Repositório Comunidade: CDF_GRFCDF_GRFhttps://hdl.handle.net/1822/18832024-03-29T05:32:37Z2024-03-29T05:32:37ZEncapsulation of agrochemicals in polymeric microcapsules coated with photocatalytic nanomaterialsForte, Marta Adriana Félixhttps://hdl.handle.net/1822/811502022-12-15T11:55:56Z2022-12-15T11:55:56ZTítulo: Encapsulation of agrochemicals in polymeric microcapsules coated with photocatalytic nanomaterials
Autor: Forte, Marta Adriana Félix
Resumo: Excessive use of agricultural land using agrochemicals (AC) for human livelihood results in excessive pollution of soils and food chains. The nutritional deregulation of soils causes damage that takes years to restore. Therefore, it is urgent to reduce the amount and/or concentration of ACs and to create solutions for their gradual release.
Microencapsulation systems may help to reduce this problem as they protect the AC from external actions like water, light, and temperature. This work developed two controlled release systems. (1) Polymethyl methacrylate microcapsules (PMMA-MCs), using the solvent evaporation technique with double emulsion, followed by ZnO and TiO2 coatings by atomic layer deposition (ALD) to degrade the PMMA-MCs and release the AC. Energy-dispersive X-ray spectrometry (EDX) proved the microcapsules configuration, as also the presence of the AC. (2) Gelatin microspheres (MSs) by gelification and crosslinking methods.
The ALD deposition depends on the substrate glass transition temperature (Tg) and on the pre-treatment with ozone. The studied PMMA has a Tg = 114 ºC, resulting from a combination of tacticities determined by the three different proton and carbon peaks in 1D and 2D NMR, from each tactic structure. The syndiotactic PMMA is predominant because intense peaks were identified in UV-vis (212.8 nm) and FTIR (750, 915, and 1062 cm-1).
ALD permits to do ozonation as an in situ pre-treatment. The reactivity from the metallic precursor indicates the intensity of the pre-treatment. For titanium tetraisopropoxide it was necessary more 300 O3 ALD cycles than for the diethylzinc. The X-ray diffractometer experiments revealed the amorphous structure of TiO2 as the pattern shows the same diffractogram as for PMMA-MCs, coincident with the PDF card (00-064-1603). The ZnO coating resulted in a wurtzite structure coincident with the PDF card 04-022-5463. Moreover, ZnO can be used as a seed layer to further deposit TiO2. The TiO2 coatings have a low photocatalytic activity. However, 400 ZnO ALD cycles degraded 95 % of the dye solution after 9 hours of UV irradiation.
A controlled release was lightly observed for ALD coated PMMA microcapsules after 24h, under Xe lamp irradiation, but it was not possible to quantify it. On the other side, the gelatin and polyvinyl alcohol microspheres allowed the AC release by swelling and diffusion, and the process took more than 8h to occurs entirely.; O uso excessivo de agroquímicos (AQs) é vital para a obtenção de alimentos, todavia é uma fonte de poluição dos solos, cursos de água e cadeias alimentares. A desregulação nutricional dos solos causa danos que levam anos a serem reestabelecidos. Assim, é urgente reduzir a quantidade e/ou concentração de agroquímicos nos solos, promovendo a sua libertação gradual. Os sistemas de microencapsulação conseguem solucionar esta falha, protegendo os AQ de ações externas como água, luz e temperatura. Neste trabalho foram desenvolvidos dois sistemas de libertação controlada. (1) Síntese de microcápsulas de polimetil metacrilato (MCs-PMMA), usando a evaporação do solvente associada à dupla emulsão, sendo seguidamente revestidas com ZnO e TiO2 por deposição em camada atómica (DCA) para degradar as MCs-PMMA e posteriormente libertar o AQ. A espectrometria de raio-X por dispersão em energia provou a estrutura das MCs e a presença do AQ. (2) Formação de microesferas de gelatina por gelificação e crosslinking.
