Dye-sensitized solar cells (DSCs) have attained considerable attention during the last decade because of the potential of becoming a low cost alternative to silicon based solar cells. Although efficiencies exceeding 10% in full sunlight have been presented, major improvements of the system are however limited. Electron transport is one of the processes in the cell and is of major importance for the overall performance. It is further a complex process because the transport medium is a mesoporous film and the pores are completely filled by an electrolyte with high ionic strength, resulting in electron-ion interactions. Therefore, present models describing electron transport include simplifications, which limit the practical use, in terms of improving the DSC, because the included model parameters usually have an effective nature. This thesis focuses in particular on the influence of the mesoporous film on electron transport and also on the influence of electron-ion interactions. In order to model diffusion, which is assumed to be the transport process for electrons in the DSC, Brownian motion simulations were performed and spatial restrictions, representing the influence of the mesoporous film, were introduced by using representative models for the structure. The simulations revealed that the diffusion coefficient is approximately half the value for electrons and ions in mesoporous systems. To study the influence of ions, a simulation model was constructed in where electric fields were calculated with respect to the net charge densities, resulting from the different charge carrier distributions. The simulations showed that electron transport is highly dependent on the nature of the ions, supporting an ambipolar diffusion transport model. Experimentally, it was found that the transport process is dependent on the wavelength of the incident light; we found that the extracted current was composed of two components for green light illumination, one fast and one slow. The slow component showed similar trends as the normal current. Also we found that the transport coefficient scaled linearly with film thickness for a fixed current, which questions diffusion as transport process. Other experiments, investigating various effects in the DSC, such as the effect of different cations in the electrolyte, are also presented. / QC 20100708

During the last decade, the dye sensitised solar cell (DSC) has attracted much attention. The technology has a potential to act as a new generation of photovoltaic device, it has also increased our knowledge within the field of photoelectrochemistry. The materials used in the DSC have been used in other technologies, such as electrochromic displays. This thesis examines how such systems can be analysed to understand their properties from their components. Both of the considered device technologies consist of a thin mesoporous semiconductor film immersed in an electrolyte. The study starts by investigating some of the fundamental properties of the mesoporous semiconductor and its interface with the electrolyte. This gives rise to the charge-voltage relationship for the devices, which is related to the chemical capacitance and electronic energy levels for the materials. In particular,special attention is given to the DSC and the properties of the charge carriers in the semiconductor. For the DSC, several techniques have been developed in order to understand the processes of transport and recombination for the charge carriers in the semiconductor film, which are vitally important for performance. In this thesis, particular focus is given to light modulation techniques and electrical analysis with impedance spectroscopy. The transportproperties show for both techniques a nonlinear behaviour, which is explained with the trapping model. The DSC solar cell is analysed in order to interpret the transport measurements for film thickness optimisation. DSC cells with new semiconductor materials, such as ZnO, were analysed with impedance measurements to provide new insights into the optimisation of the performance of the photoelectrochemical solar cell technology. / QC 20100804

Calcium phosphates are the most frequently used ceramics for bone regeneration due to their biocompatibility and favorable resorption properties. Their performance can however be improved if they are associated to growth factors. In order to control the release of growth factors, we have inted to synthesize calcium phosphates with controlled mesoporosity. This thesis represents the first work that combines mesoporous calcium phosphates with the growth factors TGF and VEGF. To obtain hydroxyapatite with controlled mesoporosity, we propose new synthesis pathways: the hydroxyapatite is synthesized inside the porosity of silica or carbon templates by infiltration of aqueous precursor solutions. The template is eliminated by chemical etching with NaOH (silica template) or by selective oxidation (carbon template). Six ceramics have been chosen for the analysis of their protein adsorption and release properties. First, the experimental protocol is defined using the model proteins BSA and Cytochrom C. Then, the growth factors TGF and VEGF have been used. By this study, we were able to determine which samples were the most efficient in terms of protein adsorption and release.

This master thesis aimed to create and characterize multilayer coatings upon mesoporous silica particles (MSP). The properties of the coating aimed for, was to have a triggerable controlled release, where a targeted enzyme within the intestine, alpha-amylase, is supposed to degrade the coating. The coating was created from a bilayer consisting of DOTAP and DOPC in a 1:3 molar ratio, which serves as a protective coating. The second layer interacting with the surroundings consisted of a starch component, amylopectin, which is degraded by alpha-amylase. The study of the coating was performed with ellipsometry, where the adsorption of the different layers of the coating on a planar silica surface and the enzyme-triggered degradation was recorded. The adsorbed amount of DOTAP/DOPC was 4,22 ± 0,11 mg/m2 and amylopectin 1,82 ± 0,94. The effects of different pH where performed, simulating the coated particle going through the gastro-intestinal system. Two enzymes alpha-amylase and phospholipase A2 (PLA2) where used for degradation of the coating. The knowledge from ellipsometry was applied to coating mesoporous silica particles and it was confirmed that the two layers had formed with zeta- potential measurement.

