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Membranas de biocelulose como substrato para o crescimento de nanofios de ZnO: síntese e aplicação / Biocellulose membranes as substrate for Growth of Zinc Oxide nanowires: applications and synthesisAmaral, Thais Silva do [UNESP] 12 May 2015 (has links)
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Previous issue date: 2015-05-12 / Polímeros derivados do petróleo como polietileno tereftalato (PET) e polietileno naftalato (PEN), são utilizados em larga escala como substratos em diversos dispositivos eletrônicos. A crescente preocupação com o meio ambiente nos leva a buscar alternativas sustentáveis na utilização de materiais para fabricação de novas tecnologias. Neste trabalho, com o intuito de avaliar a viabilidade da substituição destes substratos por polímeros naturais, foi explorada uma biocelulose, a celulose bacteriana (CB), secretada por bactérias Acetobacter xylinum, que é um polímero de obtenção ―verde‖, não gerando resíduos ou altos impactos ambientais para ser produzida, além de possuir características desejáveis para ser utilizado como substrato em novos materiais, como resistência mecânica com módulo de Young de 134 GPa, tamanho nanométrico das fibras e transparência. Membranas funcionais foram obtidas pelo crescimento de nanofios de óxido de zinco na sua superfície. Os nanofios de ZnO foram obtidos com comprimento médio de 1,69 ± 0,08 μm e diâmetro de 37,2 ± 4,2 nm. Os materiais foram avaliados estruturalmente pela Difratometria de Raios-x (DRX) e Microscopia Eletrônica de Transmissão de Alta Resolução (HRTEM), e quimicamente utilizando Espectroscopia de Espalhamento Raman e Espectroscopia Vibracional na Região do Infravermelho (FT-IR). Também foram realizadas de medidas de Impedância Elétrica e Análise termogravimétrica (TG/DTG). Por fim os materiais foram testados em três diferentes aplicações: como membrana para fotodegradação de corantes, sensor piezoelétrico e substrato removível para obtenção de fios de ZnO não suportados que se mostraram aplicações viáveis para o material. / Petroleum-derived polymers such as Polyethylene Terephthalate (PET) and Polyethylene Naphthalate (PEN), are largely used as substrates in various electronic devices. The growing concern with the environment leads us to seek sustainable alternatives in the use of materials for the manufacture of new technologies. In this work, in order to assess the feasibility of replacing these substrates by natural polymers, bacterial cellulose (BC) was explored, secreted by bacteria Acetobacter xylinum is a ―green‖ polymer that don’t generate waste or high environmental impacts to be produced, and has desirable characteristics for use as new substrate materials, such as mechanical strength with Young's modulus of 134 Gpa, nano-sized fibers and transparency. Functional membranes were prepared by growing ZnO nanowires on the BC dried membranes surface. The obtained ZnO nanowires presented an average length of 1.69 ± 0.08 m and diameter of 37.2 ± 4.2 nm. Materials were evaluated structurally by X-ray Diffraction (XRD) and High-resolution Transmission Electron Microscopy (HRTEM), chemically using Raman Scattering spectroscopy and Vibrational Spectroscopy in the Infrared Region (FT-IR). Electrical Impedance measurements and thermal gravimetric analysis (TG / DTG) were performed as well. Finally the materials were tested in three different applications: as a membrane for dyes photodegradation, piezoelectric sensor and removable substrate for obtaining unsupported ZnO nanowires that are viable applications for the material.
