MFI type heteroatom zeolite molecular sieve nanosheet and synthesis method thereof
The preparation of MFI-type heteroatomic zeolite molecular sieve nanosheets from the bottom up method solves the problem of difficulty in preparing single-layer, low-thickness and large-size nanosheets in the prior art, realizes an efficient and simple preparation process, improves the performance and purity of the product, and expands its application in the fields of catalysis and membrane separation.
Patent Information
- Application Number
- CN202411727770.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-28
- Publication Date
- 2025-03-04
AI Technical Summary
The prior art is difficult to prepare MFI-type heteroatomic zeolite molecular sieve nanosheets with single layers, low thickness and large size, and heteroatoms are not easy to be introduced, which limits its application in the fields of catalysis, membrane separation, etc.
The bottom-up method was used to use silicon source, solid metal salt, alkali, template agent and deionized water as starting materials, and the gel was obtained after stirring and aging. After filtration, the MFI type zeolite molecular sieve seed crystals were added and hydrothermal reaction was carried out to prepare heteroatomic zeolite molecular sieve nanosheets.
The MFI-type heteroatomic zeolite molecular sieve nanosheets with single layer, low thickness and large size were successfully prepared, which simplified the operation process, reduced the reaction temperature and time, improved the purity and performance of the product, and met its needs in scientific experiments, membrane preparation and catalysis.
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Figure CN119551685A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of two-dimensional inorganic material synthesis, and specifically relates to an MFI type heteroatom zeolite molecular sieve nanosheet and a synthesis method thereof. Background Art
[0002] Zeolite molecular sieves are a type of crystalline material containing ordered multidimensional pores. In 1756, Swedish mineralogist AFCronstedt discovered zeolites in natural ores, and researchers subsequently discovered their functions and characteristics. There are nearly three hundred types of zeolite molecular sieves currently available. Zeolite molecular sieves have a stable structure, and different types of zeolite molecular sieves have pores of different sizes and types, so they have unique shape selection and catalytic properties, and are therefore widely used in catalysis, adsorption separation and other fields. MFI zeolite molecular sieves are a type of high-silicon or even pure-silicon zeolite molecular sieve widely used in the industrial field. They have straight pores in the b direction, which enables them to have good sieving ability in the b direction. Traditional MFI zeolite molecular sieves are usually coffin-shaped in shape, and the size in the b direction is relatively thick. In order to achieve a better adsorption and separation effect, the preparation of thinner, large-size MFI zeolite nanosheets in the b direction has become a research hotspot in the field of adsorption and separation today. However, compared with conventional zeolites, the morphology of MFI zeolite molecular sieve nanosheets is quite different, and they often have higher requirements on the structure of the template, the synthesis formula, the synthesis conditions, etc. In addition, due to the different hydrolysis rates of different heteroatoms with silicon during the aging process, it is difficult to introduce heteroatoms into MFI zeolite molecular sieve nanosheets, further limiting their application in catalysis, membrane separation and other fields.
[0003] At present, there have been many advances in the synthesis of MFI zeolite nanosheets; there are two main methods for the synthesis of MFI zeolite nanosheets, "top-down" and "bottom-up", but the MFI zeolite molecular sieve nanosheets prepared by the two methods have their own advantages and disadvantages. Among them, for the "bottom-up" method to prepare MFI zeolite nanosheets, the synthesis method is simple, the time is short, the cost is low, and the obtained MFI zeolite molecular sieve nanosheets are large in size, thin in thickness, and have a single crystal structure and are all single-layer. To this end, the present invention provides a method for synthesizing MFI heteroatom zeolite molecular sieve nanosheets from the bottom up, filling the technical gap in the preparation of single-layer heteroatom-containing zeolite molecular sieve nanosheets. Summary of the invention
[0004] The technical problem to be solved by the present invention is to provide an MFI type heteroatom zeolite molecular sieve nanosheet and a synthesis method thereof, so as to solve the technical gap in the prior art for preparing heteroatom zeolite molecular sieve nanosheets, so as to obtain samples of heteroatom zeolite nanosheets for functional molecular sieve separation, catalytic membrane materials and laboratory research.
