Seeking for clean and renewable energy resource has been a research focus for the past decades. Carbon-based fuel, the current primary energy resource, will be depleted in the near future. The environmental concern coming with the consumption of fossil fuel is more significant than ever. The sunlight incident on the earth's surface reaches as high as 1000W/m2, far exceeding the human energy needs. If an efficient and environmental benign solar energy conversion and utilization could be achieved, the energy problem will be eventually solved.

Since the first reported UV light activated photocatalyst TiO2, many materials have been synthesized and studied for their photocatalytical activity. Among of them, researchers are especially interested in these which could make H2 from water efficiently under visible light irradiation, since the energy of visible light take up a large proportion of solar energy.

Herein, we investigated the Ti3+-doped TiO2 by a facile one-step combustion method. It is found that Ti3+ extends the photoresponse of TiO2 from the UV to the visible light region, which leads to high visible-light photocatalytic activity for the generation of hydrogen gas from water.

We further studied how the synthetic conditions such as crystallinity, surface area, particle size, crystal facets distribution and etc. affected the photocatalytic activity of the partially reduced TiO2.

In addition, we found that the partially reduced TiO2 with highly active facets could be fabricated by a facile hydrothermal treatment of the Ti powder and hydrochloric acid. Without any additional reducing agent and surfactant, Ti3+ was successfully incorporated into the product, and more importantly, highly active facets developed preferentially, which is supported by the electron paramagnetic resonance (EPR) spectra and transmission electron microscopy (TEM), respectively. The as-synthesized single crystal sample shows a great improvement in the photocatalytic H2 production activity over our previously prepared particles. It is inferred that the active facets play a crucial role for this enhancement. Measurement of the photocatalytic activity over an extended time period proved the excellent stability of the reduced TiO2 made by this approach.

In this work, I concentrated on the development of porous materials using different design strategies or methods for a range of applications. Among these porous materials, the metal-organic frameworks (MOFs) are the focus of this work. First, on the aspect of different design strategies, I have proposed a “multi-level” division MOFs design strategy and combined it with the pore space partition (PSP) strategy and the bioisosteric replacement (BIS) strategy to develop a series of new MOFs belonging to partitioned acs topology (pacs) type. These new pacs type MOFs achieved the same symmetry at different levels. Given the close connection between the nature of chemical moiety and its symmetry, such unique perspective on ligand symmetry and sub-symmetry in MOF design implicitly translates into the influences on MOF properties. Also, these new pacs type MOFs have excellent water stability, light hydrocarbons and benzene/cyclohexane selective adsorption capacities. These MOFs possess great application prospect. Second, on the aspect of different synthesis methods, I have developed the solvent-free method to synthesize MOFs, as well as carbon materials prepared by using solvent-free-synthesized MOFs as starting materials. I also combined the strategy of “multi-module” with the solvent-free synthesis method. I synthesized a series of complex multi-module pacs type MOFs using the solvent-free method, which has the advantages of short synthesis time, convenient activation, high stability, and good C2H2/CO2 selective adsorption capacity. Carbon materials prepared using the solvent-free method synthesized MOFs also exhibit good oxygen reduction reaction (ORR) and light hydrocarbons selective adsorption capacities. Finally, I also studied the “one-pot” in situ synthesis of MOFs containing complex ligands, and obtained a new type of MOF with chirality and helicity based on covalent organic framework (COF) fragments.

The open framework materials have emerged as a highly active and rapidly developing domain of research because their rich host-guest chemistry could be utilized to develop promising materials such as absorbents, catalysts, sensors and substrates for mechanistic studies into fundamental surface interactions and catalytic mechanisms.

To better understand, predict and design materials with desired properties and functions, it is often essential to know the detailed structures, crystalline materials with well-defined periodic arrangements that allow for structural studies at the atomic resolution are of special importance. In addition, some properties such as uniform porosity and associated shape- or size-selectivity can be best designed with crystalline materials.

Unlike some other materials such as semiconductors in which properties can be dramatically altered by simple doping, properties of open-framework materials are closely correlated with their general chemical compositions, and structural and geometrical features. As such, a great emphasis has been placed on creating materials with new crystal structures, in contrast with doping of well-known structure types. Hence the focus of this study is on the introduction of novel chemical-physical functions to the crystalline porous solids by fully exploring and understanding fundamental structural features and their possible correlation to properties and functions.

