EFFICIENT CAPTURE AND RELEASE OF THE RARE-EARTH ELEMENTS USING COVALENT ORGANIC FRAMEWORKS
20250282713 ยท 2025-09-11
Inventors
- Levi M. STANLEY (Ames, IA, US)
- Wenyu HUANG (Ames, IA, US)
- Alexander VOLKOV (Ames, IA, US)
- Puranjan CHATTERJEE (Ames, IA, US)
- Aaron J. Rossini (Ames, IA, US)
- Jiashan MI (Ames, IA, US)
Cpc classification
International classification
C07C233/88
CHEMISTRY; METALLURGY
Abstract
The present disclosure is directed to a covalent organic framework comprising repeating units of a moiety comprising Formula (I):
##STR00001##
wherein X, Y, R, R, n.sub.1, and n.sub.2 are as described herein. The present disclosure is also directed to a method of making the covalent organic frameworks and a method of separating rare-earth elements using the covalent organic frameworks.
Claims
1. A covalent organic framework comprising repeating units of a moiety comprising Formula (I): ##STR00043## wherein --- is a single or a double bond; X is independently selected at each occurrence thereof from N or N(R.sup.3), wherein at least one X is N(R.sup.3); Y is independently selected at each occurrence thereof from C(R.sup.1)(R.sup.2) or C(R.sup.1); R is independently selected at each occurrence thereof from H or OC.sub.1-6 alkyl; R is independently selected at each occurrence thereof from H, OH, NO.sub.2, heteroaryl, wherein heteroaryl can be optionally substituted 1 to 3 times with C.sub.1-6 alkyl; R.sup.1 is H; R.sup.2 is optional and, if present, is C(O)NHR.sup.4; R.sup.3 is C(O)R.sup.5; R.sup.4 is independently selected at each occurrence thereof from the group consisting of cycloalkyl, (CH.sub.2).sub.mC(O)OC.sub.1-6 alkyl, and (CH.sub.2).sub.mC(O)NH(CH.sub.2).sub.kNH.sub.2, wherein (CH.sub.2).sub.mC(O)NH(CH.sub.2).sub.kNH.sub.2 can be optionally substituted 1 to 3 times with R.sup.7; R.sup.5 is selected from the group consisting of C.sub.1-12 alkyl, C.sub.2-12 alkenyl, or C.sub.2-12 alkynyl, wherein C.sub.1-12 alkyl can be optionally substituted 1 to 3 times with R.sup.6; R.sup.6 is independently selected at each occurrence thereof from N.sub.3, C(O)OC.sub.1-6 alkyl, C(O)NH(CH.sub.2).sub.kNH.sub.2, wherein C(O)NH(CH.sub.2).sub.kNH.sub.2 can be optionally substituted 1 to 3 times with R.sup.7; R.sup.7 is (CH.sub.2).sub.k1NH.sub.2 optionally substituted with C(O)(CH.sub.2).sub.k2O(CH.sub.2).sub.k3C(O)OH, C(O)(CH.sub.2).sub.k2N[(CH.sub.2).sub.k3C(O)OH](CH.sub.2).sub.k4N((CH.sub.2).sub.k5C(O)OH).sub.2, C(O)(CH.sub.2).sub.k2N[(CH.sub.2).sub.k3C(O)OH](CH.sub.2).sub.k4N[(CH.sub.2).sub.k5C(O)OH](CH.sub.2).sub.k6N((CH.sub.2).sub.k7C(O)OH).sub.2, or C(O)(CH.sub.2).sub.k2N((CH.sub.2).sub.k3P(O)(OH).sub.2).sub.2; n.sub.1 is 0, 1, 2, 3, or 4; n.sub.2 is 0, 1, 2, 3, or 4; m is 1, 2, 3, 4, 5, or 6; k is 1, 2, 3, 4, 5, or 6; k.sub.1 is 1, 2, 3, 4, 5, or 6; k.sub.2 is 1, 2, 3, 4, 5, or 6; k.sub.3 is 1, 2, 3, 4, 5, or 6; k.sub.4 is 1, 2, 3, 4, 5, or 6; k.sub.5 is 1, 2, 3, 4, 5, or 6; k.sub.6 is 1, 2, 3, 4, 5, or 6; and k.sub.7 is 1, 2, 3, 4, 5, or 6.
2. The covalent organic framework according to claim 1, wherein m is 1, k is 2, k.sub.1 is 2, k.sub.2 is 1, and k.sub.3 is 1.
3. The covalent organic framework according to claim 1, wherein R is H.
4. The covalent organic framework according to claim 1, wherein the repeating units of a moiety comprise Formula (I): ##STR00044##
5. The covalent organic framework according to claim 1, wherein the repeating units of a moiety comprise a structure selected from the group consisting of: ##STR00045## ##STR00046##
6. The covalent organic framework according to claim 1, wherein the repeating units of a moiety have a structure of Formula (Ia): ##STR00047## wherein ##STR00048## is the point of attachment of the moiety of Formula (Ia) to ##STR00049## of another moiety of Formula (Ia); Z is selected from the group consisting of C, CH, ##STR00050## and p is 2 or 3.
7. The covalent organic framework according to claim 1, wherein the repeating units of a moiety have a structure of Formula (Ib): ##STR00051## wherein W is selected from the group consisting of X, ##STR00052## and Q is optional, and if present, is NHC(O) or C(O)NH.
8. The covalent organic framework according to claim 1, wherein the covalent organic framework comprises a moiety of Formula (Ic): ##STR00053##
9. A method of separating rare-earth elements comprising: providing a sample comprising a rare-earth element; providing a covalent organic framework according to claim 1; contacting the sample with the covalent organic framework under conditions effective to separate the rare-earth elements from the sample.
10. The method of claim 9, wherein the sample contains Nd(NO.sub.3).sub.3.
11. The method of claim 9, wherein the sample contains two or more rare-earth elements.
12. The method of claim 9, wherein said contacting the sample with the covalent organic framework results in capture of the rare earth element inside the covalent organic framework.
13. The method of claim 12, wherein the sample contains two or more rare-earth elements.
14. The method of claim 13, wherein said contacting the sample with the covalent organic framework results in more effective capture of one rare-earth element over another rare-earth element.
15. The method of claim 14, wherein the sample contains Nd(NO.sub.3).sub.3 and Dy(NO.sub.3).sub.3.
16. The method of claim 15, wherein Dy ions are captured more effectively than Nd ions.
17. The method of claim 14, further comprising: isolating the covalent organic framework containing the rare-earth elements from the sample.
18. The method of claim 17, wherein said isolating is carried out by filtration.
19.-20. (canceled)
21. A method of making a covalent organic framework comprising repeating units of a moiety comprising Formula (I): ##STR00054## wherein --- is a single or a double bond; X is independently selected at each occurrence thereof from N or N(R.sup.3), wherein at least one X is N(R.sup.3); Y is independently selected at each occurrence thereof from C(R.sup.1)(R.sup.2) or C(R.sup.1); R is independently selected at each occurrence thereof from H or OC.sub.1-6 alkyl; R is independently selected at each occurrence thereof from H, OH, NO.sub.2, heteroaryl, wherein heteroaryl can be optionally substituted 1 to 3 times with C.sub.1-6 alkyl; R.sup.1 is H; R.sup.2 is optional and, if present, is C(O)NHR.sup.4; R.sup.3 is C(O)R.sup.5; R.sup.4 is independently selected at each occurrence thereof from the group consisting of cycloalkyl, (CH.sub.2).sub.mC(O)OC.sub.1-6 alkyl, and (CH.sub.2).sub.mC(O)NH(CH.sub.2).sub.kNH.sub.2, wherein (CH.sub.2).sub.mC(O)NH(CH.sub.2).sub.kNH.sub.2 can be optionally substituted 1 to 3 times with R.sup.7; R.sup.5 is selected from the group consisting of C.sub.1-12 alkyl, C.sub.2-12 alkenyl, or C.sub.2-12 alkynyl, wherein C.sub.1-12 alkyl can be optionally substituted 1 to 3 times with R.sup.6; R.sup.6 is independently selected at each occurrence thereof from N.sub.3, C(O)OC.sub.1-6 alkyl, C(O)NH(CH.sub.2).sub.kNH.sub.2, wherein C(O)NH(CH.sub.2).sub.kNH.sub.2 can be optionally substituted 1 to 3 times with R.sup.7; R.sup.7 is (CH.sub.2).sub.k1NH.sub.2 optionally substituted with C(O)(CH.sub.2).sub.k2O(CH.sub.2).sub.k3C(O)OH, C(O)(CH.sub.2).sub.k2N[(CH.sub.2).sub.k3C(O)OH](CH.sub.2).sub.k4N((CH.sub.2).sub.k5C(O)OH).sub.2, C(O)(CH.sub.2).sub.k2N[(CH.sub.2).sub.k3C(O)OH](CH.sub.2).sub.k4N[(CH.sub.2).sub.k5C(O)OH](CH.sub.2).sub.k6N((CH.sub.2).sub.k7C(O)OH).sub.2, or C(O)(CH.sub.2).sub.k2N((CH.sub.2).sub.k3P(O)(OH).sub.2).sub.2; n.sub.1 is 0, 1, 2, 3, or 4; n.sub.2 is 0, 1, 2, 3, or 4; m is 1, 2, 3, 4, 5, or 6; k is 1, 2, 3, 4, 5, or 6; k.sub.1 is 1, 2, 3, 4, 5, or 6; k.sub.2 is 1, 2, 3, 4, 5, or 6; k.sub.3 is 1, 2, 3, 4, 5, or 6; k.sub.4 is 1, 2, 3, 4, 5, or 6; k.sub.5 is 1, 2, 3, 4, 5, or 6; k.sub.6 is 1, 2, 3, 4, 5, or 6; and k.sub.7 is 1, 2, 3, 4, 5, or 6; said method comprises: providing a covalent organic framework comprising repeating units of a moiety comprising Formula (II): ##STR00055## and reacting the covalent organic framework comprising repeating units of a moiety comprising Formula (II) under conditions effective to produce the covalent organic framework.
22.-30. (canceled)
31. A method of making a modified covalent organic framework comprising repeating units of a moiety comprising Formula (Ia): ##STR00056## wherein R is independently selected at each occurrence thereof from H or OC.sub.1-6 alkyl; R is independently selected at each occurrence thereof from H, OH, NO.sub.2, heteroaryl, wherein heteroaryl can be optionally substituted 1 to 3 times with C.sub.1-6 alkyl; R.sup.4 is (CH.sub.2).sub.mC(O)NH(CH.sub.2).sub.kNH.sub.2 substituted 1 to 3 times with R.sup.7; R.sup.5 is C.sub.1-12 alkyl substituted with R.sup.6; R.sup.6 is C(O)NH(CH.sub.2).sub.kNH.sub.2 substituted 1 to 3 times with R.sup.7; R.sup.7 is (CH.sub.2).sub.k1NH.sub.2 substituted with C(O)(CH.sub.2).sub.k2O(CH.sub.2).sub.k3C(O)OH, C(O)(CH.sub.2).sub.k2N[(CH.sub.2).sub.k3C(O)OH](CH.sub.2).sub.k4N((CH.sub.2).sub.k5C(O)OH).sub.2, C(O)(CH.sub.2).sub.k2N[(CH.sub.2).sub.k3C(O)OH](CH.sub.2).sub.k4N[(CH.sub.2).sub.k5C(O)OH](CH.sub.2).sub.k6N((CH.sub.2).sub.k7C(O)OH).sub.2, or C(O)(CH.sub.2).sub.k2N((CH.sub.2).sub.k3P(O)(OH).sub.2).sub.2; n.sub.1 is 0, 1, 2, 3, or 4; n.sub.2 is 0, 1, 2, 3, or 4; m is 1, 2, 3, 4, 5, or 6; k is 1, 2, 3, 4, 5, or 6; k.sub.1 is 1, 2, 3, 4, 5, or 6; k.sub.2 is 1, 2, 3, 4, 5, or 6; k.sub.3 is 1, 2, 3, 4, 5, or 6; k.sub.4 is 1, 2, 3, 4, 5, or 6; k.sub.5 is 1, 2, 3, 4, 5, or 6; k.sub.6 is 1, 2, 3, 4, 5, or 6; and k.sub.7 is 1, 2, 3, 4, 5, or 6; said method comprises: providing a covalent organic framework comprising repeating units of a moiety comprising Formula (Ib): ##STR00057## wherein R.sup.4 is (CH.sub.2).sub.mC(O)NH(CH.sub.2).sub.kNH.sub.2 substituted 1 to 3 times with (CH.sub.2).sub.k1NH.sub.2; R.sup.5 is C.sub.1-12 alkyl substituted with R.sup.6; and R.sup.6 is C(O)NH(CH.sub.2).sub.kNH.sub.2 substituted 1 to 3 times with (CH.sub.2).sub.k1NH.sub.2; and reacting the covalent organic framework comprising repeating units of a moiety comprising Formula (Ib) under conditions effective to produce the modified covalent organic framework.
32.-40. (canceled)
Description
BRIEF DESCRIPTION OF THE DRAWINGS
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[0120] Ugi-COF-DGA.
[0121] Ugi-COF-DGA.
[0122] Ugi-COF-DGA: (left) N and Nd EDS maps overlapped with STEM image; (center) Nd EDS image; (right) N EDS image.
[0123] Ugi-COF-DGA.
