The use of metal-organic structures to generate metal-organic structures and H2.

Abstract

The present invention relates to metal-organic frameworks (MOFs) containing a trimetallic center and having pyrazole as a ligand in their structure. In particular, the present invention relates to MOFs containing units of formula (I). The present invention also relates to a photocatalytic method for producing H2, starting from liquid water or water vapor, using said materials. [Formula 1] JPEG2023544605000005.jpg81169

Description

Detailed description of the invention

[0001] This invention describes a metal-organic structure having in its structure a ligand (or connector between metal nodes) formed by three metal centers linked to a pyrazole, and its use for generating H2 under exposure to sunlight.

[0002] [Latest technological standards] Metal-organic structures (MOFs) are crystalline and porous materials whose structure is formed by nodes containing one or more metal atoms, linked by coordination bonds and Coulomb interactions with rigid organic ligands. M6O4(OH)4 12- The metal nodes of these MOFs, which are composed of units of Zr, are known in the art, where M is, for example, Zr +4 Ce 4+ and Hf 4+ These are tetrapositive metal cations, and the organic ligands are trimesic acid and 1,3,5(4-carboxyphenyl)benzene (Liu, Q. et al., Mesoporous Cages in Chemically Robust MOF Created by Large Number of Vertices with Reduced Connectivity. Journal of American Chemical Society). These are tricarboxylic acid aromatic compounds, such as those listed in 2019, 141, 488-496. These components define a porous structure corresponding to a solid exhibiting X-ray diffraction, as shown in Figure 1 accompanying the document. These MOF materials possess various properties derived from their surface area and composition, including their high gas adsorption capacity and catalytic activity.

[0003] In direct relation to the present invention, it is known in the art that some MOF materials exhibit photocatalytic activity when irradiated with photons of wavelengths corresponding to the UV-visible or near-infrared region, which can accelerate chemical reactions. The specific case of using MOFs as photocatalysts concerns the case where the irradiation source is natural sunlight reaching the Earth's surface. The spectrum of solar radiation on the Earth's surface corresponds to a photon distribution having wavelengths in the UV region above 380 nm, in addition to photons in the visible region between 400 nm and 800 nm, which contribute about 48% of the solar energy, and the remaining low-energy photons in the near-infrared region, in addition to wavelengths in the UV region above 380 nm, which contribute about 4% of the total energy.

[0004] Of the photocatalytic reactions described for MOF-type metal-organic materials, those particularly relevant to the present invention are the production of H2 by irradiation of these materials in contact with water, either in the liquid or vapor phase. A rare and exceptional case is the photocatalytic production of H2 using distilled water, fresh water, or seawater, in which amounts of H2 and O2 are simultaneously produced depending on the composition of the water. This type of process is known in the current state of the art as photocatalytic water splitting, and the evidence described shows that water acts simultaneously as both an electron donor and an electron acceptor compound. The reaction occurring in photocatalytic water splitting is represented by the following equation, which also includes the enthalpy change of the process.

[0005]

number

[0006] In light of non-fossil fuel-based renewable energy, the above reaction could be useful as a way to convert sunlight as a primary energy source into chemical energy, specifically into H2, which can be used as an energy vector in fuel cells or combustion systems. Furthermore, H2 can function as a chemical reagent in hydrogenation or reduction reactions.

[0007] Nevertheless, despite the potential of photocatalytic production of H2 starting from H2O, state-of-the-art MOF materials have been described that have very low and still insufficient efficiency for use in any industrial process (A. Dhakshinamoorthy, Z. Li, H. Garcia., Catalysis and photocatalysis by metal organic frameworks, Chem. Soc. Rev. 2018, 47, 8134-8172). Furthermore, the described MOF-based photocatalysts require noble metals and especially platinum to enhance their photocatalytic performance in the production of H2. Since platinum is an expensive metal, including it in the MOF material makes the material significantly more expensive and reduces the economic attractiveness of the process. Moreover, the photocatalytic activity of the MOF materials described to date drops significantly to less than 50% of their efficiency when irradiation is carried out exclusively with visible light and not with ultraviolet light, so the solar radiation of these materials is very inefficient.

[0008] Considering the state of the art, the development of MOF materials as photocatalysts for the efficient production of H2, in which the presence of noble metals is not required in their composition and whose photocatalytic response mainly originates from irradiation in the visible or near-infrared region of the electromagnetic spectrum, is considered important.

