The importance of porous materials has risen substantially in the last few decades due to their ability to reduce the size and cost of bioanalytical devices and fuel cells. First, this work aims to describe the fabrication of nanoporous gold (NPG) electrodes that are resistant to electrode passivation due to fibrinogen biofouling in redox solutions. The effect on potentiometric and voltammetric experiments was seen as a deviation from ideal behavior on planar gold electrodes, whereas NPG electrodes were consistently behaving in a Nernstian fashion at low concentrations of ferri-ferrocyanide (£100 mM). An improvement in electrode behavior on NPG electrodes versus planar gold was seen in solutions containing ascorbic acid as well as blood plasma. Second, cost effective NPG electrodes were fabricated using a glass substrate to test the response in the presence of a variety of redox molecules. The optical transparency of these electrodes allowed for microdroplet measurements to be made using an inverted microscope in several redox solutions for validation and subsequent biological applicability. Nernstian behavior was demonstrated for all one- and two-electron transfer systems in both poised and unpoised solutions. All experiments were conducted using volumes between 280 and 1400 pL producing rapid results in less than one minute. Third, in order to decrease the requirement for complex instrumentation, microdroplet fabrication technique was used to create mini-nanoporous gold (mNPG) electrodes on glass capillary tubes. The cylindrical shape of the electrodes allowed for testing in sample volumes of 100 mL. The response to ferri-ferrocyanide, ascorbic acid, cysteine, and uric acid was then investigated with Nernstian behavior shown. However, the mNPG electrodes were insensitive to glucose and hydrogen peroxide. In order to increase the sensitivity of the electrodes, a minimal amount of platinum was electrodeposited onto the NPG surface using a low concentration of platinum salt (0.75 mM) for a short deposition time (2 seconds) producing a Nernstian response to both glucose and hydrogen peroxide. Lastly, to test the viability of crossover applications, the platinum incorporated NPG electrode was employed as a fuel cell anode material, testing their oxidation capability with methanol, ethanol, and formic acid.

Many highly effective drugs display serious side-effects. To limit them, one can contain the drug in tiny containers, which are subsequently delivered toward targets inside the body. The entrapment of drug molecules prevents them from coming in contact with and thus causing damage to normal cells. Inherently, it is difficult to reach 100% efficiency of drug trapping and release when employing physical caps to seal the vehicles. Instead, we propose drug trapping inside the nanopores of hydrophobic silica particles by "hydrophobic trapping". This phenomenon is associated with the repulsive "force field" generated inside nanometer-sized hydrophobic channels that completely prevents aqueous solutions from entering the channels. We demonstrate the excellent trapping efficiency using C18-modified silica particles with 10 nm pores and the anticancer drug doxorubicin. The major challenge in using hydrophobic particles in biological applications is their tendency to cluster in aqueous media. To overcome it, we use surfactants as solubilization means. We have developed protocols that effectively solubilize the outer surface of the particles while preventing surfactant micelles from entering nanopores. Consequently, particles become well-dispersible in aqueous solutions, with the pre-loaded drug safely contained inside nanopores. Nanomaterials exhibit heterogeneity on their surfaces that impact their functional applications. Although techniques such as atomic force microscopy are great tools for studying nanomaterials with their excellent spatial resolution, they cannot probe the inner surface of porous structures. We have established a method of single-molecule ratiometric imaging that is currently the only technique able to provide the nanopolarity of adsorption sites located on the pore surface. We analyze the polarity distribution of adsorptions events for the solvatochromic probe Nile Red at the C18/acetonitrile interface and discover at least two different populations of adsorption sites. One of them corresponds to the polarity of surface silanol groups while the other sites have a polarity consistent with the environment inside the C18 organic layer. We also discover an additional adsorption mode situated at a polarity higher than exposed silanol surface that could presumably be linked to a different ionization state of the silanol groups. We are developing a method for resolving spectra of complex samples using two-dimensional hetero-correlation spectroscopy by correlating the intensity fluctuations in optical spectra to those of completely separated peaks in analytical separations. We demonstrate this methodology for fluorescence spectra and electrophoregrams of mixtures anthracene-pyrene. All the individual vibronic features that overlap in mixtures are cleanly extracted in cross-sections of the two-dimensional asynchronous spectrum.

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.