DETAILED DESCRIPTION
[0124] One aspect of the present disclosure relates to a covalent organic framework comprising repeating units of a moiety comprising Formula (I):
##STR00007##
where [0125] --- is a single or a double bond; [0126] X is independently selected at each occurrence thereof from N or N(R.sup.3), wherein at least one X is N(R.sup.3); [0127] Y is independently selected at each occurrence thereof from C(R.sup.1)(R.sup.2) or CR); [0128] R is independently selected at each occurrence thereof from H or OC.sub.1-6 alkyl; [0129] R is independently selected at each occurrence thereof from H, OH, NO.sub.2, heteroaryl, wherein heteroaryl can be optionally substituted 1 to 3 times with C.sub.1-6 alkyl; [0130] R.sup.1 is H; [0131] R.sup.2 is optional and, if present, is C(O)NHR.sup.4; [0132] R.sup.3 is C(O)R.sup.5; [0133] R.sup.4 is independently selected at each occurrence thereof from the group consisting of cycloalkyl, (CH.sub.2).sub.mC(O)OC.sub.1-6 alkyl, and (CH.sub.2).sub.mC(O)NH(CH.sub.2).sub.kNH.sub.2, wherein (CH.sub.2).sub.mC(O)NH(CH.sub.2).sub.kNH.sub.2 can be optionally substituted 1 to 3 times with R.sup.7; [0134] R.sup.5 is selected from the group consisting of C.sub.1-12 alkyl, C.sub.2-12 alkenyl, or C.sub.2-12 alkynyl, wherein C.sub.1-12 alkyl can be optionally substituted 1 to 3 times with R.sup.6; [0135] R.sup.6 is independently selected at each occurrence thereof from N.sub.3, C(O)OC.sub.1-6 alkyl, C(O)NH(CH.sub.2).sub.kNH.sub.2, wherein C(O)NH(CH.sub.2).sub.kNH.sub.2 can be optionally substituted 1 to 3 times with R.sup.7; [0136] R.sup.7 is (CH.sub.2).sub.k1NH.sub.2 optionally substituted with C(O)(CH.sub.2).sub.k2O(CH.sub.2).sub.k3C(O)OH, C(O)(CH.sub.2).sub.k2N[(CH.sub.2).sub.k3C(O)OH](CH.sub.2).sub.k4N((CH.sub.2).sub.k5C(O)OH).sub.2, C(O)(CH.sub.2).sub.k2N[(CH.sub.2).sub.k3C(O)OH](CH.sub.2).sub.k4N[(CH.sub.2).sub.k5C(O)OH](CH.sub.2).sub.k6N((CH.sub.2).sub.k7C(O)OH).sub.2, or C(O)(CH.sub.2).sub.k2N((CH.sub.2).sub.k3P(O)(OH).sub.2).sub.2; [0137] n.sub.1 is 0, 1, 2, 3, or 4; [0138] n.sub.2 is 0, 1, 2, 3, or 4; [0139] m is 1, 2, 3, 4, 5, or 6; [0140] k is 1, 2, 3, 4, 5, or 6; [0141] k.sub.1 is 1, 2, 3, 4, 5, or 6; [0142] k.sub.2 is 1, 2, 3, 4, 5, or 6; [0143] k.sub.3 is 1, 2, 3, 4, 5, or 6; [0144] k.sub.4 is 1, 2, 3, 4, 5, or 6; [0145] k.sub.5 is 1, 2, 3, 4, 5, or 6; [0146] k.sub.6 is 1, 2, 3, 4, 5, or 6; and [0147] k.sub.7 is 1, 2, 3, 4, 5, or 6.
[0148] As used above, and throughout the description herein, the following terms, unless otherwise indicated, shall be understood to have the following meanings. If not defined otherwise herein, all technical and scientific terms used herein have the same meaning as is commonly understood by one of ordinary skill in the art to which this technology belongs. In the event that there is a plurality of definitions for a term herein, those in this section prevail unless stated otherwise.
[0149] In this specification and the appended claims, the singular forms a, an, and the include plural references unless the context clearly dictates otherwise.
[0150] The terms comprising, comprises, and comprised of as used herein are synonymous with including, includes, or containing, contains, and are inclusive or open-ended and do not exclude additional, non-recited members, elements, or method steps.
[0151] The terms comprising, comprises, and comprised of also encompass the term consisting of The transitional term comprising, which is synonymous with including, containing, or characterized by, is inclusive or open-ended and does not exclude additional, un-recited elements or method steps. By contrast, the transitional phrase consisting of excludes any element, step, or ingredient not specified in the claim. The transitional phrase consisting essentially of limits the scope of a claim to the specified materials or steps and those that do not materially affect the basic and novel characteristic(s) of the claimed subject matter. In some embodiments or claims where the term comprising is used as the transition phrase, such embodiments can also be envisioned with replacement of the term comprising with the terms consisting of or consisting essentially of
[0152] Terms of degree such as substantially, about, and approximately and the symbol as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed. These terms of degree should be construed as including a deviation of at least 0.1% (and up to 1%, 5%, or 10%) of the modified term if this deviation would not negate the meaning of the word it modifies. Unless otherwise clear from context, all numerical values provided herein are modified by the term about. All numerical values provided herein that are modified by terms of degree set forth in this paragraph (e.g., substantially, about, approximately, and ) are also explicitly disclosed without the term of degree. For example, about 1% is also explicitly disclosed as 10.
[0153] The term and/or as used herein means that the listed items are present, or used, individually or in combination. In effect, this term means that at least one of or one or more of the listed items is used or present.
[0154] The recitation of numerical ranges by endpoints includes all numbers and fractions subsumed within the respective ranges, as well as the recited endpoints. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a non-limiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc. As will also be understood by one skilled in the art all language such as up to, at least, and the like include the number recited and refer to ranges which can be subsequently broken down into subranges as discussed above. Finally, as will be understood by one skilled in the art, a range includes each individual member.
[0155] The term alkyl means an aliphatic hydrocarbon group which may be straight or branched having about 1 to about 12 carbon atoms in the chain. For example, straight or branched carbon chain could have 1 to 6 carbon atoms. Branched means that one or more lower alkyl groups such as methyl, ethyl or propyl are attached to a linear alkyl chain. Exemplary alkyl groups include methyl, ethyl, n-propyl, i-propyl, n-butyl, t-butyl, n-pentyl, and 3-pentyl.
[0156] The term alkenyl means an aliphatic hydrocarbon group containing a carbon-carbon double bond and which may be straight or branched having about 2 to about 12 carbon atoms in the chain. Particular alkenyl groups have 2 to about 6 carbon atoms in the chain. Branched means that one or more lower alkyl groups such as methyl, ethyl, or propyl are attached to a linear alkenyl chain. Exemplary alkenyl groups include ethenyl, propenyl, n-butenyl, and i-butenyl. The term alkenyl may also refer to a hydrocarbon chain having 2 to 6 carbons containing at least one double bond and at least one triple bond.
[0157] The term alkynyl means an aliphatic hydrocarbon group containing a carbon-carbon triple bond and which may be straight or branched having about 2 to about 12 carbon atoms in the chain. Particular alkynyl groups have 2 to about 6 carbon atoms in the chain. Branched means that one or more lower alkyl groups such as methyl, ethyl, or propyl are attached to a linear alkynyl chain. Exemplary alkynyl groups include ethynyl, propynyl, n-butynyl, 2-butynyl, 3-methylbutynyl, and n-pentynyl.
[0158] The term cycloalkyl means a non-aromatic mono- or multicyclic ring system of about 3 to about 12 carbon atoms, preferably of about 3 to about 8 carbon atoms. Exemplary monocyclic cycloalkyls include cyclopentyl, cyclohexyl, cycloheptyl, bicyclo[1.1.1]pentyl, and the like.
[0159] The term heteroaryl means an aromatic monocyclic or multicyclic ring system of about 5 to about 14 ring atoms, preferably about 5 to about 10 ring atoms, in which one or more of the atoms in the ring system is/are element(s) other than carbon, for example, nitrogen, oxygen, or sulfur. In the case of multicyclic ring system, only one of the rings needs to be aromatic for the ring system to be defined as Heteroaryl. Preferred heteroaryls contain about 5 to 6 ring atoms. The prefix aza, oxa, thia, or thio before heteroaryl means that at least a nitrogen, oxygen, or sulfur atom, respectively, is present as a ring atom. A nitrogen atom of a heteroaryl is optionally oxidized to the corresponding N-oxide. Representative heteroaryls include pyridyl, 2-oxo-pyridinyl, pyrimidinyl, pyridazinyl, pyrazinyl, triazinyl, furanyl, pyrrolyl, thiophenyl, pyrazolyl, imidazolyl, oxazolyl, isoxazolyl, thiazolyl, isothiazolyl, triazolyl, oxadiazolyl, thiadiazolyl, tetrazolyl, indolyl, isoindolyl, benzofuranyl, benzothiophenyl, indolinyl, 2-oxoindolinyl, dihydrobenzofuranyl, dihydrobenzothiophenyl, indazolyl, benzimidazolyl, benzooxazolyl, benzothiazolyl, benzoisoxazolyl, benzoisothiazolyl, benzotriazolyl, benzo[1,3]dioxolyl, quinolinyl, isoquinolinyl, quinazolinyl, cinnolinyl, pthalazinyl, quinoxalinyl, 2,3-dihydro-benzo[1,4]dioxinyl, benzo[1,2,3]triazinyl, benzo[1,2,4]triazinyl, 4H-chromenyl, indolizinyl, quinolizinyl, 6aH-thieno[2,3-d]imidazolyl, 1H-pyrrolo[2,3-b]pyridinyl, imidazo[1,2-a]pyridinyl, pyrazolo[1,5-a]pyridinyl, [1,2,4]triazolo[4,3-a]pyridinyl, [1,2,4]triazolo[1,5-a]pyridinyl, thieno[2,3-b]furanyl, thieno[2,3-b]pyridinyl, thieno[3,2-b]pyridinyl, furo[2,3-b]pyridinyl, furo[3,2-b]pyridinyl, thieno[3,2-d]pyrimidinyl, furo[3,2-d]pyrimidinyl, thieno[2,3-b]pyrazinyl, imidazo[1,2-a]pyrazinyl, 5,6,7,8-tetrahydroimidazo[1,2-a]pyrazinyl, 6,7-dihydro-4H-pyrazolo[5,1-c][1,4]oxazinyl, 2-oxo-2,3-dihydrobenzo[d]oxazolyl, 3,3-dimethyl-2-oxoindolinyl, 2-oxo-2,3-dihydro-1H-pyrrolo[2,3-b]pyridinyl, benzo[c][1,2,5]oxadiazolyl, benzo[c][1,2,5]thiadiazolyl, 3,4-dihydro-2H-benzo[b][1,4]oxazinyl, 5,6,7,8-tetrahydro-[1,2,4]triazolo[4,3-a]pyrazinyl, [1,2,4]triazolo[4,3-a]pyrazinyl, 3-oxo-[1,2,4]triazolo[4,3-a]pyridin-2(3H)-yl, and the like. The term heteroarylene refers to a group obtained by removal of a hydrogen atom from a heteroaryl group. Exemplary heteroarylene groups include, but are not limited to, groups derived from the heteroaryl groups described above.
[0160] The term monocyclic used herein indicates a molecular structure having one ring.
[0161] The term polycyclic or multicyclic used herein indicates a molecular structure having two or more rings, including, but not limited to, fused, bridged, or spiro rings.
[0162] Compounds described herein may contain one or more asymmetric centers and may thus give rise to enantiomers, diastereomers, and other stereoisomeric forms. Each chiral center may be defined, in terms of absolute stereochemistry, as (R)- or (S)-. This technology is meant to include all such possible isomers, as well as mixtures thereof, including racemic and optically pure forms. Optically active (R)- and (S)-, ()- and (+)-, or (D)- and (L)-isomers may be prepared using chiral synthons or chiral reagents, or resolved using conventional techniques. When the compounds described herein contain olefinic double bonds or other centers of geometric asymmetry, and unless specified otherwise, it is intended that the compounds include both E and Z geometric isomers. Likewise, all tautomeric forms are also intended to be included.
[0163] In some embodiments of the covalent organic framework, m is 1, k is 2, k.sub.1 is 2, k.sub.2 is 1, and k.sub.3 is 1.
[0164] In some embodiments, R is H.
[0165] According to the present disclosure, X in the covalent organic framework comprising repeating units of a moiety comprising Formula (I) is independently selected at each occurrence thereof from N or N(R.sup.3), wherein at least one X is N(R.sup.3). In some embodiments, X is N(R.sup.3).
[0166] According to the present disclosure, from about 1% to about 100% of X in the covalent organic framework comprising repeating units of a moiety comprising Formula (I) is NR.sup.3. In some embodiments, from about 1% to about 10%, from about 1% to about 20%, from about 1% to about 30%, from about 1% to about 40%, from about 1% to about 50%, from about 1% to about 60%, from about 1% to about 70%, from about 1% to about 80%, from about 1% to about 90%, from about 10% to about 20%, from about 10% to about 30%, from about 10% to about 40%, from about 10% to about 50%, from about 10% to about 60%, from about 10% to about 70%, from about 10% to about 80%, from about 10% to about 90%, from about 10% to about 100%, from about 20% to about 30%, from about 20% to about 40%, from about 20% to about 50%, from about 20% to about 60%, from about 20% to about 70%, from about 20% to about 80%, from about 20% to about 90%, from about 20% to about 100%, from about 30% to about 40%, from about 30% to about 50%, from about 30% to about 60%, from about 30% to about 70%, from about 30% to about 80%, from about 30% to about 90%, from about 30% to about 100%, from about 40% to about 50%, from about 40% to about 60%, from about 40% to about 70%, from about 40% to about 80%, from about 40% to about 90%, from about 40% to about 100%, from about 50% to about 60%, from about 50% to about 70%, from about 50% to about 80%, from about 50% to about 90%, from about 50% to about 100%, from about 60% to about 70%, from about 60% to about 80%, a from about 60% to about 90%, from about 60% to about 100%, %, from about 70% to about 80%, from about 70% to about 90%, from about 70% to about 100%, from about 80% to about 90%, from about 80% to about 100%, or from about 90% to about 100% of X in the covalent organic framework comprising repeating units of a moiety comprising Formula (I) is NR.sup.3.
