METHOD FOR PREPARING A TITANIUM-BASED METAL-ORGANIC MONOLITHIC MATERIAL

Abstract

This disclosure relates to a method for preparing a monolithic metal-organic framework characterized in that it comprises the following steps: mixing a titanium(IV) metal precursor, a salt of a divalent or trivalent metal element, and a tricarboxylic ligand L in a polar solvent Z to obtain a reaction mixture, wherein the concentrations of the titanium(IV) metal precursor and the salt of a metal element are between 0.1 and 3 M; heating the reaction mixture to temperatures above 80 °C for at least 12 hours to obtain a colloidal solution; washing the colloidal solution with a solvent; centrifuging the washed solution for at least 10 minutes at a relative centrifugal force of between 1500 and 4000 g; and allowing the centrifuged solution to dry at a temperature between 25 and 100 °C in a container. This disclosure also relates to the monolithic framework obtained according to the method described.

Description

METHOD FOR PREPARING A MONOLITHIC METAL-ORGANIC MATERIAL BASED ON TITANIUM FIELD OF TECHNOLOGY The present invention relates to a method for preparing a titanium-based metal-organic monolithic material. The present invention also relates to the monolithic material obtained according to the method described and to a metal-organic monolithic material resulting from the combination of Ti(IV) with other metals. BACKGROUND OF THE INVENTION Over the past two decades, research and development of metal-organic frameworks (MOFs) has been extensive, with more than 100,000 structures registered in the Crystallographic Data Center. However, one of the reasons why the vast majority of these materials have not progressed beyond laboratory applications is the difficulty of handling them, as MOFs are generally produced in powder form. At an industrial level, these powders have several drawbacks, such as limitations in mass transfer, the generation of considerable pressure drops, and the lack of a homogeneous flow distribution in the bed. Therefore, for large-scale applications, granular structures are preferred, which can be shaped into pellets, granules, monoliths, or films. To address this need, there is currently a growing interest in densifying MOFs through processing methods that increase their bulk density while maintaining their high surface area and porosity. One strategy used to densify these materials is through the shaping of monolithic structures from a dense sol-gel colloidal dispersion. The main advantage of these materials in monolithic form is that their high surface area and porosity can be maintained without resorting to the addition of external chemical agents (surfactants) or more aggressive physical shaping methods (extrusion, pelletizing, granulation, film formation) that could cause structural collapse and / or partial pore blockage. One strategy for producing structured MOFs is by depositing the material onto a polymeric support, ceramic monolith, fibers, or foams. However, the resulting materials generally exhibit low adsorption capacities due to the incorporation of the second component. For example, in Yao, P. et al. (Green Chemical Engineering, 4 (4) , 439-447 (2023) ), a monolithic mesoporous titanium material in combination with a polymer (PEG, PVA and PAM) obtained by frozen melting in liquid nitrogen is described. A second method employed is pelletizing through mechanical compression or extrusion. However, the working pressure must be carefully selected, as in some cases this can induce a loss of crystallinity and microporosity in the material. The introduction of a binder is an alternative to reduce this loss, but this can lead to a decrease in its adsorption capacity. Recently, a new strategy has emerged involving the self-generation of monoliths from a sol-gel colloidal dispersion. Sol-gel monoliths form spontaneously and exhibit a single phase at both the macro and micro scales, increasing their density and mechanical strength. The main advantage of this method is that forming the monolith does not require binders or high pressures that could compromise the material's intrinsic structure. This, in principle, allows its adsorption, porosity, and density properties to remain intact. This technique involves four stages: supersaturation, nucleation, growth, and Ostwald maturation. The final properties of the monolith depend primarily on the size and quantity of particles formed during the nucleation stage.Therefore, to achieve the optimal textural properties of the material, careful control of certain synthesis parameters is required (concentration, solvent, reaction time, crystallization temperature, modulators, drying temperature). In the last decade, through the use of this sol-gel technique, it has been possible to synthesize monoliths of the following materials: UiO-66, UiO-66-NH2, HKUST-1, NU-1000, MIL100 (Fe) , ZIF-8, ZIP-4, TPB-DMTP, Zr-Fumarate, SRh@ZIF-8, SnO2@ monoZIF-8 and Au@ZIF-67. For example, Tian et al. (Journal of the American Chemical Society, 2022, 144, 13729-13739) successfully synthesized HKUST-1 monoliths with particle sizes between 51-73 ± 10 nm without compromising their monolithic structure. This material was tested for methane adsorption, demonstrating a high volumetric adsorption capacity of 259 cm³ (STP) at 65 bar, making it the first material to meet the target set by the U.S. Department of Energy (DOE) for natural gas storage. Subsequently, Madden et al. tested this same material for H₂ storage, achieving the highest reported capacity (46 g L⁻¹ at 100 bar and 77 K) using actual densities under DOE conditions. In Connolly et al. (Nature Communications, 2019, 10:2345) Zirconium-based monoliths called monoUiO-66, monoUiO-66-NH2, and monoNU-1000 were synthesized. Among them, monoUiO-66 stands out with a volumetric capacity for CH4 of 296 cm3 cm-3 at 100 bar, being comparable to the adsorption of HKUST-1. A very important step towards the application of these materials on an industrial scale was achieved by Çamur et al. (Adv. Mater.2023, 35, 2209104) when they described the multigram scale-up of Zr-Fumarate. The scale-up of 1 L of Zr-Fumarate allowed the production of 67 g of product while maintaining its porosity and crystallinity properties intact. Therefore, there is a need for a methodology for manufacturing a monolithic material from heterometallic materials based on other metals on an industrial scale, with high efficiency and low cost. DESCRIPTION OF THE INVENTION The present invention has been made taking into account the prior art and described above, the object of the present invention being a method for preparing a monolithic metal-organic material based on the combination of titanium (IV) with other metals In a first aspect, the present invention describes a method for preparing a monolithic metal-organic material characterized in that it comprises the following steps: a) mixing a titanium(IV) metal precursor, a salt of a divalent or trivalent metal element, and a tricarboxylic ligand L in a polar solvent Z to obtain a reaction mixture, wherein the concentrations of the titanium(IV) metal precursor and the salt of a metal element are between 0, 1, and 3 M; b) heating the reaction mixture to temperatures above 80°C for at least 12 hours to obtain a colloidal solution; c) washing the colloidal solution with a solvent; d) centrifuging the washed solution for at least 10 minutes at a relative centrifugal force of between 1500 and 4000 g; and e) allowing the centrifuged solution to dry at a temperature between 25 and 100°C in a container. In the context of the present invention, a metal-organic framework (MOF) refers to a type of material composed of metal ions or metal clusters linked together by organic molecules (ligands) forming a highly ordered, three-dimensional structure. A metal-organic framework according to the present invention is what is known as a MOF. In the context of the present invention, a monolithic metal-organic material refers to a metal-organic material (or MOF) structure generated as a solid, discrete, and continuous piece, as opposed to metal-organic material structures composed of particles or crystals. In a monolithic metal-organic framework, the structure is designed to form a solid, cohesive block, rather than a granular or powdered form. This structure can be advantageous in certain applications where a continuous, robust material is needed, or where a durable and shape-stable material is required. In particular, the concentration of titanium(IV) metal precursor and the metal salt (between 0.1 and 3 M) defined in the reaction mixture, along with the centrifugation of the resulting colloidal solution, has enabled the inventors to obtain a surprisingly stable, monolithic titanium(IV)-based material, never before described in the prior art. The technical characteristics defined in the method according to the invention thus allow for optimal densification of the metal-organic framework obtained by reacting the metal precursor with the metal salt and the subsequent colloidal solution to produce a monolithic material that retains the high adsorption capacities of the powdered material. In the method according to the present invention, the mixture defined in step a) may also comprise an acid. The acid acts as a catalyst in the method defined in the present invention. Preferably, the acid is selected from the group consisting of hydrochloric acid, formic acid, acetic acid, propanoic acid, benzoic acid and derivatives thereof. In the method according to the present invention, the metallic precursor of titanium (IV) is selected from a titanium (IV) salt, preferably from the group consisting of Ti (IV) isopropoxide, Ti (IV) methoxide, Ti (IV) ethoxide, Ti (IV) n-propoxide, Ti (IV) n-butoxide, Ti (IV) triethanolamine isopropoxide, Ti (IV) tert-butoxide, Ti (IV) oxo diacetylacetonate, Ti (IV) tetrachloride, bis (cyclopentadienyl) Ti (IV) dichloride, cyclopentadienyl Ti ​​(IV) trichloride, Ti (IV) oxosulfate, or an air-stable Ti (IV) polynuclear compound such as a Ti (IV) hexanuclear complex. The combination of titanium (IV) with divalent or trivalent metals, varying the identity and relative proportion in the structure of the monolithic metal-organic material, allows for the provision of a family of stable monoliths with advantageous properties. In particular, the divalent or trivalent metallic element may be selected from the group consisting of magnesium, calcium, strontium, barium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, cadmium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, and combinations thereof.These divalent or trivalent metals are found in their corresponding valence; that is, the divalent or trivalent metallic element can be selected from the group consisting of magnesium (II), calcium (II), strontium (III), barium (II), vanadium (III), chromium (II), chromium (III), manganese (II), manganese (III), iron (II), iron (III), cobalt (II), cobalt (III), nickel (II), nickel (III), copper (II), zinc (II), cadmium (II), lanthanum (III), cerium (III), praseodymium (III), neodymium (III), promethium (III), samarium (III), europium (III), gadolinium (III), terbium (III), dysprosium (III), holmium (III) , erbium (III) , thulium (III) , ytterbium (III) , lutetium (III) and combinations thereof. Furthermore, in the method according to the present invention, the salt of a divalent or trivalent metallic element is preferably a fluoride, chloride, bromide, iodide, nitrate, perchlorate, tetrafluoroborate, isocyanate, hydroxide, acetate, benzoate, sulfate, or carbonate. The molar ratio between the acid and the salt of a divalent or trivalent metallic element is preferably between 5 and 500 equivalents; that is, for every 5 to 500 moles of acid, there is one mole of divalent or trivalent metallic element. Preferably, the molar ratio is between 10 and 200, more preferably between 50 and 100. Preferably, the polar solvent Z is selected from the group consisting of N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, methanol, ethanol, isopropanol, n-propanol, water, and combinations thereof. The choice of solvent determines the final structure of the monolithic material. In the method according to the present invention, the Ti (IV) precursor and the salt of a divalent or trivalent metallic element are preferably in a molar ratio between 99:1 and 15:85, more preferably between 99:1 and 50:50. Preferably, in the method according to the present invention, the tricarboxylic ligand L is selected from an aryl-C6 tricarboxylic acid, an aryl-C3N3 tricarboxylic acid, or a derivative thereof of the type (aryl-C6)3-aryl-C6 tricarboxylic acid or (aryl-C6)3-aryl-C3N3 tricarboxylic acid. More preferably, the tricarboxylic ligand L has one of the following structures A, B, C or D, where A is a C6 aryl tricarboxylic acid: where R1 is -COOH and R2 is selected from the group -H, C1-C5 alkyl, -NH2, -OH, NO2, -COOH and halogen B is an aryl-C3N3 tricarboxylic acid: where R1 is -COOH C is a (aryl-C6)3-aryl-C6 tricarboxylic: where R1 is selected from: and R2 is selected from the group -H, C1-C5 alkyl, -NH2, -OH, NO2, -COOH and halogen D is a (aryl-C6) 3-aryl-C3N3 tricarboxylic where R1 is selected from: and R2 is selected from the group -H, C1-C5 alkyl, -NH2, -OH, NO2, -COOH and halogen. More preferably, the L tricarboxylic ligand is 1,3,5-benzene-tricarboxylic acid or trimesic acid. In another embodiment, in the method according to the present invention, the stoichiometric ratio between the salt of a divalent or trivalent metallic element and the tricarboxylic ligand L is between 1:1 and 1:6. Preferably, in the method according to the present invention, the reaction mixture is heated to temperatures between 80ºC and 200ºC. Preferably, in the method according to the present invention, the reaction mixture is heated for between 12 and 72 hours. Preferably, in the method according to the present invention, the metallic precursor of Ti(IV) is a Ti(IV) heterometallic metal-organic solid, a Ti(IV) MOF. In a second aspect of the present invention, the monolithic metal-organic material obtained according to the method described above is also described. Furthermore, in a third aspect of the present invention, a monolithic metal-organic compound of Ti(IV) is also described, characterized in that it comprises a tricarboxylic ligand L as the organic part of the metal-organic compound, Ti(IV), and at least one divalent or trivalent metal M, wherein the Ti(IV) and the at least the divalent or trivalent metal M are homogeneously distributed at the atomic level in the structure of the