A co9s8 / fe2o3 heterojunction composite catalyst and a preparation method and application thereof

Abstract

The application discloses a Co9S8 / Fe2O3 heterojunction composite catalyst and a preparation method and application thereof, and belongs to the field of nanocomposites, material science and photocatalysis technology. The composite catalyst takes Fe2O3 obtained by calcining MIL-88A(Fe) as a precursor, uniformly disperses Co9S8 nanoparticles on the surface of tubular Fe2O3 to form a Schottky heterojunction structure. The application is prepared by a MOFs derivation-sulfidation two-step method, takes cobalt nitrate as a cobalt source, takes thioacetamide as a sulfidation agent, and takes Fe2O3 derived from MIL-88A(Fe) as a substrate, so that the uniform dispersion of cobalt ions and the directional growth of Co9S8 phases are promoted. The application utilizes porous Fe2O3 generated by pyrolysis of MIL-88A(Fe) as an active main body, introduces Co9S8 as an electron transmission bridge through a sulfidation reaction, and reasonably constructs a Co9S8 / Fe2O3 heterojunction photo-Fenton catalytic system. The system can efficiently activate PMS to generate active free radicals under light excitation, exhibits excellent degradation performance and cycle stability for the second generation of neonicotinoid pesticides, and shows a good practical application prospect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of material science and photocatalysis technology, and mainly relates to a Co9S8 / Fe2O3 heterojunction composite catalyst and a preparation method and photocatalytic application thereof. BACKGROUND

[0002] With the rapid development of modern agriculture, the problem of pests and diseases poses a serious threat to crop growth, prompting the development and application of pesticides such as insecticides. Among them, neonicotinoid insecticides stand out with their unique mechanism of action and high insecticidal effect, and have a strong development momentum. Reasonable use of this type of insecticide can effectively prevent and control pests and diseases, and improve the yield and quality of crops.

[0003] However, neonicotinoid insecticides have good water solubility and are easily penetrated into the groundwater environment through the soil during production and use, causing a heavy burden on the ecological system. In addition, they are difficult to degrade and eliminate, further exacerbating the damage to the ecological environment and causing serious environmental pollution problems. In addition, this type of pesticide contains a large amount of toxic substances, which may endanger human life and health safety. Thiamethoxam, as a commonly used second-generation neonicotinoid insecticide, is widely used in agriculture and horticulture. It acts by stimulating the nicotinic acetylcholine receptor in the body, leading to damage to the nervous system and even death. Studies have shown that thiamethoxam residues can cause human discomfort, and in severe cases can cause respiratory distress, palpitations, convulsions and other toxic reactions; excessive or long-term use can also pollute the soil and water sources and destroy the ecological balance. Therefore, the development and exploration of degradation and detoxification technology for neonicotinoid pesticides is of great significance for expanding the means of repairing polluted environments

[0004] Separation technology has been widely used in the field of pesticide wastewater treatment, among which distillation, extraction, adsorption, precipitation, biological method, reverse osmosis and activated carbon-biofilm method have developed rapidly in recent years. However, it should be noted that the separation technology in the conventional treatment method can only realize the separation of inorganic pollutants (such as various toxic metals and their oxides, acids, bases, salts, sulfides, halides, etc.) between two phases, and cannot effectively realize the phase transformation and toxicity reduction of pollutants, so it is difficult to further degrade organic pollutants. In contrast, advanced oxidation processes (AOPs) based on reactive oxygen species (ROS) have attracted widespread attention due to their high efficiency in degrading organic pollutants and strong practicability. Among the many AOPs, photocatalysis technology is considered to be a promising technology in the field of energy production and environmental remediation by using solar energy as a renewable energy source to drive the reaction. The photocatalytic performance depends on the separation efficiency of electron-hole pairs in the semiconductor and the utilization rate of sunlight, and the construction of heterojunction photocatalytic system is one of the important ways to solve the above problems. Among them, the Schottky junction formed by n-type semiconductor and metal is often used to induce one-way transfer of electrons to enhance the photocatalytic activity of bare semiconductors. Metal organic frameworks (MOFs) have a porous nanostructure and uniformly dispersed metal atoms, making them excellent precursors for preparing transition metal oxides, for example, it is feasible to use iron-based MOFs as precursors to prepare iron oxide (Fe2O3). As a widely studied n-type semiconductor photocatalyst, Fe2O3 has the advantages of narrow band gap (≈2.1 eV), good visible light response, diverse morphology, high thermodynamic stability, low cost, high natural abundance and environmental friendliness. However, the catalytic activity of Fe2O3 still needs to be improved, and the construction of Schottky junction photocatalytic system is an effective means to enhance its activity.

