A hollow cubic high-entropy oxide and its controllable synthesis method and application

Abstract

The present invention relates to the field of novel nano-morphology nano-materials and controlled synthesis, and a method for controllably synthesizing hollow cubic high-entropy oxides, comprising: dissolving CuSO4·5H2O and sodium citrate in water, then adding sodium hydroxide and ascorbic acid aqueous solution to obtain a first solid; washing and drying the first solid to obtain nano-cubic Cu2O; after dispersing the nano-cubic Cu2O, adding polyvinylpyrrolidone, mixing, adding different metal M salts, stirring, and then adding sodium thiosulfate solution to obtain a second solid; washing and drying the second solid to obtain hollow M-OH, and annealing M-OH to obtain Ni a Co b Fe c Cd d Cr e La f Sn g Zn h O4. A high-entropy hydroxide precursor is synthesized at room temperature by the hard and soft acid-base reaction method, and a single-phase high-entropy oxide is formed through an annealing process at a relatively low temperature. The finally obtained high-entropy oxide exhibits a hollow cubic morphology structure, which is beneficial to the progress of the catalytic reaction.

Description

Technical Field

[0001] The present invention relates to the field of nanomaterials with novel nano-morphologies and controlled synthesis, and particularly to a hollow cubic high-entropy oxide and its controllable synthesis method and application. Background Art

[0002] As a new type of oxide, high-entropy oxide belongs to the derivative system of high-entropy alloy materials. It has become a research hotspot due to its unique structure, component mixing, excellent properties and the existence of oxygen sites. The unique properties of high-entropy oxides benefit from the interaction, synergy and entropy promotion effects of different combinations of multiple elements, and have broad application prospects in environmental governance, chemical catalysis, energy and other aspects. Therefore, it is very necessary to explore and develop fast and controllable synthesis technologies for exploring new element combinations and applications of high-entropy oxides.

[0003] At present, the synthesis of high-entropy oxides mainly focuses on high-temperature and high-energy-driven synthesis methods, which need to be synthesized under long-term heating, high temperature and high-energy conditions. Usually, it needs to be heated to a temperature of 1000 °C or even higher, and the morphology is uncontrollable, mostly in bulk shape, and the element composition is uncontrollable, which is easy to cause phase segregation. For example, when synthesizing high-entropy oxides, metal salts are mixed and then rapidly heat-treated to a temperature of 1000 °C or even higher to sinter them into one phase. However, this method has relatively large limitations. For example, in terms of morphology, due to its rapid high-temperature sintering, it is easy to form a molten bulk morphology, which is not conducive to the exposure of active sites and the progress of catalytic reactions.

[0004] It is also worth noting that the hydrogenation of nitroaromatic compounds is one of the most widely used catalytic processes in organic chemistry and bulk chemical industry. Hydrogenation also provides a way to reduce the environmental pollution risk of nitroaromatic compounds. However, most metal-based catalysts for reducing nitroaromatic compounds highly rely on precious metals, and due to the scarcity and high cost of precious metals, it hinders their practical applications. Therefore, many scholars are committed to developing cheap transition metal materials to replace precious metal catalysts. Therefore, synthesizing novel non-precious metal-based high-entropy oxides by a simple method and applying them to the catalytic hydrogenation of p-nitrophenol is a valuable research field. Summary of the Invention

[0005] The purpose of the present invention is to provide a preparation method with controllable morphology, mild conditions, adjustable components and strong universality, used to synthesize transition metal-based high-entropy oxides with a hollow structure, and further develop its application in the hydrogenation degradation of p-nitrophenol to solve the above problems.

[0006] To achieve the above object, the present invention is implemented according to the following technical solutions:

[0007] A controllable synthesis method of hollow cubic high-entropy oxides, comprising the following steps:

[0008] S1. Prepare nano-cubic Cu2O:

[0009] Dissolve CuSO4·5H2O and sodium citrate in water, add sodium hydroxide, mix evenly, then add an aqueous solution of ascorbic acid, and stir and mix to obtain a first solid; centrifuge and wash the obtained first solid, and vacuum dry it to obtain nano-cubic Cu2O;

[0010] S2. Prepare high-entropy hydroxide M-OH:

[0011] Disperse the nano-cubic Cu2O in an aqueous solution of ethanol, add polyvinylpyrrolidone, mix evenly, then add different metal M salts, stir evenly, and then add a sodium thiosulfate solution to obtain a second solid; centrifuge and wash the second solid, and then freeze-dry it to obtain hollow cubic high-entropy hydroxide M-OH;

[0012] S3. Prepare hollow cubic high-entropy oxide Ni a Co b Fe c Cd d Cr e La f Sn g Zn h O4:

[0013] Anneal M-OH to obtain hollow cubic high-entropy oxide Ni a Co b Fe c Cd d Cr e La f Sn g Zn h O4;

[0014] where a + b + c + d + e + f + g + h = 3, and a > 0, b > 0, c > 0, d ≥ 0, e ≥ 0, f ≥ 0, g ≥ 0, h ≥ 0.

[0015] Preferably, in the step S1, the mass ratio of CuSO4·5H2O, sodium citrate, and sodium hydroxide is 0.75:0.3:2; in the step S1, the mass-volume ratio of CuSO4·5H2O to water is 0.75:200, and the unit of the mass-volume ratio is g:ml.

[0016] Preferably, in the step S1, the volume ratio of water to the aqueous solution of ascorbic acid is 2:1; the concentration of the aqueous solution of ascorbic acid is 0.03 mol / L.

[0017] Preferably, in step S2, in the aqueous solution of ethanol, the volume ratio of water to absolute ethanol is 1:1; the concentration of the sodium thiosulfate solution is 1 mol / L.

[0018] Preferably, in step S2, the mass ratio of the nano-cubic Cu2O to polyvinylpyrrolidone is 4:66.66; the mass-to-volume ratio of the nano-cubic Cu2O to the sodium thiosulfate solution is 5:4, and the unit of the mass-to-volume ratio is mg:ml.

