Mixed carbon self-assembly electrode loaded with self-source iron and preparation method and application thereof

Abstract

The invention relates to a mixed carbon self-assembly electrode loaded with self-source iron as well as a preparation method and application of the mixed carbon self-assembly electrode. The preparation method comprises the following steps: preparing a mixed solution from graphene oxide and a commercially available carbon nanotube containing residual iron, immersing a metal base material into the mixed solution, and standing to obtain the mixed carbon material self-assembled electrode material containing self-source iron. When the material is applied to electro-Fenton, generation of hydrogen peroxide and removal of refractory organic pollutants can be efficiently catalyzed. The carbon nanotube raw material used by the electrode material is low in purity and pretreatment requirements, and low in manufacturing and use cost; and the preparation method is simple and easy for large-scale production.

Description

Technical Field

[0001] The invention relates to an electrode material and a preparation method and application thereof, and belongs to the field of electrochemical catalysis. Background Art

[0002] In the process of electro-Fenton pollutant removal, the performance of the cathode material is crucial. On the one hand, the cathode material determines the in-situ generation efficiency of oxygen reduction to hydrogen peroxide. On the other hand, the cathode material determines the regeneration of divalent iron and the activation efficiency of hydrogen peroxide, which directly affects the production of active oxygen species and the removal effect of pollutants. Therefore, an excellent electro-Fenton cathode material needs to have at least three characteristics: high mass transfer, high charge transfer, and high-performance hydrogen peroxide generation sites. Chemical oxidation is usually used to introduce oxygen functional groups on carbon materials as active sites for catalyzing hydrogen peroxide generation, but this operation also usually leads to the destruction of the crystal structure of the carbon material, the decrease of hydrophobicity, and the attenuation of oxygen and charge transfer rates. Therefore, when the oxygen content of the material is too high, the generation of hydrogen peroxide and the removal efficiency of pollutants will be reduced. Therefore, the trade-off between oxygen functional groups and crystal structure integrity is the difficulty and key point in constructing high-performance electro-Fenton carbon-based cathode materials and achieving efficient removal of pollutants.

[0003] At present, there are four main methods for preparing cathodes based on carbon materials that catalyze the reduction of oxygen to hydrogen peroxide: the first is to mix the oxidized carbon nanomaterials with fluorinated polymer binders such as perfluorosulfonic acid resin and polytetrafluoroethylene, and then coat them on the substrate material to form a cathode with a binder (Angew. Chem. Int. Ed. 2019, 58, 1100-1105); the second is to deposit graphene oxide or oxidized carbon nanotubes containing a large number of oxygen functional groups on an active metal substrate in the aqueous phase based on the self-assembly mechanism to form a self-assembled cathode (Adv. Mater. Technol. 2022, 7, 2100708). The preparation of such self-assembled electrodes relies on the chemical reaction between oxygen functional groups and the active metal surface to form a large number of chemical bonds, thereby fixing graphene oxide or oxidized carbon nanotubes on the electrode; the third method is to use chemical catalysis or hydrothermal conditions to assemble graphene oxide and oxidized carbon nanotubes into carbon hydrogels, and then freeze-dry to form carbon aerogel electrodes (Electrochim. Acta 2016,200, 75–83); the fourth method is to use polytetrafluoroethylene membrane carriers to pressurize and filter oxidized carbon nanotubes and reduce graphene oxide to form carbon film electrodes (J. Membr. Sci. 2021, 623, 119069). Compared with cathodes with binders, self-assembled cathodes do not use binders, thus avoiding the release of dangerous elements such as fluorine; compared with cathodes with binders and carbon aerogel electrodes, the preparation process of self-assembled cathodes is simpler; compared with carbon film electrodes, the preparation of self-assembled cathodes does not require pressurized filtration operations, has lower energy consumption, and does not use fluorine-containing substrates, thus avoiding the release of dangerous elements such as fluorine.

[0004] When considering the activation of hydrogen peroxide, the electro-Fenton carbon cathode can be divided into two categories according to the source of iron: the first category is that the carbon cathode does not contain active iron. In electro-Fenton applications, the cathode catalyzes the reduction of oxygen to hydrogen peroxide, and additional divalent iron or ultraviolet light is required to activate hydrogen peroxide (Adv. Mater. Technol. 2022, 7, 2100708); the second category is that additional iron is added during the manufacture of the carbon cathode to form an iron-loaded carbon cathode (J. Membr. Sci. 2021,623, 119069). In electro-Fenton applications, no additional divalent iron or ultraviolet light is required to activate hydrogen peroxide. There are also photo-Fenton materials with similar components to the latter, which use oxygen-containing carbon nanotubes, graphene oxides and iron salts to heat and hydrolyze and then freeze-dry to form aerogels (Appl. Catal. B Environ. 2017, 213, 74–86). However, the function of this material in photo-Fenton applications is only to provide heterogeneous iron and promote iron valence state cycling, so additional addition of hydrogen peroxide is required.

