A single polymer electrolyte membrane fuel cell (PEMFC) is comprised of several sub-millimetre thick layers of varying porosity sandwiched together. The thickness of each layer, which typically ranges from 10 to 200μm, is kept small in order to minimize the transport resistance of heat, mass, electrons, and protons, that limit reaction rate. However, the thickness of these materials presents a significant challenge to engineers characterizing the transport properties through them, which is of considerable importance to the development and optimization of fuel cells. The objective of this research is to address the challenges associated with measuring the heat conduction and gas diffusion transport properties of thin porous media used in PEMFCs. An improvement in the accuracy of the guarded heat flow technique for measuring thermal conductivity and the modified Loschmidt Cell technique for measuring gas diffusivity are presented for porous media with a sub-millimetre thickness. The improvement in accuracy is achieved by analyzing parameters in each apparatus that are sensitive to measurement error and have the largest contribution to measurement uncertainty, and then developing ways to minimize the error. The experimental apparatuses are used to investigate the transport properties of the gas diffusion layer (GDL) and the microporous layer (MPL), while the methods would also be useful in the study of the catalyst layer (CL). Gas diffusion through porous media is critical for the high current density operation of a PEMFC, where the electrochemical reaction becomes rate-limited by the diffusive flux of reactants reaching reaction sites. However, geometric models that predict diffusivity of the GDL have been identified as inaccurate in current literature. Experimental results give a better estimate of diffusivity, but published works to date have been limited by high measurement uncertainty. In this thesis, the effective diffusivity of various GDLs are measured using a modified Loschmidt cell and the relative differences between GDLs are explained using scanning electron microscopy and the method of standard porosimetry. The experimental results from this study and others in current literature are used to develop a generalized correlation for predicting diffusivity as a function of porosity in the through-plane direction of a GDL. The thermal conductivity and contact resistance of porous media are important for accurate thermal analysis of a fuel cell, especially at high current densities where the heat flux becomes large. In this thesis, the effective through-plane thermal conductivity and contact resistance of the GDL and MPL are measured. GDL samples with and without a MPL and coated with 30%-wt. PTFE are measured using the guarded steady-state heat flow technique described in the ASTM standard E 1225-04. Thermal contact resistance of the MPL with the iron clamping surface was found to be negligible, owing to the high surface contact area. Thermal conductivity and thickness of the MPL remained constant for compression pressures up to 15bar at 0.30W/m°K and 55μm, respectively. The thermal conductivity of the GDL substrate containing 30%−wt. PTFE varied from 0.30 to 0.56W/m°K as compression was increased from 4 to 15bar. As a result, the GDL contain- ing MPL had a lower effective thermal conductivity at high compression than the GDL without MPL. At low compression, differences were negligible. The constant thickness of the MPL suggests that the porosity, as well as heat and mass transport properties, remain independent of the inhomogeneous compression by the bipolar plate. Despite the low effective thermal conductivity of the MPL, thermal performance of the GDL can be improved by exploiting the excellent surface contact resistance of the MPL while minimizing its thickness.

<p>Carbon nanomaterials have a wide range of promising and exciting applications. One of the most heavily investigated carbon nanomaterial in recent history has been the carbon nanotube. The intense interest in carbon nanotubes can be attributed to the many exceptional characteristics which give them great potential to revolutionize modern mechanical, optical and electronic technologies. However, controlling these characteristics in a scalable fashion has been extremely difficult. Although some progress has been made in controlling the quality, diameter distribution and other characteristics of carbon nanotube samples, several issues still remain. The two major challenges which have stood in the way of their mainstream application are controlling their orientation and their electronic characteristics. Developing and understanding a Chemical Vapor Deposition based carbon nanotube synthesis method has been the major focus of the research presented here. Although several methods were investigated, including the so-called "fast-heating, slow-cooling" and large feeding gas flowrate methods, it was ultimately found that high-quality, perfectly aligned carbon nanotubes from a variety of metal catalysts could be grown on quartz substrates. Furthermore, it was found that using MeOH could selectively etch small-diameter metallic carbon nanotubes, which ultimately led to the productions of perfectly aligned single-walled carbon nanotube samples consisting almost entirely of semiconducting carbon nanotubes. Thiophene was utilized to investigate and support the hypothesized role of MeOH in producing these selectively gown semiconducting carbon nanotube samples. Additionally, this sulfur-containing compound was used for the first time to demonstrate a two-fold density enhancement in surface grown carbon nanotube samples. This method for selectively producing perfectly aligned semiconducting carbon nanotubes represents a major step towards the integration of carbon nanotubes into mainstream applications.