A method for green low-temperature preparation of pure-phase CuMn2O4-based high-entropy spinel oxide

Abstract

The application discloses a method for preparing pure-phase CuMn2O4-based high-entropy spinel oxide at low temperature in a green way, and the method comprises the following steps: collecting plant leaves, washing, drying, weighing, bagging and leaching to obtain a plant extract; adding nitrate precursors of copper, zinc, manganese, aluminum and chromium into the plant extract, stirring and drying to obtain a dry gel; and calcining (as low as 350 DEG C) the dry gel to obtain the pure-phase CuMn2O4-based high-entropy spinel oxide. The synthesis process of the pure-phase high-entropy spinel oxide is simple, the plant extract is used, the pure-phase high-entropy spinel oxide has the advantages of green environmental protection, low cost and energy consumption reduction, and is beneficial to the green preparation and large-scale production of the spinel oxide.

Description

Technical Field

[0001] This invention relates to the field of high-entropy metal oxide preparation, and particularly to a green, low-temperature method for preparing pure-phase CuMn2O4-based spinel-type high-entropy metal oxides. Background Technology

[0002] High entropy metal oxides (HEOs) are a class of oxides composed of five or more metal elements. They possess strong electronic correlation, multi-metal synergy, flexible composition, and entropy increase effects, endowing them with advantages such as structural stability, high thermal stability, and strong corrosion resistance. They are an emerging functional material with great potential in energy storage, fuel cells, and catalysis. HEOs are considered solid solution phases and can be classified into rock salt, fluorite, spinel, and perovskite structures. Among them, spinel-type oxides have the general formula AB₂O₄ (e.g., CuMn₂O₄), where A is a divalent cation and B is a trivalent cation. Therefore, spinel-type HEOs have highly flexible composition (A and B can be various metals) and flexible valence states (A and B can have variable valences), making them highly sought after.

[0003] Currently, the reported methods for preparing spinel-type HEOs are mainly: solid-state synthesis, wet chemical methods, and vapor deposition. The solid-state method is one of the most commonly used methods for synthesizing HEOs. Generally, five or more metal oxides or metal salts are weighed as precursors according to appropriate stoichiometry, and then homogenized (e.g., dry grinding, ball milling, or mechanical mixing) and sintered at high temperature to obtain HEOs. The solid-state method is not complex and the operation is relatively simple, but it requires high temperatures (≥1000 °C) and long times, resulting in high energy consumption and the possibility of agglomeration during high-temperature, long-term sintering. The wet chemical method typically involves adding metal salts to create a homogenized solution to adjust the proportions of various elements at the atomic level. The mixture is then subjected to a chemical reaction at a suitable temperature, followed by the removal of the solvent and other reagents, ultimately forming a single-phase HEO. Common wet chemical methods include sol-gel methods, hydrothermal methods, solvothermal methods, solution combustion methods, coprecipitation methods, and spray pyrolysis methods. In contrast, wet chemical methods can not only significantly reduce the formation temperature of single-phase HEOs, but also control the morphology, particle size, and elemental distribution of HEOs. Wang first prepared high-entropy (Co, Cu, Fe, Mn, Ni)3O4 oxides with a spinel structure at temperatures as low as 400 °C using a solvothermal-low-temperature calcination method. However, the preparation process required ethanol as a solvent, polyethylene glycol-polypropylene glycol-polyethylene glycol and ethylene glycol as surfactants, and hexamethylenetetramine as a precipitant and fuel (J. Mater. Chem. A, 2019, 7, 24211-24216). He et al. first prepared high-entropy spinel-type oxides (Fe...) using a low-temperature solution combustion method. 0.2 Co 0.2 Ni0.2 Cr 0.2 Mn 0.2 To obtain the target product, they first mixed a metal nitrate precursor with citric acid and dissolved it in ethanol. After thorough mixing, the solution was ignited in a fume hood, and stirring continued until the flame extinguished. A large amount of deionized water was then rapidly added for cooling and quenching. The product was subsequently washed with deionized water and dried to obtain the target product (Chem. Eng. J., 2023, 460: 141675.). Although this method operates at room temperature, it requires ethanol and citric acid as fuels, generating a large amount of heat during combustion, which poses certain risks (such as fire or explosion). Furthermore, the combustion process may be non-uniform, resulting in uneven particle size and distribution of the product, making it difficult to obtain high-purity, monodisperse nanoparticles. Post-combustion processing may be required to obtain the final product. Patent (CN202211418410.9) provides a method for preparing high-entropy spinel-type iron-cobalt-nickel oxides using sodium alginate and metal nitrates as raw materials via hydrothermal treatment or low-temperature carbonization (180 °C) at 160-240 °C. Although the operating temperature is lower, the entire process involves the preparation of small spherical gels, hydrothermal reaction, freeze-drying (12 or 48 h), and carbonization (12 h), which is time-consuming and relatively cumbersome. For other methods, such as vapor deposition (Small, 2025, 21(50). DOI:10.1002 / smll.202508297.) and electrospinning (patent CN202411340092.8), although they can reduce the formation temperature of high-entropy metal oxides to some extent, most methods still require high-temperature treatment (≥700 °C), and the operation is relatively complex and inefficient.

