京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第21797号 / 工博第4614号 / 新制||工||1719(附属図書館) / 京都大学大学院工学研究科合成・生物化学専攻 / (主査)教授 杉野目 道紀, 教授 松田 建児, 教授 大内 誠 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

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Five systems consisting of different sorbate-sorbent combinations were studied using experimental volumetric adsorption techniques. Multiple adsorption isotherms were measured at low temperatures and low pressures for all of the systems studied which included CO2 adsorption on single walled carbon nanotubes (CO2 – SWCNT), Ethane adsorption on closed carbon nanohorns (Ethane-cNH), Ar adsorption on open carbon nanohorns (Ar – oNH), CO2 adsorption on zeolitic imidazolate framework-8 (CO2 – ZIF-8), and O2 adsorption on ZIF-8 (O2 – ZIF-8). Each of these systems offers a unique study of the relationship between the physical properties of the adsorbate and substrate and the effects of these properties on the thermodynamics and kinetics of adsorption. In addition to being of fundamental interest, the thermodynamics and kinetics of adsorption are important to understand for practical considerations in research fields such as gas storage and gas separation via adsorption processes, among other applications. CO2 – SWCNT is a system with a small linear molecular adsorbate with a permanent quadrupole moment adsorbing on a substrate with quasi-1D grooves and convex outer adsorption sites. Ethane-cNH is a system with a linear alkane adsorbing on a substrate with conical pores and convex outer adsorption sites. Ar – oNH is a system with a spherical atom sorbing in a substrate with two different groups of conical adsorption sites and both convex and concave surface sites. CO2 – ZIF-8 and O2 – ZIF-8 are both systems with small linear molecules sorbing in a flexible microporous scaffold-like substrate. Adsorption isotherms were analyzed to identify features corresponding to adsorbate-adsorbate and adsorbate-substrate interactions. Namely, the presence of substeps in the semi-logarithmic data were identified and interpreted to correspond to groups of adsorption sites of similar binding energy which likely depend on the morphology and/or structural flexibility of the substrates. All of the systems, with the exception of CO2 - SWCNTs, yielded at least some isotherms with substeps at pressures below that corresponding to saturation. Effective specific surface areas for all adsorbent-substrate combinations were calculated using the BET and Point-B methods for the sake of comparison. These surface area measurements are very dependent on the porosity and morphology of the substrate as well as the size and shape of the adsorbate atoms/molecules and therefore the values vary greatly between the different systems. The isosteric heat of adsorption was calculated using isotherms over the full range of temperatures for each system. A variant of the Clausius-Clapeyron equation was used for this purpose and the results were analyzed based on adsorbate-adsorbate and adsorbate-substrate interactions. Plateaus in the isosteric heat data for Ethane – cNH and Ar – oNH were related to the morphology of the substrates and properties of the adsorbate species. For CO2 – SWCNTs, the isosteric heat at all but the lowest coverages is below the latent heat of deposition. This is due to the quadrupole moment of CO2. For both of the studies of adsorption on ZIF-8, the isosteric heat contains peaks in the data which likely are the result of the flexibility of the ZIF-8 structure. The kinetics of adsorption (or, the rates at which the adsorption systems approach equilibrium) were analyzed as functions of isotherm temperature and coverage, vapor pressure, and fractional uptake point by point along individual isotherms using the linear driving force model. Certain trends in the kinetics of adsorption are consistent for all the systems studied and others vary depending on the specific adsorbate-substrate combination. As with the thermodynamic results, trends in the kinetics of adsorption are discussed in terms of the effects of adsorbate-adsorbate and adsorbate-substrate interactions.