</p><p>Although extremely useful in a variety of technologies, carbon nanotubes have proven impractical for use in H₂ storage applications. As such, microporous carbons have been heavily investigated for such ends. Microporous carbons have distinguished themselves as excellent candidates for H₂ storage media. They are lightweight and have a net-capacity of almost 100%, meaning that nearly all of the H₂ stored in these materials is easily recoverable for use in devices. However, developing a microporous carbon with the appropriately small pore diameters (~1nm), large pore volumes (>1cm<super>3</super>) and large surface areas (&#8805;3000m<super>2</super>/g) has proven exceedingly difficult. Furthermore, maintaining the ideal graphitic pore structure has also been an unresolved issue in many production means. Several microporous carbon synthesis methods were investigated herein, including inorganic and organically templated production schemes. Ultimately, thermally treating poly (etherether ketone) in CO₂ and steam environments was found to produce large surface area porous carbons (&#8805;3000m<super>2</super>/g) with the appropriately small pore diameters (<3nm) and large pore volumes (>1cm<super>3</super>) necessary for optimized storage of H2. Furthermore, the surface chemistry of these pores was found to be graphitic. As a result of these ideal conditions, these porous carbons were found to store ~5.8wt.% H₂ at 77K and 40bar. This represents one of the most promising materials presently under investigation by the United States Department of Energy H₂ Sorption Center of Excellence. </p><p>The success of both of these materials demonstrates the diversity and promise of carbon nanomaterials. It is hoped that these materials will be further developed and will continue to revolutionize a variety of vital technologies.</p> / Dissertation

Microporous organic polymers (MOPs) are porous materials. Owing to their high surface area, tunable pore sizes and high physicochemical stability, they are studied for applications including gas capture and separation and heterogeneous catalysis. In this thesis, a series of imine/azo-linked MOPs were synthesized. The MOPs were examined as potential CO2 sorbents and as supports for heterogeneous catalysis. The MOPs were synthesized by Schiff base polycondensations and oxidative couplings. The porosities of the imine-linked MOPs were tunable and affected by a range of factors, such as the synthesis conditions, monomer lengths, monomer ratios. All the MOPs had ultramicropores and displayed relatively high CO2 uptakes and CO2-over-N2 selectivities at the CO2 concentrations relevant for post-combustion capture of CO2. Moreover, the ketimine-linked MOPs were moderately hydrophobic, which might increase their efficiency for CO2 capture and separation. The diverse synthesis routes and rich functionalities of MOPs allowed further post-modification to improve their performance in CO2 capture. A micro-/mesoporous polymer PP1-2, rich in aldehyde end groups, was post-synthetically modified by the alkyl amine tris(2-aminoethyl)amine (tren). The tethered amine moieties induced chemisorption of CO2 on the polymer, which was confirmed by the study of in situ infrared (IR) and solid-state 13C nuclear magnetic resonance (NMR) spectroscopy. As a result, the modified polymer PP1-2-tren had a large CO2 capacity and very high CO2-over-N2 selectivity at low partial pressures of CO2. Pd(II) species were incorporated in the selected MOPs by means of complexation or chemical bonding with the imine or azo groups. The Pd(II)-rich MOPs were tested as heterogeneous catalysts for various organic reactions. The porous Pd(II)-polyimine (Pd2+/PP-1) was an excellent co-catalyst in combination with chiral amine for cooperatively catalyzed and enantioselective cascade reactions. In addition, the cyclopalladated azo-linked MOP (Pd(II)/PP-2) catalyzed Suzuki and Heck coupling reactions highly efficiently. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Accepted. Paper 7: Manuscript.</p>

