Síntese e caracterização de nanoestruturas compósitas


Semiconductor nanocomposites present a high technological importance due to their size dependent properties. Application in photocatalysis, fungicides, biomedicine or in optoelectronic devices are expected for these materials. In the first chapter a contextualization on the subject Nanotechnology and Nanoscience is made describing synthetic strategies, the nanomateriais and their possible applications. The metal chalcogenides deposition on inorganic particles is investigated using a mild temperature chemical method, comprising the chemical decomposition of dithiocarbamates or diselenocarbamates complexes. Nanostructures of SiO2/ME (M=Zn, Cd, Bi, Pb, Ag, Au and E=S or Se) are presented in chapter 2. Due to some particularities associated to the SiO2/ZnS system, a systematic study was preformed to understand the chemical mechanism of the synthesis of the ZnS nanophase by the dialkyldithiocarbamate decomposition in the presence of an amine. In chapter 3 the nanocomposites TiO2/ME are described. The TiO2 (anatase) is a well known photocatalyst and with this in mind some preliminaries photocatalysis studies were preformed using the nanocomposite TiO2/Ag2S in the decomposition of phenol under UV-vis light. Nanostructure thin films of CdS, CdSe organically caped and Bi2S3/SiO2 were used to fabricate LbL multilayers (chapter 4). In our study, hydrophobic QD’s dispersed in toluene have been successfully deposited on glass and quartz substrates previously treated with PAH. This study supports the idea that other interactions rather than electrostatic attraction may constitute the driving force to fabricate stable LbL films. In chapter 5 is described the chemical synthesis of transparent, flexible and photoluminescent di-ureasil based nanocomposites by a sol-gel method, in the presence of CdS, CdSe and ZnS coated CdSe QDs. For the latter a new and alternative process has been investigated that involves the coating of previously prepared CdSe QDs with ZnS shells derived from a ligand mixed amine-alkyldithiocarbamate Zn(II) complex. The incorporation of such CdSe/ZnS QDs into the d-U(600) di-ureasil hybrid host result in final nanocomposites with emission quantum yields up to 0.11 displaying a huge increase in the lifetime of the QDs, relatively to that of the isolated ones, induced by d-U(600)-to-CdSe/ZnS QDs energy transfer active channels.




Márcia Carvalho Neves

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