The first part of this work presented here is on creating pure inorganic framework structures, specifically metal-chalcogenide supertetrahedral-cluster-based frameworks, together with a discussion on their structure-property relationships. A series of such molecular architectures have been built by directed assembly of supertetrahedral clusters that can be viewed as artificial atoms with tunable radii. A new class of "hollowed-out bulk semiconductor" materials has been achieved. Both experimental evaluations and theoretical simulations on some pure phase compounds have been performed. Based on these new structures, the relationship between materials' structural features and their optoelectronic properties is discussed.

The later parts of the work presented here deal with hybrid porous solids, specifically synthesis, characterizations and novel functions of metal-organic framework materials (MOF). By designed synthesis, one MOF material with unusual 4-level structural hierarchy was assembled. Its magnetic property was evaluated, revealing an interesting geometry-induced magnetic frustration mechanism. Also, a catalytically active MOF was synthesized and characterized. Most importantly, single-crystal X-ray crystallography has been employed to capture the detailed molecular conformations of reaction intermediates on the active sites, which represents a powerful example of using a MOF-based novel methodology to elucidate catalytic mechanisms.

Metal-organic frameworks (MOFs) represent a large family of crystalline porous materials which have been extensively studied during the past decade. Due to their great porosity, precise and uniform pore size and functional organic linkers, they have found applications in the area of gas storage, separation, ion-exchange, catalysis and sensors. While previous studies in this area emphasize more on transition metal based MOFs, the main group metal based MOFs have been relatively less explored, which, however, may bring improved properties and novel structures. This dissertation focuses on two categories of metal-organic frameworks based on the s-block metal Li and p-block metal In, respectively. The design, synthesis, structure and properties will be discussed.

Lithium is the lightest metallic element and is therefore desired for construction of ultralight MOFs with the expectation of improved gas sorption properties. In addition, the appropriate binding energy between lithium and H₂ make it an ideal candidate for H₂ storage. Nonetheless, almost all Li-MOFs to date have shown quite dense structures. There is no effective strategy for construction of lithium based open frameworks. In this work, we have intentionally introduced lithium cubane cluster into framework design as a versatile secondary building unit (SBU). Through this method, a series of open-framework materials were obtained, among which even a highly symmetric zeolitic framework was achieved. Surprisingly, except the coordination compounds, a series of H-bonded frameworks have also been observed in this system. In addition, a mixed multivalent ligand route has also been successfully applied for construction of 4-connected lithium imidazolate frameworks. H₂ and CO₂ sorption properties have been studied upon these compounds.

In-MOF represents another area that has recently attracted researcher's attention due to its higher charge and bigger coordination sphere that differs from the traditional divalent transition metals. In this work, we have developed a series of indium based charged frameworks in two opposite categories, indium trimer based cationic frameworks (ITCs) and indium monomer based anionic frameworks (IMAs). Especially, it is found that the introduction of intrinsically positively charged indium trimer SBUs can be an effective way for systematical synthesis of cationic frameworks, which are less common in the MOFs study. The ion-exchange of a series of organic dyes upon the nanogated cationic frameworks has been studied in detail. The size and charge dependent behaviors make the reported MOF a promising candidate for the stationary phase materials of ion-exchange based separation process.

First reported in 1992, ordered mesoporous materials exhibit unique features, such as regular pore geometry, high surface area, and large pore volume, and have shown great potential in various applications. This dissertation combines the knowledge from the field of ordered mesoporous materials and several other research areas to design advanced hybrid porous materials for controlled release and catalysis applications.

