Titanium heterometallic metal-organic solids, method for obtaining them and their uses
11787824 · 2023-10-17
Assignee
Inventors
- Carlos Marti Gastaldo (Valencia, ES)
- Javier CASTELLS GIL (Valencia, ES)
- Natalia MUÑOZ PADIAL (Granada, ES)
Cpc classification
International classification
Abstract
The present invention relates to a new family of titanium heterometallic structured metal-organic materials (MOFs) having, among other characteristics, high porosity, stability in an aqueous medium and photocatalytic activity under visible light and UV radiation. The new family of materials has a structural unit that combines tetravalent titanium with multiple combinations of divalent metals with a homogeneous distribution at atomic level in the MOF structure. The invention also relates to methods for obtaining them with high yields, in addition to their uses in the generation of solar fuels, photoactivated degradation, photoreduction of CO.sub.2, heterogeneous catalysis, as a component or part of an electronic component and/or as a porous or photoactive coating for controlling pollutants, inter alia.
Claims
1. A crystalline and porous Ti(IV) heterometallic MOF solid, characterised in that it comprises a ligand L of the general structure of: Compound (A): ##STR00007## wherein R.sub.1=—COOH; and R.sub.2=—H, —(CH.sub.2).sub.0-5—CH.sub.3, —NH.sub.2, —OH, —NO.sub.2, —COOH or halogen; or Compound (B): ##STR00008## wherein R.sub.1=—COOH; as the organic part of the MOF, and Ti.sup.IV with at least one, and up to 5 divalent metals (M.sup.II) in the structural unit as the inorganic part of the MOF, wherein Ti.sup.IV and the at least one, and up to 5 divalent metals (M.sup.II) divalent metal M.sup.II.sub.(1-5) are homogeneously distributed at atomic level, and wherein the MOF solid also includes at least one polar solvent S molecule selected from N,N′-dimethylformamide, N,N′-diethylformamide, N,N′-dimethylacetamide, N-methyl-2-pyrrolidone, methanol, ethanol, isopropanol, n-propanol, water and mixtures thereof.
2. The Ti(IV) heterometallic MOF solid, according to claim 1, wherein the inorganic part includes a proportion of titanium less than or equal to 50%, with divalent metal(s) making up the remaining part until 100%.
3. The Ti(IV) heterometallic MOF solid, according to claim 1, wherein the proportion of titanium is comprised between 50% and 15%, with divalent metal(s) making up the remaining part until 100%.
4. The Ti(IV) heterometallic MOF solid, according to claim 1, wherein Ti.sup.IV and the at least one, and up to 5 divalent metals (M.sup.II) jointly form a metal cluster interconnected with the ligand L to give a crystalline and porous three-dimensional structure.
5. The Ti(IV) heterometallic MOF solid, according to claim 1, wherein: the at least one divalent, and up to 5 metals (M.sup.II) are each independently selected from, mg.sup.2+, ca.sup.2+, sr.sup.2+, Ba.sup.2+, Ti.sup.2+, v.sup.2+, cr.sup.2+, Mn.sup.2+, Fe.sup.2+, Co.sup.2+, Ni.sup.2+, cu.sup.2+, zn.sup.2+ or cd.sup.2+.
6. A Ti(IV) heterometallic MOF solid comprising a ligand selected from Compound (A): ##STR00009## wherein R.sub.1=—COOH; and R.sub.2=—H, —(CH.sub.2).sub.0-5—CH.sub.3, —NH.sub.2, —OH, —NO.sub.2, —COOH or halogen; or Compound (B): ##STR00010## wherein R.sub.1=—COOH, as the organic part of the MOF, and Ti.sup.IV with at least one, and up to 5 divalent metals (M.sup.II) in the structural unit as the inorganic part of the MOF, wherein Ti.sup.IV and the at least one, and up to 5 divalent metals (M.sup.II) are homogeneously distributed at atomic level, and wherein the MOF solid also includes at least one polar solvent S molecule selected from N,N′-dimethylformamide, N,N′-diethylformamide, N,N′-dimethylacetamide, N-methyl-2-pyrrolidone, methanol, ethanol, isopropanol, n-propanol, water and mixtures thereof.
