Preparation method and application of amorphous / crystalline phase hybrid iron sulfide electro-Fenton catalyst

Abstract

The invention discloses an amorphous / crystalline phase hybrid iron sulfide catalyst as well as a preparation method and application thereof. The catalyst takes an amorphous iron-based metal organic framework as a precursor, an amorphous / crystal phase synergistic structure is obtained through sulfur source solvothermal reaction time regulation and control, and an amorphous / crystal interface action effect is formed, so that electron transport and Fe (II) / Fe (III) circulation are promoted, Fe (II) active sites are stabilized, and the heterogeneous electro-Fenton reaction efficiency is remarkably improved. In an electrochemical reaction, the catalyst preferentially generates surface-bound hydroxyl radicals under a neutral condition, so that efficient removal of pollutants is realized. Compared with a single amorphous or crystalline phase catalyst, the catalyst disclosed by the invention has higher degradation rate and lower energy consumption, shows a good application effect in electro-Fenton removal reaction of various pollutants, and still keeps an excellent removal effect after being recycled for multiple times. The limitation that traditional electro-Fenton depends on acidic conditions is broken through, a new technical approach is provided for electro-Fenton water treatment under the neutral condition, and the method has wide engineering application prospects.

Description

Technical Field

[0001] This invention relates to the field of water pollution control and electrochemical advanced oxidation catalysis, specifically to a method for preparing an amorphous / crystalline hybrid iron sulfide catalyst and its application in heterogeneous electro-Fenton water treatment. Background Technology

[0002] Electro-Fenton (EF) technology is widely used for the removal of recalcitrant organic pollutants because it can generate H₂O₂ in situ via electrochemical processes and combine it with Fe(II) to activate hydroxyl radicals (·OH). However, traditional EF systems typically rely on acidic conditions for efficient operation, with a significant decrease in reaction efficiency under neutral conditions. This is mainly due to the slow Fe(II) / Fe(III) cycle kinetics in a neutral environment, which leads to the easy precipitation and deactivation of iron ions, resulting in low H₂O₂ utilization and high energy consumption, thus severely limiting the application of this technology in practical water treatment.

[0003] Current research has attempted to improve the electro-Fenton efficiency under neutral conditions by developing iron-based solid catalysts to replace homogeneous Fe(II). Amorphous iron-based materials possess abundant active sites, but their electron transport performance is poor and their stability is limited. While crystalline iron sulfides exhibit some electron conductivity, their limited number of reactive sites results in insufficient overall catalytic performance. Therefore, single-phase catalysts still have significant shortcomings in terms of activity, stability, and energy consumption, making it difficult to meet the demands for efficient purification in complex water bodies.

[0004] Therefore, how to achieve efficient and stable electro-Fenton reaction of iron-based catalysts under neutral conditions through structural design is a technical problem that urgently needs to be solved. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing an amorphous / crystalline hybrid iron sulfide catalyst and its application in heterogeneous electro-Fenton water treatment, thereby solving the problems of low reaction efficiency, high energy consumption, and insufficient catalyst stability in existing electro-Fenton technologies under neutral conditions. The catalyst of this invention can efficiently activate electrogenerated H₂O₂ under neutral pH conditions, preferentially generating surface-bound hydroxyl radicals (·OH). surf. This enables the efficient removal of organic pollutants.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: An amorphous / crystalline hybrid iron sulfide catalyst is characterized in that the catalyst simultaneously comprises an amorphous phase region and a crystalline phase region, the crystalline phase being Fe3S4, and the amorphous phase being rich in sulfur vacancies and SO functional groups. The two form a charge transport effect at the interface, thereby promoting heterogeneous electro-Fenton reaction and effectively degrading organic pollutants.

[0007] The method for preparing the catalyst includes the following steps: (1) A brownish-yellow powder was obtained by reacting FeSO4·7H2O and 2-methylimidazole in methanol solution with a molar ratio of 1:5.3 with magnetic stirring for 24 h and then drying by centrifugation. This powder is an amorphous iron-based metal-organic framework (A-Fe-MOF) and is used as a precursor. (2) The obtained A-Fe-MOF and thioacetamide were mixed in an ethanol solution at a mass ratio of 1:4. After the reaction was carried out in a hydrothermal reactor at 120 °C, the precipitate was obtained by centrifugation of ethanol and deionized water and then dried in a vacuum drying oven.

[0008] Catalysts with different crystalline phases were obtained based on different reaction times (1-24 h). A reaction time of 1 h yielded a pure amorphous iron sulfide; reaction times of 2 h and 4 h yielded amorphous / crystalline hybrid iron sulfides; after 8 h, the reaction gradually evolved into a predominantly crystalline iron sulfide; and after 24 h, a pure crystalline Fe3S4 was obtained. Catalysts were labeled according to reaction time: 1 h was designated A-Fe. x S-1,2 h is AC-Fe x S-2,4 h is AC-Fe x S-4, 8 h is C-Fe x S-8, 24 h is C-Fe x S-24.

