Thesis advisor: Dunwei Wang / Metal nanocrystals with size and shape control have great potential in heterogeneous catalysis. Controllable encapsulation of well-defined metal nanoparticles into the novel porous materials results in new multifunctional nanomaterials. The core-shell nanostructure can enhance the selectivity, durability, or reactivity of the catalysts and even provide additional functionalities. Metal-organic frameworks (MOFs) are a class of novel crystalline nanoporous materials, with well-defined pore structures and distinctive chemical properties. Using MOFs as the encapsulating porous materials has drawn great interest recently due to their tunable structures and properties. However, it could be challenging to grow another porous material layer on metal surface due to the unfavorable interfacial energy. In this work we develop a new concept of colloidal synthesis to synthesize the metal@MOF core-shell nanostructures, in which a layer of self-assembled molecules directed the growth and alignment between two materials. Surfactant cetyltrimethylammonium bromide (CTAB) is designated to facilitate the overgrowth of MOF onto metal surface, and an alignment between the {100} planes of the metal and {110} planes of the MOF can be observed. By utilizing the same concept, a third layer of mesoporous silica could also be coated on the MOF shell with assistance of CTAB. And our method could be a general strategy to fabricate multiple-layer MOF materials. / Thesis (MS) — Boston College, 2015. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Thesis advisor: Chia-Kuang (Frank) Tsung / Exchange reactions have enabled a new level of control in the rational, stepwise preparation of metal-organic framework (MOF) materials. However, their full potential is limited by a lack of understanding of the molecular mechanisms by which they occur. This dissertation describes our efforts to understand this important class of reactions in two parts. The first reports our use of a linker exchange process to encapsulate guest molecules larger than the limiting pore aperture of the MOF. The concept is demonstrated, along with evidence for guest encapsulation and its relation to a dissociative linker exchange process. The second part describes our development of the first quantitative kinetic method for studying MOF linker exchange reactions and our application of this method to understand the solvent dependence of the reaction of ZIF-8 with imidazole. This project involved the collection of the largest set of rate data available on any MOF linker exchange reaction. The combination of this dataset with small molecule encapsulation experiments allowed us to formulate a mechanistic model that could account for all the observed kinetic and structural data. By comparison with the kinetic behavior of complexes in solution, we were able to fit the kinetic behavior of ZIF-8 into the broader family of coordination compounds. Aside from the specific use that our kinetic data may have in predicting the reactivity of ZIF linker exchange, we hope that the conceptual bridges made between MOFs and related metal−organic compounds can help reveal underlying patterns in behavior and advance the field. / Thesis (PhD) — Boston College, 2017. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

This thesis is built upon two areas of research concerning metal-organic frameworks (MOFs). The first focuses on the functionalisation of MOFs via post-synthetic modification (PSM). The second involves the investigation on the potential of MOFs as hosts for insect pheromones. Chapter 1 introduces the field of MOF chemistry, and covers their properties along with a brief description of their applications. The concept of PSM is introduced and a review of recent literature given. The aims of the thesis are also detailed at the end of this chapter. Chapter 2 describes the PSM of [Zr6O4(OH)4(BDC-NH2)6], UiO-66-NH2, via Aza-Michael reactions. Different functionalities were successfully introduced into its pores and the degrees of conversion were determined via 1H NMR spectroscopy. Gas sorption measurements (CO2 and N2) of the PSM products were carried out and compared. In particular, two PSM products were shown to exhibit higher CO2 over N2 selectivity than that for the starting MOF, UiO-66-NH2. Chapter 3 describes a new PSM route in obtaining azole-functionalised MOFs via Mannich reactions. The amino groups in three different MOFs were converted into a range of azole-functionalised MOFs with conversions up to 100%. In particular, one of the PSM reactions afforded a new material, formulated as [Zn3(BDC-NH2)1.32(BDC-NHCH2N2C3H3)1.68(C6H12N2)], based on single crystal X-ray crystallography, 1H NMR and TGA analyses. Gas sorption studies demonstrate increased selectivity for CO2 over N2 for the PSM products. One of the modified MOFs was shown to exhibit a high Hg(II) uptake from aqueous solutions. Chapter 4 introduces the concept of using MOFs as hosts for ant pheromones. The factors which influenced the pheromone loading in zinc and zirconium based MOFs were investigated. The MOFs containing the linker BDC-NHPr (2-(propylamino)benzene-1,4-dicarboxylate) were found to be effective at hosting two types of ant pheromones, 3-octanone and (S)-4-methyl-3-heptanone.

