METAL ORGANIC FRAMEWORK AND USE THEREOF FOR GENERATING H2

Abstract

The present invention relates to metal-organic frameworks (MOFs) which contain trimetallic centres with pyrazole as a ligand in the structure thereof. Particularly, it relates to MOFs which contain units of formula (I). The present invention also relates to a photocatalytic method for generating H.sub.2 starting from liquid water or vapour using said materials.

##STR00001##

Claims

1. A use of a metal organic framework characterised in that it comprises units of formula (I) in the structure thereof: ##STR00003## wherein M.sub.1, M.sub.2 and M.sub.3 are metal cations selected from the list comprising: Co and Cu, wherein M.sub.1, M.sub.2 and M.sub.3 are equal to each other; X is a substituent selected from the list comprising: H, CH.sub.3, OCH.sub.3, SO.sub.3.sup., F, Cl, Br, I, NH.sub.2, CF.sub.3; Y is COO.sup.; Z is a substituent selected from the list comprising: H, CH.sub.3, OCH.sub.3, SO.sub.3.sup., F, Cl, Br, I, NH.sub.2, CF.sub.3; L.sub.1, L.sub.2, L.sub.3 and L.sub.4 are groups independently selected from the list comprising: O.sup.2, OH.sup., H.sub.2O and halide; n.sub.1, n.sub.2, n.sub.3 and n.sub.4 are numbers independently selected from 0 or 1, as a catalyst for the photocatalytic production of hydrogen starting from water.

2. The use, according to claim 1 wherein X is H and Z is other than H.

3. The use, according to any of the preceding claims 1 to 2 wherein X and Z are H.

4. The use, according to any of the preceding claims 1 to 3, wherein L.sub.1, L.sub.2, L.sub.3 and L.sub.4 are independently selected from Cl.sup. and OH.sup..

5. The use, according to any of the preceding claims 1 to 4, wherein M.sub.1, M.sub.2 and M.sub.3 are Cu cations; X and Z are H, Y is CO.sub.2H and L.sub.1, L.sub.2, L.sub.3 and L.sub.4 is Cl.sup., OH.sup. or is not present.

6. The use, according to any of the preceding claims 1 to 5, wherein the proportion of units of formula (I) in the structure is between 15% and 100%, in moles with respect to the total of ligands.

7. The use, according to claim 1 wherein the unit cell of the material comprises the following formula:
[M.sup.IV.sub.6(.sub.3-O).sub.4(.sub.3-OH).sub.4(OH).sub.6(H.sub.2O).sub.6(formula (I)).sub.2].sub.p.Math.(solvent).sub.m wherein M.sup.IV is a tetravalent metal selected from Zr or Hf o or combinations thereof; p is an integer between 1 and 1000; the solvent is selected from the list comprising: H.sub.2O, dimethylformamide, diethylformamide or formamide.

8. The use, according to claim 1 wherein the unit cell of the material comprises the formula:
[Zr.sub.6(.sub.3-O).sub.4(.sub.3-OH).sub.4(OH).sub.6(H.sub.2O).sub.6][Cu.sub.3(.sub.3-O)(-Py-4-CO.sub.2).sub.3(OH)(H.sub.2O).sub.2].sub.2.
[Hf.sub.6(.sub.3-O).sub.4(.sub.3-OH).sub.4(OH).sub.6(H.sub.2O).sub.6][Cu.sub.3(.sub.3-O)(-Py-4-CO.sub.2).sub.3(OH)(H.sub.2O).sub.2].sub.2
or
[Zr.sub.6(.sub.3-O).sub.4(.sub.3-OH).sub.4(OH).sub.6(H.sub.2O).sub.6][Cu.sub.3(-Py-4-CO.sub.2).sub.3].sub.2.