[0019] Preferably, in step S2, the addition amount of the metal M salt is n1 mmol of Ni salt, n2 mmol of Co salt, n3 mmol of Fe salt, n4 mmol of Cd salt, n5 mmol of Cr salt, n6 mmol of La salt, n7 mmol of Sn salt, n8 mmol of Zn salt; where n1>0, n2>0, n3>0, n4≥0, n5≥0, n6≥0, n7≥0, n8≥0, and n1:n2:n3:n4:n5:n6:n7:n8 = a:b:c:d:e:f:g:h.

[0020] Preferably, in step S2, the mass-to-amount-of-substance ratio of the nano-cubic Cu2O to the metal M salt is 40:0.06 - 0.12, and the unit of the mass-to-amount-of-substance ratio is mg:mmol.

[0021] Preferably, in step S3, the annealing temperature is 600 °C and the annealing time is 2 h.

[0022] The present invention also relates to the application of hollow cubic high-entropy oxide Ni a Co b Fe c Cd d Cr e La f Sn g Zn h O4 in the catalytic reduction degradation of p-nitrophenol.

[0023] Specifically, when the metal M salt includes Ni salt, Co salt, Fe salt, Cd salt, and Cr salt, the prepared hollow cubic high-entropy oxide is Ni a Co b Fe c Cd d Cr e O4 in the catalytic reduction degradation of p-nitrophenol.

[0024] Specifically, the controllable synthesis method of the hollow cubic high-entropy oxide includes the following steps:

[0025] S1, preparing nano-cubic Cu2O:

[0026] Dissolve 0.75 g of CuSO4·5H2O and 0.3 g of sodium citrate completely in 200 mL of water under stirring; then, add 2 g of NaOH (solid powder) to the above solution and stir for 0.5 h, add 100 mL of 0.03 M ascorbic acid (it can be added dropwise), stir for 0.5 h, and then let it stand; centrifuge and wash the obtained solid, and vacuum dry it in an oven at 60 °C for 12 h to obtain nano-cubic Cu2O; the stirring process in step S1 is carried out at room temperature. The water in step S1 is deionized water or ultrapure water.

[0027] S2, prepare high-entropy hydroxide M-OH:

[0028] Disperse the Cu2O (40 mg) synthesized in step S1 by ultrasonic stirring in a solution of 80 mL of water and anhydrous ethanol mixed evenly (the volume ratio of water to anhydrous ethanol is 1:1), first add 0.6666 g of polyvinylpyrrolidone (PVP, K30) and stir magnetically to dissolve for 15 min; then dissolve different component metal M salts in the above solution and stir for 15 min; finally, drop 32 mL of 1 M Na2S2O3 solution into the above solution system drop by drop, stir and react for 0.5 h to obtain a second solid; centrifuge and wash many times to separate the second solid, and carry out vacuum freeze-drying; obtain high-entropy hydroxide M-OH; the addition order of PVP and metal salts is that PVP is added first, and after stirring and dissolving, the metal salts are added; the stirring process in step S2 is carried out at room temperature.

[0029] In step S2, the total addition amount of metal M salts is 0.06 - 0.12 mmol; M salts include Ni salts, Co salts, Fe salts; or M salts include Ni salts, Co salts, Fe salts, and at least one of Cd salts, Cr salts, La salts, Sn salts, Zn salts.

[0030] S3, prepare hollow-cubic high-entropy oxide Ni a Co b Fe c Cd d Cr e La f Sn g Zn h O4:

[0031] Anneal the freeze-dried M-OH powder in a tube furnace at 600 °C in an air atmosphere for 2 h to obtain high-entropy oxide Ni a Co b Fe c Cd d Cr e La f Sn g Zn h O4.

[0032] Further, when the metal M salt includes Ni salt, Co salt, and Fe salt, the prepared hollow cube high-entropy oxide is Ni a Co b Fe c O4; where the values of a, b, and c satisfy: 1 / 3 ≤ a ≤ 4 / 3, 1 / 3 ≤ b ≤ 4 / 3, 1 / 3 ≤ c ≤ 4 / 3, and the sum of a, b, and c is 3.

[0033] Further, when the metal M salt includes Ni salt, Co salt, Fe salt, Cd salt, and Cr salt, the prepared hollow cube high-entropy oxide is Ni a Co b Fe c Cd d Cr e O4; where the values of a, b, c, d, and e satisfy: 1 / 5 ≤ a ≤ 4 / 5, 1 / 5 ≤ b ≤ 4 / 5, 1 / 5 ≤ c ≤ 4 / 5, 1 / 5 ≤ d ≤ 4 / 5, 1 / 5 ≤ e ≤ 4 / 5, and the sum of a, b, c, d, and e is 3.

[0034] Further, when the metal M salt includes Ni salt, Co salt, Fe salt, and Cd salt, when obtained, the prepared hollow cube high-entropy oxide is Ni a Co b Fe c Cd d O4; where the values of a, b, c, and d satisfy: 1 / 4 ≤ a ≤ 1, 1 / 4 ≤ b ≤ 1, 1 / 4 ≤ c ≤ 1, 1 / 4 ≤ d ≤ 1, and the sum of a, b, c, and d is 3.

[0035] Further, when the metal M salt includes Ni salt, Co salt, Fe salt, and Cr salt, the prepared hollow cube high-entropy oxide is Ni a Co b Fe c Cr e O4; where the values of a, b, c, and e satisfy: 1 / 4 ≤ a ≤ 1, 1 / 4 ≤ b ≤ 1, 1 / 4 ≤ c ≤ 1, 1 / 4 ≤ e ≤ 1, and the sum of a, b, c, and e is 3.

[0036] Further, when the metal M salt includes Ni salt, Co salt, Fe salt, Cd salt, Cr salt, and La salt, the prepared hollow cube high-entropy oxide is Ni a Co b Fe c Cd d Cr e La fO4; where the values of a, b, c, d, e, f satisfy: 1 / 6 ≤ a ≤ 2 / 3, 1 / 6 ≤ b ≤ 2 / 3, 1 / 6 ≤ c ≤ 2 / 3, 1 / 6 ≤ d ≤ 2 / 3, 1 / 6 ≤ e ≤ 2 / 3, 1 / 6 ≤ f ≤ 2 / 3, and the sum of a, b, c, d, e, f is 3.

