Process for preparing aluminum-based metallo-organic networks

Abstract

The invention relates to a method for preparing a metal-organic network (MOF) comprising a step of synthesizing the metal-organic network (MOF) comprising contacting at least one aluminum alkoxide with at least one bidentate organic ligand in the presence of an aqueous solvent, thereby obtaining a colloidal suspension comprising said MOF and an alcohol, and a step of coating a support with said colloidal suspension, thereby depositing a thin layer of said MOF on said support.

Description

Title of the invention: Process for preparing aluminum-based metallo-organic networks. TECHNICAL FIELD OF THE INVENTION

[0001] The present invention belongs to the field of materials chemistry, and more particularly to the field of organometallic chemistry. The present invention relates to a process for preparing aluminum-based metallo-organic networks, comprising in particular a coating step on a support. STATE OF THE ART

[0002] Metal-organic networks, also known as MOFs, are crystalline hybrid porous structures composed of metal nodes (inorganic metal ions) coordinated by organic ligands. Such organic ligands are generally multidentate and coordinate the metal ions through functional groups such as carboxylate or amine groups. The nature of the metal ions and organic compounds has a significant influence on the MOF structure, notably impacting the size and shape of the pores, which in turn affects the material properties. Consequently, there is a wide variety of MOF structures due to the extensive range of combinable metal entities and organic ligands.

[0003] Due to their microporous and / or mesoporous architecture, MOFs are characterized by a large specific surface area, combined with good thermal stability, enabling various applications such as the storage, separation, and controlled release of chemical elements in diverse fields like energy (batteries, supercapacitors, membranes for fuel cells) or healthcare (controlled drug release). These materials are thus attracting increasing interest due to their high modularity and numerous properties.

[0004] Certain aluminum-based MOFs (Al-MOFs), such as MIL-53(A1) and aluminum fumarate, are distinguished by their remarkable moisture stability and are therefore excellent candidates for water vapor adsorption, with demonstrated stability over more than 150 and 4500 adsorption / desorption cycles, respectively. Thus, such MOFs have strong potential in applications requiring humidity control, such as air conditioning, desalination, or atmospheric water harvesting. Furthermore, aluminum-based MOFs can be stored more easily without performance loss due to moisture-induced degradation.

[0005] Moreover, aluminium is one of the most abundant metals and has less toxicity compared to other metals, which is compatible with large-scale industrial production.

[0006] MOF synthesis generally consists of mixing metal salts and organic ligands in a solvent. This is usually carried out via hydrothermal or solvothermal processes, which require a significant energy input (heat) to solubilize the precursors and crystallize the MOF, thus imposing significant constraints on the industrialization of its production. Furthermore, such syntheses require the use of organic solvents such as dimethylformamide (DMF), dimethoxyethane (DME), dimethylacetamide (DMA), or diethylformamide (DEF), which exhibit significant toxicity to humans and the environment. Therefore, MOF syntheses in aqueous media have been developed and are known in the prior art.

[0007] US patent 2012 / 0082864 Al discloses the synthesis of aluminum fumarate in aqueous media. The solvent used is preferably exclusively water, provided that the medium is basic, for example, by adding sodium hydroxide. The metallic precursor used as a reagent is an aluminum salt, in particular aluminum sulfate. This process may also include a step of atomizing the filter cake containing the MOF, which shapes the MOF, resulting in a narrower particle size distribution. The process according to US patent 2012 / 0082864 Al further discloses an optional step of atomizing the filter cake containing the MOF, which shapes the MOF, resulting in a narrower particle size distribution.

[0008] Although the process described in US patent 2012 / 0082864 Al does not require the use of highly toxic organic solvents, it necessarily involves rinsing and filtration steps of the resulting MOF to remove the generated saline byproducts and aluminum salt residues. These rinsing and filtration steps are time-consuming and significantly hinder the scaling up of these processes to industrial levels and the productivity of the synthesis process.

[0009] Thus, there is a considerable need to develop new processes for producing MOFs on an industrial scale, which would not include steps for eliminating co-products by reprocessing solvents. Description of the invention

[0010] In the context stated above, the present invention aims to remedy all or part of the drawbacks of the prior art mentioned above. The inventors were surprised to discover that it is possible to prepare a metal-organic network (MOF) from aluminum alkoxides (also called aluminum alkoxides or aluminum alkyls) in aqueous media, advantageously in that such a synthesis does not generate saline co-products such as sulfates, chlorides, nitrates, which would require filtration and washing steps to extract these co-products from the solvent, and does not require the use of organic solvents. Such a synthesized MOF can be advantageously applied directly by coating onto a substrate to form a thin layer.

[0011] Thus, the invention relates to a process for preparing a metal-organic network (MOF) comprising a step of synthesizing the metal-organic network (MOF) comprising contacting at least one aluminum alkoxide with at least one bidentate organic ligand in the presence of an aqueous solvent, thereby obtaining a colloidal suspension comprising said MOF and an alcohol; and a step of coating a support with said colloidal suspension, thereby depositing a thin layer of said MOF on said support.

