Method for in-situ growth of cobalt-iron-lanthanum ternary hydrotalcite phosphorus removal electrode on carbon felt

Abstract

The invention discloses a method for in-situ growth of a cobalt-iron-lanthanum ternary hydrotalcite phosphorus removal electrode on a carbon felt, and belongs to the technical field of capacitive deionization electrode preparation. The ternary hydrotalcite cobalt-iron-lanthanum hydrotalcite is synthesized on the commercial carbon felt by adopting a one-step hydrothermal method, and the preparation method does not need to use a binder and a conductive agent, and can better expose active sites of an active material, so that the phosphorus removal efficiency is improved, the economic benefit is remarkable, and the application prospect is wide.

Description

Technical Field

[0001] The invention belongs to the technical field of capacitor deionization electrode preparation, and in particular relates to a method for in-situ growth of a cobalt-iron-lanthanum ternary hydrotalcite dephosphorization electrode on carbon felt. Background Art

[0002] The enrichment of phosphorus in water bodies can easily lead to deterioration of water quality, which in turn destroys the ecological balance and restricts social development. How to solve the imminent problem of eutrophication of water bodies has aroused global discussion. As one of the main nutrients, phosphorus removal in wastewater is particularly important. Traditional methods for phosphorus removal from wastewater can be roughly divided into three categories: chemical method, biological method, and physical adsorption method. The chemical method precipitates phosphorus in the water body by adding a large amount of chemical agents, which has significant results, but the subsequent sludge treatment is prone to secondary pollution. The biological method degrades phosphorus in the water body through polyphosphate bacteria, which is clean and environmentally friendly, but the biological method has strict requirements on equipment and is costly. Capacitive deionization water treatment technology (CDI) has attracted widespread attention due to its advantages such as convenient operation, simple equipment, and low energy consumption. Its principle is to apply a low-voltage electric field as the driving force for anions and cations in the water body, and anions and cations are adsorbed on the anode and cathode respectively, and the target ions can be selectively removed by customizing different anions and cations. Currently, there are few technologies that use capacitive deionization to remove phosphate. The most fundamental reason lies in the electrodes. Traditional electrode materials are mainly carbon-based materials. Carbon-based material electrodes do not have the selective adsorption of phosphates and have limited adsorption performance. Furthermore, traditional capacitive deionization electrode preparation methods use coating or tableting methods, which are not conducive to exposing the active sites for adsorbing phosphates and will make the internal resistance of the capacitive deionization system large, which is not conducive to phosphate adsorption.

[0003] Existing electrodes made of zinc-aluminum hydrotalcite and zinc-zirconium hydrotalcite are prepared by mixing active materials with conductive agents and binders into slurry, coating it on a current collector such as a graphite plate, carbon paper, titanium plate, etc., and drying it to form an electrode. The electrodes prepared by this method have problems such as poor conductivity and shielding of active sites. Summary of the invention

[0004] The object of the present invention is to provide a preparation method for in-situ growing ternary hydrotalcite on carbon felt and using it as a capacitor deionization electrode. The preparation method does not require the use of a binder and a conductive agent, and can better expose the active sites of the active material, thereby significantly improving the phosphorus removal efficiency.

[0005] To achieve the above object, the present invention adopts the following technical solution:

[0006] A method for preparing a carbon felt cobalt iron lanthanum ternary hydrotalcite composite electrode comprises the following steps:

[0007] (1) Pretreatment of commercial carbon felt: The commercial carbon felt was ultrasonically washed with ethanol and deionized water in sequence and vacuum dried;

[0008] (2) Preparation of composite electrode: Dissolve cobalt nitrate, iron nitrate, lanthanum nitrate and urea in deionized water and mix them evenly by ultrasonication; immerse the dry carbon felt obtained in step (1) in the mixed solution, perform ultrasonication for 20 minutes, perform hydrothermal reaction, repeatedly wash with deionized water, and dry at 60° C. to obtain the carbon felt cobalt iron lanthanum ternary hydrotalcite composite electrode.

[0009] In step (1), the mass fraction of ethanol is 95%, the ultrasonic washing time of ethanol is 10 to 20 minutes, the ultrasonic washing time of deionized water is 10 to 20 minutes, the vacuum drying temperature is 60 to 80° C., and the drying time is 6 to 12 hours.

[0010] In step (2), the molar ratio of urea, cobalt nitrate, iron nitrate and lanthanum nitrate is 5-10:1.5-1:0.375-0.125:0.125-0.375.

[0011] In step (2), the temperature of the hydrothermal reaction is 80 to 180° C., and the reaction time is 12 to 24 hours.

