Preparation method of double perovskite La2CoFeO6 and its application in degrading odor pollutants

Abstract

This invention relates to a method for preparing double perovskite La2CoFeO6 and its application in degrading odorous pollutants, comprising the following steps: dissolving La(NO3)3·6H2O, Co(NO3)2·6H2O, and Fe(NO3)3·9H2O in a mixed solution of deionized water and ethylene glycol or deionized water and citric acid, adjusting the pH, and then mixing thoroughly; placing them separately in a high-pressure reactor and heating or evaporating the moisture and drying in an oven to obtain precursor powder or dry gel; then calcining at high temperature and cooling to obtain double perovskite La2CoFeO6 powder. The R3c phase La2CoFeO6 material provided in this application, by combining crystal structure regulation with oxygen vacancy defect engineering, establishes a synergistic enhancement mechanism of "structure optimization + defect regulation" for double perovskite materials, significantly improving the photoresponse capability and catalytic performance of the material, providing a new technical path and material design idea for the design of subsequent high-performance photocatalysts for odor pollution control.

Description

Technical Field

[0001] This invention relates to the field of aquaculture wastewater treatment technology, and in particular to a method for preparing double perovskite La2CoFeO6 and its use in degrading odorous pollutants. Background Technology

[0002] During livestock and poultry farming, a large amount of organic matter decomposes under anaerobic conditions, producing various malodorous pollutants. Among them, 3-methylindole (3-MI) is a typical nitrogen-containing heterocyclic compound. This substance mainly originates from the decomposition of tryptophan and has a distinct and persistent pungent odor, commonly found in livestock wastewater, manure accumulation, and sludge treatment systems. Due to its extremely low odor perception threshold, even low concentrations can easily cause noticeable odors. Therefore, 3-methylindole has become one of the key targets for malodor control in livestock farms. Meanwhile, the concentration of this substance in livestock wastewater is usually high. If discharged directly without treatment, it will not only affect the surrounding air quality and water environment but may also have adverse effects on the human respiratory system and the ecosystem.

[0003] Currently, the main technologies for treating 3-methylindole include biodegradation, physical adsorption, and chemical oxidation. Biological methods typically rely on specific microorganisms to metabolically degrade the target pollutant. While offering advantages such as being environmentally friendly and having low operating costs, practical applications are often limited by factors such as the difficulty in selecting suitable strains, demanding cultivation conditions, and long reaction cycles, making it difficult to meet the needs for rapid treatment of high-concentration pollutants. Physical adsorption methods primarily utilize porous materials such as activated carbon, zeolite, and charcoal to enrich and remove pollutants. However, these methods primarily achieve pollutant transfer rather than complete decomposition, and the adsorption materials are prone to saturation, regeneration difficulties, and high treatment costs after long-term use.

[0004] In contrast, advanced oxidation technologies, such as photocatalysis, are considered an ideal approach for the complete mineralization of recalcitrant organic pollutants due to their ability to generate strong oxidizing free radicals (such as superoxide radicals and hydroxyl radicals) in situ under mild conditions, thereby rapidly oxidizing and degrading them. This method offers advantages such as thorough reaction, wide applicability, minimal secondary pollution, and good environmental compatibility, demonstrating promising application potential in the treatment of aquaculture wastewater. Existing research has shown that photocatalysis can achieve highly efficient removal of 3-methylindole under the synergistic effect of light and oxidants, confirming its feasibility in treating this type of odorous pollutant. However, existing photocatalytic systems generally suffer from cumbersome preparation processes, high material costs, and difficulties in recycling, hindering large-scale promotion and engineering applications. Therefore, developing novel photocatalytic materials with simple preparation processes, high catalytic efficiency, environmental friendliness, and ease of recycling has become an important research direction in this field.

[0005] In recent years, double perovskite oxides have gradually become a research hotspot in photocatalytic materials due to their unique crystal structure and tunable electronic properties. These materials not only possess excellent structural stability and suitable band gaps, but also effectively broaden the visible light absorption range through the synergistic effect of metal ions. Compared with traditional semiconductor materials, double perovskite oxides have certain advantages in improving the separation efficiency of photogenerated electrons and holes and enhancing surface reactivity, thus showing great application potential in fields such as organic pollutant degradation and water treatment. However, existing double perovskite photocatalytic materials still have certain limitations, such as the rapid recombination of photogenerated carriers, the lack of sufficient active sites on the surface, and limited visible light utilization efficiency, making it difficult to further improve their actual catalytic performance. Therefore, it is necessary to further develop novel double perovskite photocatalytic materials that deeply couple crystal regulation with defect engineering to achieve efficient degradation of malodorous organic pollutants such as 3-methylindole. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for preparing double perovskite La2CoFeO6 and its use in degrading malodorous pollutants.

