Preparation method of a multi-level pore structure bentonite

Abstract

The present invention relates to a preparation method of a bentonite adsorption material. The method first acidifies bentonite to form Al<supgt;3+< / supgt; ions and active sites. Then the acidified bentonite is mixed with a metal-organic amine precursor. During the mixing process, the metal-organic amine precursor binds to the active sites on the surface of bentonite through coordination, thereby forming a metal-organic framework (MOF). At the same time, aluminum hydroxide sol is also formed. These sols can penetrate between bentonite particles and bond the particles together to form a stable structure. Untreated bentonite is added again, and these newly added bentonite particles will be coated by the formed aluminum hydroxide sol, thereby forming a hierarchical structure. This hierarchical structure not only retains the original excellent properties of bentonite, but also further improves the application performance of bentonite in the fields of adsorption, separation, and catalysis through the introduction of MOF and aluminum hydroxide sol.

Description

Technical Field

[0001] The present invention relates to new materials, and particularly to a preparation method of bentonite with a hierarchical pore structure. Background Art

[0002] The bentonite structure only has relatively large internal pore diameters and can be used for pollutant adsorption. However, its overall pore size is relatively single and it cannot comprehensively adsorb pollutant molecules of various sizes. In existing research, it is generally considered that size matching is an important influencing factor for pollutant molecule adsorption. Therefore, existing bentonite materials have good adsorption capacity for most pollutant molecules with larger sizes. However, in actual applications, the composition of pollutants is complex and the molecular size distribution is also wide. Current bentonite adsorption materials cannot achieve comprehensive adsorption of all pollutants, especially small molecule pollutants. There is an urgent need to develop an adsorption material with a hierarchical pore structure.

[0003] In addition, bentonite is a layered silicate clay mineral with a typical two-dimensional sheet structure and it is difficult to directly obtain a three-dimensional porous structure through chemical modification. Compared with the three-dimensional porous structure, in the granulation process of the two-dimensional layered bentonite structure, its agglomeration strength is often inferior to that of the three-dimensional structure, and it is prone to particle breakage and disintegration to form a large amount of dust during actual use. In the prior art, it is necessary to add a binder to bentonite during the granulation process to enhance the agglomeration strength of bentonite particles and reduce the dust problem. Commonly used binders mainly include corn starch, water glass, wood fiber, silica gel, guar gum, etc., with complex compositions and cumbersome processes. Summary of the Invention

[0004] The purpose of the present invention is to provide a bentonite with a hierarchical pore structure and its preparation method in view of the deficiencies of the prior art, so as to achieve comprehensive adsorption of pollutant molecules of different sizes, more efficient pollutant adsorption, and further prepare highly stable bentonite particles through a binder-free granulation process.

[0005] Specifically, the bentonite prepared by the present invention has a hierarchical pore structure of macropores - mesopores - micropores; moreover, the present invention introduces amino organic groups into the MOF structure, which can not only provide the alkaline conditions for the formation of aluminum hydroxide substances, but also more effectively adsorb acidic odor sources such as hydrogen sulfide; moreover, in the disk granulation process, granulation is formed through an alumina network structure as a self-binder, avoiding the use of an external binder and having higher production efficiency; moreover, the particulate matter obtained after the disk granulation loses water will form a gel system when encountering water and cause the particulate matter to agglomerate.

[0006] To achieve the above object, the present invention adopts the following technical solutions: A preparation method of bentonite with a hierarchical pore structure, the method comprising:

[0007] 1) Take 2 parts by weight of bentonite and disperse it in a solution containing 6 parts by weight of citric acid. Stir and acidify the bentonite at 50 °C for 3 hours, with a stirring speed of 100 r / min. After the acidification treatment, centrifuge at 8000 r for 5 min. Add water and centrifuge and wash at the same speed until the pH value of the washing liquid is 6.5 - 7.5.

[0008] 2) Mix the product obtained after centrifugal washing in step 1 with 1 part by weight of the precursor of the metal - organic amine ligand. The precursor of the metal - organic amine ligand is a metal salt and an organic amine ligand. Specifically, mix the centrifuged product with the solution of the metal salt and the solution of the organic amine ligand, and stir and react at 110 - 150 °C for 20 - 48 hours. Filter out the solvent to obtain agglomerated bentonite particles.

[0009] 3) Take another 1 part by weight of bentonite and mix it with the bentonite particles in step 2. Granulate by disk at room temperature, with a disk rotation speed of 25 r / min and a rounding time of 3 min to obtain granular bentonite with a multi - pore structure.

