Graphene features a unique combination of exceptional properties and has emerged as one of the most promising nanomaterials for a variety of applications. The ability to structurally modify graphene with nanoscale precision enables the properties to be further extended. By introducing nanopores in the graphene lattice, nanoporous graphene can be used in high-performance electronic devices or as selective membranes for efficient molecular filtering. Although methods for deterministic nanopatterning already exists, key for the implementation of nanoporous graphene is the development of a scalable and customisable method of patterning graphene that does not require any lithographic mask that is introducing defects. In this project, a novel approach using a nanoporous mask and a broad beam of 20 keV Ar ions has been investigated. Masks with 60-600 nm circular pores have been fabricated, and by irradiating suspended graphene membranes grown by chemical vapor deposition (CVD) through the mask, nanoporous graphene has been deterministically generated. The masks are fabricated using electron beam lithography, and the pattern is highly customisable regarding pore size, pore distribution and areal coverage. In addition to perforating the graphene, the ion beam is also observed to significantly reduce the level of contamination on the graphene membrane. The proposed mechanism is the combination of electronic  sputtering of surface contaminants and the random diffusion that follows, with a low nuclear sputtering yield and to-site pinning of contaminants. An extension of this study could include a more comprehensive characterization of the nanoporous graphene obtained as well as further studies on the dependency of beam parameters.

Porous materials have long been a research interest due to their practical importance in traditional chemical industries such as catalysis and separation processes. The successful synthesis of porous materials requires further understanding of the fundamental physics that govern the formation of these materials. In this thesis, we apply molecular modeling methods and develop novel models to study the formation mechanism of ordered porous materials. The improved understanding provides an opportunity to rational control pore size, pore shape, surface reactivity and may lead to new design of tailor-made materials. To attain detailed structural evolution of silicate materials, an atomistic model with explicitly representation of silicon and oxygen atoms is developed. Our model is based on rigid tetrahedra (representing SiO4) occupying the sites of a body centered cubic (bcc) lattice. The model serves as the base model to study the formation of silica materials. We first carried out Monte Carlo simulations to describe the polymerization process of silica without template molecules starting from a solution of silicic acid in water at pH 2. We predicted Qn evolutions during silica polymerization and good agreement was found compared with experimental data, where Qn is the fraction of Si atoms with n bridging oxygens. The model captures the basic kinetics of silica polymerization and provides structural evolution information. Next we generalize the application of this atomic lattice model to materials with tetrahedral (T) and bridging (B) atoms and apply parallel tempering Monte Carlo methods to search for ground states. We show that the atomic lattice model can be applied to silica and related materials with a rich variety of structures including known chalcogenides, zeolite analogs, and layered materials. We find that whereas canonical Monte Carlo simulations of the model consistently produce the amorphous solids studied in our previous work, parallel tempering Monte Carlo gives rise to ordered nanoporous solids. The utility of parallel tempering highlights the existence of barriers between amorphous and crystalline phases of our model. The role of template molecules during synthesis of ordered mesoporous materials was investigated. Implemented surfactant lattice model of Larson, together with atomic tetrahedral model for silica, we successfully modeled the formation of surfactant-templated mesoporous silica (MCM-41), with explicit representation of silicic acid condensation and surfactant self-assembly. Lamellar and hexagonal mesophases form spontaneously at different synthesis conditions, consistent with published experimental observations. Under conditions where silica polymerization is negligible, reversible transformation between hexagonal and lamellar phases were observed by changing synthesis temperatures. Upon long-time simulation that allows condensation of silanol groups, the inorganic phases of mesoporous structures were found with thicker walls that are amorphous and lack of crystallinity. Compared with bulk amorphous silica, the wall-domain of mesoporous silicas are less ordered withlarger fractions of three- and four-membered rings and wider ring-size distributions. It is the first molecular simulation study of explicit representations of both silicic acid condensation and surfactant self-assembly.