[0005] In the study of aqueous self-assembled cathodes, highly oxidized graphene oxide or oxidized carbon nanotubes can be self-deposited on metal substrates. Under the same oxidation conditions, carbon nanotubes have better mass transfer capacity than graphene oxide because they have stronger rigidity and inner tube pore structure, and they are more potential as electric Fenton cathodes. However, in the process of preparing highly oxidized graphene oxide carbon nanotubes, since the tubular structure of carbon nanotubes is very stable, high-temperature and high-pressure acid treatment or laser etching and other high-demand processing processes are required to produce enough oxygen functional groups on carbon nanotubes, which leads to high manufacturing costs on the one hand, and on the other hand, it leads to a decrease in oxygen mass transfer and charge conduction capacity, and the self-source metal of carbon nanotubes is removed. Therefore, the electric Fenton cathode based on highly oxidized carbon nanotubes has no self-source metal for activating hydrogen peroxide, and iron needs to be added additionally, and polytetrafluoroethylene coating needs to be added to improve oxygen mass transfer, resulting in additional manufacturing costs and use costs, which is not conducive to promotion and application. In summary, there is no report on the use of carbon nanotubes and their self-source iron to synthesize iron-loaded electric Fenton cathodes through self-assembly. Summary of the invention

[0006] The object of the present invention is to provide a mixed carbon self-assembled electrode carrying self-source iron and a preparation method and application thereof. Low-cost commercially available carbon nanotubes containing residual iron are selected and mixed with graphene oxide, and the carbon nanotubes are co-deposited on a metal substrate based on π-π interaction. The mixed carbon self-assembled electrode obtained based on this co-self-assembly process carries self-source iron, which can be used as a donor of divalent iron, and no additional divalent iron is required in electrode synthesis and electro-Fenton applications. In addition, graphene oxide provides oxygen functional groups as active sites to catalyze the generation of hydrogen peroxide, and the crystal structure of the carbon nanotubes is well maintained, which can maintain a higher material and electron transfer rate, promote the regeneration of divalent iron and the activation of hydrogen peroxide, thereby realizing low-cost electro-Fenton cathode manufacturing and use, and obtaining efficient active oxygen species generation and pollutant removal. Therefore, a self-assembled high-performance electro-Fenton cathode material can be obtained through a simple synthesis process, solving the problem that the existing electro-Fenton cathode needs to use a binder and additional iron addition, resulting in high manufacturing and use costs, which is more conducive to actual production and wide application.

[0007] According to a first aspect of the present invention, the present invention provides a method for preparing a mixed carbon self-assembled electrode loaded with self-source iron, characterized in that it comprises the following steps: Step 1: Dispersing graphene oxide in water under normal temperature, pressure and air conditions to form a dispersion; Step 2: adding commercially available carbon nanotubes containing residual iron to the dispersion obtained in step 1 and mixing thoroughly; Step 3: Immerse the clean and uncontaminated metal substrate in the dispersion obtained in step 2 to allow sufficient time for self-assembly; Step 4: Take out the mixed carbon self-assembled metal material loaded with self-source iron obtained in step 3 and dry it to obtain a mixed carbon self-assembled electrode loaded with self-source iron.

[0008] The commercially available carbon nanotubes containing residual iron are grown by catalytic growth of an iron-based catalyst, and residual iron nanoparticles are distributed inside and outside the tubes.

[0009] Preferably, the oxygen content of the graphene oxide is not less than 20%.

[0010] Preferably, the metal substrate is copper, iron, nickel, or a mixed substrate thereof with other metals.

[0011] Preferably, in step 2, the mixing mass ratio of the commercially available carbon nanotubes containing residual iron to graphene oxide is 1:0.1 to 1:100.

[0012] According to the second aspect of the present invention, the present invention provides a mixed carbon self-assembled electrode loaded with self-source iron, characterized in that its oxygen functional groups are mainly distributed on graphene oxide, iron nanoparticles are distributed inside and outside the carbon nanotubes, and are loaded on a metal substrate together with graphene oxide, and the formed self-assembled electrode has rich micropores and mesoporous structures.

[0013] According to the third aspect of the present invention, the present invention provides a mixed carbon self-assembled electrode loaded with self-source iron for use in electro-Fenton.