[0005] The technical solution of the present invention is:
[0006] A method for synthesizing MFI type heteroatom zeolite molecular sieve nanosheets, the preparation method comprising: using a silicon source, a solid metal salt, an alkali, a template agent and deionized water as starting materials, stirring and aging to obtain a gel; filtering the gel, adding MFI type zeolite molecular sieve seed crystals and mixing them evenly; then adding the mixed gel into a hydrothermal kettle for hydrothermal reaction, and finally preparing the heteroatom zeolite molecular sieve nanosheets.
[0007] In the present invention, the heteroatom is one or more of the four elements of aluminum, tin, titanium and gallium.
[0008] Furthermore, the solid metal salt is selected from one or more of tetraethyl titanate, titanium tetrachloride, potassium stannate, tin tetrachloride pentahydrate, and sodium aluminate; preferably, the solid metal salt is selected from tetraethyl titanate, potassium stannate, or tin tetrachloride pentahydrate; further preferably, the heteroatom source is selected from one or more of tetraethyl titanate and tin tetrachloride pentahydrate.
[0009] Furthermore, the silicon source is selected from one or more of colloidal silicon dioxide, tetraethyl silicate, and water glass; preferably, the silicon source is selected from tetraethyl orthosilicate.
[0010] Furthermore, the template agent (SDA) is selected from tetrapropylammonium hydroxide TPAOH, tetrapropylammonium bromide TPABr, dC5, and dC6. Preferably, the template agent is selected from dC5 and dC6; further preferably, the template agent is selected from dC5.
[0011] Furthermore, the base is selected from one or more of NaOH, KOH, and CsOH; preferably, the alkaline solution is selected from KOH solution.
[0012] Furthermore, the MFI type zeolite molecular sieve seed crystals are prepared by the method of the reference document, and the reference document is: Nature, 2017, 543, 690-694. The specific method for preparing the MFI type zeolite molecular sieve seed crystals is: 8.93g of 1.0M TPAOH solution, 0.16g of deionized water, and 0.127g of NaOH are dissolved and dispersed; 2.5g of silicic acid is added as a silicon source. All the mixtures were stirred overnight at room temperature, then allowed to stand at 50°C for 6d, and the solution was injected and filtered with a 0.45μm polypropylene filter membrane; the filtrate was allowed to stand at 100°C for 3d. The MFI crystals were centrifuged at 14500RCF for 1h and then decanted. The solid was redispersed in deionized water by ultrasound, and the washing was repeated twice. The concentration of the MFI type zeolite molecular sieve seed crystals finally obtained was 0.0924g / mL.
[0013] The molar ratio of the heteroatom zeolite molecular sieve nanosheet synthesis formula is: Si:M:SDA:KOH:H2 O=80:x:3.75:20:9500, wherein M is a metal salt, and the range of x is 0.4-2.4, preferably, the range of x is 0.8-1.6.
[0014] Wherein, the reaction temperature of the gel preparation process is 20-100°C, preferably, the reaction temperature of the gel preparation process is 20-60°C.
[0015] Wherein, the hydrothermal reaction temperature is 140-180°C, preferably, the hydrothermal reaction temperature is 140-160°C.
[0016] Wherein, the hydrothermal reaction time is 4-30 days, preferably, the hydrothermal reaction time is 4-21 days.
[0017] The post-treatment method of the heteroatom zeolite molecular sieve nanosheet product is as follows: the pH value of the liquid after the reaction is measured with a pH test paper. After removing the liquid, the final product is centrifuged and washed to neutrality to remove KOH and other soluble substances. Whether the sample needs to be treated with impurities is determined by characterization, and finally the pure sample is dispersed in deionized water.