The use of interference microscopy has enabled the direct observation of transient concentration profiles generated by intracrystalline transport diffusion in nanoporous materials. The thus accessible intracrystalline concentration profiles contain a wealth of information which cannot be deduced by any macroscopic method. In this paper, we illustrate five different ways for determining the concentration-dependent diffusivity in one-dimensional systems and two for the surface permeability. These methods are discussed by application to concentration profiles evolving during the uptake of methanol by the zeolite ferrierite and of methanol by the metal organic framework (MOF) manganese(II) formate. We show that the diffusivity can be calculated most precisely by means of Fick’s 1st law. As the circumstances permit, Boltzmann’s integration method also yields very precise results. Furthermore, we present a simple procedure that enables the estimation of the influence of the surface barrier on the overall

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Within this general context, this talk will consider the use of novel nanoporous materials as the basis for adsorption based separations [3] that will range from concentrated mixtures to direct capture of carbon dioxide from air. An overview of different classes of materials will show how these can be tailored to such a wide range of conditions. The sheer scale of the task leads to having to optimize systems and speed up processes, which in turn brings in diffusion limitations.

Hydrogen storage remains a major technological barrier to the widespread adoption of hydrogen as an energy source. Organic polymers offer one potential route to useful hydrogen storage materials. Recently, Frechet and his coworkers described a series of hypercrosslinked polymers with high surface area and studied their surface properties and hydrogen storage capacities. McKeown and his coworkers studied a class of materials termed Polymers of Intrinsic Microporosity (PIMs) which are also based on a "hypercrosslinked" concept. We enchained N-substituted maleimide and functionalized stilbene alternating copolymers into a "hypercrosslinked system" to achieve high rigidity, high surface areas, high aromatic content and good thermal stability. Hypercrosslinked copolymers of N-(3-methylphenyl)maleimide (3MPMI), 4-methyl stilbene (4MSTBB), vinylbenzyl chloride (VBC) and divinyl benzene (DVB) were synthesized. Scanning electron micrographs (SEM) show the copolymers are porous and some examples have shown surface areas over 1200 m²/g. We have also found the incorporation of 3MPMI and 4MSTBB improves the thermal stability and raises the glass transition temperature of the copolymer. However, the incorporation of 3MPMI and 4MSTBB decreases the hypercrosslinking density and therefore causes a decrease in the copolymer surface area. The systematic study of styrene (STR) – vinylbenzyl chloride (VBC) – divinyl benzene (DVB) networks indicates that a low density of chloromethyl groups leads to a decrease in surface area. Therefore, we are continuing to investigate other monomers, such as N-substituted maleimide and functionalized stilbene containing chloromethyl groups, in order to enhance thermal stability while maintaining surface area. In order to increase the enthalpy of hydrogen adsorption and thus raise the temperature of hydrogen storage, the monomer N,N-dimethyl-N',N'-diethyl-4,4'-diaminostilbene (4,4'DASTB-3MPMI) which contains electron donating groups was incorporated into hypercrosslinked polymer particles. Hypercrosslinked polymer (4,4'DASTB-3MPMI)1.0(VBC)98.5(DVB).50 exhibits a surface area of 3257 m²/g. / Master of Science

