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 as well as an alcohol and a step of recovering the synthesized MOF.

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. PRIOR TECHNIQUE

[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] Document WO 2013 / 050402 A1 relates to a process for preparing a MOF by atomization, in which this atomization step allows both the contacting of metal ions and the organic ligand to synthesize the MOF, and the drying of the latter. Document WO 2017 / 158165 A1 proposes an improvement to the previously described process, in that it includes a step of contacting the metal ions with the organic ligand in a solvent at a temperature between 70°C and 150°C, prior to the atomization step. Even though such processes include an atomization step, they still generate saline by-products requiring reprocessing, for example, filtration steps.

[0010] 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

[0011] 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 alkoxides) in aqueous media, advantageously in that such a synthesis does not generate saline co-products such as sulfates, chlorides, and nitrates, which would require filtration and washing steps at the end to extract said co-products from the solvent, and does not require the use of organic solvents.

[0012] 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 recovering the synthesized MOF.

[0013] 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.

[0014] 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. According to 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.

[0015] 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. According to a particular embodiment, the process according to the invention further comprises a distillation step in which said at least one alcohol produced during the MOF synthesis step is extracted from the aqueous solvent.

[0016] 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.

[0017] 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 recovered directly from it. In a particular embodiment, the recovery step of the synthesized MOF consists of a drying step, by which the synthesized MOF is obtained in the form of a powder, for example, a crystalline powder. Such a drying step may include spray drying, drying in supercritical CO2, drying at ambient pressure (for example, in an oven), or freeze-drying.

[0018] According to a particularly preferred embodiment, the drying step comprises atomization, during which the colloidal suspension comprising the MOF is dispersed as fine droplets, which are dried by circulating a stream of hot gas, for example air or nitrogen. This step advantageously allows obtaining a MOF in the form of solid grains of calibrated sizes, and enabling the size of these grains to be selected by varying the size of the droplets generated during atomization.

[0019] The invention also relates to a metallo-organic network that can be obtained by a process according to the invention. BRIEF DESCRIPTION OF THE FIGURES

[0020] 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).

[0021] 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°.

[0022] Figure 3 shows the nitrogen adsorption isotherms at 77 K for four Al-fumarate samples (batches B1, B2, B3 and B4) prepared according to example IA. The specific surface areas (BET) calculated from these isotherms are 1050 m² / g, 1020 m² / g, 1040 m² / g and 1015 m² / g respectively.

[0023] Fig. 4 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).

[0024] Figures 5A and 5B represent the nitrogen adsorption isotherms at 77 K for two MIL-110(Al) samples prepared according to Example 2A (Figure 5A corresponds to lot C and Figure 5B to lot D). The BET specific surface areas calculated from these isotherms are 870 m² / g (lot C) and 775 m² / g (lot D).

[0025] Fig. 6A and Fig. 6B represent the X-ray diffraction spectra of MIL-16O(A1) samples prepared according to Example 3A (Fig. 6A corresponds to lot E and Fig. 6B corresponds to lot F). These spectra reveal a main peak around an angle of 8°, and secondary peaks around angles of 9°, 15° and 22° (20).

[0026] Figures 7A and 7B represent the nitrogen adsorption isotherms at 77 K for two MIL-16O(A1) samples prepared according to Example 3A (Figure 7A corresponds to lot E and Figure 7B to lot F). The BET specific surface areas calculated from these isotherms are 830 m² / g (lot E) and 760 m² / g (lot F).

[0027] Fig. 8 is an image of aluminium fumarate prepared according to example IA (batch A) observed by SEM at a magnification of 1x00.0. The scale shown on the image corresponds to 100.00 pm. DETAILED DESCRIPTION OF THE INVENTION

[0028] Definitions:

[0029] 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 network according to the present invention is aluminum-based, also known as an "Al-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). .