[0005] Noble metals are the traditional components of Schottky junction, in theory, when the work function of the metal is greater than that of Fe2O3, a Schottky junction can be formed at the contact interface between the two, thereby inhibiting the reverse transmission of photo-generated electrons captured by the metal. However, noble metals are too expensive, so it is urgent to find suitable substitutes to construct a Schottky junction system. So far, a variety of co-catalysts have been proven to enhance photocatalytic performance, including Ti3C2, ReS2, NiB, CoP, MoS2 and CuS, etc. In recent years, Co9S8 has attracted widespread attention as a non-noble metal co-catalyst, which has shown outstanding performance in enhancing photocatalytic activity. Studies have shown that Co9S8 can act as an efficient co-catalyst to significantly enhance photocatalytic activity by promoting the separation and transfer of photo-generated charges.

[0006] The coupling of photocatalysis with other advanced oxidation technologies such as the Fenton reaction, persulfate activation, and electrochemical oxidation can produce a synergistic effect, significantly enhancing the overall activity of the reaction system and exhibiting a "1+1>2" enhancement characteristic. Among them, advanced oxidation technologies (AOPs) based on persulfate monosulfate (PMS) have become an efficient and convenient means to remove recalcitrant organic pollutants due to their environmental friendliness, mild reaction conditions, and strong oxidizing power. After activation, PMS can generate free radicals and non-radical species with high redox potentials, thereby efficiently degrading target pollutants. The synergistic effect of photocatalysis and PMS activation is manifested in a two-way promotion: PMS can act as an electron acceptor to capture photogenerated electrons generated during photocatalysis, not only achieving self-activation through electron transfer but also improving the charge separation efficiency of the photocatalytic system. In addition, iron-based semiconductors and cobalt-based catalysts have shown good application potential in PMS activation. As heterogeneous catalysts, they can drive PMS activation through the valence state cycle of Fe(III) / Fe(II) and Co(II) / Co(III), significantly improving the activation efficiency.

[0007] Under illumination, the Schottky junction formed at the Fe2O3-Co9S8 interface acts as an electron trap, transferring photogenerated electrons from Fe2O3 to the Co9S8 surface and suppressing electron backflow. Co9S8, in turn, acts as an electron transport channel, transferring electrons to the PMS (Polymerase Activation System), driving its efficient activation. Currently, there are no photocatalysts combining Fe2O3 and Co9S8 to degrade pesticide residues in water. This dual-system coupling strategy exhibits excellent redox capabilities and reaction kinetics. Therefore, this novel approach of constructing a Schottky junction-mediated dual-coupled PMS activation system provides an effective strategy for improving charge transfer efficiency and PMS activation performance. Summary of the Invention

[0008] This invention addresses the problems of low degradation efficiency and poor stability of existing photo-Fenton catalysts for thiamethoxam by providing a MIL-88A-derived Co9S8 / Fe2O3 Schottky heterojunction composite material. By controlling the material structure and interfacial interactions, efficient and stable degradation of thiamethoxam can be achieved.

[0009] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0010] This invention provides a method for dispersing Co9S8 nanoparticles on the surface of Fe2O3 obtained by calcination using MIL-88A(Fe) as a template to form a heterojunction structure; the mass ratio of Fe2O3 to Co9S8 nanoparticles is 3~19:1. This ratio can be controlled by adjusting the amount of Co(NO3)3•6H2O.

[0011] In the above technical solution, the average length of the MIL-88A (Fe) is 4~5 μm, and the average length of the porous Fe2O3 obtained after calcination remains almost unchanged.