The exploration of functional materials to store renewable, clean, and efficient energies for electric vehicles (EVs) has become one of the most popular topics in both material chemistry and electrochemistry. Rechargeable lithium batteries and fuel cells are considered as the most promising candidates, but they are both facing some challenges before the practical applications. For example, the low discharge capacity and energy density of the current lithium ion battery cannot provide EVs expected drive range to compete with internal combustion engined vehicles. As for fuel cells, the rapid and safe storage of H2 gas is one of the main obstacles hindering its application. In this thesis, novel mesoporous/nano functional materials that served as cathodes for lithium sulfur battery and lithium ion battery were studied. Ternary lithium transition metal nitrides were also synthesized and examined as potential on-board hydrogen storage materials for EVs. Highly ordered mesoporous carbon (BMC-1) was prepared via the evaporation-induced self-assembly strategy, using soluble phenolic resin and Tetraethoxysilane (TEOS) as precursors and triblock copolymer (ethylene oxide)106(propylene oxide)70(ethylene oxide)106 (F127) as the template. This carbon features a unique bimodal structure (2.0 nm and 5.6 nm), coupled with high specific area (2300 m2/g) and large pore volume (2.0 cm3/g). The BMC-1/S nanocomposites derived from this carbon with different sulfur content exhibit high reversible discharge capacities. For example, the initial capacity of the cathode with 50 wt% of sulfur was 995 mAh/g and remains at 550 mAh/g after 100 cycles at a high current density of 1670 mA/g (1C). The good performance of the BMC-1C/S cathodes is attributed to the bimodal structure of the carbon, and the large number of small mesopores that interconnect the isolated cylindrical pores (large pores). This unique structure facilitates the transfer of polysulfide anions and lithium ions through the large pores. Therefore, high capacity was obtained even at very high current rates. Small mesopores created during the preparation served as containers and confined polysulfide species at the cathode. The cycling stability was further improved by incorporating a small amount of porous silica additive in the cathodes. The main disadvantage of the BMC-1 framework is that it is difficult to incorporate more than 60 wt% sulfur in the BMC-1/S cathodes due to the micron-sized particles of the carbon. Two approaches were employed to solve this problem. First, the pore volume of the BMC-1 was enlarged by using pore expanders. Second, the particle size of BMC-1 was reduced by using a hard template of silica. Both of these two methods had significant influence on improving the performance of the carbon/sulfur cathodes, especially the latter. The obtained spherical BMC-1 nanoparticles (S-BMC) with uniform particle size of 300 nm exhibited one of the highest inner pore volumes for mesoporous carbon nanoparticles of 2.32 cm3/g and also one of the highest surface areas of 2445 m2/g with a bimodal pore size distribution of large and small mesopores of 6 nm and 3.1 nm. As much as 70 wt% sulfur was incorporated into the S-BMC/S nanocomposites. The corresponding electrodes showed a high initial discharge capacity up to 1200 mAh/g and 730 mAh/g after 100 cycles at a high current rate 1C (1675 mA/g). The stability of the cells could be further improved by either removal of the sulfur on the external surface of spherical particles or functionalization of the C/S composites via a simple TEOS induced SiOx coating process. In addition, the F-BMC/S cathodes prepared with mesoporous carbon nanofibers displayed similar performance as the S-BMC/S. These results indicate the importance of particle size control of mesoporous carbons on electrochemical properties of the Li-S cells. By employing the order mesoporous C/SiO2 framework, Li2CoSiO4/C nanocomposites were synthesized via a facile hydrothermal method. The morphology and particle size of the composites could be tailored by simply adjusting the concentrations of the base LiOH. By increasing the ratio of LiOH:SiO2:CoCl2 in the precursors, the particle size decreased at first and then went up. When the molar ratio is equal to 8:1:1, uniform spheres with a mean diameter of 300-400 nm were obtained, among which hollow and core shell structures were observed. The primary reaction mechanism was discussed, where the higher concentration of OH- favored the formation of Li2SiO3 but hindered the subsequent conversion to Li2CoSiO4. According to the elemental maps and TGA of the Li2CoSiO4/C, approximately 2 wt% of nanoscale carbon was distributed on/in the Li2CoSiO4, due to the collapse of the highly ordered porous structure of MCS. These carbons played a significant role in improving the electrochemical performance of the electrode. Without any ball-mill or carbon wiring treatments, the Li2CoSiO4/C-8 exhibited an initial discharge capacity of 162 mAh/g, much higher than that of the sample synthesized with fume silica under similar conditions and a subsequent hand-mixing of Ketjen black. Finally, lithium transition metal nitrides Li7VN4 and Li7MnN4 were prepared by high temperature solid-state reactions. These two compounds were attempted as candidates for hydrogen storage both by density functional theory (DFT) calculations and experiments. The results show that Li7VN4 did not absorb hydrogen under our experimental conditions, and Li7MnN4 was observed to absorb 7 hydrogen atoms through the formation of LiH, Mn4N, and ammonia gas. While these results for Li7VN4 and Li7MnN4 differ in detail, they are in overall qualitative agreement with our theoretical work, which strongly suggests that both compounds are unlikely to form quaternary hydrides.

