O presente trabalho teve como objetivo principal estudar os processos de intercalação e esfoliação do niobato lamelar H2K2Nb6O17 em soluções aquosas de n-hexilamina, n-propilamina e hidróxido de tetrabutilamônio (TBAOH). Procurou-se avaliar a influência do agente esfoliante no processo de separação das lamelas do niobato. Para tanto, uma quantidade fixa de H2K2Nb6O17 foi suspensa em solução do agente esfoliante, nas razões molares amina/H+-niobato iguais a 0,25, 0,50, 0,75 e 1,0, e mantida sob agitação à temperatura ambiente por 2 semanas. O sólido depositado foi separado do sobrenadante opaco (isto é, do sólido esfoliado). Para a caracterização do sólido depositado, determinou-se a composição química e registrou-se o difratograma de raios-X, a curva termogravimétrica e os espectros vibracionais no IV e Raman. A dispersão de partículas esfoliadas foi caracterizada por espectroscopia eletrônica enquanto o sólido esfoliado, por DRX, medidas de área superficial, MEV e HRTEM. Nos sólidos depositados, as alquilaminas se encontram intercaladas em um arranjo de monocamada e praticamente orientadas perpendicularmente em relação às lamelas do niobato. As suspensões contendo as razões molares amina/H+-niobato = 0,5 para a n-hexilamina e 1,0 para a n-propilamina produziram a maior quantidade de sólido esfoliado (ca. 35%). As micrografias revelam que o sólido esfoliado é formado por partículas flexíveis em um arranjo desorganizado, muito diferente da morfologia do K4Nb6O17. Os difratogramas mostram perfil de material com organização somente no eixo de empilhamento das lamelas e, ainda, que nessas partículas as aminas mantêm o arranjo de monocamadas. As partículas esfoliadas contêm 50% e 70% de n-hexilamina e n-propilamina, respectivamente, neutralizando os íons H+ do niobato. Esses dados mostram que a insaturação das lamelas em relação às aminas favorecem a estabilização dos sistemas esfoliados, uma vez que diminuem as interações de van der Waals entre as cadeias carbônicas e promovem a hidratação da superfície das lamelas. Os sólidos depositados em suspensão de TBAOH não possuem espécie orgânica intercalada e as suspensões contendo as razões TBA+/H+-niobato ? 0,5 produziram maior quantidade de sólido disperso (ca. 65%). O sólido esfoliado isolado da suspensão com razão 0,75 contém 10% de TBA+ neutralizando os íons H+ do niobato. À medida que o pH das suspensões é diminuído, o TBA+ é substituído por H3O+ e as partículas planas começam a encaracolar. Observou-se a formação de nanotubos nas razões molares TBA+/H+-niobato = 0,5 e 1,0, que tiveram o pH alterado para 1 e 7 respectivamente. A amostra isolada em pH 1 apresenta área específica de 139 m²g?¹ enquanto o K4Nb6O17 possui apenas 2 m²g?¹ . Os sistemas contendo tanto partículas tabulares quanto tubulares possuem potencial aplicação na área de (foto)catálise e de sensores. / The main aim of this work was to study the intercalation and exfoliation processes of the layered niobate H2K2Nb6O17 in aqueous solutions of n-hexylamine, n-propylamine and tetra-n-butylammonium hydroxide (TBAOH). It was evaluated the influence of the exfoliation agent in the process of separation of the niobate layers. A fixed amount of H2K2Nb6O17 was suspended in solution of the exfoliation agent, in the molar ratios amine/H+-niobate 0.25, 0.50, 0.75 and 1.0, and maintained under stirring at room temperature for 2 weeks. The deposited solid was separated from the opaque suspension (i.e., the exfoliated solid). For the characterization of the deposited solid, it was determined the chemical composition and the X-ray diffractogram, the termogravimetric curve and the infrared and Raman vibrational spectra were recorded. The dispersion of exfoliated particles was characterized by electronic spectroscopy while the exfoliated solid, for XRD, surface area measurement, SEM and HRTEM. Considering the deposited solids, the alkylamines are