[0012] Fe2O3 retains the morphology of MIL-88A, with an average length of 4~5 μm and abundant mesoporous structure; Co9S8 nanoparticles are uniformly distributed on the surface of Fe2O3, with a particle size of 20~50 nm, forming a tight interfacial contact with Fe2O3; the formation of Schottky heterojunction can promote the transfer of photogenerated electrons from Fe2O3 (n-type semiconductor) to Co9S8 (conductor) and suppress carrier recombination.

[0013] This invention also provides a method for preparing a Co9S8 / Fe2O3 heterojunction composite catalyst, using Fe2O3 obtained by calcination of MIL-88A (Fe) as a support, and dispersing Co9S8 nanoparticles on the Fe2O3 to form a heterojunction structure; the mass ratio of Fe2O3 to Co9S8 nanoparticles is 3~19:1, and the catalyst achieves activation of PMS under light and degradation of THX in aqueous solution; the preparation method includes the following steps:

[0014] (1) Preparation of MIL-88A precursor: FeCl3•6H2O and fumaric acid were dissolved in water and stirred until dissolved. The reaction was carried out at 55-70 °C for 9-11 h in a solvothermal environment. After centrifugation and washing, the product was dried under vacuum to obtain MIL-88A nanorods.

[0015] (2) Preparation of Fe2O3 nanotubes: Fe2O3 was obtained by pyrolysis of MIL-88A (Fe);

[0016] (3) Sulfurization treatment: Take the Fe2O3 and Co(NO3)3•6H2O prepared above and dissolve them in 30-40 mL of ethylene glycol. After complete dissolution, add thioacetamide and stir until dissolved. Transfer to a polytetrafluoroethylene reactor and hydrothermally heat at 180-200 °C for 8 h. Centrifuge and wash the obtained sample with distilled water 3-4 times and dry at 60-70 °C.

[0017] In the above scheme, the molar ratio of FeCl3•6H2O to fumaric acid in step (1) is 1:1.

[0018] In the above technical solution, further, step (1) involves mixing and stirring at 50-60 ℃ for a stirring time of not less than 20 min.

[0019] In the above technical solution, the Fe2O3 is further obtained by pyrolysis of MIL-88A (Fe); the pyrolysis temperature is 500-600 ℃, the heating rate is 5-10 ℃ / min, the pyrolysis time is 4 h, and the atmosphere is air.

[0020] In the above technical solution, further, in step (2), the mass ratio of Fe2O3 to Co(NO3)3•6H2O is 1:0.3~1:1.1, and the molar ratio of thioacetamide (calculated as S) to Co9S8 (calculated as Co) is 1:1.

[0021] This invention also provides the application of the aforementioned method for preparing the Co9S8 / Fe2O3 heterojunction composite catalyst in the photocatalytic activation of PMS for the degradation of neonicotinoid pesticides.

[0022] In the above technical solution, the neonicotinoid pesticide is further selected from THX.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] (1) The present invention is low cost and easy to prepare: MOFs are used as precursors, the preparation process is simple and controllable, the raw materials are cheap and readily available, and it is suitable for large-scale production.

[0025] (2) This invention provides a novel method for synthesizing Co9S8 / Fe2O3 heterojunction composite materials. The Schottky heterojunction promotes photogenerated electron transfer, while Fe... 3+ / Fe 2+ With Co 3+ / Co 2+ The synergistic cycle accelerates the decomposition of PMS, generating a large amount of reactive oxygen species. The degradation rate of 5 mg / L thiamethoxam can reach more than 75% within 30 min, which is 2.3 times that of pure Fe2O3 and pure Co9S8.