The demand for better treatment of illness has led to ever-increasing efforts in the development of efficient drug delivery system that can transport drug molecules to the targeted site and release the loading in a controlled manner. The emerging ordered mesostructured materials exhibit great potential in controlled release because of their stable structures, large surface areas, tunable pore sizes and pore volumes, well-defined surface properties, and biocompatibility. The great diversity in surface functionalization offers mesoporous silica a unique advantage in site-specific delivery and stimuli-responsive release. My research is focused on developing novel controlled release systems using physiologically compatible chemical or physical stimuli by integrating organic materials with inorganic nanostructured porous materials. The release system uses mesoporous materials as reservoir and functional organic or nanomaterials as valves to perform the controlled responsive functionalities. With this strategy, a series of stimuli responsive and physiologically compatible release systems have been developed, which provide a promising new direction in the bio-applications of nanostructured materials.

Poly(4-vinyl pyridine) is coated on mesoporous silica through facile "grafting to" method. The grafted polymer nanoshell works as pH-sensitive barrier to control the release of trapped molecules from mesoporous silica. We also use nanoparticle as capping agent to block the silica mesopore by pH-responsive acetal linker to obtain acid-sensitive delivery system. By designing a polymeric network (capable of being cross-linked and de-cross-linked) as a "gatekeeper" at the pore opening of mesoporous silica-based materials, a series of hybrid porous materials for controlled release have been developed. For example, the pore of silica materials loaded with guest molecules are blocked by the addition of cystamine, a disulfide-based bifunctional primary amine, which allows polymer chains around the silica surface to be cross-linked. The polymeric network thus formed around the pore opening can be reopened by cleaving the disulfide bond of cystamine in the presence of disulfide reducing agents such as dithiothreitol (DTT), leading to the redox-controlled release. The further introduction of cyclodextrin introduced into the polymer network expands the responsive diversity by supramolecular host-guest interaction, which is sensitive to photoirradiation, redox signal, or competitive binding.. In addition, cavitands are introduced into the hybrid system and work as supramolecular releasing trigger.

Sulfonated ordered mesoporous carbons have been synthesized by covalent attachment of sulfonic acid containing aryl radicals on the surface of mesoporous carbons. The hybrid materials work as novel solid acid catalysts, which show stable and highly efficient catalytic performance in biodiesel production.

The increasing demand for renewable energy is driving innovations in both science and technology. Hydrogen has been broadly identified as a potential clean energy carrier due to its high energy capacity (enthalpy of combustion is as high as 286 kJ/mol) and environmental friendliness (the only product after burning is water). Meanwhile, solar energy is renewable, abundant and easily available. Solar-driven H2 production from water has therefore attracted global attention in the past decades since the first report of photoelectrochemical (PEC) water splitting based on an n-type TiO2 photoanode. Many semiconductor-based materials have been synthesized and studied for their photocatalytic or PEC performance.

Among them, visible-light-active photocatalytsts are more promising since the energy of the visible-light region takes up a large proportion of the whole solar spectrum. Herein, we found two novel groups of compounds, e.g. copper borates and boron carbides. We investigated the origins and performances of their photocatalytic water splitting under visible light irradiation. It is found that the visible light activities of the two groups are resulted from different band-gap engineering mechanisms.

For the two copper borates compounds, e.g. CuB2O4 and Cu3B2O6, we found that the visible light activity is from the intrinsic midgap states in the two compounds. Both midgap states serve as an electron acceptor level, but they function very differently in the two copper borates. For CuB2O4, the midgap states facilitate the visible light absorption for photocatalytic water splitting, while for Cu3B2O6, the midgap states trap electrons and reduce the photocatalytic activity.

For the two boron carbides, e.g. B4.3C and B13C2, they exhibit efficient photocatalytic H2 evolution and PEC H2 evolution as a stable photocathode under visible light irradiation. Interestingly, it is found that the inherent defects and structural distortions in B4.3C cause a continuum downshift of its conduction band (CB) edge that facilitates visible-light absorption and water splitting based on density functional theory (DFT) calculations. In B13C2, however, the more complicated structural defects and distortions result in a large number of midgap states between the CB and the valence band (VB), which reduce its overall photocatalytic and PEC water splitting efficiency by promoting charge recombination.

Zeolites have played essential roles in a number of industrial processes and technological applications. The intensive research in crystalline microporous materials has successfully extended such traditional inorganic zeolites to semiconducting open-framework metal chalcogenides and hybrid porous coordination polymers. Our research group has made a number of key advances in the development of metal chalcogenide clusters and their self-assembled open frameworks. Some of these key advances resulted from this thesis work and are described here. This dissertation also deals with the synthesis of some unique families of porous frameworks based on coordination polymers.

