Orientadores: Ana Flávia Nogueira, Teresa Dib Zambon Atvars / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-19T07:00:55Z (GMT). No. of bitstreams: 1 Alves_JoaoPaulodeCarvalho_M.pdf: 2190959 bytes, checksum: a321ebe05ad04c15ea1e77782b12c743 (MD5) Previous issue date: 2011 / Resumo: Células solares orgânicas apresentam-se como uma alternativa promissora para conversão de energia solar. Muitos desses dispositivos são produzidos pela mistura de um polímero condutor e um derivado fulereno. O polímero condutor atua como absorvedor de luz, doador de elétrons e transportador de buracos, enquanto o fulereno atua como transportador e aceitador de elétrons. Esses dispositivos destacam-se pela possibilidade de deposição em substratos flexíveis, transparência, diversidade em cores e uso de materiais recicláveis, além do baixo custo. No entanto, células solares orgânicas apresentam baixa mobilidade de carga e absorção em pequena faixa espectral da energia solar quando comparadas aos dispositivos fotovoltaicos baseados em semicondutores inorgânicos. A adição de CdSe ao sistema P3HT/PCBM promoveu o decréscimo na eficiência e fotocorrente dos dispositivos. Esses resultados são diferentes dos observados para o sistema PFT/PCBM, previamente reportado. A diferença observada para os dispositivos com os polímeros P3HT e PFT foram associados com as diferentes interações polímero-nanopartícula, como evidenciado pelas medidas de absorção e emissão e pelos espectros de RMN. A elevada concentração de tiofeno no P3HT pode contribuir fortemente na formação de um complexo entre polímero e CdSe e na desativação do processo de transferência de elétrons entre polímero e PCBM. Para investigar um possível efeito de morfologia pela introdução de CdSe ao sistema P3HT/PCBM, foram obtidas imagens de microscopia de força atômica e microscopia óptica. Há um aumento da rugosidade e tamanho de grãos do sistema com o acréscimo de nanopartículas de CdSe, que pode inibir o processo de separação de cargas e de formação de redes de percolação / Abstract: Organic solar cells are presented as a promising alternative for solar energy conversion. Many of these devices are produced by mixing a conductive polymer and a fullerene derivative. The conducting polymer acts as a light absorber, electron donor and hole transporter, while the fullerene acts as acceptor and electron shuttle. These devices call attention due to the possibility to produce flexible solar cells with high transparency and different colors, allied to the use of recyclable materials and low cost. However, organic solar cells have lower charge mobility and narrower spectral range absorption of solar energy compared to inorganic-based photovoltaic devices. The addition of CdSe to the P3HT/PCBM system promoted the decrease in efficiency and photocurrent of the devices. These results are different from those observed for the PFT/PCBM system, previously reported. The difference observed for the devices with P3HT and PFT was associated with different polymer-nanoparticle interactions, as evidenced by absorption and emission measurements. The high concentration of thiophene in P3HT contributes in the formation of a complex between polymer-CdSe and the deactivation of the electron transfer process between the polymer and PCBM. To investigate the possible contribution of a morphological effect induced by CdSe in P3HT/PCBM system, Atomic Force Microscopy (AFM) images were obtained. There is an increase of roughness and grain size of the system with the addition of CdSe nanoparticles, which can inhibit the charge separation process and formation of percolation networks / Mestrado / Quimica Inorganica / Mestre em Química

Humankind’s tremendous industrial and technological progress over the last two centuries has been driven by the natural abundance and availability of fossil fuels. As those reserves deplete, the prudent course of action would be to develop other readily available fuel sources. Some research efforts using biomolecules involve the hydrogenases and nitrogenases with the goal of evolving dihydrogen. At the nitrogenase active site, the iron-molybdenum cofactor (FeMo-co) catalyzes the reduction of dinitrogen and protons to form ammonia and dihydrogen. Toward the goal of producing dihydrogen passively as an alternative fuel, a novel advanced material has been developed. CdSe nanoparticles complexed with FeMo-co, in both aqueous and organic solvent systems showed complex formation. When the system was interrogated by EPR spectroscopy, evidence of electron transfer was observed. The CdSeMSA●NafY●FeMo-co system when illuminated with visible light evolved dihydrogen consistently in four different experimental sets under the same reaction conditions. NifEN protein plays an important role in the biosynthesis of FeMo-co in addition to the involvement of NifU, NifS, NifB, NifX, NifH and NafY. After NifB synthesizes a FeMo-co precursor, 6-Fe NifB-co, NifEN further incorporates additional Fe, S, Mo, and (R)-homocitrate to complete the synthesis of FeMo-co. Molybdenum is provided to NifEN as its oxoanion, Mo(VI)O4 2- ; however, in FeMo-co molybdenum is in the oxidation state of Mo(IV). EPR spectroscopic investigation of NifEN turnover samples showed a signal at g = 2.00 that was dependent on molybdate concentration. Power and temperature profiles gave evidence that the g iv = 2.00 EPR signal was distinct from the Fe-S clusters in NifEN. The species observed at g = 2.00 was assigned to the reduction of Mo(VI) to Mo(V). How to utilize the effectiveness of FeMo-co and complex it to photoactive materials for the purpose of evolving dihyrogen upon illumination, thus providing a sustainable alternative energy source is one subject of this dissertation. A related subject is to gain an understanding of the biosynthetic pathway of FeMo-co by investigation of NifEN turnover experiments. This understanding should contribute towards the development of improved catalysts for meeting future energy demands.