[0026] (3) In this invention, Fe2O3 obtained by calcining MIL-88A (Fe) is used as a carrier. The strong interfacial interaction between Co9S8 and Fe2O3 inhibits the dissolution of metal ions. After being recycled 5 times, the degradation rate still remains above 60%. Attached Figure Description

[0027] Figure 1 The SEM and TEM characteristics of MIL-88A (Fe), Fe2O3 and Co9S8 / Fe2O3 composite materials are shown. Figure 1 (a) is a SEM image of MIL-88A(Fe); Figure 1 (b) is a SEM image of calcined Fe2O3; Figure 1 (c) and Figure 1 (d) is a SEM image of the Co9S8 / Fe2O3 composite material; Figure 1 (e) and Figure 1 (f) is a TEM image of the Co9S8 / Fe2O3 composite material.

[0028] Figure 2XRD and BET characterization of Fe2O3, Co9S8 and Co9S8 / Fe2O3 composites; Figure 2 (a) is the XRD characterization. Figure 2 (b) is a BET representation.

[0029] Figure 3 The graph shows the photocatalytic activation of PMS for THX degradation and the photoelectric properties of Fe2O3, Co9S8 and composite materials with different ratios of Co9S8 / Fe2O3. Figure 3 (a) is a graph showing the THX degradation performance. Figure 3 (b) is the pseudo-first-order reaction kinetics fitting diagram. Figure 3 (c) is a bar chart of the reaction rate constant. Figure 3 (d) is the CSF-20 cyclic experimental diagram. Figure 3 (e) is the EIS spectrum. Figure 3 (f) is the transient photocurrent response curve.

[0030] Figure 4 UV-vis DRS characterization, Tauc plot and Mott-Schottky curve of Fe2O3, Co9S8 and composites of different proportions of Co9S8 / Fe2O3; Figure 4 (a) is the UV-vis DRS characterization. Figure 4 (b) is a Tauc diagram. Figure 4 (c) is the Mott-Schottky curve of Fe2O3. Figure 4 (d) is the Mott-Schottky curve of Co9S8.

[0031] Figure 5 This is a schematic diagram of the photocatalytic activation of PMS to degrade THX by the Co9S8 / Fe2O3 heterojunction composite catalyst. Detailed Implementation

[0032] The present invention will be further described below with reference to specific embodiments, but this does not limit the present invention in any way.

[0033] To enable those skilled in the art to better understand the technical solution of the present invention, the preparation method and application of a Co9S8 / Fe2O3 heterojunction composite catalyst provided by the present invention are described in detail below with reference to embodiments. The following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0034] Example 1: Preparation of Co9S8 / Fe2O3 heterojunction composite catalyst

[0035] The preparation method includes the following steps:

[0036] (1) Preparation of MIL-88A (Fe) by hydrothermal method: Take 1.3515 g FeCl3•6H2O, add it to 30 mL of distilled water, and slowly add 0.5804 g of transbutadiene acid under heating at 55 ℃. After complete dissolution, transfer it to a polytetrafluoroethylene reactor and hydrothermally react at 65 ℃ for 10 h. The obtained sample is centrifuged and washed 3-4 times with distilled water. The brownish-red product is placed in a vacuum oven and dried at 70 ℃ to obtain MIL-88A (Fe).

[0037] (2) Preparation of Fe2O3 nanotubes: MIL-88A (Fe) was calcined in a muffle furnace at 600 °C for 4 h to obtain Fe2O3.

[0038] (3) Co9S8 / Fe2O3 heterojunction composite catalyst: 0.1 g of the Fe2O3 prepared above was added to 30 mL of ethylene glycol. After complete dissolution, different amounts of Co(NO3)3•6H2O were added, and the mixture was ultrasonicated for 30 min to promote dissolution. After complete dissolution, different amounts of thioacetamide were added, and the mixture was stirred for 30 min. The mixture was then transferred to a polytetrafluoroethylene reactor and hydrothermally heated at 200 ℃ for 8 h. The resulting sample was centrifuged and washed 3-4 times with distilled water and dried at 60 ℃. The amounts of Co(NO3)3•6H2O and thioacetamide used in different proportions of the catalyst are shown in the table. The catalyst ratio is the mass ratio of Co9S8 to the total.