We have investigated the chemical sensitivity of nanoporous (NP) alumina-coated surface acoustic wave (SAW) devices that have been surface-modified with polymeric mediating films. The research in this dissertation covers the refinement of the NP alumina coating, development of dendrimer and/or polymer surface modifications, design of composite ultrathin vapor-phase analyte gates, and preparation of selectively permeable, polymeric films that mediate analyte transport. Nanoporous alumina SAW devices were fabricated from planar Al SAW devices using an anodization process that yields a high-surface-area transduction platform. Refinement of the anodization process results in a homogeneously porous substrate capable of ~40 times the analyte sensitivity of conventional planar SAW devices. Attempts to directly impart selective gas-phase analyte permeation with monolayers of amine-terminated, poly(amidoamine) (PAMAM) dendrimer films were investigated with and without secondary functionalization. We also prepared and characterized pore-bridging polymeric composite ultrathin films (~12 nm) of PAMAM dendrimers and poly(maleic anhydride)-c-poly(methyl vinylether) (Gantrez). Access to the underlying pores of the NP alumina coating can be modulated through the sequential deposition of the composite film. These tailorable ultrathin films result in impermeable surface- modifications which fully gate the analyte response without filling the porous structure. Thin spin-cast films (40 nm) of polydimethylsiloxane (PDMS) were developed to simultaneously provide selective sorption and permeation characteristics towards vapor-phase analytes. The porous nature of the underlying alumina coating provides for this real-time evaluation of sorption and permeation. The results suggest that the thin films offer preferential sorption of non-polar organics and selective permeability towards water vapor.

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.

abstract: Mesoporous materials that possess large surface area, tunable pore size, and ordered structures are attractive features for many applications such as adsorption, protein separation, enzyme encapsulation and drug delivery as these materials can be tailored to host different guest molecules. Films provide a model system to understand how the pore orientation impacts the potential for loading and release of selectively sized molecules. This research work aims to develop structure-property relationships to understand how pore size, geometry, and surface hydrophobicity influence the loading and release of drug molecules. In this study, the pore size is systematically varied by incorporating pore-swelling agent of polystyrene oligomers (hPS) to soft templated mesoporous carbon films fabricated by cooperative assembly of poly(styrene-block-ethylene oxide) (SEO) with phenolic resin. To examine the impact of morphology, different compositions of amphiphilic triblock copolymer templates, poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO-PPO-PEO), are used to form two-dimensional hexagonal and cubic mesostructures. Lastly, the carbonization temperature provides a handle to tune the hydrophobicity of the film. These mesoporous films are then utilized to understand the uptake and release of a model drug Mitoxantrone dihydrochloride from nanostructured materials. The largest pore size (6nm) mesoporous carbon based on SEO exhibits the largest uptake (3.5&mu;g/cm2); this is attributed to presence of larger internal volume compared to the other two films. In terms of release, a controlled response is observed for all films with the highest release for the 2nm cubic film (1.45 &mu;g/cm2) after 15 days, but this is only 56 % of the drug loaded. Additionally, the surface hydrophobicity impacts the fraction of drug release with a decrease from 78% to 43%, as the films become more hydrophobic when carbonized at higher temperatures. This work provides a model system to understand how pore morphology, size and chemistry influence the drug loading and release for potential implant applications. / Dissertation/Thesis / M.S. Chemical Engineering 2011

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Yes / Objectives This work investigated the impact of spray drying variables such as feedconcentration, solvent composition and the drying mode, on the micromeriticproperties of chlorothiazide sodium (CTZNa) and chlorothiazide potassium(CTZK).Methods Microparticles were prepared by spray drying and characterised usingthermal analysis, helium pycnometry, laser diffraction, specific surface area analysisand scanning electron microscopy.Key findings Microparticles produced under different process conditions pre-sented several types of morphology.To systematise the description of morphology ofmicroparticles, a novel morphology classification system was introduced. The shapeof the microparticles was described as spherical (1) or irregular (2) and the surfacewas classified as smooth (A) or crumpled (B). Three classes of morphology of micro-particles were discerned visually: class I, non-porous; classes II and III, comprisingdiffering types of porosity characteristics. The interior was categorised as solid/continuous (a), hollow (b), unknown (g) and hollow with microparticulate content(d). Nanoporous microparticles of CTZNa and CTZK, produced without recircula-tion of the drying gas, had the largest specific surface area of 72.3 and 90.2 m2/g,respectively, and presented morphology of class 1BIIIa.Conclusions Alteration of spray drying process variables, particularly solvent com-position and feed concentration can have a significant effect on the morphology ofspray dried microparticulate products. Morphology of spray dried particles may beusefully described using the morphology classification system. / The Irish Research Council for Science and Engineering Technology (IRCSET), the Solid State Pharmaceutical Cluster (SSPC), supported by Science Foundation Ireland under grant number [07/SRC/B1158] and the Irish Drug Delivery Research Network, a Strategic Research Cluster grant (07/SRC/B1154) under the National Development Plan co-funded by EU Structural Funds and Science Foundation Ireland.

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