This thesis documents efforts to synthesize Metal-Organic Frameworks (MOFs) and study their charge transport, electrocatalytic, and photoredox catalytic properties. Chapter 1 introduces concepts of pre-synthetic and post-synthetic metalation of MOFs. A series of four chemically identical but structurally different hydrolytically robust ZrIV-MOFs constructed from tetrakis(4-carboxyphenyl) porphyrinato iron (III) are examined to understand the influence of topological construction on redox hopping conductivity. The structural variation fixes center-to-center distances in the four MOFs and defines the hopping rate. The spin-state variation of the central metal in the porphyrin unit helps in further tuning the TCPP(FeIII/II) reorganization energy of the self-exchange process. The hopping rate significantly increased upon axial coordination of 1-methyl imidazole to the iron center, which converts a weakly halide bound five-coordinated high-spin (HS) TCPP(FeIII/II) to the six-coordinated low-spin (LS) complex. The population of LS vs HS species is shown to be a function of topology in the presence of an excess ligand. Chapter 2 investigates this idea further by using MOFs for electrocatalytic oxygen reduction reaction (ORR). Two cobalt-centered porphyrin-based MOFs are synthesized and deposited on various substrates to afford working electrodes that can be used in an electrochemical cell to catalyze the ORR. Chapter 3 investigates the linker-dependent photoredox catalytic activity of MOFs that possess the same topology. This is the first MOF-based study wherein a heavy metal like ruthenium is not employed to carry out the visible light-dependent photoredox catalysis.

Surface phenomena are an integral part of everyday life -- whether in the appearance of bubbles in the sink after washing one's hands or in the design of water-repellent clothing. Surface phenomena also find application in industrial processes, such as catalysis, fluid purification, or separation. For industrial application, materials with huge surface-to-volume ratios are preferred. Solids with pores in the nanometer range (i.e. nanoporous solids) are such materials, and of these, metal-organic frameworks are the most versatile class. Metal-organic frameworks have already received a high level of attention. The modular structure -- MOFs consist of inorganic nodal building blocks that are connected by organic linking building blocks -- allows almost continuous adjustment of pore size, shape, and environment. However, many aspects of surface phenomena in or on metal-organic frameworks are not yet fully understood. For example, it is known that entropy favors the accumulation of smaller guest molecules in nanoporous solids at high loading. But does entropy also favor the accumulation of water in metal-organic frameworks with internal hydrophobicity? Speaking of which, how is the hydrophobicity of the internal and external surface of metal-organic frameworks related? And how can modern visualization techniques, such as virtual reality, help in studying metal-organic frameworks and the guest molecules within them? This thesis aims to shed light on these questions using classical molecular simulations. Molecular simulations are a helpful tool for studying surface phenomena, because they can complement experiments by providing insights at the microscopic level, and offer the possibility of exploring surface phenomena that can only rarely be investigated in experiments, plus help to improve the efficiency of experiments by predicting metal-organic frameworks with desired properties.

Metal Organic Frameworks (MOFs) are a class of porous materials that are predominantly obtained as powders and have been investigated as a solid sorbent for gas separation or carbon capture applications from combustion exhaust gases. The manufacturing of products with MOFs to use them for real life applications is still a major problem. The most common productization method used is to form pellets of the powder MOFs. This has a limitation on the product shape which makes it difficult for it to be used in gas separation applications. This study focuses on using additive manufacturing technique to give MOFs a lattice (mesh-like) geometry which is useful for gas separation applications as the mixture of gases would be able to pass through the lattice structure and be separated due to the inherent MOF properties and characteristics. Two MOFs based on magnesium and manganese salts have been studied in this project. An extrudable paste developed using alginate gel as a binder with these MOFs. With alterations in paste formulations and 3D printer parameters, lattice structures were printed using the two MOFs. CO2 and N2 gas uptakes were measured showing that the structure adsorbs CO2 gas to a higher extend which results in the separation of N2 gas in both materials. When compared to their pristine powder form, other properties of the MOFs such as crystallinity, microstructure, reusability and surface area remain to be preserved after being 3D printed in both cases.

