Multi-metal-component high-entropy metal organic framework material, preparation thereof and application of multi-metal-component high-entropy metal organic framework material in azo dye degradation

Abstract

The invention discloses a multi-metal-component high-entropy metal organic framework material and a preparation method thereof, and belongs to the technical field of new material technology development and environmental governance, and the multi-metal-component high-entropy metal organic framework material is mainly used as a photocatalysis and photo-Fenton material for degrading azo dye pollutants. The high-entropy metal organic framework is prepared by taking various transition metal ions as inorganic components in the framework and polycarboxylic acid functional group ligands as organic components of a framework material, and heating the inorganic components and the organic components in a mixed solvent under the protection of nitrogen to coordinate and self-assemble the inorganic components and the organic components. The selected metal ions and organic ligands are low in cost, the preparation condition is simple, the yield is high, and the obtained multi-metal-component high-entropy metal organic framework material has good photocatalysis and photo-Fenton degradation performance on monoazo dyes under the visible light wave band; the problems of wide band gap, low response to visible light, poor photon-generated carrier separation capability and the like of conventional monometal component MOFs are solved, and a new scheme is provided for an environment restoration material.

Description

Technical Field

[0001] The present invention relates to a multi-metal component high entropy metal organic framework material and a preparation method thereof, which is mainly used as a photocatalytic and photo-Fenton material for the degradation of azo dye pollutants, and belongs to the technical field of new material technology development and environmental governance. Background Art

[0002] In the process of social development, various pollutants including azo dyes inevitably flow into the environment, posing a potential threat to ecology and human health. Pollutants in the environment are complex and intensifying, and the control of highly toxic organic pollutants is urgent. At present, photocatalysis is considered to be one of the most promising ways to control environmental pollutants. However, the current mainstream photocatalysts are generally limited by defects such as wide band gap, only responding to ultraviolet light, high recombination rate of photogenerated carriers, and insufficient surface active sites, which seriously restrict their practical application. Metal-organic framework materials (MOFs) composed of metal ions and organic ligands have shown theoretical advantages in the fields of heterogeneous photocatalysis / photo-Fenton due to their designable pore structure, high specific surface area and photosensitivity of metal sites. However, typical single-metal component MOFs also face many challenges in application and are difficult to meet the degradation needs of complex pollutants. The development of multi-metal MOFs has opened up new ways for the precise regulation of photocatalytic performance. When five or more heterogeneous metal elements are anchored in the framework at a similar molar ratio (5% to 35%), the extremely chaotic unit cell structure (configuration entropy above 1.5R) will also construct a multi-metal component framework material with high entropy characteristics and give it a "cocktail effect" in performance. The introduction of more types of metal sites can effectively expand the spectral response range of the material. In addition, the atomically dispersed multi-metals in the framework also bring more possibilities for adjusting the band structure and optimizing the catalytic active sites. Summary of the invention

[0003] The object of the present invention is to provide a multi-metal component high entropy metal organic framework material and a preparation method thereof; Another object of the present invention is to apply the prepared material to the photocatalytic degradation of pollutants including azo dyes in the environment.

[0004] 1. Preparation method of multi-metal component high entropy metal organic framework materials Add a polycarboxylic acid linker ligand and a metal salt into a mixed reaction solvent system containing a regulator, and ultrasonically stir for 5 - 30 minutes to dissolve the metal salt and the polycarboxylic acid linker ligand, and filter the reaction solution using a filter membrane; Load the mixed reaction solution containing the metal salt and the carboxylic acid linker ligand into a Schlenk tube resistant to high temperature and high pressure, and introduce an inert gas into it. After sealing, heat it to 100 - 180 °C and react for 12 - 144 hours; After the reaction is completed, wash it successively with N,N-dimethylformamide, deionized water, and ethanol, centrifuge, perform solvent replacement for 3 days to 1 week, and dry it under vacuum. The obtained product is the multi-metal high-entropy metal-organic framework material.

[0005] Among them, the metal salt is a nitrate, a chloride, an acetate, or a combination of multiple of them; the valence state of the metal salt is +1, +2, +3, +4, or a combination of corresponding multiple valence states. The metal types of the metal salt are selected from combinations of five or more of Ag, Ca, Mg, Mn, Fe, Co, Ni, Cu, Zn, Cd, Cr, Al, Sc, Zr, Ti, In, Ru, Pt, Ce, Nd, Ho, Yb. The molar ratio of each metal salt participating in the mixture is 1:1 - 1:6; the concentration of the metal salt in the mixed reaction system is 0.5 - 12 mmol / L.

