Solar energy is a sustainable resource which has substantial potential to meet the increasing demand for renewable energy. Though there has been some success in harvesting solar energy for electricity production, converting solar energy to chemical energy as fuels is still a challenge due to low efficiency. Since the discovery of TiO2 photocatalysts for splitting water (4) and reducing CO2 (5) to form useful chemical feedstock such as H2, CO and CH4, much research has been done to increase the efficiency of photocatalysts. However, the current conversion efficiency of photocatalysts remains low (~5%) (6, 7). Issues being addressed include the wide bandgap and mismatched band edge for reactions (thermodynamic energy for reaction), poor quantum efficiency of the photon collector systems, high recombination of e-/h+ pairs and limitation in the rate of charge transfer from photocatalyst to reactants. This work focuses on improving efficiency of photocatalysts for fuel production through several approaches: (1) engineering a metal-organic-framework (MOF) to have proper band gaps and band edges for targeted reactions and for enhancing photoadsorption in the visible light range, (2) tuning an ABO3-type perovskite for desired bandgaps and thermodynamically favored bandedges for CO2 reduction with water in visible light range. A porphyrin-based Ti-MOF is studied for CO2 photoreduction to gaseous chemical fuels such as CH4 and CO. The porphyrin linkers allow porphyrin-based MOF-525 to achieve narrow bandgap (Eg = ~1.7eV) to absorb visible light, indicating its ability to harvest more solar energy than conventional TiO2. Ti/Zr-MOF-525 also exhibited the appropriate energy level alignment for CO2 and H2O redox reaction for CO and CH4 production. Its CO2 photoreactivity under visible light was demonstrated in a photoreaction, illuminated by 150W Xenon solar simulator. Interestingly, Ti/Zr-MOF-525 demonstrates a selectivity toward CH4, a more valuable fuels than CO. The gas phase reaction condition is an advance over liquid photoreaction. The catalyst stability was also studied and presented. After 3 cycles of reactions, Ti/Zr-MOF-525 is relatively stable for CO2 photoreduction and able to maintain its photoreactivity at about 60-65% of fresh catalyst. The reduction of reactivity is due to a less stable fresh catalyst. When investigating LaCr1-xFexO3 perovskite oxides for photocatalyst, it was found that when replacing Cr ions at the B sites of LaCrO3 by Fe ions, the bandgap does not follow a linear trend in regards to metal ratio composition but rather reflects the smaller bandgap of LaFeO3. Bandedges were successfully measured for the new synthesized materials. At x = 0.25, the conduction band potential remains similar with x = 0. However, at x = 0.75, the conduction band potential was more negative than either perovskites at x = 0 or x = 1. Future simulation of density of state could address this interesting observation. CO2 reduction relativities of each perovskites were predicted well by their measured bandgaps and bandedges. Among five studied perovskites, synthesized LaCr0.25Fe0.75O3 (x = 0.75) is the most active for CO2 photoreduction under visible illumination at room temperature thanks to its small bandgap (2.0 eV) and its suitable bandedges for CO2 photoreduction.

Reducing anthropogenic carbon dioxide emissions from coal-fired power plants is an important step in mitigating climate change. To implement carbon dioxide capture technologies, materials capable of removing carbon dioxide efficiently are required. Currently, liquid amine technology is used for carbon dioxide capture. However, the mechanism for carbon dioxide removal in liquid amine requires extraordinary amounts of energy input. Alternatively, solid sorbents such as metal-organic frameworks (MOFs) show promising potentials as a type of material for carbon dioxide capture. Due their varying structural properties, MOFs can be configured for specific purposes. Certain MOFs carry a net charge on their frameworks, which may allow for increased interactions with carbon dioxide molecules. In this work, charged MOFs were studied for their potential in carbon dioxide capture. Due to the massive number of MOFs available, computational methods were employed for the study. This project includes three major components: (1) the development of novel computational methods to simulate the gas adsorption properties in charged materials, (2) a diverse database of 47,244 hypothetical charged MOFs was constructed to represent the capabilities of charged MOFs, and (3) screening of high performing charged MOFs for carbon capture application by combining the previous two portions of the project. The methods developed in this work include fitting intermolecular interaction parameters to quantum mechanical calculations in periodic systems with net charges. No methods have been reported in literature for such parameter fittings, even in well studied materials such as zeolites. Therefore, the gas adsorption estimation method for charged materials developed in this work is proprietary. Also, databases of hypothetical MOFs with framework net charges have never been reported previously in literature. By screening the charged MOFs in the database with the methods developed, gas adsorption capabilities were evaluated. The adsorption properties of a neutral group of hypothetical MOFs were also obtained for a baseline comparison. Between the two groups of MOFs, charged MOFs were found to outperform neutral MOFs in three key aspects. Firstly, charged MOFs were able to adsorb an average of three times as much carbon dioxide than the neutral group. Secondly, charged MOFs were capable of removing twice the amount of carbon dioxide per adsorption/desorption cycle than the neutral MOFs. Lastly, charged MOFs were able to selectively adsorb much more carbon dioxide over other gasses present in the carbon dioxide capture situations. Specific structural features that resulted in the selectiveness of adsorption in charged MOFs were identified. Also, positive correlations were found between the adsorption of carbon dioxide and the charge present in the MOFs. As seen in the results, charges present in MOFs can greatly increase their ability to remove carbon dioxide. Charged MOFs in the hypothetical database not only outperformed neutral MOFs, certain top performers were also found to exceed the requirements for post-combustion carbon capture application. Therefore, charged MOFs were shown to be a possible material for future carbon dioxide capture. The proprietary methods developed in this work can not only be used to simulate gas adsorptions in charged MOFs, but also for other porous materials, regardless of net charges presented in their systems. Also, the database constructed in this work can be utilized in multiple ways. Aside from carbon dioxide capture capabilities, the charged MOFs in the database can be screened for other gas separations and catalysis via high throughput screening. The database and the computational methods developed in this work pave the way for discovering the capabilities of charged materials.