The society profits from a variety of electronic devices, which rely on electrons and holes as the charge carriers for information transmission and processing. In contrast, biological systems operate via ions of varying size to handle complicated tasks, including massive parallel information sensing, processing, storing, and behavior controlling in nature, which inspire the development of iontronics (such as ionic transistors, ionic diodes, and ionic resistive memristors) for further bioelectronic interface, in-memory computing, and artificial intelligence hardware.[1] In recent years, the electric double layer (EDL) formation has proven a powerful tool for the coupling of ions and electrons in iontronics. EDL electrically adsorbs/desorbs ions on the surface of electrodes to balance and store opposite charges in a controllable manner, which enables to operate ions and build iontronic devices. Nanoporous carbons with higher specific surface areas compared to widely-used metal electrodes in iontronics feature the higher volume and specific capacitances along with fine compatibility with biological systems, which are promising for ion manipulation in iontronics.[2,3] In recent years, a series of carbon-based capacitive iontronics were developed to realize the functions of conventional diodes and transistors.[4,5] Due to the demand of high performance (energy and power density) in above devices, toxic electrolytes were applied as the electrolytes,[4,5] which limits the implementation in biological applications. Various functionally bioactive ions are a requisite for complicated psychological, physiological, and behavioral processes, such as neurotransmitters (ranging from amino acids (e.g., glycine (Gly) and gamma-aminobutyric acid (GABA)), biogenic amines (e.g., dopamine and acetylcholine), to peptides (e.g., vasopressin and somatostatin)).[6] Moreover, some bioactive ions such as sodium ibuprofen (NaIbu) and sodium salicylate (NaSal) are common analgesic and inflammation drugs for the human health.[7,8] So far, there have been few reports about applying bioactive ions as the charge carriers in carbon-based EDL iontronics. A deep molecular-level mechanism of the adsorption of bioactive ions and the deliberate concentration control via nanoporous carbons with and without polarization remain unclear and unsolved, but are crucial for the design of neuromorphic devices, neurotransmitter sensors, and transmitter delivery. Given the varying sizes and structures of bioactive ions and the varying porosity structures of nanoporous carbons, there are some open questions for the interaction mechanism of bioactive ions and nanoporous carbons in the EDL devices as shown in the following: a) the influence of porosity structures of nanoporous carbons for the adsorption kinetics and thermodynamics of bioactive ions; b) the difference of the electrosorption and physisorption and their roles for manipulating ion behaviors; c) the influence of bioactive ion structure for the adsorption process; d) the adsorption mechanisms for electroneutral and charged neurotransmitters; e) the effects of the surface polarity and functional groups of nanoporous carbons for the bioactive ion adsorption process. This thesis focuses on revealing the interaction behaviors of bioactive ion electrolytes and nanoporous carbon electrodes from four main parts, with the aid of electrochemical methods and spectroscopic analyses. In Chapter 5.1, the adsorption kinetics of bioactive choline chloride (ChCl) in ACC with a narrow pore size distribution (PSD) and ROX with a broad PSD is explored. The comparison indicates a faster diffusion process of ChCl in ROX with a broad PSD. The evaluation of physisorption and electrosorption of ChCl in ROX with a broad PSD is conducted, which show that the amount of physically adsorbed ChCl in ROX is less than 6 μmol/g, while the amount of electrosorption-induced concentration changes in the polarized ROX electrode is up to 30 μmol/g. Electrosorption dominates the adsorption process for ChCl. Consequently, it can be concluded that the capture and release of ChCl in aqueous solutions can be easily manipulated via electrochemical techniques. Chapter 5.2 builds on the investigation of the ChCl interaction behavior in the ROX carbon. The investigation is extended to a series of ammonium-based ionic liquid salts with different alkyl chain lengths paired with Cl- anions (CxAmOMCl, where x=2, 6, and 12). The increasing physisorption of these cations in the ROX carbon is observed with the alkyl chain length increasing. The role of alkyl chain is clarified in bioactive cations for the adsorption in nanoporous carbons. However, the