[0009] 〔Description of the Invention〕 The inventors have demonstrated that a MOF material containing, within its structure, a unit (represented by the following formula (I)) formed by a trimetallic center linked to pyrazole has photocatalytic activity for decomposing water into H2 and O2 upon irradiation with sunlight.

[0010] The unit formed by the trimetallic center linked to pyrazole acts as a ligand or linker between the metal nodes of the structure of the material, and each unit coordinates to three metal nodes of the structure by coordination bonds and / or Coulombic interactions.

[0011] Thus, a first aspect of the present invention relates to the use of a metal-organic framework as a catalyst for the photocatalytic production of hydrogen starting from water, characterized in that it comprises units of formula (I) in its structure:

[0012]

Chemical formula

[0013] M1, M2 and M3 are metal cations selected from a list comprising Co and Cu, and M1, M2 and M3 are equal to each other; X is a substituent selected from a list comprising H, CH3, OCH3, SO3 - , F, Cl, Br, I, NH2, and CF3; Y is COO - ; Z is a substituent selected from a list comprising H, CH3, OCH3, SO3 - , F, Cl, Br, I, NH2, and CF3, L1, L2, L3 and L4 are groups independently selected from a list comprising O 2- , OH - , H2O and halides, n1, n2, n3 and n4 are numbers independently selected from 0 or 1, Formula (I) contains the required L1, L2, L3 and L4 groups (which may be from 0, i.e., when n1, n2, n3 and n4 are all 0, to 4, i.e., when n1, n2, n3 and n4 are all 1), and compensates for the charge of the metal cation.

[0014] The term "halide" relates to F - , Cl - , Br - or I - .

[0015] In certain embodiments, X and Z are H.<|

[0016] In a particular embodiment, L1, L2, L3, and L4 are Cl - and OH - It is selected independently of others.

[0017] In a preferred embodiment, M1, M2, and M3 are Cu cations; X and Z are H, Y is -CO2H, and L1, L2, and L3 are Cl - And L4OH - or O 2- It is either true or not true.

[0018] In certain embodiments, the material comprises up to 30% by weight of L1, L2, and L3 groups, where L1, L2, and L3 groups are selected from acetates, benzoates, pyridinecarboxylates, or combinations thereof.

[0019] The material used in this invention has an X-ray diffraction pattern as shown in Figure 1.

[0020] These units of formula (I) act in MOFs as tricarboxylic acid organic ligands of the same type as trimesic acid, as discussed in the latest level of technology classification, and coordinate to metal nodes. Among the metal nodes to which these ligands can be coordinated are (Zr6O4(OH)4) 12+ (Hf6O4(OH)4) 12+ There are other known nodes in the latest state of the art, and these are also possible. Preferably, the node is (Zr6O4(OH)4) 12+ It is a unit.

[0021] Furthermore, at these nodes, it is possible to replace one or more metal cations with other metals. For example, at the node (Zr6O4(OH)4) 12+ Zr 4+ One or more cations are Ce 4+ or action 4+Alternatively, it may have a combination of six cations, replaced by a combination of those. Similarly, other metal nodes may contain two or more different metals.

[0022] The use of the present invention also relates to MOF materials containing the unit (ligand) of formula (I) in combination with another tricarboxylic acid ligand having similar molecular dimensions. The proportion of the unit (ligand) of formula (I) can vary between 15% and 100% molarly relative to the total number of ligands, and is more preferably between 10% and 25% molarly relative to the total number of ligands. In addition to the unit of formula (I), non-limiting examples of possible ligands include polycarboxyaromatic acids such as tris(4-carboxyphenyl)methane, tris(4-carboxyphenyl)amine, and 1,3,5-tris(4-carboxyphenyl)benzene.

[0023] In a preferred embodiment, The metal-organic structure is [Zr 6 (μ 3 -O) 4 (μ 3 -OH) 4 (OH) 6 (H 2 O) 6 -[Cu 3 (μ 3 -O)(μ-PyC) 3 (H 2 O) 6 ] 2 where PyC represents Py-4-CO 2 .

[0024] Another In a preferred embodiment, metal-organic structure is [Hf 6 (μ 3 -O) 4 (μ 3 -OH) 4 (OH) 6 (H 2 O) 6 -[Cu 3 (μ 3 -O)(μ-PyC) 3 (H 2 O) 6 ] 2 where PyC represents Py-4-CO 2 .

[0025] In another preferred embodiment, The metal-organic structure is [Zr 6 (μ 3 -O) 4 (μ 3 -OH) 4 (OH) 6 (H 2 O) 6 -[Co 3 (μ 3 -O)(μ-PyC) 3 (H 2 O) 6 ] 2 where PyC represents Py-4-CO 2 .

