Solarzellen auf Basis von hybriden Perowskiten, wie zum Beispiel Methylammoniumbleitriiodid (CH3NH3PbI3), stellen eine der vielversprechendsten Solarzellenkonzepte dar. Dabei wurden Wirkungsgrade über 20 % gezeigt. Perowskite werden durch verschiedene lösungsbasierte Techniken abgeschieden. Daher konzentriert sich der erste Teil dieser Dissertation auf die Bildung von hybriden Perowskiten in der Lösung, während der zweite Teil der Stabilität von hybriden Perowskiten gewidmet ist. Im ersten Teil, wird die Bildung von Polyiodidplumbaten aus PbI2 in Lösung nachgewiesen. Die Bildung dieser Polyiodidplumbate konnte unabhängig von dem gewählten Lösungsmittel sowie unabhängig von der Beigabe von Methylammoniumiodid (CH3NH3I) beobachtet werden. Die Polyiodidplumbate zeigten, ähnlich wie CH3NH3PbI3, ein Photolumineszenzmaximum bei einer Wellenlänge von 760 nm, was auf einen gemeinsamen Ursprung des angeregten Zustands in PbI2-Komplexen und CH3NH3PbI3 hindeutet. Im zweiten Teil wurden darüber hinaus die Lichtbeständigkeit sowie die thermische und kompositionelle Stabilität untersucht. Die Untersuchung der thermischen Stabilität hat gezeigt, dass Tempern bei T <190 °C zu einer Verbesserung der Morphologie und der optoelektronischen Eigenschaften führt. Oberhalb einer Temperatur von 190 °C kam es dabei zur Zersetzung des Materials. Die Stabilität der Komposition wurde anhand von CsPb(I[1-x]Br[x])3-Perowskiten untersucht. Die Herstellung von Perowskiten mit einer großen Bandlücke war zunächst nicht möglich, da es bei den dafür notwendigen Kompositionen (0,3<x<1) zur Phasentrennung kommt. Im Gegensatz dazu konnte durch den Zusatz von Ethylendiammoniumdiodid (EDDI) zu CH3NH3PbI3 die Bandlücke zwischen 1,6 und 1,8 eV variiert werden. Die Lichtstabilität von CH3NH3PbI3, CH(NH2)2PbI3 sowie gemischt Perowskiten wurde mittels in-situ Infrarotspektroskopie analysiert. Die Zersetzung des Materials war durch die lichtinduzierte Spaltung der N-H-Bindungen bei hv ≥ 2,72 eV gekennzeichnet. / Hybrid perovskites such as methylammonium lead iodide, CH3NH3PbI3, are one of the most promising absorber materials for photovoltaic energy conversion with demonstrated power conversion efficiencies beyond 20 %. In addition, hybrid perovskites can be deposited by various solution-based fabrication techniques. Therefore, the first part of this dissertation is focused on the formation of hybrid perovskites in the precursor solution, while the second part is dedicated to the study of the stability of hybrid perovskites. In the first part of this thesis, the formation of polyiodide plumbates between molecules of PbI2 was detected. Importantly, the formation of polyiodide plumbates was observed independently of the solvent choice or the presence of CH3NH3I. The polyiodide plumbates exhibited a photoluminescence peak located at 760 nm, similarly to CH3NH3PbI3, which suggests a common origin of the excited state in PbI2 complexes and CH3NH3PbI3. In the second part of this thesis, the thermal, compositional, and photostability of perovskite thin films were evaluated. The study of the thermal stability has shown that post-annealing at T < 190 °C leads to the improvement of morphology and optoelectronic properties. Above 190 °C, CH3NH3PbI3 was found to degrade. Next, the compositional stability of mixed CsPb(I[1-x]Br[x])3 perovskites was investigated. A fundamental miscibility gap between 0.3 < x <1 was demonstrated, that impedes the preparation of high band-gap perovskites. To overcome this intrinsic instability, a new approach for band-gap engineering was developed. An addition of ethylenediammonium diiodide (EDDI) allowed to alter the band gap of CH3NH3PbI3 from 1.6 to 1.8 eV. Finally, the influence of light on the stability of hybrid perovskites was studied. A degradation of CH3NH3PbI3, CH(NH2)2PbI3, as well as mixed perovskites, was observed through photo-dissociation of N-H bonds with hν ≥ 2.72 eV by means of in-situ Fourier-transform infrared spectroscopy.