intercalated in a monolayer arrangement and practically oriented perpendicularly in relation to the niobate layers. The suspensions containing the molar ratios amine/H+-niobate 0.5 for the n-hexylamine and 1.0 for the n-propylamine produced the highest amount of exfoliated solid (ca. 35%). SEM images reveal that exfoliated solid is formed by flexible particles in a disorganized arrangement, very different from the K4Nb6O17 morphology. The diffractograms profile show a solid with organization only in the axis of piling up of the layers and also that in these particles the amines maintain the monolayer arrangement. The exfoliated particles contain 50% and 70% of n-hexylamine and n-propylamine, respectively, neutralizing the H+ ions of the niobate. These data show that the layers insaturation in relation to the amines seems to favor the stabilization of the exfoliated systems, once it reduces the van der Waals interactions among the carbon chains and facilitate the hydration of the layer surfaces. The deposited solids in suspension of TBAOH do not possess organic species intercalated and the suspensions containing the ratio TBA+/H+-niobate ? 0.5 produce the highest amount of dispersed solid (ca. 65%). The exfoliated solid isolated from suspensions with ratio 0.75 contains 10% of TBA+ neutralizing the H+ ions of the niobate. As the pH of the suspensions is decreased, TBA+ ion is replaced by H3O+ and the tabular particles begin to scroll. The nanotubes formation was observed to molar ratios TBA+/H+-niobate = 0.5 and 1.0, which pH values were changed to 1 and 7 respectively. The sample isolated at pH 1 presents specific area of 139 m²g?¹ while K4Nb6O17 possesses only 2 m²g?¹ . The systems containing plate and tubular particles possesses potential application in (photo)catalysis and sensors areas.

Projects were undertaken investigating the functionalisation of polyaromatic cores (chrysene, pyrene and perylene) for use in organic electronics and aqueous graphene stabilisation. In each case an iridium-catalysed aromatic C-H borylation formed a key synthetic step, allowing access to unique substitution patterns. The development of strategies for the orthogonal and asymmetric functionalisation of polyaromatic hydrocarbons was explored. In a key synthetic step 4,10-dichlorochrysene was regioselectively borylated in high yields at the 2,8-positions though C-H activation chemistry. The subsequent application of sequential palladium-catalysed Suzuki and Kumada coupling reactions to this intermediate enabled the synthesis of a series of chrysene derivatives with a unique orthogonal "A2B2" 2,8- and 4,10-substitution pattern. In addition the application of a trifluoromethylation at the borylated 2,8-positions enabled the synthesis of a donor-acceptor chrysene derivative. The effect of these substitution patterns on the photophysical and electrochemical properties of these derivatives was investigated and their potential use as organic semiconducting materials evaluated. In particular the synthesised chrysene derivatives displayed broadened UV-vis absorption spectra, redshifted fluorescence spectra, increased HOMO levels and decreased band gaps. In an extension of these aromatic substitution methodologies, pyrene and perylene aromatic cores were functionalised to perform as stabilisers for aqueous graphene dispersions, investigating asymmetric motifs that may maximise performance. A series of amphiphilic pyrene- and perylene-based alkylsulfonic acid salts were synthesised via their intermediate hydroxyalkyl derivatives. In addition the application of the previously explored aromatic C-H borylation allowed access to 7- and 5,8,11- asymmetrically substituted pyrene and perylene derivatives. Through collaboration, initial steps have been undertaken to compare and evaluate these novel stabilisers for their ability exfoliate graphite to graphene in aqueous solution.