A single polymer electrolyte membrane fuel cell (PEMFC) is comprised of several sub-millimetre thick layers of varying porosity sandwiched together. The thickness of each layer, which typically ranges from 10 to 200μm, is kept small in order to minimize the transport resistance of heat, mass, electrons, and protons, that limit reaction rate. However, the thickness of these materials presents a significant challenge to engineers characterizing the transport properties through them, which is of considerable importance to the development and optimization of fuel cells. The objective of this research is to address the challenges associated with measuring the heat conduction and gas diffusion transport properties of thin porous media used in PEMFCs. An improvement in the accuracy of the guarded heat flow technique for measuring thermal conductivity and the modified Loschmidt Cell technique for measuring gas diffusivity are presented for porous media with a sub-millimetre thickness. The improvement in accuracy is achieved by analyzing parameters in each apparatus that are sensitive to measurement error and have the largest contribution to measurement uncertainty, and then developing ways to minimize the error. The experimental apparatuses are used to investigate the transport properties of the gas diffusion layer (GDL) and the microporous layer (MPL), while the methods would also be useful in the study of the catalyst layer (CL). Gas diffusion through porous media is critical for the high current density operation of a PEMFC, where the electrochemical reaction becomes rate-limited by the diffusive flux of reactants reaching reaction sites. However, geometric models that predict diffusivity of the GDL have been identified as inaccurate in current literature. Experimental results give a better estimate of diffusivity, but published works to date have been limited by high measurement uncertainty. In this thesis, the effective diffusivity of various GDLs are measured using a modified Loschmidt cell and the relative differences between GDLs are explained using scanning electron microscopy and the method of standard porosimetry. The experimental results from this study and others in current literature are used to develop a generalized correlation for predicting diffusivity as a function of porosity in the through-plane direction of a GDL. The thermal conductivity and contact resistance of porous media are important for accurate thermal analysis of a fuel cell, especially at high current densities where the heat flux becomes large. In this thesis, the effective through-plane thermal conductivity and contact resistance of the GDL and MPL are measured. GDL samples with and without a MPL and coated with 30%-wt. PTFE are measured using the guarded steady-state heat flow technique described in the ASTM standard E 1225-04. Thermal contact resistance of the MPL with the iron clamping surface was found to be negligible, owing to the high surface contact area. Thermal conductivity and thickness of the MPL remained constant for compression pressures up to 15bar at 0.30W/m°K and 55μm, respectively. The thermal conductivity of the GDL substrate containing 30%−wt. PTFE varied from 0.30 to 0.56W/m°K as compression was increased from 4 to 15bar. As a result, the GDL contain- ing MPL had a lower effective thermal conductivity at high compression than the GDL without MPL. At low compression, differences were negligible. The constant thickness of the MPL suggests that the porosity, as well as heat and mass transport properties, remain independent of the inhomogeneous compression by the bipolar plate. Despite the low effective thermal conductivity of the MPL, thermal performance of the GDL can be improved by exploiting the excellent surface contact resistance of the MPL while minimizing its thickness.

Gegenstand der Arbeit ist die PFG NMR (nuclear magnetic resonance with pulsed field gradients), wobei speziell die apparativen und experimentellen Bedingungen untersucht werden, welche sich durch die Verwendung ultra-hoher gepulster magnetischer Feldgradienten von bis zu 35T/m ergeben. Motiv für die Arbeit ist die Untersuchung von Diffusionserscheinungen in mikroporösen Wirtssystemen mit inneren magnetischen Feldgradienten oder/und kurzen T2-Relaxationzeiten. Nach Zusammenstellung der notwendigen Werkzeuge zur mathematischen Beschreibung von PFG NMR-Experimenten werden die aus der Literatur bekannten Impulssequenzen kritisch untersucht und durch eigene Weiterentwicklungen ergänzt. Für wichtige PFG NMR-Impulssequenzen wird eine verallgemeinerte Schreibweise vorgestellt und auf beliebige Formen der gepulsten magnetischen Feldgradienten ausgedehnt. Weiterhin werden Störeinflüsse auf das PFG NMR-Experiment untersucht und zunächst in allgemeiner Form Möglichkeiten zu deren Beseitigung bzw. Unterdrückung dargestellt. Die so gewonnenen Erkenntnisse fanden konkrete Anwendung bei der Konzeption und dem Bau des PFG NMR-Spektrometers Fegris 400 NT. Dieses Gerät wird, soweit es den Gegenstand der Arbeit berührt, ebenfalls beschrieben und in der Anlage dokumentiert. Abschließend sind einige Untersuchungen, die mit dem Fegris 400 NT durchgeführt wurden und in der dargestellten Form erst mit diesem Gerät möglich waren, kurz skizziert, wobei für weitergehende Informationen auf die entsprechenden Veröffentlichungen verwiesen wird.