metal-organic compound; wherein the metal-organic compound of Ti(IV) has a general formula selected from one of the following: - [Ti (IV) 3M3 (O) 3L4]·Z where M is selected from the group of cations consisting of Mg2+, Ca2+, Sr2+, Ba2+, Ti2+, V2+, Cr2+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, La3+, Ce3+, Pr3+, Nd3+, Pm3+, Sm3+, Eu3+, Gd3+, Tb3+, Dy3+, Ho3+, Er3+, Tm3+, Yb3+, Lu3+ or combinations thereof; L is a tricarboxylic ligand; and Z is a molecule of N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, methanol, ethanol, isopropanol, n-propanol, or water; The particle size of the material is less than 200 nm; and the density of the material is at least 40% of the density of the same material in single crystal form. In the context of the present invention, "homogeneous distribution at the atomic level" of the metal atoms means that the atomic ratio between the different metals integrated into the solid is the same regardless of the area of ​​the crystalline solid that is examined. In the context of the present invention, "single crystal" means a solid material in which the atoms, ions, or molecules are arranged in a continuous, ordered, and repeating pattern throughout the entire structure. A single crystal is composed of a single crystal, meaning that all its atoms or molecules are arranged in a regular and periodic pattern throughout the material. Furthermore, the atomic arrangement is free from defects such as dislocations, grain boundaries, or other defects that may be present in polycrystalline materials. Therefore, according to the present invention, the proposed monolithic material has a density of at least 40% of the density that the same material would have in single-crystal form. Furthermore, in the general formula [Ti (IV) 3M3 (O) 3L4]·Z of the monolithic material defined in the present invention, the Ti (IV) and the at least one divalent or trivalent metal are in a molar ratio Ti (IV) :M between 50:50 and 99:1. In a preferred embodiment, the tricarboxylic ligand L is selected from the group consisting of an aryl-C6 tricarboxylic acid, an aryl-C3N3 tricarboxylic acid or a derivative thereof, of the type (aryl-C6) 3-aryl-C6 tricarboxylic acid or (aryl-C6) 3-aryl-C3N3 tricarboxylic acid. More preferably, the tricarboxylic ligand L has one of the following structures A, B, C or D, where A is a C6 aryl tricarboxylic acid: where R1 is -COOH and R2 is selected from the group -H, C1-C5 alkyl, -NH2, -OH, NO2, -COOH and halogen B is an aryl-C3N3 tricarboxylic acid where R1 is -COOH C is a (aryl-C6)3-aryl-C6 tricarboxylic where R1 is selected from: and R2 is selected from the group -H, C1-C5 alkyl, -NH2, -OH, NO2, -COOH and halogen D is a (aryl-C6) 3-aryl-C3N3 tricarboxylic: where R1 is selected from: and R2 is selected from the group -H, C1-C5 alkyl, -NH2, -OH, NO2, -COOH and halogen. Furthermore, more preferably, the L tricarboxylic ligand is 1,3,5-benzenetricarboxylic acid or trimesic acid. The described method, the way the monolithic material is prepared, and the monolithic material itself represent an improvement over the state of the art. In particular, an example of a heterometallic monolith based on Titanium (IV) using the sol-gel methodology, according to the method defined in the present invention, has not been previously described. Furthermore, the densification of the metal-organic material (MOF type) in the form of monoliths has been achieved without resorting to the addition of external chemical agents (surfactants) or more aggressive methods of physical modeling (extrusion, pelletizing, granulating, films), which could cause structural collapse and / or partial blockage of the pores. Furthermore, the heterometallic titanium (IV) monoliths are synthesized in a single stage (onepot reaction), improving porosity, increasing density and mechanical strength compared to their powder analogue. It is also worth noting that, with the method described here, monolithic structures of Ti(IV)-M-based metal-organic frameworks (MOFs) (M = Mg, Ca, Sr, Ba, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) can be prepared with high chemical stability in acidic / basic media and high porosities of up to 1000 m²·g⁻¹. Materials with variable formulations can be obtained by directly controlling the proportion of Ti(IV) and the other metals in the material, not being limited solely to binary combinations; titanium can be combined with up to 5 different types of metals in the same material. Furthermore, the method described here allows for precise control over the nanoparticle size distribution, ranging from tens of nanometers to 200 nm, enabling optimal control of crystal growth to form a structured metal-organic framework (MOF). It has also been possible to directly modulate the properties of porosity, mechanical strength, chemical stability, and optical, electronic, and catalytic