Patent Grant
11786890
The accumulation of carbon dioxide in the atmosphere as a result of human activity is one of the largest contributing factors in the gradual warming of the Earth [1]. The Earth has a natural system of negative feedback processes to balance these accumulations, primarily by carbon fixation through photosynthesis. The amount of carbon dioxide already in the atmosphere is far too large for natural photosynthesis to reduce its accumulation in the short term. Therefore, it is urgent that technologies be developed that are capable of fixating large quantities of CO2 into organic matter, which are both energetically efficient and capable of creating a usable feedstock of reduced carbon (so-called solar fuel) [2]. These new technologies can use a naturally abundant and sustainable source of energy. Early transition metal oxides, in particular titanium oxides, are capable of reducing CO2 when excited by UV light [3]. Using sunlight to reduce CO2 directly would be ideal; however, the majority of the sun's rays are in the visible-IR range [4], which is too low energy to induce photoreduction with these materials, limiting their applicability on environmentally relevant scales. Thus, materials that are able to reduce CO2 with the use of visible light are an imminent and currently unfulfilled need. The materials discussed herein address these and other needs.
Disclosed herein are metal-organic frameworks. Metal-organic frameworks (MOFs) are a class of crystalline porous materials that exhibit high surface area and large pore volume. Metal-organic frameworks [5] are a class of porous materials composed of metal-oxide clusters connected through organic links forming highly crystalline open structures that offer a promising alternative to metal-oxide semiconductor photocatalysis. Research in the design and synthesis of new MOFs (reticular chemistry [6]) has allowed for the creation of functional materials with unprecedented high porosity (surface areas up to 10 000 m2 g−1) [7] and exceptional chemical and thermal stability, with applications in gas storage [8], gas separation [9], heterogeneous catalysis [10], payload release [11], and sensing [12], among others. MOFs are materials with extraordinary chemical and functional versatility, because both the organic and inorganic components can be systematically varied towards targeted applications in a systematic manner [13].
Titanium based MOFs in particular combine the photocatalytic activity of titanium oxide clusters with the light absorption properties of organic linkers, producing materials that can be photocatalytically active under UV-visible light [14]. These catalytic reactions are facilitated through either oxidative [14a, 15], or reductive [16] photoinduced electron transfer within the Ti-MOF under irradiation. MIL-125-NH2 (MIL=Materials Institut Lavoisier) is a titanium-based MOF constructed from 2-aminoterephthalate and a Ti8O12 ring-shaped cluster (
In accordance with the purposes of the disclosed compositions and methods, as embodied and broadly described herein, the disclosed subject matter relates to compositions and methods of making and using the compositions. More specifically, according to the aspects illustrated herein, disclosed are metal-organic frameworks and methods of making and use thereof.
Additional advantages of the disclosed compositions and methods will be set forth in part in the description which follows, and in part will be obvious from the description. The advantages of the disclosed compositions will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosed compositions, as claimed.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.
The accompanying figures, which are incorporated in and constitute a part of this specification, illustrate several aspects of the disclosure, and together with the description, serve to explain the principles of the disclosure.
The metal-organic frameworks and methods described herein may be understood more readily by reference to the following detailed description of specific aspects of the disclosed subject matter and the Examples included therein.
Before the present metal-organic frameworks and methods are disclosed and described, it is to be understood that the aspects described below are not limited to specific synthetic methods or specific reagents, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting.
Also, throughout this specification, various publications are referenced. The disclosures of these publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art to which the disclosed matter pertains. The references disclosed are also individually and specifically incorporated by reference herein for the material contained in them that is discussed in the sentence in which the reference is relied upon.
In this specification and in the claims that follow, reference will be made to a number of terms, which shall be defined to have the following meanings.
Throughout the description and claims of this specification the word “comprise” and other forms of the word, such as “comprising” and “comprises,” means including but not limited to, and is not intended to exclude, for example, other additives, components, integers, or steps.
As used in the description and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a composition” includes mixtures of two or more such compositions, reference to “an agent” includes mixtures of two or more such agents, reference to “the component” includes mixtures of two or more such components, and the like.
“Optional” or “optionally” means that the subsequently described event or circumstance can or cannot occur, and that the description includes instances where the event or circumstance occurs and instances where it does not.
Ranges can be expressed herein as from “about” one particular value, and/or to “about” another particular value. By “about” it is meant within 5% of the value, e.g., within 4, 3, 2, or 1% of the value. When such a range is expressed, another aspect includes from the one particular value and/or to the other particular value, the range beginning and end value are both included of the possible values, i.e., the range is mathematically a close rectangle. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another aspect. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint.
It is understood that throughout this specification the identifiers “first” and “second” are used solely to aid in distinguishing the various components and steps of the disclosed subject matter. The identifiers “first” and “second” are not intended to imply any particular order, amount, preference, or importance to the components or steps modified by these terms.
References in the specification and concluding claims to parts by weight of a particular element or component in a composition denotes the weight relationship between the element or component and any other elements or components in the composition or article for which a part by weight is expressed. Thus, in a compound containing 2 parts by weight of component X and 5 parts by weight component Y, X and Y are present at a weight ratio of 2:5, and are present in such ratio regardless of whether additional components are contained in the compound.
A weight percent (wt. %) of a component, unless specifically stated to the contrary, is based on the total weight of the formulation or composition in which the component is included.
As used herein, the term “substituted” is contemplated to include all permissible substituents of organic compounds. In a broad aspect, illustrative substituents include, acyclic and cyclic, branched and unbranched, carbocyclic and heterocyclic, and aromatic and nonaromatic substituents of organic compounds. Further examples of the permissible substituents will be described below. The permissible substituents can be one or more and the same or different for appropriate organic compounds. For purposes of this disclosure, the heteroatoms, such as nitrogen, can have hydrogen substituents and/or any permissible substituents of organic compounds described herein which satisfy the valencies of the heteroatoms. This disclosure is not intended to be limited in any manner by the permissible substituents of organic compounds. Also, the terms “substitution” or “substituted with” include the implicit proviso that such substitution is in accordance with permitted valence of the substituted atom and the substituent, and that the substitution results in a thermodynamically stable compound, e.g., a compound that does not spontaneously undergo transformation such as by rearrangement, cyclization, elimination, etc.
“Z1,” “Z2,” “Z3,” and “Z4” are used herein as generic symbols to represent various specific substituents. These symbols can be any substituent, not limited to those disclosed herein, and when they are defined to be certain substituents in one instance, they can, in another instance, be defined as some other substituents.
The term “aliphatic” as used herein refers to a non-aromatic hydrocarbon group in which carbon atoms form an open chain, and includes branched and unbranched, alkyl, alkenyl, or alkynyl groups.
As used herein, the term “alkyl” refers to saturated, straight-chained or branched saturated hydrocarbon moieties. Unless otherwise specified, C1-C24 (i.e., moieties containing one (1) to twenty-four (24) carbon atoms)) alkyl groups are intended. Examples of alkyl groups include methyl, ethyl, propyl, 1-methyl-ethyl, butyl, and their homologues and isomers. Alkyl substituents may be unsubstituted or substituted with one or more chemical moieties. The alkyl group can be substituted with one or more groups including, but not limited to, hydroxyl, halogen, acyl, alkyl, alkoxy, alkenyl, alkynyl, aryl, heteroaryl, aldehyde, amino, cyano, carboxylic acid, ester, ether, ketone, nitro, phosphonyl, silyl, sulfo-oxo, sulfonyl, sulfone, sulfoxide, or thiol, as described below, provided that the substituents are sterically compatible and the rules of chemical bonding and strain energy are satisfied.