[0004] In summary, although researchers have developed several strategies for the low-temperature synthesis of high-entropy spinel-type metal oxides, most still require temperatures above 700 °C. While some methods can lower the temperature to around 200 °C, these strategies often require auxiliary reagents, and the preparation process is relatively cumbersome and lengthy, with low efficiency. Therefore, developing a low-temperature, green, convenient, and efficient method for synthesizing high-entropy spinel-type metal oxides is of great significance. Summary of the Invention

[0005] In view of the above problems, the purpose of this invention is to provide a green low-temperature method for preparing pure phase CuMn2O4-based high-entropy spinel oxides. This method uses metal nitrates as the metal source and plant extracts as the complexing agent, and prepares pure phase CuMn2O4-based high-entropy spinel metal oxides by calcination at temperatures as low as 350 °C using a sol-gel method.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A green, low-temperature method for preparing pure-phase CuMn2O4-based high-entropy spinel oxides includes the following steps: (1) Prepare plant leaves: Collect, wash, dry and bag the plant leaves; (2) Preparation of plant extract: Soak the bagged plant leaves in boiling water to obtain plant extract; (3) Preparation of dry gel: Add metal precursor to plant extract, then stir and dry; (4) Sample preparation: Calcine the dried sample to obtain the target product.

[0007] Preferably, the plant leaves in step (1) can be fresh green leaves or fallen dead leaves, and can be leaves of herbaceous plants, shrubs or trees.

[0008] Preferably, the washing process in step (1) involves rinsing with tap water 2 to 4 times, followed by washing with deionized water 1 to 2 times, with a ratio of tap water or deionized water (mL) to plant leaves (g) of 5 to 20: 1.

[0009] Preferably, the drying temperature in step (1) is 80~120 ℃ and the time is 12~48 h.

[0010] Preferably, in step (1), the bagging involves weighing 0.5 to 4.0 g of dried leaves and packing them into a nylon yarn bag.

[0011] Preferably, the soaking in step (2) uses deionized water at 70~100 ℃ and the volume of water is 20 mL.

[0012] Preferably, the soaking time in step (2) is 0.5 to 10 min.

[0013] Preferably, the metal precursor in step (3) is a nitrate, namely, a mixture of copper nitrate, zinc nitrate, manganese nitrate, aluminum nitrate and chromium nitrate, with a total metal content of 0.006 mol, of which the total content of copper nitrate and zinc nitrate is 0.002 mol, the total content of manganese nitrate, aluminum nitrate and chromium nitrate is 0.004 mol, and the molar percentage of each metal in the total metal is 12.50~33.33%.

[0014] Preferably, the drying temperature in step (3) is 80~120 ℃ and the time is 6~12 h.