"Porous materials have been a focus of researchers for their applications as molecular storage, molecular sensing, catalysis, asymmetric synthesis and host materials. Metal-organic frameworks (MOFs) represent a promising new class of porous crystalline solids because they exhibit large pore volumes, high surface areas, permanent porosity, high thermal stability, and feature open channels with tunable dimensions and topology. We are currently investigating the design, synthesis, and structures of a new family of MOFs derived from transition metals complexes of 4-(imidazole-1-yl)benzoic acids. Here we present our effort in continuing design and synthesis MOFs composed of 4-(imidazole-1-yl)benzoic acids to expand our knowledge about 4-(imidazole-1-yl)benzoic acid MOF family. A series of ligands are synthesized and Cu MOF-3N, 4, 5 and Cd MOF-3 were synthesized, structure determination found out metal-ligand complex follows our proposal, while Cu MOF-4,5 exhibit porous framework structure via absolute structure determination. Sorption behavior is a key focus in MOF application because the great potential applications MOF bears. Here we carry out a fundamental study about MOF texture and selectivity on MOF-5 and Cd MOF-2. Non-polar polyaromatic hydrocarbons such as naphthalene, phenanthrene, and pyrene, polar molecules such as 2-naphthol, ibuprofen were selected to test our hypothesis that sorption is influenced by the degree of tight fitting, and guest-host interaction such as van der waals and hydrogen bonding. By determining Langmuir isotherms of selected guest molecules, we are able to demonstrate our hypothesis that tighter the fit of the guest molecule and the pores, the higher the amount it would sorb. The sorption difference of non-polar and polar molecules suggest hydrogen bonding is not involved in guest sorption and the dominating force of sorption is hydrophobic interaction. Polymorphism is an interesting phenomenon that bears great value in pharmaceutical industry. Here we report the first case for MOF to serve as a heterogeneous surface that induced nucleation of indomethacin. It is also a first report of this polymorph form of indomethacin. PXRD, DSC, TGA, NMR are conducted as our initial investigation effort. This polymorph exhibits exceptionally thermal stability and low solubility, indicating an unusual tight binding between indomethacin and ethanol solvate. "

The electrochemical growth of metal-organic framework (MOF) coatings, utilising the anodic dissolution method, has been investigated as a means of preparing MOF coated electrodes for various electrochemical applications. A mechanistic understanding of the formation of the electrode coatings has been further developed. This understanding has been utilised to expand the scope of this technique; to allow for the electrochemical formation of Zn and Co zeoliticimidazolate framework (ZIF) coatings which was hitherto not believed to bepossible. Electrodes coated with Co and Zn ZIFs via this methodology were assessed for their capacitive behaviour and the Co ZIFs exhibited the highest, pure MOF areal capacitance values reported to date. This was attributed to the method of coating formation, which provides well adhered coatings of MOF particles integrated into the electrode surface providing a good electrical connection between the coating and the electrode. Incorporation of GO, via electrophoretic deposition during the coating growth, is shown to improve this capacitance still further. Thecorresponding Zn ZIFs exhibited resistances orders of magnitude higher than their Co analogues; modelling can explain this behaviour with the Co analogue of a given ZIF calculated to have a greater metal contribution to its LUMO leading to a more delocalised electronic structure. Electrodes coated with the Cu MOF HKUST-1 have enabled for the first time the use of MOFs as a template for the electrodeposition of anisotropic metal nanostructures. Such MOF encapsulated metal nanostructures are demonstrated to have applications in surface enhanced Raman spectroscopy (SERS). In addition the same MOF has been discovered to display a redox based hysteresis which allows for the rewritable storage of small amounts of electrically accessible data.

