CN117208926B - High-crystallinity two-dimensional MWW zeolite molecular sieve and preparation method thereof - Google Patents
High-crystallinity two-dimensional MWW zeolite molecular sieve and preparation method thereofInfo
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- CN117208926B CN117208926B CN202311173825.9A CN202311173825A CN117208926B CN 117208926 B CN117208926 B CN 117208926B CN 202311173825 A CN202311173825 A CN 202311173825A CN 117208926 B CN117208926 B CN 117208926B
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- C01B39/04—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof; Direct preparation thereof; Preparation thereof starting from a reaction mixture containing a crystalline zeolite of another type, or from preformed reactants; After-treatment thereof using at least one organic template directing agent, e.g. an ionic quaternary ammonium compound or an aminated compound
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Abstract
本发明提供了一种高结晶性的二维MWW沸石分子筛的制备方法，包括以下步骤：步骤S1，将二维材料的粉末加入反应容器，滴加有机结构导向剂并混合均匀，得混合液，对混合液依次进行超声处理和离心处理后取上层清液，得液相剥离后的薄层二维材料分散液；步骤S2，将薄层二维材料分散液、去离子水、碱金属源和铝源配制成溶液，在溶液中缓慢加入硅源，搅拌溶解，陈化处理，得溶胶凝胶；步骤S3，溶胶凝胶进行水热晶化后，得反应产物，进行洗涤、离心和干燥处理后，得高结晶性的二维MWW沸石分子筛。本发明中采用六方氮化硼或硫化钼作为外延生长二维沸石的模板，无需额外添加除六亚甲基亚胺或哌啶之外的有机模板剂，合成得到结晶性好且横纵比大的二维MWW型沸石。
The present invention provides a method for preparing a two-dimensional MWW zeolite molecular sieve with high crystallinity, comprising the following steps: step S1, adding a powder of a two-dimensional material to a reaction vessel, dripping an organic structure directing agent and mixing evenly to obtain a mixed solution, and taking the supernatant after ultrasonic treatment and centrifugal treatment of the mixed solution in sequence to obtain a thin layer of two-dimensional material dispersion after liquid phase peeling; step S2, preparing a solution of a thin layer of two-dimensional material dispersion, deionized water, an alkali metal source and an aluminum source, slowly adding a silicon source to the solution, stirring and dissolving, and aging treatment to obtain a sol-gel; step S3, after the sol-gel is hydrothermally crystallized, a reaction product is obtained, and after washing, centrifugation and drying treatment, a highly crystalline two-dimensional MWW zeolite molecular sieve is obtained. In the present invention, hexagonal boron nitride or molybdenum sulfide is used as a template for epitaxial growth of two-dimensional zeolite, and no additional organic template agent other than hexamethyleneimine or piperidine is required to synthesize a two-dimensional MWW zeolite with good crystallinity and a large aspect ratio.
Description
Technical Field
The invention belongs to the technical field of synthesis of two-dimensional zeolite molecular sieves, and particularly relates to a high-crystallinity two-dimensional MWW zeolite molecular sieve and a preparation method thereof.
Background
Zeolite is a crystalline aluminosilicate having excellent adsorption and catalytic properties. Particularly in the petrochemical industry, zeolite is used as a commonly used heterogeneous catalyst, and has very important application in the fields of catalytic cracking, hydrocracking, reforming and the like of petroleum refining. With the increasing exhaustion of petroleum resources worldwide and the increasing trend of global petroleum resource heaviness and inferior quality, the demand for zeolite-catalyzed macromolecular reactions is growing. However, the conventional zeolite is a three-dimensional rigid material, on one hand, macromolecules are difficult to enter the internal acid sites through pore channels and gaps, the accessibility of molecules is poor, and on the other hand, serious diffusion limitation exists in the pore channels, and the diffusion speed of reactant molecules and products is low, so that the catalytic efficiency and catalytic activity of the zeolite are reduced, and the catalytic effect of the zeolite cannot be fully exerted.
In view of this, the synthesis of two-dimensional zeolite molecular sieve nanoplatelets that expose more active sites and have shorter diffusion lengths has become a hotspot of great interest. The MWW zeolite has a layered structure, the thickness of a single layer is only 2.5nm, the specific surface area and a special twelve-membered ring super-cage structure are realized, the opening of a lamellar layer is improved, more active sites are increased by constructing the thin-layer two-dimensional MWW zeolite, and the diffusion of macromolecular reactants in pore channels and the contact with the active sites are facilitated, so that the MWW zeolite shows excellent shape selectivity and catalytic activity in macromolecular reactions.
Currently, the methods commonly used for two-dimensional MWW zeolite synthesis mainly include post-treatment methods and direct synthesis methods. The post-treatment method mainly comprises the steps of stripping zeolite by swelling ultrasonic, and has complex process, complicated steps, low yield and serious damage to zeolite structure and morphology. The direct synthesis method mainly synthesizes the two-dimensional zeolite directly by designing a special template agent with a complex molecular structure, however, the special template agent is complex and expensive in design, not beneficial to industrialization, and the synthesized zeolite sheets are mutually crossed and stacked for growth, so that the shape selectivity effect of zeolite pore channels cannot be exerted. Therefore, there is a great need to develop a highly efficient, low cost process for the preparation of two-dimensional zeolites with high crystallinity and consistent planar orientation.
Disclosure of Invention
The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a two-dimensional MWW zeolite molecular sieve having high crystallinity and a method for producing the same.
The invention provides a preparation method of a high-crystallinity two-dimensional MWW zeolite molecular sieve, which is characterized by comprising the following steps of S1, adding powder of a two-dimensional material into a reaction container, then dripping an organic structure directing agent and uniformly mixing to obtain a mixed solution, sequentially carrying out ultrasonic treatment and centrifugal treatment on the mixed solution, and taking supernatant to obtain a thin-layer two-dimensional material dispersion liquid after liquid phase stripping;
S2, preparing a thin-layer two-dimensional material dispersion liquid, deionized water, an alkali metal source and an aluminum source into a solution, slowly adding a silicon source into the solution, stirring for dissolution, and aging to obtain sol gel;
And S3, carrying out hydrothermal crystallization on the sol-gel to obtain a reaction product, and sequentially washing, centrifuging and drying the reaction product to obtain the high-crystallinity two-dimensional MWW zeolite molecular sieve, wherein the concentration of the two-dimensional material contained in the thin-layer two-dimensional material dispersion liquid is 0.005-0.06 mg/mL, the transverse dimension of the two-dimensional material is 0.5-3 mu m, the thickness is 10-30 nm, the ageing treatment time is 1-6 h in the step S2, the molar ratio of the silicon source to the aluminum source to the alkali metal source to the structure directing agent to the deionized water is 22:0.2-1.5:1-6.5:2-10:400-1000, and the crystallization temperature is 120-180 ℃ and the crystallization time is 7-14 days in the step S3.
The preparation method of the high-crystallinity two-dimensional MWW zeolite molecular sieve provided by the invention can be characterized in that in the step S1, the two-dimensional material is hexagonal boron nitride or molybdenum sulfide, and the organic structure directing agent is hexamethyleneimine or piperidine.