[0014] The beneficial effects of the present invention are embodied in: (1) The raw materials and pretreatment costs of commercially available carbon nanotubes containing residual iron are low, and the co-self-assembly synthesis process is simple, which is conducive to large-scale production. Compared with cathodes with binders and carbon aerogel electrodes, the preparation process of self-assembled cathodes is simpler; compared with the high energy consumption of directly oxidizing carbon nanotubes to produce oxygen functional groups for self-assembly, the co-self-assembly synthesis process only uses graphene oxide with low oxidation energy consumption, and based on the pp interaction, the carbon nanotubes are pulled to co-self-assemble onto the metal substrate. The oxidation degree of carbon nanotubes with high oxidation energy consumption is low, and even additional oxidation treatment is not required, which reduces the manufacturing cost. In addition, carbon nanotubes contain self-source iron that can be used to activate hydrogen peroxide, and no divalent iron needs to be added in electro-Fenton applications, so their use cost is lower; (2) Compared with electrodes using binders, the self-deposition electrode provided by the present invention does not contain a binder. Compared with carbon film electrodes, the self-deposition electrode provided by the present invention does not use a fluorine-containing substrate, thereby avoiding the risk of electrodes with binders and carbon film electrodes releasing their own fluorine elements in electro-Fenton applications. Compared with the electro-Fenton carbon cathode that does not contain iron, the self-deposition electrode provided by the present invention has its own iron source, and no divalent iron needs to be added in the electro-Fenton application. Therefore, on the one hand, the iron sludge generated during electro-Fenton water treatment is reduced, and on the other hand, it is unnecessary to adjust the acid and alkali, which has a lower cost of use and reduces the impact on the salinity of the water body; (3) Compared with the carbon film electrodes and the self-deposited highly oxidized graphene electrodes prepared by the high-pressure filtration method, which are mainly micropores (<2 nm), and the self-deposited highly oxidized carbon nanotubes, which are mainly macropores (>50 nm) formed by stacking tubes, the co-self-deposited carbon nanotubes and graphene oxide provided by the present invention can use flexible planes to cut the stacked macropores of the tubular structure to produce more mesopores (2 ~ 50 nm), and improve the exposure of active sites and mass transfer efficiency based on abundant micropores and mesopores. In addition, the oxygen functional groups on the graphene can be used as active sites, and the carbon nanotubes with more complete crystal structures can be used to promote charge transfer efficiency and hydrogen peroxide activation, thereby achieving more efficient generation of active oxygen species and electro-Fenton removal of pollutants; (4) The present invention can directly use relatively low-purity commercially available carbon nanotubes containing residual iron, and does not require strict control of the carbon nanotube production process, which can reduce the cost of electrode production. It is more valuable for promotion and application in application scenarios where a large number of electrodes need to be used and replaced in sewage treatment. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 This is a physical picture of the mixed carbon self-assembled electrode loaded with self-source iron obtained in Example 1; Figure 2 This is a pore structure distribution diagram of the mixed carbon self-assembled electrode loaded with self-source iron obtained in Example 1; Figure 3 This is a physical picture of the carbon nanotube self-assembled electrode obtained in Comparative Example 1; Figure 4 This is an electron microscope image of the graphene oxide self-assembled electrode obtained in Comparative Example 2; Figure 5 This is the pore structure distribution diagram of the graphene oxide self-assembled electrode obtained in Comparative Example 2. DETAILED DESCRIPTION In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings. The following content is only an example and explanation of the concept of the present invention. The technicians in the field may make various modifications or supplements to the specific implementation cases described, or replace them with similar methods, as long as they do not deviate from the concept of the invention or exceed the scope defined by the claims, they should all fall within the scope of protection of the present invention.

[0017] Example 1 The preparation process of the mixed carbon self-assembled electrode loaded with self-source iron comprises the following steps: Step 1: Disperse 20 mg of graphene oxide in water under normal temperature, pressure and air conditions, and fully ultrasonically disperse to form a dispersion; Step 2: Add 20 mg of commercially available carbon nanotubes containing residual iron to the dispersion obtained in step 1, and mix thoroughly by ultrasonication; Step 3: After cleaning the nickel foam with ethanol and dilute hydrochloric acid, immerse it in the dispersion obtained in step 2 to allow for sufficient self-assembly; Step 4: Take out the mixed carbon self-assembled nickel foam material loaded with self-source iron obtained in step 3 and dry it naturally to obtain a mixed carbon self-assembled electrode loaded with self-source iron. Figure 1 shown.

[0018] Its pore structure is Figure 2 As shown, there is a higher proportion of micropores and mesopores.

[0019] Using the mixed carbon self-assembled electrode loaded with self-source iron in this example as the cathode, the platinum wire as the anode, the silver / silver chloride electrode as the reference electrode, and 0.1 mol / L Na2SO4 as the electrolyte, levofloxacin was removed in the electrolytic cell, and 96% of levofloxacin could be removed within 20 minutes.