9. The use, according to any of the preceding claims 1 to 8, wherein the material contains one or more species housed in the pores which act as cocatalysts favouring the H.sub.2 photocatalytic generation reaction wherein said cocatalysts are selected from the list comprising: nanoparticles of the metals platinum, gold, iridium, silver, rhodium and nickel, palladium and combinations thereof, nanoparticles of metal oxides that are selected from cobalt, copper, ruthenium, molybdenum, strontium, zirconium and combinations thereof. Nanoparticles of metal chalcogenides based on sulphides, selenides or tellurides combined with molybdenum, cadmium, zinc, lead, indium, copper, tungsten and combinations thereof. Metal complexes wherein the metal is chrome, manganese, iron, cobalt, nickel, copper, ruthenium, rhodium, palladium, silver, platinum and iridium and the organic ligand contains amine-, imine- or heterocyclic-type nitrogen atoms, and combinations thereof.

10. A photocatalytic method for producing hydrogen starting from water which comprises contacting a metal-organic framework, as described in any of claims 1 to 9, with water in liquid or vapour state and in the presence of sunlight or artificial light.

11. The method according to claim 10 wherein the metal-organic framework is deposited in the form of a thin film between 1 and 20 microns thick and a bed of water between 0.5 and 12 cm thick is made to flow over said film at a temperature between 4 and 40 C. and at a rate between 0.1 and 2 ml/h, said film being exposed to sunlight or artificial light.

12. The method according to claim 10 wherein the metal-organic framework is deposited in the form of a thin film several microns thick and a flow of water vapour at a temperature between 100 and 150 C. is made to flow over said film at a rate between 0.1 and 2 ml/h and wherein said film is exposed to sunlight or artificial light.

13. A metal-organic framework characterised in that it comprises the formula:
[M.sup.IV.sub.6(.sub.3-OH).sub.4(.sub.3-OH).sub.4(OH).sub.6(H.sub.2O).sub.6(formula (I)).sub.2].sub.p.Math.(solvent).sub.m wherein M.sup.IV is a tetravalent metal selected from Zr or Hf or combinations thereof; p is an integer between 1 and 1000 and m is an integer between 0 and 50; the solvent is selected from the list comprising: H.sub.2O, dimethylformamide, diethylformamide or formamide; wherein formula (I) refers to the unit of formula (I) as described in any of claims 1 to 9, with the proviso that the material does not comprise the formula: [Zr.sub.6(.sub.3-O).sub.4(.sub.3-OH).sub.4(OH).sub.6(H.sub.2O).sub.6][Cu.sub.3(.sub.3-O)(-PyC).sub.3(H.sub.2O).sub.6].sub.2.

14. A metal-organic framework, according to claim 13 selected from:
[Hf.sub.6(.sub.3-O).sub.4(.sub.3-OH).sub.4(OH).sub.6(H.sub.2O).sub.6][Cu.sub.3(.sub.3-O)(-Py-4-CO.sub.2).sub.3(OH)(H.sub.2O).sub.2].sub.2
or
[Zr.sub.6(.sub.3-O).sub.4(.sub.3-OH).sub.4(OH).sub.6(H.sub.2O).sub.6][Cu.sub.3(-Py-4-CO.sub.2).sub.3].sub.2.

Description

DESCRIPTION OF THE FIGURES

[0065] FIG. 1. X-ray powder diffractogram corresponding to the materials object of the present invention recorded by means of a Philips X'Pert equipment.

EXAMPLES

[0066] Having generally presented the present invention and the materials containing units of formula (I) in the crystal framework of a metal-organic structure capable of promoting complete water splitting, some examples are described below that show how the generation of H.sub.2 can be carried out according to the present invention.

Example 1. Photocatalytic Water Splitting Using a MOF with Formula [Zr.SUB.6.(.SUB.3.-O).SUB.4.(.SUB.3.-OH).SUB.4.(OH).SUB.6.(H.SUB.2.O).SUB.6.][Cu.SUB.3.(.SUB.3.-O)(-PyC).SUB.3.(H.SUB.2.O).SUB.6.].SUB.2 .(PvC Refers to Py-4-CO.SUB.2.) by Irradiation with Sunlight in Suspension in Aqueous Phase at pH 7