7. The Ti(IV) heterometallic MOF solid, according to claim 6, wherein the ligand L is 1,3,5-benzenetricarboxylic acid.
8. The Ti(IV) heterometallic MOF solid, according to claim 1, wherein the MOF solid has the general formula (MUV-10): [Ti.sup.IV.sub.3M.sup.II.sub.3(O).sub.3L.sub.4]S, and each of M.sup.II is independently a Mg.sup.2+, Ca.sup.2+, Sr.sup.2+, Ba.sup.2+, Ti.sup.2+, V.sup.2+, Cr.sup.2+, Mn.sup.2+, Fe.sup.2+, Co.sup.2+, Ni.sup.2+, Cu.sup.2+, Zn.sup.2+ or Cd.sup.2+ cation.
9. The Ti(IV) heterometallic MOF solid, according to claim 8, wherein Ti.sup.IV and the at least one and up to 5 divalent metals (M.sup.II) are in a ratio between 50:50 and 99:1.
10. The Ti(IV) heterometallic MOF solid, according to claim 1, wherein the MOF solid has the general formula (MUV-101): [Cu.sup.II.sub.(3-2z)Ti.sup.IV.sub.z(L).sub.2]S wherein: z is a rational number comprised between a value greater than 0 and less than 1.5; L is a ligand having the general structure of Compound (A): ##STR00011## wherein R.sub.1=—COOH; and R.sub.2=—H, —(CH.sub.2).sub.0-5—CH.sub.3, —NH.sub.2, —OH, —NO.sub.2, —COOH or halogen; or Compound (B): ##STR00012## wherein R.sub.1=—COOH; and S is at least one molecule of N,N′-dimethylformamide, N,N′-diethylformamide, N,N′-dimethylacetamide, N-methyl-2-pyrrolidone, methanol, ethanol, isopropanol, n-propanol, water or mixtures thereof.
11. The Ti(IV) heterometallic MOF solid, according to claim 10, wherein Ti.sup.IV and Cu.sup.II are in a ratio between 15:85 and 99:1.
12. The Ti(IV) heterometallic MOF solid, according to claim 1, wherein the MOF solid has the general formula (MUV-102): [Ti.sup.IV.sub.(3-w)M.sup.II.sub.wO(L).sub.2X.sub.(3-w)]S wherein: w is a rational number comprised between a value greater than 0 and less than 3; X is, independently, a F.sup.−, Cl.sup.− or OH.sup.− anion; each of M.sup.II is independently a Mg.sup.2+, Ca.sup.2+, Sr.sup.2+, Ba.sup.2+, Ti.sup.2+, V.sup.2+, Cr.sup.2+, Mn.sup.2+, Fe.sup.2+, Co.sup.2+, Ni.sup.2+, Cu.sup.2+, Zn.sup.2+ or Cd.sup.2+ cation; L is a ligand having the general structure of Compound (A): ##STR00013## wherein R.sub.1=—COOH; and R.sub.2=—H, —(CH.sub.2).sub.0-5—CH.sub.3, —NH.sub.2, —OH, —NO.sub.2, —COOH or halogen; or Compound (B): ##STR00014## wherein R.sub.1=—COOH; and S is at least one molecule of N,N′-dimethylformamide, N,N′-diethylformamide, N,N′-dimethylacetamide, N-methyl-2-pyrrolidone, methanol, ethanol, isopropanol, n-propanol, water or mixtures thereof.
13. The Ti(IV) heterometallic MOF solid, according to claim 12, wherein Ti.sup.IV and the at least one and up to 5 divalent metals (M.sup.II) are in a ratio comprised between 99:1 and 33:67.
14. A method for synthesising a crystalline and porous Ti(IV) heterometallic MOF solid, according to claim 6, characterised in that intrinsic doping of Ti(IV) and at least one and up to 5 divalent metals (M.sup.II) is carried out by one-pot synthesis as follows: (i) mixing: a polar solvent, S: a Ti(IV) precursor, at least one salt of a divalent metal of formula MX.sub.2 or MY, wherein: M is Mg.sup.2+, ca.sup.2+, sr.sup.2+, Ba.sup.2+, Ti.sup.2+, v.sup.2+, cr.sup.2+, Mn.sup.2+, Fe.sup.2+, Co.sup.2+, Ni.sup.2+, cu.sup.2+, zn.sup.2+ or Cd.sup.2+; X is F.sup.−, Cl.sup.−, Br, I.sup.−, NO.sub.3.sup.−, ClO.sub.4.sup.−, BF.sub.4.sup.−, SCN.sup.−, OH.sup.−, CH.sub.3COO.sup.− or C.sub.5H.sub.7O.sub.2.sup.−, Y is SO.sub.4.sup.2− or CO.sub.3.sup.2−, a ligand L having the structure of Compound (A): ##STR00015## wherein R.sub.1=—COOH; and R.sub.2=—H, —(CH.sub.2).sub.0-5—CH.sub.3, —NH.sub.2, —OH, —NO.sub.2, —COOH or halogen; or Compound (B): ##STR00016## wherein R.sub.1=—COOH, wherein the stoichiometric relationship between the at least one divalent metal salt and the ligand is comprised between 1:1 and 1:6, and, optionally, an inorganic acid or an acid selected from the group consisting of formic acid, acetic acid, propanoic acid, benzoic acid, and derivatives thereof in a molar relationship comprised between 5 and 500 gram equivalent/mole of salt MX.sub.2 or MY; and, next, (ii) heating the reaction mixture to give the MOF solid, wherein Ti.sup.IV and the at least one divalent metal M.sup.II.sub.(1-5) jointly form an interconnected metal cluster with the ligand L, wherein Ti.sup.IV and the at least one divalent metal M.sup.II.sub.(1-5) homogeneously distributed at atomic level in the MOF.