[0167] In some embodiments, the repeating units of a moiety comprise Formula (I):
##STR00008##
[0168] In some embodiments, the repeating units of a moiety comprise a structure selected from the group consisting of:
##STR00009## ##STR00010##
[0169] In some embodiments, the repeating units of a moiety comprise a structure selected from the group consisting of:
##STR00011## ##STR00012## ##STR00013##
[0170] In some embodiments, the repeating units of a moiety have a structure of Formula (Ia):
##STR00014##
where
##STR00015##
is the point of attachment of the moiety of Formula (Ia) to
##STR00016##
of another moiety of Formula (Ia); [0171] Z is selected from the group consisting of C, CH,
##STR00017## and [0172] p is 2 or 3.
[0173] In some embodiments, the repeating units of a moiety have a structure of Formula (Ib):
##STR00018##
where [0174] W is selected from the group consisting of X,
##STR00019## and [0175] Q is optional, and if present, is NHC(O) or C(O)NH.
[0176] In some embodiments, the covalent organic framework comprises a moiety of Formula (Ic):
##STR00020##
[0177] Another aspect of the present disclosure relates to method of separating rare-earth elements. This method comprises providing a sample comprising a rare-earth element, providing a covalent organic framework according to the present disclosure, and contacting the sample with the covalent organic framework under conditions effective to separate the rare-earth elements from the sample.
[0178] Suitable rare earth elements that can be present in the sample include La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, and Sc. In some embodiments, the sample contains Nd, La, Lu, Pr, or Dy salts, such as nitrates, chlorides, and/or acetates. In some embodiments, the sample contains Dy(NO.sub.3).sub.3 or Nd(NO.sub.3).sub.3. In one embodiment, the sample contains Nd(NO.sub.3).
[0179] In some embodiments, the sample contains two, three, four, or more rare-earth elements. In some embodiments, the sample contains two or more rare-earth elements. In some embodiments, the sample contains Nd(NO.sub.3).sub.3 and Dy(NO.sub.3).sub.3.
[0180] In some embodiments, contacting the sample with the covalent organic framework results in the capture (adsorption) of the rare earth element inside the covalent organic framework. In some embodiments, when the sample contains two or more rare-earth elements, contacting the sample with the covalent organic framework results in more effective capture (adsorption) of one rare-earth element over another rare-earth element. In some embodiments one rare-earth element is selectively captured in the presence of another rare-earth element. For example, one rare-earth element can be selectively captured in the presence of another rare-earth element in a ratio of about 1.5:1, about 2:1, about 2.5:1, about 3:1, about 3.5:1, about 4:1, about 4.5:1, about 5:1, about 5.5:1, about 6:1, about 6.5:1, about 7:1, about 7.5:1, about 8:1, about 8.5:1, about 9:1, about 9.5:1, or about 10:1.
[0181] In some embodiments Dy ions are captured more effectively than Nd ions. For example, in some embodiments, Dy ions are selectively captured in the presence of Nd ions in a ratio of about 1.5:1, about 2:1, about 2.5:1, about 3:1, about 3.5:1, about 4:1, about 4.5:1, about 5:1, about 5.5:1, about 6:1, about 6.5:1, about 7:1, about 7.5:1, about 8:1, about 8.5:1, about 9:1, about 9.5:1, or about 10:1.
[0182] In some embodiments, the method further comprises isolating the covalent organic framework containing the rare-earth elements from the sample. In some embodiments, such isolation is carried out by filtration.
[0183] In some embodiments, the method further comprises recovering the rare-earth element from the covalent organic framework.
[0184] In some embodiments, the recovering is carried out by suspending the covalent organic framework containing the rare-earth elements in an inorganic acid, such as nitric acid, at about 25 C. for about 20 hours and filtering the covalent organic framework. For example, in some embodiments, the covalent organic framework containing the rare-earth elements can be suspended in an inorganic acid, such as nitric acid, at about 20 C., about 21 C., about 22 C., about 23 C., about 24 C., about 25 C., about 26 C., about 27 C., about 28 C., about 29 C., or about 30 C. for about 15 hours, about 16 hours, about 17 hours, about 18 hours, about 19 hours, about 20 hours, about 21 hours, about 22 hours, about 23 hours, about 24 hours, or about 25 hours and then filtered.
[0185] The general scheme for the covalent organic framework of the present disclosure is shown in Scheme 1.
##STR00021##
[0186] Reaction between an amine comprising a moiety having a Formula 1 and an aldehyde comprising a moiety having a Formula 2 leads to formation of a covalent organic framework comprising repeating units of a moiety comprising Formula 3. The reaction can be carried out in a variety of solvents, for example in methanol, ethanol, acetonitrile, water, toluene, mesitylene, methylene chloride (CH.sub.2Cl.sub.2), tetrahydrofuran (THF), dimethylformamide (DMF), or other such solvents or in the mixture of such solvents. This reaction can be carried out at room temperature or at elevated temperatures. Ugi reaction between the covalent organic framework 3, isocyanate (4), and carboxylic acid (5) leads to formation of the covalent organic framework comprising repeating units of a moiety comprising Formula (I). The reaction can be carried out in a variety of solvents, for example in water, methanol, ethanol, acetonitrile, methylene chloride (CH.sub.2Cl.sub.2), tetrahydrofuran (THF), dimethylformamide (DMF), or other such solvents or in the mixture of such solvents. This reaction can be carried out at room temperature or at elevated temperatures.
[0187] The general scheme for the modified covalent organic framework of the present disclosure is shown in Scheme 2.
##STR00022##
[0188] Reaction between an amine comprising a moiety having a Formula 1 and an aldehyde comprising a moiety having a Formula 2 leads to formation of a covalent organic framework comprising repeating units of a moiety comprising Formula 3. The reaction can be carried out in a variety of solvents, for example in methanol, ethanol, acetonitrile, water, toluene, mesitylene, methylene chloride (CH.sub.2Cl.sub.2), tetrahydrofuran (THF), dimethylformamide (DMF), or other such solvents or in the mixture of such solvents. This reaction can be carried out at room temperature or at elevated temperatures. Ugi reaction between the covalent organic framework 3, an isocyanate (4a), and a carboxylic acid (5a) leads to formation of a covalent organic framework comprising repeating units of a moiety comprising Formula (6). The reaction can be carried out in a variety of solvents, for example in water, methanol, ethanol, acetonitrile, methylene chloride (CH.sub.2Cl.sub.2), tetrahydrofuran (THF), dimethylformamide (DMF), or other such solvents or in the mixture of such solvents. This reaction can be carried out at room temperature or at elevated temperatures. Amidation of the covalent organic framework (6) leads to formation of a covalent organic framework comprising repeating units of a moiety comprising Formula (7). The reaction can be carried out in a variety of solvents, for example in methanol, water, methylene chloride (CH.sub.2Cl.sub.2), tetrahydrofuran (THF), dimethylformamide (DMF), or other such solvents or in the mixture of such solvents. This reaction can be carried out room temperature or at elevated temperatures. Acylation of the covalent organic framework (7) leads to formation of the covalent organic framework comprising repeating units of a moiety comprising Formula (Ia). Any suitable acylating agent can be used. The reaction can be carried out in a variety of solvents, for example in methanol, water, methylene chloride (CH.sub.2Cl.sub.2), tetrahydrofuran (THF), dimethylformamide (DMF), or other such solvents or in the mixture of such solvents. This reaction can be carried out room temperature or at elevated temperatures.
[0189] Another aspect of the present disclosure relates to method of making a covalent organic framework comprising repeating units of a moiety comprising Formula (I):
##STR00023##
where [0190] --- is a single or a double bond; [0191] X is independently selected at each occurrence thereof from N or N(R.sup.3), wherein at least one X is N(R.sup.3); [0192] Y is independently selected at each occurrence thereof from C(R.sup.1)(R.sup.2) or C(R.sup.1); [0193] R is independently selected at each occurrence thereof from H or OC.sub.1-6 alkyl; [0194] R is independently selected at each occurrence thereof from H, OH, NO.sub.2, heteroaryl, wherein heteroaryl can be optionally substituted 1 to 3 times with C.sub.1-6 alkyl; [0195] R.sup.1 is H; [0196] R.sup.2 is optional and, if present, is C(O)NHR.sup.4; [0197] R.sup.3 is C(O)R.sup.5; [0198] R.sup.4 is independently selected at each occurrence thereof from the group consisting of cycloalkyl, (CH.sub.2).sub.mC(O)OC.sub.1-6 alkyl, and (CH.sub.2).sub.mC(O)NH(CH.sub.2).sub.kNH.sub.2, wherein (CH.sub.2).sub.mC(O)NH(CH.sub.2).sub.kNH.sub.2 can be optionally substituted 1 to 3 times with R.sup.7; [0199] R.sup.5 is selected from the group consisting of C.sub.1-12 alkyl, C.sub.2-12 alkenyl, or C.sub.2-12 alkynyl, wherein C.sub.1-12 alkyl can be optionally substituted 1 to 3 times with R.sup.6; [0200] R.sup.6 is independently selected at each occurrence thereof from N.sub.3, C(O)OC.sub.1-6 alkyl, C(O)NH(CH.sub.2).sub.kNH.sub.2, wherein C(O)NH(CH.sub.2).sub.kNH.sub.2 can be optionally substituted 1 to 3 times with R.sup.7; [0201] R.sup.7 is (CH.sub.2).sub.k1NH.sub.2 optionally substituted with C(O)(CH.sub.2).sub.k2O(CH.sub.2).sub.k3C(O)OH, C(O)(CH.sub.2).sub.k2N[(CH.sub.2).sub.k3C(O)OH](CH.sub.2).sub.k4N((CH.sub.2).sub.k5C(O)OH).sub.2, C(O)(CH.sub.2).sub.k2N[(CH.sub.2).sub.k3C(O)OH](CH.sub.2).sub.k4N[(CH.sub.2).sub.k5C(O)OH](CH.sub.2).sub.k6N((CH.sub.2).sub.k7C(O)OH).sub.2, or C(O)(CH.sub.2).sub.k2N((CH.sub.2).sub.k3P(O)(OH).sub.2).sub.2; [0202] n.sub.1 is 0, 1, 2, 3, or 4; [0203] n.sub.2 is 0, 1, 2, 3, or 4; [0204] m is 1, 2, 3, 4, 5, or 6; [0205] k is 1, 2, 3, 4, 5, or 6; [0206] k.sub.1 is 1, 2, 3, 4, 5, or 6; [0207] k.sub.2 is 1, 2, 3, 4, 5, or 6; [0208] k.sub.3 is 1, 2, 3, 4, 5, or 6; [0209] k.sub.4 is 1, 2, 3, 4, 5, or 6; [0210] k.sub.5 is 1, 2, 3, 4, 5, or 6; [0211] k.sub.6 is 1, 2, 3, 4, 5,or 6; and [0212] k.sub.7 is 1, 2, 3, 4, 5, or 6.
[0213] This method comprises providing a covalent organic framework comprising repeating units of a moiety comprising Formula (II):
##STR00024##
and [0214] reacting the covalent organic framework comprising repeating units of a moiety comprising Formula (II) under conditions effective to produce the covalent organic framework.
[0215] In some embodiments, the reacting comprises providing a compound of Formula (III):
R.sup.4NC(III);
providing a compound of Formula (IV):
R.sup.5COOH(IV); and [0216] reacting the covalent organic framework comprising repeating units of a moiety comprising Formula (II) with the compound of Formula (III) and the compound of Formula (IV) to produce the covalent organic framework.
[0217] In some embodiments, the reacting the covalent organic framework comprising repeating units of a moiety comprising Formula (II) with the compound of Formula (III) and the compound of Formula (IV) is carried out at a temperature from about 20 C. to about 200 C. For example, in some embodiments, the reacting of the covalent organic framework comprising repeating units of a moiety comprising Formula (II) with the compound of Formula (III) and the compound of Formula (IV) is carried out at a temperature from about 20 C. to about 40 C., about 20 C. to about 60 C., about 20 C. to about 80 C., about 20 C. to about 100 C., about 20 C. to about 120 C., about 20 C. to about 140 C., about 20 C. to about 160 C., or about 20 C. to about 180 C., about 30 C. to about 50 C., about 35 C. to about 45 C., or about 40 C. to about 50 C.
[0218] In some embodiments, the reacting the covalent organic framework comprising repeating units of a moiety comprising Formula (II) with the compound of Formula (III) and the compound of Formula (IV) is carried out for at least 8 hours without stirring. For example, in some embodiments, the reacting is carried out for at least 8 hours, at least 10 hours, at least 12 hours, at least 14 hours, at least 16 hours, or at least 24 hours.
[0219] In some embodiments, the compound of Formula (III) is
##STR00025##
[0220] According to the present disclosure, the reaction between the covalent organic framework comprising repeating units of a moiety comprising Formula (II), the compound of Formula (III), and the compound of Formula (IV) results in the formation of the covalent organic framework comprising repeating units of a moiety comprising Formula (I) that contains from about 1% to about 100% of X being NR.sup.3. In some embodiments, from about 1% to about 10%, from about 1% to about 20%, from about 1% to about 30%, from about 1% to about 40%, from about 1% to about 50%, from about 1% to about 60%, from about 1% to about 70%, from about 1% to about 80%, from about 1% to about 90%, from about 10% to about 20%, from about 10% to about 30%, from about 10% to about 40%, from about 10% to about 50%, from about 10% to about 60%, from about 10% to about 70%, from about 10% to about 80%, from about 10% to about 90%, from about 10% to about 100%, from about 20% to about 30%, from about 20% to about 40%, from about 20% to about 50%, from about 20% to about 60%, from about 20% to about 70%, from about 20% to about 80%, from about 20% to about 90%, from about 20% to about 100%, from about 30% to about 40%, from about 30% to about 50%, from about 30% to about 60%, from about 30% to about 70%, from about 30% to about 80%, from about 30% to about 90%, from about 30% to about 100%, from about 40% to about 50%, from about 40% to about 60%, from about 40% to about 70%, from about 40% to about 80%, from about 40% to about 90%, from about 40% to about 100%, from about 50% to about 60%, from about 50% to about 70%, from about 50% to about 80%, from about 50% to about 90%, from about 50% to about 100%, from about 60% to about 70%, from about 60% to about 80%, a from about 60% to about 90%, from about 60% to about 100%, %, from about 70% to about 80%, from about 70% to about 90%, from about 70% to about 100%, from about 80% to about 90%, from about 80% to about 100%, or from about 90% to about 100% of X in the covalent organic framework comprising repeating units of a moiety comprising Formula (I) is NR.sup.3.