[0015] Preferably, the calcination temperature in step (4) is 350~900 ℃, the calcination heating rate is 1~15 ℃ / min, and the calcination constant temperature time is 30~300 min.

[0016] As can be seen from the above technical solution, the present invention has the following beneficial effects: (1) The pure phase high-entropy spinel oxide prepared by this method requires a temperature as low as 350 °C, which can not only reduce energy consumption, but also prevent high-temperature sintering of the material; (2) This method uses inexpensive, readily available, green and environmentally friendly plant extracts in the preparation process, and the process is simple and easy to operate, which is conducive to large-scale production. Attached Figure Description

[0017] Figure 1 The XRD patterns of the samples prepared in Example 1 and Comparative Example 1 are shown.

[0018] Figure 2 The XRD patterns of the samples from Example 2 at different calcination temperatures are shown.

[0019] Figure 3 The image shows the EDS spectrum of the sample prepared in Example 2 at a calcination temperature of 600 °C.

[0020] Figure 4 The XRD patterns of samples prepared with different concentrations of Bidens pilosa extract in Example 3 are shown.

[0021] Figure 5 The XRD patterns of samples prepared from different plants at low temperatures in Example 4 are shown.

[0022] Figure 6 The XRD patterns of CuMn2O4-based high-entropy spinel oxides with different Cr contents are shown in Example 5.

[0023] Figure 7 The XRD patterns of CuMn2O4-based high-entropy spinel oxides with different Cu contents are shown in Example 6.

[0024] Figure 8 The image shows the XRD pattern of the univariate sample in Comparative Example 2.

[0025] Figure 9 The image shows the XRD pattern of the binary sample in Comparative Example 2.

[0026] Figure 10 The image shows the XRD pattern of the ternary sample in Comparative Example 2.

[0027] Figure 11 The image shows the XRD pattern of the quaternary sample in Comparative Example 2. Detailed Implementation

[0028] To better understand the present invention, the following description is based on embodiments. However, the scope of protection of the present invention is not limited to the scope shown in the embodiments.

[0029] Example 1 (Green Low-Temperature Preparation of Pure-Phase CuMn2O4-Based High-Entropy Spinel Oxides) Pure-phase CuMn2O4-based high-entropy spinel oxides were prepared using Bidens pilosa extract at a green, low-temperature environment. (1) Preparation of plant leaves: Pick fresh Bidens pilosa leaves, wash them 3 times with tap water, then wash them 2 times with deionized water, place them on a tray and dry them in an oven at 120 ℃ for 12 h. Weigh 2.0 g of dried Bidens pilosa leaves, crush them, and put them into a nylon gauze bag for later use; (2) Preparation of plant extract: Add the plant leaves prepared in (1) to 20 mL of 100 ℃ deionized water and soak at a constant temperature for 5 min. Then remove the nylon gauze bag (plant leaves) to obtain Bidens pilosa leaf extract.

[0030] (3) Preparation of dry gel: Weigh 0.1914 g Cu(NO3)2, 0.3005 g Zn(NO3)2·6H2O, 0.3842 g Mn(NO3)2·4H2O, 0.5628 g Al(NO3)3·9H2O, and 0.4042 g Cr(NO3)3·9H2O (the molar ratio of Cu is Cu 2+ :Zn 2+ :Mn 2+ Al 3+ :Cr 3+ =1: 1: 1.5: 1.5: 1) Add to the Bidens pilosa leaf extract prepared in (2), stir at room temperature for 15 min, put into an oven to dry at 120 ℃ for 6 h to obtain precursor dry gel.

[0031] (4) Sample preparation: Transfer the precursor dry gel to a crucible, place it in a muffle furnace, raise the temperature from room temperature to 350 ℃ at a rate of 5 ℃ / min and hold it at that temperature for 2 h. After naturally cooling to room temperature, the final sample is obtained. The sample name is: Bidens pilosa extract, calcined at 350 ℃.

