GB2595204A

GB2595204A - Metal organic framework material

Info

Publication number: GB2595204A
Application number: GB2003447.6A
Authority: GB
Inventors: Ghita Oana; Chen Binling; Davies Richard
Original assignee: University of Exeter
Current assignee: University of Exeter
Priority date: 2020-03-10
Filing date: 2020-03-10
Publication date: 2021-11-24
Also published as: GB202003447D0; WO2021180564A1; GB2593555A; GB202010047D0

Abstract

A MOF material is described comprising a polymer material upon a surface of which MOF crystals are located. In a preferred embodiment, the MOF crystals are formed in-situ on the polymer surface. The polymer surface should be capable of forming chemical bods with the ligands of the MOF. Preferably the material is in powder or granulated form. The polymer is preferably chosen from Polyamide-12, polypropylene and polyaryletherketones. Preferred MOFs for use in the invention are ZIF-8, MIL-125, MOF-5, HKUST-1, MIL-100, MOF-74 or UIO-66. The composite material may be used in an additive manufacturing process and is preferably used to form porous structures. The material may be made by combining a metal salt, an alcoholic solution of an appropriate ligand, and the polymer and allowing the MOF crystals to form on the surface of the polymer.

Description

METAL ORGANIC FRAMEWORK MATERIAL

This invention relates to a metal organic framework (MOF) material, and in particular to a MOF material that is suitable for use in the fabrication of products using additive manufacturing techniques.

Additive manufacturing techniques are in increasingly wide use in the fabrication of products. The techniques allow the fabrication of products by adding up material layers by layers as opposed to conventional manufacturing techniques. Additive manufacturing thus allows the manufacture of complex products.

A known additive manufacturing technique (powder bed fusion) involves laying down a layer of material from which a product is to be fabricated, and by laser melting or sintering the parts of the powder layer that are form part of the product By repeating this process a number of times, a finished product can be built up. In use, the material from which the product is to be fabricated must be capable of being laser sintered. Typical materials used in this method include a number of polymeric and metallic materials.

Some MOF materials are advantageous in that they are capable of adsorbing significant quantities of carbon dioxide (CO2), hydrogen (H2) and other gases. However, the incorporation of MOF materials into products is difficult, and they are unsuitable for use directly in traditional additive manufacturing methods of the type outlined hereinbefore. It is known to dry mix certain MOF materials with polymer materials suitable for use in additive manufacturing processes, and to subsequently fabricate products by additive manufacturing using the mixture, but such techniques have the disadvantages that the MOF materials may be non-uniformly distributed within the product, and fully embedded into the polymers, hence reducing the active sites of MOF materials. Therefore, this can negatively impact upon the performance of the product.

It is an object of the invention to provide a MOF material suitable for use in such applications and in which at least some of the disadvantages associated with known materials are overcome or are of reduced effect. Another object of the invention is to provide a method of manufacture of the MOF material. It is another object of the invention to provide a product incorporating such a MOF material.

According to a first aspect of the invention there is provided a MOF material comprising a polymer material upon a surface of which MOF crystals are located.

The MOF crystals are preferably nucleated and grown in situ upon the polymer material. The polymer material preferably takes the form of a powder or granular material and is preferably suitable for use in an additive manufacturing technique.

By growing MOF crystals upon a polymer material, and in particular a polymer material that is suitable for use in the fabrication of products using additive manufacturing techniques, it will be appreciated that MOF crystals may be relatively uniformly distributed, or more uniformly distributed within the fabricated product.

The polymer material conveniently comprises Polyamide 12. However, the invention is not restricted in this regard, and other polymer materials may be used. By way of example, the polymer material may take the form of polyaryletherketones (PAEKs) or polypropylene (PP). These materials represent just example materials that may be used in accordance with the invention, and other polymer materials may be used.

The MOF crystals are conveniently of ZIF-67. However, other MOF crystals that may be used without departing from the scope of the invention. By way of example, suitable MOF crystals include ZIF-8, MIL-125, MOF-5, HKUST-1, MIL-100(Fe), MOF-74(Zn) and Ui0-66. Again, these merely represent example materials that may be used in accordance with the invention and it will be appreciated that other materials may be used.

It is thought that in order to promote the nucleation and growth of MOF crystals upon the surface of the polymer material, the surface of the polymer should have a roughness that allows enhanced attachment of the MOF crystals thereto. Alternatively, or additionally, the organic ligands of the MOFs should be compatible with the polymer material to enhance bonding therebetween, for example to promote the formation of hydrogen bonds therebetween.

It will be appreciated that as the MOF material of the invention takes the form of MOF crystals located upon the surface of a polymer material, the material can be used in the fabrication of products using additive manufacturing techniques in much the same manner as if the polymer material alone were being used in the fabrication of such products. The use of the MOF material may result in the CO2 adsorption properties of the product being considerably enhanced as compared to products fabricated using just the polymer material.