The preparation method of the high-crystallinity two-dimensional MWW zeolite molecular sieve provided by the invention can be further characterized in that in the step S1, the ultrasonic treatment time is 6-12 h, the rotating speed during centrifugal treatment is 800-10000 rpm, and the time is 10-30 min.
The preparation method of the high-crystallinity two-dimensional MWW zeolite molecular sieve provided by the invention can also be characterized in that in the step S2, the alkali metal source is sodium hydroxide or potassium hydroxide, the aluminum source is sodium metaaluminate, aluminum isopropoxide, aluminum chloride or aluminum sulfate octadecanoate, and the silicon source is silica sol aqueous solution, water glass or white carbon black.
The preparation method of the high-crystallinity two-dimensional MWW zeolite molecular sieve provided by the invention can be characterized in that in the step S2, the dropping speed of a silicon source is 0.5-1.5 mL/min, and when stirring and dissolving, the silicon source is stirred for 1-3 hours at room temperature under the rotating speed of 400-800 r/min.
The preparation method of the high-crystallinity two-dimensional MWW zeolite molecular sieve provided by the invention can be characterized in that in the step S3, the hydrothermal crystallization mode is dynamic crystallization or static crystallization, and the dynamic crystallization is hydrothermal crystallization at a rotating speed of 15-30 rpm.
The preparation method of the high-crystallinity two-dimensional MWW zeolite molecular sieve provided by the invention can be characterized in that in the step S3, during washing and centrifuging, the two-dimensional MWW zeolite molecular sieve is centrifuged for 3min to 5min at 3000rpm to 5000rpm, then the two-dimensional MWW zeolite molecular sieve is washed by deionized water, the operation is repeated for 3 to 4 times until the centrifuged upper solution becomes clear, and the two-dimensional MWW zeolite molecular sieve is dried at a constant temperature in a vacuum drying oven at 50 ℃ to 100 ℃ for 12h to 24h during drying.
The invention also provides a high-crystallinity two-dimensional MWW zeolite molecular sieve, which has the characteristics that the high-crystallinity two-dimensional MWW zeolite molecular sieve is prepared by the preparation method of the high-crystallinity two-dimensional MWW zeolite molecular sieve, wherein the high-crystallinity two-dimensional MWW zeolite molecular sieve is of a hexagonal sheet structure, the transverse dimension is 500-1000 nm, and the thickness is 2.5-25 nm.
Effects and effects of the invention
According to the high-crystallinity two-dimensional MWW zeolite molecular sieve and the preparation method thereof, a thin layer two-dimensional material dispersion liquid is obtained by a liquid phase stripping method, and then the dispersion liquid and zeolite synthesis raw materials are mixed and aged, and the mixture is subjected to hydrothermal crystallization and heating growth for a certain time to obtain the high-crystallinity two-dimensional MWW zeolite molecular sieve.
According to the principle of lattice symmetry matching, the two-dimensional MWW zeolite with consistent c-axis orientation is epitaxially grown by taking hexagonal boron nitride or molybdenum sulfide as a template. Compared with the interpenetration grown zeolite structure obtained by the traditional direct synthesis method, the two-dimensional MWW zeolite molecular sieve which is epitaxially grown in the invention is of a flat structure with consistent orientation, has a thin layer thickness of 2.5-15 nm, a large transverse dimension of 500-1000 nm and a high transverse-longitudinal ratio. Meanwhile, the high-crystallinity two-dimensional MWW zeolite molecular sieve prepared by the epitaxial growth method has high crystallinity and skeleton opening degree, has high diffusion rate and selectivity for xylene molecules, and has wide application prospect in the fields of catalysis and gas separation.
Drawings
FIG. 1 is a schematic illustration of a preparation flow of a method for preparing a highly crystalline two-dimensional MWW zeolite molecular sieve in accordance with an embodiment of the present invention;
FIG. 2 is a transmission electron micrograph and an atomic force micrograph of two-dimensional hexagonal boron nitride obtained by liquid phase exfoliation in example 1 of the present invention;
FIG. 3 is a scanning electron microscope image of the MWW zeolite obtained in example 1 of the present invention epitaxially grown on a hexagonal boron nitride substrate;
FIG. 4 is a transmission electron microscope and a scanning electron microscope image of a two-dimensional MWW zeolite molecular sieve of high crystallinity prepared in example 1 of the present invention;
FIG. 5 is a transmission electron microscope of a cross section of a two-dimensional MWW zeolite molecular sieve of high crystallinity, an atomic force microscope view of the two-dimensional MWW zeolite molecular sieve, and a thickness statistical chart prepared in example 1 of the present invention;
FIG. 6 is an XRD pattern of a two-dimensional MWW zeolite molecular sieve of high crystallinity and a conventional three-dimensional MCM-22P zeolite prepared in example 1 of the present invention.
FIG. 7 is a graph showing adsorption diffusion rates of o-xylene and P-xylene for a two-dimensional MWW zeolite molecular sieve having high crystallinity and a conventional three-dimensional MCM-22P zeolite prepared in example 1 of the present invention.
Detailed Description
The invention relates to a preparation method of a high-crystallinity two-dimensional MWW zeolite molecular sieve, which comprises the following steps:
step S1, adding powder of the two-dimensional material into a reaction container, then dropwise adding an organic structure directing agent, uniformly mixing to obtain a mixed solution, sequentially carrying out ultrasonic treatment and centrifugal treatment on the mixed solution, and taking supernatant to obtain a thin-layer two-dimensional material dispersion liquid after liquid phase stripping.
The concentration of the two-dimensional material contained in the thin-layer two-dimensional material dispersion liquid is 0.005 mg/mL-0.06 mg/mL, the transverse dimension of the two-dimensional material is 0.5 mu m-3 mu m, and the thickness is 10nm-30nm. Preferably, the concentration of the two-dimensional material dispersion liquid is 0.03mg/mL, the transverse dimension of the two-dimensional material is 1 mu m, the thickness is 10nm, the template effect of the two-dimensional material is improved, and the large-size two-dimensional MWW zeolite monocrystal is obtained.
In the step S1, the two-dimensional material is hexagonal boron nitride or molybdenum sulfide, and the organic structure directing agent is hexamethyleneimine or piperidine.
In the step S1, the ultrasonic treatment time is 6-12 h, the rotating speed during the centrifugal treatment is 8000-10000 rpm, and the ultrasonic treatment time is 10-30 min. Further, the power during ultrasonic treatment is 200W-400W, and the frequency is 20-40 KHz. Preferably, the ultrasonic treatment is carried out for 10 hours, the centrifugal treatment is carried out for 20 minutes, the power during ultrasonic treatment is 400W, and the frequency is 40KHz.
In the step S1, when the ultrasonic treatment is carried out, the reactor is placed in an ultrasonic instrument, the two-dimensional material powder is stripped by utilizing the shearing force generated by the ultrasonic and the polarity of the solvent, and the thickness and the yield of the stripped two-dimensional material can be regulated and controlled by regulating the ultrasonic power and the ultrasonic time, so that the two-dimensional material dispersion liquid with proper concentration is obtained.