bioactive anions with long alkyl chains showed a quite weaker adsorption in the ROX carbon, compared with bioactive cations with long alkyl chains. These results illustrate the synergistic effect of the hydrophobic interaction and electrostatic attraction for the bioactive ions strong adsorption in nanoporous carbons. In Chapter 5.3, the adsorption and charge balancing mechanism of electroneutral amino acids are further explored in ROX carbon electrodes. The weak physisorption of four amino acids (with linear structures) is observed, which results from the hydrophilic end groups and electroneutral properties. The charge balance mechanism of these electroneutral zwitterions (with amine and carboxylic acid groups) is clarified as the dissociation reaction of amino acid zwitterions, which produces anions to balance positive charges and cations to balance negative charges. In the buffered environment, the deliberate uptake and release of inhibitory neurotransmitters (Gly and GABA) are achieved by polarizing porous carbon electrodes, which implies the powerful abilities of electrosorption for controlling the concentration of neurotransmitters in aqueous and phosphate-buffered saline (PBS) solutions. In Chapter 5.4, we investigate the impurity effects for the carbon properties and bioactive ion adsorption processes. The impurity contents are very high in some commercial porous carbons. The washing process leads to the decrease of O and N contents, and reduces wettability of porous carbons. Moreover, some O, N, and other non-carbon contents, which are commonly considered as surface functional groups of carbons, are not bonded but adsorbed inorganic impurities on the carbon surface. In-situ UV-Vis experiments clarify that the adsorbed ionic impurities play a role in the charge balance process during the electric polarization, which partly explains the capacitances of porous carbons in pure water electrolytes. The questions addressed in this thesis provide a fundamental basis for the understanding of the interaction of various bioactive ions with nanoporous carbons, which benefit the development of EDL iontronics. Based on two different interaction modes (weak and strong adsorption), the interaction theory is further applied in the construction of iontronic devices. For weak adsorption, EDL transistors are deeply explored using bioactive ions (ChCl, NaIbu, Gly, and GABA). The capacitance switching behavior is confirmed in a 3D printed carbon-based ionic transistor. The concentration manipulation of bioactive ions in aqueous environments are promising for various potential applications, such as toxic ion removal, drug delivery, plant regulation, and bioelectronic devices. For strong adsorption, the confined cations with long alkyl chains (cations of C12AmOMCl) are irreversibly adsorbed and fixed on the porous carbon surface. The electric polarization cannot desorb confined cations, causing anion depletion and anion enrichment during electric polarization, which leads to the favorable memristive behavior for promising ionic memristors and in-memory computing applications in the future. References [1] C. Wan, K. Xiao, A. Angelin, M. Antonietti, X. Chen, Advanced Intelligent Systems 2019, 1, 1900073. [2] S. Z. Bisri, S. Shimizu, M. Nakano, Y. Iwasa, Advanced Materials 2017, 29, 1607054. [3] Y.-Z. Zhang, Y. Wang, T. Cheng, L.-Q. Yao, X. Li, W.-Y. Lai, W. Huang, Chemical Society Reviews 2019, 48, 3229. [4] S. Lochmann, Y. Bräuniger, V. Gottsmann, L. Galle, J. Grothe, S. Kaskel, Advanced Functional Materials 2020, 30, 1910439. [5] E. Zhang, N. Fulik, G.-P. Hao, H.