[0012] Advantageously, such a preparation process takes place in an aqueous medium and does not require the use of organic solvents, such as dimethylformamide, diethylformamide, dimethyl sulfoxide, or dimethoxyethane, which are known to be toxic and impose particularly burdensome recovery, recycling, or disposal steps for manufacturers. According to a particular embodiment, the aqueous solvent used in the process according to the invention comprises water, preferably consisting of water, for example, tap water or demineralized water. The aqueous solvent, preferably consisting of water, can thus be easily disposed of or recycled, with an optional step of pH neutralization, when the pH is not neutral, by adding a strong acid, for example, sulfuric acid, or a strong base, for example, sodium hydroxide.According to a particular embodiment, the aqueous solvent used in the process according to the invention has a neutral pH, for example between 5 and 9, preferably between 6 and 8, particularly preferably between 6.5 and 7.5. Advantageously, when, at the end of the MOF synthesis step, the pH of the aqueous solvent is neutral, the solvent can be disposed of or recycled without requiring a neutralization step.

[0013] Advantageously, the MOF preparation process according to the invention takes place under pressure and temperature conditions close to ambient. The process according to the invention is thus a gentle synthesis, of the sol-gel (or solution-gelation) type. Such a gentle synthesis is suitable for large-scale industrial production. In a particular embodiment, the MOF synthesis step of the process according to the invention is carried out at a temperature between 20°C and 100°C, preferably between 70°C and 95°C, under stirring.

[0014] The preparation of a MOF from at least one aluminum alkoxide according to the invention is particularly advantageous in that it generates only at least one alcohol in the reaction medium. Such at least one alcohol can be easily removed from the aqueous solvent by evaporation, for example by a distillation step.

[0015] The preparation of a MOF according to the invention may also include a step of activating said MOF by heat treatment, by which the solvent trapped in the porous system of said MOF is removed.

[0016] Advantageously, the MOF preparation process according to the invention does not require filtration or rinsing steps of the synthesized MOF, which would lead to high solvent consumption and significantly impact the productivity of the manufacturing process by increasing its duration. The MOF synthesized in the process according to the invention, in the advantageous form of a colloidal suspension, can therefore be directly coated onto a support, whereby a thin layer of said MOF is deposited on said support.

[0017] Advantageously, such a process does not require the addition of stabilizing agents to the solution, nor a pH adjustment step before coating onto the support.

[0018] The invention also relates to a part comprising a thin layer of a MOF that can be obtained by a process according to the invention. BRIEF DESCRIPTION OF THE FIGURES

[0019] Fig. 1 shows a process for preparing Al-fumarate as described in Example IA. Step 1 shows the reaction of metallic aluminum (Al0) with isopropanol to form aluminum isopropylate (aluminum triisopropoxide). Step 2 shows the reaction of aluminum isopropylate and fumaric acid in aqueous medium to produce aluminum fumarate (Al-fumarate), isopropanol, and water. The reaction products are in the form of a colloidal suspension that can be atomized to separate the solid Al-fumarate (obtained as a powder), water, and isopropanol (solvent). The water and isopropanol can then be separated in a distillation step. The isopropanol thus recovered can be reused in step 1) and the water can be reused as a solvent in step 2).

[0020] Fig. 2 represents an X-ray diffraction spectrum of an Al-fumarate sample (batch A) prepared according to example IA. This spectrum reveals a main peak between 8° < 20 < 12°, as well as several secondary peaks around 15°, 21°, 32° and 42°.

[0021] Fig. 3 represents an X-ray diffraction spectrum of a sample of MIL-110(Al) (batch C) prepared according to example 2A. This spectrum reveals two main peaks around 4° and 8°(20).

[0022] Fig. 4 represents the nitrogen adsorption isotherm at 77 K for the MIL-1llO(Al) batch C sample prepared according to example 2A. The BET specific surface area calculated from this isotherm is 870 m² / g (batch C).

[0023] Fig. 5 represents the X-ray diffraction spectrum of a MIL-16O(A1) lot E sample prepared according to Example 3A. This spectrum reveals a main peak around an angle of 8°, and secondary peaks around angles of 9°, 15° and 22° (20).