[0039]

[0040] The FeCl3•6H2O, fumaric acid, and Co(NO3)3•6H2O used in this invention are all analytical grade with a purity ≥99.0%; ethylene glycol is analytical grade; and thioacetamide is analytical grade with a purity ≥98.0%. The different proportions of Co9S8 / Fe2O3 heterojunction composite catalysts prepared in this invention are labeled as CSF-5, CSF-15, CSF-20, and CSF-25.

[0041] Figure 1 SEM and TEM images of MIL-88A(Fe), Fe2O3, and Co9S8 / Fe2O3 composite materials are presented. The scanning electron microscope (SEM) images show that MIL-88A(Fe) has a distinct hexagonal rod-like morphology, with an average length of approximately 4 μm and a width of approximately 500 nm. Figure 1 (a) Fe2O3 obtained after calcination in air has a slightly rough surface, see Figure 1 (b) This is more conducive to compounding with other substances. After the introduction of Co9S8, the original morphology of Fe2O3 remained unchanged, and it was observed that the Co9S8 particles were firmly attached to the Fe2O3 surface. Figure 1 (c) andFigure 1 (d) This indicates that Co9S8 has been successfully loaded into the structure of Fe2O3. Furthermore, high-resolution transmission electron microscopy (TEM) shows that nanoparticles are attached to the surface of Fe2O3, see... Figure 1 (e). Two distinct lattice fringes are visible. Figure 1 (f). The fringe spacing of Fe2O3 is 0.368 nm, corresponding to the (012) crystal plane. The fringe spacing of Co9S8 is 0.175 nm, corresponding to the (440) crystal plane.

[0042] Figure 2 (a) shows the XRD pattern of the synthesized catalyst. Pure Co9S8 exhibits relatively low diffraction peaks, but diffraction peaks are visible at 29.8° and 52.1°, corresponding to the (311) and (440) crystal planes, respectively (JCPDS#86-2273). For Fe2O3, multiple diffraction peaks were detected at 24.1°, 33.1°, 35.6°, 40.8°, 49.4°, 54.1°, 62.4°, and 64.0°, corresponding to the (012), (104), (110), (113), (024), (116), (214), and (300) crystal planes, respectively (JCPDS #84-0306). The presence of typical Co9S8 and Fe2O3 diffraction peaks in the composite catalyst is consistent with the crystal planes observed by transmission electron microscopy, fully demonstrating the successful preparation of the Co9S8 / Fe2O3 composite material.

[0043] Figure 2 (b) N2 adsorption-desorption isotherms for Fe2O3, Co9S8, and CSF-20 are shown. All three exhibit a type III isotherm and an H3-type hysteresis loop, indicating a mesoporous structure. The specific surface areas of Fe2O3, Co9S8, and CSF-20 are 7.371 m², respectively. 2 / g, 3.511 m 2 / g and 10.626 m 2 / g. The specific surface area of ​​all samples was relatively small, indicating that the adsorption effect of the samples may not be significant. See the corresponding pore size distribution diagrams. Figure 2 (b) As shown in the illustration, the average pore size of CSF-20 is 24.017 nm, which is much larger than the average geometric radius of the contaminants and activators. This large-size pore structure provides a rapid mass transport pathway for the PMS activation process, promoting contact between reactants and active sites. Therefore, it effectively promotes catalytic reaction kinetics and improves overall catalytic performance.

[0044] Example 2: Photocatalytic PMS activation reaction for the degradation of THX in water

[0045] The photocatalytic degradation of THX in water using PMS activation was carried out in a jacketed glass reactor. Tap water was circulated through the jacket to maintain a constant room temperature throughout the reaction process. For each degradation experiment, 100 mL of a 5 mg / L THX solution was added to the reactor. Timing began after adding 10 mg of catalyst to the solution. The first 30 minutes were the adsorption phase. Every 10 minutes, 3 mL of the reaction solution was pipetted using a dropper and filtered through a 0.22 μm water-washed filter membrane into a quartz cuvette. The cuvette was then placed in a double-beam spectrophotometer (TU-1901) to measure the absorbance at 255 nm to determine the THX concentration.