[0030] By "organic ligands" is meant 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 metal centers by aluminum. The organic ligand can, for example, be bidentate (i.e., possessing two functional groups), tridentate (i.e., possessing three functional groups), or tetradentate (i.e., possessing four functional groups). For the purposes of this invention, the organic ligands that can be used are di- and tricarboxylic acids, i.e., acids comprising two or three carboxylic acid groups (-COOH), respectively; polycarboxylic acids, i.e., acids comprising at least two carboxylic acid groups (-COOH), preferably said polycarboxylic acids being mono-aromatic or non-aromatic; and 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, benzentricarboxylic acids, benzentetracarboxylic 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, it is preferable to avoid benzendicarboxylic acids (phthalic acid, isophthalic acid and terephthalic acid) and polyaromatic acids such as 4,4'-bibenzoic acid or 2,6-naphthalenedicarboxylic acid.

[0031] Preferably, an organic ligand that is at least bidentate is fumaric acid, 1,3,5-benzenetricarboxylic acid or 2,5-furandicarboxylic acid.

[0032] The terms "alkoxide," "alkoxide," 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. Metallic 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 skeleton will be considered. Aluminum alkoxides can be, for example. 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, aluminum tert-pentylate. Preferably, aluminum alkoxides with an associated alcohol having a boiling point below 100°C (to facilitate distillation of the alcohol produced during synthesis) will be considered. Preferably, an aluminum alkoxide usable in a process according to the invention is chosen from aluminum methylate, aluminum ethoxide, aluminum isopropylate, aluminum sec-butylate or aluminum tert-butylate, preferably the aluminum alkoxide is aluminum isopropylate.

[0033] 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 comprise 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 distinguished from true solutions, where the dissolved particles (solutes) are of molecular size and cannot be filtered through a conventional filter, and from suspensions, where the particles are large enough to settle. Preferably, the colloidal solution comprises suspended particles smaller than 10 µm, preferably less than 1 µm, and particularly preferably less than 750 nm, 500 nm, 250 nm, or 100 nm.

[0034] By "percentage of dry matter" is meant the proportion of solids present in a given sample once all the water or moisture has been removed. The percentage of dry matter can be calculated according to the following formula:

[0035] [Math.l] S(%) = g^*100 v • r,*tofale Where mtotaie is the combined mass of solvent and dry matter in the system.

[0036] 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.

[0037] The term "recovery" or "recovery step" in a process for preparing a MOF according to the invention refers to all the operations performed to isolate and / or purify the MOF produced during the synthesis step. This step makes it possible, in particular, to separate the MOF from other substances present in the reaction medium, such as unreacted reagents, by-products, or solvents. The compound can be recovered by several methods, including drying methods.

[0038] By "drying" or "drying step" in a process according to the invention, we mean a process which consists of removing the aqueous solvent so as to recover the MOF. Such drying can be carried out in various ways, for example by spray drying, by freeze-drying, by drying under atmospheric pressure, or by drying in a supercritical fluid (for example, in CO2 under supercritical conditions).

[0039] 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 measurement of the total amount of accessible internal surface area per unit mass of material. Specific surface area is a key indicator of material porosity. It is expressed in m² / g. Techniques for measuring specific surface area are well known to those skilled in the art. A preferred method for measuring specific surface area may be the so-called BET technique by gas adsorption, such as nitrogen at 77 K (the so-called BET technique, after 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 the surface area and pore size distribution (THOMMES and al, 2015). The method consists of measuring the amount of gas adsorbed at different pressures and using this data to estimate the total surface accessible to the gas from the analysis of the linear region of the isotherm.

[0040] Method according to the invention:

[0041] 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 recovering the synthesized MOF.

[0042] 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.

[0043] 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 the temperature of the water-alcohol azeotrope corresponding to the composition of the mixture.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] According to a particular embodiment, the MOF prepared by a process according to the invention is aluminum fumarate (Al-fum). In this embodiment, the at least bidentate organic ligand used as a reagent in the synthesis step is fumaric acid.

[0055] 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).

[0056] 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).

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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-benzentetracarboxylic acid.

[0061] 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.

[0062] According to a particular embodiment, said at least one bidentate organic ligand and said at least one aluminium 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.

[0063] 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 yields a colloidal suspension comprising the synthesized MOF and an alcohol. The colloidal suspension may include suspended particles, for example, particles smaller than 1 µm.

[0064] 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.