This thesis was about finding a recovery method for TiO2, using a TiO2 recovery technology, which was high enough to be economical ($10 - $15 per 1,000 gallons) to be adopted by wastewater treatment plants. When comparing recovery technologies, the top three which were investigated further through experimentation were a centrifuge, sedimentation tank, and microfilter membrane. Upon experimentation and research, the TiO2 recovery efficiencies of these technologies were 99.5%, 92.5%, and 96.3%, respectively. When doing economic analysis on these technologies comparing TiO2 efficiencies and capital and operational costs, the centrifuge was the most preferred economic option. Also, its cost did were in the economical range ($10 - $15/1,000 gallons) which makes even this technology economical. Besides that, important and valuable information about TiO2: settling behavior, particle size and zeta potential, interactions with COD, and filter operations (particle characterization) were discovered for future research and future testing on this issue. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2015. / FAU Electronic Theses and Dissertations Collection

This thesis deals with the investigation of the first hyperpolarizabilities (β) of a large number of molecules linked to other molecules either covalently or noncovalently. Chapter 1 gives a brief introduction to supramolecular chemistry and Nonlinear Optics (NLO). A survey of literature pertinent to noncovalently interacting supramolecular assembly and their NLO properties as well as NLO properties of oligomeric systems has been presented. The scope of the present investigation has been described at the end of the chapter. Chapter 2 discusses all the methods used in carrying out this thesis work. The first hyperpolarizabilities (β) of all the compounds have been measured by the hyper Rayleigh scattering (HRS) technique; the experimental details of which are written in this chapter. Various spectroscopic techniques such as NMR, IR, UV-Vis, etc. that were used in the investigation have been presented. The subsequent chapters 3-5 deal with the actual results obtained in this work. In chapter 3 first hyperpolarizabilities of o-, m-, and p-aminobenzoic acids and their oligomers viz., dimer, trimer and tetramer (covalently linked) have been studied. The compounds are synthesized and characterized by various spectroscopic methods and their β values have been measured by HRS. The hyperpolarizability increases in going from the monomer to the dimer but decreases subsequently from the dimer to the trimer to the tetramer. This unexpected trend in β has been attributed to the formation of molecular aggregates in the trimers and tetramers. Further evidences of aggregation come from the results of1H NMR spectroscopy and conductivity measurements. In chapter 4, synthesis, characterization and HRS investigation to probe the formation, dissociation and binding constants of hydrogen bonded supramolecular complexes (noncovalent interaction) formed in solution between 6-amino-2-(pivaloylamino)pyridine and ferrocene functionalized barbituric acid and 5-methoxy-N,N′-bis(6-amino-2-pyridinyl)-1,3-benzenedicarboxamide and ferrocenyl barbituric acid have been described. From the HRS data the stoichiometry of the supramolecular complexes has been determined and compared to that from the NMR data. Some of the complex stoichiometries that are measured by HRS have not been seen in the NMR data and vice versa. The results have been rationalized in terms of the strengths and weaknesses of various spectroscopic methods as applied to this problem. Many fold increase in the β value has been realized in the supramolecular complex formation process. Depolarized HRS experiments have been carried out to obtain structural information on the complexes. In the last chapter the synthesis, characterization and measurements on the first hyperpolarizabilities of unsubstituted tetraphenylporphyrin and its metallated complexes have been presented. Synthesis of supramolecular complexes of ferrocenyl barbituric acid with functionalized porphyrin compounds has been carried out although the amount of the final complex was insufficient for HRS measurements. This chapter ends with a perspective for the future work in the direction.

Ceramic membrane processes are a rapidly emerging technology for water treatment, yet virtually no information on the performance and fouling mechanisms is available to the industry. Ceramic microfiltration of model feed solutions and a synthetic river water was examined, and a systematic comparison with polymeric counterpart was performed. The results suggested that the models which have been applied to polymeric membranes agreed well with the ceramic membrane filtration data. The fouling was characterized by the initial pore blocking mechanism and transition to the cake filtration mechanism at a later phase. Cake resistance was dominant and readily removable by physical cleaning. The effects of solution chemistry including ionic strength, divalent ion concentration and pH on the flux behavior were comparatively evaluated for ceramic and polymeric ultrafiltration of synthetic water containing model natural organic matter. Experimental evaluations further included resistance-in-series model analysis, organic matter fouling visualization using quantum dots, batch adsorption test, and contact angle measurement, and provided a quantitative a quantitative comparison of fouling characteristics between ceramic and polymeric membranes. The results collectively suggested that the effects of solution chemistry on the fouling behavior with ceramic membranes were mostly similar with polymeric membranes in terms of trends, while the extents varied depending on water quality parameters. Less fouling tendency and better cleaning efficiency were observed with the ceramic membranes, which was a promising finding for ceramic membrane application to surface water treatment. The study further examined a coagulation-ceramic membrane process as a robust option for surface water treatment. The performance of the hybrid system was evaluated using selected surface waters by varying coagulation conditions and types of coagulants. Results suggested that ceramic membranes experienced relatively less fouling and had better cleaning efficiency than polymeric counterpart. The results of this study provide critical information to guide the industry practitioners, consultants, and regulatory agents considering early adoption of this new technology as well as fundamental knowledge upon which further in-depth studies can be built.