[0006] The polycarboxylic acid linker ligand includes 2,5-dihydroxyterephthalic acid, pyromellitic acid, biphenyltetracarboxylic acid, 1,3,5-tris(3,5-dicarboxyphenyl)benzene, and its benzene ring substituted derivatives; the molar ratio of the polycarboxylic acid linker ligand to the metal salt is 1:1 - 8:1; the concentration of the polycarboxylic acid linker ligand in the mixed reaction system is 0.5 - 28 mmol / L.

[0007] The mixed reaction solvent system is a mixed solution of water, methanol, and N,N-dimethylformamide. The volume percentages of each component are: water 5% - 35%, methanol 20% - 50%, and N,N-dimethylformamide 25% - 75%.

[0008] The regulator is formic acid, acetic acid, sodium formate, sodium acetate, sodium carbonate, ammonium formate, or ammonium acetate; the concentration of the regulator in the mixed reaction system is 0.02 - 5 mmol / L.

[0009] The inert gas introduced is to isolate oxygen and includes nitrogen, argon; the solvent used for solvent replacement is a low-boiling organic reagent, including but not limited to methanol, ethanol, or a mixture of them, and the replacement period is 8 - 24 hours.

[0010] II. Characterization of the multi-metal component high-entropy metal-organic framework material Figure 1PXRD diffraction patterns of the multi-metal component high-entropy metal-organic frameworks prepared in Examples 1-3 of the present invention and the single-metal component and four-metal component MOFs for comparison. Figure 1 a is a comparison chart of the PXRD peak patterns of each metal component MOF. The main diffraction peak of the single-metal component Co-MOF (PMA) is located at 8.12°, and there are also obvious diffraction peak signals at 10.55°, 14.34°, 15.97°, 17.24°, etc. The series of MOF products obtained by mixing other metal components show similar diffraction peak patterns at the same positions. In addition, compared with the single-metal component Co-MOF (PMA), the absolute diffraction peak intensities of each mixed-metal component MOF are weaker, especially the six-metal component ZnCoNiMnFe-MOF containing Fe(Ⅲ), which has the worst crystallinity. Figure 1 b is a partially enlarged comparison image of the corresponding PXRD. Compared with the single-metal component Co-MOF (PMA), the main XRD diffraction peaks of the mixed-metal component MOFs show different degrees of shift, which is due to the different degrees of distortion of the unit cell in the crystal structure caused by the incorporation of metals with different atomic radii.

[0011] Figure 2 Transmission electron microscope (TEM) images of the multi-metal component high-entropy metal-organic frameworks prepared in Examples 1-3 of the present invention and the single-metal component and four-metal component MOFs for comparison. Figure 2 a-e are TEM images of the single-metal component Co-MOF (PMA), the four-metal component ZnCoNiMn-MOF, and the high-entropy metal-organic frameworks ZnCoNiMnCu-MOF, ZnCoNiMnFe-MOF, and ZnCoNiMnFeCu-MOF at the same magnification. The framework materials synthesized using the same polyacid organic linker ligand show similar nanorod-like morphologies. By comparison, it can be found that the rod-like structures of Co-MOF (PMA), ZnCoNiMn-MOF, and ZnCoNiMnCu-MOF are longer and more ordered, while the nanorods of ZnCoNiMnFe-MOF and ZnCoNiMnFeCu-MOF are thinner, shorter, and stacked together. This is related to the metal components in the framework material. The coordination of different valence states of Fe(Ⅲ) makes the crystallinity of ZnCoNiMnFe-MOF and ZnCoNiMnFeCu-MOF poor, affecting the overall order.

[0012] Figure 3The simulated structure diagram of the six-metal component ZnCoNiMnFeCu-MOF prepared in Example 3 of the present invention in different views. The synthesized multi-metal component framework material has typical hexagonal crystal characteristics and can be attributed to the R-3 (148) space group. The relevant unit cell parameters are a=b=25.883 Å, c=6.851 Å, and the unit cell angles are α=β=90°, γ=120°.