[0046] The relative content in solution. After 30 min of adsorption, 20 mg of PMS was added to the system and a 300 W Xe lamp (without a cutoff filter) was turned on. During the photoreaction, 3 mL of solution was aspirated every 5 min and the absorbance was measured. The rotor speed was maintained at 500 rpm throughout the reaction. For the cycle stability experiment, the catalyst after the photocatalytic reaction was centrifuged, washed with deionized water, and dried at 70 °C before the next experiment. If the amount of recovered catalyst is insufficient, multiple parallel degradation experiments are required.

[0047] The catalysts used were the Co9S8 / Fe2O3 heterojunction composite catalyst prepared in Example 1 and Co9S8 and Fe2O3, respectively.

[0048] Figure 3 (a) demonstrates the performance of the synthesized catalyst in degrading THX. The degradation efficiency of the composite material initially increases significantly with increasing Co9S8 content, peaking at 20% Co9S8 content, and then begins to decline when the content increases to 25%. We hypothesize the following mechanism: when the Co9S8 content is insufficient, Co... 2+ The reduced formation of Co9S8 hinders the regeneration of active sites, thus reducing degradation efficiency. Conversely, when Co9S8 is in excess, it may accumulate on the Fe2O3 surface. This accumulation not only weakens photocatalytic performance and PMS activation but also fails to form more active sites, ultimately leading to a decline in overall degradation performance. The CSF-20 composite material exhibits excellent degradation performance in the photo / PMS system, achieving a THX degradation rate of 75.2% within 30 minutes. In contrast, the degradation rates of pure Fe2O3 and pure Co9S8 are only 33.6% and 33.4%, respectively. This result clearly demonstrates that the CSF-20 composite material has a significantly higher THX degradation efficiency than the two single components. We then fitted the degradation reaction rate constant using the integral form of the pseudo-second-order reaction kinetic differential equation, which is shown in... Figure 3 (b) and Figure 3(c) Among them, the reaction rate constant of CSF-20 is the largest at 0.0491 mg. -1 ‧L‧min -1 Fe2O3 (0.0136 mg) -1 ‧L‧min -1 ) and Co9S8 (0.0137 mg) -1 ‧L‧min -1 3.6 times that of ). Figure 3 (d) shows the cyclic stability experiment of CSF-20. After 5 consecutive reactions, the activity of CSF-20 can still be maintained at 61.5%, indicating that CSF-20 has a certain degree of catalytic stability.

[0049] Example 3 Photoelectric properties of the synthesized catalyst

[0050] The photoelectric performance of the synthesized catalyst was tested on an electrochemical workstation (CHI760D). The test involved assembling a three-electrode system: a Pt electrode as the counter electrode and a silver chloride electrode as the reference electrode. The working electrode was prepared as follows: 50 mg of catalyst was uniformly dispersed in 2 mL of ethanol and 30 μL of perfluorinated resin aqueous solution, and ground in a mortar until the solution thickened. The viscous liquid was then uniformly coated onto the conductive side of an FTO conductive glass using a pipette. This catalyst-coated conductive glass was further dried in an infrared oven for 20 min to prevent the catalyst coating from peeling off during the test. The electrolyte solution was a 0.5 M Na₂SO₄ solution. A 300 W xenon lamp was used as the light source for the photocurrent test.

[0051] The catalysts used were the Co9S8 / Fe2O3 heterojunction composite catalyst prepared in Example 1 and Co9S8 and Fe2O3, respectively.

[0052] Figure 3 (e) shows the EIS spectra of the synthesized catalysts. The EIS curves of different materials differ significantly. The EIS curves of Co9S8 / Fe2O3 catalysts with different proportions in the figure generally follow the same direction. The diameter of the semicircle in the figure represents the resistance to charge transfer during photocatalysis; the smaller the semicircle diameter, the lower the catalyst impedance. As shown in the figure, CSF-20 has the smallest Nyquist radius, indicating a significant reduction in charge transfer impedance, which accelerates the separation and transfer of photogenerated electrons and holes, thereby improving the catalyst's catalytic performance. Figure 3Figure (f) shows the change in photocurrent over time for different proportions of catalysts, reflecting the ability of the catalyst material to generate and collect photogenerated carriers under illumination. As can be seen from the figure, there are significant differences among the different catalyst materials. The Co9S8 / Fe2O3 catalyst, through different proportions of composite materials, alters the band structure and interfacial properties of the catalyst itself, thereby affecting the generation, separation, and transport of photogenerated carriers, leading to corresponding changes in photocurrent. Figure 3 As can be seen from (f), Fe2O3 and Co9S8 have the weakest photocurrents, but the CSF-20 catalyst can quickly generate a large photocurrent response at the beginning of illumination and can remain relatively stable for a period of time. This indicates that the catalyst can effectively absorb light energy and convert it into electrical energy, and has good photogenerated carrier separation and transport performance.