[0037] Furthermore, when the metal M salt includes Ni salt, Co salt, Fe salt, Cd salt, Cr salt, La salt, Sn salt, the prepared hollow cubic high-entropy oxide is Ni a Co b Fe c Cd d Cr e La f Sn g O4; where the values of a, b, c, d, e, f, g satisfy: 1 / 7 ≤ a ≤ 4 / 7, 1 / 7 ≤ b ≤ 4 / 7, 1 / 7 ≤ c ≤ 4 / 7, 1 / 7 ≤ d ≤ 4 / 7, 1 / 7 ≤ e ≤ 4 / 7, 1 / 7 ≤ f ≤ 4 / 7, 1 / 7 ≤ g ≤ 4 / 7, and the sum of a, b, c, d, e, f, g is 3.

[0038] Furthermore, when the metal M salt includes Ni salt, Co salt, Fe salt, Cd salt, Cr salt, La salt, Sn salt, Zn salt, when obtained, the prepared hollow cubic high-entropy oxide is; where the values of a, b, c, d, e, f, g, h satisfy: 1 / 8 ≤ a ≤ 1 / 2, 1 / 8 ≤ b ≤ 1 / 2, 1 / 8 ≤ c ≤ 1 / 2, 1 / 8 ≤ d ≤ 1 / 2, 1 / 8 ≤ e ≤ 1 / 2, 1 / 8 ≤ f ≤ 1 / 2, 1 / 8 ≤ g ≤ 1 / 2, 1 / 8 ≤ h ≤ 1 / 2, and the sum of a, b, c, d, e, f, g, h is 3.

[0039] Principle of action:

[0040] Aiming at the technical problems existing in the prior art, the present invention is committed to overcoming the limitations of high temperature and high energy, controlling the morphology and composition, and designing and preparing high-entropy oxide materials with good morphology, high activity, significant catalytic efficiency and simple and mild synthesis methods, which is of great significance for its practical application, but it is still a huge challenge.

[0041] Based on the principle of greatly shortening the heat treatment temperature and time, the present invention develops a highly universal, rapid and controllable synthesis strategy. At the same time, by broadening the element combination of high-entropy oxides and combining favorable morphology regulation, the compositional advantages of high-entropy materials can be greatly stimulated, enabling them to have more efficient catalytic activity for degrading p-nitrophenol.

[0042] The present invention aims to address the limitations of the synthesis method of high-entropy oxides, mainly involving three aspects: (1) Controllable morphology: The method adopted can enable the high-entropy oxides to finally exhibit a hollow cubic morphology structure, which is more conducive to subsequent development and application; (2) Controllable composition: By adjusting the synthesis method conditions and metal ion components, multi-component transition metal-based ternary Ni a Co b Fe c O4 (the sum of a, b, and c is 3) to octa-component Ni a Co b Fe c Cd d Cr e La f Sn g Zn h O4 (the sum of a, b, c, d, e, f, g, and h is 3) oxides can be prepared; (3) Mild conditions: After synthesizing the precursor at room temperature, a single-phase high-entropy oxide can be formed by undergoing a relatively low annealing temperature.

[0043] Generally speaking, the present invention relates to a mild, simple, morphology-controllable, and composition-controllable technical method for preparing hollow-structured nano-cubic high-entropy oxides, and ultimately can achieve the controllable synthesis of ternary to octa-component high-entropy oxides. Moreover, the prepared high-entropy oxides have excellent activity and stability in the application of catalytic reduction and degradation of p-nitrophenol.

[0044] The design and synthesis of high-entropy oxide catalysts follow two criteria: forming a single phase and uniform element mixing. Therefore, inventing an effective precursor synthesis method is of great significance for generating high-entropy oxides. The present invention adopts a template-assisted method to synthesize well-defined, multi-component, high-quality, and different-component hydroxide hollow nano-cube precursors through a coordination etchant at room temperature, and then heat-treats the high-entropy hydroxide to obtain high-entropy oxides.

[0045] The present invention designs and successfully prepares a novel five-component high-entropy oxide Ni a Co b Fe c Cd d Cr e O4, which can be used as a catalyst for the hydrogenation of p-nitrophenol with NaBH4.

[0046] The implementation method of the present invention uses solid cubic cuprous oxide as a soft acid and sodium thiosulfate as a soft base. Through the coordination etching between the two, the hydroxide ions continuously generated by the hydrolysis of thiosulfate ions coordinate with metal ions to form metal hydroxides, which are gradually deposited on the surface of the cuprous oxide shell layer. The cuprous oxide is gradually consumed, and finally a hollow high-entropy hydroxide precursor is formed. After the heat treatment annealing process, hollow nanocubic high-entropy oxides are prepared.

[0047] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0048] (1) A high-entropy hydroxide precursor of hollow nanoboxes was synthesized at room temperature by the hard-soft acid-base reaction method. After an annealing process at a relatively low temperature, a single-phase high-entropy oxide was formed. The finally obtained high-entropy oxide exhibited a hollow cubic morphology structure, which was beneficial to the progress of the catalytic reaction;

[0049] (2) By adjusting the synthesis method conditions and metal components, high-entropy oxides of transition metal-based ternary to octonary can be finally prepared, which is of great significance for controlling and broadening the components of high-entropy oxides;

[0050] (3) The prepared high-entropy quinary Ni a Co b Fe c Cd d Cr e O4 catalyst showed excellent performance in the hydrogenation of p-nitrophenol, and the rate constant (k) was as high as 1.79 min -1 . In addition, Ni a Co b Fe c Cd d Cr e O4 also showed excellent stability. After 10 cycles, the activity loss was not obvious, and the conversion rate could be maintained above 95%. Description of the Drawings

[0051] Figure 1 Synthesis route diagram of the quinary high-entropy oxide (Ni a Co b Fe c Cd d Cr e O4) prepared in Example 1;

[0052] Figure 2 Characterization diagram of Cu2O prepared in Example 1; among them, (a) is the scanning electron microscope (SEM) image of Cu2O prepared in Example 1; (b) is the X-ray diffraction (XRD) pattern of Cu2O; (c-e) are the transmission electron microscope (TEM) images of Cu2O; (f) is the element distribution (EDS) map of Cu2O;

