Crystalline membranes
In certain aspects, the invention features methods for forming crystalline membranes (e.g., a membrane of a framework material, such as a zeolite) by inducing secondary growth in a layer of oriented seed crystals. The rate of growth of the seed crystals in the plane of the substrate is controlled to be comparable to the rate of growth out of the plane. As a result, a crystalline membrane can form a substantially continuous layer including grains of uniform crystallographic orientation that extend through the depth of the layer.
1. A method of forming a film, the method comprising:
obtaining a layer of oriented seed crystals; and
growing the oriented seed crystals to form a film defining a surface, wherein the seed crystals growth rate parallel to the surface is substantially the same as their growth rate normal to the surface,
wherein growing the seed crystals comprises exposing the layer of oriented seed crystals to a solution that comprises a first structure directing agent.
2. The method of claim 1 , wherein the solution is an aqueous solution.
3. The method of claim 1 , further comprising forming the seed crystals using a seed structure directing agent.
4. The method of claim 3 , wherein the first structure directing agent is the same as the seed structure directing agent.
5. The method of claim 1 , wherein the oriented seed crystal layer is obtained by disposing seed crystals on a surface of a substrate.
6. The method of claim 5 , further comprising applying a coupling agent to the surface of the substrate before disposing the seed crystals wherein the coupling agent bonds to the substrate surface and to the seed crystals.
7. The method of claim 6 , wherein the coupling agent covalently bonds to the substrate surface and to the seed crystals.
8. The method of claim 1 , wherein the layer of oriented seed crystals is substantially a monolayer.
9. The method of claim 1 , wherein the seed crystals comprise a framework material.
10. The method of claim 9 , wherein the framework material is a zeolite.
11. The method of claim 1 , wherein the seed crystals are disc-shaped.
12. The method of claim 11 , wherein each seed crystal has a first crystallographic axis and for a majority of the seed crystals the first crystallographic axes are substantially parallel to each other.
13. The method of claim 12 , wherein the first crystallographic axis is the b-axis.
14. The method of claim 1 , wherein during the growth of the oriented seed crystal layer, the seed crystals growth rate parallel to the surface is between about 0.5 and two times the growth rate normal to the surface.
15. The method of claim 1 , wherein during the growth of the seed crystals, substantially no crystal nucleation occurs in the solution or on a surface of the seed crystals.
16. A method of forming a film, the method comprising:
disposing anisotropic seed crystals on a surface of a substrate, wherein each seed crystal has a short axis; and
exposing the seed crystals to a solution to grow the seed crystals, the solution comprising a structure directly agent,
wherein the growth rate of each seed crystal along its short axis is substantially the same as the growth rate along another axis.
17. The method of claim 16 , wherein the seed crystals form an oriented seed crystal layer on the substrate surface.
18. The method of claim 17 , wherein for a majority of the seed crystals, the short axis is oriented substantially orthogonal to the substrate surface.
19. The method of claim 16 , wherein the seed crystals are exposed to the solution for sufficiently long to form a substantially continuous layer of the seed crystal material.
20. An article comprising:
a porous substrate having a surface; and
a layer of a framework material bound to the surface,
wherein the framework material layer is substantially continuous, and comprises a plurality of crystal grains that extend through the depth of the layer such that a lateral dimension of adjacent crystal grains is substantially the same at different depths through the layer and grain boundaries between adjacent crystal grains are oriented substantially perpendicular with respect to the surface.
21. The article of claim 20 , wherein the framework material is a zeolite.
22. The article of claim 20 , wherein the framework material is a porous framework material.
23. The article of claim 22 , wherein the porous framework material comprises channels that run through the depth of the layer.
24. The article of claim 20 , wherein the crystalline grains have an oriented crystallographic axis.
25. The article of claim 24 , wherein the oriented crystallographic axis is the b-axis.
26. The article of claim 20 , wherein an average ratio of the layer thickness to the crystalline grains' maximum size parallel to the substrate surface is less than about two.
27. The article of claim 20 , wherein the layer is substantially intergrown.
28. The article of claim 20 , wherein the framework material has an MFI structure.
29. The article of claim 20 , wherein the framework material is covalently bound to the substrate surface.
30. The article of claim 20 , wherein the article is in the form of a membrane.
31. An article comprising:
a substrate having a surface; and
a layer of a framework material disposed on the surface,
wherein the article has a para-xylene permeance of at least about 1,000×10− 10 mol/m 2 sPa and a para-xylene to ortho-xylene separation factor of at least about 100:1.