[0012] An application of the carbon felt cobalt iron lanthanum ternary hydrotalcite composite electrode prepared by the method as described above in a capacitive deionization electrode: the electrode is used to remove phosphate.

[0013] The beneficial effects of the present invention are as follows: the electrode preparation method of the present invention abandons the binder and conductive agent used in the traditional CDI electrode preparation, reducing the use of chemicals. At the same time, a one-step hydrothermal method is used to synthesize a ternary hydrotalcite cobalt iron lanthanum hydrotalcite on commercial carbon felt. Compared with the traditional cobalt iron hydrotalcite, this method introduces the rare earth element lanthanum to increase the affinity of the electrode for phosphorus. The prepared electrode has better conductivity and faster mass transfer process than the electrode prepared by the traditional coating method, so that the electrode has a higher phosphorus removal rate and lower energy consumption than the electrode prepared by the traditional coating method. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 SEM images of the materials, including surface SEM images: (a) CF; (b) CF / CoFeLa-LDH; (c) CoFeLa-LDH; cross-sectional SEM images: (d) CF; (e) CF / CoFeLa-LDH.

[0015] Figure 2 This is the EDS spectrum of CF / CoFeLa-LDH.

[0016] Figure 3 XRD patterns of CF, CF / CoFeLa-LDH, and CoFeLa-LDH. DETAILED DESCRIPTION

[0017] In order to make the contents of the present invention easier to understand, the technical solution of the present invention is further described below in conjunction with specific implementation methods, but the present invention is not limited thereto.

[0018] Example 1

[0019] The ternary cobalt-iron-lanthanum hydrotalcite-carbon felt composite electrode is prepared by the following method:

[0020] Weigh 3g urea, 4.365g cobalt nitrate hexahydrate, 1.51g ferric nitrate nonahydrate, and 0.54g lanthanum nitrate hexahydrate into a beaker, add 100 ml deionized water to form a mixed solution A, and ultrasonicate for 10 minutes. Soak the pretreated 4*5 square centimeters of carbon felt in mixed solution A and ultrasonicate again for 20 minutes. Transfer the carbon felt and mixed solution A to the lining of the hydrothermal reactor and hydroheat in an oven at 120°C for 18 hours. After the reaction is completed, wash the excess cobalt, iron, lanthanum hydrotalcite on the surface of the carbon felt with deionized water, and put it in a 60°C vacuum drying oven to dry for 8 hours for use.

[0021] The prepared cobalt iron lanthanum carbon felt electrode was applied to the CDI system test. After 6 hours, samples were taken and the results were detected and calculated by ammonium molybdate spectrophotometry. The P removal rate and energy consumption of the cobalt iron lanthanum carbon felt electrode prepared in this example were 88% and 0.0067 KWh / gP, respectively.

[0022] Example 2

[0023] The ternary cobalt-iron-lanthanum hydrotalcite-carbon felt composite electrode is prepared by the following method:

[0024] Weigh 3g urea, 2.91g cobalt nitrate hexahydrate, 1.515g ferric nitrate nonahydrate, and 0.541g lanthanum nitrate hexahydrate into a beaker, add 100 ml of deionized water to form a mixed solution A, and ultrasonicate for 10 minutes. Soak the pretreated 4*5 square centimeters of carbon felt in mixed solution A and ultrasonicate again for 20 minutes. Transfer the carbon felt and mixed solution A to the lining of the hydrothermal reactor and hydroheat in an oven at 120°C for 18 hours. After the reaction is completed, wash the excess cobalt, iron, lanthanum hydrotalcite on the surface of the carbon felt with deionized water, and put it in a 60°C vacuum drying oven to dry for 8 hours for use.

[0025] The prepared cobalt iron lanthanum carbon felt electrode was applied to the CDI system test. After 6 hours, samples were taken and the results were detected and calculated by ammonium molybdate spectrophotometry. The P removal rate and energy consumption of the cobalt iron lanthanum carbon felt electrode prepared in this example were 92% and 0.0063 KWh / gP, respectively.

[0026] Example 3

[0027] The ternary cobalt-iron-lanthanum hydrotalcite-carbon felt composite electrode is prepared by the following method:

[0028] Weigh 3g urea, 4.365g cobalt nitrate hexahydrate, 1.51g ferric nitrate nonahydrate, and 0.54g lanthanum nitrate hexahydrate into a beaker, add 100 ml deionized water to form a mixed solution A, and ultrasonicate for 10 minutes. Soak the pretreated 4*5 square centimeters of carbon felt in mixed solution A and ultrasonicate again for 20 minutes. Transfer the carbon felt and mixed solution A to the lining of the hydrothermal reactor and hydroheat in an oven at 120°C for 18 hours. After the reaction is completed, wash the excess cobalt, iron, lanthanum hydrotalcite on the surface of the carbon felt with deionized water, and put it in a 60°C vacuum drying oven to dry for 8 hours for use.