[0053] Example 4: Band structure of the synthesized catalyst

[0054] The band structure of the synthesized catalyst was determined by UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS) and Mott-Schottky curve (MS curve), using Lambda 355 and CHI760D, respectively.

[0055] Figure 4 (a) UV-Vis DRS of the synthesized catalyst. The pristine Fe₂O₃ exhibits a significant absorption band edge at approximately 642 nm. In contrast, see […]. Figure 4 (a) Black Co9S8 exhibits a broad absorption peak in the 200-800 nm wavelength range. Compared to pure Fe2O3, the absorption edge of the composite material shows a significant red shift, which significantly improves its photocatalytic performance. The band gaps of Fe2O3 and CSF-20 were then determined using the Tauc plot method, see [reference needed]. Figure 4 (b), where the band gap values ​​of Fe2O3 and CSF-20 were determined to be 1.56 eV and 1.77 eV, respectively.

[0056] To obtain the band structure of Fe2O3, the flat band potentials of Fe2O3 at multiple frequencies (1 kHz, 1.5 kHz, 2 kHz) were measured based on the Mott-Schottky diagram, such as... Figure 4 As shown in (c), the curve slope is positive, indicating that Fe2O3 is an n-type semiconductor. The intersection of the tangent with the x-axis represents the flat-band potential of Fe2O3 as -0.58 V vs. SSC. Converting this to a standard hydrogen electrode yields E... CB (Fe₂O₃) = -0.58 V vs .NHE. Furthermore, through the binding of Fe₂O₃ with E... g and E VB =E CB +E gE is derived VB (Fe₂O₃) = 1.19V vs. NHE. Similarly, to obtain the complete band structure of Co₉S₈, the flat band potentials of Co₉S₈ at multiple frequencies (1 kHz, 1.5 kHz, 2 kHz) were tested based on the Mott-Schottky plot, such as... Figure 4 As shown in (d), the intersection of the tangent with the x-axis indicates that the flat-band potential of Co9S8 is 0.76 V vs. SSC. The flat-band potential can represent the Fermi level of the semiconductor, thus yielding E... f (Co9S8) = 0.96 V vs. NHE, and similarly, E can be obtained. f (Fe2O3)=-0.38 V vs. NHE.

[0057] Example 5: Mechanism of photocatalytic PMS activation and degradation of THX by Co9S8 / Fe2O3 heterojunction composite material

[0058] Based on the above characterization results and analysis, we have roughly described the mechanism of photocatalytic PMS activation and degradation of THX in Co9S8 / Fe2O3 heterojunction composite materials, such as... Figure 5 As shown, under illumination, Fe2O3 and Co9S8 form a tight interfacial contact, with photoelectrons from Fe2O3 migrating to Co9S8, thus forming a Schottky junction at the interface. This structure not only suppresses electron backflow but also helps improve the separation efficiency of photogenerated carriers. Under illumination, carrier separation mainly occurs on the Fe2O3 surface, where photogenerated electrons are excited from the valence band to the conduction band and then rapidly migrate to the Co9S8 surface through the interfacial Schottky junction in the heterojunction. Because Co9S8 exhibits excellent conductivity and strong catalytic activity towards PMS, it can effectively activate PMS to generate •SO5. - This leads to 1 O2 ultimately degrades THX into H2O and CO2. Meanwhile, [the process continues...] Figure 5 It can be seen that Fe2O3 and Co9S8 form a Schottky heterojunction, and the holes left on Fe2O3 can directly degrade thiamethoxam into smaller molecules. The conduction band potential of Fe2O3 (-0.58 eV) is more negative than that of O2 / •O2. - With a potential of -0.33 eV, some electrons on Fe2O3 can fully react with O2 to generate •O2. - This process degrades thiamethoxam into H2O and CO2.