-Y. Zhang, K. Kaneko, L. Borchardt, E. Brunner, S. Kaskel, Angewandte Chemie International Edition 2019, 58, 13060. [6] S. E. Hyman, Current Biology 2005, 15, R154. [7] S. A. Hawley, M. D. Fullerton, F. A. Ross, J. D. Schertzer, C. Chevtzoff, K. J. Walker, M. W. Peggie, D. Zibrova, K. A. Green, K. J. Mustard, B. E. Kemp, K. Sakamoto, G. R. Steinberg, D. G. Hardie, Science 2012, 336, 918. [8] N. Azum, A. Ahmed, M. A. Rub, A. M. Asiri, S. F. Alamery, Journal of Molecular Liquids 2019, 290, 111187.:Table of Contents I Abbreviations IV 1. Motivation 1 2. Background and Introduction 5 2.1. Biology and Ion-controlled Devices 5 2.2. Ion-related Biological Processes 5 2.2.1. Sensing and Signaling 5 2.2.2. Memory and Computing 7 2.2.3. Actuation Components 9 2.3. Bioinspired Iontronics 10 2.3.1. Ionic Diodes 11 2.3.2. Ionic Transistors 12 2.3.3. Ionic Resistive Memristors 14 2.4. Carbon-based Capacitive Iontronics 15 2.4.1. The Mechanism of Carbon-based Supercapacitors 15 2.4.2. Electrolytes for Supercapacitors 18 2.4.3. Nanoporous Carbons 22 2.4.4. Carbon-based Ionic Diodes 23 2.4.5. Carbon-based Ionic Transistors 24 2.4.6. The Interaction Mechanism of Bioactive Ions with Porous Carbons 26 3. Electrochemical Methods 28 3.1. Linear Sweep Voltammetry (LSV) 28 3.2. Cyclic Voltammetry (CV) 30 3.3. Electrochemical Impedance Spectroscopy (EIS) 31 4. Experimental Section 35 4.1. List of Used Chemicals 35 4.2. List of Used Materials 36 4.3. Preparation and Characterizations 37 4.3.1. Carbon Preparation 37 4.3.2. Electrode Preparation 38 4.3.3. 2-electrode Cells 38 4.3.4. 3-electrode Cells 38 4.3.5. 4-terminal Setups 39 4.3.6. Local pH Measurement 39 4.3.7. EIS Measurement 40 4.3.8. In-situ UV-Vis Measurement 40 4.3.9. Raman Spectroscopy 41 4.3.10. NMR and MS Measurement 41 4.3.11. Ninhydrin Reaction 42 4.3.12. Nitrogen Physisorption 42 4.3.13. Electrosorption Evaluation 42 5. Results and Discussion 43 5.1. Pore Structure and Ion Adsorption Kinetics 43 5.1.1. Introduction 43 5.1.2. Physiochemical Properties of Two Nanoporous Carbons 43 5.1.3. ChCl Physisorption Mechanism in Nanoporous Carbons 45 5.1.4. ChCl Electrochemical Stability and Performance 48 5.1.5. ChCl Electrosorption Mechanism in Nanoporous Carbons 52 5.1.6. Switchable Capacitive Transistor Analogues in Printed Structures 60 5.1.7. Summary 63 5.2. Ion Structures and Adsorption Kinetics 64 5.2.1. Introduction 64 5.2.2. Synthesis and Characterization of Ammonium-based ILs 65 5.2.3. Adsorption Behavior of Ammonium-based ILs in Nanoporous Carbons 67 5.2.4. Electrochemical Performance of Ammonium-based ILs 76 5.2.5. Adsorption Behavior of Organic Salts in Nanoporous Carbons 78 5.2.6. Strong Interaction and Ionic Memristor Behaviors 82 5.2.7. Weak Interaction and Ionic Transistor Applications 86 5.2.8. Summary 89 5.3. Electroneutral Neurotransmitter Adsorption Mechanism 90 5.3.1. Introduction 90 5.3.2. Amino Acid Physisorption Mechanism in Nanoporous Carbons 92 5.3.3. Amino Acid Electrochemical Behaviors in Electrically-polarized Nanoporous Carbons 96 5.3.4. Mechanism Investigation of Zwitterions in Electrically-polarized Nanoporous Carbons 99 5.3.5. Local pH Measurement of Amino Acid Electrolytes during Electric Polarization 105 5.3.6. Electrosorption-induced Capture and Release of Amino Acid Neurotransmitters 109 5.3.7 Neurotransmitter-based Bioinspired Iontronic Devices 113 5.3.8. Summary 115 5.4. Porous Carbon Impurities for Bioactive Ion Adsorption 116 5.4.1. Introduction 116 5.4.2. Qualitative Analysis of the Impurity Release from Porous Carbons 118 5.4.3. Electrochemical Evaluation for Ionic Impurities in Porous Carbons 121 5.4.4. The Effect of Adsorbed Ionic Impurities for Carbon Properties 126 5.4.5. The Charge Balance Mechanism of Ionic Impurities for Bioactive Ion Controlling 135 5.4.6. Summary 137 6. Conclusion and Outlook 139 7. References 142 A. Bibliography 152 B. List of Publications 154 C. Acknowledgements 155 D. Appendix 157 E. Versicherung und Erklärung 161

La conversion thermoélectrique a suscité un regain d'intérêt en raison des possibilités d'augmenter l'efficacité tout en exploitant les effets de taille. Par exemple, les nanofils montrent théoriquement une augmentation des facteurs de puissance ainsi qu'une réduction du transport des phonons en raison d'effets de confinement et/ou de taille. Dans ce contexte, le diamètre des nanofils devient un paramètre crucial à prendre en compte pour obtenir des rendements thermoélectriques élevés. Une approche habituelle consiste à réduire la conductivité thermique phononique dans les nanofils en améliorant la diffusion sur les surfaces tout en réduisant les diamètres.Dans ce travail, la caractérisation thermique d'une forêt dense de nanofils de silicium, germanium, silicium-germanium et alliage Bi2Te3 est