Preparation and application of FeS-loaded alginate-derived carbon shell-encapsulated Fe3O4 cathode

Abstract

The application discloses a preparation method of a FeS-loaded alginate-derived carbon shell-coated Fe3O4 catalyst (FeS / Fe3O4@C) and loading of the catalyst on a cathode for efficient removal of pollutants by heterogeneous electro-Fenton water treatment. Sodium alginate, carbon black and FeSO4 are mixed as a carbon source and an iron source respectively, and a three-dimensional gel synthesized by one-step cross-linking is pyrolyzed in situ, so that the obtained catalyst realizes deposition of FeS on the surface of carbon-coated Fe3O4 particles and exhibits multi-layer structure and multi-reaction active centers. The bifunctional electro-Fenton catalyst prepared in the application is low in cost and high in catalyst stability, the H2O2 selectivity of the cathode catalyst can reach 90%-95%, and the iron dissolution is extremely low (<0.18 mg / L ‑1 ), the cathode has good reusability, and meanwhile, the method has excellent catalytic performance in degradation of pollutants in the pH range of 3-11, and has wide application prospect in the field of actual water treatment.

Description

Technical Field

[0001] This invention relates to the fields of materials and environment. Specifically, this invention relates to a method for preparing a Fe3O4 cathode encapsulated in an alginate-derived carbon shell loaded with FeS and its application in heterogeneous electric Fenton. Background Technology

[0002] Heterogeneous electro-Fenton advanced oxidation technology, as a novel electrochemical advanced oxidation technology, generates H2O2 in situ through a two-electron redox reaction at the cathode, and uses iron-containing materials as a heterogeneous catalyst to provide Fe. 2+ In recent years, the cathode electro-Fenton process, which has seen continuous development in the field of water treatment technology, involves loading the Fenton catalyst onto the cathode, avoiding catalyst recovery and effectively reducing the formation of iron sludge. However, the catalyst surface is easily oxidized and deactivated, and Fe... 2+ The hindered dissolution of iron significantly limits the reaction rate of heterogeneous electro-Fenton catalysts. Currently developed iron-based catalysts utilize heterogeneous catalysts as the electro-Fenton cathode, where oxygen undergoes a reduction reaction to produce H₂O₂. Simultaneously, the active sites in the iron-based catalyst decompose H₂O₂ to generate free radicals that degrade pollutants. However, this technology still faces certain challenges. Many catalysts exhibit a four-electron water generation process, and significant iron dissolution reduces the catalyst's reusability.

[0003] Bifunctional cathodes simultaneously generate H2O2 and catalyze the degradation of pollutants, which can further improve the utilization efficiency of H2O2 and the recyclability of the catalyst. However, they still face challenges such as the required high cathode potential, low H2O2 yield, and significant iron dissolution. Furthermore, conventional cathode-fenton catalysts such as Fe2O3, Fe3O4, and FeOOH are easily deactivated under alkaline conditions. Therefore, constructing cathode-fenton catalysts suitable for a wide pH range is of significant environmental importance. Among the currently developed catalyst preparation methods, coating the catalyst surface with a carbon shell to construct a core-shell catalyst can effectively reduce the dissolution of the Fe-based core and improve catalyst stability. However, methods for constructing iron-based core-shell Fenton catalysts mainly involve pyrolysis of iron-based MOFs or embedding the catalyst in a carbon aerogel electrode, which suffers from high raw material costs, complex synthesis processes, and poor catalyst stability, limiting their practical industrial application. Heteroatom-doped porous carbon nanomaterials with unique structures and chemical compositions have been synthesized using the inherent characteristics of natural biomass. These biomass-derived functionalized carbon nanomaterials have advantages such as high conductivity, abundant heteroatoms, high specific surface area, and large pore volume, and have broad application prospects in the field of electrochemistry. Summary of the Invention

[0004] This invention addresses the problems of low H2O2 selectivity, poor catalyst stability, and pH limitation in current electro-Fenton processes. The aim is to provide a green, environmentally friendly, low-cost, highly active, and stable FeS-supported alginate-derived carbon shell-encapsulated Fe3O4 cathode (FeS / Fe3O4@C), which is then applied to heterogeneous electro-Fenton water treatment to achieve efficient H2O2 generation and effective pollutant removal at lower potentials.

