Porous organic polymers (POPs) received great attention in recent years because of their novel properties such as permanent porosity, adjustable chemical nature, and remarkable thermal and chemical stability. These attractive features make POPs very promising candidates for use in gas separation and storage applications. In particular, CO2 capture and separation from gas mixtures by POPs have been intensively investigated in recent years because of the greenhouse nature of CO2, which is considered a leading cause for global warming. CO2 chemical absorption by amine solutions from the flue gas of coal-fired power plants suffers from several challenges such as high-energy consumption in desorption, chemical instability, volatility, and corrosive nature, limiting the widespread use of this technology. To mitigate these limitations, new adsorbents with improved CO2 capturing properties need to be designed, synthesized, and tested. Alternatively, the use of cleaner fuels such as methane can reduce CO2 release or completely eliminates it in the case of hydrogen. However, the on-board storage of methane and hydrogen for automotive applications remains a great challenge. With these considerations in mind, our research goals in this dissertation focus on the systematic design and synthesis of N-rich POPs and their use in small gas (H2 and CH4) storage as well as selective CO2 capture from gas mixtures. In particular, we have studied the effect of integrating pyrene and triazine building units into benzimidazole-linked polymers (BILPs) and covalent organic frameworks (COFs) on gas storage and separation. We have found that pyrene-based BILPs exhibit remarkable selective CO2 capturing capacities under industrial settings (VAS, PSA). However the methane and hydrogen storage capacities of BILPs were found to be only modest especially at high pressure due to their moderate surface area and pore volume. We addressed these limitations by the synthesis of a highly porous imine-linked COF (ILCOF-1), which has very high surface area and improved hydrogen and methane uptakes when compared to BILPs. We have demonstrated that the use of pyrene in BILPs and COFs can direct frameworks growth through - stacking and improve porosity and pore volume whereas the use of triazine is instrumental in improving the binding affinity of the frameworks towards CO2.

Global climate change is one of the most challenging problems that human beings are facing. The large anthropogenic emission of CO2 in the atmosphere is one of the major causes for the climate change. Coal-fired power plants are the single-largest anthropogenic emission sources globally, accounting for approximately one third of the total CO2 emissions. It is therefore necessary to reduce CO2 emission from coal-fired power plants. Current technologies for the post-combustion CO2 capture from flue gas streams can be broadly classified into the three categories: absorption, adsorption, and membrane processes. Despite challenges, CO2 capture by adsorption using solid sorbents and membranes offers opportunities for energy-efficient capture and storage of CO2. Nanoporous materials have attracted tremendous interest in research and development due to their potential in conventional applications such as catalysis, ion-exchange, and gas separation as well as in advanced applications such as sensors, delivery, and micro-devices. In the first part of this dissertation, we will study the synthesis of membranes using an emerging class of nanoporous materials, metal-organic frameworks (MOFs) for carbon dioxide (CO2) separations. Due to the unique chemistry of MOFs which is very different from that of zeolites, the techniques developed for the synthesis of zeolite membranes cannot be used directly. In order to overcome this challenge, a couple of novel techniques were developed: 1) "thermal seeding" for the secondary growth and 2) "surface modification" for the in situ growth. Membranes of HKUST-1 and ZIF-8, two of the most important MOFs, were prepared on porous α-alumina supports using thermal seeding and the surface modification techniques, respectively. The second part of this dissertation demonstrates a simple and commercially viable application of nanoporous materials (zeolite 5A and amine-functionalized mesoporus silica), storing CO2 as a micro-fire extinguishers in polymers. Materialist is observed that by dispersing these highly CO2-philic nanoporous materials in polymer matrices, the propagation of flame was greatly retarded and extinguished. This flame retarding behavior is attributed to the fact that CO2 released from the sorbents (zeolite 5A and mesoporous silica), blocks the flow of oxygen, therefore causing the fire to be effectively extinguished. Our results suggest that the binding strength of CO2 on sorbents play an important role. If the binding strength of CO2 is too low, CO2 releases too early, thereby ineffective in retarding the flame.

