Production method of zeolite film in which one axis is completely vertically oriented, using steam under synthetic gel-free condition

Abstract

Provided are a method for preparing a thin film or a thick film, including: a first step of providing a porous substrate capable of supplying silicon; a second step of applying zeolite seed crystals onto the surface of the porous substrate; a third step of coating the seed crystals-applied porous substrate with an aqueous solution containing a structure-directing agent; and a fourth step of forming and growing a film from the seed crystals by the secondary growth above a temperature at which moisture inside the seed crystals-applied porous substrate prepared in the third step can form steam, and a film prepared by the method. The film manufacturing method of the present invention is a simple manufacturing process, and thus has high reproducibility and high throughput. Since a synthetic gel is not used and a solution is used, the unnecessary consumption of materials, environmental pollution, and waste of a synthetic gel can be prevented while not necessitating drying and washing of a film.

Claims

1. A method for producing a film, the method comprising the steps of: (1) providing a porous substrate capable of supplying silicon; (2) applying zeolite seed crystals to the surface of the porous substrate; (3) coating the porous substrate, having the seed crystals applied thereto, with an aqueous solution containing a structure-directing agent, which does not contain a silicon source; and (4) forming and growing a film from the seed crystals by a secondary growth at or above a temperature at which moisture in the porous substrate, having applied thereto the seed crystals and prepared in step (3), is capable of forming steam.

2. The method of claim 1, wherein the material of the porous substrate capable of supplying silicon is an amorphous porous material.

3. The method of claim 1, wherein the material of the porous substrate capable of supplying silicon is porous silica.

4. The method of claim 1, wherein the porous substrate in step (1) is swollen with water.

5. The method of claim 1, wherein the seed crystals and the formed film are made of zeolite or zeotype molecular sieve.

6. The method of claim 5, wherein the zeolite or the zeotype molecular sieve has an MFI structure.

7. The method of claim 5, wherein the zeolite or the zeotype molecular sieve is selected from the group consisting of ZSM-5, silicalite, TS-1, AZ-1, Bor-C, boralite C, encilite, FZ-1, LZ-105, monoclinic H-ZSM-5, mutinaite, NU-4, NU-5, TSZ, TSZ-III, TZ-01, USC-4, USI-108, ZBH, and ZKQ-1B.

8. The method of claim 1, wherein the size of the seed crystals is greater than the size of pores and voids of the porous substrate so that the seed crystals lie flat on the surface of the porous substrate.

9. The method of claim 1, wherein the silicon-containing seed crystals in step (2) are arranged on the porous substrate so that one or more or all of the a-, b- and c-axes of the seed crystals are oriented according to a predetermined rule.

10. The method of claim 9, wherein the seed crystals in step (2) are arranged in a manner such that all the a-axes of the seed crystals are oriented parallel to one another, or all the b-axes of the seed crystals are oriented parallel to one another, or all the c-axes of the seed crystals are oriented parallel to one another, or according to a combination thereof.

11. The method of claim 10, wherein the seed crystals in step (2) are arranged such that the a-, b- or c-axes are oriented perpendicular to the substrate surface.

12. The method of claim 9, wherein the seed crystals, one or more or all of the a-, b- and c-axes of which have been oriented according to the predetermined rule, form a monolayer on the substrate in step (2).

13. The method of claim 1, wherein the seed crystals in step (4) are two-dimensionally connected to one another by the secondary growth from the seed crystal surface while they vertically grow three-dimensionally, thereby forming the film.

14. The method of claim 1, wherein the formed film has a thickness of 100 nm to 500 nm.

15. The method of claim 1, wherein the structure-directing agent used in step (3) is tetrapropylammonium hydroxide (TPAOH), tetraethylammonium hydroxide (TEAOH), tetramethylammonium (TMA), tetrabutylammonium (TBA), or a mixture of two or more thereof.

16. The method of claim 1, wherein the structure-directing agent used in step (3) is a material inducing only the secondary growth from the surface of the seed crystals but not capable of inducing crystal nucleation on the surface of the seed crystals.

17. The method of claim 1, wherein the seed crystals are ordered porous materials.

18. The method of claim 9, wherein the seed crystals are applied to the porous substrate such that at least the b-axes are oriented according to the predetermined rule, and the film, formed in an area in which the orientations of the b-axes of the adjacent seed crystals are the same, has either a channel continuously extending in an axial direction parallel to the substrate surface or a channel extending in an axial direction perpendicular or inclined with respect to the substrate surface.

