A method for growing cobalt-iron-lanthanum ternary hydrotalcite in-situ on carbon felt to remove phosphorus

Abstract

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

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrode preparation of capacitive deionization, and particularly relates to a method for preparing a cobalt-iron-lanthanum ternary hydrotalcite electrode for removing phosphorus in-situ grown on carbon felt. BACKGROUND

[0002] The enrichment of phosphorus in water bodies can easily lead to water quality deterioration, further destroy the ecological balance and limit the development of society. How to solve the problem of water eutrophication, which is imminent, has caused discussions worldwide. As one of the main nutrients, the removal of phosphorus in wastewater is particularly important. The traditional methods for removing phosphorus in wastewater can be roughly divided into three categories: chemical method, biological method and physical adsorption method. The chemical method can make the phosphorus in the water body precipitate by adding a large amount of chemical agent, and the effect is significant, but the subsequent sludge treatment can easily cause secondary pollution. The biological method can degrade the phosphorus in the water body by using phosphorus-accumulating bacteria, and is clean and environmentally friendly, but the biological method has high requirements for equipment and high cost. The capacitive deionization water treatment technology (CDI) has attracted widespread attention due to its convenient operation, simple equipment and low energy consumption. The principle is to apply a low-voltage electric field as the driving force for anions and cations in water, and the anions and cations are adsorbed on the anode and cathode respectively, and different anode and cathode can be customized to selectively remove target ions. At present, there are few technologies for removing phosphate by capacitive deionization. The most fundamental reason is the electrode. The traditional electrode material is mainly carbon-based material. The carbon-based electrode does not have selective adsorption of phosphate and has limited adsorption performance. In addition, the traditional preparation method of capacitive deionization electrode adopts the coating method or the pressing method, which is not conducive to exposing the active sites for adsorbing phosphate and can increase the internal resistance of the capacitive deionization system, which is not conducive to the adsorption of phosphate.

[0003] The existing electrodes prepared from zinc-aluminum hydrotalcite and zinc-zirconium hydrotalcite are obtained by mixing active material, conductive agent and binder into slurry, coating the slurry on a current collector such as graphite plate, carbon paper, titanium plate, and then drying to form an electrode. The electrode prepared by this method has problems such as poor conductivity and shielding of active sites. SUMMARY

[0004] The purpose of the present application is to provide a preparation method of a ternary hydrotalcite grown in-situ on carbon felt and used as a capacitive deionization electrode. The preparation method does not need to use a binder and a conductive agent, and can better expose the active sites of the active material, so that the removal efficiency of phosphorus is significantly improved.

[0005] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0006] A preparation method of a carbon felt cobalt-iron-lanthanum ternary hydrotalcite composite electrode, comprising the following steps:

[0007] (1) Pretreatment of commercial carbon felt: the commercial carbon felt is sequentially ultrasonically washed with ethanol and deionized water, and vacuum dried;

[0008] (2) Preparation of composite electrode: cobalt nitrate, iron nitrate, lanthanum nitrate and urea are dissolved in deionized water, and ultrasonically mixed uniformly; the dried carbon felt obtained in step (1) is immersed in the mixed solution, ultrasonically for 20 minutes, hydrothermally reacted, repeatedly washed with deionized water, and dried at 60 DEG 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 10-20 minutes, the ultrasonic washing time of deionized water is 10-20 minutes, the vacuum drying temperature is 60-80 DEG C, and the drying time is 6-12 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 hydrothermal reaction is 80-180 DEG C, and the reaction time is 12-24 hours.

[0012] The carbon felt cobalt iron lanthanum ternary hydrotalcite composite electrode prepared by the method is applied to the capacitor deionization electrode: the electrode is used for removing phosphate.