Thin nanoporous films are attractive for many potential uses for example gas separation, catalysis, filtration of viruses, ore flotation, or as low-dielectric-constant materials. Zeolite and mesoporous materials are the two important nanoporous material classes. In this thesis, we synthesized and characterized two different thin nanoporous films; (i) mesostructured films at the mica-solution interface; (ii) mechanical exfoliated zeolites. The mesoporous materials are well-defined pore shoe and size, and exhibit various morphologies, such as thin films, etc. In contrast, zeolites are a kind of perfect crystal and the morphologies are strongly related to their structures and are difficult to control. Therefore, first we synthesis mesostructured films at mica-solution interface in acidic solution. In-situ Atomic Force Microscopy (AFM) has been used to reveal the formation process of organic and inorganic mesophase films at the molecular level. Then, we synthesized two-dimensional zeolite structures via mechanical exfoliation process that does not involve any chemical intervention and can be applicable to a wide variety of structures with different chemical makeup. Three different zeolite structure nanosheets related to the structure code MWW, UTL, and MFI have been prepared. AFM and TEM have been used to characterized the exfoliated single nanosheet. In order to broaden the application of the single zeolite nanosheet, platinum nano-clusters are encapsulated within mechanical exfoliated zeolite MFI nanosheets by ion exchange from aqueous solution of [Pt(NH3)4](NO3)2. High-angle annular dark field scanning transmission electron microscopy has been used to indicate the Pt clusters in the zeolite MFI structures. Because of the property of the mechanically as-synthesised exfoliated MFI nanosheets that is the long hydrocarbon chains are essentially intact on both sides of the inorganic layer, and can prevent thickening of the zeolite MFI nanosheets along b-axis, we use the mechanically exfoliated MFI as seeds for further growth to form large scale MFI membrane with uniform nano-thickness. Encapsulating noble metals within the channels or cavities of zeolites has already drawn numerous attentions because the well-defined zeolite structure is able to constrain the metal nanoparticle (NPs) aggregation size and enhance the diversity and activity for catalysis. We use the organic surfactant (C22-6-6Br2) and [Pt(NH3)4](NO3)2 as the structure and metal precursor to form Pt-containing nanowires; and use F- to inhibit the premature precipitation of Pt precursors. After involving F-, the Pt-containing nanowire structures were generated.

O presente trabalho teve como objetivo principal estudar os processos de intercalação e esfoliação do niobato lamelar H2K2Nb6O17 em soluções aquosas de n-hexilamina, n-propilamina e hidróxido de tetrabutilamônio (TBAOH). Procurou-se avaliar a influência do agente esfoliante no processo de separação das lamelas do niobato. Para tanto, uma quantidade fixa de H2K2Nb6O17 foi suspensa em solução do agente esfoliante, nas razões molares amina/H+-niobato iguais a 0,25, 0,50, 0,75 e 1,0, e mantida sob agitação à temperatura ambiente por 2 semanas. O sólido depositado foi separado do sobrenadante opaco (isto é, do sólido esfoliado). Para a caracterização do sólido depositado, determinou-se a composição química e registrou-se o difratograma de raios-X, a curva termogravimétrica e os espectros vibracionais no IV e Raman. A dispersão de partículas esfoliadas foi caracterizada por espectroscopia eletrônica enquanto o sólido esfoliado, por DRX, medidas de área superficial, MEV e HRTEM. Nos sólidos depositados, as alquilaminas se encontram intercaladas em um arranjo de monocamada e praticamente orientadas perpendicularmente em relação às lamelas do niobato. As suspensões contendo as razões molares amina/H+-niobato = 0,5 para a n-hexilamina e 1,0 para a n-propilamina produziram a maior quantidade de sólido esfoliado (ca. 35%). As micrografias revelam que o sólido esfoliado é formado por partículas flexíveis em um arranjo desorganizado, muito diferente da morfologia do K4Nb6O17. Os difratogramas mostram perfil de material