Porous zeolitic metal imidazolate frameworks can be considered as integrating features of both traditional inorganic zeolites and porous coordination polymers because the Si-O-Si angle in zeolites is coincident with that of the bridging angle formed by the Metal-Imidazolate-Metal unit. In this thesis work, two different strategies are employed. The first is the use of mixed, sterically tuned and complementary imidazole ligands, which results in several novel zeolitic topologies with both 3-ring and large rings (>12). The second is the use of novel tetrahedral nodes (e.g., Li and B), which leads to a new family of boron imidazolate open-framework materials.

Open-framework metal chalcogenides are a new generation of inorganic porous materials because their semiconducting properties could expand the utility of inorganic porous materials into areas in which traditional insulating inorganic zeolite materials have had little impact. Key synthetic discoveries made in this thesis work include (1) synthesis of a family of Sn- and/or S-doped Zn-Ga-Se clusters and frameworks and demonstration of site-selective doping chemistry controlled by the interplay of multiple fundamental chemical and geometrical factors, (2) synthesis of two selenide 3D superlattices based on dual-sized supertetrahedral clusters and demonstration of charge density tuning of chalcogenide clusters using three types of charge-complementary and yet geometry-matching metal cations (di-, tri-, and tetravalent ions), (3) synthesis of the largest discrete chalcogenide clusters with tunable band gaps, which further blurs the boundary between molecular clusters and colloidal nanoparticles, and (4) the synthesis of a new family of 3D covalent arrays of supertetrahedral clusters and negatively-charged imidazolate ligands.

The introduction of C3-symmetric pore-partitioning agents, in the form of either molecular ligand such as 2,4,6-tri(4-pyridinyl)-1,3,5-triazine (tpt) or metal-complex clusters, into hexagonal channels of MIL-88/MOF-235 type (the acs net) to create pacs-type (partitioned acs) crystalline porous materials is an effective strategy to develop high-performance gas adsorbents. In the first part, inspired by the synthetic chemistry of COF-1, we developed integrated COF-MOF chemistry through co-assembly of [B3O3(py)3] COF-type trimers and [(M3(OH)(COO)6] MOF-type trimers as a new method for pore-space partition. With this strategy, the coordination-driven assembly of the acs framework occurs concurrently with the COF-1-type condensation of pyridine-4-boronic acid into a C3-symmetric trimeric boroxine molecule leading to a new family of pacs materials. The new boroxine-based pacs materials exhibit dramatically enhanced NH3 sorption properties. In the second part, we further explored and utilized the method in the first part to let the self-assembly of the acs framework react simultaneously with the trimerization of three different monomers. Three monomers including 4-cyanopyridine, 4-vinylpyridine, and pyridine-4-boronic acid trimerized into 2,4,6-tri(pyridin-4-yl)-1,3,5-triazine (TPT), 1,3,5-tri(pyridin-4-yl)-cyclohexane (TPC), and 2,4,6-tri(4-pyridinyl)-1,3,5-boroxine (TPB) during the pacs materials formation. New materials exhibit excellent C2H2/CO2 gas separation performance. In the third part, we lengthened the monomer from pyridine-4-boronic acid to 4-(pyridin-4-yl) phenyl boronic acid and prepared two new pacs compounds with similar surface areas. C3H8 and C3H6 isothermal adsorption studies on these two compounds revealed the host-guest interaction sites in structures. In summary, the pore-space partition of crystalline porous materials by monomer trimerization in this dissertation is a novel and efficient method for gas captures and host-guest interaction studies.

Porous Materials are an important class of materials due to their large-scale industrial applications in gas adsorption, gas separation, heterogeneous catalysis and so on. Among many kinds of porous materials, metal organic frameworks (MOFs) have emerged as one of the favorites in the past fifteen years. MOFs are crystalline porous materials that are mainly made of inorganic metal containing units (secondary building units, also called SBUs), organic ligands and templates.