[0032] Comparative Example 1 (Comparative sample prepared by conventional chemical method) A comparative sample was prepared using a chemical method with citric acid as a complexing agent. The same nitrate (same mass, same chemical reagent) as in Example 1 (3) was weighed, and 1.5130 g of citric acid was added (the molar ratio was citric acid: Cu). 2+ Zn 2+ :Mn 2+ Al 3+ : Cr 3+= 7.2: 1: 1: 1.5: 1.5: 1), add 20 mL of deionized water, stir at room temperature for 15 min, put it in an oven to dry at 120 ℃ for 6 h, repeat the above process to obtain two identical precursor dry gels, and calcine them at 350 ℃ and 600 ℃ respectively using the same calcination method as in Example 1 (4) to obtain the final samples. The sample names are: citric acid, calcined at 350 ℃; citric acid, calcined at 600 ℃.

[0033] Figure 1 The XRD patterns of the samples prepared in Example 1 and Comparative Example 1 are shown in the figures. As can be seen from the figures, the XRD diffraction peaks of the green low-temperature synthesized sample (Bidens pilosa extract, calcined at 350 °C) match well with the CuMn2O4 standard card (PDF#84-0543), and no other impurity peaks were observed. This indicates that this method can obtain pure-phase CuMn2O4-based high-entropy spinel oxides under calcination conditions as low as 350 °C. In contrast, the XRD peaks of samples prepared by traditional chemical methods at different temperatures do not match the CuMn2O4 standard card. 1.5 Mn 1.5 The product is consistent with the O4 standard card (PDF#70-0260), and impurity peaks can be observed at positions such as 2θ=32.81 and 60.47 °, indicating that the main crystalline phase of the product is Cu. 1.5 Mn 1.5 O4, and contains other impurities. Therefore, even with high-temperature calcination (600 °C), the traditional chemical method using citric acid as a complexing agent cannot yield a pure phase CuMn2O4-based high-entropy spinel oxide, which demonstrates the inventiveness of this invention.

[0034] Example 2 (Green preparation of CuMn2O4-based high-entropy spinel oxides at different calcination temperatures) Samples were prepared by repeating the method of Example 1, except that the calcination temperatures of the precursors were 400, 450, 500, 600, 700, and 800 °C, respectively.

[0035] Figure 2 The figures show the XRD patterns of samples from Example 2 at different calcination temperatures. As can be seen from the figures, the XRD diffraction peaks of the samples prepared at different temperatures generally match the CuMn2O4 standard card (PDF#84-0543), indicating that the prepared samples mainly form a spinel structure. With increasing calcination temperature, the diffraction peaks gradually strengthen and become sharper, indicating that the degree of crystallization continuously improves and the crystal structure becomes more complete. Furthermore, even when the calcination temperature is increased to 800 °C, the sample still maintains a pure phase, indicating that the prepared CuMn2O4-based high-entropy spinel oxide has good thermal stability.

[0036] Figure 3The image shows the EDS spectrum of the sample prepared in Example 2 at a calcination temperature of 600 °C. Characteristic peaks for O, Cu, Zn, Mn, Al, and Cr can be observed in the spectrum, and the elemental proportions are close to the theoretical values, indicating that five metallic elements (Cu, Zn, Mn, Al, and Cr) were successfully introduced into the sample. The sample successfully constructed a high-entropy spinel oxide system containing these five metallic elements.

[0037] Example 3 (Green preparation of CuMn2O4-based high-entropy spinel oxide with different concentrations of Bidens pilosa extract) The samples were prepared using the method described in Example 1, except that the calcination temperature was 600 °C and the mass of dried Bidens pilosa packed in nylon gauze bags was 0.5, 1.0, 1.5, 2.0, and 2.5 g, respectively.