com organização somente no eixo de empilhamento das lamelas e, ainda, que nessas partículas as aminas mantêm o arranjo de monocamadas. As partículas esfoliadas contêm 50% e 70% de n-hexilamina e n-propilamina, respectivamente, neutralizando os íons H+ do niobato. Esses dados mostram que a insaturação das lamelas em relação às aminas favorecem a estabilização dos sistemas esfoliados, uma vez que diminuem as interações de van der Waals entre as cadeias carbônicas e promovem a hidratação da superfície das lamelas. Os sólidos depositados em suspensão de TBAOH não possuem espécie orgânica intercalada e as suspensões contendo as razões TBA+/H+-niobato ? 0,5 produziram maior quantidade de sólido disperso (ca. 65%). O sólido esfoliado isolado da suspensão com razão 0,75 contém 10% de TBA+ neutralizando os íons H+ do niobato. À medida que o pH das suspensões é diminuído, o TBA+ é substituído por H3O+ e as partículas planas começam a encaracolar. Observou-se a formação de nanotubos nas razões molares TBA+/H+-niobato = 0,5 e 1,0, que tiveram o pH alterado para 1 e 7 respectivamente. A amostra isolada em pH 1 apresenta área específica de 139 m²g?¹ enquanto o K4Nb6O17 possui apenas 2 m²g?¹ . Os sistemas contendo tanto partículas tabulares quanto tubulares possuem potencial aplicação na área de (foto)catálise e de sensores. / The main aim of this work was to study the intercalation and exfoliation processes of the layered niobate H2K2Nb6O17 in aqueous solutions of n-hexylamine, n-propylamine and tetra-n-butylammonium hydroxide (TBAOH). It was evaluated the influence of the exfoliation agent in the process of separation of the niobate layers. A fixed amount of H2K2Nb6O17 was suspended in solution of the exfoliation agent, in the molar ratios amine/H+-niobate 0.25, 0.50, 0.75 and 1.0, and maintained under stirring at room temperature for 2 weeks. The deposited solid was separated from the opaque suspension (i.e., the exfoliated solid). For the characterization of the deposited solid, it was determined the chemical composition and the X-ray diffractogram, the termogravimetric curve and the infrared and Raman vibrational spectra were recorded. The dispersion of exfoliated particles was characterized by electronic spectroscopy while the exfoliated solid, for XRD, surface area measurement, SEM and HRTEM. Considering the deposited solids, the alkylamines are intercalated in a monolayer arrangement and practically oriented perpendicularly in relation to the niobate layers. The suspensions containing the molar ratios amine/H+-niobate 0.5 for the n-hexylamine and 1.0 for the n-propylamine produced the highest amount of exfoliated solid (ca. 35%). SEM images reveal that exfoliated solid is formed by flexible particles in a disorganized arrangement, very different from the K4Nb6O17 morphology. The diffractograms profile show a solid with organization only in the axis of piling up of the layers and also that in these particles the amines maintain the monolayer arrangement. The exfoliated particles contain 50% and 70% of n-hexylamine and n-propylamine, respectively, neutralizing the H+ ions of the niobate. These data show that the layers insaturation in relation to the amines seems to favor the stabilization of the exfoliated systems, once it reduces the van der Waals interactions among the carbon chains and facilitate the hydration of the layer surfaces. The deposited solids in suspension of TBAOH do not possess organic species intercalated and the suspensions containing the ratio TBA+/H+-niobate ? 0.5 produce the highest amount of dispersed solid (ca. 65%). The exfoliated solid isolated from suspensions with ratio 0.75 contains 10% of TBA+ neutralizing the H+ ions of the niobate. As the pH of the suspensions is decreased, TBA+ ion is replaced by H3O+ and the tabular particles begin to scroll. The nanotubes formation was observed to molar ratios TBA+/H+-niobate = 0.5 and 1.0, which pH values were changed to 1 and 7 respectively. The sample isolated at pH 1 presents specific area of 139 m²g?¹ while K4Nb6O17 possesses only 2 m²g?¹ . The systems containing plate and tubular particles possesses potential application in (photo)catalysis and sensors areas.