[0065] The process according to the invention also includes a step for recovering the MOF synthesized during the MOF synthesis step. Such a recovery step advantageously allows the synthesized MOF to be separated from the aqueous solvent and at least one alcohol produced during MOF synthesis, while preserving the integrity of the porous structure and the functionality of the MOF.

[0066] According to a particular embodiment, the recovery step is a drying step. Such a drying step may include spray drying, supercritical CO2 drying, ambient pressure drying, or freeze-drying.

[0067] In a particularly preferred manner, the drying step includes atomization. Such atomization advantageously converts the colloidal suspension obtained during the MOF synthesis step into a dry powder and can be carried out in an atomizer. The suspension containing the MOF crystals to be atomized is directed to an atomization chamber, where it is sprayed through a high-pressure nozzle or using a rotary atomizer. This step nebulizes the colloidal suspension, creating a mist of fine droplets. A stream of hot gas, for example air or nitrogen, then encounters this nebulized suspension and rapidly evaporates the solvent. Advantageously, the hot gas stream is at a controlled temperature that does not alter the physicochemical structure of the MOF.The particle size and morphology of the final product can be adjusted by modifying process parameters such as air temperature, flow rate, spray pressure, or atomizer rotation speed. The dry particles can then be collected from the atomization chamber outlet stream, often using a cyclone separator or filtration system.

[0068] Such an atomization step is particularly advantageous, as it allows the production of a homogeneous powder with a large specific surface area, while reducing the risk of thermal or chemical degradation of the MOFs. This step is crucial to ensure that the characteristics of the MOF, such as specific reactivity, storage capacity, or capture selectivity, are preserved in the final product.

[0069] The colloidal suspension obtained during the MOF synthesis may advantageously have a viscosity compatible with a spray-drying step, i.e., a viscosity sufficiently low so as not to clog the pipes or the nozzle of the atomizer. The viscosity of a colloidal suspension obtained during a MOF synthesis step according to the invention is preferably lower than a viscosity limit defined according to the characteristics of the atomizer used, as well as the temperature at which the atomization step takes place.

[0070] Any atomizer can be used to implement a spray-drying step in a process according to the invention. Preferably, an industrial-type atomizer is used. Such an industrial-type atomizer advantageously allows for To produce large quantities of crystalline Al-MOF powder synthesized by the process according to the invention. An atomizer may include one or more nozzles suitable for nebulizing the colloidal suspension to be atomized. Advantageously, such an atomizer includes a large-capacity drum suitable for collecting the crystalline powder produced, and includes a powder collection device coupled to said drum. Such a device advantageously allows the powder to be removed from the drum at regular intervals, so as to enable continuous production. Thus, according to a particular embodiment, the drying step of the colloidal suspension produced in a process according to the invention is carried out continuously.

[0071] The temperature inside the atomizer can vary between 20 °C and 350 °C, preferably between 50 °C and 250 °C, more particularly between 60 °C and 200 °C, preferably between 80 °C and 200 °C, and even more preferably between 100 °C and 180 °C, for example between 120 °C and 180 °C. According to a particular embodiment, the temperature inside the atomizer is approximately 150 °C.

[0072] The drying time inside the atomizer required for the formation of a crystalline MOF powder is advantageously less than 1 hour. According to a particular embodiment, the atomization drying time required for the formation of a crystalline MOF powder is between 10 s and 1 h. For example, such a drying time can be between 10 s and 30 min, between 10 s and 15 min, between 20 s and 10 min, between 20 s and 5 min, between 10 s and 2 min, between 10 s and 1 min, between 10 s and 40 s, or between 10 s and 30 s.

[0073] A person skilled in the art knows how to adjust the parameters of such a spray-drying step according to the colloidal suspension to be dried, such as the hot gas flow rate, the feed rate, or the temperature. In particular, the concentration of the colloidal suspension can be adjusted to give it a viscosity compatible with its use in a spray gun. Preferably, the viscosity of the colloidal suspension does not exceed a threshold value. Such a viscosity threshold value may depend on the characteristics of the spray gun used, or on the parameters specific to the spray-drying step, for example, the temperature. By way of example, a maximum viscosity threshold value may be 500 cP.

[0074] According to an alternative embodiment, the drying step includes drying at ambient pressure, for example carried out in an oven. 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.