15. The synthesis method, according to claim 14, wherein the stoichiometric relationship between the at least one divalent metal salt and the ligand is comprised between 1:1.1 and 1:6, such that the ligand is in stoichiometric excess.
16. The synthesis method, according to claim 14, wherein the inorganic acid is hydrochloric acid.
17. The Ti(IV) heterometallic MOF solid, according to claim 6, wherein the ligand L is trimesic acid; the divalent metal is Fen; and the polar solvent S is N,N′-dimethyl-formamide.
18. The synthesis method, according to claim 14, wherein the Ti(IV) precursor and the at least one salt of a divalent metal of formula MX.sub.2 or MY are added to the mixture in a ratio comprised between 99:1 and 50:50.
19. The synthesis method, according to claim 14, wherein the Ti(IV) precursor is selected from a Ti(IV) organometallic precursor, a Ti(IV) alkoxide, Ti(IV) isopropoxide, Ti(IV) methoxide, Ti(IV) ethoxide, Ti(IV) n-propoxide, Ti(IV) n-butoxide, Ti(IV) (triethanolanninato)isopropoxide, Ti(IV) tert-butoxide, Ti(IV) oxyacetylacetonate, Ti(IV) tetrachloride, bis-(cyclopentadienyl)-Ti(IV) dichloride, cyclopentadienyl-Ti(IV) trichloride, Ti(IV) oxosulphate, a Ti(IV) polynuclear compound stable in the air, a Ti(IV) hexanuclear complex, a Ti(IV) heterometallic MOF solid, or a Ti(IV) heterometallic MOF solid of the formula [Ti.sup.IV.sub.3M.sup.II.sub.3(O).sub.3L.sub.4]S wherein: each of M.sup.II is independently a Mg.sup.2+, Ca 2+, Sr.sup.2+, Ba 2+, Ti.sup.2+, V.sup.2+, Cr.sup.2+, Mn.sup.2+, Fe.sup.2+, Co.sup.2+, Ni.sup.2+, Cu.sup.2+, Zn.sup.2+, or Cd.sup.2+, cation; S is at least one molecule of N, N′-dimethylformamide, N, N′-diethylformamide, N, N′-dimethylacetamide, N-methyl-2-pyrrolidone, methanol, ethanol, isopropanol, n-propanol, water, and mixtures thereof.
20. The synthesis method, according to claim 14, wherein the ligand L is 1,3,5-benzenetricarboxylic acid.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) In order to better understand the description made, a set of drawings has been provided which, schematically and solely by way of non-limiting example, represent a practical case of embodiment.
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
(10)
(11)
DETAILED DESCRIPTION OF THE INVENTION
(12) Preferred embodiments of the present invention are disclosed below.
(13) The problem that the present invention aims to address is that of providing new crystalline and porous materials based on Ti(IV) using Ti-M heterometallic clusters as species with controlled reactivity to enable the formation of multiple metal-organic architectures by combining Ti(IV)-M(II) clusters (M=Mg, Ca, Sr, Ba, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd) and ligands based on low-cost polyaromatic carboxylic acids.