Throughout the specification “alkyl” is generally used to refer to both unsubstituted alkyl groups and substituted alkyl groups; however, substituted alkyl groups are also specifically referred to herein by identifying the specific substituent(s) on the alkyl group. For example, the term “halogenated alkyl” specifically refers to an alkyl group that is substituted with one or more halides (halogens; e.g., fluorine, chlorine, bromine, or iodine). The term “alkoxyalkyl” specifically refers to an alkyl group that is substituted with one or more alkoxy groups, as described below. The term “alkylamino” specifically refers to an alkyl group that is substituted with one or more amino groups, as described below, and the like. When “alkyl” is used in one instance and a specific term such as “alkylalcohol” is used in another, it is not meant to imply that the term “alkyl” does not also refer to specific terms such as “alkylalcohol” and the like.
This practice is also used for other groups described herein. That is, while a term such as “cycloalkyl” refers to both unsubstituted and substituted cycloalkyl moieties, the substituted moieties can, in addition, be specifically identified herein; for example, a particular substituted cycloalkyl can be referred to as, e.g., an “alkylcycloalkyl.” Similarly, a substituted alkoxy can be specifically referred to as, e.g., a “halogenated alkoxy,” a particular substituted alkenyl can be, e.g., an “alkenylalcohol,” and the like. Again, the practice of using a general term, such as “cycloalkyl,” and a specific term, such as “alkylcycloalkyl,” is not meant to imply that the general term does not also include the specific term.
As used herein, the term “alkenyl” refers to unsaturated, straight-chained, or branched hydrocarbon moieties containing a double bond. Unless otherwise specified, C2-C24 (i.e., moieties containing two (2) to twenty-four (24) carbons)) alkenyl groups are intended. Alkenyl groups may contain more than one unsaturated bond. Examples include ethenyl, 1-propenyl, 2-propenyl, and their homolouges and isomers. The term “vinyl” refers to a group having the structure —CH═CH2; 1-propenyl refers to a group with the structure-CH═CH—CH3; and 2-propenyl refers to a group with the structure —CH2—CH═CH2. Asymmetric structures such as (Z1Z2)C═C(Z3Z4) are intended to include both the E and Z isomers. This can be presumed in structural formulae herein wherein an asymmetric alkene is present, or it can be explicitly indicated by the bond symbol C═C. Alkenyl substituents may be unsubstituted or substituted with one or more chemical moieties. Examples of suitable substituents include, for example, alkyl, alkoxy, alkenyl, alkynyl, aryl, heteroaryl, acyl, aldehyde, amino, cyano, carboxylic acid, ester, ether, halide, hydroxyl, ketone, nitro, phosphonyl, silyl, sulfo-oxo, sulfonyl, sulfone, sulfoxide, or thiol, as described below, provided that the substituents are sterically compatible and the rules of chemical bonding and strain energy are satisfied.
As used herein, the term “alkynyl” represents straight-chained or branched hydrocarbon moieties containing a triple bond. Unless otherwise specified, C2-C24 (i.e., moieties containing one (1)) to twenty-four (24) carbons) alkynyl groups are intended. Alkynyl groups may contain more than one unsaturated bond. Examples include C2-C6-alkynyl, such as ethynyl, 1-propynyl, 2-propynyl (or propargyl), 1-butynyl, and their homolouges and isomers. Alkynyl substituents may be unsubstituted or substituted with one or more chemical moieties. Examples of suitable substituents include, for example, alkyl, alkoxy, alkenyl, alkynyl, aryl, heteroaryl, acyl, aldehyde, amino, cyano, carboxylic acid, ester, ether, halide, hydroxyl, ketone, nitro, phosphonyl, silyl, sulfo-oxo, sulfonyl, sulfone, sulfoxide, or thiol, as described below.
As used herein, the term “aryl,” as well as derivative terms such as aryloxy, refers to groups that include a monovalent aromatic carbocyclic group of from 3 to 50 carbon atoms. Aryl groups can include a single ring or multiple condensed rings. In some embodiments, aryl groups include C6-C10 aryl groups. Examples of aryl groups include, but are not limited to, benzene, phenyl, biphenyl, naphthyl, tetrahydronaphtyl, phenylcyclopropyl, phenoxybenzene, and indanyl. The term “aryl” also includes “heteroaryl,” which is defined as a group that contains an aromatic group that has at least one heteroatom incorporated within the ring of the aromatic group. Examples of heteroatoms include, but are not limited to, nitrogen, oxygen, sulfur, and phosphorus. The term “non-heteroaryl,” which is also included in the term “aryl,” defines a group that contains an aromatic group that does not contain a heteroatom. The aryl substituents may be unsubstituted or substituted with one or more chemical moieties. Examples of suitable substituents include, for example, alkyl, alkoxy, alkenyl, alkynyl, aryl, heteroaryl, acyl, aldehyde, amino, cyano, carboxylic acid, ester, ether, halide, hydroxyl, ketone, nitro, phosphonyl, silyl, sulfo-oxo, sulfonyl, sulfone, sulfoxide, or thiol as described herein. The term “biaryl” is a specific type of aryl group and is included in the definition of aryl. Biaryl refers to two aryl groups that are bound together via a fused ring structure, as in naphthalene, or are attached via one or more carbon-carbon bonds, as in biphenyl.
The term “cycloalkyl” as used herein is a non-aromatic carbon-based ring composed of at least three carbon atoms. Examples of cycloalkyl groups include, but are not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, etc. The term “heterocycloalkyl” is a cycloalkyl group as defined above where at least one of the carbon atoms of the ring is substituted with a heteroatom such as, but not limited to, nitrogen, oxygen, sulfur, or phosphorus. The cycloalkyl group and heterocycloalkyl group can be substituted or unsubstituted. The cycloalkyl group and heterocycloalkyl group can be substituted with one or more groups including, but not limited to, alkyl, alkoxy, alkenyl, alkynyl, aryl, heteroaryl, acyl, aldehyde, amino, cyano, carboxylic acid, ester, ether, halide, hydroxyl, ketone, nitro, phosphonyl, silyl, sulfo-oxo, sulfonyl, sulfone, sulfoxide, or thiol as described herein.
The term “cycloalkenyl” as used herein is a non-aromatic carbon-based ring composed of at least three carbon atoms and containing at least one double bound, i.e., C═C. Examples of cycloalkenyl groups include, but are not limited to, cyclopropenyl, cyclobutenyl, cyclopentenyl, cyclopentadienyl, cyclohexenyl, cyclohexadienyl, and the like. The term “heterocycloalkenyl” is a type of cycloalkenyl group as defined above, and is included within the meaning of the term “cycloalkenyl,” where at least one of the carbon atoms of the ring is substituted with a heteroatom such as, but not limited to, nitrogen, oxygen, sulfur, or phosphorus. The cycloalkenyl group and heterocycloalkenyl group can be substituted or unsubstituted. The cycloalkenyl group and heterocycloalkenyl group can be substituted with one or more groups including, but not limited to, alkyl, alkoxy, alkenyl, alkynyl, aryl, heteroaryl, acyl, aldehyde, amino, cyano, carboxylic acid, ester, ether, halide, hydroxyl, ketone, nitro, phosphonyl, silyl, sulfo-oxo, sulfonyl, sulfone, sulfoxide, or thiol as described herein.
The term “cyclic group” is used herein to refer to either aryl groups, non-aryl groups (i.e., cycloalkyl, heterocycloalkyl, cycloalkenyl, and heterocycloalkenyl groups), or both. Cyclic groups have one or more ring systems that can be substituted or unsubstituted. A cyclic group can contain one or more aryl groups, one or more non-aryl groups, or one or more aryl groups and one or more non-aryl groups.
The term “acyl” as used herein is represented by the formula —C(O)Z1 where Z1 can be a hydrogen, hydroxyl, alkoxy, alkyl, alkenyl, alkynyl, aryl, heteroaryl, cycloalkyl, cycloalkenyl, heterocycloalkyl, or heterocycloalkenyl group described above. As used herein, the term “acyl” can be used interchangeably with “carbonyl.” Throughout this specification “C(O)” or “CO” is a short hand notation for C═O.