[0059] By constructing heterojunctions between semiconductors and conductors, not only are the defects of individual semiconductors compensated for, which is beneficial to the target reaction, but also the working principle of heterojunctions can be better understood, guiding the development of heterojunction catalysts. This invention uses Fe2O3 obtained by calcining MIL-88A(Fe) as a support, and disperses Co9S8 nanoparticles on the surface of rod-shaped Fe2O3 to form a heterojunction structure. The synergistic effect of Fe2O3 and Co9S8 achieves maximum separation of photogenerated electrons and holes, further enhancing the photocatalytic activation performance of PMS in degrading THX in aqueous solution.

[0060] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention, and these changes should also be considered within the scope of protection of the present invention.

Claims

1. A Co9S8 / Fe2O3 heterojunction composite catalyst, characterized in that, Using Fe2O3 obtained by calcination of MIL-88A(Fe) as a carrier, Co9S8 nanoparticles are dispersed on Fe2O3 to form a heterojunction structure; the mass ratio of Fe2O3 to Co9S8 nanoparticles is 3~19:1; The MIL-88A (Fe) is rod-shaped with an average length of 4~5 μm, and the Fe2O3 obtained after calcination still has an average length of 4~5 μm.

2. A method for preparing the Co9S8 / Fe2O3 heterojunction composite catalyst according to claim 1, characterized in that, Includes the following steps: (1) Preparation of MIL-88A precursor: FeCl3•6H2O and fumaric acid were dissolved in water and stirred until dissolved. The reaction was carried out at 55-70℃ for 9-11 h in a solvothermal manner. After centrifugation and washing, the product was dried under vacuum to obtain MIL-88A nanorods. (2) Preparation of Fe2O3 nanotubes: Fe2O3 was obtained by pyrolysis of MIL-88A (Fe); (3) Sulfurization treatment: Take the Fe2O3 and Co(NO3)3•6H2O prepared above and dissolve them in 30-40 mL of ethylene glycol. After complete dissolution, add thioacetamide and stir until dissolved. Transfer to a polytetrafluoroethylene reactor and hydrothermally heat at 180-200℃ for 8 h. Centrifuge and wash the obtained sample with distilled water 3-4 times and dry at 60-70℃.

3. The preparation method of the Co9S8 / Fe2O3 heterojunction composite catalyst according to claim 2, characterized in that, In step (1), the molar ratio of FeCl3•6H2O to fumaric acid is 1:

1.

4. The preparation method of the Co9S8 / Fe2O3 heterojunction composite catalyst according to claim 2, characterized in that, In step (1), FeCl3•6H2O and fumaric acid are mixed at 50-60 °C and stirred for at least 20 min.

5. The method for preparing the Co9S8 / Fe2O3 heterojunction composite catalyst according to claim 2, characterized in that, In step (2), the pyrolysis temperature is 500-600 ℃, the heating rate is 5-10 ℃ / min, the pyrolysis time is 4 h, and the atmosphere is air.

6. The preparation method of the Co9S8 / Fe2O3 heterojunction composite catalyst according to claim 2, characterized in that, In step (3), the mass ratio of Fe2O3 to Co(NO3)3•6H2O is 1:0.3~1:1.1, and the molar ratio of thioacetamide (calculated as S) to Co(NO3)3•6H2O (calculated as Co) is 1:

1.

7. The application of the Co9S8 / Fe2O3 heterojunction composite catalyst according to claim 1 or the Co9S8 / Fe2O3 heterojunction composite catalyst obtained by the preparation method according to any one of claims 2 to 6 in the photocatalytic activation of PMS to degrade neonicotinoid pesticides.

8. The application according to claim 7, characterized in that, The neonicotinoid pesticides are selected from THX.

Images