Cette thèse est consacrée à la production de matériaux 2D en phase liquide, en utilisant des approches pouvant permettre la production en masse de graphène et de matériaux apparentés. Notre objectif est de surmonter certains problèmes critiques pour le traitement et l'utilisation pratique des encres à base de matériaux 2D et de fournir une compréhension approfondie de la relation structure-propriétés dans ces matériaux, constituant des étapes obligatoires pour leurs applications futures. Cette thèse porte principalement sur l'UILPE et l'exfoliation électrochimique du graphène et du disulfure de molybdène (MoS2), qui ont été choisis comme matériaux prototypes à 2 dimensions. Les approches synthétiques sont combinées à une caractérisation physico-chimique des matériaux produits, à l'aide de techniques telles que l'AFM, la microscopie électronique, la spectroscopie XPS et Raman, ainsi qu'à une caractérisation électrique. Des applications dans le domaine de la détection et de l'électronique ont été explorées et ont permis de démontrer que des approches d'exfoliation en phase liquide pouvaient être utilisées pour obtenir un contrôle précis des propriétés des matériaux 2D ouvrant la voie à leur intégration en tant que matériaux actifs dans de nouveaux dispositifs multifonctionnels. / This thesis is devoted to the production in liquid-phase of two-dimensional materials, by using approaches that may enable mass production of graphene and related materials. We aim to overcome some issues that are critical for the processing and practical use of 2D materials-inks and to provide a deep understanding of the structure-properties relationship in such materials being mandatory steps toward their future applications. This thesis mainly focuses on ultrasound-induced liquid-phase exfoliation and electrochemical exfoliation of graphene and molybdenum disulfide, which have been chosen as prototypical 2D materials. The synthetic approaches have been combined with a multiscale physico-chemical and electrical characterization of the produced materials, by employing techniques such as AFM, XPS and Raman spectroscopy. Applications in the field of sensing and electronics have been explored and allowed to demonstrate that liquid-phase exfoliation approaches can be conveniently employed to achieve a fine control on the properties of 2D materials paving the way to their integration as active materials in novel multifunctional devices.

This research aimed to develop technology and processes to further beneficiate two southern African bentonites for applications in polymer/clay nanotechnology. The bentonites were from the Koppies mine in South Africa, and the Boane mine in Mozambique. The work was divided into two parts: (i) preparation of organomodified nanoparticulate smectite clays, and (ii) preparation of their poly(ethylene-co-vinylacetate) nanocomposites. Nanoparticulate organobentonites were prepared using purified bentonites. The conventional organomodification process uses a very low concentration of bentonites at 80 oC. In this study, a novel method was developed: concentrated slurries of naturally occurring Ca-bentonite partially activated with soda ash in the presence of a proprietary dispersant were contacted at ambient temperature with quaternary ammonium surfactants. A known amount of bentonite dispersion was placed in a planetary mixer before the mixture. Likewise, a known amount of surfactant, up to 50% excess, based on the estimated cation exchange capacity (CEC) of the bentonites, was added while mixing the dispersion. The surfactants added were either in solution or in powdered form. The intercalated bentonite was recovered by centrifugation and washed repeatedly with water until halide ions could not be detected using a 1M silver nitrate solution. The solids were dried at ambient temperature and humidity, and then crushed and milled into a fine powder using a mortar and pestle. Several instrumental techniques were used to characterise and examine the properties of the bentonite samples before and after organic treatment.The X-ray diffraction (XRD) results were consistent with: (i) paraffin-type extended chain intercalation; and (ii) interdigitated monolayer intercalation of the C12 and C14 single-chain alkyl surfactants and bilayer intercalation of the single-chain C16 surfactant and the surfactants with double alkyl chains. Fourier transform infrared (FTIR) spectroscopy analysis of the organobentonite powders confirmed disordered chain conformations. XRD also detected significant amounts of cristobalite in the samples of Boane bentonite (from Mozambique). This impurity could not be removed cost-effectively. The onset decomposition temperature ofthe present organobentonites was around 200 ºC, which is within the typical range of polymer/organoclay processing temperatures. The thermal stability of the organobentonites was independent of both the number of alkyl chain substituents and their length, and also independent of the degree of clay intercalation. SURFACTANT INTERCALATED KOPPIES AND BOANE BENTONITES FOR POLYMER NANOTECHNOLOGY ii Poly(ethylene-co-vinylacetate) nanocomposites were prepared with South African Koppies bentonite, organomodified with single-chain C12 (and polar 2-hydroxyethyl side chain) and double-chains C18 alkyl ammonium cationic surfactants. The later surfactant was intercalated both below and above the clay CEC. Nanocomposites were prepared by twin-screw melt compounding. Transmission electron microscopy (TEM) indicated the presence of mixed nanoand micron-sized clay morphologies. XRD studies revealed that the crystallinity of the particles improved and that the d-spacing values increased on incorporation of the modified bentonites in the polymer matrix. It is postulated that, rather than indicating polymer co-intercalation, this was caused by further intercalation of either excess surfactants or surfactant residues that were released by shear delamination of the clays during compounding. Improved mechanical properties were realised, especially when using the bentonite containing the longer double-chains surfactant intercalated at levels in excess of the CEC of the clay. The nanocomposites showed improved tensile modulus and elongation at break values at the expense of a reduction in impact strength, while tensile strength was about the same as for the neat polymer. / Thesis (PhD)--University of Pretoria, 2013. / gm2014 / Chemistry / unrestricted