Ce travail est une étude de l'adsorption/condensation de gaz simples (Ar, Kr, N2) dans le silicium mésoporeux (Si-p). Nous montrons par microscopie électronique<br />en transmission et analyse par faisceau d'ions que ce matériau présente des nanopores tubulaires, de section polygonale et dissymétrique (désordre morphologique) non connectés (pas de désordre topologique). Ces propriétés placent le Si-p entre les nanopores réguliers<br />MCM41 et les verres mésoporeux (Vycor). La taille moyenne et la longueur des pores du Si-p est contrôlée par les paramètres de la synthèse électrochimique. L'invasion du Si-p par une vapeur met en évidence le phénomµene de condensation capillaire ainsi que son<br />irréversibilité (hystérésis) dans la courbe isotherme d'adsorption. Les pressions de condensation expérimentales sont, pour la taille des pores du Si-p (10-40 nm), plus basses que celles prédites théoriquement pour des pores cylindriques. Nous avons réalisé des simulations Monte Carlo pour étudier à l'échelle moléculaire l'adsorption/condensation d'Ar à<br />77 K dans des pores de différentes géométries et formes. La présence d'une constriction (défaut morphologique étendu) modifie fondamentalement le mécanisme de remplissage du pore et abaisse fortement la pression de condensation. En préparant des substrats Si-p<br />avec des pores ouverts µa une ou aux deux extrémités, nous montrons que les cycles d'adsorption sont irréversibles dans chaque cas. Ce résultat est en contradiction avec la conjecture de Cohan prévoyant la réversibilité dans le cas des pores ouverts à une extrémité et que nous validons par simulation. De plus, la dissymétrie de la boucle d'hystérésis expérimentale n'est pas attendue pour un ensemble de mésopores non-connectés. Nos résultats obtenus pour différents gaz et tailles de pore semblent indiquer que cette dissymétrie n'est pas due à la présence d'éventuelles constrictions. Nous proposons alors qu'il puisse exister un couplage entre pores lors de la désorption.

The workshop program will focus on adsorption measurement techniques and methodologies for the assessment of adsorption properties and textural/structural characterization of novel nanoporous materials including zeolites, carbons, MOFs as well as materials consisting of hierarchically structured pore networks. A major point will be the correlation of textural properties, adsorption behavior, catalytic reaction pathways as well as transport properties with applications in gas and energy storage, separations and catalysis. Within this framework, the workshop will offer a platform for scientific discussions and for a knowledge transfer between various scientific areas where diffusion and transport properties of porous materials are of importance.

With reference to these advantages, the poster goes the other way round and identifies a couple of similarities where, on looking at molecular diffusion in nanoporous materials, one is able to recognize features of spreading, which may occur in quite different fields of research. The examples presented include (i) considering molecular uptake and release with nanoporous particles as a model for, respectively, occupation of a habitat by a new species and, vice versa, for the loss of a species in this habitat [2], (ii) the effect of additional highways on overall mass transfer [3,4], (iii) transport impediment (and enhancement!) by diffusant interference [5], (iv) invader-induced changes in the host system [2] and (v) host-induced changes of the invaders [6].

Successful design and application of nanoporous materials are essentially dependent on the molecular diffusion. Two mechanisms, i.e. surface barriers and intracrystalline diffusion, may dominate the mass transport. In the previous studies, these two mechanisms are difficult to determine with certainty by dual resistance model [1] (DRM). Here, we derive an expression of uptake rate relying solely on surface permeability, which provides a method to directly quantify the surface barriers. Subsequently, the effects of surface barriers and intracrystalline diffusion could be identified separately.

