酸性配位高分子の合理的な設計、およびそのプロトン伝導性と選択的吸着特性

京都大学0048新制・課程博士博士(理学)甲第16653号理博第3765号新制||理||1545(附属図書館)29328京都大学大学院理学研究科化学専攻(主査)教授 北川 宏, 准教授 植田 浩明, 教授 矢持 秀起学位規則第4条第1項該当Doctor of ScienceKyoto UniversityDA

A significant change in selective adsorption behaviour for ethanol by flexibility control through the type of central metals in a metal-organic framework

Closed-open structural transformations in flexible metal-organic frameworks (MOFs) are of interest for potential applications such as separation, because of their complete selectivity for the adsorption of specific guest molecules. Here, we report the control of the adsorption behaviour in a series of flexible MOFs, (H2dab)[M2(ox)3] (H2dab = 1, 4-diammoniumbutane, M = Fe, Co, Ni, Zn, or Mg), having different central metals with analogous crystal structures. We found that a significant change in the selective adsorption behaviour for EtOH over MeCHO and MeCN is caused by the type of central metals, without changes in the crystal structures of all phases (except the Ni compound). A systematic study of adsorption measurements and structural analyses of the analogous MOFs reveals for the first time that the framework flexibility around the central metals of MOFs is truly related to the selective adsorption behaviour

Proton Conductivity Control by Ion Substitution in a Highly Proton-Conductive Metal–Organic Framework

Proton conductivity through two-dimensional (2-D) hydrogen-bonding networks within a layered metal–organic framework (MOF) (NH₄)₂(H₂adp)­[Zn₂(ox)₃]·3H₂O (H₂adp = adipic acid; ox = oxalate) has been successfully controlled by cation substitution. We synthesized a cation-substituted MOF, K₂(H₂adp)­[Zn₂(ox)₃]·3H₂O, where the ammonium ions in a well-defined hydrogen-bonding network are substituted with non-hydrogen-bonding potassium ions, without any apparent change in the crystal structure. We successfully controlled the proton conductivity by cleavage of the hydrogen bonds in a proton-conducting pathway, showing that the 2-D hydrogen-bonding networks in the MOF truly contribute to the high proton conductivity. This is the first example of the control of proton conductivity by ion substitution in a well-defined hydrogen-bonding network within a MOF

Support Effect of Metal-Organic Frameworks on Ethanol Production through Acetic Acid Hydrogenation

We present a systematic study on the support effect of metal-organic frameworks (MOFs), regarding substrate adsorption. A remarkable enhancement of both catalytic activity and selectivity for the ethanol (EtOH) production reaction through acetic acid (AcOH) hydrogenation (AH) was observed on Pt nanoparticles supported on MOFs. The systematic study on catalysis using homogeneously loaded Pt catalysts, in direct contact with seven different MOF supports (MIL-125-NH2, UiO-66-NH2, HKUST-1, MIL-101, Zn-MOF-74, Mg-MOF-74, and MIL-121) (abbreviated as Pt/MOFs), found that MOFs having a high affinity for the AcOH substrate (UiO-66-NH2 and MIL-125-NH2) showed high catalytic activity for AH. This is the first demonstration indicating that the adsorption ability of MOFs directly accelerates catalytic performance using the direct contact between the metal and the MOF. In addition, Pt/MIL-125-NH2 showed a remarkably high EtOH yield (31% at 200 degrees C) in a fixed-bed flow reactor, which was higher by a factor of more than 8 over that observed for Pt/TiO2, which was the best Pt-based catalyst for this reaction. Infrared spectroscopy and a theoretical study suggested that the MIL-125-NH2 support plays an important role in high EtOH selectivity by suppressing the formation of the byproduct, ethyl acetate (AcOEt), due to its relatively weak adsorption behavior for EtOH rather than AcOH

Promotion of Low-Humidity Proton Conduction by Controlling Hydrophilicity in Layered Metal–Organic Frameworks

We controlled the hydrophilicity of metal–organic frameworks (MOFs) to achieve high proton conductivity and high adsorption of water under low humidity conditions, by employing novel class of MOFs, {NR₃(CH₂COOH)}­[MCr­(ox)₃]·<i>n</i>H₂O (abbreviated as <b>R-MCr</b>, where R = Me (methyl), Et (ethyl), or Bu (<i>n</i>-butyl), and M = Mn or Fe): <b>Me-FeCr</b>, <b>Et-MnCr</b>, <b>Bu-MnCr</b>, and <b>Bu-FeCr</b>. The cationic components have a carboxyl group that functions as the proton carrier. The hydrophilicity of the cationic ions was tuned by the NR₃ residue to decrease with increasing bulkiness of the residue: {NMe₃(CH₂COOH)}⁺ > {NEt₃(CH₂COOH)}⁺ > {NBu₃(CH₂COOH)}⁺. The proton conduction of the MOFs increased with increasing hydrophilicity of the cationic ions. The most hydrophilic sample, <b>Me-FeCr</b>, adsorbed a large number of water molecules and showed a high proton conductivity of ∼10^–4 S cm^–1, even at a low humidity of 65% relative humidity (RH), at ambient temperature. Notably, this is the highest conductivity among the previously reported proton-conducting MOFs that operate under low RH conditions