[0024] Fig. 6 represents the nitrogen adsorption isotherms at 77 K for a MIL-16O(A1) batch E sample prepared according to example 3A. The BET specific surface area calculated from this isotherm is 830 m² / g (batch E). DETAILED DESCRIPTION OF THE INVENTION

[0025] Definitions:

[0026] The term “metal-organic network” or “MOF” refers to a class of materials composed of coordination polymers made up of metal ions (or metal centers) and organic ligands, thus forming three-dimensional structures with high porosity. The metal ions (or metal clusters) form metal nodes or sites within the material. These ions can originate from various metallic elements of the periodic table, including transition metals such as copper (Cu), zinc (Zn), iron (Fe), nickel (Ni), chromium (Cr), and cobalt (Co); lanthanides such as cerium (Ce) or europium (Eu); actinides such as uranium (U); alkaline earth metals (such as calcium (Ca) and magnesium (Mg)); or post-transition metals such as aluminum (Al) or titanium (Ti).Metal ions can exist in various oxidation states and coordination forms, which influences the geometry of the MOF structure and its functional properties. The combination of metal centers and organic ligands through coordination bonds creates the lattice structure of MOFs, with a characteristic arrangement of lattices and pores. The shapes and sizes of these pores can be adjusted by selecting the metal and ligand, allowing the creation of MOFs with specific characteristics (pore size, surface functionality, stability, etc.) for targeted applications. In particular, a metal-organic lattice according to the present invention is aluminum-based, also designated "A1-MOF".Non-limitingly, an aluminum-based metal–organic network can be Al-Fumarate (Al-Fum), Al-MIL-53-NH2, CAU-1-NH2(A1), CAU-lO(Al), DUT-5, MIL-1O1(A1)-NH2, MIL-1(l-Al), MILA(l), MIL-llO(Al), MIL-16O(A1), MOF-253, PCN-333(A1), MIL-68(A1), . MOF-303(A1), 467-MOF(Al), Al-PMOF, CAU-21(A1), MIL-lOO(Al) or MIL-96(A1). Preferably, an aluminum-based metal–organic network according to the invention can be Al-Fumarate (Al-Fum), MIL-lOO(Al) or MIL-16O(A1).

[0027] By “organic ligands,” we mean organic molecules that bind to metal centers via electron-pair donor groups, typically oxygen, nitrogen, or sulfur atoms in functional groups such as carboxylates, pyridines, imidazoles, or phosphonates. An organic ligand within the meaning of the invention is at least “bidentate,” that is, it has at least two functional groups capable of coordinating with the aluminum metal centers. The organic ligand may, for example, be bidentate (i.e., having two functional groups), tridentate (i.e., having three functional groups), or tetradentate (i.e., having four functional groups).For the purposes of the invention, the organic ligands that can be used are di- and tri-carboxylic acids, i.e. acids comprising respectively 2 or 3 carboxylic acid functions (-COOH); polycarboxylic acids, i.e. acids comprising at least two carboxylic acid functions (-COOH), preferably said polycarboxylic acids are mono-aromatic or non-aromatic; polycarboxylic acids comprising one or more amine groups (-NH2); dicarboxylic acids such as terephthalic acid (BDC or benzene-1,4-dicarboxylic acid), isophthalic acid (or benzene-1,3-dicarboxylic acid) or 2,6-naphthalenedicarboxylic acid. Examples of organic ligands include fumaric acid, furandicarboxylic acid, benzenetricarboxylic acids, benzenetetracarboxylic acids, muconic acid, aspartic acid, and glutamic acid.Preferably, an organic ligand suitable for preparing a MOF according to the invention is fumaric acid, trimesic acid, or furandicarboxylic acid. Such carboxylic compounds are well known to those skilled in the art, who know how to produce them on a large scale. Fumaric acid and furandicarboxylic acid can advantageously be produced from biomass. Fumaric acid may also be preferred due to its lack of toxicity. Conversely, benzenedicarboxylic acids (phthalic acid, isophthalic acid, and terephthalic acid) and polyaromatic acids such as 4,4'-bibenzoic acid or 2,6-naphthalenedicarboxylic acid are preferable to avoid.

[0028] Preferably, an organic ligand that is at least bidentate is fumaric acid, 1,3,5-benzenetricarboxylic acid or 2,5-furandicarboxylic acid.

[0029] The terms "alkoxide," "alcoholate," or "alkoxide" may be used interchangeably and refer to a type of organometallic compound derived from the reaction of an alcohol with an alkali or alkaline earth metal. The formation of the alkoxide also generates hydrogen gas. Alcoholates are characterized by their alkoxyl (OR) group, where the oxygen is covalently bonded to the metal. Consequently, they are considered organic salts of alcohols and, in solution, can act as strong bases. Metal alkoxides are sensitive to moisture and air, in that they can react with water to reform an alcohol and a metal hydroxide. Because of this sensitivity, they are generally handled under an inert atmosphere in anhydrous conditions. In the context of the present invention, alkoxides are limited to aluminum alkoxides. Preferably, alcohol-based alkoxides with fewer than five carbon atoms in their backbone will be considered.Examples of aluminum alkoxides include aluminum methylate, aluminum ethylate, aluminum propylate, aluminum isopropylate, aluminum butylate, aluminum sec-butylate, aluminum isobutylate, aluminum tert-butylate, aluminum 1-pentylate, aluminum 2-pentylate, aluminum 3-pentylate, aluminum sec-pentylate, aluminum isopentylate, aluminum 2-isopentylate, aluminum 2,2-dimethyl-1-propylate, and aluminum tert-pentylate. Preferably, aluminum alkoxides with an associated alcohol having a boiling point below 100°C are preferred (to facilitate the distillation of the alcohol produced during synthesis).Preferably, an aluminium alkoxide usable in a process according to the invention is chosen from aluminium methylate, aluminium ethoxide, aluminium isopropylate, aluminium sec-butylate or aluminium tert-butylate, preferably the aluminium alkoxide is aluminium isopropylate.