[0005] The technical principle of its wastewater treatment is as follows: This invention proposes a multi-reactive active center among C, O, S, and Fe components, and a composite structure at the FeS and Fe3O4@C interface, which not only promotes the adsorption and conversion of O2, but also significantly enhances the overall activity of the catalyst. The principle of its organic matter treatment method is as follows: The FeS / Fe3O4@C modified cathode can undergo a 2-electron reduction reaction with oxygen in the air to synthesize H2O2 in situ. This cathode has high H2O2 synthesis efficiency and low energy consumption. The generated H2O2 can be absorbed by the encapsulated Fe3O4 and the ≡Fe in the FeS on the catalyst surface. 2+ Catalytic Fenton reaction produces • OH and Fe 3+ Under moderately alkaline conditions, H2O2 reacts with Fe on the catalyst surface. 2+ The reaction produces Fe IV O 2+ And water; in addition, O2 is also reduced to water via single-electron transfer. • O2 − Further generation 1 O2 is used to achieve the co-catalytic degradation of pollutants by multiple active species. The FeS in this invention can regulate the pH of the reaction system, thereby broadening the applicable pH range. The core-shell encapsulation structure formed by the catalyst can reduce iron dissolution, thus achieving high reusability.

[0006] The specific method described in this invention is as follows: Specifically, the method for preparing FeS-loaded alginate-derived carbon shell-encapsulated Fe3O4 (FeS / Fe3O4@C) cathode and its application in heterogeneous electro-Fenton water treatment technology includes the following steps:

[0007] 20 g / L sodium alginate and carbon black were mixed and stirred evenly at a mass ratio of 5:1 to 20:1. Then, the mixture was added to a 20 g / L ferrous sulfate heptahydrate solution at a volume ratio of 1:2. The resulting composite gel was freeze-dried at -40 °C.

[0008] Furthermore, the obtained composite gel was placed in a tube furnace under an inert gas atmosphere for pyrolysis. The temperature was increased to 400 °C at a rate of 3-5 °C / min and kept at the same temperature for 1.5-2.5 h. Then, the temperature was increased to 800 °C at a rate of 8-12 °C / min and kept at the same temperature for 1.5-2.5 h to obtain FeS / Fe3O4@C catalyst with FeS supported on an alginate-derived carbon shell encapsulating Fe3O4.

[0009] Further, the obtained FeS / Fe3O4@C catalyst powder was weighed into a 1:1 mixture of ethanol and water, and 20% PTFE emulsion was added and shaken to mix thoroughly, controlling the loading to 15-20 mg / cm³. -1 Loaded onto the substrate electrode, after natural drying, it can be calcined in a tube furnace at 360 ℃ for 30 min to be used as a cathode; adjust the pH of the wastewater to be treated to 3-11.

[0010] The present invention has the following outstanding features and beneficial effects:

[0011] (1) The catalyst preparation method is simple and easy to implement, with high yield, and exhibits a H2O2 selectivity of over 90% and extremely low iron dissolution (<0.2 mg / L). -1 The characteristics of )

[0012] (2) This catalyst exhibits structural features such as multiple reactive sites and interfacial composites between FeS and Fe3O4@C, which can effectively promote the electron transfer rate on the catalyst surface and Fe 2+ The dissolution of FeS on the surface can provide a favorable pH environment for the electro-Fenton through the reaction, thereby broadening the pH range of applicability.

[0013] (3) The cross-linking effect between sodium alginate biomass, metal ions and carbon black is used to make the graphite carbon and metal catalytic components in the final product have a strong covalent bond, which improves the heterogeneous electro-Fenton catalytic performance by promoting electron transport.

[0014] (4) By using FeS / Fe3O4@C modified carbon felt as the cathode, H2O2 can be continuously generated in situ during the reaction process without the need for additional addition, thus solving the problems of H2O2 transportation and storage and greatly reducing operating costs.

[0015] (5) The biomass raw materials used in this invention are widely available and inexpensive. The reaction operation is simple and the conditions are easy to control. This heterogeneous electro-Fenton process can achieve efficient removal of pollutants in the pH range of 3-11, and its reusability can reach more than 10 times, which has good practical application prospects. Attached Figure Description

[0016] Figure 1 The X-ray photoelectron spectrum of the FeS / Fe3O4@C catalyst prepared in this invention;

[0017] Figure 2 Transmission electron microscopy image of the FeS / Fe3O4@C catalyst prepared in this invention;

[0018] Figure 3 The effect of the FeS / Fe3O4@C catalyst with a sodium alginate to carbon black mass ratio of 10:1 prepared in this invention on the in-situ degradation of 50 mg / L tetracycline in a heterogeneous electro-Fenton process is shown in the figure.

[0019] Figure 4 The effect of FeS / Fe3O4@C cathode with sodium alginate and carbon black in a mass ratio of 10:1 prepared for this invention on the degradation of tetracycline at different pH values;

[0020] Figure 5 The effect of the FeS / Fe3O4@C catalyst with a sodium alginate to carbon black mass ratio of 5:1 prepared in this invention on the in-situ degradation of 50 mg / L tetracycline in a heterogeneous electro-Fenton process is shown in the figure.