[0038] Figure 4 The XRD patterns of samples prepared with different concentrations of Bidens pilosa extract in Example 3 are shown. Samples prepared under different concentrations of Bidens pilosa leaf extract all exhibited similar diffraction peak positions, and their main characteristic peaks basically corresponded to the CuMn2O4 standard card (PDF#84-0543), indicating that within the investigated concentration range, all samples could form the same target crystal phase. This shows that the target product can be prepared within a relatively wide range of plant extract concentrations, demonstrating that this green preparation method has good adaptability to plant leaf extract concentrations.

[0039] Example 4 (Green preparation of CuMn2O4-based high-entropy spinel oxide from different plant extracts) The sample was prepared using the same method as in Example 1, except that the calcination temperature was 600 °C and banyan leaves or arborvitae leaves were used.

[0040] Figure 5 The XRD patterns of samples prepared from different plants in Example 4 are shown. As can be seen from the figures, the samples prepared with the assistance of extracts from Platycladus orientalis or Ficus microcarpa leaves all exhibit similar diffraction peak positions, which match those of the CuMn2O4 standard card (PDF#84-0543). This indicates that pure-phase CuMn2O4-based high-entropy spinel oxides can be prepared using different plant extracts. Therefore, the method provided by this invention has good universality.

[0041] Example 5 (Green preparation of CuMn2O4-based high-entropy spinel oxides with different Cr contents) Samples were prepared using the same method as in Example 1, except that the calcination temperature was 600 °C and the proportion of nitrates used was different, designed according to Cr accounting for 8.33%, 12.50%, 16.67%, 25.00%, and 33.33% of the total metal content, as detailed below: (1) Cr accounts for 8.33% of the total metal content. Weigh 0.1914 g Cu(NO3)2, 0.3005 g Zn(NO3)2·6H2O, 0.4483 g Mn(NO3)2·4H2O, 0.6566 g Al(NO3)3·9H2O, and 0.2021 g Cr(NO3)3·9H2O.

[0042] (2) Cr accounts for 12.50% of the total metal content. Weigh 0.1914 g Cu(NO3)2, 0.3005 g Zn(NO3)2·6H2O, 0.4162 g Mn(NO3)2·4H2O, 0.6096 g Al(NO3)3·9H2O, and 0.3031 g Cr(NO3)3·9H2O.

[0043] (3) Cr accounts for 16.67% of the total metal content. Weigh 0.1914 g Cu(NO3)2, 0.3005 g Zn(NO3)2·6H2O, 0.3842 g Mn(NO3)2·4H2O, 0.5628 g Al(NO3)3·9H2O, and 0.4042 g Cr(NO3)3·9H2O.

[0044] (4) Cr accounts for 25.00% of the total metal content. Weigh 0.1914 g Cu(NO3)2, 0.3005 g Zn(NO3)2·6H2O, 0.3202 g Mn(NO3)2·4H2O, 0.4690 g Al(NO3)3·9H2O, and 0.6063 g Cr(NO3)3·9H2O.

[0045] (5) Cr accounts for 33.33% of the total metal content. Weigh 0.1914 g Cu(NO3)2, 0.3005 g Zn(NO3)2·6H2O, 0.2561 g Mn(NO3)2·4H2O, 0.3752 g Al(NO3)3·9H2O, and 0.8084 g Cr(NO3)3·9H2O.

[0046] Figure 6The XRD patterns of CuMn2O4-based high-entropy spinel oxides with different Cr contents are shown in Example 5. As can be seen from the figures, the main diffraction peaks of each sample generally correspond to the CuMn2O4 standard card (PDF#84-0543), indicating that the prepared samples mainly formed a CuMn2O4-type spinel structure. However, the Cr-8.33% sample, in addition to corresponding to the CuMn2O4 standard card, also exhibits characteristic diffraction peaks of the ZnAl2O4 standard card (PDF#74-1138), indicating the presence of a ZnAl2O4 impurity phase in this sample, and the failure to form a pure-phase spinel structure. This demonstrates that the Cr content has a significant impact on the phase composition of the system. When the Cr content is low, the system easily forms a ZnAl2O4 impurity phase, while as the Cr content increases, Cr helps suppress the formation of impurity phases, thereby promoting the formation of pure-phase CuMn2O4-based high-entropy spinel.