Hydrogen storage is a developing technology that can be used as an energy vector for sustainable energy applications such as fuel cells for transport applications or for supplying power to the grid in moments of high demand. However, before hydrogen can be used as a practical energy vector, hydrogen storage issues, such as low gravimetric storage density, need to be addressed. One possible solution could be using nanoporous materials to physically adsorb hydrogen at low temperatures and moderate pressures. Hydrogen adsorption excess isotherms in solid-state porous materials can be obtained experimentally. However, the total amount stored in them, a quantity of more practical interest, cannot be measured by experimental techniques. Therefore, a model developed at the University of Bath is used to predict the total amount of hydrogen contained in nanoporous materials from their experimentally derived excess isotherm data. According to inelastic neutron scattering experiments (TOSCA, ISIS, RAL, Oxfordshire), solid-like hydrogen is likely to exist within the pores. The model is applied in this work in order to search for relationships between intrinsic properties of the materials (BET surface area, pore volume and pore size) and the predicted total hydrogen capacity of the materials. The model assumes adsorbed hydrogen at a constant density within the pore (defined as the absolute), also taking bulk hydrogen in the pore (amount that is not considered to be adsorbed by the adsorbent), into account. Several MOF datasets have been used to search for these relations, since they are the materials that have the highest hydrogen uptake in solid-state adsorption. Different MOFs and MOF families have been tested in order to widen the range of the correlations. Also, different strategies, such as fixing the pore volume when applying the fittings, relying on experimental data, or using high pressure hydrogen isotherm data to increase the robustness of the model have been researched. These MOFs have been either synthesized and characterized at the University of Bath or their datasets obtained from literature. Some of these MOFs with zeolitic structure exhibited unreported flexibility, being their structures further characterized. Changes on accessible pore size for hydrogen storage were also investigated using C60 in IRMOF-1. The final aim of this work is to find possible correlations between BET surface area, pore volume and pore size to find out what the values of these parameters have to be in a specific material to fulfil the DOE hydrogen storage requirements.

Nanoporous materials have attracted tremendous interest, investment and effort in research and development due to their potential applications in various areas such as membranes, catalysis, sensors, delivery, and micro devices. Controlling a nanoporous material’s microstructure is of great interest due to the strong influence on efficiency and performance. For particles, microstructure refers to particle size, shape, surface morphology, and composition. When discussing thin films, microstructure includes film thickness, crystal orientation and grain boundaries. In this respect, we focus to develop novel methods for the synthesis and characterization of nanoporous materials and their films, which are capable of controlling the microstructure of material. This dissertation is composed of two main sections and each explores the fabrication of a different nanoporous material: 1) A simple fabrication method for producing oriented MFI zeolite membranes with controlled thickness, orientation, and grain boundary; 2) A microfluidic synthesis of ordered mesoporous silica particles with controllable size, shape, surface morphology, and composition. The first section of this dissertation demonstrates a simple and commercially viable method termed the micro-tiles-and-mortar method to make continuous b-oriented MFI membranes with controlled membrane microstructure. This simple method allows for control of the thickness of the membrane by using plate-like seed crystals with different thicknesses along the b-axis (0.5 μm to 2.0 μm), as well as to manipulate the density and structure of grain boundaries. Microstructural effects of silicalite-1 membranes on the gas separation are investigated by measuring the permeation and separation for xylene isomers. In the second section of this dissertation, a new synthesis method for the ordered mesoporous silica particles with controllable microstructure is demonstrated. This novel method combines a microfluidic emulsification technique and nonaqueous inorganic synthesis with a diffusion-induced self-assembly (DISA). The systematic control of the particle microstructure such as size, shape, and surface morphology is shown by adjusting microfluidic conditions.