(14) To date this type of materials could not be efficiently generated due to the limitations intrinsic to the synthesis of the titanium MOFs expounded in the background of the invention section. This problem was addressed by the inventors through the use of another metal precursor M(II), in addition to Ti(IV), under certain conditions determined in the synthesis of these materials. This enables the generation of Ti.sup.IV-M.sup.II heterometallic MOFs with high chemical stability that makes it possible to combine both types of metals in the structure in variable proportions to generate multiple combinations and architectures with variable porosity. Ti.sup.IV-M.sup.II.sub.(1-5) MOF solids can be obtained on a large scale, easily and controlling both crystal size and morphology. Ti.sup.IV-M.sup.II.sub.(1-5) MOF solids with variable formulations can be generated by directly controlling the proportion of Ti and the other metals in the material. The control is not only limited to binary combinations, but rather titanium can be combined with up to 5 different types of metals in the same material. As opposed to the extrinsic doping methodologies disclosed to date -synthesis of the material and subsequent incorporation of other metals in a second stage—the methods disclosed herein enable the combination of Ti with divalent metals in a single stage, precisely controlling their distribution in the MOF and the desired proportion to precisely control the electronic, catalytic and photoactive properties of the final MOF.
(15) In a preferred embodiment, the Ti.sup.IV-M.sup.II.sub.(1-5) MOF solids family is prepared using the general formula (MUV-10): [Ti.sup.IV.sub.3M.sup.II.sub.3(O).sub.3L.sub.4]S
(16) MUV-10 Family
(17) These materials have a sodalite-type structure wherein the Ti.sup.IV-M.sup.II heterometallic units are joined together by the trimesic acid to form a three-dimensional neutral network with two types of pores, one with octahedral geometry and another with dodecahedral geometry.
(18) Said Ti.sup.IV-M.sup.II.sub.(1-5) solids are prepared by direct reaction of Ti(IV) organometallic precursors, generally using Ti(IV) alkoxides (for example, Ti(IV) isopropoxide, Ti(IV) methoxide, Ti(IV) ethoxide, Ti(IV) n-propoxide, Ti(IV) n-butoxide, Ti(IV) (triethanolaminato)isopropoxide, Ti(IV) tert-butoxide, Ti(IV) oxyacetylacetonate, among others) or other commercial Ti(IV) precursors (Ti(IV) tetrachloride, bis(cyclopentadienyl)-Ti(IV) dichloride, cyclopentadienyl-Ti(IV) trichloride or Ti(IV) oxosulphate), as well as other non-commercial Ti(IV) polynuclear compounds and that are stable at air such as the Ti(IV) hexanuclear complexs; and simple MX.sub.2 salts (X=F, Cl, Br, I, NO.sub.3.sup.−, ClO.sub.4.sup.−, BF.sub.4.sup.−, SON.sup.−, OH.sup.−, acetate or acetylacetonate) or MY (Y=SO.sub.4.sup.2−, CO.sub.3.sup.2−) of divalent metals (M.sup.II=Mg, Ca, Sr, Ba, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd), such that it makes it possible to maintain the neutrality of the network, with trimesic acid in a stoichiometric ratio of 1:3 in polar solvents with a boiling point of more than 80° C., such as N,N-dimethyl-formamide, N,N-diethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, water. An inorganic acid which acts as a crystalline growth modulator is added to said solution in variable proportions, typically between 5 and 500 gram equivalents/mol, depending on the inorganic acid used, and is maintained under stirring until the reagents are completely dissolved.
(19) This reaction mixture is heated at a temperature of more than 80° C. for a period greater than or equal to 24 hours.
(20) Once this time has elapsed, the mixture is cooled to room temperature and the solid obtained is separated by centrifugation, thoroughly washed with organic solvents to remove the material which has not reacted and left to dry in a vacuum all night. The method is adequate for any of the metal precursors described above and can be scaled to produce grams of material in reactors with a volume of up to 1 litre. The resulting MOF is isolated in the form of crystals with well-defined morphologies which can be controlled by temperature, reaction time and proportion of inorganic acid added. Said size may vary from hundreds of nanometres to 250 μm, while the morphology of the crystals may vary from cubic to octahedral, passing through different intermediate morphologies there between (
(21) The crystalline structure of the Ti.sup.IV-M.sup.II.sub.(1-5) MOF solid and the homogeneous distribution of the metals throughout the crystal is always the same, regardless of the morphology and size of the crystals (
(22) These Ti.sup.IV-M.sup.II.sub.(1-5) MOF solids can be prepared using any type of tricarboxylic ligand, i.e. tricaboxylic C.sub.6-aryl acid-type ligands (for example, trimesic acid (1,3,5-benzenetricarboxylic acid)) or tricarboxylic C.sub.3N.sub.3-aryl acid-type ligands (for example, 2,4,6-triazine-tricarboxylic acid) and derivatives thereof of the tricarboxylic (C′.sub.6-aryl).sub.3-C.sub.6-aryl or (C′.sub.6-aryl).sub.3-C.sub.3N.sub.3-aryl acid type.