Advances in flexible and functional metal–organic frameworks (MOFs), also called soft porous crystals, are reviewed by covering the literature of the five years period 2009–2013 with reference to the early pertinent work since the late 1990s. Flexible MOFs combine the crystalline order of the underlying coordination network with cooperative structural transformability. These materials can respond to physical and chemical stimuli of various kinds in a tunable fashion by molecular design, which does not exist for other known solid-state materials. Among the fascinating properties are so-called breathing and swelling phenomena as a function of host–guest interactions. Phase transitions are triggered by guest adsorption/desorption, photochemical, thermal, and mechanical stimuli. Other important flexible properties of MOFs, such as linker rotation and sub-net sliding, which are not necessarily accompanied by crystallographic phase transitions, are briefly mentioned as well. Emphasis is given on reviewing the recent progress in application of in situ characterization techniques and the results of theoretical approaches to characterize and understand the breathing mechanisms and phase transitions. The flexible MOF systems, which are discussed, are categorized by the type of metal-nodes involved and how their coordination chemistry with the linker molecules controls the framework dynamics. Aspects of tailoring the flexible and responsive properties by the mixed component solid-solution concept are included, and as well examples of possible applications of flexible metal–organic frameworks for separation, catalysis, sensing, and biomedicine.

Ligand-protected metal nanoclusters (NCs), which are ultra-small nanoparticles marked by their atomic precision, are distinctly importance for contemporary nanomaterials. NCs have attracted significant research attention for utilizing their novel optical and physicochemical properties in various applications, including fluorescence sensing, catalysis, and biomedical applications. This dissertation deals with ligand-protected atomically precise silver NCs and is divided into two main parts. The first part is focused on the exploration and design of well-defined silver NCs through surface co-ligand engineering. The second part is related to the development of silver NC-based frameworks (NCFs). In the first part, we designed a synthetic strategy based on engineering the structure of the phosphine co-ligands with thiols to generate the large box-shaped [Ag67(SPhMe2)32(PPh3)8]3+ (referred to as Ag67) NC. The strategy demonstrates that the combined use of judiciously chosen thiol and phosphine co-ligands can result in stable highly anisotropic box-like shapes. The optical absorption spectrum of the Ag67 NC displays highly structured multiple sharp peaks. The crystal structure shows a Ag23 core formed of a centered cuboctahedron (an unprecedented core geometry in silver clusters), which is encased by a layer with a composition of Ag44S32P8 arranged in the shape of a box. The electronic structure of this box-shaped cluster resembles a jellium box model with 32 free electrons. In the second part, a novel approach is developed for the assembly and linkage of atomically precise Ag NCs into one-dimensional (1D) and two-dimensional (2D) NC-based frameworks (NCFs) with atomic-level control over cluster size and dimensionality. With this approach three novel, but related, crystal structures (one silver NC and two NCFs) were synthesized. These structures have the same protecting ligands, and also the same organic linker. The three structures exhibit a similar square gyrobicupola geometry of the building NC unit with only a single Ag atom difference. The critical role of using a chloride template in controlling the NC’s nuclearity was demonstrated, as well as the effect of a single Ag atom difference in the NC’s size on the NCF’s dimensionality, optical properties, and thermal stability.