[0007] This invention is achieved through the following technical solution: A method for preparing double perovskite La2CoFeO6 includes the following steps: S1. Weigh out La(NO3)3·6H2O, Co(NO3)2·6H2O, and Fe(NO3)3·9H2O in a molar ratio of 1.8-2.2:0.8-1.2:0.8-1.2 and dissolve them in a mixed solution of deionized water and ethylene glycol or deionized water and citric acid. Adjust the pH and mix thoroughly. S2. Place the product in a high-pressure reactor and heat or evaporate the moisture and dry it in an oven to obtain precursor powder or dry gel; S3. The precursor powder or dry gel is calcined at high temperature and cooled to obtain double perovskite La2CoFeO6 powder.

[0008] According to the above technical solution, preferably, step S1 includes: Weigh out La(NO3)3·6H2O, Co(NO3)2·6H2O, and Fe(NO3)3·9H2O in a molar ratio of 1.8-2.2:0.8-1.2:0.8-1.2 and dissolve them in a mixed solution of deionized water and ethylene glycol. After adjusting the pH to 10-12, mix thoroughly and transfer to a high-pressure reactor.

[0009] According to the above technical solution, preferably, step S2 includes: Seal the high-pressure reactor and react it in an oven at 190-210℃ for 22-26 hours; After the reaction, the precipitate was collected by centrifugation, washed 2-4 times, and then dried in a vacuum drying oven at 50-80℃ for 8-12 h to obtain the precursor powder.

[0010] According to the above technical solution, preferably, in step S1, La(NO3)3·6H2O, Co(NO3)2·6H2O, and Fe(NO3)3·9H2O with a molar ratio of 1.8-2.2:0.8-1.2:0.8-1.2 are weighed and dissolved in a mixed solution of deionized water and ethylene glycol, wherein the ratio of deionized water to ethylene glycol is between 3.5:1 and 4.5:1.

[0011] According to the above technical solution, preferably, step S1 includes: Weigh out La(NO3)3·6H2O, Co(NO3)2·6H2O, Fe(NO3)3·9H2O and citric acid in a molar ratio of 1.8-2.2:0.8-1.2:0.8-1.2 and dissolve them in deionized water to form a mixed solution; The molar ratio of (La+Co+Fe) to citric acid is 1:2 to 1:3, and the pH is adjusted to 6-8 before mixing thoroughly.

[0012] According to the above technical solution, preferably, step S2 includes: The water content was evaporated by heating in a water bath at 70-90℃ to obtain a wet gel. Transfer to an oven at 140-160℃ and dry for 48-50 h to obtain a dry gel, then grind and set aside.

[0013] According to the above technical solution, preferably, in step S1, La(NO3)3·6H2O, Co(NO3)2·6H2O, and Fe(NO3)3·9H2O with a molar ratio of 1.8-2.2:0.8-1.2:0.8-1.2 are weighed and dissolved in 300 mL of deionized water with citric acid to form a mixed solution, so that the molar ratio of (La+Co+Fe) to citric acid is 1:2 to 1:3.

[0014] According to the above technical solution, preferably, in step S3, the precursor powder or dry gel is calcined in a muffle furnace at a heating rate of 5℃ / min to 950-1050℃ for 10-12 h, and then cooled to obtain double perovskite La2CoFeO6 powder.

[0015] This application also discloses the use of double perovskite La2CoFeO6 in degrading malodorous pollutants. Based on the above-mentioned method for preparing double perovskite La2CoFeO6, the double perovskite La2CoFeO6 powder catalytically degrades 3-methylindole under natural light conditions.

[0016] According to the above technical solution, preferably, the R3c phase double perovskite La2CoFeO6 powder under light irradiation Co 2+ / Co 3+ with Fe 3+ / Fe 2+ The double redox reaction, combined with the alteration of the electronic structure of the Fe-O-Co bond by combining oxygen vacancies, catalyzes the degradation of 3-methylindole.

[0017] The beneficial effects of this invention are: This application constructs a precursor via hydrothermal or sol-gel method, and successfully constructs a double perovskite La2CoFeO6 material with an R3c phase structure by high-temperature calcination. The R3c phase structure, with its narrower band gap and superior visible light absorption, exhibits significantly better catalytic performance than the Pbnm+I4 / mmm composite phase structure in the degradation of 3-methylindole. This allows it to make fuller use of solar energy under natural light conditions, enhance the generation efficiency of photogenerated electrons and holes, and thus improve the photocatalytic degradation ability of 3-methylindole.

[0018] Meanwhile, Co in R3c phase La2CoFeO6 material 2+ / Co 3+ with Fe 3+ / Fe 2+ A synergistic dual redox cycle is formed, which can continuously promote electron transfer and the generation of reactive oxygen species under light conditions. The introduction of oxygen vacancies into the material further alters the electronic structure around the Fe-O-Co bonds, reducing the electron-hole recombination probability, improving carrier separation and migration efficiency, and enhancing the generation capacity of reactive species such as superoxide radicals and hydroxyl radicals. This results in the prepared La2CoFeO6 photocatalyst exhibiting a faster reaction rate and higher degradation efficiency in the degradation of 3-methylindole.