Made available in DSpace on 2014-12-17T14:06:51Z (GMT). No. of bitstreams: 1 ThiagoC.pdf: 1828528 bytes, checksum: f789d02379757a5c26566b00a092e4c1 (MD5) Previous issue date: 2009-02-03 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / heterogeneous catalyst such as a silicoaluminophosphate, molecular sieve with AEL (Aluminophosphate eleven) structure such as SAPO-11, was synthesized through the hydrothermal method starting from silica, pseudoboehmite, orthophosphoric acid (85%) and water, in the presence of a di-isopropylamine organic template. For the preparation of SAPO-11 in a dry basis it was used as reactants: DIPA; H3PO4; SiO4; Pseudoboehmite and distilled water. The crystallization process occurred when the reactive hydrogel was charged into a vessel and autoclaved at 200?C for a period of 72 hours under autogeneous pressure. The obtained material was washed, dried and calcined to remove the molecular sieves of DIPA. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared spectroscopy (FT-IR), nitrogen adsorption (BET) and thermal analysis (TG/DTG). The acidic properties were determined using adsorption of nbutylamine followed by programmed thermodessorption. This method revealed that SAPO-11 shows an acidity that ranges from weak to moderate. However, a small quantity of strong acid sites could be detected there. The deactivation of the catalysts was conducted by artificial coking followed by the cracking of the n-hexane in a fixed bed with a continuous flow micro-reactor coupled on line to a gas chromatograph. The main products obtained were: ethane, propane, isobutene, n-butane, n-pentane and isopentane. The Vyazovkin (model-free) kinetics method was used to determine the regeneration and removal of the coke / Um catalisador heterog?neo do tipo silicoaluminofosfato, peneira molecular com estrutura AEL (Aluminophosphate eleven), como o SAPO-11, foi sintetizado pelo m?todo hidrot?rmico a partir de alumina hidratada (pseudobohemita), ?cido fosf?rico 85%, s?lica gel, ?gua e di-isopropilamina (DIPA) usada como direcionador estrutural org?nico. Para a prepara??o de SAPO-11 em base seca foram necess?rias como reagentes: DIPA; H3PO4:; SiO4; Pseudoboehmita e ?gua destilada. O processo de cristaliza??o ocorreu ? temperatura de 200 0C durante 72 h, quando foi poss?vel obter a fase pura para o SAPO-11. O material obtido foi lavado com ?gua deionizada, seco e calcinado para remover as mol?culas do direcionador. Posteriormente a amostra foi caracterizada por difra??o de raios-X (DRX), microscopia eletr?nica de varredura (MEV), espectroscopia de absor??o na regi?o do infravermelho (FT-IR), adsor??o de nitrog?nio (BET) e an?lise t?rmica via TG/DTG. As propriedades ?cidas foram determinadas usando adsor??o de n-butilamina seguida de termodessor??o programada. Este m?todo revelou que a amostra SAPO-11 apresenta uma acidez tipicamente fraca a moderada. Entretanto, uma pequena quantidade de s?tios ?cidos fortes foi detectada. A desativa??o dos catalisadores foi conduzida pelo coqueamento artificial da amostra, seguida da rea??o de craqueamento do n-hexano em um microrreator catal?tico de leito fixo com fluxo cont?nuo acoplado em linha com um cromat?grafo a g?s. Como principais produtos foram obtidos: etano, propano, isobutano, n-butano,e n-pentano, isopentano. Para determinar a regenera??o e a remo??o do coque foi aplicado o m?todo cin?tico Vyazovkin (Model Free Kinetics)

Submitted by Ana Hilda Fonseca (anahilda@ufba.br) on 2014-10-29T23:28:41Z No. of bitstreams: 1 Tese_Doutorado_Saulo.pdf: 12043320 bytes, checksum: 9e747c238576b9219840bfcd38f02a2e (MD5) / Approved for entry into archive by Ana Hilda Fonseca (anahilda@ufba.br) on 2014-10-30T02:15:21Z (GMT) No. of bitstreams: 1 Tese_Doutorado_Saulo.pdf: 12043320 bytes, checksum: 9e747c238576b9219840bfcd38f02a2e (MD5) / Made available in DSpace on 2014-10-30T02:15:21Z (GMT). No. of bitstreams: 1 Tese_Doutorado_Saulo.pdf: 12043320 bytes, checksum: 9e747c238576b9219840bfcd38f02a2e (MD5) / FINEP, CNPq / As restrições difusionais aos reagentes, causadas pelos microporos, limitam o uso das zeólitas no processamento de moléculas pesadas. Isto demanda o desenvolvimento de materiais que combinem as propriedades de zeólitas com as de materiais mesoporosos. Um número significativo de procedimentos experimentais, pré ou pós síntese, vem sendo sugerido para a obtenção de zeólitas hierarquicamente estruturadas. As metodologias de síntese mais bem sucedidas envolvem o uso de agentes geradores de mesoporosidade (agentes orgânicos e nanopartículas) ou nanomoldes (moldagem em nanoespaços), que geram sólidos com mesoporosidade intracristalina com uma estreita distribuição de tamanho de poros; isto resulta em sólidos contendo mesoporos, além dos microporos intrínsecos das zeólitas. Entretanto, ainda não existem estudos sistemáticos, que