A DCA depende da temperatura de transição vítrea (Tg) e do pré-tratamento com ozono. O PMMA estudado tem Tg = 114ºC, e é a combinação de taticidades que foram determinadas pelos respetivos picos de protão e carbono em 1D e 2D RMN. O PMMA é predominantemente sindiotático, com picos intensos em UV-vis (212.8 nm) e FTIR (750, 915 e 1062 cm-1).
A DCA permite fazer ozonação como um pré-tratamento in situ. A reatividade do percursor metálico dita a intensidade do pré-tratamento. Para o tetraisopropóxido de titânio foram precisos mais 300 ciclos de O3 do que para o dietilzinco. Através da difração de raios-X determinou-se que o TiO2 é amorfo uma vez que o difractograma é semelhante ao das MCs-PMMA, coincidente com a carta PDF 00-064-1603. O revestimento de ZnO tem a estrutura da wurtzite (carta PDF 04-022-5463). Adicionalmente, o ZnO pode ser usado como camada semente para crescer o TiO2. Os revestimentos de TiO2 têm uma baixa atividade fotocatalítica. Todavia, 400 ciclos de ZnO degradaram 95% de solução de corante após irradiação com luz UV durante 9h.
A libertação controlada foi testada sob irradiação com uma lâmpada de Xe, verificando-se este efeito em 24h, porém com variações ligeiras e difíceis de quantificar. As microesferas de gelatina e álcool polivinílico foram criadas para libertar o AQ por inchamento e difusão, e o processo demora mais de 8h.
Descrição: Programa doutoral em Engenharia de Materiais e Processamento Avançados
<b>Tipo</b>: doctoralThesis2022-12-15T11:55:56ZSurface plasmon resonance effect on the optical properties of TiO2 doped by noble metals nanoparticlesTorrell, M.Adochite, R. C.Cunha, L.Barradas, N. P.Alves, E.Beaufort, M. F.Rivière, J. P.Cavaleiro, A.Dosta, S.Vaz, F.https://hdl.handle.net/1822/789762022-07-25T19:46:50ZTítulo: Surface plasmon resonance effect on the optical properties of TiO2 doped by noble metals nanoparticles
Autor: Torrell, M.; Adochite, R. C.; Cunha, L.; Barradas, N. P.; Alves, E.; Beaufort, M. F.; Rivière, J. P.; Cavaleiro, A.; Dosta, S.; Vaz, F.
Resumo: Nanocomposite thin films composed of a TiO2 matrix doped with noble metals nanoparticles (MNPS), Au and Ag, were deposited on Si (100) and glass substrates by dc magnetron sputtering. The samples were annealed in a protective atmosphere at temperatures
ranging from 200 to 700 ºC. The main goal of this work is to characterize and compare the Surface Plasmon Resonance (SPR) behaviour in both systems. The studies have been focused on the growth of the nanoclusters and on their role on the optical properties of the films. Size, shape and distribution of the nanoclusters embedded on the titanium oxide dielectric matrix are reported as key factors on the SPR behaviour in both systems (Au:TiO2 and Ag:TiO2). The MNPs grew due to diffusion mechanisms, which were led by the annealing treatments, even at the highest annealing temperatures. Evidences of the correlation between the nanocomposite film structural changes and the evolution of the optical properties due to the SPR activity are reported. The SPR phenomenon manifests itself as a wide band on the visible range on the absorption spectra, and it is confirmed by
an important change on the surface colour tones of the samples.