[0026] In another preferred embodiment, the material used in the present invention is: The pore contains one or more species that act as co-catalysts that are advantageous to the H2 photocatalyst generation reaction. The co-catalysts may be: • Nanoparticles of the aforementioned metals: platinum, gold, iridium, silver, rhodium, nickel, palladium, and combinations thereof. • Nanoparticles of metal oxides selected from cobalt, copper, ruthenium, molybdenum, strontium, zirconium, and combinations thereof. Nanoparticles of metal chalcogenides based on sulfides, selenides, or tellurides, combined with molybdenum, cadmium, zinc, lead, indium, copper, tungsten, and combinations thereof. The metal is chromium, manganese, iron, cobalt, nickel, copper, ruthenium, rhodium, palladium, silver, platinum, and iridium, and the organic ligand is a metal complex comprising an amine-type, imine-type, or heterocyclic nitrogen atom, and combinations thereof.

[0027] In this invention, the term "nanoparticles" refers to particles having dimensions between 10 nm and 100 nm.

[0028] In a preferred embodiment, the material used in the present invention contains 1% by weight of platinum and 1% by weight of ruthenium oxide as co-catalysts contained within its pores (the pores having a size between 0.5 nm and 5 nm).

[0029] These MOF materials, which contain units of formula (I) in their composition, may consist of particles of micrometer size or smaller, on a nanometer scale. They may also have geometric shapes defined as octahedrons, cubes, or irregular forms, and these materials may also have a high aspect ratio between the lateral dimension and the thickness.

[0030] In an unexpected way that cannot be inferred from the current state of technology, these materials containing the unit of formula (I) exhibit photocatalytic activity in water splitting that is more than an order of magnitude higher than the activity known to the current state of technology for other MOFs. Similar to the center of O2 generation in the natural photosynthetic systems present in green plants, the unexpected photocatalytic activity of the materials described herein may derive from the cooperative action of the three metal ions at the center of formula (I). Thus, successively, the photon energy can facilitate a continuous change in the oxidation state of the three metal ions coordinated to the same O atom, promoting O2 generation through protonation and deprotonation processes.

[0031] The present invention further relates to a photocatalytic method for producing hydrogen, starting from water, which includes contacting a metal-organic structure with water in a liquid or vapor state in the presence of light, preferably sunlight, as described in the first aspect of the present invention.

[0032] All preferred embodiments of the materials shown in the first embodiment of the present invention are also applicable to the present embodiment of the present invention relating to a photocatalytic method.

[0033] Photocatalytic generation of H2 by irradiation of an MOF material containing the unit of formula (I) can be carried out by suspending an appropriate amount of the material in an aqueous medium and exposing the suspension to the direct action of sunlight. The aqueous medium is 10 × 10 -6 W -1 ·m -1 Distilled water having the following ionic conductivity, or other types of natural water from rivers and wells, or seawater and brackish water may be used. The reaction must be carried out in a sealed container that allows for the collection and convenient separation or treatment of the formed gas. The reaction can be carried out at room temperature, either above or below 25°C. Alternatively, radiation can be carried out by exposing a photocatalytic film on a MOF substrate to water vapor. The reaction can similarly be carried out with natural light or focused sunlight using mirrors, lenses, or other optical devices. Radiation can also be carried out with artificial light having various wavelengths in the ultraviolet, visible, or near-infrared regions, or combinations thereof. Irradiation sources may be incandescent lamps or discharge lamps, as well as light-emitting diodes. The radiation may also be monochromatic, for example, from a laser source.

[0034] Irradiation can be carried out by contacting the photocatalyst with water in the liquid or gas phase. MOFs comprising formula (I) can be dispersed in suspensions in both liquid and vapor fluids, or immobilized in the form of films or coatings. The reaction can be carried out at temperatures above or below 25°C, within the thermal stability range of the material up to 150°C.

[0035] Irradiation can be carried out at both atmospheric pressure and pressures lower or higher than atmospheric pressure between 0.01 MPa and 5 MPa. In both cases, the irradiation can be carried out by a batch method, in which a certain amount of water is introduced and left to stand until the conversion occurs, and then liquid or gaseous water flows continuously in contact with the photocatalyst.

[0036] In a preferred embodiment of this method, the material of the present invention is deposited in the form of a thin film with a thickness of between 1 micron and 20 microns, and a bed of water with a thickness of between 0.5 cm and 12 cm is configured to flow over the film at a temperature between 4°C and 40°C and a rate between 0.1 ml / hour and 2 ml / hour, and the film is exposed to sunlight or artificial light.