[0021] Figure 6 The effect of the FeS / Fe3O4@C catalyst with a sodium alginate to carbon black mass ratio of 20:1 prepared in this invention on the in-situ degradation of 50 mg / L tetracycline in a heterogeneous electro-Fenton process is shown in the figure.

[0022] Figure 7 The H2O2 selectivity of the FeS / Fe3O4@C catalyst with a sodium alginate to carbon black mass ratio of 10:1 prepared in this invention and the control group is shown in the figure.

[0023] Figure 8 The graph shows the effect of the FeS / Fe3O4@C catalyst with a sodium alginate to carbon black mass ratio of 10:1 prepared in this invention and the control group on the in-situ degradation of 50 mg / L tetracycline in a heterogeneous electro-Fenton process.

[0024] Figure 9 This is a diagram of hydroxyl radicals and singlet oxygen generated by the FeS / Fe3O4@C cathode prepared in this invention;

[0025] Figure 10 The graph shows the effect of the FeS / Fe3O4@C cathode prepared in this invention on the PMSO2 conversion rate during the PMSO degradation process at different initial pH values.

[0026] Figure 11 The image shows the effect of the FeS / Fe3O4@C cathode prepared in this invention being reused 10 times to degrade tetracycline.

[0027] Figure 12The image shows the effect of iron leaching after the FeS / Fe3O4@C cathode prepared in this invention is reused 10 times. Detailed Implementation

[0028] The present invention will be further described in detail below through specific embodiments, examples of which are shown in the accompanying drawings. The embodiments described below with reference to the drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0029] A mixed solution of sodium alginate and carbon black at a mass ratio of 10:1 was added dropwise to a ferrous sulfate heptahydrate solution. The resulting composite gel was then subjected to cold drying at -40 °C for 24 h. The composite gel was then placed in an inert gas atmosphere and heated to 400 °C at a rate of 3-5 °C / min, and held at that temperature for 1.5-2.5 h. The temperature was then increased to 800 °C at a rate of 8-12 °C / min, and held at that temperature for 1.5-2.5 h to obtain a FeS-supported alginate-derived carbon shell-encapsulated Fe3O4 catalyst (FeS / Fe3O4@C).

[0030] Implementation Case 1

[0031] The composition and properties of the FeS / Fe3O4@C catalyst were characterized by X-ray photoelectron spectroscopy, and the results are shown in the figure. Figure 1 The catalyst mainly consists of C, O, S, and Fe elements. Transmission electron microscopy revealed a multilayer structure of FeS / Fe3O4@C, confirming that the bifunctional catalyst consists of Fe3O4-supported FeS particles encapsulated in an alginate-derived carbon shell (see results). Figure 2 ).

[0032] Implementation Case 2

[0033] The FeS / Fe3O4@C cathode catalytic performance test of this embodiment is as follows: 200 mL of solution containing 50 mg L... -1 A 50 mM sodium sulfate solution of tetracycline at pH 7. When the FeS / Fe3O4@C loading is 0.02 g cm⁻¹ -2 When the cathode potential is -0.4V (vs. the reversible hydrogen electrode), from Figure 3 It can be seen that when the mass ratio of sodium alginate to carbon black is 10:1, 98% of tetracycline can be removed after 2 hours of reaction.

[0034] refer to Figure 4 The system exhibited tetracycline removal rates exceeding 80% across solution pH ranges from 3 to 11, with optimal results observed at pH 3. Furthermore, the tetracycline removal rates were similar at pH 5 and 7, indicating that the FeS / Fe3O4@C cathode performs better under moderately alkaline conditions.

[0035] Implementation Case 3

[0036] The steps in Implementation Case 3 are basically the same as those in Implementation Case 1, except that FeS / Fe3O4@C is prepared with a sodium alginate and carbon black mass ratio of 5:1. When this catalyst is used as the cathode, the removal of tetracycline is 79% after 2 hours. The results are shown in […]. Figure 5 .

[0037] Implementation Case 4

[0038] The steps in Implementation Case 3 are basically the same as those in Implementation Case 1, except that the mass ratio of sodium alginate to carbon black is 20:1 for FeS / Fe3O4@C. When this catalyst is used as the cathode, the removal of tetracycline is 72% after 2 hours. The results are shown in […]. Figure 6 .

[0039] Implementation Case 5

[0040] CB-800 and FeS @C, obtained by calcining separate carbon black in a tube furnace using the same method as for preparing FeS / Fe3O4@C catalysts, were physically-mechanically mixed at a ratio of 10:1. The results were compared with those of the FeS / Fe3O4@C prepared in Example 1 during rotating disk electrode testing. The results showed that the prepared FeS / Fe3O4@C catalyst exhibited excellent electron transfer processes, with calculated H2O2 selectivity exceeding 90%. (See attached figures). Figure 7 The H2O2 selectivity of the CB-800 and FeS@C mechanically mixed catalyst was only 76%, indicating that FeS / Fe3O4@C is a good catalyst for achieving two-electron ORR to generate H2O2.