The primary focus of this research is to utilize cellular and polymeric membranes for biomedical applications: To date, several organic and inorganic materials have been used to synthesize nanoparticles (NPs). The question arises as to which criteria and design principles should be considered while selecting the best material. Based on the results of testing, three key roles of NPs have been identified. First, NPs need enough circulation time to reach their target. Then these NPs must be able to target diseased tissue while leaving healthy tissue unaffected. Finally, NPs must be biodegradable and easily eliminated from the body. Biomimetic nanoparticles based on cell membranes have been developed as an efficient way to fulfill the needs of drug delivery goals and achieve targeted delivery by actively interacting and communicating with the biological environment. In the first project, genome editing machinery was delivered to particular cells using biomimetic cancer cell coated zeolitic imidazolate frameworks. MCF-7 cells demonstrated the highest uptake of C3-ZIFMCF compared to HeLa, HDFn, and aTC cells. In terms of genome editing, MCF-7 cells transfected with C3-ZIFMCF showed 3-fold EGFP repression compared to C3-ZIFHELA cells transfected with 1-fold EGFP repression. In vivo tests demonstrated C3-ZIFMCF's affinity for MCF-7 tumor cells. This demonstrates the biomimetic approach's ability to target cells specifically, which is definitely the most essential step in future genome editing technology translation. In the second project, multimodal therapeutic nanowires (NWs D-ZIF) MCF-7 cancer cells were developed. D-ZIF coated NWs had higher cellular uptake and photothermal treatment efficiency than non-coated NWs. (NWs D-ZIF) MCF accumulates in MCF-7 tumor cells and enhances photothermal capability. On the other hand, chiral separation of enantiomers is becoming more important, particularly in pharmaceuticals. Because enzyme activities and other biological processes are stereoselective, chiral drugs' enantiomers often have different metabolic effects, pharmacological activity, metabolic rates, and toxicities. In an attempt to address this issue, we decided in the final project to study the capability of chiral polyamide membrane for efficient and energy-free chiral separation. In particular, to separate essential amino acid critical to all living organisms (DL-tryptophan).

Anthropogenic emission of greenhouse gases has long been suspected to contribute to global warming and climate change. Most greenhouse gases are emitted in a mixture, so efficient methods and materials to separate and capture the gases are in demand in order to reduce emissions. A promising material group for this purpose is metal-organic frameworks (MOFs). This class of material have the ability to selectively adsorb green house gases due to its high porosity and high surface area. Zeolitic imidazolate frameworks (ZIFs) are a subclass of MOFs that are topologically similar to zeolites and are known for their good chemical and thermal stability.   The aim of this project was to investigate if the greenhouse gas (i.e. CO2 and SF6) capture performance of ZIFs could be improved and tuned using a mixed-linker approach with seven different imidazolate-based organic linkers of different sizes or with various functional groups. As well as to investigate the processability of MOFs using 3D printing. ZIFs composed of different ratios of 2-methylimidazolate as base linker and a second linker of imidazolate, benzimidazolate, 2-aminobenzimidazolate, 5,6-dimethylbenzimidazolate, and 4,5-dichloroimidazolate were succesfully made. The materials were all found to be crystalline, however, mixed-linker ZIFs containing 2-aminobenzimidazole, 5,6-dimethylbenzimidazole and dichloroimidazole were observed to contain more than a single phase. All samples showed to be somewhat porous towards CO2 and SF6, and there seem to be a trend where a low % of a bulkier linker (eg. bIm, ambIm) resulted in a higher uptake of SF6 whereas a high % resulted in a higher uptake of CO2. For dcIm it was the other way around, a low % showed a higher uptake for CO2  whereas a high % showed a higher uptake for SF6. For CO2, the ZIF containing 80% benzimidazolate showed the highest uptake of 9.81 wt%. For SF6, the 25% 4,5-dichloroimidazolate showed the highest uptake of 17.73 wt%. Furthermore, direct ink writing (DIW) 3D printing was also successfully utilized to process and structure a Mn-based MOF using carbopol as binder. The printed structure was found to have similar properties to the pristine MOF in regards to crystallinity and porosity.

The analysis of empirical sorption equilibrium datasets is still vital to gain insights into material–property relationships as computational methods remain in development, especially for complex materials such as flexible MOFs. Therefore, the Dubinin-based universal adsorption theory (D-UAT) was revisited and evaluated as a simple visualization, analysis, and prediction tool for sorption equilibrium data. Within the theory, gas properties are normalized into corresponding states using the critical temperatures of the respective sorptives. The study shows theoretically and experimentally that the D-UAT is able to condense differences of sorption data visualized in reduced Dubinin plots to just three governing parameters: (a) the accessible pore volume, (b) the reduced enthalpy of sorption, and (c) the framework’s reduced free energy differences (in case of flexible behavior). This makes the theory a fast visualization and analysis tool, the use as a prediction tool depends on rough assumptions, and thus is not recommended.