permitam estabelecer o efeito das variáveis de preparação sobre as características dos sólidos finais. A fim de superar essa dificuldade, neste trabalho foi estudado o efeito do tempo e da temperatura de cristalização do gel de síntese sobre as características de materiais baseados em mordenita com estrutura hierárquica de poros. Na preparação das amostras, adicionou-se um organossilano gerador de mesoporosidade (TPOAC, cloreto de [3- (trimetoxissilil)propil]octadecildimetilamônio), ao gel de síntese da mordenita, que foi cristalizado por diferentes períodos e em distintas temperaturas. Os sólidos obtidos foram submetidos à troca iônica com cloreto de amônio e posterior calcinação, de modo a obter a forma ácida do material. As amostras foram caracterizadas por termogravimetria, espectroscopia no infravermelho com transformada de Fourier, difração de raios X, análise textural por adsorção de nitrogênio, ressonância magnética nuclear de 29Si e de 27Al, microscopia eletrônica de varredura e medidas de acidez por dessorção de amônia à temperatura programada. Observou-se que a formação da mordenita contendo mesoporos é influenciada pelo tempo e temperatura de cristalização do gel da zeólita. O emprego de tempos relativamente curtos ou baixas temperaturas favorece a formação de um sólido amorfo, enquanto longos tempos ou elevadas temperaturas favorecem a formação de mesoporos intracristalinos na mordenita. Por outro lado, tempos e temperaturas intermediárias favoreceram a formação da mordenita com uma estrutura hierárquica de poros e mesoporos desordenados. O aumento da cristalinidade da mordenita acarreta uma diminuição na área e no volume de mesoporos, mas promove um acréscimo na área e no volume de microporos. A área externa também tende a diminuir devido ao aumento do tamanho do cristal da mordenita em função da cristalinidade. Os sólidos obtidos foram susceptíveis à desaluminação durante a etapa de calcinação. A extensão da desaluminação diminuiu com o aumento do tempo ou da temperatura de cristalização, devido à inserção dos átomos de alumínio na rede da zeólita em formação. Porém, em tempos de cristalização longos e temperaturas altas, pode ocorrer a redispersão dos átomos de alumínio. Todos os sólidos apresentaram elevada acidez que aumentou com a cristalinidade. Entretanto, nas amostras preparadas em tempos curtos e temperaturas baixas, a maioria dos sítios apresentou força ácida moderada, enquanto aquelas obtidas em tempos longos e temperaturas altas apresentaram maior quantidade de sítios ácidos fortes. / The diffusion restrictions of the reactants caused by the micropores limit the use of zeolites for processing heavy molecules. This demands for the development of materials that can combine the properties of zeolites and of mesoporous materials. A significant number of experimental procedures, pre or post synthesis, has been suggested for obtaining hierarchically structured zeolites. The most successful synthesis involve the use of mesoporosity generating agents (nanoparticles and organic agents) or nanotemplates (templating in nanospaces), which generate solids with intracristaline mesoporosity with a narrow pore size distribution. This results in solids containing mesoporous besides the intrinsic zeolite micropores. However, there is not any systematic study which allows to state the effect of crystallization time and temperature of the synthesis gel on the properties of the final solid. In order to overcome this difficulty, the effect of time and temperature of the synthesis gel on the properties of mordenite-based materials with hierarchical pore structure was studied in this work. In the samples preparation a mesoporosity generating organosilane (TPOAC, [3-(trimethoxysilyl) propyl] octadecyldimethylammonium chloride) was added to the synthesis gel of mordenite, which was crystallized for different times and temperatures. The solids were then submitted to ion exchange with ammonium chloride and further calcination to obtain the acidic form of the zeolite. The samples were characterized by thermogravimetry, Fourier transformed infrared spectroscopy, X-ray diffraction, textural analysis by nitrogen adsorption, 29Si and 27Al NMR, scanning electron microscopy and acidity measurements by ammonia desorption. It was observed that the formation of mordenite containing mesoporous is affected by the time and temperature of crystallization of the zeolite gel. The use of relatively short times and low temperatures favors the formation of an amorphous solid, while long times or high temperatures favor the formation of intracristaline mesoporosity in the mordenite. On the other hand, intermediate times and temperatures favor the formation of mordenite with hierarchical pore structure and disordered mesopores. The increase in mordenite crystallinity leads to a decrease