[0009] The application of the catalyst is characterized by its application in a heterogeneous electro-Fenton system, enabling the simultaneous utilization of H2O2 through electrosynthesis and mitigating the risks associated with H2O2 storage and transportation. Under neutral conditions (pH=7) during the electro-Fenton reaction, ·OH is preferentially generated. surf. This enables the efficient removal of organic pollutants.

[0010] Compared with the prior art, the present invention has the following beneficial effects: (1) Amorphous / crystalline hybrid iron sulfides possess both amorphous and crystalline phase characteristics, constructing a hybrid interface with efficient electron transport, which significantly improves the EF reaction efficiency.

[0011] (2) It can efficiently generate ·OH under neutral conditions. surf. The formation efficiency is 228.5 times and 39.5 times that of simple amorphous iron sulfides and crystalline iron sulfides, respectively.

[0012] (3) The catalyst exhibits high degradation efficiency, high mineralization rate, and low energy consumption for organic pollutants in neutral heterogeneous electro-Fenton technology. It can achieve 100% removal rate within 15 min, with a degradation rate constant of 0.2508 min.-1 With a mineralization rate of 72.3%, the power consumption is only 0.0219 kWh / g. TOC .

[0013] (4) The reaction system is suitable for the degradation of a variety of different organic pollutants, and the degradation efficiency can still be maintained at more than 95% after multiple cycles, showing broad engineering application prospects. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the preparation method of the amorphous / crystalline hybrid iron sulfide catalyst of the present invention; Figure 2 The X-ray diffraction (XRD) patterns of the catalysts obtained at different hydrothermal reaction times are used to characterize the formation of amorphous, crystalline, and amorphous / crystalline hybrid structures. Figure 3 The image shows a transmission electron microscope (TEM) image of the catalyst of the present invention, displaying the bonding between the amorphous phase and the crystalline phase at the interface and its microstructural features. Figure 4 Comparison curves of the degradation efficiency of bisphenol A by different catalysts in the electro-Fenton reaction, including amorphous, crystalline and amorphous / crystalline hybrid catalysts; Figure 5 The results are from electron paramagnetic resonance (EPR) detection, showing a comparison of the intensity of the ·OH signal generated by different catalysts in the electro-Fenton reaction; Figure 6 The results are from a quantitative analysis of the ·OH generation amount of different catalysts by the dimethyl sulfoxide-2,4-dinitrophenylhydrazine derivatization method. Figure 7 A comparison of the energy efficiency of different catalysts in the electro-Fenton reaction, with TOC removal rate as a function of energy consumption (kWh / g). TOC ) are used as evaluation indicators; Figure 8 The results show the comparison of the removal rates of the catalyst of this invention in the degradation of various typical organic pollutants; Figure 9 The results show the cyclic stability test of the catalyst of this invention in the bisphenol A degradation experiment. Specific Implementation Cases

[0015] The present invention will be further described below with reference to the embodiments, but the present invention is not limited to the following embodiments.

[0016] Implementation Case 1 See Figure 1This is a flowchart of the preparation method of the amorphous / crystalline hybrid iron sulfide catalyst provided in the embodiments of this application. The preparation method includes: step (1), dissolving FeSO4·7H2O and 2-methylimidazolium in methanol solution at a molar ratio of 1:5.3, mixing and stirring for 24 h, and then centrifuging, washing and drying to obtain a brownish-yellow powder; step (2), weighing A-Fe-MOF and thioacetamide at a mass ratio of 1:4, mixing them in ethanol solution, stirring to form a uniform suspension, transferring to a polytetrafluoroethylene (PTFE) lined reactor, sealing and carrying out a hydrothermal reaction at 120 ℃ for 2-8 h, centrifuging, washing and drying to obtain a blackish-gray powder, and storing it in a sealed and dry environment for later use.