And S2, preparing a solution from the thin-layer two-dimensional material dispersion liquid, deionized water, an alkali metal source and an aluminum source, slowly adding a silicon source into the solution, stirring for dissolution, and aging to obtain sol gel.
In the step S2, when a solution is prepared by using a thin layer two-dimensional material dispersion liquid, deionized water, an alkali metal source and an aluminum source, stirring for 10-30 min at room temperature (for example, at room temperature of 15-35 ℃) under the rotating speed of 100-800 r/min, and uniformly mixing to prepare an alkali solution.
The ageing treatment time is 1h-6h. Preferably, the aging treatment is carried out for a period of time ranging from 1h to 3h.
In the sol gel, the molar ratio of the silicon source to the aluminum source to the alkali metal source to the structure directing agent to the deionized water is 22:0.2-1.5:1-6.5:2-10:400-1000. Further, the silicon-aluminum ratio of the material in the preparation system is 15-110, the water-silicon ratio is 18-45, the alkalinity is OH -：SiO2 =0.05-0.3, and the ratio of the silicon source to the structure directing agent is 2-11.
Wherein, the aluminum source consumes alkali of the system, thereby changing the alkalinity of the system, the alkalinity can influence the generation of silicon and aluminum short chain polymers, and the alkalinity is increased in a low-alkali system, the number of crystal nucleus in initial gel can be increased, and the crystallization process is promoted. At high water levels, however, the solubility of the silica-alumina species decreases, and the saturation of the system decreases, resulting in a decrease in the number of nucleation sites and an increase in zeolite size. The structure directing agent can induce the silicon aluminum species to form primary and secondary structural units, and the increase of the content of the structure directing agent in the system can increase the nucleation number, thereby accelerating the crystallization process. Preferably, the silicon-aluminum ratio of the feed in the preparation system of the invention is 25, the water-silicon ratio is 25, the alkalinity is OH -：SiO2 =0.15, and the ratio of the silicon source to the structure directing agent is 5.
In the step S2, the alkali metal source is sodium hydroxide or potassium hydroxide, the aluminum source is sodium metaaluminate, aluminum isopropoxide, aluminum chloride or aluminum sulfate octadecanoate, and the silicon source is silica sol water solution, water glass or white carbon black. Further, the silica sol aqueous solution is 25-40% by mass. Preferably, when the aluminum source is sodium metaaluminate, 40% of silica sol aqueous solution is used as the silicon source, when the aluminum source is aluminum sulfate octadecatried, water glass is used as the silicon source, silicon aluminum and aluminum are respectively dissolved, then the silicon source is slowly dripped into the aluminum source, the ratio of the silicon to the aluminum is 18-45, the solubility of silicon aluminum species is improved, the formation of an initial sol-gel system is facilitated, and the yield of MWW zeolite is improved.
In the step S2, the dropping speed of the silicon source is 0.5-1.5 mL/min, and when stirring and dissolving are carried out, stirring is carried out for 1-3 hours at room temperature under the rotating speed condition of 400-800 r/min. Preferably, the dropping rate of the silicon source is 1mL/min, and when stirring and dissolving, the silicon source is stirred for 2 hours at room temperature under the rotating speed condition of 600r/min, so that the slow release of the silicon source and the full combination with the aluminum source are facilitated, a more uniform sol-gel system is formed, and the dropping rate of the liquid phase silicon source is controlled and regulated by a dropping funnel.
And S3, carrying out hydrothermal crystallization on the sol-gel to obtain a reaction product, and washing, centrifuging and drying the reaction product in sequence to obtain the high-crystallinity two-dimensional MWW zeolite molecular sieve.
In the step S3, when the hydrothermal crystallization is carried out, the crystallization temperature is 120-180 ℃ and the crystallization time is 7-14 days.
In step S3, the hydrothermal crystallization mode is dynamic crystallization or static crystallization, and the dynamic crystallization is hydrothermal crystallization at a rotation speed of 15-30 rpm.
In the step S3, during washing and centrifuging, centrifuging for 3min to 5min at the rotating speed of 3000rpm to 5000rpm, washing with deionized water, repeating the operation for 3 to 4 times until the centrifuged upper solution becomes clear, and during drying, drying for 12h to 24h at constant temperature in a vacuum drying box at 50 ℃ to 100 ℃. Preferably, in step S3, dynamic crystallization is performed for 10 days at a rotation speed of 25rpm, deionized water washing is performed, and centrifugation is performed for 3min at 5000rpm, so that dynamic crystallization can promote migration and mass transfer of silica-alumina species in the sol, and thin-layer two-dimensional MWW zeolite with uniform particle size distribution can be obtained.
The high-crystallinity two-dimensional MWW zeolite molecular sieve prepared by the preparation method of the high-crystallinity two-dimensional MWW zeolite molecular sieve is of a hexagonal platy structure, the transverse dimension is 500-1000 nm, the thickness of the synthesized two-dimensional zeolite is obviously reduced by a two-dimensional template effect, the thickness is 2.5-25 nm (1-10 layers), preferably, the thickness is 2.5-15 nm, the average thickness is 10nm, the openness of a zeolite framework is greatly improved, more internal active sites are exposed, the transverse-longitudinal ratio is up to 50-100, and the preparation and the application of a gas separation membrane are facilitated.
Meanwhile, the high-crystallinity two-dimensional MWW zeolite molecular sieve prepared by the invention has strong MWW zeolite (300) and (500) characteristic peaks.
Furthermore, the high-crystallinity two-dimensional MWW zeolite molecular sieve prepared by epitaxial growth has high diffusion rate and selectivity for xylene molecules due to good crystallinity and skeleton opening degree, and can be applied to diffusion separation of xylene molecules.
In order to make the technical means, creation characteristics, achievement purposes and effects achieved by the present invention easy to understand, the following examples specifically describe a two-dimensional MWW zeolite molecular sieve with high crystallinity and its preparation method by referring to the accompanying drawings.
Example 1 ]
The preparation method of the two-dimensional MWW zeolite molecular sieve with high crystallinity comprises the following steps:
step S1, adding powder of a two-dimensional material into a reaction container, then dripping an organic structure directing agent, uniformly mixing to obtain a mixed solution, sequentially carrying out ultrasonic treatment and centrifugal treatment on the mixed solution, and then taking supernatant to obtain a thin-layer two-dimensional material dispersion liquid after liquid phase stripping, wherein the specific process is as follows:
25mg of commercial hexagonal boron nitride powder (PT 110) and 5mL of hexamethyleneimine (98%) are added into a reaction vessel, stirred for 30min at 400r/min, uniformly mixed to obtain a mixed solution, ultrasonic treatment is carried out on the mixed solution, hexagonal boron nitride is peeled off from the liquid phase, the ultrasonic power is 400W, the frequency is 40KHz, the time period is 10h, and the temperature of an ultrasonic instrument is kept constant at 20 ℃ in the ultrasonic process. After the ultrasonic treatment is finished, transferring the mixed solution of hexagonal boron nitride and hexamethyleneimine after the ultrasonic treatment into a 50mL centrifuge tube, centrifuging at 10000rpm for 10 minutes, taking supernatant, centrifuging at 10000rpm again for 10 minutes, taking supernatant, obtaining a two-dimensional hexagonal boron nitride dispersion liquid, putting the dispersion liquid into a 20mL glass bottle, and putting the glass bottle into a vacuum drying oven for standby, wherein the concentration of hexagonal boron nitride in the dispersion liquid is 0.006mg/mL.