réalisée par une méthode 3-omega très sensible. Ces forêts de nanofils pour le silicium, le germanium et les alliages silicium-germanium ont été fabriqués selon une technique "bottom-up" suivant le mécanisme Vapeur-Liquide-Solide en dépôt chimique en phase vapeur. La croissance assistée par matrice et la croissance par catalyseurs en or des nanofils à diamètres contrôlés ont été réalisés à l'aide d'alumine nanoporeuse comme matrice. Les nanofils sont fabriqués selon la géométrie interne des nanopores, dans ce cas le profil de surface des nanofils peut être modifié en fonction de la géométrie des nanopores. Profitant de ce fait, la croissance à haute densité de nanofils modulés en diamètre a également été démontrée, où l'amplitude et la période de modulation peuvent être facilement contrôlées pendant la fabrication des matrices. Même en modulant les diamètres pendant la croissance, les nanofils ont été structurellement caractérisés comme étant monocristallins par microscopie électronique à transmission et analyse par diffraction des rayons X.La caractérisation thermique de ces nanofils a révélé une forte diminution de la conductivité thermique en fonction du diamètre, dont la réduction était principalement liée à une forte diffusion par les surfaces. La contribution du libre parcours moyen à la conductivité thermique observée dans ces matériaux "bulk" varie beaucoup, Bi2Te3 ayant une distribution en libre parcours moyen (0,1 nm à 15 nm) très faible par rapport aux autres matériaux. Même alors, des conductivités thermiques réduites (~40%) ont été observées dans ces alliages attribuées à la diffusion par les surfaces et par les impuretés. D'autre part, le silicium et le germanium ont une conductivité thermique plus élevée avec une plus grande distribution de libre parcours moyen. Dans ces nanofils, une réduction significative (facteur 10 à 15 ) a été observée avec une forte dépendance avec la taille des nanofils.Alors que les effets de taille réduisent la conductivité thermique par une meilleure diffusion sur les surfaces, le dopage de ces nanofils peut ajouter un mécanisme de diffusion par différence de masse à des échelles de longueur atomique. La dépendance en température de la conductivité thermique a été déterminée pour les nanofils dopés de silicium afin d'observer une réduction de la conductivité thermique à une valeur de 4,6 W.m-1K-1 dans des nanofils de silicium fortement dopés avec un diamètre de 38 nm. En tenant compte de la conductivité électrique et du coefficient Seebeck calculé, on a observé un ZT de 0,5. Avec l'augmentation significative de l'efficacité du silicium en tant que matériau thermoélectrique, une application pratique réelle sur les appareils n'est pas loin de la réalité. / Thermoelectric conversion has gained renewed interest based on the possibilities of increasing the efficiencies while exploiting the size effects. For instance, nanowires theoretically show increased power factors along with reduced phonon transport owing to confinement and/or size effects. In this context, the diameter of the nanowires becomes a crucial parameter to address in order to obtain high thermoelectric efficiencies. A usual approach is directed towards reducing the phononic thermal conductivity in nanowires by achieving enhanced boundary scattering while reducing diameters.In this work, thermal characterisation of a dense forest of silicon, germanium, silicon-germanium and Bi2Te3 alloy nanowires is done through a sensitive 3ω method. These forest of nanowires for silicon, germanium and silicon-germanium alloy were grown through bottom-up technique following the Vapour-Liquid-Solid mechanism in Chemical vapour deposition. The template-assisted and gold catalyst growth of nanowires with controlled diameters was achieved with the aid of tuneable nanoporous alumina as templates. The nanowires are grown following the internal geometry of the nanopores, in such a case the surface profile of the nanowires can be modified according to the fabricated geometry of nanopores. Benefiting from this fact, high-density growth of diameter-modulated nanowires was also demonstrated, where the amplitude and the period of modulation can be easily