III-nitride nanostructures have generated tremendous scientific and technological interests in studying and engineering their low dimensional physics phenomena. Among these, 2D planar, free standing III-nitride nanomembranes are unrivalled in their scalability for high yield manufacture and can be mechanically manipulated. Due to the increase in their surface to volume ratio and the manifestation of quantum phenomena, these nanomembranes acquire unique physical properties. Furthermore, III-nitride membranes are chemically stable and biocompatible. Finally, nanomembranes are highly flexible and can follow curvilinear surfaces present in biological systems. However, being free-standing, requires especially new techniques for handling nanometers or micrometers thick membrane devices. Furthermore, effectively transferring these membrane devices to other substrates is not a direct process which requires the use of photoresists, solvents and/or elastomers. Finally, as the membranes are transferred, they need to be properly attached for subsequent device fabrications, which often includes spin coating and rinsing steps. These engineering complications have impeded the development of novel devices based on III-nitride membranes. In this thesis, we demonstrate the versatility of III-nitride membranes where we develop a thermal bio-sensor nanomembrane and solar energy photo-anode membrane. First, we present a novel preparation technique of nanomembranes with new characteristics; having no threading dislocation cores. We then perform optical characterization to reveal changes in their defect densities compared to the bulk crystal. We also study their mechanical properties where we successfully modulate their bandgap emission by 55 meV through various external compressive and tensile strain fields. Furthermore, we characterize the effect of phonon-boundary scattering on their thermal properties where we report a reduction of thermal conductivity from 130 to 9 W/mK. We employ these modifications to develop a thermal biosensor, which conformally gets attached to cells to measure their thermal properties. We also assess the statistical significance of our measurements to differentiate between different cell lines based on their measured thermal properties. Finally, we demonstrate the application of nanomembranes in solar-based water-splitting by merging them with nanowires to form nanowire membranes which are used to fabricate membrane photo-anodes. Finally, through optical, chemical and electrochemical measurements, we demonstrate their superior operations compared to typical fabrication techniques.

El presente trabajo de investigación es un estudio de prefactibilidad para la constitución de una empresa productora de jabones artesanales. Este trabajo consta de dos partes importantes. En primer lugar, se presenta la validación del modelo de negocio, donde se analizó el problema que existe y nuestra propuesta de solución con el uso de jabones artesanales. Además, se estimó el tamaño de mercado de los productos y se elaboraron diferentes Productos Mínimos Viables (MVP) que validaron el producto y su forma de presentación al consumidor final, así como también se pudo recabar la información necesario para comenzar las ventas presenciales y realizar una proyección de ventas. En segundo lugar, se desarrolló el plan de negocios donde se hizo la declaración de la visión y misión de la empresa, así como sus objetivos y estrategias a corto y largo plazo. Asimismo, se evaluó el plan de operaciones, el de recursos humanos, de marketing y de responsabilidad social empresarial junto con el detalle de sus respectivos presupuestos. Gracias a la definición de estas estimaciones se logró elaborar el plan financiero del proyecto de acuerdo con los ingresos y egresos que se realizarían durante los años de operación. Todo ello se evaluó de indicadores financieros como el COK, WACC y TIR, los cuales validaron la viabilidad del proyecto. / This reasarch work is a prefeasibility study for the constitution of a handmade soaps. This work consists of two important parts. In the first place, we presented the validation of the business model, where the existing problem is analyzed and our solution proposal with the use of handmade soaps is presented. Furthermore, the market size of the products was estimated and many different Minimum Viable Products (MVP) were developed in order to validate the product and its presentation to the consumer. Additionally, we collected the information needed to begin face-to-face sales and perform A sales projection. Secondly, the business plan was developed in which the company's vision and mission statement was made, as well as its short and long-term objectives and strategies. Likewise, the operations plan, the human resources, marketing and corporate social responsibility plan were evaluated along with the details of their respective budgets. Thanks to the definition of these estimates, the project's financial plan was prepared according to the income and expenses that would be made during the years of operation. The entire financial structure was evaluated with indicators such as COK, WACC and TIR, which validated the viability of the project. / Trabajo de investigación

No description available.