Step S2, preparing a thin-layer two-dimensional material dispersion liquid, deionized water, an alkali metal source and an aluminum source into a solution, slowly adding a silicon source into the solution, stirring and dissolving, and aging to obtain sol gel, wherein the specific process is as follows:
28.2675g of deionized water is added into a 100mL reactor, 0.2532g of flaky sodium hydroxide is added, stirring and dissolving are carried out for 5 minutes, the rotating speed is controlled at 500rpm, 0.2360g of sodium metaaluminate powder is added, stirring and dissolving are carried out for 5 minutes at 500rpm, 1.25g of the two-dimensional hexagonal boron nitride dispersion prepared in the step S1 is added, stirring and mixing are carried out uniformly, a clear solution is obtained, and stirring is carried out for 30 minutes at 500 rpm. Then, an aqueous silica sol solution of 40% by mass was slowly added dropwise to the solution through a dropping funnel at a rate of 1mL/min, and aged for 2 hours with vigorous stirring at 800rpm until there was no solid deposit at the bottom, to obtain a sol gel. The mol ratio of each component in the sol gel is SiO 2:Al2O3:NaOH:HMI:H2 O=22:0.44:3.3:4.4:660.
Step S3, after hydrothermal crystallization of sol-gel, obtaining a reaction product, and after washing, centrifuging and drying the reaction product in sequence, obtaining the high-crystallinity two-dimensional MWW zeolite molecular sieve, wherein the specific process is as follows:
And subpackaging the aged sol gel into a stainless steel reaction kettle with 25mL polytetrafluoroethylene as a lining, transferring the reaction kettle into a dynamic rotary oven, performing hydrothermal crystallization at the rotating speed of 25rpm and at the temperature of 150 ℃ for 10 days, and then taking out and naturally cooling to obtain a crystallized product. Washing the crystallized product by using deionized water, centrifuging for 5 minutes at a rotation speed of 5000rpm, and repeating washing and centrifuging for 3-4 times until the product turns white and the pH of the supernatant is neutral. The centrifuged bottom product was then dried in a vacuum oven at 85 ℃ for 12 hours to give a fully crystalline two-dimensional MWW zeolite molecular sieve.
Fig. 1 is a schematic illustration of a preparation flow of a preparation method of a two-dimensional MWW zeolite molecular sieve with high crystallinity in an embodiment of the invention.
As shown in fig. 1, in this embodiment, hexagonal boron nitride with alternately distributed surface charges is used as a two-dimensional template, hexamethyleneimine is used as an organic structure guiding agent, silicon aluminum and an aluminum source are subjected to hydrothermal crystallization under the induction of the organic structure guiding agent to form a silicon aluminum precursor, and under the action of the hexagonal boron nitride template, a thin-layer high-crystallinity two-dimensional MWW zeolite molecular sieve is epitaxially grown through electrostatic interaction and lattice symmetry matching, and the two-dimensional MWW zeolite molecular sieve has a regular planar hexagonal structure.
Fig. 2 is a transmission electron micrograph and an atomic force micrograph of two-dimensional hexagonal boron nitride obtained by liquid phase exfoliation in example 1 of the present invention. Fig. 2 (a) is a transmission electron microscopic image of two-dimensional hexagonal boron nitride obtained by liquid phase exfoliation in example 1 of the present invention, and (b) is an atomic force microscopic image of two-dimensional hexagonal boron nitride obtained by liquid phase exfoliation in example 1 of the present invention.
As shown in FIG. 2, the size of the hexagonal boron nitride is 500nm, the thickness is 10nm, and in the embodiment, the organic structure directing agent hexamethyleneimine is used as a stripping solvent of the hexagonal boron nitride (h-BN), so that the hexagonal boron nitride with a thin layer is successfully stripped, and the quick epitaxial growth of the formed silicon aluminum tetrahedron the h-BN template is guided by HMI at the initial stage of crystallization.
Fig. 3 is a scanning electron microscope image of the MWW zeolite obtained in example 1 of the present invention epitaxially grown on a hexagonal boron nitride substrate.
As shown in fig. 3, on a hexagonal boron nitride (h-BN) substrate, MWW zeolite is parallel to each other, has uniform crystal orientation, and realizes epitaxial growth of two-dimensional MWW zeolite.
FIG. 4 is a transmission electron microscope and a scanning electron microscope image of a two-dimensional MWW zeolite molecular sieve of high crystallinity prepared in example 1 of the present invention. Wherein, (a), (b) and (c) in fig. 4 are transmission electron microscopes of the high-crystallinity two-dimensional MWW zeolite molecular sieve prepared in example 1 of the present invention at different magnifications, and (d), (e) and (f) in fig. 4 are scanning electron microscopes of the high-crystallinity two-dimensional MWW zeolite molecular sieve prepared in example 1 of the present invention at different magnifications.
As shown in FIG. 4, the high-crystallinity two-dimensional MWW zeolite molecular sieve prepared in the embodiment has a regular hexagonal structure and uniform planar spreading orientation, and the transverse dimension is 500nm.
FIG. 5 is a transmission electron microscope of a cross section of a two-dimensional MWW zeolite molecular sieve having high crystallinity, an atomic force microscope view of the two-dimensional MWW zeolite molecular sieve, and a thickness statistical chart, which were prepared in example 1 of the present invention. Fig. 5 (a) shows a transmission electron microscope of a cross section of a two-dimensional MWW zeolite molecular sieve having high crystallinity prepared in example 1 of the present invention, (b) shows an atomic force microscope view of a two-dimensional MWW zeolite molecular sieve having high crystallinity prepared in example 1 of the present invention, and (c) shows a thickness statistical graph of a two-dimensional MWW zeolite molecular sieve.
As shown in FIG. 5, the number of epitaxially grown two-dimensional MWW layers is mainly concentrated in 3-6 layers, and the average thickness is 10nm.
FIG. 6 is an XRD pattern of a two-dimensional MWW zeolite molecular sieve of high crystallinity and a conventional three-dimensional MCM-22P zeolite prepared in example 1 of the present invention.
As shown in fig. 6, the two-dimensional MWW zeolite molecular sieve prepared in this example has (300) and (500) MWW zeolite characteristic peaks at 2θ=21.8° and 35.6 °, half widths of 0.334 ° and 0.246 °, respectively, which are high in-plane crystallinity of the two-dimensional MWW zeolite caused by epitaxial growth.