[0047] Example 6 (Green preparation of CuMn2O4-based high-entropy spinel oxides with different Cu contents) Samples were prepared using the same method as in Example 1, except that the calcination temperature was 600 °C and the nitrate ratio was different, designed according to Cu content of 8.33%, 16.67%, and 25.00% of the total metal content, as detailed below: (1) Cu accounts for 8.33% of the total metal content. Weigh 0.0947 g Cu(NO3)2, 0.4507 g Zn(NO3)2·6H2O, 0.3842 g Mn(NO3)2·4H2O, 0.5628 g Al(NO3)3·9H2O, and 0.4042 g Cr(NO3)3·9H2O.

[0048] (2) Cu accounts for 16.67% of the total metal content. Weigh 0.1914 g Cu(NO3)2, 0.3005 g Zn(NO3)2·6H2O, 0.3842 g Mn(NO3)2·4H2O, 0.5628 g Al(NO3)3·9H2O, and 0.4042 g Cr(NO3)3·9H2O.

[0049] (3) Cu accounts for 25.00% of the total metal content. Weigh 0.2842 g Cu(NO3)2, 0.1502 g Zn(NO3)2·6H2O, 0.3842 g Mn(NO3)2·4H2O, 0.5628 g Al(NO3)3·9H2O, and 0.4042 g Cr(NO3)3·9H2O.

[0050] Figure 7The XRD patterns of CuMn2O4-based high-entropy spinel oxides with different Cu contents are shown in Example 6. As can be seen from the figure, the positions of the diffraction peaks of each sample are basically consistent with those of the CuMn2O4 standard card (PDF#84-0543), and no obvious impurity phase diffraction peaks were observed, indicating that pure phase CuMn2O4-based high-entropy spinel oxides were successfully formed in the samples under different Cu contents.

[0051] Comparative Example 2 (Preparation of Comparative Samples with Different Components) To investigate the effects of various metal components on the formation and properties of high-entropy spinel oxides, mono-, binary, ternary, and quaternary comparative samples were further prepared based on the conditions described in Example 1. Except for the metal salt composition, metal ion ratio, and type of complexing agent, the preparation steps were the same as in Example 1.

[0052] (1) Preparation of univariate samples The monometallic samples were prepared using the same method as in Example 1, except that the calcination temperature was 600 °C and only a single metal precursor was used. Specifically, the precursors were 1.1483 g Cu(NO3)2, 1.8029 g Zn(NO3)2·6H2O, 1.5370 g Mn(NO3)2·4H2O, 2.2510 g Al(NO3)3·9H2O, and 2.4252 g Cr(NO3)3·9H2O. The prepared samples were labeled as 1 metal-Cu, 1 metal-Zn, 1 metal-Mn, 1 metal-Al, and 1 metal-Cr, respectively.

[0053] (2) Preparation of binary samples Using CuMn2O4 as a model sample, it was prepared by both green preparation with Bidens pilosa extract and traditional chemical methods. 0.3828 g of Cu(NO3)2 and 1.0245 g of Mn(NO3)2·4H2O were weighed.

[0054] The sample was prepared using the same method as in Example 1, except that the calcination temperature was 600 °C and the added metal nitrates were the weighed Cu(NO3)2 and Mn(NO3)2·4H2O mentioned above. The resulting sample was labeled as Bid-CuMn2O4.

[0055] Using a traditional chemical method, 1.2608 g of citric acid was weighed, 20 mL of deionized water was added, and the weighed metal salt was added. The mixture was stirred at room temperature for 15 min, then dried in an oven at 120 °C for 6 h to obtain a precursor dry gel. This gel was then treated under the same calcination conditions as in Example 1, and the resulting sample was labeled Chem-CuMn2O4.