[0019] Therefore, the double perovskite La2CoFeO6 material provided in this application can achieve efficient, rapid and green degradation of 3-methylindole under natural light conditions, providing a novel photocatalytic material that is easy to prepare, has excellent performance and is environmentally friendly for the treatment of aquaculture wastewater and odor pollution. Attached Figure Description

[0020] Figure 1 This is a scanning electron microscope (SEM) image of LCF-1 in this invention.

[0021] Figure 2 This is a scanning electron microscope (SEM) image of LCF-2 in this invention.

[0022] Figure 3This is a scanning electron microscope (SEM) image of LCF-3 in this invention.

[0023] Figure 4 These are transmission electron microscope (TEM) and inverse Fourier transform (IFFT) images of LCF-1 in this invention.

[0024] Figure 5 These are transmission electron microscope (TEM) and inverse Fourier transform (IFFT) images of LCF-2 in this invention.

[0025] Figure 6 These are transmission electron microscope (TEM) and inverse Fourier transform (IFFT) images of LCF-3 in this invention.

[0026] Figure 7 These are the electron spin resonance (EPR) fitting spectra of LCF-1, LCF-2, and LCF-3 in this invention.

[0027] Figure 8 These are the X-ray photoelectron spectroscopy (XPS) O 1s spectra of LCF-1, LCF-2 and LCF-3 in this invention.

[0028] Figure 9 This is a schematic diagram illustrating the photocatalytic degradation capabilities of 3-methylindole under dark and light conditions, and under light + H2O2 conditions for LCF-1, LCF-2, and LCF-3 in this invention.

[0029] Figure 10 This is a schematic diagram of the ultraviolet-visible (UV-Vis) diffuse reflectance detection of LCF-1, LCF-2 and LCF-3 in this invention.

[0030] Figure 11 This is a graph showing the processing and analysis of ultraviolet-visible (UV-Vis) diffuse reflectance detection data of LCF-1, LCF-2, and LCF-3 in this invention.

[0031] Figure 12 This is a schematic diagram of the X-ray photoelectron spectroscopy derived valence band spectra of LCF-1, LCF-2, and LCF-3 in this invention.

[0032] Figure 13 The work function graphs are obtained from ultraviolet photoelectron spectroscopy (UPS) of LCF-1, LCF-2 and LCF-3 in this invention.

[0033] Figure 14 This is a schematic diagram of the band structure of LCF-1, LCF-2 and LCF-3 in this invention.

[0034] Figure 15 This is an analysis diagram of the instantaneous photocurrent response of LCF-1, LCF-2 and LCF-3 in this invention.

[0035] Figure 16 These are the electrochemical impedance spectroscopy (EIS) and Tafel slope diagrams of LCF-1, LCF-2, and LCF-3 in this invention.

[0036] Figure 17 This is the steady-state photoluminescence (PL) spectrum of LCF-1, LCF-2 and LCF-3 in this invention.

[0037] Figure 18 These are the time-resolved emission spectra (TRPL) of LCF-1, LCF-2, and LCF-3 in this invention.

[0038] Figure 19 This is a graph showing the change in surface potential of the sample after illumination using Kelvin probe force microscopy (KPFM) with the LCF-1 in this invention.

[0039] Figure 20 This is a graph showing the change in surface potential of the sample after illumination using Kelvin probe force microscopy (KPFM) with LCF-2 in this invention.

[0040] Figure 21 This is a graph showing the change in surface potential of the sample after illumination using Kelvin probe force microscopy (KPFM) with LCF-3 in this invention.

[0041] Figure 22 This is the Co 2p spectrum of the in situ X-ray photoelectron spectroscopy (in situ XPS) of LCF-1 in this invention.

[0042] Figure 23 This is the Fe 2p spectrum of the in situ X-ray photoelectron spectroscopy (in situ XPS) of LCF-1 in this invention.

[0043] Figure 24 This is the Co 2p spectrum of the in situ X-ray photoelectron spectroscopy (in situ XPS) of LCF-2 in this invention.

[0044] Figure 25 This is the Fe 2p spectrum of the in situ X-ray photoelectron spectroscopy (in situ XPS) of LCF-2 in this invention.

[0045] Figure 26 This is the Co 2p spectrum of the in situ X-ray photoelectron spectroscopy (in situ XPS) of LCF-1 in this invention.

[0046] Figure 27 This is the Fe 2p spectrum of the in situ X-ray photoelectron spectroscopy (in situ XPS) of LCF-1 in this invention.