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Hollow magnetic and semiconductor micro/nanostructures : synthesis, physical properties and applicationPomar, César Augusto Díaz January 2018 (has links)
Orientador: Prof. Dr. José Antonio Souza / Tese (doutorado) - Universidade Federal do ABC, Programa de Pós-Graduação em Nanociências e Materiais Avançados, Santo André, 2018. / O objetivo deste trabalho e sintetizar materiais magneticos e semicondutores ocos
micro/nanoestruturados hierarquicamente, para obter um melhor entendimento das
propriedades fisicas e explorar aplicacoes tecnologicas. Inicialmente, microtubos de hematita
e magnetita foram sintetizados por oxidacao termica juntamente com uma corrente eletrica
aplicada e utilizando-se o microfio de ferro metalico como precursor. A fraccao volumetrica
de Fe2O3(hematite) e Fe3O4(magnetite) nos microtubos e a formacao das nanoestruturas de
hematite na superficie pode ser controlada por alteracoes sistematicas dos parametros de
sintese tais como temperatura, rampa de aquecimento, tempo de aquecimento e valor da
corrente electrica. A reacao quimica de oxidacao envolve um processo onde uma fina camada
de oxido e formada primeiro na superficie do metal, seguida por difusao simultanea de ions
metalicos atraves da camada oxida e difusao de oxigenio da atmosfera para o interior. A
difusao para fora e mais rapida, levando a criacao de vacancias que coalescem em poros
formando os microtubos. Medidas de resistividade eletrica in situ foram realizadas durante o
processo de oxidacao mostrando todo o processo de formacao do microtubo. Imagens de
microscopia eletronica de varredura mostram a morfologia do microtubo com diametro
variando de 40 ¿Êm a 100 ¿Êm e comprimento de 5 mm. Medidas de difracao de raios-X em po
evidenciam a presenca de fases cristalinas de hematita (Fe2O3) e magnetita (Fe3O4) nos
microtubos. Nanoestruturas de hematita aparecem em forma de bastoes e fios dispersos
homogeneamente ao redor da superficie do microtubo com diametros de 80-300 nm e
comprimento de 1-5 ¿Êm. Experimentos in vitro envolvendo aderencia, migracao e
proliferacao de culturas de celulas de fibroblastos na superficie dos microtubos indicaram a
ausencia de citotoxicidade para este material. Tambem o calculo do torque e da forca
magnetica desses microtubos com nanofios em funcao do gradiente de campo magnetico
externo, mostrou que ele e robusto, abrindo a possibilidade para fabricacao de bio-microrobos magneticos para aplicacao em biotecnologia. Por outro lado, microarquiteturas ocas de
SnS e ZnS decoradas com nanoestruturas foram sintetizadas por evaporacao termica livre de
catalisadores utilizando microfios de metal e po de enxofre como materiais de partida. Para o
SnS, observamos formacao de uma estrutura oca composta por uma camada metalica de Sn na
superficie interna, e uma camada de SnS de estrutura ortorrombica com nanoestruturas de SnS
na superficie. Para o ZnS, descobrimos a formacao de uma esfera oca com uma camada
metalica na parte interna, uma camada de ZnS com fase cubica, e sobre ela nanoestruturas de
ZnS com fase cristalina hexagonal cresceram homogeneamente. O diametro da microsfera e
de 415 ¿Êm e os nanofios tem um diametro e comprimento medio de 70 nm e 7 ¿Êm,
respectivamente. As microestruturas ocas semicondutoras de ZnS e SnS exibiram atividade
eficiente para degradar azul de metileno sob irradiao com luz solar simulada. Os resultados
revelam que essas nano/microestruturas possuem alta fotoatividade para degradacao organica. / The aim of this work is to synthesize hierarchically micro/nanostructured hollow
magnetic and semiconductor materials, to obtain a better understanding on the physical
properties, and find technological applications. Initially, hematite and magnetite microtubes
were synthesized by thermal oxidation process along with the presence of an applied electrical
current and using metallic iron microwire as a precursor. The volume fraction of both Fe2O3
(hematite) and Fe3O4 (magnetite) phase on microtubes can be controlled as well as surface
nanostructures formation of hematite by systematic change of the synthesis parameters such
as temperature, heating rate, annealing time and electrical current value. The oxidation
chemical reaction involves a process where a thin oxide layer is formed first on the metal
surface, followed by simultaneous outward diffusion of metal ions through the oxide scale
and inward diffusion of oxygen from the atmosphere into the core. In our case, the outward
diffusion is faster leading to the creation of vacancies which coalesce into voids forming the
microtubes. In situ electrical resistivity measurements were carried out during the oxidation
process showing the whole process of the microtube formation. Scanning electron microscopy
images show microtube morphology with diameter ranging from 40 ìm to 100 ìm and length
of 5 mm. X-ray powder diffraction measurements evidence the presence of hematite (Fe2O3)
and magnetite (Fe3O4) crystal phases comprising microtubes. Nanostructures of hematite
appear in form of sticks and wires homogeneously dispersed on the microtube surface with
diameters ranking from 80 nm to 300 nm and length of 1 to 5 ìm. In vitro experiments
involving adherence, migration, and proliferation of fibroblasts cell culture on the surface of
the microtubes indicated the absence of immediate cytotoxicity for this material. We have also
calculated both torque and driving magnetic force for these microtubes with nanowires as a
function of external magnetic field gradient which were found to be robust opening the
possibility for magnetic bio micro-robot device fabrication and application in biotechnology.