Metal-organic nanotubular (MON) materials have garnered significant attention in the recent years not only due to the aesthetic architecture but also due to the interesting chemical and physical properties that have been reported for these compounds. The number of MONs reported in the literature are limited compared to metal organic frameworks due to synthetic challenges and difficulties in crystal engineering. These types of materials are of interest given their one-dimensional channels that lead to their potential application in advanced membrane technologies. In Forbes group, a uranium-based metal-organic nanotube (UMON) was synthesized using zwitterionic like iminodiacetic acid (IDA) as the ligand. IDA ligand chelates to the U(VI) metal center in a tridentate fashion and doubly protonated IDA linker connects the neighboring uranyl moieties until it forms hexameric macrocycles. These macrocycles stack into a nanotubular array due to supramolecular interactions. Single crystal X-ray diffraction studies displayed there are two crystallographically unique water molecules that can be removed reversibly at 37 °C. UMON indicated selectivity to water, the selectivity of this material was analyzed using solvents with different polarities, sizes, and shapes. In the current body of work, dehydrated UMON crystallites were exposed to these solvents (in liquid and vapor phase) and studied using TGA coupled FTIR set up, confirming the highly selective nature of UMON. Kinetic studies were also conducted using an in-house built vapor adsorption setup confirmed the water uptake rate of the nanotube depends on the humidity of the environment. Uptake rates were estimated using a simple kinetic model and indicated enhanced hydration compared to other porous materials. One of the hypotheses regarding the interesting properties of UMON is that the uranium metal center might play a central role in the selectivity of this material. To test this hypothesis, a similar uranium based metal-organic nanotube containing 2,6-pyridine dicarboxylic acid (UPDC) as the ligand was synthesized and its properties were compared to that of the UMON material. UPDC did display some selectivity based upon size exclusion but did not exhibit the same selectivity to water that is observed for UMON. Different transition metals were also incorporated into the nanotubular structures to determine the influence of dopants on the observable properties. Only small amounts of transition metal dopants were incorporated into the structure, but it increased the stability under high humid environment. Attempts to incorporate transition metal dopants in the UPDC led to the formation of novel chain structures.