[0053] Figure 3 Characterization diagrams of NiCoFeCdCr-OH prepared in Example 1; where (a) is the TEM image of NiCoFeCdCr-OH prepared in Example 1; (b) is the XRD pattern of NiCoFeCdCr-OH; (c) is the elemental distribution map of NiCoFeCdCr-OH;

[0054] Figure 4 TEM and elemental distributions of the hollow cubic high-entropy oxides prepared in Examples 1 to 7: corresponding to (a) Ni a Co b Fe c O4; (b) Ni a Co b Fe c Cd d O4; (c) Ni a Co b Fe c Cr e O4; (d) Ni a Co b Fe c Cd d Cr e O4; (e) Ni a Co b Fe c Cd d Cr e La f O4; (f) Ni a Co b Fe c Cd d Cr e La f Sn g O4; (g) Ni a Co b Fe c Cd d Cr e La f Sn g Zn h O4 (scale bar: 200 nm);

[0055] Figure 5 XRD pattern of the quinary high-entropy oxide Ni a Co b Fe c Cd d Cr e O4 prepared in Example 1;

[0056] Figure 6 Performance graphs of the high-entropy oxides prepared in Examples 1 to 4 for the catalytic reduction of p-nitrophenol to p-aminophenol at 25 °C: Among them, (a) shows the change in the absorbance of the p-nitrophenol solution with the reaction time by the high-entropy oxide of Example 1; (b) shows the graph of ln(C t / C0) of the high-entropy oxides of Examples 1 to 4 with the reaction time of the catalyst; (c) shows the bar graph of the corresponding rate constants of the high-entropy oxides of Examples 1 to 4; (d) shows 10-cycle experiments of the high-entropy oxide of Example 1 for the hydrogenation of p-nitrophenol. Detailed implementation manners

[0057] The present invention will be further described below with specific examples. The illustrative examples and explanations of this invention are used to explain the present invention, but do not limit the present invention.

[0058] For all raw materials of the present invention, there is no particular limitation on their sources, which are purchased on the market or prepared by conventional methods well-known to those skilled in the art.

[0059] Regarding the devices involved in the present invention, those without particular limitations are commonly used devices in the art, and those skilled in the art are familiar with their operations and usage methods.

[0060] The present invention will be further described below with specific examples. The illustrative examples and explanations of this invention are used to explain the present invention, but do not limit the present invention.

[0061] Example 1

[0062] A controllable synthesis method of a hollow cubic high-entropy oxide:

[0063] (1) Dissolve 0.75 g of CuSO4·5H2O and 0.3 g of sodium citrate in 200 mL of ultrapure water. Then, add 2 g of NaOH to the above solution and stir for 0.5 h, and then add 100 mL of 0.03 M ascorbic acid. After stirring for 0.5 h, centrifuge, wash and separate the Cu2O nanocubes, and vacuum dry them in an oven at 60 °C for 12 h.

[0064] (2) Ultrasonically stir and disperse the synthesized Cu₂O (40 mg) in a solution of 80 mL of water and anhydrous ethanol mixed evenly. First, add 0.6666 g of polyvinylpyrrolidone and stir to dissolve for 15 min. Then, dissolve 4.8 mg of NiCl₂·6H₂O (0.02 mmol), 4.8 mg of CoCl₂·6H₂O (0.02 mmol), 5.6 mg of FeSO₄·7H₂O (0.02 mmol), 4.6 mg of CdCl₂·2.5H₂O (0.02 mmol), and 8 mg of Cr(NO₃)₃·9H₂O (0.02 mmol) in the above solution and stir for 15 min. Finally, slowly drop 32 mL of 1 M Na₂S₂O₃ into the above solution system. After reacting for 0.5 h under stirring, centrifuge and wash multiple times to separate the high-entropy hydroxide NiCoFeCdCr-OH, and perform vacuum freeze-drying.

[0065] (3) Anneal the freeze-dried NiCoFeCdCr-OH powder in a tube furnace at 600 °C for 2 h in an air atmosphere to obtain the high-entropy oxide Ni a Co b Fe c Cd d Cr e O₄ (the sum of a, b, c, d, and e is 3, and the values of a, b, c, d, and e range from 1 / 5 to 4 / 5).

[0066] Specifically, in this example, the actual obtained high-entropy oxide has a = 3 / 5, b = 3 / 5, c = 3 / 5, d = 3 / 5, and e = 3 / 5, that is, the obtained product is Ni 3 / 5 Co 3 / 5 Fe 3 / 5 Cd 3 / 5 Cr 3 / 5 O₄.

[0067] The Ni a Co b Fe c Cd d Cr e O₄ synthesized in Example 1 is a novel high-entropy penta-oxide with a hollow nanocube structure, which is prepared based on the hard-soft base reaction theory. Specifically, first prepare solid cube cuprous oxide as a soft acid, and the prepared sodium thiosulfate as a soft base. According to the principle that soft acids react preferentially with soft bases, coordination etching occurs between the two. Cuprous oxide is gradually consumed and coordinates with thiosulfate to form soluble [Cu₂(S₂O₃) x 2-2x diffusing into the solution system. At this time, thiosulfate continuously hydrolyzes to produce OH - ​It coordinates with metal ions to form tiny metal hydroxide nanosheets, which gradually deposit on the surface of the cuprous oxide shell and finally form a hollow high-entropy hydroxide precursor. After a heat treatment annealing process at 600 degrees Celsius, hollow nano-cubic high-entropy oxides are obtained.

[0068] As Figure 1 shown, it is the synthesis route of the high-entropy oxide Ni a Co b Fe c Cd d Cr e O4 in Example 1 of the present invention.

[0069] As Figure 2 shown, the synthesized Cu2O sample in step 1) involved in the technical solution of the present invention has a solid nano-cubic morphology ( Figure 2 a), and the XRD diffraction peaks can be well matched with Cu2O (JCPDS card number 05-0667) ( Figure 2 b), indicating that cuprous oxide with high crystallinity and purity is successfully prepared. The TEM image shows that the average size of the Cu2O solid nano-cubes is 300 nm ( Figure 2 c-e), and the distributions of O and Cu elements are very uniform ( Figure 2 f).