[0013] Figure 4 This is an energy dispersive X-ray (EDX) spectrum of the six-metal component ZnCoNiMnFeCu-MOF prepared in Example 3 of the present invention. The multi-metal component framework material shows characteristic signals of zinc, cobalt, nickel, manganese, iron, and copper metal elements that were synthesized, and the proportion of each metal component was calculated, including Zn 5.20%, Co 19.33%, Ni 15.21%, Mn 22.58%, Fe17.57%, and Cu 20.11%.

[0014] Figure 5 N2 adsorption-desorption curves and corresponding pore size distribution diagrams of the multi-metal component high entropy metal organic frameworks prepared in Examples 1 to 3 of the present invention and the single-metal component and four-metal component MOFs used for comparison. Figure 5 a is the nitrogen adsorption-desorption curve of MOF with different metal components. The single metal Co-MOF (PMA) with good crystallinity measured 526.57m 2 Higher S / g BET , which is a typical type IV adsorption isotherm. In the relatively low pressure range of P / P0 from 0.05 to 0.1, the N2 adsorption amount shows a rapid increase, which is due to the rapid filling of gas molecules in the micropores. In the subsequent P / P0 range, the adsorption curve is nearly horizontal, indicating that the micropores are full. When P / P0 increases to close to 1, the adsorption amount further increases, and an H1-type hysteresis loop appears during N2 gas desorption, indicating the presence of mesopores in the material. The multi-metal ZnCoNiMn-MOF, ZnCoNiMnCu-MOF, ZnCoNiMnFe-MOF, and ZnCoNiMnFeCu-MOF have similar topological structures to Co-MOF (PMA), so similar type IV adsorption-desorption curves are obtained. However, compared with Co-MOF (PMA), the incorporation of various metals reduces the crystallinity of each MOFs, S BET Only 273.49, 242.79, 212.18, 179.10 m respectively 2 / g; Figure 5Figures b and c are the pore size distribution comparison diagrams of each metal component MOF. Co-MOF (PMA) has mesopores at 9.24 nm and shows concentrated micropores at 1.26 nm. For the multi-metal component ZnCoNiMn-MOF, ZnCoNiMnCu-MOF, ZnCoNiMnFe-MOF, and ZnCoNiMnFeCu-MOF, due to the less ideal framework crystallinity, the volume of micropores in each metal component MOF is relatively small. Additionally, the measured micropore sizes are 1.34, 1.48, 1.49, and 1.52 nm respectively.

[0015] Figure 6 The solid ultraviolet-visible diffuse reflectance (UV-vis DRS) absorption spectra and the deduced band gap width diagrams of the multi-metal component high-entropy metal-organic frameworks prepared in Examples 1 to 3 of the present invention and the single-metal component and four-metal component MOFs for comparison are shown. By comparing each MOF, it can be found that the addition of each metal will change the light absorption ability of the framework material to varying degrees. In particular, the addition of Cu and Fe metal elements significantly improves the optical properties of the material. In the visible light band, Co-MOF (PMA) only has a little absorption in the 450 - 650 nm band range. For the four-metal component ZnCoNiMn-MOF prepared by adding zinc, nickel, and manganese in addition, the light absorption band edge undergoes a slight red shift, but the absorption in the visible light band is limitedly improved. For the five-metal component ZnCoNiMnCu-MOF with an additional copper element, the light absorption band edge shows an obvious red shift. This will reduce the band gap width, but the absorption effect on visible light is still limited. The five-metal component ZnCoNiMnFe-MOF containing iron in the framework shows the strongest light absorption ability among these materials, which is beneficial to the utilization of visible light. The ZnCoNiMnFeCu-MOF containing six metals also has excellent light absorption effects.