in mesopore area and volume but promotes an increase in micropore area and volume. The external area also tends to decrease due to the increased crystal size as a function of mordenite crystallinity. The solids obtained were susceptible to dealumination during the calcination step. The degree of dealumination decreased with the increasing crystallization time or temperature due to the insertion of aluminum atoms in the zeolite lattice. However, at long crystallization times and high crystallization temperatures the redispersion of aluminum atoms can occur. All solids showed high acidity which increased as a function of crystallinity. However, the samples prepared at short times and low temperatures showed the majority of moderate acid sites of medium strength, whereas those obtained at long times and high temperatures have more strong acid sites. Thus, intermediate times and temperatures favor the formation of solids having zeolitic characteristics and high mesoporosity.

abstract: Membrane-based gas separation is promising for efficient propylene/propane (C3H6/C3H8) separation with low energy consumption and minimum environment impact. Two microporous inorganic membrane candidates, MFI-type zeolite membrane and carbon molecular sieve membrane (CMS) have demonstrated excellent thermal and chemical stability. Application of these membranes into C3H6/C3H8 separation has not been well investigated. This dissertation presents fundamental studies on membrane synthesis, characterization and C3H6/C3H8 separation properties of MFI zeolite membrane and CMS membrane. MFI zeolite membranes were synthesized on &#945;-alumina supports by secondary growth method. Novel positron annihilation spectroscopy (PAS) techniques were used to non-destructively characterize the pore structure of these membranes. PAS reveals a bimodal pore structure consisting of intracrystalline zeolitic micropores of ~0.6 nm in diameter and irregular intercrystalline micropores of 1.4 to 1.8 nm in size for the membranes. The template-free synthesized membrane exhibited a high permeance but a low selectivity in C3H6/C3H8 mixture separation. CMS membranes were synthesized by coating/pyrolysis method on mesoporous &#947;-alumina support. Such supports allow coating of thin, high-quality polymer films and subsequent CMS membranes with no infiltration into support pores. The CMS membranes show strong molecular sieving effect, offering a high C3H6/C3H8 mixture selectivity of ~30. Reduction in membrane thickness from 500 nm to 300 nm causes an increase in C3H8 permeance and He/N2 selectivity, but a decrease in the permeance of He, N2 and C3H6 and C3H6/C3H8 selectivity. This can be explained by the thickness dependent chain mobility of the polymer film resulting in final carbon membrane of reduced pore size with different effects on transport of gas of different sizes, including possible closure of C3H6-accessible micropores. CMS membranes demonstrate excellent C3H6/C3H8 separation performance over a wide range of feed pressure, composition and operation temperature. No plasticization was observed at a feed pressure up to 100 psi. The permeation and separation is mainly controlled by diffusion instead of adsorption. CMS membrane experienced a decline in permeance, and an increase in selectivity over time under on-stream C3H6/C3H8 separation. This aging behavior is due to the reduction in effective pore size and porosity caused by oxygen chemisorption and physical aging of the membrane structure. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2015

abstract: ABSTRACT Large-pore metal-organic framework (MOF) membranes offer potential in a number of gas and liquid separations due to their wide and selective adsorption capacities. A key characteristic of a number of MOF and zeolitic imidazolate framework (ZIF) membranes is their highly selective adsorption capacities for CO2. These membranes offer very tangible potential to separate CO2 in a wide array of industrially relevant separation processes, such as the separation from CO2 in flue gas emissions, as well as the sweetening of methane. By virtue of this, the purpose of this dissertation is to synthesize and characterize two linear large-pore MOF membranes, MOF-5 and ZIF-68, and to study their gas separation properties in binary mixtures of CO¬2/N2 and CO2/CH4. The three main objectives researched are as follows. The first is to study the pervaporation behavior and stability of MOF-5; this is imperative because although MOF-5 exhibits desirable adsorption and separation characteristics, it is very unstable in atmospheric conditions. In determining its stability and behavior in pervaporation, this material can be utilized in conditions wherein atmospheric levels of moisture can be avoided. The second objective is to synthesize, optimize and characterize a