properties. These optimized properties, directly applied to monolithic structures, are what distinguish these systems in storage, separation, and catalysis applications. Thus, with a single production method, we can obtain materials relevant to multiple applications at a low production cost. Furthermore, by starting from formulations optimized to stoichiometric ratios and commercial organic reagents, the production cost is minimized, resulting in greater ease in transferring its synthesis to an industrial scale, which has been verified at the pilot plant level (10L). These and other intrinsic properties of Ti(IV)-based monolithic metal-organic materials make them relevant for use, according to a fourth aspect of the invention, in gas capture and storage, solar fuel generation, photoactivated degradation, CO2 photoreduction, water purification, or organophosphorus compound degradation. In a fifth aspect of the invention, Ti(IV)-based monolithic metal-organic materials can also be used as a component or part of an electronic component, or as a porous or photoactive coating for contaminant control. BRIEF DESCRIPTION OF THE FIGURES The above and other features and advantages will be more fully understood from the following detailed description of some examples of implementation, which are merely illustrative and not limiting, with reference to the accompanying figures, in which: FIG.1: Optical image of the monolithic structure of MUV-10 (Ca), showing that it maintains the shape of the container where it was prepared. FIG.2: X-ray diffractogram of the monolithic material MUV-10 (Ca) powder. FIG.3: SEM images (3A) and particle size distribution (3B) of the MUV-10 (Ca) monolith family monoA. FIG.4: N2 adsorption isotherm at 77K of the MUV-10 (Ca) monoB family monolith. FIG.5: MUV-10 (Ca) pore size distributions obtained by Hg porosimetry showing the variations in meso (20-500 Å diameter) and macro (> 500 Å diameter) porosity between monolithic materials and powder. FIG.6: MUV-10 (Ca) pore size distributions obtained by Hg porosimetry showing the variations in meso (20-500 Å diameter) and macro (> 500 Å diameter) porosity among monolithic materials of different particle sizes. FIG. 7: Measurement of mechanical properties of MUV-10 (Ca) monoliths using load-displacement curves obtained using a Berkovich type nanoindenter for MUV-10 (Ca) monoA exchanged with DMF (20nm) (FIG. 7A), MUV-10 (Ca) monoB exchanged with methanol (20nm) (FIG.7B) and MUV-10 (Ca) monoC (exchanged with methanol (135 nm) (FIG. 7C) . DETAILED DESCRIPTION OF THE INVENTION The following describes preferred embodiments for carrying out the present invention, in particular an example based on obtaining a heterometallic monolith of the MUV-10 (Ca) family. The process described herein allows for the production of titanium-based heterometallic monoliths in a single step, avoiding the use of external agents (surfactants) and / or mechanical methods (high pressures) that could negatively affect their adsorption properties. The results shown below focus on the MUV-10 (Ca) material as a model reaction, but the present invention applies to all types of Ti(IV)-M-based heterometallic metal-organic materials, as described above. In general, MUV-10 (Ca) monoliths are synthesized by the stoichiometric reaction of Ti(IV) metal precursors and a CaCl2 salt with trimesic acid in a mixture of DMF and acetic acid. This reaction mixture is heated to 80–120°C, preferably 120°C, for 6–48 hours, preferably 48 hours. Subsequently, the colloidal solution is washed with DMF and / or methanol, centrifuged (3500 rpm, 1718 g) in the desired container, and finally dried at 25°C when washed with methanol, or at 40–60°C when washed with DMF. The resulting material is isolated as a monolith (FIG. 1). Powder X-ray diffraction results confirm the presence of peaks characteristic of the crystalline structure of the MUV-10 material family (FIG. 2). It is important to highlight that the particle size of the obtained material is on the nanoscale, which offers significant advantages compared to its micrometric equivalents. First, reducing the particle size to the nanoscale can contribute to better pore accessibility, potentially improving adsorption capacity and interaction with host molecules, making it ideal for gas storage or CO2 capture applications. Furthermore, nanometric MOFs can improve dispersion properties in liquid and solid media, which is beneficial in catalytic applications as it allows for more homogeneous distribution. Another key advantage is the higher rate of molecular diffusion within the pores, accelerating adsorption, desorption, and chemical reaction processes. Nanometric MOFs also have greater potential in biomedical applications, such as controlled drug release, due to their ability to enter and act at the cellular level, a characteristic that their micrometric counterparts