[0037] In another preferred embodiment, the material of the present invention is deposited in the form of a thin film with a thickness of several microns, and a flow of water vapor at a temperature between 100°C and 150°C is configured to flow over the film at a speed between 0.1 ml / hour and 2 ml / hour, and the film is exposed to sunlight or artificial light.

[0038] The final aspect of the present invention relates to a metal-organic material characterized by including a unit of formula (I) in its structure, as described in the present invention, formula: [Zr6(μ3-O)4(μ3-OH)4(OH)6(H2O)6]-[Cu3(μ3-O)(μ-PyC)3(H2O)6]2 Provided that it does not contain [specific compound], "PyC" refers to Py-4-CO2.

[0039] All preferred embodiments of the material shown in the first embodiment of the present invention are also applicable to this final embodiment of the present invention relating to the material itself.

[0040] [Material properties]: The materials of the present invention are crystalline and porous solids of the so-called metal-organic structure type, which contain units of formula (I) in their structure and may further contain co-catalysts housed within pores. Accordingly, these materials are characterized by a combination of chemical analysis techniques, X-ray diffraction, gas adsorption, and spectroscopic measurements.

[0041] Chemical analysis of these materials can be performed after they have been completely dissolved in a suitable medium, such as concentrated HF in an aqueous medium. After dissolving the materials, the resulting liquid is subjected to inductively coupled plasma (ICP) analysis, and the signal is measured by atomic emission spectroscopy (AES) or mass spectrometry to quantify the signal against a calibration pattern.

[0042] The crystallinity and structure of the material are determined by the X-ray diffraction pattern, and the diffraction peaks are recorded with the determined angular value and intensity based on the crystal structure. Figure 1 shows the X-ray diffraction pattern of a material corresponding to the present invention.

[0043] The surface area can be determined by nitrogen adsorption at a temperature of 77K, and the volume of this adsorbed gas can be determined at various relative pressures. In addition to adsorption, desorption measurements can also be performed. Micropore volume and pore dimensions can be established by fitting experimental adsorption values ​​to a theoretical model (BJH-Barrett-Jolenda-Halenda). A typical value for the surface area in the material of the present invention is 500 m². 2 / g -1 ~2000m 2 / g -1 It is between these two points.

[0044] X-ray photoelectron spectroscopy enables the detection and quantification of the units of formula (I) present in the material, thereby allowing the relative ratio of each atom to be established by signal correction.

[0045] The material of the present invention, including a co-catalyst contained within pores, can be analyzed by transmission microscopy. Transmission microscopy allows observation of the presence of nanoparticles and determination of the dimensional dispersion of these nanoparticles. The co-catalyst, along with metal nodes containing more than one cation, contributes to increasing the efficiency of photocatalytic processes for hydrogen and oxygen evolution.

[0046] Ultraviolet-visible absorption spectroscopy allows for the determination of the wavelengths of photons absorbed by a material. These spectra can be recorded in diffuse reflectance mode. In diffuse reflectance mode, a solid material is packed into a sample holder, and the sample holder is positioned so that it forms an integrating sphere at the focal point. The interior of this sphere is illuminated by the absorbed radiation, and the absorbed intensity is determined by comparison with a barium sulfate pattern. Photoresponse and photocurrent measurements allow for the determination of the wavelengths of radiation, which are connected to an external circuit and lead to the generation of a current between an anode and cathode immersed in a common electrolyte. These photocurrent measurements are performed by depositing a thin layer of material containing the unit of equation (I) onto a transparent conductive electrode. This electrode is electrically connected to a potentiostat, which allows for the determination of the current measurement and ultimately the application of a bias voltage to the electrode. The working electrode is also connected to a potentiostat, which may be a platinum plate and a reference electrode whose potential value is known.

[0047] The stability of a material with respect to pH and temperature can be established by dispersing the solid sample in an aqueous solution at a known pH that can be subjected to heating between 25°C and 100°C, and the metal content in the solution is measured by elemental analysis over time. The material of the present invention is stable in the pH range of 4 to 8 and stable at temperatures up to 80°C for more than 24 hours.

[0048] The thermal stability of a material can be established by thermogravimetric measurements on a thermobalance. In these measurements, weight loss is determined according to the temperature of the system, and this weight loss is due to the decomposition of the material. It has been observed that the material of the present invention can be stable up to 150°C.