[0030] The terms "colloidal solution," "colloidal suspension," or "colloid" refer to a mixture in which very fine particles (on the order of a few nanometers to a few tens or even hundreds of micrometers) of a substance are uniformly dispersed in another medium without dissolving completely. The dispersed particles are also called the dispersed phase, while the medium in which they are dispersed is called the continuous phase or dispersing phase. The particles in a colloidal suspension are small enough to remain suspended in the dispersion medium through physical interactions, and often due to electrical charges on their surface, which prevent their aggregation or sedimentation. The dispersed phase can be in a solid, liquid, or gaseous state. The continuous phase can also be in a solid, liquid, or gaseous state.Thus, there are different types of colloidal suspensions, which can be classified according to the state of the dispersing and dispersed phases. One example is gels, which contain colloidal systems in which the liquid is so tightly bound to the solids that the system is in a semi-solid state, easily deformable but not easily flowable. Colloids are distinct from true solutions, where the dissolved particles (solutes) are molecular in size and cannot be filtered through. a conventional filter, and suspensions, where the particles are large enough to settle. Preferably, the colloidal solution comprises suspended particles smaller than 10 pm, preferably less than 1 pm, particularly preferably less than 750 nm, 500 nm, 250 nm, or 100 nm.

[0031] By "aqueous solvent" is meant a solution in which water acts as the principal solvent. Alcohols, for example, at least one alcohol produced during the synthesis of the MOF according to the invention, are advantageously soluble in water. Preferably, the aqueous solvent is demineralized water (by permutation or distillation), that is, water free of mineral salts, contaminants, and other impurities. The aqueous solvent may also be tap water or reverse osmosis water, that is, water that has been filtered by a reverse osmosis process using a semi-permeable membrane to remove ions and undesirable molecules.

[0032] By "coating" or "coating step" in a process for preparing a MOF according to the invention, we mean all the operations performed to cover the surface of a substrate or part with a uniform layer of colloidal solution prepared during the process according to the invention, comprising a MOF. The coating is carried out by various methods allowing the MOF to be deposited on the desired substrate. By way of example, the coating can be carried out by immersion: The substrate to be coated is immersed in the colloidal solution comprising the MOF, then withdrawn at a controlled speed, and dried so as to allow the solvent to evaporate, leaving a thin layer of MOF on the surface. The coating can also be carried out by centrifugation. In this case, the colloidal solution comprising the MOF is deposited onto the center of the substrate to be coated.Rapid rotation of the substrate allows the solution to spread across it, forming a thin layer thanks to centrifugal force. Coating can also be carried out by spraying. In this case, the colloidal solution is sprayed onto the substrate to be coated, for example, using a sprayer, so as to cover the surface of the substrate evenly. Coating can also be carried out by scraping. In this case, the colloidal solution is applied in excess to the surface of the substrate to be coated. The solution is then spread with a blade to obtain a thin, uniform layer of MOF on the substrate.

[0033] By "drying" or "drying step" in a process according to the invention, one means a process which consists of removing the aqueous solvent so that a solid layer of MOF is formed on the surface of the coated substrate. Such drying can be carried out in various ways, for example under atmospheric pressure conditions.

[0034] By "specific surface area" with reference to a material, for example a MOF prepared by a process according to the present invention, is meant the measure of the total amount of accessible internal surface area per unit mass of material. The specific surface area is Specific surface area is a key indicator of material porosity. It is expressed in m² / g. Specific surface area measurement techniques are well known to those skilled in the art. A preferred method for measuring specific surface area is the BET technique using gas adsorption, such as nitrogen at 77 K (the BET technique, according to Brunauer, Emmett, and Teller). The implementation of such a measurement method is detailed in ISO 9277:2022, based on the recommendations of 1TUPAC published in 2015 in the technical report on gas physisorption, with particular reference to the evaluation of surface area and pore size distribution (THOMMES et al., 2015). The method consists of measuring the amount of gas adsorbed at different pressures and using this data to estimate the total gas-accessible surface area from the analysis of the linear region of the isotherm.

[0035] Method according to the invention:

[0036] A first object of the invention relates to a process for preparing a metal-organic network (MOF) comprising a step of synthesizing the metal-organic network (MOF) comprising contacting at least one aluminum alkoxide with at least one bidentate organic ligand in the presence of an aqueous solvent, thereby obtaining a colloidal suspension comprising said MOF and an alcohol; and a step of coating a support with said colloidal suspension, thereby depositing a thin layer of said MOF on said support.