The term “acetal” as used herein is represented by the formula (Z1Z2)C(═OZ3)(═OZ4), where Z1, Z2, Z3, and Z4 can be, independently, a hydrogen, halogen, hydroxyl, alkyl, alkenyl, alkynyl, aryl, heteroaryl, cycloalkyl, cycloalkenyl, heterocycloalkyl, or heterocycloalkenyl group described above.
As used herein, the term “alkoxy” as used herein is an alkyl group bound through a single, terminal ether linkage; that is, an “alkoxy” group can be defined as to a group of the formula Z1—O—, where Z1 is unsubstituted or substituted alkyl as defined above. Unless otherwise specified, alkoxy groups wherein Z1 is a C1-C24 (i.e., moieties containing one (1)) to twenty-four (24) carbons) alkyl group are intended. Examples include methoxy, ethoxy, propoxy, 1-methyl-ethoxy, butoxy, and their homolouges and isomers.
The term “aldehyde” as used herein is represented by the formula —C(O)H. Throughout this specification “C(O)” is a short hand notation for C═O.
The terms “amine” or “amino” as used herein are represented by the formula —NZ1Z2Z3, where Z1, Z2, and Z3 can each be substitution group as described herein, such as hydrogen, an alkyl, alkenyl, alkynyl, aryl, heteroaryl, cycloalkyl, cycloalkenyl, heterocycloalkyl, or heterocycloalkenyl group described above.
The terms “amide” or “amido” as used herein are represented by the formula —C(O)NZ1Z2, where Z1 and Z2 can each be substitution group as described herein, such as hydrogen, an alkyl, alkenyl, alkynyl, aryl, heteroaryl, cycloalkyl, cycloalkenyl, heterocycloalkyl, or heterocycloalkenyl group described above.
The term “carboxylic acid” as used herein is represented by the formula —C(O)OH. A “carboxylate” or “carboxyl” group as used herein is represented by the formula —C(O)O−.
The term “cyano” as used herein is represented by the formula —CN.
The term “ester” as used herein is represented by the formula —OC(O)Z1 or —C(O)OZ1, where Z1 can be an alkyl, alkenyl, alkynyl, aryl, heteroaryl, cycloalkyl, cycloalkenyl, heterocycloalkyl, or heterocycloalkenyl group described above.
The term “ether” as used herein is represented by the formula Z1OZ2, where Z1 and Z2 can be, independently, an alkyl, alkenyl, alkynyl, aryl, heteroaryl, cycloalkyl, cycloalkenyl, heterocycloalkyl, or heterocycloalkenyl group described above.
The term “ketone” as used herein is represented by the formula Z1C(O)Z2, where Z1 and Z2 can be, independently, an alkyl, alkenyl, alkynyl, aryl, heteroaryl, cycloalkyl, cycloalkenyl, heterocycloalkyl, or heterocycloalkenyl group described above.
The term “halide” or “halogen” or “halo” as used herein refers to fluorine, chlorine, bromine, and iodine.
The term “hydroxyl” as used herein is represented by the formula —OH.
The term “nitro” as used herein is represented by the formula —NO2.
The term “phosphonyl” is used herein to refer to the phospho-oxo group represented by the formula —P(O)(OZ1)2, where Z1 can be hydrogen, an alkyl, alkenyl, alkynyl, aryl, heteroaryl, cycloalkyl, cycloalkenyl, heterocycloalkyl, or heterocycloalkenyl group described above.
The term “silyl” as used herein is represented by the formula —SiZ1Z2Z3, where Z1, Z2, and Z3 can be, independently, hydrogen, alkyl, alkoxy, alkenyl, alkynyl, aryl, heteroaryl, cycloalkyl, cycloalkenyl, heterocycloalkyl, or heterocycloalkenyl group described above.
The term “sulfonyl” or “sulfone” is used herein to refer to the sulfo-oxo group represented by the formula —S(O)2Z1, where Z1 can be hydrogen, an alkyl, alkenyl, alkynyl, aryl, heteroaryl, cycloalkyl, cycloalkenyl, heterocycloalkyl, or heterocycloalkenyl group described above.
The term “sulfide” as used herein is comprises the formula —S—.
The term “thiol” as used herein is represented by the formula —SH.
“R1,” “R2,” “R3,” “Rn,” etc., where n is some integer, as used herein can, independently, possess one or more of the groups listed above. For example, if R1 is a straight chain alkyl group, one of the hydrogen atoms of the alkyl group can optionally be substituted with a hydroxyl group, an alkoxy group, an amine group, an alkyl group, a halide, and the like. Depending upon the groups that are selected, a first group can be incorporated within second group or, alternatively, the first group can be pendant (i.e., attached) to the second group. For example, with the phrase “an alkyl group comprising an amino group,” the amino group can be incorporated within the backbone of the alkyl group. Alternatively, the amino group can be attached to the backbone of the alkyl group. The nature of the group(s) that is (are) selected will determine if the first group is embedded or attached to the second group.
Unless stated to the contrary, a formula with chemical bonds shown only as solid lines and not as wedges or dashed lines contemplates each possible molecular conformation, including but not limited to enantiomer, stereoisomer or mixtures thereof
Reference will now be made in detail to specific aspects of the disclosed materials, compounds, compositions, formulations, articles, and methods, examples of which are illustrated in the accompanying Examples and Figures.
Herein, the synthesis of a family of titanium MOFs isoreticular to MIL-125-NH2 is described, where the amine functionality is decorated with alkyl chains of varying length and connectivity, i.e., methyl, ethyl, isopropyl, n-butyl, cyclopentyl, cyclohexyl, and n-heptyl (
In specific embodiments, disclosed herein are metal-organic frameworks comprising titanium oxide clusters connected through an organic linker, wherein the organic linker comprises:
wherein R1 and R2 are independently selected from the group consisting of H, substituted or unsubstituted C1-C14 alkyl, and substituted or unsubstituted C1-C14 cycloalkyl.
In some examples, R1 and R2 are independently selected from H, unsubstituted linear or branched C1-C14 alkyl, and unsubstituted C1-C14 cycloalkyl. In some examples, R1 is H and R2 is selected from the group consisting of unsubstituted linear or branched C1-C7 alkyl and unsubstituted C1-C7 cycloalkyl. In some examples, R1 is H and R2 is selected from the group consisting of methyl, ethyl, isopropyl, n-butyl, cyclopentyl, cyclohexyl, and n-heptyl.
In some examples, the titanium oxide clusters comprise Ti8O12 ring shaped clusters.
Also disclosed herein are metal-organic frameworks comprising:
wherein R1 and R2 are independently selected from the group consisting of H and substituted or unsubstituted C1-C14 alkyl.
In some examples, R1 and R2 are independently selected from H, unsubstituted linear or branched C1-C14 alkyl, and unsubstituted C1-C14 cycloalkyl. In some examples, R1 is H and R2 is selected from the group consisting of unsubstituted linear or branched C1-C7 alkyl and unsubstituted C1-C7 cycloalkyl. In some examples, R1 is H and R2 is selected from the group consisting of methyl, ethyl, isopropyl, n-butyl, cyclopentyl, cyclohexyl, and n-heptyl.
In some examples, the metal-organic framework can have a crystal structure in the high symmetry tetragonal I4/mmm space group with low residuals.
In some examples, the metal-organic framework can have a BET surface area of from 100 m2/g to 2000 m2/g (e.g., from 200 m2/g to 1000 m2/g).
In some examples, the metal-organic framework can have a total pore volume of from 0.05 cm3/g to 1.5 cm3/g (e.g., from 0.09 cm3/g to 0.73 cm3/g).
In some examples, the metal-organic framework can have an adsorption capacity for CO2 gas of from 5 to 500 cm3 of CO2 gas per g of metal-organic framework (e.g., from 19 to 225 cm3 of CO2 gas per g of metal-organic framework).