<b>Tipo</b>: articleLocal variation of the dielectric properties of poly(vinylidene fluoride) during the alpha- to beta-phase transformationMartins, P.Nunes, Jivago Serrado Gomes AguiarHungerford, GrahamMiranda, D.Ferreira, Armando José BarrosSencadas, Vítor João Gomes SilvaLanceros-Méndez, S.https://hdl.handle.net/1822/783302022-06-09T13:34:30ZTítulo: Local variation of the dielectric properties of poly(vinylidene fluoride) during the alpha- to beta-phase transformation
Autor: Martins, P.; Nunes, Jivago Serrado Gomes Aguiar; Hungerford, Graham; Miranda, D.; Ferreira, Armando José Barros; Sencadas, Vítor João Gomes Silva; Lanceros-Méndez, S.
Resumo: The phase transformation from the non-polar alpha-phase to the polar electroactive beta-phase of polyvinylidene fluoride (PVDF) has been investigated using the fluorescence from Nile red. Films of alpha-PVDF doped with Nile red were stretched at controlled rates at a temperature of 80 degrees C to produce the alpha- to beta-phase transition. The thermo/mechanical dependent changes in the crystalline structure are related to the physical rotation of the polar (CH2-CF2) group, which can he monitored by steady state fluorescence techniques. The degree of phase transformation is related to variation in the fluorescence, which ill turn is linked to local dielectric constant of the polymer. The variation of the refractive index is more associated to the alignment of the polymeric chains than to the phase transformation. Thus, fluorescence is a suitable technique to monitor phase transitions coupled to a variation in the polarity of the dielectric medium. (C) 2008 Elsevier B.V. All rights reserved.
<b>Tipo</b>: articlePoly[(vinylidene fluoride)-co-trifluoroethylene] Membranes Obtained by Isothermal Crystallization from SolutionFerreira, Armando José BarrosSilva, JaimeSencadas, Vítor João Gomes SilvaGomez Ribelles, Jose LuisLanceros-Méndez, S.https://hdl.handle.net/1822/783292022-06-09T13:35:02ZTítulo: Poly[(vinylidene fluoride)-co-trifluoroethylene] Membranes Obtained by Isothermal Crystallization from Solution
Autor: Ferreira, Armando José Barros; Silva, Jaime; Sencadas, Vítor João Gomes Silva; Gomez Ribelles, Jose Luis; Lanceros-Méndez, S.
Resumo: Electroactive macroporous poly[(vinylidene fluoride)-co-trifluoroethylene] membranes have been produced by solvent evaporation at room temperature, starting with a diluted solution of the copolymer in dimethylformamide. The pore architecture consists of interconnected spherical pores. This architecture is independent of the membrane thickness. The thickness of the membranes ranges from a few to several hundred mu m, using spin coating and evaporation in static conditions, respectively. The pore structure is explained by a spinodal decomposition of the liquid/liquid phase separation and crystallization in the copolymer-rich phase.
<b>Tipo</b>: articleDesign of new biocompatible osseointegrated and antimicrobial dental implantFialho, Luísa Isabel Serra Glóriahttps://hdl.handle.net/1822/755452022-01-17T14:46:51Z2022-01-17T14:46:50ZTítulo: Design of new biocompatible osseointegrated and antimicrobial dental implant
Autor: Fialho, Luísa Isabel Serra Glória
Resumo: Como alternativa aos implantes dentários convencionais de Ti, foi realizada uma biofuncionalização de superfícies de Ta por diferentes tratamentos de superfície de modo a aumentar a bioatividade da superfície bem como dotá-la de capacidade bactericida. Para alcançar este design inovador, a estratégia adotada prendeu-se com duas etapas principais: i) desenvolvimento de uma superfície bioativa baseada no efeito sinergético da camada anódica de Ta2O5 com (nano a micro) porosidades e enriquecida por elementos osteocondutores; ii) desenvolvimento do sistema antimicrobiano pela deposição, por pulverização catódica, de NPs de Zn/ZnO na superfície de Ta2O5, com ou sem uma fina camada de carbono.