[0016] Figure 7 The photoluminescence (PL) spectra, time-resolved fluorescence decay spectra, electrochemical impedance (EIS), and transient photocurrent response curve diagrams of the multi-metal component high-entropy metal-organic frameworks prepared in Examples 1 to 3 of the present invention and the single-metal component and four-metal component MOFs for comparison are shown. Figure 7 Figure a is the comparison diagram of the PL spectra of each metal component MOF. Among them, Co-MOFs (PMA) has the highest fluorescence intensity, indicating its electron-hole (e - -h +)High composite efficiency, releasing energy in the form of photons. The fluorescence intensity of MOFs with different metal components is significantly weakened, and the intensity relationship is ZnCoNiMn-MOF > ZnCoNiMnFe-MOF > ZnCoNiMnFeCu-MOF > ZnCoNiMnCu-MOF. The five-metal-component MOF ZnCoNiMnCu-MOF containing copper element exhibits the lowest PL intensity, followed by the six-metal-component ZnCoNiMnFeCu-MOF; Figure 7 b is the fluorescence lifetime decay curve of MOFs with each metal component. The calculated fluorescence lifetimes of Co-MOF (PMA), ZnCoNiMn-MOF, ZnCoNiMnCu-MOF, ZnCoNiMnFe-MOF, and ZnCoNiMnFeCu-MOF are 1.71, 1.99, 1.81, 2.37, and 2.09 ns respectively. The longer the time, the slower the recombination rate of photo-generated carriers in the material, which is more conducive to charge separation, indicating that the incorporation of various metals affects the fluorescence lifetime of the framework material; Figure 7 c is the electrochemical impedance (EIS) diagram of MOFs with each metal component. The arc radius size is Co-MOF (PMA) > ZnCoNiMn-MOF > ZnCoNiMnFe-MOF > ZnCoNiMnFeCu-MOF > ZnCoNiMnCu-MOF. The smaller the curve radius, the smaller the charge transfer resistance of the material, and the result has a good correspondence with the characteristics of the PL spectrum; Figure 7 d is the transient photocurrent response curve diagram of MOFs with each metal component. The change in the photocurrent density of the single-metal-component Co-MOF (PMA) is very small, and that of the four-metal-component ZnCoNiMn-MOF is not obvious either. This is related to the serious charge recombination of Co-MOF (PMA) and the poor photo-generated charge transfer ability of ZnCoNiMn-MOF. However, ZnCoNiMnCu-MOF, ZnCoNiMnFe-MOF, and ZnCoNiMnFeCu-MOF have obvious photocurrent responses. Among them, ZnCoNiMnCu-MOF and ZnCoNiMnFeCu-MOF with copper metal elements have the highest change in current density, indicating that they have good charge separation and migration and transport capabilities.

[0017] III. Applications of multi-metal-component high-entropy metal-organic framework materials Taking the multi-metal-component high-entropy metal-organic framework material ZnCoNiMnFeCu-MOF prepared in Example 3 of the present invention as an example, it is used for the photocatalytic degradation and removal of azo dyes.

[0018] The typical monoazo dye Chrome Azurol R was selected as the degradation target, and the photocatalytic and photo-Fenton performance of the prepared multi-metal high-entropy MOFs framework materials was studied. Under the condition of keeping other conditions the same, a blank control group without catalyst illumination, illumination plus H2O2 without catalyst, and three experimental groups were set up: MOFs + darkness (adsorption), MOFs + light source (photocatalysis), MOFs + light source + H2O2 (photo-Fenton), to evaluate the removal performance of the monoazo dye MB 17 in different systems.

[0019] As Figure 8 shown, in the investigation of ZnCoNiMnFeCu-MOF, under the condition of simulated visible light source (λ>420 nm), MB 17 in the solution did not degrade spontaneously when only illuminated. When H2O2 was added without adding the MOFs catalyst, only slight degradation of the MB 17 dye in the solution occurred, which can be attributed to the decomposition of H2O2 itself in the visible light band, and thus only a slight decrease in the dye concentration occurred. In the experimental group with the addition of MOFs material as the catalyst, an obvious decrease in the dye concentration occurred. Under the condition of stirring in the dark for 10 min, ZnCoNiMnFeCu-MOF could remove about 10% of the dye, which was attributed to the physical adsorption of MOFs. Subsequently, stirring was further carried out in the dark without turning on the light, and 14.6% of MB 17 was finally removed after 60 min of the process ended.

[0020] In contrast, under the condition of ZnCoNiMnFeCu-MOF + light source (photocatalysis), the concentration of the dye MB 17 decreased rapidly. In the same 60 min, 62.5% of the MB 17 dye in the solution was removed. In the ZnCoNiMnFeCu-MOF + light source + H2O2 (photo-Fenton) degradation system, the degradation of the azo dye was more significant. About 88% of MB17 could be removed in about 40 min, and then it tended to be flat. When the 60 min degradation process ended, 92.3% of the dye was finally degraded. The solution changed from the deep purple of the dye to the yellow-brown of the framework material before and after the reaction, and the solution was basically decolorized after filtration.

