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The adsorption isotherms can be used to study the properties of a sorbent and to determine the binding energy between a sorbent and a gas that is adsorbed on it. This study that was carried out on a metal organic framework called "Zeolitic imidazolate framework-8" (ZIF-8) as the sorbent. ZIF -8 is known to have a flexible structure and it has shown structural transformation during gas adsorption, at different temperatures. During this study, ZIF-8 was explored using Xenon adsorption. The range of temperatures for the Xenon adsorption isotherms was between 138 K and 157.56 K. During the adsorption of Xenon on ZIF -8 the lowest two isotherms (138 K and 140.39 K) showed two steps. The lower pressure step represents adsorption of Xenon on the "as - produced" ZIF-8. The extra step reflects the structural transition ("gate opening") that occurs due to the re-orientation of the organic linkers in ZIF-8. These changes increase the diameter of the apertures in the structure, and allow more gas molecules to enter in to the ZIF -8 structure. The Xenon adsorption isotherms were also used to determine the effective surface area of ZIF -8 by employing the "point B" method. The binding energy between Xenon and ZIF -8 was found using the isosteric heat for Xenon on ZIF-8 at low coverage. The kinetics of the Xenon adsorption was also studied during this experiment.

Rapid industrial globalization and technological development and energy consumption across the globe has significantly increased in response to mounting energy needs. The necessity for alternative and sustainable energy conversion devices has become apparent with the growth of energy utilization. In recent years, many research efforts have been made in the development of low-cost, efficient, environmentally friendly energy conversion devices. One type of energy conversion device, polymer electrolyte membrane fuel cells (PEMFCs), uses hydrogen oxidation at the anode and oxygen reduction at the cathode, with a solid-state proton conducting membrane between to generate energy with water as a by-product. PEMFCs use Nafion®, a sulfonated fluoropolymer-copolymer for proton transport; however, temperature restraints and the need for hydration limits the efficacy of this polymer. Moreover, the kinetics of oxygen reduction (ORR) are significantly slower at the cathode than the anode. Platinum is currently the industry standard, but these materials have limited resources, are expensive, and can be sensitive to carbon monoxide poisoning. Platinum is also the preferred catalyst for hydrogen evolution reactions (HER)—critical electrochemical reactions at the cathode for water splitting applications for the generation of hydrogen. Metal-Organic Frameworks (MOFs) have been explored for proton conductivity and as electrode catalysts. The tunability of metal ions and organic linkers both in situ and post-synthesis allows for the targeted design of specific surface areas and topologies while fine tuning selective functionality. Furthermore, due to morphology retention upon pyrolysis, MOFs are good platforms for logical design both pre- and post- carbonization. Taking advantage of the amendable design, along with tunable porosity and growth in controlled dimensions, this work explores the modification of a zinc based MOF as a possible candidate for proton conduction, as well modification of zinc, cobalt, and iron based MOFs for ORR catalysis. Post-synthetic modification was employed as a technique to oxidize the imidazolate ligand to include carboxylic acid functionality of a zinc based MOF. Proton conductivity generally arises from the mobility of the charge carriers present (i.e. carboxylates and phosphates). The incorporation of Brønsted acidity by way of free carboxylates is often challenging, as these are generally sites of coordination in the framework. Herein, we report the successful augmentation of Brønsted acidity with retention of framework crystallinity in a robust MOF. Additionally, the effects of metal content and carbonization temperature of MOFs were explored for ORR and HER. Cobalt and iron were doped either pre- or post-synthesis and carbonized in an inert atmosphere at various temperatures to generate MOF-derived carbons with catalytically active centers without the need for additional support. Carbons with parent MOFs containing moderate amounts of cobalt doping in a bimetallic Co/Zn MOF, or carbons that contained no zinc in the parent material, showed excellent electrocatalytic performance for ORR when carbonized at temperatures just at or above the boiling point of zinc. Zinc based MOFs were doped with various amounts of iron post-synthesis and prior to carbonization in an inert atmosphere. The formation of iron nanoflakes and nanorods on the surface of these carbons generated from the pyrolysis of these iron doped MOFs yielded high surface areas and outstanding electrochemical performance for ORR in both acidic and alkaline media. Likewise, excellent HER catalysis was exhibited by the MOF-derived carbon matrix with the highest iron loading pre-carbonization and more disperse nanorods. Not only does the amenability of MOFs make them a good platform for the direct inclusion of essential electrochemically active moieties, but it also allows for more targeted, nuanced, and rational design of materials needed to enhance proton conduction and electrochemical performance, particularly in cases on non-precious metal electrocatalysts where mechanisms are often not well-understood.