The goal of this project is the design of heterogeneous catalysts to facilitate the oxygen evolution reaction (OER). Considering the industrial feasibility for this reaction, first-row transition-metal-based materials are good candidates since they are cheap, abundant and possess variable oxidation states. However, most of them give only moderate catalytic activities, compared with noble-metal-based materials. To achieve efficient catalysts while maintaining low cost, it is important to discover and modify new systems based on the study of existing materials.In chapter 3 we present a study of the effect of surface reduction of birnessite on catalytic activity. A sample of birnessite was reduced by stirring with sodium dithionite, in which case the oxidation states of surface Mn decreased faster than those of inside Mn. We characterized the difference between the oxidation states of Mn of surface and inside (ΔAOS) and further investigate the effect of ΔAOS on catalysis. The catalytic activity was examined by reaction of birnessite samples with ceric ammonium nitrate, and O2 evolution was monitored using a dissolved oxygen probe with respect to time. The most reduced samples with ΔAOS of 0.15 was found to possess a turnover number (TON) of 36 mmol O2 per mol Mn, a value 10-fold higher than the unmodified sample. This result suggests oxidation state differential across layers aids the catalysis. In chapter 4, a more rigorous study is conducted by the examination of few-layer catalysts constructed by manganese oxide sheets with different oxidation states. We stacked low-AOS manganese oxide sheets with high-AOS manganese oxide sheets in various ordered combinations to obtain few-layer birnessite samples with non-uniform distribution of Mn(III). We found samples with more variation in AOS had a lower overpotential (~510 mV) in electrochemical OER catalysis than uniform stacks of the parent manganese oxide sheets (~750 mV for low-AOS sheets, >1000 mV for high-AOS sheets. The result indicates that the distribution of Mn(III) in stacking direction was the dominant factor for OER catalysis in birnessite and is more important than the overall Mn(III) content. We also found the band structures via scanning tunneling microscopy (STM) and provide an electronic-structure-based explanation of the observed activity. In chapter 5 an analogous strategy to that used in chapter 4 is applied to optimize lithium cobalt oxide (LCO) and lithium nickel oxide (LNO) layered catalysts. LCO and LNO contains various oxidation states (or spin states) of cobalt and nickel atoms. With alternatively stacking a high-AOS and a low-AOS cobalt (or nickel) oxide sheets one by one, the electrochemical OER catalytic activity of the obtained few layer LCO (or LNO) sample was enhanced. The results indicated that the structural feature of the alternating distribution of oxidation states affected not only the birnessite catalysts but also both cobalt and nickel oxide materials. In chapter 6 we incorporated both cobalt and nickel oxide sheets into layered heterostructured catalysts. We present findings that mixed transition metal oxide material K-CoxNiyO2 with alternating distribution of cobalt and nickel oxide layers showed enhanced activity mixed Ni-Co metal oxides with homogeneously distributed transition metals. The overpotential of the sample K-Co0.5Ni0.5O2 with alternating distribution of Co and Ni is 460 mV, 190 mV smaller than that of the sample with homogeneously distributed Co and Ni, even though they had a similar elemental composition. / Chemistry