19. The method of claim 1, wherein step (3) and step (4) are repeated at least twice.

Description

DESCRIPTION OF DRAWINGS

(1) FIG. 1 schematically shows MFI crystals having a structure-directing agent inserted therein.

(2) FIG. 2 shows SEM images of anisotropic coffin-shaped silicalite-1 crystals and anisotropic leaf-shaped silicalite-1 crystals and the crystal axes thereof. The left SEM image shows coffin-shaped silicalite-1 crystals, and the right SEM image shows anisotropic leaf-shaped silicalite-1 crystals.

(3) FIG. 3 is an electron micrograph (an image viewed from the top) of a glass plate having silicalite-1 seed crystals attached thereto using a rubbing method (Korean Patent No. 0789661), in which the b-axes of the attached seed crystals are oriented perpendicular to the glass plate, but the a- and c-axes are oriented randomly.

(4) FIG. 4 is a set of SEM images of silicon wafers having micro-pattern depressions formed thereon using photoresist (PR) such that all the crystal axes can be uniformly oriented while each of the a-, b- and c-axes of the seed crystals can be oriented perpendicular to the wafer surface.

(5) FIG. 5 is a schematic process view showing a film production method according to one embodiment of the present invention.

(6) FIG. 6A shows an SEM image and XRD pattern of a crystal monolayer of silicalite-1 particles, the b-axes of which have been oriented perpendicular to a porous SiO.sub.2 substrate.

(7) FIG. 6B shows an SEM image and XRD pattern of a thin film formed by the secondary growth using a porous substrate having the silicalite-1 crystal monolayer of FIG. 6A according to one embodiment of the present invention.

(8) FIG. 7 is a set of SEM images of films formed by the secondary growth from silicalite-1 seed crystals, the b-axes of which were oriented perpendicular to porous silica (SiO.sub.2) substrates, by performing a steaming reaction at 190 C. for various times using a TPAOH-containing aqueous solution according to the same embodiment as shown in FIG. 6B.

(9) FIG. 8 is a set of SEM images of films formed by the secondary grown from silicalite-1 seed crystals, the b-axes of which were oriented perpendicular to porous silica (SiO.sub.2) substrates, using aqueous solutions containing various concentrations of TPAOH by performing a steaming reaction at 190 C. for 48 hours.

(10) FIG. 9 is a set of SEM images of films formed by the secondary growth from silicalite-1 seed crystals, the b-axes of which were oriented perpendicular to porous silica (SiO.sub.2) substrates, using an aqueous solution containing TPAOH and TEAOH and a steaming reaction at 190 C. for various times.

(11) FIG. 10A is an SEM image of films formed by the secondary growth from silicalite-1 seed crystals, the b-axes of which were oriented perpendicular to a glass substrate, using an aqueous solution containing TPAOH and TEAOH and a steaming reaction at 190 C. for 48 hours; FIG. 10B is an SEM image of films formed by the secondary growth from silicalite-1 seed crystals, the b-axes of which were oriented perpendicular to a silicon wafer, using an aqueous solution containing TPAOH and TEAOH and a steaming reaction at 190 C. for 48 hours. When the glass substrate was used (FIG. 10A), secondary growth did not easily occur.

(12) FIG. 11 is a set of SEM images of silicalite membranes (images B to D) formed by the secondary growth of silicalite nanoparticles (image A) having a size of 800 nm on porous silica (SiO.sub.2) substrates (surface particle size: 500-600 nm) and a steaming reaction at 190 C. for various times. The structure-directing agent used is an aqueous solution containing TPAOH and TEAOH.

(13) The size of the seed crystals is similar to the size scale of particles forming the porous substrate surface, and thus a secondary membrane, the crystal axes of which have been oriented randomly, is formed. Accordingly, only when the average particle size of seed crystals is 2-3 m, the seed crystals can lie flat on a porous substrate, and thus at least one axis of the seed crystals can be oriented perpendicular to the substrate, and a secondary membrane, at least one crystal axis of which has been oriented perpendicular to the substrate, can be formed from the seed crystals.

(14) FIG. 12A is an SEM image of a porous silica substrate (surface particle size: 500-600 nm); FIG. 12B is an SEM image of a smooth surface after rubbing 70 nm SiO.sub.2 beads; FIG. 12C is an SEM image of a film formed by secondary growth using an aqueous solution containing TEAOH and TPAOH and a steaming reaction at 190 C. for 48 hours; and FIG. 12D is an XRD pattern of the film shown in FIG. 12C. From FIG. 12D, it can be seen that no new crystals were formed.