[0049] [Brief explanation of the drawing] Figure 1. X-ray powder diffraction pattern corresponding to the target material of the present invention, recorded by a Philips X'Pert instrument.

[0050] [Examples] The present invention and a material containing a unit of formula (I) in a metal-organic crystalline structure that can promote complete water splitting have been outlined, and several examples demonstrating how H2 can be produced according to the present invention are described below.

[0051] <Example 1. Photocatalytic water splitting of a suspension in an aqueous phase at pH 7 by irradiation with sunlight, using an MOF having the formula [Zr6(μ3-O)4(μ3-OH)4(OH)6(H2O)6]-[Cu3(μ3-O)(μ-PyC)3(H2O)6]2 (where "PyC" means Py-4-CO2)> The material was prepared in advance following a procedure slightly modified from the latest technological standards (Liu, Q. et al. Journal of the American Chemical Society 2019, 141, 488-496), and its X-ray pattern corresponds to that shown in Figure 1, and its formula is consistent with the chemical analysis. Briefly, 1 ml each of three solutions containing Cu(NO3)2·3H2O (0.2 mmol; 48.3 mg), H-pyrazole-4-carboxylic acid (0.2 mmol; 23.5 mg), and ZrOCl2·8H2O (0.12 mmol; 38.7 mg) was sequentially mixed with N,N-dimethylformamide (DMF) in a 20 ml glass vial, to which 450 μl of acetic acid was added. The vial was sealed and placed in a preheated oven at 100°C for 12 hours. After that, the vial was cooled to room temperature and the supernatant was separated. The obtained solid is washed with DMF (3 × 5 ml) and then with acetonitrile (3 × 5 ml). The solid material is stored in acetonitrile for use. 50 mg of this material is dispersed in 50 ml of distilled water by magnetic stirring and placed inside a 70 ml Pyrex glass reactor that can be sealed. Before the start of irradiation, the reactor solution and free volume were purged by a 1 ml / min argon flow bubbling through the reactor for at least 1 hour before the start of the reaction to reduce the amount of O2 present in the system. The system is irradiated by exposure to a beam from a solar simulator consisting of a Xe lamp with an AM 1.5 filter, simulating sunlight irradiation on the Earth's surface. The radiant power is 100 mW·cm. 2 The exposed surface of the reactor was 13 cm 2The distance between the beam outlet of the solar simulator and the photoreactor was approximately 10 cm. The temperature of the system during radiation varied between 25°C and 35°C. Exposure to simulated sunlight was performed for 24 hours, and the composition of the free volume of the reactor was analyzed by a gas chromatograph capable of detecting and quantifying the presence of H2 and O2. After 24 hours, the values ​​of H2 and O2 under these conditions were 6 mmol and 2.5 mmol, respectively. The material [Zr6(μ3-O)4(μ3-OH)4(OH)6(H2O)6]-[Cu3(μ3-O)(μ-PyC)3(H2O)6]2 is stable under these reaction conditions, and the production of H2 and O2 of the same values ​​listed above was observed when the system was purged with argon after the first use until the presence of H2 was no longer detectable in volume, and then this process was repeated for another 24 hours.

[0052] <Example 2. Photocatalytic water splitting by sunlight irradiation in a suspension in an aqueous phase at pH 7, using [Zr6(μ3-O)4(μ3-OH)4(OH)6(H2O)6]2 containing platinum nanoparticles as the photocatalyst> Prior to the photocatalytic reaction of the platinum-containing material [Zr6(μ3-O)4(μ3-OH)4(OH)6(H2O)6]-[Cu3(μ3-O)(μ-PyC)3(H2O)6]2, a material was prepared starting from an MOF containing the unit Cu3(Py-4-CO2H)3OH from Example 1. Pt is deposited by photodeposition using chloroplatinic acid. Thus, 50 mg of MOF was dispersed in water-methanol in a 3:1 volume ratio, where 3 mg of chloroplatinic acid was pre-dissolved in water and introduced into a quartz tube. Next, a photocatalytic test was performed as shown in Example 1. After 24 hours, the H2 and O2 values ​​under these conditions were 10 mmol × g, respectively. -1 and 4.5 mmol × g -1The material [Zr6(μ3-O)4(μ3-OH)4(OH)6(H2O)6]-[Cu3(μ3-O)(μ-PyC)3(H2O)6]2, which contains platinum nanoparticles, is stable under these reaction conditions, and after the first use, if the system is purged with argon until the presence of H2 is no longer detected in the volume of the photoreactor, and then the process is repeated for a further 24 hours, the production of H2 and O2 at the same values ​​listed above will be observed.