Promotion of Low-Humidity Proton Conduction by Controlling Hydrophilicity in Layered Metal–Organic Frameworks

We controlled the hydrophilicity of metal–organic frameworks (MOFs) to achieve high proton conductivity and high adsorption of water under low humidity conditions, by employing novel class of MOFs, {NR₃(CH₂COOH)}­[MCr­(ox)₃]·<i>n</i>H₂O (abbreviated as <b>R-MCr</b>, where R = Me (methyl), Et (ethyl), or Bu (<i>n</i>-butyl), and M = Mn or Fe): <b>Me-FeCr</b>, <b>Et-MnCr</b>, <b>Bu-MnCr</b>, and <b>Bu-FeCr</b>. The cationic components have a carboxyl group that functions as the proton carrier. The hydrophilicity of the cationic ions was tuned by the NR₃ residue to decrease with increasing bulkiness of the residue: {NMe₃(CH₂COOH)}⁺ > {NEt₃(CH₂COOH)}⁺ > {NBu₃(CH₂COOH)}⁺. The proton conduction of the MOFs increased with increasing hydrophilicity of the cationic ions. The most hydrophilic sample, <b>Me-FeCr</b>, adsorbed a large number of water molecules and showed a high proton conductivity of ∼10^–4 S cm^–1, even at a low humidity of 65% relative humidity (RH), at ambient temperature. Notably, this is the highest conductivity among the previously reported proton-conducting MOFs that operate under low RH conditions

Proton-Conductive Magnetic Metal–Organic Frameworks, {NR₃(CH₂COOH)}[M_a^IIM_b^III(ox)₃]: Effect of Carboxyl Residue upon Proton Conduction

Proton-conductive magnetic metal–organic frameworks (MOFs), {NR₃(CH₂COOH)}­[M_a^IIM_b^III(ox)₃] (abbreviated as <b>R–M</b>_<b>a</b><b>M</b>_<b>b</b>: R = ethyl (Et), <i>n</i>-butyl (Bu); M_aM_b = MnCr, FeCr, FeFe) have been studied. The following six MOFs were prepared: <b>Et–MnCr</b>·2H₂O, <b>Et–FeCr</b>·2H₂O, <b>Et–FeFe</b>·2H₂O, <b>Bu–MnCr</b>, <b>Bu–FeCr</b>, and <b>Bu–FeFe</b>. The structure of <b>Bu–MnCr</b> was determined by X-ray crystallography. Crystal data: trigonal, <i>R</i>3<i>c</i> (#161), <i>a</i> = 9.3928(13) Å, <i>c</i> = 51.0080(13) Å, <i>Z</i> = 6. The crystal consists of oxalate-bridged bimetallic layers interleaved by {NBu₃(CH₂COOH)}⁺ ions. <b>Et–MnCr</b>·2H₂O and <b>Bu–MnCr</b> (R–MnCr MOFs) show a ferromagnetic ordering with <i>T</i>_C of 5.5–5.9 K, and <b>Et–FeCr</b>·2H₂O and <b>Bu–FeCr</b> (R–FeCr MOFs) also show a ferromagnetic ordering with <i>T</i>_C of 11.0–11.5 K. <b>Et–FeFe</b>·2H₂O and <b>Bu–FeFe</b> (R–FeFe MOFs) belong to the class II of mixed-valence compounds and show the magnetism characteristic of Néel N-type ferrimagnets. The Et-MOFs (<b>Et–MnCr</b>·2H₂O, <b>Et–FeCr</b>·2H₂O and <b>Et–FeFe</b>·2H₂O) show high proton conduction, whereas the Bu–MOFs (<b>Bu–MnCr</b>, <b>Bu–FeCr</b>, and <b>Bu–FeFe</b>) show moderate proton conduction. Together with water adsorption isotherm studies, the significance of the carboxyl residues as proton carriers is revealed. The R–MnCr MOFs and the R–FeCr MOFs are rare examples of coexistent ferromagnetism and proton conduction, and the R–FeFe MOFs are the first examples of coexistent Néel N-type ferrimagnetism and proton conduction