[0010] Preferably, in step 1), the acidification treatment uses an aqueous solution of citric acid with a concentration of 0.1 - 1.0 mol / L;

[0011] Preferably, in step 2), the metal salt solution is a soluble salt solution of zinc (Zn) and / or cobalt (Co) and / or copper (Cu) and / or iron (Fe) and / or manganese (Mn) and / or silver (Ag) and / or titanium (Ti) and / or zirconium (Zr);

[0012] Preferably, in step 2), the metal salt solution is a soluble salt solution of zinc and iron; the molar ratio of zinc ions to iron ions in the metal salt solution is (7 - 9):1.

[0013] Preferably, in step 3), the organic amine ligand is 2 - aminoterephthalic acid (H2BDC - NH2) and / or 5 - aminoisophthalic acid (5 - AIPA); as common general knowledge in the art, the molar amount of the organic amine ligand used is 1 - 4 times the molar amount of the metal ions contained in the metal salt solution used in step 2. On the premise of knowing the mass of the target metal - organic amine ligand, preparing metal salt solutions and organic amine ligand solutions with corresponding concentrations is common general knowledge in the art.

[0014] The present invention also provides the bentonite with a multi - pore structure obtained by one of the above methods, which can comprehensively adsorb pollutant molecules of different sizes.

[0015] In the technical solution of the present invention, the interlayer of bentonite is activated by acid solution, the pore diameter increases, and interlayer cations can be precipitated, enabling it to have a channel for the diffusion of adsorbed substances. At the same time, H +Entering the interlayer of the bentonite layer can weaken the interlayer force of the bentonite layer and increase the cation exchange capacity. Acidification not only promotes the splitting of some macromolecules in the bentonite into smaller fragments, enhancing its adsorption property, but also promotes the formation of crosslinks between small molecules, resulting in the rearrangement of porous materials and larger structural units to form crosslinked particles, enabling the bentonite to form a skeleton with sufficient space to ensure the entry of metal ions into the interlayer and access to active sites, and then being able to form MOF structures in the bentonite interlayer. At the same time, the activation temperature and citric acid concentration will affect the effect of organic chelated metals. Too low activation temperature causes insufficient free radicals and poor activity of the formed MOF structure. Too high activation temperature easily leads to the breakage of chemical bonds on the hydrates formed by chelation, and excessive Zn 2+ crosslinks with the sites, and in an acidic environment, metals mostly exist in ionic form and will exist as stable metal oxides or precipitates as the pH increases, thus affecting the activity of the MOF structure. Therefore, the present invention should control the acid solution concentration and the temperature during the acidification process.

[0016] The present invention uses zinc (Zn) and / or cobalt (Co) and / or copper (Cu) and / or iron (Fe) and / or manganese (Mn) and / or silver (Ag) and / or titanium (Ti) and / or zirconium (Zr) as the metal center of the MOF and simultaneously as the antibacterial active center. The growth of bacteria is inhibited by the slow release of metal ions. The metal ions can crosslink with proteins and DNA to generate active groups such as singlet oxygen and hydroxyl groups, inhibiting the normal life activities of bacteria. Research shows that most metal-organic framework materials exhibit good antibacterial effects through metal cations. However, most metal cations have certain biological toxicity. Although there are usage effects, there are still certain safety hazards. Among them, some metal cations such as Cu, Ag, and Zn have low biological toxicity, but Ag is expensive, and Cu has a higher reaction selectivity with the amino organic ligand 2-aminoterephthalic acid, which easily causes excessive consumption of 2-aminoterephthalic acid. Therefore, Zn is preferably the optimal metal center in the present invention. At the same time, the Zn cation metal-organic framework structure has a high specific surface area and clear metal nodes. In addition to this conventional feature, the most important thing is that its pore size can be adjusted, forming a crystal structure similar to MOF-5. Through the experiments of researchers in this field, it is found that its microstructure presents a microporous-mesoporous composite pore structure. After further characterization, it shows that Zn can be successfully loaded and the distributions of Zn, C, and O elements are uniform. Moreover, the constant temperature time has a great influence on its microstructure. If the reaction time is too long, the particles gradually grow and the surface roughness increases, even presenting a flower-like cluster. In addition, on the premise that Zn is used as the metal center, the addition of a small amount of Fe ions can further improve the bactericidal performance. The bactericidal performance of intrinsic Fe ions is low, but after introducing a small amount of iron sites into the Zn-based MOF material, the MOF nanoparticles have weak magnetism and stronger adsorption on the surface of the charged cell membrane of bacteria, further improving the bactericidal performance. The present invention successfully introduces a central metal with ion bactericidal properties into the MOF structure, which can provide a significant bactericidal effect on various bacteria such as Staphylococcus aureus and Escherichia coli through the release of metal ions. By using the hydroxyl organic ligand 2,5-dihydroxyterephthalic acid and the amino organic ligand 2-aminoterephthalic acid, acidic and basic organic groups are introduced, and odor substances are adsorbed through acid-base adsorption. The amino group adsorbs acidic substances such as H2S and uric acid, and the deodorization performance is better. In the MOF structure, the Zn atom forms a bidentate coordination with the carboxyl group of the organic ligand, and the carboxyl group bridges with Zn, playing a supporting role in the interlayer pore channels, forming a rigid crosslinked structure, ensuring a high degree of stability of the ion exchange space. At the same time, the organic ligand can enhance its bactericidal effect by inducing a large number of oxygen free radicals.