[0053] <Example 3. Photocatalytic water splitting by sunlight irradiation in a suspension in an aqueous phase at pH 7 using [Zr6(μ3-O)4(μ3-OH)4(OH)6(H2O)6]2 containing platinum and ruthenium oxide> Before the H2 and O2 generation starting from water, a MOF material containing the unit Cu3(Py-CO2)3OH is fabricated, this time including platinum and ruthenium oxide nanoparticles as co-catalysts. x The preparation is carried out by simultaneously depositing both metals, starting with chloroplatinic acid and potassium perthenate dissolved in water, into an aqueous solution prepared by dispersing 50 mg of the MOF used in Example 1 in a 3:1 volume ratio in water-methanol. After purging the system with argon, the mixture is irradiated for 4 hours using a visible-ultraviolet lamp. Next, a photocatalytic test is performed as shown in Example 1. After 24 hours, the H2 and O2 values ​​under these conditions were 12 mmol × g, respectively. -1 and 5.5 mmol × g -1 The material [Zr6(μ3-O)4(μ3-OH)4(OH)6(H2O)6]-[Cu3(μ3-O)(μ-PyC)3(H2O)6]2, using platinum and ruthenium nanoparticles, is stable under these reaction conditions. After the initial use, purging the system with argon until the presence of H2 is no longer detectable in the reactor, and then repeating the process for a further 24 hours, results in the same production of H2 and O2 as listed above.

[0054] <Example 4. [Zr 6 (μ 3 -O)4 (μ 3 -OH) 4 (OH) 6 (H 2 O) 6 -[Co 3 (μ 3 -O)(μ-PyC) 3 (H 2 O) 6 ] Photocatalytic water splitting by sunlight irradiation in a suspension in an aqueous phase at pH 7 using method 2. The flexibility in MOF structure compositions is demonstrated by the possibility of substituting Cu with Co in the trispyrazolyl units. The production of this material is carried out according to the latest technological standards for the production of Cu compounds, but with the substitution of tris(2-carboxy)pyrazolyl copper with tris(2-carboxy)pyrazolyl cobalt, followed by the steps outlined in the latest technological standards (Liu, Q. et al. Journal of the American Chemical Society 2019, 141, 488-496). Thus, the procedure is as shown in Example 1, but with the substitution of the copper material with other similar materials, here with copper replaced by cobalt. The photocatalytic hydrolysis method under the indicated conditions was 3 mmol × g each. -1 and 1.2 mmol × g -1 This produces H2 and O2 values.

[0055] <Example 5. Approximately 20cm each connected in series 2 1m including 6 modules 2 Deposited on a board [Zr 6 (μ 3 -O) 4 (μ 3 -OH) 4 (OH) 6 (H 2 O) 6 -[Cu 3 (μ 3 -O)(μ-PyC) 3 (H 2 O) 6 ] Continuous photocatalytic water splitting using method 2 > material is [Zr 6 (μ 3 -O) 4 (μ 3 -OH) 4(OH) 6 (H 2 O) 6 -[Cu 3 (μ 3 -O)(μ-PyC) 3 (H 2 O) 6 ] 2 (μ First, to deposit the MOF in each module, a paste containing Nafion and ethanol is prepared by manually dispersing 100 mg of MOF in 5 ml of a commercially available 5% Nafion solution in ethanol in a mortar. This paste is then deposited onto a Teflon support and spread with a blade that provides a very thin thickness according to a method known as a razor blade. The plate is then dried at 100°C for 24 hours. H2 generation is carried out by irradiating the aqueous phase at pH 7 with natural sunlight, which, under ambient conditions measured on a sunny day in Valencia, produces 400 ml of H2.

[0056] <Example 6. A plate deposited on a plate as described in Example 5 [Zr 6 (μ 3 -O) 4 -OH) 3 (OH) 4 -[Cu 6 (H 2 O) 6 (μ 3 -O)(μ-PyC) 3 (μ 3 (H 2 O) 6 ] Photocatalytic water splitting in the gas phase using method 2 > H2 is generated using 0.5 ml x min as a carrier gas. -1 Using an N2 stream, the experiment was conducted by irradiating the sample with water vapor at 60°C and natural sunlight, yielding 600 ml of H2 measured under ambient conditions.