[0018] Wherein, the structures of the template agents dC5 and dC6 are respectively as shown in the following formula 1 and formula 2;
[0019]
[0020] The preparation method of the heteroatom zeolite molecular sieve nanosheet sample is based on the tin-doped zeolite molecular sieve nanosheet Sn-MFI-NS-50 as an example. The specific operation details of different heteroatom zeolite molecular sieve nanosheets are different, including:
[0021] Step 1: Add 0.1658 g KOH and 0.0589 g SnCl into a 100 mL tetrafluoroethylene reaction vessel. 4 .5H 2 O;
[0022] Step 2, according to the stoichiometry of the heteroatom zeolite molecular sieve nanosheets, weigh out 0.2406 g of the template dC5, and add the powder into the container of step 1;
[0023] Step 3: Use a pipette to add 17.97 mL of deionized water to the solid mixture in step 2, and stir until the solid is completely dissolved;
[0024] Step 4: Take 1.85 mL of tetraethyl silicate with a pipette, add it to the solution in step 3, and continue stirring for 16 hours under open ventilation conditions to obtain a precursor gel;
[0025] Step 5, filtering the precursor gel with a 0.45 μm polypropylene filter membrane to remove insoluble matter, and transferring the precursor gel to a polytetrafluoroethylene liner of a hydrothermal reactor;
[0026] Step 6, adding 28.1 μL of MFI zeolite seed suspension to the precursor gel in step 5 and shaking evenly;
[0027] Step 7, encapsulating the precursor gel of step 6 in a hydrothermal reactor, crystallizing at 140° C. for 4 days, and cooling to room temperature after the reaction is completed;
[0028] Step 9, the pH value of the obtained product is measured with pH test paper, washed to neutrality by centrifugation, and the product is added to a mixed solution of 0.1M KOH and 2M KCl to remove impurities;
[0029] After the impurities of the products in step 10 and step 9 are removed, they are washed by centrifugation until the pH is neutral and dispersed in deionized water.
[0030] Compared with the prior art, the present invention has the following advantages:
[0031] Compared with other artificially synthesized MFI type heteroatom zeolite molecular sieves, the present invention prepares MFI type heteroatom zeolite molecular sieve nanosheets with single layer, low thickness and large size; the preparation method of the present invention has obvious advantages such as simple operation process, short reaction time and low reaction temperature, and the obtained MFI type heteroatom zeolite molecular sieve nanosheets have excellent performance such as high purity proved by various characterizations, which can fully meet the needs in the fields of scientific experiments, membrane preparation, catalysis, etc. The method provides important sample guarantee for the measurement of physical property parameters of MFI type heteroatom zeolite molecular sieve nanosheets, breaking through the technical bottleneck of the existing synthesis of heteroatom zeolite molecular sieve nanosheets. BRIEF DESCRIPTION OF THE DRAWINGS
[0032] Figure 1 SEM images of heteroatom zeolite molecular sieve nanosheets in Examples 1-4; wherein (a)-(f) are Sn-MFI-NS-50, Sn-MFI-NS-100, Ti-MFI-NS-low pH and Ti-MFI-NS-high pH, respectively;
[0033] Figure 2 XRD patterns of heteroatom zeolite molecular sieve nanosheets in Examples 1-4;
[0034] Figure 3 Flow chart of the synthesis of heteroatom zeolite molecular sieve nanosheets in Example 1-2;
[0035] Figure 4 Flow chart of the synthesis of heteroatom zeolite molecular sieve nanosheets in Example 3-4. DETAILED DESCRIPTION
[0036] The present invention will be further described in detail below in conjunction with specific embodiments, but the embodiments of the present invention are not limited thereto. For process parameters not particularly noted, conventional techniques may be used.