Compared to commercial inorganic porous materials, zeolites, which are based on Al3+ and Si4+, MOFs can accommodate most types of metal ions and a large number of organic ligands. This makes it possible for MOFs to adopt some fantastic features: (1) in principle the pore size and the surface area of MOFs can be tuned by changing the organic linkers, which allows MOFs to have a wider range of pore size and surface area than zeolites; (2) functionality can be built into linkers; (3) in MOFs, the solvents have weak interaction with frameworks and therefore can easily leave the structure at relatively low temperature, which will provide useful and readily accessible porosity. Furthermore, the removal of coordinated solvent molecules can provide unsaturated metal centers, which are quite meaningful for gas adsorption and catalysis.

We focus on developing MOFs with zeolite topologies and analyzing how different factors affect the construction of the final products. We also evaluated the potential applications of synthesized MOFs in gas adsorption/separation, proton conductivity and oxygen reduction reaction.

In chapter 2, we reported a rare MOF in which two zeolitic frameworks (SOD and ACO) are within one MOF. The bent angle of the ligand plays an important role in the construction of this fantastic structure. This MOF showed selective adsorption of CO2 over H2. The work also proved how important the bent angle of ligands is in the synthesis of MOFs.

In chapter 3, by using the same ligand, and varying synthetic conditions (especially In3+/FDA ratio), we obtained three unique building blocks of indium, demonstrating charge-switching from positive trimer to negative monomer and leading to synthesis of In-MOFs with tunable framework charge. We further demonstrated the variations of gas sorption properties and proton conduction behaviors in such materials.

In chapter 4, we developed a series of zirconium-porphyrin frameworks. The frameworks are constructed by Zr4+ and TCBPP. Different metal ions (Zn, Co, Fe) are trapped within phorphyrin rings. The frameworks have exceptional stability and uniform pores. These make them become excellent candidates for being the precursors of catalysis for oxygen reduction reaction (ORR). This work demonstrated a novel method to develop noble metal free catalysts for electrochemical reactions.

The current global heavy dependency on fossil fuels gives rise to two critical problems: I) fossil fuels will be depleted in the near future; II) the release of green house gas CO2 generated by the combustion of fossil fuels contributes to global warming. To potentially address both problems, this dissertation documents three primary areas of investigation related to the development of alternative energy sources: electrocatalysts for fuel cells, photocatalysts for hydrogen generation, and photoreduction catalysts for converting CO2 to CH4.

Fuel cells could be a promising source of alternative energy. Decreasing the cost and improving the durability and power density of Pt/C as a catalyst for reducing oxygen are major challenges for developing fuel cells. To address these concerns, we have synthesized a Nitrogen-Sulfur-Iron-doped porous carbon material. Our results indicate that the synthesized catalyst exhibits not only higher current density and stability but also higher tolerance to crossover chemicals than the commercial Pt/C catalyst. More importantly, the synthetic method is simple and inexpensive.

Using photocatalysts and solar energy is another potential alternative solution for energy demand. We have synthesized a new biomimetic heterogeneous photocatalyst through the incorporation of homogeneous complex 1 [(í-SCH2)2NC(O)C5H4N]-Fe2(CO)6] into the highly robust zirconium-porphyrin based metal-organic framework (ZrPF). As photosensitizer ZrPF absorbs the visible light and produces photoexcited electrons that can be transferred through axial covalent bond to di-nuclear complex 1 for hydrogen generation.

Additionally, we have studied the photoreduction of CO2 to CH4 using self-doped TiO2 (Ti+3@TiO2) as photocatalytic materials. The incorporation of Ti3+ into TiO2 structures narrows the band gap, leading to significantly increased photocatalytic activity for the reduction of CO2 into renewable hydrocarbon fuel in the presence of water vapor under visible light.

Finally, we demonstrate that open-framework chalcogenides can also be used as efficient photocatalysts for the reduction of CO2 to CH4. These materials contain covalent superlattices of nanosized supertetrahedral clusters, which can be made with different metal cations to provide high electrical conductivity and current density as well as materials with different band gaps. The ability in incorporating different metal cations further enhances the material’s photocatalytic activity, which could possibly provide alternative technologies for reducing CO2 in the atmosphere and simultaneously producing fuel.