[0037] The MOF synthesis step in the process according to the invention is advantageously a mild synthesis of the "sol-gel" (solution-gelation) type. This synthesis step therefore takes place under temperature and pressure conditions close to ambient conditions.

[0038] According to a particular embodiment, the MOF synthesis step takes place at a temperature between 20°C and 150°C, preferably between 70°C and 110°C, and even more preferably between 70°C and 100°C. For example, the MOF synthesis step can take place at a temperature of approximately 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, or 110°C. The MOF synthesis step can also take place at a temperature below 100°C; preferably, the MOF synthesis step takes place at a water-alcohol azeotrope temperature corresponding to the composition of the mixture.

[0039] A person skilled in the art knows how to implement laboratory techniques and common industrial synthesis techniques at these temperatures. For example, the MOF synthesis step of the process according to the invention can be carried out in any type of suitable container or reactor. The MOF synthesis step of the process according to the invention can be carried out under reflux, that is to say, the vapors from the heated reaction medium are condensed and fall back into the reaction medium.

[0040] Advantageously, the MOF synthesis step is carried out under stirring, for example, under mechanical stirring, preferably with a TURRAX or ULTRA-TURRAX agitator-disperser. The stirring speed can be chosen according to the viscosity or volume of the reaction medium. For example, the mechanical stirring speed is between 120 rpm and 480 rpm.

[0041] The duration of the MOF synthesis step of a process according to the invention is variable and can be between 4 and 24 hours, for example, between 8 a.m. and 10 p.m., between 10 p.m. and 12 p.m., between 12 p.m. and 2 p.m., between 2 p.m. and 4 p.m., between 4 p.m. and 6 p.m., between 6 p.m. and 8 p.m., between 8 p.m. and 10 p.m., or between 10 p.m. and 12 a.m. Advantageously, the duration of the MOF synthesis step is less than 24 hours.

[0042] The MOF synthesis step of a process according to the invention is advantageously carried out at ambient pressure, i.e. at atmospheric pressure, without deliberate pressure control.

[0043] Advantageously, the MOF synthesis step of a process according to the invention is carried out in an aqueous solvent. According to a particular embodiment, such an aqueous solvent comprises water, preferably consisting of water, for example demineralized water or reverse osmosis water.

[0044] The MOF synthesis step can be carried out in aqueous media, at a neutral pH, for example between 5 and 9, preferably between 6 and 8, particularly preferably between 6.5 and 7.5.

[0045] According to a particular embodiment, the MOF prepared by a process according to the invention is an aluminum-based MOF (Al-MOF). In the context of the invention, the nature of the MOF prepared will depend on the at least one bidentate organic ligand used as a reagent in the synthesis step.

[0046] According to a particular embodiment, said at least one bidentate organic ligand used in a process according to the invention is chosen from di- and tri-carboxylic acids, mono-aromatic or non-aromatic polycarboxylic acids and polycarboxylic acids comprising at least one amine group.

[0047] According to a preferred embodiment, said at least one bidentate organic ligand used in a process according to the invention is selected from fumaric acid, furandicarboxylic acid, benzenetricarboxylic acids, benzenetetracarboxylic acids, muconic acid, aspartic acid and glutamic acid.

[0048] According to an even more preferred embodiment, said at least one bidentate organic ligand is fumaric acid, 1,3,5-benzenetricarboxylic acid or 2,5-furandicarboxylic acid.

[0049] According to a particular embodiment, the MOF prepared by a process according to the invention is aluminum fumarate (Al-fum). In this embodiment, the ligand The only at least bidentate organic compound used as a reagent in the synthesis step is fumaric acid.

[0050] According to a particular embodiment, the MOF prepared by a process according to the invention is MIL-110(Al). In this embodiment, the at least bidentate organic ligand used as a reagent in the synthesis step is 1,3,5-benzenetricarboxylic acid (1,3,5-BTC).

[0051] According to a particular embodiment, the MOF prepared by a process according to the invention is MIL-16O(A1). In this embodiment, the at least bidentate organic ligand used as a reagent in the synthesis step is 2,5-furandicarboxylic acid (2,5-FDCA).

[0052] According to a particular embodiment, the MOF prepared by a process according to the invention is Al-adipate. In this embodiment, the at least bidentate organic ligand used as a reagent in the synthesis step is adipic acid.

[0053] According to a particular embodiment, the MOF prepared by a process according to the invention is MIL-101(Al) or MIL-53(A1). In this embodiment, the at least bidentate organic ligand used as a reagent in the synthesis step is terephthalic acid.

[0054] According to a particular embodiment, the MOF prepared by a process according to the invention is CAU-10. In this embodiment, the at least bidentate organic ligand used as a reagent in the synthesis step is isophthalic acid.

[0055] According to a particular embodiment, the MOF prepared by a process according to the invention is MIL-121(A1). In this embodiment, the at least bidentate organic ligand used as a reagent in the synthesis step is 1,2,4,5-benzenetetracarboxylic acid.