[0221] In some embodiments, providing a covalent organic framework comprising repeating units of a moiety comprising Formula (II) comprises providing a dialdehyde comprising a moiety of Formula (V):
##STR00026## [0222] providing an amine comprising a moiety of Formula (VI):
##STR00027##
and [0223] reacting the dialdehyde comprising a moiety of Formula (V) with the amine comprising a moiety of Formula (VI) under conditions effective to produce the covalent organic framework comprising repeating units of a moiety comprising Formula (II).
[0224] In some embodiments, the amine has a Formula (VIa) or Formula (VIb):
##STR00028## [0225] where [0226] Z is selected from the group consisting of C, CH,
##STR00029## [0227] p is 2 or 3; [0228] R.sup.a is NH.sub.2 or
##STR00030## and [0229] Q is optional, and if present, is NHC(O) or C(O)NH.
[0230] In some embodiments, the amine is selected from the group consisting of
##STR00031## ##STR00032##
[0231] In some embodiments, the aldehyde has a Formula (Va)
##STR00033##
[0232] In some embodiments, the aldehyde is
##STR00034##
[0233] Another aspect of the present disclosure relates to a method of making a modified covalent organic framework comprising repeating units of a moiety comprising Formula (Ia):
##STR00035##
where [0234] R is independently selected at each occurrence thereof from H or OC.sub.1-6 alkyl; [0235] R is independently selected at each occurrence thereof from H, OH, NO.sub.2, heteroaryl, wherein heteroaryl can be optionally substituted 1 to 3 times with C.sub.1-6 alkyl; [0236] R.sup.4 is (CH.sub.2).sub.mC(O)NH(CH.sub.2).sub.kNH.sub.2 substituted 1 to 3 times with R.sup.7; [0237] R.sup.5 is C.sub.1-12 alkyl substituted with R.sup.6; [0238] R.sup.6 is C(O)NH(CH.sub.2).sub.kNH.sub.2 substituted 1 to 3 times with R.sup.7; [0239] R.sup.7 is (CH.sub.2).sub.k1NH.sub.2 substituted with C(O)(CH.sub.2).sub.k2O(CH.sub.2).sub.k3C(O)OH, C(O)(CH.sub.2).sub.k2N[(CH.sub.2).sub.k3C(O)OH](CH.sub.2).sub.k4N((CH.sub.2).sub.k5C(O)OH).sub.2, C(O)(CH.sub.2).sub.k2N[(CH.sub.2).sub.k3C(O)OH](CH.sub.2).sub.k4N[(CH.sub.2).sub.k5C(O)OH](CH.sub.2).sub.k6N((CH.sub.2).sub.k7C(O)OH).sub.2, or C(O)(CH.sub.2).sub.k2N((CH.sub.2).sub.k3P(O)(OH).sub.2).sub.2; [0240] n.sub.1 is 0, 1, 2, 3, or 4; [0241] n.sub.2 is 0, 1, 2, 3, or 4; [0242] m is 1, 2, 3, 4, 5, or 6; [0243] k is 1, 2, 3, 4, 5, or 6; [0244] k.sub.1 is 1, 2, 3, 4, 5, or 6; [0245] k.sub.2 is 1, 2, 3, 4, 5, or 6; [0246] k.sub.3 is 1, 2, 3, 4, 5, or 6; [0247] k.sub.4 is 1, 2, 3, 4, 5, or 6; [0248] k.sub.5 is 1, 2, 3, 4, 5, or 6; [0249] k.sub.6 is 1, 2, 3, 4, 5, or 6; and [0250] k.sub.7 is 1, 2, 3, 4, 5, or 6.
[0251] This method comprises providing a covalent organic framework comprising repeating units of a moiety comprising Formula (Ib):
##STR00036## [0252] where [0253] R.sup.4 is (CH.sub.2).sub.mC(O)NH(CH.sub.2).sub.kNH.sub.2 substituted 1 to 3 times with (CH.sub.2).sub.k1NH.sub.2; [0254] R.sup.5 is C.sub.1-12 alkyl substituted with R.sup.6; and [0255] R.sup.6 is C(O)NH(CH.sub.2).sub.kNH.sub.2 substituted 1 to 3 times with (CH.sub.2).sub.k1NH.sub.2; and reacting the covalent organic framework comprising repeating units of a moiety comprising Formula (Ib) under conditions effective to produce the modified covalent organic framework.
[0256] In some embodiments, reacting comprises providing an acylating reagent, and reacting the covalent organic framework comprising repeating units of a moiety comprising Formula (Ib) with the acylating reagent to produce the modified covalent organic framework. Any suitable acylating agent can be used. Suitable acylating agents include, but are not limited to,
##STR00037##
[0257] In one embodiment, the acylating reagent is a compound of Formula (VII):
##STR00038##
[0258] In some embodiments, the reacting of the covalent organic framework comprising repeating units of a moiety comprising Formula (Ib) with the acylating reagent is carried out at a temperature from about 20 C. to about 200 C. For example, in some embodiments, the reacting is carried out at a temperature from about 40 C. to about 180 C., about 60 C. to about 160 C., about 70 C. to about 140 C., about 80 C. to about 120 C., or about 90 C. to about 110 C.
[0259] In some embodiments, the reacting of the covalent organic framework comprising repeating units of a moiety comprising Formula (Ib) with the acylating reagent is carried out for at least 6 hours. For example, in some embodiments, the reacting is carried out for at least for at least 6 hours, at least 8 hours, at least 10 hours, at least 12 hours, at least 14 hours, at least 16 hours, or at least 24 hours.
[0260] In some embodiments, the providing a covalent organic framework comprising repeating units of a moiety comprising Formula (Ib) comprises providing a covalent organic framework comprising repeating units of a moiety comprising Formula (I):
##STR00039## [0261] providing a compound of Formula (VIII):
##STR00040## [0262] and reacting the covalent organic framework comprising repeating units of a moiety comprising Formula (I) with the compound of Formula (VIII) to produce the covalent organic framework comprising repeating units of a moiety comprising Formula (Ib).
[0263] In some embodiments, the reacting of the covalent organic framework comprising repeating units of a moiety comprising Formula (I) with the compound of Formula (VIII) is carried out at a temperature from about 20 C. to about 200 C. For example, in some embodiments, the reacting is carried out at a temperature from about about 40 C. to about 180 C., about 40 C. to about 160 C., about 40 C. to about 140 C., about 40 C. to about 120 C., about 40 C. to about 100 C., about 40 C. to about 80 C., about 50 C. to about 100 C., about 50 C. to about 90 C., about 50 C. to about 80 C., or about 50 C. to about 70 C.
[0264] In some embodiments, the reacting of the covalent organic framework comprising repeating units of a moiety comprising Formula (I) with the compound of Formula (VIII) is carried out for at least 6 hours. For example, in some embodiments, the reacting is carried out for at least for at least 6 hours, at least 8 hours, at least 10 hours, at least 12 hours, at least 14 hours, at least 16 hours, or at least 24 hours.
[0265] In some embodiments, providing a covalent organic framework comprising repeating units of a moiety comprising Formula (I) comprises providing a covalent organic framework comprising repeating units of a moiety comprising imine groups of Formula (II):
##STR00041## [0266] and [0267] reacting the covalent organic framework comprising repeating units of a moiety comprising imine groups of Formula (II) under conditions effective to produce the covalent organic framework comprising repeating units of a moiety comprising Formula (I).
[0268] In some embodiments, the reacting comprises providing a compound of Formula (IIIa):
CN(CH.sub.2).sub.mC(O)OC.sub.1-6 alkyl(IIIa); [0269] providing a compound of Formula (IV):
R.sup.5COOH(IV); and [0270] reacting the covalent organic framework comprising repeating units of a moiety comprising imine groups of Formula (II) with the compound of Formula (IIIa) and the compound of Formula (IV) to produce the covalent organic framework comprising repeating units of a moiety comprising Formula (I).
[0271] The above disclosure is general. A more specific description is provided below in the following examples. The examples are described solely for the purpose of illustration and are not intended to limit the scope of the present disclosure. Changes in form and substitution of equivalents are contemplated as circumstances suggest or render expedient. Although specific terms have been employed herein, such terms are intended in a descriptive sense and not for purposes of limitation.
EXAMPLES
[0272] The following Examples are presented to illustrate various aspects of the present disclosure, but are by no means intended to limit its scope.
Example 1Materials and Instrumentation for Examples 2-3
Materials
[0273] Mesitylene and dioxane were purchased from Millipore Sigma. Methanol, acetone, tetrahydrofuran (THF), n-hexane, and acetic acid were purchased from Fisher. 4-Aminophenylboronic acid pinacol ester, 3,5-dibromobenzaldehyde, and 4-pentynoic acid were purchased from Combi-Blocks. 3-Bromopropionic acid, cyclohexyl isocyanide, palladium(0) tetrakis(triphenylphosphine), and 4-pentenoic acid were purchased from Oakwood Chemical. 1,3,5-Tris(4-aminophenyl)benzene (TAPB) (Mancheno et al., Introduction to Covalent Organic Frameworks: An Advanced Organic Chemistry Experiment, J. Chem. Educ., 96(8):1745-1751 (2019), which is hereby incorporated by reference in its entirety), (E)-3,3,5,5-tetrakis(4-aminophenyl)stilbene (TAPS) (Lyle et al., Multistep Solid-State Organic Synthesis of Carbamate-Linked Covalent Organic Frameworks, J. Am. Chem. Soc., 141(28):11253-11258 (2019), which is hereby incorporated by reference in its entirety), 2,5-dimethoxyterephthalaldehyde (DMTP) (Kang et al., Aggregated Structures of Two-Dimensional Covalent Organic Frameworks, J. Am. Chem. Soc., 144(7):3192-3199 (2022), which is hereby incorporated by reference in its entirety), 3-azidopropionic acid (Schmitz et al., Cathepsin B Inhibitors: Combining Dipeptide Nitriles with an Occluding Loop Recognition Element by Click Chemistry, ACS Med. Chem. Lett., 7(3):211-216 (2016), which is hereby incorporated by reference in its entirety), and 1-(2-methoxyphenyl)-N-phenylmethanimine (Cardinale et al., Photoredox-Catalyzed Synthesis of -Amino Acid Amides by Imine Carbamoylation, Org. Lett., 24(2):506-510 (2022), which is hereby incorporated by reference in its entirety) were synthesized according to previously reported protocols.
Sonication
[0274] Sonication was performed with a Branson 2510 Ultrasonic Cleaner with a frequency of 40 kHz.
Fourier-Transform Infrared (FTIR) Spectroscopy
[0275] Infrared spectra were collected using an Agilent Technologies Cary 600 Series FTIR Spectrometer equipped with a Diamond ATR accessory.
Thermogravimetric Analysis (TGA)
[0276] TGA was measured on Netzsch STA449 F1 over the temperature range from 40 to 900 C. The analysis was carried out under an argon atmosphere with a heating rate of 10 C./min using an empty Al.sub.2O.sub.3 crucible as the reference.
Powder X-Ray Diffraction (PXRD)
[0277] Powder X-ray diffraction patterns were collected using a Bruker D8-Advance diffractometer in parallel beam geometry employing Cu K (1.5418 ) line-focused radiation at 40 kV/40 mA power and equipped with a position-sensitive detector. Covalent organic framework (COF) samples were loaded on zero background sample holders (MTI Corporation, ZeroSi32D20C1cavity10D) by dropping the powders from a metal spatula and leveling the sample. In the case of TAPS-DMTP-COF and its derivatives, powders were drop-casted onto the sample holder using THF to disrupt the preferred orientation of crystals. Samples were rotated at a rate of 15 rpm. Data were collected from 1.0 2 to 30.0 2 with 0.03 2 per step (983 steps) and an exposure time of 7 s per step, for a total acquisition time of 126 min.
X-Ray Photoelectron Spectra (XPS)
[0278] The XPS measurements were performed using a Kratos Amicus/ESCA 3400 instrument. The sample was irradiated with 240 W unmonochromated Mg K x-rays, and photoelectrons emitted at 0 from the surface normal were energy analyzed using a DuPont type analyzer. The pass energy was set at 150 eV and a Shirley baseline was removed from the spectra. CasaXPS was used to process raw data files.
Nuclear Magnetic Resonance (NMR) Spectroscopy
[0279] .sup.1H NMR and .sup.13C NMR spectra were recorded at 25 C. on Varian 400 MHz. The spectra were calibrated using residual solvent as internal reference (CDCl.sub.3: 7.26 ppm for .sup.1H NMR, 77.00 ppm for .sup.13C NMR).
Scanning Electron Microscopy (SEM)
[0280] SEM images were taken on JEOL JSM-IT200 Scanning Electron Microscope. Samples were dispersed in ethanol or acetone and drop-casted on the silicon wafer substrate.
Gas Sorption Isotherms
[0281] Nitrogen physisorption experiments were conducted on a Micromeritics Tristar Analyzer using 80-100 mg samples in dried and tared analysis tubes equipped with filler rods and capped with a Transeal. Samples were heated to 100 C. for 6 hours and degassed using nitrogen gas flow. Each tube was weighed again to determine the mass of the activated sample and transferred to the analysis port of the instrument. UHP-grade (99.999% purity) N.sub.2 was used for all sorption measurements. N.sub.2 sorption isotherms were generated by incremental exposure to nitrogen up to 760 mmHg (1 atm) at 77 K (liquid N.sub.2 bath). The Brunauer-Emmett-Teller (BET) method was utilized to calculate the specific surface areas.