In some examples, the metal-organic framework has a bandgap of from 2.15 eV to 2.9 eV
Methods of Making
Also disclosed herein are methods of making the metal-organic frameworks disclosed herein. The methods can, for example, comprise contacting a titanium oxide cluster with an organic linker to form the metal-organic framework. In some examples, the metal-organic framework can be formed at room temperature.
Methods of Use
Also disclosed herein are methods of use of the metal-organic frameworks described herein. The methods can comprise using the metal-organic framework as a catalyst in the photocatalytic reduction of CO2. For example, the methods can comprise contacting the metal-organic framework with CO2 to form a mixture and illuminating the mixture with light that at least partially overlaps with the bandgap of the metal-organic framework. In some examples, the CO2 can be reduced at an initial rate of reaction of from 5.5×10−6 to 1.25×10−5 mol L−1 h−1. In some examples, the apparent quantum yield is from 0.3% to 1.8%.
Also disclosed herein are CO2 reduction catalysts, the catalysts comprising the metal-organic frameworks described herein.
A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.
The examples below are intended to further illustrate certain aspects of the systems and methods described herein, and are not intended to limit the scope of the claims.
The following examples are set forth below to illustrate the methods and results according to the disclosed subject matter. These examples are not intended to be inclusive of all aspects of the subject matter disclosed herein, but rather to illustrate representative methods and results. These examples are not intended to exclude equivalents and variations of the present invention which are apparent to one skilled in the art.
Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts, temperature, etc.) but some errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, temperature is in ° C. or is at ambient temperature, and pressure is at or near atmospheric. There are numerous variations and combinations of measurement conditions, e.g., component concentrations, temperatures, pressures and other measurement ranges and conditions that can be used to optimize the described process.
A series of metal-organic frameworks (MOFs) isoreticular to MIL-125-NH2 were prepared, where the 2-amino-terephthalate organic links feature N-alkyl groups of increasing chain length (from methyl to heptyl) and varying connectivity (primary and secondary). The prepared materials display reduced optical bandgaps correlated to the inductive donor ability of the alkyl substituent as well as high photocatalytic activity towards the reduction of carbon dioxide under blue illumination operating over 120 h. Secondary N-alkyl substitution (isopropyl, cyclopentyl and cyclohexyl) exhibit larger apparent quantum yields than the primary N-alkyl analogs directly correlated to their longer lived excited-state lifetime. In particular, MIL-125-NHCyp (Cyp=cyclopentyl) exhibits a small bandgap (Eg=2.30 eV) and the larger apparent quantum yield (Φapp=1.80%) compared to the parent MIL-125-NH2 (Eg=2.56 eV, Φapp=0.31%), making it a promising candidate for the next generation of photocatalysts for solar fuel production based on earth-abundant elements.
All starting materials and solvents, unless otherwise specified, were obtained from commercial sources (Aldrich, Fisher, VWR) and used without further purification. All reactions were performed at ambient laboratory conditions, and no precautions were taken to exclude oxygen or atmospheric moisture unless otherwise specified. Anhydrous N,N-dimethylformamide (DMF) and tetrahydrofuran (THF) were purified using a custom-built alumina-column based solvent purification system (Inovative Technology). Anhydrous methanol was obtained from Aldrich (Sureseal). Mesitylene and hexamethylphosphoramide (HMPA) were dried over activated 4 Å molecular sieves. Deuterated solvents (CDCl3, DMSO, D2O, CD3CN, NaOD 40% in D2O) were obtained from Cambridge Isotope Lab.
High-resolution 1H and 13C nuclear magnetic resonance (NMR) spectra were collected using Bruker AVANCE-III 400 MHz spectrometer. The chemical shifts are reported relative to solvent residual signal. NMR data analysis was preformed using MestReNova (v. 10.0.2). Liquid chromatography-mass spectra (LC-MS) were recorded using Agilent 6230 TOF with an Agilent Zorbax SB-C18 analytical column. Fourier-transform infrared (FTIR) spectra were performed using a Perkin Elmer Spectrum ONE Universal FT-IR ATR. 32 scans were collected for each sample at a resolution of 0.5 cm−1 from 4000-650 cm−1. Scanning electron microscopy (SEM) was conducted using a JEOL JSM 6480 microscope on low-vacuum with an accelerating voltage of 20 kV. Sample preparation involved the dispersion of samples upon carbon tape attached to stainless steel sample holder.
Powder X-ray diffraction (PXRD) data was collected using a Rigaku MiniFlex 600 θ-2θdiffractometer in Bragg-Brentano geometry with a 300 mm goniometer diameter, Ni-filtered CuKα radiation (λ=1.5418 Å) at 600 W power (40 kV, 15 mA), equipped with a NaI(Tl) SC-70 scintillation detector, 5.0° incident and receiving Soller slits, a 0.625° divergent slit, a 1.25° scattering slit, a 0.3 mm receiving slit and a Ni-CuKβ filter. Samples were analyzed from 3 to 40 2θ-degrees with 0.02° per step and a scan rate of 0.25 2θ-degrees min−1. Samples were prepared by dropping the powder sample in a glass sample holder and pressing the powder with a razor blade spatula forming a smooth surface. Crystal models were created using Materials Studio modeling suite [21] starting from the published crystal of MIL-125 (CCDC code RUPRUQ) [14a] by adding the corresponding N-alkyl chains.
Crystal modeling and Rietveld refinements. Rietveld refinements were performed in GSAS-II [22] with the experimental diffractograms, and the respective crystal model generated in Materials Studio. Refinements were performed using a Thomson-Cox-Hasting modified pseudo-Voigt function with 6 terms, and Finger-Cox-Jephcoat peak asymmetry with 1 parameter. Crystallographic information for the Rietveld Refinement are summarized in Table 1-Table 3.
Gas adsorption isotherm analysis was performed using a Micromeritics ASAP 2020 surface area and porosimetry analyzer. Measurements were performed at 77 K (liquid N2 bath) for N2(g), and at 273, 283 and 293 K (water circulator bath) for CO2 (g) on thermally activated samples. Brunauer-Emmet-Teller (BET) surface areas were obtained by performing a Rouquerol analysis over the linear isotherm to determine the upper limits of the BET model from the N2 isotherms. Least squares linear fitting over the BET plot provided the parameter for the volume of the monolayer, BET surface area and C-constant were obtained following the recommendation by Snurr et al. for determination of the surface area in MOFs [23]. Differential enthalpies of CO2 adsorption were obtained by fitting the isotherms at the three measured temperatures into a virial equation using the Micromeritics data processing software.
Solid-state absorption spectra were collected at room temperature using an Edinburgh FLS980 spectrometer with the integrating sphere accessory. Light output from a housed 450 W Xe lamp was passed through a single grating (1800/mm, 250 nm blaze) Czerny-Turner monochromator and then into the integrating sphere containing powder MIL-125-NHR sample or scattering reference (BaSO4). The output from the integrating sphere was passed through a single grating (1800λ/mm, 500 nm blaze) Czerny-Turner and finally detected by a peltier-cooled Hamamatsu R928 photomultiplier tube. Synchronous spectral scans were performed with both excitation and emission monochromators, with zero wavelength offset, stepping through the pre-set spectral range. Absorbance was then calculated using Edinburgh's F900 software package. Tauc plots were obtained assuming α(hν)=(Ahν)2.