Mesoporous silica materials containing microporous cavities provided by covalently bound ¦Â-cyclodextrin (CD ICS) were synthesized by co-condensation of a ¦Â-CD functionalized triethoxy silane (CD ICL) with tetraethyl orthosilicate (TEOS) by using neutral amine surfactants as structure directing agents (SDA). CD ICL was prepared by reacting ¦Â-CD with 3-isocyanatopropyltriethoxysilane. IR spectroscopy of CD ICL showed complete disappearance of isocyanato group at 2270 cm-1. 1H NMR results indicate an average of four isocyanate linkers covalently attached to random hydroxyl substituents of each molecule of ¦Â-CD. <p> Nine different CD ICS materials were synthesized using dodecylamine, tetradecylamine or hexadecylamine with ¦Â-CD (2, 4, and 6 mol %) with respect to TEOS. The incorporation of ¦Â-CD within the mesoporous framework was supported by IR, Raman, MALDI TOF MS, solid state 13C NMR CP-MAS and TGA results. Small angle X-ray diffraction results showed a peak at 2¦È ¡Ö 2.20, supporting the presence of an ordered silica mesostructure framework. For materials with same CD loading, the surface area and pore volume doubled as the surfactant from dodecylamine to hexadecylamine. However, as the CD loading increased from 2% to 6%, the surface area decreases by a factor of ~ 1.5. <p>MALDI TOF mass spectrometry showed two peaks at m/z 1157 a.m.u. and 1173 a.m.u. for [¦Â-CD + Na]+ and [¦Â-CD + K]+ respectively due to desorption of ¦Â-CD from the walls of the silica matrix. The 13C NMR CP MAS results showed 13C signals in the region ¦Ä=60-110 ppm due to the nuclei of ¦Â-CD. CD ICS materials were found to be effective as a sorbent in both gas and aqueous phases, respectively. The sorption capacity (mmol/g) of p-nitrophenol increased from 61% to 84% with an increase of CD loading from 2% to 6% and as the alkyl chain length of the SDA increases from dodecylamine to hexadecylamine. The adsorption isotherm of CH3Cl in the gas phase and that of p-nitrophenol in the aqueous phase at ambient temperature adopts a multilayer model of adsorption.