[0047] Figure 28This is a diagram showing the percentage of valence state changes in the in-situ X-ray photoelectron spectroscopy (in situ XPS) of LCF-1 in this invention.

[0048] Figure 29 This is a diagram showing the percentage of valence state changes in the in-situ X-ray photoelectron spectroscopy (in situ XPS) of LCF-2 in this invention.

[0049] Figure 30 This is a diagram showing the percentage of valence state changes in the in-situ X-ray photoelectron spectroscopy (in situ XPS) of LCF-3 in this invention.

[0050] Figure 31 This is a schematic diagram illustrating the photocatalytic degradation ability of LCF-1 on 3-methylindole under different pH values ​​under light + H2O2 conditions in this invention.

[0051] Figure 32 This is a schematic diagram illustrating the photocatalytic degradation ability of LCF-1 on 3-methylindole under light + H2O2 conditions with different H2O2 dosages.

[0052] Figure 33 This is a schematic diagram illustrating the photocatalytic degradation ability of LCF-1 on 3-methylindole under light + H2O2 conditions with different catalyst dosages in this invention.

[0053] Figure 34 This is a schematic diagram illustrating the photocatalytic degradation ability of LCF-1 on 3-methylindole under light + H2O2 conditions with the addition of a cation coexisting substance.

[0054] Figure 35 This is a schematic diagram illustrating the photocatalytic degradation ability of LCF-1 on 3-methylindole under light + H2O2 conditions with the addition of anionic coexisting substances.

[0055] Figure 36 This is a schematic diagram illustrating the photocatalytic degradation ability of LCF-1 on 3-methylindole under light + H2O2 conditions in this invention after 6 cycles.

[0056] Figure 37 This is a schematic diagram showing the leaching rates of La, Co, and Fe ions after 6 cycles of LCF-1 under light + H2O2 conditions in this invention.

[0057] Figure 38 This is a comparison of X-ray diffraction (XRD) images of the long-term stability of LCF-1 in this invention.

[0058] Figure 39 This is a schematic diagram of the photocatalytic degradation ability of LCF-1 for different pollutants under light + H2O2 conditions in this invention.

[0059] Figure 40This is a schematic diagram illustrating the photocatalytic degradation capability of LCF-1 on wastewater from four aquaculture farms under light + H2O2 conditions in this invention. Detailed Implementation

[0060] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and preferred embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0061] Example 1: This invention provides a method for preparing double perovskite La2CoFeO6, comprising the following steps: S11. Weigh 0.02 mol La(NO3)3·6H2O, 0.01 mol Co(NO3)2·6H2O, and 0.01 mol Fe(NO3)3·9H2O and dissolve them in a mixed solution of 40 mL deionized water and 10 mL ethylene glycol. Adjust the pH to 12, mix thoroughly, and transfer to a stainless steel high-pressure reactor lined with polytetrafluoroethylene (filling degree controlled at 70-80%). S12. Seal the high-pressure reactor and react it in an oven at 200°C for 24 hours. After the reaction, collect the precipitate by centrifugation (3000 rpm, 5 min), wash it 2-3 times alternately with deionized water and anhydrous ethanol, and dry it at 100°C for 12 hours to obtain the precursor powder.

[0062] S13. Place the precursor powder into a muffle furnace and calcine it at 1000℃ for 10h. After annealing, allow it to cool naturally to room temperature to obtain double perovskite La2CoFeO6 powder, denoted as La2CoFeO6-1 (LCF-1).

[0063] Example 2: This invention provides a method for preparing double perovskite La2CoFeO6, comprising the following steps: S21. Weigh 0.02 mol La(NO3)3·6H2O, 0.01 mol Co(NO3)2·6H2O, 0.01 mol Fe(NO3)3·9H2O, and 0.1 mol citric acid and dissolve them in 300 mL of deionized water to form a mixed solution, making the molar ratio of La+Co+Fe to citric acid 1:2.5. Adjust the pH to 7 and mix thoroughly. S22. Transfer to a constant temperature water bath at 80℃ to evaporate the water and obtain a wet gel. Place it in an oven at 120℃ and dry for 48 hours to obtain a dry gel. Grind it and set it aside for later use.

[0064] S23. Place the ground dry gel into a muffle furnace (heating rate set to 5℃·min). -1In the process of calcining at 1000℃ for 10h, after annealing, the mixture was naturally cooled to room temperature to obtain double perovskite La2CoFeO6 powder, denoted as La2CoFeO6-3 (LCF-3).