[0021] In summary, the high-entropy metal-organic framework of the present invention uses a variety of transition metal ions as the inorganic components in the framework and polycarboxylic acid functional group ligands as the organic components of the framework material, and the two are coordinated and self-assembled by heating in a mixed solvent under nitrogen protection. The metal ions and organic ligands selected in the present invention are low-cost, the preparation conditions are simple and the yield is high. The obtained multi-metal component high-entropy metal-organic framework material has good photocatalytic and photo-Fenton degradation performance for monoazo dyes in the visible light band, solves the problems of wide bandgap, low visible light response, and poor photogenerated carrier separation ability of conventional single-metal component MOFs, and provides a new solution for environmental remediation materials. Description of the Drawings

[0022] Figure 1 Actual powder X-ray diffraction (PXRD) spectra of single-metal-component Co-MOF(PMA), four-metal-component ZnCoNiMn-MOF, and high-entropy metal-organic frameworks ZnCoNiMnCu-MOF, ZnCoNiMnFe-MOF, and ZnCoNiMnFeCu-MOF; (b) corresponding enlarged local comparison images of PXRD.

[0023] Figure 2 Transmission electron microscopy (TEM) comparison images of (a) single-metal-component Co-MOF(PMA), (b) four-metal-component ZnCoNiMn-MOF, and high-entropy metal-organic frameworks (c) ZnCoNiMnCu-MOF, (d) ZnCoNiMnFe-MOF, and ZnCoNiMnFeCu-MOF.

[0024] Figure 3 Structural diagram simulated for six-metal-component ZnCoNiMnFeCu-MOF.

[0025] Figure 4 Energy-dispersive X-ray (EDX) spectrum of six-metal-component ZnCoNiMnFeCu-MOF.

[0026] Figure 5 (a) N2 adsorption-desorption curves and (b), (c) corresponding pore size distributions of single-metal-component Co-MOF(PMA), four-metal-component ZnCoNiMn-MOF, and high-entropy metal-organic frameworks ZnCoNiMnCu-MOF, ZnCoNiMnFe-MOF, and ZnCoNiMnFeCu-MOF.

[0027] Figure 6 (a) Solid-state ultraviolet-visible diffuse reflectance (UV-vis DRS) absorption spectra and (b) corresponding deduced band gap width comparison diagrams of single-metal-component Co-MOF(PMA), four-metal-component ZnCoNiMn-MOF, and high-entropy metal-organic frameworks ZnCoNiMnCu-MOF, ZnCoNiMnFe-MOF, and ZnCoNiMnFeCu-MOF.

[0028] Figure 7Comparative diagrams of (a) photoluminescence (PL) spectra, (b) corresponding time-resolved fluorescence decay spectra, (c) electrochemical impedance (EIS), and (d) transient photocurrent response curves for single-metal-component Co-MOF(PMA), four-metal-component ZnCoNiMn-MOF, and high-entropy metal-organic frameworks ZnCoNiMnCu-MOF, ZnCoNiMnFe-MOF, and ZnCoNiMnFeCu-MOF.

[0029] Figure 8 Degradation of azo dye Chrome Azurol S (MB17) by high-entropy metal-organic framework ZnCoNiMnFeCu-MOF under different conditions. Detailed implementation methods

[0030] The preparation of multi-metal-component high-entropy metal-organic framework materials and their application in the degradation of azo dye pollutants in the present invention are further described below through specific examples.

[0031] Example 1 Dissolve 0.222 g of Zn(NO3)2·6H2O, 0.292 g of Co(NO3)2·6H2O, 0.219 g of Ni(NO3)2·6H2O, 0.251 g of Mn(NO3)2·4H2O, and 0.241 g of Cu(NO3)2 in 25 mL of a mixed solution of water / methanol / DMF (1:1:1 v / v / v) (solution A). Weigh 1 mmol of pyromellitic acid as a polyacid linker ligand and dissolve it in 30 mL of a mixed solution of water / methanol / DMF (1:1:1 v / v / v) containing 5 mL of acetic acid as a regulator (solution B). Ultrasonically stir for 15 minutes to dissolve the metal salts and organic linker ligands. After filtering with a filter membrane, slowly pour solution A into a Schlenk tube containing solution B, and heat to 120 °C in a nitrogen protection atmosphere for 72 hours. After the reaction, wash and centrifuge the gray product successively with DMF, deionized water, and ethanol, then perform solvent replacement in pure methanol for 3 days, and dry in a vacuum drying oven to obtain a five-metal-component high-entropy metal-organic framework ZnCoNiMnCu-MOF with a yield of 78.3%.