(23) The incorporation of different metals to the structure makes it possible to modulate the absorption of radiation to make these systems active under visible light and, consequently, improve their photocatalytic activity.
(24) Chemical stability experiments were conducted to verify the resilience of these materials against aqueous solutions at different pH values. All the materials studied were found to be stable in water between pH values comprised between 2 and 12, without observing any sign of degradation in their structure or in their N.sub.2 adsorption properties at 77 K with surface areas of close to 1,000 m.sup.2/g (
(25) Mixing the Ti.sup.IV-M.sup.II.sub.(1-5) MOF solids with a divalent metal salt solution under adequate reaction conditions also enables the post-synthetic transformation of the structure of the MUV-10 family into other structures (MUV-101, MUV-102 families) with controlled Ti.sup.IV:M.sup.II ratios, as disclosed in the examples below.
(26) In another embodiment, the Ti.sup.IV-M.sup.II.sub.(1-5) MOF solids family is prepared using the general formula (MUV-101): [Cu.sup.II.sub.(3-2z)Ti.sup.IV.sub.z(L).sub.2]S
(27) MUV-101 Family
(28) These materials have the same structure as the compound known as HKUST-1, with formula Cu.sub.3(btc).sub.2, wherein btc makes reference to trimesic acid. The main difference lies in the introduction of variable percentages of Ti(IV) replacing the dimetallic units of Cu(II) present in the originally disclosed material.
(29) The preparation of the materials of the MUV-101 family is carried out by direct reaction of Ti(IV) organometallic precursors, such as those disclosed earlier for the MUV-10 family, with trimesic acid in the presence of a simple Cu(II) salt (CuF.sub.2, CuCl.sub.2, CuBr.sub.2, Cul.sub.2, Cu(OAc).sub.2 CuSO.sub.4, Cu(NO.sub.3).sub.2, CuCO.sub.3) in polar solvents such as N,N′-dimethylformamide, N,N′-diethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, methanol, ethanol, isopropanol, n-propanol, water and at temperatures of more than 100° C.
(30) Once the reaction has finished, the resulting solid is separated by centrifugation and is thoroughly washed with organic solvents and vacuum dried.
(31) The resulting family of materials we call MUV-101 are isolated in the form of crystals with cubic morphology, surface areas comprised between 1,000-2,000 m.sup.2/g and variable Ti.sup.IV:Cu.sup.II ratios between 99:1 and 15:85 according to the Ti.sup.IV:Cu.sup.II ratio initially used (
(32) These systems are stable in water in the presence of acid and bases in pH ranges between 1 and 10.
(33) This Ti.sup.IV-M.sup.II.sub.(1-5) MOF solid can also be prepared using preformed materials of the MUV-family based on Ti(IV) and M(II) as precursors.
(34) These are subjected to a post-synthetic transformation method, not disclosed to date, in the presence of simple Cu.sup.II salts (CuF.sub.2, CuCl.sub.2, CuBr.sub.2, Cul.sub.2, Cu(OAc).sub.2 CuSO.sub.4, Cu(NO.sub.3).sub.2,
(35) CuCO.sub.3) using different polar solvents such as N,N-dimethylformamide, N,N′-diethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, methanol, ethanol, isopropanol, n-propanol, water, at temperatures below 100° C.
(36) Once the reaction has finished, the new material is isolated by centrifugation, washed with the solvent and vacuum dried.
(37) The MUV-101 family of materials thus synthesised are isolated in the form of crystals with cubic morphology, cubic surface areas comprised between 1,000-2,000 m.sup.2/g and variable Ti.sup.IV:Cu.sup.II ratios between 99:1 and 15:85 according to the time and reaction temperature.
(38) In another embodiment, the Ti.sup.IV-M.sup.II.sub.(1-5) MOF solids family is prepared using the general formula (MUV-102): [Ti.sup.IV.sub.(3-w)M.sup.II.sub.wO(L).sub.2X.sub.(3-w)]S
(39) MUV-102 Family
(40) The materials have the same zeolite-type structure with MTN topology disclosed earlier for the MIL-100 MOF family. As opposed to these, the materials of the invention incorporate Ti.sup.IV-M.sup.II heterometallic clusters, replacing the disclosed homometals M(III) (M=Cr, Al, Fe).