O primeiro tratamento funcional consistiu em duas etapas de anodização. A anodização inicial revelou-se sensível à concentração do eletrólito levando a uma curva j-t instável, ao aumento de temperatura do eletrólito e a uma morfologia final porosa ordenada e homogénea. A segunda anodização teve como finalidade incorporar elementos osteocondutores (Ca; P e/ou Mg) com uma razão de Ca/P biomimética. Duas abordagens foram propostas: anodização e/ ou polarização inversa. Os elementos osteocondutores foram incorporados na camada porosa de Ta2O5 sem comprometer a morfologia, porém a secção transversal das superfícies revelou uma estrutura lamelar inviável para aplicações biomédicas. Numa segunda abordagem, foi adotado o processo de oxidação por micro-arco onde foi possível otimizar uma estrutura (micro+nano) -porosa de Ta2O5 com Ca e P. Posteriormente, NPs de Zn (Zn/ZnO – core/shell) foram depositadas por pulverização catódica nas superfícies bioativas com (ou sem) uma camada adicional de carbono para controlar a libertação dos iões Zn²⁺.
A adesão celular inicial foi garantida em todas as superfícies, destacando-se a superfície de Ta2O5 com NPs e a camada de carbono, que traduziu a maior taxa de proliferação celular. As duas superfícies com NPs apresentaram atividade antibacteriana contra S. aureus e a maior inibição das bactérias sésseis foi observada na superfície com as NPs Zn/ZnO sem a camada de carbono. Graças ao excelente desempenho in vitro das superfícies de Ta nanoestruturadas com elementos osteocondutores, este trabalho é um progresso na estratégia para desenvolver uma nova geração de implantes dentários simultaneamente capazes de promover a osteointegração e prevenir infeções implantares.; As alternative to the conventional Ti dental implants surfaces, Ta surface biofunctionalization was investigated using different surface treatments in order to enhance the surface bioactivity as well as endow it with bactericidal ability. To achieve this innovative design, the adopted strategy was accomplished in two main steps: i) development of a bioactive surface based on the synergetic effect of anodic Ta2O5 with multilevel porosity (nano to micro) with osteoconductive elements incorporated; ii) development of an antimicrobial delivery system by deposition, by magnetron sputtering, of Zn/ZnO nanoparticles deposited onto the anodic Ta2O5 structured surface with or without an additional thin carbon layer.
The first functional treatment consisted of two anodization steps. The initial anodization-step was sensible to the electrolyte concentration leading to an unstable j-t curve and to a strong electrolyte temperature increase and a quite ordered and homogeneous porous nanopattern. A second anodization was carried out to obtain a porous structure enriched with osteoconductive elements (Ca, P and/or Mg), attaining a biomimetic Ca/P ratio. Two approaches were proposed: anodization and/or reverse polarization. The osteoconductive elements were successfully incorporated onto the porous Ta2O5 layer without compromising the nanostructure, however the cross-sectional analysis revealed an unsuitable lamellar structure for biomedical applications. As second approach, micro-arc oxidation process was adopted where it was possible to optimize a (micro+nano)porous CaP-containing Ta2O5 surface. Afterwards, Zn NPs (Zn/ZnO core-shell structure) were deposited by magnetron sputtering onto the bioactive surfaces with (or without) an additional carbon layer, for Zn²⁺ ions release control.
The initial osteoblasts adhesion was ensured on all surfaces, but the porous Ta2O5 surface with the Zn/ZnO NPs and the carbon layer stood out, which also translated to a higher proliferation rate. Both Zn-containing surfaces presented antibacterial activity against S. aureus and the greatest sessile bacteria inhibition was observed on the surface with the Zn/ZnO NPs without the carbon layer. Due to the excellent in vitro performance of the nanostructured Ta surface with osteoconductive elements, this work is clearly a progress on the strategy to develop a new generation of dental implants that can simultaneously promote osseointegration and prevent implant’s infection.
Descrição: Programa Doutoral em Engenharia de Materiais
<b>Tipo</b>: doctoralThesis2022-01-17T14:46:50Z