[0075] According to a particular embodiment, the process for preparing an MOF according to the invention may further comprise an MOF activation step. Such an activation step may take place after the drying step, and advantageously allows to remove the solvent (e.g., water and / or alcohol) trapped in the MOF's porous system. Such an activation step may include heat treatment, for example, heat treatment under reduced pressure. In one particular embodiment, the MOF activation step in a process according to the invention comprises heat treatment at a temperature of 100 °C to 250 °C, preferably 120 °C to 240 °C, most preferably 130 °C to 230 °C, and even more preferably 140 °C to 220 °C. In a preferred embodiment, the MOF activation step in a process according to the invention comprises heat treatment at a temperature of approximately 180 °C.

[0076] According to a particular embodiment, the process according to the invention further comprises a distillation step in which said at least one alcohol produced during the MOF synthesis step is extracted from the aqueous solvent. Advantageously, said at least one alcohol thus extracted from the solvent can thereby be reused, for example, to form an aluminum alkoxide from metallic aluminum. Also advantageously, the aqueous solvent thus recovered, for example, water, can also be reused in the process according to the invention.

[0077] 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.

[0078] The invention also relates to a metallo-organic network that can be obtained by a process according to the invention.

[0079] According to a particular embodiment, the MOF obtainable by a process according to the invention is an aluminum-based MOF (Al-MOF). By way of example, an aluminum-based MOF could be Aluminum Fumarate (Al-Fum), MIL-100(Al), or MIL-160(Al).

[0080] The embodiments exemplified below are given only as illustrations and do not in any way constitute a limitation of the present invention.

[0081] Example 1: Preparation of Aluminium fumarate and characterization

[0082] IA. Preparation of Aluminium fumarate by a process according to the invention

[0083] The preparation of Al-fumarate according to the process of the present invention is illustrated in [Fig. 1].

[0084] A first batch A of Al-fumarate recovered by oven drying is prepared according to the following protocol.

[0085] 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, the isopropylate Aluminium can be prepared by dissolving metallic aluminium in an aqueous solution of isopropanol, as illustrated in [Fig.1], reaction 1.

[0086] 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.

[0087] The resulting colloidal suspension takes the form of a white, difficult-to-filter liquid gel. The colloidal suspension is collected, centrifuged for 5 minutes at 8000 rpm, and then dried for 24 hours in an oven at 80°C. The solvent remaining after centrifugation is thus evaporated, and the aluminum fumarate is recovered.

[0088] Four other batches (Bl, B2, B3, B4) of aluminium fumarate are also produced according to the following protocol.

[0089] Four batches of aqueous aluminum isopropylate solutions at concentrations of 333 g / L (batches B1 and B2) or 320 g / L (batches B3 and B4) are prepared from aluminum isopropyl oxide (ABCR) powder. The resulting aluminum isopropylate solutions are heated to 70 °C. 25 kg of fumaric acid (ABCR) are added to each of these four aluminum isopropylate solutions while stirring. The stoichiometric ratio of aluminum isopropylate to fumaric acid is thus approximately 1.1:1. The mixture is kept under stirring at this temperature for 36 h for batch B1, 60 h for batch B2, and 20 h for batch B4. Batch B3 is kept under stirring at room temperature for 20 h.

[0090] The colloidal suspensions thus obtained take the form of a white liquid gel with a viscosity compatible with spray drying, for example, a viscosity of less than 500 cP. The industrial spray dryer (GEA) used for the drying step has a drying chamber 10.5 m high and 2 m in diameter and is capable of producing powders containing organic fillers and operating in a closed system under nitrogen. The colloidal suspensions are nebulized (dispersed into fine droplets) by passing through a single-fluid SDx 39 injection nozzle at a pressure of 8 bar to obtain an atomization flow rate of 60 kg / h, using a nitrogen flow of 1600 m³ / h. For batch B1, the atomizer inlet temperature is 170°C and the atomizer outlet temperature is 110°C. For batches B2, B3, and B4, the atomizer inlet temperature is 185°C and the atomizer outlet temperature is 115°C.The solvent is thus eliminated in this way. atomization step and aluminium fumarate is recovered as a dry powder composed of polycrystalline particles with a diameter of 50 to 100 pm.