[0017] In addition, the bentonite structure is a 2:1 type crystal structure composed of two silicon-oxygen tetrahedrons sandwiching a layer of aluminum-oxygen octahedrons. During the process of citric acid acidifying bentonite, through H +The exchange reaction with the aluminum octahedron in the bentonite structure can form aluminum citrate. During the further synthesis process of MOFs, with the use of organic amine ligands, through the chemical interaction between partial aluminum citrate and organic amine, aluminum hydroxide sol is formed. At the same time, while the metal and the organic amine ligand form the MOF structure through self-assembly reaction, the layered bentonite structure is induced by the metal cations between its layers and crosslinked and assembled on the periphery of the MOF structure to form a hierarchical pore structure of bentonite-MOFs. During the further granulation process, another portion of bentonite is mixed with the bentonite-MOFs hierarchical pore structure containing aluminum hydroxide sol, and water is added for disk granulation. By using the polycondensation reaction of aluminum hydroxide gel, dehydration condensation forms an alumina network structure, and this is used as a spontaneous binder to fix the MOFs-bentonite with a hierarchical pore structure in the network structure, forming a stable MOFs-bentonite particle structure, avoiding the use of a binder, and being coated with bentonite on the periphery of the network structure, providing more macroporous structures for pollutant adsorption, resulting in a bentonite with a hierarchical pore structure. Compared with the externally added binder, the self-generated binder omits the binder blending step, has higher production efficiency, and at the same time has a tighter combination with bentonite and MOFs-bentonite particles, stronger agglomeration effect, and is not prone to phenomena such as hardening expansion and cracking and disintegration often occurring with externally added binders, having higher application value.

[0018] The bentonite adsorbent material prepared by the present invention constructs a hierarchical pore structure of macropores-mesopores-micropores. The macropores come from the swollen binder and the interlayer structure of bentonite, the mesopores are the grain boundary gaps existing between MOF crystals, and the micropores are the intrinsic porosity within MOF crystals. Compared with the existing bentonite adsorbent materials, the present invention can achieve comprehensive adsorption of pollutants with different sizes through the hierarchical pores, and the pollutant adsorption is more efficient.

[0019] The beneficial effects of the present invention are as follows: The present invention successfully prepares a bentonite adsorbent material with a hierarchical pore structure, which can adsorb pollutant molecules with different sizes and has a strong adsorption effect. At the same time, the present invention avoids the externally added binder during the granulation process, has higher production efficiency. Compared with the commercially available bentonite adsorbent materials, the bentonite adsorbent material prepared by the present invention has a small amount of dust during transportation, is not easily pulverized after getting wet and agglomerates, is convenient for cleaning excrement, and has good antibacterial and deodorant properties. Description of the Drawings

[0020] Figure 1 It is the SEM characterization diagram of the bentonite adsorbent material prepared in Example 1 of the present invention;

[0021] Figure 2 It is the antibacterial experimental performance diagram of the bentonite adsorbent material obtained by the present invention. Detailed Embodiments

[0022] The present invention first acidifies bentonite. Through the action of acid, a protonation reaction occurs on the surface of bentonite, forming Al 3+ ions and active sites. These active sites provide binding points for subsequent reactions, enhancing the reaction activity of bentonite. At the same time, the acidification treatment can also form pores inside bentonite. These pores not only increase the specific surface area of bentonite but also help improve the adsorption performance and ion exchange capacity of bentonite. In addition, the acidification treatment can weaken the interlayer force of bentonite, making the bentonite particles easier to disperse and subsequent treatment.