[0041] refer to Figure 8 When the catalyst of CB-800 and FeS@C mechanically mixed was used as the cathode, tetracycline removal was only 50%, while electroadsorption and carbon felt substrate alone achieved only 8.6% and 30.2% removal rates for tetracycline, respectively, while iron dissolution increased from 0.18 mg / L. -1 Increased to 2.16 mg L -1 These findings indicate that the FeS / Fe3O4@C cathode prepared in this invention is a good bifunctional cathode that can catalytically decompose in-situ generated H2O2 into active oxygen species, thereby achieving the removal of pollutants.

[0042] Implementation Case 6

[0043] The steps in Implementation Case 6 are basically the same as in Implementation Case 1, comparing the effects of adding different inhibitors to the catalytic reaction system on the generation of free radicals in the system without adding contaminants. (Reference) Figure 9 It can be observed that after adding TBA or N2 to replace O2, the reaction system...• The OH signal disappeared after adding SOD and CAT. • The decrease in OH signal indicates that H2O2 and • O2 − All produced • OH. However, H2O2 is not produced. 1 The main source of O2, because after the addition of CAT... 1 O2 did not change significantly. And when • When OH is captured by TBA, 1 The signal of O2 increases. Therefore, it can be considered that O2 and • O2 − It is produced 1 The source of O2, O V It can promote • O2 − The generation of free radicals.

[0044] Implementation Case 7

[0045] The steps in Implementation Case 6 are basically the same as in Implementation Case 1, using PMSO as a probe to investigate the presence of Fe(IV). Since pH affects the formation of Fe in the Fenton reaction... • OH or Fe(IV) substances were used, therefore different initial pH values ​​were adjusted to verify the degradation of PMSO by the FeS / Fe3O4@C cathode. (Reference) Figure 10 To investigate the role of Fe(IV), the conversion rate of PMSO2 was calculated by the ratio of PMSO2 generated to PMSO2 consumed. It was found that the PMSO2 conversion rate was below 40% at pH 3-7, while it was greater than 43.7% at pH 9 and greater than 52.6% at pH 11, indicating that Fe(IV) is readily formed at high pH values ​​in this system.

[0046] Implementation Case 8

[0047] The steps for implementing Case 7 are basically the same as those for Case 1. (See reference) Figure 11 Even after the FeS / Fe3O4@C cathode was reused 10 times, tetracycline removal still reached 87%, and the dissolved iron concentration was consistently below 0.18 mg / L. -1 ( Figure 12 Therefore, this demonstrates that the FeS / Fe3O4@C cathode can be reused and reduces iron leaching, thereby reducing the generation of iron sludge.

[0048] The above description is merely one embodiment of the present invention and does not constitute any limitation on the present invention. Anyone skilled in the art can readily implement the present invention based on the accompanying drawings and the description above. However, any modifications, alterations, or variations made by those skilled in the art without departing from the scope of the present invention are equivalent embodiments of the present invention. Furthermore, any equivalent modifications, alterations, or variations made to the above embodiments based on the essential technology of the present invention are within the protection scope of the present invention.

Claims

1. A method for preparing an Fe3O4 cathode encapsulated in an alginate-derived carbon shell loaded with FeS, characterized in that, Includes the following steps: (1) 20 g / L sodium alginate and carbon black are mixed and stirred evenly at a mass ratio of 5:1 to 20:1, and then added to a 20 g / L ferrous sulfate heptahydrate solution at a volume ratio of 1:2 to obtain a composite gel. The composite gel is then freeze-dried at -40℃. (2) The composite gel obtained in step (1) was placed in a tube furnace under argon protection for pyrolysis. The temperature was increased to 400 ℃ at a rate of 3-5 ℃ / min and kept at the temperature for 1.5-2.5 h. Then the temperature was increased to 800 ℃ at a rate of 8-12 ℃ / min and kept at the temperature for 1.5-2.5 h to obtain FeS / Fe3O4@C Fe3O4 catalyst with alginate-derived carbon shell loaded with FeS. (3) Disperse the FeS / Fe3O4@C catalyst powder obtained in step (2) in a mixed solution of ethanol and water at a volume ratio of 1:1, and add 20% PTFE emulsion and shake to mix evenly, at a concentration of 15-20 mg / cm³. 2 The loading amount is applied to the surface of a carbon substrate, and after natural drying, it is calcined in a tube furnace at 360 °C for 30 min to obtain the cathode.

2. The preparation method according to claim 1, characterized in that, The carbon substrate is carbon felt, carbon cloth, carbon paper, or carbon fiber.

3. The preparation method according to claim 1, characterized in that, In step (1), the mass ratio of sodium alginate to carbon black is 10:1.

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