[0067] The material is previously prepared according to a slightly modified procedure from the state of the art (Liu, Q. et al. Journal of the American Chemical Society 2019, 141, 488-496) and the X-ray pattern of which corresponds to that shown in FIG. 1 and the formula of which coincides with the chemical analysis. Briefly, 1 ml of three dissolutions of Cu(NO.sub.3).sub.2.Math.3H.sub.2O (0.2 mmol; 48.3 mg), H-pyrazole-4-carboxylic acid (0.2 mmol; 23.5 mg) and ZrOCl.sub.2.Math.8H.sub.2O (0.12 mmol; 38.7 mg) are consecutively mixed in N, N-dimethylformamide (DMF) in a 20 ml glass vial to which 450 l of acetic acid are added. The vial is hermetically sealed and placed in a preheated oven at 100 C. for 12 h. After that time, the vial is allowed to cool to ambient temperature, separating the supernatant liquid. The resulting solid is washed with DMF (35 ml) and then with acetonitrile (35 ml). The solid material is stored in acetonitrile for use thereof. 50 mg of this material are dispersed by magnetic stirring in 50 ml of distilled water and is placed inside a 70 ml Pyrex glass reactor capable of being hermetically sealed. Prior to the start of the irradiation the solution and the free volume of the reactor were purged by means of a stream of argon of 1 ml/min that was bubbled through the reactor for at least 1 hour before the start of the reaction in order to reduce the amount of O.sub.2 present in the system. The system is irradiated by exposure to the beam of a solar simulator consisting of an Xe lamp with an AM 1.5 filter that simulates the solar irradiation of the earth's surface. The radiation power was 100 mW.Math.cm.sup.2 and the exposed surface of the reactor was 13 cm.sup.2. The distance between the exit of the beam of the solar simulator and the photoreactor was about 10 cm. The temperature of the system during radiation varied between 25 and 35 C. Exposure to simulated sunlight is carried out for 24 hours, analysing the composition of the free volume of the reactor by means of a gas chromatograph that enables the detection and quantification of the presence of H.sub.2 and O.sub.2. After 24 hours the values of H.sub.2 and O.sub.2 under these conditions were 6 and 2.5 mmol, respectively. The material [Zr.sub.6(.sub.3-O).sub.4(.sub.3-OH).sub.4(OH).sub.6(H.sub.2O).sub.6][Cu.sub.3(.sub.3-O)(-PyC).sub.3(H.sub.2O).sub.6].sub.2 was stable under these reaction conditions and when the system is purged with argon after the first use until the presence of H.sub.2 is not detected in the volume and then the process is repeated for another 24 hours, the same values of H.sub.2 and O.sub.2 production are observed as those listed above.

Example 2. Photocatalytic Water Splitting Using [Zr.SUB.6.(.SUB.3.-O).SUB.4.(.SUB.3.-OH).SUB.4.(OH).SUB.6.(H.SUB.2.O).SUB.6.][Cu.SUB.3.(.SUB.3.-O)(-PyC).SUB.3.(H.SUB.2.O).SUB.6.].SUB.2 .Containing Platinum Nanoparticles as Photocatalyst by Irradiation with Sunlight in Suspension in Aqueous Phase at pH 7

[0068] Prior to the photocatalytic reaction of the material [Zr.sub.6(.sub.3-O).sub.4(.sub.3-OH).sub.4(OH).sub.6(H.sub.2O).sub.6][Cu.sub.3(.sub.3-O)(-PyC).sub.3(H.sub.2O).sub.6].sub.2 containing platinum, the material is prepared starting from MOF containing units Cu.sub.3(Py-4-CO.sub.2H).sub.3OH from Example 1 wherein Pt is deposited by the photodeposition method using chloroplatinic acid. Thus, 50 mg of MOF are dispersed in water-methanol in a 3 to 1 volume ratio wherein 3 mg of chloroplatinic acid have been previously dissolved in water and introduced in a quartz tube. Next, the photocatalytic test is carried out as indicated in Example 1. After 24 hours the values of H.sub.2 and O.sub.2 under these conditions were 10 and 4.5 mmolg.sup.1, respectively. The material [Zr.sub.6(.sub.3-O).sub.4(.sub.3-OH).sub.4(OH).sub.6(H.sub.2O).sub.6][Cu.sub.3(.sub.3-O)(-PyC).sub.3(H.sub.2O).sub.6].sub.2 with platinum nanoparticles was stable under these reaction conditions and when the system is purged with argon after the first use until the presence of H.sub.2 is not detected in the volume of the photoreactor and then the process is repeated for another 24 hours, the same values of H.sub.2 and O.sub.2 production are observed as those listed above.