[0070] As Figure 3 shown, after the coordination etching process in step 2), the Cu2O nano-cubes are consumed to form high-entropy NiCoFeCdCr-OH hollow nano-boxes with fine M-OH nanosheets on the surface ( Figure 3 a), and the XRD results show that the diffraction peaks match with classical hydroxides ( Figure 3 b). The EDS results show that Ni, Co, Fe, Cd, and Cr are evenly distributed in the NiCoFeCdCr-OH nano-boxes, and since the Cu element always exists in the solution system and is very likely not to be completely consumed, inevitably there is still a part of Cu residue ( Figure 3 c).

[0071] After the heat treatment in air at 600 °C in step 3), high-entropy oxide Ni a Co b Fe c Cd d Cr e O4 is formed. The TEM image shows that the morphology and structure of the hollow nano-box are maintained after the heat treatment. The tiny nanosheets on the surface have a slight shrinkage but the overall structure remains unchanged, indicating that the structure has good stability. In addition, the EDS results show that the element distributions are uniform ( Figure 4 d), preliminarily indicating the formation of the high-entropy phase. In addition, as Figure 5The XRD results show that the as-prepared high-entropy oxide is a single-phase high-entropy oxide with a spinel structure, which can match well with the standard card of the cobalt ferrite spinel phase oxide ( Figure 5 ), and no other elemental oxide phases are formed, indicating no phase segregation, further demonstrating the successful synthesis of the high-entropy quinary Ni a Co b Fe c Cd d Cr e O4. It should be noted that in addition to the spinel oxide phase, there is also a CuO phase formed by the annealing of the residual Cu in the system. Generally speaking, a quinary single-phase high-entropy oxide can be obtained by implementing the technical solution of the present invention.

[0072] As Figure 6 shown, in order to investigate the catalytic ability of the catalyst, the catalytic performance of the synthesized material was tested: the catalytic reduction of p-nitrophenol. Excessive NaBH4 was selected to catalyze the hydrogenation of p-nitrophenol at 298 K to investigate the catalytic performance of the prepared catalyst. Usually, 0.1898 g of NaBH4 was dissolved in 20 mL of ultrapure water, and the NaBH4 solution was added to 20 mL of 2 mM p-nitrophenol. After stirring for 5 min, 20 μL of the dispersed catalyst suspension (2 mg·mL -1 ) was quickly injected into the system to initiate the hydrogenation reaction. Subsequently, during the reaction, 0.5 mL of the solution in the system was diluted to 10 mL every certain time interval (30 s), and then monitored by a UV-vis spectrometer. For the recycling experiment, after the reduction reaction was completed, the catalyst was separated by a filtration device and dried, and then the performance test was carried out again under the same experimental conditions. Ten consecutive cycle tests were carried out. According to the Lambert-Beer law: A = KbC (where A represents absorbance, C is the concentration of the light-absorbing substance, K is the molar extinction coefficient, and b is the thickness of the absorption layer). In addition, the degradation kinetics of p-nitrophenol in the present invention was fitted with a pseudo-first-order model, and the rate constant k can be calculated by the formula: ln(C t / C0) = ln(A t / A0) = -kt, where k is the apparent rate constant, t is the reaction time, and the higher the degradation rate, the larger the value of the rate constant k, indicating that the catalytic efficiency of the catalyst is better during the catalytic process.

[0073] For the synthesized high-entropy oxide Ni a Co b Fe c Cd d Cr eThe catalytic ability of O4 for the degradation of p-nitrophenol. The results show that after adding the catalyst to the solution, the absorbance of p-nitrophenol decreases, and a new peak of p-aminophenol appears in the region around 310 nm, proving that the catalyst can effectively hydrogenate and degrade p-nitrophenol into p-aminophenol. The typical absorbance change of p-nitrophenol at 25 °C is shown ( Figure 6 a), Ni a Co b Fe c Cd d Cr e O4 can achieve a p-nitrophenol conversion efficiency of nearly 100% within 150 s. Compared with the ternary Ni a Co b Fe c O4 (0.242 min -1 ), the quaternary Ni a Co b Fe c Cd d O4 (0.635 min -1 ), and the quaternary Ni a Co b Fe c Cr e O4 (1.00 min -1 ), the highly efficient quinary high-entropy Ni a Co b Fe c Cd d Cr e O4 catalyst has a rate constant (k) of 1.79 min -1 ( Figure 6 b, c), indicating that Ni a Co b Fe c Cd d Cr e O4 has the fastest catalytic reaction rate and high reactivity for the hydrogenation of p-nitrophenol. In addition, Ni a Co b Fe c Cd d Cr e O4 also exhibits excellent stability, with insignificant activity loss after 10 cycles, and the conversion rate can be maintained above 95%( Figure 6 d).

[0074] Based on the hard-soft-acid-base (HSAB) strategy, the present invention prepared a single-phase high-entropy oxide with uniform element distribution using soft acid Cu2O as a template. Specifically, as shown in the synthesis route Figure 1 , when the soft base S2O3 2- etches the soft acid Cu2O, OH will be released- , M(OH) x began to form a shell-like structure by synchronous precipitation, and Cu2O was gradually consumed. Finally, the high-entropy hydroxide (NiCoFeCdCr-OH) was converted into high-entropy oxide (Ni a Co b Fe c Cd d Cr e O4, where the sum of a, b, c, d, and e is 3).

[0075] Example 2:

[0076] A controllable synthesis method of hollow cubic high-entropy oxide:

[0077] (1) Dissolve 0.75 g of CuSO4·5H2O and 0.3 g of sodium citrate in 200 mL of ultrapure water. Then, add 2 g of NaOH to the above solution and stir for 0.5 h, and then add 100 mL of 0.03 M ascorbic acid. After stirring for 0.5 h, the Cu2O nanocubes were separated by centrifugation, washed, and vacuum-dried in an oven at 60 °C for 12 h.