[0091] The aqueous solvent containing the isopropanol produced during the MOF synthesis, recovered during the oven-drying or spray-drying step, can undergo a distillation step. The isopropanol can thus be recovered and, if necessary, reused to form aluminum isopropylate from metallic aluminum, as illustrated in [Fig. 1]. After the distillation step, the aqueous solvent devoid of isopropanol can also be reused, as shown in [Fig. 1], for example, in the preparation of the reaction medium for the MOF synthesis presented in step 2) of [Fig. 1].

[0092] 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.

[0093] IB. X-ray diffraction analysis of the aluminum fumarate batches synthesized in IA

[0094] 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 identifying the atomic and molecular structure of an 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, and to obtain information on the size and geometry of the material's pores.

[0095] 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.

[0096] X-ray diffraction analysis of a sample from batch A, the 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.

[0097] The diffraction profiles of samples B1 to B4 correspond to the profile obtained for batch A.

[0098] IC. Analysis of the specific surface area of ​​the aluminum fumarate synthesized in IA

[0099] Batches Bl, B2, B3 and B4 of MOF synthesized and spray-dried according to Example IA are characterized by the BET (Brünauer, Emett and Teller) method in order to measure their specific surface areas. To implement this measurement method, a MINIX (BELSORP) device is used to measure nitrogen adsorption at 77 K of MOF batches synthesized after activation at 150°C under reduced pressure for 12 hours. A person 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).

[0100] The nitrogen adsorption isotherms at 77 K for batches B1 to B4 of Al-fumarate produced according to Example 1 are shown in [Fig. 3]. These isotherms exhibit a type I shape, which is characteristic of exclusively nano- and microporous materials. The specific surface areas calculated for the four Al-fumarate samples from the isotherms are 1050 m² / g, 1020 m² / g, 1040 m² / g, and 10¹⁵ m² / g (which represents a very small variation). These results are close to the specific surface area reported in the literature for Aluminium-fumarate, for example, 10¹⁰ m² / g (Alvarez et al. The Structure of the Aluminum Fumarate Metal-Organic Framework A520. Angew. Chem. Int. Ed. 2015, 54 (12)). This low variability between samples allows us to conclude that the process developed by the inventors as described in example IA is robust, reproducible, and not very sensitive to variations in conditions, particularly stoichiometry.

[0101] 1D. Characterization of the aluminum fumarate synthesized in AI by microscopy electronic

[0102] The aluminum fumarate synthesized according to Example IA (batch Bl) is characterized by scanning electron microscopy (Hitachi S4800) after spray drying. Scanning electron microscopy advantageously allows observation of the external morphology of the MOF (size, shape, texture, presence of specific facets), verification of the uniformity and purity of the MOF, and confirmation of whether the material particles aggregate or assemble in a specific manner.

[0103] Figure 8 shows an image of the aluminum fumarate prepared according to Example 1, observed by SEM at a magnification of 1x00.0. The scale shown in the image represents 100.00 pm. This image shows that the spray-drying step produces aluminum fumarate in the form of micrometric beads of calibrated size and regular shape. As a result, the aluminum fumarate powder obtained exhibits good flowability and does not cause caking problems during use.

[0104] Example 2: Preparation of MIL-1llO(Al) and characterization

[0105] 2A. Preparation of MIL-11O(Al) by a process according to the invention

[0106] A first batch C of MIL-110(Al) is prepared and recovered by oven drying according the following protocol.

[0107] 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.

[0108] 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 molar stoichiometric ratio between aluminum isopropylate and 1,3,5-BTC is thus 0.44:1. The synthesized MOF is then recovered by oven drying, according to the protocol described in Example IA.

[0109] A second batch D of MIL-110( Al) is prepared and recovered by atomization according to the following protocol.

[0110] 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.