The invention further relates to a method of manufacture of the MOF material described hereinbefore, the method comprising the steps of dissolving an organic ligand material in a liquid solvent to form a solution, adding a polymer material to the solution, adding a metal ion containing material to the solution, allowing the organic ligand material and the metal ion containing material to form MOF crystals, the MOF crystals nucleating and growing upon the surface of the polymer material, filtering powders from the solution and drying the powders.

The dried powders take the form of the polymer material, upon the surface of which MOF crystals have formed, and so take the form of the above described MOF material.

The process may include a further step of locating the dried powders in a further MOF based solution, to promote the growth of additional MOF crystals upon the material. The process may also include a further step of locating a laser sintered product manufactured using the material in a further MOF based solution, to promote the growth of additional MOF crystals on the surface of the product.

Depending upon the nature of the desired MOF crystals, the organic ligand may take the form of, for example, methylimidazole, terephthalic acid, 1,4-benzenedicarboxylic acid, 1,3,5-benzenetricarboxylic acid, 2,5-dioxide-1,4-benzenedicarboxylate. The solvent may comprise water, or alternatively could comprise methanol, dimethylformamide, trimethylamine or ethanol. The metal ion may be, for example, Co', Zn2, Tizt CU2+ or Fe". It will be appreciated that the nature of the metal ion, organic ligand, solvent and polymer used need to be selected in such a manner as to be compatible with one another and to result in the formation of the desired MOF crystals.

The invention further relates to a product fabricated by using the above described MOF material in an additive manufacturing process. The product may include built-in and size-controlled pores, ranging from micrometer to millimeter. It will be appreciated that such a structure is advantageous in that it is of large effective surface area. Where manufactured from the MOF material described hereinbefore which is of enhanced gas adsorbing capability, it will be appreciated that by providing the product with an increased effective surface area, additional enhancements in the gas adsorbing properties of the product may be achieved.

The invention will further be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagram illustrating steps in the method for manufacture of a MOF material in accordance with an embodiment of the invention; Figure 2 is a series of views illustrating the MOF material manufactured using the method of Figure 1; Figure 3 illustrates a product manufactured using the material of Figure 2; and Figures 4 to 7 are views, similar to Figure 2, at a range of different levels of magnification, illustrating several different MOF materials in accordance with embodiments of the invention.

Referring firstly to Figure 1, steps in a method of manufacture of a MOF material 20 in accordance with an embodiment of the invention are illustrated. The method shown in Figure 1 is intended for use in the manufacture of a MOF material 20 in the form of ZIF-67 crystals 22 located upon the surface of Polyamide 12 powder granules 24. Whilst the method illustrated in Figure 1 relates to the manufacture of this specific material, it will be appreciated that by substitution of different materials, and making appropriate consequential modifications to the process, substantially the same process may be used in the manufacture of a number of other similar MOF materials.

As illustrated, the method involves dissolving an organic ligand material in the form of Methylimidazole (MIM) 10 in distilled water 12 to form a solution 14. A quantity of polymer material in the form of granules 24 of PA2200 (polyamide 12) 16 is added to the solution 14, and gentle mixing of the solution 14 is undertaken. Next a metal ion containing material, in this case cobalt nitrate hexahydrate 18, is added to the solution 14, and mixing of the solution for a period of 24 hours is undertaken. During this time, nucleation and growth of MOF crystals 22, in this case ZIF-67 crystals, upon the polymer granules 24 takes place. The solid polymer granules 24 with ZIF-67 crystals 22 located on the surfaces thereof are then removed from the solution by filtration, and are washed. They are then dried by placing them in an oven at a temperature of 80°C for several hours.

Figure 2 is a series of images showing (a) the granules 24 prior to the formation of the MOF crystals 22 thereon, (b) the surface of the granules 24 under a higher level of magnification, (c) the granules 24 after the formation of the MOF crystals 22 thereon, and (d) the surface of the granules 24 after the formation of the MOF crystals 22 under a higher level of magnification. Comparing Figure 2(d) with Figure 2(b), the presence of the MOF crystals 22 on the surface of the granules 24 is readily apparent, and it is clear from Figure 2(d) that the MOF crystals 22 are reasonably uniformly distributed upon the surface of the granules 24.

The MOF material 20 manufactured in this manner may then be used in the fabrication of products using a traditional additive manufacturing technique. By way of example, a powder bed based, laser sintering technique may be used. However, this represents just one example of an additive manufacturing method or technique by which a product may be fabricated using the MOF material 20, and it will be appreciated that the invention is not restricted in this regard but rather encompasses the use of the MOF material 20 in the fabrication of products of a range of designs using any suitable additive manufacturing technique.