Metal-organic frameworks (MOFs) or porous coordination polymers (PCPs) have become the focus of intense study over the past decade due to their potential for advancing a variety of applications including air purification, gas storage, adsorption separations, catalysis, gas sensing, drug delivery, and so on. These materials have some distinct advantages over traditional porous materials such as the well-defined structures, uniform pore sizes, chemically functionalized sorption sites, and potential for post-synthetic modification, etc. Thus, synthesis and adsorption studies of porous MOFs have increased substantially in recent years. Among various prospective applications, air purification is one of the most immediate concerns, which has urgent requirements to improve current nuclear, biological, and chemical (NBC) filters involving commercial and military purposes. Thus, the major goal of this funded project is to search, synthesize, and test these novel hybrid porous materials for adsorptive removal of toxic industrial chemicals (TICs) and chemical warfare agents (CWAs), and to install the benchmark for new-generation NBC filters. The objective of this study is three-fold: (i) Advance our understanding of coordination chemistry by synthesizing novel MOFs and characterizing these porous coordination polymers; (ii) Evaluate porous MOF materials for gas-adsorption applications including CO2 capture, CH4 storage, other light gas adsorption and separations, and examine the chemical and physical properties of these solid adsorbents including thermal stability and heat capacity of MOFs; (iii) Evaluate porous MOF materials for next-generation NBC filter media by adsorption breakthrough measurements of TICs on MOFs, and advance our understanding about structure-property relationships of these novel adsorbents.

The controlled assembly of molecular building blocks is an emerging strategy that allows for the preparation of materials with tailor-made properties. This involves the precise combination of molecular subunits that interact with one another via specifically designed reactive sites. Such a strategy has produced materials exhibiting remarkable properties, including those based on metal-organic frameworks and single-molecule magnets. The present Thesis aims to highlight how such metal-organic assemblies can be engineered at the molecular level to promote certain desired functionalities. Specifically, Chapter 2 will focus on the confinement effects of a crystalline sponge on a ferrocene-based guest molecule that is nanostructured within the porous cavities of a host material. In doing so, we evaluate how one can exert some level of control over the binding sites of the guest molecule, through the addition of electron-withdrawing groups, as well as tuning the physical properties of the guest itself through molecular encapsulation. Notably, we demonstrate a distinct change in the dynamic rotational motion of the ferrocene molecules once confined within the crystalline sponge. In Chapter 3, we investigate the generation of slow relaxation of the magnetization from a Co(II)-based metal-organic framework. We compare this to a closely related 2D Co(II) sheet network, and how slight changes in the crystal field, probed through computational methods, can impact the magnetic behaviour. This type of study may be particularly beneficial in the optimization of single-ion magnets, by sequestering metal centres in select chemical environments, and minimizing molecular vibrations that may offer alternative magnetic relaxation pathways. We extend these principles in Chapter 4, through the use of a nitrogen-rich ligand that acts as a scaffold for Ln(III) ions, thereby yielding 0D and 1D architectures. The coordination chemistry of Ln(III) ions with N-donor ligands remains scarce, especially when evaluated from a magnetic perspective, and therefore, we sought to determine the magnetic behaviour of such compounds. The monomeric unit displays clear single-molecule magnet behaviour with an energetic barrier for the reversal of the magnetization, while the 1D chain displays weaker magnetic characteristics. Nevertheless, such compounds incorporating nitrogen-rich ligands offer much promise in the design of environmentally-friendly energetic materials. In Chapter 5, we take a look at different two different systems that involve the formation of radical species. On one hand, we can promote enhanced magnetic communication between Ln(III) ions, which is typically quite challenging to achieve given the buried nature of the 4f orbitals, and on the other hand, we rely on a redox-active ligand to design stimuli-responsive metal-organic assemblies. The latter case provides access to “smart” molecular materials that can respond to changes in their environment. Here, a multi-stimuli responsive nanobarrel was studied, which displayed sensitivity to ultraviolet radiation, heat and chemical reduction. Lastly, Chapter 6 provides a new method for the systematic generation of cationic frameworks, termed Asymmetric Ligand Exchange (ALE). This strategy focuses on the replacement of linear dicarboxylates with asymmetric linkers that features one less negative charge, in order to tune the ionicity of porous frameworks. This allows for the retention of the structural topology and chemical reactivity of the original framework, representing distinct advantages over other similar strategies. Methods to retain permanent porosity in such cationic frameworks are also proposed. Altogether, these studies highlight how the directed assembly of ordered networks can generate varied properties of high scientific interest.