do not achieve with the same efficiency. Therefore, it is very important to control the particle size of the material. A key factor is ensuring its large-scale production while maintaining a homogeneous particle size distribution of less than 100 nm. In the example shown in FIG. 3, the average particle size is 20 nanometers with a homogeneous distribution. The nitrogen adsorption properties of the material are shown in Figure 4. From this figure, it can be inferred that the isotherm corresponds to a Type IV, characterized by high adsorption at relative pressure (P / P) values ​​below 0.1, suggesting significant microporosity (<2 nm). Likewise, significant N2 adsorption is observed at comparatively high pressures (P / P0 > 8), indicating the presence of mesoporosity (2–50 nm). These results confirm that the self-generation of the monolith does not affect the adsorption properties of the powdered material, resulting in a high BET surface area of ​​604 m²g⁻¹. Density measurements were performed using Hg porosimetry. The densification calculation was obtained from calculations regarding the density of the single crystal (in English, single cr and stal) which is 1.039 g·cm-3. The density of MOF monoliths is a crucial factor in determining their efficiency in various applications, especially those requiring high adsorption capacity, such as gas storage and CO2 capture. A high-density MOF monolith contains a greater amount of active material per unit volume, increasing its adsorption capacity in confined spaces—ideal for compact devices. Furthermore, higher density improves the monolith's structural integrity, allowing it to maintain its shape and functionality under demanding operating pressure and temperature conditions. Therefore, controlling and optimizing the density of MOF monoliths is essential to maximizing their performance and viability in industrial applications. Table 1 presents the results of the apparent density (bulk) calculation of the samples obtained by Hg porosimetry. From these results it can be inferred that the exchange with high boiling point solvents, such as DMF, allows the densification of the material to be improved up to 92% with respect to the theoretical density of the single crystal (or single cr and stal). Table 1. Textural properties of MUV-10 (Ca) monoliths To further study the density and pore size distribution (PSD) in the meso- and macropore regions, Hg porosimetry is used. Figure 5 shows the variations in meso (2–50 nm diameter) and macro (>50 nm diameter) porosity between the densified materials and the powder. As already mentioned, a determining factor for obtaining highly densified materials is particle size control. Figure 6 shows how the particle size of the materials directly influences the variations in meso- and macropore size. Synthesizing materials with particle sizes smaller than 100 nm is of particular interest because they also exhibit a higher apparent density. Indeed, one of the most important advantages of MOF densification using the sol-gel technique is that these materials maintain high porosity and, at the same time, possess the appropriate density that allows them to withstand external forces without compromising their adsorption or catalytic capacity. Finally, to measure the mechanical properties of the monoliths at the nanoscale, the nanoindentation technique was used. Figure 7 shows the results of the measurements using a Berkovich-type nanoindenter for the MUV-10 (Ca) mono samples. These results are consistent with those obtained from the porosimetry of Hg and confirm that monoliths with particle sizes smaller than 100 nm exhibit greater mechanical strength. Properties such as the modulus of elasticity and hardness are critical parameters that help understand the behavior of these materials under operating conditions involving resistance to loads and / or pressures. Table 2 details the results of the determination of the elastic modulus (E, GPa) and hardness (H, GPa) using a Berkovich-type nanoindenter. Table 2. Mechanical properties of MUV-10 (Ca) monoliths calculated from Berkovich nanoindentation data. Hardness (H, GPa) and Young's modulus (E, GPa) were calculated from Berkovich nanoindentation data. Mean values ​​and standard deviations were calculated from an indentation depth range of 300–4500 nm. Measurements obtained in the penetration range below 250 nm were excluded to eliminate errors due to surface defects / tip artifacts. As can be seen, monoliths with particle sizes smaller than 100 nm improve mechanical properties by an order of magnitude. This ability of MOF monoliths to withstand stress and maintain their porous structure without collapsing is fundamental for gas storage and transportation applications where a combination of strength and durability is required. The scope of the present invention is defined in the appended claims.