[0023] Next, the acidified bentonite is mixed with a metal-organic amine precursor. During the mixing process, the metal-organic amine precursor binds to the active sites on the surface of bentonite through coordination, and then a metal-organic framework (MOF) is formed. The formation of MOF not only further increases the specific surface area and pore structure of bentonite but also endows bentonite with more excellent adsorption and separation performance. At the same time, aluminum hydroxide sol is formed during the mixing process. These sols can penetrate between bentonite particles and bond the particles together to form a stable structure.

[0024] Then, untreated bentonite is added again. These newly added bentonite particles will be coated by the formed aluminum hydroxide sol. The bonding effect of the sol makes the bentonite particles form a tight connection, and then a hierarchical structure is formed. This hierarchical structure not only retains the original excellent properties of bentonite but also further improves the application performance of bentonite in the fields of adsorption, separation, and catalysis through the introduction of MOF and aluminum hydroxide sol.

[0025] The following further clearly and detailedly describes the present invention in combination with specific embodiments and the accompanying drawings of the specification. Those of ordinary skill in the art will be able to implement the present invention based on these descriptions. In addition, the embodiments of the present invention involved in the following description are usually only a part of the embodiments of the present invention, rather than all the embodiments. Therefore, all other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0026] Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commercially available or raw materials that can be obtained by those skilled in the art; unless otherwise specified, the methods used in the embodiments of the present invention are all methods mastered by those skilled in the art.

[0027] Example 1

[0028] A preparation method of a bentonite adsorbent material, the method comprising:

[0029] 1) Take 10g of bentonite, mix well, add to 30mL of citric acid solution containing 30g of citric acid, heat to 80℃ and stir for 5h at a stirring speed of 100r / min; wash by centrifugation with deionized water until the pH of the eluate is 7;

[0030] 2) With the goal of preparing 10g of Zn@MOFs particles, weigh its precursors: zinc nitrate and 2-aminoterephthalic acid; dissolve zinc nitrate in water to prepare a 0.5mol / L zinc salt solution, and dissolve 2-aminoterephthalic acid in N,N-dimethylformamide to prepare a 0.2mol / L organic amine ligand solution. Stir the product obtained by centrifugation in step 1 with the zinc salt solution and the organic amine ligand solution in a 50°C water bath for 60 minutes to fully mix, heat to 120°C to react for 24 hours, and after the reaction is completed, filter out the pre-product bentonite adsorption material;

[0031] The obtained pre-product was characterized by SEM, and the characterization results are as follows Figure 1 As shown. Figure 1 It can be clearly seen that the bentonite adsorption material prepared by the present invention effectively realizes the loading of regular Zn@MOFs particles. Zn@MOFs basically presents a double tetrahedral pyramid shape and effectively retains the pore characteristics of the original zeolite bentonite-based carrier. Zn@MOFs are distributed on the microscopic surface of the multi-level pore size bentonite and partially at the pore mouth and in the pore, but do not cause serious blockage to the pore, thereby retaining the adsorption characteristics of its carrier.

[0032] 3) Take another 10 g of bentonite, mix it with the pre-product of step 2, and granulate it with a disc at room temperature, with a disc speed of 25 r / min and a rounding time of 3 min to obtain bentonite particles with a particle size of 2 to 3 mm.

[0033] At room temperature, the performance of the bentonite adsorption material obtained in this example was tested using the following method.

[0034] 1. Ammonium ion concentration

[0035] Take 10 g of the bentonite adsorption material obtained by the method of this example, and pour an excess of 50 mL of a solution with an ammonium ion concentration of 31 mg / L into it, filter to obtain a filtrate, repeat three times in parallel, detect the ammonium ion concentration in the filtrate and record the average value.

[0036] 2. Agglomeration strength (I):

[0037] After the test (1) is completed, take the agglomerated part and record whether the agglomerate produces debris without the influence of external force. If the agglomerate test result is complete, it is marked as ○, and if it produces debris, it is marked as ×. It is allowed to fall freely at a height of 0.8 meters from the ground. If it falls to the ground in the drop test and does not scatter in particles, it is marked as PASS, and if it scatters, it is marked as FAIL.