[0056] Advantageously, said at least one aluminum alkoxide (also called aluminum alkyl) used in a process according to the invention is selected from aluminum methylate, aluminum ethoxide, aluminum isopropylate, aluminum sec-butylate, and aluminum tert-butylate. In a particularly preferred embodiment, said at least one aluminum alkoxide is aluminum isopropylate.

[0057] According to a particular embodiment, said at least one bidentate organic ligand and said at least one aluminum alkoxide during the MOF synthesis step of the process according to the invention are supplied in the reaction medium in a stoichiometric molar ratio (ligand: alkoxide) of between 0.4:1 and 1.5:1. According to a preferred embodiment, the stoichiometric ratio (ligand: alkoxide) is 1:1.

[0058] The MOF synthesis step of a process according to the invention, comprising contacting at least one aluminum alkoxide with at least one bidentate organic ligand in the presence of an aqueous solvent, advantageously allows obtaining a colloidal suspension comprising the synthesized MOF and an alcohol. The colloidal suspension may include suspended particles, for example, smaller than 1 pm.

[0059] According to a particular embodiment, the process for preparing an MOF according to the invention may include, prior to the MOF synthesis step, a step for preparing an aluminum alkoxide from metallic aluminum and at least one alcohol.

[0060] The process according to the invention also includes a step of coating a support with said colloidal suspension, whereby a thin layer of said MOF is deposited on said support.

[0061] According to a particular embodiment, the process according to the invention further comprises a post-coating drying step for the substrate. Such a drying step can be carried out at ambient pressure, for example in an oven. Advantageously, such a drying step allows the solvent to be removed and gives the MOF thin layer good adhesion to the substrate. Preferably, such drying at ambient pressure is carried out at a temperature between 60 °C and 100 °C, for example at a temperature of about 80 °C, and can last from 12 to 48 hours, for example 24 hours.

[0062] According to a particular embodiment, the process for preparing a MOF according to the invention may further include an activation step of the MOF. Such an activation step may take place after the drying step and advantageously allows the removal of the solvent (for example, water and / or alcohol) trapped in the porous system of the MOF. Such an activation step may include a heat treatment, for example, a heat treatment under reduced pressure. According to a particular embodiment, the MOF activation step in a process according to the invention comprises a heat treatment at a temperature of 100 °C to 250 °C, preferably from 120 °C to 240 °C, most preferably from 130 °C to 230 °C, and even more preferably from 140 °C to 220 °C. According to a preferred embodiment, the MOF activation step in a process according to the invention includes a heat treatment at a temperature of about 180 °C.

[0063] According to a particular embodiment, the process for preparing a MOF according to the invention does not include a washing step for the synthesized MOF, nor a filtration step. Advantageously, such steps are unnecessary thanks to the process according to the invention, which is carried out in an aqueous medium, without organic solvents, and which does not generate aluminum salt-type co-products.

[0064] The invention also relates to a part comprising a thin layer made of a MOF obtainable by a process according to the invention. According to a particular embodiment, the thin layer of a part according to the invention includes an aluminum-based MOF (Al-MOF). For example, an aluminum-based MOF could be Aluminium-Fumarate (Al-Fum), MIL-100(Al), MIL-160(A1).

[0065] A part or support within the meaning of the invention can be of various kinds. By way of example, such a part can be used in a heat exchanger, in a gas sensor, in a catalytic support, in a filtration membrane, in an electrode or even in any type of composite material.

[0066] The embodiments exemplified below are given only as illustrations and do not in any way constitute a limitation of the present invention.

[0067] Example 1: Preparation of Aluminium fumarate and characterization

[0068] IA. Preparation of Aluminium fumarate by a process according to the invention

[0069] The preparation of Al-fumarate according to the process of the present invention is illustrated in [Fig. 1].

[0070] A batch A of Al-fumarate in an oven is prepared according to the following protocol.

[0071] An aqueous solution of aluminum isopropylate at a concentration of 160 g / L (also called aluminum triisopropoxide) is prepared from an Al-isopropoxide powder (Sigma Aldrich). Alternatively, aluminum isopropylate can be prepared by dissolving metallic aluminum in an aqueous isopropanol solution, as illustrated in [Fig. 1], reaction 1.

[0072] The aluminum isopropylate solution is heated to a temperature of 95 °C under magnetic stirring at 800 rpm. 31.4 g of fumaric acid (Sigma Aldrich) are added to 250 ml of the aluminum isopropylate solution, whereby, after 24 h of reaction, a colloidal suspension is obtained comprising the synthesized Al-fumarate as well as isopropanol, as illustrated in [Fig. 1], reaction 2. The stoichiometric ratio between aluminum isopropylate and fumaric acid is thus 1.38:1.

[0073] The resulting colloidal suspension takes the form of a white, difficult-to-filter liquid gel. This can be used to coat a substrate, for example, a metal plate. For the purpose of characterizing the MOF produced, the colloidal suspension is collected and then dried for 24 hours in an oven at 80°C. The solvent is thus evaporated, and the aluminum fumarate is recovered.