[0065] Comparative Example: Weigh an appropriate amount of La2O3 and calcine it in a muffle furnace at 700℃ for 2 hours. Accurately weigh 0.2 mol of La2O3, 0.67 mol of Co3O4, and 0.1 mol of Fe2O3 according to the stoichiometric ratio and place them in a ball mill jar. Add zirconium oxide balls and anhydrous ethanol as grinding media. The ball-to-material ratio is 10:1. Use a planetary ball mill for 24 hours and a ball speed of 400 r / min to obtain a uniformly mixed raw material powder. Transfer the powder to an alumina crucible and calcine it in a high-temperature furnace at 900℃ for 10 hours, and then calcine it at 1000℃ for 10 hours to synthesize the material. After the synthesized material is naturally cooled to room temperature, it is ground again. The above steps are repeated to obtain powder, which is then placed in a muffle furnace for secondary sintering at 1000℃ for 10 hours. After sintering, the powder is naturally cooled to room temperature to obtain a powder sample, which is denoted as La2CoFeO6-2 (LCF-2).

[0066] LCF-1 and LCF-3 both crystallized into rhombohedral structures (R-3c), while LCF-2 was a composite phase structure consisting of 65.47% orthorhombic crystal (Pbnm) and 34.53% tetragonal crystal (I4 / mmm). The morphology and microstructure of the samples were analyzed and evaluated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The three samples were viewed under scanning electron microscopes at magnifications from low to high (…). Figure 1-3 The samples showed varying degrees of particle aggregation, with the density order being LCF-1 > LCF-3 > LCF-2. The overall shapes of LCF-1, LCF-2, and LCF-3 were spherical, irregularly spherical, and plate-like, respectively. Transmission electron microscopy (TEM) further revealed the lattice state of the samples. Figure 4-6 All three samples exposed the (112) crystal plane, with measured spacings of 0.274, 0.282, and 0.278 nm, all slightly larger than the standard values ​​on the PDF card. This is mainly due to lattice distortion caused by the difference in radii between Co and Fe ions at the B site, and the trend is consistent with XRD. To further visualize the lattice defects, the TEM images were processed using inverse Fourier transform (IFFT), such as... Figure 4-6 As shown in the attached figure, local blurring caused by the bending of lattice fringes can be clearly observed, mainly due to lattice distortion caused by the coexistence of bimetals at B sites.

[0067] To investigate the presence and distribution of oxygen vacancies (OVs), they were characterized using electron paramagnetic resonance (EPR) spectroscopy. Figure 7As shown, all three samples exhibit a typical Lorentz-type signal at g=2.003, which is a characteristic response of OV-related unpaired electrons. The signal intensity order is LCF-1>LCF-3>LCF-2, indicating that the OV concentration in the R3c phase sample is higher than that in the composite phase, and LCF-1 has the highest defect density. To directly assess the relative OV concentration, the O 1s spectrum was fitted, where O... ads / O lat It is an effective indicator for assessing the relative concentration of OV in a sample. Figure 8 The composite ratio is 1.01, and LCF-1 (1.20) in the R3c phase is higher than LCF-3 (1.04), which further verifies that the R3c structure is more conducive to OV formation.

[0068] Example 3: This application also discloses the use of double perovskite La2CoFeO6 in degrading odorous pollutants. Based on the above-mentioned method for preparing double perovskite La2CoFeO6, the double perovskite La2CoFeO6 powder catalytically degrades 3-methylindole under natural light conditions. Specifically, the R3c phase double perovskite La2CoFeO6 powder, under light irradiation, Co... 2+ / Co 3+ with Fe 3+ / Fe 2+ The double redox reaction, combined with the alteration of the electronic structure of the Fe-O-Co bond by combining oxygen vacancies, catalyzes the degradation of 3-methylindole.

[0069] Figure 9 compares the performance differences of the three samples in photocatalytic degradation of 3-MI. It was found that the photocatalytic performance of the R3c phase was better than that of the composite phase (78.61%), and the R3c phase with more OV, LCF-1 (100%), was better than LCF-3 (89.87%).

[0070] The results of ultraviolet-visible absorption spectroscopy (UV-vis DRS) show that ( Figure 10 The R3c phase LCF exhibits higher light absorption intensity across the entire visible light region than the composite phase, indicating a stronger light-harvesting ability and greater potential for the generation of photogenerated electron-hole pairs. Notably, the LCF-1 phase displays a distinct characteristic absorption peak in the 350-400 nm range compared to LCF-3. This characteristic absorption can be attributed to OV-induced defect level transitions, further confirming the highest OV concentration in LCF-1.