[0056] (3) Preparation of ternary samples The ternary sample was prepared using the same green preparation method as in Example 1, except that the calcination temperature was 600 ℃ and the composition and ratio of nitrates were different, as detailed below: ① 0.3828 g Cu(NO3)2, 0.5123 g Mn(NO3)2·4H2O, 0.7503 g Al(NO3)3·9H2O ② 0.1914 g Cu(NO3)2, 0.3005 g Zn(NO3)2·6H2O, 1.0245 g Mn(NO3)2·4H2O ③ 0.1914 g Cu(NO3)2, 0.5123 g Mn(NO3)2·4H2O, 0.8084 g Cr(NO3)3·9H2O The final samples were labeled as: 3 metal-CuMnAl, 3 metal-CuZnMn, and 3 metal-CuMnCr.

[0057] (4) Preparation of quaternary samples The quaternary sample was prepared using the same green preparation method as in Example 1, except that the calcination temperature was 600 ℃ and the composition and ratio of the nitrates were different, as detailed below: ① 0.1914 g Cu(NO3)2, 0.3005 g Zn(NO3)2·6H2O, 0.5123 g Mn(NO3)2·4H2O, 0.7503 g Al(NO3)3·9H2O ② 0.1914 g Cu(NO3)2, 0.3005 g Zn(NO3)2·6H2O, 0.5123 g Mn(NO3)2·4H2O, 0.8084 g Cr(NO3)3·9H2O ③ 0.3828 g Cu(NO3)2, 0.3842 g Mn(NO3)2·4H2O, 0.5628 g Al(NO3)3·9H2O, 0.4042 g Cr(NO3)3·9H2O The final samples were labeled as: 4 metal-CuZnMnAl, 4 metal-CuZnMnCr, and 4 metal-CuMnAlCr.

[0058] Figure 8The XRD patterns of the monometallic samples in Comparative Example 2 are shown. Comparison of the XRD patterns of each monometallic sample with their corresponding standard cards shows that the diffraction peaks of the 1 metal-Zn, 1 metal-Mn, 1 metal-Cu, and 1 metal-Cr samples largely correspond to the standard cards for ZnO (PDF#80-0074), Mn₂O₃ (PDF#71-0636), CuO (PDF#72-0629), and Cr₂O₃ (PDF#06-0504), respectively, indicating that each sample formed its corresponding metal oxide crystalline phase. However, the 1 metal-Al sample did not show obvious characteristic crystalline phase peaks, indicating that it is mainly amorphous alumina.

[0059] Figure 9 The XRD patterns of the binary samples in Comparative Example 2 are shown. The figures show that the diffraction peaks of both the Bid-CuMn2O4 and Chem-CuMn2O4 samples correspond to the CuMn2O4 standard card (PDF#84-0543), indicating that both methods can form the CuMn2O4 phase. However, both samples have diffraction peaks corresponding to the Mn2O3 standard card (PDF#76-0150), indicating that neither sample yielded a pure phase and both contained Mn2O3 impurities. The Mn2O3-related impurity peaks are more pronounced in the Bid-CuMn2O4 sample, while they are relatively weaker in the Chem-CuMn2O4 sample, suggesting that neither the traditional citric acid complexation method nor the green low-temperature preparation method can produce pure-phase samples.

[0060] Figure 10 The XRD patterns of the ternary samples in Comparative Example 2 are shown. As can be seen from the figures, the main diffraction peaks of the 3-metal-CuMnCr sample basically correspond to the CuCrMnO4 standard card (PDF#76-1565), indicating that the sample mainly formed the CuCrMnO4 related crystalline phase. The diffraction peaks of the 3-metal-CuMnAl sample correspond to the CuAl2O4 standard card (PDF#33-0448) and the MnAl2O4 standard card (PDF#10-0310), respectively, indicating that both CuAl2O4 and MnAl2O4 crystalline phases exist in the sample. The diffraction peaks of the 3-metal-CuZnMn sample correspond to the ZnMn2O4 standard card (PDF#71-2499) and the CuMn2O4 standard card (PDF#84-0543), respectively, indicating that both ZnMn2O4 and CuMn2O4 crystalline phases are formed in the sample. The above results indicate that the introduction of different third metals has a significant impact on the phase formation behavior of the ternary system. The CuMnCr system mainly forms the CuCrMnO4 phase, while the CuMnAl and CuZnMn systems exhibit the coexistence of two related oxide crystal phases.