[0017] Implementation Case 2 The catalysts obtained at different reaction times were subjected to X-ray diffraction (XRD) tests. It was observed that the 1-h sample showed only broad, diffuse peaks (amorphous structure); the 2-h and 4-h samples showed both diffuse peaks and crystalline phase diffraction peaks (amorphous / crystalline hybrid structure); the 8-h sample showed a significant enhancement of the crystalline phase signal, indicating a crystallization trend; the 24-h sample showed clear Fe3S4 crystalline phase characteristic peaks, indicating that the product is a pure crystalline iron sulfide. (See results below) Figure 2 ) Implementation Case 3 AC-Fe was studied using transmission electron microscopy (TEM). x Observations using S-4 images show that the amorphous and crystalline phases are tightly bonded at the interface, forming a clear structural transition that facilitates efficient electron transport between the interfaces. (See results below) Figure 3 ) Implementation Case 4 A 10 mg / L bisphenol A solution (pH=7.0) was prepared in a 100 mL quartz electrolytic cell, and 100 mg / L of different catalysts were added. A current of 5 mA was applied. The results are as follows. Figure 5 As shown, bisphenol A is completely degraded within 15 min, and the apparent rate constant is higher than that of pure amorphous or pure crystalline catalysts. (See results below) Figure 4 ) Implementation Case 5 Under neutral conditions (pH=7), using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a spin trap, the active species generated during the electro-Fenton reaction were detected using electron paramagnetic resonance (EPR) technology. A typical DMPO-·OH signal peak shape was observed, indicating the formation of hydroxyl radicals (·OH) in the reaction system. Compared with pure amorphous or pure crystalline iron sulfide catalysts, the amorphous / crystalline hybrid catalyst of this invention exhibited a stronger signal intensity, indicating a higher ability to generate active species under neutral conditions, thus endowing the system with superior organic pollutant degradation performance. (Results are shown in...) Figure 5 ) Implementation Case 6 The ·OH in the reaction system was quantitatively analyzed using a dimethyl sulfoxide-2,4-dinitrophenylhydrazine derivatization method. Under neutral conditions (pH=7), the ·OH formation in the electro-Fenton reaction was compared using different catalysts, and the results are as follows: Figure 5 As shown, the amorphous / crystalline hybrid catalyst (AC-FexS-4) of this invention produces a ·OH concentration of 6.17 μM, significantly higher than the control sample. Its apparent formation rate constant reaches 0.309 μmol / L / min, far exceeding that of amorphous or crystalline catalysts. These results indicate that the catalyst of this invention can preferentially generate ·OH under neutral conditions. surf. It maintains a high level of ·OH production, thereby achieving efficient degradation of organic pollutants. (See results) Figure 6 ) Implementation Case 7 The energy efficiency performance of different catalysts was compared under the same conditions, and the results are as follows: Figure 7 As shown. The amorphous / crystalline hybrid catalyst (AC-Fe) of the present invention. x S-4 achieves efficient TOC removal while consuming only 0.0219 kWh / g TOC The energy consumption level was significantly lower than that of the amorphous or crystalline control catalyst, indicating that this catalyst can combine excellent organic matter removal rate and low energy consumption under neutral conditions. (See results below) Figure 7 ) Implementation Case 8 Under neutral conditions (pH=7), typical organic pollutants were subjected to electro-Fenton degradation experiments, including bisphenol A (BPA), tetracycline (TC), sulfamethoxazole (SMX), rhodamine B (RhB), and atrazine (ATZ). The experimental conditions were: initial pollutant concentration 10 mg / L, catalyst concentration 100 mg / L, and a constant current of 5 mA. The results are as follows: Figure 7 As shown, the amorphous / crystalline hybrid catalyst (AC-Fe) of the present invention x S-4) can achieve efficient removal of multiple pollutants in a short time, with removal rates generally exceeding 95%. These results indicate that the catalyst of this invention, under neutral conditions, is not only suitable for treating single pollutants but also for the efficient degradation of many typical organic pollutants, demonstrating broad application potential. (See results...) Figure 8 ) Implementation Case 9 Under neutral conditions (pH=7), with bisphenol A (10 mg / L) as the target pollutant, the amorphous / crystalline hybrid iron sulfide catalyst (AC-Fe) of this invention was used. x S-4) was subjected to cyclic degradation experiments. After 5 consecutive cycles, AC-Fex The degradation efficiency of S-4 remained above 97%, indicating that the catalyst possesses good structural stability and recyclability, making it suitable for long-term operation and practical engineering applications. (See results below) Figure 9 ).

Claims

1. An amorphous / crystalline hybrid iron sulfide heterogeneous electro-Fenton catalyst, characterized in that: It is prepared by sulfidation reaction using amorphous iron-based metal-organic frameworks (A-Fe-MOF) as a precursor. The specific preparation process includes the following two steps: (1) A-Fe-MOF was prepared by reacting FeSO4·7H2O with 2-methylimidazole in a molar ratio of 1:5.

3. After mixing them in methanol solution, the mixture was stirred in a magnetic stirrer for 24 h and then centrifuged and vacuum dried. (2) The brownish-yellow powder obtained in process (1) was mixed with thioacetamide in an ethanol solution at a mass ratio of 1:4 and then transferred to a reaction vessel lined with polytetrafluoroethylene. The reaction time was controlled at 120 °C for 2-8 h. After the reaction was completed, the mixture was washed with ethanol and deionized water and centrifuged. Then it was dried under vacuum to obtain a blackish-gray powder catalyst.

2. A method for applying the heterogeneous electro-Fenton catalyst as described in claim 1 in water treatment, characterized in that, In the electro-Fenton water treatment process, 20-200 mg / L of the above-mentioned amorphous / crystalline hybrid iron sulfide is added. The PTFE and carbon black modified air diffusion electrode is used as the cathode, and the shape-stabilized electrode is used as the anode. The pH of the wastewater to be treated is adjusted to 7, and the current is controlled at 1-20 mA for wastewater treatment.

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