京都大学 / 新制・論文博士 / 博士(理学) / 乙第13396号 / 論理博第1575号 / 新制||理||1678(附属図書館) / (主査)教授 北川 宏, 教授 吉村 一良, 教授 有賀 哲也 / 学位規則第4条第2項該当 / Doctor of Science / Kyoto University / DGAM

京都大学 / 新制・課程博士 / 博士(工学) / 甲第23233号 / 工博第4877号 / 新制||工||1761(附属図書館) / 京都大学大学院工学研究科化学工学専攻 / (主査)教授 宮原 稔, 教授 佐野 紀彰, 教授 松坂 修二 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

Since the discovery of size-selective metal-organic frameworks (MOF) researchers have tried to manufacture them into gas separation membranes. ZIF-8 became the most studied MOF for membrane applications mainly because of its simple synthesis, good chemical and thermal stability, recent commercial availability and attractive pore size. The aim of this work is to develop convenient methods for growing ZIF thin layers on polymer supports to obtain defect-free ZIF membranes with good gas separation properties. We present new approaches for ZIF membranes preparation on polymers. We introduce zinc oxide nanoparticles in the support as a secondary metal source for ZIF-8 growth. Initially the ZnO particles were incorporated into the polymer matrix and later on the surface of the polymer by magnetron sputtering. In both cases, the ZnO facilitated to create more nucleation opportunities and improved the ZIF-8 growth compared to the synthesis without using ZnO. By employing the secondary seeded growth method, we were able to obtain thin (900 nm) ZIF-8 layer with good gas separation performance. Next, we propose a metal-chelating polymer as a suitable support for growing ZIF layers. Defect-free ZIF-8 films with a thickness of 600 nm could be obtained by a contra-diffusion method. ZIF-8 membranes were tested for permeation of hydrogen and hydrocarbons, and one of the highest selectivities reported so far for hydrogen/propane, and propylene/propane was obtained. Another promising method to facilitate the growth of MOFs on polymeric supports is the chemical functionalization of the support surface with functional groups, which can complex metal ions and which can covalently bond the MOF crystals. We functionalized the surface of a common porous polymeric membrane with amine groups, which took part in the reaction to form ZIF-8 nanocrystals. We observed an enhancement in adhesion between the ZIF layer and the support. The effect of parameters of the contra-diffusion experiment (such as temperature lower than room temperature and synthesis times shorter than 1 hour) on ZIF-8 membrane properties was evaluated. We could prepare one of the thinnest (around 200 nm) yet selective ZIF-8 films reported.

This diploma thesis builds on the already published work, in which phosphinate analogs of terephthalic acid were used to prepare new stable metal-organic frameworks (MOFs) Fe-ICR- 2 and Fe-ICR-4. With the use of analogous biphenylene linkers, two new Fe-MOFs were prepared - Fe-ICR-6 and Fe-ICR-7. Isoreticular MOFs were also prepared using Al3+ metal centers. These materials were characterized by X-ray powder diffraction and adsorption isotherm measurements. Their solvothermal stability was measured after shaking and refluxing in water, ethanol, and toluene and activation from water. Furthermore, their thermal stability and the disintegration mechanism in air were determined by thermal analysis. Keywords: coordination polymer, metal-organic framework, stability, phosphinate

Metal organic frameworks (MOFs) is a quite recently discovered porous material group which shows potential in many different areas. One of these areas is carbon capture; the framework structure of the porous materials allows gas molecules to adsorb to the surface of the pores. MOFs are conventionally synthesised at high temperatures and with hazardous solvents. The goal of this projectwas to synthesise highly porous MOFs at room temperature with water as the main solvent, using environmentally friendly and non-hazardous precursors. As well as the room temperature synthesis, conventional synthesis methods were used with the same precursors as comparison. The materials were characterised with X-ray diffraction, thermogravimetrical methods and IR-spectroscopy. To assess the porosity of the materials, gas adsorption evaluation was performed with CO2, N2, SF6, and CH4 at 20⁰C. In the end, three novel porous magnesium-based materials and one zirconium-based material were successfully synthesised. One of the magnesium-based materials showed a moderately high CO2 adsorption (2.38mmol/g), and could be synthesised at room temperature. The zirconium-based material showed a remarkably high selectivity (17.7) for SF6 over N2 and a high surface area (550m2/g)

京都大学 / 0048 / 新制・論文博士 / 博士(工学) / 乙第12846号 / 論工博第4103号 / 新制||工||1601(附属図書館) / 31429 / (主査)教授 北川 進, 教授 杉野目 道紀, 教授 松田 建児 / 学位規則第4条第2項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM