binder is 8:1:1. The conductive agent is one of carbon black, graphite, and acetylene black. The binder is one of styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), and polyvinylidene fluoride (PVDF). The binder solvent is one of N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAC), and dimethyl sulfoxide (DMSO). The vacuum drying oven temperature is 60–80°C, and the drying time is 5–6 hours.

[0028] The present invention provides a method for preparing a ZnFe-PANI composite carbon material electrode using the pseudocapacitor to prepare a ZnFe-PANI / CNT electrode.

[0029] The electrode provided by the present invention is used as an anode, and the activated carbon electrode is used as a cathode to construct a capacitive deionization device.

[0030] Furthermore, the specific method of removing phosphate from water by electrosorption using the capacitive deionization device is as follows:

[0031] The capacitive deionization reactor consists of a titanium plate current collector, an electrosorption module, a non-conductive polyethylene mesh separator, and a regulated power supply. The distance between the electrodes is 2.0 mm, and a suitable flow rate is maintained. A predetermined amount of phosphate solution is pumped to the bottom and then flows out of the top of the capacitive deionization module. A small amount of the solution is sampled at regular intervals to determine the phosphate concentration. The applied voltage is 1.2 V, and the electrosorption time is less than 3 hours.

[0032] Furthermore, the initial concentration of phosphate is 6-10 mg / L, the pH value of the phosphate water body is 5-9, and the volume of the phosphate water body is 70-100 mL.

[0033] Furthermore, the flow rate of the capacitive deionization device is 10-30 mL / min, and the electrode size is 3 cm×3 cm.

[0034] The present invention has achieved the following beneficial effects:

[0035] 1. The ZnFe-PANI / CNT composite electrode of the present invention uses carbon nanotubes as a conductive network, which is loaded with uniformly dispersed ZnFe-PANI particles. It has a rich pore structure and a large specific surface area, providing more active sites for phosphate ions.

[0036] 2. The ZnFe-PANI / CNT composite material electrode of the present invention exhibits obvious Faraday pseudocapacitive characteristics, and has the advantages of good conductivity, high specific capacitance, fast ion diffusion rate, and good stability. It can be used as a capacitive deionization electrode to remove phosphate from water and achieve rapid ion removal.

[0037] 3. The ZnFe-PANI / CNT composite electrode of the present invention has a higher phosphate adsorption capacity than CNT and ZnFe-PANI. Furthermore, after 2 hours of electrosorption, the ZnFe-PANI / CNT composite electrode achieved a phosphate removal rate of 97%, with an effluent concentration of 0.16 mg / L, meeting the primary standard (0.5 mg phosphate / L) of the Integrated Wastewater Discharge Standard (GB18918-2002). BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solution of the present application, the following is a brief introduction to the drawings required for use in the embodiments. Obviously, each drawing described below is for some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0039] Figure 1This is a scanning electron microscope image of the ZnFe-PANI / CNT composite material of the present invention;

[0040] Figure 2 cyclic voltammetry curves of the ZnFe-PANI / CNT composite electrode, the ZnFe-PANI electrode, and the CNT electrode of the present invention;

[0041] Figure 3 This is a dynamic effect diagram of the ZnFe-PANI / CNT composite electrode of the present invention adsorbing phosphate;

[0042] Figure 4 This is a dynamic effect diagram of the ZnFe-PANI electrode of the present invention adsorbing phosphate;

[0043] Figure 5 This is a dynamic effect diagram of the CNT electrode of the present invention adsorbing phosphate;

[0044] Figure 6 This is a graph of the electrical adsorption capacity of the ZnFe-PANI / CNT composite electrode with different ZnFe ratios of the present invention. DETAILED DESCRIPTION

[0045] The present invention discloses a method for preparing a ZnFe-PANI composite carbon material electrode based on pseudocapacitance and its removal of phosphate in a capacitive deionization system, and relates to the technical fields of composite materials and wastewater treatment. The ZnFe-PANI composite carbon material electrode described in the present invention is prepared by dispersing ZnFe-PANI nanoparticles in a carbon nanotube network using a precipitation method, and is applied to capacitive deionization to adsorb phosphate. The ZnFe-PANI composite carbon material electrode provided by the present invention has the advantages of large specific surface area, good electrical conductivity, high specific capacitance, and fast ion transmission. In the electrical adsorption experiment, it shows strong phosphate adsorption performance, high removal efficiency and fast rate, so that the phosphate concentration in the water body reaches the first-level standard (0.5mg P / L) of the Comprehensive Wastewater Discharge Standard (GB18918-2002) in a relatively short time, and has wide application potential.