(15) FIG. 13 is a graphic diagram showing the void area (%) of zeolite films (SL membranes) as a function of react ion time, when the zeolite films were produced by secondary growth in steam at 190 C. using different structure-directing agents (TEAOH, TPAOH+TEAOH, and TPAOH) without using a gel-type silicon source, according to the present invention. Void area % means a portion of the substrate, on which zeolite is not located. When the aqueous solution containing the TPAOH structure-directing agent was used, the zeolite film grew fastest, and the growth rate of the zeolite film was faster in the order of use of the TPAOH+TEAOH structure-directing agent-containing aqueous solution and use of the TEAOH structure-directing agent-containing aqueous solution.

(16) The left photograph of FIG. 14 shows a randomly oriented MFI zeolite thin film produced by a conventional method of growing a zeolite film using an MFI synthesis gel. It can be seen that fluorescence was observed in cracks, because the cracks occurred in the calcining step for removal of TPAOH during the production process. On the other hand, the right photograph shows a film, the crystal axis orientations of which have been maintained uniformly, produced by the method of the present invention without using a synthesis gel. In this case, no fluorescence was observed, because no crack occurred and the film grew uniformly (observed by Plan-Apochromat 20/0.8 M27, zoom: 1.0, mater gain: 585, laser: 488 nm, 2.6%).

(17) FIG. 15 shows that a zeolite thin film, one axis of which has been oriented vertically, can be grown into a 200 nm thin film using steam under synthesis gel-free conditions according to the method of the present invention.

(18) FIG. 16 is a set of SEM images showing the results of observing the growth of a film as a function of time, when zeolite seed crystals were applied to a molded material (that is a porous substrate capable of supplying silicon according to the present invention) obtained by filling amorphous silica particles into a mold and compressing the filled particles, and were then subjected to secondary growth using an aqueous solution containing the TPAOH structure-directing agent.

(19) FIG. 17 is a set of SEM images showing that silica beads supply silicon for the growth of seed crystals while being etched during a streaming reaction, when zeolite seed crystals were placed on a molded material (that is a porous substrate capable of supplying silicon according to the present invention) obtained by filling 50 nm silica (SiO.sub.2) beads into a mold and compressing the filled beads, and were then subjected to secondary growth using a steaming reaction.

(20) FIG. 18 is a set of SEM images showing silicalite (SL) films formed on silica particle supports by secondary growth using a TPAOH TEACH structure-directing agent-containing aqueous solution and a steaming reaction at different reaction temperatures for different reaction times. (a) 160 C. for 8 hr, (b) 175 C. for 8 hr, (c) 190 C. for 8 hr, and (d) 190 C. for 18 hr. Scale bar: 5 m.

(21) FIG. 19 is a set of SEM images showing silicalite (SL) films formed on silica particle supports by secondary growth using a TPAOH structure-directing agent-containing aqueous solution and a steaming reaction at different reaction temperatures for different reaction times. (a) 160 C. for 8 hr, (b) 175 C. for 8 hr, (c) 190 C. for 8 hr, and (d) 190 C. for 18 hr. Scale bar: 5 m.

(22) FIG. 20 is a set of SEM images showing silicalite (SL) films on silica particle supports by secondary growth using aqueous solutions containing various concentrations (0.01M (a), 0.02M (b), 0.04M (c), and 0.05M (d)) and a steaming reaction at 190 C. for 48 hours.

(23) FIG. 21 is a set of SEM images showing silicalite films formed on a glass support (a), a cleaned silicon wafer (b) and an amorphous SiO.sub.2-coated silicon wafer by secondary growth using an aqueous solution containing a TPAOH+TEAOH structure-directing agent and a steaming reaction at 190 C. for 48 hours. Scale bar: 5 m.

MODE FOR INVENTION

(24) Hereinafter, the present invention will be described in further detail with reference to examples. It will be obvious to those skilled in the art that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

(25) Scanning Electron Microscope (SEM) Analysis

(26) Platinum/palladium was coated on a produced thin film to a thickness of about 15 nm and imaged by a scanning electron microscope (Hitachi S-4300 FE-SEM) to obtain an SEM image.

(27) X-Ray Powder Diffraction (XRD) Analysis

(28) In order to examine the crystal orientations of thin films produced in the following examples, X-ray powder diffraction patterns were obtained by an X-ray diffractor (Rigaku diffractor D/MAX-1C, Rigaku) using CuK X-rays.

Example 1: Synthesis of Seed Crystals

(29) Experimental Materials

(30) TPAOH 35% (Alfa), TPAOH 1M (Sigma-Aldrich), (NH.sub.4).sub.2SiF.sub.6 98% (Sigma-Aldrich), and tetraethylorthosilicate (TEOS 98%, Acros-Organic).