Example 3. Photocatalytic Water Splitting Using [Zr.SUB.6.(.SUB.3.-O).SUB.4.(.SUB.3.-OH).SUB.4.(OH).SUB.6.(H.SUB.2.O).SUB.6.][Cu.SUB.3.(.SUB.3.-O)(-PyC).SUB.3.(H.SUB.2.O).SUB.6.].SUB.2 .Containing Platinum and Ruthenium Oxide by Irradiation with Sunlight in Suspension in Aqueous Phase at pH 7

[0069] Prior to the H.sub.2 and O.sub.2 generation reaction starting from water, the MOF material is prepared containing units Cu.sub.3(Py-CO.sub.2).sub.3OH in turn containing nanoparticles of platinum and ruthenium oxide as cocatalysts. The preparation of PtRuO.sub.x is carried out by simultaneously depositing both metals starting from chloroplatinic acid and potassium perruthenate dissolved in water in a solution wherein 50 mg of MOF used in example 1 are dispersed in water methanol in a 3 to 1 volume ratio. After purging the system with argon, this mixture is irradiated with a lamp that emits visible-ultraviolet light for 4 hours. Next, the photocatalytic test is carried out as indicated in Example 1. After 24 hours the values of H.sub.2 and O.sub.2 under these conditions were 12 and 5.5 mmolg.sup.1, respectively. The material [Zr.sub.6(3-O).sub.4(.sub.3-OH).sub.4(OH).sub.6(H.sub.2O).sub.6][Cu.sub.3(.sub.3-O)(-PyC).sub.3(H.sub.2O).sub.6].sub.2 with platinum and ruthenium nanoparticles was stable under these reaction conditions and when the system is purged with argon after the first use until the presence of H.sub.2 is not detected in the reactor and then the process is repeated for another 24 hours, the same values of H.sub.2 and O.sub.2 production are observed as those listed above.

Example 4. Photocatalytic Water Splitting Using [Zr.SUB.6.(.SUB.3.-O).SUB.4.(.SUB.3.-OH).SUB.4.(OH).SUB.6.(H.SUB.2.O).SUB.6.(Co.SUB.3.(Py-CO.SUB.2.).SUB.3.).SUB.2.] by Irradiation with Sunlight in Suspension in Aqueous Phase at pH 7

[0070] The flexibility in the composition of the MOF structure is illustrated by the possibility of replacing the Cu of the trispyrazolyl unit by Co. The preparation of this material is carried out following the state of the art for the preparation of the Cu compound, but substituting tris(2-carboxy)pyrazolyl copper with tris(2-carboxy)pyrazolyl cobalt and following the steps indicated in the state of the art (Liu, Q. et al. Journal of the American Chemical Society 2019, 141, 488-496). Thus, the procedure is as indicated in Example 1 but substituting the copper material with another similar one wherein the copper has been substituted with cobalt. The method of photocatalytic water splitting under the indicated conditions gives rise to values of H.sub.2 and O.sub.2 of 3 and 1.2 mmolg.sup.1, respectively.

Example 5. Continuous Photocatalytic Water Splitting Using [Zr.SUB.6.(3-OH).SUB.4.(OH).SUB.6.(H.SUB.2.O).SUB.6.(Cu.SUB.3.(.SUB.3.-O)(-PyC).SUB.3.(H.SUB.2.O).SUB.6.].SUB.2 .Deposited on a 1 m.SUP.2 .Plate Containing 6 Modules of about 20 cm.SUP.2 .Each One Connected in Series

[0071] The material [Zr.sub.6(.sub.3-O).sub.4(.sub.3-OH).sub.4(OH).sub.6(H.sub.2O).sub.6(Cu.sub.3(Py-CO.sub.2).sub.3).sub.2] corresponds to that used in Example 4. Initially, to deposit the MOF in each module, a paste with Nafion and ethanol is prepared by manually dispersing in a mortar 100 mg of MOF with 5 ml of a commercial 5% Nafion solution in ethanol. This paste is subsequently deposited on a Teflon support spreading it with a blade that provides a very thin thickness, according to the method known as razor blade. Subsequently, the plate is dried at 100 C. for 24 h. The generation of H.sub.2 is carried out by irradiation with natural sunlight in aqueous phase at pH 7, generating 400 ml of H.sub.2 on a sunny day in Valencia measured under ambient conditions.