In this example, adsorption diffusion comparison of para-xylene and ortho-xylene was also performed using the prepared two-dimensional MWW zeolite molecular sieve with a conventional three-dimensional MCM-22P zeolite molecular sieve, and fig. 7 is a graph showing adsorption diffusion rates of para-xylene and para-xylene for the two-dimensional MWW zeolite molecular sieve with high crystallinity and the conventional three-dimensional MCM-22P zeolite prepared in example 1 of the present invention.
As shown in FIG. 7, the two-dimensional MWW zeolite molecular sieve with higher openness prepared in this example had higher diffusion rates, whether para-xylene or ortho-xylene, and the diffusion rates of ortho-xylene and para-xylene in the two-dimensional MWW zeolite molecular sieve were 43 times and 203 times, respectively, as high as those of the MCM-22 zeolite molecular sieve at room temperature. And the selectivity of the two-dimensional MWW zeolite molecular sieve to o-xylene/p-xylene is 10 times of that of the MCM-22 zeolite molecular sieve according to the ideal solution adsorption theory.
Further, the two-dimensional MWW zeolite molecular sieve prepared in the embodiment has good crystallinity and high transverse-longitudinal ratio, and the exposed 10-membered ring channels (0.55 nm) in more zeolite can enable paraxylene with the absolute diameter of 0.41nm to easily diffuse into the zeolite, but the 0.53nm o-xylene has larger diffusion resistance, so that the diffusion speed and selectivity of the two-dimensional MWW zeolite to paraxylene are greatly improved.
Example 2 ]
The preparation method of the two-dimensional MWW zeolite molecular sieve with high crystallinity comprises the following steps:
Step S1, adding 20mg of commercial hexagonal boron nitride powder (PT 110) and 20mL of deionized water into a reaction container, stirring for 30min at 400r/min, uniformly mixing to obtain a mixed solution, carrying out ultrasonic treatment on the mixed solution, stripping hexagonal boron nitride from the liquid phase, wherein the ultrasonic power is 400W, the frequency is 40KHz, the duration is 10h, and the temperature of an ultrasonic instrument is kept constant at 20 ℃ in the ultrasonic process. After the ultrasonic treatment is finished, transferring the mixed solution of hexagonal boron nitride and deionized water after the ultrasonic treatment into a 50mL centrifuge tube, centrifuging at 10000rpm for 10 minutes, taking supernatant, centrifuging at 10000rpm again for 10 minutes, taking supernatant to obtain a two-dimensional hexagonal boron nitride dispersion liquid, placing the dispersion liquid into a 20mL glass bottle, and placing the glass bottle into a vacuum drying box for standby, wherein the concentration of hexagonal boron nitride in the dispersion liquid is 0.030mg/mL.
Step S2, adding 28.2675g of two-dimensional hexagonal boron nitride dispersion liquid into a 100mL reactor, adding 0.2532g of flaky sodium hydroxide, stirring and dissolving for 5 minutes, controlling the rotating speed at 500rpm, adding 0.2360g of sodium metaaluminate powder, stirring and dissolving for 5 minutes at 500rpm, adding 1.25g of hexamethyleneimine, stirring and mixing uniformly to obtain a clear solution, and stirring for 30 minutes at 500 rpm. Then, an aqueous silica sol solution of 40% by mass was slowly added dropwise to the solution through a dropping funnel at a rate of 1mL/min, and aged for 2 hours with vigorous stirring at 800rpm until there was no solid deposit at the bottom, to obtain a sol gel. The mol ratio of each component in the sol gel is SiO 2:Al2O3:NaOH:HMI:H2 O=22:0.44:3.3:4.4:660.
In this example, the subsequent preparation steps are the same as step S3 of example 1, and finally a two-dimensional MWW zeolite molecular sieve with high crystallinity is prepared.
Example 3 ]
The preparation method of the two-dimensional MWW zeolite molecular sieve with high crystallinity in the embodiment is based on the specific preparation steps same as those in the embodiment 1, and the hydrothermal crystallization mode in the step S3 is replaced by static crystallization, and specifically comprises the following steps:
And subpackaging the aged sol gel into a stainless steel reaction kettle with 25mL polytetrafluoroethylene as a lining, transferring the reaction kettle into an oven, carrying out hydrothermal crystallization for 10 days at 150 ℃, and then taking out and naturally cooling to obtain a crystallized product. And subsequent preparation was performed using the same preparation conditions based on the preparation procedure of example 1, to finally prepare a highly crystalline two-dimensional MWW zeolite molecular sieve having a lateral dimension of 500nm to 1500nm and an average thickness of 25 nm.
Example 4 ]
The preparation method of the two-dimensional MWW zeolite molecular sieve with high crystallinity in this example is based on the same specific preparation steps as in example 1, and only the usage amount of the flaky sodium hydroxide in step S2 is adjusted, specifically as follows:
Adding 28.2675g of deionized water into a 100mL reactor, adding 0.1688g of flaky sodium hydroxide, stirring and dissolving for 5 minutes, controlling the rotating speed at 500rpm, adding 0.2360g of sodium metaaluminate powder, stirring and dissolving for 5 minutes at 500rpm, adding 1.25g of the two-dimensional hexagonal boron nitride dispersion prepared in the step S1, stirring and mixing uniformly to obtain a clear solution, and stirring for 30 minutes at 500 rpm. Then, an aqueous silica sol solution of 40% by mass was slowly added dropwise to the solution through a dropping funnel at a rate of 1mL/min, and aged for 2 hours with vigorous stirring at 800rpm until there was no solid deposit at the bottom, to obtain a sol gel. The mol ratio of each component in the sol gel is SiO 2:Al2O3:NaOH:HMI:H2 O=22:0.44:2.2:4.4:660. And carrying out subsequent preparation by using the same preparation conditions based on the preparation step of example 1, and finally preparing the high-crystallinity two-dimensional MWW zeolite molecular sieve.
Example 5]
The preparation method of the two-dimensional MWW zeolite molecular sieve of the embodiment is based on the specific preparation step same as that of the embodiment 1, and the concentration of hexagonal boron nitride in the two-dimensional hexagonal boron nitride dispersion liquid prepared in the step S1 is replaced by 0.0015mg/mL from 0.006mg/mL, specifically as follows:
25mg of commercial hexagonal boron nitride powder (PT 110) and 20mL of hexamethyleneimine (98%) are added into a reaction vessel, stirred for 30min at 400r/min, uniformly mixed to obtain a mixed solution, ultrasonic treatment is carried out on the mixed solution, hexagonal boron nitride is peeled off from the liquid phase, the ultrasonic power is 400W, the frequency is 40KHz, the time period is 10h, and the temperature of an ultrasonic instrument is kept constant at 20 ℃ in the ultrasonic process. After the ultrasonic treatment is finished, transferring the mixed solution of hexagonal boron nitride and hexamethyleneimine after the ultrasonic treatment into a 50mL centrifuge tube, centrifuging at 10000rpm for 10 minutes, taking supernatant, centrifuging at 10000rpm again for 10 minutes, taking supernatant, obtaining a two-dimensional hexagonal boron nitride dispersion liquid, putting the dispersion liquid into a 20mL glass bottle, and putting the glass bottle into a vacuum drying oven for standby, wherein the concentration of hexagonal boron nitride in the dispersion liquid is 0.0015mg/mL. And subsequent preparation was performed using the same preparation conditions based on the preparation procedure of example 1, to finally prepare a two-dimensional MWW zeolite molecular sieve.