Conventional Solid-State Spinning NMR Spectroscopy
[0282] Room-temperature magic angle spinning (MAS) .sup.13C solid-state NMR experiments were performed with a 9.4 T widebore Bruker NMR spectrometer (n.sub.0 (.sup.13C) 100.7 MHz) equipped with an Avance III HD console, and a Bruker 4 mm MAS probe configured in double resonance .sup.1H-.sup.13C mode. .sup.13C solid-state NMR spectra were acquired with cross-polarization (CP) for signal enhancement (Pines et al., Proton-Enhanced Nuclear Induction Spectroscopy. A Method for High Resolution NMR of Dilute Spins in Solids, Chem. Phys., 56(4):1776-1777 (1972); Schaefer and Stejskal, Carbon-13 Nuclear Magnetic Resonance of Polymers Spinning at the Magic Angle, J. Am. Chem. Soc., 98(4):1031-1032 (1976), which are hereby incorporated by reference in their entirety). .sup.1H-.sup.13C CP matching conditions were optimized on an external standard of adamantane. CP experiments on COF materials used a 2 ms CP contact time. 65,536 scans were acquired each for the kag-COF and kag-Ugi-COF-OAc-[1.0]. A 1.0 s recycle delay was employed in both cases to maximize sensitivity. .sup.1H saturation recovery experiments indicated that the .sup.1H T.sub.1 was approximately 0.7 s for both COF materials. The magic angle spinning (MAS) frequency was 10 kHz. All .sup.1H CP spin-lock RF fields were linearly ramped from 90% to 100% amplitude (Metz et al., Ramped-Amplitude Cross Polarization in Magic-Angle-Spinning NMR, J. magn. reson., Ser. A, 110(2):219-227 (1994), which is hereby incorporated by reference in its entirety) to broaden the Hartman-Hahn match condition. The .sup.1H-.sup.13C CP experiments used spin lock pulses with RF fields of ca. 34 kHz and 44 kHz for .sup.1H and .sup.13C, respectively. SPINAL-64 heteronuclear decoupling (Fung et al., An Improved Broadband Decoupling Sequence for Liquid Crystals and Solids, J. Magn. Reson., 142(1):97-101 (2000), which is hereby incorporated by reference in its entirety) with a .sup.1H RF field of 100 kHz was applied during the acquisition.
Dynamic Nuclear Polarization Solid-State NMR Spectroscopy
[0283] In general, ca. 10 mg of hex-COF samples were weighed out and placed in a watch glass, where ca. 20 mL of a 16 mM TEKPol TCE solution was added by impregnation. The impregnated sample was then packed into a 3.2 mm DNP sapphire rotor, then capped with a Teflon insert and zirconia drive cap. .sup.13C and .sup.15N SSNMR DNP experiments were conducted on a 9.4 T Bruker 400 MHz/263 GHz DNP NMR system (Rosay et al., Solid-State Dynamic Nuclear Polarization at 263 GHz: Spectrometer Design and Experimental Results, Phys. Chem. Chem. Phys., 12(22):5850-5860 (2010), which is hereby incorporated by reference in its entirety) equipped with a Bruker Avance III console and a Bruker 3.2 mm HXY MAS DNP-NMR probe configured in triple resonance HCN mode. The main magnetic field was set on a standard sample of TEKPol TCE solution so that microwave irradiation gave a maximum positive DNP enhancement. The sample temperature was approximately 110 K for all experiments. The magic angle spinning (MAS) frequency was 10 kHz. .sup.1H-.sup.15N cross polarization (CP) was optimized on an external standard of .sup.13C, .sup.15N labeled glycine. All .sup.1H CP spin-lock RF fields were linearly ramped from 90% to 100% amplitude (Metz et al., Ramped-Amplitude Cross Polarization in Magic-Angle-Spinning NMR, J. magn. reson., Ser. A, 110(2):219-227 (1994), which is hereby incorporated by reference in its entirety) to broaden the Hartman-Hahn match condition. The .sup.1H-.sup.13C CP experiments used spin lock pulses with RF fields of ca. 65 kHz and 50 kHz for .sup.1H and .sup.13C, respectively, and a 2 ms contact time. The .sup.1H-.sup.15N CP experiments used spin lock pulses with RF fields of ca. 70 kHz and 42 kHz for .sup.1H and .sup.15N, respectively, and 5 ms contact times. Recycle delay of 7.5 s and 6.5 s were used for hex-COF and hex-Ugi-COF-OAc-[1.0], respectively. These recycle delays were chosen for optimal sensitivity, based upon DNP signal build-up times measured with .sup.1H-.sup.13C CP saturation recovery experiments (
Example 2Synthetic Procedures
Synthesis of TAPB-DMTP-COF (Hex-COF)
[0284] Hex-COF was prepared according to a previously reported procedure (Xu et al., Stable, Crystalline, Porous, Covalent Organic Frameworks as a Platform for Chiral Organocatalysts, Nat. Chem., 7(11):905-912 (2015), which is hereby incorporated by reference in its entirety) with some modifications. TAPB (56.2 mg, 0.16 mmol) and DMTP (46.6 mg, 0.24 mmol) were charged in a prescored glass ampule (20 mL). Mesitylene (3.2 mL) and dioxane (0.8 mL) were added, and the solution was sonicated for 5 min to produce a homogenous suspension. Acetic acid (0.4 mL, 6.0 M) was added. The ampule was degassed through three freeze-pump-thaw cycles, flash frozen at 77 K (liquid N.sub.2 bath), evacuated to an internal pressure of 100 mTorr, and flame sealed. The reaction mixture was allowed to warm up to room temperature and heated at 120 C. for 72 hours without disturbance. Upon cooling the reaction to room temperature, the yellow precipitate was isolated by filtration and washed with acetone. While still activated, the product was transferred to the Soxhlet extractor for further purification with THF for 24 hours. Afterward, the powder was collected by filtration, washed with acetone, and dried at 100 C. under reduced pressure (100 mTorr) for 24 hours, affording the product as a bright yellow powder (80 mg, 81% yield).
Synthesis of TAPS-DMTP-COF (Kag-COF)
[0285] Kag-COF was prepared according to a previously reported procedure (Lyle et al., Multistep Solid-State Organic Synthesis of Carbamate-Linked Covalent Organic Frameworks, J. Am. Chem. Soc., 141(28):11253-11258 (2019), which is hereby incorporated by reference in its entirety) with some modifications. TAPS (87.2 mg, 0.16 mmol) and DMTP (62.1 mg, 0.32 mmol) were charged in a prescored glass ampule (20 mL). Mesitylene (2.8 mL) and dioxane (1.2 mL) were added, and the solution was sonicated for 5 min to produce a homogenous suspension. Acetic acid (0.4 mL, 6.0 M) was added. The ampule was degassed through three freeze-pump-thaw cycles, flash frozen at 77 K (liquid N.sub.2 bath), evacuated to an internal pressure of 100 mTorr, and flame sealed. The reaction mixture was allowed to warm up to room temperature and heated at 120 C. for 72 hours without disturbance. Upon cooling the reaction to room temperature, the yellow precipitate was isolated by filtration and washed with acetone. While still activated, the product was transferred to the Soxhlet extractor for further purification with THF for 24 hours. Afterward, the powder was collected by filtration, washed with acetone, and dried at 100 C. under reduced pressure (100 mTorr) for 24 hours, affording the product as a bright yellow powder (120 mg, 83% yield).
Ugi Multicomponent Reaction
Synthesis of N-Cyclohexyl-2-phenyl-2-(N-(2-methoxy-phenyl)acetamido)acetamide (Model Compound)
##STR00042##
[0286] 1-(2-Methoxyphenyl)-N-phenylmethanimine (105 mg, 0.5 mmol) was charged to a 1-dram glass vial. Methanol (0.41 mL), acetic acid (30 mg, 0.5 mmol, 1.0 equiv), and cyclohexyl isocyanide (54 mg, 0.5 mmol, 1.0 equiv) were added in this order, and the vial was sealed with a Teflon cap. The precipitate formed within minutes, but the reaction was allowed to proceed for additional 24 hours at room temperature. The product was isolated by filtration, washed with n-hexane, and dried under reduced pressure, affording the model compound as a white solid (155 mg, 96%). .sup.1H NMR (400 MHz, CDCl.sub.3): 7.10-7.18 (m, 5H), 7.01 (dd, J=7.6, 2.0 Hz, 1H), 6.73 (d, J=8.0 Hz, 1H), 6.67 (td, J=7.6, 1.2 Hz, 1H), 6.33 (s, 1H), 5.46 (d, J=8.0 Hz, 1H), 3.89-3.78 (m, 1H), 3.76 (s, 3H), 2.01-1.92 (m, 1H), 1.87 (m, 1H), 1.86 (s, 3H), 1.73-1.52 (m, 3H), 1.41-1.26 (m, 2H), 1.18-1.07 (m, 2H), 1.07-0.94 (m, 1H) (
Synthesis of TAPB-DMTP-Ugi-COF-OAc-[1.0](hex-Ugi-COF-OAc-[1.0])
[0287] Hex-COF (10.0 mg, 0.0085 mmol, MW=1177.38 g/mol) was charged to a 1-dram glass vial. Methanol (0.21 mL), acetic acid (15 mg, 0.25 mmol, 5.0 equiv6 imine bonds per unit cell), and cyclohexyl isocyanide (28 mg, 0.25 mmol, 5.0 equiv6 imine bonds per unit cell) were added in this order, and the vial was sealed with a Teflon cap. Hence, the concentration of the acid and the isocyanide reaction components was kept at 1.0 M each. The reaction was placed in a metal block preheated to 40 C. and maintained at that temperature for 24 hours without stirring. The progress of the reaction was monitored using the color-responsive nature of the conjugated COF framework: upon initial addition of the acetic acid, the material turned dark red (imine protonation), followed by a gradual color change to light orange or yellow (Ugi adduct formation), which indicated the reaction competition. The product was isolated by filtration, washed with a copious amount of acetone, and dried at 100 C. under reduced pressure (100 mTorr) for 24 hours, affording hex-Ugi-COF-OAc-[1.0] as a yellow powder (12 mg).
Synthesis of TAPB-DMTP-Ugi-COF-OAc-[1.5](hex-Ugi-COF-OAc-[1.5])
[0288] The product was prepared according to the previously described procedure using hex-COF (10 mg, 0.0085 mmol), methanol (0.19 mL), acetic acid (23 mg, 0.38 mmol, 7.5 equiv6 imine bonds per unit cell), and cyclohexyl isocyanide (42 mg, 0.38 mmol, 7.5 equiv6 imine bonds per unit cell). Hence, the concentration of the acid and the isocyanide reaction components was kept at 1.5 M each. The reaction afforded hex-Ugi-COFOAc-[1.5] as a yellow powder (14 mg).
Synthesis of TAPB-DMTP-Ugi-COF Derivatives (Hex-Ugi-COF-R)
[0289] Functionalized hex-Ugi-COF derivatives were prepared according to the previously described procedure using hex-COF (10 mg, 0.0085 mmol), methanol (0.19 mL), corresponding carboxylic acid (3-azidopropionic acid, 4-pentynoic acid, or 4-pentenoic acid) (0.38 mmol, 7.5 equiv6 imine bonds per unit cell), and cyclohexyl isocyanide (42 mg, 0.38 mmol, 7.5 equiv6 imine bonds per unit cell). In each case, the concentration of the acid and the isocyanide reaction components was kept at 1.5 M each. The reaction afforded hex-Ugi-COFN.sub.3 (14 mg), hex-Ugi-COFCC (14 mg), or hex-Ugi-COFCC (14 mg) as yellow powders.
Synthesis of TAPS-DMTP-Ugi-COF-OAc-[1.0](kag-Ugi-COF-OAc-[1.0]).
[0290] Kag-COF (7.6 mg, 0.0085 mmol, MW=897.05 g/mol) was charged to a 1-dram glass vial. Methanol (0.21 mL), acetic acid (15 mg, 0.25 mmol, 15.0 equiv2 imine bonds per unit cell), and cyclohexyl isocyanide (28 mg, 0.25 mmol, 15.0 equiv2 imine bonds per unit cell) were added in this order, and the vial was sealed with a Teflon cap. Hence, the concentration of the acid and the isocyanide reaction components was kept at 1.0 M each. The reaction was placed in a metal block preheated to 40 C. and maintained at that temperature for 24 hours without stirring. The progress of the reaction was monitored using the color-responsive nature of the conjugated COF framework: upon initial addition of the acetic acid, the material turned dark red (imine protonation), followed by a gradual color change to light orange or yellow (Ugi adduct formation), which indicated the reaction completion. The product was isolated by filtration, washed with a copious amount of acetone, and dried at 100 C. under reduced pressure (100 mTorr) for 24 hours, affording hex-Ugi-COF-OAc-[1.0] as a yellow powder (12 mg).
Synthesis of TAPS-DMTP-Ugi-COF Derivatives (kag-Ugi-COF-R)
[0291] Functionalized kag-Ugi-COF derivatives were prepared according to the previously described procedure using kag-COF (7.6 mg, 0.0085 mmol), methanol (0.21 mL), corresponding carboxylic acid (3-azidopropionic acid, 4-pentynoic acid, or 4-pentenoic acid) (0.25 mmol, 15.0 equiv2 imine bonds per unit cell), and cyclohexyl isocyanide (28 mg, 0.25 mmol, 15.0 equiv2 imine bonds per unit cell). In each case, the concentrations of the acid and the isocyanide reaction components were kept at 1.0 M each. The reaction afforded kag-Ugi-COFN.sub.3 (8 mg), kag-Ugi-COFCC (8 mg), or kag-Ugi-COFCC (8 mg) as yellow powders.