Claims

1. A method for preparing a monolithic metal-organic framework characterized in that it comprises the following steps: a) mixing a titanium(IV) metal precursor, a salt of a divalent or trivalent metal element, and a tricarboxylic ligand L in a polar solvent Z to obtain a reaction mixture, wherein the concentrations of the titanium(IV) metal precursor and the salt of a metal element are between 0, 1, and 3 M; b) heating the reaction mixture to temperatures above 80°C for at least 12 hours to obtain a colloidal solution; c) washing the colloidal solution with a solvent; d) centrifuging the washed solution for at least 10 minutes at a relative centrifugal force of between 1500 and 4000 g; and e) allowing the centrifuged solution to dry at a temperature between 25 and 100°C in a container.

2. The method according to claim 1, wherein an acid is also added to the mixture defined in step a).

3. The method according to claim 1 or 2,wherein the titanium(IV) metal precursor is selected from the group consisting of Ti(IV) isopropoxide, Ti(IV) methoxide, Ti(IV) ethoxide, Ti(IV) n-propoxide, Ti(IV) n-butoxide, triethanolamineto-Ti(IV) isopropoxide, Ti(IV) tert-butoxide, Ti(IV) oxo di-acetylacetonate, Ti(IV) tetrachloride, bis(cyclopentadienyl)-Ti(IV) dichloride, cyclopentadienyl-Ti(IV) trichloride, Ti(IV) oxosulfate or an air-stable polynuclear Ti(IV) compound such as a hexanuclear Ti(IV) complex.

4. The method according to any one of the preceding claims, wherein the divalent or trivalent metallic element is selected from the group consisting of magnesium, calcium, strontium, barium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, cadmium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium,lutetium and combinations thereof.

5. The method according to any one of the preceding claims, wherein the salt of a divalent or trivalent metallic element is a fluoride, chloride, bromide, iodide, nitrate, perchlorate, tetrafluoroborate, isocyanate, hydroxide, acetate, benzoate, sulfate, or carbonate.

6. The method according to any one of claims 2 to 5, wherein the acid is selected from the group consisting of hydrochloric acid, formic acid, acetic acid, propanoic acid, benzoic acid, and derivatives thereof.

7. The method according to any one of claims 2 to 6, wherein the molar ratio between the acid and the salt of a divalent or trivalent metallic element is between 5 and 500 equivalents.