Les travaux décris dans cette thèse rapportent la conception de Metal-Organic Frameworks (MOFs) photoactifs et leur immobilisation sur surface dans le but d’obtenir et d’étudier des SurMOFs (Surface anchored Metal-Organic Frameworks) propices aux processus photoinduits dans le cadre de la photosynthèse artificielle. Pour accomplir cela, nous avons synthétisé différents ligands photoactifs et réalisé leur immobilisation sur surface à l’aide de la croissance épitaxiale en phase liquide. Ainsi, différents SurMOFs à base de zinc(II), présentant tous une structure de type SurMOF-2, ont été préparés avec succès. Les premiers matériaux obtenus à base de ligands rylènes (naphtalène dimide : NDI et pérylène diimide : PDI) ont mis en avant de fortes interactions  entre les chromophores au sein du SURMOF, causant une perte de la luminescence. Une deuxième génération de ligands plus encombrés a été synthétisée. Ils ont conduit à des SurMOFs luminescents et siège de transferts d’énergie interligands. Ces premiers travaux ont mis en avant l’impact de la disposition des ligands dans le matériau sur les propriétés photoniques. Par ailleurs, des SurMOFs constitués de ligands dicétopyrrolopyrrole (DPP) et d’anthracène (ADP) ont été synthétisés. L’étude de leurs propriétés photoniques alliée à des calculs théoriques ont montré que le transfert d’énergie au sein de ce SurMOF ne se fait pas de manière isotrope. Enfin, un SurMOF à partir de ligand DPP portant des fonctions réactives (azoture) a été synthétisé et nous avons pu greffer différentes molécules par réaction de cyclo-addition de type Huisgen, dont un accepteur d’électron, à sa périphérie par modification post-synthétique. / The aim of this thesis was the development of photoactive Metal-Organic Frameworks (MOFs) and their immobilizations on surface to obtain and study SurMOFs (Surface anchored Metal-Organic Frameworks) to investigate photoinduced processes in the context of the artificial photosynthesis. Towards this goal, we have synthesized photoactive ligands and immobilized them on surfaces using liquid phase epitaxy (LPE) in a layer-by-layer (LbL) fashion. Thus, different zinc (II) based SurMOFs, featuring a SurMOF-2 structure, were successfully prepared. The first rylene- (naphthalene diimide: NDI and perylene diimide: PDI) based SurMOFs described in this thesis showed strong  interactions between the chromophores within the MOF, causing the quenching of the luminescence. A second generation of ligands, sterically hindered, was then synthesized. They lead to luminescent SurMOFs showing efficient ligand-to-ligand energy transfer. These first results highlight the impact of linker arrangement within the material on its photonic properties. Furthermore, diketopyrrolopyrrole (DPP) and anthracene (DPA) based SurMOFs were prepared. The study of their photonic properties coupled with theoretical calculations showed that energy transfers, occurring within SurMOF-2 type materials, were not isotropic. Finally, a SurMOF, made out of a DPP ligand bearing reactive moieties (azide), was synthesized and was functionalized with different kinds of molecules, including an electron acceptor, at the periphery by post-synthetic modification using the Huisgen cycloaddtion reaction.

The morphology evolution of high-temperature grown AlN nucleation layers on (111) silicon has been studied using atomic force microscopy (AFM). The structure and morphology of subsequently grown GaN film were characterized by optical microscopy, scanning electron microscopy, x-ray diffraction, and photoluminescence measurement. It was found that a thicker AlN buffer layer resulted in a higher crystalline quality of subsequently grown GaN films. The GaN with a thicker buffer layer has a narrower PL peak. Cracks were found in the GaN film which might be due to the formation of amorphous SiNx at the AlN and Si interface. / Singapore-MIT Alliance (SMA)

AlN nucleation layers are being investigated for growth of GaN on Si. The microstructures of high-temperature AlN nucleation layers grown by MOCVD on Si (111) substrates with trimethylaluminium pre-treatments have been studied using atomic force microscopy (AFM) and transmission electron microscopy (TEM). The AFM results show that with TMA pre-treatments, AlN grows in a pseudo-2-dimensional mode because the lateral growth rate of AlN is increased, and the wetting property of the AlN on silicon is improved. Also, no amorphous SiNx layer was observed at the interface with TMA pre-treatments and AlN films with good epitaxial crystalline quality were obtained. Transmission electron diffraction patterns revealed that the AlN and Si have the crystallographic orientation relationship AlN [0001]║Si[111] and AlN[11 2 0] ║Si[110]. High resolution transmission electron microscopy indicates a 5:4 lattice matching relationship for AlN and Si along the Si [110] direction. Based on this observation, a lattice matching model is proposed. / Singapore-MIT Alliance (SMA)

The periodic silane burst technique was employed during metalorganic chemical vapor deposition of epitaxial GaN on AlN buffer layers grown on Si (111). Periodic silicon delta doping during growth of both the AlN and GaN layers led to growth of GaN films with decreased tensile stresses and decreased threading dislocation densities, as well as films with improved quality as indicated by x-ray diffraction, micro-Raman spectroscopy, atomic force microscopy, and transmission electron microscopy. The possible mechanism of the reduction of tensile stress and the dislocation density is discussed in the paper. / Singapore-MIT Alliance (SMA)