[0032] Take 8 mg of MOFs as a catalyst and add it to 40 mL of a 50 mg / L concentration of Chrome Azurol S azo dye solution. After stirring in the dark for 10 minutes, start the photocatalytic reaction. The reaction beaker is placed in a circular water tank with circulating water, and the height of the xenon light source (λ>420 nm) is controlled at 15 cm from the liquid surface of the beaker. Under continuous light irradiation and stirring, take 2 mL of water samples every 5 minutes, filter with a filter membrane, and measure the concentration using a UV-visible spectrophotometer. 49.6% of the azo dye can be degraded within 60 minutes.

[0033] 8 mg of MOFs as a catalyst was added to a 50 mg / L solution of Chrome Azurol S azo dye in 40 mL (containing 1 mM H2O2). After stirring for 10 minutes in the dark, the photo-Fenton reaction was initiated. Under continuous light irradiation and stirring, 2 mL of water samples were taken every 5 minutes, filtered through a membrane filter, and the concentration was measured using a UV-visible spectrophotometer. 65.7% of the azo dye could be degraded within 60 minutes.

[0034] Example 2 0.222 g of Zn(NO3)2·6H2O, 0.292 g of Co(NO3)2·6H2O, 0.219 g of Ni(NO3)2·6H2O, 0.251 g of Mn(NO3)2·4H2O, and 0.4 g of Fe(NO3)3·9H2O were dissolved together in a 25 mL mixture of water / methanol / DMF (1:1:1 v / v / v) (solution A). 1 mmol of pyromellitic acid was weighed as a polyacid linker ligand and dissolved in a 30 mL mixture of water / methanol / DMF (1:1:1 v / v / v) containing 5 mL of acetic acid as a regulator (solution B). The mixture was ultrasonically stirred for 15 minutes to dissolve the metal salts and the organic linker ligand. After filtration using a membrane filter, solution A was slowly poured into a Schlenk tube containing solution B, and the temperature was raised to 140 °C under a nitrogen protection atmosphere for 72 hours. After the reaction, the brown product was washed and centrifuged successively with DMF, deionized water, and ethanol, and then solvent-exchanged in pure ethanol for 3 days to obtain a high-entropy metal-organic framework ZnCoNiMnFe-MOF with a five-metal component and a yield of 81.8%.

[0035] 8 mg of MOFs as a catalyst was added to a 50 mg / L solution of Chrome Azurol S azo dye in 40 mL. After stirring for 10 minutes in the dark, the photocatalytic reaction was initiated. The reaction beaker was placed in a circular water bath with circulating water, and the height of the xenon light source (λ>420 nm) was controlled at 15 cm from the liquid surface of the beaker. Under continuous light irradiation and stirring, 2 mL of water samples were taken every 5 minutes, filtered through a membrane filter, and the concentration was measured using a UV-visible spectrophotometer. 49.6% of the azo dye could be degraded within 60 minutes.

[0036] 8 mg of MOFs as a catalyst was added to a 50 mg / L solution of Chrome Azurol S azo dye in 40 mL (containing 1 mM H2O2). After stirring for 10 minutes in the dark, the photo-Fenton reaction was initiated. Under continuous light irradiation and stirring, 2 mL of water samples were taken every 5 minutes, filtered through a membrane filter, and the concentration was measured using a UV-visible spectrophotometer. 65.7% of the azo dye could be degraded within 60 minutes.