Combustion of fossil fuels has contributed to many environmental problems including acid deposition. The Clean Air Act (CAA) was created to reduce ecological problems by cutting emissions of sulfur and nitrogen. Reduced emissions and rainfall concentrations of acidic ions have been observed since the enactment of the CAA, but soils continue to receive some acid inputs. Soils sensitive to acid deposition have been found to have low pH, a loss of base cations and a shift in the mineral phase controlling the activity of Al3+ and/or SO42-. If inputs continue, soil may be depleted of base cations and saturated with Al and could cause low forest productivity. Soil solutions from lysimeters were taken in the Daniel Boone National Forest to evaluate potential impacts of acid deposition. In addition, tree-ring growth and chemical analysis created a timeline of forest health and ion accumulation. Physicochemical characteristics of the soils revealed that sites were very low in base saturation and pH and high in exchangeable acidity. Soil solution data indicated that sites periodically received high acid inputs leading to saturation of Al in soils and the formation of Al-hydroxy-sulfate minerals. Given these conditions, long-term changes in soil chemistry from acid deposition are acknowledged.

This thesis studied the viability of recycling filter substrates as soil amendments after being used in on-site systems for phosphorus (P) removal from wastewater. Focus was put on the materials Filtra P and Polonite, which are commercial products used in compact filters in Sweden. A prerequisite for this choice was to review filter materials and P sorption capacity. The filter substrates (Filtra P, Polonite and wollastonite tailings) were recycled from laboratory infiltration columns as soil amendments to a neutral agricultural soil and to an acid meadow soil to study their impacts on soil properties and yield of barley and ryegrass. The amendments tended to improve the yield and showed a liming effect, significantly increasing soil pH and the availability of P. In another experiment, samples of Filtra P and Polonite were equilibrated in batch experiments with the two soils in order to study the P dynamics in the soil-substrate system.  Batch equilibrations confirmed the liming potential of Filtra P and Polonite and showed that improved P availability in soils was strongly dependent on substrate P concentration, phase of sorbed P, and soil type. Finally, samples of Polonite used for household wastewater treatment were recycled as soil amendments to a mountain meadow and to an agricultural field for wheat cropping. The liming effect of Polonite was confirmed under field conditions and the results were similar to those of lime for the mountain meadow soil. However, the results were quite different for the agricultural field, where Polonite did not affect soil pH or any other chemical and physical soil properties investigated and had no impact on wheat yield and quality. The results from field experiments suggested that Polonite can be safely recycled to meadows and cropping fields at rates of 5-10 ton ha-1 but long-term studies are needed to forecast the effects of accumulation. / QC 20100708