[0071] The band gap of each sample was calculated using the Tauc plot method, such as... Figure 11As shown, the band gaps of the R3c phase LCF-1 and LCF-3 are 2.63 and 2.76 eV, respectively, significantly narrower than the 2.86 eV of the composite phase LCF-2. This difference indicates that the crystal structure has a decisive influence on the band structure, and LCF-1, being rich in OV, further compresses the band gap width, thereby effectively broadening the visible light response range and improving solar energy utilization. XPS valence band spectroscopy was used to confirm the valence band positions of the samples. The valence band potentials of the LCF-1, LCF-2, and LCF-3 samples are -0.16 eV, -0.07 eV, and -0.13 eV, respectively. Figure 12 The work functions (Φ) measured by combined ultraviolet photoelectron spectroscopy (UPS) were 3.36, 4.17, and 3.40 eV, respectively. Figure 13 The lower work function means that the Fermi level is closer to the conduction band, and electrons are more easily excited to the conduction band by light. Therefore, the R3c phase is more likely to achieve efficient carrier excitation and separation under visible light irradiation. Based on the above results, schematic diagrams of the band structures of three LCF samples were constructed, as shown below. Figure 14 As shown.

[0072] Instantaneous photocurrent response test ( Figure 15 The results showed that all three samples exhibited fast and repeatable photocurrent signals. The photocurrent density of the R3c phase was significantly higher than that of the composite phase, and LCF-1 showed the highest and most stable response intensity, indicating that its electron-hole pair separation efficiency was optimal. This result directly confirms the synergistic effect of crystal structure modulation and OV introduction in promoting carrier separation. Electrochemical impedance spectroscopy (EIS) further revealed the interfacial charge transfer characteristics (…). Figure 16 The LCF-1 has the smallest radius, corresponding to the lowest charge transfer resistance, indicating that it has the most efficient interface charge migration capability, which is consistent with the UPS results. Tafel slope analysis ( Figure 16 Furthermore, it was shown that the Tafel slope of LCF-1 was higher than that of LCF-2 and LCF-3, indicating that its surface reaction kinetics were faster, which further verified the positive regulatory role of structure and OV on photocatalytic activity.

[0073] To further quantify carrier recombination behavior, steady-state and time-resolved photoluminescence tests were performed. Figure 17 As shown, all samples exhibited a broadband emission peak at 450 nm, originating from radiative recombination of defect states within the bandgap. The PL intensity of LCF-1 was significantly lower than that of other samples, indicating that non-radiative recombination of photogenerated carriers was effectively suppressed, resulting in a significant improvement in separation efficiency. The TRPL decay curve fitting results show ( Figure 18The average fluorescence lifetimes of LCF-1 (1.0366 ns) and LCF-3 (1.0886 ns) were lower than those of LCF-2 (1.3044 ns), indicating that a more efficient charge transport channel was formed within the R3c phase, enabling photogenerated carriers to rapidly migrate to the surface and participate in redox reactions, thus preventing recombination. In particular, LCF-1 had the shortest radiative lifetime (τ1) and non-radiative lifetime (τ2), further confirming that high concentrations of OV can accelerate the photoinduced charge transfer process. The surface potential changes of the samples after illumination were observed using Kelvin probe force microscopy (KPFM). Figure 19-21 As can be seen, the positive and negative potential differences on the surfaces of the three samples were 96.84 mV, 30.79 mV, and 52.51 mV, respectively, which directly demonstrates that LCF-1 accumulated the most photogenerated charge. This is attributed to its abundant OV (off-voltage) surface acting as an electron trap, effectively promoting charge separation. Therefore, LCF-1 exhibited the strongest charge separation capability, followed by LCF-2, consistent with the photocatalytic activity results.

[0074] In-situ XPS spectroscopy ( Figure 22-30 As can be seen, the La 3d peak position remained almost constant throughout the illumination process, indicating that the La at site A... 3+ Ions, acting as lattice framework components, do not participate in redox processes but only play a role in stabilizing the structure. In stark contrast, the valence states of the B-site transition metals Co and Fe exhibit highly dynamic and reversible periodic changes; after 15 minutes of illumination, the binding energy of Co shifts to higher values, corresponding to... 2+ To Co 3+ During the oxidation process, the Fe 2p peak shifts to lower binding energies, reflecting the Fe... 3+ Reduced to Fe 2+ When continuously exposed to light for 30 minutes, the migration trend was opposite to that described above. 3+ Reduced, Fe 2+ The periodic dynamic change of re-oxidation clearly and directly visualizes Co in LCF-1. 2+ / Co 3+ with Fe 3+ / Fe 2+ A synergistic cycling mechanism of two redox pairs. Under visible light excitation, photogenerated holes preferentially oxidize Co. 2+ To Co 3+ Photogenerated electrons are rapidly transferred to Fe via a Co–O–Fe superexchange bridge shared by B sites. 3+ Sites, reducing them to Fe 2+ Subsequently, it was enriched in Fe. 2+ Electrons from the site are rapidly transferred to the sample surface via surface oxygen species (such as OV or adsorbed H2O / O2) to activate O2 generation. -Or it may directly participate in the reductive cleavage of 3-MI molecules. As surface reactions consume electrons, Fe... 2+ It is re-oxidized, while Co 3+ Receive return electronic recovery as Co 2+ This completes a full internal charge cycle.