[0037] Example 3 Dissolve 0.296 g of Zn(NO3)2·6H2O, 0.291 g of Co(NO3)2·6H2O, 0.290 g of Ni(NO3)2·6H2O, 0.251 g of Mn(NO3)2·4H2O, 0.241 g of Cu(NO3)2, and 0.4 g of Fe(NO3)3·9H2O together in 25 mL of a mixed solution of water / methanol / DMF (1:1:1 v / v / v) (solution A). Weigh 1 mmol of pyromellitic acid as a polyacid linker ligand and dissolve it in 30 mL of a mixed solution of water / methanol / DMF (1:1:1 v / v / v) containing 5 mL of acetic acid as a regulator (solution B). Ultrasonically stir for 15 minutes to dissolve the metal salts and the organic linker ligand. After filtering with a filter membrane, slowly pour solution A into a Schlenk tube containing solution B and heat to 150 °C in a nitrogen-protected atmosphere for 72 hours. After the reaction, wash and centrifuge the yellow product successively with DMF, deionized water, and ethanol, and then perform solvent exchange in pure methanol for 3 days to obtain a high-entropy metal-organic framework ZnCoNiMnFeCu-MOF with a six-metal component and a yield of 73.6%.

[0038] Take 5 mg of the dose of MOFs as a catalyst and put it into 40 mL of a 50 mg / L concentration of chrome azurol S azo dye solution. After stirring in the dark for 10 minutes, start the photocatalytic reaction. The reaction beaker is placed in a circular water tank with circulating water, and the height of the xenon light source (λ>420 nm) is controlled at 15 cm from the liquid surface of the beaker. Under continuous light irradiation and stirring, take 2 mL of water samples every 5 minutes. After filtering with a filter membrane, use a UV-visible spectrophotometer to measure the concentration, and 62.5% of the azo dye can be degraded within 60 minutes.

[0039] Take 5 mg of the dose of MOFs as a catalyst and put it into 40 mL (containing 1 mM H2O2) of a 50 mg / L concentration of chrome azurol S azo dye solution. After stirring in the dark for 10 minutes, start the photo-Fenton reaction. Under continuous light irradiation and stirring, take 2 mL of water samples every 5 minutes. After filtering with a filter membrane, use a UV-visible spectrophotometer to measure the concentration, and 93.2% of the azo dye can be degraded within 60 minutes.

[0040] Example 4 Dissolve 0.370 g of Zn(NO3)2·6H2O, 0.365 g of Co(NO3)2·6H2O, 0.363 g of Ni(NO3)2·6H2O, 0.313 g of Mn(NO3)2·4H2O, 0.310 g of Cu(NO3)2 and 0.5 g of Fe(NO3)3·9H2O together in 25 mL of a mixed solution of water / methanol / DMF (1:1:1 v / v / v) (solution A). Weigh 1.5 mmol of pyromellitic acid as a polyacid linker ligand and dissolve it in 45 mL of a mixed solution of water / methanol / DMF (1:1:1 v / v / v) containing 7.5 mL of acetic acid as a regulator (solution B). Ultrasonically stir for 15 minutes to dissolve the metal salts and the organic linker ligand. After filtering with a filter membrane, slowly pour solution A into a Schlenk tube containing solution B, and heat to 160 °C in a N2-protected atmosphere and react for 72 hours. After the reaction, wash and centrifuge the yellow product successively with DMF, deionized water and ethanol, and then perform solvent exchange in pure ethanol for 3 days to obtain a six-metal-component high-entropy metal-organic framework ZnCoNiMnFeCu-MOF with a yield of 76.7%.

[0041] Put 10 mg of the dose of MOFs as a catalyst into 40 mL of a 50 mg / L concentration of chrome azurol S azo dye solution. After stirring in the dark for 10 minutes, start the photocatalytic reaction. The reaction beaker is placed in a circular water tank with circulating water, and the height of the xenon light source (λ>420 nm) is controlled at 15 cm from the liquid surface of the beaker. Under continuous light irradiation and stirring, take 2 mL of water samples every 5 minutes. After filtering with a filter membrane, use a UV-visible spectrophotometer to measure the concentration, and 86.8% of the azo dye can be degraded within 60 minutes.

[0042] Put 10 mg of the dose of MOFs as a catalyst into 40 mL (containing 1 mM H2O2) of a 50 mg / L concentration of chrome azurol S azo dye solution. After stirring in the dark for 10 minutes, start the photo-Fenton reaction. Under continuous light irradiation and stirring, take 2 mL of water samples every 5 minutes. After filtering with a filter membrane, use a UV-visible spectrophotometer to measure the concentration, and 97.4% of the azo dye can be degraded within 60 minutes.