Example 6. Photocatalytic Water Splitting in the Vapour Phase Using [Zr.SUB.6.(.SUB.3.-O).SUB.4.(.SUB.3.-OH).SUB.4.(OH).SUB.6.(H.SUB.2.O).SUB.6.(Cu.SUB.3.(.SUB.3.-O)(-PyC).SUB.3.(H.SUB.2.O).SUB.6.].SUB.2 .Deposited on Plates as Described in Example 5

[0072] The generation of H.sub.2 is carried out by irradiation with natural sunlight and water vapour at a temperature of 60 C., using a N.sub.2 flow of 0.5 mlmin.sup.1 as carrier gas, obtaining 600 ml of H.sub.2 measured under ambient conditions.

Example 7. Photocatalytic Water Splitting Using [Zr.SUB.6.(.SUB.3.-O).SUB.4.(.SUB.3.-OH).SUB.4.(OH).SUB.6.(H.SUB.2.O).SUB.6.Cu.SUB.3.(.SUB.3.-O)(-PyC).SUB.3.(H.SUB.2.O).SUB.6.].SUB.2 .by Irradiation with Sunlight in Suspension in Aqueous Phase at pH 7 at High Temperatures

[0073] 50 mg of the material previously synthesised and the X-ray pattern of which corresponds to that shown in FIG. 1 are dispersed by means of magnetic stirring in 50 ml of distilled water and are placed inside a 70 ml glass reactor capable of being hermetically sealed. Prior to the start of the radiation the solution and the free volume of the reactor were purged by means of a stream of argon of 1 ml/min that was bubbled through the reactor for at least 1 hour before the start of the reaction in order to reduce the amount of O.sub.2 present in the system. The system is irradiated by exposure to the beam of a solar simulator consisting of an Xe lamp with an AM 1.5 filter that simulates the solar irradiation of the earth's surface. The radiation power was 100 mW.Math.cm.sup.2 and the exposed surface of the reactor was 13 cm.sup.2. The distance between the exit of the beam of the solar simulator and the photoreactor was about 10 cm. The temperature of the system during radiation varied between 20 and 100 C. Exposure to simulated sunlight is carried out for 24 hours, analysing the composition of the free volume of the reactor by means of a gas chromatograph that enables the detection and quantification of the presence of H.sub.2 and O.sub.2. After 24 hours the values of H.sub.2 and O.sub.2 under these conditions were 2 and 0.9 mmols of H.sub.2 and O.sub.2 at 100 C., respectively. The material [Zr.sub.6(.sub.3-O).sub.4(.sub.3-OH).sub.4(OH).sub.6(H.sub.2O).sub.6(Cu.sub.3(Py-CO.sub.2).sub.3).sub.2] was stable under these reaction conditions and when the system is purged with argon after the first use until the presence of H.sub.2 is not detected in the volume of the reactor and then the process is repeated for another 24 h the same values of H.sub.2 and O.sub.2 production are observed as those listed above.

Example 8. Photocatalytic Splitting of Salt Water Using [Zr.SUB.6.(.SUB.3.-O).SUB.4.(.SUB.3.-OH).SUB.4.(OH).SUB.6.(H.SUB.2.O).SUB.6.(Cu.SUB.3.(.SUB.3.-O)(-PyC).SUB.3.(H.SUB.2.O).SUB.6.].SUB.2 .by Irradiation with Sunlight in Suspension in Aqueous Phase at pH 7

[0074] Next, the photocatalytic test is carried out as indicated in Example 1 using salt water. After 24 hours, the values of H.sub.2 and O.sub.2 under these conditions were 4 and 2.5 mmolg.sup.1, respectively. The material [Zr.sub.6(.sub.3-O).sub.4(.sub.3-OH).sub.4(OH).sub.6(H.sub.2O).sub.6(Cu.sub.3(Py-CO.sub.2).sub.3).sub.2] was stable under these reaction conditions and when the system is purged after the first use with argon until the presence of H.sub.2 is not detected in the volume of the photoreactor and then the process is repeated for another 24 hours, the same values of H.sub.2 and O.sub.2 production are observed as those listed above.