[0111] The aluminum isopropylate solution is heated to 70 °C under magnetic stirring at 800 rpm. 1.8 g of 1,3,5-benzenetricarboxylate (1,3,5-BTC, Sigma-Aldrich) are added to 100 mL of the aluminum isopropylate solution, whereby, after 24 h, a colloidal suspension is obtained comprising the synthesized MIL-11O(Al) and isopropanol. The molar stoichiometric ratio between aluminum isopropylate and 1,3,5-BTC is thus 0.44:1. The synthesized MOF is then recovered by atomization using a spray dryer (MINI SPRAY-DRYER B-290, BÜCHI LABORTECHNIK AG).

[0112] 2B. X-ray diffraction analysis of MIL-11O(Al) synthesized in 2A

[0113] 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.

[0114] X-ray diffraction analysis for this sample is shown in [Fig.4]. 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.).

[0115] 2C. Analysis of the specific surface area of ​​MIL-llO(Al) synthesized in 2A

[0116] The specific surface area of ​​the MOF MIL-110(Al) batches C and D 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. 5A] and for batch D in [Fig. 5B]. The specific surface area calculated from the isotherm of batch C of MIL-110(Al) is 870 m² / g, and the specific surface area calculated from the isotherm of batch D of MIL-110(Al) is 775 m² / g. This result is close to the specific surface area that can be found 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 Vapour. Nanomaterials 2022,12 (12), 2092).

[0117] Example 3: Preparation of MIL-16O(A1) and characterization

[0118] 3A. Preparation of MIL-16O(A1) by a process according to the invention

[0119] A first batch E of MIL-16O(A1) is prepared and recovered by oven drying according the following protocol.

[0120] 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.

[0121] 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 molar stoichiometric ratio between aluminum isopropylate and 2,5-FDCA is thus 1:1. The synthesized MOF is then recovered by oven drying, as explained in Example IA.

[0122] A second batch F of MIL-16O(A1) is prepared and recovered by atomization according to the following protocol.

[0123] 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.

[0124] The aluminum isopropylate solution is heated to 70 °C under magnetic stirring at 800 rpm. 3.06 g of 2,5-furandicarboxylic acid (2,5-FDCA, Sigma-Aldrich) are added to 100 mL of the aluminum isopropylate solution, whereby, after 24 h, a colloidal suspension is obtained comprising the synthesized MIL-16O(A1) and isopropanol. The molar stoichiometric ratio between aluminum isopropylate and 2,5-FDCA is thus 1:1. The MOF synthesized is then recovered by atomization, using an atomizer (MINI SPRAY-DRYER B-290, BÜCHI LABORTECHNIK AG).

[0125] 3B. X-ray diffraction analysis of MIL-16O(A1) synthesized in 3A

[0126] The MIL-16O(A1) MOFs E and F synthesized according to Example 3A are characterized by X-ray diffraction (XRD), according to the protocol stated in Example IB.

[0127] X-ray diffraction analysis of batch E of MIL-16O(A1) prepared according to Example 3A is shown in [Fig. 6A] and that of batch F of MIL-16O(A1) is shown in [Fig. 6B]. 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).

[0128] 3C. Analysis of the specific surface area of ​​MIL-16O(A1) synthesized in 3A

[0129] The specific surface area of ​​the MOFs MIL-16O(A1) batches E and F 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. 7A] and for batch F in [Fig. 7B]. 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 recovering the synthesized MOF.

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 ethoxide, 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, furandicarboxylic acid, benzenetricarboxylic acids, benzenetetracarboxylic acids, muconic acid, aspartic acid and glutamic acid, preferably said at least one bidentate organic ligand is fumaric acid, 1,3,5-benzenetricarboxylic acid and 2,5-furandicarboxylic acid.

7. 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 pm.

8. 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.

9. A method for preparing an MOF according to any one of the preceding claims, wherein the step of recovering the synthesized MOF consists of a drying step.

10. A method for preparing a MOF according to claim 9, wherein the drying step comprises spray drying, supercritical CO2 drying, ambient pressure drying or freeze-drying, preferably spray drying.

11. A method for preparing an MOF according to any one of the preceding claims, said method further comprising a distillation step in which said at least one alcohol produced during the MOF synthesis step is extracted from the aqueous solvent.

12. A method for preparing an MOF according to any one of the preceding claims, said method further comprising a step of activating said MOF by heat treatment.

13. Metal-organic networks that can be obtained by the process as defined in any one of claims 1 to 12.

Images