[0020] Comparative Example 1 Compared with Example 1, the commercially available carbon nanotubes containing residual iron were treated with 9 mol / L nitric acid at 120°C for 6 h to introduce oxygen functional groups. The pretreated carbon nanotubes were directly ultrasonically dispersed in water for self-deposition. The obtained carbon nanotube self-assembled electrode is shown in the figure below. Figure 3 As shown. Due to the small amount of oxygen functional groups contained, the deposition amount of carbon nanotubes is low, and the nickel foam substrate is not completely covered. When used as an electro-Fenton cathode, not only does it require additional divalent iron, but the removal rate of levofloxacin is only 30%.

[0021] Example 2 The preparation process of the mixed carbon self-assembled electrode loaded with self-source iron comprises the following steps: Step 1: Disperse 100 mg of graphene oxide in water under normal temperature, pressure and air conditions, and fully ultrasonically disperse to form a dispersion; Step 2: Add 50 mg of commercially available carbon nanotubes containing residual iron to the dispersion obtained in step 1, and mix thoroughly by ultrasonication; Step 3: After cleaning the copper foam with isopropyl alcohol and dilute hydrochloric acid, immerse it in the dispersion obtained in step 2 to allow for sufficient self-assembly; Step 4: Take out the mixed carbon self-assembled copper foam material loaded with self-source iron obtained in step 3 and dry it naturally to obtain a mixed carbon self-assembled electrode loaded with self-source iron.

[0022] Comparative Example 2 Compared with Example 2, the cleaned nickel foam is directly immersed in the graphene oxide dispersion obtained in step 1 for self-assembly to obtain a graphene oxide self-assembled electrode, the scanning electron microscope image of which is as follows: Figure 4 The pore size distribution diagram is shown in Figure 5 As shown. It can be seen that the graphene layers on the surface of the graphene oxide self-assembled electrode are densely stacked, with more micropores and almost no mesopores. When used as an electro-Fenton cathode, not only does it require additional divalent iron, but also due to the lack of mesopores and the strong hydrophilicity of the electrode, the mass transfer rate of the reactant oxygen is low, resulting in a reduced generation rate of hydrogen peroxide. Therefore, in this system, the removal kinetics of levofloxacin is reduced by half, and the removal rate is 85%.

[0023] The above are only exemplary embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A mixed carbon self-assembled electrode loaded with self-source iron, characterized in that: Its oxygen functional groups are mainly distributed on graphene oxide. Iron nanoparticles are distributed inside and outside the carbon nanotubes and are loaded on a metal substrate together with graphene oxide. The formed self-assembled electrode has rich microporous and mesoporous structures.

2. A method for preparing a mixed carbon self-assembled electrode loaded with self-source iron as claimed in claim 1, characterized in that: The following steps are involved: Step 1: Dispersing graphene oxide in water under normal temperature, pressure and air conditions to form a dispersion; Step 2: adding commercially available carbon nanotubes containing residual iron to the dispersion obtained in step 1 and mixing thoroughly; Step 3: Immerse the clean and uncontaminated metal substrate in the dispersion obtained in step 2 to allow sufficient time for self-assembly; Step 4: Take out the mixed carbon self-assembled metal material loaded with self-source iron obtained in step 3 and dry it to obtain a mixed carbon self-assembled electrode loaded with self-source iron.

3. The method for preparing the mixed carbon self-assembled electrode loaded with self-source iron according to claim 2, characterized in that: The commercially available carbon nanotubes containing residual iron are grown by catalytic growth of an iron-based catalyst, and residual iron nanoparticles are distributed inside and outside the tubes.

4. The method for preparing the mixed carbon self-assembled electrode loaded with self-source iron according to claim 2, characterized in that: The oxygen content of the graphene oxide is not less than 20%.

5. The method for preparing a mixed carbon self-assembled electrode loaded with self-source iron according to claim 2, characterized in that: The metal substrate in step 3 is copper, iron, nickel and a mixture of other metals. The surface of the substrate is clean and pollution-free and has no organic matter or severe oxidation.

6. The method for preparing a mixed carbon self-assembled electrode loaded with self-source iron according to claim 2, characterized in that: In the step 2, the mixing mass ratio of the commercially available carbon nanotubes containing residual iron to graphene oxide is 1:0.1 to 1:

100.

7. A mixed carbon self-assembled electrode loaded with self-source iron prepared according to any one of claims 2 to 6, characterized in that: Iron nanoparticles are distributed inside and outside the carbon nanotubes and are loaded together with graphene oxide on a metal substrate. The self-assembled electrode formed has rich microporous and mesoporous structures.

8. Use of the mixed carbon self-assembled electrode loaded with self-source iron according to claim 7 in electrochemical catalysis.

9. The use according to claim 8, characterized in that: The application is to perform electro-Fenton degradation of pollutants.

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