[0078] (2) Ultrasonically stir and disperse the Cu2O (40 mg) synthesized in step (1) in a solution of 80 mL of water and anhydrous ethanol mixed evenly. First, add 0.6666 g of polyvinylpyrrolidone and stir to dissolve for 15 min. Then, dissolve 4.8 mg of NiCl2·6H2O (0.02 mmol), 4.8 mg of CoCl2·6H2O (0.02 mmol), and 5.6 mg of FeSO4·7H2O (0.02 mmol) in the above solution and stir for 15 min. Finally, 32 mL of 1 M Na2S2O3 was added dropwise to the above solution system. After reacting for 0.5 h under stirring, it was centrifuged and washed multiple times to separate the high-entropy hydroxide NiCoFe-OH, and then vacuum freeze-dried.

[0079] (3) Anneal the freeze-dried NiCoFe-OH powder in a tube furnace at 600 °C in an air atmosphere for 2 h to obtain the high-entropy oxide Ni a Co b Fe c O4 (where the sum of a, b, and c is 3, and the values of a, b, and c range from 1 / 3 to 4 / 3).

[0080] Specifically, in this example, a = 1, b = 1, and c = 1 in the actually obtained high-entropy oxide, that is, the obtained product is NiCoFeO4

[0081] TEM images and EDS results show( Figure 4 a), ternary Ni a Cob Fe c The O4 transition metal-based oxide exhibits a hollow nanobox morphology structure and the distribution of each component element is uniform, indicating the successful synthesis of the ternary Ni a Co b Fe c O4 metal oxide.

[0082] Example 3:

[0083] A controllable synthesis method of hollow cubic high-entropy oxide:

[0084] (1) Dissolve 0.75 g of CuSO4·5H2O and 0.3 g of sodium citrate in 200 mL of ultrapure water. Then, add 2 g of NaOH to the above solution and stir for 0.5 h, and then add 100 mL of 0.03 M ascorbic acid. After stirring for 0.5 h, centrifuge, wash and separate the Cu2O nanocubes, and vacuum dry them in an oven at 60 °C for 12 h.

[0085] (2) Ultrasonically stir and disperse the Cu2O (40 mg) synthesized in step (1) in a solution of 80 mL of water and anhydrous ethanol mixed evenly. First, add 0.6666 g of polyvinylpyrrolidone and stir to dissolve for 15 min, and then dissolve 4.8 mg of NiCl2·6H2O (0.02 mmol), 4.8 mg of CoCl2·6H2O (0.02 mmol), 5.6 mg of FeSO4·7H2O (0.02 mmol) and 4.6 mg of CdCl2·2.5H2O (0.02 mmol) in the above solution and stir for 15 min. Finally, drop 32 mL of 1 M Na2S2O3 into the above solution system drop by drop. After reacting for 0.5 h under stirring, centrifuge and wash many times to separate the high-entropy hydroxide NiCoFeCd-OH, and perform vacuum freeze-drying.

[0086] (3) Anneal the freeze-dried NiCoFeCd-OH powder in a tube furnace at 600 °C for 2 h in an air atmosphere to obtain the high-entropy oxide Ni a Co b Fe c Cd d O4 (the sum of a, b, c, and d is 3, and the values of a, b, c, and d are 1 / 4 to 1).

[0087] TEM images and EDS results show ( Figure 4 b), the quaternary Ni a Co b Fe c Cd d O4 transition metal-based oxide exhibits a hollow nanobox morphology structure and the distribution of each element is uniform, indicating the quaternary Ni a Cob Fe c Cd d The successful synthesis of metal oxides of O4.

[0088] Specifically, in this example, for the high-entropy oxide actually obtained, a = 3 / 4, b = 3 / 4, c = 3 / 4, d = 3 / 4, that is, the obtained product is Ni 3 / 4 Co 3 / 4 Fe 3 / 4 Cd 3 / 4 O4.

[0089] Example 4:

[0090] A method for controllable synthesis of hollow cubic high-entropy oxides:

[0091] (1) Dissolve 0.75 g of CuSO4·5H2O and 0.3 g of sodium citrate in 200 mL of ultrapure water. Then, add 2 g of NaOH to the above solution and stir for 0.5 h, and then add 100 mL of 0.03 M ascorbic acid. After stirring for 0.5 h, centrifuge, wash, and separate the Cu2O nanocubes, and vacuum dry them in an oven at 60 °C for 12 h.

[0092] (2) Ultrasonically stir and disperse the synthesized Cu2O (40 mg) in a solution of 80 mL of water and anhydrous ethanol mixed evenly. First, add 0.6666 g of polyvinylpyrrolidone and stir to dissolve for 15 min. Then, dissolve 4.8 mg of NiCl2·6H2O (0.02 mmol), 4.8 mg of CoCl2·6H2O (0.02 mmol), 5.6 mg of FeSO4·7H2O (0.02 mmol), and 8 mg of Cr(NO3)3·9H2O (0.02 mmol) in the above solution and stir for 15 min. Finally, slowly drip 32 mL of 1 M Na2S2O3 into the above solution system. After reacting for 0.5 h under stirring, centrifuge and wash multiple times to separate the high-entropy hydroxide NiCoFeCr-OH, and perform vacuum freeze-drying.

[0093] (3) Anneal the freeze-dried NiCoFeCr-OH powder in a tube furnace at 600 °C in an air atmosphere for 2 h to obtain the high-entropy oxide Ni a Co b Fe c Cr e O4 (the sum of a, b, c, and d is 3, and the values of a, b, c, and d range from 1 / 4 to 1).

[0094] TEM images and EDS results show ( Figure 4 c), the quaternary Ni a Co b Fe c Cre The O4 transition metal-based oxide exhibits a hollow nanobox morphology structure with uniform distribution of each component element, indicating the successful synthesis of the quaternary Ni a Co b Fe c Cr e O4 metal oxide.

[0095] Specifically, in this example, a = 3 / 4, b = 3 / 4, c = 3 / 4, e = 3 / 4 in the actually obtained high-entropy oxide, that is, the obtained product is Ni 3 / 4 Co 3 / 4 Fe 3 / 4 Cr 3 / 4 O4.

[0096] Example 5:

[0097] A method for controllable synthesis of hollow cubic high-entropy oxide:

[0098] (1) Dissolve 0.75 g of CuSO4·5H2O and 0.3 g of sodium citrate in 200 mL of ultrapure water. Then, add 2 g of NaOH to the above solution and stir for 0.5 h, and then add 100 mL of 0.03 M ascorbic acid. After stirring for 0.5 h, centrifuge and wash the Cu2O nanocubes to separate them, and vacuum dry them in an oven at 60 °C for 12 h.