(41) The MOF solids of this family have the general formula included above. The heterometallic clusters are connected by trimesate ligands to form a porous three-dimensional network with two pore sizes having a diameter of 2.4 and 2.9 nm. As in the case of the MUV-10 family, these materials can be prepared by direct reaction of the Ti(IV) organometallic precursors and simple MX.sub.2 or MY divalent metal salts with trimesic acid in polar solvents with a boiling point of more than 80° C., such as N,N′-dimethylformamide, N,N-diethylformamide, N,N′-dimethylacetamide, N-methyl-2-pyrrolidone, water.
(42) An inorganic acid which acts as a crystalline growth modulator is added to said solution in variable proportions, typically between 5 and 500 gram equivalent/mol, depending on the inorganic acid used, and is maintained under stirring until the reagents are completely dissolved.
(43) This reaction mixture is heated at a temperature of more than 80° C. for a period greater than or equal to 48 hours. Once this time has elapsed, the mixture is cooled to room temperature and the solid obtained is separated by centrifugation, thoroughly washed with organic solvents to remove the material which has not reacted and left to dry in a vacuum all night.
(44) The method is adequate for any of the metal precursors described above and can be scaled to produce grams of material in reactors with a volume of up to 1 litre.
(45) The resulting family of materials we call MUV-102 are isolated in the form of crystals with octahedral morphology, variable Ti.sup.IV:M.sup.II ratios between 99:1 and 33:67 according to the used (
(46) These materials can also be prepared by post-synthetic transformation of the MUV-10 family similarly to the MUV-101 family disclosed above. In this method, heterometallic MOFs of the family based on Ti.sup.IV-M.sup.II are suspended in a solution of a simple salt MX.sub.2 or MY of divalent metals in polar solvents such as N,N-dimethylformamide, N,N′-diethylformamide, N,N′-dimethylacetamide, N-methyl-2-pyrrolidone, methanol, ethanol, isopropanol, n-propanol, water, at temperatures below 100° C.
(47) Once the reaction has finished, the material is separated by centrifugation and thoroughly washed with the organic solvent used, in order to remove the non-reacted residues.
(48) Once again, the resulting MUV-102 MOF solids are isolated as particles with octahedral morphology and with variable Ti.sup.IV:M.sup.II ratios between 99:1 and 33:67, according to reaction time and temperature, and with the concentration of the solution of the metal used. As opposed to the post-synthetic metal exchange methodologies disclosed earlier, this post-synthetic transformation ensures a homogeneous distribution of the metals throughout the crystal (
(49) As disclosed in the descriptive part of the invention, systems integrated by Ti(IV) heterometallic MOF solids of the invention have the following advantages: Use of Ti(IV) heterometallic clusters as a structural unit of the MOF. Ti(IV) heterometallic MOF solids with variable formulations through the direct control of the proportion of Ti(IV) and other divalent metals that form the structural unit of the MOF. Up to five types of different divalent metals in addition to titanium with homogeneous distribution at atomic level in the MOF. Precise control over the distribution of the metals in the MOF and the desired proportion of Ti.sup.IV-M.sup.II for severe control over the electronic, catalytic and photoactive properties of the final MOF material. Control of the morphology and size of the Ti(IV) heterometallic MOF solid, essential for the adequate dispersal of the MOFs in organic solvents and processing in the manufacture of functional coatings. One-pot synthesis methods by direct reaction with multiple metal precursors and/or by post-synthetic transformation of a titanium heterometallic MOF solid defined in the invention. In both cases, the synthesis method is easily scalable at reactor sizes of at least one litre in volume. Intrinsic doping in a single stage and using cheaper precursors for obtaining titanium heterometallic MOFs. Improved photocatalytic activity under visible light. High chemical stability. The Ti(IV) heterometallic MOF solids remain intact when immersed in water, even in the presence of acids or bases (range of pH 2-12), without this treatment affecting its crystalline structure or its properties.
EXAMPLES
Example 1: Synthesis of MUV-10(Ca)
(50) 125 mg of trimesic acid (595 μmol) are dissolved in a mixture of 12 mL of N,N-dimethyl-formamide (DMF) and 3.5 mL of acetic acid. 36 μL of Ti(IV) isopropoxide [Ti(O.sup.i)Pr).sub.4] (120 μmol) and 26 mg of calcium chloride (120 μmol) are added to this solution under an inert atmosphere and in the absence of humidity. The mixture is stirred until the complete dissolution of the reagents and heated in an oven at 120° C. for 48 hours. Once this time has elapsed, the solid obtained is separated by centrifugation, washed with corresponding portions of DMF and methanol, and vacuum dried.