Transient Absorption (TA) Measurements:
Samples for TA were prepared by suspending MIL-125-NHR in ˜3.0 mL of MeCN in a 1 cm×1 cm quartz cuvette (A≈0.2 O.D.). Measurements were performed on a spectrometer composed of a Continuum Surelite EX Nd:YAG laser combined with a Continuum Horizon OPO (λex=405 nm, 5-7 ns, operated at 1 Hz, beam diameter ˜0.5 cm, 5 mJ/pulse) integrated into a commercially available Edinburgh LP980 laser flash photolysis spectrometer. White light probe pulses generated by a pulsed 150 W Xe lamp were passed through the sample, focused into the monochromator, and then, for full spectrum data, were detected by intensified Andor iStar CCD camera. Single wavelength kinetic absorption at 500 nm were detected by a photomultiplier tube with a 435 nm long pass filter placed before the detector to reject unwanted scattered light. Detector outputs were processed using a Tektronix TDS3012C Digital Phosphor Oscilloscope interfaced to a PC. Single wavelength kinetic data were the result of averaging 50 laser shots. Detector outputs were processed using Edinburgh's L900 (version 8.2.3, build 0) software package. Time-resolved absorption data were fit with the exponential function in Equation 1:
I=Ioe−t/τ eq. (1)
where τ is the lifetime.
The isoreticular family of MOFs was prepared via SN2 reaction of 2-amino terephthalate dimethyl ester (Scheme 1) with the corresponding alkyl iodide in basic conditions forming intermediates 1a-d and 1g in moderate yields. Specifically, 2-amino-terepthlate dimethyl ester (2.00 g, 9.56 mmol) was suspended in anhydrous DMF (20 mL) and stirred until fully dissolved (HMPA was used instead of DMF for 1g). K2CO3 (5.30 g, 38.2 mmol) was added, followed by dropwise addition of alkyl iodide (14.3 mmol), and the mixture was stirred for 18 h at 100° C. The reaction mixture was then cooled to room temperature and quenched with 2 M HCl (aq) to a pH=3. The mixture was extracted with EtOAc (3×50 mL), the combined organic extracts were washed with brine (3×50 mL), dried over anhydrous MgSO4, filtered through celite and the solvent was removed using a rotary evaporator. The obtained crude was purified using flash chromatography (SiO2, 15% v/v EtOAc:hexanes, dry loading).
Conditions: ia (R=Me, Et, iPr, Bu, hep) RI, K2CO3, DMF/HPMA, 100° C., 18 h. ib (R=Cyp, Cy) cycloketone, TMSCl, NaBH4, DMF, N2 (g), 0° C., 15 min. ii. NaOH, THF, 70° C., 8 h. iii. Ti(OiPr)4, DMF, MeOH, 150° C., 48 h.
Compound 1a: Yellow solid, yield 0.89 g (45%). 1H NMR (400 MHz, CDCl3) δ=7.84 (dd, J=8.3, 1.7 Hz, 1H), 7.61 (br, NH), 7.24 (s, br, 1H), 7.11 (d, J=8.3 Hz, 1H), 3.85 (s, 3H), 3.79 (s, 3H), 2.88 (d, J=5.2 Hz, 3H) (
Compound 1b: Yellow solid, yield 0.80 g (40%). 1H NMR (400 MHz, CDCl3) δ=7.89 (d, J=8.3 Hz, 1H), 7.59 (br, NH), 7.29 (d, J=1.7 Hz, 1H), 7.13 (dd, J=8.3, 1.6 Hz, 1H), 3.87 (s, 3H), 3.83 (s, 3H), 3.24 (qd, J=7.2, 4.9 Hz, 2H), 1.30 (t, J=7.2 Hz, 3H) (
Compound 1c: Yellow solid, yield 0.67 g (34%). 1H NMR (400 MHz, CDCl3) δ=7.91 (d, J=8.3 Hz, 1H), 7.68 (br, NH), 7.35 (s, 1H), 7.13 (d, J=8.4 Hz, 1H), 3.89 (s, 3H), 3.84 (s, 3H), 3.79 (m, 1H), 1.27 (d, J=6.3 Hz, 6H) (
Compound 1d: Yellow solid, yield 0.75 g (38%). 1H NMR (400 MHz, CDCl3) δ=7.87 (d, J=8.4 Hz, 1H), 7.67 (br, NH), 7.29 (s, 1H), 7.12 (d, J=8.2 Hz, 1H), 3.87 (s, 3H), 3.83 (s, 3H), 3.23-3.17 (m, 2H), 1.69-1.61 (m, 2H), 1.50-1.40 (m, 3H), 0.97-0.92 (t, J=7.4, 3H). 13C NMR (100 MHz, CDCl3) δ=168.55, 166.92, 150.91, 135.08, 131.70, 114.47, 112.69, 112.44, 52.24, 51.66, 42.62, 31.22, 20.36, 13.87. HRMS (ESI-TOF) m/z calculated for C6H13NO3 [M+H]+: 266.1387, found 266.1364.
Compound 1g: Yellow liquid, yield 0.53 g (42%). 1H NMR (400 MHz, Chloroform-d) δ=7.93 (d, J=8.3 Hz, 1H), 7.70 (br, NH), 7.34 (d, J=1.6 Hz, 1H), 7.17 (dd, J=8.3, 1.6 Hz, 1H), 4.12 (t, J=6.7 Hz, 2H), 3.92 (s, 3H), 3.87 (s, 3H), 1.56 (d, J=6.4 Hz, 2H), 1.38-1.22 (m, 8H), 0.89 (t, J=3.1 Hz, 3H). 13C NMR (100 MHz, CDCl3) δ=168.75, 167.15, 151.07, 135.24, 131.88, 114.61, 112.86, 112.64, 52.45, 51.86, 43.11, 31.91, 29.20, 28.84, 27.29, 22.78, 14.20.
Intermediates 1e-f were synthesized via reductive amination with cyclopentanone or cyclohexanone in the presence of NaBH4/TMSCl in cold DMF in high yields (Scheme 1). Under N2 (g) in a 25 mL two-neck round bottom flask with a magnetic stir bar, 2-aminoterepthlate dimethyl ester (1.00 g, 4.78 mmol) was suspended in anhydrous DMF (3.2 mL) and stirred until fully dissolved. TMSCl (1.30 g, 11.95 mmol) and the corresponding cyclic ketone (5.25 mmol) were added to the solution and the mixture was cooled to 0° C. in an ice bath. NaBH4 (0.18 g, 4.78 mmol) was added cautiously over 5 min. The mixture was then allowed to warm up to room temperature and monitored by TLC until disappearance of starting material. The mixture was quenched with saturated NaHCO3 (aq.) followed by extraction with EtOAc (3×10 mL). The combined organic fractions were then washed with brine (3×10 mL) and dried over MgSO4, filtered through celite and the solvent was removed using a rotary evaporator. The obtained crude was purified using flash chromatography (SiO2, 5-10% v/v EtOAc:hexanes, dry loading).
Compound 1e: Yellow liquid, yield 1.20 g (89%). 1H NMR (400 MHz, CDCl3) δ=7.92 (d, J=8.3 Hz, 1H), 7.79 (br, NH), 7.38 (d, J=1.6 Hz, 1H), 7.15 (dd, J=8.3, 1.6 Hz, 1H), 3.95 (dd, J=9.2, 3.8 Hz, 1H), 3.91 (s, 3H), 3.86 (s, 3H), 2.14-2.00 (m, 2H), 1.81-1.71 (m, 2H), 1.72-1.62 (m, 2H), 1.57 (tdd, J=12.2, 6.2, 3.2 Hz, 2H). 13C NMR (100 MHz, CDCl3) δ=168.73, 167.11, 150.55, 135.09, 131.87, 114.42, 113.41, 112.82, 53.82, 52.42, 51.81, 33.57, 24.16.