[0038] 3. Antibacterial property:

[0039] The bentonite adsorption material obtained in this example was subjected to microbial detection. Four common cat pathogenic bacteria, namely Yersinia enterocolitica, Shigella dysenteriae, Staphylococcus aureus, and Escherichia coli, were transferred into a common nutrient agar medium with a sterile pipette and incubated in a constant temperature incubator at 37 °C for 24 h. Four typical colonies on the incubated nutrient agar plate were picked with a sterile cotton swab and placed in a sterile LB liquid medium, thoroughly mixed, and incubated at 37 °C and 200 r / min for 24 h. The bacterial cells were centrifuged out, and a bacterial suspension with a concentration of 10 3 cfu / mL was prepared with sterile MH broth. After grinding the product prepared in this example through a 120-mesh sieve, 2 g of the product was added to 20 mL of the prepared bacterial suspension (the experimental group without adding the product was used as the control experimental group), and it was incubated in a constant temperature incubator at 37 °C for 24 h. 1.0 mL was taken from the completed culture medium, diluted 100-fold, quantitatively (50 μL) spread on an MH agar plate, and the total number of colonies was counted. The cultivation results are as Figure 2 shown. Figure 2 The left figure in the middle is the control experimental group, and the right figure is the experimental result of the bentonite adsorption material in this example.

[0040] 4. Acid and alkali tolerance test:

[0041] 1 wt% brine was prepared. The pH value of the brine was adjusted to 5.5 with hydrogen sulfide as the acidic test solution, and the pH value was adjusted to 8.0 with ammonia water as the alkaline test solution. Equal amounts of the product prepared in this example were placed in different sealed containers, and the acidic test solution and the alkaline test solution were respectively added dropwise to the product in the sealed containers according to the ratio of 15 mL / 10 g of the product (experimental group). Subsequently, the sealed containers (without placing the product) with equal amounts of the acidic test solution and the alkaline test solution added dropwise were used as the blank control. The hydrogen sulfide gas content and ammonia content in the sealed containers were characterized and recorded after 30 min, and the percentage decrease in the hydrogen sulfide gas content (△H2S) and ammonia content (△NH3) of the experimental group (the acidic experimental group with the acidic test solution added dropwise and the alkaline experimental group with the alkaline test solution added dropwise) compared with the blank control group was recorded.

[0042] 5. Caking strength (II):

[0043] After the detection in (4) was completed, the caked part was taken. Without the influence of external force, it was recorded whether the caked part produced debris. If the caking test result was a complete cake, it was recorded as ○, and if debris was produced, it was recorded as ×. It was freely dropped from a height of 0.8 m above the ground. In the dropping test, if it did not scatter in a granular form on the ground, it was recorded as PASS, and if it scattered, it was recorded as FAIL.

[0044] The results of various characterizations are as follows.

[0045]

[0046]

[0047] According to the results in the table, the bentonite adsorption material prepared by the present invention can effectively adsorb ammonium ions, has a fast caking speed and high strength. The liquid is adsorbed by multiple adjacent particles, and the binder dispersed between the particles becomes harder when encountering water, which can cement the loose particles into a whole and develop strength, effectively avoiding caking and pulverization. In addition, the bentonite adsorption material has high antibacterial property. Moreover, the product of the present invention has good acid and alkali resistance. However, it can also be seen that under the action of acidic test solution, the caking strength of the product of the present invention is weakened to some extent.

[0048] Example 2

[0049] A preparation method of a bentonite adsorption material, the specific preparation process is the same as that of Example 1, the difference is that:

[0050] Other metal salt solutions with the same metal cation concentration are used to replace the metal salt solution used in step 2). The cobalt (Co), copper (Cu), iron (Fe), and manganese (Mn) metal salts used are all soluble chlorides, silver (Ag) uses silver nitrate, and the titanium salt and zirconium salt are both nitrates and stabilizers are added respectively to avoid their precipitation. And the same tests as in Example 1 are carried out, and the test results are shown in the following table.

[0051]

[0052] It can be seen from the above characterization results that different metal cations will produce significantly different preparation effects. Among them, the main effects are on the absorption capacity of ammonia and hydrogen sulfide and the overall antibacterial property. It can be seen from the data in the table that in terms of adsorption capacity and antibacterial property, Cu, Ag, and Mn are the best, and their effects are better than Zn ions. However, all three of them will have different degrees of influence on the caking strength of the product. Among them, the caking strength of the product under acidic conditions decreases significantly after Cu and Ag ions form MOFs, which may be related to the fact that copper ions and silver ions enhance the acidity of the microenvironment system to a certain extent. The Mn@MOFs structure makes the interlayer structure of bentonite loose and the strength weakened, and the caking strength under alkaline conditions also decreases.