(51) The same previous methodology was repeated, except that in this case bis-cyclopentadienyltitanium (IV) dichloride [Cp.sub.2TiCl.sub.2] was added instead of titanium (IV) isopropoxide.
(52) The same previous methodology was repeated, except that in this case hexanuclear titanium (IV) [Ti.sub.6] complex was added instead of bis-cyclopentadienyltitanium (IV).
(53) The different morphologies, homogeneous distribution of metals, crystallinity and chemical stability of the MUV-10 family of materials are shown in
Example 2: Synthesis of MUV-10 (Ca+Mn)
(54) 125 mg of trimesic acid (595 μmol) were dissolved in a mixture of 12 mL of N,N-dimethyl-formamide (DMF) and 3.5 mL of acetic acid. 36 μL of Ti(IV) isopropoxide [Ti(Oi)Pr).sub.4] (120 μmol) and an equimolar amount of divalent metal salts were added to this solution: 13 mg of calcium chloride (60 μmol) and 12 mg of manganese chloride (60 μmol) under an inert atmosphere and in the absence of humidity. The mixture was stirred until the complete dissolution of the reagents and heated in an oven at 120° C. for 48 hours. Once this time had elapsed, the solid obtained was separated by centrifugation, washed with corresponding portions of DMF and methanol and vacuum dried.
(55) Scanning electron microscopy (SEM) photographs were taken of the MOF obtained, whose homogeneous morphology and homogeneous distribution of the metals can be observed in
(56) The data obtained from the EDX trial, also represented in
(57) Spectrum: 1
(58) TABLE-US-00001 Normalised Normalised atomic atomic percentage percentage Error Element (p %) (atomic %) (p %) Titanium 51.26 50.98 0.6 Calcium 21.09 25.06 0.3 Manganese 27.65 23.96 0.4 Total 100.00 100.00
(59) The results obtained in the table demonstrate the presence of three different metals in a single MOF with homogeneous distribution.
Example 3: Synthesis of MUV-101 Ti—Cu by Direct Reaction
(60) 125 mg of trimesic acid (595 μmol) are dissolved in a mixture of 12 mL of N,N-dimethyl-formamide (DMF) and 3 mL of acetic acid. 17 μL of Ti(IV) isopropoxide (54 μmop and 41 mg of Cu(II) chloride (306 μmop are added to this solution. The mixture is stirred until the complete dissolution of the reagents and heated in an oven at 120° C. for 48 hours. Once this time has elapsed, the solid obtained is separated by centrifugation, washed with corresponding portions of DMF and methanol, and vacuum dried.
Example 4: Synthesis of MUV-101 Ti—Cu by Post-Synthetic Transformation (PST) of MUV-10
(61) 100 mg of MUV-10(Ca) are suspended in 10 mL of a solution of 0.005 M of Cu(II) chloride in a mixture of DMF:NMP 1:1. The mixture is introduced in an oven preheated at 65° C. for a maximum period of 15 days. Once this time has elapsed, the solid obtained is separated by centrifugation, washed with corresponding portions of DMF and methanol, and vacuum dried.
(62) The morphology, crystallinity and porosity of the MUV-101 family of materials is shown in
Example 5: Synthesis of MUV-102 Ti—Fe by Direct Reaction
(63) 125 mg of trimesic acid (595 μmol) are dissolved in a mixture of 12 mL of N,N-dimethyl-formamide (DMF) and 3 mL of acetic acid. 36 μL of Ti(IV) isopropoxide (120 μmop and 48 mg of Fe(II) chloride (240 μmop are added to this solution in a dry box or in the absence of oxygen. The mixture is stirred until the complete dissolution of the reagents and heated in an oven at 120° C. for 48 hours. Once this time has elapsed, the solid obtained is separated by centrifugation, washed with corresponding portions of DMF and methanol, and vacuum dried.
Example 6: Synthesis of MUV-102 Ti—Fe by Post-Synthetic Transformation (PST) of MUV-10
(64) 100 mg of MUV-10(Ca) are suspended in 10 mL of a solution of 0.005 M of Fe(II) chloride in a mixture of DMF:NMP 1:1 in the absence of oxygen. The mixture is introduced in an oven preheated at 65° C. for a maximum period of 10 days. Once this time has elapsed, the solid obtained is separated by centrifugation, washed with corresponding portions of DMF and methanol, and vacuum dried.