linear, more stable MOF membrane, ZIF-68. The final objective is to study in tandem the high-pressure gas separation behavior of MOF-5 and ZIF-68 in binary gas systems of both CO2/N2 and CO2/CH4. Continuous ZIF-68 membranes were synthesized via the reactive seeding method and the modified reactive seeding method. These membranes, as with the MOF-5 membranes synthesized herein, both showed adherence to Knudsen diffusion, indicating limited defects. Organic solvent experiments indicated that MOF-5 and ZIF-68 were stable in a variety of organic solvents, but both showed reductions in permeation flux of the tested molecules. These reductions were attributed to fouling and found to be cumulative up until a saturation of available bonding sites for molecules was reached and stable pervaporation permeances were reached for both. Gas separation behavior for MOF-5 showed direct dependence on the CO2 partial pressure and the overall feed pressure, while ZIF-68 did not show similar behavior. Differences in separation behavior are attributable to orientation of the ZIF-68 membranes. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2015

The anthropogenic carbon dioxide (CO2) emission into the atmosphere, mainly through the combustion of fossil fuels, has resulted in a balance disturbance of the carbon cycle. Overwhelming scientific evidence proves that the escalating level of atmospheric CO2 is deemed as the main culprit for global warming and climate change. It is thus imperative to develop viable CO2 capture and sequestration (CCS) technologies to reduce CO2 emissions, which is also essential to avoid the potential devastating effects in future. The drawbacks of energy-cost, corrosion and inefficiency for amine-based wet-scrubbing systems which are currently used in industry, have prompted the exploration of alternative approaches for CCS. Extensive efforts have been dedicated to the development of functional porous materials, such as activated carbons, zeolites, porous organic polymers, and metal-organic frameworks (MOFs) to capture CO2. However, these adsorbents are limited by either poor selectivity for CO2 separation from gas mixtures or low CO2 adsorption capacity. Therefore, it is still highly demanding to design next-generation adsorbent materials fulfilling the requirements of high CO2 selectivity and enough CO2 capacity, as well as high water/moisture stability under practical conditions. Metal-organic frameworks (MOFs) have been positioned at the forefront of this area as a promising type of candidate amongst various porous materials. This is triggered by the modularity and functionality of pore size, pore walls and inner surface of MOFs by use of crystal engineering approaches. In this work, several effective strategies, such as incorporating 1,2,3-triazole groups as moderate Lewis base centers into MOFs and employing flexible azamacrocycle-based ligands to build MOFs, demonstrate to be promising ways to enhance CO2 uptake capacity and CO2 separation ability of porous MOFs. It is revealed through in-depth studies on counter-intuitive experimental observations that the local electric field favours more than the richness of exposed nitrogen atoms for the interactions between MOFs and CO2 molecules, which provides a new perspective for future design of new MOFs and other types of porous materials for CO2 capture. Meanwhile, to address the water/moisture stability issue of MOFs, remote stabilization of copper paddlewheel clusters is achieved by strengthening the bonding between organic ligands and triangular inorganic copper trimers, which in turn enhances the stability of the whole MOF network and provides a better understanding of the mechanism promoting prospective suitable MOFs with enhanced water stability. In contrast with CO2 capture by sorbent materials, the chemical transformation of the captured CO2 into value-added products represents an alternative which is attractive and sustainable, and has been of escalating interest. The nanospace within MOFs not only provides the inner porosity for CO2 capture, but also engenders accessible room for substrate molecules for catalytic purpose. It is demonstrated that high catalytic efficiency for chemical fixation of CO2 into cyclic carbonates under ambient conditions is achieved on MOF-based nanoreactors featuring a high-density of well-oriented Lewis active sites. Furthermore, described for the first time is that CO2 can be successfully inserted into aryl C-H bonds of a MOF to generate carboxylate groups. This proof-of-concept study contributes a different perspective to the current landscape of CO2 capture and transformation. In closing, the overarching goal of this work is not only to seek efficient MOF adsorbents for CO2 capture, but also to present a new yet attractive scenario of CO2 utilization on MOF platforms.