In one example, the MOF material manufactured using the method described hereinbefore may be used in the fabrication of a product 26 of the form illustrated in Figure 3. In this arrangement, the product 26 is of generally cubic form, having a series of passages 28 formed therein with the result that the product effectively includes a series of hollow voids, each of which communicates with the exterior of the product 26, resulting in the product 26 being of enhanced effective surface area. By fabricating the product 26 from the above described MOF material which is of enhanced CO2 adsorbing properties, and by designing the product in such a manner that it is of enhanced effective surface area, it will be appreciated that the product may form an effective CO2 adsorbing structure. By way of example, compared to a normal polymer material, the MOF material of the invention may have a CO2 capacity that is, for example, 4 to 7 times that of a typical polymer material. The MOF material 20 may be used in the fabrication of a range of products, for example for use in carbon capture applications and the like.

By substitution of the polyamide 12 polymer material for another polymer, it will be appreciated that a number of other forms of MOF material 20 may be manufactured. By way of example, the polymer material could take the form of polyaryletherketones (PAEKs), polypropylene (PP) or the like. Similarly, by substitution of the methylimidazole organic ligand material for a different organic ligand material, substituting the metal ion material for a different metal ion material, and appropriate selection of the solvent, MOF materials 20 including a range of other MOF crystals 22 may be formed. The following table provides an indication of a number of MOF materials 20 that may be fabricated using the method of the invention.

Figures 4 to 7 are views illustrating certain of the above MOF materials 20 under a range of magnifications, clearly demonstrating that MOF materials 20 manufactured using a range of different polymer material granules 24 and upon which MOF crystals 22 of a range different materials can be formed through the use of the invention.

The particle size distribution, results of powder rheology tests and thermal analysis have shown that the MOF material 20 is suitable for use in additive manufacturing techniques in substantially the same manner as the base polymer material.

Not only is the MOF material 20 advantageous in that it permits the fabrication of products in such a manner that the MOF crystals are substantially uniformly disbursed therein, but the material is also advantageous in that the MOF crystals 22 are anchored to the powder granules ri.,>\4% \\;k 1/4*kSk\ r-*s, ny?: ^*N * N Wa's \+*A *k\: NS\ St*ft.

\%& *> S** *

N

'' ,*'.\\\ kS * tA* N**"*** ** CS'',.*<, 24 and so are relatively easy to handle. Risks associated with airborne dispersal of the MOF crystals, in use, can thus be reduced or avoided.

Whilst specific embodiment of the invention are described hereinbefore, it will be appreciated that a wide range of modifications and alterations may be made to the MOF material, the method of manufacture thereof and the products manufactured using the material without departing from the scope of the invention as defined by the appended claims.

Claims

CLAIMS: 1. A MOF material comprising a polymer material upon a surface of which MOF crystals are located.
2. A material according to Claim 1, wherein the MOF crystals are nucleated and grown in situ upon the polymer material.
3. A material according to Claim 1 or Claim 2, wherein the polymer material takes the form of a powder or granular material.
4. A material according to any of the preceding claims, wherein the polymer material is suitable for use in an additive manufacturing technique.
5. A material according to any of the preceding claims, wherein the polymer material comprises Polyamide 12, polyaryletherketones (PAEKs), or polypropylene (PP).
6. A material according to any of the preceding claims, wherein the MOF crystals are of ZIF-67, ZIF-8, MIL-125, MOF-5, HKUST-1, MIL-100(Fe), MOF-74(Zn) or Ui0-66.
7. A material according to any of the preceding claims, wherein in order to promote the nucleation and growth of MOF crystals upon the surface of the polymer material, the surface of the polymer has a roughness that allows enhanced attachment of the MOF crystals thereto.
8. A material according to any of the preceding claims, wherein the organic ligands of the MOFs are compatible with the polymer material to enhance bonding therebetween.
9. A method of manufacture of a MOF material, the method comprising the steps of dissolving an organic ligand material in a liquid solvent to form a solution, adding a polymer material to the solution, adding a metal ion containing material to the solution, allowing the organic ligand material and the metal ion containing material to form MOF crystals, the MOF crystals nucleating and growing upon the surface of the polymer material, filtering powders from the solution and drying the powders.
10. A method according to Claim 9, further including a further step of locating the dried powders in a further MOF based solution, to promote the growth of additional MOF crystals upon the material.
11. A method according to Claim 9 or Claim 10, wherein the organic ligand takes the form of methylimidazole, terephthalic acid, 1,4-benzenedicarboxylic acid, 1,3,5-benzenetricarboxylic acid, or 2,5-dioxide-1,4-benzenedicarboxylate.
12. A method according to any of Claims 9 to 11, wherein the solvent comprises water, methanol, dimethylformamide, trimethylamine or ethanol.
13. A method according to any of Claims 9 to 12, wherein the metal ion comprises Co2*, zn2+, CU2+ or Fe3+.
14. A product fabricated by using the MOF material of any of Claim 1 to 8 in an additive manufacturing process.
15. A product according to Claim 14, and including one or more hollows, with passages provided to provide communication between the hollows defined by the product and the exterior thereof.