(65) The morphology, crystallinity, chemical stability and homogeneous distribution of metals of the MUV-102 family of materials are shown in
Example 7: Application of MUV-10(Ca) and MUV-10 (Mn) for Generating H.SUB.2
(66) The photocatalytic activity of two different MUV-10, MUV-10 (Ca) and MUV-10 (Mn), was assessed for the generation of fuels under visible radiation. To this end, a suspension of each MOF in a mixture of H.sub.2O:MeOH (4:1) was irradiated with a Xenon lamp (300 W). The results obtained relative to the amount of H.sub.2 generated per gram of material are shown in
(67) Study of the Properties of the MUV-10 Solid
(68) The distribution of pore size obtained from N.sub.2 adsorption isotherms confirmed a homogeneous pore diameter of 10.3 Å, which is consistent with the theoretical value of 12.0 Å calculated from the structure.
(69) The hydrolytic stability of the material between pH 2 and 12 was analysed. In accordance with the refinement of the diffraction pattern and N.sub.2 adsorption measurements, the immersion of the MUV-10(Ca) solid in concentrated solutions of HCl and NaOH.sub.(aq) for 24 hours did not affect its crystallinity or its surface area.
(70) In addition to its chemical stability, the photoactivity of the MOFs of the invention under ultraviolet (UV) light was also studied. To this end, the electronic structure of MUV-10(Ca) was computationally calculated using the density functional theory (DFT). In accordance with its density of states diagram, this Ti.sup.IV—Ca.sup.II MOF is a semi-conductor with a band gap of 3.1 eV, consistent with the optical band gap estimated using diffuse reflectance spectroscopy. As in other MOFs of the state of the art, the conduction band (CB) is dominated by the 3d orbitals of the Ti, while the valence band (VB) is mainly populated by the 2p orbitals of the carbon and oxygen atoms in the aromatic ligand. To test the photoactivity of MUV-10(Ca), the solid suspended in deoxygenated tetrahydrofuran (THF) was irradiated with UV-B radiation (λ=280-315 nm). This gave rise to a change in colour, from white to dark brown, in less than 2 hours. This change remained stable over time and was reverted immediately after exposure of the solid to air. The electron paramagnetic resonance (EPR) spectrum of MUV-10(Ca) before and after the irradiation confirmed the presence of two signals exclusively for the irradiated sample. A wide signal at 0.35 T with parameters g adjusted to g.sub.II=1.975 and g.sub.I=1.946, characteristic of the species Ti(III), and a narrower signal better defined to the lower fields with g=2.00, which can be attributed to the formation of photoexcited radicals of the trimesate ligand. This fact confirmed that the photoreduction of titanium in the MOF occurs through the generation of an excited state of the ligand that transfers the charge to the Ti(IV) centres in the MOF metal clusters by means of a ligand-metal charge transfer mechanism.
(71) The photoactivity under visible light of the heterometallic MOFs of the invention that incorporate metals with d electrons in their valence layer to improve their photoactivity under visible light. To this end, a MUV-10(Mn) solid was prepared by direct reaction following the same methodology as for a MUV-10(Ca) solid, detailed in the examples. In accordance with theoretical calculations (equivalent to those detailed above for the same material with Ca), the incorporation of Mn to the material significantly reduces the band gap (2.6 eV) as a result of the introduction of d electrons to the conduction band. Next, the activity of the MUV-10(Mn) solid under visible light was demonstrated. To this end, the activity of the MOF solid as a photocatalyst for generating H.sub.2 was studied. A suspension of the solid in a mixture of H.sub.2O:CH.sub.3OH was irradiated with a xenon lamp (300 W), confirming that the MUV-10(Mn) phase produces 6,500 μmol/g.sup.1 of H.sub.2, more than double the amount generated by the material MUV-10(Ca), after 24 hours of irradiation, without altering the structure or porosity of the solid. This fact confirms the possibility of modifying the electronic structure and photoactivity of the solid by adequately choosing the metals incorporated to its structure. Despite the fact that reference has been made to a specific embodiment of the invention, it is evident to a person skilled in the art that the solvent type or the titanium (IV) precursor, for example, inter alia, are susceptible of variations and modifications, and that the aforementioned details can be replaced with other technically equivalent ones, without falling outside the scope of protection defined by the attached claims.