[0046] The following examples of the present application will clearly and completely describe the technical solution. Obviously, the described examples are only some preferred embodiments of the present application, not all embodiments. Based on the examples in the present application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0047] The polyaniline (PANI) solution used in the present examples was homemade and prepared by preparing 50 mL of a 0.06 mol / L aniline solution and an ammonium persulfate solution, respectively, using a 1 mol / L hydrochloric acid solution as a solvent. The ammonium persulfate solution was slowly added dropwise to the aniline solution in an ice bath and allowed to react for 24 hours to slowly polymerize the polyaniline, thereby obtaining the polyaniline solution.

[0048] In the following examples of the present invention, unless otherwise specified, the materials and instruments used are purchased products.

[0049] Example 1

[0050] The preparation process of the ZnFe-PANI composite carbon material electrode provided in this embodiment is as follows:

[0051] (1) Preparation of composite materials

[0052] Preparation of ZnFe-PANI:

[0053] Dissolve 0.01 M terephthalic acid in 30 mL of deionized water, and adjust the pH of the resulting solution to 8 by adding 2 mol / L NaOH solution. This solution is labeled Solution A. Dissolve 9 mmol / L ZnCl2·6H2O and 3 mmol / L FeCl3 in 40 mL of water, then add 4 mL of polyaniline solution and continue stirring for 15 minutes. This solution is labeled Solution B.

[0054] Then, solution B and solution A were mixed and vigorously stirred for 1 hour, maintaining the pH of the mixed solution at 8. The resulting material was aged at 70°C for 6 hours, washed by centrifugation, and dried at 80°C for 24 hours. The final product was ground into a powder and labeled as ZnFe-PANI.

[0055] Preparation of ZnFe-PANI composite carbon materials:

[0056] 0.01 mol / L terephthalic acid was dissolved in 30 mL of deionized water, and the pH of the resulting solution was adjusted to 8 by adding 2 mol / L NaOH solution (denoted as Solution A). 9 mmol / L ZnCl2·6H2O and 3 mmol / L FeCl3 were dissolved in 40 mL of water, followed by the addition of 4 mL of polyaniline solution and continuous stirring for 15 minutes. Then, 30 mL of the CNT mixed solution (0.3 g) that had been sonicated for 30 minutes was added (denoted as Solution B).

[0057] Solution B and Solution A were then mixed and vigorously stirred for 1 hour, maintaining the pH of the mixed solution at 8. The resulting material was aged at 70°C for 6 hours, washed by centrifugation, and then dried at 80°C for 24 hours. The final product was ground into a powder and labeled as ZnFe-PANI / CNT. Furthermore, ZnFe(x)-PANI / CNT with different ZnFe ratios (x = 2:1, 4:1) were also prepared under the same conditions.

[0058] (2) Preparation of electrodes

[0059] The above-prepared composite material, acetylene black and PVDF / NMP binder were mixed into a slurry in a ratio of 8:1:1 and coated on carbon paper. The slurry was dried at 60°C for 2 hours and then vacuum-dried at 80°C for 6 hours. The obtained electrode was used as the electrode anode and the activated carbon electrode was used as the electrode cathode.

[0060] The electrochemical properties of the electrodes were measured using 1 mol / L sodium dihydrogen phosphate solution as the electrolyte. Table 1 shows the specific capacitance of different electrodes measured at a scan rate of 2 mV / s:

[0061] Table 1 Specific capacitance of different electrodes

[0062]

[0063] Test data showed that ZnFe-PANI / CNT had better electrochemical performance than ZnFe-PANI and CNT, indicating a larger phosphate storage capacity.

[0064] Example 2

[0065] The composite material electrodes prepared in the above embodiment were subjected to capacitive deionization adsorption experiments. The composite material electrode was used as the anode and the activated carbon electrode was used as the cathode. The distance between the two electrodes was 2.0 mm and the flow rate was maintained at 20 mL / min. At a voltage of 1.2 V, 70 mL of phosphate was transported to the capacitive adsorption device by a peristaltic pump, and the solution then flowed back into the feed liquid pool. Water samples were taken at intervals to test the phosphate concentration. The initial concentration of phosphate was 6 mg / L, the adsorption time was 2 h, and the adsorption pH was 7.

[0066] Example 3

[0067] The conditions were the same as in Example 2, except that the initial concentration of phosphate was 8 mg / L.

[0068] Example 4

[0069] The conditions were the same as in Example 2, except that the initial concentration of phosphate was 10 mg / L.

[0070] like Figure 3-5As shown, the ZnFe-PANI / CNT electrode has higher adsorption performance than both ZnFe-PANI and CNT. Furthermore, the phosphate concentration in the effluent from the capacitive deionization system remains below 0.5 mg / L, meeting Class I wastewater discharge standards. The adsorption time is only 2 hours, significantly shortening treatment time and saving costs.

[0071] like Figure 6 As shown in the figure, the highest phosphate adsorption capacity is achieved when the ZnFe ratio is 3:1, which can give full play to the pseudocapacitive characteristics of the ZnFe-PANI / CNT electrode and adsorb more phosphate faster.