[0037] The preparation method of the MFI zeolite molecular sieve seed crystals used in the following examples is as follows: 8.93g of 1.0MTPAOH solution, 0.16g of deionized water, and 0.127g of NaOH are dissolved and dispersed; 2.5g of silicic acid is added as a silicon source. All mixtures are stirred overnight at room temperature, then allowed to stand at 50°C for 6d, and the solution is injected filtered with a 0.45μm polypropylene filter membrane; the filtrate is allowed to stand at 100°C for 3d. The MFI crystals are centrifuged at 14500RCF for 1h and then decanted. The solid is re-dispersed in deionized water by ultrasound, and the washing is repeated twice. The concentration of the MFI zeolite molecular sieve seed crystals finally obtained is 0.0924g / mL.
[0038] Example 1: Synthesis of Sn-MFI-NS-50
[0039] Synthesis method reference Figure 3 , with tetraethyl silicate (Si(OC 2 H 5 ) 4 ) and tin tetrachloride pentahydrate (SnCl 4 ·5H 2 O) were silicon source and heteroatom metal salt, respectively, and heteroatom zeolite molecular sieve nanosheets were prepared by hydrothermal method. 0.1754 g KOH and 0.0589 g SnCl 4 ·5H 2 O was added to a 100 mL polytetrafluoroethylene beaker, 0.2406 g dC5 was added as a template, and then 17.97 mL deionized water was added and stirred until the solid was completely dissolved. 1.85 mL Si(OC 2 H 5 ) 4 , stirring was continued for 16 hours at 25°C, the obtained gel was filtered through a 0.45μm polypropylene filter membrane, and the obtained clear solution was transferred to a 50mL polytetrafluoroethylene hydrothermal kettle, and 28.1μL of MFI zeolite molecular sieve seed suspension was added, and the seed suspension was evenly dispersed in the gel. The gel liquid was encapsulated in a hydrothermal kettle, transferred to an oven and hydrothermally reacted at 140°C for 4 days, cooled and centrifuged to neutral pH to obtain a crude product. In order to remove impurities in the product, the product was dispersed in a mixed solution of 0.1M KOH and 2M KCl and stirred for 24 hours. After the end, it was centrifuged and washed to neutral pH. The obtained product was dispersed in deionized water for characterization and identification. Figure 1 (a) is a scanning electron microscope image of the sample; Figure 2 The XRD of the sample shows that the structure of the sample is consistent with MFI zeolite molecular sieve; the results of ICP-OES prove that Si / Sn is 690.
[0040] Example 2: Synthesis of Sn-MFI-NS-100
[0041] Synthesis method reference Figure 3 , with tetraethyl orthosilicate (Si(OC 2 H 5 ) 4 ) and tin tetrachloride pentahydrate (SnCl 4 ·5H 2 O) were silicon source and heteroatom metal salt, respectively, and heteroatom zeolite molecular sieve nanosheets were prepared by hydrothermal method. 0.1474g KOH and 0.0292g SnCl 4 ·5H 2 O was added to a 100 mL polytetrafluoroethylene beaker, 0.2406 g dC5 was added as a template, and then 17.97 mL deionized water was added and stirred until the solid was completely dissolved. 1.85 mL Si(OC 2 H 5 ) 4 , stirring was continued for 16 hours at 25°C, the obtained gel was filtered through a 0.45μm polypropylene filter membrane, and the obtained clear solution was transferred to a 50mL polytetrafluoroethylene hydrothermal kettle, and 28.1μL of MFI zeolite molecular sieve seed suspension was added, and the seed suspension was evenly dispersed in the gel. The gel liquid was encapsulated in a hydrothermal kettle, transferred to an oven and hydrothermally reacted at 140°C for 4 days, cooled and centrifuged to neutral pH to obtain a crude product. In order to remove impurities in the product, the product was dispersed in a mixed solution of 0.1M KOH and 2M KCl and stirred for 24 hours. After the end, it was centrifuged and washed to neutral pH. The obtained product was dispersed in deionized water for characterization and identification. Figure 1 (b) is a scanning electron microscope image of the sample;
[0042] Figure 2 The XRD of the sample shows that the structure of the sample is consistent with MFI zeolite molecular sieve; the results of ICP-OES prove that Si / Sn is 2700.