[0057] <Example 7. [Zr 6 (μ 3 -O) 4 -OH) 3 (OH) 4 -[Cu 6 (H 2 O) 6 (μ 3 -O)(μ-PyC) 3(μ 3 (H 2 O) 6 ] Photocatalytic water splitting of a suspension in an aqueous phase at pH 7 at high temperature using method 2, by irradiation with sunlight. 50 mg of a pre-synthesized material, whose X-ray pattern corresponds to that shown in Figure 1, is dispersed in 50 ml of distilled water using a magnetic stirring device and placed in a 70 ml glass reactor that can be sealed. Before the start of irradiation, to reduce the amount of O2 present in the system, the solution and the free volume of the reactor were purged for at least 1 hour before the start of the reaction by bubbling a 1 ml / min argon stream through the reactor. The system is irradiated by exposure to a beam from a solar simulator consisting of a Xe lamp with an AM1.5 filter, simulating sunlight irradiation on the Earth's surface. The radiant power is 100 mW·cm. 2 The exposed surface of the reactor was 13 cm 2 The distance between the beam outlet of the solar simulator and the photoreactor was approximately 10 cm. The temperature of the system during radiation varied between 20°C and 100°C. Exposure to simulated sunlight was performed for 24 hours, and the composition of the free volume of the reactor was analyzed by a gas chromatograph capable of detecting and quantifying the presence of H2 and O2. After 24 hours, the values ​​of H2 and O2 under these conditions were 2 mmol of H2 and 0.9 mmol of O2, respectively, at 100°C. [Zr 6 (μ 3 -O) 4 -OH) 3 (OH) 4 -[Cu 6 (H 2 O) 6 (μ 3 -O)(μ-PyC) 3 (μ 3 (H 2 O) 6 ] Compound 2 is stable under these reaction conditions, and the same values ​​of H2 and O2 production are observed, as described above, when purging the system with argon after the first use until the presence of H2 is no longer detected in the reactor volume, and then repeating the process for a further 24 hours.

[0058] <Example 8. [Zr 6 (μ 3 -O) 4 -OH) 3 (OH) 4 -[Cu 6 (H 2 O) 6 (μ 3 -O)(μ-PyC) 3 [[ID=]](μ 3 (H 2 O) 6 ] Photocatalytic hydrolysis of brine in a suspension in an aqueous phase at pH 7 using method 2, by irradiation with sunlight. Next, the photocatalytic test was performed using saline solution as shown in Example 1. After 24 hours, the H2 and O2 values ​​under these conditions were 4 mmol × g, respectively. -1 and 2.5 mmol × g -1 It was. Materials [Zr 6 (μ 3 -O) 4 -OH) 3 (OH) 4 -[Cu 6 (H 2 O) 6 (μ 3 -O)(μ-PyC) 3 [Hf 3 (H 2 O) 6 ] Compound 2 is stable under these reaction conditions, and the same values ​​of H2 and O2 production are observed, as described above, when the system is purged with argon after the first use until the presence of H2 is no longer detected in the volume of the photoreactor, and then when the process is repeated for a further 24 hours.

[0059] <Example 9. Formula> (μ 6 (μ 3 -O) 4 -OH) 3 (OH) 4 -[Cu 6 (H 2 O) 6 (μ 3 -O)(μ-PyC) 3 [Hf 3 (H 2 O) 6 ] Photocatalytic water splitting of a suspension in an aqueous phase at pH 7 by irradiation with sunlight using an MOF containing 2. To further clarify the flexibility of the MOF material compositions described herein for photocatalytic water splitting, the Zr at the nodal positions was determined according to the synthesis method described in the latest state of the art (Liu, Q. et al. Journal of the American Chemical Society 2019, 141, 488-496). IV to Hf IV It can be replaced with: Materials (μ 6 (μ 3 -O) 4 -OH) 3 (OH) 4 -[Cu 6 (H 2 O) 6 (μ 3 -O)(μ-PyC) 3 (μ 3 (H 2 O) 6 ] Figure 2 shows the efficiency of H2 generation by sunlight irradiation, identical to the material described in Example 1. Furthermore, the following process is comparable to the processes shown in Examples 2, 3, and 4, and allows for the incorporation of Pt or Pt-RuO2 into the pores of the material, and also allows for the substitution of Cu with Co in the composition, while maintaining the same structure corresponding to the X-ray diffraction pattern shown in Figure 1.