[0099] (2) Ultrasonically stir and disperse the Cu2O (40 mg) synthesized in step (1) in a solution of 80 mL of water and anhydrous ethanol mixed evenly. First, add 0.6666 g of polyvinylpyrrolidone and stir to dissolve for 15 min. Then, dissolve 3.6 mg of NiCl2·6H2O (0.015 mmol), 3.6 mg of CoCl2·6H2O (0.015 mmol), 4.2 mg of FeSO4·7H2O (0.015 mmol), 3.4 mg of CdCl2·2.5H2O (0.015 mmol), 6 mg of Cr(NO3)3·9H2O (0.015 mmol) and 4.9 mg of La(NO3)3·nH2O (0.015 mmol) into the above solution and stir for 15 min. Finally, slowly drop 32 mL of 1 M Na2S2O3 into the above solution system. After stirring and reacting for 0.5 h, centrifuge and wash multiple times to separate the high-entropy hydroxide NiCoFeCdCrLa-OH, and perform vacuum freeze-drying.

[0100] (3) Anneal the freeze-dried NiCoFeCdCrLa-OH powder in a tube furnace at 600 °C in an air atmosphere for 2 h to obtain the high-entropy oxide Ni a Co b Fe c Cd dCr e La f O4 (the sum of a, b, c, d, e, and f is 3, and the values of a, b, c, d, e, and f range from 1 / 6 to 2 / 3).

[0101] This example proves that in the present invention, in addition to being able to synthesize ternary to quinary oxides, the oxide components can also be expanded, such as the hexavalent NiCoFeCdCrLa oxide in this example.

[0102] TEM images and EDS results show ( Figure 4 e), the high-entropy hexavalent Ni a Co b Fe c Cd d Cr e La f O4 transition metal-based oxides also exhibit a hollow nanobox morphology structure and the distribution of each component element is uniform, further demonstrating the successful synthesis of the hexavalent Ni a Co b Fe c Cd d Cr e La f O4 high-entropy oxide.

[0103] Specifically, in this example, the actual obtained high-entropy oxide has a = 1 / 2, b = 1 / 2, c = 1 / 2, d = 1 / 2, e = 1 / 2, f = 1 / 2; that is, the obtained product is Ni 1 / 2 Co 1 / 2 Fe 1 / 2 Cd 1 / 2 Cr 1 / 2 La 1 / 2 O4.

[0104] Example 6:

[0105] A method for controllable synthesis of hollow cubic high-entropy oxides:

[0106] (1) Dissolve 0.75 g of CuSO4·5H2O and 0.3 g of sodium citrate in 200 mL of ultrapure water. Then, add 2 g of NaOH to the above solution and stir for 0.5 h, and add 100 mL of 0.03 M ascorbic acid. After stirring for 0.5 h, centrifuge and wash the Cu2O nanocubes for separation, and vacuum dry them in an oven at 60 °C for 12 h.

[0107] (2) The synthesized Cu2O (40 mg) in step 1) was ultrasonically stirred and dispersed in a solution of 80 mL of water and anhydrous ethanol mixed evenly. First, 0.6666 g of polyvinylpyrrolidone was added and stirred to dissolve for 15 min. Then, 3.6 mg of NiCl2·6H2O (0.015 mmol), 3.6 mg of CoCl2·6H2O (0.015 mmol), 4.2 mg of FeSO4·7H2O (0.015 mmol), 3.4 mg of CdCl2·2.5H2O (0.015 mmol), 6 mg of Cr(NO3)3·9H2O (0.015 mmol), 4.9 mg of La(NO3)3·nH2O (0.015 mmol), and 3.4 mg of SnCl2·2H2O (0.015 mmol) were dissolved in the above solution and stirred for 15 min. Finally, 32 mL of 1 M Na2S2O3 was added dropwise to the above solution system. After reacting for 0.5 h under stirring, it was centrifuged and washed multiple times to separate the high-entropy hydroxide NiCoFeCdCrLaSn-OH, and then vacuum freeze-dried.

[0108] (3) The freeze-dried NiCoFeCdCrLaSn-OH powder was annealed in a tube furnace at 600 °C for 2 h in an air atmosphere to obtain the high-entropy oxide Ni a Co b Fe c Cd d Cr e La f Sn g O4 (the sum of a, b, c, d, e, f, g is 3, and the values of a, b, c, d, e, f, g range from 1 / 7 to 4 / 7).

[0109] TEM images and EDS results show that( Figure 4 f), the high-entropy heptanary Ni a Co b Fe c Cd d Cr e La f Sn g O4 transition metal-based oxide also exhibits a hollow nanobox morphology structure and the distribution of each element is uniform, further indicating that the heptanary Ni a Co b Fe c Cd d Cr e La f Sn g O4 high-entropy oxide can also be successfully prepared.

[0110] Specifically, in this embodiment, in the actually obtained high-entropy oxide, a = 3 / 7, b = 3 / 7, c = 3 / 7, d = 3 / 7, e = 3 / 7, f = 3 / 7, g = 3 / 7; that is, the obtained product is Ni 3 / 7 Co 3 / 7 Fe 3 / 7 Cd 3 / 7 Cr 3 / 7 La 3 / 7 Sn 3 / 7 O4.

[0111] Example 7:

[0112] A method for controllable synthesis of hollow cubic high-entropy oxide:

[0113] (1) Dissolve 0.75 g of CuSO4·5H2O and 0.3 g of sodium citrate in 200 mL of ultrapure water. Then, add 2 g of NaOH to the above solution and stir for 0.5 h, and then add 100 mL of 0.03 M ascorbic acid. After stirring for 0.5 h, centrifuge, wash and separate the Cu2O nanocubes, and vacuum dry them in an oven at 60 °C for 12 h.