[0029] The prepared cobalt iron lanthanum carbon felt electrode was applied to CDI system test. After 6 hours, samples were taken and detected by ammonium molybdate spectrophotometry. The results showed that the P removal rate and energy consumption of the cobalt iron lanthanum carbon felt electrode prepared in this example were 85% and 0.0065 KWh / gP, respectively.

[0030] The morphology of CF, CF / CoFeLa-LDH and CoFeLa-LDH was characterized by field emission electron microscopy. Figure 1 As shown. Figure 1 It can be seen that the commercial CF (carbon felt) has a smooth surface, and CoFeLa-LDH particles are generated on its surface and inside after the hydrothermal reaction.

[0031] The EDS spectrum of the CF / CoFeLa-LDH electrode was scanned, and the results were as follows: Figure 2 As shown in Figure 2, the C, O, Co, Fe, and La elements of the synthesized CF / CoFeLa-LDH electrode are evenly distributed, indicating that CoFeLa-LDH was successfully grown on the CF substrate.

[0032] The CF, CF / CoFeLa-LDH, and CoFeLa-LDH electrodes were analyzed by X-ray diffractometer. Figure 3 The synthesized CoFeLa-LDH is highly matched with the CoFe-LDH standard card, and the characteristic peak of La(OH)3 appears near 2θ=27.5,50. Although the peak on the CF / CoFeLa-LDH electrode is not obvious (probably affected by CF), its approximate position corresponds to that of CoFeLa-LDH.

[0033] In summary, it was confirmed that CoFeLa-LDH was successfully synthesized on CF to form a composite electrode CF / CoFeLa-LDH.

[0034] Comparative Example 1

[0035] The coated electrode is prepared according to the traditional active material: conductive agent: binder = 1:1:1, and the method is as follows:

[0036] 1. Weigh 10 mg of PVDF (polyvinylidene fluoride, binder) powder and dissolve it in 400 μL DMF (N,N-dimethylformamide) as solution A.

[0037] 2. Weigh 80 mg of CoFeLa-LDH powder (active material) and 10 mg of acetylene black (conductive agent) and add them to solution A, and shake and stir to form a uniform slurry B.

[0038] 3. Apply slurry B evenly on the reaction area 4*5cm 2 The graphite plate was placed in a vacuum drying oven at 60°C and dried for later use.

[0039] Table 1 Raw material ratio and performance of electrode

[0040]

[0041] It can be seen from the above table that the performance of the cobalt-iron-lanthanum hydrotalcite electrode grown in situ on carbon felt is higher than that of the cobalt-iron-lanthanum hydrotalcite electrode prepared by the traditional coating method.

[0042] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A method for preparing a carbon felt cobalt iron lanthanum ternary hydrotalcite composite electrode, characterized in that: The following steps are involved: (1) Pretreatment of commercial carbon felt: The commercial carbon felt was ultrasonically washed with ethanol and deionized water in sequence, and then vacuum dried; (2) Preparation of composite electrode: dissolve cobalt nitrate, iron nitrate, lanthanum nitrate and urea in deionized water and mix them evenly by ultrasonication; immerse the dry carbon felt obtained in step (1) in the mixed solution, ultrasonicate for 20 minutes, perform hydrothermal reaction, repeatedly wash with deionized water, and dry at 60° C. to obtain the carbon felt cobalt iron lanthanum ternary hydrotalcite composite electrode.

2. The method according to claim 1, characterized in that: In step (1), the mass fraction of ethanol is 95%, the ultrasonic washing time of ethanol is 10 to 20 minutes, the ultrasonic washing time of deionized water is 10 to 20 minutes, the vacuum drying temperature is 60 to 80°C, and the drying time is 6 to 12 hours.

3. The method according to claim 1, characterized in that: In step (2), the molar ratio of urea, cobalt nitrate, iron nitrate and lanthanum nitrate is 5-10:1.5-1:0.375-0.125:0.125-0.

375.

4. The method according to claim 1, characterized in that: In step (2), the temperature of the hydrothermal reaction is 80-180° C., and the reaction time is 12-24 hours.

5. A carbon felt cobalt iron lanthanum ternary hydrotalcite composite electrode prepared by the method according to any one of claims 1 to 4.

6. An application of a carbon felt cobalt iron lanthanum ternary hydrotalcite composite electrode prepared by the method according to any one of claims 1 to 4 in a capacitive deionization electrode, characterized in that: The electrode is used for removing phosphate.

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