Thesis advisor: Chia-Kuang Tsung / Thesis advisor: Eranthie Weerapana / Metal-Organic Frameworks (MOFs) are crystalline porous materials constructed of metal ions and organic linkers, and have been widely utilized in gas storage, sensing, and chromatographic separation. The combination of MOF nanoparticles with other materials will broaden the utilization of MOF materials to a great extent. Several approaches for creating composites with the MOF, Zeolitic Imidazolate Framework-8 (ZIF-8), have been developed: dye and model drug molecules were encapsulated in ZIF-8 pores for potential drug delivery; mesoporous silica monolayer was epitaxially grown on the ZIF-8 surface for structural stability enhancement and hollow structure formation; UiO-66, another MOF subclass, was hierarchically encased inside ZIF-8 for double-phase gas separation and heterogeneous catalysis. By exploring the versatile ZIF-8 platform, these nanocomposites could have great applications in fields such as heterogeneous catalysis and drug delivery. / Thesis (MS) — Boston College, 2015. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Metal-organic frameworks (MOFs) are crystalline hybrid materials with interesting chemical and physical properties. This thesis is focused on the synthesis and characterization of different MOFs and their use in heterogeneous catalysis. Zeolitic imidazolate frameworks (ZIFs), including ZIF-4, ZIF -7 and ZIF -62, Ln(btc)(H2O) (Ln: Nd, Sm, Eu, Gd, Tb, Ho, Er and Yb), Ln2(bpydc)3(H2O)3, (Ln: Sm, Gd, Nd, Eu, Tb, Ho and Er), MOF-253-Ru and Zn(Co-salophen) MOFs were synthesized. Various characterization techniques were applied to study the properties of these MOFs. X-ray powder diffraction (XRPD), single crystal X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) were extensively used. The effect of synthesis parameters, such as batch composition and temperature, on the formation and morphology of ZIF-7 and ZIF-62 was studied. Structural transformation and flexibility of two series of lanthanide-based MOFs, Ln(btc)(H2O) (Ln: Nd, Ho and Er) and Ln2(bpydc)3(H2O)3, (Ln: Sm and Gd) upon drying and heating were characterized. Relations between metal coordination, structure flexibility and thermal stability among the Sm2(bpydc)3(H2O)3, Nd(btc)(H2O) and MOF-253 were investigated. Salophen- and phenanthroline-based organic linkers were designed, synthesized and characterized. Metal complexes were coordinated to these linkers to be used as catalytic sites within the MOFs. Catalytic studies using two MOF materials, Ln(btc) and MOF-253-Ru, as heterogeneous catalysts in organic transformation reactions were performed. The heterogeneous nature and recyclability of these MOFs were investigated and described. / <p>At the time of doctoral defence the following papers were unpublished and had a status as follows: Paper nr 4: Submitted; Paper nr 5: Submitted</p>

Propylene is one of the most important feedstocks of the petrochemical industry with an estimated 2015 worldwide demand of 100 million tons. Retrofitting conventional C3 splitters is highly desirable due to the huge amount of thermal energy required to separate propylene from propane. Membrane separation is among the alternatives that both academia and industry have actively studied during the past decades, however; many challenges remain to advance membrane separation as a scalable technology for energy-efficient propylene/propane separations. The overarching goal of this research is to provide a framework for development of scalable ZIF-based mixed-matrix membrane that is able to deliver attractive transport properties for advanced gas separations. Zeolitic imidazolate frameworks (ZIFs) were pursued instead of conventional molecular sieves (zeolites and carbon molecular sieves) to form mixed-matrix membrane due to their intrinsic compatibility with high Tg glassy polymers. A systematic study of adsorption and diffusion in zeolitic imidazolate framework-8 (ZIF-8) suggests that this material is remarkably kinetically selective for C3 and C4 hydrocarbons and therefore promising for membrane-based gas separation and adsorptive separation. As a result, ZIF-8 was used to form mixed-matrix dense film membranes with polyimide 6FDA-DAM at varied particle loadings and it was found that ZIF-8 significantly enhanced propylene/propane separation performance beyond the “permeability-selectivity” trade-off curve for polymeric materials. Eventually, this research advanced ZIF-based mixed-matrix membrane into a scalable technology by successfully forming high-loading dual-layer ZIF-8/6FDA-DAM asymmetric mixed-matrix hollow fiber membranes with attractive propylene/propane selectivity.

This thesis presents the synthesis, properties, and applications of two important classes of metal-organic frameworks (MOFs); lanthanide MOFs and hierarchical porous zeolitic imidazolate frameworks (ZIFs). The materials have been characterized using a wide range of techniques including diffraction, imaging, various spectroscopic techniques, gas sorption, dynamical light scattering (DLS) and thermogravimetric analysis (TGA). In Chapter 1, the unique features of MOFs and ZIFs as well as their potential applications are summarized. In Chapter 2, different characterization techniques are presented. Chapter 3 describes a family of new isoreticular lanthanide MOFs synthesized using tri-topic linkers of different sizes, H3L1-H3L4, denoted SUMOF-7I-IV (Ln) (SU; Stockholm University, Ln = La, Ce, Pr, Nd, Sm, Eu and Gd, Paper I). The SUMOF-7I-III (Ln) contain permanent pores and exhibit exceptionally high thermal and chemical stability. The luminescence properties of SUMOF-7IIs are reported (Paper II). The influences of Ln ions and the tri-topic linkers as well as solvent molecules on the luminescence properties are investigated. Furthermore, the potential of SUMOF-7II (La) for selective sensing of Fe (III) ions and the amino acid tryptophan is demonstrated (Paper III).  Chapter 4 presents a simple, fast and scalable approach for the synthesis of hierarchical porous zeolitic imidazolate framework ZIF-8 and ZIF-67 using triethylamine (TEA)-assisted approach (Paper IV). Organic dye molecules and proteins are encapsulated directly into the ZIFs using the one-pot method. The photophysical properties of the dyes are improved through the encapsulation into ZIF-8 nanoparticles (Paper IV). The porosity and surface area of the ZIF materials can be tuned using the different amounts of dye or TEA. To further simplify the synthesis of hierarchical porous ZIF-8, a template-free approach is presented using sodium hydroxide, which at low concentrations induces the formation of zinc hydroxide nitrate nanosheets that serve as in situ sacrificial templates (Chapter 5, Paper V). A 2D leaf-like ZIF (ZIF-L) is also obtained using the method. The hierarchical porous ZIF-8 and ZIF-L show good performance for CO2 sorption. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 5: Manuscript.</p>

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.

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