[0060] <Example 10. [Zr 6 (μ 3 -O) 4 -OH) 3 (OH) 4 -[Cu 6 (H 2 O) 6 (μ 3 -O)(μ-PyC) 3 (μ 3 (H 2 O) 6 ] A comparative study comparing the efficiency of method 2 with that of a known related material, Zr6(μ3-O)4(μ3-OH)4(BDC-NH2)3(BDC-NH2:2-amino-1,4-benzenedicarboxylate), using the latest technological standards. Surprisingly, this invention describes the high photocatalytic activity of an organic structure containing formula I in the generation of H2. [Zr 6 (μ 3 -O) 4-OH) 3 (OH) 4 -[Cu 6 (H 2 O) 6 (μ 3 -O)(μ-PyC) 3

Figure 1

[0061] ​ X-ray powder diffraction pattern corresponding to the material of the present invention, recorded by a Philips X'Pert instrument.

Claims

1. The use of a metal-organic structure characterized by including a unit of formula (I) in its structure: 【Chemistry 1】 M １ M ２ and M ３ M is a metal cation selected from a list consisting of Co and Cu. １ M ２ and M ３ They are equal to each other; X and Z are H; Y is COO － And; L １ 、 L ２ 、 L ３ and L ４ are groups independently selected from the list consisting of O ２－ , OH － and H ２ O, and are radicals selected independently from the list consisting of O, OH and H. n １ , n ２ , n ３ and n ４ is a number that is independently selected from 0 and 1. Use of metal-organic structures as catalysts for photocatalytic hydrogen production starting from water.

2. L １ , L ２ , L ３ and L ４ However, OH － The use described in claim 1.

3. M １ M ２ and M ３ is a Cu cation; X and Z are H, Y is -CO2-, and L １ , L ２ , L ３ and L ４ oh － The use according to claim 1 or 2, which is either true or false.

4. The proportion of units of formula (I) in the above structure is The use according to any one of claims 1 to 3, wherein the amount is between 15% and 100% in moles relative to the total amount of ligands.

5. The aforementioned metal-organic structure is [Zr ６ (μ ３ -O) ４ (μ ３ -OH) ４ (OH) ６ (H ２ O) ６ ]-[Cu ３ (μ ３ -O)(μ-PyC) ３ (H ２ O) ６ ] ２ 、 I ６ (μ ３ -9) ４ (μ ３ -O() ４ (98) ６ (8) ２ 9) ６ ]-Co ３ (μ ３ -O)(µ-PyC) ３ (8) ２ 9) ６ ) ２ および [Hf ６ (μ ３ -O) ４ (μ ３ -OH) ４ (OH) ６ (H ２ O) ６ ]-[Cu ３ (μ ３ -O)(μ-PyC) ３ (H ２ O) ６ ] ２ Selected from a list consisting of, The aforementioned PyC is Py-4-CO ２ To show, The use described in claim 1.

6. The metal-organic structure comprises H ２ It contains one or more species contained within pores that act as co-catalysts that are advantageous in the photocatalytic generation reaction, The co-catalyst is selected from the following list, for use according to any one of claims 1 to 5: - Nanoparticles of metals selected from platinum, gold, iridium, silver, rhodium, nickel, palladium, and combinations thereof. Nanoparticles of metal oxides selected from cobalt, copper, ruthenium, molybdenum, strontium, zirconium, and combinations thereof. Nanoparticles of metal chalcogenides based on sulfides, selenides, or tellurides, combined with molybdenum, cadmium, zinc, lead, indium, copper, tungsten, and combinations thereof, as well as - A metal complex wherein the metal of the metal complex is chromium, manganese, iron, cobalt, nickel, copper, ruthenium, rhodium, palladium, silver, platinum, and iridium, and the organic ligand of the metal complex comprises an amine-type, imine-type, or heterocyclic nitrogen atom, and combinations thereof.

7. A water-start photocatalytic method for producing hydrogen, comprising contacting a metal-organic structure according to any one of claims 1 to 6 with water in a liquid or vapor state in the presence of sunlight or artificial light.

8. The aforementioned metal-organic structure is deposited in the form of a thin film with a thickness between 1 micron and 20 microns, A bed of water with a thickness of 0.5 cm to 12 cm is configured to flow over the membrane at a temperature of 4°C to 40°C and a speed of 0.1 ml / hour to 2 ml / hour. The method according to claim 7, wherein the film is exposed to sunlight or artificial light.

9. It is characterized by including the following formula: [Hf ６ (μ ３ -O) ４ (μ ３ -OH) ４ (OH) ６ (H ２ O) ６ ]-[Cu ３ (μ ３ -O)(μ-PyC) ３ (H ２ O) ６ ] ２ ; The PyC is Py-4-CO ２ indicating Metal-organic structures.

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