Example 9. Photocatalytic Water Splitting Using a MOF with Formula [Hf.SUB.6.(.SUB.3.-O).SUB.4.(.SUB.3.-OH).SUB.4.OH).SUB.6.(H.SUB.2.O).SUB.6.(Cu.SUB.3.(Py-CO.SUB.2.).SUB.3.).SUB.2.] by Irradiation with Sunlight in Suspension in Aqueous Phase at pH 7

[0075] In order to illustrate again the flexibility in the composition of the MOF materials described herein for the photocatalytic water splitting, it is possible to substitute Zr.sup.IV in nodal positions with Hf.sup.IV following the synthesis methods described in the state of the art (Liu, Q. et al. Journal of the American Chemical Society 2019, 141, 488-496). The material [Hf.sub.6(.sub.3-O).sub.4(.sub.3-OH).sub.4(OH).sub.6(H.sub.2O).sub.6(Cu.sub.3(Py-CO.sub.2).sub.3).sub.2] shows an efficiency in the generation of H.sub.2 by irradiation with sunlight identical to that described in Example 1. Additionally, following processes parallel to those indicated in examples 2, 3 and 4, it is possible to incorporate Pt or PtRuO.sub.2 in the pores of the material and also substitute Cu with Co in the composition, maintaining the same structure corresponding to the X-ray diffractogram indicated in FIG. 1.

Example 10. Comparative Study of the Efficiency of [Zr.SUB.6.(.SUB.3.-O).SUB.4.(.SUB.3.-OH).SUB.4.(Cu.SUB.3.(OH)(Py-CO.SUB.2.).SUB.3.).SUB.2.] (H.SUB.2.O).SUB.6 .Compared to a Related Material Zr.SUB.6.(.SUB.3.-O).SUB.4.(.SUB.3.-OH).SUB.4.(BDC-NH.SUB.2.).SUB.3 .(BDC-NH.SUB.2.: 2-amino-1,4-benzenedicarboxylate) Known in the State of the Art

[0076] The present invention surprisingly describes the high photocatalytic activity of organic frameworks containing formula I in the generation of H.sub.2. Comparison between the photocatalytic efficiency of [Zr.sub.6(.sub.3-O).sub.4(.sub.3OH).sub.4(Cu.sub.3(OH)(Py-CO.sub.2).sub.3).sub.2] (H.sub.2O).sub.6 with that of Zr.sub.6(.sub.3-O).sub.4(.sub.3-OH).sub.4(BDC-NH.sub.2).sub.3 (A. Dhakshinamoorthy, Z. Li, H. Garca., Catalysis and photocatalysis by metal organic frameworks, Chem. Soc. Rev. 2018, 47, 8134-8172) demonstrates inventive step. Thus, the material corresponding to example 1 under the irradiation conditions described in that example has a production of H.sub.2 and O.sub.2 after 24 h of 6 and 2.5 mmol, respectively. By comparison, the similar material Zr.sub.6(.sub.3-O).sub.4(.sub.3-OH).sub.4(BDC-NH.sub.2).sub.3 prepared as described in the state of the art produces 0.125 and 0.031 mmol of H.sub.2 and O.sub.2 under the same conditions, respectively. The material Zr.sub.6(.sub.3-O).sub.4(.sub.3-OH).sub.4(BDC-NH.sub.2).sub.3 is prepared by mixing 2-aminoterephthalic acid (1.0 mmol) with ZrCl.sub.4 (0.233 g, 1 mmol) in a Teflon-coated autoclave containing 3 ml of dimethylformamide. The autoclave is heated at a temperature of 100 C. for 24 h. The System is allowed to cool to ambient temperature and the resulting precipitate is collected, washed with dimethylformamide and introduced in a Soxhlet continuous extraction equipment using methanol as solvent. Lastly, the solid is dried in an oven at 100 C. for 24 h.