Compound 1f: Yellow liquid, yield 1.24 g (92%). 1H NMR (400 MHz, Chloroform-d) δ=7.93 (d, J=8.3 Hz, 1H), 7.81 (br, NH), 7.12 (dd, J=8.3, 1.6 Hz, 1H), 3.91 (s, 3H), 3.86 (s, 3H), 3.50 (dtd, J=12.6, 8.4, 7.9, 3.6 Hz, 1H), 2.02 (td, J=7.8, 7.3, 3.8 Hz, 2H), 1.77 (dq, J=13.0, 4.2 Hz, 2H), 1.62 (ddt, J=14.1, 9.6, 4.5 Hz, 1H), 1.51-1.22 (m, 5H). 13C NMR (101 MHz, CDCl3) δ=168.79, 167.19, 150.14, 135.18, 132.08, 114.21, 113.06, 112.70, 52.45, 51.82, 50.50, 32.93, 25.96, 24.69
The alkylated diester 1a-f (0.50 g) was dissolved in THF (25 mL), followed by addition of 1 M NaOH (aq, 12.8 mL). The solution was heated to 70° C. and stirred for 8 h. The mixture was concentrated in a rotary evaporator at 45° C. to remove the excess THF. The mixture was cooled to room temperature followed by addition of 1 M HCl (aq) until a pH=3. The observed precipitate was isolated by filtration, rinsed with water, and dried in air at room temperature for 6 h.
Compound 2a: Yellow solid, yield 0.46 g (92%). 1H NMR (400 MHz, DMSO-d6) δ=7.86 (d, J=8.2 Hz, 1H), 7.21 (d, J=1.6 Hz, 1H), 7.09 (dd, J=8.2, 1.6 Hz, 1H), 2.88 (s, 3H) (
Compound 2b: Yellow solid, yield 0.45 g (90%). 1H NMR (400 MHz, DMSO-d6) δ=7.87 (d, J=8.2 Hz, 1H), 7.23 (d, J=1.6 Hz, 1H), 7.08 (dd, J=8.2, 1.6 Hz, 1H), 3.23 (q, J=7.2 Hz, 2H), 1.23 (t, J=7.1 Hz, 3H). 13C NMR (100 MHz, DMSO-d6) δ=169.46, 167.15, 150.35, 135.78, 131.96, 114.30, 112.91, 111.71, 36.70, 14.26. HRMS (ESI-TOF) m/z calculated for C6H13NO3 [M+H]+: 210.0761, found 210.0746.
Compound 2c: Yellow solid, yield 0.47 g (94%). 1H NMR (400 MHz, DMSO-d6) δ=7.87 (d, J=8.2 Hz, 1H), 7.25 (d, J=1.6 Hz, 1H), 7.05 (dd, J=8.2, 1.6 Hz, 1H), 3.74 (hept, J=6.4 Hz, 1H), 1.21 (d, J=6.3 Hz, 6H). 13C NMR (100 MHz, DMSO-d6) δ=169.57, 167.19, 149.58, 135.75, 132.11, 114.08, 113.04, 112.14, 42.74, 22.46. HRMS (ESI-TOF) m/z calculated for C6H13NO3 [M+H]+: 224.0917, found 224.0924.
Compound 2d: Yellow solid, yield 0.48 g (96%). 1H NMR (400 MHz, DMSO-d6) δ=7.85 (d, J=8.2 Hz, 1H), 7.24 (d, J=1.5 Hz, 1H), 7.07 (dd, J=8.2, 1.6 Hz, 1H), 3.20 (t, J=7.0 Hz, 2H), 1.60 (m, 2H), 1.40 (m, 2H), 0.93 (t, J=7.1 Hz, 3H). 13C NMR (100 MHz, DMSO-d6) δ=169.52, 167.15, 150.51, 135.77, 131.96, 114.25, 112.90, 111.74, 41.72, 30.58, 19.71, 13.68. HRMS (ESI-TOF) m/z calculated for C6H13NO3 [M+H]+: 238.1074, found 238.1058.
Compound 2e: Yellow solid, yield 0.47 g (93%). 1H NMR (400 MHz, DMSO-d6) δ=7.86 (d, J=8.2 Hz, 1H), 7.27 (d, J=1.5 Hz, 1H), 7.07 (dd, J=8.2, 1.5 Hz, 1H), 3.88 (p, J=6.1 Hz, 1H), 2.02 (dq, J=12.1, 6.0, 5.1 Hz, 2H), 1.65 (dqd, J=22.4, 7.8, 3.7 Hz, 4H), 1.45 (dq, J=11.6, 5.5 Hz, 2H). 13C NMR (100 MHz, DMSO) δ=169.60, 167.21, 150.05, 135.72, 132.05, 114.28, 112.99, 112.58, 53.08, 32.92, 23.57. HRMS (ESI-TOF) m/z calculated for C13H16NO4 [M+H]+: 250.1079, found 250.1041.
Compound 2f: Yellow solid, yield 0.46 g (92%). 1H NMR (400 MHz, DMSO-d6) δ=7.98 (br, NH), 7.86 (d, J=8.2 Hz, 1H), 7.25 (s, 1H), 7.04 (dd, J=8.3, 1.4 Hz, 1H), 3.45 (d, J=8.9 Hz, 2H), 1.93 (dt, J=12.6, 3.9 Hz, 2H), 1.68 (dt, J=13.3, 4.3 Hz, 2H), 1.58 (dt, J=10.0, 4.3 Hz, 1H), 1.49-1.34 (m, 2H), 1.34-1.19 (m, 3H). 13C NMR (100 MHz, DMSO) δ=169.67, 167.23, 149.54, 135.74, 132.15, 114.02, 112.11, 49.54, 32.23, 25.33, 23.97. HRMS (ESI-TOF) m/z calculated for C14H18NO4 [M+H]+: 264.1235, found 264.1189.
Compound 2g: Yellow solid, yield 0.48 g (96%). 1H NMR (400 MHz, DMSO-d6) δ=7.86 (d, J=8.2 Hz, 1H), 7.23 (d, J=1.6 Hz, 1H), 7.07 (dd, J=8.2, 1.5 Hz, 1H), 3.19 (t, J=7.0 Hz, 2H), 1.61 (p, J=7.0 Hz, 2H), 1.44-1.20 (m, 8H), 0.92-0.80 (m, 3H)13C NMR (100 MHz, DMSO) δ=169.54, 167.16, 150.52, 135.77, 131.97, 114.25, 112.89, 111.75, 42.02, 31.20, 28.41, 28.36, 26.45, 22.01, 13.94. HRMS (ESI-TOF) m/z calculated for C15H22NO4 [M+H]+: 280.1548, found 280.1500.
N,N-2-dimethyl amino-terephthalic acid (2.00 g, 9.56 mmol) was suspended in anhydrous DMF (20 mL) and stirred until fully dissolved. K2CO3 (5.30 g, 38.2 mmol) was added, followed by dropwise addition of methyl iodide (7.66 g, 54.0 mmol), and the mixture was stirred for 18 h at 60° C. The reaction mixture was then cooled to room temperature and quenched with 2 M HCl (aq) to a pH=3. The mixture was extracted with EtOAc (3×50 mL), the combined organic extracts were washed with brine (3×50 mL), dried over anhydrous MgSO4, filtered through celite and the solvent was removed using a rotary evaporator. The obtained crude was purified using flash chromatography (SiO2, 15% v/v EtOAc:hexanes, dry loading).
Compound S1: Yellow solid, yield 0.69 g (31%). 1H NMR (400 MHz, CDCl3) δ=7.65 (d, J=5.9 Hz, 1H), 7.60 (s, 1H), 7.45 (d, J=7.5 Hz, 1H), 3.91 (d, J=3.8 Hz, 6H), 2.89 (d, J=3.1 Hz, 6H). 13C NMR (100 MHz, CDCl3) δ=168.69, 166.90, 151.95, 133.26, 131.59, 124.43, 119.19, 117.73, 52.44, 43.57.
The alkylated diester (0.50 g) was dissolved in THF (25 mL), followed by addition of 1 M NaOH (aq, 12.8 mL). The solution was heated to 70° C. and stirred for 8 h. The mixture was concentrated in a rotary evaporator at 45° C. to remove the excess THF. The mixture was cooled to room temperature followed by addition of 1 M HCl (aq) until a pH=3. The observed precipitate was isolated by filtration, rinsed with water, and dried in air at room temperature for 6 h.