[0075] The mechanism by which the double perovskite La2CoFeO6 powder provided in this application catalytically degrades 3-methylindole under natural light conditions is as follows: Under visible light irradiation, LCF-1 is excited to generate photogenerated electron-hole pairs, LCF-1 + hv → e - +h + Photogenerated electrons rapidly transfer through the Co-O-Fe oxygen bridge at the B site, forming a bimetallic redox cycle: Co 2+ It loses electrons and is oxidized to Co. 3+ , And Fe 3+ The captured electrons are reduced to Fe 2+ , Then the reverse steps occur: , This dual redox synergistic cycle achieves efficient spatial separation of photogenerated electrons and holes. Simultaneously, electrons migrating to the surface efficiently activate dissolved oxygen and H2O2, resulting in O2 + e-. - → O2 - H2O2+e - → OH+OH - , The most active species attack the nitrogen-containing heterocyclic structure of the 3-MI molecule, mineralizing it into CO2 and H2O through a series of reactions including ring-opening and hydroxylation. O2 - / h + / 1 O2 / OH+Pollutant→H2O+CO2+Smallmolecules.

[0076] Meanwhile, the performance of LCF-1 in degrading 3-MI in the light + H2O2 system was further evaluated by changing the reaction conditions. Solution pH is an important parameter for the practical application of catalysts. Figure 31 LCF-1 exhibited the best degradation performance (100%) at pH=9, while excessively acidic or alkaline conditions led to a decrease in degradation rate. Therefore, subsequent experiments were conducted under the optimal condition of pH=9.

[0077] H2O2 concentration is an important indicator of the economic benefits of the light + H2O2 system. For example... Figure 32As shown, as the H2O2 concentration increases to 2 mM, the k value changes from 0.03039 min... -1 Rise to 0.04098 min -1 Further increasing the H2O2 concentration actually decreased the k-value to 0.01700 min. -1 This is attributed to the fact that excessive H2O2 quenches free radicals, leading to a reduction in effective active species.

[0078] The amount of catalyst added is also an important criterion for measuring catalytic efficiency. Figure 33 The degradation rate was 100% when the dosage was 5 mg. The degradation rate decreased when the dosage was too low (2 mg) or too high (10 mg). The former was due to insufficient active sites, while the latter may be due to particle aggregation blocking light absorption and enhanced light scattering.

[0079] Coexisting substances are an important indicator for evaluating the effectiveness of catalysts in actual wastewater treatment. Figure 34 The addition of cations inhibited the reaction to some extent. This is mainly because when the solution pH is 9, which is much higher than the zero charge of LCF-1, the material surface carries a negative charge. Cations will be attracted and adsorbed on the surface due to electrostatic attraction, occupying active sites and thus inhibiting the reaction. Figure 35 The effects of common anions on catalyst activity were investigated. HA, as a natural organic compound, had no significant effect on the reaction rate, indicating good tolerance to common organic matter in water. Other anions had no significant promoting or inhibiting effect, confirming that LCF-1 has good degradation stability in complex water bodies.

[0080] The stability and repeatability of the catalyst are key indicators for its practical application. LCF-1 maintains a removal rate of over 99% even after six consecutive cycles of use. Figure 36 It exhibits good reusability, and the ion leaching rate is far below the allowable limit. Figure 37 To address the phase instability issue of lanthanide double perovskites, LCF-1 was stored at room temperature and pressure in air for 8 months. XRD analysis showed no significant changes in its phase composition and crystallinity. Figure 38 This confirms the excellent stability of its structure.

[0081] like Figure 39 As shown, the degradation rates of TC, CIP, SMX, β-E2, EE2 and indole were all 100% within 90 min in the light + H2O2 system, confirming its wide applicability. Figure 40The actual degradation efficiency of wastewater from four aquaculture farms under the LCF-1 photo + H2O2 system was measured. The degradation rate of 3-MI after photocatalysis reached 76.14-91.73% when the concentration of 3-MI was 1.37-4.37 mg / L. At the same time, the test results of the actual samples showed that the pH of the aquaculture wastewater was weakly alkaline (≥7.5), which matched the optimal photocatalytic performance of LCF-1 at pH=9. This fully demonstrates that LCF-1 shows good practical application potential in treating 3-MI pollution in complex aquaculture wastewater under the photo + H2O2 system.