Example 3Results and Discussion for Examples 1-2
[0292] A typical Ugi reaction involves the multicomponent reaction of imine, isocyanide, and carboxylic acid reagents to generate a bis-amide product (Rocha et al., Review on the Ugi Multicomponent Reaction Mechanism and the Use of Fluorescent Derivatives as Functional Chromophores, ACS Omega, 5(2):972-979 (2020); Fouad et al., Two Decades of Recent Advances of Ugi Reactions: Synthetic and Pharmaceutical Applications, RSC Adv., 10(70):42644-42681 (2020), which are hereby incorporated by reference in their entirety). High concentrations of the above components in polar protic solvents usually lead to higher yields of the Ugi adduct (Domling et al., Multicomponent Reactions with Isocyanides, Angew. Chem., Int. Ed., 39(18):3168-3210 (2000); Marcaccini and Torroba, The Use of the Ugi Four-Component Condensation, Nat. Protoc., 2(3):632-639 (2007); Bradley et al., Optimization of the Ugi Reaction Using Parallel Synthesis and Automated Liquid Handling, J. Vis. Exp., 21:942 (2008), which are hereby incorporated by reference in their entirety). To test the feasibility of this reaction, N-cyclohexyl-2-phenyl-2-(N-(2-methoxy-phenyl)acetamido)acetamide (model compound) was first synthesized from N-(2-methoxybenzylidene)aniline, cyclohexyl isocyanide, and acetic acid in methanol at room temperature in 10 minutes with quantitative yield. Inspired by the preliminary success, these reaction conditions were applied to the COF materials, obtaining the TAPB-DMTP-Ugi-COF (hex-Ugi-COF) and TAPS-DMTP-Ugi-COF (kag-Ugi-COF). During optimization, it was found that the concentrations of isocyanide and carboxylic acid must be at least 1.0 M to achieve more than 50% functionalization of the porous materials. However, running the reaction at 2.0 M resulted in an almost complete conversion of the imine bonds to the Ugi bis-amide but lead to a PXRD-silent profile of the Ugi-COFs. Hence, the concentration of 1.5 M was identified to lead to the highest degree of functionalization while retaining the crystallinity of the material.
[0293] For routine assessment, Fourier-transform infrared (FTIR) spectroscopy was utilized to confirm the formation of the Ugi adduct at the backbone of the COFs. In the case of hex-Ugi-COF-OAc-[1.0] obtained from the reaction of hex-COF (
[0294] To introduce functional group handles in the COFs, the acetic acid was replaced with either 3-azidopropionic acid, 4-pentynoic acid, or 4-pentenoic acid in Ugi reactions with cyclohexyl isocyanide and hex-COF in a 1.5 M solution of methanol. In addition to the previously described FTIR features of the hex-Ugi-COF-OAc materials, the corresponding functionalized hex-Ugi-COFN.sub.3-[1.5] material showed a presence of strong azide frequency at 2103 cm.sup.1 (N.sub.3) (
[0295] To confirm the retention of crystallinity throughout the Ugi reaction, powder X-ray diffraction (PXRD) patterns of as-synthesized hex-COF (
[0296] Scanning Electron Microscopy (SEM) imaging was utilized to assess the retention of morphology for COF material before and after the Ugi transformation. For as-synthesized hex-COF crystals, the material was isolated mostly as islands of spherical particles (
[0297] To better understand the effect of the Ugi transformation on the permanent porosity of the COFs, the Brunauer-Emmett-Teller (BET) measurements for the materials before and after the Ugi reaction were obtained. The BET surface area of as-synthesized hex-COF was measured at 1610 m.sup.2/g, while for the hex-Ugi-COF-OAc-[1.0] and hex-Ugi-COFOAc-[1.5], the BET surface areas were measured at 325 and 230 m.sup.2/g, respectively (
[0298] The N 1s X-ray photoelectron spectroscopy (XPS) profiles of the hex-COF and kag-COF before and after the Ugi reaction provided a handle for quantifying the efficiency of the multicomponent coupling reaction. After fitting the N 1s XPS spectra, both as-synthesized hex-COF (
[0299] Additional confirmation of the imine nitrogen transformation to the Ugi amide nitrogen was obtained by using magic angle spinning (MAS) dynamic nuclear polarization (DNP) to enhance solid-state NMR sensitivity (Maly et al., Dynamic Nuclear Polarization at High Magnetic Fields, Chem. Phys., 128(5):052211 (2008); Ni et al., High Frequency Dynamic Nuclear Polarization, Acc. Chem. Res., 46(9):1933-1941 (2013), which are hereby incorporated by reference in their entirety) and enable .sup.1H.fwdarw..sup.15N cross-polarization MAS (CPMAS) SSNMR experiments. The DNP-enhanced .sup.15N CPMAS NMR spectra verified the nitrogen functional groups present in the frameworks before and after functionalization. DNP has been used previously to enhance the sensitivity of solid-state NMR experiments on a variety of porous materials such as silica (Lesage et al., Surface Enhanced NMR Spectroscopy by Dynamic Nuclear Polarization, J. Am. Chem. Soc., 132(44):15459-15461 (2010); Grning et al., Molecular-Level Characterization of the Structure and the Surface Chemistry of Periodic Mesoporous Organosilicates Using DNP-Surface Enhanced NMR Spectroscopy, Phys. Chem. Chem. Phys., 15(32):13270-13274 (2013), which are hereby incorporated by reference in their entirety), MOF (Rossini et al., Dynamic Nuclear Polarization Enhanced Solid-State NMR Spectroscopy of Functionalized Metal-Organic Frameworks, Angew. Chem. Int. Ed., 51(1):123-127 (2012); Kobayashi et al., DNP-Enhanced Ultrawideline Solid-State NMR Spectroscopy: Studies of Platinum in Metal-Organic Frameworks, J. Phys. Chem. Lett., 7(13):2322-2327 (2016), which are hereby incorporated by reference in their entirety), COF (Cao et al., Exploring Applications of Covalent Organic Frameworks: Homogeneous Reticulation of Radicals for Dynamic Nuclear Polarization, J. Am. Chem. Soc., 140(22):6969-6977 (2018), which is hereby incorporated by reference in its entirety), polymers (Blanc et al., Dynamic Nuclear Polarization NMR Spectroscopy Allows High-Throughput Characterization of Microporous Organic Polymers, J. Am. Chem. Soc., 135(41):15290-15293 (2013), which is hereby incorporated by reference in its entirety, and zeolites (Wolf et al., NMR Signatures of the Active Sites in Sn- Zeolite, Angew. Chem. Int. Ed., 53(38):10179-10183 (2014); Gunther et al., Dynamic Nuclear Polarization NMR Enables the Analysis of Sn-Beta Zeolite Prepared with Natural Abundance .sup.119Sn Precursors, J. Am. Chem. Soc., 136(17):6219-6222 (2014), which are hereby incorporated by reference in their entirety). To perform DNP experiments on the COF materials, they were impregnated with a 16 mM solution of the nitroxide biradical TEKPOl (Zagdoun et al., Large Molecular Weight Nitroxide Biradicals Providing Efficient Dynamic Nuclear Polarization at Temperatures up to 200 K, J. Am. Chem. Soc., 135(34):12790-12797 (2013), which is hereby incorporated by reference in its entirety) dissolved in tetrachloroethane (Lesage et al., Surface Enhanced NMR Spectroscopy by Dynamic Nuclear Polarization, J. Am. Chem. Soc., 132(44):15459-15461 (2010); Zagdoun et al., Non-Aqueous Solvents for DNP Surface Enhanced NMR Spectroscopy, Chem Comm, 48(5):654-656 (2012), which are hereby incorporated by reference in their entirety). .sup.1H.fwdarw..sup.13C CPMAS experiments performed with and without microwaves showed indirect .sup.1H CPMAS DNP enhancements (.sub.C cp) of zz11 and 4 for the hex-COF and hex-Ugi-COFOAc-[1.0], respectively. .sup.1H.fwdarw..sup.13C CPMAS saturation recovery experiments showed that the .sup.1H DNP signal build-up times (T.sub.DNP) were on the order of 5 s for the framework .sup.1H spins (
[0300] The .sup.15N CPMAS spectra were acquired with a 5 ms CP contact time to observe .sup.15N NMR signals from both protonated and non-protonated nitrogen sites. The .sup.1H.fwdarw..sup.15N CPMAS spectrum of the hex-COF shows intense NMR signals at 67 ppm, 243 ppm, 319 ppm, and 340 ppm that are assigned to imine, aromatic amide, amine, and ammonium (likely, from the acetate salt) nitrogen sites, respectively (
[0301] A gradient in DNP enhancements would likely preferentially enhance the intensity of amide and amine groups that are expected to be associated with incompletely condensed linkers present at the surface of the COF particles prior to Ugi functionalization. Regardless, the .sup.1H.fwdarw..sup.15N CPMAS spectrum of hex-Ugi-COF-OAc-[1.0] shows that all imine signals are absent and that the most Intense .sup.15N NMR signals are now present at amide chemical shifts (
[0302] To verify the bulk functionalizations of the Ugi-COF materials, .sup.13C CPMAS solid-state NMR spectroscopy was employed. Comparison of the .sup.13C solution-state NMR spectrum of the model compound (
[0303] In addition to confirming the incorporation of the Ugi adduct in both COFs, .sup.13C CPMAS, NMR spectroscopy was used to more accurately quantify the efficiency of the Ugi modification in the hex-Ugi-COF-OAc-[1.0] and kag-Ugi-COF-OAc-[1.0]. .sup.13C CPMAS solid-state NMR will be much more quantitative than DNP .sup.15N CPMAS NMR spectra because only the .sup.1H.fwdarw..sup.13C CP dynamics will affect the relative peak intensities. A 2 ms CP contact time was used to obtain all .sup.13CPMAS spectra, which typically results in differences of ca. 15% or less in the integrated intensity relative to the atom ratio for all types of carbon atoms (Alemany et al., Cross Polarization and Magic Angle Sample Spinning NMR Spectra of Model Organic Compounds. 1. Highly protonated molecules, J. Am. Chem. Soc., 105(8):2133-2141 (1983), which is hereby incorporated by reference in its entirety). Signals at 152.5 ppm, 147.1 ppm, and 139.0 ppm in as-synthesized hex-COF were assigned to the aromatic carbon (B), imine carbon (I), and aromatic carbon (C), respectively (
[0304] Thermogravimetric analysis (TGA) curves of hex-COF and hex-Ugi-COF-OAc-[1.0] are shown in
[0305] The same analysis was applied to the .sup.13C CPMAS solid-state NMR spectra of as-synthesized kag-COF and kag-Ugi-COF-OAc-[1.0]. Signals at 153.3 ppm, 147.5 ppm, 142.8-133.3 ppm were identified as aromatic carbon (B), imine carbon (I), and aromatic carbons (C), respectively, in kag-COF (
[0306] TGA curves of kag-COF and kag-Ugi-COF-OAc-[1.0] are shown in
[0307] Note that the presented Ugi-COF materials were produced with a relatively high degree of functionalization for the purpose of efficient characterization. However, for most COF applications, the optimal active site loading varies between 20% to 30% (Xu et al., Catalytic Covalent Organic Frameworks via Pore Surface Engineering, Chem Comm, 50(11):1292-1294 (2014); Xu et al., Stable, Crystalline, Porous, Covalent Organic Frameworks as a Platform for Chiral Organocatalysts, Nat. Chem, 7(11):905-912 (2015), which are hereby incorporated by reference in their entirety). The strategy described herein meets this requirement and provides fine control over the functional group loading by tuning the concentration of the Ugi reaction conditions. Decreasing the functionalization degree of the Ugi-COFs would also help preserve most of its porous architecture.
[0308] In conclusion, a general strategy for the modification of imine-based COFs with functional group handles has been developed using the Ugi multicomponent reaction. The current facile approach to derivatize COFs with valuable functional group handles provides a gateway for the scientific community to advance the exploration of these crystalline porous materials. The potential of the operationally straightforward Ugi modifications in COFs, coupled with the versatile reactivity of the azide, alkyne, and vinyl functional handles, can result in the rapid production of highly customizable platforms that are poised to expand the applications of these materials in catalysis, separation, and molecular sensing.
Example 4Materials and Instrumentation for Examples 5-8
Materials
[0309] Benzonitrile, mono-methyl succinate, tris(2-aminoethyl)amine, and neodymium(III) nitrate (Nd(NO.sub.3).sub.3) were purchased from Millipore Sigma. Methanol, acetone, diethyl ether, and tetrahydrofuran were purchased from Fisher. Ethyl isocyanoacetate was purchased from Oakwood Chemical. Diglycolic anhydride was purchased from Combi-Blocks. 1,3,5-Tris(4-aminophenyl)benzene (TAPB) (Mancheno et al., Introduction to Covalent Organic Frameworks: An Advanced Organic Chemistry Experiment, J. Chem. Educ., 96(8):1745-1751 (2019), which is hereby incorporated by reference in its entirety) and 2,5-dimethoxyterephthalaldehyde (DMTP) (Kang et al., Aggregated Structures of Two-Dimensional Covalent Organic Frameworks, J. Am. Chem. Soc., 144(7):3192-3199 (2022), which is hereby incorporated by reference in its entirety) were synthesized according to previously reported protocols.
Sonication
[0310] Sonication was performed with a Branson 2510 Ultrasonic Cleaner with a frequency of 40 kHz.
Fourier-Transform Infrared (FTIR) Spectroscopy
[0311] Infrared spectra were collected using an Agilent Technologies Cary 600 Series FTIR Spectrometer equipped with a Diamond ATR accessory.
Thermogravimetric Analysis (TGA)
[0312] TGA was measured on Netzsch STA449 F1 over the temperature range from 40 to 900 C. The analysis was carried out under an argon atmosphere with a heating rate of 10 C./min using an empty Al.sub.2O.sub.3 crucible as the reference.