[0074] Such a process for preparing Al-fumarate can thus be described as "zero waste", since the isopropanol co-produced during the synthesis and the aqueous solvent can be easily recycled.

[0075] IB. X-ray diffraction analysis of batches of aluminum fumarate synthesized in IA

[0076] Batch A of MOF synthesized according to Example 1 is characterized by X-ray diffraction (XRD). X-ray diffraction is a well-known technique for Identify the atomic and molecular structure of a MOF. This method makes it possible to determine the precise arrangement of metal ions and organic ligands in space, to verify the purity and homogeneity of the MOF, or to obtain information on the size and geometry of the material's pores.

[0077] This method is implemented in the present example using a diffractometer (D8 ADVANCE, BRUKER). The radiation source is Cu k al and a2 radiation, and the signal is captured using a LYNXEYE detector. The measurement range is 4° < 20 < 80° with a measurement step of 0.02° and a time per step of 0.5 seconds.

[0078] X-ray diffraction analysis of a sample of batch A of Al-fumarate prepared according to Example 1 is shown in [Fig. 2]. This reveals a main peak between 8° < 20° < 12°, as well as several secondary peaks around 15°, 21°, 32° and 42°. Such a diffraction profile corresponds to what is described in the literature for aluminum fumarate, thus validating the preparation process according to the invention.

[0079] IC. Analysis of the specific surface area of ​​the aluminum fumarate synthesized in IA

[0080] Aluminum fumarate synthesized according to Example IA can be characterized by the BET (Brünauer, Emett, and Teller) method to measure its specific surface area. To implement this measurement method, a MINIX instrument (BELSORP) is used to measure the nitrogen adsorption at 77 K of MOF batches synthesized after activation at 150°C under reduced pressure for 12 hours. Those skilled in the art can calculate the specific surface area of ​​a porous solid from a nitrogen adsorption isotherm curve at 77 K, for example, by following the guidelines of the IUP AC technical report on gas physisorption, with particular reference to the evaluation of the surface area and pore size distribution (THOMMES et al., 2015).

[0081] Example 2: Preparation of MIL-1llO(Al) and characterization

[0082] 2A. Preparation of MIL-11O(Al) by a process according to the invention

[0083] A batch C of MIL-110(Al) is prepared according to the following protocol.

[0084] An aqueous solution of aluminum isopropylate (also called aluminum triisopropoxide) at 40 g / L is prepared from an Al-isopropoxide (Sigma-Aldrich) powder. Alternatively, aluminum isopropylate can be prepared by dissolving metallic aluminum in an aqueous isopropanol solution.

[0085] The aluminum isopropylate solution is heated to 90 °C under magnetic stirring at 800 rpm. 0.91 g of 1,3,5-benzenetricarboxylate (1,3,5-BTC, Sigma-Aldrich) is added to 50 mL of the aluminum isopropylate solution, whereby, after 24 h, a colloidal suspension is obtained comprising the synthesized MIL-11O(Al) and isopropanol. The stoichiometric ratio The molar ratio between aluminum isopropylate and 1,3,5-BTC is thus 0.44:1. The resulting colloidal suspension takes the form of a white, difficult-to-filter liquid gel. This can be used to coat a substrate, for example, a metal plate. For characterization purposes, the synthesized MOF can be recovered by oven drying, according to the protocol described in Example IA.

[0086] 2B. X-ray diffraction analysis of MIL-11O(Al) synthesized in 2A

[0087] The MOF MIL-110(Al) lot C synthesized according to Example 2A is characterized by X-ray diffraction (XRD), according to the protocol stated in Example IB.

[0088] X-ray diffraction analysis for this sample is presented in [Fig.3]. This reveals two main peaks around angles of 4.8° and 8.5°, and are in accordance with the literature (Dao, X. et al. Al-Based Coordination Polymer Nanotubes: Simple Preparation, Post-Modification and Application in Fe 3+ Ions Sensing. Dalton Trans. 2017, 46 (16), 5373-5383.).

[0089] 2C. Analysis of the specific surface area of ​​MIL-llO(Al) synthesized in 2A

[0090] The specific surface area of ​​the MIL-110(Al) MOF batch C synthesized according to Example 2A is characterized according to the protocol stated in Example IC. The nitrogen adsorption isotherm at 77 K for batch C of MIL-110(Al) is shown in [Fig. 4]. The specific surface area calculated from the isotherm of batch C of MIL-110(Al) is 870 m² / g. This result is close to the specific surface area reported in the literature for MIL-110(Al), for example, 780 m² / g (Celic et al. New Insight into Sorption Cycling Stability of Three Al-Based MOF Materials in Water Vapor. Nanomaterials 2022, 12(12), 2092).

[0091] Example 3: Preparation of MIL-16O(A1) and characterization

[0092] 3A. Preparation of MIL-16O(A1) by a process according to the invention

[0093] A first batch E of MIL-16O(A1) is prepared and recovered by oven drying according to the following protocol.