Example 6 ]
The preparation method of the two-dimensional MWW zeolite molecular sieve in the embodiment is based on the specific preparation steps same as those in the embodiment 1, and the hydrothermal crystallization time in the step S3 is replaced by 4 days from 10 days, and specifically comprises the following steps:
And subpackaging the aged sol gel into a stainless steel reaction kettle with 25mL polytetrafluoroethylene as a lining, transferring the stainless steel reaction kettle into a dynamic rotary oven, carrying out hydrothermal crystallization for 4 days at the rotating speed of 25rpm and at the temperature of 150 ℃, and then taking out and naturally cooling the sol gel to obtain a crystallized product. And subsequent preparation was performed using the same preparation conditions based on the preparation procedure of example 1, to finally prepare a two-dimensional MWW zeolite molecular sieve.
Comparative example 1]
The preparation method of the two-dimensional MWW zeolite molecular sieve of the comparative example comprises the following steps:
Step S1, adding 28.2675g of deionized water into a 100mL reactor, adding 0.2532g of flaky sodium hydroxide, stirring and dissolving for 5 minutes, controlling the rotating speed to be 500rpm, adding 0.2360g of sodium metaaluminate powder, stirring and dissolving for 5 minutes at the rotating speed of 500rpm, adding 1.25g of hexamethyleneimine, stirring and mixing uniformly to obtain a clear solution, and stirring for 30 minutes at the rotating speed of 500 rpm. Then, an aqueous silica sol solution of 40% by mass was slowly added dropwise to the solution through a dropping funnel at a rate of 1mL/min, and aged for 2 hours with vigorous stirring at 800rpm until there was no solid deposit at the bottom, to obtain a sol gel. The mol ratio of each component in the sol gel is SiO 2:Al2O3:NaOH:HMI:H2 O=22:0.44:3.3:4.4:660.
In this comparative example 1, the two-dimensional hexagonal boron nitride dispersion was not added during the preparation, and the subsequent preparation steps were the same as step S3 of example 1, to finally prepare a two-dimensional MWW zeolite molecular sieve.
Comparative example 2]
The preparation method of the two-dimensional MWW zeolite molecular sieve of the comparative example comprises the following steps:
Step S1, adding 25mg of commercial mica powder and 5mL of hexamethyleneimine (98%) into a reaction container, stirring for 30min at 400r/min, uniformly mixing to obtain a mixed solution, carrying out ultrasonic treatment on the mixed solution, carrying out liquid phase mica stripping, wherein the ultrasonic power is 400W, the frequency is 40KHz, the duration is 10h, and keeping the temperature of an ultrasonic instrument constant at 20 ℃ in the ultrasonic process. After the ultrasonic treatment is finished, transferring the mixed solution of mica and hexamethyleneimine after the ultrasonic treatment into a 50mL centrifuge tube, centrifuging at 10000rpm for 10 minutes, taking supernatant, centrifuging at 10000rpm again for 10 minutes, taking supernatant to obtain a two-dimensional mica dispersion, placing the dispersion into a 20mL glass bottle and placing the glass bottle into a vacuum drying box for standby, wherein the concentration of mica in the dispersion is 0.006mg/mL.
And S2, adding 28.2675g of deionized water into a 100mL reactor, adding 0.2532g of flaky sodium hydroxide, stirring and dissolving for 5 minutes, controlling the rotating speed at 500rpm, adding 0.2360g of sodium metaaluminate powder, stirring and dissolving for 5 minutes at 500rpm, adding 1.25g of mica dispersion prepared in the step S1, stirring and mixing uniformly to obtain a clear solution, and stirring for 30 minutes at 500 rpm. Then, an aqueous silica sol solution of 40% by mass was slowly added dropwise to the solution through a dropping funnel at a rate of 1mL/min, and aged for 2 hours with vigorous stirring at 800rpm until there was no solid deposit at the bottom, to obtain a sol gel. The mol ratio of each component in the sol gel is SiO 2:Al2O3:NaOH:HMI:H2 O=22:0.44:3.3:4.4:660.
Step S3, the specific procedure of step S3 in this comparative example is the same as in example 1, and finally a two-dimensional MWW zeolite molecular sieve is prepared.
In this comparative example, based on the specific preparation procedure of example 1, mica was replaced with hexagonal boron nitride, and the subsequent preparation procedure was the same as step S3 of example 1, finally preparing a two-dimensional MWW zeolite molecular sieve.
Comparative example 3]
The preparation method of the two-dimensional MWW zeolite molecular sieve of the comparative example comprises the following steps:
Step S1, adding 25mg of commercial hexagonal boron nitride powder (PT 110) and 5mL of aniline (99%) into a reaction container, stirring for 30min at 400r/min, uniformly mixing to obtain a mixed solution, carrying out ultrasonic treatment on the mixed solution, carrying out liquid phase stripping on hexagonal boron nitride, wherein the ultrasonic power is 400W, the frequency is 40KHz, the duration is 10h, and the temperature of an ultrasonic instrument is kept constant at 20 ℃ in the ultrasonic process. After the ultrasonic treatment is finished, transferring the mixed solution of hexagonal boron nitride and aniline after the ultrasonic treatment into a 50mL centrifuge tube, centrifuging at 10000rpm for 10 minutes, taking supernatant, centrifuging at 10000rpm again for 10 minutes, taking supernatant to obtain a two-dimensional hexagonal boron nitride dispersion, placing the dispersion into a 20mL glass bottle, and placing the glass bottle into a vacuum drying box for standby, wherein the concentration of hexagonal boron nitride in the dispersion is 0.006mg/mL.
In this comparative example, based on the specific preparation procedure of example 1, the structure directing agent was replaced with aniline from hexamethyleneimine, and the subsequent preparation procedure was the same as both step S2 and step S3 of example 1, to finally obtain a two-dimensional MWW zeolite molecular sieve.
Comparative example 4]
The preparation method of the two-dimensional MWW zeolite molecular sieve of the comparative example comprises the following steps:
Step S1, adding 28.2675g of deionized water into a 100mL reactor, adding 0.2532g of flaky sodium hydroxide, stirring and dissolving for 5 minutes, controlling the rotating speed to be 500rpm, adding 0.2360g of sodium metaaluminate powder, stirring and dissolving for 5 minutes at the rotating speed of 500rpm, adding 1.25g of hexamethyleneimine, adding 0.025g of hexagonal boron nitride powder (PT 110), stirring and mixing uniformly to obtain a clear solution, and stirring for 30 minutes at the rotating speed of 500 rpm. Then, an aqueous silica sol solution of 40% by mass was slowly added dropwise to the solution through a dropping funnel at a rate of 1mL/min, and aged for 2 hours with vigorous stirring at 800rpm until there was no solid deposit at the bottom, to obtain a sol gel. The mol ratio of each component in the sol gel is SiO 2:Al2O3:NaOH:HMI:H2 O=22:0.44:3.3:4.4:660.