Powder X-Ray Diffraction (PXRD)
[0313] Powder X-ray diffraction patterns were collected using a Bruker D8-Advance diffractometer in parallel beam geometry employing Cu K (1.5418 ) line-focused radiation at 40 kV/40 mA power and equipped with a position-sensitive detector. COF samples were loaded on zero background sample holders (MTI Corporation, ZeroSi32D20C1cavity10D) by dropping the powders from a metal spatula and leveling the sample. Samples were rotated at a rate of 15 rpm. Data were collected from 1.0 20 to 30.0 20 with 0.03 20 per step (983 steps) and an exposure time of 7 s per step, for a total acquisition time of 126 min.
X-Ray Photoelectron Spectra (XPS)
[0314] The XPS measurements were performed using a Kratos Amicus/ESCA 3400 instrument. The sample was irradiated with 240 W unmonochromated Mg K x-rays, and photoelectrons emitted at 0 from the surface normal were energy analyzed using a DuPont-type analyzer. The pass energy was set at 150 eV, and a Shirley baseline was removed from the spectra. CasaXPS was used to process raw data files.
Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES)
[0315] Agilent 5800 ICP-OES instrument was used to measure the rare-earth elements in the solution and consequent quantification of the adsorption/desorption capacities of the COFs. The intensity of 401.2 nm wavelength of Nd was used in the radial viewing mode for all the quantifications using a known calibration curve. A calibration curve consisting of 6 data points was constructed using 0-10 ppm Nd(NO.sub.3).sub.3 solution in a 2% HNO.sub.3 every time before analyzing the samples. All samples were diluted using a 2% HNO.sub.3 solution before the analysis.
Zeta Potential Measurements
[0316] The zeta potential measurements of the materials were performed in a Malvern Zetasizer NS using Smoluchowski equation and water as the dispersant. The refractive index of the COFs was assumed to be the same as the refractive index values of the carbon for all measurements.
Scanning Transmission Electron Microscopy (STEM)
[0317] STEM images, high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images, and energy dispersive X-ray spectroscopy (EDS) were acquired on a FEI Titan Themis Probe Cs corrected scanning transmission electron microscope under 200 kV accelerating voltage. For experiments, 1 mg of the sample was dispersed in 2 mL ethanol, and then 50 L mixture was dried on a TEM grid (Formvar/Carbon 200 mesh, Copper, TED PELLA, Inc.).
Atomic Force Microscopy (AFM)
[0318] AFM images were acquired in AC mode using a CypherES (Oxford Instrument) using TESPA (Bruker) probes. All images were acquired in the open air. Samples were prepared by adding materials to 100% pure ethanol, followed by a 5-minute sonication and allowing the solution to rest for 5 minutes at room temperature. Next, a 5-L droplet taken from the upper 10% of the sample solution was placed on a polished silicon surface (Ted Pella #16006), and ethanol was allowed to evaporate completely. AFM images were post-processed using the flattening (first order) technique. Height measurements were taken via cross-section within the Asylum software (v19.12.70).
Gas Sorption Isotherms
[0319] Nitrogen physisorption experiments were conducted on a Micromeritics Tristar Analyzer using 80-100 mg samples in dried and tared analysis tubes equipped with filler rods and capped with a Transeal. Samples were pretreated at 100 C. for 6 hours under nitrogen gas flow. Each tube was weighed again to determine the mass of the activated sample and transferred to the analysis port of the instrument. UHP-grade (99.999% purity) N.sub.2 was used for all sorption measurements. N.sub.2 sorption isotherms were generated by incremental exposure to nitrogen up to 760 mmHg (1 atm) at 77 K (liquid N.sub.2 bath). The Brunauer-Emmett-Teller (BET) method was utilized to calculate the specific surface areas.
Conventional Solid-State Spinning NMR Spectroscopy
[0320] Room-temperature magic angle spinning (MAS).sup.13C solid-state NMR experiments were performed with a 9.4 T widebore Bruker NMR spectrometer (.sub.0(.sup.13C)=100.7 MHz) equipped with an Avance III HD console, and a Bruker 4 mm MAS probe configured in double resonance .sup.1H-.sup.13C mode. .sup.13C solid-state NMR spectra were acquired with cross-polarization (CP) for signal enhancement (Pines et al., Proton-Enhanced Nuclear Induction Spectroscopy. A Method for High Resolution NMR of Dilute Spins in Solids, Chem. Phys., 56(4):1776-1777 (1972); Schaefer and Stejskal, Carbon-13 Nuclear Magnetic Resonance of Polymers Spinning at the Magic Angle, J. Am. Chem. Soc., 98(4):1031-1032 (1976), which are hereby incorporated by reference in their entirety). .sup.1H-.sup.13C CP matching conditions were optimized on an external standard of adamantane. CP experiments on COF materials used a 2 ms CP contact time. The magic angle spinning (MAS) frequency was 10 kHz. All .sup.1H CP spin-lock RF fields were linearly ramped from 90% to 100% amplitude (Metz et al., Ramped-Amplitude Cross Polarization in Magic-Angle-Spinning NMR, J. magn. reson., Ser. A, 110(2):219-227 (1994), which is hereby incorporated by reference in its entirety) to broaden the Hartman-Hahn match condition. The .sup.1H-.sup.13C CP experiments used spin lock pulses with RF fields of ca. 34 kHz and 44 kHz for .sup.1H and .sup.13C, respectively. SPINAL-64 heteronuclear decoupling (Fung et al., An Improved Broadband Decoupling Sequence for Liquid Crystals and Solids, J. Magn. Reson., 142(1):97-101 (2000), which is hereby incorporated by reference in its entirety) with a .sup.1H RF field of 100 kHz was applied during the acquisition.
Example 5Synthetic Procedures
Synthesis and Post-Synthetic Modifications of COFs
Synthesis of Imine-COF
[0321] The imine-COF was prepared according to a previously reported single-crystalline protocol (Natraj et al., Single-Crystalline Imine-Linked Two-Dimensional Covalent Organic Frameworks Separate Benzene and Cyclohexane Efficiently, J. Am. Chem. Soc., 144(43):19813-19824 (2022), which is hereby incorporated by reference in its entirety), with some modifications. Benzonitrile (9.0 mL) was added to a scintillation vial (20 mL) containing benzoic acid (2.69 g, 22 mmol) and DMTP (56.0 mg, 0.28 mmol). The reaction vial was placed in a metal block and heated to 100 C. to fully dissolve the solids. Aniline (43 mg, 0.46 mmol) and TAPB (67.0 mg, 0.19 mmol) were separately dissolved in benzonitrile (1.0 mL and 2.0 mL, respectively), preheated to 100 C., and sequentially added to the reaction vial, with aniline modulator first, followed by the TAPB linker. The reaction was undisturbed for 10 min, maintaining the temperature at 100 C., followed by cooling to room temperature over the next 10 min. The solution was diluted with methanol, and the yellow precipitate was isolated by filtration, washed with copious amounts of methanol and acetone, and dried at 120 C. under reduced pressure (100 mTorr) for 24 hours, affording the product as a bright yellow powder (77 mg, 75% yield).
Synthesis of Ugi-COF
[0322] In a 1-dram glass vial, the imine-COF (50 mg, 0.042 mmol, MW=1177.38 g/mol) was thoroughly mixed with mono-methyl succinate (101 mg, 0.76 mmol, 3 equiv6 imine bonds per unit cell), followed by the addition of methanol (0.21 mL) and ethyl isocyanoacetate (86 mg, 0.76 mmol, 3 equiv6 imine bonds per unit cell). Hence, the concentration of the acid and the isocyanide components was kept at 2.0 M each. The reaction was sealed with a Teflon cap and heated to 40 C. in a metal block for 12 hours without stirring. The progress of the reaction was monitored using the conjugated color-responsive structure of the COF: upon the initial addition of the acid, the material turned dark red (imine protonation), followed by a gradual change to light orange or yellow color (Ugi adduct formation), which indicated the reaction competition. The product was isolated by filtration, washed with methanol and diethyl ether, and dried at 120 C. under reduced pressure (100 mTorr) for 24 hours, affording Ugi-COF as an orange-yellow powder (99 mg, 88% yield).
Synthesis of Ugi-COFNH.SUB.2
[0323] In a 1-dram glass vial, the Ugi-COF (99 mg, 0.037 mmol, MW=2648.76 g/mol) was suspended in tris(2-aminoethyl)amine (0.5 mL, 3.57 mmol, 16 equiv6 Ugi adducts per unit cell), sealed with a Teflon cap and heated to 60 C. in a metal block for 12 hours without stirring. The product was isolated by filtration, washed with methanol and diethyl ether, and dried at 120 C. under reduced pressure (100 mTorr) for 24 hours, affording Ugi-COFNH.sub.2 as a light coral powder (132 mg, 90% yield).
Synthesis of Ugi-COF-DGA
[0324] In a 1-dram glass vial, the Ugi-COFNH.sub.2 (132 mg, 0.034 mmol, MW=3934.95 g/mol) was thoroughly mixed with diglycolic anhydride (0.473 mg, 4.08 mmol, 4 equiv4 amine groups per Ugi adduct x 6 Ugi adducts per unit cell), sealed with a Teflon cap and heated to 100 C. in a metal block for 12 hours without stirring. The unreacted diglycolic anhydride was extracted thrice with hot tetrahydrofuran, and the product was isolated by filtration, washed with tetrahydrofuran, and dried at 120 C. under reduced pressure (100 mTorr) for 24 hours, affording Ugi-COF-DGA as a beige-brown powder (132 mg, 90% yield). Assuming quantitative functionalization at each step, the molecular weight of as-synthesized Ugi-COF-DGA was calculated to be 6630.47 g/mol. Hence, the effective loading of the diglycolic acid was determined at 3.62 mmol/g (1 g6630.47 g/mol4 DGA groups per Ugi adduct6 Ugi adducts per unit cell1000 mmol/1 mol).
Example 6Adsorption Experiments and Characterization
Ree Batch Adsorption Experiments
[0325] 10 mg of the dried COF materials were precisely weighed and added in a 50 mL centrifuge tube. The COFs were then mixed with 50 ppm (50 mL) Nd(NO.sub.3).sub.3 solution at a pH=6.20.3 and sonicated for 1 min. The mixture was then stirred at 500 rpm for 20 hours at 25 C. After that, the COFs were separated by centrifugation, and the supernatant was diluted using 2% HNO.sub.3 and analyzed by ICP-OES to obtain the adsorption capacity (q.sub.e) of the materials.
Here, C.sub.0=initial Nd concentration, C.sub.e=equilibrium concentration, V=total volume of the solution, m=mass of COF adsorbent.
[0326] Each experiment was done in triplicates to obtain the average q.sub.e value and the associated standard deviation. Unless stated otherwise, similar parameters were used for all studies. For the Ugi-COF-DGA, the following additional adsorption studies were conducted: pH-dependent Nd adsorption, Nd adsorption kinetics, and concentration dependent Nd adsorption.
Ph-Dependent Nd Adsorption
[0327] Using similar conditions, the pH of the systems was adjusted from ca. 3.7 to ca. 6.2 by the addition of 0.1 M HNO.sub.3 or 0.1 M NaOH solution, and the q.sub.e was measured to obtain a pH-dependent adsorption trend for the Ugi-COF-DGA. With the increase in the pH, the q.sub.e increased for the material.
Nd Adsorption Kinetics
[0328] The contact time (contact time=sonication+stirring+centrifugation time) of the Ugi-COF-DGA with the Nd(NO.sub.3).sub.3 solution was adjusted from 4 to 130 min to obtain the time-dependent adsorption trend. The material seemed to reach an adsorption equilibrium within ca. 70 min of contact time.
Concentration Dependent Nd Adsorption
[0329] Keeping all other conditions the same, the initial Nd concentration was varied from 50 to 1000 ppm to obtain the concentration-dependent adsorption trend and the maximum adsorption capacity (q.sub.max) for the Ugi-COF-DGA. For these experiments, apart from analyzing the supernatant, the COF adsorbent was also analyzed to obtain accurate q.sub.e values for a higher concentration regime. After the separation of COF by centrifugation, the material was dried under vacuum (0.05 mBar). The dried material was precisely weighed and stirred with 2.0 M HNO.sub.3 for 20 hours to desorb the adsorbed Nd. This solution was then analyzed by ICP-OES to obtain the concentration-dependent q.sub.evalues.
Nd Concentration Dependent Zeta Potential Measurements
[0330] In a 15 mL centrifuge tube, ca. 2 mg of Ugi-COF-DGA was mixed with 5 mL of Nd(NO.sub.3).sub.3 solutions of different concentrations from 0 to 200 ppm. The pH was adjusted at 6.20.3 by the addition of 0.1 M NaOH, and the mixture was sonicated for 1 min. Thereafter, the zeta potential was measured for each of the samples in triplicates to obtain the average zeta potential value for specific Nd concentrations.
Accessible Surface Area from Adsorption Experiments
[0331] The accessible surface area of the Ugi-COF-DGA material to the Nd ions in an aqueous solution was estimated. First, the mass of the Nd atoms adsorbed by the Ugi-COF-DGA was converted to mol of Nd:
Next, given the radius of the hydrated Nd(III) ion (249 pm or 24910.sup.12 m (Rudolph et al., On the Hydration of the Rare Earth Ions in Aqueous Solution, Journal of Solution Chemistry 49:316-331 (2020), which is hereby incorporated by reference in its entirety)), the area covered by each Nd atom was calculated as follows:
Then, the total area occupied by 0.00459 mol Nd atoms was calculated according to the formula below:
Therefore, the estimated accessible surface area of the Ugi-COF-DGA to Nd atoms was 2154 m.sup.2/g, which was in the same order of magnitude as the surface area of 2383 m.sup.2/g for the pristine imine-COF. Some loss in the accessible surface area can be attributed to the newly installed functionality of the DGA groups and/or waters of hydration surrounding the Nd ions during adsorption.