[0043] Example 3: Synthesis of Ti-MFI-NS-low pH
[0044] Synthesis method reference Figure 4 , with tetraethyl silicate (Si(OC 2 H 5 ) 4 ) and tetrabutyl titanate (Ti(OC 4 H 9) 4 ) are silicon source and heteroatom metal salt, respectively, and heteroatom zeolite molecular sieve nanosheets are prepared by hydrothermal method. 0.1178g KOH is added to a 100mL polytetrafluoroethylene beaker, 0.2406g dC5 is added as a template, and then 17.97mL deionized water is added, stirred until the solid is completely dissolved, and stored in an ice bath at 0℃. 1.85mL Si(OC 2 H 5 ) 4 and 57 μL Ti(OC 4 H 9 ) 4 Mix and stir for 15 minutes, then gradually add dropwise to the above mixed solution. After complete dropwise addition, place the mixed solution at 25°C and continue stirring for 16 hours. The obtained gel is filtered through a 0.45μm polypropylene filter membrane to obtain a clear solution. The clear solution is transferred to a 50mL polytetrafluoroethylene hydrothermal kettle liner, and 28.1μL of MFI zeolite molecular sieve seed suspension is added. Oscillate to evenly disperse the seed suspension in the gel. Encapsulate the gel liquid in a hydrothermal kettle, transfer to an oven and hydrothermally react at 140°C for 4 days, cool and centrifuge to neutral pH, and disperse the obtained product in deionized water for characterization and identification. Figure 1 (c) is a scanning electron microscope image of the sample; Figure 2 The XRD of the sample shows that the structure is consistent with MFI zeolite molecular sieve; the results of ICP-OES prove that Si / Ti is 440.
[0045] Example 4: Synthesis of Ti-MFI-NS-high pH
[0046] Synthesis method reference Figure 4 , with tetraethyl orthosilicate (Si(OC 2 H 5 ) 4 ) and tetrabutyl titanate (Ti(OC 4 H 9 ) 4 ) are silicon source and heteroatom metal salt, respectively, and heteroatom zeolite molecular sieve nanosheets are prepared by hydrothermal method. 0.1744g KOH is added to a 100mL polytetrafluoroethylene beaker, 0.2406g dC5 is added as a template, and then 17.97mL deionized water is added, stirred until the solid is completely dissolved, and stored in an ice bath at 0℃. 1.85mL Si(OC 2 H 5 ) 4 and 57 μL Ti(OC 4 H 9 ) 4Mix and stir for 15 minutes, gradually add dropwise to the above mixed solution, after complete dropwise addition, place the mixed solution at 25°C and continue stirring for 16 hours, filter the obtained gel through a 0.45μm polypropylene filter membrane, and transfer the obtained clear solution to a 50mL polytetrafluoroethylene hydrothermal autoclave, add 28.1μL of MFI zeolite molecular sieve seed suspension, and oscillate to evenly disperse the seed suspension in the gel. Encapsulate the gel liquid in a hydrothermal autoclave, transfer to an oven and hydrothermally react at 140°C for 4 days, cool and centrifuge and wash until the pH is neutral, and disperse the obtained product in deionized water for characterization and identification. Figure 1 (d) is a scanning electron microscope image of the sample; Figure 2 The XRD of the sample shows that the structure of the sample is consistent with MFI zeolite molecular sieve; the results of ICP-OES prove that Si / Sn is 880.