Compound 3: Yellow solid, yield 0.45 g (90%). 1H NMR (400 MHz, DMSO-d6) δ=7.99 (d, J=1.8 Hz, 1H), 7.95-7.89 (m, 1H), 7.76-7.71 (m, 1H), 2.86 (s, 6H). 13C NMR (100 MHz, DMSO) δ=167.11, 166.43, 150.74, 134.69, 130.85, 127.29, 124.41, 120.82, 43.85.
Assembling of the Building Blocks into MOFs
General Procedure for Solvothermal MOF Crystallization in Flame-Sealed Glass Tube Vessel.
A meter-long borosilicate glass tube measuring 10×8 mm (o.d×i.d), was divided into six equal portions with a marker. Using a glass cutter, the long tube was cut into three shorter tubes by only cutting every other mark. The cut ends of the tube were etched using an oxygen-propane torch. The final glass tubes were made by melting the intermediate glass tubes at the mark with the torch. After the reactants and solvents were loaded into to the glass tubes, a hose adaptor was used to connect the glass tube to a high vacuum (10 mtorr) using a Schlenk line constructed by fitting the open end of the tube inside a short length of standard rubber hose that was further affixed to a ground glass tap which could be closed to isolate this assembly from dynamic vacuum. The mixture was flash frozen at 77 K (liquid N2), evacuated to an internal pressure of 150 mtorr (±10 mtorr), and sealed under static vacuum. Upon sealing, the length of the tube was reduced to 18-20 cm; the reactant mixture was allowed to thaw and placed in an isothermal oven inside a sand bath. After the reaction was complete, the tube was allowed to cool to room temperature, the tube was opened using a glass cutter, and the solids were isolated by filtration.
Compounds 2a-f (0.41 mmol) were placed in 20 mL scintillation vials with anhydrous DMF (4.90 mL) and anhydrous MeOH (0.35 mL). The mixture was mixed thoroughly by immersing the vial in an ultra-sonic bath for 1 min then transferred into a borosilicate glass tube and bubbled with N2 (g) for 5 min. Ti(OiPr)4 (0.031 mL, 0.106 mmol) was added to the tube via syringe, immediately flash frozen in liquid N2, and flame sealed. The sealed tube was heated to 150° C. for 48 h. After cooling to room temperature, the formed powder was isolated by filtration and rinsed with DMF (3×) and CHCl3 (3×). The powder was immersed in CHCl3 and stored for 3 d in a desiccator, replacing the solvent during this time (8×). The solvent was removed by decantation and the solvent-wet powder was dried under dynamic vacuum (10 mtorr) for 48 h at room temperature. The degassed yellow solid was stored under N2 in a desiccator.
MIL-125-NHMe.
Yellow solid. Yield: 0.015 g [66% yield based on Ti8O12(C9H7NO4)6]. FTIR (ATR, cm−1) 3388.88, 2923.01, 1717.1, 1538.36, 1505.04, 1484.73, 1456.67, 1408.86, 1384.32, 1311.53, 1278.29, 1163.53, 1080.44, 1062.15, 1036.26, 950.04, 882.39, 768.58, 632.14, 583.12, 553.84, 507.68, 460.66
MIL-125-NHEt.
Yellow solid. Yield: 0.015 g [63% yield based on Ti8O12(C10H9NO4)6]. FTIR (ATR, cm−1) 3364.35, 2969.06, 2927.83, 2871.17, 1622.55, 1574.24, 1538.33, 1504.43, 1480.27, 1454.32, 1385.56, 1304.75, 1279.43, 1269.21, 1157.09, 1081.55, 1058.47, 983.03, 950.64, 886.9, 768.8, 665.76, 630.17, 585.19, 512.73
MIL-125-NHiPr.
Yellow solid. Yield: 0.014 g [56% yield based on Ti8O12(C11H11NO4)6]. FTIR (ATR, cm−1) 3354.94, 2965.73, 2927.26, 1622.02, 1573.66, 1538.12, 1503.89, 1454.54, 1445.82, 1410.07, 1384.84, 1279.16, 1246.65, 1117.76, 1006.2, 951.41, 888.56, 850.56, 768.24, 665.95, 636.51, 613.79, 600.93, 538.98, 482.13
MIL-125-NHBu.
Yellow solid. Yield: 0.015 g [57% yield based on Ti8O12(C12H13NO4)6]. FTIR (ATR, cm−1) 3362.48, 2955.93, 2927.6, 2870.25, 1622.53, 1573.94, 1537.91, 1503.55, 1451.88, 1386.73, 1314.03, 1304.04, 1280.91, 1259.32, 1115.87, 970.85, 951.52, 906.68, 885.87, 837.9, 769.03, 731, 633.97, 616.57, 583.52, 534.70, 503.04
MIL-125-NHCyp.
Yellow solid. Yield: 0.010 g [39% yield based on Ti8O12(C13H13NO4)6]. FTIR (ATR, cm−1) 3365.09, 2956.52, 2870.11, 1622.59, 1572.58, 1533.02, 1499.83, 1453.63, 1409.16, 1385.58, 1323.65, 1276.65, 1184.97, 1115.98, 1060.09, 980.45, 951.9, 886.01, 768.43, 620.1, 597.1, 523.84, 470.79
MIL-125-NHCy.
Yellow solid. Yield: 0.011 g [42% yield based on Ti8O12(C14H15NO4)6]. FTIR (ATR, cm−1) 3352.11, 2927.79, 2853.15, 1620.61, 1571.39, 1532.66, 1501.01, 1453.71, 1383.93, 1322.94, 1281.56, 1248.78, 1187.03, 1150.25, 1073.88, 994.46, 959.79, 887.69, 767.44, 664.76, 631.11, 602.49, 526.78, 479.16
MIL-125-NHhept.
Yellow solid. Yield: 0.015 g [52% yield based on Ti8O12(C15H19NO4)6]. FTIR (ATR, cm−1) 3373.41, 2953.73, 2926, 2854.98, 1622.82, 1573.83, 1537.73, 1532.36, 1504.52, 1454.97, 1403.36, 1385.54, 1311.73, 1278.64, 1123.5, 1063.3, 982.81, 954.74, 884.31, 768.1, 665.83, 617.89, 582.38, 548.52, 505.48
Attempts to prepare a double methylated aminoterephthalate MIL-125-NMe2 using linker 3 were unsuccessful (Scheme 3) due to the decomposition of the linker into the monomethylated species 2a, with 80% conversion while forming non-porous amorphous solids. The steric constrain imposed by the double substitution can impede the crystallization of the MOF, while Ti+4 induces N-dealkylation, similar to Zr-based MOFs, and thus only single N-alkylated MOFs were successfully synthesized.
Note: Attempts to prepare this MOF under the same conditions as in mono N-substituted MOFs resulted in N-demethylation of the linker with formation of amorphous non-porous samples.
MOF Characterization
Activation procedure for gas adsorption. The dried MOF powder was placed in a sample tube for gas adsorption, evacuated to ˜5 mtorr at room temperature and then heated up to 120° C. under dynamic vacuum for 18 h.