[0061] Figure 11The image shows the XRD pattern of the quaternary sample in Comparative Example 2. As can be seen from the figure, for the 4 metal-CuZnMnAl sample, its diffraction peaks correspond to the Al2CuO4 standard card (PDF#76-2995) and the MnAl2O4 standard card (PDF#29-0880), respectively. A weak impurity peak is also present, corresponding to the Mn2O3 standard card (PDF#76-0150). This indicates that the 4 metal-CuZnMnAl sample mainly consists of Al2CuO4 and MnAl2O4 crystal phases, with a small amount of Mn2O3 impurity phase. For the 4 metal-CuMnAlCr sample, the diffraction peaks generally correspond to Cu… 1.5 Mn 1.5 The diffraction peaks generally correspond to the CuMn2O4 standard card (PDF#70-0260) and show no impurity peaks. For the 4 metal-CuZnMnCr sample, the diffraction peaks generally correspond to the CuMn2O4 standard card (PDF#84-0543) and show no obvious impurity peaks. A comprehensive comparison shows that the introduction of Cr makes it easier for the sample to form a pure-phase spinel structure, indicating that Cr plays a crucial role in the phase stability and pure-phase formation of this high-entropy system.

[0062] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A green, low-temperature method for preparing pure-phase CuMn2O4-based high-entropy spinel oxides, characterized in that, Includes the following steps: (1) Prepare plant leaves: Collect, wash, dry and bag the plant leaves; (2) Preparation of plant extract: Soak the bagged plant leaves in boiling water to obtain plant extract; (3) Preparation of dry gel: Add metal precursor to plant extract, then stir and dry; (4) Sample preparation: The dried sample was calcined to obtain pure phase CuMn2O4-based high-entropy spinel oxide.

2. The method as described in claim 1, characterized in that, The plant leaves mentioned are fresh green leaves or fallen dead leaves, including leaves of herbaceous plants, shrubs, or trees.

3. The method as described in claim 1, characterized in that, The washing process involves rinsing with tap water 2-4 times, followed by washing with deionized water 1-2 times. The ratio of tap water or deionized water to plant leaves is 5-20: 1 mL / g.

4. The method as described in claim 1, characterized in that, In step (1), the drying temperature is 80~120 ℃ and the time is 12~48 h.

5. The method as described in claim 1, characterized in that, The bagging process involves weighing 0.5 to 4.0 g of dried leaves and placing them into a nylon mesh bag.

6. The method as described in claim 1, characterized in that, The soaking process uses deionized water at 70~100 ℃, with a water volume of 20 mL and a soaking time of 0.5~10 min.

7. The method as described in claim 1, characterized in that, The metal precursor is a mixture of copper nitrate, zinc nitrate, manganese nitrate, aluminum nitrate, and chromium nitrate, with a total metal content of 0.006 mol, of which the total content of copper nitrate and zinc nitrate is 0.002 mol, and the total content of manganese nitrate, aluminum nitrate, and chromium nitrate is 0.004 mol. The molar percentage of each metal in the total metal content is 12.50~33.33%.

8. The method as described in claim 1, characterized in that, In step (3), the drying temperature is 80~120 ℃ and the time is 6~12 h.

9. The method as described in claim 1, characterized in that, The calcination temperature is 350~900 ℃, the calcination heating rate is 1~15 ℃ / min, and the calcination holding time is 30~300 min.

10. CuMn2O4-based high-entropy spinel oxide prepared by the method according to any one of claims 1-9.

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