Example 1-1: Anisotropic Coffin-Shaped Silicalite-1 Crystals

(31) 22.5 g of TEOS was added to a PP bottle containing 247.7 mL of DDW, 22.5 mL of TPAOH and 37.2 g of ethylene glycol (EG) to prepare a gel. The mixture was stirred for 24 hours to form a clear gel, and then 6.168 mL of TEACH was added thereto and stirred for 12 hours. The obtained clear gel had a final molar composition of 1 TEOS/0.15 TPAOH/0.1 TEACH/4 EtOH/100 H.sub.2O/4 EG. After aging, the gel was filtered through Whatman Grade No. 2 filter paper and transferred into a Teflon-lined autoclave equipped with a clean stirring bar. The autoclave was sealed, heated by jacket heater at 150 C. and stirred with a magnetic stirrer at 500 rpm. After a hydrothermal reaction for 12 hours, the autoclave was cooled in tap water. The clean solution in the upper layer was removed by decantation, thereby obtaining a solid product. The solid product was washed with a large amount of DDW and dried at 100 C. for 24 hours, thereby obtaining coffin-shaped silicalite-1 seeds having a size of abc=2.6 m1.2 m5.0 m (see FIG. 2).

Example 1-2: Anisotropic Leaf-Shaped Silicalite-1 Crystals

(32) The reaction conditions described in the paper Angew. Chem. Int. Ed., 2006, 45, 1154-1158 were used. 1.696 g of TEOS was added to a PP bottle containing 1.019 g of Trimer-TPA.sup.3+-3I.sup., 0.295 g of KOH and 34.2 g of DDW to prepare a clean gel. The obtained gel had a final molar composition of 8 TEOS/1 (Trimer-TPA.sup.3+-3I.sup.)/5 KOH/1900 H.sub.2O. After aging for 24 hours, the gel was filtered through Whatman Grade No. 2 filter paper and transferred into a Teflon-lined autoclave. The gel was subjected to a hydrothermal reaction at 175 C. for 24 hours. The product was collected, washed with a large amount of DDW and dried at 100 C. for 24 hours, thereby obtaining leaf-shaped silicalite-1 powder (see FIG. 2).

Example 2: Preparation of Porous Silica Substrate

(33) Silica particles having a size ranged from 50 nm to-500 nm, synthesized according to the method of Stober (W. Stober et al. J. Colloid Interface Sci. 26, 62 1968), were used to prepare a porous silica substrate.

(34) Specifically, 10 g of 350 nm SiO.sub.2 beads and 10 g of 550 nm SiO.sub.2 beads were mixed with each other in a food mixer. 0.5 wt % Na.sub.2SiO.sub.3 aqueous solution (DDW) was added dropwise to the mixed silica beads, which were then ground in a food mixer. 1.8 g of the mixture was placed in a household stainless mold and compressed with a pressure of 150 kgf/cm.sup.2 to prepare a porous silica support. The silica support was sintered at 1,025 C. at a heating rate of 100 C./h for 2 hours. After cooling to room temperature, both surfaces of the porous silica disc were polished with SiC sandpaper (Presi, grit size P800). To make the surface smooth, both surfaces of the porous silica disc were re-polished with SiC sandpaper (Presi, grit size P1200). The diameter and thickness of the porous silica disc were 20 mm and 3 mm, respectively. The porous silica disc had an average pore size of 250 nm and a porosity of 45.5% as measured by a mercury porosimeter.

(35) A drop of DDW was added dropwise to the porous silica disc. Meanwhile, 70 nm silica beads were prepared and sintered at 550 C. for 24 hours. The porous silica disc was rubbed with the sintered 70 nm silica beads until the surface became glossy, whereby large cracks in the porous silica substrate made from the 350 nm beads were filled with the sintered beads. The resulting porous silica substrate having a smooth surface was dried overnight at room temperature and sintered in a muffle furnace at 550 C. for 8 hours. The temperature was increased to 550 C. for 8 hours and decreased to room temperature for 4 hours. An acetone solution of epoxy resin (10 wt %) was spin-coated on the porous silica substrate at 3,000 rpm for 15 seconds and cured at 80 C. for 30 minutes. The epoxy coating functions to prevent seed crystals from being randomly inclined by cracks of the porous substrate surface when the seed crystals are to be arranged later on the porous substrate surface in a predetermined direction.