Fitting of Nd Adsorption Isotherm Data
[0332] The experimental Nd isotherm data was fitted to the linear form of the Langmuir adsorption model using the following equation:
where C.sub.e=equilibrium adsorption concentration, q.sub.e=corresponding adsorption capacity at that specific C.sub.e value, q.sub.max=maximum adsorption capacity of the material, k.sub.L=Langmuir constant. Upon fitting the experimental isotherm data to the Langmuir model, a good fit (R.sup.2=0.988) was obtained, and the predicted q.sub.max value from the fitting was 667 mg/g, which is within the range of the experimentally obtained maximum adsorption capacity of 66329 mg/g.
Ugi-COF-DGA Recyclability Studies
[0333] Ugi-COF-DGA (10 mg) was precisely weighed and added in a 50 mL centrifuge tube. The COFs were then stirred at 500 rpm in 50 mL of 50 ppm solution of Nd(NO.sub.3).sub.3 at a pH=6.20.3 for 20 hours at 25 C. After that, the COFs were separated by centrifugation, and the supernatant was diluted using 2% HNO.sub.3 and analyzed by ICP-OES to obtain the adsorption capacity (q.sub.e) of the materials. After the separation of COF by centrifugation, the material was dried under vacuum (0.05 mBar) at 25 C. The dried material was precisely weighed and stirred with 2.0 M HNO.sub.3 for 20 hours at 25 C. to desorb Nd. This solution was then analyzed by ICP-OES to obtain the desorption capacity of the material. After the desorption treatment, the material was washed with DI H.sub.2O twice and dried under vacuum (0.05 mBar) at 25 C. overnight (ca. 16 hours). The dried COF was then utilized for the next consecutive adsorption-desorption cycles, and similar treatments were done after each adsorption or desorption experiment. Each experiment was done at least in triplicates to obtain the average q.sub.e and the associated standard deviation for each cycle. Any adsorbent mass loss during recycling was addressed by adjusting the
ratio of the system.
Fitting of Nd Adsorption Kinetics Data
[0334] The experimental Nd adsorption kinetics data was fitted to the linear form of the standard pseudo-first-order and pseudo-second-order models. More details on the models are provided below:
where q.sub.eq=adsorption capacity (q.sub.e) at the equilibrium, q.sub.e=adsorption capacity at a specific time point, k.sub.1=pseudo-first-order rate constant, k.sub.2=pseudo-second-order rate constant, and t=contact time. Upon fitting the data to both of these standard kinetics models, a better fit was obtained for the pseudo-2.sup.nd order model (R.sup.2=0.989) over the pseudo-1.sup.st order model (R.sup.2=0.966).
Time-Dependent Nd Desorption Studies
[0335] NdUgi-COF-DGA samples were prepared by soaking Ugi-COF-DGA in 50 mL of 50 ppm solution of Nd(NO.sub.3).sub.3 at pH=6.20.3 for 2 hours while stirring at 500 rpm at 25 C. The material was separated by centrifugation, and the supernatant was quantified by ICP-OES. The average Nd adsorption capacity for this material was 204 mg/g. The Nd
Ugi-COF-DGA was then dried overnight under vacuum (0.05 mBar), suspended in 10 mL 2.0 M HNO.sub.3 solution, and stirred at 500 rpm at 25 C. for different amounts of time (7 min to 240 min). Aliquots of 100 L were taken out at each of the time points for quantification by ICP-OES to determine the desorption capacity of the material. Triplicate runs were done for each time point to determine the average desorption capacity and the standard deviation.
Example 7Nd-Dy Binary Mixture Adsorption by Ugi-COF-DGA
[0336] Nd and Dy are both critical materials with significant real-world applications. Recycled electronics and permanent magnet feeds can serve as potential cheap sources for Nd/Dy mixtures along with natural sources of these REEs. However, separating them can be challenging due to their similar physico-chemical properties. Therefore, the novel Ugi-COF-DGA materials were utilized to target this mixture in order to observe selective REE capture.
[0337] In a 50 mL plastic centrifuge tube, Nd-Dy binary mixture solution (50+50 ppm) was added. The solution was acidified by adding 400 L of 0.1M HNO.sub.3. Then, 10 mg Ugi-COF-DGA and a magnetic stir bar were added to this mixture. The centrifuge tube was then sealed and sonicated for 2-3 minutes to finely suspend the COF. The mixture was stirred at 500 rpm for 2 hours at room temperature (25 C.). After 2 hours, the mixture was centrifuged, and the supernatant was analyzed using ICP-OES to obtain the adsorption capacities of Nd and Dy by the COF.
[0338] The procedure was repeated in triplicates to obtain the average adsorption capacities for Nd and Dy along with the standard deviations. The adsorption capacities of Nd and Dy were 9.91.6 mg/g and 57.43.3 mg/g, respectively (
Example 8Results and Discussion for Examples 4-7
Design and Characterization of COFs
[0339] To incorporate the DGA motif for the first time in a COF, a chemically robust and highly crystalline COF (imine-COF) produced by the condensation of 1,3,5-tris(4-aminophenyl)benzene with 2,5-dimethoxyterephthalaldehyde via the single-crystalline synthetic protocol was selected (Natraj et al., Single-Crystalline Imine-Linked Two-Dimensional Covalent Organic Frameworks Separate Benzene and Cyclohexane Efficiently, J. Am. Chem. Soc., 144(43):19813-19824 (2022), which is hereby incorporated by reference in its entirety). To obtain the best material for REE adsorption, a series of post-synthetically modified COFs were rationally designed and tested, ultimately leading to the production of the Ugi-COF-DGA (
[0340] The successful synthetic transformation at each step was confirmed by Fourier-transform infrared (FTIR) spectroscopy and .sup.13C cross-polarization magic angle spinning (CPMAS) solid-state nuclear magnetic resonance (SSNMR) spectroscopy. For the Ugi-COF, the FTIR spectrum revealed new amide frequencies at 1671 cm.sup.1 (CO) and 3407 cm.sup.1 (NH), as well as the ester frequency at 1743 cm.sup.1 (CO) (
[0341] The FTIR spectrum of the Ugi-COFNH.sub.2 displayed an intense amide frequency at 1670 cm.sup.1 (CO), as well as a full disappearance of the ester frequency (CO) (
[0342] In the case of the Ugi-COF-DGA, further amplification of the amide frequency at 1692 cm.sup.1 (CO) was observed, as well as significant attenuation of the aliphatic amine frequency (NH). A new frequency appeared at 1745 cm.sup.1 (CO), corresponding to the DGA carboxylic acid functional group (
[0343] A complete loss of porosity of the Ugi-COFs in dry form was observed after the initial Ugi reaction on the imine-COF. In particular, the Brunauer-Emmett-Teller (BET) surface area of 2383 m.sup.2/g was recorded for the imine-COF, while only 3 m.sup.2/g was measured for the Ugi-COF and the Ugi-COFNH.sub.2, and 2 m.sup.2/g for the Ugi-COF-DGA (
REE Adsorption Studies of COFs
[0344] The performance of the COF materials for the REE adsorption was evaluated by mixing 10 mg of the adsorbent in 50 mL of 50 ppm solution of neodymium(III) nitrate (Nd(NO.sub.3).sub.3) at a pH of ca. 6.4 with stirring at 25 C. for 20 hours. A preliminary assessment of the imine-COF revealed a minimal Nd adsorption capacity (q.sub.e) of ca. 5 mg of Nd per gram of COF (mg/g) despite the high porosity and crystallinity of the material (
[0345] Favorable ionic interactions between negatively charged carboxylates of the DGA moiety and positively charged metal ions should bolster the adsorption capacity of the Ugi-COF-DGA. To verify this hypothesis, a pH-dependent Nd adsorption study was conducted for the Ugi-COF-DGA material (
[0346] One of the critical properties distinguishing a promising adsorbent for REE capture is the material's ability to amplify the uptake of metal ions in a more concentrated solution of REEs. To evaluate the q.sub.e response of the Ugi-COF-DGA to higher REE concentrations, an isotherm plot was generated using Nd solutions of 50 mL with initial concentrations ranging from 50 to 2000 ppm, while keeping the amount of adsorbent constant at 10 mg. Ugi-COF-DGA demonstrated an increase in the q.sub.e value with a higher concentration of the Nd ions, varying from ca. 205 mg/g for the 50 ppm solution to 66329 mg/g for the 2000 ppm solution (
[0347] Consistently high performance and chemical stability of the material over multiple adsorption/desorption cycles are important factors for sustainable REE recovery. Hence, the recyclability of the Ugi-COF-DGA was evaluated over five adsorption/desorption cycles, and each data point was repeated thrice. Adsorption experiments were performed using 10 mg of the Ugi-COF-DGA in 50 mL of 50 ppm solution of Nd. After adsorption, Nd-loaded Ugi-COF-DGA (NdUgi-COF-DGA) was isolated by filtration and suspended in 10 mL of 2.0 M nitric acid (HNO.sub.3) at 25 C. for 20 hours with stirring, to ensure equilibrium was reached. Under these conditions, there was a near complete release of the adsorbed Nd (
TABLE-US-00001 TABLE 1 Solid Adsorbents of Neodymium
[0348] Fast adsorption kinetics is another attractive feature of a solid adsorbent for practical applications. Adsorption kinetics of the Ugi-COF-DGA were assessed by varying the contact time of 10 mg of COF material with 50 mL of 50 ppm solution of Nd. Ugi-COF-DGA reached its equilibrium q.sub.e value within 70 minutes of contact time (Ugi-COF-DGA were thoroughly washed with deionized water to remove excess REEs, dried in vacuo, and subjected to time-dependent desorption studies in 2.0 M HNO.sub.3. The release of the REE ions by Nd
Ugi-COF-DGA was almost immediate (
[0349] To assess the effect of the COF architecture as a solid support for the DGA ligand, the highest q.sub.e value of the Ugi-COF-DGA was compared with the maximum adsorption capacities reported for other DGA-functionalized solid materials (Florek et al., Selective Recovery of Rare Earth Elements Using Chelating Ligands Grafted on Mesoporous Surfaces, RSC Adv., 5(126):103782-103789 (2015), Pereao et al., Adsorption of Ce.sup.3+ and Nd.sup.3+ by Diglycolic Acid Functionalised Electrospun Polystyrene Nanofiber from Aqueous Solution, Sep. Purif Technol., 233:116059 (2020); Arrambide et al., Extraction and Recovery of Rare Earths by Chelating Phenolic Copolymers Bearing Diglycolamic Acid or Diglycolamide Moieties, React. Funct. Polym., 142:147-158 (2019); Pereao et al., Synthesis and Characterisation of Diglycolic Acid Functionalised Polyethylene Terephthalate Nanofibers for Rare Earth Elements Recovery, J. Environ. Chem. Eng., 9(5):105902 (2021); Li et al., Selective Extraction and Column Separation for 16 Kinds of Rare Earth Element Ions by Using N, N-dioctyl Diglycolacid Grafted Silica Gel Particles as the Stationary Phase, J. Chromatogr. A, 1627:461393 (2020); Bai et al., Preparation of Elastic Diglycolamic-Acid Modified Chitosan Sponges and Their Application to Recycling of Rare-Earth from Waste Phosphor Powder, Carbohydr. Polym., 190:255-261 (2018); Hamada et al., Poly(vinyl diglycolic acid ester)-Grafted Polyethylene/Polypropylene Fiber Adsorbent for Selective Recovery of Samarium, ACS Appl. Polym. Mater., 4(3):1846-1854 (2022); Momen et al., Extraction Chromatographic Materials for Clean Hydrometallurgical Separation of Rare-Earth Elements Using Diglycolamide Extractants, Ind. Eng. Chem. Res., 58(43):20081-20089 (2019); Ogata et al., Immobilization of Diglycol Amic Acid on Silica Gel for Selective Recovery of Rare Earth Elements, Chem. Lett., 43(9):1414-1416 (2014); Wang et al., Preparation of Pyrrolidinyl Diglycolamide Bonded Silica Particles and its Rare Earth Separation Properties, J. Chromatogr. A, 1681:46339 (2022), which are hereby incorporated by reference in their entirety). The newly developed Ugi-COF-DGA offers the highest adsorption capacity, the q.sub.c value four times higher than the next best-reported DGA-modified supports (
[0350] To verify the presence of Nd on the solid adsorbent, the Ndgi-COF-DGA sample was recovered from the 1000 ppm Nd adsorption experiment, washed thoroughly with deionized water to remove excess REEs, dried in vacuo, and characterized. The FTIR spectrum of the Nd
Ugi-COF-DGA exhibited apparent shifts of the carboxylic acid and amide carbonyl stretches to a lower frequency at 1500 cm.sup.1, suggesting the weakening of the CO bonds due to coordination to Nd (
Ugi-COF-DGA showed the presence of the Nd peak at 122 eV, which appeared at a lower binding energy than the Nd(NO.sub.3).sub.3 salt peak at 123 eV (
Ugi-COF-DGA revealed a homogeneous distribution of the N and Nd atoms in the sample without apparent clustering of the metal ions, suggesting their successful adsorption by the COF material rather than precipitation from the solution (
[0351] In conclusion, it was demonstrated that the Ugi PSM strategy could be used to transform an imine-based COF into a readily customizable platform for efficient and recyclable adsorption of REEs. The novel Ugi-COF-DGA displayed the highest adsorption capacity among other DGA-functionalized solid supports, can be recycled at least five times without compromising the performance of the material, and had fast adsorption and desorption kinetics. Future studies will be focused on optimizing the Ugi-COFs reticular and molecular design to achieve selective REE capture and integrating these materials into devices for capture or separation of REE ions from solution. This work could serve as a general strategy for the expansion of the functional diversity in imine-based COFs and inspire further exploration of these materials as promising adsorbents for efficient and recyclable capture of the REEs.
[0352] Although preferred embodiments have been depicted and described in detail herein, it will be apparent to those skilled in the relevant art that various modifications, additions, substitutions, and the like can be made without departing from the spirit of the invention and these are therefore considered to be within the scope of the invention as defined in the claims which follow.