[0047] Comparative example: Synthesis of pure silica zeolite molecular sieve nanosheets (reference: Nature, 2017, 543, 690-694)
[0048] Tetraethyl orthosilicate (Si(OC 2 H 5 ) 4 ) was used as Si source, and zeolite molecular sieve nanosheets were prepared by hydrothermal method. 0.1120g KOH was added to a 100mL polytetrafluoroethylene beaker, 0.2406g dC5 was added as template, and then 17.97mL deionized water was added and stirred until the solid was completely dissolved. 1.85mL (Si(OC 2 H 5 ) 4 ) was added to the above mixed solution, and the mixed solution was placed at 25°C and stirred for 16 hours. The obtained gel was filtered through a 0.45μm polypropylene filter membrane, and the obtained clear solution was transferred to a 50mL polytetrafluoroethylene hydrothermal kettle, and 28.1μL of MFI zeolite molecular sieve seed suspension was added, and the seed suspension was evenly dispersed in the gel by oscillation. The gel liquid was encapsulated in a hydrothermal kettle, transferred to an oven and hydrothermally reacted at 150°C for 4 days, cooled and centrifuged to neutral pH, and the obtained product was dispersed in deionized water.
[0049] The above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.
Claims
1. A method for synthesizing MFI type heteroatom zeolite molecular sieve nanosheets, characterized in that: Silicon source, solid metal salt, alkali, template and deionized water are used as starting materials, stirred evenly and aged to obtain gel; after filtering the gel, MFI type zeolite molecular sieve seed crystals are added and mixed evenly; the mixed gel is added into a hydrothermal kettle for hydrothermal reaction to prepare heteroatom zeolite molecular sieve nanosheets.
2. The method for synthesizing an MFI type heteroatom zeolite molecular sieve nanosheet according to claim 1, characterized in that: The thickness of the heteroatom zeolite molecular sieve nanosheet is 5-20nm; the solid metal salt is one or more of tetraethyl titanate, titanium tetrachloride, potassium stannate, tin tetrachloride pentahydrate, sodium aluminate and gallium nitrate.
3. The method for synthesizing an MFI type heteroatom zeolite molecular sieve nanosheet according to claim 1, characterized in that: The silicon source is one or more of colloidal silicon dioxide, tetraethyl silicate and water glass.
4. The method for synthesizing MFI type heteroatom zeolite molecular sieve nanosheets according to claim 1, characterized in that: The template agent is one or more of tetrapropylammonium hydroxide TPAOH, tetrapropylammonium bromide TPABr, dC5, and dC6.
5. The method for synthesizing MFI type heteroatom zeolite molecular sieve nanosheets according to claim 1, characterized in that: The base is one or more of KOH, NaOH and CsOH.
6. The method for synthesizing MFI type heteroatom zeolite molecular sieve nanosheets according to claim 1, characterized in that: The substance ratio of the starting materials is Si:M:template:base:H2O=80:0.4-2.4:3.75:20:9500, wherein M is a heteroatom metal salt.
7. The method for synthesizing MFI type heteroatom zeolite molecular sieve nanosheets according to claim 1, characterized in that: The stirring time of the gel is 8-32 hours; the reaction temperature of the gel is 20-60°C.
8. The method for synthesizing MFI type heteroatom zeolite molecular sieve nanosheets according to claim 1, characterized in that: The hydrothermal reaction temperature is 140-160° C.; the hydrothermal reaction duration is 4-21 days.
9. The method for synthesizing MFI type heteroatom zeolite molecular sieve nanosheets according to claim 1, characterized in that: The post-treatment method of the heteroatom zeolite molecular sieve nanosheets is as follows: the pH value of the liquid after the reaction is measured with a pH test paper, after removing the liquid, the final product is centrifuged and washed until the liquid is neutral, the structure is identified by characterization means to determine whether to perform an impurity treatment step, and finally, the heteroatom zeolite molecular sieve nanosheets are dispersed in deionized water.
10. Obtain MFI type heteroatom zeolite molecular sieve nanosheets by the synthesis method described in any one of claims 1 to 9.