[0114] (2) Ultrasonically stir and disperse the Cu2O (40 mg) synthesized in step (1) in a solution of 80 mL of water and anhydrous ethanol mixed evenly. First, add 0.6666 g of polyvinylpyrrolidone and stir to dissolve for 15 min. Then, dissolve 3.6 mg of NiCl2·6H2O (0.015 mmol), 3.6 mg of CoCl2·6H2O (0.015 mmol), 4.2 mg of FeSO4·7H2O (0.015 mmol), 3.4 mg of CdCl2·2.5H2O (0.015 mmol), 6 mg of Cr(NO3)3·9H2O (0.015 mmol), 4.9 mg of La(NO3)3·nH2O (0.015 mmol), 3.4 mg of SnCl2·2H2O (0.015 mmol) and 4.3 mg of ZnSO4·7H2O (0.015 mmol) in the above solution and stir for 15 min. Finally, dropwise add 32 mL of 1 M Na2S2O3 into the above solution system. After stirring and reacting for 0.5 h, centrifuge and wash multiple times to separate the high-entropy hydroxide NiCoFeCdCrLaSnZn-OH, and perform vacuum freeze-drying.

[0115] (3) Anneal the freeze-dried NiCoFeCdCrLaSnZn-OH powder in a tube furnace at 600 °C in an air atmosphere for 2 h to obtain the high-entropy oxide Ni a Co b Fe c Cd d Cr e Laf Sn g Zn h O4 (the sum of a, b, c, d, e, f, g, and h is 3, and the values of a, b, c, d, e, f, g, and h range from 1 / 8 to 1 / 2).

[0116] Specifically, in this example, the actually obtained high-entropy oxide has a = 3 / 8, b = 3 / 8, c = 3 / 8, d = 3 / 8, e = 3 / 8, f = 3 / 8, g = 3 / 8, h = 3 / 8; that is, the obtained product is Ni 3 / 8 Co 3 / 8 Fe 3 / 8 Cd 3 / 8 Cr 3 / 8 La 3 / 8 Sn 3 / 8 Zn 3 / 8 O4.

[0117] TEM images and EDS results show ( Figure 4 g), the extended component octa - Ni a Co b Fe c Cd d Cr e La f Sn g Zn h O4 high - entropy oxide can also maintain the hollow - cube structure and the element distribution is uniform, indicating the successful synthesis of octa - Ni a Co b Fe c Cd d Cr e La f Sn g Zn h O4 high - entropy oxide.

[0118] In summary, the synthesis method described in the present invention is applicable to the synthesis of ternary Ni a Co b Fe c O4 to octa - Ni a Co b Fe c Cd d Cr e La f Sn g Zn h O4 high - entropy oxides, and shows excellent catalytic activity and stability for the reaction of hydrogenation degradation of p - nitrophenol.

[0119] The technical solution of the present invention is not limited to the limitations of the above specific embodiments. Any technical deformation made according to the technical solution of the present invention falls within the protection scope of the present invention.

Claims

1. A controllable synthesis method of hollow cubic high entropy oxide, characterized in that: The following steps are involved: S1, preparation of nanocubic Cu2O: Dissolving CuSO4·5H2O and sodium citrate in water, adding sodium hydroxide, mixing evenly, adding ascorbic acid aqueous solution, stirring and mixing to obtain a first solid; washing the obtained first solid by centrifugation, and vacuum drying to obtain nanocube Cu2O; S2, preparation of high entropy hydroxide M-OH: The nanocubic Cu2O is dispersed in an aqueous solution of ethanol, polyvinyl pyrrolidone is added, different metal M salts are added after being mixed evenly, sodium thiosulfate solution is added after being stirred evenly, and a second solid is obtained; the second solid is centrifuged, washed, and freeze-dried to obtain a hollow cubic high entropy hydroxide M-OH; S3, Preparation of hollow cubic high entropy oxide Ni a Co b Fe c Cd d Cr e La f Sn g Zn h O4: After annealing M-OH, hollow cubic high entropy oxide Ni a Co b Fe c Cd d Cr e La f Sn g Zn h O4; Where a+b+c+d+e+f+g+h=3, and a>0, b>0, c>0, d≥0, e≥0, f≥0, g≥0, h≥0; In step S1, the mass ratio of CuSO4·5H2O, sodium citrate and sodium hydroxide is 0.75:0.3:2; the mass volume ratio of CuSO4·5H2O to water is 0.75:200, and the unit of the mass volume ratio is g:ml; In the step S1, the volume ratio of water to ascorbic acid aqueous solution is 2:1; the concentration of ascorbic acid aqueous solution is 0.03 mol / L; In the step S2, the mass ratio of nanocube Cu2O to polyvinyl pyrrolidone is 4:66.66; the mass volume ratio of nanocube Cu2O to sodium thiosulfate solution is 5:4, and the unit of the mass volume ratio is mg:ml; In the step S2, the mass molar ratio of the nanocube Cu2O to the metal M salt is 40:0.06-0.12, and the unit of the mass molar ratio is mg:mmol.

2. The controllable synthesis method of a hollow cubic high entropy oxide according to claim 1, characterized in that: In the step S2, in the aqueous solution of ethanol, the volume ratio of water to anhydrous ethanol is 1:1; and the concentration of the sodium thiosulfate solution is 1 mol / L.

3. The controllable synthesis method of a hollow cubic high entropy oxide according to claim 1, characterized in that: In the step S2, the added amount of the metal M salt is n1 mmol of Ni salt, n2 mmol of Co salt, n3 mmol of Fe salt, n4 mmol of Cd salt, n5 mmol of Cr salt, n6 mmol of La salt, n7 mmol of Sn salt, and n8 mmol of Zn salt; wherein n1>0, n2>0, n3>0, n4≥0, n5≥0, n6≥0, n7≥0, n8≥0, and n1:n2:n3:n4:n5:n6:n7:n8=a:b:c:d:e:f:g:h.

4. The controllable synthesis method of a hollow cubic high entropy oxide according to claim 1, characterized in that: In step S3, the annealing temperature is 600° C. and the annealing time is 2 hours.

5. Hollow cubic high entropy oxide Ni synthesized by the synthesis method according to any one of claims 1 to 4 a Co b Fe c Cd d Cr e La f Sn g Zn h O4.

6. The hollow cubic high entropy oxide Ni according to claim 5 a Co b Fe c Cd d Cr e La f Sn g Zn h Application of O4 in catalytic reduction degradation of p-nitrophenol.

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