[0072] The embodiments described above are merely specific implementations of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be imagined by any person skilled in the art within the technical scope disclosed in the present application without resorting to creative effort should be included within the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims in the present application.

Claims

1. A method for preparing a ZnFe-PANI composite carbon material electrode, characterized in that: The following steps are involved: S1. Preparation of polyaniline: Using hydrochloric acid solution as solvent, equal amounts of aniline solution and ammonium persulfate solution are prepared respectively, and the two solutions are mixed and stirred in an ice bath to slowly polymerize polyaniline to obtain a polyaniline solution; S2. Preparation of ZnFe-PANI composite carbon nanotubes, including steps S201-S205: S201, adding terephthalic acid to an appropriate amount of deionized water, adjusting the resulting solution to alkaline by adding NaOH solution, and continuously stirring to completely dissolve it, to obtain solution A; S202, dissolving zinc chloride and ferric chloride in deionized water, then adding the polyaniline solution prepared in step S1, and continuously stirring to obtain solution B; S203, dispersing carbon nanotubes in deionized water, dissolving them by ultrasonication, then adding them to solution B, and mixing them by ultrasonication to obtain solution C; S204, slowly adding solution C to the continuously stirred solution A, maintaining the pH of the mixed solution at a pH value of 8-10, and continuing stirring until the reaction is complete; S205, aging the obtained mixed solution in an oven, centrifuging and washing, and drying to obtain the desired ZnFe-PANI / CNT composite material; S3. Preparation of electrodes: The electrode material ZnFe-PANI / CNT composite material, conductive agent and binder are mixed into slurry, coated on a plane, and vacuum dried to form an electrode.

2. The method for preparing the ZnFe-PANI composite carbon material electrode according to claim 1, characterized in that: In step S1, the hydrochloric acid solution is 0.5-1.0 mol / L, the aniline solution and the ammonium persulfate solution are 0.04-0.08 mol / L, and the ice bath reaction time is 3-10 h. Equal amounts refer to equal amounts of substances.

3. The method for preparing the ZnFe-PANI composite carbon material electrode according to claim 1, characterized in that: In step S2, the concentration of terephthalic acid is 0.01-0.03 mol / L; The concentration of NaOH solution is 2 mol / L; The molar ratio of zinc chloride to ferric chloride is (2–4):1, the volume of polyaniline is 3–6 mL, and stirring is continued for 15 min; The molar ratio of terephthalic acid to ferric chloride is (2–4):1; The mass of the carbon nanotubes is 0.2-0.5 g, and the ultrasonic time is 0.5-1 h.

4. The method for preparing the ZnFe-PANI composite carbon material electrode according to claim 1, characterized in that: In step S204, the pH of the mixed solution is maintained at 8-10, and the stirring time is 1-2 hours; In step S205, the aging temperature is 60-70°C, the aging time is 6-8 hours, the temperature of the blast drying oven is 70-80°C, and the drying time is not less than 12 hours.

5. The method for preparing the ZnFe-PANI composite carbon material electrode according to claim 1, characterized in that: In step S3, the ratio of the composite material, the conductive agent and the binder is 8:1:1; The conductive agent is any one of carbon black, graphite, and acetylene black; The binder is one of styrene-butadiene rubber, carboxymethyl cellulose and polyvinylidene fluoride; The solvent of the binder is one of N-methylpyrrolidone, N,N-dimethylacetamide and dimethyl sulfoxide; The vacuum drying oven temperature is 60–80°C and the drying time is 5–6 h.

6. A ZnFe-PANI composite carbon material electrode, characterized in that: The electrode is prepared by the method according to claim 5, and the size of the electrode is 3 cm×3 cm.

7. An application of the ZnFe-PANI composite carbon material electrode prepared according to claim 6 in removing phosphate from wastewater in a capacitive deionization (CDI) device, characterized in that: The ZnFe-PANI composite carbon material electrode is used as the anode, and the molar ratio of Zn to Fe is 2:1 to 4:1, and the activated carbon electrode is used as the cathode; the distance between the anode and the cathode in the capacitive deionization device is 2.0 mm, the influent phosphate concentration is 6-10 mg / L, the pH is 5-9, the flow rate is 10-30 mL / min, the voltage is 1.2 V, and the operating time is less than 3 hours.

8. The use according to claim 7, characterized in that The ZnFe-PANI composite carbon material electrode has a phosphate removal rate of up to 97%, and an effluent concentration of 0.16 mg / L.

9. The use according to claim 7 or 8, characterized in that The device is used to treat phosphate-containing water bodies and remove phosphate in the water body through electrical adsorption; the phosphate-containing wastewater is adjusted to a pH of 5-9, and the water inlet volume is 70-100 mL; at a voltage of 1.2 V, the anode specifically adsorbs phosphate anions through the pseudocapacitive effect of ZnFe-PANI, and the cathode synchronously adsorbs sodium ions to maintain charge balance.

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