Orientador: Maria Isabel Felisberti / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-26T22:37:44Z (GMT). No. of bitstreams: 1 Marques_RosalvadosSantos_D.pdf: 38406911 bytes, checksum: 574d251b2b2578b4a3d9fd0b4e82fcf7 (MD5) Previous issue date: 2014 / Resumo: Neste trabalho, estudou-se o comportamento de fases de soluções binárias e ternárias de poliolefinas funcionalizadas com hidroxilas (EVOH) e ácido carboxílico (PEAA) nos solventes dimetilformamida e álcool benzílico. Utilizou-se EVOH contendo 27 e 44 mol % e PEAA contendo 80 mol % de etileno. As soluções exibem o comportamento de fases do tipo UCST, apresentando separações de fases líquido-líquido (L-L) e sólido-líquido (S-L). As temperaturas de separação de fases L-L e S-L, TL-L e TS-L, respectivamente, foram determinadas para soluções com diferentes composições por inspeção visual e por DSC, respectivamente. Enquanto TS-L para as soluções binárias de EVOH varia fortemente da com a composição das soluções binárias, TS-L para as soluções binárias de PEAA é praticamente constante. Estes resultados foram interpretados sob a ótica de um modelo em que a cristalização do PEAA, que envolve os segmentos de etileno do copolímero, ocorre quase na ausência de solvente. Já a cristalização do EVOH, que envolve os segmentos hidroxilados, ocorre em meio ao solvente, em uma condição em que o potencial químico do polímero varia com a composição da solução. Este modelo pode ser comprovado por estudos de fluorescência empregando-se o pireno e o acetato de uranila como sondas hidrofóbica e hidrofílica, respectivamente. Estes estudos de fluorescência permitiram também acessar transições não detectáveis por DSC. As soluções ternárias homogêneas apresentam mais de uma separação de fases L-L quando submetidas a resfriamento. O diagrama de fases ternário foi construído determinando-se as composições das soluções em equilíbrio, decorrentes da primeira separação de fases L-L, por termogravimetria de alta resolução. Os diagramas de fases das soluções ternárias resultantes das combinações possíveis entre os diferentes polímeros e solventes apresentam regiões de miscibilidade limitadas localizadas em regiões próximas aos vértices, sendo as composições das fases em equilíbrio características de cada combinação nas soluções ternárias. Os materiais resultantes da evaporação do solvente de soluções submetidas ao processo TIPS (Temperature Induced Phase Separation) são compactos ou porosos, dependendo da afinidade polímero-solvente. Entretanto, as morfologias dos materiais resultantes de soluções ternárias submetidas ao processo TIPS são únicas e características do par polímero-polímero, demonstrando que a estratégia de combinação de polímeros para controlar a morfologia é viável / Abstract: The phase behavior of binary and ternary solutions of functionalized poliolefins with hydroxyls (EVOH) and carboxylic acid (PEAA) were studied using dimethylformamide and benzyl alcohol as solvents. PEAA containing 80 mol % and EVOH containing 27 and 44 mol % of ethylene were used. The binary and ternary solutions present a typical UCST behavior associated to liquid-liquid (L-L) and solid-liquid (S-L) phase separation. The temperatures related to L-L and S-L phase separation, TL-L e TS-L, respectively, were determined visually and using DSC, respectively. While TS-L depends on the EVOH solution composition, it is practically constant for PEAA solutions. These results were explained using a model in which the crystallization of PEAA from the solution occurs in absence of solvent, once it involves the polyethylene segments. On the contrary, the crystallization of EVOH from the solution, that involves the hydroxylated segments, occurs in presence of the solvent. This condition leads to the decrease of the chemical potential of EVOH in the solution. The models could be proved by fluorescence experiments using pyrene and uranyl acetate as hydrophobic and hydrophilic probes, respectively. Moreover, the fluorescence experiments allow accessing other transitions not detectable by DSC for ternary solutions. The homogeneous ternary solutions present more than one L-L phase separation by cooling. The ternary diagram was determined by the first L-L phase separation using the composition data accessed by high resolution thermogravimetry. The ternary solutions of all possible combination of polymers and solvents show a restricted miscibility window in the regions near the vertices. The composition of the phases in equilibrium is characteristic of each ternary solution, as well as, the morphology of the materials resulting from the evaporation of the solvent after the solution being subjected to TIPS (Temperature Induced Phase Separation) process. This process applied to binary and ternary solutions resulted in dense or porous materials depending on the polymer-solvent affinity. However, the morphology resulting from ternary solutions subjected to TIPS process and solvent evaporation is unique, showing that the strategy of combining different polymers is a viable route to control the morphology of polymers / Doutorado / Físico-Química / Doutora em Ciências

This thesis is focused on carbide ceramics synthesis, more specifically on the synthesis of a Ti2AlC MAX Phase carbide using solution chemistry rather than powder metallurgy. Chloride and nitrate precursors have been used as a source of metals and citric acid as a source of carbon for carbothermal reduction and as a complexing agent. A new route of precursor synthesis has been developed based on peroxo-titanic acid, which helps retain aluminium. The syntheses were performed using the SPS facility to ensure high heating rates. Al4C3 and TiC carbides and their mixtures were prepared successfully. However, the Ti2AlC phase was not synthesized under used conditions. The phase composition, structure and grain sizes of the samples were investigated by powder X-ray diffraction, X-ray fluorescence and electron microscopy. The contents of carbon in the precursors were determined by thermogravimetric analysis.

No description available.

State of the art conductivity equipment has been used to measure deuterium isotope effects on the molar conductivity of strong electrolytes in the temperature range of 298 K to 598 K as a means of exploring solvation effects under hydrothermal conditions. Individual ionic contributions were determined by extrapolation of published transference number data to elevated temperature. The temperature dependence of the Walden product ratio indicates that there is little difference in the transport of ions between light and heavy water . Excess conductivity observed in hydrogen and deuterium compounds arising from proton hopping in hydrogen-bonded networks has been determined in the temperature range of 318 K to 598 K for the first time