tuned during the fabrication of the templates. Even while modulating the diameters during growth, the nanowires were structurally characterised to be monocrystalline through transmission electron microscopy and X-ray diffraction analysis.The thermal characterisation of these nanowires revealed a strong diameter dependent decrease in the thermal conductivity, where the reduction was predominantly linked to strong boundary scattering. The mean free path contribution to the thermal conductivity observed in the bulk of fabricated nanowire materials vary a lot, where Bi2Te3 has strikingly low mean free path distribution (0.1 nm to 15 nm) as compared to the other materials. Even then, reduced thermal conductivities (~40%) were observed in these alloys attributed to boundary and impurity scattering. On the other hand, silicon and germanium have higher thermal conductivity with a larger mean free path distribution. In these nanowires, a significant reduction (10-15 times) was observed with a strong dependence on the size of the nanowires.While size effects reduce the thermal conductivity by enhanced boundary scattering, doping these nanowires can incorporate mass-difference scattering at atomic length scales. The temperature dependence of thermal conductivity was determined for doped nanowires of silicon to observe a reduction in thermal conductivity to a value of 4.6 W.m-1K-1 in highly n-doped silicon nanowires with 38 nm diameter. Taking into account the electrical conductivity and calculated Seebeck coefficient, a ZT of 0.5 was observed. With these significant increase in the efficiency of silicon as a thermoelectric material, a real practical application to devices is not far from reality.

Doctor of Philosophy / Department of Chemistry / Takashi Ito / Self-organized nanoporous materials have drawn a lot of attention because the uniform, highly dense, and ordered cylindrical nanopores in these materials provide a unique platform for chemical separations and chemical sensing applications. Here, we explore self-organized nanopores of PS-b-PMMA diblock copolymer thin films and anodic gallium oxide for chemical separations and sensing applications. In the first study, cyclic voltammograms of cytochrome c on recessed nanodisk-array electrodes (RNEs) based on nanoporous films (11, 14 or 24 nm in average pore diameter; 30 nm thick) derived from polystyrene-poly(methylmethacrylate) diblock copolymers were measured. The faradic current of cytochrome c was observed on RNEs, indicating the penetration of cytochrome c (hydrodynamic diameter ≈ 4 nm) through the nanopores to the underlying electrodes. Compared to the 24-nm pores, the diffusion of cytochrome c molecules through the 11- and 14-nm pores suffered significantly larger hindrance. The results reported in this study will provide guidance in designing RNEs for size-based chemical sensing and also for controlled immobilization of biomolecules within nanoporous media for biosensors and bioreactors. In another study, conditions for the formation of self-organized nanopores of a metal oxide film were investigated. Self-organized nanopores aligned perpendicular to the film surface were obtained upon anodization of gallium films in ice-cooled 4 and 6 M aqueous H2SO4 at 10 V and 15 V. The average pore diameter was in the range of 18 ~ 40 nm, and the anodic gallium oxide was ca. 2 µm thick. In addition, anodic formation of self-organized nanopores was demonstrated for a solid gallium monolith incorporated at the end of a glass capillary. Nanoporous anodic oxide monoliths formed from a fusible metal will lead to future development of unique devices for chemical sensing and catalysis. In the final study, surface chemical property of self-organized nanoporous anodic gallium oxide is explored through potentiometric measurements. The nanoporous anodic and barrier layer gallium oxide structures showed slow potentiometric response only at acidic pH (≤ 4), in contrast to metallic gallium substrates that exhibited a positive potentiometric response to H⁺ over the pH range examined (3-10). The potentiometric response at acidic pH probably reflects some chemical processes between gallium oxide and HCl.