Metalle werden oft während ihrer Anwendung korrosiven Bedingungen ausgesetzt, was ihre Alterungsbeständigkeit reduziert. Deswegen werden korrosionsanfällige Metalle, wie Aluminiumlegierungen mit Schutzbeschichtungen versehen, um den Korrosionsprozess aktiv oder passiv zu verhindern. Die klassischen Schutzbeschichtungen funktionieren als physikalische Barriere zwischen Metall und korrosiver Umgebung und bieten einen passiven Korrosionsschutz nur, wenn sie unbeschädigt sind. Im Gegensatz dazu kann die Korrosion auch im Fall einer Beschädigung mittels aktiver Schutzbeschichtungen gehemmt werden. Chromathaltige Beschichtungen bieten heutzutage den besten aktiven Korrosionsschutz für Aluminiumlegierungen. Aufgrund ihrer Giftigkeit wurden diese weltweit verboten und müssen durch neue umweltfreundliche Schutzbeschichtungen ersetzt werden. Ein potentieller Ersatz sind Schutzbeschichtungen mit integrierten Nano- und Mikrobehältern, die mit ungiftigem Inhibitor gefüllt sind. In dieser Arbeit werden die Entwicklung und Optimierung solcher aktiver Schutzbeschichtungen für die industriell wichtige Aluminiumlegierung AA2024-T3 dargestellt Mesoporöse Silika-Behälter wurden mit dem ungiftigen Inhibitor (2-Mercaptobenzothiazol) beladen und dann in die Matrix anorganischer (SiOx/ZrOx) oder organischer (wasserbasiert) Schichten dispergiert. Zwei Sorten von Silika-Behältern mit unterschiedlichen Größen (d ≈ 80 and 700 nm) wurden verwendet. Diese haben eine große spezifische Oberfläche (≈ 1000 m² g-1), eine enge Porengrößenverteilung mit mittlerer Porenweite ≈ 3 nm und ein großes Porenvolumen (≈ 1 mL g-1). Dank dieser Eigenschaften können große Inhibitormengen im Behälterinneren adsorbiert und gehalten werden. Die Inhibitormoleküle werden bei korrosionsbedingter Erhöhung des pH-Wertes gelöst und freigegeben. Die Konzentration, Position und Größe der integrierten Behälter wurden variiert um die besten Bedingungen für einen optimalen Korrosionsschutz zu bestimmen. Es wurde festgestellt, dass eine gute Korrosionsschutzleistung durch einen Kompromiss zwischen ausreichender Inhibitormenge und guten Barriereeigenschaften hervorgerufen wird. Diese Studie erweitert das Wissen über die wichtigsten Faktoren, die den Korrosionsschutz beeinflussen. Somit wurde die Entwicklung effizienter, aktiver Schutzbeschichtungen ermöglicht, die auf mit Inhibitor beladenen Behältern basieren. / Metals are often used in environments that are conducive to corrosion, which leads to a reduction in their mechanical properties and durability. Coatings are applied to corrosion-prone metals such as aluminum alloys to inhibit the destructive surface process of corrosion in a passive or active way. Standard anticorrosive coatings function as a physical barrier between the material and the corrosive environment and provide passive protection only when intact. In contrast, active protection prevents or slows down corrosion even when the main barrier is damaged. The most effective industrially used active corrosion inhibition for aluminum alloys is provided by chromate conversion coatings. However, their toxicity and worldwide restriction provoke an urgent need for finding environmentally friendly corrosion preventing systems. A promising approach to replace the toxic chromate coatings is to embed particles containing nontoxic inhibitor in a passive coating matrix. This work presents the development and optimization of effective anticorrosive coatings for the industrially important aluminum alloy, AA2024-T3 using this approach. The protective coatings were prepared by dispersing mesoporous silica containers, loaded with the nontoxic corrosion inhibitor 2-mercaptobenzothiazole, in a passive sol-gel (SiOx/ZrOx) or organic water-based layer. Two types of porous silica containers with different sizes (d ≈ 80 and 700 nm, respectively) were investigated. The studied robust containers exhibit high surface area (≈ 1000 m² g-1), narrow pore size distribution (dpore ≈ 3 nm) and large pore volume (≈ 1 mL g-1) as determined by N2 sorption measurements. These properties favored the subsequent adsorption and storage of a relatively large amount of inhibitor as well as its release in response to pH changes induced by the corrosion process. The concentration, position and size of the embedded containers were varied to ascertain the optimum conditions for overall anticorrosion performance. Attaining high anticorrosion efficiency was found to require a compromise between delivering an optimal amount of corrosion inhibitor and preserving the coating barrier properties. This study broadens the knowledge about the main factors influencing the coating anticorrosion efficiency and assists the development of optimum active anticorrosive coatings doped with inhibitor loaded containers.