8. The method according to any one of the preceding claims, wherein the polar solvent Z is selected from the group consisting of N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, methanol, ethanol, isopropanol,n-propanol, water, and combinations thereof.

9. The method according to any one of the preceding claims, wherein the Ti(IV) precursor and the salt of a divalent or trivalent metal element are in a molar ratio of between 99:1 and 15:

85.

10. The method according to any one of the preceding claims, wherein the tricarboxylic ligand L is selected from an aryl-C6 tricarboxylic acid, an aryl-C3N3 tricarboxylic acid, or a derivative thereof of the type (aryl-C6)3-aryl-C6 tricarboxylic acid or (aryl-C6)3-aryl-C3N3 tricarboxylic acid.

11. The method according to any one of the preceding claims, wherein the stoichiometric ratio between the salt of a divalent or trivalent metal element and the tricarboxylic ligand L is between 1:1 and 1:

6.

12. The method according to any one of the preceding claims,wherein the reaction mixture is heated to temperatures between 80 and 200°C.

13. The method according to any one of the preceding claims, wherein the mixture is heated for between 12 and 72 hours.

14. The method according to any one of the preceding claims, wherein the metallic precursor of Ti(IV) is a heterometallic metal-organic solid of Ti(IV).

15. Monolithic metal-organic material obtained according to the method defined in claims 1 to 14.

16. Monolithic metal-organic material of Ti(IV) characterized in that it comprises a tricarboxylic ligand L as the organic part of the metal-organic compound, Ti(IV), and at least one divalent or trivalent metal M.wherein Ti(IV) and at least the divalent or trivalent metal M are homogeneously distributed at the atomic level in the structure of the metal-organic compound; the Ti(IV) metal-organic compound has a general formula selected from one of the following: - [Ti(IV)3M3(O)3L4]·Z wherein M is selected from the group of cations consisting of Mg2+, Ca2+, Sr2+, Ba2+, Ti2+, V2+, Cr2+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, La3+, Ce3+, Pr3+, Nd3+, Pm3+, Sm3+, Eu3+, Gd3+, Tb3+, Dy3+, Ho3+, Er3+, Tm3+, Yb3+, Lu3+ or combinations thereof; L is a tricarboxylic ligand; and Z is a molecule of N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, methanol, ethanol, isopropanol, n-propanol, or water; the particle size of the material is less than 200 nm; and furthermore, the density of the material is at least 40% of the density of the same material in single-crystal form.

17. The material according to claim 16,wherein in the general formula [Ti(IV)3M3(O)3L4]·X, the Ti(IV) and the at least one divalent or trivalent metal are in a Ti(IV):M molar ratio between 50:50 and 99:

1.

18. The material according to claim 16 or 17, wherein the tricarboxylic ligand L is selected from the group consisting of an aryl-C6 tricarboxylic acid, an aryl-C3N3 tricarboxylic acid or a derivative thereof, of the type (aryl-C6)3-aryl-C6 tricarboxylic acid or (aryl-C6)3-aryl-C3N3 tricarboxylic acid.

19. The material according to any one of claims 16 to 18, wherein the tricarboxylic ligand L has one of the following structures A, B, C or D, wherein A: where R1 is -COOH and R2 is selected from the group -H, C1-C5 alkyl, -NH2, -OH, NO2, -COOH and halogen B: where R1 is -COOH C: where R1 is selected from: and R2 is selected from the group -H, C1-C5 alkyl, -NH2, -OH, NO2, -COOH and halogen D: where R1 is selected from: and R2 is selected from the group -H, C1-C5 alkyl, -NH2, -OH,NO2, -COOH and halogen.

20. The material according to any one of claims 16 to 19, wherein the tricarboxylic ligand L is 1,3,5-benzene-tricarboxylic acid.

21. Use of a material according to any one of claims 15 to 20 for gas capture and storage, solar fuel generation, photoactivated degradation, CO2 photoreduction, water purification and / or degradation of organophosphorus compounds.

22. Use of a material according to any one of claims 15 to 20 as a component or part of an electronic component, or as a porous or photoactive coating for contaminant control.