Blue LED photochemical reactor setup and calibration. Photocatalytic reactions were carried out in a home-built reactor using a 60 W blue LED strip (5 m long, MEILI, product #CNMX-Hardlines-464321) with λ=466 nm (fwhm=20 nm), the strip was coiled and glued inside a 20 cm diameter tin can and mounted on top of a magnetic stirrer. The temperature inside the photo reactor was kept at 25° C. with the aid of an attached fan and a thermometer. The photon flux of the photoreactor was determined by chemical actionometry though standard photoreduction of K3[Fe(C2O4)3] to Fe((C2O4)22− at 466 nm following the protocol by Parker et al. [24]. After the preparation of a calibration curve of ferrous iron (
The radiation dose of a photoreactor using blue LED can be obtained by using the IUPAC recommended protocol by Serpone et al. [25] and the recommended quantum efficiency of 0.925 in the following equation:
where Φλ is the photochemical quantum yield, Rin is the initial rate of the photochemical reaction, and Ro,λ, is the incident volumetric photon flux. The obtained photon flux in the photoreactor is Ro,λ=1.92×10− mol (photons) L−1 h−1.
Photochemical reduction of carbon dioxide to formate were performed under ambient conditions in the photoreactor described above. MIL-125-NHR (3-5 mg) was loaded in a 3 mL borosilicate vial with a magnetic stirrer. 1.5 mL of a CO2-bubbled stock solution containing triethanolamine (TEOA, 0.30 mol L−1) and mesitylene (1.5 mmol L−1) in MeCN-d3 was added to the vial and tightly capped with a PTFE/rubber septum. A flow of CO2 (g) was bubbled into the vial with the aid of a needle with an input positive pressure of 1 psi for 30 min previous to photoirradiation. During irradiation, 40 μL aliquots were sampled every 12 h with the aid of a syringe, the aliquot was filtered through a 0.2 am PTFE syringe membrane into an NMR tube. The filtrate was diluted with CDCl3 (˜0.6 mL) and a total of 256 transients were measured for each time point. Kinetic plots were obtained in both concentration and turnover number in the ordinate axis. The concentration was obtained by addition of the intensity of the photoreduced-CO2 signals (formate+HEF+BHEF) and normalizing with respect to the internal standard, and the turnover number was determined as the total number of moles of photoreduced-CO2 (mol CO2+mol HEF+mol BHEF) per mol of photocatalyst (with respect to the organic linker). The initial rate of the reaction was obtained by fitting a third order polynomial function using linear least squares then evaluating their first derivative at t=0.
In summary, the isoreticular family of MOFs was prepared via SN2 reaction of 2-amino terephthalate dimethyl ester (Scheme 1) with the corresponding alkyl iodide in basic conditions forming intermediates 1a-d and 1g in moderate yields. Intermediates 1e-f were synthesized via reductive amination with cyclopentanone or cyclohexanone in the presence of NaBH4/TMSCl in cold DMF in high yields. Hydrolysis of the dimethyl esters in NaOH/THF afforded linkers 2a-g, and solvothermal MOF crystallization with Ti(OiPr)4 in DMF/MeOH in flame sealed borosilicate tubes produced the desired MOFs in high yields. The molecular integrity of the linkers within the MOFs was determined using 1H NMR by dissolving the synthesized MOFs in NaOD 0.1 M in D2O (
The MOFs were obtained as microcrystalline powders that were analyzed by scanning electron microscopy (SEM) and powder X-ray diffraction (PXRD) crystallography. SEM images (
The porosity of the MOFs was determined using N2 gas adsorption at 77 K. All isotherms display IUPAC Type II isotherm behavior that corresponds to microporous materials with fully reversible adsorption behavior
The total cumulative pore volume, obtained from non-local density functional theory (NLDFT) fitting of the N2 isotherms, resulted in a decreasing pore volumes consistent with increased substitution (
The UV-visible absorption spectra for crystalline powder of the MIL-125-NHR series were acquired using an integrating sphere and the results can be seen in
The photocatalytic rates and efficiencies of MIL-125-NHR MOFs can be dependent on the lifetime of the photo generated charge-separated state [18]. To gain insights into the excited state dynamics, nanosecond transient absorption spectroscopy was performed on suspensions of selected MIL-125-NHR in MeCN and the results can be seen in
The photocatalytic activity of the isoreticular MOFs towards CO2 photoreduction using blue irradiation (Scheme 4) was examined. A LED light source was utilized because of its accessibility, low cost, high irradiance, low power needs and narrow emission profile, compared to Xe-based lamps [28]. Moreover, using a narrow band aids in circumventing photocatalysis by any residual titanium oxide formed during the MOF synthesis, as these phases require light in the UV region (λ<350 nm) [3]. Irradiating MIL-125-NHR suspensions in MeCN-d3 under a flow of CO2 and in the presence of triethanolamine, TEOA (a reducing agent), and mesitylene (an internal standard) with blue light (λ=466 nm) resulted in the formation of formate as the product of CO2 reduction, which displays a 1H NMR signal at 8.45 ppm (
Note: HEF and BHEF appear as formate reacts with hydrolyzed products of oxidized triethanolamine [29].
No trend or correlation was observed between the photocatalytic rates/efficiency and the gas adsorption properties of the MOFs. Electronic effects from N-alkyl substitution can determine the photocatalytic efficiency with little effect from mass transport. This assessment is consistent with the reaction mechanism proposed by Fu et al. [17], who propose that upon photoexcitation, an electron is promoted from the π-cloud in terephthalate to a Ti d-state and is further transferred to CO2, reducing it to formate. The MOF catalyst is then regenerated by oxidizing TEOA (the latter also serving as proton source). The observed correlation between excited-state lifetime and apparent quantum yield herein suggest that the rate-limiting step of the reduction is the electron transfer from Ti+3 to CO2. The chemical stability of the MIL-125-NHR MOFs was assessed by PXRD and 1H NMR after 120 h of photoreaction. No changes in the PXRD patterns were observed, suggesting stability of the crystalline framework (
An isoreticular series of titanium-based MOF photocatalysts were prepared by increasing the N-alkyl substitution in MIL-125-NHR, where R varies from methyl, to ethyl, isopropyl, n-butyl, cyclopentyl, cyclohexyl, and n-heptyl. The isoreticular nature of their crystal structure was studied by powder X-ray crystallography and gas adsorption. Their photophysical and photocatalytic properties were studied displaying a gradual decrease in the optical bandgap from 2.56 eV in MIL-125-NH2 to 2.29 eV in MIL-125-NHCy, consistent with increased electron density around the organic linker via inductive effects of the N-alkyl chain. The photocatalytic efficiency of the MOFs towards reduction of carbon dioxide under blue LED light was explored, displaying increased reaction rates and quantum yields consistent with the increased alkyl substitution. The CO2 photoreduction quantum yield is higher for MOFs with increased excited-state lifetime, particularly with secondary N-alkyls substituents, and it was concluded that from the current proposed mechanism, the electron transfer from Ti+3 to CO2 can be the rate-limiting step in the photoreduction. The results herein indicate that small variations in the organic linker of the MOF can result in tuning of the photophysical and photocatalytic properties of the materials, solely by selection of specific substituents in the organic links.
Other advantages which are obvious and which are inherent to the invention will be evident to one skilled in the art. It will be understood that certain features and sub-combinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and is within the scope of the claims. Since many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.
The methods of the appended claims are not limited in scope by the specific methods described herein, which are intended as illustrations of a few aspects of the claims and any methods that are functionally equivalent are intended to fall within the scope of the claims. Various modifications of the methods in addition to those shown and described herein are intended to fall within the scope of the appended claims. Further, while only certain representative method steps disclosed herein are specifically described, other combinations of the method steps also are intended to fall within the scope of the appended claims, even if not specifically recited. Thus, a combination of steps, elements, components, or constituents may be explicitly mentioned herein or less, however, other combinations of steps, elements, components, and constituents are included, even though not explicitly stated.
This invention was made with government support under Grant No. CHE-1531629 awarded by the National Science Foundation. The government has certain rights in the invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2018/026137 | 4/4/2018 | WO |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2018/187507 | 10/11/2018 | WO | A |
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| Number | Date | Country | |
|---|---|---|---|
| 20200188896 A1 | Jun 2020 | US |
| Number | Date | Country | |
|---|---|---|---|
| 62481268 | Apr 2017 | US |