[0013] The electrode preparation method of the application discards the binder and conductive agent used in the preparation of traditional CDI electrode, and reduces the use of chemical medicines. Meanwhile, the ternary hydrotalcite cobalt iron lanthanum hydrotalcite is synthesized on the commercial carbon felt by one-step hydrothermal method, compared with the traditional cobalt iron hydrotalcite, the method introduces the rare earth element lanthanum to increase the affinity of the electrode to phosphorus. The prepared electrode has better conductivity and faster mass transfer process compared with the electrode prepared by the traditional coating method, so that the electrode has higher phosphorus removal rate and lower energy consumption compared with the electrode prepared by the traditional coating method. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 It is the SEM graph of the material, wherein the surface SEM graph: (a) CF; (b) CF / CoFeLa-LDH; (c) CoFeLa-LDH; the cross-section SEM graph: (d) CF; (e) CF / CoFeLa-LDH.

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

[0016] Figure 3 It is the XRD graph of CF, CF / CoFeLa-LDH and CoFeLa-LDH. DETAILED DESCRIPTION

[0017] In order to make the content of the present application more convenient to understand, the technical solutions of the present application are further described below in combination with specific embodiments, but the present application is not limited to this.

[0018] Example 1

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

[0020] 3g of urea, 4.365g of cobalt nitrate hexahydrate, 1.51g of iron nitrate nonahydrate, and 0.54g of lanthanum nitrate hexahydrate are weighed into a beaker, 100ml of deionized water is added to form a mixed solution A, and ultrasonic treatment is performed for 10 minutes. The pretreated 4*5 square centimeter carbon felt is immersed in the mixed solution A and ultrasonic treatment is performed again for 20 minutes. The carbon felt and the mixed solution A are transferred into the inner liner of a hydrothermal reaction kettle, and hydrothermal treatment is performed in an oven at a temperature of 120℃ for 18 hours. After the reaction is completed, the excess cobalt-iron-lanthanum hydrotalcite on the surface of the carbon felt is washed away with deionized water, and the carbon felt is placed in a 60℃ vacuum drying oven for drying for 8 hours for standby use.

[0021] The prepared cobalt-iron-lanthanum carbon felt electrode is applied to CDI system testing, and after 6 hours, sampling is performed for detection by the ammonium molybdate spectrophotometric method. It is calculated that the P removal rate and energy consumption of the cobalt-iron-lanthanum carbon felt electrode prepared in this example are 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] 3g of urea, 4.365g of cobalt nitrate hexahydrate, 1.51g of iron nitrate nonahydrate, and 0.54g of lanthanum nitrate hexahydrate are weighed into a beaker, 100ml of deionized water is added to form a mixed solution A, and ultrasonic treatment is performed for 10 minutes. The pretreated 4*5 square centimeter carbon felt is immersed in the mixed solution A and ultrasonic treatment is performed again for 20 minutes. The carbon felt and the mixed solution A are transferred into the inner liner of a hydrothermal reaction kettle, and hydrothermal treatment is performed in an oven at a temperature of 120℃ for 18 hours. After the reaction is completed, the excess cobalt-iron-lanthanum hydrotalcite on the surface of the carbon felt is washed away with deionized water, and the carbon felt is placed in a 60℃ vacuum drying oven for drying for 8 hours for standby use.

[0025] The prepared cobalt-iron-lanthanum carbon felt electrode is applied to CDI system testing, and after 6 hours, sampling is performed for detection by the ammonium molybdate spectrophotometric method. It is calculated that the P removal rate and energy consumption of the cobalt-iron-lanthanum carbon felt electrode prepared in this example are 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] 3g of urea, 4.365g of cobalt nitrate hexahydrate, 1.51g of iron nitrate nonahydrate, and 0.54g of lanthanum nitrate hexahydrate are weighed into a beaker, 100ml of deionized water is added to form a mixed solution A, and ultrasonic treatment is performed for 10 minutes. The pretreated 4*5 square centimeter carbon felt is immersed in the mixed solution A, and ultrasonic treatment is performed again for 20 minutes. The carbon felt and the mixed solution A are transferred into the inner liner of a hydrothermal reaction kettle, and hydrothermal treatment is performed at a temperature of 120℃ for 18 hours. After the reaction is completed, the excess cobalt-iron-lanthanum hydrotalcite on the surface of the carbon felt is washed away with deionized water, and the carbon felt is placed in a 60℃ vacuum drying box for drying for 8 hours for standby use.