[0094] An aqueous solution of aluminum isopropylate (also called aluminum triisopropoxide) at 40 g / L is prepared from an Al-isopropoxide (Sigma-Aldrich) powder. Alternatively, aluminum isopropylate can be prepared by dissolving metallic aluminum in an aqueous isopropanol solution.

[0095] The aluminum isopropylate solution is heated to 90 °C under magnetic stirring at 800 rpm. 1.53 g of 2,5-furandicarboxylic acid (2,5-FDCA, Sigma-Aldrich) is added to 50 mL of the aluminum isopropylate solution, whereby, after 24 h, a colloidal suspension is obtained comprising the synthesized MIL-16O(A1) and isopropanol. The stoichiometric molar ratio between aluminum isopropylate and 2,5-FDCA is thus 1:1. The resulting colloidal suspension is a white, difficult-to-filter liquid gel. This can be used to coat a substrate, for example a metal plate. For characterization purposes, the synthesized MOF can be recovered by oven drying, according to the protocol described in example IA.

[0096] 3B. X-ray diffraction analysis of MIL-16O(A1) synthesized in 3A

[0097] The MIL-16O(A1) MOF batch E synthesized according to example 3A are characterized by X-ray diffraction (XRD), according to the protocol stated in example IB.

[0098] X-ray diffraction analysis of batch E of MIL-16O(A1) prepared according to example 3A is shown in [Fig. 5]. These reveal a main peak around an angle of 8.2°, and secondary peaks around angles of 9.2°, 15° and 23°, in accordance with the literature (Cui, S. et al. Heat Properties of a Hydrophilic Carboxylate-Based MOF for Water Adsorption Applications. Applied Thermal Engineering 2019, 161, 114135. and Solovyeva, M. MIL-160 as an Adsorbent for Atmospheric Water Harvesting. Energies 2021, 14 (12), 3586).

[0099] 3C. Analysis of the specific surface area of ​​MIL-16O(A1) synthesized in 3A

[0100] The specific surface area of ​​the MOF MIL-16O(A1) batch E synthesized according to Example 3A is characterized according to the protocol stated in Example IC. The nitrogen adsorption isotherm at 77 K for batch E of MIL-16O(A1) is shown in [Fig. 6]. The specific surface area calculated from the isotherm of batch E of MIL-16O(A1) is 830 m² / g, and the specific surface area calculated from the isotherm of batch F of MIL-16O(A1) is 760 m² / g. This result is close to the specific surface area that can be found in the literature for MIL-16O(A1), for example 1070 m2 / g (Cadiau et al. Design of Hydrophilic Metal Organic Framework Water Adsorbents for Heat Reallocation. Adv. Mater. 2015, 27 (32), 4775-4780).

Claims

Demands

1. A process for preparing a metal-organic network (MOF) comprising: 1) A step of synthesizing the metal-organic network (MOF) comprising contacting at least one aluminum alkoxide with at least one bidentate organic ligand in the presence of an aqueous solvent, thereby obtaining a colloidal suspension comprising said MOF and an alcohol; 2) a step of coating a support with said colloidal suspension, thereby depositing a thin layer of said MOF on said support.

2. A method for preparing an MOF according to claim 1, wherein the MOF synthesis step is carried out at a temperature between 20°C and 100°C, preferably between 70°C and 95°C, under stirring.

3. A method for preparing a MOF according to any one of claims 1 or 2, wherein the aqueous solvent consists of water.

4. A method for preparing an MOF according to any one of the preceding claims, wherein said at least one aluminum alkoxide is selected from aluminum methylate, aluminum ethylate, aluminum isopropylate, aluminum sec-butylate and aluminum tert-butylate, preferably said at least one aluminum alkoxide is aluminum isopropylate.

5. A method for preparing an MOF according to any one of the preceding claims, wherein said at least one bidentate organic ligand is selected from di- and tri-carboxylic acids, mono-aromatic or non-aromatic polycarboxylic acids, and polycarboxylic acids comprising at least one amine group.

6. A method for preparing a MOF according to claim 5, wherein said at least one bidentate organic ligand is selected from fumaric acid, furanedicarboxylic acid, benzenetricarboxylic acids, benzenetetracarboxylic acids, muconic acid, aspartic acid and glutamic acid, preferably said at least one bidentate organic ligand

7.

8.

9.

10. is fumaric acid, 1,3,5-benzenetricarboxylic acid and 2,5-furandicarboxylic acid. A method for preparing a MOF according to any one of the preceding claims, wherein the colloidal suspension comprises suspended particles of sizes less than 1 µm. A method for preparing a MOF according to any one of the preceding claims, said method further comprising a step of preparing an aluminum alkoxide from metallic aluminum and at least one alcohol. A method for preparing a MOF according to any one of the preceding claims, said method further comprising a step of activating said MOF by heat treatment. Part comprising a thin layer comprising a MOF capable of being obtained by a process as defined in any one of claims 1 to 9.

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