[0082] In summary, traditional methods are easily limited by solid-phase diffusion, leading to uneven local concentrations of Co / Fe, which in turn easily forms composite phases at high temperatures. However, hydrothermal and sol-gel methods enable uniform atomic complexation and co-precipitation of La, Co, and Fe precursors in the liquid phase, forcing bimetallic ions into the same crystal framework and effectively preventing composite phase formation. The double perovskite La2CoFeO6 material provided in this application can achieve efficient, rapid, and green degradation of 3-methylindole under natural light conditions, providing a novel photocatalytic material that is easy to prepare, has excellent performance, and is environmentally friendly for the treatment of aquaculture wastewater and odor pollution. This application establishes a synergistic enhancement mechanism of "structure optimization + defect control" for double perovskite materials by combining crystal structure regulation with oxygen vacancy defect engineering. This not only significantly improves the material's photoresponse capability and catalytic performance but also provides a new technical path and material design ideas for the design of subsequent high-performance photocatalysts for odor pollution treatment.

[0083] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing double perovskite La2CoFeO6, characterized in that, Includes the following steps: S1. Weigh out La(NO3)3·6H2O, Co(NO3)2·6H2O, and Fe(NO3)3·9H2O in a molar ratio of 1.8-2.2:0.8-1.2:0.8-1.2 and dissolve them in a mixed solution of deionized water and ethylene glycol or deionized water and citric acid. Adjust the pH and mix thoroughly. S2. Place the product in a high-pressure reactor and heat or evaporate the moisture and dry it in an oven to obtain precursor powder or dry gel; S3. The precursor powder or dry gel is calcined at high temperature and cooled to obtain double perovskite La2CoFeO6 powder.

2. The method for preparing a double perovskite La2CoFeO6 according to claim 1, characterized in that, Step S1 includes: Weigh out La(NO3)3·6H2O, Co(NO3)2·6H2O, and Fe(NO3)3·9H2O in a molar ratio of 1.8-2.2:0.8-1.2:0.8-1.2 and dissolve them in a mixed solution of deionized water and ethylene glycol. After adjusting the pH to 10-12, mix thoroughly and transfer to a high-pressure reactor.

3. The method for preparing a double perovskite La2CoFeO6 according to claim 2, characterized in that, Step S2 includes: Seal the high-pressure reactor and react it in an oven at 190-210℃ for 22-26 hours; After the reaction, the precipitate was collected by centrifugation, washed 2-4 times, and then dried in a vacuum drying oven at 50-80℃ for 8-12 h to obtain the precursor powder.

4. The method for preparing a double perovskite La2CoFeO6 according to claim 2 or 3, characterized in that, In step S1, La(NO3)3·6H2O, Co(NO3)2·6H2O, and Fe(NO3)3·9H2O with a molar ratio of 1.8-2.2:0.8-1.2:0.8-1.2 are weighed and dissolved in a mixed solution of deionized water and ethylene glycol, with the ratio of deionized water to ethylene glycol being between 3.5:1 and 4.5:

1.

5. The method for preparing a double perovskite La2CoFeO6 according to claim 1, characterized in that, Step S1 includes: Weigh out La(NO3)3·6H2O, Co(NO3)2·6H2O, Fe(NO3)3·9H2O, and citric acid, and dissolve them in deionized water to form a mixed solution, so that the molar ratio of (La+Co+Fe) to citric acid is 1:2 to 1:3, and adjust the pH to 6-8 before mixing thoroughly.

6. The method for preparing a double perovskite La2CoFeO6 according to claim 5, characterized in that, Step S2 includes: The water content was evaporated by heating in a water bath at 70-90℃ to obtain a wet gel. Transfer to an oven at 140-160℃ and dry for 48-50 h to obtain a dry gel, then grind and set aside.

7. The method for preparing a double perovskite La2CoFeO6 according to claim 5 or 6, characterized in that, In step S1, weigh out La(NO3)3·6H2O, Co(NO3)2·6H2O, and Fe(NO3)3·9H2O in a molar ratio of 1.8-2.2:0.8-1.2:0.8-1.2, and dissolve citric acid in 300 mL of deionized water to form a mixed solution, so that the molar ratio of (La+Co+Fe) to citric acid is 1:2 to 1:

3.

8. The method for preparing a double perovskite La2CoFeO6 according to claim 1, characterized in that, In step S3, the precursor powder or dry gel is calcined in a muffle furnace at a heating rate of 5°C / min to 950-1050°C for 10-12 hours, and then cooled to obtain double perovskite La2CoFeO6 powder.

9. The use of a double perovskite La2CoFeO6 for degrading odorous pollutants, based on the preparation method of a double perovskite La2CoFeO6 according to claim 1, characterized in that, The double perovskite La2CoFeO6 powder catalytically degrades 3-methylindole under natural light conditions.

10. The use of the double perovskite La2CoFeO6 according to claim 9 for degrading odorous pollutants, characterized in that, The R3c phase of the double perovskite La2CoFeO6 powder under light irradiation Co 2+ / Co 3+ with Fe 3+ / Fe 2+ The double redox reaction, combined with the alteration of the electronic structure of the Fe-O-Co bond by combining oxygen vacancies, catalyzes the degradation of 3-methylindole.

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