In this comparative example, a two-dimensional hexagonal boron nitride dispersion was not prepared and used at the time of preparation, hexagonal boron nitride powder and hexamethyleneimine were directly added at the time of preparation, and the subsequent preparation steps were the same as step S3 of example 1, to finally prepare a two-dimensional MWW zeolite molecular sieve.
XRD spectra and morphology data were obtained for the two-dimensional MWW zeolite molecular sieves prepared in examples 1-6 and comparative examples 1-4, respectively, and the specific data are shown in Table 1.
TABLE 1 XRD spectra and morphology data for two-dimensional MWW zeolite molecular sieves
In Table 1, "-" indicates that zeolite has a structure of interpenetrated growth, and performance index cannot be measured.
As can be seen from Table 1, the high-crystallinity two-dimensional MWW zeolite molecular sieves prepared by the preparation method of the present invention in examples 1-3 each have (300), (500) characteristic peaks. Meanwhile, the prepared two-dimensional MWW zeolite molecular sieves with high crystallinity have regular hexagonal structures, the larger transverse dimension is 500-1000 nm, and the two-dimensional MWW zeolite molecular sieves have higher transverse-longitudinal ratio.
In examples 4 to 6, although hexagonal boron nitride was also used as a template for epitaxially growing a two-dimensional zeolite, the two-dimensional MWW zeolite molecular sieves prepared at a two-dimensional hexagonal boron nitride dispersion concentration of 0.0015mg/mL, a hydrothermal crystallization period of 4 days, and an basicity of oh—: sio2=0.1 did not have (300), (500) characteristic peaks, respectively.
Further, in comparative examples 1 and 2, hexagonal boron nitride was not used, in comparative example 3, hexagonal boron nitride was used and aniline was used as a structure directing agent, in comparative example 4, hexagonal boron nitride powder and hexamethyleneimine were directly added to prepare the two-dimensional MWW zeolite molecular sieves prepared by the preparation methods of comparative examples 1 to 4, the characteristic peaks of (300) and (500) were not present, and the prepared two-dimensional MWW zeolite molecular sieves were all of an interpenetrated growth structure.
Effects and effects of the examples
As is clear from comparison of example 1 and example 2, when preparing a thin layer two-dimensional hexagonal boron nitride dispersion, different stripping solvents affect the stripping effect, and in example 1, using hexamethyleneimine as an organic structure directing agent as a stripping solvent for h-BN, a thin layer h-BN was successfully stripped and a two-dimensional hexagonal boron nitride dispersion with a concentration of 0.006mg/mL was obtained, and in example 2, deionized water was used as a stripping solvent for h-BN, a two-dimensional hexagonal boron nitride dispersion with a concentration of 0.030mg/mL was obtained. Therefore, in this example, the use of hexamethyleneimine and water as the stripping solvent for the two-dimensional hexagonal boron nitride provides a superior stripping effect, and a thin layer of two-dimensional hexagonal boron nitride dispersion can be successfully stripped. Further, when HMI is selected as a stripping reagent, a large amount of HMI adsorbs the surface of the h-BN, so that the quick epitaxial growth of the formed silicon aluminum tetrahedron on the h-BN template is guided by the HMI in the initial crystallization stage;
According to comparison of the embodiment 1 and the embodiment 3, the average transverse dimension of the two-dimensional MWW zeolite molecular sieve prepared in a dynamic crystallization mode is 50-500 nm, the dynamic crystallization mode can promote migration and mass transfer of silica-alumina species in an accelerating sol, and is favorable for obtaining thin-layer two-dimensional MWW zeolite with uniform particle size distribution, the two-dimensional MWW zeolite molecular sieve prepared in a static crystallization mode is larger in transverse dimension, but uneven in particle size distribution and obviously increased in zeolite layer thickness, the average thickness is 25nm, the average transverse dimension of the prepared MWW zeolite is 1000nm, and the transverse-longitudinal ratio is 40. Therefore, the difference of hydrothermal crystallization modes can influence the transverse dimension and the transverse-longitudinal ratio of the prepared two-dimensional MWW zeolite molecular sieve, and the transverse dimension of the zeolite becomes larger but the longitudinal direction becomes thicker under the static crystallization condition.
As is evident from comparison of example 1 and example 4, in the preparation system of this example, alkalinity affects the formation of short chain polymers of silicon and aluminum, and in a low alkali system, the increase in alkalinity increases the number of nuclei in the initial gel, promoting crystallization process, but the particle size decreases. When the alkalinity is OH < - > SiO 2 =0.15, the average transverse dimension of the prepared two-dimensional MWW zeolite molecular sieve is 500nm, the transverse-longitudinal ratio is 50, the two-dimensional MWW zeolite molecular sieve has a complete hexagonal structure and (300) and (500) characteristic peaks, when the alkalinity is OH < - > SiO 2 =0.1, the average transverse dimension of the prepared two-dimensional MWW zeolite molecular sieve is 1000nm, the transverse-longitudinal ratio is 100, but the two-dimensional MWW zeolite molecular sieve has a broken structure and does not have (300) and (500) characteristic peaks. Therefore, the alkalinity in the system can influence the structure and the size of the prepared two-dimensional MWW zeolite molecular sieve, and when the alkalinity is prepared under the condition of OH < - > SiO 2 =0.1, the structure is not a complete regular hexagon although the transverse-longitudinal ratio is increased, and the (300) and (500) characteristic peaks of XRD are not provided.
According to comparison of the embodiment 1 and the embodiment 5 and the embodiment 6, the two-dimensional MWW zeolite molecular sieve with the regular hexagonal structure can be prepared by taking hexagonal boron nitride as a template for epitaxially growing the two-dimensional zeolite, but the concentration of the two-dimensional material dispersion liquid and the hydrothermal crystallization time length can influence the synthesis result, and the two-dimensional MWW zeolite molecular sieve with high crystallinity, larger transverse dimension and larger transverse-longitudinal ratio can be obtained only under the preparation condition that the concentration of the two-dimensional material dispersion liquid is 0.005 mg/mL-0.06 mg/mL and the hydrothermal crystallization time length is 7-14 days.
According to comparison of example 1 and comparative examples 1 to 4, only under the preparation method of this example, by using hexamethyleneimine as an organic structure directing agent as a stripping solvent for hexagonal boron nitride, the thin layer hexagonal boron nitride obtained by stripping is beneficial to guiding the rapid epitaxial growth of the silicon aluminum tetrahedron formed by the hexamethyleneimine on the hexagonal boron nitride template in the initial stage of crystallization, and finally, the two-dimensional MWW zeolite molecular sieve with regular hexagonal structure, larger transverse dimension and high transverse-longitudinal ratio and high crystallinity can be successfully prepared.
In summary, according to the two-dimensional MWW zeolite molecular sieve with high crystallinity and the preparation method thereof, which are related to the embodiment, a thin layer two-dimensional material dispersion liquid is obtained by a liquid phase stripping method, and then the two-dimensional MWW zeolite molecular sieve with high crystallinity can be obtained after the dispersion liquid and zeolite synthesis raw materials are mixed and aged and then subjected to hydrothermal crystallization and heating growth for a certain time.