On the other hand, SnS and ZnS hollow microarchitectures decorated with
nanostructures were synthesized by catalysis free thermal evaporation technique using metal
microwires and sulfur powder as starting materials. For SnS, we observed a hollow formation
comprised of a thin metallic Sn layer in the inner surface, SnS orthorhombic structure thick
layer with SnS nanostructures on the top. For ZnS, we found out the formation of hollow
sphere with a thin metallic layer in the inner part, a thick cubic phase layer of ZnS, and on this
second phase, nanostructures of ZnS hexagonal crystal phase grew up homogeneously. The
microsphere diameter is about 415 ìm and the nanowires on the surface have average
diameter of 70 nm and length 7 ìm. ZnS and SnS hollow semiconducting microstructures
have exhibited efficient activity to degrade the methylene blue under simulated sunlight
irradiation. The results reveal that these nano/microstructures have high photoactivity to
organic degradation.
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Antimicrobial activity and dye photodegradation of titanium dioxide nanoparticles immobilized on polyacrylonitrile-cellulose acetate polymer blended nanofibers.Nkabinde, Sibongile Chrestina January 2019 (has links)
M. Tech. (Department of Chemistry, Faculty of Applied and Computer Sciences), Vaal University of Technology. / Electrospinning is a method that has gained more attention due to its capability in spinning a wide variety of polymeric fibers and nanoparticles embedded in polymer fibers. Polymer blending has been considered the most appropriate way for creating new materials with fused properties which improve poor chemical, mechanical, thermal and dynamic mechanical properties of each polymer. Hence, in this study, electrospinning technique was used to fabricate polyacrylonitrile (PAN) nanofibers at concentrations of (10, 12 and 14 wt%) and cellulose acetate (CA) nanofibers at concentrations of (14, 16 and 18 wt%). 10wt% of PAN and 16 wt% of CA were blended together and the optimum blend ratio was found to be 80/20 PAN/CA. TiO2 nanoparticles (0.2 and 0.4 wt%) were incorporated into CA nanofibers and (1, 2 and 3 wt%) were incorporated into PAN and PAN/CA blended polymers, respectively. Applied voltages of 20, 22 and 24 kV were varied at a spinning distance of 15cm and the optimum voltage for the fabrication of composite was 22 kV. The sol-gel method was used to synthesise the TiO2 nanoparticles at different calcination temperatures of 400, 500 and 600 ºC. The fabricated composite nanofibers were tested for antibacterial and photocatalytic activities. The synthesised nanomaterials were characterized using SEM, TEM, EDX, UV-Vis, PL, FTIR spectroscopy, XRD and TGA. The absorption and emission spectra illustrated the formation of TiO2 nanoparticles and the increase in absorption band edges. TEM showed the spherical morphology of the nanoparticles with average diameter of 12.2 nm for nanoparticles calcined at 500 ºC. SEM illustrated the diameter and morphology of the nanofibers and composites with the average diameter of 220, 338, 181, 250, 538, 294 nm for PAN, CA, PAN-TiO2, CA-TiO2, PAN/CA and PAN/CA-TiO2, respectively. XRD revealed anatase phase as the dominant crystalline phase of the synthesised nanoparticles. FTIR spectroscopy and EDX signified that the formation of composite nanofibers and the presence of TiO2 nanoparticles corresponded to the Ti-O stretching and Ti-O-Ti bands on the FTIR spectra. The antimicrobial activity of the composite nanofibers were tested against E. coli, S. aureus and C. albicans microorganisms. The photocatalytic activity of the nanomaterials was tested using methyl orange dye. PAN/CA-TiO2 composite nanofibers revealed the greatest antibacterial activity against selected microorganisms as compared to the other nanocomposites. PAN/CA-TiO2 nanocomposite (44%) showed greater rate of photodegradation of methyl orange than PAN-TiO2 nanofibers (28%) and TiO2 nanoparticles (12%) under visible light irradiation.
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