Claims

1. A preparation method of a multi-metal component high-entropy metal-organic framework is to add a polycarboxylic acid linker ligand and metal salts into a mixed reaction solvent system containing a regulator, ultrasonically stir to dissolve the metal salts and the polycarboxylic acid linker ligand, and filter the reaction solution using a filter membrane; load the mixed reaction solution containing the metal salts and the carboxylic acid linker ligand into a Schlenk tube resistant to high temperature and high pressure, introduce an inert gas into it, seal it, and heat it to 100~180 °C for reaction for 12~144 hours; after the reaction is completed, wash it successively with N,N-dimethylformamide, deionized water and ethanol, centrifuge, perform solvent replacement for 3 days to 1 week, and dry it under vacuum. The obtained product is the multi-metal high-entropy metal-organic framework material.

2. The preparation method of the multi-metal component high-entropy metal-organic framework according to claim 1, wherein: The metal salts are nitrates, chlorides, acetates or combinations thereof; the valence states of the metal salts are +1, +2, +3, +4 or combinations of corresponding multiple valence states; the metal types are selected from combinations of five or more of Ag, Ca, Mg, Mn, Fe, Co, Ni, Cu, Zn, Cd, Cr, Al, Sc, Zr, Ti, In, Ru, Pt, Ce, Nd, Ho, Yb, and the molar ratio of each metal salt is 1:1~1:6; the concentration of the metal salts in the mixed reaction system is 0.5~12 mmol / L.

3. The preparation method of the multi-metal component high-entropy metal-organic framework according to claim 1, characterized in that: The polycarboxylic acid linker ligands include 2,5-dihydroxyterephthalic acid, pyromellitic acid, biphenyltetracarboxylic acid, 1,3,5-tris(3,5-dicarboxyphenyl)benzene and its benzene ring substituted derivatives; the molar ratio of the polycarboxylic acid linker ligand to the metal salt is 1:1~8:1; the concentration of the polycarboxylic acid linker ligand in the mixed reaction system is 0.5~28 mmol / L.

4. The preparation method of a multi-metal component high-entropy metal-organic framework according to claim 1, characterized in that: The mixed reaction solvent system is a mixed solution of water, methanol, and N,N-dimethylformamide, and the volume percentages are: water 5%~35%, methanol 20%~50%, N,N-dimethylformamide 25%~75%.

5. The preparation method of the multi-metal component high-entropy metal-organic framework according to claim 1, wherein: The regulator is formic acid, acetic acid, sodium formate, sodium acetate, sodium carbonate, ammonium formate or ammonium acetate; the concentration of the regulator in the mixed reaction system is 0.02~5 mmol / L; The inert gas is nitrogen or argon; the solvent used for solvent replacement is methanol, ethanol or a mixture thereof, and the replacement period is 8~24 hours.

6. A multi-metal component high-entropy metal-organic framework material prepared by any of the methods of claims 1~5, characterized in that: The material contains five or more metal elements, the configurational entropy ≥ 1.5R, the crystal structure is hexagonal system (R-3 space group), the unit cell parameters are a = b = 25.883 Å, c = 6.851 Å, α = β = 90°, γ = 120°; the specific surface area is 179~527 m² / g, and the pore size distribution includes 1.2~1.6 nm micropores and 9~10 nm mesopores.

7. According to the multi-metal component high-entropy metal-organic framework material of claim 6, characterized in that: The metal elements include Zn, Co, Ni, Mn, Fe, and Cu, and the mass percentages of the respective elements are Zn 5-25%, Co 15-25%, Ni 10-20%, Mn 15-25%, Fe 10-20%, and Cu 15-25%.

8. Application of the multi-metal component high-entropy metal-organic framework material prepared by the method described in claim 1 or the multi-metal component high-entropy metal-organic framework material described in claim 6 or 7 in the photocatalytic degradation of azo dyes.

9. The application according to claim 8, characterized in that: The photocatalytic degradation of azo dyes includes the following steps: (1) Put the multi-metal component high-entropy metal-organic framework material as a catalyst into a solution containing azo dyes and stir in the dark for 8-15 minutes; (2) Carry out photocatalysis or photo-Fenton reaction under visible light (λ>420 nm) irradiation, and the concentration of H2O2 in the reaction system is 0-5 mM; (3) The degradation rate of azo dyes is ≥60% within 60 minutes.

10. The application according to claim 8 or 9, characterized in that: The azo dye is Chrome Blue Black R, the catalyst dosage is 0.1-0.5 mg / mL, and the degradation rate of the photo-Fenton system is ≥90%.

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