[0029] The prepared cobalt-iron-lanthanum carbon felt electrode is applied to a CDI system test, and after 6 hours, sampling is performed, and the P removal rate and energy consumption of the cobalt-iron-lanthanum carbon felt electrode prepared in the example are 85% and 0.0065 KWh / g P, respectively, which are calculated by the ammonium molybdate spectrophotometric method.

[0030] The CF, CF / CoFeLa-LDH, and CoFeLa-LDH are characterized by field emission scanning electron microscopy, and the results are shown in Figure 1 It can be seen from Figure 1 that the surface of the commercial CF (carbon felt) is smooth, and CoFeLa-LDH particles are generated on the surface and inside after hydrothermal reaction.

[0031] The CF / CoFeLa-LDH electrode is subjected to EDS energy spectrum scanning, and the results are shown in Figure 2 The C, O, Co, Fe, and La elements of the synthesized CF / CoFeLa-LDH electrode are uniformly distributed, indicating that CoFeLa-LDH is successfully grown on the CF substrate.

[0032] The CF, CF / CoFeLa-LDH, and CoFeLa-LDH electrodes are analyzed by X-ray diffractometer, and the results are shown in Figure 3 The synthesized CoFeLa-LDH matches the CoFe-LDH standard card in height, 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 (may be affected by CF), but the approximate position corresponds to CoFeLa-LDH.

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

[0034] Comparative Example 1

[0035] The preparation of the coated electrode is prepared according to the conventional active material: conductive agent: binder = 1:1:1, as follows:

[0036] 1. 10 mg of PVDF (polyvinylidene fluoride, binder) powder was weighed and dissolved in 400 μL of DMF (N,N-dimethylformamide) to form solution A.

[0037] 2. 80 mg of CoFeLa-LDH powder (active material) and 10 mg of acetylene black (conductive agent) were weighed and added to solution A to form a uniform slurry B.

[0038] 3. The slurry B was uniformly coated on a graphite plate with a reaction area of 4*5 cm 2 , and placed in a 60°C vacuum drying box for drying.

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

[0040]

[0041] As can be seen from the above table, the performance of the cobalt-iron-lanthanum ternary hydrotalcite electrode grown in-situ on the carbon felt is higher than that of the conventional coated cobalt-iron-lanthanum hydrotalcite electrode.

[0042] The above description is only the preferred embodiment of the present application, and any equivalent changes and modifications made within the scope of the patent application of the present application shall be included in the scope of the present application.

Claims

1. A method for preparing a carbon felt Co-Fe-La ternary hydrotalcite composite electrode, characterized by comprising the following steps: The method comprises the following steps: ​ (1) Pretreatment of commercial carbon felt: the commercial carbon felt is sequentially ultrasonically washed with ethanol and deionized water, and vacuum dried; (2) Preparation of the composite electrode: cobalt nitrate, iron nitrate, lanthanum nitrate and urea are dissolved in deionized water and ultrasonically mixed uniformly; the dried carbon felt obtained in step (1) is immersed in the mixed solution, ultrasonically for 20 minutes, hydrothermally reacted, repeatedly washed with deionized water, and dried at 60 DEG C to obtain the carbon felt cobalt-iron-lanthanum ternary hydrotalcite composite electrode; 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; In step (2), the temperature of the hydrothermal reaction is 80-180 DEG C, and the reaction time is 12-24 hours.

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

3. A carbon felt cobalt-iron-lanthanum ternary hydrotalcite composite electrode prepared by the method according to any one of claims 1-2.

4. Use of the carbon felt Co-Fe-La hydrotalcite ternary composite electrode prepared according to the method of any one of claims 1-2 in a capacitive deionization electrode, characterized in that: The electrode is used for removing phosphate.

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