Example 3: Production of Silicalite Monolayer on Porous Silica Substrate by Rubbing

(36) An ethanol solution of polyethyleneimine (PEI, 0.1 wt %) was spin-coated on the epoxy-coated porous silica substrate at a spin speed of 2,500 rpm for 15 seconds. Silicalite crystals (1.00.51.4 m.sup.3) were placed on the porous silica substrate and rubbed with the finger so that the silicalite crystals were aligned into a monolayer such that the b-axes were completely oriented (FIG. 6A). The silicalite crystal monolayer supported on the porous silica substrate is expressed as SLM/p-SiO.sub.2. The SLM/p-SiO.sub.2 substrate was sintered in air in a tubular furnace at 550 C. for 24 hours, whereby the organic polymer layer was removed and the silicalite monolayer on the porous silica substrate was fixed by formation of SiOSi bonds. The temperature was increased at a rate of 65 C./h and decreased at a rate of 100 C./h.

(37) The sintered SLM/p-SiO.sub.2 substrate was allowed to stand in a chamber at a specific humidity so that the substrate absorbed H.sub.2O in order for steam to be easily formed from moisture of the porous substrate in a subsequent process. The hydrated SLM/p-SiO.sub.2 substrate was soaked in NH.sub.4F solution (0.2 M) for 5 hours in order to remove fine powder that came out of the seed crystals by the rubbing process. The NH.sub.4F-treated SLM/p-SiO.sub.2 substrate was soaked in fresh DDW for 1 hour and dried at room temperature for 24 hours.

Example 4: Formation and Growth of Film by Secondary Growth from Silicalite Seed Crystals, the b-Axes of which have been Completely Oriented

(38) An aqueous solution of a mixture of TEACH (0.00-0.05 M) and TPAOH (0.00-0.05 M) as a structure-directing agent (template) was placed in a plastic beaker.

(39) Specifically, an aqueous solution of TEACH, an aqueous solution of TPAOH and TEACH, and an aqueous solution of TPAOH were used.

(40) The SLM/p-SiO.sub.2 substrate was coated with the above-described structure-directing agent by a slip-coating process in the following manner (see FIG. 5). Specifically, the clean SLM/p-SiO.sub.2 substrate was brought into gentle contact with the structure-directing agent containing solution. Herein, the silicalite monolayer surface was faced downward, and about of the thickness of the porous silica substrate was soaked in the structure-directing agent containing solution. After soaking for 10-20 seconds, the SLM/p-SiO.sub.2 substrate was lifted slowly. This process was repeated three times. After coating with the structure-directing agent, the SLM/p-SiO.sub.2 substrate was kept horizontally in a Petri dish at room temperature for 5 second to remove an excess of water.

(41) Finally, the SLM/p-SiO.sub.2 substrate coated with the structure-directing agent was transferred into a Teflon-lined autoclave in such as manner that the silicalite monolayer faced upward. A secondary growth reaction was performed without adding a synthesis gel or water. Specifically, the closed autoclave was placed in a preheated oven. The reaction was performed at a temperature of from 160 C. to 190 C. for 18-48 hours. After a predetermined reaction time, the autoclave was cooled in tap water.

(42) The resulting film was taken out of the autoclave and allowed to stand at room temperature for from 6 to 12 hours. Next, it was sintered in air at 440 C. for 8 hours to remove the structure-directing agent. Herein, the heating rate was 60 C./h, and the cooling rate was 90 C./h.

(43) An SEM image and XRD pattern of the thin film obtained by secondary growth using the porous SiO.sub.2 substrate having the silicalite crystal monolayer as described above are shown in FIG. 6B.

(44) In addition, the zeolite thin film could be produced as a thin film having a thickness of 200 nm by controlling the reaction time and temperature in the above-described production step (FIG. 15).

Test Example 1: Test for Uniformity of Film Formed by Secondary Growth

(45) A randomly oriented MFI zeolite thin film produced by a conventional method of growing zeolite using an MFI synthesis gel was observed with a fluorescence microscope (Plan-Apochromat 20/0.8 M27, zoom: 1.0, mater gain: 585, laser: 488 nm, 2.6%). In the thin film produced by the conventional method, fluorescence was observed in cracks, because the cracks occurred in the calcining step for removal of TPAOH during the production process.

(46) On the other hand, in the film, the crystal axis orientations of which have been maintained uniformly, prepared by the method of the present invention without using a synthesis gel, no fluorescence was observed, because no crack occurred and the film grew uniformly (FIG. 14).

(47) Although the present invention has been described in detail with reference to the specific features, it will be apparent to those skilled in the art that this description is only for a preferred embodiment and does not limit the scope of the present invention. Thus, the substantial scope of the present invention will be defined by the appended claims and equivalents thereof.