<p>In this doctoral project, a relatively new form of carbon material, with unique narrow pore size distribution around 7 Å and with uniform structure, has been electrochemically characterised using the single particle microelectrode technique. The carbon has been used as electrode material for supercapacitors. This type of capacitors is used as high power energy buffers in hybrid vehicles and for stationary power backup. The principle for the microelectrode technique consists of connecting a carbon particle with a carbon fibre by means of a micromanipulator. The single particle and carbon fibre together form a microelectrode. Combination of this technique with electroanalytical methods such as cyclic voltammetry and potential step measurements allows for the survey of electrochemical phenomena and for the determination of ion transport parameters inside the nanopores.</p><p>A mathematical model based on Fick’s second law, for diffusion of ions inside the nanopores at non steady state, was used for the determination of effective diffusion coefficients (Deff). The coefficients were calculated from an asymptotic solution of Fick’s equation, applied for a thin layer adjacent to the external surface of the carbon particles and valid for the current response in a short time region. Another asymptotic solution was obtained, using spherical geometry and valid for the current response in a long time region.</p><p>In this doctoral work, the carbon particles have been exposed to potential cycling, which mimics that of large electrodes during operation of a double layer capacitor. The potential-current response, E-I, for the nanoporous carbon, shows a pure capacitive behaviour between –0.5 V and 0.1 V vs. the Hg|HgO reference electrode. The detection of the faradaic processes beyond these potentials was possible by lowering of the voltammometric sweep rate. The electrochemical processes occurring at positive and at negative potential were investigated separately.</p><p>Cyclic voltammometric measurements showed that the chemisorption of hydroxyl groups, occurring between 0.1 and 0.3 V, leads to a mild oxidation of the carbon structure, resulting in surface groups containing an oxygen atom at a specific carbon site (e.g., phenolic or quinine type). These oxygen-containing surface groups caused an increase of the specific capacitance, which remained constant throughout a number of voltammometric cycles. The Deff decreased on the other hand with the number of cycles. The Deff decreases also with the positive potential. The evaluation of Deff indicates adsorption of hydroxyl groups and an increase of the effective tortuosity of the pore system.</p><p>The oxidation of the carbon particles, between 0 and 0.5 V, leads to more extensive oxidation and to surface groups containing two oxygen atoms at a single carbon site, followed by formation of carbonate ions. The oxygen-containing surface groups and carbonate ions formed at these potentials do not contribute to the specific capacitance and drastically retard or obstruct the ion transport inside the nanopores.</p><p>At negative potentials the carbon particles show a dominantly capacitive behaviour. The faradaic processes taking place below –0.5 V vs. Hg|HgO reference electrode are generation and adsorption of hydrogen. These processes do not perturb significantly the electrochemical and ion transport properties of the nanoporous carbon particles. It was found that hydrogen generation occurs at –0.5 V vs. Hg|HgO and that two hydrogen oxidation processes take place at positive potentials. The results indicate that the weakly adsorbed hydrogen undergoes oxidation between 0 and 0.1 V and that the strongly adsorbed hydrogen is oxidised at more positive potentials.</p><p>The single particle technique was adapted for the determination of diffusion coefficients of an organic electrolyte. The different size of the anions and cations caused different transport characteristics at negative and positive potentials. Slow cycling was found important for ion penetration inside the nanopores and for the evaluation of the effective diffusion coefficients.</p><p>The effective diffusion coefficients for the nanoporous carbon using aqueous 6M KOH and 0.1M TEABF4 in acetonitrile were estimated to 1.4 (±0.8).10-9 cm2 s-1 and 1.3 (±0.4) 10-8 cm2 s-1, respectively.</p>