In this example, according to the principle of lattice symmetry matching, a two-dimensional MWW zeolite with consistent c-axis orientation was epitaxially grown using hexagonal boron nitride as a template. Compared with the interpenetrated and grown zeolite structure obtained by the traditional direct synthesis method, the two-dimensional MWW zeolite molecular sieve which is in epitaxial growth in the embodiment is of a flat structure with consistent orientation, has a thin layer thickness of 2.5-15 nm, a large transverse dimension of 500-1000 nm and a high transverse-longitudinal ratio.
The two-dimensional MWW zeolite molecular sieve prepared by the embodiment has high crystallinity, the two-dimensional MWW zeolite obtained by an epitaxial growth method has a regular planar hexagonal structure and good structural integrity, the two-dimensional MWW zeolite molecular sieve not only has characteristic peaks of the traditional MWW zeolite, but also has sharp and strong characteristic peaks of the MWW zeolite (300) and (500) in an XRD spectrum, and the two-dimensional MWW zeolite with high in-plane crystallinity is obtained by epitaxial growth by taking hexagonal boron nitride as a template and lattice symmetry matching, has a complete framework structure, fewer defects of silicon-aluminum species and good stability and crystallinity.
Meanwhile, the high-crystallinity two-dimensional MWW zeolite molecular sieve prepared by the epitaxial growth method in the embodiment has high diffusion rate and selectivity for xylene molecules due to good crystallinity and skeleton opening degree, the diffusion rates of o-xylene and p-xylene in the two-dimensional MWW zeolite molecular sieve at room temperature are respectively 43 times and 203 times of that of a conventional molecular sieve MCM-22, and the selectivity of the two-dimensional MWW zeolite for o-xylene/p-xylene calculated according to an ideal solution adsorption theory is 10 times of that of MCM-22. Therefore, the high-crystallinity two-dimensional MWW zeolite molecular sieve prepared by the method has wide application prospect in the field of catalysis and gas separation.
The above embodiments are preferred examples of the present invention, and are not intended to limit the scope of the present invention.
Claims (7)
1. The preparation method of the two-dimensional MWW zeolite molecular sieve with high crystallinity is characterized by comprising the following steps of:
Step S1, adding powder of a two-dimensional material into a reaction container, then dropwise adding an organic structure directing agent, uniformly mixing to obtain a mixed solution, sequentially carrying out ultrasonic treatment and centrifugal treatment on the mixed solution, and then taking supernatant to obtain a thin-layer two-dimensional material dispersion liquid after liquid phase stripping;
S2, preparing a solution from the thin-layer two-dimensional material dispersion liquid, deionized water, an alkali metal source and an aluminum source, slowly adding a silicon source into the solution, stirring for dissolution, and aging to obtain sol gel;
step S3, after hydrothermal crystallization of the sol-gel, obtaining a reaction product, washing, centrifuging and drying the reaction product in sequence to obtain the high-crystallinity two-dimensional MWW zeolite molecular sieve,
Wherein in the step S1, the two-dimensional material is hexagonal boron nitride or molybdenum sulfide,
The organic structure directing agent is hexamethyleneimine,
The concentration of the two-dimensional material contained in the thin-layer two-dimensional material dispersion liquid is 0.005 mg/mL-0.06 mg/mL, the transverse dimension of the two-dimensional material is 0.5 mu m-3 mu m, the thickness is 10nm-30nm,
In the step S2, the ageing treatment time is 1-6 h, in the sol-gel, the molar ratio of the silicon source to the aluminum source to the alkali metal source to the structure directing agent to the deionized water is 22:0.2-1.5:3.3-6.5:2-10:400-1000,
In the step S3, when the hydrothermal crystallization is carried out, the crystallization temperature is 120-180 ℃ and the crystallization time is 7-14 days.
2. The method for preparing a high-crystallinity two-dimensional MWW zeolite molecular sieve according to claim 1, characterized in that:
in the step S1, the ultrasonic treatment lasts for 6-12 hours, the rotating speed during centrifugal treatment is 8000-10000 rpm, and the time is 10-30 min.
3. The method for preparing a high-crystallinity two-dimensional MWW zeolite molecular sieve according to claim 1, characterized in that:
wherein in the step S2, the alkali metal source is sodium hydroxide or potassium hydroxide,
The aluminum source is sodium metaaluminate, aluminum isopropoxide, aluminum chloride or aluminum sulfate octadecanoate,
The silicon source is silica sol water solution, water glass or white carbon black.
4. The method for preparing a high-crystallinity two-dimensional MWW zeolite molecular sieve according to claim 1, characterized in that:
wherein in the step S2, the dropping speed of the silicon source is 0.5mL/min-1.5mL/min,
And stirring and dissolving at room temperature for 1-3 hours under the rotating speed of 400-800 r/min.
5. The method for preparing a high-crystallinity two-dimensional MWW zeolite molecular sieve according to claim 1, characterized in that:
In step S3, the hydrothermal crystallization is dynamic crystallization or static crystallization, and the dynamic crystallization is performed at a rotation speed of 15rpm to 30 rpm.
6. The method for preparing a high-crystallinity two-dimensional MWW zeolite molecular sieve according to claim 1, characterized in that:
wherein in the step S3, during washing and centrifuging, centrifuging for 3min to 5min at a rotating speed of 3000rpm to 5000rpm, washing with deionized water, repeating the operation for 3 to 4 times until the upper layer solution after centrifuging becomes clear,
And (3) drying at a constant temperature in a vacuum drying oven at 50-100 ℃ for 12-24 hours during drying treatment.
7. A two-dimensional MWW zeolite molecular sieve with high crystallinity, which is characterized in that the two-dimensional MWW zeolite molecular sieve with high crystallinity is prepared by the preparation method of the two-dimensional MWW zeolite molecular sieve with high crystallinity according to any one of claims 1 to 6,
The high-crystallinity two-dimensional MWW zeolite molecular sieve is of a hexagonal platy structure, the transverse dimension is 500-1000 nm, and the thickness is 2.5-25 nm.
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| CN102602957B (en) * | 2012-04-13 | 2013-10-30 | 华东师范大学 | Preparation method for mordenite with high Si/Al ratio and small crystal particle |
| CN103922296B (en) * | 2014-04-30 | 2015-10-28 | 辽宁大学 | A kind of spherical boron nitride and application thereof |
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| CN117208926B (en) * | 2023-09-12 | 2025-07-15 | 复旦大学 | High-crystallinity two-dimensional MWW zeolite molecular sieve and preparation method thereof |
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2023
- 2023-09-12 CN CN202311173825.9A patent/CN117208926B/en active Active
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2024
- 2024-09-11 WO PCT/CN2024/118297 patent/WO2025055948A1/en active Pending
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| Epitaxial Growth of Two-Dimensional MWW Zeolite;Hongbin Li et al.;《J.Am.Chem.Soc.》;20240316;第146卷;第8520-8527页 * |
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