[0053] It can be seen that to maintain good adsorption and caking strength, the optimal choice should be to use four metal cations of Cu, Zn, Ag, and Fe.

[0054] Comparative Example 1

[0055] Commercially available bentonite adsorption material. The same tests as in Example 1 are carried out on the commercially available bentonite adsorption material for characterization. The characterization results are as follows:

[0056]

[0057] From the above characterization results, it can be seen that the commercially available bentonite adsorption material also has good caking property and certain adsorption capacity. However, the caking strength is extremely low under acidic conditions. The acid solution experimental group is extremely dispersed without external force, making it difficult to effectively agglomerate. At the same time, the antibacterial property is also relatively limited.

[0058] Comparing with the foregoing embodiments, it can be found that the zeolite component and M@MOFs structure used in the present invention have significant beneficial effects on improving the caking strength, adsorption property and antibacterial property.

[0059] Example 3

[0060] A preparation method of a bentonite adsorption material, the method comprising:

[0061] 1) Take 10 g of bentonite, mix it evenly, and add it to 30 mL of a citric acid solution containing 30 g of citric acid. Heat it to 80 °C and stir at a constant temperature for 5 h, with a stirring speed of 100 r / min; wash it with deionized water by centrifugation until the pH of the washing liquid is 7;

[0062] 2) Aiming at preparing 10 g of Zn-Fe@MOFs particles, weigh its precursors: zinc chloride, iron chloride and 5-aminoisophthalic acid; among them, zinc chloride and iron chloride are dissolved in deionized water at a molar ratio of 7:1 to prepare a zinc-iron salt solution with a concentration of 0.15 mmol / L, and 5-aminoisophthalic acid is dissolved in N,N-dimethylformamide to prepare an organic modification solution with a concentration of 0.2 mol / L. The product obtained by centrifuging in step 1, the organic modification solution and the zinc-iron salt solution are stirred in a water bath at 50 °C for 60 min and then heated to 110 °C for reaction for 24 h. After the reaction is completed, filter out the product to obtain agglomerated bentonite particles.

[0063] 3) Take another 10 g of bentonite, mix it with the pre-product in step 2, and granulate it on a disc at room temperature. The disc rotation speed is 25 r / min, and the rounding time is 3 min to obtain bentonite particles with a particle size of 2-3 mm.

[0064] Perform the same test as in Example 1, and the test results are shown in the following table.

[0065]

[0066] Comparing the above test results with those of Example 1 and Comparative Example 3, it can be found that when appropriate iron and zinc ions are combined in a certain proportion, while maintaining the adsorption performance and caking strength of the present invention under alkaline conditions, the adsorption capacity and caking strength under acidic conditions can be significantly improved, so that the agglomeration does not disperse under acidic conditions, and the acidic components can be more effectively adsorbed, greatly improving the acid-base tolerance of the bentonite-based material.

Claims

1. A method for preparing bentonite with a multi-level pore structure, characterized in that: The method comprises: 1) Take 2 parts by weight of bentonite and disperse it in a solution containing 6 parts by weight of citric acid. Stir and acidify the bentonite at 80°C for 5 hours at a stirring speed of 100 r / min. After acidification, centrifuge at 8000 r / min for 5 minutes. Add water and centrifuge at the same speed to wash the solution until the pH value of the eluate is 6.5-7.

5. 2) Mixing the product obtained by centrifugation in step 1 with 1 part by weight of a MOF precursor, wherein the MOF precursor is a metal salt and an organic amine ligand; specifically, mixing the centrifugal product with a solution of the metal salt and a solution of the organic amine ligand, stirring and reacting at 110-150° C. for 20-48 hours; filtering off the solvent to obtain bonded bentonite particles; the organic amine ligand is 2-aminoterephthalic acid and / or 5-aminoisophthalic acid; the metal salt is a Zn salt, or a mixed salt of a Zn salt and a Fe salt; 3) Take another 1 part by weight of bentonite, mix it with the bentonite particles in step 2, and granulate it with a disc at room temperature, with a disc speed of 25 r / min and a granulation time of 3 min to obtain granular bentonite with a multi-level pore structure.

2. The preparation method according to claim 1, characterized in that: The metal salt is a mixed salt of Zn salt and Fe salt, and the molar ratio of zinc ion to iron ion is (7-9):1.

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