Mesoporous silica materials containing microporous cavities provided by covalently bound ¦Â-cyclodextrin (CD ICS) were synthesized by co-condensation of a ¦Â-CD functionalized triethoxy silane (CD ICL) with tetraethyl orthosilicate (TEOS) by using neutral amine surfactants as structure directing agents (SDA). CD ICL was prepared by reacting ¦Â-CD with 3-isocyanatopropyltriethoxysilane. IR spectroscopy of CD ICL showed complete disappearance of isocyanato group at 2270 cm-1. 1H NMR results indicate an average of four isocyanate linkers covalently attached to random hydroxyl substituents of each molecule of ¦Â-CD. <p> Nine different CD ICS materials were synthesized using dodecylamine, tetradecylamine or hexadecylamine with ¦Â-CD (2, 4, and 6 mol %) with respect to TEOS. The incorporation of ¦Â-CD within the mesoporous framework was supported by IR, Raman, MALDI TOF MS, solid state 13C NMR CP-MAS and TGA results. Small angle X-ray diffraction results showed a peak at 2¦È ¡Ö 2.20, supporting the presence of an ordered silica mesostructure framework. For materials with same CD loading, the surface area and pore volume doubled as the surfactant from dodecylamine to hexadecylamine. However, as the CD loading increased from 2% to 6%, the surface area decreases by a factor of ~ 1.5. <p>MALDI TOF mass spectrometry showed two peaks at m/z 1157 a.m.u. and 1173 a.m.u. for [¦Â-CD + Na]+ and [¦Â-CD + K]+ respectively due to desorption of ¦Â-CD from the walls of the silica matrix. The 13C NMR CP MAS results showed 13C signals in the region ¦Ä=60-110 ppm due to the nuclei of ¦Â-CD. CD ICS materials were found to be effective as a sorbent in both gas and aqueous phases, respectively. The sorption capacity (mmol/g) of p-nitrophenol increased from 61% to 84% with an increase of CD loading from 2% to 6% and as the alkyl chain length of the SDA increases from dodecylamine to hexadecylamine. The adsorption isotherm of CH3Cl in the gas phase and that of p-nitrophenol in the aqueous phase at ambient temperature adopts a multilayer model of adsorption.

ABC type amphiphilic triblock copolymers, polyethylene-b-poly(ethylene oxide)-b-poly (£`-caprolactone) (PE-b-PEO-b-PCL), were synthesized through ring-opening polymerization. We have successfully synthesized hierarchical mesoporous silicas using a simple evaporation-induced self-assembly (EISA) strategy. Two blocks of hydrophobic segment (PE and PCL) in the triblock copolymer (PE-b-PEO-b-PCL) involved in two-type mesepores after calcinations. We recognized the PE segment attributed to face centered cubic (f. c. c.) morphology (spherical pore) and the PCL segment attributed to tetragonal cylinder structure (cylinder pore) by small angle X-ray scattering (SAXS), transmission electron microscopy (TEM) and specific surface area & pore size distribution analyzer (BET), respectively. We also investigated the effect on pore size and morphology with changing the molecular weight of PCL and the ratios of TEOS/template/HCl. We also synthesized the mesoporous phenolic resin by triblock copolymer poly(ethylene oxide)-b-poly(£`-caprolactone)-b-poly(L-lactide) (PEO-b-PCL-b-PLLA). After curing and calcinations, we also explored the morphology and pore size distribution of mesoporous phenolic by SAXS, TEM, BET. Because of the sequence of hydrophobic segment PCL and PLLA lay in the same side, so we could only observe hexagonal cylinder structure and one pore size.

Solubility-based membrane separation, in which the more soluble species preferentially permeates across the membrane, has attracted considerable recent attention due to both economic and environmental concerns. This solubility-selective mode is particularly attractive over a diffusivity-selective mode in applications in which the heavier species are present in dilute concentrations. Examples include the recovery of volatile organic components (VOCs) from effluent streams and the removal of higher hydrocarbons from natural gas. Recently, nanocomposites have shown great promise as possible membrane materials for solubility-selective separations. The chemical derivatization of inorganic mesoporous substrates has been explored to synthesize organic-inorganic nanocomposite membranes. The most exciting feature of this approach is that it enables the rational engineering of membrane nano-architecture with independent control over the free volume and chemistry to create membranes with highly customizable permselectivity properties. In this study, we synthesized the organic-inorganic nanocomposite membranes by decorating the surfaces of commercially available mesoporous alumina substrates, and surfactant-templated highly ordered mesoporous silicate thin films placed on commercially available macroporous inorganic substrates, with a selective organic material that is physically or chemically anchored to the porous surfaces. Hyperbranched melamine-based dendrimers, with nanometer dimension and chemical composition designed to target certain components, were used as filling agents. We evaluated these membranes for several environmentally relevant separations, such as the recovery of the higher hydrocarbon from air and the removal of trace VOCs from air or water, while exploring the impact of organic oligomer size, chemistry, and surface coverage, as well as substrate pore size and structure, on membrane performance. First, we did a model study to verify the feasibility of dendrimer growth inside mesopores by using ordered mesoporous silica. Alumina-ordered mesoporous silica (alumina-OMS) hybrid membranes were prepared as new inorganic porous substrates. Finally, we synthesized dendrimer-ceramic nanocomposite membranes by growing several generations of melamine-based dendrimers with diverse functional groups directly off the commercial alumina membranes. Composite membranes show very high propane/nitrogen selectivity up to 70.